A comparative study based on the mandibular movement track and the movement parameters of the virtual articulator in simulating occlusal adjustment / 华西口腔医学杂志

OBJECTIVES@#This study aimed to compare the effects of virtual adjustment on occlusal interferences in mandibular posterior single crown and three-unit bridge restorations by using the mandibular movement track and the movement parameters of a virtual articulator.@*METHODS@#Twenty-two participants were recruited. Digital casts of the maxillary and mandibular arches were obtained using an intraoral scanner, and the jaw registration system was used to record the data of the mandibular movement track and the movement parameters of the articulator. Four kinds of restorations with 0.3 mm occlusal interferences were designed with dental design software. In particular, single crowns were designed for teeth 44 and 46, whereas three-unit bridges were designed for teeth 44-46 and 45-47, and the corresponding natural teeth were virtually extracted. Virtual adjustment of the restorations was performed using two dynamic occlusal recordings, namely, the mandibular movement track and the movement parameters of the virtual articulator. A reverse-engineering software was used to measure the root-mean-square of the three-dimensional deviation of the occlusal surfaces between natural teeth and the adjusted restorations. The differences between the two methods of virtual-occlusion adjustment were compared and analyzed.@*RESULTS@#For the same group of restorations, the three-dimensional deviation of the mandibular movement track group were lower than those of the virtual articulator group, and the differences were statistically significant (P<0.05). For the four groups of restorations adjusted by the same method, the three-dimensional deviation of the 46-tooth single crown was the largest and the smallest three-dimensional deviation was that of the 44-tooth single crown. Statistical differences existed between the 44-tooth single crown and the other groups (P<0.05).@*CONCLUSIONS@#For the occlusal design of posterior single crown and three-unit bridge, the mandibular movement track could be a more effective approach to virtual occlusal adjustment than the movement parameters of the virtual articulator.

The assessment of resting tongue posture in different sagittal skeletal patterns

ABSTRACT Introduction: Resting tongue posture affects the surrounding structures and, theoretically, may result in altered arch form and jaw relationship. Objective: The objective of the present study was to investigate the association between resting tongue posture as observed in lateral cephalometric radiograph, sagittal jaw relationship and arch form. Methods: The study was conducted on pretreatment lateral cephalograms and dental casts of 90 subjects. Subjects were equally divided into three groups, based on sagittal jaw relationship (Class I, II and III). Tongue posture was determined in terms of tongue-to-palate distances at six different points (distances 1 to 6) using ViewPro-X software, according to the method described by Graber et al in 1997. The arch widths (intercanine and intermolar widths) were evaluated on pretreatment dental casts. Results: Tongue-to-palate distances were found to be comparable among different study groups. Significant differences were found in intercanine and intermolar widths at the cuspal and gingival levels among the study groups, except for intercanine width at cuspal level in maxilla and intermolar width at cuspal level in mandible. Moderate positive correlation was found between arch widths ratios at distances 3 and 4 in skeletal Class III group. Effect size was found to be moderate to large in different sagittal skeletal patterns and arch widths. Conclusion: The results of the current study showed no significant differences in the resting tongue posture among the groups, and moderate to weak correlation between tongue posture and dental arch widths.

RESUMO Introdução: a postura da língua em repouso pode afetar as estruturas adjacentes e resultar em mudanças no formato das arcadas e na relação maxilomandibular. Objetivo: o presente estudo teve como objetivo avaliar a associação entre a postura da língua em repouso (observada em radiografias cefalométricas laterais), o padrão esquelético e o formato da arcada. Métodos: a amostra incluiu radiografias cefalométricas laterais e modelos de estudos iniciais de 90 pacientes, os quais foram divididos em três grupos, conforme a relação esquelética: Classe I, Classe II e Classe III. A postura da língua foi avaliada com o software ViewPro-X, de acordo com o método descrito por Graber et al. em 1997, medindo-se a distância entre o palato e a língua em seis pontos diferentes (distâncias 1 a 6). A largura das arcadas (distâncias intercaninos e intermolares) foi medida nos modelos de gesso iniciais. Resultados: as distâncias aferidas foram semelhantes entre os grupos. Diferenças significativas entre os grupos foram encontradas para as distâncias intercaninos e intermolares, nos níveis das cúspides e da gengiva, com exceção da distância intercaninos superiores ao nível das cúspides e distância intermolares inferiores ao nível das cúspides. No grupo Classe III, foi observada uma correlação positiva moderada entre as proporções das larguras das arcadas nas distâncias 3 e 4. O tamanho do efeito apresentou-se de moderado a alto nos diferentes padrões esqueléticos e larguras das arcadas. Conclusão: os resultados do presente estudo mostraram ausência de diferenças significativas na postura da língua em repouso entre os diferentes grupos, e uma correlação moderada a fraca entre a postura da língua e o formato das arcadas.

Dentoalveolar compensation according to skeletal discrepancy in Normal occlusion / 대한치과교정학회지

The purpose of this study was to investigate the dentoalveolar compensation according to anteroposterior skeletal discrepancy in normal occlusion and to evaluate cephalometric parameters that quantitatively describe dental compensations. The study consisted of 90 subjects (50 males, 40 females) who were selected among specimens of normal occlusion at Seoul National University Dental Hospital, Dept. of Orthodontics. Lateral cephalograms in centric occlusion were traced and digitized for each subject. According to the anteroposterior skeletal pattern, the sample was divided into three groups. Cephalometric data were analyzed for the three groups using the SPSS program. Independent t-test, correlation analysis and regression analysis were carried out. The results were as follows: Dentoalveolar compensation was found in upper and lower incisor inclination and occlusal plane inclination. As the mandible located anterior to the maxilla, the maxillary incisors inclined more labially, the mandibular incisors more lingually, and the occlusal plane continued to flatten. The dental parameters most correlated with anteroposterior skeletal discrepancy were L1 to SN and L1 to FH. Among the compensatory dentoalveolar changes, lower incisor inclination was strongly related to the anteroposterior jaw relationship and played an important role in obtaining a normal incisor relationship. U1 to PtGn and L1 to APog were constant irrelevant to anteroposterior skeletal discrepancy.