The mandible at different ages and importance of proximal spaces

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descriptive dental anatomy, mandibular descrition

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The mandible at different ages and importance of proximal spaces

  1. 1. Descriptive dental anatomy Mandible at different ages Name:Mahmoud Zakaria
  2. 2. Mandible at different ages The Mandible at birth: I. The Mandible at birth is made up of two separate halves, they are united later on by fibrous tissue at the midline. The two halves of the Mandible joint at an area called symphysis menti. II. At birth there are no teeth, the size of the Mandible bone is too small to carry any teeth but it carries the tooth germ of both the decidious and permanent teeth in its bony crypts. III. The mandibular canal runs near the lower border of the mandible while the mental foramen opens below the crypt of the lower D. IV. There is no mental protuberance present at that age. V. The sigmoid notch is very shallow, the ramus bone is small and makes an angle of 170 degrees with the body of the mandible this angle is called the mandibular angle VI. The coronoid process is higher than the condyle. The condyle is present at the same line with the upper border of the mandible.
  3. 3. The Mandible at age of 3 years: I. The two halves of the mandible joint together at the end of the first year or beginning of the second year of children. II. The body of the mandible bone starts growing to be able to occupy the decidious and after that the permanent teeth, also the body increases in height by the growth of the alveolar bony socket and the growth of the first decidious teeth III. The mandibular angle becomes smaller than at birth and closer to the adult mandibular angle as it changes from 170 degrees to 140 degrees
  4. 4. The Mandible at the age of six years: I. The mixed dentition starts by the eruption of the first permanent molar. II. The mandibular canal is placed above the mylohyoid line. III. The opening of the mental foramen lies midway between the upper and lower border of the body of the mandible. IV. The mandibular angle more closer to the adult mandibular angle. V. The growth of the mandibular bone causes bone remodeling, the remodeling of the bone means resorption in certain regions accompanied with apossition in other regions.
  5. 5. Dental Model of Mixed Dentition
  6. 6. • The Mandible at Adult age: I. The height and length of the mandible increase by the increase of size of the alveolar bone and the eruption of the permanent teeth. II. The mandibular canal is in a parallel position to the mylohyoid line. III. The mandibular canal and mental foramen are both positioned midway to the upper and lower borders of the mandible, usually the mental foramen lies below the sockets lower 5 or lower 4 but in some rare cases it lies between both sockets. IV. The appearance of mental protuberance gives the chin appearance in adults. V. The coronoid is at a lower level than the condyle. VI. The sigmoid notch becomes deeper VII. The mandibular angle becomes from 110-120 degrees.
  7. 7. Mandible at old age: I. There is a decrease in the size of the mandible due to lose of permanent teeth and the resorption of the alveolar process. II. The loss of the permanent teeth and decrease in size of the mandible cause the mental foramen and mandibular canal to become positioned near the upper border of the mandible. III. The mandibular angle becomes bigger than at adult age because due to the loss of teeth the person tries to bring the lower and upper jaws near each other for mastication, also the ramus becomes oblique for the same reason. IV. The mandibular angle becomes 140 degrees. V. the condyle bends backward and become in lower level than the coronoid process. VI. The sigmoid notch is shallower than adult.
  8. 8. The Physiologic Tooth Form Protecting The Peridontium What is the Peridontium? The peridontium is the supporting system of the tooth the peridontium is formed of:  Gigiva  Periodontal ligament  Alveolar bone proper  Cementum
  9. 9. The teeth have certain outline and curvatures that serve in supporting the teeth and that curvature is so finely drawn that any changes in these dimensions may seriously injure the tooth in the future. There are certain factors that may affect the periodontum: I. Direct factors II. Indirect factors
  10. 10. 1. The direct factors consist of: • The proximal contact area • The interproximal spaces • Embrasures or spillway • Facial and lingual contours of the crown • Curvature of the cervical line mesially and distally 2. The indirect factors consist of: • Cusp forms • Root forms • Root/Crown ratio • Angle of the tooth axis in the jaw bone • Self cleansing ability of the tooth which consists of: 1. The smooth rounded surface of tooth and brushing activity of tongue and cheeks. 2. The flushing activity of saliva. 3. The friction of food material during mastication. 4. The efficient use of tooth brush during home care of teeth.
  11. 11. 1.The proximal contact area: A. What is the proximal contact area? The proximal contact area is the spot on the proximal tooth surface where the tooth touches the tooth adjacent to it in the same dental arch The proper location of the contact areas can be observed from: • The labial or buccal aspect • The incisal or occlusal aspect B. The normal location of the contact areas are: • Every tooth has distal contact area in a more cervical area the the mesial contact area • The contact area is wider in posterior teeth than in anterior teeth and more cevically in postion • The contact area is centered labioligually in anterior teeth while in posterior teeth it is deviated more bucally
  12. 12. C. What are the importance's of the proximal contact area? • It stabilizes the tooth within the alveolus which thereby stabilizes the dental arches • It helps prevent food impaction which can lead to decay and periodontal problems • It protects the interdental papillae of the gingival
  13. 13. 2. The interproximal spaces: A. What is the definition of interproximal spaces? The interproximal space is a triangular space between adjacent teeth cervical to their contact, the sides of the triangle are the proximal surfaces of the adjacent teeth and the apex of the triangle is the area of contact of two teeth. This space is occupied by the interdental papilla B. What are the importance’s of the interproximal spaces: • The healthy interdental papilla is smooth and elastic tissue that prevent food stagnation • Interproximal space gives sufficient space for the alveolar bone between the neighboring teeth to support them in their sockets
  14. 14. 3. The embrasure or spillway: A. What are embrasures? Embrasures are triangle shaped space or area between two adjacent teeth in the same dental arch, where their proximating surface diverge from the area of contact facially, lingually, and oclussaly. Also there is a good relation between the location of contact areas and the embrasures: • The lingual embrasures are larger than the facial ones since most teeth are narrower on the lingual side than the facial side, the lingual embrasures also are larger than the buccal embrasures in posterior teeth more than in anterior teeth. • The incisal embrasure is shallow and narrow faciolingually on the anterior teeth but broad in posterior teeth this is because the contact area is more cervical in the posterior teeth than in the anterior teeth.
  15. 15. B. The importance of the embrasure’s are as follows: • They make a spillway for the escape of food during mastication thus reducing the forces upon the teeth. • They make the teeth self cleansing because the rounded smooth surface of the crowns are more exposed to the cleansing action of foods, fluids and the friction of the tongue, lips, and cheeks. If there was no escape way for the food the lodgement of food would cause to very poor oral hygiene. • They allow proper stimulation for the gingival by permitting the proper degree of frictional massage during mastication.
  16. 16. 4. Facial and lingual contours of the crown. A. The location of the facial and lingual contours: • The height of contour on both labial and lingual surfaces of all the anterior teeth is located in the cervical third. • The height of contour of the buccal surfaces of all posterior teeth is located in the cervical third. • The height of contour of the lingual surfaces of all posterior teeth is located in the middle third except the lower second premolar where it is located at the oclusal third.
  17. 17. B. The physiological importance of these uniform curvature: • The curvature holds the gingival under definite tension. • They protect the gingival margin by deflecting food away from it during mastication. • The proper curvature will deflect food over the gingival margin preventing unnecessary frictional irritation, but will allow some massage to soft tissue. C. If the proper curvature of teeth was replaced by improper contour by unsuccessful dental restoration the following will occur: • If the proper contour are absent or too small the gingival tissue will be pushed apically and gingival recession will occur. • If the curvature is too great there will be too much protection of the gingival from proper massage and also the gingival will lose it’s tone. The food material will accumulate around the gingival area resulting in chronic inflammation.
  18. 18. 5. Curvature of the cervical line mesially and distally. A. The curvature of the cervical line from different aspects: • The curvature of the cervical line mesially and distally differs in different teeth generally speaking this curvature is greater in the anterior teeth than in the posterior teeth . • In individual tooth it’s greater mesially than distally. • It tends to be straight buccolingually in the distal surface or even the mesial surfaces of some molars.
  19. 19. B. The importance of the curvature of the cervical line mesially and distally: • The importance of the curvature of the cervical line is due to the face that it is the site of attachment of the gingival to the tooth by means of a structure called the attachment epithelium . • If the teeth are in normal alignment and contact, the attachment epithelium follows the curvature of the cervical line but not necessarily at the same level. Any break in this epithelium will result in major injury to the periodontium due to the penetration of the bacteria and their toxins causing damage to the investing tissue of the tooth.
  20. 20. Thank you!!

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