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Normal dentition

Class I normal dentition

Class I normal dentition

 

A normal dentition is characterized by an ideal alignment of the upper and lower teeth and by an intermaxillary relationship (between both jaws) showing neither anterior-posterior nor transverse discrepancies. The upper canine is aligned with the embrasure between the lower canine and the lower first molar (blue arrows). The first corner (mesiobuccal cusp) of the upper first molar is aligned with the center (mesiobuccal groove) of the lower first molar (red arrows). The maxillary arch midline fits with the mandibular arch midline. The overjet of the upper incisors is minimal (about 2 mm), just like the overbite.

Occlusal view

 

Upper and lower occlusal views

Seen from above, the teeth do not show any rotation and every tooth touches each other, leaving no interdental space between them. The shape of the arch is a parabolic arch. You can see a wire bonded to the inside (on the lingual side) of the top and bottom teeth from canine to canine. This is often called a fixed or bonded lingual retainer.

Cephalometric profile view

Class I orthognathic profile view

On this cephalometric X-ray, the upper teeth are over the lower teeth by about 2 mm. This is possible because the size of the lower jaw matches the upper jaw. The height of the face is in proportion with the size of the maxilla and allows the lips to touch without muscular contraction.

This profile shows a class I relationship of the teeth and a normal (class I) skeletal relationship of the maxilla and the mandible. This relationship is called “skeletal orthognathy”.

 

Panoramic view

Complete dentition

An ideal dentition shows the teeth parallel from one another. You can see the interdental alveolar bone level in which the roots are located. The small black line visible in a few areas surrounding the roots represents the periodontal ligament. This ligament, composed of connective tissue fibers, holds the teeth and distributes the forces generated by chewing of foods in the bony support. A white line, the lamina dura, represents the lining of the tooth socket to which the periodontal ligament is attached. The ligament is attached to the tooth by the cementum which covers the dental root.

 

You can see 32 teeth on this X-ray. There are 4 upper and 4 lower incisors. The canines are beside the incisors. There are four of them, one per quadrant. There are 8 premolars, the first and second premolars, on each side of the canines. Humans have 12 molars, 3 on each side on each arch. They are the first molars that appear in the mouth at about 6-7 years of age, the second molars appear at about 12-14 years of age and finally, the third molars erupt, when they are able to, at about 17-20 years of age. The third molars, better known as wisdom teeth, are therefore the last teeth on the farthest left and right ends of both the upper and lower arches. The white line that is shown is the lingual retainer bonded to the lingual side of the anterior upper and lower teeth.

 

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