Laboratory studies of visible-light cured fissure sealants: setting times and depth of polymerization

Effect of curing method and curing time on the microhardness and wear of pit and fissure sealants

OBJECTIVE

To evaluate the effects of a light source, polymerization time and storage time on the microhardness and wear of pit and fissure sealants.

METHODS

Five commercial pit and fissure sealants (Fissurit F [FF], Teethmate F1 [TF], Apollo Seal [AS], Concise [CC], and Ultraseal XT Plus [US]) were used. Specimens were cured with a conventional visible light curing unit (Curing Light XL 3000) for 10, 20, 30, 40s or with a plasma arc light curing unit (Apollo 95E) for 3, 6, 9, 12s. The specimens were kept dry in light-shielded bottles at 37 degrees C for 1 week, then half of them were thermocycled. The rest of them were stored in distilled water in light-shielded bottles for another 30 days, which were kept in an incubator at 37 degrees C, followed by thermocycling. Microhardness and wear of the specimens were measured.

RESULTS

Similar degree of microhardness was achieved with the shorter curing time with the plasma arc light curing unit as with the conventional visible light-curing unit. With conventional visible light curing, the microhardness of the top surface was higher than that of the bottom surface (P<0.05). With plasma arc light curing, the microhardness of the top surface was higher than that of the bottom surface for AS and CC, but for FF, TF and US, the microhardness of the top surface was lower than that of the bottom surface, except in the 3-s curing of US. For FF, AS, CC and US, wear in the 6s curing with plasma arc light was similar to or less than that of the 30s curing with conventional visible light, but for TF, wear of the 9s curing with plasma arc light was similar to that of the 20s curing with conventional visible light. After storage in distilled water for 30 days followed by thermocycling, there was a tendency towards a decrease in microhardness and an increase in wear. There was a significant negative correlation between microhardness and wear (P<0.01).

SIGNIFICANCE

The tested curing methods differed significantly in their curing capacity. This study suggested that a plasma arc light curing unit needs shorter curing time than a visible light curing unit to achieve similar mechanical properties of the pit and fissure sealants tested.

Interface dimensions of CEREC-2 MOD inlays

OBJECTIVES

To quantify the width of the cement interface between ceramic inlays generated by the CEREC-2 CAD-CAM system and the tooth, and to determine the effect of cement viscosity on the interface width.

METHODS

Standardised MOD cavities were cut in 15 human premolar teeth using a custom paralleling device. A ceramic inlay was made with a CEREC-2 CAD-CAM machine for each tooth. The inlays were cemented using one of three resin-based composite systems of varying viscosity; a hybrid microfilled posterior composite, a compomer restorative and a dual-cure luting composite. The teeth were subsequently sectioned and measurements were taken at 21 key points with the aid of an image-analysis light microscopy system.

RESULTS

Statistical significance tests were applied to examine for difference in interface dimensions at specific points within each of the cement-groups and amongst groups. The interface space at the occlusal walls has a distinct wedge shape, being narrower at the external interface (50 microns, SD 15) than internally (211 microns, SD 38). There is no statistically significant difference in the interface dimensions of the gingival floor between the boxes that lie above and below the CEJ. There is no statistically significant difference in the width of the interface at any given point between the three cement groups.

SIGNIFICANCE

There is a significant improvement in the fit of CEREC-2 restorations when compared with the original CEREC system. Cements of varying viscosity (within the measured range) may be used for cementation of these inlays, without adversely affecting the width of the interface. Caution must be exercised with light-activated composite cements to ensure adequate transmission of light through the ceramic and the underlying composite cement.

Light-activated restorative materials: a method of determining effective radiation times

The aim of this investigation was to develop a test method that allows an operator to determine the appropriate radiation time for any light-activated material, irrespective of the characteristics of the light-activation unit or material to be cured. A computer-based radiometer was used to monitor the radiation energy transmitted through a number of light-activated materials during irradiation, and a method was devised to determine the predicted radiation time for any given material/shade/light unit combination based upon the change in transmission against time that occurred as the material polymerized. Additional test samples were cured for the predicted radiation times and upper and lower surface microhardness measurements were taken to verify the validity of the test method. Predicted times varied from 16 to 44 s for 2 mm thick samples of the materials/shade/light-activation units used. This method may allow operators to determine appropriate radiation times for any new light-activated restorative they decide to use with their own light-activation unit.

Pit and fissure sealant application: updating the technique

Dental sealants have proved an effective way to prevent caries development. The authors discuss available options in sealant materials and placement. They also outline key points in sealant application.

Evaluating intensity output of curing lights in private dental offices

Dentists in private offices were using inadequate curing lights, according to these study results. Many were unaware that the output of the lights was inadequate to completely cure composite resins.

Variables affecting the spectral transmittance of light through porcelain veneer samples

The spectral transmittance of porcelain laminate veneers was measured at three different thicknesses (0.50, 0.75, and 1 mm) and three different opacities (25%, 75%, and 100%). The results indicated that the thickness of the porcelain veneer was the primary factor affecting light transmission and not the opacity. The measured values of transmittance were then used to estimate the setting time for light-cured luting agents of a porcelain veneer.

An investigation into the microhardness of a light cured composite when cured through varying thicknesses of porcelain

An investigation was carried out to measure the completeness of cure of samples of a composite resin, light cured for 40s and 60s through porcelain discs of varying thickness. Once cured, each specimen was subjected to Vickers microhardness testing to assess the completeness of cure. Composite resin specimens cured without an intervening porcelain disc were used to establish a baseline. The results showed that increasing the thickness of the porcelain disc produced a statistically significant decrease in microhardness of the composite resin. Increasing the cure time from 40s to 60s produced a significant increase in microhardness. The increase in microhardness with increased cure time was more pronounced when the discs of thickness 1 mm and 2 mm were used, and when there was no overlying porcelain disc.

An investigation of the polymerization of orthodontic adhesives by the transillumination of tooth tissue

Prepared samples of light-activated composite were cured by transillumination of tooth tissue in healthy volunteers. Positioning of the samples and the direction of illumination was designed to simulate curing during direct bonding. The effectiveness of curing was investigated by determination of surface microhardness. The degree of polymerization of the specimens cured by transillumination was found to be reduced compared to the control samples cured by direct exposure to the light source.