The ideal occlusion (bite); The points of the upper teeth fit
into the grooves of the lower teeth, the defining teeth are
the upper and lower first molars. How the first molars fit together
is how the bite is classified. The first molars each have two points
and one grove, ideally the first point of the upper first molar will
fit into the groove of the lower first molar. Also, in an ideal bite
the midline, an imaginary line going inbetween the upper and lower
front teeth, is straight.
Class I: The first molars are in a normal relationship. Crowding or spacing may occur.
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Class II: The lower first molars are too far forward in relation to the first upper molars.
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Class III: The first lower molars are too far back in relation to the first upper molars.
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Crowding: Crowding can be due to heredity and/or environment. Heredity determines the tooth and jaw size relationship; larger teeth in a normal or smaller jaw results in crowding. Environment can also be a factor, the premature loss of a tooth can cause a lack of space for the permanent tooth due to unfavorable drifting and prolonged retention of the baby teeth can cause a lack of space due to deflection, or the displaced eruption of the permanent tooth.
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Spacing: Spacing can be due to heredity and/or environment. Heredity determines the tooth and jaw size relationship; smaller teeth in a normal or larger jaw results in spacing. Environment can play a part in spacing as well. A strong tongue can push the teeth apart, and excessive amounts of gum tissue between the teeth or a thumb or finger habit can cause spacing of the teeth.
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