Karyna Martins do Valle-Corotti

Comparative in vitro study of the shear bond strength of brackets bonded with restorative and orthodontic resins

The aim of this study was to evaluate the shear bond strength of brackets bonded with different restorative systems and compare it with that afforded by an established orthodontic bonding system. Seventy human bicuspids were used, divided into five different groups with 14 teeth each. Whereas a specific orthodontic bonding resin (Transbond™ XT) was used in the control group, the restorative systems Charisma, Tetric Ceram, TPH Spectrum and Z100 were used in the other four groups. Seven days after bonding the brackets to the samples, shear forces were applied under pressure in a universal testing machine. The data collected was evaluated using the ANOVA test and, when a difference was identified, the Tukey test was applied. A 5% level of significance was adopted. The mean results of the shear bond strength tests were as follows: Group 1 (Charisma), 14.98 MPa; Group 2 (Tetric Ceram), 15.16 MPa; Group 3 (TPH), 17.70 MPa; Group 4 (Z100), 13.91 MPa; and Group 5 or control group (Transbond™ XT), 17.15 MPa. No statistically significant difference was found among the groups. It was concluded that all tested resins have sufficient bond strength to be recommended for bonding orthodontic brackets.

Determination of the force systems produced by different configurations of tear drop orthodontic loops

OBJECTIVE To determine the mechanical characteristics of teardrop loop with and without helix fabricated using different metal alloy compositions (stainless steel and beta-titanium), submitted to different intensities of bends preactivation (0° and 40°), and with different cross-sectional dimension of the wire used to build these loops (0.017 x 0.025-in and 0.019 x 0.025-in). METHODS Eighty loops used to close spaces were submitted to mechanical tests. The magnitudes of horizontal force, the moment/force ratio, and the load/deflection ratio produced by the specimens were quantified. Loops were submitted to a total activation of 5.0 mm and the values were registered for each 1.0 mm of activation. For statistic data analysis, a analysis of variance was performed and a Tukeys Multiple Comparison test was used as supplement, considering a 5% level of significance. RESULTS In general, teardrop loops with helix produced lower magnitudes of horizontal force and load/deflection ratio, and higher moment/force ratio than teardrop loops without helix. Among all analyzed variables, metal alloy composition presented greater influence in the horizontal force and in the load/deflection ratio. The moment/force ratio showed to be more influenced by the preactivation of loops for space closure.

Avaliação da resistência ao cisalhamento de braquetes da técnica lingual colados sobre superfície cerâmica

OBJETIVO: avaliar a resistencia ao cisalhamento de braquetes metalicos (American Orthodontics) utilizados na tecnica lingual, colados em facetas de cerâmica. METODOS: foram utilizados 40 corpos de prova divididos em quatro grupos de 10, de acordo com o material de colagem e do preparo da porcelana: Grupo I -resina Sondhi Rapid-Set e acido fluoridrico; Grupo II -resina Sondhi Rapid-Set e oxido de aluminio; Grupo III -resina Transbond XT e acido fluoridrico; e Grupo IV -resina Transbond XT e oxido de aluminio. Previamente a colagem, os braquetes foram preparados com base de resina de carga pesada (Z-250) e as facetas de cerâmica receberam aplicacao de silano. O teste de cisalhamento foi realizado por uma maquina de ensaios Kratos a uma velocidade de 0,5mm/min. RESULTADOS: os resultados obtidos foram analisados estatisticamente atraves do teste de Tukey (p<0,05) e demonstraram diferenca significativa entre os grupos I (2,77MPa) e IV (6,00MPa), e entre os grupos III (3,33MPa) e IV. CONCLUSOES: concluiu-se que a colagem de braquetes da tecnica lingual em superficie de cerâmica foi mais resistente ao cisalhamento com o uso de oxido de aluminio associado as duas resinas utilizadas neste estudo, porem a resina Transbond XT apresentou maior resistencia que a Sondhi Rapid-Set.

Avaliação comparativa do espaçamento anterior em nipo-brasileiros e leucodermas, na dentição decídua

OBJECTIVE: To carry out a comparative evaluation of the prevalence of anterior spacing characteristics in Japanese-Brazilian and white children in primary dentition. METHODS: Two selected samples of children aged 2-6 years were: 405 Japanese-Brazilians from 36 schools in the State of Sao Paulo and 510 white children from 11 public institutions in Sao Paulo city. The spacing features in the maxillary and mandibular arches were assigned to four categories: generalized spacing; only primate spaces; no spacing; and crowding. Logistic regression was used to analyze the effect of age, gender and ethnic group on the prevalence of the occlusal characteristics (α=0.05). RESULTS: In Japanese-Brazilians, generalized spacing was the most prevalent trait in the maxillary (46.2%) and mandibular (53.3%) arches. The frequency of primate spaces was higher in the maxillary arch (28.2% versus 15.3%). Concerning no spacing (21.7-26.4%) and crowding (4.0-4.9%), the variation between arches was relatively small. In white children, no spacing and exclusive presence of primate spaces showed distributions similar to that observed in Japanese-Brazilians. Generalized spacing was diagnosed in approximately 50% of the arches. Crowding prevalence was higher in the mandibular arch (12.8% versus 3.9%). The regression model adjusted for crowding prevalence was the only significant one. Only racial factor was significant (p<0.001). CONCLUSION: It may be suggested that anterior spacing features in primary dentition would not be influenced by age or gender. Nevertheless, white children would have 2.8 times more chances of presenting crowding in the mandibular arch, in comparison with Japanese-Brazilians.