Part 2 book “Textbook of preclinical conservative dentistry” has contents: Principles of tooth preparation, tooth preparation for amalgam and composite restorations, tooth preparation for primary teeth, dental materials, adhesive dentistry,… and other contents.
Trang 1Tooth preparation is the mechanical alteration of a
defective, injured or diseased tooth in order to best receive
a restorative material which will re-establish the healthy
state of the tooth including esthetic correction when
indicated along with normal form and function
PURPOSE OF TOOTH PREPARATION
Earlier when the affected tooth was prepared because
of caries, cutting of tooth was referred to as cavity
preparation But nowadays many indications other than
caries lead to preparation of the tooth Hence, the term
cavity preparation has been replaced by tooth preparation
Tooth preparation is done for:
Tooth preparation is classified according to location of the
tooth defect (Fig 8.1).
Class I is the only pit and fissure preparation whereas rest are smooth surface preparations.
r Class I: Pit and fissure preparations occur on the
occlusal surfaces of premolars and molars, the occlusal two-third of buccal and lingual surface of molars and
lingual surface of incisors (Figs 8.2A and B) r Class II: Preparations on the proximal surface of premolars and molars are class II (Figs 8.3A and B) r Class III: Preparations on the proximal surface of anterior
teeth and not involving the incisal angles are class III
(Figs 8.4A and B)
r Class IV: Preparations on the proximal surface of
anterior teeth also involving the incisal angle falls under
class IV (Figs 8.5A and B) r Class V: Preparations on gingival third of facial and
lingual or palatal surfaces of all teeth came under Class V
(Figs 8.6A and B)
Principles of Tooth Preparation
Trang 2Figures 8.3A and B: (A) Clinical picture of Class II lesion; (B) Schematic representation of Class II lesion
Figures 8.2A and B: (A) Clinical picture of class I lesion; (B) Schematic representation of class I lesion showing caries on occlusal
surface of molars and premolars, lingual surface of incisors and occlusal third of buccal and lingual surface of molars
B A
Figure 8.1: Schematic representation showing GV Black’s classification of dental caries
Trang 3Figures 8.5A and B: (A) Clinical picture of Class IV lesion; (B) Schematic representation of Class IV lesion
Trang 4Figure 8.7: Schematic representation of MOD preparation
Figures 8.8A and B: (A) Clinical picture of Class VI lesion;
(B) Schematic representation of class VI lesion
Figures 8.9A and B: Photograph and schematic representation
showing simple tooth preparation involving one tooth surface only
Figures 8.10A and B: Photograph and schematic representation
showing compound tooth preparation involving two surfaces
Modification of Black’s classification was made to
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r Class II: Preparations on the single or both proximal
surface of premolar and molar teeth When there is
involvement of both proximal surfaces, it is called
mesio-occlusodistal (MOD) preparation (Fig 8.7)
r Class VI: Preparations on incisal edges of anterior and
cusp tips of posterior teeth without involving any other
surface (Figs 8.8A and B) come under Class VI.
DEFINITIONS
Simple Tooth Preparation
A tooth preparation involving only one tooth surface
is termed simple preparation (Fig 8.9), for example,
occlusal preparation
Compound Tooth Preparation
A tooth preparation involving two surfaces is termed as
compound tooth preparation (Fig 8.10), for example,
mesio-occlusal or disto-occlusal preparation
Complex Tooth Preparation
A tooth preparation involving more than two surfaces
is called as complex tooth preparation (Fig 8.11), for
example, MOD preparation
For communication and records purpose, surface
of tooth preparation is abbreviated by using first letter,
It is a wall in the preparation, which is not extended to the
external tooth surface (Fig 8.12)
External Wall
An external wall is a wall in the prepared tooth that
extends to the external tooth surface (Fig 8.13) External
wall takes the name of the tooth surface towards which it
is situated
Trang 5Figures 8.11A and B: Photograph and schematic representation
showing complex tooth preparation involving more than two surfaces
Pulpal Wall
A pulpal wall is an internal wall that is towards the pulp
and covering the pulp (Fig 8.14) It may be both vertical
and perpendicular to the long axis of tooth
(Fig 8.16).
Cavosurface Angle Margin
Cavosurface angle is formed by the junction of a prepared tooth surface wall and external surface of the tooth
(Fig 8.17) The acute junction is referred to as preparation
margin or cavosurface margin
Line Angle
It is a junction of two surfaces of different orientations along the line Its name is derived from the involved surfaces
Point Angle
It is a junction of three plane surfaces or three line angles of different orientations Its name is derived from its involved surfaces or line angles
NUMBER OF LINE AND POINT ANGLES
Number of line angles and point angles in different tooth
preparations are enumerated in Table 8.1.
Line and point angles of class I to class V tooth preparations are enlisted as following
Facts
When two or more surfaces are combined, the –al ending of the prefix word is changed to an –o The angle formed by lingual and gingival wall is termed as “linguogingival” line angle An MOD preparation is called mesio-occlusodistal preparation.
Figure 8.12: Schematic representation of internal and
external wall of tooth preparation
Figure 8.13: Schematic representation of
external wall of tooth preparation
Figure 8.14: Schematic representation of pulpal floor and axial wall
Trang 6Figure 8.15: Schematic representation showing class III tooth
preparation depicting axial wall
Figure 8.16: Schematic representation showing pulpal and gingival
floor of class II preparation
Figure 8.17: Schematic representation showing cavosurface angle is
angle formed by junction of prepared tooth surface and external
sur-face of the tooth
Table 8.1 ¨Number of line angles and point angles in different
tooth preparation designs
Type of tooth preparation Line angles Point angles
Class I Tooth Preparation
For simple class I tooth preparation involving only occlusal surface of molars eight line angles and four point angles
are named as follows (Fig 8.18):
Line Angles
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Point Angles
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Class II Tooth Preparation
For class II preparation (mesio-occlusal or disto-occlusal)
11 line angles and 6 point angles are as follows (Fig 8.19).
The following is the nomenclature for mesio-occlusal tooth preparation
Line Angles
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Point Angles
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Trang 7r "YJPMJOHVPQVMQBMQPJOUBOHMF
r %JTUPMJOHVPQVMQBMQPJOUBOHMF
Class III Tooth Preparation
For class III preparation on anterior teeth, 6 line angles
and 3 point angles are as follows (Fig 8.20):
Figure 8.18: Schematic representation of class I tooth preparation
showing line angles and point angles
Figure 8.19: Schematic representation of class II tooth preparation
showing line and point angles
Figure 8.20: Schematic representation of class III preparation
show-ing line and point angles
Figure 8.21: Schematic representation of class IV preparation
show-ing line and point angles
Figure 8.22: Schematic representation of class V preparation
show-ing line and point angles
Line Angles
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Point Angles
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Class IV Tooth Preparation
For class IV tooth preparation on anterior teeth, 11 line
angles and 6 point angles are as follows (Fig 8.21):
Trang 8Class V Tooth Preparation
For class V preparation, 8 line angles and 4 point angles are
For optimal restoration, tooth preparation involves basic
mechanical and physical principles which should be
followed in an orderly sequence Tooth preparation is
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Steps in Tooth Preparation
r Stage I: Initial tooth preparation steps
– Outline form and initial depth– Primary resistance form– Primary retention form – Convenience form
r Stage II: Final tooth preparation steps
infected dentin and/or old restorative material, if indicated
– Pulp protection, if indicated– Secondary resistance and retention form – Procedures for finishing the external walls of the tooth preparation
– Final procedures: Cleaning, inspecting and sealing.Under special conditions these sequences can be changed
INITIAL STAGE
Outline Form and Initial Depth
Definition
Outline form means:
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Outline form includes the external outline form and
internal outline form External outline form is established
first to extend all margins into sound tooth tissue while NBJOUBJOJOHUIFJOJUJBMEFQUIPGmNNJOUPUIFEFOUJO
towards the pulp (Fig 8.23) During tooth preparation, the
margins of preparation not only extend into sound tooth tissue but also involve adjacent deep pits and fissures
in preparation This was referred to as ‘extension for prevention’ by GV Black
Factors Affecting the Outline and Initial Depth form of Tooth Preparation
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Trang 9margins to healthy tooth structure
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enamel margins
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preparation, otherwise prepared as separate tooth
preparations
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areas, such as cusp eminences
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fissures which cannot be managed by enameloplasty
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dentin, though the actual depth of preparation may
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slopes and thickness of the enamel
External outline form
r Consists of smooth curves, straight lines and rounded
line and point angles (Fig 8.25)
r Weak unsupported enamel should be removed since it
is liable to fracture
Internal outline form
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cavosurface angle to the pulpal floor
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from the cavosurface margin to the pulpal floor and at
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strength to resist fracture due to masticatory forces
(Fig 8.26).
Figures 8.23A and B: Schematic representation showing initial
depth of preparation should be 0.2–0.8 mm into dentin
Figure 8.25: Clinical picture showing that outline form should
con-sist of smooth curves, rounded line and point angles
Figures 8.24A and B: Schematic representation showing removal of
all undermined enamel
Outline form for Smooth Surface Lesions—Outline form
of Proximal Caries (Class II, III and IV lesions)
A class II tooth preparation consists of:
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Trang 10Rules for Making Outline form for
Proximal Preparation
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structure is reached (Fig 8.27)
Rules for Class V Cavities
occlusally and gingivally till sound tooth structure is
reached
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Enameloplasty
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enamel margins of the enamel surface by ‘rounding’
or ‘saucering’ it and converting it into a smooth groove
making it self-cleansable area
r Enameloplasty does not extend the outline form This
procedure should not be used unless a fissure can
be made into a groove with a saucer base with mild
removal of enamel
Primary Resistance Form
Definition
Primary resistance form is that shape and placement
of preparation walls to best enable both the tooth and
Figure 8.26: Schematic representation showing that preparation
depth should be at least 1.5–2 mm from the cavosurface margin and
at least 0.2–0.5 mm into dentin
Figure 8.27: Schematic representation showing that outline form
should include all the carious lesion and undermined enamel
Figure 8.28: Schematic representation showing that depth of axial
wall should be restricted 0.2–0.8 mm into dentin
restoration to withstand, without fracture, the stresses of masticatory forces delivered principally along the long axis of the tooth
Features of Resistance Form
r Box-shaped preparation with flat pulpal and gingival floor: This helps the tooth to resist occlusal loading by virtue of being prepndicular to the masticatory forces directed
along the long axis of the tooth (Figs 8.32A and B)
Trang 11Figure 8.29: Schematic representation showing that axial wall
should be parallel to external surface of tooth
Figure 8.30: Schematic representation showing that proximal tooth
preparation, gingival margin should clear adjacent tooth by 0.5 mm
Figure 8.31: Schematic representation showing 0.5 mm
clearance from adjacent tooth
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on its respective compressive and tensile strengths
to prevent the fracture of both the remaining tooth
structure and restoration (Box 8.1)
width of anterior teeth, to establish the resistance
concentration points in tooth preparation (Fig 8.34)
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amount of remaining tooth structure
Factors Affecting Resistance Form
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Primary Retention Form
Definition
Primary retention form is that form, shape and configuration
of the tooth preparation that resists the displacement or removal of restoration from the preparation under lifting
and tipping masticatory forces (Box 8.2).
Factors Affecting Retention Form
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restorationr ǔJDLOFTTPGUIFSFTUPSBUJPO
Figures 8.32A and B: Schematic representation showing (A)
Resistance form of tooth provided by flat pulpal and gingival floor;
(B) In case of rounded pulpal floor, the rocking motion of restoration results in wedging force which may result in failure of restoration
Trang 12Figure 8.33: Schematic representation showing restriction of the
extensions of external wall so as to have strong marginal ridge area
Figure 8.34: Schematic representation showing sharp line angle and
cavosurface margins can lead to poor resistance form because of
con-centration of stresses at that point
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Features of Convenience Form
walls to gain adequate access to the deeper portion of the preparation
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surface for convenience formr 1SPYJNBM DMFBSBODF JT QSPWJEFE GSPN UIF BEKPJOJOHtooth during class II tooth preparation
the proximal caries in posterior teeth is approached through a tunnel initiating from the occlusal surface and ending on carious lesion on the proximal surface without cutting the marginal ridge
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r 4UBSU SFNPWBM PG DBSJFT GSPN UIF MBUFSBM CPSEFST PG UIFlesion Force for removal of infected dentin should be directed laterally and not towards the center of the carious lesion
Box 8.2: Retention form for different restorations
Restoration Primary retention form
Amalgam class I
and II
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(about 2°–5°) t $POTFSWBUJPOPGNBSHJOBMSJEHFT t 0DDMVTBMEPWFUBJM
Amalgam class III
and IV retention grooves/coves are the primary
retention forms Cast metals t 1BSBMMFMMPOHJUVEJOBMXBMMTXJUITMJHIU
occlusal divergence of 2–5°
t 0DDMVTBMEPWFUBJM skirts and dentin slot Composites t .JDSPNFDIBOJDBMCPOEJOHCFUXFFOFUDIFE
and primed surface with composites t &OBNFMCFWFMT
Direct filling gold t &MBTUJDDPNQSFTTJPOPGEFOUJOBOETUBSUJOH
point in dentin provides retention by proper condensation
Trang 13Pulp protection is a very important step in adapting the
preparation for final restoration although actually it is
not a step of tooth preparation When remaining dentin
thickness is less, pulpal injury can occur because of heat
production, high speed burs with less effective coolants,
irritating restorative materials, galvanic currents due to
restoration of dissimilar metals, excessive masticatory
forces transmitted through restorative materials to the
dentin and ingress of microorganisms and their noxious
products through microleakage
Pulp protection is achieved using liners, varnishes and
bases depending upon—
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Liners and varnishes are used where preparation depth
is shallow and remaining dentin thickness is more than
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– Barrier to protect remaining dentin and pulp
– Galvanic and thermal insulation
Table 8.3TVNNBSJ[FTEJŀFSFOUXBZTPGQVMQQSPUFDUJPOunder various restorative materials depending upon remaining dentin thickness
Secondary Resistance and Retention Forms
This step is needed in complex and compound tooth preparations where added preparation features are used to improve the resistance and retention form of the prepared tooth These are as follows:
Mechanical Features
Many mechanical features are added in the tooth preparation to provide additional retention and resistance form These can be:
Grooves and Coves
Coves are small conical depressions prepared in healthy dentin to provide additional retention These are normally prepared in the proximal walls of class II preparations at the axiofacial and axiolingual line angles, thus reducing proximal displacement of the restoration More than one groove per wall should be avoided as they may weaken the wall Grooves are especially useful for cast restorations
Table 8.4 enlists type of tooth preparation and location
of retention grooves
Slot or Internal Box
ǔFTFBSFmNNEFFQCPYMJLFHSPPWFTQSFQBSFEJOdentin to increase the surface area These are prepared in occlusal box, buccoaxial, linguoaxial and gingival walls
Table 8.2 ¨Difference between infected and affected dentin
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Shallow (RDT>
2.0 mm)
Moderately deep (RDT >0.5–2 mm)
Glass JPOPNFS
Trang 14(Fig 8.35) For cast restorations these are prepared by
tapered fissure bur to avoid undercuts and for plastic
restorative materials like amalgam, these are prepared by
inverted cone bur to create slight undercuts in dentin
Locks
Locks are usually prepared for class II amalgam
restorations for increasing resistance and retention form
(Fig 8.36).
Pins
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to provide additional retention in amalgam, composite
and cast restorations
Skirts
Skirts are prepared for providing additional retention in
cast restorations They increase the total surface area of the
preparation Skirts can be prepared on one or all four sides
of the preparation depending upon the required retention
(Fig 8.37) Skirts have shown to improve both resistance
and retention form
Amalgapins
Amalgapins are vertical posts of amalgam anchored in
dentin Dentin chamber is prepared by using inverted
DPOF CVS PO HJOHJWBM ëPPS NN JO EFOUJO XJUI UP
NN EFQUI BOE UP NN XJEUI (Fig 8.38) Amalgam
pins increase the retention and resistance of complete
restoration
Treatment of the Preparation Walls
Treatment of the preparation walls by beveling, etching
and priming increases the adhesive property of tooth
preparation
Beveled Enamel Margins
Beveling of preparation, margins increases the surface
area and thus, the retention in composite restorations
Enamel Wall Etching
Etching results in microscopic roughness, which increases
the surface area and thus helps in enhancing the
Figure 8.35: Schematic representation of slot
Figure 8.36: Schematic representation of retention locks
Figure 8.37: Schematic representation of skirt in cast restoration
helps in increasing retention
Figure 8.38: Schematic representation showing amalgapins increase
retention of the restoration
Trang 15for proper finishing of the preparation margins At the margins, all the enamel walls should have full length rods
supported by dentin (Fig 8.39) To remove unsupported
enamel rods near gingival margins, it should be slightly beveled In case of cast gold restorations, a short bevel is given and an ultrashort bevel is given in case of gold foil
Table 8.5 shows differences between butt joint and lap
joint
VIVA QUESTIONS
Q.1 What is tooth preparation?
Ans It is a mechanical alteration of a defective, injured or
diseased tooth in order to best receive a restorative material which will re-establish the healthy state
of the tooth including esthetic correction when indicated along with normal form and function
Q.2 What are different causes of loss of tooth structure?
Ans Most common cause is dental caries Other causes
can be trauma resulting in tooth fracture, attrition,
Dentin Conditioning (Etching and Priming)
Etching and priming of the dentin surface increases the
retention
Adhesive Luting Cements
Adhesive luting cements increase the retention of indirect
restorations
Procedures for Finishing the External
Walls of the Tooth Preparation
Definition
Finishing of a tooth preparation walls is further
development of a specific cavosurface design and degree
of smoothness which produces maximum effectiveness of
the restorative material being used
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structure
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restoration at and near the margins
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Final Procedures: Cleaning, Inspecting and Sealing
Final step in tooth preparation is cleansing of the
preparation This includes the removal of debris, drying
of the preparation, and final inspection before placing
restorative materials
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pellets
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alcohol free disinfectant: Use of mild disinfectant in
tooth preparation serves the purpose of disinfection
Degree of Smoothness of Walls
It depends upon type of restoration used For example,
for cast metal restorations, a very smooth surface is
required whereas for direct gold, amalgam and composite
restorations, slight roughness is needed in the preparation
walls
Location of the Margins
During finishing of the preparation walls and margins, one
should follow the principles of paralleling the direction of
enamel wall The knowledge of enamel rods is necessary
Figure 8.39: Schematic representation showing that at the margins,
all the enamel walls should have full length rods supported by dentin
Table 8.5 ¨Showing differences between butt joint and lap joint
Butt joint Lap/Slip joint
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Trang 16abrasion, erosion, tooth malformation, hypoplasia,
tooth resorption, etc
Q.3 What is simple, compound and complex tooth
preparations?
Ans A tooth preparation involving only one tooth surface
is termed as simple preparation For example,
mesial, distal, occlusal, buccal, lingual tooth
preparation
A tooth preparation involving two surfaces
is termed as compound tooth preparation For
example, mesio-occlusal (MO), disto-occlusal
(DO), mesiolingual (ML), or distobuccal (DB) tooth
preparation
A tooth preparation involving more than two
surfaces is called as complex tooth preparation
For example, mesio-occlusodistal (MOD),
facio-occlusolingual (FOL) or mesioincisodistal (MID)
tooth preparation
Q.4 Define class I tooth preparation.
Ans Class I preparations occur on the occlusal surfaces
of premolars and molars, the occlusal two-third of
buccal and lingual surface of molars and lingual
surface of incisors
Q.5 Define class II tooth preparation.
Ans Preparations on the proximal surface of premolars
and molars are class II
Q.6 Define class III tooth preparation.
Ans Preparations on the proximal surface of anterior
teeth and not involving the incisal angles are class
III
Q.7 Define class IV tooth preparation.
Ans Preparations on the proximal surface of anterior
teeth also involving the incisal angle falls under
class IV
Q.8 Define class V tooth preparation.
Ans Preparations on gingival third of facial and lingual
or palatal surfaces of all teeth came under Class V
Q.8 Define class VI tooth preparation.
Ans Preparations on incisal edges of anterior and cusp
tips of posterior teeth without involving any other
surface come under Class VI
Q.10 What are different walls and floors of a tooth
Q.12 What is floor of the cavity?
Ans Floor is the flat surface of prepared cavity which
is perpendicular to the occlusal forces which are directed occlusogingivally
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Q.13 What should be the isthmus width of amalgam cavity?
Ans 1/4thof intercuspal disatance
Q.14 What is ideal depth of amalgam cavity?
Ans. mNNUPUBMEFQUImNNJOUPUIFEFOUJOF
Q.15 Define a line angle.
Ans It is a junction of two surfaces of different
orientations along the line Its name is derived from the involved surfaces
Q.16 What is a point angle?
Ans It is a junction of three plane surfaces or three line
angles of different orientations Its name is derived from its involved surfaces or line angles
Q.17 Do we have line angle at cavosurface margin?
Ans No, because line angle is the junction between two
prepared parts of tooth preparation Cavosurface margin is the junction of prepared tooth with unprepared tooth surface
Q.18 If class II tooth preparation involves only proximal surface, why do we make occlusal preparation also?
Ans Occlusal preparation is done for convenience form
Since directly reaching the affected area with bur is difficult because of close proximity of the adjacent tooth therefore an occlusal preparation is made through which proximal surface is reached
Q.20 Why is class VI added to Black’s classification?
Trang 17Ans Black classified the cavities according to some order
and pattern of caries in affected teeth But he did not
include the areas which he assumed might not be
attacked by caries, though in reality they might be
affected Simon later modified Black’s classification
and added class VI The class VI are the tooth
preparations which occur in the areas not covered
by any of the other five classes like cusp tips, incisal
two-third of anterior teeth, etc
Q.21 What is enamel and dentinal wall?
Ans Enamel wall is portion of prepared external wall
consisting of enamel
Dentinal wall is portion of prepared external wall
consisting of dentin
Q.22 What will be the treatment if caries involve
proximal surface of anterior tooth without
involving incisal edge and caries at palatal pit?
Ans If lesions are not interconnected they are treated as
separate preparations
But if they are connected, the preparation is class
III with lingual extension
Q.23 What is treatment for caries present on buccal
surface and proximal surface of a molar?
Ans If lesions are not interconnected and small, they are
treated as separate class II and class I preparations
But if lesions are large and interconnected, it is
treated as proximo-occlusobuccal preparation
Q.24 What is similarity between class II, III, IV and V
preparations?
Ans All occur on smooth surfaces
Q.25 What is common between class II, III, IV
preparations?
Ans All these occur on proximal surfaces.
Q.26 How is tooth preparation done?
Ans It is done by use of hand and rotary instruments.
Q.27 What are different steps of tooth preparation?
Ans A Stage I
Initial tooth preparation steps:
1 Outline form and initial depth
6 Pulp protection, if indicated
7 Secondary resistance and retention form
8 Procedures for finishing the external walls of the tooth preparation
9 Cleaning, inspecting and sealing
Q.28 Define outline form List the factors influencing the outline form?
Ans The outline form means:
Q.29 What is extension for prevention?
Ans This concept was given by GV Black which advocated
involvement of all pits and fissures even if they are unaffected by caries
Q.30 What do you mean by breaking the contact?
Ans In case of class II, and III and IV caries, there is always
a contact with the adjacent tooth In these cases, whether caries are below or above the contact, the contact has to be broken so as to bring preparation margins into the embrasures for easy cleansability
If preparation margins end in non-cleansable areas, food stagnation in those areas may result in secondary caries
Q.31 What should be ideal depth of the preparation?
Ans.
for non-adhesive materials Since enamel is inelastic, it cannot be used for providing retentive and resistance form So depth of preparation should be increased till elastic dentin is reached Preparation should not end at dentinoenamel
Trang 18junction This area is sensitive because of lateral
branching of dentinal tubules and cytoplasmic
extensions of odontoblasts
Q.32 How does convenience form affects outline from?
Ans This is specially seen in case of class II, III and IV
preparations where adjacent tooth is present In
these cases it is impossible to reach the proximal
area without cutting occlusal surface, otherwise
adjacent tooth is cut
But if adjacent tooth is missing, one can gain entry
to proximal box without cutting the occlusal surface
Q.33 What is meant by cuspal contour?
Ans Cuspal contour means making preparation at
uniform depth providing equal dentin thickness
between pulp and the preparation Since cusps are
conical in shape, if pulpal floor is made straight it
may result in uneven dentin thickness The areas
where less of dentin is present, preparation will be
closer to pulp, resulting in its damage
Q.34 Why should not preparation have sharp angles?
Ans If preparation has sharp angles, it leads to
concentration of stresses at those areas which
may fracture the restoration So to avoid stress
concentration, preparation should have gentle
curves and smooth walls
Q.35 What is significance of stress bearing areas?
Ans When opposing teeth come in contact, they contact
only some areas of occlusal surfaces These areas
where they contact are stress bearing areas
Significance: Preparation margins should not end
at stress bearing areas otherwise stresses are met
partially by the tooth and partially by restoration
resulting in separation between the two This can
fracture the restoration or may result in marginal
leakage So preparation margin should be avoided
at stress bearing areas They should be kept entirely
either on tooth surface or on restorative material
Q.36 How is outline form affected by direction of
enamel rods?
Ans. &OBNFM SPET FYUFOE QFSQFOEJDVMBS GSPN %&+ UP
enamel in a slightly wavy course In vertical direction,
whereas they diverge as they move towards cusp tip
GSPNUIF%&+
%&+UPXBSETPVUFSTVSGBDF
Because of the direction of enamel rods, following walls are flared externally:
1 Buccal and lingual walls of proximal box
FTJBM BOE EJTUBM XBMMT PG CVDDBM BOE MJOHVBM
boxes of class I extensions
3 All walls of class V preparation
If these walls are made to converge towards each
other, this will result in unsupported enamel rods which may fracture later on
Q.37 How does esthetics affect outline form?
Ans
intact
r 1SFQBSBUJPO NBSHJOT TIPVME CF LFQU JOUP
embrasures for better esthetics
r 3FWFSTFDVSWFJTHJWFOJONBYJMMBSZQSFNPMBST
Q.38 How does age affect outline form?
Ans Because of presence of deep pits and fissures, young
teeth are more caries prone, therefore for a young patient, a conventional preparation is indicated
For older patients, a conservative preparation
is indicated In these patients teeth become less susceptible to caries because of following reasons:
a Attrition of teeth
b Cumulative effect of fluoride from food, water supply, dentifrices, etc
c Older patient may follow oral instructions better
Q.39 Define resistance form.
Ans It is that shape and placement of preparation
walls to best enable both the tooth and restoration
to withstand, without fracture the stresses of masticatory forces delivered principally along long axis of the tooth
Q.40 What are factors affecting resistance form?
Ans. r "NPVOUPGPDDMVTBMTUSFTTFT
r 5ZQFPGSFTUPSBUJPOVTFE
r "NPVOUPGSFNBJOJOHUPPUITUSVDUVSF
Q.41 What is extension for resistance?
Ans When outline is extended for reinforcing the
weakened tooth structure, it is referred as extension for resistance For example, when preparation involves more than one-half of the cusp, outline
is extended in which cusp is reduced and cuspal coverage is done
Trang 19Q.42 Why is floor of preparation made perpendicular
to occlusal forces?
Ans When masticatory forces are applied perpendicular
to floor, there is equal and opposite force offered by
preparation floor to resist the masticatory forces
If pulpal floor is made at an angle, it will split
occlusal forces into two components:
a Perpendicular component which is resisted
by occlusal forces, this helps in seating of the
restoration
b Lateral component of force along the surface of
floor
Q.43 Is pulpal floor always horizontal?
Ans No the mandibular premolar has a lingual tilt, so the
pulpal floor is also made with lingual tilt
Q.44 Why should a restorative material have bulk?
Ans To have resistance form a restorative material should
have sufficient bulk, for example for amalgam, at
MFBTUmNNPGEFQUIJTSFRVJSFE
Q.45 Why should be unsupported enamel removed
from the preparation?
Ans If enamel is not supported by dentin, it can fracture
by masticatory forces because of its brittle nature
Q.46 What is as isthmus and its significance?
Ans Isthmus is the narrow connection between two
portions of a preparation (occlusal and proximal)
Most of the restoration failures occur at isthmus
area If it is very narrow, restoration will be very weak
at that area If isthmus is very wide, the remaining
tooth structure will become very weak
Q.47 When should two adjacent preparation be
connected??
Ans If healthy tooth structure between two preparations
are joined to form one large preparation For
example, mesial and distal pits of maxillary first
molar
Q.48 What is retention form?
Ans It is that form, shape and configuration of the tooth
preparation that resists the displacement or removal
of restoration from the preparation under lifting and
tipping masticatory forces
Q.49 Classify retention form
Ans. r *U NFBOT JOUFSOBM PVUMJOF GPSN JT HSFBUFS UIBO
external outline form with pulpoocclusal convergence of the preparation walls
r *U JT JOEJDBUFE GPS JODSFNFOUBMMZ BEEFE EJSFDU
restoration material like amalgam
Q.54 How does dentin help in retention?
Ans Due to elastic nature of dentin, there is microscopic
movement of dentinal walls (away from each other) when a restorative material is being condensed in the preparation Once the restorative material sets, dentin comes back to its original position resulting
in better retention and more gripping action
Q.55 What is significance of dovetail?
Ans It helps in retention in proximal direction In other
words, dovetail holds the proximal restoration from dislodging proximally
Q.56 What is undercut?
Ans Undercut is a mode of retention which is prepared
with an inverted cone bur in line angles of the preparation While preparing undercut, one should take care to make the cut in the wall and not into the floor While restoration, one should take care that
Trang 20only the restorative material should be filled in the
undercut area, and not the base
Q.57 What are secondary means of retention?
Q.58 What is convenience form?
Ans The convenience form is that form which facilitates
and provides adequate visibility, accessibility and
ease of operation during preparation and restoration
of the tooth
Q.59 What is meant by convenience for access?
Ans In case of class II and III preparations, due to
presence of adjacent tooth, one has to cut the
occlusal or labial surface This outline for gaining
access to carious lesion is called as convenience for
access
Q.60 What do you mean by removal of remaining
caries?
Ans In some teeth, if any caries remain on the deeper part
of preparation after gaining resistance and retention
form, these are removed carefully without causing
any harm to pulp If attempts are made for complete
caries removal at the initial stages only, one might
end up for over cutting so it is always advised to
incorporate retentive and resistance features before
complete caries removal is done
Q.61 Which instrument is used for removal of
remaining caries?
Ans r -PXTQFFEIBOEQJFDFXJUIUIFSPVOECVS
r 4QPPOFYDBWBUPS
Q.62 Difference between affected and infected dentin?
Ans Infected dentin:
Ans Use slow-speed handpiece with the round bur or
spoon excavator that will fit in the carious lesion used with light force and a wiping motion
Forces for removal of infective dentin should be
directed laterally and not towards the center of the carious lesion
Q.64 Which instrument is used for removal of unsupported enamel rods ?
Ans Chisel, hoe or hatchet is used for removal of
unsupported rods
Q.65 For smoothening the gingival seat which instrument is used?
Ans GMT is used for making gingival seat
Q.66 How do you check convenience form?
Ans After tooth preparation, insert the small amalgam
condenser into all parts of preparation If even the small instrument does not enter some parts of tooth preparation, tooth preparation is widened
Q.67 Is breaking of contact also required for insertion
of matrix band?
Ans No, the main reason for breaking a contact is to bring
the preparation margins in self cleansable area For matrix band insertion, teeth can be separated using separators rather than cutting natural teeth structure
Q.68 For preparations near gingival margins, where should be gingival seat located?
Ans As we know gingival area is a delicate area, any
irritant present at tooth–gingival interface can cause inflammation of soft tissue and epithelial attachment One should always try to keep the gingival margins supragingivally for easy
Trang 21cleansability Subgingival margins are given only
Q.70 Why are marginal ridge/transverse or oblique
ridges preserved during tooth preparation?
Ans Since ridges are the strongest areas with high density
of dentin as compared to others, these act as stress
bearing areas and thus, need to be preserved
Q.71 What is minimal gingival clearance between teeth
in class II tooth preparation?
Ans. NN
Q.72 What is minimal facial and lingual clearance
between teeth in class II tooth preparation?
Ans. mNN
Q.73 Why should be the contact point broken in class II
preparation?
Ans Contact has to be broken so as to bring cavity
margins outside the contact area into the embrasure
both occlusogingivally and buccolingually for easy
cleansability If contact area is not broken, it can
lead to debris accumulation and therby secondary
caries
Q.74 What are stress bearing areas in cavity
preparation?
Ans During occlusion, some areas of occlusal surface
come in contact either in centic or eccentric
position, these are stress bearing areas
Significance: Cavity margins should not be placed
on stress bearing areas as this may lead to stress
distribution both to tooth and restoration resulting
in their separation
Q.75 Why should not the pulpal floor be placed on
DEJ?
Ans Because of branching of dentinal tubules and
cytoplasmic branches, this area is very sensitive, so QVMQBMëPPSTIPVMECFBWPJEFEPO%&+
Q.76 What should be the width of gingival seat?
Ans. NNNNJOFOBNFMBOENNJOEFOUJO
Q.77 What is ideal depth of tooth preparation for amalgam restoration? What happens with increase or decrease in depth?
Ans. mNN *G NN *OBEFRVBUF TQBDF GPSamalgam: poor resistance and retention form If
NN 3FTVMUT JO EFDSFBTFE SFNBJOJOH EFOUJOthickness: increased sensitivity and post operative pain
Q.78 What is ideal width of tooth preparation for amalgam restoration? What happens with increase or decrease in width?
Q.80 Where should be the gingival seat placed in class
II tooth preparation?
Ans It is placed below contact point so as to break contact
with the adjacent tooth and to have restoration with self cleansable margins
Q.81 What will happen if gingival seat is placed very shallow at the same level with pulpal floor?
Ans Inadequate removal of the proximal carious lesion
and inadequate retention form
Q.82 What should be the clearance from adjacent tooth
in class II tooth preparation?
Ans. NN$MFBSBODF NNFYDFTTJWFMPTTPGUPPUIstructure, unesthetic display of amalgam facially and chances of damaging interdental gingival
$MFBSBODF NNJOBEFRVBUFDBSJFTSFNPWBMBOEdifficulty in placement of matrix band
Trang 22Tooth Preparation for Amalgam and Composite Restorations
9
Introduction
Preparation for Amalgam Restoration
t Class I Tooth Preparation
t Class II Tooth Preparation
t Class V Tooth Preparation
Tooth Preparation for Composite Restoration
t Class III Tooth Preparation t Class IV Tooth Preparation t Class V Tooth Preparation t Class I Tooth Preparation t Class II Tooth Preparation
Viva Question
CHAPTER OUTLINE
INTRODUCTION
As we know tooth preparation is mechanical alteration of
a defective, injured or diseased tooth structure to receive
a restorative material which will best return the tooth
and area to proper form, function and esthetics We have
already discussed fundamentals of tooth preparation in
chapter 9 In this chapter, we will discuss class I to V tooth
preparation for amalgam and composite
PREPARATION FOR AMALGAM
RESTORATION
Class I Tooth Preparation
Class I caries are caries occurring in pits and fissures of the
occlusal surfaces of premolars and molars, the occlusal
two-third of buccal and lingual surfaces of molars and
lingual surface of incisors
Outline Form
r Take No 245 bur for tooth preparation Its dimensions
help in guiding ideal tooth preparation, i.e depth of
tooth preparation 1.5 mm (half the length of bur, i.e
3mm), to preserve marginal ridge width 1.6–2 mm
(double the width of bur, i.e 0.8mm), rounded internal
line angles and convergent external walls (due to pear
shape with rounded corners of the bur) (Fig 9.1)
r Keep 245 bur parallel to the long axis of the tooth
structure to make a ditch in carious lesion (Figs 9.2
and 9.3)
Figure 9.1: Photograph showing No 245 bur It’s dimensions and
shape guide the tooth preparation viz; depth of 1.5 mm (half the length of bur), marginal ridge width of 1.6–2 mm (double the width), rounded internal line angles and convergent external walls (due to pear shape with rounded corners)
Nisha Garg, Poonam Bogra
Trang 23Figure 9.2: Schematic representation showing no 245 bur oriented
parallel to long axis of tooth crown for entry Dotted line indicates the
long axis of tooth crown and the direction of the bur
Figure 9.5: Schematic representation showing mesiodistal section
depicting flat pulpal floors but may follow the rise and fall of the clusal surface
oc-Figure 9.6: Schematic representation of tooth preparation showing
convergent buccal and lingual walls for retention form
Figures 9.7A and B: Schematic representation showing removal of
remaining caries Remove only deep carious lesion with the help of spoon excavator or round bur instead of deepening of whole floor
Figure 9.4: Schematic representation showing that minimal
width of the marginal ridge should be 1.6mm Incline the bur
dis-tally to establish proper occlusal divergence to proximal wall to
pre-vent removal of the dentin supporting the marginal ridge enamel
Figure 9.3: Schematic representation of punch cut of 1.5–2 mm
into the central fissure
Trang 24r Initial punch cut should be 1.5 mm deep While
maintaining the same depth and bur orientation, move
the bur to extend the outline to include the central
fissure Width of the cavity should be 1/3rd–1/4th of
intercuspal distance
r Extend the margin mesially and distally but do not
involve marginal ridges While working towards mesial
and distal surface, orient the bur towards respective
marginal ridge This results in slight divergence of
mesial and distal walls which helps to provide dentinal
support for marginal ridges (Fig 9.4).
Primary Resistance Form
Check for following features to have resistance form for
amalgam restoration
r Box-shaped preparation with flat floor (to resist
occlusal masticatory forces without any displacement)
(Fig 9.5)
r Minimum depth of preparation 1.5–2.0 mm
r Rounded internal line angles
r 90° cavosurface angle (butt joint)
r Strong marginal ridge areas with sufficient dentin
support
r Inclusion of all weakened tooth structure
r Cusp capping for preserving cuspal strength
Primary Retention Form
Check for following features to have retention form for
It is checked by moving a condenser in the cavity It should
be able to pass the preparation even in its narrowest
portion
Final Tooth Preparation
To remove remaining caries, use spoon excavator or slow-
speed round bur Remove only that portion of the tooth
which is affected by caries leaving the remaining floor
untouched (Fig 9.7).
Preparation of Buccal Pit for Mandibular Molars
r Keep no 245 perpendicular to the tooth surface (Fig 9.8)
r Make a depth cut 1.5 mm deep into the dentinr Extend the outline form for convenience form and to remove remaining caries, if present
r Prepare undercut in dentin using no.1/4 burr In case of occlusobuccal or occlusopalatal extension, after completing the occlusal preparation, the inclination of bur is changed to establish the correct axial wall depth.The axial wall depth should be 0.2–0.5
mm into the dentin (Fig 9.9)
r Figures 9.8 to 9 16 are showing class I tooth
prepara-tions on plaster models
Class II Tooth Preparation
Class II restoration involves the proximal (mesial or distal) surfaces of premolars and molars
Outline form
Occlusal Preparation
r Occlusal portion is prepared same as that for pit and fissure caries except that outline is extended proximally
towards defective proximal surface (Fig 9.17)
r Prepare occlusal dovetail in unaffected proximal margin It prevents displacement of the restoration to the affected proximal side
Preparation of Proximal Box
r While maintaining established pulpal depth, extend the preparation towards proximal surface of tooth, ending 0.8 mm short of cutting through affected marginal ridge r Keep the bur on DEJ in the pulpal floor adjacent to affected proximal side It should be placed 2/3rd in dentin (0.5 mm) and 1/3rd in enamel (0.3 mm) (Fig 9.18)
r Prepare reverse curve specially in teeth with broader contacts It is given to the proximal walls by curving them inwards towards the contact area Reverse curve helps in conserving the tooth structure Moreover, flare
of the proximal wall leaves tangent to that outer tooth surface at 90° angle, this further increases the resistance form
r Create a proximal ditch cut by moving the bur gingivally Keep a small slice of enamel at the contact area to
prevent accidental damage to adjacent tooth (Fig 9.19)
Trang 25Figures 9.8:A to C: Photograph showing (A) Mandibular molar
show-ing carious buccal pit; (B) Position of bur perpendicular to the tooth
surface for entry; (C) Outline form of buccal pit
Figures 9.10A and B: Photograph showing (A) Outline form of class I
preparation in mandibular molar; (B) Class I tooth preparation in
man-dibular molar
Figures 9.11A and B: Photograph showing (A) Outline form of class
I preparation in mandibular premolar; (B) Tooth preparation in dibular premolar
Figure 9.13: Photograph showing (A) Outline form of conservative
tooth preparation of mandibular premolar (B) Outline form of tional tooth preparation of mandibular premolar
Figures 9.12A and B: Photograph showing; (A) Carious palatal pit;
(B) Outline form of palatal pit in maxillary lateral incisor
Figure 9.9: Schematic representation showing that in occlusobuccal
tooth preparation, after occlusal preparation, inclination of the bur is
altered to establish the correct axial wall depth (0.2–0.5 mm into the
dentin)
Trang 26Figure 9.15: Photograph showing outline form of maxillary first
molar with carious distal pit involving palatal fissure
Figures 9.16A and B: Photograph showing (A) Outline form of
buc-cal pit extension of mandibual molar; (B) Photograph showing tooth
preparation of buccal pit extension of mandibular first molar
r Move the bur faciolingually to just clear the contact areas and diverge the proximal cut gingivally It results in greater faciolingual dimension at gingival surface than occlusal surface (provide retention and conservation of
marginal ridge) (Fig 9.20)
r Gingival floor should be located below contact point
so as to have clearance from the adjacent tooth and
to have margins of restoration self cleansable Ideal clearance of facial and lingual margins of the proximal
box should be 0.2–0.5 mm from the adjacent tooth (Fig
9.21) Wedge is kept in the gingival embrasure area
while preparing proximal box to protect interdental gingival tissue
r Fracture the slice of enamel in the region of the contact area with a small chisel or enamel hatchet
r With the help of gingival marginal trimmer round off the axiopulpal line angle (to avoid stress concentration) and bevel the gingival margin (to remove unsupported
enamel margins) (Fig 9.22).
Primary Resistance Form
Include following features to have retention form for amalgam restoration:
r Box-shaped preparation with flat pulpal and gingival floor
r Rounded axiopulpal angler Bevelled gingival marginr Reverse curve
r Inclusion of all weakened tooth structurer Cusp capping for preserving cuspal strength
Primary Retention Form
Include following features to have retention form for amalgam restoration:
r Occlusal convergence of buccal and lingual wallsr Occlusal dovetail
Convenience Form
r It is checked by moving a condenser in the cavity
It should be able to pass the preparation even in its narrowest portion
Final Tooth Preparation
r To remove remaining caries, use spoon excavator or slow-speed round bur Remove only that portion of the tooth which is affected by caries leaving the remaining floor untouched
Figures 9.14A to C: Photograph showing maxillary first molar
(A) Outline form for conservative tooth preparation; (B) Outline form
for conventional tooth preparation involving oblique ridge; (C)
Out-line form for conventional class I involving palatal fissure
Trang 27Figures 9.17A and B: Schematic representation showing that Class II
preparation outline form of the cavity is similar to class I Make entry with
no.245 bur parallel to long axis of the tooth and prepare class I cavity
Figure 9.18: Schematic representation showing how bur is to be kept
DEJ, 0.5 mm in dentin 0.3 mm in enamel to create a proximal ditch cut
by moving the bur gingivally
Figure 9.19: Schematic representation showing that a small slice of
enamel is to be kept at the contact area to prevent damage to adjacent
tooth
Secondary retention and resistance form
r Place retention grooves and locks in the proximal box
(Fig 9.23)
r If required, place slots and pot holes in gingival floor
Modifications in Class II Design
Factors affecting modifications in Class II preparations:
Figure 9.20: Schematic representation showing that greater
facio-lingual dimension at gingival surface than occlusal surface provides retention form
Figure 9.21: Schematic representation showing that there should be
0.2–0.5 mm clearance of facial and lingual margins of the proximal box from the adjacent tooth
r Extent of caries: For extensive caries, complex amalgam restorations and full coverage restorations are indicated
In small proximal caries, only proximal box can dor Esthetic requirement: In maxillary premolars, minimal facial extension is done so as to display less amalgamr Relationship with adjacent tooth: If adjacent tooth is missing, slot preparations can be done
r Rotated teeth: Here preparation is modified according
to contact with adjacent tooth
Figures 9.22A and B: Schematic representation showing rounding
off of the axiopulpal line angle and bevelling of gingival margin
Trang 28Following modifications can be made in class II design
(Fig 9.24):
r Slot preparation
r Simple box preparation
r Tunnel preparation
Figures 9.25 to 9.28 are showing class II tooth
preparation on plaster models
Class V Tooth Preparation
Class V lesion is present on the gingival third of facial and
lingual surfaces of all teeth Amalgam is not indicated for
anterior teeth except when esthetics is least concerned
Initial Tooth Preparation
r Outline form is dictated by extension of caries Outline
resembles kidney or bean shape (Fig 9.29)
r Preparation is started using 169L or 271 tapered-fissure
bur keeping perpendicular to long axis of tooth
r Initial axial wall depth is maintained 0.5 mm into the
dentin Axial wall depth at the occlusal wall should be
more than that at the gingival wall This results in a
convex axial wall as the contour of tooth
Figures 9.24A to C: Schematic representation of modifications in class II design; (A) Slot preparation; (B) Simple box preparation;
(C) Tunnel preparation
Figures 9.23A and B: Schematic representation showing the
retention grooves and locks in the proximal box
Figures 9.25A and B: Photograph showing (A) Outline form of class II
tooth preparation of maxillary premolar; (B) Class II tooth preparation
of maxillary premolar
Figures 9.26A and B: Photograph showing (A) Outline form of class
II tooth preparation of mandibular molar; (B) Class II tooth preparation
of mandibular molar
Trang 29r Extend the preparation incisally, gingivally, mesially and distally till the cavosurface margins are placed on sound tooth structure.
Final Tooth Preparation
r Remove any remaining caries using a round burr Retention is achieved by giving grooves incisally and gingivally along axioincisal and axiogingival line angles using an inverted cone bur
r Use hoe and chisel to finish the mesial, distal and gingival walls
TOOTH PREPARATION FOR COMPOSITE RESTORATION
Things to be kept in mind while doing tooth preparation for composite restoration:
r Retention comes primarily from micromechanical mode of retention (bonding to enamel and dentin)r Flat pulpal floor, or wall surfaces not as critical as for amalgam restoration
r Retention grooves not necessary unless margin is on root surface or preparation is very large
r 90 degree or greater (beveled) cavosurface marginsr Isolation is extremely important Use rubber damn especially when restoring
Class III Tooth Preparation
Class III preparations are present on proximal surface of anterior teeth and not involving the incisal angles
For gaining entry into the lesion, bur is entered from palatal side
Advantages of palatal access:
r Preservation of estheticsr Color matching not critical r Unsupported facial enamel can be preserved for bonding with composite resin
Indications for labial approach
r Involvement of labial enamelr Rotated teeth where lingual approach is difficultr Malaligned teeth
Conventional Class III Tooth Preparation
Indication
r Lesion present on the root surfacer Tooth preparation on root is done in conventional method whereas on the crown, it is prepared in beveled conventional or modified type
Figure 9.27: Photograph showing; (A) Outline form of class II cavity in
maxillary 1st molar; (B) Class II tooth preparation of maxillary 1st molar
Figures 9.28A and B: Photograph showing (A) Outline form of MOD
tooth preparation of mandibular molar; (b) MOD tooth preparation of
mandibular molar
Figure 9.29: Photograph showing kidney-shaped class V tooth
preparation of mandibular incisor
Trang 30Outline form
r Outline form depends on extent of caries and
convenience form
r Approach carious area palataly with no ½, 1 or 2
round bur and move the bur in incisogingival direction
(Fig 9.30) Initial depth of axial wall should be 0.75
mm deep gingivally and 1.25 mm deep incisally This
results in the axial wall depth of 0.5 mm into the dentin
Primary Resistance and Retention form
r Conventional preparation is done with 90 degrees
cavosurface margins (Fig 9.31)
r If required, prepare retentive grooves and coves along
gingivoaxial line angle and incisoaxial line angle,
respectively, with the help of no 1/4 or 1/2 round burs
Depth of these grooves should be 0.2–0.5 mm into the
dentin
Retention in conventional tooth preparation is attained
by—
r Roughening of the preparation surface
r Parallelism or convergence of opposing external walls
r Giving retention grooves and coves
r Grooves should be located at least 1 mm from tooth
surface and at least 0.5 mm deep into dentin
Beveled Conventional Class III Tooth Preparation
Indications
r For replacing an existing defective restoration on crown
portion of an anterior tooth
r For restoration of large preparations
Steps
r Approach carious area lingually with a no ½, 1 or 2
round bur and move the bur in incisogingival direction
r Shape of the tooth preparation should be identical to
the shape of existing carious lesion
Figure 9.30: Schematic representation showing presentation with
round bur palataly and movement of the bur in incisogingival direction
r Initial depth of axial wall should be 0.75 mm deep gingivally and 1.25 mm deep incisally This results
in the axial wall depth of 0.2–0.5 mm into the dentin Axial wall should follow the contour of tooth, i.e shape
of axial wall should be convex outwardlyr In final tooth preparation, remove all remaining infected dentin or defective restoration using spoon excavator or slow-speed round bur
r Keep external walls of tooth preparation perpendicular
to the enamel surface with all enamel margins beveled Prepare bevels using flat end tapering fissure diamond bur at cavosurface margins Bevel should be 0.2–0.5
mm wide at an angle of 45 degree to external tooth
Figure 9.31: Schematic representation showing that conventional
preparation is done with 90 degrees cavosurface margins Axial wall should be 0.2 mm into the dentin
Figures 9.32A and B: Schematic representation showing bevelled
preparation: Bevel should be 0.2–0.5 mm wide at an angle of 45 gree to external tooth surface
Trang 31Figure 9.33: Schematic representation showing modified tooth
preparation: ‘Scooped-out’ appearance
Figures 9.34A and B: Schematic representation showing beveled
Class IV preparation
Modified (Conservative) Class III Tooth Preparation
It is the most conservative type of tooth preparation used
for composites
Indication
r Small to moderate class III lesion
r In this tooth preparation, basically infected carious area
is removed as conservatively as possible by “scooping”
out This results in ‘scooped-out’ or ‘concave’
appearance of the preparation (Fig 9.33).
Steps
r Make initial entry through palatal surface with a small
round bur
r Design and extent of preparation is determined by
extent of carious lesion
r Modified preparation does not have definite axial wall
depth and walls diverge externally from axial depth in a
scoop shape
r Finally check the preparation after cleaning and provide
pulp protection
Class IV Tooth Preparation
Class IV preparations are present on proximal surface of
anterior teeth involving the incisal angles
Conventional Tooth Preparation
Features of Conventional Class IV Preparation for
Composites
r Box-like preparation with facial and lingual walls
parallel to long axis of tooth
r Retention obtained by means of dovetail or grooves
placed gingivally and incisally in the axial wall using
number 1/4 round bur
Beveled Tooth Preparation
Beveled preparation is indicated for treatment of a large
lesion Initial axial wall depth should be kept 0.5 mm into
dentin Bevels are prepared at 45 degree angle to tooth
surface with a width of 0.25–2 mm, depending on the
amount of retention required (Fig 9.34).
Modified (Conservative) Tooth Preparation
Modified class IV preparation is done in small class
IV lesions or for treatment of small traumatic defects
Preparation for modified class IV preparation should be
done conservatively without removing the normal tooth
structure (Fig 9.35).
Figures 9.35A and B: Schematic representation showing
conserva-tive class IV tooth preparation for composite
B A
Figure 9.36: Schematic representation showing conventional class V
tooth preparation for composites
Trang 32Class V Tooth Preparation
Conventional Tooth Preparation
Indication
r If caries is present completely or mainly on root surface
r If lesion is partly on crown and partly on root, then
crown portion is prepared using beveled conventional
or modified preparation design and the root surface
lesion is prepared by conventional method
Steps of Tooth Preparation
In conventional class V tooth preparation, shape of the
preparation is kidney shaped (Fig 9.36).
1 Isolate the area and use tapered fissure bur to make
entry at 45 degree angle to tooth surface initially
2 After this, keep long axis of bur perpendicular to the
external surface in order to get a cavosurface angle of 90
degree
3 During initial tooth preparation, keep the axial depth of
0.75 mm into the dentin
4 After achieving the desired distal extension, move the
bur mesially, incisally (occlusally) and gingivally for
placing the preparation margins onto the sound tooth
surface while maintaining a cavosurface margin of 90
degree
5 Axial wall should follow the contour of facial surface
incisogingivally and mesiodistally
6 During final tooth preparation, remove any remaining
infected dentin, restoration material using spoon
excavator or slow-speed round bur
7 If additional retention is required, place retention
grooves all along the whole length of incisoaxial and
gingivoaxial line angles using a no 1/4 or 1/2 round
bur 0.25 mm deep into the dentin At this stage, all the
external walls appear outwardly divergent
Beveled Conventional Tooth Preparation
Indications
1 For replacing defective existing restoration
2 For restoring a large, carious lesion
– Initial axial wall depth should be limited to only 0.25
mm into the dentin, when retention grooves are not
placed and 0.5 mm when retention groove is placed
– After this, bevel the enamel margins 0.25–0.5 mm
wide at 45 degree to external surface When class
V lesion extends onto the root surface, gingival
preparation has conventional class V design with the
initial axial depth of 0.75 mm Beveling is done only
on enamel cavosurface margins (Fig 9.37)
Figure 9.37: Schematic representation showing beveled class V
walls and axial wall either in enamel or dentin (Fig 9.38).
Class I Tooth Preparation
r Fundamentals of tooth preparation are similar to that
of amalgam except for following differences (Fig 9.39)
r Small faciolingual dimensions of preparation (¼th of intercuspal distance)
r No need to prepare dovetail or other retention featuresr Flame-shaped diamond instruments are used to bevel the enamel cavosurface margins Bevel is 0.5 mm wide placed at 45 degrees to external enamel surface
Trang 33r If the marginal ridge is not supported by dentin,
remaining weakened enamel may be left, provided
there is no heavy centric contact on this area
r Unsupported marginal ridge will be strengthened by
composite restoration
Class II Tooth Preparation
Steps
r Use No 330 or 245 pear-shaped bur parallel to long axis
of the tooth to start preparation in a pit opposite to the
affected proximal side
r Keep the outline as conservative as possible Maintain
the depth of pulpal floor 1.5 mm from central groove
area Make the occlusal walls converging and occlusal
cavosurface obtuse (Fig 9.40)
r For proximal box preparation, extend the occlusal
preparation using straight fissure bur into marginal
ridge Keep bur perpendicular to the pulpal floor
r Thin out the marginal ridge and deepen the preparation
towards the gingival direction as to give proximal ditch
cut This will form the width of 1.0–1.5 mm
r For small carious lesion, proximal walls can be left in
the contact but for large carious lesion, contact area is
broken
r Keep gingival floor flat with butt joint cavosurface angle
Whether or not to give gingival beveling, depends on
location and the width of gingival seat If gingival seat
is supragingival and above cementoenamel junction,
beveling can be done but if gingival seat is close to
cementoenamel junction, beveling is avoided so as to
preserve the enamel present in this area
Features of Class II Composite Tooth Preparation
r Decreased pulpal depth of axial wall which allows
greater conservation of tooth structures
r Occlusal and proximal walls converge occlusally and provide additional retention form
r Proximal box preparation has cavosurface angle at right angles to the enamel surface facially and linguallyr Gingival floors should clear the contact apically and they should be butt joined
VIVA QUESTIONS
Q.1 What is class I tooth preparation?
Ans Class I preparations occur on the occlusal surfaces
of premolars and molars, the occlusal two-third of buccal and lingual surface of molars and lingual surface of incisors
Q.2 What is class II tooth preparation.
Ans Class II preparations occur on the proximal surface
of premolars and molars
Q.3 Define class III tooth preparation.
Ans Preparations on the proximal surface of anterior
teeth and not involving the incisal angles are class III
Q.4 Define class IV tooth preparation.
Ans Preparations on the proximal surface of anterior
teeth also involving the incisal angle falls under class IV
Q.5 Define class V tooth preparation.
Ans Preparations on gingival third of facial and lingual
or palatal surfaces of all teeth came under Class V
Q.6 What is ideal depth of amalgam cavity?
Ans 1.5–2.0mm total depth 0.2–0.5mm into the dentin.
Q.7 What should be the isthmus width of amalgam cavity?
Ans 1/4th of intercuspal distance.
Figure 9.40: Schematic representation showing class II tooth
prepa-ration for composites
Figure 9.39: Schematic representation of class I tooth preparation
for composite restoration
Trang 34Q.8 What is extension for prevention?
Ans Given by GV Black, it advocates involvement of all
pits and fissures to bring the preparation margins
into self cleanseable areas
Q.9 Why should preparations not have sharp angles?
Ans Sharp angles of preparation lead to stress
concentration at these areas which may result in
restoration fracture
Q.10 What is resistance form.
Ans It is that shape and placement of preparation
walls to best enable both the tooth and restoration
to withstand, without fracture the stresses of
masticatory forces delivered principally along long
axis of the tooth
Q.11 Why should a preparation have flat floor?
Ans When masticatory forces are applied perpendicular
to floor, there is equal and opposite force offered by
preparation floor to resist the masticatory forces
Q.12 What is an isthmus?
Ans Isthmus is the narrow joint between occlusal and
proximal part of tooth preparation
Q.13 What is retention form?
Ans It is that form, shape and configuration of the tooth
preparation that resists the displacement or removal
of restoration from the preparation under lifting and
tipping masticatory forces
Q.14 How is retention achieved in amalgam
Q.15 What is importance of dovetail?
Ans Dovetail holds the proximal restoration from
dislodging proximally
Q.16 How are remaining caries removed from prepared
tooth?
Ans With the help of low-speed handpiece using round
bur and spoon excavator in lateral scrapping
motion
Q.17 Which instrument is used for smoothening of
gingival seat?
Ans Gingival marginal trimmer.
Q.18 How is convenience form checked?
Ans Insert the small end of amalgam condenser into
prepared tooth It should be able to enter all parts of the preparation
Q.19 What is the main reason for breaking a contact in class II preparation?
Ans To bring the preparation margins in self cleansable
Q.21 What is minimal gingival clearance between teeth
in class II tooth preparation?
Ans 0.5mm.
Q.22 What should be the width of gingival seat?
Ans 0.8mm.i.e 0.3 mm in enamel and 0.5mm in dentin.
Q.23 What are differences in cavity preparation for amalgam and composite resin
Outline form r *ODMVEFBMMQJUTBOE
r 'PSDMBTT**UPPUI
DPOUBDUOFFEOPUCF CSPLFOJOBMMUIFDBTFT 1VMQBMEFQUI r 4IPVMECFNBJOUBJOFE
retention form
Ans 1 For replacing defective existing restoration.
2 For restoring a large, carious lesion
Trang 35Tooth Preparation for Primary Teeth
10
Introduction
Rationale for Tooth Preparation
Principles of Tooth Preparation
Classification of Dental Caries
Tooth Preparation
Matrix Bands and Retainers
Steps for Amalgam Restoration for Primary Teeth
Viva Question
Chapter Outline
IntroductIon
According to American Academy of Pediatric Dentistry
(AAPD) guidelines, tooth preparation should include
the removal of caries or improperly developed or
unsound tooth structure to establish appropriate outline,
resistance, retention and convenience form compatible
with the restorative material to be utilized The decision
to use amalgam should be based upon the needs of each
individual patient Amalgam restorations often require
removal of healthy tooth structure to achieve adequate
resistance and retention Glass ionomer or resin restorative
materials might be a better choice for conservative
restorations, thereby retaining healthier tooth structure
ratIonale for tooth preparatIon
• Restoration of carious teeth
• Treatment of malformed, fractured or traumatized teeth
• Replacement of old, defective restorations
• Esthetic improvement for discolored and unesthetic teeth
prIncIples of tooth preparatIon
• Removal and inclusion of carious areas
• Susceptibility of remaining tooth structure to be involved
• Preservation of sound tooth structure
Restoration of deciduous teeth is a challenge for the dentist because of the following reasons:
• Compromised retention form: Early spread of caries
in primary teeth leads to loss of major part of tooth structure This compromises retention form
• Modifications in cavity designs: Different anatomical
and morphological features make cavity preparation different
• Behaviour management: Children in dental operatory
behave differently Therefore, behavior problems can result in inefficient dental care
Usually, a primary tooth is smaller form of its counterpart permanent tooth, but there are some anatomic and histological differences between the two which demand special type of restorative care
Basic differences in primary and permanent dentitions affecting tooth preparation
in primary teeth
• Shorter clinical crown: Cervicoincisal length is smaller
than mesiodistal diameter in primary teeth, whereas the converse is true in permanent teeth (Fig 10.1).
Clinical significance: It affects the ability of primary
teeth to adequately support and retain intracoronal restorations
Madhu Garg, Priya Verma Gupta, Bhumika Ahuja
Trang 36• Thin enamel: Enamel has around 1 mm thickness in
primary teeth as compared to 2–3 mm in permanent
teeth
Clinical significance:
– Small burs used
– Less pressure is applied during tooth preparation
• High pulp horns:
Pulp horns in primary teeth are more near to the surface
than permanent teeth (Fig 10.2)
Clinical significance:
– Spread of dental caries is faster with early pulpal
involvement
– Tooth preparation has to be more conservative to
avoid pulp involvement
– Isthmus must be narrow to avoid pulp exposure
– To reduce failure of restorative material, pulpoaxial
line angle is deepened to increase bulk of material
• Less mineralized enamel and dentin: Enamel
and dentin are less mineralized in primary teeth as
compared to permanent teeth
Clinical significance: More time is needed for acid-etching
of primary teeth Time is 45–60 seconds in primary teeth
as compared to 15–20 seconds in permanent teeth
• Direction of enamel rods: Enamel rods of primary
teeth in cervical third of the crown extend in an occlusal
direction from DEJ, whereas in permanent teeth, rods
incline in apical direction (Figs 10.3A and B).
Clinical significance: In case of permanent teeth,
gingival bevel is given in class II restoration to remove
unsupported enamel rods but there is no requirement
of a gingival bevel in primary teeth, since there is little
danger of rods being unsupported
• Marked cervical constriction: There is a marked
cervical constriction in primary teeth (giving them bell
shaped appearance) which is lacking in permanent
teeth (Fig 10.4).
Clinical significance:
– Tendency to make floor of box too deep
– Forces to re-establish floor by moving axial wall
towards pulp
– Due to exaggerated cervical bulge, matrix adaptation
is difficult It requires the construction of a custom
matrix to fit the teeth
• Broad, flat proximal contact areas: Primary teeth have
broad, flat proximal contact areas Moreover, contact
areas are situated gingivally
Clinical significance:
– Proximal box has to be wider so as to make buccal and
lingual line angles of the proximal box self-cleansable
figures 10.1a and B: Schematic representation showing mesiodistal
dimensions of primary teeth (A) are more than permanent teeth (B)
figures 10.2a and B: Schematic representation showing primary
teeth (A) have high pulp horns as compared to permanent teeth (B)
figures 10.3a and B: Schematic representation showing cervical
third of the crown: (A) Enamel rods are inclined occlusally in primary teeth; (B) Rods incline apically in permanent teeth
figures 10.4a and B: Schematic representation showing primary (A)
tooth with prominent cervical bulge than permanent teeth (B)
Trang 37– Proximal box is to be extended far gingivally, so as to
clear the contact
• Narrow occlusal table: Occlusal table is somewhat
narrower in primary teeth Occlusal surfaces are much
flatter than permanent teeth (Fig 10.5).
Clinical significance:
To avoid weakening of cusps by overextending
bucco-lingual dimensions, conservative tooth preparation is
desirable
Young permanent teeth also exhibit characteristics
that need to be considered in restorative procedures, such
as large pulp chambers and broad contact areas that are
proximal to primary teeth
classIfIcatIon of dental carIes
Black’s classification
Class I: (All pit and fissure restorations)
• Restorations on occlusal surface of premolars and
molars
• Restorations on occlusal two-thirds of the facial and
lingual surfaces of molars
• Restorations on lingual surface of maxillary incisors
Class II: Restorations on the proximal surfaces of posterior
teeth
Class III: Restorations on the proximal surfaces of anterior
teeth that do not involve the incisal edge.
Class IV: Restorations on the proximal surfaces of anterior
teeth that involve the incisal edge
Class V: Restorations on the gingival third of the facial or
lingual surfaces of all teeth
Class VI: (Simon’s modification) Restorations on the
incisal edge of anterior teeth or the occlusal cusp heights
of posterior teeth
finn’s Modification
Class I: Cavities involving the pits and fissures of molar
teeth and buccal and lingual pits of all teeth
Class II: Cavities involving proximal surfaces of molars
with access established from occlusal surfaces
Class III: Cavities involving proximal surfaces of anterior
teeth which may or may not involve a labial or lingual extension
Class IV: Cavities of proximal surface of an anterior tooth
which involve restoration of an incisal angle
Class V: Cavities present on the cervical third of all teeth,
including proximal surface where the marginal ridge is not included in the cavity preparation
tooth preparatIon
class I tooth preparation
Class I caries are caries occurring in pits and fissures of the occlusal surfaces of premolars and molars, the occlusal two-third of buccal and lingual surfaces of molars and lingual surface of incisors
Outline Form
• Take no 330 bur for tooth preparation Keep it parallel
to the long axis of the tooth structure to make a ditch
in carious lesion Initial punch cut should be 1.5 mm deep Use No 330 bur’s shank as depth marker It is approximately 1.5 mm from the bur tip to the shank
• While maintaining the same depth and bur orientation, move the bur mesial and distal to extend the outline to include the central fissure Width of the cavity should
be 1/3rd of intercuspal distance
• Extend the margin mesially and distally but do not involve marginal ridges
Primary Resistance Form
• Use No 330 bur for rounding of the internal line angles These rounded line angles are easier to condense amalgam into and reduce the stress concentration
• Slightly concave or round the pulpal floor
• Minimum depth of preparation should be 1.5 mm (0.5
mm into the dentin)
• Establish sharp 90° cavosurface angle in lateral walls using No 169L bur Watch the tip of 169 L bur to prevent scoring the floor of preparation
figures 10.5a and B: Schematic representation showing primary
tooth (A) has narrow occlusal table than permanent tooth (B)
Trang 38figure 10.6: Schematic representation showing external outline
form of class I cavity of primary teeth
figure 10.7: Schematic representation showing internal outline
form of class I cavity of primary teeth
• Keep strong marginal ridge areas with sufficient dentin
support
Primary Retention Form
• Occlusal convergence of buccal and lingual walls
Convenience Form
• It is checked by moving a condenser in the cavity
It should be able to pass the preparation even in its
narrowest portion
Final Tooth Preparation
• To remove remaining caries, use spoon excavator or
slow speed round bur
• Remove only that portion of the tooth, which is affected
by caries leaving the remaining floor untouched
Figures 10.6 and 10.7 are showing external and internal
outline form of class I cavity in primary teeth
primary Mandibular first Molar
• Central pit of mandibular primary first molar is more
frequently involved than the mesial pit So the outline
form should include central pit with adjacent buccal
and lingual grooves and distal triangular fossa It
is not advised to cross the enamel ridge joining the
mesiobuccal and mesiolingual cusps (Figs 10.8A and
B) because of proximity of mesiobuccal pulp horn and
strength imparted by intact central ridge
primary Mandibular second Molar
• When buccal or lingual fissures are carious then buccal
or lingual extension is required Here the buccal
or lingual walls of the cavity should be straight and
converging occlusally (Figs 10.9A and B).
primary Maxillary second Molar
• Usual areas of involvement are central pit, distal pit,
lingual pit and the groove that separates the cusp of
Carabelli from the mesiolingual cusp
• Distal developmental groove sometimes extends
through to the lingual surface Its continuity with lingual
developmental groove and distal pit make the area
susceptible to caries This demands lingual extension of
class I cavity
figures 10.8a and B: Schematic representation showing (A) Occlusal
anatomy of primary mandibular 1st molar; (B) While tooth tion enamel ridge joining the mesiobuccal and mesiolingual cusps should not be crossed
prepara-Abbreviations: MBc, mesiobuccal cusp; cDG, central developmental
groove; DBc, distobuccal cusp; BDG, buccodistal groove; cP, central pit; DLc, distolingual cusp; LDG, linguodistal groove; MLc, mesiolin- gual groove; MP, mesial pit
• Oblique ridge of the maxillary second primary molar is not crossed when treating small lesions (Figs 10.10A and B)
• Cavity walls should be straight or converging
(Fig 10.10C).
Trang 39surface than occlusal surface (provide retention and conservation of marginal ridge)
• Axial wall should follow the contour of the tooth to avoid pulp exposure
• Gingival seat should be located below contact point so
as to have clearance form the adjacent tooth and to have margins of restoration self-cleansable Ideal clearance
of facial and lingual margins of the proximal box should
be 0.2–0.5 mm from the adjacent tooth Keep a wedge in the gingival embrasure area while preparing proximal box to protect interdental gingival tissue
• In cervical area, direction of enamel rods is horizontal
or occlusal So to have fully supported enamel rods with dentin, gingival seat should not be beveled
• Fracture the slice of enamel in the region of the contact area with a small chisel or enamel hatchet Rinse and clean the cavity
Primary Resistance Form
Include following features to have retention form for amalgam restoration:
• Rounded axiopulpal angle
• Sharp cavosurface angle of 90°
• Isthmus of 1/3rd of intercuspal width
• Inclusion of all weakened tooth structure
• Proximal box in occlusogingival direction roughly parallel to the long axis of tooth
Primary Retention Form
• Occlusal convergence of buccal and lingual walls
Convenience Form
• It is checked by moving a condenser in the cavity
It should be able to pass the preparation even in its narrowest portion
Figures 10.11 and 10.12 showing characteristic features
of external and internal outline form of class II preparation
of primary teeth
Final Tooth Preparation
• To remove remaining caries, use spoon excavator or slow speed round bur Remove only that portion of the tooth which is affected by caries leaving the remaining floor untouched
Figures 10.13A and B show class II tooth preparation
for maxillary and mandibular primary molars
figures 10.9a and B: Schematic representation showing (A) Occlusal
anatomy of primary mandibular 2nd molar; (B) class I tooth
prepara-tion in primary mandibular 2nd molar
Abbreviations: MBc, mesiobuccal cusp; DBc, distobuccal cusp; cP,
central pit; Dc, distal cusp, DBDG, distobuccal developmental groove;
DP, distal pit; cDG, central developmental groove; DLc, distolingual
cusp; LDG, linguodistal groove, MLc, mesiolingual groove; MP, mesial
pit; MBDG, mesiolingual developmental groove
figures 10.10a to c: Schematic representation showing (A)
Occlu-sal anatomy of primary maxillary 2nd molar; (B) conservative class I
tooth preparation in primary maxillary 2nd molar (c) Schematic
rep-resentation showing walls of tooth preparation should be straight or
converging
Abbreviations: DBc, distobuccal cusp; cDG, central developmental
groove; MBc, mesiobuccal cusp; BDG, buccodistal groove; MTF mesial
triangular fossa; MP, mesial pit; MLc, mesiolingual groove; cP, central
pit; DLc, distolingual cusp; DTF, distal triangular fassa; DDG, distal
development groove
class II tooth preparation
Occlusal Preparation
• Prepare the occlusal portion using No.330 bur same as
that for pit and fissure caries
Preparation of Proximal Box
• Extend occlusal outline to the marginal ridge using
No 330 bur Sweep the bur buccolinually in pendulum
motion and in gingival direction
• Move the bur faciolingually to just clear the contact
areas and diverge the proximal cut gingivally It
results in greater faciolingual dimension at gingival
Trang 40class III
The most common area for class III in primary dentition is mesial surface of the primary incisors (Fig 10.14)
• Pear shaped bur (No.330) is used for cavity preparation
• Outline form should be triangular with the base of the triangle at the gingival aspect of the cavity
• Buccal and lingual walls of the cavity should parallel the external surfaces of the tooth
• Gingival cavity wall is inclined occlusally to form parallelism with direction of enamel rods
• Depth of cavity into dentin is 0.5-1 mm
• If contact area is open, there is no need of dovetail lock, caries is accessed labially
In case of closed contact, a dovetail lock is made to facilitate access and retention Dovetail extends to the middle of the tooth cervicoincisally
class IV
Cavity outline is similar to class III
• Sometimes, along with the proximal surface, labial
or lingual surfaces also show carious involvement,
figure 10.12: Schematic representation showing internal outline
form of class II preparation
figure 10.14: Schematic representation showing class III tooth
preparation in primary teeth
figure 10.15: Schematic representation showing class IV tooth
preparation in primary teeth
figure 10.16: Schematic representation showing class V tooth
preparation
figure 10.11: Schematic representation showing external outline
form of class II preparation
figures 10.13a and B: Schematic representation showing class II
preparation; (A) Primary maxillary 2nd molar; (B) Primary mandibular
2nd molar