Thermal cycling procedures for laboratory testing of dental restorations

Objectives: Exposure of restorations in extracted teeth to cyclic thermal f luctuations to simulate one of the many factors in the oral environment has been common in many tracer penetration, marginal gap and bond strength lab oratory tests. Temperature changes used have rarely been substantiated with temperature measurements made in vivo and vary considerably between report s. Justification and standardization of regimen are required. Data, sources and study selection: An assessment of reports describing temp erature changes of teeth in vivo is followed by an analysis of 130 studies of laboratory thermal cycling of teeth by 99 first authors selected from 25 journals. A clinically relevant thermal cycling regimen was derived from t he in vivo information, and is suggested as a benchmark standard. Conclusions: Variation of regimens used was large, making comparison of rep orts difficult. Reports of testing the effects of thermal cycling were ofte n contradictory, but generally leakage increased with thermal stress, altho ugh it has never been demonstrated that cyclic testing is relevant to clini cal failures. However, should this be done, the standard cyclic regimen def ined is: 35 degrees C (28 s), 15 degrees C (2 s), 35 degrees C (28 s), 45 d egrees C (2 s). No evidence of the number of cycles likely to be experience d in vivo was found and this requires investigation, but a provisional esti mate of approximately 10 000 cycles per year is suggested. Thermal stressin g of restoration interfaces is only of value when the initial bond is alrea dy known to be reliable. This is not the case for most current restorative materials. (C) 1999 Elsevier Science Ltd. All rights reserved.