Mandible at Different Ages - Dentition

1. بسم الله الرحمن الرحيم

2. Prof: Dr : Rawya Hassan Professor Oral biology Cairo university

3. Mandible at different ages

4. Condyle process at the level of the upper border of mandible. Coronoid process at higher level than condyloid . Mental foramen near the lower border under the crypt of D Mandibular canal near lower border Sigmoid notch is shallow Mandible two half till the end of the first year . Angle of the mandible 170 degree . Mandible during the neonatal life(at birth) Symphyseal cartilage ( Symphysis of mandibule +mental ossicals ) 2parts fuse at 1 year Mental foramen Mandibular canal Condyloid cartilage: 14WIUL-20Y give condyle + posterior part of the ramus Coronoid cartilage : 14WIU- --6MIU give coronoid process + anterior part of the ramus

5. Mandible at childhood period Coronoid process higher than condyloid process. Mental foramen midway between upper& lower border. Mandibular canal slightly above mylohyoid line. Sigmoid notch more deeper. Angle of the mandible 140 degree. Chin is poorly developed. Increase in length by bone remodeling make room for permanent molars Increase in height by eruption of teeth +alveolar bone formation+ bone deposition at lower border of the mandible Growth Condyle cartilage Alveolar bone Posterior border of ramus Increase in length of ramus Increase in height Increase in length

6. Mandible at the adult period Condyle process at a higher level than coronoid process. Sigmoid notch deepest. Mental foramen mid way between upper & lower border under the socket of lower 5. Angle of the mandible 110-120 degree. Chin is significantly prominent ----- mental protuberance. Condyloid process Coronoid process Sigmoid notch Ramus Body Mental foramen Mental protuberance

7. Mandible at old age Condyloid process at a lower level than coronoid process Sigmoid notch is shallower. Mental foramen near the upper border of the mandibule . Mandibular canal near the upper border. Angle of the mandible 140 and the ramus inclined posterior. Body of the mandible has reduction in height due to loss of teeth and alveolar process. Condyloid process Coronoid process Mental foramen Mental protuberance Mandibular canal

8. Mandible at different ages At birth At childhood At adult period At old age

9. Bonwill triangle Bonwill described the mandible and the mandibular dental arch form occlusal view as an equilateral triangle of 4 inches length. The apex of the triangle is at the mesial contact area of lower central incisors and the angles of the base at the centers of the condyles .

10. Compensating curvature of the dental arch (curved occlusal planes) 1- Curve of Spee . 2- Curve of Wilson. 3- Curve of Monson. 1- These are the curved plane to which the teeth are arranged in the dental arch. 2- They provide balance in all mandibular movement.

11. The curve of Spee in sagittal plane (Lateral view) . Spee stated that when the upper and lower jaws are examined from a point opposite the first molar buccally the incisal ridges of anterior teeth and the buccal cusps of posterior teeth follow a curve that end at the anterior surface of the condyle . ) Curve of Spee condyloid coronoid Sigmoid notch Oblique line Mandibular angle Mental foramen 110-120

12. Curve of Spee allows for the normal functional protrusive movement of the mandible. Curve of Spee : *Curve of the mandibular arch is concave from the level of occlusion. *Curve of the maxillary arch is convex.

13. In coronal Plane (posterior view) (transverse ) Curve of Wilson

14. Crowns of the upper posterior teeth are inclined buccally so lingual cusps appear longer than buccal cusps. Crowns of the lower posterior teeth are inclined lingually so buccal cusps appear longer than lingual cusps. If a line is drawn from the buccal cusps of a posterior tooth on one side to a buccal cusp of the same tooth on the other side of the same arch, it will follow a curve parallel to the coronal plane. This is the curve of Wilson . Curve of Wilson

15. Curve of Wilson The curve formed by an imaginary line touching the buccal and lingual cusp tips of similar teeth on each side of the mandibular arch. The inclination of the posterior teeth increase in backward direction so the curve of wilson is more curved in backward direction Typically, viewed in the frontal plane (However, to improve visibility, this image is viewed from the posterior)

16. Curve of Wilson: * Allows for those exquisite movements which are used in chewing functions. * The elevated buccal cusps prevent food from going past the occlusion table Curve of Wilson : convex in maxillary arch & concave in mandibular arch change from first molar to third molar and with wear of the dentition.

17. What is the difference between the curve of Spee and the curve of Wilson? The buccal cusp tips of posterior teeth , seen in alignment from a lateral view , conform to the curve of Spee in an anterior to posterior direction. The curve of Wilson is a transverse occlusal curve which exists for posterior teeth in a direction from right to left as seen from a posterior view. Curve of Spee : Anteroposterior curvature of the incisal & occlusal surfaces Buccal - Lingual Curvature. For mastication. the Curve of Wilson. Clinically, it relates to the anterior overbite: the deeper the curve, the deeper the overbite. 4” radius

18. Curve of Monson : Curve of Monson is the curve of occlusion in which each tooth cusp and incisal edge touches or conform to a segment of a surface of a sphere 8 inches (20 cm) in diameter, with its center in the region of the glabella .

19. When teeth are properly aligned in the dental arches, their incisal and occlusal surfaces adapt themselves to curved planes. The occlusal surfaces of the mandibular teeth form a concave plane .Those of maxillary teeth form a convex plane .In centric occlusion these planes become identical . Curve of Monson Monson stated that the curved occlusal surfaces of the dental arches conform to a segment of a sphere of 4 inches radius. The center of this sphere is in the glabella . Curve of Monson is a combination of curve of Spee and curve of Wilson. The importance of these curved planes is to assist the path of condyles of the mandible in its movement.

20. Sphere of Monson It is a combination of Spee and Wilson curves , these curves are studies in a three dimension occlusal model the cusps tips of posterior teeth resting on a sphere . Sphere of Monson :sphere existed with a radius of 4 inches glabella Center of Monson’s Sphere ( located in the gabella above the condyles )

21. The functional form of the crown at incisal and occlusal third, is manifested by elevations and depressions. Elevations of the crown in one dental arch occlude with depressions on the opposing teeth during centric occlusion (self occluding design). Ridge to fossa : I ncisal ridge of lower 1& 2 rest in the lingual fosse of upper 1& 2. Cusp to fossa : MLC of upper molars rest in central fossae of lower molars & DBC of lower molars rest in central fossae of upper molars. Cusp to ridge: BC of lower 4& 5 hits MMR of upper 4&5 in centric occlusion. Cusp to sulcus : the triangular ridge of the MBC of upper molar are accommodated to the BG of the lower molars . Cusp to embrasure : the DBC of the maxillary molars lie in the B. embrasure between lower molars . Escapement spaces : the rounded surfaces of teeth make escapement of food during mastication. 5-Functional form of the teeth at their incisal and occlusal thirds

22. Cusp- fossa (tooth-to-tooth) occlusion Ridge to fossa

23. It is the contact relation of upper and lower teeth when they are in the maximum inter cuspation and the condyles are in the most retruded unstrained position in glenoid fossa . Centric occlusion: 6- Facial and lingual relation of each tooth in one arch to its antagonist in the opposing arch during centric occlusion

24. The first permanent tooth to develop & erupt. The largest of the permanent teeth. Their eruption is guided distal to the deciduous teeth. Their eruption is not disturbed as they have no deciduous predecessors. The upper 6 is more important as a key of occlusion as it is attached to a fixed bone (the maxilla). Key of occlusion: the upper&lower 6 6 6

25. In centric occlusion 1- each tooth contacts 2 teeth from the other arch except lower 1and upper 8. 2- All upper teeth overlap the lower teeth vertically and it called overbite. 3- All upper teeth have a labial relation to the lower teeth in centric occlusion and it called overjet.

26. Guiding cusps : cusps free of contact during centric occlusion (buccal cusps of upper teeth & lingual cusps of lower). Supporting cusps : cusps that occlude with fossae or marginal ridges of opposing teeth in centric occlusion (palatal cusps of upper teeth & buccal cusps of lower teeth). Centric stops : points of occlusal contact made by supporting cusps with opposing teeth in centric occlusion.

27. Centric stops guiding cusps Supporting cusps

28. Buccal surface 1-Buccal of upper (guiding cusps) - incisal edge of upper anterior & buccal cusps of upper premolars & molars are all free of contact. - Cusp of upper canine, Buccal cusps of upper premolars & disto-buccal cusp of 7 lie in the buccal embrasure. - Buccal cusps of 6 & mesio-buccal cusp of 7 & 8 lie in the buccal groove.

29. 2- Buccal of lower : (supporting cusps ) Buccal cusps of lower 4 & 5 hit the MMR of opposing teeth having the same number. Mesio-buccal cusps of lower 6 & 7 hit the MMR of upper teeth having the same number + the DMR of the tooth before. Mesio-buccal cusp of lower 8 hits the mesial triangular fossa of the 8 . - Disto - buccal cusps of lower molars hit the central fossae of upper molars. - distal cusp of lower 6 rest in the distal triangular fossa of 6 . MBC DBC MBC DBC DBC MBC DC

30. Lingual surface (Guiding cusps): - Cingulum of lower 2, 3 & lingual cusps of posterior teeth are free of contact . - L ing ual cusps of lower premolars & mesio - lingual cusps of lower molars lie lingual to the lingual embrasure. Disto -lingual cusps of lower molars lie lingual to the lingual grooves of upper molars. MLC MLC MLC

31. lingual surface (Supporting cusps): - Lingual cusps of upper 4 & 5 hit the DMR of lower 4 & 5. - In case of 3 cusp type lower 5 the lingual cusp of upper 5 contact the disto-occlusal cusp slope of the disto lingual cusp. MLC of upper molars contact the central fossae of the lower molars. - DLC of upper 6 hits the MMR of lower 7. DLC of upper 7 & 8 hit the distal cusp ridge of lower 7 & DMR of lower 8 respectively.

32. Movements of the mandible: * Bilaterally symmetrical *Bilaterally asymmetrical *Depression &Elevation. *Right lateral. *Protrusion & Retrusion. *Left lateral. All mandibular movements start from and terminate to centric occlusion. 8-Occlusal contact and intercusp relation of all teeth during various mandibular movements:

33. 1-The mandible is depressed. 2-Moves forward ( Pro trusive movement ) bring teeth together in the best position for incision (the lower teeth are in anterior relation to centric occlusion). During protrusive movement

34. 1- The mandible is depressed. 2- Retrusion of the mandible : placement of the teeth posterior to centric occlusion (non functioning occlusion). 3- Retrusive is limited by the compressibility of the tissues posterior to the condyles. During retrusive movement

35. MASTICATORY cycle of anterior teeth *The mandible moves in downward and forward direction to make lower anterior teeth in anterior relation to the upper teeth. * The functioning side is located at anterior teeth & balancing side at posterior teeth. * The incisal edge of lower teeth are in contact with lingual third of upper teeth (working side) *Posterior teeth in anterior relation of the lower teeth to the upper teeth (balancing side) Then the mandibule glides upward and backward

36. 1-Tthe mandible is depressed (the dental arches are free). 2-Moves to a right position to centric occlusion. 3-The right side is termed the working side * The buccal cusp of maxillary & mandibular teeth are in contact *The lingual cusps of lower posterior teeth contact the lingual cusps of upper posterior teeth lingually. 4-The left side is termed the balancing side : * The lingual cusps of maxillary teeth contact the buccal cusps of mandibular teeth. During right lateral mandibular movement (Occlusal cycle of posterior teeth) Right movement Balancing side Working side

37. The left lateral movement is similar to the right one in opposite direction the left side is the (working side & the right side is the balancing side) Working side Balancing side Right movement 5-Return to centric occlusion by sliding of teeth against each other in a direction nearly parallel to the oblique ridge of upper 6. 6-The lateral movement is repeated again till grinding of the food

38. The cycle of occlusal movement Initial occlusal contact in right lateral occlusal relation Centric occlusion relation Final contact after leaving centric relation before the mandible drops away to begin another cycle

39. The lower anterior teeth strike the upper anterior teeth lingually above their incisal ridges. Upper A: lower A&m1/3 of lower B. Upper B: d 2/3 of lower B and mesial part of lower C (mesial to its cusp tip). Upper C: d part of lower C (distal to cusp tip) and m part of lower D. Upper D: d 2/3 of lower D and m part of lower E. At the age of 4&5 years diastema due to jaw growth and increase with further growth. Occlusion is supported by eruption of permanent first molar at 6 years. Normal occlusion of deciduous teeth at three years