Các biến thể giải phẫu được gặp hàng ngày bởi những chuyên gia đi vào khoang miệng (ví dụ: nha sĩ và bác sĩ phẫu thuật miệng) và các vùng lân cận. Do đó, để thực hành lâm sàng hàng ngày một cách tối ưu, cả thực tập sinh và chuyên gia trong các lĩnh vực này và những người khác (ví dụ: bác sĩ nội nha, bác sĩ nha chu, bác sĩ cấy ghép, bác sĩ giải phẫu, bác sĩ phẫu thuật hàm mặt, bác sĩ tai mũi họng, sinh viên nha khoa và bác sĩ vệ sinh nha khoa) nên biết về các biến thể phổ biến nhất được tìm thấy trong khoang miệng. Các Biến thể Giải phẫu trong Nha khoa Lâm sàng tìm cách cung cấp tài liệu tham khảo về chủ đề này. Cuốn sách bắt đầu bằng cách giới thiệu cho người đọc các biến thể giải phẫu theo quan điểm của các bác sĩ lâm sàng khác nhau — bác sĩ phẫu thuật răng hàm mặt, bác sĩ nha chu và bác sĩ nội nha. Các kiến thức giải phẫu mới nhất và các biến thể sau đó lần lượt được trình bày cho các xoang hàm trên, hàm trên, vòm miệng cứng, sàn miệng, môi, khớp thái dương hàm và răng. Trong mỗi chương, các chú thích lâm sàng được đưa vào để nâng cao hiểu biết về các mối quan hệ giữa phẫu thuật và giải phẫu. Các tác giả nổi tiếng quốc tế của văn bản đã được lựa chọn cẩn thận về chuyên môn của họ.
Mandible 4 Anatomy and Variations of the Pterygomandibular Space
J Iwanaga, R S Tubbs (eds.), Anatomical Variations in Clinical Dentistry, https://doi.org/10.1007/978-3-319-97961-8_1
Dental and Oral Medical Center, Kurume University School of Medicine, Kurume, Japan e-mail: kusukawa@med.kurume-u.ac.jp
Anatomical Variations Relevant to Oral and Maxillofacial Surgeons
Anatomy is the cornerstone of surgery, serving as the fundamental science essential for all surgical specialties It plays a crucial role in addressing diagnostic challenges and is vital for the development of surgical procedures Thus, a strong understanding of anatomy is a prerequisite for anyone pursuing a career in surgery.
Oral and maxillofacial surgery focuses on the treatment of various conditions affecting the oral cavity, jaws, face, and surrounding structures Surgeons in this field must possess specialized skills and a comprehensive understanding of the anatomical relationships involved in surgical procedures A lack of detailed anatomical knowledge can lead to significant complications and suboptimal cosmetic or functional outcomes Therefore, a strong grasp of clinical anatomy, particularly in relation to practical surgery, is essential for improving diagnostic accuracy and ensuring safe, effective operations Additionally, it is important to consider anatomical changes due to aging and individual variations to enhance surgical outcomes.
Tooth loss leads to disuse atrophy of the alveolar and jaw bones, complicating the surgeon's ability to identify key anatomical landmarks such as the piriform aperture, anterior nasal spine, incisive papilla, hamular notch, and neural foramina The reduction in alveolar ridge height heightens the risk of damaging nerves and blood vessels that exit through the neural foramina, including the greater palatine foramen, infraorbital foramen, and mental foramen Additionally, the narrowing of the alveolar ridge increases the likelihood that surgical instruments may inadvertently cut too deeply, moving beyond the alveolar crest.
Furthermore, anatomical variations complicate the situation of the operation Such variations are potential risk factors in oral and maxillofacial surgery In
Injuries to specific variations of nerves and blood vessels pose significant risks, including life-threatening uncontrollable bleeding and the potential for permanent nerve damage, which can severely impact a patient's quality of life.
To avoid such complications, surgeons should be familiar with anatomical varia- tions as well as preventive care.
Third molar surgery is the most frequently performed procedure by dentists and oral surgeons, with a significant concern being the risk of inferior alveolar nerve (IAN) injury, which has a permanent incidence rate of 0.35% to 8.4% Beyond third molar extractions, the IAN can also be compromised during other oral surgeries, such as jaw cyst and implant surgeries The IAN enters the mandible through the mandibular foramen, traverses the mandibular canal, and exits via the mental foramen, branching into the mental nerve (MN) that innervates the lower lip and mental area Understanding the variations in the IAN and MN pathways is crucial to prevent complications, as the relationship between the third molar's position and the mandibular canal significantly affects the likelihood of IAN injury Additionally, the occurrence of accessory mental foramina, which ranges from 2.0% to 13.0%, poses a potential risk for lower lip and mental region paresthesia.
Lingual nerve (LN) paralysis is a significant complication that can arise during oral surgery The LN travels along the lingual side of the mandible and extends to the tongue through the floor of the mouth, making it susceptible to injury during various surgical procedures, such as third molar extraction, jaw resection, alveolar crest grafting, and salivary gland surgery.
Fig 1.1 Greater palatine foramen (arrow), nerve, and artery
The placement of implants and tumor excision can lead to complications, with incidence rates varying between 0.04% and 22% (Dias et al 2015) While nerve injury is infrequent, it can have serious consequences for the patient.
The sublingual artery (SLA), a key branch of the lingual artery, supplies the floor of the mouth and may enter the mandible through lingual bony canals, posing a risk of injury during intraosseous surgeries like implant placement Such injuries can lead to significant hematoma formation and potentially life-threatening airway obstruction Similarly, the posterior superior alveolar artery (PSAA), a terminal branch of the maxillary artery, provides blood to the lateral wall of the maxillary sinus and its floor membrane Injury to the PSAA during sinus-related surgeries, such as sinus floor augmentation, can result in severe perioperative bleeding Therefore, accurately locating these blood vessels before surgery is essential to prevent complications.
To ensure safe and reliable surgical operations, surgeons must accurately identify anatomical variations before surgery, alongside a thorough understanding of normal structures However, the preoperative detection of soft tissue anatomical variations remains limited Key imaging modalities such as angiography, CT angiography, and magnetic resonance angiography (MRA) are essential for this purpose.
Fig 1.2 Mandibular lingual canal in the canine-premolar region
(arrow) Additional buccal bony canal in the incisal region (arrowhead)
Fig 1.3 Left posterior superior alveolar artery
1 Anatomical Variations Relevant to Oral and Maxillofacial Surgeons
Detecting vascular distribution and its variations is often invasive and costly, making it a challenging process Furthermore, identifying nerves within soft tissue poses significant difficulties The most reliable method for nerve detection and management during surgery is direct visualization Utilizing anatomical landmarks can enhance the safety and efficiency of surgical procedures.
Radiographic imaging is essential for identifying anatomical variations in bone, particularly through the use of orthopantomograms (OPG) OPGs are traditionally employed to assess the jaws, including critical structures such as the maxillary sinus, mandibular canal, and mental foramen, along with their relationships to teeth However, one limitation of OPG is that it does not allow for a three-dimensional (3D) evaluation of these structures or the visualization of lingual canals.
CT and cone beam CT (CBCT) offer high-resolution visualization of osseous architecture, enhancing surgical accuracy through multiplanar reconstruction (MPR) imaging, which provides detailed anatomical information in both 2D and 3D views While MPR imaging is a recent advancement for dentists and oral and maxillofacial surgeons, it significantly boosts diagnostic efficiency The integration of digital technology, including computer-aided design/computer-aided manufacturing (CAD/CAM), further refines surgical planning by enabling the creation of surgical guides and 3D models for procedures like implant placement and tumor resection Looking ahead, the incorporation of robotic surgery and artificial intelligence promises to enhance the safety and precision of oral and maxillofacial surgeries However, despite these technological advancements, a solid understanding of anatomy remains crucial for surgeons to achieve success in this field.
Dias GJ, de Silva RK, Shah T et al (2015) Multivariate assessment of site of lingual nerve Br J Oral Maxillofac Surg 53:347–351
Güncü GN, Yildirim YD, Wang HL et al (2011) Location of posterior superior alveolar artery and evaluation of maxillary sinus anatomy with computerized tomography: a clinical study Clin Oral Implants Res 22:1164–1167
Iwanaga J, Saga T, Tabira Y et al (2015) The clinical anatomy of accessory mental nerves and foramina Clin Anat 28:848 https://doi.org/10.1002/ca.22597
Maridati P, Stoffella E, Speroni S et al (2014) Alveolar Antral artery isolation during sinus lift procedure with the double window technique Open Dent J 8:95–103
Sahman H, Ercan A, Elif S et al (2014) Lateral lingual vascular canals of the mandible: a CBCT study of 500 cases Surg Radiol Anat 36:865–870
The systematic review by Sarikov and Juodzbalys (2014) highlights the prevalence of inferior alveolar nerve injury (IANI) following the extraction of mandibular third molars, noting an incidence rate between 0.35% and 8.4% The study identifies risk factors such as age over 24, horizontal impactions, and extractions performed by less experienced surgeons, while emphasizing that most injuries recover within 4 to 8 weeks Furthermore, the review underscores the importance of radiographic assessments in predicting IANI risks during surgery In a related study, Tepper et al (2001) focus on the use of computed tomography for accurately diagnosing and localizing bone canals in the mandibular interforaminal region, which is crucial for preventing bleeding complications during implant surgeries.
J Iwanaga, R S Tubbs (eds.), Anatomical Variations in Clinical Dentistry, https://doi.org/10.1007/978-3-319-97961-8_2
Department of Periodontics, Indiana University School of Dentistry, Indianapolis, IN, USA e-mail: danshin@iu.edu
Anatomical Variations from the Point of View of the Periodontist
Periodontal surgery involves various surgical therapies aimed at restoring the natural form and function of damaged dental structures Key procedures include open flap debridement, osseous resective surgery, guided tissue regeneration (GTR), and soft tissue augmentation A skilled periodontist must possess strong clinical judgment and technical proficiency, alongside a deep understanding of anatomical variations in the surgical field Recognizing these variations is crucial for planning and executing safe surgical procedures This chapter focuses on common anatomical variations encountered in periodontal and implant surgeries, with further details available in subsequent chapters of the textbook.
2.2 Common Anatomical Variations Relevant to Periodontal
The maxillary palate demands careful attention due to the variability in the location of the greater palatine neurovascular bundle and its foramen Surgical incision depth and the method of flap elevation are determined by the positioning of the greater palatine foramen and the neurovascular bundle.
2.2.1 Greater Palatine Foramen and Greater Palatine
Maxillary Sinus 8 Anatomy and Variations of the Floor of the Maxillary Sinus
J Iwanaga, R S Tubbs (eds.), Anatomical Variations in Clinical Dentistry, https://doi.org/10.1007/978-3-319-97961-8_4
Department of Anatomy, Jagiellonian University Medical College, Krakow, Poland
Anatomy and Variations of the Pterygomandibular Space
Iwona M Tomaszewska, Matthew J Graves, Marcin Lipski, and Jerzy A Walocha
The pterygomandibular space (PM) is a triangular area composed mainly of connective tissue and muscle, housing vital neurovascular structures, including the inferior alveolar nerve, artery, and vein, as well as the lingual nerve It is bordered laterally by the medial surface of the mandibular ramus, medially by the medial pterygoid muscle and fascia, and superiorly by the lateral pterygoid muscle, with the parotid gland located posteriorly and the buccinator and superior pharyngeal constrictors anteriorly Understanding the anatomy and variations of the PM is crucial for successfully performing inferior alveolar nerve blocks and avoiding potential iatrogenic injuries during dental procedures in this region This chapter will explore the common anatomy of the PM, its variants, and their clinical implications.
The PM is rich in neurovascular structures and surrounded by numerous soft tissue components Its medial border features the interpterygoid fascia, which is located next to the medial pterygoid muscle.
The medial pterygoid muscle, a key component of the masticator muscles, is covered superiorly by the interpterygoid fascia, which also encompasses the medial border of the lateral pterygoid muscle and the superior border of the pterygoid muscle (PM) Notably, the lateral pterygoid is unique among the muscles of mastication as it facilitates mouth opening The lateral wall of the PM consists of the medial surface of the mandibular ramus, highlighting important anatomical features such as the lingula, sulcus colli, and temporal crest The posterior boundary is defined by the stylomandibular membrane, situated between the styloid process and the posterior border of the mandible, along with the medial portion of the parotid gland Anteriorly, the PM is bordered by various structures, with the temporalis muscle tendons being closest to the inferior alveolar neurovascular bundle, followed by the temporopterygoid fascia.
1972) The ligamentous pterygomandibular raphe serves as an attachment for the buccinator muscle anteriorly and the superior pharyngeal constrictor posteriorly (Barker and Davies 1972).
Fig 4.1 Inferior alveolar nerve block
Fig 4.2 Intraoral dissection of pterygomandibular space (light green) and parapharyngeal space
(light blue) MPM medial pterygoid muscle, SPCM superior pharyngeal constrictor muscle, T tongue
The maxillary artery (MA) can sometimes be found within the pterygomandibular (PM) region, specifically within the interpterygoid fascia that covers the lateral pterygoid muscle (Barker and Davies 1972) Understanding the relationship between the lateral pterygoid muscle and the MA is vital for surgical procedures, particularly during bilateral sagittal split osteotomy If the MA is located laterally to the lateral pterygoid muscle, it is at a significant risk of injury during the medial horizontal bony incision of the ramus (Fig 4.4) The internal course of the MA has varying incidence rates, reported as 3.6–10.1% in Japanese populations, 44.7% in the United Kingdom, 45.6% among Caucasians in the United States, and 91.5% in Australians (Iwanaga et al 2017a).
Medial surface of ramus of mandible
Fig 4.3 Schematic drawing of pterygomandibular space (superior view)
Fig 4.4 Lateral course right maxillary artery IAA inferior alveolar artery, MA maxillary artery, LPM lateral pterygoid muscle,
4 Anatomy and Variations of the Pterygomandibular Space
Anatomic variants of the mandibular artery (MA) have been documented, including a case involving a cadaver with a divided mandibular nerve that entrapped the MA through two branches, which later reunited into the inferior alveolar nerve (Anil et al 2003) This entrapment can cause pain and numbness in the sensory distribution of the nerve, potentially due to arterial pulsations or direct compression (Wolf et al 2016).
4.4 Inferior Alveolar Nerve, Artery, and Vein
The inferior alveolar neurovascular bundle, which includes the inferior alveolar nerve, artery, and vein encased in a fibrous sheath, is typically located in a posterolateral position relative to the lingula of the mandible This bundle runs along the medial side of the mandibular ramus, averaging 60% of the distance from the anterior border of the ramus in relation to its total width.
The inferior alveolar nerve (IAN), a sensory branch of the mandibular nerve (CN V3), is crucial for the somatosensory innervation of the mandibular teeth It branches off alongside the lingual nerve beneath the lateral pterygoid muscle and enters the pterygomandibular space as distinct structures from the medial pterygoid's lateral surface Although the IAN appears as a single trunk, it actually consists of two branches: the mental nerve and the incisive branches Its external morphology varies, with one-third of IANs exhibiting round, oval, or flat shapes, located approximately 2 mm above the lingula At the lingula level, the IAN is positioned in the anterior part of the sulcus colli, leading to the mandibular foramen The lingula, located just superior to the temporal crest, serves as a protective bony ridge for the IAN during block procedures Despite the emergence of various mandibular anesthesia techniques, the IAN block remains a fundamental approach for many clinicians.
The inferior alveolar nerve (IAN) blockade often encounters a failure rate of nearly 20%, as noted by Kaufman et al (1984) Variations in clinician techniques and patient anatomy may lead to simultaneous anesthesia of the lingual nerve during an IAN blockade, which can be beneficial in specific situations (Khoury et al 2010) Clinicians should consider that the average distance between the IAN and the lingual nerve ranges from 5.3 to 8.5 mm, which can assist in determining the appropriate needle withdrawal technique (Khoury et al 2010; Iwanaga et al.).
2018) A notable variant is the presence of communicating branches between IANs
Anatomic variations, such as the presence of accessory mandibular foramina, can complicate the traditional understanding of mandibular nerve anatomy, leading to bifid inferior alveolar nerves (IANs) Surgical procedures, particularly those involving the extraction of third molars, pose a risk of IAN damage, with reported incidence rates as high as 8% These complications may contribute to the significant failure rate of IAN blockades Additionally, collateral sensory innervation from nerves like the mylohyoid nerve may further complicate the effectiveness of these anesthetic techniques A thorough understanding of the spatial arrangement and depth of anatomical structures in the posterior mandible can enhance the efficacy of local anesthetic administration.
The inferior alveolar artery (IAA) arises from the maxillary artery and typically runs alongside the inferior alveolar nerve (IAN) Research indicates that in 79% of cases, the IAA is positioned posteriorly or posterolaterally to the IAN, which has been the most frequently observed spatial arrangement in historical studies This anatomical positioning of the IAA within the posterior mandible (PM) offers procedural benefits, potentially reducing the risk of vascular aspirations and minimizing unnecessary vascular trauma during IAN block procedures.
2010) Case reports have demonstrated that hematoma may occur as a complication from an IAN blockade (Traeger 1979) Hematoma formation from a small vessel lingula
Fig 4.5 Lingula and mandibular foramen
4 Anatomy and Variations of the Pterygomandibular Space
The inferior alveolar artery (IAA) is typically associated with larger structures like the maxillary veins and pterygoid venous plexus, particularly when high needle placement is used (Shaw and Fierst 1988; Traeger 1979) There have been documented cases of aberrant IAA origins, including instances where it originates from the external carotid artery (Jergenson et al 2005) Additionally, the positioning of the inferior alveolar vasculature, which rarely lies medial to the inferior alveolar nerve (IAN), may contribute to a lower risk of intravascular injection of local anesthetics (Khoury et al.).
2010) It should be noted however that approximately 15% of IAN blocks are aspi- ration positive (Taghavi Zenouz et al 2008).
The inferior alveolar vein (IAV) is typically located as the most posterior component of the inferior alveolar neurovascular bundle, being positioned posteriorly or posterolaterally to the inferior alveolar artery (IAA) in 71% of observed cases (Khoury et al 2010).
The inferior alveolar vein (IAV) ultimately drains into the pterygoid venous plexus, which is closely linked to the lateral pterygoid muscle Recent studies indicate that the pterygoid venous plexus may extend inferiorly, potentially serving as a plexus around the inferior alveolar artery (IAA) Traditionally viewed as a single entity, the IAV is now recognized to commonly present as two distinct veins based on cadaveric examinations Additionally, the IAV, being the most posterior structure within the inferior alveolar neurovascular sheath, may receive less osseous protection compared to its arterial and neural counterparts.
2010) Procedurally, it is recommended withdrawing anesthetic needles 1–2 mm prior to performing an aspiration as to avoid pinning of the IAV to the mandible (Khoury et al 2010).
Fig 4.6 Right inferior alveolar nerve (IAN) and inferior alveolar artery
(IAA) Upper part of mandibular ramus removed LN lingual nerve
The lingual nerve (LN), a branch of the mandibular nerve, provides somatic sensory innervation to the anterior two-thirds of the tongue and receives special sensory taste fibers and parasympathetic fibers from the facial nerve (CN VII) It is also believed to convey proprioceptive information about the tongue's position The LN joins the inferior alveolar nerve (IAN) at their common origin within the mandibular nerve and is accompanied by special sensory fibers from the chorda tympani The nerve travels through the pterygomandibular space along the anterolateral aspect of the medial pterygoid muscle before entering the submandibular area Morphologically, the LN resembles the IAN, with about one-third of the nerves exhibiting oval, flat, or circular shapes at a level of 2 mm above the lingula.
Fig 4.7 Origin of the left mandibular nerve
Upper part of mandibular ramus removed ATN auriculotemporal nerve,
CT chorda tympani, FO foramen ovale, IAN inferior alveolar nerve,
LN lingual nerve, MN mandibular nerve
4 Anatomy and Variations of the Pterygomandibular Space
Research indicates a 47% concordance in external morphology between the inferior alveolar nerve (IAN) and the lingual nerve (LN) (Tan et al 2014) Variations in the LN, including communicating branches with the IAN in up to 33% of cases, have been documented (Rácz and Maros 1981) Additional connections to other nerves, such as the nerve to mylohyoid, auriculotemporal nerve, and hypoglossal nerve, have also been reported (Al-Amery et al 2016; Piagkou et al 2011; Păduraru and Rusu 2013) Surgical procedures in the oral cavity can lead to LN injuries, resulting in sensory disturbances, including loss of taste (Al-Amery et al 2016) The risk of lingual nerve injury is particularly high during lower third molar extractions due to its close proximity (McGeachie 2002), with retraction of the lingual flap further increasing this risk (Baqain et al 2016).