Influence of the hyrax expander screw position on stress distribution in the maxilla: A study with finite elements.

INTRODUCTION: Our objective was to evaluate the stress and deformation distribution patterns on the maxillary bone structure using the finite element method by simulation of different vertical and anteroposterior positions of the expansion screw on the hyrax expander appliance. METHODS: Part of the maxilla with anchorage teeth, midpalatal suture, and the hyrax appliance were modeled, and 6 distinct finite element method models were created to simulate different positions of the expansion screw. There were 2 vertical positions at distances of 20 and 15 mm from the occlusal plane. Another 3 positions were anteroposterior, with the center of the screw placed between and equidistant from the mesial face of the first molar and the distal face of the first premolar, aligned to the center of the crown of the first molar, and the anterior edge of the screw aligned to the distal face of the first molar. The initial activations of the expanders were simulated, and the stress distributions on the maxilla in each model were registered. RESULTS: The stress was concentrated in the anterior region of the models, close to the incisive foramen, dissipating through the palate in the posterior and lateral orientations, in the direction of the pterygoid pillar, diverting from the midpalatal suture region. When the expander screw was simulated closer to the occlusal plane and in a more anterior position, more stress was located around the incisive foramen and distributed through the midpalatal suture to its posterior portion. More posterior positions resulted in concentrated stress around the pterygoid pillars. At all simulations, the midpalatal suture showed a V-shaped expansion, with the vertex superior in the coronal view and posterior in the axial view. CONCLUSIONS: Different positions of the expander screw interfered with stress intensity and distribution patterns. When the expansion screw was simulated in a more occlusal and anterior position, it was more efficient to transfer the mechanical effects from the appliance to the bone structures.

Evaluation of the prototype of a new bracket-positioning gauge.

OBJECTIVE: The purposes of this study were to present a prototype of a bracket-positioning gauge, which makes vertical inclination of the instrument difficult, allowing a reduction of vertical bracket positioning error, and to test its accuracy in bracket positioning by groups of individuals with different clinical experience and in specific groups of teeth. METHODS: For the testing of the prototype, four groups of six participants each were used: Group 1 was composed of undergraduate students in the dental school, who had no previous experience in bonding orthodontic attachments; Group 2 was composed of orthodontic graduate students in the dental school; Group 3 consisted of orthodontists with a maximum of 5 years of clinical experience; Group 4 comprised orthodontists with more than 5 years of clinical experience. A typodont was simulated with a Class I crowded malocclusion, which reproduced the same occlusal characteristics for all groups to be bonded. All participants were instructed to bond 0.022×0.028-in Edgewise brackets on the labial surfaces of the upper and lower incisors, canines, and premolars at a height of 4 mm from the incisal edge or the labial cusp tip. RESULTS: Only the mean value of Group 1 showed statistically significant difference in the comparison with the standard measurement. In the groups of teeth, the difference was significant for the premolar and incisor groups. CONCLUSION: Clinical experience interfered with the accuracy of vertical positioning of orthodontic attachments. As for the groups of teeth, premolars, followed by canines and incisors had the closest mean values to the standard measurement.

Evaluation of the prototype of a new bracket-positioning gauge

ABSTRACT Objective: The purposes of this study were to present a prototype of a bracket-positioning gauge, which makes vertical inclination of the instrument difficult, allowing a reduction of vertical bracket positioning error, and to test its accuracy in bracket positioning by groups of individuals with different clinical experience and in specific groups of teeth. Methods: For the testing of the prototype, four groups of six participants each were used: Group 1 was composed of undergraduate students in the dental school, who had no previous experience in bonding orthodontic attachments; Group 2 was composed of orthodontic graduate students in the dental school; Group 3 consisted of orthodontists with a maximum of 5 years of clinical experience; Group 4 comprised orthodontists with more than 5 years of clinical experience. A typodont was simulated with a Class I crowded malocclusion, which reproduced the same occlusal characteristics for all groups to be bonded. All participants were instructed to bond 0.022×0.028-in Edgewise brackets on the labial surfaces of the upper and lower incisors, canines, and premolars at a height of 4 mm from the incisal edge or the labial cusp tip. Results: Only the mean value of Group 1 showed statistically significant difference in the comparison with the standard measurement. In the groups of teeth, the difference was significant for the premolar and incisor groups. Conclusion: Clinical experience interfered with the accuracy of vertical positioning of orthodontic attachments. As for the groups of teeth, premolars, followed by canines and incisors had the closest mean values to the standard measurement.

RESUMO Objetivos: os objetivos deste estudo foram apresentar um protótipo de posicionador de braquetes ortodônticos que dificulte a inclinação no sentido vertical, possibilitando a redução dos erros de altura no posicionamento desses acessórios; além de testar sua precisão na colagem, realizada por grupos de indivíduos com diferentes tempos de experiência clínica em Ortodontia e em grupos específicos de dentes. Métodos: para os testes do protótipo desenvolvido, quatro grupos de seis participantes foram formados. O Grupo 1 foi composto por alunos do curso de Odontologia sem qualquer prática com colagem em Ortodontia; o Grupo 2, por estudantes em Ortodontia; o Grupo 3, por ortodontistas com menos de cinco anos de experiência clínica; e o Grupo 4, por ortodontistas com mais de cinco anos de experiência clínica em Ortodontia. Em um typodont, foi simulada uma má oclusão Classe I com apinhamento, com as mesmas características para todas as colagens realizadas. Todos os participantes foram instruídos a colar braquetes Edgewise 0,022" x 0,028" na superfície vestibular dos incisivos, caninos e pré-molares superiores e inferiores, na altura de 4mm da borda incisal ou cúspide vestibular. Resultados: somente a média do Grupo 1 apresentou diferença estatisticamente significativa na comparação com a medida padrão. Nos grupos de dentes, a diferença foi significativa para o grupo dos pré-molares e incisivos. Conclusão: o tempo de experiência clínica interferiu na precisão do posicionamento vertical do acessório ortodôntico e, quanto aos grupos de dentes, as médias mais próximas à medida padrão foram dos pré-molares, seguidas pelos caninos e incisivos.

Evaluation of the vertical accuracy of bracket placement with the Boone gauge.

INTRODUCTION: In this study, we aimed to evaluate the influence of clinical experience and the type of tooth (incisors, canines, and premolars) on the vertical accuracy of bracket placement with the Boone gauge. METHODS: For this analysis, 4 groups were defined. Group 1 was composed of undergraduate students from the dental school with no previous experience in bonding orthodontic attachments; group 2 was composed of graduate students in the dental school; group 3 consisted of orthodontists with a maximum of 5 years of clinical experience; and group 4 comprised orthodontists with more than 5 years of clinical experience. Each group included 6 participants. A typodont was simulated with a Class I crowded malocclusion that reproduced the same occlusal characteristics for all groups to be bonded. All participants were instructed to bond 0.022 × 0.028-in edgewise brackets on the labial surfaces of the maxillary and mandibular incisors, canines, and premolars at a height of 4 mm from the incisal edge or the labial cusp tip. After each bonding procedure, all teeth were photographed after being removed from the typodont and positioned in a stabilizing device adapted to a camera stand. RESULTS: The analyses of the variations showed that group 1 had the closest mean to 4 mm. However, this group also showed the greatest variance (0.433) (P <0.001). The smallest variations were observed in group 2 (variance, 0.093), followed by group 4 (variance, 0.094). The comparison of the means obtained in the groups of teeth at 4 mm demonstrated that the incisors showed a statistically significant difference (P <0.001), whereas canines (P = 0.133) and premolars (P = 0.913) did not. CONCLUSIONS: Operators are prone to fail in the placement of orthodontic attachments with the Boone gauge, despite their clinical experience in orthodontics. In the comparison of the groups of teeth, the incisors showed a statistically significant difference in relation to the height suggested for bracket placement with the Boone gauge.