Kỹ thuật chẩn đoán của William Clark trong chỉnh nha

Kesling  It’s a procedure in which teeth are removed and replaced in positions they will occupy after experiencing mesial migration in an orthodontic environment...  Factors influenc

D iagnostic Set up

Panoramic Radiography Xeroradiography

Clark’s technique

DIAGNOSTIC SET UP

 Practical aid in treatment planning and diagnosis.

 Proposed by H.D Kesling

 It’s a procedure in which teeth are

removed and replaced in positions they will occupy after experiencing mesial

migration in an orthodontic environment.

www.dainha.com

Advantages –

1 To determine and visualise the resultant

occlusion before the teeth have been extracted

2 Possible to change the treatment plan on the

model by replacing some and removing other teeth so that one can thoroughly examine all possible occlusions.

3 Mainly useful in asymmetric extraction and

combined surgical orthodontic treatment.

4 Tooth size – arch length discrepancies can be

visualised by means of set up.

5 Also a step in construction of tooth positioner.

6 Patient can be motivated

www.dainha.com

 A 004 inch ribbon saw blade is used to cut through the contact areas and separate teeth.

 The lower first permanent molars are replaced to a new position they will occupy by mesial migration.

 Deciding lower first molar position is the most important decision in constructing the set up

 Factors influencing position of first molar set up

are –

– Size of the teeth

– Presence or absence of tooth crowding mesial to anchor

 After all the above points have been considered, the

orthodontist must anticipate the behaviour of anchor

molar during treatment

 At this stage by studying the set up one can analyse

that- If anterior teeth – too far forward – Extraction – If already extracted – more extraction

 If anterior teeth – lingual – Eliminate planned

extraction

www.dainha.com

 Maxillary teeth are arranged according to mandibular teeth to obtain best possible occlusion.

 In most cases, same no and type of teeth are removed from maxillary arch as mandibular arch

 Exception –

– Badly broken down teeth

– Congenitally missing or deformed teeth.

– Single tooth extraction in lower arch

‘A Simplified wax set up technique’

by R.W Knierim JCO- 1975

According to his procedure –

 Plaster is filled to about 4 mm over gingival margin of impression

 As the plaster sets rough grooves are made in near set plaster to depth of 2mm

 When plaster is set it is removed and teeth are

numbered

www.dainha.com

 Teeth are then separated using discs on a lathe to slice root area, most teeth will now snap apart

 Root areas are then trimmed

 The impression are saved and kept moist

 The trimmed dies are then reinserted in air dried alginate impression

www.dainha.com

 Melted wax is then poured in impression holding the dies, it should flow well in grooves.

.

 Similar grooves are then placed in surface of wax

as it hardens

 Plaster is poured over wax surface to make base for model

www.dainha.com

‘ A simplified Diagnostic set up technique.’ by Dr Barry N Resnick; 1979 JCO

 According to his procedure –

 The plaster is poured in impression only to the extent of clinical crown

 Soft wax of 5 mm thickness is poured over crown dies

 Remainder of impression is poured with plaster and

 Original study model.

www.dainha.com

 Alginate impression with selected teeth poured up

in stone to the extent of their clinical crowns

 Dental units and model base connected by

periphery wax

www.dainha.com

 Diagnostic set up with mandibular left lateral incisor removed and remaining teeth aligned.

Panoramic Radiography

www.dainha.com

Panoramic Radiography

 Also called as Ortho pantomograph (OPG)

 Rotational Radiography.

single image of facial structures that includes both maxillary and mandibular arches and their supporting structures.

Advantages-1 Broad anatomic coverage

2 Simple procedure

3 Better tolerated by pts with gagging problems

4 Low radiation dose

5 Convenience of the examination.

6 Useful in pts who are unable to open their mouth

7 Full mouth IOPA – 15 mins and OPG – 3-4

mins.

www.dainha.com

Disadvantages

1 Magnification, Geometric distortion and overlapped

images

2 Resolution of fine anatomic details of peri-apical area

and periodontal structures is less

3 Poor image is obtained when sharp inclination of

anterior teeth towards labial or lingual side

4 The spinal cord superimpose on anterior region

5 Common to have overlapped teeth images ,

particularly in premolar area

6 Artifacts are common and may easily be

misinterpreted

7 Expensive

3 Presence or absence of permanent teeth: their size,

shape, position and relative state of development

4 To view ankylosed and impacted teeth

5 To diagnose presence of supernumerary teeth or

congenital absence of teeth

6 To study the character of alveolar bone and

immediate lamina dura and periodontal membrane

www.dainha.com

7 To study morphology and angulations of roots of

permanent teeth

8 To study the path of eruption of teeth

9 To diagnose fractures or pathologies of jaw

10 To diagnose caries, periapical infections root

fractures etc

11 Useful aid in serial extraction to study status of

eruption of teeth

12 Can assess TMJ and Sinuses

13 Assess shape, size and symmetry of condyles

 To interpret OPG competently one

must have a thorough understanding

of the following :

1 Principles of Panoramic image formation.

2 Techniques for Patient positioning with head

alignment and their rationale.

3 Radiographic appearance of normal anatomic

structures.

www.dainha.com

Principles of Panoramic image formation

 First described by Numata and independently by

Paatero in late 1940s.

Movement of the film and objects about 2 fixed centers of rotation.

Movement of film and X- ray source about one fixed center of rotation.

 While disc 2 moves, the film on this disc rotates past the slit

 It is critical that speed of the film passing the collimator slit is maintained equal to the speed at which x-ray beam sweeps through the object of interest

www.dainha.com

Movement of the film and x-ray source about the shifting center of rotation.

 Structures near the film will be sharply imaged

 Structures which are near x-ray source get magnified and distorted and resultant image is not discrete

Rotational Panaromic radiographic machines.

www.dainha.com

 Objects out of focal trough are blurred

magnified/ reduced or distorted

 The shape of focal trough varies

with brands of machines used

Patient positioning and Head alignment.

 Prepration of Patients.

– Removal of earrings or any other metallic objects in head and neck region.

– Instruct patients to remain still.

– Drape with lead apron.

 Patient Positioning

– Place the pt so that dental arches are located in middle of focal trough.

– A-P positioning – by biting at bite block.

– Proper mid sagittal plane –proper head positioning –

If anterior teeth are located behind the FT

- Blurred

- Wide anterior teeth

If anterior teeth are located infront of the FT

-Blurred

-Narrow anterior teeth

www.dainha.com

If skull tipped too far backward

Position the skull according to FH plane and check for

Correct position using bite block

www.dainha.com

If skull tipped too far forward

Position the skull according to FH plane and check for

Deviation in mid sagittal plane

Asymmetric image

www.dainha.com

Positioning of the Tongue

Pt should press tongue against palate

Radiation dose reduction

 By using rare-earth intensifying screens

 Reduce the output by using filters infront of x-ray tube

Eg Lanex screens

www.dainha.com

Positioning in mixed dentition stage

•The tooth buds should be in FT

•If additional supernumerary teeth

or impacted teeth has to be shown the

pt must be positioned with occlusal plane steeply dorsally

Radiographic appearance of normal Anatomy

www.dainha.com

The four Diagnostic regions in OPG

Dentoalveolar region

Maxillary region

Mandibular region

TMJ,including retromaxillary

Maxillary region

www.dainha.com

Mandibular region

Dentoalveolar region

• Shape and angulation of roots

• Alveolar bone and periodontium

• Shows gentle curve of occlusal plane

• Missing 3rd molars and

• Presence of metallic restorations.www.dainha.com

Soft tissue images

Air spaces

www.dainha.com

Xeroradiography

 Xeroradiography is the recording of

radiologic images by a photoelectric process

rather than the photochemical one used in

conventional radiography.

 An electrostatic image of object is formed on a

‘ Xeroplate’ , a metallic plate coated with

Selenium.

 An electrostatic image is printed on a paper in

such a manner that xeroradiograph is obtained.

www.dainha.com

 Pronounced edge enhancement

 A choice of positive and negative display

 Good detail

 Wide exposure latitude

 No need of silver halide coated films.

Disadvantages

 High radiation exposure

Types of Xeroradiographic systems

– Also been used for Cephalometric

radiography and Tomography of TMJ

2 The Dental 110 system

 Designed for dental Xeroradiographs

www.dainha.com

Medical Xeroradiography

 Conventional X-ray source is needed.

 Image is recorded on Selenium coated plate.

 Before use, Selenium photoreceptors which are

stored in a unit called conditioner are given a

uniform electrostatic charge

Processing of Xeroplate before exposure

www.dainha.com

Exposure of Xeroplate

Latent image

Latent image is converted to visible image by

process called Development, in unit called

Processor

Development of Image

www.dainha.com

Positive Image

 Darkest areas corresponds to most dense parts of anatomy

 Darkest areas corresponds to least dense parts of anatomy and dense objects appear white.

Negative image

www.dainha.com

Dental xeroradiographic processor.

www.dainha.com

Dental Xeroradiographic procedure.

Radiologic exposure conditions and resultant skin doses

in application of Xeroradiography to Orthodontic

diagnosis AJO-DO, 1980 by Akihiko Nakasima (Japan )

 Minimum xeroradiologic exposure conditions for Skull projections, Schuller’s and TMJ

projections and Hand projections were

 The advantages

were-– finer and clearer images due to edge effect and wider

latitude

– Landmarks on cephlaogram such as Sella,

ANS,Basion, etc were more clear and exactly set

– Outline of condylar process and articular fossa, the trabecular pattern of mandible and interdental crestal bone edges were more clear and distinct

 The main hazard was unavoidable larger skin radiation

dose It was 2.4 to 16.2 times larger than conventional film techniques

A cephalometric appraisal of Xeroradiography

by Chate – AJO-DO 1980

Aim : To estimate the effect of xeroradiographic technique on the

degree of inter and intra observer error in cephalometric landmarks identification.

Method

This study involved identification by four observers of 16

cephalometric landmarks on 12 xeroradiographs & on 12

radiographs, on 2 separate occasions.

Conclusion

 Neither technique provided a significant decrease in interobserver differences

 However, for 8 of 32 variables, xeroradiography produced a

significant reduction in intraobserver error in comparison to

radiography.

www.dainha.com

Clark’s technique

2 Tube shift/cone shift principle or Clark’s

technique or buccal object rule or SLOB rule.

 Mainly used in Orthodontia to locate position

of impacted canine.

www.dainha.com

Clark’s technique

 C.A Clark described it in 1910.

 Its based on Parallax principle.

 In this , 2 periapical films are taken,

– First, standard orthoradial projection,

– Second, employs a vertical or horizontal change in central ray projection

 The apparent movement of the object in this

radiograph will provide clue to its exact

location.

 According to rule of thumb objects which moves with central ray movement are actually behind the reference object.

 Its basis of SLOB rule, that is Same side

Lingual Opposite side Buccal

www.dainha.com

Horizontal shift of central ray

Distal shift of cone

Standard Cone shift

Standard

Vertical shift of central ray

Standard Vertical shift

Standard Vertical shift

www.dainha.com

INDICES

According to Russell, an index is defined as

‘A numerical value describing the relative status

of the population on a graduated scale with definite upper and lower limits which is designed to permit and facilitate comparison with other population classified with the same criteria and the method.’

In the orthodontic context index is described as –

‘A rating or categorizing system that assigns a

numeric score or alpha numeric label to a person’s

occlusion.’

www.dainha.com

Requirements of ideal orthodontic index are –

(Jamison H.D and Mc Millan R.S )

1 Simple, reliable and reproducible.

2 Objective and yield quantitative data.

3 Differentiate b/w handicapping and non

Types of Indices ( according to WHO)

 Occlusal Classification

– Angle’s classification by Angle in 1899

– Incisor classification by Ballard and Wayman, 1964

 Skeletal classification by Houston et al, 1993

 Malocclusion

– Occlusal index by Summers 1966

– Handicapping Malocclusion Assessment Record (HMAR) by Salzmann, 1968

– Index of Treatment Need by Evans and Shaw 1987

www.dainha.com

 Treatment assessment

– Little’s irregularity index by Little 1975

– Peer Assessment rating by Richmond et al, 1992

 Cleft Outcome

– Goslon Yardstick by Mars et al, 1987

– 5Year olds’ Index by Atack et al ,1997

 Periodontal

– Plaque Index by Stilness & Loe , 1964

– Gingival Index by Loe & Stilness, 1963

 Treatment need ( Treatment priority) indices.

– Categorize malocclusion according to levels of treatment needs.

– Eg 1 Index Of Treatment Need (IOTN)

2 Draker’s Handicapping Labio – Lingual Deviation index (HLD)

3 Grainger’s Treatment Priority Index.(TPI)

4 Salzmann’s Handicapping Malocclusion Index

 Treatment outcome indices.

– Assesssment of changes resulting from treatment

– Eg 1 Peer Assessment Rating index

2 Summer’s index

 Treatment complexity index

– Index of Complexity Outcome and Need (ICON)

Various indices of Occlusion

 Master and Frankel (1951)

– Count the number of teeth displaced or

Handicapping Labio – Lingual deviation index

 Proposed to select subjects with severe or handicapping malocclusions and dentofacial anomalies

 Applicable only to permanent dentition

 First Orthodontic index to meet administrative needs of programme planners

 Made use of weighting factors developed by trial and error

 Had 9 components

Conditions observed HLD score

1 Cleft palate Score 15

2 Severe Traumatic deviations Score 15

3 Overjet in mm

4 Overbite in mm

5 Mandibular protrusion in mm x 5

6 Open bite in mm x 4

7 Ectopic eruption ,Anteriors only x 3

8 Anterior crowding : Maxilla

9 Anterior crowding : Mandible

TOTAL

www.dainha.com

Handicapping Labio – Lingual deviation index

by Draker (1960)

 Modification of earlier used HLD index

 Main aim is to find presence or absence and degree

of handicap caused by components of index

7 conditions of HLD index are

7 Labio Lingual spread

Following codes are used –

 ‘O’ = condition present

 ‘X’ = condition absent

 ‘M’= mixed dentition

 ‘A’= Clinical approval

 ‘D’=Clinical disapprovalwww.dainha.com