Normal Occlusion 1 / orthodontic courses by Indian dental academy

Department of Orthodontics & Dentofacial Orthopedics

NORMAL OCCLUSION INDIAN DENTAL ACADEMY

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INTRODUCTION :The study and practice of most branches of dentistry should be based on a strong foundation of knowledge of occlusion.The orthodontist should know what constitutes normal occlusion in order to be able to recognize abnormal occlusion.Normal in physiology is always a range, never a point. A balanced, stable, healthy and esthetically attractive occlusion is also conceivable normal even if minor rotation are present.



And yet, what may be abnormal for one age may be normal for another.The curve of spee, compensatory curve, cusp height and facial relation of each tooth to its antagonist and other characteristics of occlusion may all vary within a broad range and still be normal.It may be equally normal for one child to have a marked overbite and overjet and procumbent incisors and for another to have little overbite or overjet.



Good examples of the time-linked nature of normally are such transient malocclusion, as crowding during, eruption of incisors, the ugly duckling flaring of maxillary lateral incisors, the Class II first molar relationship tendencies before loss of second deciduous molars. Original concept of occlusion were those of a complete act literally an anatomic approach, a description of how the teeth meet when the jaws are closed. clusion means closing and oc means up thus occlusion is closing up.



DEVELOPMENT OF CONCEPT OF OCCLUSION The development of the idea of occlusion can be traced through fiction and hypothesis to fact. The fictional approach, in a philosophical sense, was convenient arrangement of series of observed and thoughts more or, less logically arrange.The hypothetical attack on the problem of occlusion was based on a provisional acceptance of certain logical entities. As Simon said, a hypothesis can be maintained only if it does not contradict the facts of experience. This is just the opposite of fiction.



Fact is reality, what has really happened. Fact is a truth known by actual experience or observation. Both the functional and hypothetical approaches are necessary preludes to the establishment fact but must given way wherever contradiction arises.The development of concept of occlusion thus can be divided into three periods:The fictional period, prior to 1900, the hypothetical period, from 1900 to 1930, the factual period, from 1930 to the present development of concept of occlusion



DEFINITIONS Occlusion Is defined as the anatomic alignment of teeth and their relationship to the rest of the masticatory system.BSSO in 1926 defined occlusion as the relationship of the teeth in the maxilla and mandible when the jaws are closed and the condyles are at rest in the glenoid fossae.Normal occlusion This refers to an occlusion that deviates in one or more ways from ideal yet it is well adopted to that particular environment, is esthetic and shows no pathologic manifestations or dysfunction. BSSO (1926) has defined normal occlusion as the occlusion which is within the standard deviation from the ideal.



Ideal occlusion It is a preconceived theoretical concept of occlusal structural and functional relationships that includes idealized principles and characteristics that an occlusion should have.BSSO (1926) has defined ideal occlusion as a hypothetical standard of occlusion based on morphology of the teeth.



COMPENSATORCURVES OF THE DENTAL ARCHES 1) Curve of spee 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 arc through the condyle. If the curve is extended, it would form a circle of about 4 inch diameter. This curvature is within the sagittal plane only.The curve of spee given by F. Graf Von Spee in Germany in 1890.



2) Curve of WilsonThis is a curve that contacts the buccal and lingual cusp tips of mandibular buccal teeth. The curve of Wilson is medio-lateral on each side of the arch. It results from inward inclination of the lower posterior teeth.Curve of Wilson helps in two ways.

Teeth are aligned parallel to the direction of medial pterygoid for optimum resistance to masticatory forces.The elevated buccal cusps prevent food from going past the occlusal table.www.indiandentalacademy.com


3) Curve of Monson Manson (1920), at a later date, connected the curve of spee and curve of Wilson to all cusps and incisal edges, and suggested that the mandibular arch adopted itself to the curved segment of a sphere of a 4 inch radius.



POSITION OF TEETH IN THE DENTAL ARCH

1) Contact point The point of contact of teeth should be situated at their greatest mesio-distal diameter.

2) Anteroposterior positionThe posterior teeth normally in contact with each other mesiodistallyThe anterior teeth should have their incisal edges along a smooth curve. This is usually the case for the lower incisors because of their relative equal size.The maxillary lateral and central incisors however, do not have the same labiolingual thickness, which causes the lateral incisors edges to be slightly lingual to those of central.



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

3) Vertical position The tips of cusps of all the teeth are situated approximately on a segment of a sphere, the centre of which is located about 10mm above the crista galli in the cranial base. i.e. the curve of spee. In attritional dentition, when reduction is confined to the cusp, the same curve is maintained

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



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



ANDREWS SIX KEYS TO NORMAL OCCLUSION - Andrews gathered data from 1960 to 1964 of non-orthodontic normal models.Key I Molar relationshipthe distal surface of distobuccal cusp of upper first permanent molar occluded with the mesial surface of the mesiobuccal cusp of the 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.



Key II Crown angulation (Tip)The gingival portion of the long axis of the all crowns was more distal than the incisal portion.The degree of crown tip is the angle between the long axis of crown and a line bearing 90 from the occlusal plane.It varied with each tooth type, but within each type tip patterns was consistent from individual to individual.



Key III Crown inclination crown inclination refers to the labiolingual or buccolingual inclination of long axis of the crown, not to the inclination of long axis of entire tooth. Crown inclination is expressed in plus or minus degrees. A plus reading is given if the gingival portion of the crown is lingual to the incisal portion. A minus reading is recorded when the gingival portion of the crown is labial to the incisal portion. a) Anterior crown inclination: properly inclined anterior crowns contribute to normal overbite and posterior occlusion, when too straight-up and down they lose their functional hormony and overeruption results. Inclination should be positive in this categary of teeth.



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



Key IV RotationsThe fourth key to normal occlusion is that the teeth should be free of undesirable rotations.Key V Tight contacts The fifth key is that the contact points should be tight (no spaces).Key VI Occlusal plane or curve of speeThe planus of occlusion found on normal models ranged crown flat to slight curves of Spee.Even though not all of the non-orthodontic normal had flat planes of occlusion, flat plane should be a treatment goal as a form of over-treatment. There is a natural tendency for curve of Spee to deepen with time.Intercuspation of teeth is best when the plane of occlusion is relatively flat.



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Normal Occlusion 1 / orthodontic courses by Indian dental academy

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