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[Long-term changes of hard-tissue in borderline cases with extraction vs. non-extraction treatment]
Yan Liu1, Wei Huang, Tian Min Xu
1Department of Orthodontics, Peking University School and Hospital of Stomatology, Beijing, China.
Objective:
To investigate hard-tissue changes in borderline cases with extraction and non-extraction during treatment and follow-up stages.
Methods:
Five associate professors, who were from Peking University School and Hospital of Stomatology, were asked to make judgment on the cases with full pre-treatment records for discriminating the borderline cases from extraction and non-extraction cases. Fifty-four borderline cases with full treatment records which had been out of treatment for at least 2 years were followed. Twenty-one cases with follow-up records were collected including 8 extraction cases and 13 non-extraction cases. Cephalometric measurements were preceded in IDAS (Image and Database Analysis System) software program.
Results:
In extraction group, significant changes of SNB, SNPg in A-P direction and that of ArGo/ANSMe, MP/SN in vertical direction were present during the follow-up stage, while the overjet was stable. In non-extraction group, only decrease of proclination of lower incisor and increase of overjet were present without any skeletal changes during the follow-up stage. In comparison of the two groups, no skeletal and dental changes showed statistically significant difference except for MP/SN and ArGoGn in pre-treatment stage, while dental characteristics in relation to upper and lower incisor (L1/NB, L1-NB, L1-AP, U1-AP, U1/L1) showed statistically significant difference between the two groups after treatment. But in follow-up stage, the skeletal and dental pattern tended to be similar for both groups only except for the proclination of lower incisor.
Conclusion:
The similarities of skeletal and dental pattern are demonstrated in extraction and non-extraction group before treatment. Dental changes are the major post-treatment changes in the two groups. In follow-up stage, counter-clockwise rotation of mandible is unique in extraction group, which is likely a helpful factor for stability of overjet, while lingual tipping of lower incisor in non-extraction group without skeletal changes may contribute to overjet relapse.
