Title: 0390 - Longitudinal Study of the Maxillary First Molar Physiological Mesial Displacement


tingting feng (Presenter)
Peking University School of Stomatology

Tianmin Xu, Peking University School of Stomatology


Objectives: To observe the mesial displacement and tipping of the maxillary first molar (U6) during growth, and to explain this phenomenon by studying the growth and rotation of the jaws.

Methods: A longitudinal sample of 30 adolescents with normal occlusion from Cranial-facial Growth Study Center of Peking University School of Stomatology was selected. Averagely from 10 years old to 16, 3 to 6 lateral cephalograms were taken. These cephalograms were traced and superimposed using “pitchfork” analysis raised by Johnston. When the maxillae were superimposed, the displacement and the tipping of U6 , inclination of functional occlusal plane(FOP), distances of maxilla and mandible forward growth were measured. And L6 displacement and tipping were measured when mandibles superimposed. The rotation of jaws were measured when anterior cranial bases superimposed. All the distances were measured along the functional occlusion plane of age 12.

Results: The average mesial tipping angle of U6 was 10.97±3.40°and the average mesial displacement of U6 mesial-buccal cusp was 5.70±1.31mm from 10 to 15 years old. The tipping of L6 showed no significant change and the average mesial displacement of L6 mesial-buccal cusp was 2.25±1.18mm. The maxilla moved forward 4.39±1.72mm relative to the anterior cranial base and rotated 1.47±1.96° counter-clockwise (with no statistical significance). The mandible moved forward 6.97±4.64mm relative to maxilla and rotated 6.37±2.37° counter-clockwise relative to the anterior cranial base. The inclination of FOP decreased 4.59±1.66°. In the five years we studied, U6 moved and tipped at the fastest rate from 10 to 12 years old.

Conclusions: For the individuals with growth potential, U6 will tip and move mesially without mechanical force, as the mandible moved forward and rotated counter-clockwise relative to the maxilla, which deserves serious consideration in anchorage control in orthodontic treatment.

Student Presenter

This abstract is based on research that was funded entirely or partially by an outside source:
International Science and Technology Cooperation Program of China (No. 2014DFA31800)

Disclosure Statement:
The submitter must disclose the names of the organizations with which any author have a relationship, the nature of the relationship, and the clinical or research area involved. The following is submitted: NONE