It is the contact relation ship of upper & lower teeth during various mandibular movements.

The study of occlusion includes the following items:1- Dental arch formation.2- Compensating curvatures of the dental arch( curved

occlusal planes).3- Compensatory curvatures of individual teeth (curved

tooth axes). 4-Angulation of teeth in relation to various planes.5- functional form of the teeth at their incisal and

occlusal third.6-Facial and lingual relation of each tooth in one arch

to its antagonist in the opposing arch during centric occlusion.

7- Occlusal contact and inter-cusp relation of all teeth during various mandibular movement.

(Arrangement or Alignment of teeth)

Parabolic curve. From an occlusal view the facial and lingual outlines of the

dental arch conform to a Parabolic curve. The maxillary arch is larger than the mandibular arch

giving a horizontal space between upper and lower teeth during occlusion called overjet.

Phases of development of permanent dental arch. Bonwill triangle.

parabolic curve. 1-Anterior segment:

Semicircular and

equally bisected by the midline.

Facial surfaces of anterior teeth and the first premolar of both sides.

2- Middle segment: Straight line and

continuous with the anterior segment in buccal direction. Included the first and second premolars and the mesial half of the first molar.

Anterior segment

straight

Posterior segment

semicircular

Middle segment

3- Posterior segment:

Straight line parallel to the midline slightly directed to the midline in the

maxillary dental arch.

Middle segment

Posterior segment

Middle segment

Anterior segment

First phase: Second phase: At 6 years eruption of

the first permanent molars lead to increase the masticatory efficiency and jaw growth.

Eruption of the permanent incisors.

Third phase: Fourth phase: Premolars replace the

deciduous molars and spacing of teeth occur due to smaller size of premolars than deciduous molars.

The canines and the second permanent molar erupted nearly at the same time. The arch is considered to be physiologically complete.

Fifth phase:

Eruption of the third molar.

Fifth phase

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.

The curve follows a sagittal plane. 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.

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.

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.

Importance: -Occlusal balance and stability of teeth during normal occlusion. -Promote mesial drift of teeth.

Any line bisecting the tooth from any aspect will form a curve.

The curves made by teeth in either dental arch, is parallel to those in the opposing dental arch.

The curves made by anterior teeth, premolars and first molar form equal circles.

The second and third molars form smaller circles.

Each tooth is positioned in the dental arch at an angle that best withstands the forces of mastication.

The axial angulation of the incisors is about 60 degrees to the horizontal plane.

The axis of the maxillary incisor forms acute angle with the axis of the mandibular incisor.

The angle becomes less acute in the canines and first premolars.

The maxillary and mandibular second premolar and the first molar have their axes parallel to each other.

The second and third molars have their axes at an angle more acute to the horizontal plane than the first molar.

Function: - Stabilize proximal contact.

-Promotes mesial drift.

Angulation of the teeth

Maxillary incisors

Maxillary premolar

Maxillary molars

Mandibular incisors

Mandibular premolars

Mandibular molars

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 crown depression on the opposing dental arch 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.

6-Facial and lingual relations of each tooth in one arch to its antagonist in the

opposing arch in centric occlusion

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).

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.

4- All incisal ridges of upper incisors, buccal cusps of upper premolars and molars are free of contact.

* The cusp of the upper 3,buccal cusps of upper 4&5 and the DBC of the upper molars are labial to the labial embrasure of the tooth having the same no and the next tooth.

* The MBC of upper molars are buccal to the BG of the tooth having the same number.

5- All incisal ridges of lower teeth, lingual cusps of lower premolars and molars are free of contact.

* the cusp of the lower 3, the lingual cusps of lower 4&5 and the MLC of 6&7&8 are lingual to the lingual embrasure of the tooth having its number and the tooth before

* The DLC of lower molars are lingual to the tooth having the same number.

6-The BC of lower 4&5 hits the MMR of the upper tooth having the same number.

7-The MBC of lower 6&7 hits MMR of the upper tooth having the same number and the DMR of the tooth before.

8-MBC of lower 8 hits MMR or MTF of the upper 8.

9-All DBC of lower molars hit CF of the upper molar having the same number.

10-All upper and lower teeth end at one line distal to the upper and lower 8.

11-All the MLC of upper molars hit the CF of the lower tooth having the same number.

12-The DLC of upper molars hit the DMR of the tooth having the same number except that of the upper 6 hit the MMR to the lower 7.

13-The LC of the upper 4 hits the DC slope of the lower 4.14-The LC of the upper 5 have two cases: * if the lower 5 is 2 cusps type it hits the DTF of the

lower 5. * if the lower 5 is 3 cusps type it hits the DC slope of

the lingual cusp of lower 5.Guiding cusps: cusps free of contact in centric occlusion (buccal

cusps of upper teeth & lingual cusps of lower).Supporting cusps: cusps making contact in centric occlusion.Centric stops: points of contact made by supporting cusps with

opposing tooth in centric occlusion.

Each tooth contact 2 teeth except lower1& upper 8.

1-Buccal of upper

-incisal edge of upper anterior & buccal cusps of upper premolars & molars are all free of contact.

-Buccal cusps of upper premolars& molars lie in the buccal embrasure or buccal groove. -1&2 , over lap lower1&2&3

-3&4&5 lie in buccal embrasure. Molars MBC lie in buccal grooves & DBC lie in buccal embrasure.

2- Buccal of lower:

Buccal cusps of lower 4 & 5 lie in MMR of opposing teeth having the same number.

Molars : DBC lie in central fossa of opposing teeth having the same number. MBC lower 6&7 lie in MMR of opposing +DMR of the tooth before. Lower 8 with MMR of 8 . N.B. distal cusp of lower 6 rest in the distal triangular fossa of 6

MBC

MBC

MBC

DBC

DBC

DBC

D

All lingual surfaces and cusps of lower teeth are free of contact: 1-lingual surface of lower:

*lingual cusps of lower 4 & 5 are free and lie in lingual embrasure

*ML cusps of lower 6& 7& 8 lie in the lingual embrasure.

*DLC of 6&7&8 lie in the lingual grooves of upper 6 & 7& 8.

2-lingual surface of upper: lingual surface of upper1& 2& 3 are free of contact.

Lingual surface of upper4&5 ,the lingual cusps contact DMR of lower 4&5 N.B.

in case of 3 cusp type lower 5 the lingual cusp ofupper5 contact the disto occlusal slope of disto lingual cusp.

MLCDLC

Lingual cusps of molars

MLC, contact central fossa of molars having the same number.

DLC, contact DMR of molars having the same number except upper 6 contact MMR of lower 7.

*N.B. cingulum of upper anterior is in the lingual embrasure of lower anterior.

*Cingulum of lower anterior is free from contact.

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.

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). 3-Retrusive movement teeth slide over each other backward and upward to centric

occlusion. The incisal ridges of upper and lower incisors contact each

other. While sliding back upper and lower incisors still contact each other until they rest in centric position.

4-The mesial cusp ridge of lower 4 contact the distal cusp ridge of upper 3.

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.

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 cusps of lower posterior teeth contact

the upper posterior teeth buccal to the buccal cusp ridge.

*The upper posterior teeth make their contact lingual to their buccal cusp ridge.

*The lingual cusps of lower posterior teeth contact the lingual cusps of upper posterior teeth lingually.

*The lingual cusps of upper posterior teeth contact the lingual cusps of the lower posterior occlusally.

4-The left side is termed the balancing side:*the occlusal slopes of the buccal cusps of lower

molars contact the occlusal slopes of the lingual cups of upper posterior teeth.

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 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

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