Basic Anatomy of the Oral Cavity

Marin Vodanović

Chapter I

Learning outcomes: œ State and explain the functions of the oral cavity œ State thea most important Slap in the oral cavity œ Explain the innervation of the oral cavity œ State the most important blood vessels in the oral cavity œ Explain the vascularisation of the oral cavity œ Distinguish phases in jaw growth and devel- Copyrightopment œ Describe the characteristics of dental arch- es œ Specify the parts of the jawbone œ Explain the Haversian canal system œ Explain the alveolar bone proper œ Explain the supporting alveolar bone œ Explain the trabecular bone œ Recognise basic structures on radiographic © Nakladimages of the maxilla and Slap

Copyright Naklada ©

2 Chapter 1 Basic Anatomy of the Oral Cavity

he oral cavity (cavum oris) is the initial part it is richly supplied with blood vessels. The Tof the digestive system and has a digestive, colour of the varies from light to phonative, sensory, protective, respiratory, dark pink. It is continuous with the skin of and social function. The digestive function in- the and the mucosa of the soft and cludes mastication, saliva secretion, preparing . The palate (palatum) constitutes bolus for deglutition, and deglutition in itself. the roof of the oral cavity and comprises a The phonation includes the creation and ar- (anterior part) and a ticulation of sounds in conjunction with other (posterior part). A longitudinal suture runs speech organs. The sensory function of the along the middle of the hard palate connect- oral cavity refers to sensations of taste, smell, ing the left and right parts of the upper jaw touch, pain, and thermal changes. The pro- (maxilla). Shallow transverse palatine folds tective function is primarily linked to the oral (rugae palatinae) can be found on the mucosa mucosa which mechanically protects deeper of the anterior part of the hard palate behind oral tissues, and to saliva which contains cer- the incisors. The soft palate is composed of a tain antimicrobial substances. During strenu- musculotendinous plate which is covered on ous physical work, when there is an increased the underside by the oral mucosa and by the need for air or in case of nasal airway obstruc- nasal mucosa superiorly. The (lingua) tion, the oral cavity assumes a respiratory is a muscular organ which is covered with oral function. The social function of the oral cavity mucosa and is involved in mastication, deglu- is realised not only through speech (phonative function) but also through facial expressions Slap and social contacts such as kissing. The oral cavity is divided into the oral vestibule and the oral cavity proper (cavum oris proprium). The oral cavity proper is also Nasal cavity referred to as the oral cavity in the narrower Hard palate sense. The entrance to the oral cavity is referred Soft palate to as oral fissure (rima oris) and is bounded by Upper Vertebral the lips. Posteriorly, the oral cavity terminates column Teeth at the entrance to the pharynx. The constitute the lateral walls of the oral cavity. Lower lip AnteriorlyCopyright and laterally, the oral cavity proper Pharynx is bounded by the U-shaped maxillary and Tongue mandibular dental arches. While the hard and soft palate constitute the roof of the oral cavity proper, the so-called diaphragma oris formed by both mylohyoid muscles, the anterior bel- ly of the two-bellied (digastric) muscles, and Windpipe Oesophagus (respiratory tract) (digestive tract) the geniohyoid andNaklada genioglossus muscles, together with parts of the tongue, constitute Figure 1.1 Cross-section of the oral cavity and the the floor of the oral cavity. The tongue consti- pharynx (Adapted from: Vodanović, M. Uvod u anato- miju i fiziologiju usne šupljine (Introduction to the Anat- tutes most of the oral cavity proper (Figures omy and Physiology of the Oral Cavity). In: Vodanović, 1.1 and© 1.2). The mucosa of the oral cavity is M. Osnove stomatologije (The Essentials of Dental Medi- relatively thick and consists of a multi-layered cine). Jastrebarsko: Naklada Slap; 2015. 19-32. Printed squamous and connective tissue; with permission of the publisher.)

3 BIOLOGY AND MORPHOLOGY OF HUMAN TEETH

Anterior palatine arch Maxillary dental arch Palatine tonsils Posterior palatine arch Hard palate Longitudinal palatine Tongue suture Mandibular dental arch Soft palate Uvula

Pharynx

Figure 1.2 The oral cavity

tition, drinking, speech, and the perception vary glands exist in pairs. The minor salivary of taste. Anatomically, the tongue is divided glands are found in the cheeks, lips, tongue, into three parts, namely, the root, the dorsum, palate, tonsils, and pharynx. and the apex. It is composed of seven muscles Slap which extend perpendicular to its surface and are transverse and parallel to its longitudinal Innervation of the oral axis. cavity The mucosa of the dorsum of the tongue is permeated by numerous visible protrusions, The oral cavity and the organs contained referred to as lingual papillae; they play a role therein are innervated by several cranial in mechanical, tactile, or gustatory recogni- nerves with their sensory and motor fibres, tion, which is important for mixing food. The which are the following: nervus trigeminus lips (labia oris) are composed of muscles and (fifth cranial ), nervus facialis (seventh connective tissue. They are richly supplied cranial nerve), nervus glossopharyngeus with Copyrightblood vessels and nerves. The red part of (ninth cranial nerve), and nervus vagus (tenth the lip is covered by mucosa which constitutes cranial nerve). the transition between the skin of the face The trigeminal nerve (nervus trigeminus) and oral mucosa. The salivary glands in the is a nerve of the first which oral cavity are divided into major and minor consists of a sensory and a motor part and salivary glands. The labial mucosa contains innervates the masticatory muscles and some minor salivary glands the size of pin heads. pharyngeal and supralingual muscles. It Nakladatransmits general sensory information from The largest part of the total saliva volume is secreted by the major salivary glands. The the face and a large part of the forehead, teeth, (glandula parotis), the subman- lips, and the nasal cavity. The main branches dibular gland (glandula submandibularis), of the trigeminal nerve are the ophthalmic and© the sublingual gland (glandula sublingua- nerve (nervus ophtalmicus), the maxillary lis) are the major salivary glands. As opposed nerve (nervus maxillaris), and the mandibular to the minor salivary glands, the major sali- nerve (nervus mandibularis).

4 Chapter 1 Basic Anatomy of the Oral Cavity

The ophthalmic nerve innervates the eye- œ the lesser palatine nerve (nervus palatinus balls, sockets, frontal sinuses, nose, forehead, minor), which innervates the soft palate and the vertex. It is the first and smallest œ the nasopalatine nerve (nervus nasopalati- branch of the trigeminal nerve and contains nus), which innervates the nose and the only sensory nerve fibres. The branches of the palatine gingiva of maxillary anterior teeth ophthalmic nerve are as follows: œ the middle superior alveolar nerve (nervus œ the lacrimal nerve (nervus lacrimalis), alveolaris superior medius), which inner- which innervates the sockets and the skin vates the maxillary sinuses and the maxil- of the upper eyelids and receives anasto- lary premolars moses from the post-ganglionic fibres of œ the anterior superior alveolar nerve (ner- the pterygopalatine ganglion via the zygo- vus alveolaris superior anterior), which in- matic nerve nervates the maxillary anterior teeth œ the frontal nerve (nervus frontalis), which œ the infraorbital nerve (nervus infraorbital- innervates the forehead and vertex is), which innervates the skin on the front œ the nasociliary nerve (nervus nasociliaris), part of the cheeks, the lower eyelids, the which innervates the eyeballs, the ethmoi- lateral nasal surfaces, the upper lip, and dal chambers, the nose, and the skin of the the upper labial mucosa nasal bridge and the tip The mandibular nerve is the third and the The maxillary nerve is the second branch largest branch of the trigeminal nerve. It pro- of the trigeminal nerve, which has purely sen- vides sensory innervationSlap to the mandibular sory fibres which innervate the cheeks, lower teeth and gingiva, the skin of the temples, a eyelids, the lateral sides of the nose, the upper part of the ear, the lower lip, the lower part of lip, teeth, the maxillary mucosa, the inlet of the face, the anterior two-thirds of the tongue, the sphenoid bone, the maxillary sinuses, the and the mucosa of the oral cavity floor. It pro- posterior ethmoidal chambers, the superior vides motor innervation to the masticatory and middle nasal conchae, the palate and pal- muscles and the other muscles which develop atine tonsils, the roof of the pharynx, and the from the first pharyngeal arch. The branches dura mater of the middle cranial fossa. The of the mandibular nerve are as follows: branches of the maxillary nerve are as follows: œ the buccal nerve (nervus buccalis), which œ the posteriorCopyright superior alveolar nerve (ner- innervates the mucosa and skin of the vus alveolaris superior posterior), which cheeks innervates the maxillary molars and the œ the (nervus lingualis), which maxillary sinuses innervates the floor of the oral cavity and œ the zygomatic nerve (nervus zygomaticus), the anterior two-thirds of the tongue which innervates the skin of the temples œ the inferior alveolar nerve (nervus alveo- and the cheeks laris inferior), which innervates all the œ the pharyngeal nerveNaklada (nervus pharyngeus), mandibular teeth and the mandibular which innervates the mucosa of the nasal gingiva part of the pharynx behind the auditory œ the mylohyoid nerve (nervus mylohyoide- tube us), which innervates the mylohyoid mus- œ the© greater palatine nerve (nervus palati- cle and the anterior belly of the digastric nus major), which innervates the hard pal- muscle ate up to the incisive foramina

5 BIOLOGY AND MORPHOLOGY OF HUMAN TEETH

œ the mental nerve (nervus mentalis), which anterior part of the nasal cavity, and the an- innervates the skin of the chin, the labial terior two-thirds of the cerebrum. As opposed area, and the labial gingiva to the internal carotid which has no œ the auriculotemporal nerve (nervus au- branches in the cervical area, the external ca- riculotemporalis), which innervates the rotid artery has several branches. The anterior parotid gland and the temporomandibular branches of the include joint the arteria thyroidea superior (for the thyroid gland and larynx), the arteria lingualis (for the The (nervus facialis) is a mixed tongue and floor of the oral cavity), and the cranial nerve which contains motor, gustatory, arteria facialis (for the submandibular salivary and parasympathetic fibres. It innervates the gland, the submental area, and the face). The mimic muscles and transmits gustatory stim- middle branch of the external carotid artery is uli from the anterior two-thirds of the tongue. the arteria pharyngea ascendens, which sup- It supplies certain cranial and cervical ganglia plies the pharynx. The posterior branches of with its preganglionic parasympathetic fibres. the external carotid artery are the arteria oc- The glossopharyngeal nerve (nervus glos- cipitalis (for the occiput area) and the arteria sopharyngeus) is a mixed cranial nerve which auricularis posterior (for the area behind the innervates the muscles of the soft palate and ears). The external carotid artery terminates pharynx, the pharyngeal mucosa, the palatine by splitting into the arteria maxillaris and the arches, and the parotid . arteria temporalis superficialis. The most im- The vagus nerve (nervus vagus) is the portant involvedSlap in the vascularisa- longest cranial nerve with the most extensive tion of the oral cavity per se are the arteria lin- distribution. It is comprised of mixed nerve gualis, arteria facialis, and arteria maxillaris. fibres and provides innervation to the head, The (arteria lingualis) splits , chest cavity, and parts of the abdominal into three parts: cavity. œ the sublingual artery (arteria sublingualis)– a branch of the lingual artery which sup- plies the floor of the oral cavity and the Vascularisation of the oral sublingual salivary glands cavity œ the dorsal lingual artery (arteria dorsalis The Copyright oral cavity is well supplied with blood linguae)–a branch of the lingual artery vessels. It is therefore vital to be aware of which supplies the deep posterior parts of the tongue its vascularisation for performing safe clini- cal work. The common carotid artery (arteria œ the deep lingual artery (arteria profunda carotis communis), which is a branch of the linguae)–the terminal branch of the lin- brachiocephalic trunk, supplies arterial blood gual artery which branches out to supply to the cranial and cervical organs. It bifurcates the lingual muscles at the level of theNaklada larynx into the external (ar- The facial artery (arteria facialis) supplies teria carotis externa) and internal carotid ar- the mimic muscles, the palatine tonsils, the teries (arteria carotis interna). The external palate, the submandibular salivary gland, and carotid artery supplies blood to all the cranial the lower and upper lips. The ascending pala- and© cervical organs except for the brain, the tine artery (arteria palatina ascendens) is a lat- eyes, and the inner ears, while the internal eral branch of the facial artery which supplies carotid artery supplies blood to the orbits, the the soft palate and the pharynx.

6 Chapter 1 Basic Anatomy of the Oral Cavity

The (arteria maxillaris) is cervical nodes; lymph from the sub- the first terminal branch of the external carot- mandibular glands drains into the deep cervi- id artery which supplies the external cerebral cal lymph nodes. membrane, the mandibular teeth, the masti- catory muscles and the temporomandibular Dental arches and the alveolar joint, the external acoustic meatus and the bone tympanum, the palate, the maxillary teeth, Teeth are placed in dental alveoli, which are and the nasal cavity. The maxillary artery arranged in the maxillary and mandibular branches extensively into the infratemporal dental arches. The shape and size of dental and pterygopalatine fossae. Its most signifi- arches change with jaw growth and develop- cant branches in the oral cavity are as follows: ment. The jaws grow and develop in several œ the inferior alveolar artery (arteria alveola- stages: ris inferior)–a branch which supplies blood œ prenatal stage to the mandibular teeth œ predental stage œ the posterior superior alveolar artery (arte- œ stage of deciduous teeth ria alveolaris superior posterior)–a branch œ mixed dentition stage which supplies blood to the maxillary mo- lars and premolars œ stage of permanent teeth œ the descending palatine artery (arteria pa- The prenatal stage in jaw growth and de- latina descendens)–a branch which sup- velopment takes place duringSlap intrauterine life, plies blood to the palate when a maxillary prognathism (the anterior œ the greater palatine artery (arteria pa- part of the maxillary alveolar process stands latina major)–a branch of the descending out over the mandibular alveolar process) is palatine artery which supplies blood to the seen during the first months. Between the hard palate second and third months of intrauterine life, embryonic progenia develops (the anterior The of the oral cavity generally fol- part of the mandibular alveolar process stands low the arteries and bear similar names. Veins out more than the maxillary alveolar process). in the palatal area drain into the pterygoid Over time, the relationship between the max- venous plexus, while the drain illa and mandible changes. Before birth, the into theCopyright internal jugular . Maxillary veins mandible once again retracts distally resulting (venae maxillares) drain the pterygoid venous in a prominent maxilla (prognathism) during plexus. birth, i.e. with a physiologically distal bite. Lymph from the upper lip, teeth, lateral The predental stage marks the jaw relation- parts of the anterior part of the tongue, and ship before the appearance of the first decidu- the gingiva drains into submandibular lymph ous teeth. In this period, the anterior part of nodes. Lymph from the lower lip and the apex the maxillary dental arch is 8 to 10 mm wide of the tongue drainsNaklada into submental lymph and flat, and a so-called incisal plane or pla- nodes. Lymph from the central and anterior teau is detected. The mandibular dental arch part of the tongue drains into deep lower is narrow and steep, which allows for sliding cervical lymph nodes, while lymph from the movements and facilitates sucking. The sub- posterior© part of the tongue drains into deep sequent stage is characterised by the eruption upper cervical lymph nodes. Parotid glands of deciduous teeth and the forward position- drain the lymph into the superficial and deep ing of the mandible. Gaps appear between the

7 BIOLOGY AND MORPHOLOGY OF HUMAN TEETH

TONGUE

Excretory ducts of sublingual Floor of oral salivary gland cavity

Transverse palatine folds

Figure 1.3 The maxillary dental arch has a semi- Figure 1.4 The mandibular dental arch has a para- elliptical shape. bolic shape.

deciduous teeth, which are referred to as phys- Slap iological diastemata. These diastemata secure space for permanent teeth. Deciduous teeth exfoliate between 5 to 7 years of age which is coincided by the eruption of the first perma- nent teeth. This marks the beginning of the mixed dentition stage which consists of two phases. In the first phase between the 5 and 9 years of age, the first permanent molars erupt, Alveolar ridge and deciduous incisors are replaced by perma- Supporting alveolar bone nent ones. In the second phase, which occurs betweenCopyright the age of 9 and 12, the canines and premolars erupt. The second permanent mo- Figure 1.5 Alveolar ridges and supporting alveolar lars erupt between 12 to 14 years of age. With bone the exfoliation of deciduous teeth, the stage of permanent dentition begins. Permanent den- tition is complete with the eruption of third molars, which usually appear at the age of 18 years, although theyNaklada can erupt earlier or much œ a wider maxillary dental arch compared to later. the mandibular arch The dental arches receive their final char- œ pronounced vestibular overlap of the max- acteristics with the eruption of the permanent illary teeth teeth.© The characteristics of dental arches œ semi-elliptical shape of the maxillary den- with properly positioned teeth (eugnathic tal arch and a parabolic mandibular dental dentition) are as follows: arch (Figures 1.3 and 1.4).

8 Chapter 1 Basic Anatomy of the Oral Cavity

œ occlusion of teeth with two antagonists Haversian canal system supplies the bone (except for mandibular central incisors with nutrients. and maxillary third molars) The alveolar and basal bones are covered œ pronounced anteroposterior occlusal curve with periosteum. The alveolar bone is divided (curve of Spee) into the alveolar bone proper and the sup- porting alveolar bone, and they are composed The alveolar bone is that part of the max- of: illa or the mandible which protects and an- chors the teeth (Figure 1.5). The alveolar bone œ fibres is also a part of the as the perio- œ cells dontal ligament connects it to the . œ intercellular substance Every mature jawbone (maxilla or mandible) œ nerves consists of two parts: œ blood vessels œ a part which contains the dental roots, i.e. œ lymphatic vessels the alveolar bone (synonyms: alveolar pro- cess or alveolar ridge) and The alveolar bone proper lines the tooth sockets. Although it is composed of com- œ a bony part which is positioned apical to pact bone, it can be considered a cribriform the root, i.e. the basal bone which consti- plate because it contains numerous cavities, tutes the body of the maxilla or mandible through which Volkmann’s canals pass from The alveolar bone consists of cells and a the alveolar bone to periodontalSlap ligament. partially calcified matrix composed of approx- The alveolar bone proper consists of com- imately 60% inorganic matter. The inorganic pact bone plates which envelop the teeth. The matter is embedded in the matrix between the thickness of the alveolar bone proper ranges bone cells and primarily consists of calcium from 0.1 to 0.5 mm. Sharpey filaments, which hydroxyapatite and components such as mag- are mineralised only in the peripheral parts, nesium, fluoride, calcium carbonate, and oth- are anchored to the alveolar bone proper (at an ers to a far lesser extent. The calcified matrix angle of 90 degrees). On a radiographs, the al- consists of collagen fibres and intercellular veolar bone proper appears as a uniform white substance. line (lamina dura) which follows the outline During the initial stages of bone forma- of the teeth. The integrity of the lamina dura tion, theCopyright unmineralized calcified bone matrix is an important feature to be considered in is referred to as osteoid, which is subjected the analyses of radiographs of teeth and per- to mineralisation. It is formed by osteoblasts iradicular space; interruptions in the continu- which are located in the periosteal surface of ity of lamina dura usually indicate pathologi- the bone surface and is 5–10 µm in thickness. cal changes. Being a layer of newly mineralised matrix, it is The alveolar ridge is the most cervical part comparable to predentine or pre-cementum. of the alveolar bone (Figure 1.6). In a healthy The matrix of the compactNaklada bone is formed in periodontium, the alveolar ridge lies 1 to 2 layers (lamellae) with osteocytes located be- mm below the cementoenamel junction. The tween the rings of the matrix. The concentric triangular part of the alveolar ridge between lamellae form the Haversian canal system. adjacent teeth is referred to as the interdental The Haversian© canal is the central vascular septum. canal containing blood vessels, nerves, and The supporting alveolar bone consists of small amounts of connective tissue. The a cortical and trabecular bone. The cortical

9 BIOLOGY AND MORPHOLOGY OF HUMAN TEETH

Radiographic appearance of the maxilla and mandible Use of radiographic equipment is an integral component of modern dentistry. Many dental Alveolar ridge procedures which follow modern standards of Alveolar bone proper dentistry are unimaginable without the use of x-ray images. These images are used in pre- operative, operative, and postoperative dental treatment starting from diagnosis and therapy Labial cortical bone planning, through intraoperative radiographic Trabecular bone Supporting evaluation, up till postoperative monitoring alveolar bone of the success of the performed procedure. Knowledge of the radiographic appearance of the maxilla and mandible constitutes the basis for analysing and interpreting intraoral and extraoral radiographs. Lingual cortical bone The differences in the way x-rays pass through different substances are of fundamen- Figure 1.6 Alveolar bone structure tal significance when recording radiographic images. Since x-rays Slapare absorbed differently in the substances they penetrate, these sub- bone (or cortical plate) consists of compact stances are depicted differently on the images. bone on the facial and lingual surfaces of the The lower the absorption of x-rays, the darker alveolar bone. The cortical bone is usually 1 the appearance on the image. For this reason, to 3 mm thicker in relation to the posterior air appears as black areas on radiographs, fatty teeth than the anterior teeth. The cortical tissue appears as grey areas, soft tissues in dif- bone is not visible on periapical or bite-wing ferent shades of grey, and mineralised tissues radiographs; it is only visible on occlusal ra- such as bones and metals appear as white ar- diographs. The trabecular bone consists of eas. During interpretation of radiographs, it spongyCopyright bone positioned between the alveolar should be borne in mind that the structures bone proper and cortical bone plates. Radio- which are closer to the radiographic film ap- graphically, the trabecular bone is visible in pear to be clearer, while those farther away are the areas between the teeth and their roots. less sharp and blurry. Since an x-ray image is a The alveolar bone between two adjacent two-dimensional depiction of a three-dimen- teeth (interdental septum) consists of the al- sional object, there occurs overlap of certain veolar bone proper and the spongy part of the structures which can make it more difficult to trabecular bone.Naklada The interdental septum is interpret these images. easy to visualise on x-ray images. The alveo- The radiographic appearance of a normal lar bone between roots of the same tooth is maxilla and mandible is depicted and de- referred© to as the interradicular septum. scribed in Figures 1.7 and 1.8.

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