Effect of orthodontic removal of mandibular first molar on the position change of third molar / 口腔疾病防治

Objective@#To investigate the effects of the first molar on the eruption of the third molar by comparing the changes of the third molar position after orthodontic treatment in different tooth extraction modes. @*Methods@#39 cases of adolescent patients were selected and divided into three groups:the first molar extraction, first premolar extraction and non-extraction.The pretreatment, posttreatment panoramic radiographs were measured to analyze the change of the third molar position among these groups.@*Results@# There were significant differences (P< 0.05) in the average annual variation of the third molar eruption space and angle. The changes in first molar extraction group were larger than that in premolar extraction group and non-extraction group. The average annual variation of the third molar eruption space, three groups were (2.38 ± 1.62) mm, (1.61 ± 0.90) mm and (1.08 ± 1.49) mm; the average annual variation of eruption angle, the three were 1.89° ± 1.93°, 1.37° ± 1.16° and 0.83° ± 1.74°.@*Conclusion @#Compared with conventional treatment, mandibular first molar extraction can significantly increase the third molar eruption space and improve its eruption angle, which is beneficial to the eruption of the third molar.

Comparison of superficial masseter muscle morphology between adult high-angle and low-angle facial skeletal types / 实用口腔医学杂志

Objective: To study the differences of the superficial masseter muscle morphology characteristics between adult high-angle and low-angle facial skeletal types. Methods: The subjects consisted of 37 yellow race adults,17 of them with high-angle facial skeletal type and 20 with low-angle. Ultrasound scanning was used to measure the perimeter, area, width, thickness, and length of masseter muscle. All the items were measured under relaxed, maximal clenching and maximal protrusive mandibular position.Results:①In the various mandibular positions, the masseter muscle size of adults with high-angle facial skeletal type was smaller than that of those with low-angle.②Except for the changes of width from the relaxed to maximal clenching position and from the relaxed to maximal protrusive position(P0.05).③Stature and weight influenced the size of the masseter muscle.Conclusion:The masseter muscle size of adult with high-angle facial skeletal type is smaller than that of those with low-angle.