Reprinting the classic article on USPHS evaluation methods for measuring the clinical research performance of restorative materials

The original article published by Cvar and Ryge in 1971 on the US Public Health Service (USPHS) Guidelines is virtually inaccessible to current scientists, despite its remarkable impact on clinical dental research. The original article described all the pilot studies that led to the choices for the final USPHS guidelines. However, many of the important basic ideas expressed in the original article, such as evaluator calibration, have been overlooked in recent years. Challenges for effective clinical testing of restorative procedures and materials that were emphasized by those authors are even more relevant today. Therefore, it is totally appropriate to republish the original article by Cvar and Ryge in this issue of Clinical Oral Investigations. This preface to the republication of the original article provides key background information and references to contributions by the many now-famous clinical investigators who were involved with pilot studies. In addition, the USPHS recommendations are critically reviewed. Clinical evaluation of restorative procedures requires (a) choices of clinically relevant criteria, (b) assessment using simple nominal scales, (c) calibration of evaluators, (d) two independent evaluations, and (e) nonparametric statistic analysis that recognizes the patient (and not the restoration) as the independent variable. Only portions of those procedures are being preserved in current clinical investigations. USPHS criteria continue in use until today as part of routine clinical evaluation and as components of standards programs such as the ADA acceptance program. However, in addition, USPHS-like criteria have been appended over the years to produce “modified USPHS guidelines.” These additional criteria include parameters such as postoperative sensitivity, fracture, interproximal contact, occlusal contact, and others. The combination of the original and modified USPHS criteria now have been accepted worldwide but are not necessarily uniformly applied. They constitute the foundation for current considerations of further development of clinical assessment methods for dental restorative procedures.