Clinical Significance of Dental Anatomy, Physiology and Occlusion

CLINICAL SIGNIFICANCE
OF
DENTAL ANATOMY,
PHYSIOLOGY AND
OCCLUSION 1

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INTRODUCTION
Thorough understanding of the anatomy, physiology and occlusal
interactions of teeth is essential in the field of restorative dentistry.
 Proper tooth form contributes to healthy supporting tissues.
 Relationship of each tooth with adjacent and opposing teeth are major
determinants of muscle function in mastication, esthetics, speech and
protection.
Sturdevant’s Art and Science of Operative Dentistry, 7th edition

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DENTITIONS
 Humans have two sets of dentitions:
i. Primary and
ii. Permanent.
 Primary Dentition consists of 5 teeth in each quadrant (total 20
teeth).
 Permanent Dentition consists of 8 teeth in each quadrant (total 32
teeth).

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 As the diet of humans consists of animal and plant foods, the human
dentition is called omnivorous.
 Human teeth are divided into four different types:
i. Incisor.
ii. Canine.
iii. Premolar.
iv. Molar.

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Different types of teeth
Source: Sturdevant’s Art and Science of Operative Dentistry, 7th edition

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INCISOR
 Located near entrance of the oral cavity.
 Used to shear (cut through) food during mastication.
 Essential for proper esthetics of the smile, facial soft tissue contours
(i.e. lip support) and speech (phonetics).

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CANINE
 Possesses the longest roots of all teeth.
 Located at the corners of the dental arches.
 Function in the seizing, piercing, tearing and cutting of food.
 Play a crucial role (along with the incisors) in the esthetics of the
smile and lip support.

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PREMOLAR
 Premolars serve a dual role:
i. Similar to canines in the tearing of food.
ii. Similar to molars in the grinding of food.
 Although less visible than incisors and canines, premolars still play an
important role in esthetics.

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MOLAR
 Large, multicusped, strongly anchored teeth.
 Located nearest to the temporomandibular joint (TMJ).
 Have a major role in the crushing, grinding and chewing of food.
 Premolars and molars are important in maintaining vertical dimension
of the face.

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PHYSIOLOGY OF TOOTH FORM
Teeth serve four main functions:
i. Mastication.
ii. Esthetics.
iii. Speech.
iv. Protection of Supporting Tissues.

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i. Mastication:
 Normal tooth form and proper alignment of teeth ensures efficiency in
the masticatory process.
 All four tooth types perform specific functions in the masticatory
process.
ii. Esthetics:
 Form and alignment of the anterior teeth are important to a person’s
physical appearance.

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iii. Speech:
 Form and alignment of teeth assists in the articulation of sounds that
have an effect on speech.
iv. Protection of Supporting Tissues:
 Proper form and alignment of teeth contributes greatly towards the
protection of gingival tissue and alveolar bone supporting them.

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CONTACTS & CONTOURS
 Facial and lingual surfaces possess a degree of convexity that affords
protection of supporting tissues during mastication.
 The convexity generally is located at the cervical third of the crown
on the facial surfaces of all teeth and the lingual surfaces of incisors
and canines.
 Lingual surfaces of posterior teeth usually have their height of
contour in the middle third of the crown.

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 Normal tooth contours must be recreated while performing
restorative dental procedures.
 Normal tooth contours act in deflecting food only to the extent that
the passing food stimulates (by gentle massage) and does not irritate
(abrade) supporting soft tissues.
 Over-contouring usually results in increased plaque retention that
leads to a chronic inflammatory state of the gingiva.

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Proximal Contour
 Proper form of the proximal surfaces of teeth is as important as the
facial and lingual surfaces for the maintenance of periodontal tissue
health.
 Improper contacts may result in food impaction between teeth which
may lead to an increased risk of periodontal disease and caries.
 Proximal contact areas typically are larger in the molar region, which
helps prevent gingival food impaction during mastication.

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Overcontour deflects food from gingiva and
results in understimulation of supporting tissues.
Undercontour of restoration may result
in irritation of soft tissue.
Correct contour permits adequate stimulation
and protection of supporting tissue.
Source: Sturdevant’s Art and Science of Operative Dentistry, 7th ed.

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 Interproximal contacts can be assessed with a thin dental floss.
 Contacts that do not allow the smooth passage of floss or result in
fraying of floss must be altered, or the restoration must be replaced,
to permit effective use of floss.
 Patient should be queried regarding any problems encountered in the
passing of floss through the contacts during home hygiene procedures.
Summit’s Fundamentals of Operative Dentistry, 4th edition

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 Benefits of an ideal contact and contour:
 Conserves health of the periodontium.
 Prevents food impaction.
 Makes the area self – cleansable.
 Improves the longevity of proximal restorations.
Sturdevant’s Art and Science of Operative Dentistry, 7th ed.

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EMBRASURES
 V – shaped spaces that originate at the proximal contact areas
between adjacent teeth.
 These embrasures are:
i. Facial.
ii. Lingual.
iii. Incisal or Occlusal.
iv. Gingival.

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Facial and Lingual embrasures shown in maxillary and mandibular teeth.

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Incisal, Occlusal and Gingival Embrasures in maxillary and mandibular teeth
Source: Sturdevant’s Art and Science of Operative Dentistry, 7th edition.

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 Correct relationships of embrasures of adjacent and opposing teeth
provide for the escape of food during mastication.
 When an embrasure is decreased in size or absent, additional stress
is created on teeth and the supporting structures during mastication.
 Too large embrasures provide little protection to the supporting
structures as food is forced into the interproximal space by an
opposing cusp.

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Improper embrasure form caused by overcontouring of restoration resulting in unhealthy
gingiva.
When the embrasure form is good, supporting tissues receive adequate stimulation
from food during mastication.

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Preservation of the curvatures of opposing cusps and surfaces in
function maintains masticatory efficiency throughout life.
Correct anatomic form renders teeth more self-cleansing because of
the smoothly rounded contours.
Radiograph showing flat contact
and resultant vertical osseous loss.
Radiograph showing restoration with
amalgam gingival excess resulting in
osseous loss & adjacent root caries.

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Embrasure form.
x: Portion of tooth that offers protection to
underlying supporting tissue during mastication.
y: Restoration fails to
establish adequate contour for good embrasure form.

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PERIODONTIUM
Periodontium consists of oral hard and soft tissues that support the
teeth.
It may be divided into:
i. Gingival unit, consisting of free and attached gingiva and the alveolar
mucosa.
ii. Attachment apparatus, consisting of cementum, periodontal
ligament and the alveolar process.

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 Clinically, the level of the gingival attachment and gingival sulcus is
an important factor in restorative dentistry.
 Soft tissue health must be maintained by teeth having the correct
anatomic form and position to prevent recession of the gingiva and
possible abrasion and erosion of the root surfaces.
 Margins of a tooth preparation should not be positioned
subgingivally unless dictated by caries, previous restoration, esthetics
or other preparation requirements.

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 Gingival esthetics should be optimal before placement of dental
restorations.
 Thin gingival margin closely adapted to the enamel with the papillae
filling the interproximal spaces is desirable.
 Gingival tissues should be firm and healthy having a pale pink color.
 Esthetics becomes a concern in cases of gingival recession, thick
margins and loss of papillae.
Principles and Practice of Operative Dentistry by Gerald T. Charbeneau, 3rd edition

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 Gingival grafting procedures to cover exposed roots of teeth with
gingival recession especially in anterior teeth are often indicated prior
to crown preparations.
 Free gingival grafts are sometimes used when there is lack of gingiva
for the abutment teeth.
 Esthetically preferable results can be obtained by thorough scaling and
root planing procedure followed by adequate maintenance care.

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 Gingival tissues adjacent to composite resin restorations extended
subgingivally are more prone to develop gingivitis even in the
presence of good oral hygiene practices.
 Common clinical observation is that rough surfaces on teeth and
restorations lead to faster and more extensive plaque formation than a
highly polished surface.
 Faulty contours or overhanging restorations pose a much greater
hazard to periodontal health.

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OCCLUSION
 Contact of teeth in opposing dental arches when the jaws are closed
(static occlusal relationship) and during various jaw movements
(dynamic occlusal relationship).
 Optimal function and absence of disease are the principal
characteristics of a good occlusion.

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Tooth contact during mandibular movement is termed dynamic
occlusal relationship.
 Gliding or sliding contacts occur during mastication and other
mandibular movements.
 Design of the restored tooth surface will have an impact on the
number and location of occlusal contacts.

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Tooth Alignment and Dental Arches
 Posterior teeth have one, two or three cusps near the facial and
lingual surfaces of each tooth.
 Cusps are separated by distinct developmental grooves and sometimes
have additional supplemental grooves on cusp inclines.
 Facial cusps are separated from the lingual cusps by a deep groove,
termed central groove.

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 Cusps in both arches are aligned in a smooth curve.
 Usually, the maxillary arch is larger than the mandibular arch, which
results in maxillary cusps overlapping mandibular cusps when the
arches are in maximal occlusal contact.
 Depressions between the cusps are termed fossae.

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 An imaginary arc connecting the facial cusps in the mandibular arch is
called the facial occlusal line.
 An imaginary line connecting the maxillary central fossae is labeled
as the central fossa occlusal line.
 Mandibular facial occlusal line and the maxillary central fossa
occlusal line coincide exactly when the mandibular arch is fully
closed into the maxillary arch.

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Maxillary lingual
occlusal line and
mandibular central
fossa line are
coincident.
Mandibular facial
occlusal line and
maxillary central
fossa line are
coincident.

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 Maximum intercuspation (MI) refers to the position of the mandible
when teeth are brought into full interdigitation with the maximal
number of teeth contacting.
 Synonyms for MI: intercuspal contact, maximum closure and
maximum habitual intercuspation.

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 Cusps that contact opposing teeth along the central fossa occlusal line
are termed functional cusps (synonyms include supporting, holding,
or stamp cusps).
 Cusps that overlap opposing teeth are termed nonfunctional cusps
(synonyms include nonsupporting or nonholding cusps).
 Mandibular facial occlusal line identifies the mandibular functional
cusps, whereas the maxillary facial cusps are nonfunctional cusps.

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 Anterior teeth are seen to have a different relationship in maximum
intercuspation (MI) position.
 Incisors are best suited to shearing food because of their overlap and
the sliding contact on the lingual surface of maxillary teeth.
 In MI, mandibular incisors and canines contact the respective lingual
surfaces of their maxillary opponents.

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 Horizontal overlap is termed as overjet.
 Vertical overlap is called overbite.
Overjet and Overbite in anterior teeth
Source: Wheeler’s Dental Anatomy, Physiology & Occlusion, 10th edition

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 Variations in the growth and development of the jaws and in the
positions of anterior teeth may prevent teeth from contacting.
 These variations can have an effect on the contacting relationships of
posterior teeth and resultant masticatory activity during various jaw
movements.
Open bite
(mandibular
deficiency)
Open bite (excessive
eruption of
posterior teeth)
Cross bite
(mandibular
growth excess)
Source: Sturdevant’Art and Science of Operative Dentistry, 7th edition

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Posterior Inter – Arch Relationship
 Cusp interdigitation pattern of the first molar teeth is used to classify
arch relationships by a classification system developed by Angle.
 Three interdigitated relationships of the first molars have been
commonly observed.
 Location of the mesiobuccal cusp of the maxillary first molar in
relation to the mandibular first molar is used as an indicator in Angle’s
classification.

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 Angle’s class I is characterized by the presence of a normal inter –
arch molar relation.
 Mesiobuccal cusp of the permanent maxillary first molar occludes in
the buccal groove of mandibular first molar.
Angle’s Class I
Orthodontics: The Art and Science by S.I. Bhalaji, 5th edition

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 Angle’s Class II is characterized by a class II molar relation wherein
the distobuccal cusp of the permanent maxillary first molar occludes
in the buccal groove of the mandibular first molar.
 Further sub-classified into two divisions, div. I and div. II.
 Class II div. I is symbolized by increased overjet.
Angle’s Class II

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 Angle’s Class III exhibits a class III molar relation where the
mesiobuccal cusp of the maxillary first molar occludes into the
distobuccal groove of mandibular first molar.
 Has the least common occurrence among all 3 classes.
Angle’s Class III

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Functional Cusps
 Cusps that contact opposing teeth along the central fossa occlusal line
are termed functional cusps (synonyms include supporting, holding,
or stamp cusps).
 Functional cusps serve to prevent drifting and passive eruption of
teeth – hence the term holding cusp.
 Functional cusps of both arches are more strong and better suited for
crushing food than nonfunctional cusps.

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 Maxillary functional cusps are located on the maxillary lingual
occlusal line.
 Mandibular functional cusps are located on the mandibular facial
occlusal line.

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 The functional cusps are characterized by five features:
1. Contact the opposing tooth in MI.
2. Maintain the vertical dimension of the face.
3. Nearer to the faciolingual center of the tooth than nonfunctional
cusps.
4. Outer (facial) incline has the potential for contact.
5. Have broader, more rounded cusp ridges with greater dentin support
than nonfunctional cusps.

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 During fabrication of restorations, it is important that functional
cusps are not contacting opposing teeth in a manner that results in
lateral deflection.
 Restorations should provide contacts on plateaus or smoothly concave
fossae.
 Masticatory forces should be directed approximately parallel to the
long axes of teeth (i.e. approximately perpendicular to the occlusal
plane).

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Non Functional Cusps
 Cusps that overlap opposing teeth are termed nonfunctional cusps
(synonyms include nonsupporting or nonholding cusps).
 Nonfunctional cusps have sharper cusp ridges that may serve to shear
food as they pass close to the functional cusp ridges during chewing
strokes.
 Position of the maxillary and mandibular nonfunctional cusps help to
prevent self – injury during chewing.

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 Nonfunctional cusps form a lingual occlusal line in the mandibular
arch.
 Form a facial occlusal line in the maxillary arch.

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 Nonfunctional cusps present with the following features:
1. Do not contact opposing tooth in MI position.
2. Keep soft tissue of tongue or cheek off the occlusal table.
3. Farther from faciolingual center of tooth than supporting cusps.
4. Outer incline has no potential for contact.
5. Have sharper cusp ridges than supporting cusps.

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Tripodization
 During complete closure, the contact point of the functional cusp is
neither at the tip of the cusp and nor it is a single point.
 Functional cusps are held in firm position by at least three contacts.
 These contacts occur on the inclines of the cusps and are called tripod
contacts, and the phenomenon is called tripodization.
Sandhu S, Lal J, Singh R, Sandhu R, Sra J. Significance of establishing occlusal anatomy in operative dentistry.
Saint Int Dent J 2016;2:7-10.

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Tripod Contacts: For cusp S1, contact points are a, b and c.
For cusp S2, contact points are b, c and d

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 Tripod contacts provide occlusal stability both buccolingually and
mesiodistally.
 There is one buccal and one lingual contact for each cusp along with
one mesial or distal contact.
 With advancing age, attrition and wear of dentition occurs due to
which the supporting cusps become more blunt.
 Tripodization does not remain as prominent with age.

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MANDIBLE & TEMPOROMANDIBULAR JOINT
 Temporomandibular joint (TMJ) is so called as it is named after the
two bones (temporal and mandible) forming its articulation.
 Mandible articulates with a depression in each temporal bone called
glenoid fossa.
Glenoid Fossa

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Mandibular Movement
 Muscles of mastication are responsible for mandibular movement.
 Classified as main and accessory muscles.
 Four pairs of muscles move the mandible during mastication:
1. Temporalis.
2. Medial Pterygoid.
3. Lateral Pterygoid.
4. Masseter.
 Buccinator is an accessory muscle of mastication.
Human Anatomy for Dental Students by M.K. Anand, 3rd edition

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All muscles are inserted in the ramus of mandible.
Muscles are innervated by branches of the mandibular nerve, which
is a branch of the trigeminal nerve.
Their vascular supply is derived from the external carotid artery.
All act on the temporomandibular joint.

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Masseter muscle
Source: BD Chaurasia’s Human Anatomy
for Dental Students, 3rd edition.

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Temporalis muscle
Source: BD Chaurasia’s Human Anatomy
for Dental Students, 3rd edition.

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Lateral Pterygoid muscle
Source: BD Chaurasia’s Human
Anatomy for Dental Students, 3rd
edition.

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Medial Pterygoid muscle
Source: BD Chaurasia’s Human
Anatomy for Dental Students, 3rd
edition.

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Buccinator
Origin Insertion Nerve Supply Action
1. Upper fibres:
Outer surface of the
alveolar process of
maxilla opposite the
molar teeth.
2. Middle fibres:
Pterygomandibular
raphe.
3. Lower fibres:
Outer surface of
alveolar process of
mandible, opposite
the molar teeth.
1. Upper fibres
pass straight to the
skin and submucosa
of upper lip.
2. Middle fibres
pass to both the
upper and lower
lips.
3. Lower fibres
pass straight to skin
and submucosa of
lower lip.
Buccal branch of
the facial nerve.
1. Flattens the cheek
against the gum and
teeth.
2.Prevents
accumulation of
food in the mouth.
3. Helps to expel the
air between the lips
from an inflated
vestibule, as in
blowing a trumpet
or whistle.

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Normal Masticatory Muscle Function
 Masticatory muscles work together to allow controlled, subtle
movements of the mandible.
 Amount of muscle activity depends on the inter – arch relationship of
the maxillary and mandibular teeth as well as the amount of resistance
to movement.

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Muscles involved in
MANDIBULAR MOVEMENTS
Anterior, Middle and
Posterior Temporalis
Superficial and Deep
Masseter
Superior and Inferior
Lateral Pterygoid
Medial Pterygoid
Digastric

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 Fine control of opening is accomplished by simultaneous mild
antagonistic activity of the medial pterygoid.
 When resistance is applied to jaw opening, mild masseter activation
allows further stabilization and fine control.
Jaw Opening
Muscles
Digastric Inferior Lateral Pterygoid

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 Once teeth come into contact, the temporalis muscle activates as
well.
 Masseter, medial pterygoid and temporalis muscles act to elevate
the mandible and are generally referred to as elevator muscles.
Jaw Closure
Muscles
Masseter Medial Pterygoid

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Clenching
Maximum
Activation
Moderate
Activation
Masseter Temporalis Medial
Pterygoid
Superior
Lateral
Pterygoid
Muscles

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Protrusion
Maximum
Activation
Moderate
Activation
Minimal
Activation
Inferior
Lateral
Pterygoid
Masseter DigastricMedial
Pterygoid
Temporalis
Superior
Lateral
Pterygoid
Muscles

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Retrusion
Maximum
Activation
Minimal
Activation
Moderate
Activation
Posterior &
Middle
Temporalis
Anterior
Temporalis
Digastric Masseter Medial
Pterygoid
Inferior
Lateral
Pterygoid
Muscles

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Movement Towards Right
Muscles
Maximum to
Moderate Activation
Moderate to
Minimal Activation
Inferior
Lateral
Pterygoid
Medial
Pterygoid
Posterior &
Middle
Temporalis
Superior
Lateral
Pterygoid
Anterior
Temporalis
Anterior
Digastric

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Wide Opening
Muscles
Maximum to
Moderate Activation
Moderate to
Minimal Activation
Minimal to
No Activation
Inferior
Lateral
Pterygoid
Anterior
Digastric
Medial
Pterygoid
Temporalis Masseter
Superior
Lateral
Pterygoid

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CLINICAL NOTE
 Sanchez GA et al (2010) studied the effects of lidocaine and
bupivacaine on Ca – ATPase on rabbit masseter and medial
pterygoid muscles.
 Results showed that both lidocaine and bupivacaine inhibit the
sarcoplasmic reticulum Ca – ATPase in masseter and medial
pterygoid muscles.
 Interactions between the anesthetics and protein might induce
masticatory muscle contraction and lead to eventual rigidity.
Sánchez GA, Takara D, Alonso GL. Local anesthetics inhibit Ca-ATPase in masticatory muscles.
J Dent Res. 2010;89(4):372-377.

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Muscle Pain
MASTICATORY MUSCLE DISORDERS
MyalgiaTendonitis Myositis Spasm
Contracture Hypertrophy
NeoplasmMovement
Disorders
Masticatory
muscle pain
attributed to
systemic/central
pain disorders
Fibromyalgia
Orofacial
Dyskinesia
Oromandibular
Dystonia
Burket’s Oral Medicine, 12th edition

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Contracture:
 Little or no pain unless involved muscle is forced to lengthen with a
limited range of motion.
Myalgia:
 Pain of muscle origin on chewing and wide opening that is affected by
jaw movement, function or parafunction.
Myositis:
 Continuous pain localized in muscle area following injury or infection
with diffuse tenderness over entire muscle.
De Rossi SS, Stern I, Sollecito TP. Disorders of the masticatory muscles. Dent Clin North Am. 2013;57(3):449-464.

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Neoplasia:
 Swelling, trismus, paresthesia and pain referred to teeth.
 Confirmed by positive findings on imaging or biopsy.
Fibromyalgia:
 Subjective pain in multiple sites.
 More than 3 months pain duration.
 Strong pain on palpation
De Rossi SS, Stern I, Sollecito TP. Disorders of the masticatory muscles. Dent Clin North Am. 2013;57(3):449-464.

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Orofacial Dyskinesia:
 Abnormal, involuntary movements of the tongue, lips and jaw.
 Ill – fitting dentures or lack of replacements may initiate dyskinesia.
Oromandibular Dystonia:
 Involuntary and excessive contractions of tongue, lip, and jaw
muscles.
 Exact etiology and pathophysiology are unknown.
Burket’s Oral Medicine, 12th edition

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Trismus
 Prolonged spasm of the jaw muscles leading to restricted mouth
opening (locked jaw).
 Trauma to the muscles is the most common causative factor
associated with local anesthetic injection.
 Excessive volumes of anesthetic solution injected in to an area may
lead to post injection trismus.
 More common after multiple missed inferior alveolar nerve blocks.
Handbook of Local Anesthesia by Stanley F. Malamed, 6th edition

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Implications of Trismus
 Reduced oral access and mandibular hypomobility that is resistant to
treatment can result in oral implications.
 Hypomobility will quite often limit the length of time for which
treatment can be undertaken.
 Frequent breaks, moments of relaxation and the use of a mouth
prop may reduce patient fatigue.
Garnett, M., Nohl, F. & Barclay, S. Management of patients with reduced oral aperture and mandibular hypomobility
(trismus) and implications for operative dentistry. Br Dent J 204, 125–131 (2008).

80
 Conservative treatment in the presence of mild to moderate
hypomobility may require a miniature sized hand piece with suitable
short shank burs.
 In presence of severe hypomobility, access to proximal and occlusal
lesions in posterior teeth may be approached through the buccal
aspect of the tooth.
 Endodontic treatment will need to be prioritized and may only be
feasible for teeth in the anterior region.

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 It may be necessary to gain access to the pulp canal via the labial
aspect of the tooth.
 Use of an apex locator could confirm working lengths and avoid the
need for periapical radiographs.
 Using rotary files of appropriate length to carry out cleaning and
shaping can allow for safer instrumentation of the canals.

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TYPES OF MOTION
 Centric Relation (CR) in a healthy TMJ refers to the location of the
mandible when the condyles are positioned superiorly and anteriorly
in the glenoid fossae.
 This position is independent of tooth contacts.

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 CR is used in dentistry as a reproducible reference position for
restorative procedures of the maxillary and mandibular occlusal
planes and also when fabricating complete dentures.
 Reproducibility of the CR position allows the establishment of
simultaneous contact of all functional cusps in maximum
intercuspation while the mandible is in CR.
 This occlusion is termed centric relation occlusion (CRO).

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 Rotation is a simple motion of an object around an axis.
 Mandible is capable of rotation about an axis through centers located
in the condyle.
 Rotation with the condyles positioned in CR is termed terminal hinge
(TH) movement.
 Maximum rotational opening in TH is limited to approximately 25
mm measured between the incisal edges of anterior teeth.

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 Translation is the bodily movement of an object from one place to
another.
 Mandible is capable of translation by anterior movement of the disc–
condyle complex from the TH position.
 Simultaneous direct anterior movement of both condyles, or
mandibular forward thrusting is termed protrusion.

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 Most of the mandibular movements during speech, chewing and
swallowing consists of rotation and translation.
 Combination of rotation and translation allows the mandible to open
50 mm approximately.

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 Posselt in 1952 recorded mandibular motion and developed a diagram
(termed Posselt’s diagram or envelope of motion) to illustrate it.

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 Every tooth in the mandible (the only moving jaw) has an envelope
of motion that outlines the outer limits to which each lower tooth can
be moved.
 TMJ has an envelope of motion that sets the path for all movements of
the teeth that are attached to the mandible.
 Lower teeth can move anywhere within the envelope of motion, but
they cannot move outside of the border paths that define the envelope
of motion.
Functional Occlusion from TMJ to Smile Design by Peter E. Dawson

89
 Digital computer techniques can reconstruct mandibular motion
simultaneously at several points, three of which are significant
clinically:
i. Incisor point: Located on the midline of the mandible at the junction
of the facial surface of mandibular central incisors and the incisal edge.
ii. Molar point: Tip of the mesiobuccal cusp of the mandibular first
molar on a specified side.
iii. Condyle point: Center of rotation of the mandibular condyle on the
specified side.

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 Mandibular pathways directed away from the midline are termed
working (synonyms include laterotrusion and functional).
 Pathways directed toward the midline are termed nonworking
(synonyms include mediotrusion, nonfunctional and balancing).
 Terms working and nonworking are based on observations of chewing
movements in which the mandible is seen to shift during closure
toward the side of the mouth containing the food bolus.

92
 Working side is used to crush food whereas the nonworking side is
without a food bolus.
 The term may also identify a specific side of the mandible (i.e., the
side toward which the mandible is moving).
 During chewing, the working side closures start from a lateral position
and are directed towards the maximum intercuspation position.

93
 Chewing movements are characterized by wide lateral movement of
the mandible to the working side during closure.
 When viewed from above, the pathways of the molar and incisor
points are typically in a figure – 8 pattern.

94
 During closure on the working side, mandibular teeth medially
approach maxillary teeth from a slightly posterior position and move
slightly anteriorly into MI position.
 During closure on the nonworking side (the contralateral side),
mandibular molar teeth approach the maxillary teeth in a medial – to
– lateral direction from a slightly anterior position and move slightly
posteriorly into MI.

95
 Vertical displacement of the mandible secondary to gliding contact of
canine teeth is termed canine guidance.
 Gliding tooth contact supplied by canine guidance provides some of
the vertical separation of posterior teeth during lateral jaw movements
and prevents potentially damaging collisions of their cusps.
 When the canine guidance is shallow, the occlusal surface of posterior
teeth must be altered to prevent potentially damaging contacts during
lateral or protrusive movements.

96
 Basic principle of canine – protected occlusion is that on laterotrusive
movements of mandible, only the canine contacts and protects
remaining dentition from adverse occlusal forces.
 Canine – protected occlusion reduces chances of temporomandibular
dysfunction, since it reduces the possibility of interfering contacts.
 Canines have a good crown root ratio capable of tolerating high
occlusal forces and shape of the palatal surface of canine is concave
which is suitable for guiding lateral movements.
Pasricha N, Sidana V, Bhasin S, Makkar M. Canine protected occlusion. Indian J Oral Sci 2012;3:13-8.

97
 Flexibility in the TMJs allows the condyles to move slightly to the
working side during the closing stroke.
 This lateral shift of the condylar head is termed Bennett shift or
lateral shift.
 Magnitude of shift in a normal TMJ varies from 0 to 1.5 and normally
has little effect on posterior teeth.
 Excessive lateral shift may be associated with morphologic changes of
the TMJ.

98
 Lateral movement of the mandible is controlled by three elements –
rotating condyle, translating condyle and the working – side canine.

99
Articulators and Mandibular Movements
Incisal Guidance (Anterior Determinant):
 When the mandible is brought forward (protrusion), the incisal edge
of lower anteriors slides along the slope of lingual surface of upper
anterior teeth.
 Lingual surface of maxillary anteriors guides the mandible during
protrusive movement and is called the incisal guidance.
Palatal slope of the incisors gives the incisal guidance
Textbook of Prosthodontics by Deepak Nallaswamy, 2nd edition

100
Condylar Guidance (Posterior Determinant):
 Path of movement taken by the condyle in the glenoid fossa.
 Condyle moves along the surface of glenoid fossa during mandibular
movement.
 Shape of the glenoid fossa which determines the path of movement of
the condyle is called the condylar guidance.
Posterior slope forms the condylar guidance
Textbook of Prosthodontics by Deepak Nallaswamy, 2nd edition

101
 Movements can be tested by comparing the cusp movement near MI
produced by the articulator with the cusp movement observed in the
patient.
 Horizontal condylar guidance setting and the medial – wall setting
of an articulator supply sufficient information to approximate the
condyle movement near MI.
 Collectively, these two settings are referred to as posterior guidance.

102
 Full – arch casts mounted in the articulator, with the use of techniques
that correctly position the maxillary cast relative to the artificial TMJs,
supply information concerning anterior guidance from canines and
incisors.
 Mechanical coupling of the anterior and posterior guidance settings
provides sufficient information to simulate the movement of posterior
teeth.
 Adjustable articulators allow establishment of patient – specific
setting of condylar inclination.

103
 Alteration of the anterior guidance may occur during dental treatment
that involves the guiding surfaces of anterior teeth.
 Loss of anterior guidance has the greatest effect when the horizontal
condylar guidance is shallow (20 degrees) and has the least effect
when the horizontal condylar guidance is steep (50 degrees).
 Articulator may be used to diagnose the need to alter the anterior
guidance and to design restorations that avoid cusp collisions in

104
 Lateral mandibular movements produce separation of posterior teeth.
 Horizontal guidance of the nonworking condyle coupled with working
– side canine guidance determines the amount of vertical separation of
posterior teeth on both sides as the mandible leaves or enters MI
during lateral movements.
 This information may be used to design restorations with the proper
cusp location and height to avoid collisions during chewing and other

105
 Increase in lateral shift of the TMJ results in significant changes in
movement of the molar point near MI.
 Effect of increasing lateral shift is to increase the likelihood of
collisions of the mesiolingual cusps of the maxillary molars with the
mandibular distobuccal cusps of the molars on the nonworking side.
 These types of undesirable contact between the opposing functional
cusps are termed nonworking interferences.

106
Tooth Contacts During Mandibular Movements
 Evaluation of the location, direction and area of tooth contacts during
mandibular movements is an essential part of the preoperative
evaluation of teeth to be restored.
 Restorations must be designed in a way that they are able to
withstand the forces of mastication.
 Anterior teeth support gliding contacts, whereas posterior teeth
support the heavy forces applied during chewing and clenching.

107
Anterior Tooth Contacts
 During anterior movement of the mandible (i.e. protrusion), the lower
anterior teeth glide along the lingual surfaces of maxillary anterior
teeth.
 With protrusion, multiple contacts occur to prevent excessive force on
any individual pair of gliding teeth.
 Articulator – mounted casts may be used to assess the MI position,
which is the critical zone for tooth contact.

108
Posterior Tooth Contacts
 Forceful contact of individual posterior tooth cusps during chewing
and clenching may lead to muscle discomfort and damage to teeth &
supporting structures or both in some patients.
 Articulator – mounted casts may be used to assess and solve
restorative problems that are difficult to manage by direct intraoral
techniques.

109
 It has been observed that buccal cusps of the maxillary premolars
and molars and lingual cusps of mandibular molars have an
increased incidence of fracture.
 This finding is consistent with the increased muscle activity that
occurs as posterior teeth come into contact and that the bulk of dentin
supporting the nonfunctional cusps is considerably less than that of
the functional maxillary and mandibular cusps.

110
Detecting and Marking Occlusal Contacts
 Occlusal contacts can be clinically marked by the following methods:
i. Articulating Papers:
 Useful for recording tooth contacts both in static and dynamic
occlusal relations.
 Occlusal pressure results in the coloured material being deposited on
the occlusal surface near or at the actual place where tooth to tooth
contact would otherwise occur.
 Reliability of the marking is related to the thickness and properties of
the articulating paper.
Warreth A, Doody K, Al-Mohsen M, Morcos O, Al-Mohsen M, Ibieyou N. Fundamentals of occlusion and restorative
dentistry. J Ir Dent Assoc. 2015;61(5):252-259.

111
 Brizuela – Velasco A et al (2015) studied the influence of articulating
paper thickness on occlusal contacts registration.
 Four different occlusal registrations were made using a 12 µm, 40
µm, 80 µm and 200 µm thickness articulating papers.
 Results showed that use of thin articulating papers (12 µm or 40 µm)
can avoid unnecessary grinding of teeth during occlusal adjustment.
 Occlusal registrations obtained with the thinnest articulating paper
were contained within the area marked on the thickest.
Brizuela-Velasco A, Álvarez-Arenal Á, Ellakuria-Echevarria J, del Río-Highsmith J, Santamaría-Arrieta G, Martín-
Blanco N. Influence of Articulating Paper Thickness on Occlusal Contacts Registration: A Preliminary Report. Int J
Prosthodont. 2015;28(4):360-362.

112
 Basic constituents of an articulating paper are a coloring agent and a
bonding agent.
 On occlusal contact, the coloring agent is expelled from the film and
the bonding agent binds it on to the tooth surface.
 Disadvantage of being easily ruined by saliva and hence requires
usage in a dry field and also produces a large number of
pseudocontact markings.
Babu RR, Nayar SV. Occlusion indicators: A review. J Indian Prosthodont Soc 2007; 7(4): 170-174

113
ii. Waxes:
 Occlusal contacts can be recorded by placing wax on the occlusal
surfaces of posterior teeth and patient closing into maximum
intercuspation.
 Cusps of the opposing occlusal surfaces penetrate the wax at the
points of occlusal contact.
 Perforations in the wax indicate actual tooth contacts.
 Should be used used only when the use of articulating paper is not
satisfactory, as when moisture control is not achievable.
Warreth A, Doody K, Al-Mohsen M, Morcos O, Al-Mohsen M, Ibieyou N. Fundamentals of occlusion and restorative
dentistry. J Ir Dent Assoc. 2015;61(5):252-259.

114
iii. Occlusal Sprays:
 Universal color indicator to test occlusal contacts, available in red,
blue, green and white colors.
 Applied at a distance of 3 – 5 cm onto the occlusal surface.
 Leaves a thin colored film which can easily be removed with water,
leaving no trace of residues.
 When testing occlusion, all contact points will be immediately
visible.
Sharma A, Rahul GR, Poduval ST, Shetty K, Gupta B , Rajora V. History of materials used for recording static and
dynamic occlusal contact marks: a literature review. J Clin Exp Dent. 2013;5(1):48-53.

iv. Shim Stock:
 Shim stock film has a metallic surface on one side and the other side
is color coded.
 Mainly indicated for use in occlusal splint therapy in order to
accurately mark contacts on the soft splint.
115

v. T Scan:
 T – Scan (Tekscan) is a Microsoft compliant occlusal analysis system
that can record a given contact sequence.
 First introduced by Mannes in 1984.
 Consists of a piezoelectric foil sensor, a sensor handle, both hardware
and software for recording, analyzing and viewing data.
 Indicated in situations where bilateral simultaneous occlusal contact is
needed.
116

 Recording handle with the sensor and arch support is placed between
central incisors of the patient.
 Recording is initiated by pressing the button on the recording handle.
 Patient is asked to close his/her mouth till complete intercuspation is
reached, without making any excursive movements.
Tekscan recording handle with sensor
placed intraorally
117

 Program can be operated in two modes:
i. Time Analysis and
ii. Force Analysis.
 Time analysis provides information on the location and timing of
contacts displayed on the screen with first, second and third contact in
different colors.
 Force analysis shows the location of contacts and their relative forces
in five different shades of colors.
Pyakurel U, Long H, Jian F, Sun J, Zhu Y, Jha H, Lai W. Mechanism, accuracy and application of T-Scan system in
dentistry – A review. J Nep Dent Assoc. 2013;13(1):1-5.
118

119
OCCLUSALADJUSTMENT
 Removal of occlusal interferences through selective tooth grinding
after the use of restorative materials (also called occlusal
equilibration).
 Aim of such an intervention is to obtain a stable occlusal relationship
with no premature contacts.
 Adjustments are generally required after performing restorations in
order to establish a better relationship with the antagonist teeth.
Lima AF, Cavalcanti AN, Martins LR, Marchi GM. Occlusal interferences: how can this concept influence the
clinical practice? Eur J Dent. 2010;4(4):487-491.

120
Ideal pattern of
centric relation
occlusion contacts
represented by dots in
the posteriors and
lines in the anteriors.

121
 Adjustment Rules:
 Narrow functional (stamp) cusps before reshaping fossae:
 If the first reshaping is directed at grinding the fossae, it unnecessarily
grinds away more enamel than would be needed to accommodate
narrower stamp cusps.
 If contouring of fossae is delayed until stamp cusps have been
reshaped, excursive interferences can then be eliminated with less
tooth reduction.

122
 Do not shorten a functional cusp:
 Instead of shortening a functional cusp, sides of the functional cusps
should be reduced.
 Avoid the cusp tip.
 Cusps should be narrowed on the side that marks when the jaw closes
to maximum intercuspation contact.

123
Reduction of the interfering tooth
surfaces is confined to areas
that are marked with red.
Black marks are not touched.

12
4
 Eliminate all posterior incline contacts:
 Any posterior incline that marks in movement should be reduced to
eliminate eccentric contacts on posterior teeth.
 Missed interferences are mostly located on the last molars often
because the interfering molars are loose enough to be easily moved by
the offending deflective inclines.
 Loose teeth just depress or move to let the rest of the teeth come
together without creating a slide.

125
 Occlusal equilibration should be verified by asking the patient to
firmly clench his/her teeth together.
 If the patient can feel discomfort in any tooth, the equilibration is
incomplete.
 Occlusion should be re – verified by making sure the teeth are dry and
a fresh marking paper is properly placed.
 If an empty mouth clench can make any posterior tooth hurt, the
equilibration has not been completed.

126
 Occlusal interferences can lead to the development of or to an
increase in the severity of Temporomandibular Joint Disorders
(TMDs).
 Several studies have evaluated the influence of occlusal interferences
on the etiology of TMDs.
 Occlusal interferences not only can affect the development and
severity of TMDs, but can also affect the body posture and
equilibrium.
Lima AF, Cavalcanti AN, Martins LR, Marchi GM. Occlusal interferences: how can this concept influence the
clinical practice? Eur J Dent. 2010;4(4):487-491.

127
CLINICALASPECTS OF OCCLUSION
 Occlusal problems are more apparent when there are restorative
aspects involved in the patient’s complaints.
 Occlusal aspects should be considered when examining a patient for
optimal management of the problem.
Alani A, Patel M. Clinical issues in occlusion. Singapore Dent J. 2014; 35: 31-38.

128
Occlusion and Tooth Surface Loss
 Attrition results from tooth – to – tooth contact resulting in well –
defined wear facets on the occluding surfaces of teeth which
correspond between the maxilla and mandible.
Attrited teeth

129
 Tooth wear more than that expected physiologically, can result in the
accelerated loss of tooth tissue, threatens pulp health and makes
future restorative management difficult due to changes in interocclusal
relationship and loss of interocclusal space.
 In the later stages, tooth may become significantly damaged resulting
in difficulties in restoration and can have pulpal involvement.
 Prognosis for survival of such teeth and their associated restorations
is likely to be questionable.

130
 Key in these situations is to identify patients with parafunctional
activity.
 Recognizing this in the early stages can protect tooth structure by
considering a long term appliance therapy.
 Conservative management would be the provision of a stabilization
splint in order to prevent further hard tissue loss.
 A soft bite guard could be made in acute cases as a way of relief.

131
 One notable risk factor for parafunctional activity is psychological
stress.
 Current research shows that prevalence of psychological stress is
increasing in the general population.
 Thorough social history should be taken which can help in treatment
planning process and aide delivery of care.

132
Occlusion and Restoring Vertical Dimension
 In cases of severe tooth surface loss, there may be an extensive loss of
the dental hard tissues.
 Teeth may appear to look grossly shorter in clinical crown height.
 Increasing the existing vertical dimension is a treatment strategy that
should be considered in such cases.

133
 Treatment methods such as surgical crown lengthening and
orthodontic intrusion have been proposed for increasing the clinical
crown height.
 These techniques should be performed with appropriate care and
planning.
 A new concept was developed further by utilizing composite resin to
restore worn teeth.

134
 Concept involved the placement of composite restorations at an
increased vertical dimension on anterior teeth leaving posterior teeth
with no occlusal contacts.
 A period of occlusal adaptation results with a combination of intrusion
of the anterior teeth and vertical migration of posterior teeth resulting
in the relinquishing of contacts over time.
Direct composite restorations placed on the
upper and lower anteriors at an increased
occlusal vertical dimension.

135
Occlusion and Mechanical Failure of Teeth
 Cracking or fracture of teeth is a problem that is increasing and is
difficult to diagnose in the early stages.
 Cracks and fractures of teeth are significantly associated with large
restorations.
 Teeth with large restorations are poorly supported with an absence of
underlying tooth tissue.

136
 As tooth bulk decreases so does the remaining tissues ability to resist
force and prevent fracture.
 This is best illustrated by MOD restorations on premolar teeth.
 Cuspal coverage of teeth with reduced tooth structure is an efficient
way to reduce the likelihood of fracture or cracking.
 Cuspal coverage has shown to provide greater resistance to fracture
than non – cuspal coverage restorations.

137
Trauma from Occlusion
 When occlusal forces exceed the adaptive capacity of the tissues,
tissue injury results.
 The resultant injury is termed trauma from occlusion, which is also
known as occlusal trauma.
 Occlusion that produces tissue injury is called a traumatic occlusion.
Carranza’s Clinical Periodontology, 13th edition

138
 Excessive occlusal forces may also disrupt the function of the
masticatory musculature and cause painful spasms, injure the
temporomandibular joint or produce excessive tooth wear.
 Can be classified according to the injurious occlusal force(s) mode of
onset (acute and chronic) or according to the capacity of the
periodontium to resist occlusal forces (primary and secondary).

139
 Acute trauma from occlusion refers to periodontal changes associated
with an abrupt occlusal impact such as that produced by biting on a
hard object.
 In addition, restorations or prosthetic appliances that interfere with
or alter the direction of occlusal forces on the teeth may also induce
acute trauma.
 Acute trauma results in tooth pain, sensitivity to percussion and
increased tooth mobility.

140
 Chronic trauma from occlusion refers to periodontal changes
associated with gradual changes in occlusion produced by tooth wear,
drifting movement and extrusion of the teeth in combination with
parafunctional habits (e.g. bruxism, clenching).
 Chronic trauma from occlusion is more common than the acute form
and of greater clinical significance.
Singh DK, Jalaluddin M, Rajeev R. Trauma from occlusion: The overstrain of the supporting structures of the teeth.
Indian J Dent Sci 2017;9:126-32.

141
 Primary trauma from occlusion refers to the condition resulting from
abnormal occlusal forces on relatively sound periodontal structure.
 Traumatic forces acting on teeth with normal support are greater than
the forces that can be withstood without injury to the periodontium.
 Classical example includes periodontal injury produced around teeth
with a previously healthy periodontium after the insertion of a high
restoration.

142
 Secondary trauma from occlusion is applied to a condition resulting
from physiologic or abnormal occlusal forces, which act on a
dentition that is seriously weakened by the loss of supporting alveolar
bone.
 Lack of periodontal support may result from effects of periodontal
disease or from excessive apical resorption.
 Periodontium becomes more vulnerable to injury and previously well
– tolerated occlusal forces become traumatic.

143
 Occlusal trauma can play a role in the progression of periodontal
disease.
 Studies have shown that occlusal trauma can play a role in the
progression of periodontal disease in a susceptible host and in the
presence of periodontal pathogens.
 Restorations in which occlusal contacts are creating occlusal trauma
should be altered or replaced as per the need.
Summit’s Fundamentals of Operative Dentistry, 4th edition

144
NEUROLOGIC CONTROL OF MASTICATION
 Control of mastication depends on sensory feedback.
 Sensory feedback serves to control the coordination of lips, tongue
and mandibular movement during manipulation of the food bolus
through all stages of mastication and preparation for swallowing.
 Sensory feedback often results in inhibition of movement (e.g.
because of pain).

145
 Group of neurons in the brainstem produces bursts of discharges at
regular intervals when excited by oral sensory stimuli.
 These bursts drive motor neurons to produce contractions of the
masticatory muscles at regular intervals, resulting in rhythmic
mandibular movement.
 Cluster of neurons in the brainstem that drives the rhythmic chewing
is termed central pattern generator.

146
 Oral sensory feedback can modify the basic central pattern generator
pattern and is essential for the coordination of the lips, tongue and
mandible.
 Sensory input from the periodontal and mucosal receptors maintains
the rhythmic chewing.
 Coactivation of the opening and closing muscles serves to protect the
dentition from excessively forceful contact, makes the mandible more
rigid and probably serves to brace the condyles while the food is
crushed.

147
OCCLUSAL DISEASE
 Process resulting in the noticeable loss or destruction of the occluding
surfaces of the teeth.
 Any disharmony between the teeth, muscles and TMJ is sufficient to
cause stress, deformation or dysfunction on any or all parts of the
masticatory system.
Mohan B, Sihivahanan D. Occlusion: The gateway to success. J Interdiscip Dentistry 2012;2:68-77

148
 Lytle in 1990 was the first to define it as “the process resulting in the
noticeable loss or destruction of the occluding surfaces of the teeth.”
 Occlusal disease is deformation or disturbance of function of any
structure within the masticatory system that are in disequilibrium
with a harmonious interrelationship between the TMJ, the masticatory
musculature and the occluding surface of the teeth.
Mohan B, Sihivahanan D. Occlusion: The gateway to success. J Interdiscip Dentistry 2012;2:68-77.

149
Examples of occlusal disease:
1. Attritional Wear:
 One of the most common untreated problems.
 Seen more frequently in the mandibular anterior teeth.
2. Painful Musculature:
 Common symptom of occlusal disease resulting from disharmony
between the occlusion and TMJ.

150
3. Splayed Teeth:
 Mandibular deflection that causes wear problems can force the upper
anterior teeth forward.
 Improperly contoured restorations that are too thick on the lingual
surfaces of upper anterior teeth or overcontoured lower restorations
are common causes of splaying.
 Oversized tongue may be the sole causative factor in some splayed
dentitions.
Splayed Teeth

151
4. Destroyed Dentition:
 Result of not intercepting occlusal disease early.
 Signs of severe wear and fractured maxillary & mandibular teeth are
typical.
5. Advanced Occlusal Disease:
 Refers to occlusal disease left undiagnosed and untreated until the
late stage of progressive damage has occurred.

152
CONCLUSION
 Knowledge of the basic principles of dental anatomy, physiology and
occlusion is vital for every dentist.
 Subject of occlusion should be given much more importance and
incorporated in our day – to – day practice.

153
THANK YOU!
Made By:
Dr. Akshat Sachdeva
MDS 2nd Year
Department of Conservative Dentistry and Endodontics
Sudha Rustagi College of Dental Sciences and Research

Clinical Significance of Dental Anatomy, Physiology and Occlusion

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