Influence of light intensity and curing cycle on microleakage of Class V composite resin restorations

Abstract

he aim of this study was to determine the effect of a softstart polymerization method from Quartz-Tungsten-Halogen (QTH) and Plasma Arc (PAC) curing units on microleakage of Class V composite resin restorations with dentin cavosurface margins. Seventy-five bovine incisors received standardized class V cavities in all dentin margins. Teeth were divided into 5 equal groups according to the curing cycle. The cavities were incrementally restored with a composite resin (Single Bond/Z-100, 3M). Light curing was applied as follows: Group I: PAC light continuous-cycle curing at 1600 mW/cm 2 for 3s; Group II: PAC light step-cycle curing (2s at 800 mW/cm 2 then 4s at 1600 mW/cm 2 ); Group III: QTH light continuous-cycle curing at 400 mW/cm 2 for 40s; Group IV: QTH light ramp-cycle curing (from 100 to 600 mW/cm 2 in 15s followed by 25s at 600 mW/cm 2 ); Group V: QTH light pulse-delay curing (200 mW/cm 2 for 3s followed by 3 min delay then 600 mW/cm 2 for 30s). Teeth were stored in distilled water at 37ºC for 30 days and then subjected to thermocycling for 500 cycles at 5 and 55ºC. Root apices were sealed and teeth coated with nail varnish before they were immersed in 0.5% fuchsine red dye solution. Teeth were then sectioned and slices were scanned with a computer scanner to determine the area of dye leakage using a computer program (Image Tools). Images of tooth slices were also visually examined under magnification and dye penetration along the tooth/restoration interface was scored. Significant differences in the degree of dye penetration and leakage were detected between groups (p<.05). Groups I and II had significantly higher values of dye penetration and leakage than groups III, IV and V. In conclusion, the use of PAC light curing in a continuous or step cycle modes resulted in increased microleakage of Class V resin composite restorations compared with medium intensity QTH light curing. Pulse, ramp and continuous-cycle curing modes with QTH light resulted in similar degrees of microleakage. Uniterms: Composite resins; Microleakage; Polymerization; Light units. objetivo deste estudo foi determinar o efeito da polimerização gradual, mediante a utilização de aparelhos de Quartzo-Tungustênio-Halógena (QTH) e Arco de Plasma de Xenônio (PAC), no selamento marginal de restaurações classe V em resina composta com margens localizadas em dentina. Setenta e cinco incisivos bovinos receberam preparos de cavidades classe V, na raiz, com o intuito de situar as margens cavitárias em dentina. Os dentes foram divididos em cinco grupos de acordo com o método de fotoativação. As cavidades, depois de condicionadas, foram tratadas com o sistema adesivo Single Bond (3M Dental) e restauradas com a resina composta Z100 (3M Dental) pela técnica incremental. A fotoativação foi realizada para cada grupo como descrito a seguir: Grupo I: PAC pelo método de fotoativação constante: 1600mW/cm 2 -3s; Grupo II: PAC pelo método de fotoativação por passos (800mW/cm 2 -2s, subindo automaticamente para 1600mW/cm 2 -4s); Grupo III: QTH pelo método de foto...

Marginal microleakage of class II composite resin restorations due to restorative techniques

“…The class II cavities were confectioned only in one part of the teeth, since the photo-curing of the resin restoration could be to influence the shrinkage stress generation on the restoration of the other side. In class II cavities, another factor that significantly influences the marginal fit is the location of cervical margin (5,17). If the margins are localized around 1.0 mm coronal to the CEJ a good marginal integrity may result following a conventional enamel acid etching (17).…”

“…Adhesive failure can also occur at the internal interface, leading to the formation of an internal gap between the material and the dentin surface (2). Such openings or gaps are considered deleterious since they allow the transit of fluid between the dentin-pulp complex and the oral environment (3,5,6). Thus, different restorative techniques have been proposed to improve the adaptation marginal, such as pre-cured CR spheres inserted with the composite increments (7), a thin layer of flowable resin applied at the gingival wall and a strip of fiberglass inserted with the increments of CR (8,9).…”

The influence of different light-curing modes on microleakage of posterior resin composites

“…[6] However, other contributing factors are concerned with light-curing intensity, restoration's insertion techniques, cavity configuration factor (C-factor), and position of cavosurface margin whether at enamel or dentin. [7,8] Microleakage was considered as a main reason for the replacement of resin composite restorations. [7] Several attempts were made to overcome the adverse effects of shrinkage and consequent microleakage in Class II composite restorations.…”

“…[18] Ramp-curing mode starts with an initial low light intensity applied for a certain period and then gradually increased to a high intensity until Journal of Adhesion Science and Technology 137 the remaining exposure time. [8] Pulse continuous mode begins with a low light intensity that gradually increased to a high intensity for a defined time and then pulsating every two seconds to a higher intensity till the remaining of exposure time. [19] The last three modes can represent soft-start curing of the continuous irradiation.…”

“…It has been found previously that curing modes greatly affect shrinkage, curing depth, and overall properties of resin composites. [8,17] Thus, the curing profile for resin composites can be altered to improve their properties and to lessen microleakage. However, application of the soft-start techniques in polymerizing dental composites was found to reduce marginal gap at tooth-restoration interface without impairing their properties.…”