OBJECTIVETo evaluate the effects of firing numbers on the total opening pore volume (TPV), translucency parameter (TP) and color of dental all-ceramic systems.

METHODSSpecimens of three kinds of all-ceramics systems were made, i.e. heat pressed all-ceramic (IPS Empress II), alumina all-ceramic (In-Cream alumina blanks) and zirconia all-ceramic (Cercon CAD/CAM zirconia). The specimens' TP, lightness (deltaL), chroma (deltaC) and TPV after 1, 3 and 5 firings were measured and calculated by spectrophotometer and surface area/porosity system. The data were analyzed statistically using SAS 8.0 software.

RESULTSThere were significant differences in TPV, TP, deltaL and deltaC for all-ceramic specimens at same number of firings (P<0.05), i.e. IPS>alumina and zirconia for TPV (P<0.05); IPS>zirconia>alumina for TP and deltaL (P<0.05); IPS and alumina>zirconia for deltaC (P<0.05). The significant differences also presented in TPV, TP, deltaL and deltaC for a same specimen at different number of firings (P<0.05). With increasing number of firings, TPV decreased, and TP, deltaL and deltaC increased gradually. There were negative linear correlation between number of firings and TPV, TP, deltaL and deltaC (P<0.05).

CONCLUSIONRepeated firings will affect TP and deltaL of all-ceramic restorations via the change of TPV.