Physiology of tooth form

 function: four main functions
 1.mastication : normal tooth form and proper
alignment ensure efficiency of mastication.
 2.esthetics :form and alignment of anterior teeth-
physical appearance
 3.speech:form and alignment of anterior and
posterior teeth assist in articulation of certain
sounds.
 4.protection of supporting tissues: form and
alignment of teeth assist in sustaining the teeth in
dental arches.

Contours
 The facial and lingual surfaces posses some
degree of convexity that afford protection and
stimulation of supporting tissues during
mastication.
 Cervical third of crown on the facial surfaces of all
teeth and lingual surfaces of incisors and canines.
 Lingual surface of posterior tooth-height of
contour-middle third of crown.
 Too great curvature-tissues receive inadequate
stimulation.
 Too little contour- trauma to attachment
apparatus.

 Over contouring-flabby ,red, chronically inflamed
gingiva and increased plaque retention.
 Proximal height of contours provide
 1-contact-prevent food impaction.
 2.Adequate embrassure space gingivally of the
contacts for gingival tissue,supporting bone, blood
vessels,nerves.

Proximal contact area
 The area of proximal height of contour of mesial and
distal surface of a tooth that touches its adjacent tooth
in the same arch.
 They promote normal healthy interdental papillae filling
of the interproximal spaces.
 Improper contacts-food impaction,carious lesion and
possible movement of teeth.
 Proximal contacts and interdigitation of teeth through
occlusal contacts stabilize and maintains integrity of
dental arches.
 Central incisors –incisal third.
 Remaining teeth-junction of incisal and middle third
/middle third.

Embrasures
 V-shaped spaces that originate at the proximal
contact areas between adjacent teeth and are
named for the direction towards which they
radiate.
 Facial,lingual, incisal/occlusal and gingival.
 Interdental papilla fills the gingival embrasure.
 In faciolingual vertical section papilla triangular in
anterior teeth
 In posterior teeth papilla shaped like a mountain
range with facial and lingual peaks and the col
lying beneath the contact area.

 When an embrasure is decreased or
absent,additional stress is created in the tooth and
supporting structures during mastication.
 Lingual embrasures are larger than facial to allow
more food to be displaced lingually.

Maxilla and mandible
 Maxilla-formed by two bones:maxilla proper and
premaxilla-forms the bulk of upper jaw and major
portion of hard palate,form the floor of orbit,sides
and base of nasal cavity.
 Mandible:forms the lower jaw.it is horse shoe
shaped and relates to skull on either side via the
TMJ.
 The mandible is composed of a body of two
horizontal portions joined at the midline symphysis
mandibulae and the rami,the vertical parts

Oral mucosa
 Is the mucous membrane that covers all oral
structures except the clinical crowns of the teeth.
 Composed of two layers-stratified squamous
epithelium and lamina propria.
 The epithelium may be keratinized, parakeratinized or
nonkeratinized.
 Lamina propria varies in thickness and supports the
epithelium.
 It may be attached to periosteum of alveolar bone or it
may be interposed over the submucosa,which may
vary in different regions of mouth.

Oral mucosa-3 functional types
 1.Masticatory mucosa
 2.Lining or reflective mucosa
 3.Specialized mucosa
 1.Masticatory mucosa-comprises of free and attached
gingiva and the mucosa of hard palate.
 Epithelium of these tissues is keratinized and lamina
propria is dense,thick,firm connective tissue
containing collagenous fibers.
 2.Lining or reflective mucosa-covers the inside of
cheek,lips,vestibule,lateral surfaces of alveolar
process,floor of mouth,soft palate and inferior surface
of tongue.

 It is a thin ,movable tissue with a relatively
thick,non keratinized epithelium and a thin lamina
propria.
 The submucosa comprises mostly thin,loose
connective tissue with muscle and collagenous
and elastic fibers.
 The junction of lining mucosa with masticatory
mucosa is the mucogingival junction.
 3.Specialized mucosa-covers the dorsum of
tongue and taste buds.
 The epithelium is non keratinized except for the
covering of the dermal filiform papillae.

Periodontium
 Consist of oral hard and soft tissues that invest
and support the teeth
 Divided into:1.gingival unit-consisting of free and
attached gingiva and alveolar mucosa.
 2.attachment apparatus-consist of
cementum,periodontal ligament and alveolar
process.
 Periodontium attaches the teeth to the maxilla
and mandible and provides a continually adapting
structure for the support of teeth during function.
 Gingival unit-
 1.free gingiva-is the gingiva from the marginal
crest to the level of base of the gingival sulcus.

 Gingival sulcus is the space between the tooth
and the free gingiva.
 Outer wall of sulcus is lined with a
thin,nonkeratinized epithelium.
 The outer aspect of free gingiva in each gingival
embrasure-gingival or interdental papilla
 The free gingival groove is a shallow groove
that runs parallel to the marginal crest of the free
gingiva and usually indicates the level of the
base of the gingival sulcus.

 2.attached gingiva-a dense connective tissue with
keratinized stratified squamous epithelium, extents
from the depth of the gingival sulcus to the
mucogingival junction.
 A dense network of collagenous fibers connects
the attached gingiva firmly to the cementum and
periosteum of alveolar process.
 3.Alveolar mucosa:is a thin soft tissue that is
loosely attached to the underlying alveolar bone.
 It is covered by thin ,nonkeratinized epithelial
layer.
 Underlying submucosa contains loosely arranged
collagen fibers,elastic tissue,fat,and muscle tissue.

 Attachment apparatus
 1.Periodontal ligament-is a complex,soft
connective tissue containing numerous cells,blood
vessels,nerves and an extracellular substance
consisting of fibers(collagen) and ground
substance(protein and polysaccharides)
 Function:1.attachment and support
 2.sensory
 3.nutritive
 4.homeostatic.

 Bundle of collagen fibers (principle fibers of the
ligament)serve to attach the cementum to alveolar
bone and act as a cushion to suspend and support the
tooth.
 The portion of principle fibers embedded in the
cementum and alveolar bone are called’ Sharpey’s
fibers’.
 2.Cementum-is a hard tissue with a calcified
intercellular substance covering the anatomic roots of
teeth.
 3.Alveolar process-a part of maxilla and
mandible,forms, supports and lines the sockets into
which the roots of the teeth fits.
 Has two parts
 1.alveolar bone proper-the innerwall of bony socket
consists of the thin lamella of bone that surrounds the
root of the tooth.(give attachment to Sharpey’s fibers)

 2.supporting alveolar bone-surrounds the alveolar
bone proper and supports the socket.
 Composed of two parts-
 a. The cortical plate-consisting of compact bone
and forming the inner(lingual) and outer(facial)
plates of alveolar process.
 b. The spongy base-that fills the area between the
plates and the alveolar bone proper.


occlusion
 Means the contact of teeth in opposing dental arches
when the jaws are closed(static occlusal relationships)
and during various jaw movements(dynamic occlusal
relationships).
 General description
 Cusps-are drawn as blunt, rounded or pointed
projections of the crowns of the teeth.
 Cusps are separated by distinct developmental
grooves and have additional supplementary grooves
on the cusp inclines.
 Facial cusps are separated from the lingual cusps by a
deep groove called central groove.

 If a toot h have multiple lingual cusps or multiple
cusps,the cusps are separated by facial or lingual
developmental groove.
 Depressions between the cusps-fossa.
 Grooves having noncoalesced enamel are
fissures.
 Noncoalesced enamel at the deepest point of a
fossa is a pit.



Tooth alignment and dental arches
 Maxillary arch is larger than mandibular
arch,resulting in the maxillary cusps overlapping
the mandibular cusps when the arches are in
maximal occlusal contact.
 Facial occlusal line-an imaginary arc connecting
the rows of facial cusps in the mandibular arch
 Central fossa occlusal line-an imaginary line
connecting the maxillary central fossae.

 These two lines coincide exactly when the mandibular
arch is fully closed into the maxillary arch
 Maximum intercuspation(MI)- is the position of
mandible when the teeth are brought into full
interdigitation with the maximum number of teeth
contacting.
 Cusps that contact the opposing teeth along the
central fossa occlusal line are termed supporting
cusps.(centric,holding or stamp cusps-mandibular
facial cusps.
 Non-supporting cusps-cusps that overlap the
opposing teeth (noncentric/nonholding cusps).-
maxillary facial cusps.
 In MI the mandibular incisors and canines contact the
respective lingual surfaces of their maxillary
opponents.

 Anterior- posterior interarch relationships.
 The cusp interdigitation pattern of the first molar
teeth is used to classify the anterior –posterior
arch relationships.
 Angles classification
 Class I -most common molar relationship.
 Mesiofacial cusp of max.1st molar occludes with
the mesiofacial groove of mand.1st molar.
 Class II -mesiofacial cusp of max.1st molar is
located in the facial embrasure between the
mand.1st molar and mand.2nd premolar.
 Class III-mesiofacial cusp of max.1st molar fits into
the distofacial groove of mand.1st molar.

Inter-arch tooth relationships
 Incisor relationships-incisal overlap considered in
two dimensions:
 Overjet -this is the horizontal distance between the
labial surface of mandibular anteriors and lingual
surface of max.anterior-horizontal overlap.
 Overbite-this the vertical distance between the
incisal edges of max. anterior and incisal edges of
mand.anteriors.
 Usual overbite and overjet varies between 2-3mm.

 Variations in incisor relationships.
 1.open bite as a result of
 a.mandibular deficiency
 b.excessive eruption of posterior teeth
 c.mandibular growth excess.
 Tooth –to-tooth relationship:mandibular facial cusp
contacting the maxillary premolar mesial marginal
ridge and max.premolar lingual cusp contacting
the mandibular distal marginal ridge.(only one
antagonist is contacted.

 Tooth-to-two –tooth contact: most stable
relationship.contact of supporting cusp tips against
the two marginal ridges
 Cusp-fossa contact:when the mandible is slightly
distal to maxilla,each supporting cusp tip occludes
in a stable relationship with the opposing mesial
or distal fossa.

Variations in molar relationships
 Facial cross bite-contact of maxillary facial cusps
in the opposing mandibular central fossa and
mandibular lingual cusps in the opposing
max.central fossa.
 Lingual cross bite results in a poor molar
relationship that provide little functional contact.

Posterior cusp characteristics
 Four cusp ridges can be identified as common
features of all cusps.
 1.outer incline(facial/lingual ridge)-is indicated by the
line that points to the outer incline of the cusp.
 2.Inner incline(triangular ridge)- the inner inclines of
posterior cusps face the central fossa /central groove
of the tooth.
 The inner incline cusp ridges are widest at the base
and become arrow as they approach the cusp tip.
 3.mesial and distal cusp ridges- extend from the cusp
tip mesially and distally and are named for their
direction.
 -extent downward from the cusp tips,forming the
characteristic facial and lingual profiles of the cusp as
viewed from the facial and lingual aspect.

 Marginal ridges- are elevated ,rounded ridges
located on the mesial and distal edges of tooth’s
occlusal surface.
 Oblique ridge-the distal cusp ridge of maxillary 1st
molar mesiolingual cusp curves facially to fuse
with the triangular ridge of distofacial cusp,this
juction forms the oblique ridge.(characteristic of
max.molars.)

Supporting cusps
 These cusps contact the opposing teeth in their
corresponding faciolingual centre on a marginal ridge
or a fossa.
 The supporting cusp central fossa contact has been
compared to a mortar and pestle becoz the supporting
cusp cuts,crushes and grinds fibrous food against the
ridges forming the concavity of the fossa of the
opposing tooth.
 Supporting cusps also serve to prevent drifting and
passive eruption of the teeth and hence the term’
centric holding cusps’
 Eg: The palatal cusps of max.posterior teeth
and buccal cusps of mand. Teeth.

Non supporting(non holding/non centric cusps)
 When viewed from the occlusal,these cusps are
farther from the faciolingual centre of tooth than
the supporting cusps.
 They have sharp cusp ridges that serve to shear
the food as they pass close to the supporting cusp
ridges during chewing strokes.
 The overlap of cusps helps to keep the soft tissue
of the tongue and cheek out from the occlusal
table preventing soft tissue injury during chewing.
 Eg: buccal cusp of max.posteriors and lingual
cusp of mand.posteriors.

Mechanics of mandibular motion
 Types of motion:
 1.Rotation-rotation is a simple motion of an object
around an axis.
 The mandible is capable of rotation about an axis
through the centres located in the condyles.
 Rotation of the condyles positioned in the centric
relation is termed ‘terminal hinge movement’.
 The maximum rotational opening in the terminal
hinge is limited to 25mm measured between the
incisal edges of anterior teeth.

 2.translation:this is the bodily movement of an
object from one place to another.
 Protrusion refers to the forward thrusting of the
mandible due to simultaneous direct anterior
movement of both the condyles.
 Protrusion is limited to approx.10 mm by the
ligamentous attachments of the masticatory
muscles and the temporomandibular joint.

 3.complex motion:this refers to a combination of
rotation and translation in a single movement.
 Most mandibular movements during chewing and
swallowing consist of both rotation and translation.
 4.Lateral movements:it is often described with
respect to only one side of the mandible for the
purpose of defining the relative motion of the
mandibular to the maxillary teeth.
Eg:during left lateral movement of the
mandible,the left mandibular teeth move away
from the midline and the right mandibular teeth
move toward the midline.

 The left lateral mandibular motion is due to rotation
of the left condyle and translation of the right
condyle.
 The mandibular pathways that are directed away from
the midline are termed ‘working/laterotrusion and
mandibular pathways directed toward the midline are
termed ‘non working’, ‘balancing’, ‘mediotrusion’.
 5.Bennett shift: this is the lateral bodily shift of the
mandible towards the working side during function.
 In normal TMJ this shift varies from 0-1.5mm and
does not have any significant effect on the posterior
teeth.
 Excessive lateral shift is associated with
morphological changes in the TMJ.

 Centric relation: described as the most retruded
position of the mandible from which lateral
movements can be made and the condyles are in the
most posterior, unstrained position in the glenoid
fossa.
 In an ideal occlusion both centric relation and centric
occlusion coincide with each other.
 But in 10% of natural dentition,centric relation does
not coincide with centric occlusion due to premature
contact or occlusal interference.
 This is compensated by proprioceptive mechanism of
periodontal fibers by allowing the mandible to
change the path of closure.
 This prevents injury to teeth and adjacent
periodontium.

Tooth contacts during mandibular movements.
 Prior to restoration of teeth,it is important to
evaluate the location,direction, and area of tooth
contact during various mandibular movements as
a preoperative procedure,
 Anterior tooth contacts: during protrusion of the
mandible,the lower anterior teeth glide along the
lingual surfaces of the maxillary anterior teeth in a
normal occlusion.
 With protrusion ,multiple contacts serve to prevent
excessive force on any individual pair of gliding
teeth.
 Posterior tooth contacts:

 In an ideal occlusion ,the posterior teeth should contact
only during maximal intercuspation.
 Forceful contact or collision of individual posterior tooth
cusps during chewing and clenching may lead to
discomfort or damage to the teeth.
 Group function occlusion:
 Occurs naturally in a worn dentition.
 In this ,there is simultaneous gliding contact of teeth in
lateral and protrusive movement.
 The working guidance in group function occurs on all the
teeth on the working side.
 The incisal edges of the mandibular anterior teeth glide
down the palatal surfaces of the maxillary anterior teeth.
 The buccal inclines of the buccal cusps of the
mand.premolars and molars glide against the palatal
inclines of the buccal cusps of maxillary premolars and
molars.

 The science of occlusion is complex.
 Understanding a few basic principles of occlusion
related to natural teeth and knowledge of the methods
of examining occlusion are of great value in preventing
failures that occur in restorations involving occlusal
surfaces of teeth.
 Any restoration placed should be in harmony with the
supporting tissues ,neuromuscular system and TMJ.

 The Art & Science of Operative Dentistry,
Sturdivant, Mosby U.S.A.
 Principle & Practice of Operative Dentistry,
Charbeneu, Varghese Publishing , Mumbai.
 WWW.WIKIPEDIA .COM

Physiology of tooth form

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