Long term skeletal and dental changes between tooth-anchored versus Dresden bone-anchored rapid maxillary expansion using CBCT images in adolescents: Randomized clinical trial.

OBJECTIVE: The aim of this study was to determine long-term skeletal and dental changes in tooth-anchored versus Dresden bone-anchored rapid maxillary expansion using CBCT images in adolescents. MATERIALS AND METHODS: In all, 29 adolescent patients (11-17 years of age) needing skeletal expansion were randomly allocated to two different groups treated by either a Dresden bone-anchored expander or a conventional hyrax expander. Patients included did not have previous orthodontic treatment, were non-syndromic and had all teeth present in mouth. CBCT images were taken before expansion and two or more years after expansion. An independent T-test was used to determine the statistical significance between treatment groups and paired T-test was used to compare the results before and after expansion in each group. RESULTS: Neither treatment group showed overall long-term different skeletal and dental changes in the transverse, anterior-posterior and vertical planes (P<0.05). Both treatment groups showed mild asymmetric skeletal expansion, but these were clinically insignificant. CONCLUSIONS: Both expanders had similar skeletal and dental results. The greatest changes were in the transverse plane. Changes in vertical and anterior-posterior were negligible.

Can pulpal floor debonding be detected from occlusal surface displacement in composite restorations?

OBJECTIVES: Polymerization shrinkage of resin composite restorations can cause debonding at the tooth-restoration interface. Theory based on the mechanics of materials predicts that debonding at the pulpal floor would half the shrinkage displacement at the occlusal surface. The aim of this study is to test this theory and to examine the possibility of detecting subsurface resin composite restoration debonding by measuring the superficial shrinkage displacements. METHODS: A commercial dental resin composite with linear shrinkage strain of 0.8% was used to restore 2 groups of 5 model Class-II cavities (8-mm long, 4-mm wide and 4-mm deep) in aluminum blocks (8-mm thick, 10-mm wide and 14-mm tall). Group I had the restorations bonded to all cavity surfaces, while Group II had the restorations not bonded to the cavity floor to simulate debonding. One of the proximal surfaces of each specimen was sprayed with fine carbon powder to allow surface displacement measurement by Digital Image Correlation. Images of the speckled surface were taken before and after cure for displacement calculation. The experiment was simulated using finite element analysis (FEA) for comparison. RESULTS: Group I showed a maximum occlusal displacement of 34.7±6.7µm and a center of contraction (COC) near the pulpal floor. Group II had a COC coinciding with the geometric center and showed a maximum occlusal displacement of 17.4±3.8µm. The difference between the two groups was statistically significant (p-value=0.0007). Similar results were obtained by FEA. The theoretical shrinkage displacement was 44.6 and 22.3µm for Group I and II, respectively. The lower experimental displacements were probably caused by slumping of the resin composite before cure and deformation of the adhesive layer. SIGNIFICANCE: The results confirmed that the occlusal shrinkage displacement of a resin composite restoration was reduced significantly by pulpal floor debonding. Recent in vitro studies seem to indicate that this reduction in shrinkage displacement could be detected by using the most accurate intraoral scanners currently available. Thus, subject to clinical validation, the occlusal displacement of a resin composite restoration may be used to assess its interfacial integrity.

Dureza e grau de conversão de resinas polimerizadas por halógeno e LED / Hardness and degree of conversion of composite polymerized with halogen and LED

Este estudo objetivou determinar a dureza Vickers e o grau de conversão de uma resina composta polimerizadas por halógeno e LED em diferentes profundidades (2,0 e 3,0 mm). Foram utilizados os aparelhos XL3000 (halógeno - 3M) e Bright Lec (LED - MM Optics). Os corpos de prova mediam 2 e 3 mm de altura e foram divididos em 4 grupos (n=8). G1: 2 mmhalógeno; G2: 2 mm-LED; G3: 3 mm-halógeno e G4: 3 mm-LED. Os corpos de prova foram submetidos ao teste de dureza Vickers, sendo que cada amostra recebeu cinco indentações (200 g durante 6 segundos), e foi medido o grau de conversão com o espectrômetro de infravermelho (Fourier). A média dos resultados da dureza Vickers (G1: 33,64; G2: 26,60; G3: 22,71; e G4: 15,46) foi submetida à análise estatística (ANOVA), e não apresentaram diferença estatisticamente significante na profundidade de 2 mm. Na profundidade de 3 mm a tecnologia halógena apresentou resultado estatisticamente superior à tecnologia LED (p<0,05). Os dados obtidos no espectrômetro de infravermelho foram submetidos à análise estatística (testes T). Os resultados do grau de conversão não diferiram estatisticamente. As médias de grau de conversão foram: G1: 65,9%; G2: 66,0%; G3: 68,4% e G4: 67,5%. Assim, conclui-se que a dureza diminuiu com o aumento da profundidade para as diferentes tecnologias emissoras de luz, e na profundidade de 3,0 mm o aparelho halógeno apresentou resultado superior ao aparelho LED. O grau de conversão não foi afetado pela profundidade e pela emissão de luz (AU).

This study aimed to evaluate the Vickers hardness and the degree of conversion of a resin composite cured by two polymerized with different technology of emission of light (halogen and LED) in different depth (2 and 3 mm). Devices were used XL3000 (halogen - 3M​) and Bright Lec (LED - MM Optics). The specimens measured 2 and 3 mm in height and were divided into 4 groups (n = 8). G1: 2 mm-halogen; G2: 2 mm-LED; G3: 3 mm-halogen; and G4: 3 mm-LED. The samples were submitted to Vickers hardness test, each sample received five indentations (200 g for 6 seconds), and measured the degree of conversion with the infrared spectrometer (Fourier). The average of the results of Vickers hardness (G1: 33.64; G2: 26.60; G3: 22.71; and G4: 15.46) was subjected to statistical analysis (ANOVA) and showed no statistically significant difference at a depth of 2 mm. In the depth of 3 mm halogen technology presented was statistically superior to LED (p <0.05). Data from the infrared spectrometer have been subjected to statistical analysis (T test). The results of the degree of conversion did not differ statistically. The average degree of conversion was: G1: 65.9%; G2: 66.0%; G3: 68.4%; and G4: 67.5%. It was concluded that the hardness decreased with increasing depth for the different technologies emitting light, and 3.0 mm in depth of the halogen unit provides results superior to the LED device. The degree of conversion was not affected by the depth and light emission (AU).