SUMMARYThis study evaluated the influence of the curing tip distance on cure depth of a resin composite by measuring Vickers microhardness and determining the degree of conversion by using FT-Raman spectroscopy. The light curing units used were halogen (500mW/cm KM Rode • Y Kawano • ML Turbino Clinical RelevanceDifferent light curing units, the thickness of the resin composite increments and the exposure distance to a curing light may change the physical properties of a restorative material and compromise its mechanical behavior under clinical loading conditions. Understanding how these factors can affect the quality of restorative products may help the dental professional in selecting the best activating source for a specific clinical application.

This in vitro study aimed to determine whether the micro-hardness of a composite resin is modified by the light units or by the thickness of the increment. Composite resin disks were divided into 15 groups (n = 5), according to the factors under study: composite resin thickness (0 mm, 1 mm, 2 mm , 3 mm and 4 mm) and light units. The light activation was performed with halogen light (HL) (40 s, 500 mW/cm(2)), argon ion laser (AL) (30 s, 600 mW/cm(2)) or light-emitting diode (LED) (30 s, 400 mW/cm(2)). Vickers micro-hardness tests were performed after 1 week and were carried out on the top surface (0 mm-control) and at different depths of the samples. Analysis of variance (ANOVA) and Tukey tests (P < or = 0.05) revealed no statistically significant difference among the light units for the groups of 0 mm and 1 mm thickness. At 2 mm depth, the AL was not statistically different from the HL, but the latter showed higher micro-hardness values than the LED. In groups with 3 mm and 4 mm thickness, the HL also showed higher micro-hardness values than the groups activated by the AL and the LED. Only the HL presented satisfactory polymerization with 3 mm of thickness. With a 4 mm increment no light unit was able to promote satisfactory polymerization.

The aim of this study was to define optimal power settings as well as curing time associated with evaluating the curing depth of a composite resin as a function of Vickers hardness. The tests were performed with a hybrid composite resin cured with a halogen lamp and argon ion laser, with different exposure times and power settings. The composite resin bulk technique was used using a black polypropylene matrix with thicknesses ranging from 1 to 4 mm and Vickers microhardness was measured on the opposite surface of the light activation. ANOVA and Tukey statistical tests were used. The results showed that the groups activated by the laser for 20 s, at 200 and 250 mW, did not present statistically significant differences regarding the halogen lamp with 1 mm thickness, but the halogen lamp showed better results with thickness values more than 2 mm (p < 0.05).

ABSTRACT:The use of argon laser (488 nm) has been suggested as a new alternative for polymerizing adhesive materials. This study aimed to evaluate the tensile bond strength of a microfilled composite (A110, 3M) inserted by incremental technique (3 increments of 1 mm) and by single increment (3 mm) polymerized by argon laser for 10, 20 and 30 seconds and halogen light for 40 seconds. Eighty (8 groups of 10 teeth) freshly extracted bovine teeth were stored in a freezer in distilled water for one week. The crowns were cross-sectioned from the roots. Pulpectomy was performed and the pulp chambers were sealed with wax. The buccal surfaces of the teeth were ground with wet sandpaper (grains: 120, 400, and 600) to expose the surface dentin, and the teeth were then included in acrylic resin. A metal device was used to fix each sample and a black propylene matrix 25 (3 mm high with an internal millimetric delimitation) was used to insert the material according to the groups studied. The polymerization intervals were of 10, 20 and 30 seconds for the laser polymerization and 40 seconds for the conventional polymerization. Tensile tests were performed by a Universal Testing Machine 4442 (Instron) at a speed of 0.5 mm/min and 500 N load. According to the methodology used, the incremental technique increased bond strength values. There was no difference between the studied polymerization techniques when resin was filled in 3 increments. DESCRIPTORS: Lasers; argon; Composite resins; Dentin; Tooth. RESUMO:O uso do laser de argônio (488 nm) tem sido sugerido como uma nova alternativa para polimerização de materiais adesivos. Este estudo tem o objetivo de avaliar a resistência adesiva de uma resina composta microparticulada (A110, 3M) inserida pela técnica incremental (3 incrementos de 1 mm) e de incremento único (3 mm) polimerizada com laser de argônio por 10, 20 e 30 segundos e com luz halógena por 40 segundos. Oitenta (8 grupos com 10 dentes) dentes bovinos recém-extraídos foram armazenados em geladeira, em água destilada, por uma semana. As coroas foram separadas das raízes. Foi realizada a pulpectomia, e as coroas foram seladas com cera. As faces vestibulares foram desgastadas com seqüência de lixas (120, 400 e 600) para expor a dentina superficial, e os dentes foram incluídos em resina acrílica. Foi utilizada uma mesa metálica para fixar cada espécime com a matriz de polipropileno preta (3 mm de altura com delimitação interna milimetrada) e inserir a resina de acordo com os grupos estudados. Os tempos de polimerização foram de 10, 20 e 30 segundos para a polimerização com laser e de 40 segundos para a polimerização convencional. Os testes de resistência adesiva foram realizados com a máquina universal de ensaios 4442 (Instron) com velocidade de 0,5 mm/min e carga de 500 N. De acordo com a metodologia usada, a técnica incremental aumentou os valores de resistência adesiva. Não houve diferença entre as técnicas de polimerização usadas quando a resina foi inserida em 3 incrementos.