CONCEPTS OF CONCEPTS OF OCCLUSIONOCCLUSION

Presented byPresented by

Dr.Maulik Patel Dr.Maulik Patel

DEPARTMENT OF

ORTHODONTICS

contentscontents• Introduction

• Development of concept of occlusion

• Definitions

• Compensatory curves of dental arches.

• Position of teeth on dental arches

•Clasification of occlusion

•Andrews six keys to normal occlusion

•Clinical significance

•Conclusion

INTRODUCTIONINTRODUCTION

The study of occlusion is an important aspect of dentistry. The study and practice of most branches of dentistry should be based on a strong foundation of knowledge of occlusion. Orthodontics is no exception to this as great many changes occur in the occlusion during orthodontic therapy.

The orthodontist should know what constitutes normal occlusion in order to be able to recognize abnormal occlusion.

THE DEVELOPMENT OF THE CONCEPTS THE DEVELOPMENT OF THE CONCEPTS OF OCCLUSIONOF OCCLUSION

The development of concept of occlusion can be The development of concept of occlusion can be traced through fiction and hypothesis to fact.traced through fiction and hypothesis to fact.

The fictional approach was a convenient The fictional approach was a convenient arrangement of a series of observation and thoughts arrangement of a series of observation and thoughts more or less logically arranged.more or less logically arranged.

The hypothetical approach was based on provisional The hypothetical approach was based on provisional acceptance of certain logical entities.acceptance of certain logical entities.

Fact is a truth known by actual experience or Fact is a truth known by actual experience or observation. Both the fictional and hypothetical observation. Both the fictional and hypothetical approach are necessary for the establishment of approach are necessary for the establishment of fact.fact.

FICTIONAL PERIODFICTIONAL PERIOD

Pioneers like Fuller, Clark and Imrie talked Pioneers like Fuller, Clark and Imrie talked of “of “AntagonismAntagonism”, “”, “MeetingMeeting” or “” or “GlidingGliding” ” of teeth.of teeth.

The creation of normal standard, a basis The creation of normal standard, a basis on which to compare departures from on which to compare departures from normal was lacking. But this served as a normal was lacking. But this served as a working hypothesis or subsequently working hypothesis or subsequently became established fact after definitive became established fact after definitive research research

Eugene Talbot published his book Eugene Talbot published his book ““Irregularities of the teeth and their Irregularities of the teeth and their treatmenttreatment” in 1903. ” in 1903.

The Talbot concept of normal occlusion The Talbot concept of normal occlusion was that it was a historical event, passed was that it was a historical event, passed in the decline of the species and normality in the decline of the species and normality was possible only with atavism or was possible only with atavism or throwback to our primitive ancestorsthrowback to our primitive ancestors

Asbell milton- brief history of orthodontics article- ajodo

HYPOTHETICAL PERIODHYPOTHETICAL PERIOD

Edward H. AngleEdward H. Angle, , – It was him, who channelised orthodontic It was him, who channelised orthodontic

thinking on occlusion and brought the real thinking on occlusion and brought the real concept out of fiction.concept out of fiction.

– In In 1907,1907, Angle summarised his views as Angle summarised his views as ‘‘occlusion shall be defied as being the occlusion shall be defied as being the normal relation of the occlusal inclined normal relation of the occlusal inclined planes of the teeth when the jaws are planes of the teeth when the jaws are closedclosed’’..

– Angle cites the example of a skull of Negro male Angle cites the example of a skull of Negro male from Broomell which he names ‘from Broomell which he names ‘Old GloryOld Glory’. In ’. In ‘‘Old GloryOld Glory’ all the teeth are present and ’ all the teeth are present and arranged in a graceful curve. He emphasizes arranged in a graceful curve. He emphasizes that all teeth are necessary for maintaining that all teeth are necessary for maintaining occlusion. He compares ‘occlusion. He compares ‘Old GloryOld Glory’ with the ’ with the profile of Appollo Belvedre a white maleprofile of Appollo Belvedre a white male

Angle furnished his ‘Angle furnished his ‘key to occlusionkey to occlusion’ and ’ and emphasizes the first permanent molars emphasizes the first permanent molars especially the upper first permanent molar and especially the upper first permanent molar and considers them to be most constant in taking considers them to be most constant in taking normal position. normal position.

From the hypothesis of constancy of first molar From the hypothesis of constancy of first molar and the ‘and the ‘line of occlusion’ line of occlusion’ , Angle developed the , Angle developed the concept that all teeth should be present if normal concept that all teeth should be present if normal occlusion is to be achived.occlusion is to be achived.

Mathew Cryer and Calvin CaseMathew Cryer and Calvin Case

Cryer pointed out that Angle showed the straight profile of Cryer pointed out that Angle showed the straight profile of Apollo Belvedre and chose a skull of negro male ‘Apollo Belvedre and chose a skull of negro male ‘Old Old GloryGlory’ to exemplify ideal occlusion. He questioned how ’ to exemplify ideal occlusion. He questioned how one could mix a prognathic denture with an orthodontic one could mix a prognathic denture with an orthodontic profile.profile.

Case accepts Angle’s hypothesis of constancy of first Case accepts Angle’s hypothesis of constancy of first molar. Case related the facile profile to each type of molar. Case related the facile profile to each type of occlusion.occlusion.

He proposed the concept of apical He proposed the concept of apical base and divided dentofacial area into base and divided dentofacial area into four segments or zones of movement.four segments or zones of movement.

He was aware of the role of nose and chin button and He was aware of the role of nose and chin button and their influence on profile.their influence on profile.

Case proposed the concept of normal and ideal Case proposed the concept of normal and ideal occlusion.occlusion.

The idea that teeth should be present to obtain normal The idea that teeth should be present to obtain normal facial contour was loosing ground.facial contour was loosing ground.

In 1908 Bennett proposed that the condylar movement In 1908 Bennett proposed that the condylar movement was primarily rotatary on opening from occlusion to rest was primarily rotatary on opening from occlusion to rest position and later on after passing this point became position and later on after passing this point became translatory. translatory.

Lischer and Paul SimonLischer and Paul Simon

They broadened the concept of occlusion by They broadened the concept of occlusion by relating the teeth to the rest of the face and relating the teeth to the rest of the face and cranium. They related teeth in occlusal contact to cranium. They related teeth in occlusal contact to cranial and facial planes outside the denture cranial and facial planes outside the denture proper. proper.

Though the concept of orbital plane as basis for Though the concept of orbital plane as basis for determining antero-posterior position of dentition determining antero-posterior position of dentition did not stand up. It introduced the idea of facial did not stand up. It introduced the idea of facial ramification of malocclusion outside the dental ramification of malocclusion outside the dental area.area.

Milo HellmanMilo Hellman

Hellman showed the racial variation in so called Hellman showed the racial variation in so called normal occlusion through anthropological normal occlusion through anthropological studies.studies.

Hellman and others studied the prognathism of Hellman and others studied the prognathism of the human dentition in relation to a cranial basethe human dentition in relation to a cranial base

FACTUAL PERIODFACTUAL PERIODIn 1930 In 1930 Holly Broadbent Holly Broadbent and and Hans Planer Hans Planer introduced an introduced an accurate technique of roentogenographic cephaolmetry. accurate technique of roentogenographic cephaolmetry. Investigators were able to follow longitudinally the Investigators were able to follow longitudinally the orofacial developmental pattern and the intricacies of orofacial developmental pattern and the intricacies of tooth formation, eruption and adjustment.tooth formation, eruption and adjustment.

Planer laid emphasis on efficiency of masticating Planer laid emphasis on efficiency of masticating mechanism. He explained physiological rest position and mechanism. He explained physiological rest position and vertical dimensionvertical dimension

A third element of occlusion, the A third element of occlusion, the TMJTMJ has been receiving has been receiving more attention. There is an intimate relationship between more attention. There is an intimate relationship between the interdigitation of the teeth, the status of controlling, the interdigitation of the teeth, the status of controlling, musculature and the integrity of the TMJ. musculature and the integrity of the TMJ.

The goal of modern orthodontics according The goal of modern orthodontics according to Profitt is “to Profitt is “the creation of best possible the creation of best possible occlusal relationship within the framework occlusal relationship within the framework of acceptable facial aesthetics and stability of acceptable facial aesthetics and stability of resultof result”.”.

Angle defined– occlusion as the normal Angle defined– occlusion as the normal relation of the occlusal inclined planes of relation of the occlusal inclined planes of the teeth when jaws are closed.the teeth when jaws are closed.

The goal of modern orthodontics according The goal of modern orthodontics according to Profitt is “to Profitt is “the creation of best possible the creation of best possible occlusal relationship within the framework occlusal relationship within the framework of acceptable facial aesthetics and stability of acceptable facial aesthetics and stability of resultof result”.”.

Angle defined– occlusion as the normal Angle defined– occlusion as the normal relation of the occlusal inclined planes of relation of the occlusal inclined planes of the teeth when jaws are closed.the teeth when jaws are closed.

Dental occlusion varies among individuals Dental occlusion varies among individuals according to tooth size and shape, tooth according to tooth size and shape, tooth position, timing and sequence of eruption, dental position, timing and sequence of eruption, dental arch size and shape and pattern of craniofacial arch size and shape and pattern of craniofacial growth.growth.

The position of the teeth within the jaws and The position of the teeth within the jaws and the mode of occlusion are determined by the mode of occlusion are determined by developmental processes that interact on the developmental processes that interact on the teeth and their associated structures during the teeth and their associated structures during the period of formation, growth and post natal period of formation, growth and post natal modification .modification .

Dental occlusion varies among individuals Dental occlusion varies among individuals according to tooth size and shape, tooth according to tooth size and shape, tooth position, timing and sequence of eruption, dental position, timing and sequence of eruption, dental arch size and shape and pattern of craniofacial arch size and shape and pattern of craniofacial growth.growth.

The position of the teeth within the jaws and The position of the teeth within the jaws and the mode of occlusion are determined by the mode of occlusion are determined by developmental processes that interact on the developmental processes that interact on the teeth and their associated structures during the teeth and their associated structures during the period of formation, growth and post natal period of formation, growth and post natal modification .modification .

TERMINOLOGIES USED IN OCCLUSION TERMINOLOGIES USED IN OCCLUSION TERMINOLOGIES USED IN OCCLUSION TERMINOLOGIES USED IN OCCLUSION

Normal Occlusion :Normal Occlusion :– Normal occlusion implies a situation commonly Normal occlusion implies a situation commonly

found in the absence of disease. It should found in the absence of disease. It should include not only a range of anatomically include not only a range of anatomically acceptable values but also physiological acceptable values but also physiological adaptability.adaptability.

– It is always a range never a point. It is always a range never a point.

Ideal Occlusion :Ideal Occlusion :– The concept of ideal or optimal occlusion refers The concept of ideal or optimal occlusion refers

both to an aesthetic and physiologic ideal. It both to an aesthetic and physiologic ideal. It includes functional harmony, stability of includes functional harmony, stability of masticatory system & Neuromuscular harmony .masticatory system & Neuromuscular harmony .

Normal Occlusion :Normal Occlusion :– Normal occlusion implies a situation commonly Normal occlusion implies a situation commonly

found in the absence of disease. It should found in the absence of disease. It should include not only a range of anatomically include not only a range of anatomically acceptable values but also physiological acceptable values but also physiological adaptability.adaptability.

– It is always a range never a point. It is always a range never a point.

Ideal Occlusion :Ideal Occlusion :– The concept of ideal or optimal occlusion refers The concept of ideal or optimal occlusion refers

both to an aesthetic and physiologic ideal. It both to an aesthetic and physiologic ideal. It includes functional harmony, stability of includes functional harmony, stability of masticatory system & Neuromuscular harmony .masticatory system & Neuromuscular harmony .

Physiologic occlusion :Physiologic occlusion :

– The occlusion that shows no signs of occlusion related The occlusion that shows no signs of occlusion related pathosis. It may not be an ideal occlusion but it is devoid pathosis. It may not be an ideal occlusion but it is devoid of any pathological manifestations in the surrounding of any pathological manifestations in the surrounding tissues.tissues.

Traumatic occlusion :Traumatic occlusion :

– The occlusion which produces abnormal occlusal stress The occlusion which produces abnormal occlusal stress which is capable of producing or has produced an injury which is capable of producing or has produced an injury to the periodontium.to the periodontium.

Therapeutic occlusionTherapeutic occlusion : :

– It is a treated occlusion employed to counteract It is a treated occlusion employed to counteract structural interrelationship related to traumatic structural interrelationship related to traumatic occlusion.occlusion.

Physiologic occlusion :Physiologic occlusion :

– The occlusion that shows no signs of occlusion related The occlusion that shows no signs of occlusion related pathosis. It may not be an ideal occlusion but it is devoid pathosis. It may not be an ideal occlusion but it is devoid of any pathological manifestations in the surrounding of any pathological manifestations in the surrounding tissues.tissues.

Traumatic occlusion :Traumatic occlusion :

– The occlusion which produces abnormal occlusal stress The occlusion which produces abnormal occlusal stress which is capable of producing or has produced an injury which is capable of producing or has produced an injury to the periodontium.to the periodontium.

Therapeutic occlusionTherapeutic occlusion : :

– It is a treated occlusion employed to counteract It is a treated occlusion employed to counteract structural interrelationship related to traumatic structural interrelationship related to traumatic occlusion.occlusion.

DYNAMIC OCCLUSIONDYNAMIC OCCLUSION

Recognition of the role played by muscles physiology and the Recognition of the role played by muscles physiology and the TMJ has firmly entrenched the dynamic functional concept. The TMJ has firmly entrenched the dynamic functional concept. The 13 muscle attachment to the mandible in addition to articular 13 muscle attachment to the mandible in addition to articular capsule and tendon provide a high degree of stability of position capsule and tendon provide a high degree of stability of position that occlusal equilibration and full mouth reconstruction can’t that occlusal equilibration and full mouth reconstruction can’t change permanentlychange permanently

The teeth are in occlusal contact only 2 to 6% of the time. The teeth are in occlusal contact only 2 to 6% of the time. Therefore 94% of the time, they are apart. The largest segment Therefore 94% of the time, they are apart. The largest segment of time is in postural rest position determined by musculature.of time is in postural rest position determined by musculature.

Postural rest position is a good place to start in an assessment Postural rest position is a good place to start in an assessment of vertical status and harmony of orofacial features. of vertical status and harmony of orofacial features.

Occlusion is a dynamic entity show variation according Occlusion is a dynamic entity show variation according to age and sex. Most girls by the age of 12 achieve to age and sex. Most girls by the age of 12 achieve relatively stable occlusion whereas boys achieve that a relatively stable occlusion whereas boys achieve that a bit later due to continuing growth pattern.bit later due to continuing growth pattern.

Three components of occlusion can be summed up asThree components of occlusion can be summed up as

1.1. Occlusal position (or) tooth contact position Occlusal position (or) tooth contact position

- Masticatory habits, tooth inclination and - Masticatory habits, tooth inclination and

malposition, shape of teeth, premature contact, malposition, shape of teeth, premature contact,

faulty restoration, tooth loss, the condition of faulty restoration, tooth loss, the condition of

periodontium affect the occlusal positions periodontium affect the occlusal positions

2.2. Postural resting positionPostural resting position

3.3. TMJTMJ

FACTORS & FORCES THAT DETERMINE FACTORS & FORCES THAT DETERMINE TOOTH POSITIONTOOTH POSITION

The alignment of the dentition in the dental The alignment of the dentition in the dental arches occur as a result of complex arches occur as a result of complex multidirectional forces acting on the teeth during multidirectional forces acting on the teeth during and after eruption. and after eruption.

• Equilibrium position of opposing forces that are given by lips and cheeks from outer side and tongue from inner side determine the (stable) position of the teeth .

Hence the labiolingual and buccolingual forces are equal.This is call “neutral position.”

• proximal and occlusal contacts are important in maintaining tooth alignment and arch integrity.

• Mastication causing buccolingual and vertical movement of teeth results in wear of proximal contacts.

• mesial drifting force helps to keep teeth in contact.

Centric cuspsCentric cusps Buccal cusps of the mandibular posterior teeth Buccal cusps of the mandibular posterior teeth

and lingual cusp of the maxillary posterior are and lingual cusp of the maxillary posterior are the centric or supporting cuspsthe centric or supporting cusps

These cusp plays major role in mastication and to maintain vertical dimension between maxilla and mandible.

Non centric cuspsThe buccal cusp of maxillary posterior teeth and lingual cusp of the mandibular posterior teeth are also called as shearing or guiding cusps.

These are responsible for- Shearing of food. Minimizing tissue impingement. Maintain bolus of food on occlusal table for masticationgives stability to mandible in full occlusion. Guide the mandible during mastication by neuromuscular feedback

The curve of spee given by F. Graf Von Spee in Germany in 1890 It refers to the antero-posterior curvature of the occlusal surfaces beginning at the tip of the mandibular cuspid and following the buccal cusps of bicuspid and molar continuing as an arch through the condyle.

Curve of spee

If the curve is extended, it would form a circle of about 4 inch diameter. This curvature is within the sagittal plane only.

Measurement of curve of spee.Measurement of curve of spee.

The maximum depth of the curve of Spee wasThe maximum depth of the curve of Spee was

measured as the maximum of the perpendicular measured as the maximum of the perpendicular distances between the buccal cusp tips of the distances between the buccal cusp tips of the mandibular teeth and a measurement plane mandibular teeth and a measurement plane described by the central incisors and the distal described by the central incisors and the distal cusp tip of the most posterior tooth in the cusp tip of the most posterior tooth in the mandibular arch.mandibular arch.

On average, the curve of Spee initially develops On average, the curve of Spee initially develops as a result of mandibular permanent first molar as a result of mandibular permanent first molar and incisor eruption. The curve of Spee and incisor eruption. The curve of Spee maintains this depth until the mandibular maintains this depth until the mandibular permanent second molars erupt above the permanent second molars erupt above the occlusal plane, when it again deepens.occlusal plane, when it again deepens.

During the adolescent dentition stage, the During the adolescent dentition stage, the curve depth decreases slightly and then remains curve depth decreases slightly and then remains relatively stable into early adulthood.relatively stable into early adulthood.

(Am J Orthod Dentofacial Orthop 2008;134:344-52(Am J Orthod Dentofacial Orthop 2008;134:344-52))

Curve of WilsonCurve of WilsonIt is a curve that contacts the buccal and lingual It is a curve that contacts the buccal and lingual cusps tips of the mandibular posterior teeth.cusps tips of the mandibular posterior teeth.It helps in two waysIt helps in two ways– Teeth aligned parallel to direction of medial Teeth aligned parallel to direction of medial

pterygoid for optimum resistance to pterygoid for optimum resistance to masticatory forces.masticatory forces.

– The elevated buccal cusps prevent food from The elevated buccal cusps prevent food from going past the occlusal table. going past the occlusal table.

Curve of Monson

Monson (1920), connected the curve of spee and

curve of Wilson to all cusps and incisal edges, which forms a sphere of a 4 inch radius, mandibular arch adopted itself to the curved

segment of a sphere.

Classification of Occlusion

Based on Mandibular Position

Centric OcclusionCentric Occlusion– It is the occlusion of teeth in centric relation. Centric It is the occlusion of teeth in centric relation. Centric

relation has been defined as the maxillomandibular relation has been defined as the maxillomandibular relationship in which condyles articulates with the relationship in which condyles articulates with the thinnest avascular portion of their respective discs with thinnest avascular portion of their respective discs with the complex in the anterosuperior position against the the complex in the anterosuperior position against the shape of articular eminence. This position is independent shape of articular eminence. This position is independent of tooth contact of tooth contact

The Importance of the centric relation in The Importance of the centric relation in orthodonticsorthodontics– In orthodontics, diagnosis and treatment planning should In orthodontics, diagnosis and treatment planning should

be performed by an evaluation of an malocclusion with be performed by an evaluation of an malocclusion with the mandible in centric relation (CR), i.e. the natural the mandible in centric relation (CR), i.e. the natural musculoskeletal position of the condyle in the fossa, in musculoskeletal position of the condyle in the fossa, in order to obtain the true maxillary - mandibular skeletal order to obtain the true maxillary - mandibular skeletal and dental relations in the three planes of space.and dental relations in the three planes of space.

– If this is overlooked an incorrect diagnosis and If this is overlooked an incorrect diagnosis and treatment plan of the actual malocclusion, along treatment plan of the actual malocclusion, along with its unfavourable consequences, may result.with its unfavourable consequences, may result.

– During every appointment a patient has to be During every appointment a patient has to be monitored in CR so that the mechanotherapy is monitored in CR so that the mechanotherapy is guided to accomplish the final ideal static and guided to accomplish the final ideal static and functional occlusion with the mandible in functional occlusion with the mandible in position. position.

– If this disregarded several prematurity that may If this disregarded several prematurity that may later cause traumatic occlusion or later cause traumatic occlusion or craniomandibular disorders may result. craniomandibular disorders may result.

Eccentric occlusionRefers to contact of teeth that occurs

during movement of mandible. Functional occlusion

Non-functional occlusion

a) Functional occlusion

Also called working side occlusion refers to tooth contacts that occurs in the segment of arch towards which the mandible moves.

According to movements functional occlusion can be of two types

Lateral functional occlusion

Protrusive functional occlusion

It includes tooth contacts that occur on canines and posterior teeth on the side towards which the mandible moves. The lateral functional occlusion can be of two types.

1. Canine guided occlusion

During lateral mandibular movement, the opposing upper and lower canines of the working side contact there by causing disclusion of all posterior teeth on the working side and balancing sides.

2. Grouped lateral occlusion –In addition to canine guidance

certain other posterior teeth on the working side also contact during lateral movement of mandible, such type of contact during lateral movement is called grouped lateral occlusion.

Protrusive functional occlusion Protrusive functional occlusion

It includes eccentric contacts that occur when the mandible moves forward. Ideally the six mandibular anterior teeth contact along the lingual inclines of the maxillary anterior teeth while the posterior disocclude.

Non-functional occlusion

They are tooth contacts that occur in the segment away from which the mandible moves. For example if the mandible is moved to the left side, contact occur on right side.

Based on relationship of first permanent molarBased on relationship of first permanent molarThe angulation of upper first permanent molar – The angulation of upper first permanent molar – the key to functional occlusion.the key to functional occlusion.– They are biggest teeth and their anchorage is They are biggest teeth and their anchorage is

strongeststrongest– Their local position in the occlusal arch supports the Their local position in the occlusal arch supports the

main masticatory functionmain masticatory function– They influence the vertical dimension of upper and They influence the vertical dimension of upper and

lower jaw, the occlusal height and esthetic proportions lower jaw, the occlusal height and esthetic proportions – They are the first erupting teeth of permanent They are the first erupting teeth of permanent

dentitiondentition– The anamolies in dental positioning are mostly due to The anamolies in dental positioning are mostly due to

more prominent disloacted positions of the crown of more prominent disloacted positions of the crown of upper permanent molar to normal. upper permanent molar to normal.

Class I : Neutro OcclusionClass I : Neutro Occlusion

Mesiobuccal cusps of the upper first permanent Mesiobuccal cusps of the upper first permanent molar occludes with the mesiobuccal groove of the lower molar occludes with the mesiobuccal groove of the lower first permanent molar. This is called the key of occlusion first permanent molar. This is called the key of occlusion

Class II : Disto OcclusionClass II : Disto Occlusion

Condition in which the mandibular first Permanent Condition in which the mandibular first Permanent molar is placed posterior in relation to the normal class I molar is placed posterior in relation to the normal class I condition condition

– Division I Division I

– Division IIDivision II

Class III : Mesio OcclusionClass III : Mesio Occlusion

Condition in which the mandibular first Permanent Condition in which the mandibular first Permanent molar is placed anterior in relation to the normal class I molar is placed anterior in relation to the normal class I condition condition

BASED ON THE ORGANISATIONBASED ON THE ORGANISATION

Canine guided (or) protected occlusionCanine guided (or) protected occlusion – during – during lateral movements only working side canine comes into lateral movements only working side canine comes into contact with the other. This result in disclusion of all contact with the other. This result in disclusion of all posterior teethposterior teeth– The canine has a good crown root ratio capable of The canine has a good crown root ratio capable of

tolerating high occlusal forcestolerating high occlusal forces– The canine root has a greater surface area then The canine root has a greater surface area then

adjacent teeth. Providing greater proprioception.adjacent teeth. Providing greater proprioception.– The shape of the palatal surface of the upper canine The shape of the palatal surface of the upper canine

is concave and is suitable for guiding lateis concave and is suitable for guiding lateral ral movement. movement.

Mutually ProtectedMutually Protected : : Posterior teeth prevent Posterior teeth prevent excessive contact of the anterior teeth in excessive contact of the anterior teeth in maximum intercuspation. Anterior teeth maximum intercuspation. Anterior teeth disengage the posterior teeth in all mandibular disengage the posterior teeth in all mandibular excursive movements.excursive movements.

Group FunctionGroup Function : : During the lateral movement During the lateral movement the buccal cusp of the posterior teeth on the the buccal cusp of the posterior teeth on the working side are in contact working side are in contact

BASED ON PATTERNBASED ON PATTERN

Cusp to fossaCusp to fossa occlusionocclusion : : Supporting Supporting cusp occluding into fossa. This produces cusp occluding into fossa. This produces an interdigitation of the cusps and fossa an interdigitation of the cusps and fossa of one teeth with the fossa of only one of one teeth with the fossa of only one opposing tooth. This is tooth-to-one-opposing tooth. This is tooth-to-one-tooth relation tooth relation

Cusp to embrasure / Marginal ridge Cusp to embrasure / Marginal ridge occlusionocclusion : Occlusion of one supporting : Occlusion of one supporting cusps into a fossa and the occlusion of cusps into a fossa and the occlusion of another cusp of the same tooth into the another cusp of the same tooth into the embrasure area of two opposing teeth. embrasure area of two opposing teeth. This is a tooth-to-two-teeth relation.This is a tooth-to-two-teeth relation.

SIX KEYS TO NORMAL OCCLUSIONSIX KEYS TO NORMAL OCCLUSION

LAWRENCE F.ANDREWS(1972)LAWRENCE F.ANDREWS(1972)

- collection of 120 models of teeth with - collection of 120 models of teeth with naturally excellent occlusion naturally excellent occlusion

Criteria for selectionCriteria for selection

1.1. Had never undergone ortho treatmentHad never undergone ortho treatment

2.2. Were straight & pleasing in appearanceWere straight & pleasing in appearance

3.3. Had a bite which looked generally correctHad a bite which looked generally correct

4.4. In his judgement, would not benefit from In his judgement, would not benefit from ortho treatmentortho treatment Andrews LF (1972). The six keys to

normal occlusion.Am J Orthod Dentofacial Orthop, 62(3): 296-309

ANDREWS SIXANDREWS SIX KEYS OF OCCLUSION KEYS OF OCCLUSION

1.1. MOLAR RELATIONSHIPMOLAR RELATIONSHIP

2.2. CROWN ANGULATIONCROWN ANGULATION

3.3. CROWN INCLINATIONCROWN INCLINATION

4.4. ROTATIONSROTATIONS

5.5. TIGHT CONTACTSTIGHT CONTACTS

6.6. OCCLUSAL PLANEOCCLUSAL PLANE

Molar relationMolar relation

Corresponds with the mesiodistal Corresponds with the mesiodistal relationship of upper first permanentrelationship of upper first permanent

molars of Angle (1899) with addition that molars of Angle (1899) with addition that the distal surface of the disto buccal cusp the distal surface of the disto buccal cusp of the upper first permanent molar should of the upper first permanent molar should made contact and occluded with the mesial made contact and occluded with the mesial surface of the mesio buccal cusp of the surface of the mesio buccal cusp of the lower second molar.lower second molar.

The closure the distal surface of buccal surface of distobuccal cusp of upper first permanent molar approaches the mesial surfaces of the M-B cusp of lower second molar, the better the opportunity for normal occlusion.

Crown angulation (Tip)Crown angulation (Tip)

The gingival portion of The gingival portion of the long axis of each crown the long axis of each crown should be distal to the should be distal to the incisal portion.incisal portion.

The degree of crown tip is the angle between the the of long axis of the crown to of long axis of the crown to a line perpendicular to the a line perpendicular to the occlusal planeocclusal plane..

A ‘plus’ reading when the gingival portion of the long axis of crown is distal to the incisal portion.

A ‘minus’ reading is when the gingival portion of the long axis of crown is mesial to the incisal portion.

Crown inclination(Torque)Crown inclination(Torque) Refers to the buccolingual inclination of the long axis of crown, not to the long axis of entire tooth. Determined by resulting angle between a line perpendicular to the occlusal plane and a line that is tangent to the middle of the labial or buccal clinical crown.

Crown inclination of teethCrown inclination of teethA ‘plus’ reading is given if the gingival portion of the tangent line is lingual to the incisal portion.

A ‘minus’ reading is recorded when the gingival portion of the tangent line is labial to the incisal portion.

Most maxillary incisors have a positive Most maxillary incisors have a positive inclination; mandibular incisors have a inclination; mandibular incisors have a slightly negative inclination.slightly negative inclination.

All posterior teeth have lingual crown All posterior teeth have lingual crown inclination (negative inclination)inclination (negative inclination)

Absence of rotationsAbsence of rotations

Arch should be devoid of Arch should be devoid of any rotated tooth.any rotated tooth.

A rotated molar occupies A rotated molar occupies more mesiodistal space.more mesiodistal space.

A rotated incisor occupies A rotated incisor occupies less space.less space.

Tight contactsTight contacts

In absence of abnormalities such as In absence of abnormalities such as genuine tooth size discrepancies, contact genuine tooth size discrepancies, contact point should be tightpoint should be tight..

It should be free of spacingIt should be free of spacing..

Occlusal planeOcclusal planeAn excessive curve of An excessive curve of spee restrict the amount spee restrict the amount of space available for of space available for the upper teeth results the upper teeth results in crowding.in crowding.

A flate curve of spee is A flate curve of spee is most receptive for most receptive for normal occlusion .(the normal occlusion .(the mandibular curve of mandibular curve of spee should not be spee should not be deeper than 1.5mm)deeper than 1.5mm)

A reverse curve of spee creates excessive space in upper jaw.

a)a) Centric relationship and Centric relationship and centric occlusion should be centric occlusion should be coincident.coincident.

b) b)

In protrusion, the incisors In protrusion, the incisors should disclude the posterior should disclude the posterior teeth, with the guidance teeth, with the guidance provided by the lower incisal provided by the lower incisal edges passing along the edges passing along the palatal contour of the upper palatal contour of the upper incisorsincisors..

Works by Roth (1981) had then addedsome functional keys to the previous six keys to normal occlusion by Andrew:

c) In lateral excursions of the mandible, thec) In lateral excursions of the mandible, the

canine should guide the working side whilst all other canine should guide the working side whilst all other teeth on that and the other side areteeth on that and the other side are

discluded.discluded.

d) When the teeth are in centric occlusion, there should d) When the teeth are in centric occlusion, there should be even bilateral contacts in the buccal segments.be even bilateral contacts in the buccal segments.

Key VII – Correct tooth size

Bennett and McLaughlin in 1993 gave seventh key to normal occlusion. I.e. the upper and lower tooth size should be correct

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ABO criteria for ideal occlusionABO criteria for ideal occlusion

A set of criteria was developed in 1998 by A set of criteria was developed in 1998 by the directors of The American Board of the directors of The American Board of Orthodontic (ABO) for objectively Orthodontic (ABO) for objectively evaluating the dental casts and panoramic evaluating the dental casts and panoramic radiographsradiographs

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Alignment.Alignment.

Attention is paid to the incisal edges and Attention is paid to the incisal edges and lingual surfaces of the maxillary anterior lingual surfaces of the maxillary anterior teeth and the incisal edges and teeth and the incisal edges and labioincisal surfaces of the mandibular labioincisal surfaces of the mandibular anterior teeth. The mesiodistal central anterior teeth. The mesiodistal central grooves of the maxillary premolars and grooves of the maxillary premolars and molars are used to assess the adequacy molars are used to assess the adequacy of alignment, as are the buccal cusps of of alignment, as are the buccal cusps of the mandibular premolars and molars. the mandibular premolars and molars.

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Marginal rides of adjacent teeth should be Marginal rides of adjacent teeth should be at the same level or within 0.5 mm of the at the same level or within 0.5 mm of the same level. Radio graphically, the same level. Radio graphically, the cemento enamel junctions should be at cemento enamel junctions should be at the same relative height, resulting in a flat the same relative height, resulting in a flat bone level between adjacent teeth bone level between adjacent teeth

Marginal RidgesMarginal Ridges

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The buccolingual inclination of the maxillary and The buccolingual inclination of the maxillary and mandibular posterior teeth is assessed by using mandibular posterior teeth is assessed by using a flat surface that is extended between the a flat surface that is extended between the occlusal surfaces of the right and left posterior occlusal surfaces of the right and left posterior teeth. There should not be a significant teeth. There should not be a significant difference between the heights of the buccal and difference between the heights of the buccal and lingual cusps of the maxillary and mandibular lingual cusps of the maxillary and mandibular premolars and molars, with all cusps within 1 premolars and molars, with all cusps within 1 mm of the straight edge. mm of the straight edge.

Buccolingual inclinationBuccolingual inclination

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The mesiobuccal cusp of the maxillary first The mesiobuccal cusp of the maxillary first molar must coincide within 1 mm of the molar must coincide within 1 mm of the buccal groove of the mandibular first buccal groove of the mandibular first molar. In addition, the buccal cusps of the molar. In addition, the buccal cusps of the maxillary molars, premolars, and canines maxillary molars, premolars, and canines must align within 1 mm of the interproximal must align within 1 mm of the interproximal embrasures of the mandibular posterior embrasures of the mandibular posterior teeth teeth

Occlusal relationshipOcclusal relationship

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Maximum intercuspation should be Maximum intercuspation should be established between the buccal cusps of established between the buccal cusps of the mandibular posterior teeth and the the mandibular posterior teeth and the lingual cusps of the maxillary posterior lingual cusps of the maxillary posterior teeth. Each functional cusp should be in teeth. Each functional cusp should be in contact with the opposing arch contact with the opposing arch

Occlusal contactsOcclusal contacts

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Posteriorly, the mandibular buccal cusps Posteriorly, the mandibular buccal cusps and the maxillary lingual cusps are used and the maxillary lingual cusps are used to determine proper position within the to determine proper position within the fossa of the opposing arch. Anteriorly, fossa of the opposing arch. Anteriorly, the mandibular incisal edges should the mandibular incisal edges should lightly contact the lingual surfaces of the lightly contact the lingual surfaces of the maxillary anterior teeth. maxillary anterior teeth.

OverjetOverjet

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All spaces within the dental arches All spaces within the dental arches should be closed. should be closed.

Interproximal contactsInterproximal contacts

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Generally, the roots of the maxillary and Generally, the roots of the maxillary and mandibular teeth should be parallel to mandibular teeth should be parallel to each other and the perpendicular to the each other and the perpendicular to the occlusal plane, as viewed in the occlusal plane, as viewed in the panoramic radiograph. If roots are panoramic radiograph. If roots are properly angulated, sufficient bone will be properly angulated, sufficient bone will be present between adjacent roots, an present between adjacent roots, an important consideration in periodontal important consideration in periodontal health health

Root angulationRoot angulation

ORTHODONTIC TREATMENT OBJECTIVESORTHODONTIC TREATMENT OBJECTIVES

CLINICAL SIGNIFICANCE

The orthodontist should know about the goal of orthodontic treatment i.e. where to stop the treatment. For this a basic knowledge of normal occlusion should know to us.

Again to know what is abnormal or malocclusion, we should first know what is normal.

Orthodontist should know about cusp fossa, relationship, normal overjet, deciduous, well as mixed dentition occlusal changes and age related changes.

 

CONCLUSION

Normal occlusion is not a rigid or static relationship. What is normal interdigitation in deciduous and mixed dentition is abnormal in permanent dentition and vice versa. Successful orthodontic treatment involves many disciplines, not all of which are always within our control. Achieving the final desired occlusion is the purpose of attending to the six keys to normal occlusion.

REFERENCES

William R. Profitt – ‘Contemporary orthodontics’ 4th edition.

Graber T.M. – Orthodontic principles and practice’

Moyers and Robert – ‘Hand book of Orthodontics’

Nanda S. – ‘The developmental basis of occlusion and malocclusion’

Ramfjord S.P. – ‘Occlusion’

Rakosi – ‘Color Atlas of diagnosis’

Graber-Vanarsdall – ‘Orthodontic-current principles and techniques’

Samir E. Bishara – ‘Textbook of Orthodontics’

Andrew L.F. – ‘The six keys to normal occlusion’. American Journal of Orthodontics. Vol 62, 1972, Pg. 296-302.

Asbell milton- brief history of orthodontics article- ajodo

Am J Orthod Dentofacial Orthop 2008;134:344-Am J Orthod Dentofacial Orthop 2008;134:344-5252