Chapter 3 Applied Anatomy PDF

CHAPTER 3 Applied anatomy Chapter 3 Applied anatomy I- Extra-oral landmarks of prosthetic importance: 1- Inter-pupillary line (Fig. 1)  It is an imaginary line running between the two pupils of the eyes whe...

CHAPTER 3 Applied anatomy Chapter 3 Applied anatomy I- Extra-oral landmarks of prosthetic importance: 1- Inter-pupillary line (Fig. 1)  It is an imaginary line running between the two pupils of the eyes when the patient is looking straight forward.  It helps in orientation of the anterior occlusal plane of the artificial teeth. 2- Ala-tragus line (Camper’s line) (Fig. 1)  It is an imaginary line running from the ala of the nose to the tragus of the ear.  It is used in orientation of the posterior occlusal plane of the artificial teeth. Fig. 1 Relationship of interpupillary line and Camper's line with occlusal plane 13 CHAPTER 3 Applied anatomy 3- Canthus-tragus line (Fig. 2)  It is an imaginary line running from the outer canthus of the eye to the tragus of the ear.  It is used in arbitrary location of the condyles (rotational axis). Fig. 2 Canthus-tragus line 4- Naso-labial sulcus (Fig.3)  It is a crease running from the ala of the nose laterally and downward to the corner of the mouth.  It becomes deeper and more prominent with aging. It can be approximately restored through proper positioning of the anterior teeth of the denture, proper establishment of occlusal vertical dimension and proper contouring of the upper denture flange. 14 CHAPTER 3 Applied anatomy Fig. 3 Extraoral landmarks 5- Vermillion border:  It is the transitional epithelium between mucous membrane of the lip and the skin of the face.  After loss of teeth and resorption of the labial alveolar bone, orbicularis oris muscle loses its support and drops inward, resulting in diminution of the amount of the vermillion border showing with relative fullness of the lower lip. Proper modification of denture flanges and position of the anterior teeth improve such appearance. 6- Mento-labial sulcus (Fig. 3)  It is a depression running horizontally between the lower lip and the chin.  Its curvature indicates the maxillo-mandibular relationship: 15 CHAPTER 3 Applied anatomy Angle Class I: In normal ridge relationship, the mento-labial sulcus shows a gentle curvature. (Fig.4a) Angle Class II: In retruded mandibular position, the mento-labial sulcus presents an acute angle. (Fig.4b) Angle Class III: In protruded maxillo-mandibular relationship, the mento-labial sulcus forms an obtuse angle (angle of 180 O). (Fig.4c) Fig.4 a. Angle Class I b. Angle Class II c. Angle Class III 7- Philtrum (Fig.3)  It is a diamond-shaped area at the center of the upper lip under the base of the nose. 16 CHAPTER 3 Applied anatomy  It is distorted with loss of teeth and alveolar bone resorption. Proper tooth arrangement and proper labial flange contouring would approximately restore the original form of the philtrum. 8- Angle of the mouth (commissure)  It is the point of meeting between upper and lower lips.  Inflammation and drooping of saliva from the angle of the mouth is termed angular cheilitis. Angular cheilitis may be the result of: (Fig.5) a. Prolonged edentulism, b. Denture with reduced vertical dimension and c. Vitamin B12 deficiency. In the first two conditions, construction of the denture with proper vertical dimension and proper positioning of the anterior teeth will support the angle of the mouth and hence improve the case. Inflammation due to vitamin B12 deficiency can be treated by administration of B12. Fig. 5 Angular cheilitis 17 CHAPTER 3 Applied anatomy 9- Modiolus (Fig.6)  It is the point of meeting of facial muscle fibers. It is a depression located below and distal to the angle of mouth.  After loss of teeth and alveolar bone resorption, the modiolus drops inward resulting in the characteristic appearance of an edentulism. Proper denture construction would restore the case. Fig. 6 Modiolus 18 CHAPTER 3 Applied anatomy II- Intra-oral landmarks of prosthetic importance: The oral cavity is divided into two compartments, the vestibule and the oral cavity proper. The vestibule is further divided into a labial vestibule and a buccal vestibule. The vestibule is bounded laterally by the mucous membrane of the lips and cheeks and medially by the outer surface of the natural teeth and the adjacent alveolar mucosa. A- In the maxilla: (Fig.7) 1- Residual alveolar ridge:  It is that portion of the alveolar process and it's covering soft tissue that remains after extraction of teeth. The highest part of the ridge is called the crest of the ridge.  It is covered with a layer of dense fibrous connective tissue that is favorable for supporting the denture. 2- Maxillary tuberosity:  It is a rounded bony prominence that is located just behind and above the distal end of the maxillary ridge.  It should be covered by the denture as it plays a role in retention and support of the maxillary denture. In some cases, extremely large tuberosities may need surgical correction before complete denture construction in order not to interfere with denture insertion. 19 CHAPTER 3 Applied anatomy Fig.7 Maxillary landmarks 3- Median palatine raphe:  It is a thin mucoperiostium with little or no submucosa that covers the median palatine suture. Its position in the palate is marked with a raised area of mucous membrane called the median palatine raphe, which may be hard or sensitive.  Lack of relief of the median palatine raphe would result in rocking of the denture with subsequent midline fracture. 20 CHAPTER 3 Applied anatomy 4- Incisive papilla:  It is pear-shaped elevation of soft tissue situated at the midline just palatal to the upper centrals. It covers the incisive foramen through which the nasopalatine nerves and vessels pass. After extraction of teeth and alveolar bone resorption, it migrates to the crest of the ridge.  It should be relieved to avoid interference with blood and nerve supply which might cause burning sensation. It also acts as a guide to the anteroposterior position of the central incisors as the labial surfaces of the upper centrals are usually located 8 to 10mm labial to the middle of the incisive papilla. (Fig.8) Fig.8 Relation of incisive papillae with incisors 21 CHAPTER 3 Applied anatomy 5- The palatine rugae:  It is irregular shaped ridges of dense connective tissue radiating from anterior one third of the hard plate on both sides of the midline. (Fig.9)  It is associated with the sense of taste and function of speech. They assist the tongue to absorb via its papillae. They also enable the tongue to form a perfect seal when it is pressed against the palate in making the linguopalatal sounds like "S" sound. When a smooth, thick artificial denture palate covers these elevations of the mucosa, difficulty is sometimes encountered with both taste and speech. Copying the rugae on the palatal surface of a denture or especially the corrugation of a thin metal palate helps to reduce the disability in some cases. Fig.9 Palatine rugae 6- Torus palatinus: (Fig. 10)  It is a bony bulge sometimes present in the midline of the palate. It varies in size and form.  If it is small, the denture base over this area should be relieved. If it is large, it is surgically removed. 22 CHAPTER 3 Applied anatomy Fig. 10 Torus palatinus 7- Fovea palatinae:  These are two small pits or depressions found on each side of the midline just posterior to the junction of hard and soft palate. They are openings of the ducts of minor salivary glands.  The posterior border of the maxillary denture should extend 2 mm posterior to the fovea palatinae. 23 CHAPTER 3 Applied anatomy B- In the mandible (Fig.11) Fig. 11 Medial and lateral surfaces of the mandible 24 CHAPTER 3 Applied anatomy 1- Residual alveolar ridge:  It is that portion of the alveolar process and it's covering soft tissue that remains after extraction of teeth. The highest part of the ridge is called the crest of the ridge. (Fig.12)  It is formed of cancellous bone, therefore unsuitable to bear stresses. Sometimes, in severely resorbed ridges, it appears as a cord like soft tissue extending throughout the crest. This case necessitates surgical intervention as it impairs denture stability. Fig.12 Crest of the ridge 2- External oblique ridge:  It is a dense bony ridge descending obliquely from the ramus of the mandible downward and forward till it fades at the mental foramen. 25 CHAPTER 3 Applied anatomy  The lower denture should cover but not extend beyond the external oblique ridge to avoid denture displacement by the powerful masseter muscle which is inserted into the lateral surface of the ramus and the anterior fibers are opposite to the external oblique ridge. 3- Buccal shelf of bone (Buccal plataeu):  It is a nearly horizontal shelf of bone that lies between the crest of the residual ridge and the external oblique ridge in the molar area. It is formed from dense compact bone. (Fig.13)  It should be covered with the denture to provide support. It is also considered as a primary stress bearing area because:- a. It is nearly perpendicular to the vertical masticatory forces and b. Its nature of bone being compact. Fig.13 Buccal shelf of bone 26 CHAPTER 3 Applied anatomy 4- Mental foramen: (Fig.14)  It is located on the buccal surface of the mandible in the premolar region between the roots of the first and second premolars and through it mental nerves and vessels pass.  Cases of severe ridge resorption, the mental foramen is usually located on the crest of the ridge. Relief of the denture in this area is necessary to avoid numbness of lower lip. Fig. 14 Mental foramen before and after teeth extraction 27 CHAPTER 3 Applied anatomy 5- Retromolar pad: (Fig. 15, 16)  It is pear shaped pad of soft tissue present bilaterally at the distal end of the residual mandibular ridge. It contains mucous glands, temporal tendon, pterygo-mandibular raphe, fibers of buccinator muscle and superior constrictor muscle of pharynx.  It should be covered by the lower denture to help for denture support. Because of its spongy nature, it acts as a cushion (shock absorbent). It also forms a splendid soft tissue seal. Fig. 15 Retromolar pad Fig. 16 Underextended denture. 28 CHAPTER 3 Applied anatomy 6- Torus mandibularis:  It is a bony prominence sometimes present on the inner surface of the mandible in the premolar region. It varies in size and shape. It is either unilateral or bilateral. (Fig. 17)  When it is covered with thin mucosa, relief of the denture base in this area could be made to avoid impingement of the mucosa. If the torus mandibularis is large and prevents proper seating of the lower denture, surgical intervention is necessary. Fig.17 Torus mandibularis 7- Internal oblique ridge (mylohyoid ridge): (Fig.18)  It is a bony ridge extending on the medial surface of the mandible from the third molar region to the lower border of the mandible near the midline. It represents the attachment of the mylohyoid muscle to the mandible.  Mylohyoid ridge should be included in the denture bearing area. Thin and sharp mylohyoid ridge should be 29 CHAPTER 3 Applied anatomy recontoured to permit better flange placement and border seal. Fig.18 Internal oblique ridge before and after extraction of teeth 30 CHAPTER 3 Applied anatomy 8- Genial tubercles or mental spine: (Fig.19)  These are two small projections located on the medial surface of the mandible, one on each side of the symphesis. They represent the attachment of the genioglossus muscle superiorly and geniohyoid muscle inferiorly.  In extreme alveolar bone resorption, genial tubercles migrate close to the crest of the ridge and become prominent, where they require relief. Fig.19 Genial tubercles before and after extraction of teeth 31 CHAPTER 3 Applied anatomy 9- Tongue:  It is a highly powerful muscle present in the floor of the mouth where the dorsum rests against the roof of the mouth and the tip rests in contact with the lingual surfaces of the lower incisor teeth. The lateral borders lie against the lingual borders of the posterior teeth.  When the teeth are extracted the tongue spreads laterally and the lips and cheeks fall in to meet it filling the space left by the teeth. Teeth have to be set on the crest of the ridge with the occlusal plane lower than the highest convexity of the tongue in order to avoid cramped tongue and allow the tongue to reflect the food on the occlusal surface. (Fig.20) Fig.20 Relation of occlusal plane with the tongue 32 CHAPTER 3 Applied anatomy III- Limiting structures of the denture: A- In the maxilla:( Fig.21) Fig. 21 Maxillary limiting structures 1- Labial frenum: (Fig.21.22)  It is a fold of mucous membrane present in the midline extending from the inner surface of the upper lip toward the crest of the residual ridge. It may be single or multiple.  Labial frenum moves with the muscles of the lips. The peripheries of the dentures must be designed to allow for these movements but such allowance must not be gross enough to spoil the peripheral seal or to produce ulceration of the frenum or displacement of the denture. 33 CHAPTER 3 Applied anatomy Fig 22 Proper contoured notch (continuous line), overcontoured notch (dotted line) 2- Labial mucous membrane reflection area (Labial vestibule):  It is the reflection of the mucosa of the lip to the mucosa of the alveolar ridge extending from the labial frenum to the buccal frenum.  The denture in this area is in relation to the orbicularis oris muscle which is the main muscle of the lip and incisive labii superioris muscle. These muscles limit thickness and length of the labial flange of the denture. 3- Buccal frenum:  It is a fold of mucous membrane that varies in size, number and position. It overlies the caninus muscle at the premolar region.  A buccal notch is made in the denture flange opposite the position of the frenum to facilitate its functional movement. Inadequate clearance in buccal flange for its movement will cause dislodgment of the denture. 34 CHAPTER 3 Applied anatomy 4- Buccal mucous membrane reflection area (Buccal vestibule):  It is the reflection of mucous membrane from the cheek to the alveolar ridge distal to the buccal frenum. In this area the denture flange is in relation to the buccinator muscle. Buccinator muscle is attached to the maxilla and mandible in the molar region and posteriorly it is attached to the pterygomandibular raphe in a horse-shoe like attachment. Due to the horizontal direction of the buccinator muscle fibers, contraction of this muscle will not displace the denture.  Denture flange must extend to rest on the attachment of this muscle in the buccal vestibule. The root of the zygomatic process (malar bone) sometimes is felt in this area as a hard bony prominence. It is located superior to the area of the first and second molar teeth. In this case, the denture flange may be notched opposite to the malar bone to avoid impingement of the oral mucosa between the denture and the bone. (Fig.23) Fig. 23 Buccinator muscle, root of zygoma and action of modiolus 35 CHAPTER 3 Applied anatomy 5- Pterygo-maxillary notch (Hamular notch):  It is a notch located between the maxillary tuberosity anteriorly and the pterygoid hamulus posteriorly. It is a band of loose connective tissue containing no muscle or ligament.  The posterior palatal seal of the denture starts from one hamular notch on one side to the other hamular notch on the other side through the vibrating line on the soft palate. 6- Vibrating line of the palate:  It is an imaginary line lying between the movable and immovable parts of the soft palate. It is also called the "Ah line" because it appears when the patient says a series of "Ah". It extends from one hamular notch to the other following the contour of the palate.  The vibrating line determines the posterior extension of the maxillary denture. 36 CHAPTER 3 Applied anatomy B- In the mandible: (Fig.24) Fig. 24 Mandibular limiting structures Starting from the midline and passing backward, the lower denture flange is related to the following structures:- 1-Labial frenum:  It is a fold of mucous membrane present in the midline extending from the inner surface of the lower lip toward the crest of the residual ridge.  Labial frenum should be opposed with labial notch in the denture border to facilitate the functional movement of 37 CHAPTER 3 Applied anatomy the frenum. Otherwise, ulceration of the frenum or displacement of the denture may occur. 2- Labial mucous membrane reflection area (labial vestibule):  It is the reflection of the mucosa of the lip to the mucosa of the alveolar ridge extending from the labial frenum to the buccal frenum.  The denture flange in this area is in relation to the orbicularis oris muscle and the incisivus labii inferioris muscle. These muscles limit thickness and length of the labial flange of the denture. 3- Buccal frenum:  It is a fold of mucous membrane overlying the triangularis muscle in the premolar region. It may or may not be present. It varies in shape, size and number.  A buccal notch is made in the denture flange opposite the position of the frenum to facilitate its functional movement. Inadequate clearance in buccal flange for its movement will cause dislodgment of the denture. (Fig.25) Fig.25 Buccal frenum opposed with buccal notch 38 CHAPTER 3 Applied anatomy 4- Buccal mucous membrane reflection area (Buccal vestibule):  It is the reflection of mucous membrane from the buccal frenum posteriorly to the outside posterior corner of the retromolar pad.  It is the reflection of mucous membrane from the cheek to the alveolar ridge distal to the buccal frenum. In this area the denture flange is in relation to the buccinator muscle. (Fig.26) Fig. 26 Relation of muscles to mandibular denture 39 CHAPTER 3 Applied anatomy 5- Masseter muscle influencing area (Masseteric notch): (Fig. 27)  The distobuccal corner of the mandibular denture is in relation to the masseter muscle.  The buccal flange of the denture in this area must converge rapidly in a medial direction to avoid displacement due to contraction of the vertical fibers of the masseter muscle. Fig. 27 Massetreric notch 40 CHAPTER 3 Applied anatomy 6- Retromolar pad and anterior border of the ramus:  Distally, the lower denture is in relation to the retromolar pad and the anterior border of the ramus.  The lower denture should extend to cover the retromolar pad till the anterior border of the ramus. On the lingual side, starting backward and passing forward, the lingual flange is related to the following structures:- 1- Palatoglossal arch: (Fig. 28)  The distolingual border of the lower denture is related to the palatoglossal arch which is formed mainly by the palatglossal muscle.  Overextension of the lingual flange in this area will cause sore-throat. Fig. 28 Lower denture should reach the palatoglossus arch (dotted line) 41 CHAPTER 3 Applied anatomy 2- Lingual pouch:  Anterior to the palatoglossal arch, the denture flange is related to the lingual pouch.  Boundaries of the lingual pouch are:- - Posteriorly: palatoglossal muscle. - Anteriorly: mylohyoid muscle. -Medially: tongue. - Laterally: medial aspect of the mandible. 3- Mylohyoid muscle influencing area: (Fig. 29)  Anterior to the lingual pouch, the denture flange is related to the mylohyoid muscle.  The lingual flange of the lower denture should extend to the mucolingual sulcus as determined by the functional movement of the mylohyoid muscle. 4- Sublingual salivary gland area: (Fig. 29)  More anteriorly, the lingual flange is related to the sublingual salivary gland. The gland is covered by reflection of the mucosa from the alveolar process to the base of the tongue.  With excessive bone resorption, the sublingual salivary gland may bulge superiorly, therefore it affects the depth of the lingual flange at this area. 42 CHAPTER 3 Applied anatomy Fig. 29 Relation of lower denture to mylohyoid and sublingual salivary gland. 5- Ligual frenum: (Fig.30)  It is a fold of mucous membrane that extends from the mucosa of the under surface of the tongue to the mucosa of the floor of the mouth. It overlies the genioglossus muscle.  A notch is made in the lingual flange to accommodate with the movement of the tongue. Fig. 30 Lingual frenum. 43