Very little light transmits through tooth structure. This is important because some dentists have been advised, when placing veneers on anterior teeth, to cure from the palatal or lingual aspect (i.e. through the back of the tooth).

Given that dentists are often provided with conflicting light curing instructions when placing ceramic restorations (e.g. veneers, crowns, inlays/onlays), it is reasonable that they question the effectiveness of various strategies for light curing of adhesives and luting cements.

Light transmission through tooth structure was recently examined in vivo by Dr. Carlos Eduardo Sabrosa (Associate Professor, University of Rio de Janeiro) in a recent study (1), using a specially designed laboratory-grade instrument from Bluelight Analytics.

Dr. Sabrosa measured the transmission of blue light through anterior teeth and found that it ranged from 0.8% to 1.5% (mean = 1.4%). The tooth shade for the majority of subjects was either A1 or B1, (see study).

In a related study (2), one of Dr. Sabrosa’s students examined light transmission through 1.5 mm blocks of CAD-CAM ceramic (shades A2, A3, A3.5). Light transmission through 1.5 mm of ceramic ranged from 13% to 24%, (see study).

It is worth noting earlier research (3) that also used a MARC resin calibrator showed that light transmission rates through zirconia dropped rapidly as thicknesses increased (transmission rates through ceramic are noted to be similar to, and perhaps slightly better than, zirconia).

This evidence suggests that substantially more light transmits through ceramic than through tooth structure. As a result, dentists should ask for evidence to support any instruction to light cure though tooth structure.

This is especially important considering the fact that light curing through tooth structure risks delivering heat more directly to pulpal tissue, and ignores the thermal insulating benefits of ceramic.

References

1. Light transmission through anterior teeth in vivo; Presented at the International Association for Dental Research, Boston, MA in March 2015.

2. Light transmission through various shades of CAD-CAM material; Presented at the International Association for Dental Research, Boston, MA in March 2015.

3. Quantification of the amount of light passing through zirconia: The effect of material shade, thickness, and curing conditions; Journal of Dentistry 42 (2014) 684-690

The image used in this post is "Light Cure Composite Restoration" by Dr. Partha Sarathi Sahana, which is licensed with CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/