Anatomy and histology

1 Anatomy and Histology 1.1 Bones The entire human body is supported by bone, with these, the vessels, the nerves and muscles run towards their groovy structures and settle in bony parts to provide the body with their function. It is essential to have a healthy bony formation on the head, for the oral cavity to function properly without any direct or indirect issues. The bones are divided into two parts, the neurocranium, which is basically a cover of the brain, and the viscerocranium, a supporting frame for the muscles of the face to rest on. The bones of the neurocranium that concern what will be mentioned in this degree thesis are the frontal

Figure 1 The skull and its parts (Source:Studyblue) bone, the temporal bone, the sphenoid bone, and for the viscerocranium are the nasal bone, the zygomatic bone, the maxilla and the mandible (1).

The mandible is probably the most important bone of the afore mentioned bones, because it is the one that holds the lower teeth on its alveolar part and with the help of the masseteric muscles, moves them against and toward the upper teeth for chewing the food particles. Without

it, a normal lifestyle is impossible. This bone is divided into head, neck, ramus and body, where the angle of mandible is formed between the ramus and the body of mandible. Due to the aid it takes from the muscles to be moved, most are inserted on structures of it (1) (2) (3) (4).

1.2 Trigerminal nerve The trigerminal nerve is one of the twelve cranial nerves, specifically the fifth and it is the one responsible for the innervation of the teeth. All cranial nerves have nuclei, from where nerve pathways arise and transport either sensory or motor innervations. Some of these nerves are solely sensory or motor and some as in the case of the trigerminal nerve, are both sensory and motor. The nuclei of the trigerminal nerve, are located in the lateral part of the pons. It provides sensory innervation for the skin and mucosa of the face, and motor innervations for the

Figure 2 The location of the nuclei of all cranial nerves (Source: Wikivet)

masticatory muscles. It divides into the Opthalmic nerve, the Maxillary nerve and the Mandibular nerve (3).

Among the many division if the Maxillary nerve, we have the infraorbital nerve which in turn divides to the posterior superior alveolar nerve that innervates the maxillary molars of the same side with the nerve, the middle superior alveolar nerve that innervates the premolars of the same side and the anterior superior alveolar nerve that innervates the frontal teeth of the same side (3).

Some of the motor divisions of the mandibular nerve are the masseteric nerves, the deep temporal nerves and the pterygoid nerves, which they supply the masticatory muscles with motor innervations as mentioned above. Furthermore, the mandibular nerve is responsible for the sensory innervations of the mandibular teeth, and this is carried out by the inferior alveolar

Figure 3 The trigerminal nerve location and its 3 primary division (Source: Medicalook)

nerve, which divides into the inferior dental branches and supplies the lower teeth of the same side (3).

1.3 Oral cavity The oral cavity is a space lined by mucous membrane and it is divided into three parts.

The first part is the oral vestibule, which is bordered in the front by the lips, laterally by the cheeks and finally by the teeth. The second part is the proper oral cavity, which is bordered by the teeth, the alveolar bone and the gingiva, on top is the palate and on the bottom is the muscular floor, on which the tongue rests in. Finally the third part are fauces, these are the glossopalatine arch and the pharyngopalatine arch, located behind and below the uvula, between the oral cavity and the oropharynx (5).

1.4 Teeth

It is important to first understand a brief division of the teeth before reading more information about their morphology. Teeth are found in the upper jaw – maxilla and the lower jaw – mandible. The teeth are divided in four sections, called quadrants, and each quadrant contains 8 teeth under normal conditions. The imaginary perpendicular lines between the first incisors of both upper and lower jaw give us those four sections. The frontal teeth are the incisors and the canines and the posterior or distal teeth are the premolars and molars. The incisors mainly function in separating parts of food and the canines in gripping and tearing of the food particles during the mastication cycle (2) (4) (6).

Figure 4 The oral cavity (Source: McGraw - Hill companies, inc.)

1.4.1 Development and eruption The eruption of teeth is done twice in a healthy human. The first process of eruption, the milky or primary dentition, starts in the first year of life, ideally in the first 6 months and the for the permanent dentition in the sixth year of life. For a tooth to be created before its eruption starts, embryological structures will come together and start its formation. It is divided into three stages: The “Bud” stage, the first stage finishes after odontogenic mesenchyme to complete. On the embryonic jaw there is a structure called the dental lamina. The dental lamina will start deviating from the jaw, in the sixth week of fetal life, with two projections that will meet and fuse, creating the odontogenic mesenchyme. In a continuous process, the mesenchyme will give rise to three structures, the dental (or enamel) organ, the dental papilla and the dental follicle and therefore completing the first stage. The difference with the permanent teeth is the location of the dental lamina before the process starts and this is the vestibular lamina, which is located labially and buccally to the dental lamina (7).

Figure 5 The cap stage after fusion of the epithelial projections (Source: BP Blogspot) Moving on to the “Cap” stage, enamel and dentine formation starts. Ameloblasts are the cells responsible for the formation of enamel and they derive from the enamel orgam. More specifically, the ameloblasts are in layers, those which are responsible for enamel deposition are located in the inner layer. After enamel deposition is complete and the crown starts to be visible, the dentine deposition starts. The cells responsible are called odontoblasts and they arise from the outer surface of the dental papilla. The deposition direction is tubular and dentine keeps this formation forever, assuming it is healthy. This formation allows a space for the future placement of the dental pulp (7).

Figure 6 The point of start, the cascade of tooth formation and the legend of structures (Source: 4Shared) The final stage of tooth formation is called the “Bell� stage.In the bell stage, the dental organ is bell-shaped and most of the cells have a star-like shape. What is particular for this stage, is the outward movement of ameloblasts and the disintegration of the dental lamina which leaves the tooth under development separated from the epithelium of the oral cavity and these two will join again when the tooth erupted. Another event of this stage, is the secretion of the organic matrix, by the cells responsible for the hard tissues, that will eventually be mineralized and get hard consistency (7).

1.4.2 Surfaces Furthermore, the teeth surfaces where each surface gets its name according to the direction it is facing. The vestibular surface is the one facing the vestibulum, a border in the mouth confined by various oral soft tissues. In the case of the frontal teeth, the surface can be referred to as labial, from the lips, and in the case of the distal teeth buccal, from the cheeks. The oral surface gets the name by pointing toward the oral cavity. For the upper teeth the surface can be called palatal, due to the hard palate and for the lower teeth lingual,

Figure 7 Two opposite quadrants of the human dentition (Source: Wistatutor)

because of the tongue. Finally the distal teeth have one extra surface, called occlusal. It is the surface where the upper distal and lower distal teeth come in contact (4) (8).

1.4.3 Morphology The human teeth, as well as the teeth in most mammals, consist of various parts where some of them are visible and some of them cannot be seen under physiologic conditions. The visible part is called clinical crown, which is basically what the eye can see. When referring to the whole structure of the crown, both hidden and visible, the term anatomical crown is used. On the visible crowns of the frontal teeth, there are the contacting parts between the upper and lower teeth, called incisal edge. The hard attachment of the teeth is facilitated by their root, a structure usually twice as big in length as the crown. The crowns and the roots are connected by the neck, or cervix, of the the teeth, the area where the teeth usually become more narrow (4) (9) (5).

Figure 8 The three main parts of the tooth (Source: Mouth and Teeth) The crown of the incisors resembles a chisel in shape for the upper incisors, or a shovel for the lower incissors, it is convex vestibularly and concave orally. In size, the maxillary central incisors are the biggest, then the maxillary lateral incisors are the second biggest, the mandibular lateral incisors follow and finally the mandibular central incisors are the smallest of all incisors.

The crown of the canine, resembles a quadrangle in the vestibular surface, which is divided into two triangles, with the distally located triangle being the biggest. Both the incisors and the canines have a structure called the “dental tubercle�, which is located on the cervical portion of the oral surface of the frontal teeth.

Moving on to the distal teeth, we find the cusps, structures that vary in number and size according to which tooth they are located on. The premolars have two cusps, one located vestibularly and the other located orally. In the case of the maxillary first premolar, the vestibular cusp is bigger with a big difference, where as in the other premolars, the difference of the cusp’s height is slight. The cusps of the premolar, give us an oval outline of the occlusalsurfaceand from that surface the crown becomes more convex toward the cervical region. Between those two cusps, a fissure is created that is well marked in the direction from the mesial to the distal sides of the crown. The maxillary first premolar is the biggest of all premolars, followed by the maxillary second premolar and the mandibular premolars. In mandible, the second premolar is bigger than the first premolar. In the molar teeth, four cusps are found, giving a rectangular outline on the occusal surface, which again becomes convex towards the cervical region, giving us a quadrilateral shape. What is noteworthy is that the third molar and final tooth in the quadrants, can show many variations or even not being present in an individual, without suffering from any certain condition. Therefore, we usually describe the first two molars as they tend to be of a similar morphology in the majority of the population. From the biggest to the smallest we get: the first maxillary molar, the second maxillary, the second manibular and the first mandibular molar. These details are all well visible in Figure 7 (4) (9) (5).

The final major structure of teeth is the root. Roots vary in number size and state according to which tooth they are located on. The frontal teeth are all one rooted teeth, with the root of the canine being the strongest and the longest of all roots in one dentition. The root of the central incisor has a small curvature sometimes, in distal or oral direction, in contrast to the other frontal roots that are inclined distally and curved on the apical part distally or orally. On the distal teeth, the first maxilarry premolar has two roots, one located vestibularly and one located orally, where the rest premolars are one rooted teeth that slightly curve in the middle of the root giving a curved shape in general. All other premolars are one rooted. The maxillary first and second molars are three rooted teeth, with one root being located mesiorally, one root being located mediodistally, and the third larger ptiside and the other root in the distal side, excluding the third molars which are once again unpredictable (4) (9) (5).

Figure 9 A cross-section of a tooth and periodontal tissue which shows the dental pulp (Source: Help your mouth)

1.4.4 Dental Pulp The dental pulp is the structure that lies in the inner part of tooth, specifically in to pulp chamber. Both are divided into coronal pulp for the part that is within the crown, and radicular pulp for the part that is within the root. Radicular pulp extends from the cervical part of the crown towards the root apex, in the conical confinement called the root canal. and it is continuous with the periapical tissues via the apical foramen. It is not uncommon for a root to

have two apices, where in this case the largest foramen is the apical foramen and the smaller is the accessory foramen. This is the point where infections are spread.

The composition of the pulp is mainly fibroblasts, odontoblasts, but also histiocytes, macrophage, granulocytes, mast cells and plasma cells exist. Finally the pulp functions in forming dentin, both primary and reparative after caries or trauma, nutrition by keeping the organic components of the surrounding mineralized tissue supplied and nutrients, sensory function by transmitting traumatic and temperature changes, perceived as pain.

1.4.5 Root Canal The root canal, as mentioned above, is the conical space within the root, continuous with the pulp chamber, that envelops the dental. The root cana is not concrete and there are many

Figure 10 Histological and anatomical structures of a tooth (Source:Medlineplus)

openings towards the side, the accessory canals. The accessory canals are predominantly in the apical third of the root and come to contact with the periodontal tissues. Although the radiographic image of the tooth is used to assess the root canal, its real morphology differs greatly.

Figure 11 A histological picture of the pulp that shows the accessory canals (Slide share – Dental Pulp)

1.4.6 Histology Histologically, the tooth is made up of three different hard tissues, the enamel, the dentine and the cementum. The enamel is the hardest tissue in the human body and it contains , around 95%, inorganic crystals, the hydroxyapatite crystals. The hydroxyapatite crystal are chemically converted to fluoroapatite crystals when in contact with fluoride, usually from the toothpastes during brushing of teeth. The remaining consistency of enamel is organic substances, around 0.5% and water. Enamel is the outermost tissue of the teeth and covers the dentine.

Dentine is also composed of inorganic material, but they make up for around 75 percent of the constituents of dentine. The rest organic material, mostly collagen fibers, around 10 percent and water. The last tissue is the cementum, which is a hard as bone and it is most prominent in the

roots. Cementum has a similar structure and consistency as bone, made from around 65 percentof inorganic material, though at the apical third of the root, the cementum is coated with a layer of cementoblasts, the cells responsible for the initial production and reproduction of cementum (4) (10) (11).

1.4.7 Differences between the two types of dentition.

The two types of the human dentition have many differences between them in a morphological, histological and also chronological aspect. Firstly, the primary dentition has a different time of development, mineralization and eruption, than the permanent. There are less teeth due to the fact that there are no premolars and no third molars and those teeth, look whiter than those of the permanent dentition. Generally milky teeth are smaller in all dimensions but thing are different when it comes to ratio. Examples of the differences in ratio are that the roots are longer in the milky teeth and also the mediodistal direction of a milky crown is greater, thus milky teeth have wider contact points (8).

Morphological differences of the roots are that the roots of frontal teeth are wider in milky dentition, even though all milky roots have thinner walls. Also there are differences in the curve a root makes as the milky roots of molars are more divergent on the coronal part of the root and more convergent on the apical part of the root and generally the roots tend to incline towards the long axis (8).

The crowns of the milky dentition, have thick enamel ridges on ocllusal surface and there are thickenings of enamel on cervical region. Also, the vestibular surfaces of milky teeth are more convex towards the occlusal surfaces, and also the buccal and lingual surfaces converge towards the occlusal surface, making the cervical diameter of the milky tooth greater than the occlusal diameter. The pulp chamber, even though the mass of tooth seems restricted, is very large with prominenent horns, therefore the narrowed area toward occlusion is made of thinner hard dental tissue (8).

1.5 Periodontium The word periodontium, refers to the structures surrounding the tooth. These structures are the gingiva, the cementun that was mentioned previously, the alveolar bone and its processes and the periodontal ligaments.

1.5.1 Gingiva The gingiva tissue surrounds a tooth, from the neck to the root. This tissue is part of the oral mucosa, and the outermost part of the periodontium on oral direction. Histologically, they contain keratin, just like the thin type of the human skin. Clinically, we divide gingiva into free marginal gingiva, and the attached gingiva (4) (12).

The free marginal gingiva surround the apical portion of the clinical crown of the tooth and provide an attachment to the crown by the junctional epithelium. Other epithelia in this region, are, from biggest to smallest, the: oral epithelium which is continuous with the attached gingival, the oral sulcular epithelium which is continuous with dentine below the contact point of

Figure 12 The gingiva anatomy (Source: Crystal Lake Dental)

two teeth and the junctional epithelium. Physiologically, the space of the juctional epithelium is approximately 2mm and several diseases which will be discussed later may cause this space to grow. Occlusaly to the marginal gingiva, are the interdental papillae, with a triangular shape in the approximal surfaces of two teeth. The inner side of an interdental papilla, is called col and its tip terminates at the contact point of two neighbouring teeth. These gingiva cover the neck of the tooth and part of the approximal surfaces and continue as attached giniva. The attached gingiva begin on the impression of the juctional epithelium towards the vestibular surface of the gingiva, also known as the free gingiva groove and continue up to the mucogingival line, which are bound, by dense collagen fibers, to the alveolar bone (4) (12).

Healthy gingiva, have a coral pink or salmon color although occasionally, gingiva with dark pigments can be found. Their surface has an appearance that resembles the peel of an orange and it is termed as stippling (4) (12).

1.5.2 Alveolar bone The alveolar bone is the thickened ridge of bone that contains the tooth sockets on maxilla and mandible. On the maxillae, the alveolar process is a ridge on the inferior surface, and on the mandible it is a ridge on the superior surface. The alveolar process contains a region of compact bone adjacent to the periodontal ligament, which is called the lamina dura when viewed on radiographs. It is this part which is attached to the cementum of the roots by the periodontal ligament. On radiographic evaluation the lamina dura is examined to assess its integrity, something which gives out the start or the complete existence of a periodontal lesion.

Figure 13 The alveolar bone histologically (Source: Syrian Clinic)

The alveolar bone or process is divided into the alveolar bone proper, the lining of the tooth surgace, also called cribriform plate due to the holes it has for the periodontal ligaments to be attached on it, and the supporting alveolar bone. Microscopically, both the alveolar bone proper and the supporting alveolar bone have the same consistency. The supporting alveolar bone consists of both cortical plates and trabecular bone. The cortical plates, consists of plates of compact bone on the facial and lingual surfaces of the alveolar bone which are about 3mm thick on the posterior teeth but not clearly defined for the anterior teeth. The trabecular bone is between the alveolar bone proper and the cortical plates. Finally the part of bone between two teeth, is the alveolar septum (11).

1.5.3 Periodontal Ligaments The periodontal ligaments, are the ligaments located at or around the apex and the apical

Figure 14 The periodontal ligament groups (Source: KCK - USM)

third of the root and they bind the tooth’s cementum to alveolar bone. They are made of collagen tissue, vascularized and cellular, with mainly fibroblasts. Other than binding, they also support the teeth against pressure, distribute the pressure load when chewing and finally they supply the root with nutrients and innervations by the nerves located there. There are two periods of the state of theses ligaments, with the first being the silent period when there is no pressure, the main fibers are shaped like the letter “S�, and when pressure is applied, is the period where they stretch.

There are five groups of ligaments and theses are: the transeptal group, which they encircle the neck area of the root below the alveolar bone, the alveolar crest group which are below junctional epithelium and oriented obliquely towards alveolar bone, the horizontal group, which lie on the root, the oblique group, the largest group of ligaments that is on the whole length of the root except the apical portion and finally the apical group of ligaments, which is only on the apex.

1.6 Salivary Glands The salivary glands are the glands responsible for the production and flow of the saliva.

There three major paired glands which are the parotid gland, the submandibular gland and the

Figure 15 The salivary gland histologically (The Digestive System of Vertebrates)

sublingual gland and an abundance of minor salivary glands. The saliva is produced in a microscopic structure of the gland, the acinous, which it may be serous or mucous or mixed, something which is defined histologicaly according to the composition and arrangement of the acini of the glands. Serous saliva contains proteins, such as: amylase and lysozyme, lactoferrin, and immunoglobulin A, which protect the oral cavity from bacteria and aid the digestion. The mucous secretion on the other hand, produces a slimy fluid which helps bacteria to stick onto surfaces of teeth and colonize, because of the many glycoproteins it contains. Saliva also contains minerals, such as: Calcium ions, Hydrogen ions, fluoride ions, inorganic phosphate After the production, the saliva is excreted through the salivary ducts (13) (2).

In summary saliva has these functions: the digestive function done by the digestive enzyme ι-amylase, where this enzyme is responsible for the breakdown of starch to maltose, that will be further fermented by oral bacteria. A following function of saliva is lubrication, facilitated by the mucin content of saliva. It is important for proper formation of food for swallowing and speech. Saliva aids in buffering too as it can neutralize the pH of the oral cavity, as after eating food, especially simple sugars, the pH levels decrease as a result of acid production by oral bacteria fermentation of sugar, causing demineralization of the tooth. At the same time, saliva assists in remineralization by elevating the pH level of the oral cavity and by being a source of ions same to the composition of the tooth’s enamel, it supplements it. Saliva is

also useful in clearing out the food debris and the cariogenic microorganism, but only in the cases where it has access, as for example in a physiologic dentition where teeth are not crowded.

Saliva contains proteins that will strongly adhere and absorbed onto the teeth, this layer of proteins is called pellicle and will protect the tooth enamel against acid dissolution. Furthermore the proteins that saliva contains act as antimicrobials. Proteins such as lysozyme, lactoferin, salivary peroxide and IgA have the ability to inhibit the metabolism, adherence and viability of cariogenic microorganisms, and therefore destroying them or leading them to destruction.

1.6.1 Minor salivary glands and Von- Ebner’s glands The minor salivary glands, are located in the oral mucosa of the lips, cheeks, palate and tongue between the fibers of its muscles. The Von-Ebner’s glands are only located in the tongue.

Their number is over 1000. These type of glands may own a duct, but it is also common that a duct is shared by more than one gland. The secretion is mucous except in the case of the VonEbner’s glands which are serous (13) (2).

1.6.2 Parotid Gland The parotid gland, the largest salivary gland is located in front of the ear on the fat pad of the masseter. It overlaps the ramus of mandible and covers the condyle of the neck of the mandible. The parotid duct passes through the buccinator muscle to the oral mucosa and empties the salivary product in the area between the first and second maxillary molars. This gland is serous (13) (2).

1.6.3 Submandibular and sublingual glands The submandibular gland, is located below the mandible, and the sublingual gland below the tongue, hence the names. The submandibular gland is surrounded by the mandible, the digastric and the mylohyoid muscles and the sublingual by the tongue and the mylohyoid muscle. The submandibular duct ascends and meets the sublingual duct, where both empty their content in through the sublingual fold. The submandibular is predominantly serous, and the sublingual is predominantly mucous (13) (2).

1.7 Temporomandibular joint The temporomanibular joint, is the joint that connects the glenoid fossa of the temporal bone and the condyle of the head of mandible, with an articular disc between them and two Figure 16 The major salivary glands and the path of their ducts (Source: ENT allergy and sinus center)

ligaments, the sphenomandibular and the stylomandibular ligament. When in function, it is like two joint are in synergy, as it seems there is an articulation between the disc and the head of mandible and an articulation between the disc and the glenoid fossa.Several movement are allowed by these joint such as opening, closing, back and forth and lateral, or in relation to the maxilla, abduction, adduction, retrusion, protrusion and lateral, also combinations of these are possible. The masticatory muscles responsible for each movement will be mentioned later, in chapter 1.9 (14).

Figure 17: The temporomandibular joint (Source: Pearson Education)

1.8 Tongue The tongue is the strongest muscular organ of the human body. It is divide into the tip, the body and the root. The anterior part of the body is conncted with the tip of the tongue via the median sulcus, and the two parts of the body are connected between them via the terminal sulcus.

Figure 18 The temporomandibular joint and the nearby structures (Source: Pearson

Figure 19: An illustration of the extrinsic muscles of the tongue (Source: Home Stead Schools)

The root of the tongue is inserted into the nearby bony structures. The whole tongue rests on the mylohyoid muscle, which arises from the mylohyoid line of the mandible and ends on the hyoid bone. The anterior two thirds of the tongue are innervated by the lingual nerve, a branch of the mandibular nerve, and the posterior one third of the tongue is innervated by the glossopharyngeal nerve, the ninth cranial nerve. The tongue functions in chewing and swallowing of food and it is also responsible for taste sensation (6) (2).

The tongue consists of a complex muscular fiber arrangement. There are four principal muscles which come into contact with nearby structures, the extrinsic muscles, and the intrinsic muscles of the tongue which are within the tongue oriented in various directions, suchs as:

superior, inferior, transverse and vertical. The extrinsic muscles of the tongue are: the genioglossus muscle, the hyoglossus muscles and the palatoglossus muscle. The genioglossus muscle is connected arises from the mental spine of mandible and interconnects with all the intrinsic muscles of the tongue. As for all the other muscles of the tongue, except the palatoglossus muscle, the motor nerve responsible for their function, is the hypoglossal nerve, the twelfth cranial nerve, and the palatoglossus form the vagus nerve, the tenth cranial nerve. The palatoglossus muscle arises from the soft palate anteriorly, it is covered by the palatoglossal arch as it descends, and merges in the body of the tongue with the transverse muscles. The hyoglossus muscle arises from the greater horn of the hyoid bone and merges with the genioglossus laterally to it. Finally the styloglossus arises from the styloid process and ends at the tip of the tongue.

The movements facilitated by the muscles of the tongue, are the forward and downward movement by the genioglossus muscle, the backward and upward movement by the hyoglossus muscle and the styloglossus (2) (6).

The sensation of the tongue, is facilitated by the papillae of tongue. The four papillae are divide according their shape. Firstly, the filliform papillae, which are threadlike and split on their top, and are located on almost the whole body of the tongue. These type of papillae are not responsible for taste but rather for tactile sensation. Another type of papillae, is the fungiform papillae, named due to their mushroom – like appearance. Fungiform papillae are distributed on most of the tongue’s area and are responsible for the perception of taste and temperature. The third type of papillae are the foliate papillae, which are located posteriorly to the tongue and arranged in lines, also responsible for taste perception. The fourth and last type of papillae is the vallate papillae, located in front of the terminal sulcus. These are the largest type of papillae and are also responsible for taste perception (2) (6).

1.9 Masticatory muscles and adjacent structures

There are four muscles that are of extreme importance for an individual’s chewing action, other muscles contribute as well but occasionally. Those four muscles are masseter, temporalis, lateral pterygoid and medial pterygoid. The lateral pterygoid muscle is present in all of the

Figure 20 The masticatory muscles and their insertion on the skull (Source: Pamibe)

movements of mandible, the medial pterygoid muscle is generally opening the mouth, but it also provides the mouth with frontal, lateral and rotational movements. The temporalis and the masseter muscles are providing closing of the mouth, with the masseter being the strongest muscle in closing of the mouth (1) (4).

The masseter mucles arises from the zygomatic arch of the zygomatic bone and it is inserted into the masseteric tuberosity of the mandible. The temporalis muscle arises from the temporal fossa of the temporal bone and it inserts on the mandible, specifically on its coronoid process and on its ramus. The lateral pterygoid muscle divides in two parts, the first part the inferior head, arises from the pterygoid bone, specifically from the outer side of the pterygoid process of that bone and it inserts into the mandible, on the pterygoid fovea. The second part of the lateral pterygoid muscle, the superior head, arises from the sphenoid bone, from its infratemporal crest and inserts into the articular disc on the head of mandible. The medial pterygoid muscle arises from the medial pterygoid bone, from the medial surface of the bone’s plate and it inserts into the thepterygoid tuberosity of the mandible (1) (4).