Statement of Problem:
Light transmission through veneers affects the degree of polymerization of light-polymerized resin luting agents.

Objective:
Light transmission through different all-ceramic veneers when irradiated by 3 types of light-polymerization units was measured to evaluate the degree of polymerization.

Materials and Methods:
The power outputs from a conventional halogen (3M Unitek), a plasma arc (Apollo 95E), and a high-intensity halogen (Kreativ Kuring Light Model 2000) light were measured by a radiometer. The light intensity (mW/cm(2) ) from these units was also measured after transmission through 0.25-, 0.40-, and 0.60-mm-thick Procera copings and through 1-mm-thick disks of feldspathic porcelain (Ceramco II), aluminous porcelain (Vitadur Alpha), and a castable pressed ceramic (IPS Empress). Two disks of each material were fabricated by a commercial laboratory in accordance with the manufacturers' recommendations. The light transmissions through these materials were compared with those through Procera-aluminous porcelain combinations. These disks were fabricated by applying appropriate thicknesses of aluminous porcelain (AllCeram). Light intensities were subjected to ANOVA and post hoc Scheffe tests at a priori alpha=.05.

Results:
Intensities of light from 3 polymerization units, conventional halogen light, high-intensity halogen light, and plasma arc, were 660, 1050, and 2475 mW/cm,(2) respectively, and these together with the ceramic veneer thickness dictated the light transmission through veneers. Mean values (+/-SD) of light transmission through Procera copings for thicknesses of 0.25, 0.40 and 0.60 mm, respectively, were as follows: Apollo plasma arc (1083 +/- 117, 843 +/- 59, and 593 +/- 132); Kreativ high-intensity halogen (425 +/- 41, 345 +/- 74, and 256 +/- 79); 3M Unitek halogen (270 +/- 102, 230 +/- 48, and 180 +/- 113). Comparable transmissions occurred with the other ceramics. Only the plasma arc and the high-intensity halogen polymerization units emitted light of sufficient energy to effect polymerization of a resin luting agent (P=.045).

Conclusion:
Within the limitations of this study, the intensity of light transmitted through ceramic veneers was dictated by the polymerization unit and the type and thickness of the ceramic. With conventional halogen polymerization units, there may be insufficient light transmission through thicker veneers or all-ceramic crowns for adequate light polymerization.

PMID: 15153851 [PubMed - indexed for MEDLINE]
Department of Restorative Dentistry, Baltimore College of Dental Surgery, University of Maryland, 21202, USA. fhr001@dental.umaryland.edu