Yukinori Nahara

ESR study of camphorquinone/amine photoinitiator systems using blue light-emitting diodes.

New light-activation units equipped with high-illuminant blue light-emitting diodes (LEDs) have recently been proposed as a replacement for the halogen units that are widely used in dentistry to polymerize light-cured resins. The photoinitiators in light-cured dental resins, typified by the camphorquinone (CQ)/amine photoinitiator system, generate primary radicals with light irradiation that attack the double bonds of resin monomers. The physical properties of the cured resins are affected by the generation of primary radicals during the initial stage of polymerization. This study examined two types of photoinitiator systems, CQ/DMPT and CQ/DMAEMA, and three types of curing units, a new LED unit and two conventional halogen units. The primary radicals generated by irradiation were quantified using electron spin resonance (ESR) spectroscopy with a trapping method, using phenyl-tert-butyl nitrone as the trapping agent. The energy efficiencies of the LED and halogen units were compared by quantifying the generated radicals and emitted light energy (J/cm(2)). The energy required to generate a given amount of radicals using the LED unit was smaller than that using the halogen units (p<0.05). These results suggest that the new LED unit performs better than conventional halogen units with respect to light energy.

The fungicidal effect of ultraviolet light on impression materials

The effects of ultraviolet (UV) light on fungi and impression materials were tested. UV light (250 microW/cm2) killed most Candida organisms (10(3) cells/ml) within 5 minutes. UV light (8000 microW/cm2) killed most C. albicans (10(7) cells/ml) within 2 minutes of exposure. The effect of UV light on dimensional change and surface roughness of impression materials (irreversible hydrocolloid, agar, and silicone rubber) was tested. The results showed that neither dimensional change nor surface roughness of the impression materials were affected. The results of this study indicate that UV light disinfects impression materials that are contaminated with Candida organisms.

Clinical evaluation of castable a tite ceramic crowns

Thirty-three castable apatite ceramic crowns were constructed for 26 patients. The crowns were clinically evaluated for anatomic form, marginal adaptation, cavosurface marginal discoloration, surface roughness, and color match for a period of 2 years at regular intervals. Results showed that all restoration had satisfactory anatomic form; all but one exhibited good marginal adaptation. Slight abrasion was noticed at the functioning cusps and all but three of the restorations demonstrated excellent color matching.

Dimensional accuracy of castable apatite ceramic crowns: The influence of heat treatment on dimensional changes and distortion of crowns

Castable apatite ceramic crowns are subjected to heat treatment during crystallizing and during coloring after casting. The dimensional accuracy of the heat-treated crowns was investigated with respect to its influence on dimensional changes in castable apatite ceramic crowns and on distortion of the interior of the crowns, using two investment techniques and a three-coordinate measuring machine. Dimensional changes were not influenced by the number of coloring firings. Distortion of the interior of crowns was slightly outward at the gingival plane. Shrinkage because of crystallizing was approximately 20 microns and the shrinkage of the gingival plane was equal to that of the occlusal plane.

Plaque accumulation on Teflon-coated metal.

This study demonstrated that plaque accumulation was reduced and plaque removal facilitated by the TFE coating. These findings suggest that the TFE coating has a practical application for pontics and the proximal and cervical surfaces of crowns. These inaccessible surfaces are not easily cleaned by brushing.