base? The trigeminal nerve has three divisions: ophthalmic, maxillary, and mandibular. The ophthalmic and maxillary exits the cranial vault through the superior orbital fissure. It supplies sensation to the upper third of the face including the forehead, scalp, upper eyelid, nose conjunctiva, and cornea. The maxillary division exits the cranial vault through the foramen rotundum and supplies sensation to the lower eyelids, cheek, and upper dentition. The mandibular division exits the cranium through the foramen ovale and supplies sensation to the lower lip, chin, jaw, and lower dentition. It also supplies the muscles of mastication including the temporalis, masseter, and pterygoids. The inferior orbital fissure contains the infraorbital and zygomatic nerves which are branches of the maxillary division of the trigeminal nerve. In addition, the inferior ophthalmic vein and infraorbital artery also pass through this fissure. The foramen spinosum transmits the middle meningeal artery and vein and the meningeal branch of the mandibular nerve (Fig. 37.1).1,2 Fig. 37.1 Primary (pediatric) dentition. (From Gilroy AM, MacPherson BR. Atlas of Anatomy. 3rd ed. Thieme, 2016.) Optic foramen Inferior orbital fissure Foramen spinosum Foramen rotundum Superior orbital fissure Foramen ovale Jugular foramen Hypoglossal foramen Jugular foramen Stylomastoid foramen Foramen spinosum
2. Neligan PC, Sharaf B. Clinical anatomy of the head and neck, and recipient vessel selection. In: Wei FC, Mardini S, eds. Flaps and Reconstructive Surgery. 2nd ed. New York, NY: Elsevier Inc.; 2017:61–74 The facial nerve exits the skull base through the stylomastoid foramen. It has a number of motor and sensory functions. It supplies voluntary control of all muscles of facial expression, the stylohyoid muscle, the stapedius, and the posterior belly of digastric. It also supplies visceral motor function to the lacrimal and sublingual glands. It supplies general sensation to the external ear (concha and external auditory canal) as well as the tympanic membrane. It is involved in specialized taste in the anterior two-thirds of the tongue. The glossopharyngeal nerve supplies sensation to the oropharynx and motor supply to the pharynx. It exits the cranium through the jugular foramen along with the vagus and accessory nerves and the sigmoid sinus, which becomes the internal jugular vein. The optic nerve supplies specialized sensation to the retina with information regarding brightness, contrast, and color. It exits the cranium through the optic foramen along with the ophthalmic artery. The hypoglossal nerve exits the skull base through the hypoglossal foramen and goes on to supply motor innervation to the tongue. The oculomotor nerve supplies motor function to the extraocular muscles: superior rectus, inferior rectus, medial rectus, inferior oblique, and the ciliary and sphincter muscles. It exits the cranium through the superior orbital fissure and can be compromised in conditions such as superior orbital fissure syndrome, leading to ptosis, proptosis, ophthalmoplegia, paresthesia, and dilated pupil (see Fig. 37.1).1,2
The mucosal covering on the alveolus of the mandible comprises the attached gingiva (gingiva proper) and mobile gingiva (alveolar mucosa). The gingiva proper is very tightly adherent to the alveolus whereas the alveolar mucosa is more loosely attached. When making incisions for access to the mandible, therefore, it is important to ensure that the length of the free end of the alveolar mucosa or loose gingiva is maximized such that there will be sufficient soft tissue to repair this to the gingiva proper at the end of the procedure. Otherwise, it is very difficult to suture the adherent and loose gingiva together because there is no space between the adherent tissue and bone. The labial frenula are midline folds of mucosa that may be incised during midline access, but preservation of tissue length is not specifically important. The oral vestibule refers to the space between the teeth and cheeks. Wharton’s duct is the term used to describe the submandibular and sublingual salivary ducts, which enter the oral cavity on the floor of mouth.1,2
The number of teeth present differs between primary and secondary dentition. The normal primary dentition includes a total of 20 teeth (10 per arch). The secondary dentition includes a total of 32 teeth (16 per arch). Adult dentition will therefore have 8 incisors, 4 canines, 8 premolars (not 4), and 12 molars. In contrast children will only have eight molar teeth and the same number of other teeth as adults.1 There are different ways to number the teeth that are uniformly recognized internationally. These are the universal numbering system, the Palmer notation numbering system, and the Federation Dentaire Internationale (FDI) numbering system.2 The universal numbering system numbers the adult teeth from the right upper third molar to the left upper third molar then continues from the left lower third molar through to the third right lower molar from 1 through 32. So the left first upper incisor is the ninth tooth from the upper right. The first adult lower molars will be numbered 19 and 30 respectively. It would be the upper first molars that would be labelled 3 and 14. The Palmer notation system uses four quadrants: right upper, left upper, right lower, and left lower, with each being given a different L notation. The left upper uses a standard L, while the right upper uses a mirror L. The left lower uses an upside down L, while the right lower uses an upside down mirrored L. Each tooth within a quadrant is then numbered 1 to 8 beginning at the midline. In this case the left upper incisor would be L1 instead of tooth 9 (Figs. 37.2 and 37.3). The FDI system again uses four quadrants. In this case the quadrants are numbered 1 through 4 with the maxillary right being labelled 1, the maxillary left being labelled 2, the mandibular left being labelled 3, and the mandibular right being labelled 4. Again the teeth within each quadrant are labelled from the midline 1 through 8. So the left upper incisor would be 11.1,2
The adult eruption sequence is commonly first molars, central incisors, lateral incisors, first premolars, canines, and second then third molars. This can be remembered as an eight-digit code: 612 453 78. Each quadrant is labeled from one to eight, commencing with the central incisor (Table 37.1).1–5 Fig. 37.3 Secondary (adult) dentition. Maxillary Mandibular Right Left Upper teeth 9. Central incisor 10. Lateral incisor 11. Canine (cuspid) 12. First premolar (first bicuspid) 13. Second premolar (second bicuspid) 15. Second molar 16. Third molar (wisdom tooth) Lower teeth 17. Third molar (wisdom tooth) 18. Second molar 20. Second premolar (second bicuspid) 21. First premolar (first bicuspid) 22. Canine (cuspid) 23. Lateral incisor 24. Central incisor Fig. 37.2 Primary (pediatric) dentition. E D C B A F G H I J T K P Q R S O N M L Right Left Upper teeth F. Central incisor G. Lateral incisor H. Canine (cuspid) J. Second molar Lower teeth K. Second molar M. Canine (cuspid) N. Lateral incisor O. Central incisor Maxillary Mandibular
Occlusion refers to the relationship of the teeth to one another. Normal occlusion is based on the relationship of the upper and lower first permanent molars. It was described by Edward Angle who identified that in normal occlusion the mesiobuccal cusp of the maxillary first molar interfaces with the buccal groove of the mandibular first molar. Malocclusion is where this relationship is altered in some way and is split into three subtypes: classes I, II, and III. The descriptions of the three classes of malocclusion are: Class I: The mesiobuccal cusp of the first maxillary molar occludes in the buccal groove of the mandibular molar but the teeth are malpositioned or malrotated. Class II: The mandibular molar is distally positioned relative to the maxillary molar. Class III: The mandibular molar is mesially positioned relative to the maxillary molar. In general terms, patients with small or retruded mandibles have a class II occlusion and patients with prognathism have class III occlusion. The patient described in this scenario has class II malocclusion which can either be subdivided as division I or division II depending on the angulation of the incisors and the degree of overjet and overbite. Overjet refers to the amount of horizontal overlap of the incisal edges, while overbite refers to the amount of vertical overlap (Fig. 37.4).1 Table 37.1 Dental Eruption and Shedding Sequences Primary Dentition Permanent Dentition Erupt Shed Erupt Maxillary Teeth Central incisor 8–12 months 6–7 years 7–8 years Lateral incisor 9–13 months 7–8 years 8–9 years Canine 16–22 months 10–12 years 11–12 years (last before 3rd molar) First premolar 10–11 years Second premolar 10–12 years First molar 13–19 months 9–11 years 6–7 years (first) Second molar 25–33 months 10–12 years 12–13 years Third molar 17–21 years Mandibular Teeth Central incisor 6–10 months (first) 6–7 years 6–7 years Lateral incisor 10–16 months 7–8 years 7–8 years Canine 17–23 months 9–12 years 9–10 years First premolar 10–12 years Second premolar 11–12 years First molar 14–18 months 9–11 years 6–7 years Second molar 23–31 months 10–12 years 11–13 years Third molar 17–21 years (Data from Zohrabian VM, Poon CS, Abrahams JJ. Embryology and anatomy of the jaw and dentition. Seminars in Ultrasound, CT, and MRI 2015;36:397–406.)
In dental terminology distal means away from the midline and mesial means toward the midline. The term buccal means toward the cheek and lingual means toward the tongue. These terms can sometimes be confusing. For example, when describing teeth, the terms distal and mesial are applied to the dental arches, and as the arches are followed from the molars to the incisors, the teeth are becoming progressively more mesial. In more traditional anatomy we might describe this relationship as the incisors being more anterior and also more medial to the molars (Fig. 37.5).1 Fig. 37.4 Classes of malocclusion. (Used with permission from Facial Analysis in Cheney M, Hadlock T, ed. Facial Surgery. Plastic and Reconstructive. 1st ed. Thieme; 2014.) A B C Mesiobuccal cusp of maxillary first molar Mesiobuccal grove of mandibular first molar ORTHOGNATHIC Class I RETROGNATHIC Class II PROGNATHIC Class III Fig. 37.5 Dental relationships. (From Marcus JR, Erdmann D, Rodriguez ED, eds. Essentials of Craniomaxillofacial Trauma. St Louis: Quality Medical Publishing, 2012.) Di st al : a w ay fr o m m id li n e MIDLINE L a bi al Fa ci al Bu cc al Mesi al: to war d m id lin e P a l a t a l
Orthognathic surgery involves correction of the components of the facial skeleton to restore proper functional and aesthetic relationships such as occlusion and normal facial appearance. The bilateral sagittal split osteotomy (BSSO) is a useful and commonly used orthognathic technique for the correction of dentofacial abnormalities such as in patients with mandibular deficiency who had Pierre Robin sequence as an infant. It can also be used to treat mandibular excess. BSSO is achieved through an intraoral approach with an incision made through the mucosa overlying the anterior border of the mandibular ramus. Extensive soft tissue dissection is performed at a subperiosteal level to adequately expose the angle, ramus, and body for the osteotomy and release of the soft tissues adequately to allow mandibular advancement (or set-back). Osteotomies are performed such that key neurovascular structures and dental roots are preserved. Once freed, the mandible can be advanced or set back as required and stabilized in place using plates and screws.1 A LeFort I osteotomy is typically performed to correct maxillary deficiency. This also involves an intraoral approach with a mucosal incision made in the upper buccal sulcus from first molar to first molar. An osteotomy is made to separate the tooth-bearing maxilla from the midface. This will extend from the piriform aperture through the anterior maxilla and posteriorly to the pterygoid plates. Again, preservation of key neurovascular structures and dental roots as well as the nasal mucosa must be ensured. Once adequate soft tissue and bone release have been achieved the desired position of the maxilla can be selected and fixation is performed with miniplates and screws.2 LeFort II and III osteotomies are not used to correct mandibular deficiencies. Intraoral vertical ramus osteotomies may be used to correct mandibular excess in some cases.
Local anesthetic blocks are very useful when performing intraoral surgery. Typically, a dental syringe is used, which gives good control for the injection and provides adequate reach for areas deeper in the oral cavity such as the posterior dentition. Lidocaine 2% is commonly used in small vials (2.2 mL each) that are combined with epinephrine 1:80,000. This concentration differs from the 1:200,000 dilution typically used and has the theoretical advantage of reducing bleeding while working in this highly vascular area. Local anesthetic blocks are not only useful for procedures where patients are fully conscious but are also useful combined with general anesthesia as they can reduce the requirements for anesthetic agents and systemic pain relief requirements such as opiates. They can also help reduce bleeding as discussed above and help with dissection of soft tissues. Knowledge of the main local anesthetic blocks, such as those described, is therefore useful in clinical practice. The infraorbital block is particularly useful when performing surgery on the nose under local anesthesia because injection at this site can reduce pain on subsequent external nasal injections. The inferior alveolar block is mainly used for dental procedures of the lower dentition, while the nasopalatine block is usually used for dental procedures of the upper dentition or in orthognathic surgery. The greater palatine block is injected into the hard palate at the level of the upper second molar to block the upper dentition and palate. A mental nerve block is also part of the inferior alveolar nerve block but can be given as an isolated block in the lower buccal sulcus at the level of the second premolar. It provides anesthesia of the buccal mucosa and gingiva anterior to the first premolar. A buccal block is performed at the mandibular ramus after withdrawing and confirming no aspiration of blood. It provides anesthesia of the buccal mucosa and gingiva anterior to the first premolar.1,2
When examining a patient with a suspected odontogenic infection, trismus may be the only indication of a parapharyngeal space abscess. Examination must include a thorough review of the oropharynx. Odontogenic infections can range from localized conditions to severe life-threatening infections. Almost all are polymicrobial and are not limited to anaerobic organisms alone. In more than half of cases, infections will be a mixed aerobic/ anaerobic combination. Odontogenic infections arise from two major sources, namely, periapical and periodontal, of which the former is most common. Although antibiotics are a component of treatment, the main management is drainage of the abscess and this is undertaken by a dentally trained professional.1
Odontogenic keratocysts are aggressively destructive lesions that arise from dental lamina and contain parakeratin. They are associated with nevoid basal cell carcinoma syndrome which is also known as Gorlin’s syndrome and have a high recurrence rate following surgical resection. On radiographs they appear with corticated, scalloped margins and expansion of cortical bone. Due to the high recurrence of these lesions, treatment may be more aggressive than simple excision and involve osseous resection with up to 1 cm bone margins. Alternatively, a two-stage decompression and enucleation may be preferred. Gorlin’s syndrome is also associated with other abnormalities including palmar and plantar pits, calcification of the falx cerebri, bifid ribs, and hypertelorism. Periapical cysts are the most common jaw cyst and occur in response to bacterial overgrowth, usually from caries or trauma. They appear as well-defined, confluent lesions on radiographs and require dental extraction and cyst enucleation if the tooth is nonviable. Dentigerous cysts are the second most common jaw cyst and arise from cystic degeneration around a tooth crown. They are well-corticated, radiolucent lesions located at the crown of a developing tooth. Treatment involves enucleation and histological analysis. Ameloblastoma is a neoplasm derived from ameloblasts. It is locally invasive and has metastatic potential. On imaging it is seen as a radiolucent uni- or multilocular lesion often with local bony distortion. It should be treated with wide resection to ensure clear margins. Major reconstruction is likely to be required with free tissue such as a fibula flap. Dental abscesses are common but are not specifically linked to Gorlin’s syndrome.1,2
The most anterior soft tissue point on the chin is the soft tissue pogonion. The menton refers to the lowest point on the contour of the soft tissue chin, while the gnathion refers to the midpoint between the pogonion and menton. The stomion superioris refers to the lowest point of the lower lip vermilion and the labrale refers to the mucocutaneous border of the lip in the midsaggital plane. Cephalometrics are an important component of orthognathic and speech surgery. Both soft tissue and bony landmarks are used for a variety of analyses. Modern technology and imaging facilitates a fully automated approach to this (Fig. 37.6).1
meatus? Bony cephalometric landmarks may be useful for analysis of the facial and cranial skeleton with reference to orthodontics and mandibular/maxillary deformity. The porion is the most superior point of the external auditory meatus. The sella turcica represents the center of the pituitary fossa. The articulare represents the junction of the basisphenoid and the posterior part of the mandibular condyle. The gonion is the point at the angle of the mandible that is directed most inferiorly and posteriorly. The nasion is the most anterior point at the junction of the nasal and frontal bones in the midsagittal plane (see Fig. 37.6).1,2
Temporomandibular (TMJ) disorders represent a spectrum of clinical problems involving the muscles of mastication, the TMJ itself or the surrounding soft tissues. They affect around 5% (not 15%) of the population and females are more commonly affected than males. Symptoms vary but can include decreased mandibular range of motion, pain in the muscles of mastication, pain in the ears or at the TMJ, joint crepitus, and jaw locking or deviation on mouth opening. TMJ problems can be subdivided into nonarticular and articular causes. Articular causes may be inflammatory or noninflammatory and include conditions such as rheumatoid arthritis (RA), ankylosing spondylitis, gout, and osteoarthritis, so are not solely attributed to RA. Nonarticular cases, which make up the majority of cases, are best treated with behavioral therapy, physical therapy, bite guards, and analgesia to try and reduce clenching and bruxism and improve symptoms. In some cases of articular causes, they are treated surgically, but this is not commonly undertaken.1
Osteoradionecrosis (ORN) and osteonecrosis (ON) of the mandible can both occur secondary to treatment for bony cancer. Radiotherapy is commonly used to treat head and neck tumors such as squamous cell carcinoma either as a primary treatment or after surgery. Radiotherapy can induce necrotic damage to the native mandible leading to soft tissue ulceration and bone exposure. Bisphosphonates can also cause necrosis of the mandible and overlying soft tissues and these are used to treat bone metastases. The underlying pathology is different as one is secondary to radiotherapy and the other to bisphosphonate use, although they may share some similarities. The initial investigations will differ and in particular it is important in ORN to exclude local tumor recurrence with a biopsy and imaging. Complete dental extraction clearance is sometimes offered to patients prior to undergoing radiotherapy of the head and neck as this can help reduce post-treatment problems with ORN. However, more often there is select dental extraction only. Prior to commencing bisphosphonates, it would be inappropriate to perform extractions for this potential risk alone. Treatment for either condition will depend on severity of symptoms and only more extreme cases will require wide resection and free tissue reconstruction. Initial treatment commences in both cases with conservative measures including maintenance of good oral hygiene and antibiotics. In some cases, debridement may be beneficial too. The use of hyperbaric oxygen therapy may be helpful in ORN or ON but still remains controversial in some circles.1,2
Arch bars may be used to stabilize dentoalveolar fractures. They provide a stable base from which to institute maxillomandibular fixation (MMF) and control occlusion in the posttraumatic period. In mandibular fractures, arch bars ideally extend two teeth proximal and distal to a fracture line when possible. When using arch bars, they are usually placed from first molar to first molar and applied starting in the midline to prevent redundancy within the arch bar. Twenty-four-gauge wires (not 5-gauge) are used and are conventionally twisted clockwise to tighten. Proper occlusion and fracture reduction must be established before complete tightening of all wires within the quadrant of the fracture to prevent malreduction. This is facilitated by tightening the wires in the fracture segment after reducing the fracture. For this reason, complete tightening of each individual wire as it is placed is not performed. Alternatives to this technique include intermaxillary screw fixation and the SMARTLock system. Intermaxillary screw fixation is faster but less rigid than arch bars. The SMARTLock system involves self-locking screws and a plate design to eliminate the need for interdental wiring.1