Mandible at Different Ages - Dentition

Mandible at different ages

• 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.

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

• 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

• 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 notchRamus

Body

Mental foramen

Mental protuberance

• 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 processCoronoid process

Mental foramen

Mental protuberance

Mandibular canal

At birthAt childhood

At adult period

At old age

• 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.

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.

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.

condyloidcoronoid

Sigmoid notch

Oblique line

Mandibular angle

Mental foramen

110-120

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.

In coronal Plane

(posterior view)(transverse)

Curve of Wilson

• 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• 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)

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 archchange from first molar to third molar and with wear of the dentition.

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

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.

• 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.

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.

Sphere of MonsonIt 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)

• 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 : Incisal 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.

Cusp-fossa

(tooth-to-tooth) occlusion

Ridge to fossa

• 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.

• 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).

6

6

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.

• 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.

• Centric stops

• guiding cusps

• Supporting cusps

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.

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 DBCMBC

DBCDBCMBC

DC

(Guiding cusps):

- Cingulum of lower 2, 3 & lingual cusps of posterior teeth are free of

contact.

- Lingual 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

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.

• 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.

1-The mandible is depressed.2-Moves forward (Protrusive movement) bring teeth together in the best position for incision

(the lower teeth are in anterior relation to centric occlusion).

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.

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

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.

Right movement

Balancing side

Working side

• 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

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

• 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.