@inproceedings{davis11,
  author = {Harry Davis and Scott A. Prahl and Jack L. Ferracane},
  title = {Reciprocity in Dental Resins and Composites},
  booktitle = {IADR/AADR/CADR 89th General Session},
  year = {2011, poster},
  volume = {90A},
  abstract = {Reciprosity, i.e. equal cure based on equal radiant exposure (mJ/cm$^2$) independent of exposure time/irradiance, has in general been shown to hold for dental composites, but with limitations. Objective: To develop depth of cure profiles to determine the limits of reciprosity for experimental dental composites having varied monomer content, photoinitiator type, and filler shape. Methods: Composites were produced with Bis-GMA:TEGDMA of 50:50, 70:30, and 90:10 with camphoroquinone (CQ)/EDMAB (1:2) or PPD (1:2; 50:50 mixture); and 62 wt\% spherical or irregular 0.4\,$\mu$m silanated glass. The same radiant exposure (5730 mJ/cm$^2$) was used to cure composites (15 mm diameter x 10 mm deep) using a Demi light (10 mm tip; Kerr) at (573 mW/cm$^2$) for 10 seconds and comparing with the same light transmitting through neutral density filters (72 mW/cm$^2$) for 80 seconds. The relatively low radiant exposure was chosen to accentuate the differences between the composites. After 24 hours, the specimens were bisected with a diamond saw and polished. Knoop Hardness (KHN) measurements were made (100 g; 15 seconds) in equidistant 1 mm squares across the width and depth (n=3/group). Regression was used to determine reciprosity (slope near 1.0 for plot of KHN 10s vs 80s). Results: Reciprosity was evident for the 70:30 and 90:10 resins (see figure-left) at nearly all measurable depths. Reciprosity only held for the 50:50 resin with CQ at 4 mm, but up to 3 mm with PPD (see figure-right). When reciprosity did not hold, longer exposure time tended to produce increased hardness at greater depths. Overall, reciprocity was less evident for composites with irregular compared to spherical fillers. Conclusions: Reciprosity was a function of monomer composition, being most evident for composites of higher viscosity (i.e. more bis-GMA), especially with spherical fillers. Longer exposure with lower irradiance was more effective for achieving depth of cure. Supported by NIH/NIDCR 1R21DE016758},
}