Digital Photoelastic Analysis of TAD-Supported Maxillary Arch Distalization

The objective of this study was to determine whether the distribution of compressional and tensional stress around tooth roots is influenced by the position of a temporary anchorage device and the length of the retraction hook during the distalization of the maxillary dentition. A photoelastic orthodontic model was made of photoelastic epoxy resin. Six combinations of three retraction hook lengths and two posterior Temporary skeletal anchorage devices (TAD) positions were established. Stress was applied through an elastic chain for each of the combinations. Digital photoelastic stress analysis measured the compression, tensional stress, and direction around the tooth root. Using this novel photoelastic model, we found that the distribution of compressional and tensional stress during the retraction of the maxillary dentition was significantly influenced by the position of the TAD and the length of the retraction hook

Comparison of arch forms between Egyptian and North American white populations

Introduction: The aim of this study was to evaluate the morphologic differences in the mandibular arches of Egyptian and North American white subjects. Methods: The sample included 94 Egyptian subjects (35 Class I, 32 Class II, and 27 Class III) and 92 white subjects (37 Class I, 29 Class II, and 26 Class III). The subjects were grouped according to arch form types (tapered, ovoid, and square) to compare their frequency distribution between ethnic groups in each Angle classification. The most facial portions of 13 proximal contact areas were digitized on scanned images of mandibular casts to estimate the corresponding clinical bracket point for each tooth. Four linear and 2 proportional measurements were taken. Results: In comparing arch dimensions, inter-molar width was narrower in Egyptians than in the whites (P = 0.001). There was an even frequency distribution of the 3 arch forms in the Egyptian group. On the other hand, the most frequent arch form was ovoid followed by tapered and square in the white group; the square arch form was significantly less frequent than the tapered and ovoid arch forms (P = 0.029). Conclusions: The arch forms of Egyptians are narrower than those of whites. The distribution of the arch form types in Egyptians showed similar frequency, but the square arch form was less frequent in whites. It is recommended to select narrower archwires from the available variations to suit many Egyptian patients. (Am J Orthod Dentofacial Orthop 2011;139:e245-e252)Partly funded by Catholic University of Korea, the alumni fund of the Department of Dentistry, and the Graduate School of Clinical Dental Science.

Evaluation of dental and basal arch forms using cone-beam CT and 3D virtual models of normal occlusion

Objectives: To evaluate the relationship between the mandibular dental and basal arches using CBCT, and to assess the correlation between basal arch dimensions derived from CBCT and 3-dimensional (3D) virtual models in a cohort sample exhibiting normal occlusions. Methods: The facial axis (FA) and root centre (RC) points of mandibular teeth were identified on 32 CBCT images. FA and WALA points were digitised on 3D models of 28 mandibular casts from the same sample. The relationships between dental and basal arch dimensions, and between the two basal depth dimensions derived from RC and WALA points were statistically assessed by Pearsons correlation. Results: Strong correlations were found between dental and basal intercanine and intermolar arch widths. Also, the basal intercanine width showed a moderate correlation with dental intermolar width and depth. The basal intercanine and intermolar widths measured on 3D models showed moderate correlations with those measurements on CBCT, whereas the basal canine and molar depths showed no correlations. Conclusions: The dental and basal anterior and posterior arch widths were strongly correlated in normal occlusion. No correlations were found between the arch depths measured from WALA points and RC points. Hence, RC points may represent more useable landmarks compared to WALA points in the evaluation of basal arch forms. It is recommended that the relationship between the dental and basal arches is evaluated during treatment planning in order to improve arch co-ordination.OAIID:oai:osos.snu.ac.kr:snu2013-01/102/0000004298/5SEQ:5PERF_CD:SNU2013-01EVAL_ITEM_CD:102USER_ID:0000004298ADJUST_YN:NEMP_ID:A072100DEPT_CD:852CITE_RATE:.281FILENAME:국윤아-백승학-호주-2013-archform-cbct.pdfDEPT_NM:치의과학과SCOPUS_YN:YCONFIRM: