Comparison of dentofacial and periodontal effects of rapid and semirapid maxillary expansion

ABSTRACTThe purpose of this study was to compare the skeletal, dentoalveolar and periodontal effects that occurred after rapid and semirapid maxillary expansion with acrylic splint bonded expansion appliance and also to compare the root resorption degree of support teeth during expansion. 19 patients (8 girl, 11 boy) who are in active growth and development, having unilateral or bilateral maxillary deficiency, Angle class I or II malocclusion with the requirement of bilateral upper premolar extraction, intact first premolars and not having a history of previous orthodontic treatment were included in our study. These patients were allocated to one of the groups. The SRME group consisted of 10 patients (5 girls, 5 boys) with a mean age of 14,05±1,46 years and the RME group consisted of 9 patients (3 girls, 6 boys) with a mean age of 13,96±0,71 years. The treatment period is mainly 61,7±20,4 days for the SRME group and 33,4±9,6 days for the RME group. The patientswere instructed to activate the screw 2 x 1/4 turn per day for first week and followed by 1 x 1/4 turn per for every other day for the SRME group and 2 x 1/4 turn per day throughout the treatment for the RME group. Lateral and posteroanterior cephalometric radiographs and periapical radiographs of upper anterior teeth by parallel technique were taken from the patients at the beginning of treatment (T0), at the end of expansion period (T1) and 3 month retention period (T2). Low dose computed tomography records were taken from the upper jaw of the patients accepted, at the beginning of treatment (T0) and at the end of 3 month retention period. And also at the end of expansion period (T1), root resorption evaluation was done with scanning electron microscope(SEM) analysis in extracted teeth. Intragroup variances were evaluated with paired t test, Mann-whitney U test were used to compare the intergroup variances. A p value of less than 0,05 was considered as statistically significant. For all possible multiple comparisons, a Bonferroni Correction was applied to control Type I error.ANB, SN-MP angle and ANS-Me value showed significant increase duringactive treatment period, while SN-MP angle showed significant decrease during retention period within SRME group. U1-SN angle showed significant decrease during both active treatment and total observation period. Posterior nasal cavity width, palatal maxillary width and the distance between palatinal roots showed significant increase in the CT measurements. SNB angle showed significant decrease while ANB and SN-MP angle showed significant increase during active treatment period within RME group. SN-MP angle showed significant decrease in retention period. Significant decrease was found in U1-SN angle during both active treatment and total observation period. In the PA cephalometric measurements, nasal cavity width and total maxillary width showed significant increase whereas right and left first molars showed significant buccal tipping during both active treatment and total observation period in both groups. Posterior nasal cavity width, palatal maxillary width, the distance between palatinal roots and the distance between incisor roots showed significant increase in the CT measurements. Buccal bone thickness decreased and palatal bone thickness increased in all molar and premolar teeth examined. The only statistically significant difference between the groups was found in the PP?U1i measurement. This measurement increased in both groups yet significantly more in the RME group. Although siginificant changes were recorded in the RME group in vertical dimension, no statistically significantdifferences were found between the two groups. According to posteroanteriorcephalometric and periapical radiographs measurements, similar changes wereobserved in both groups and no statistically significant differences were found between the two expansion procedures. In the CT measurements, significant differences were found in buccal alveolar crest levels of right and left firstmolars between groups. Root resorption was seen in both groups but no significant difference between the groups was observed. In conclusion, maxillary expansion was carried out successfully with both protocols. However, RME was superior to SRME because of the reduced active treatment period, shorter chair time and the period which the bonded appliance remains in the mouth. On the other hand, SRME protocol can be preferred in patients with increased vertical dimension and severe openbite. Even though no significant differences were found between the groups in short term, long term effects should be evaluated by further studies.Key words: Rapid maxillary expansion, semirapid maxillary expansion, computed tomography, root resorption.