Microhardness and porosity of Class 2 light-cured composite restorations cured with a transparent cone attached to the light-curing wand.

A new technique for curing class 2 composite fillings was investigated with respect to microhardness and porosity in the cervical part of the restorations. The technique is based on a plastic transparent cone that is attached to the curing wand. Before polymerizing the cervical portion, the cone is pressed down into the material in the direction of the floor of the approximal box. When the light is activated, it concentrates in the tip of the cone, from where it is distributed into the composite material. In order to compare this technique with conventional curing, standardized class 2 cavity preparations were made in brass blocks. Four different composite materials were used for 20 restorations each: Heliomolar, Herculite XR, Occlusin, and P-50. Ten restorations of each material were cured using the conventional technique (in two portions), and in the remaining 10 restorations the cervical portion was cured with the transparent cone. The irradiation time was 60 seconds in all instances. The Vickers hardness of the cervical approximal surfaces was measured after one and 24 hours. The surfaces were photographed in a stereomicroscope, and the numbers of porosities were counted on black-and-white prints.(ABSTRACT TRUNCATED AT 250 WORDS)

Strength and setting behavior of resin-modified glass ionomer cements.

Diametral tensile strength (DTS), fracture strength, and Vickers microhardness were tested in three resin-modified glass ionomer cements (GICs), one chemically set GIC, and one dental composite. For the DTS studies test discs were immersed in deionized water at 37 degrees C for 10 min, 1 day, and 28 days, respectively. Cured discs were also implanted in back muscles of rats for 28 days before testing. The effects of light irradiation time and delayed curing on the DTS of the cements were also studied. Significantly higher strength was observed in the resin-modified GICs in comparison with the chemically set GIC at all observation period. K71 showed the highest strength among the GICs. No strength reductions were detected after 28 days for the specimens in vivo. An illumination time of 20 sec was enough to obtain final strength in the PFA and K71 specimens, and 40 sec was needed in the VI specimens. The strength of the resin-modified GICs when light-cured was significantly higher than when the same cements were allowed to set without irradiation. The microhardness of the light-cured GICs was similar to that of the dental composite. Considering the improved fracture strength and surface hardness, it was concluded that the resin-modified GICs present an interesting material for further development.

Factors influencing shear strength of incrementally cured composite resins.

Factors influencing the shear strength of incremental curing of three different composite resins were examined. The first increment was cured under different surface conditions, in air, or under a coverglass. A separate experiment studied the effect of curing in nitrogen atmosphere. There was no difference in the shear strength of the specimens if the first increment was created in air or under a coverglass. One material (Heliomolar RO) showed higher shear strength when cured in increments and one when bulk-cured (Herculite XR). Curing increments in a nitrogen atmosphere increased the shear strength for two of the three materials tested (P50 and Heliomolar). The results showed that the bond strength between the increments of composites was influenced by the surface properties of the composites themselves after they had been cured under the different conditions; it was also affected by the inherent chemical and physical properties of the materials utilized.

Influence of paste temperature at curing on conversion rate and bending strength of light-cured dental composites.

Pastes of three dental composites were tempered to 20 degrees C, 37 degrees C and 60 degrees C. Test specimens (22 x 2 x 2 mm) were cured by light and stored in deionized water. Three-point bending strength was measured after 1 h and after 24 h. Degree of conversion on the surface exposed to the curing light and the opposite surfaces at the bottom of the mould was analysed by Fourier transform infrared (FTIR) after 1 h. After 1 h, specimens produced using the pastes cured at 60 degrees C showed significantly higher bending strength than the specimens produced using pastes cured at 20 degrees C and 37 degrees C. However, after 24 h the composites pretempered at the lower temperatures had developed the same level of bending strength as the composites cured at 60 degrees C. An increase in the degree of conversion with increased paste temperature was found in all materials after 1 h.

In vitro fluoride uptake by enamel and dentin. A comparative study of two varnishes.

The uptake of fluoride in enamel and dentin after application of an experimental fluoride varnish has been studied and compared with the uptake from a commercially available varnish (Duraphat). Each varnish was applied to 10 extracted human cuspid teeth. Successive etchings with perchloric acid were carried out separately in enamel and root dentin to obtain samples at three different depths. The concentrations of fluoride and calcium in the samples were determined, and the fluoride uptake was calculated. The experimental varnish gave a significantly greater fluoride uptake at all three sample depths in both enamel and dentin.

Radiographic evaluation of mandibular posterior implant sites: correlation between panoramic and tomographic determinations.

The purpose of the present study was to compare bone height determinations of implant sites by different radiographic techniques. Available bone height was measured in regions posterior to the mental foramen on panoramic radiographs, and on tomographs where the faciolingual dimension was at least 5mm. The bone heights were recorded at 401 edentulous and dentate sites in 100 patients. The overall mean bone height (m +/- SD) was 11.25 +/- 3.29 mm on panoramic radiographs and 8.81 +/- 3.38 mm on tomographs. The correlation between the two radiographic techniques ranged from 0.36 to 0.91 if the material was stratified according to factors such as height of available bone, age, gender and the presence of teeth. Gender was significantly correlated to panoramic and tomographic measurements in all regions. However, the precision of predicted tomographic measurements by using a linear regression model was not significantly increased by including gender as an explanatory variable. For evaluation of available bone height in mandibular regions posterior to the mental foramen, tomography is recommended for all prospective implant sites.