Normal Occlusion 1 / orthodontic courses by Indian dental academy

Department of Orthodontics Department of Orthodontics & Dentofacial Orthopedics& Dentofacial Orthopedics

NORMAL OCCLUSIONNORMAL OCCLUSION

INDIAN DENTAL ACADEMY

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INTRODUCTION :INTRODUCTION :• The study and practice of most The study and practice of most

branches of dentistry should be branches of dentistry should be based on a strong foundation of based on a strong foundation of knowledge of occlusion.knowledge of occlusion.

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

• Normal in physiology is always a Normal in physiology is always a range, never a point. range, never a point.

• A balanced, stable, healthy and A balanced, stable, healthy and esthetically attractive occlusion is esthetically attractive occlusion is also conceivable normal even if also conceivable normal even if minor rotation are present.minor rotation are present.


• And yet, what may be abnormal for one And yet, what may be abnormal for one age may be normal for another.age may be normal for another.

• The curve of spee, compensatory curve, The curve of spee, compensatory curve, cusp height and facial relation of each cusp height and facial relation of each tooth to its antagonist and other tooth to its antagonist and other characteristics of occlusion may all vary characteristics of occlusion may all vary within a broad range and still be normal.within a broad range and still be normal.

• It may be equally normal for one child to It may be equally normal for one child to have a marked overbite and overjet and have a marked overbite and overjet and procumbent incisors and for another to procumbent incisors and for another to have little overbite or overjet.have little overbite or overjet.


• Good examples of the time-linked nature Good examples of the time-linked nature of normally are such transient of normally are such transient malocclusion, as crowding during, eruption malocclusion, as crowding during, eruption of incisors, the ‘ugly duckling’ flaring of of incisors, the ‘ugly duckling’ flaring of maxillary lateral incisors, the Class II first maxillary lateral incisors, the Class II first molar relationship tendencies before loss molar relationship tendencies before loss of second deciduous molars. of second deciduous molars.

• Original concept of occlusion were those of Original concept of occlusion were those of a complete act – literally an anatomic a complete act – literally an anatomic approach, a description of how the teeth approach, a description of how the teeth meet when the jaws are closed. meet when the jaws are closed.

• ““clusion” means closing and “oc” means clusion” means closing and “oc” means up thus “occlusion” is closing up. up thus “occlusion” is closing up.


• DEVELOPMENT OF CONCEPT OF DEVELOPMENT OF CONCEPT OF OCCLUSION OCCLUSION

• The development of the idea of The development of the idea of occlusion can be traced through fiction and occlusion can be traced through fiction and hypothesis to fact. hypothesis to fact.

• The fictional approach, in a philosophical The fictional approach, in a philosophical sense, was convenient arrangement of series sense, was convenient arrangement of series of observed and thoughts more or, less of observed and thoughts more or, less logically arrange.logically arrange.

• The hypothetical attack on the problem of The hypothetical attack on the problem of occlusion was based on a provisional occlusion was based on a provisional acceptance of certain logical entities. As acceptance of certain logical entities. As Simon Simon said, a hypothesis can be maintained said, a hypothesis can be maintained only if it does not contradict the facts of only if it does not contradict the facts of experience. This is just the opposite of experience. This is just the opposite of fiction.fiction.


• Fact is reality, what has really Fact is reality, what has really happened. Fact is a truth known by actual happened. Fact is a truth known by actual experience or observation. Both the experience or observation. Both the functional and hypothetical approaches are functional and hypothetical approaches are necessary preludes to the establishment necessary preludes to the establishment fact but must given way wherever fact but must given way wherever contradiction arises.contradiction arises.

• The development of concept of occlusion The development of concept of occlusion thus can be divided into three periods:thus can be divided into three periods:

• The fictional period, prior to 1900, the The fictional period, prior to 1900, the hypothetical period, from 1900 to 1930, the hypothetical period, from 1900 to 1930, the factual period, from 1930 to the present factual period, from 1930 to the present development of concept of occlusion development of concept of occlusion


• DEFINITIONS DEFINITIONS • Occlusion Occlusion • Is defined as the anatomic alignment of teeth Is defined as the anatomic alignment of teeth

and their relationship to the rest of the masticatory and their relationship to the rest of the masticatory system.system.

• BSSOBSSO in in 1926 1926 defined occlusion as the defined occlusion as the relationship of the teeth in the maxilla and relationship of the teeth in the maxilla and mandible when the jaws are closed and the mandible when the jaws are closed and the condyles are at rest in the glenoid fossae.condyles are at rest in the glenoid fossae.

• Normal occlusion Normal occlusion • This refers to an occlusion that deviates in This refers to an occlusion that deviates in

one or more ways from ideal yet it is well adopted one or more ways from ideal yet it is well adopted to that particular environment, is esthetic and to that particular environment, is esthetic and shows no pathologic manifestations or dysfunction.shows no pathologic manifestations or dysfunction.

• BSSO (1926)BSSO (1926) has defined normal occlusion as has defined normal occlusion as the occlusion which is within the standard the occlusion which is within the standard deviation from the ideal.deviation from the ideal.


• Ideal occlusion Ideal occlusion • It is a preconceived theoretical concept It is a preconceived theoretical concept

of occlusal structural and functional of occlusal structural and functional relationships that includes idealized relationships that includes idealized principles and characteristics that an principles and characteristics that an occlusion should have.occlusion should have.

• BSSO (1926)BSSO (1926) has defined ideal has defined ideal occlusion as ‘a hypothetical standard of occlusion as ‘a hypothetical standard of occlusion based on morphology of the teeth.occlusion based on morphology of the teeth.


• COMPENSATORCURVES COMPENSATORCURVES OF THE DENTAL ARCHES OF THE DENTAL ARCHES

1) Curve of spee 1) Curve of spee • It refers to the antero-It refers to the antero-

posterior curvature of the posterior curvature of the occlusal Surfaces, beginning occlusal Surfaces, beginning at the tip of the mandibular at the tip of the mandibular cuspid and following the cuspid and following the buccal cusps of bicuspid and buccal cusps of bicuspid and molar continuing as an arc molar continuing as an arc through the condyle. If the through the condyle. If the curve is extended, it would curve is extended, it would form a circle of about 4 inch form a circle of about 4 inch diameter. This curvature is diameter. This curvature is within the sagittal plane within the sagittal plane only.only.

• The curve of spee given by The curve of spee given by F. Graf Von SpeeF. Graf Von Spee in in Germany Germany in in 18901890..www.indiandentalacademy.comwww.indiandentalacademy.com

2) Curve of Wilson2) Curve of Wilson• This is a curve that This is a curve that

contacts the buccal and contacts the buccal and lingual cusp tips of lingual cusp tips of mandibular buccalmandibular buccal teeth. The curve of Wilson teeth. The curve of Wilson is medio-lateral on each is medio-lateral on each side of the arch. It results side of the arch. It results from inward inclination of from inward inclination of the lower posterior teeth.the lower posterior teeth.

• Curve of Wilson helps in Curve of Wilson helps in two ways.two ways.

1.1. Teeth are aligned parallel Teeth are aligned parallel to the direction of medial to the direction of medial pterygoid for optimum pterygoid for optimum resistance to masticatory resistance to masticatory forces.forces.

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


3) Curve of Monson 3) Curve of Monson • Manson (1920)Manson (1920), at , at

a later date, connected the a later date, connected the curve curve of spee and of spee and curve of Wilson to all curve of Wilson to all cusps and incisal cusps and incisal edges, and suggested edges, and suggested that the mandibular that the mandibular arch adopted itself to arch adopted itself to the curved segment of the curved segment of a sphere of aa sphere of a 4 inch 4 inch radius.radius.


• POSITION OF TEETH IN THE DENTAL ARCH POSITION OF TEETH IN THE DENTAL ARCH 1) Contact point 1) Contact point • The point of contact of teeth should be The point of contact of teeth should be

situated at their greatest mesio-distal situated at their greatest mesio-distal diameter.diameter.

2) Anteroposterior position2) Anteroposterior position• The posterior teeth normally in contact with The posterior teeth normally in contact with

each other mesiodistallyeach other mesiodistally• The anterior teeth should have their incisal The anterior teeth should have their incisal

edges along a smooth curve. This is usually edges along a smooth curve. This is usually the case for the lower incisors because of their the case for the lower incisors because of their relative equal size.relative equal size.

• The maxillary lateral and central incisors The maxillary lateral and central incisors however, do not have the same labiolingual however, do not have the same labiolingual thickness, which causes the lateral incisors thickness, which causes the lateral incisors edges to be slightly lingual to those of central. edges to be slightly lingual to those of central.


• The canines serve as a corner stones between the The canines serve as a corner stones between the anterior and posterior. They are slightly more buccal anterior and posterior. They are slightly more buccal than first bicuspids and the lateral incisors. This is than first bicuspids and the lateral incisors. This is more accentuated in the maxillary arch than in the more accentuated in the maxillary arch than in the mandibular archmandibular arch

3) Vertical position 3) Vertical position • The tips of cusps of all the teeth are situated The tips of cusps of all the teeth are situated

approximately on a segment of a sphere, the centre of approximately on a segment of a sphere, the centre of which is located about 10mm above the crista galli in which is located about 10mm above the crista galli in the cranial base. i.e. the curve of spee. In attritional the cranial base. i.e. the curve of spee. In attritional dentition, when reduction is confined to the cusp, the dentition, when reduction is confined to the cusp, the same curve is maintainedsame curve is maintained

4) Axial inclination 4) Axial inclination • The long axis of maxillary molars and bicuspids The long axis of maxillary molars and bicuspids

tends to meet in the area of crista galli. The maxillary tends to meet in the area of crista galli. The maxillary central and lateral incisors are move inclined than the central and lateral incisors are move inclined than the buccal teeth. Their long axis convergent apically. The buccal teeth. Their long axis convergent apically. The long axis of caninelong axis of canine fallows lateral walls of nose.fallows lateral walls of nose.


• The axis of mandibular posterior teeth are The axis of mandibular posterior teeth are relatively parallel antero-posteriorly and relatively parallel antero-posteriorly and divergent apically in the transverse divergent apically in the transverse direction. This means that the apices are direction. This means that the apices are farther apart than the buccal cusps. The farther apart than the buccal cusps. The axis of canines are convergent apically in axis of canines are convergent apically in the transverse direction, as are the axis of the transverse direction, as are the axis of lower incisors, which in turn are inclined lower incisors, which in turn are inclined labially, relative to the buccal teeth.labially, relative to the buccal teeth.


• ANDREWS SIX KEYS TO NORMAL ANDREWS SIX KEYS TO NORMAL OCCLUSION OCCLUSION

• - - Andrews Andrews gathered data from gathered data from 1960 1960 to 1964 to 1964 of non-orthodontic normal models.of non-orthodontic normal models.

• Key I – Molar relationshipKey I – Molar relationship• the distal surface of distobuccal cusp of the distal surface of distobuccal cusp of

upper first permanent molar occluded with upper first permanent molar occluded with the mesial surface of the mesiobuccal cusp the mesial surface of the mesiobuccal cusp of the lower second molar. of the lower second molar.

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


• Key II Crown angulation (Tip)Key II Crown angulation (Tip)• The gingival portion of the long axis The gingival portion of the long axis

of the all crowns was more distal than of the all crowns was more distal than the incisal portion.the incisal portion.

• The degree of crown tip is the angle The degree of crown tip is the angle between the long axis of crown and a between the long axis of crown and a line bearing 90˚ from the occlusal plane.line bearing 90˚ from the occlusal plane.

• It varied with each tooth type, but It varied with each tooth type, but within each type tip patterns was within each type tip patterns was consistent from individual to individual.consistent from individual to individual.


• Key III Crown inclinationKey III Crown inclination • crown inclination refers to the labiolingual or crown inclination refers to the labiolingual or

buccolingual inclination of long axis of the crown, buccolingual inclination of long axis of the crown, not to the inclination of long axis of entire tooth. not to the inclination of long axis of entire tooth.

• Crown inclination is expressed in plus or minus Crown inclination is expressed in plus or minus degrees. A plus reading is given if the gingival degrees. A plus reading is given if the gingival portion of the crown is lingual to the incisal portion. portion of the crown is lingual to the incisal portion. A minus reading is recorded when the gingival A minus reading is recorded when the gingival portion of the crown is labial to the incisal portion. portion of the crown is labial to the incisal portion.

• a) Anterior crown inclination:a) Anterior crown inclination: properly inclined anterior crowns contribute to properly inclined anterior crowns contribute to normal overbite and posterior occlusion, when too normal overbite and posterior occlusion, when too straight-up and down they lose their functional straight-up and down they lose their functional hormony and overeruption results. Inclination hormony and overeruption results. Inclination should be positive in this categary of teeth. should be positive in this categary of teeth.


• b)Posterior crown inclination (upper)b)Posterior crown inclination (upper) :A :A minus crown inclination should exist in minus crown inclination should exist in each crown from the upper canine each crown from the upper canine through the upper second premolar . A through the upper second premolar . A slightly more negative crown inclination slightly more negative crown inclination exists in the upper first and second exists in the upper first and second molars. molars.

• c) posterior crown inclination (lower)c) posterior crown inclination (lower): A : A progressively greater minus crown progressively greater minus crown inclination exists from the lower canine inclination exists from the lower canine through lower second molar.through lower second molar.


• Key IV – RotationsKey IV – Rotations• The fourth key to normal occlusion is that The fourth key to normal occlusion is that

the teeth should be free of undesirable rotations.the teeth should be free of undesirable rotations.• Key V – Tight contacts Key V – Tight contacts • The fifth key is that the contact points The fifth key is that the contact points

should be tight (no spaces).should be tight (no spaces).• Key VI – Occlusal plane or curve of speeKey VI – Occlusal plane or curve of spee• The planus of occlusion found on normal The planus of occlusion found on normal

models ranged crown flat to slight curves of Spee.models ranged crown flat to slight curves of Spee.• Even though not all of the non-orthodontic normal Even though not all of the non-orthodontic normal

had flat planes of occlusion, flat plane should be a had flat planes of occlusion, flat plane should be a treatment goal as a form of over-treatment. treatment goal as a form of over-treatment. There is a natural tendency for curve of Spee to There is a natural tendency for curve of Spee to deepen with time.deepen with time.

• Intercuspation of teeth is best when the plane of Intercuspation of teeth is best when the plane of occlusion is relatively flat.occlusion is relatively flat.


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Normal Occlusion 1 / orthodontic courses by Indian dental academy

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