Much variation exists in the practice of dentistry with regard to diagnosis of caries and recommendations for treatment. This is a particular problem with respect to the replacement of restorations, with responsible factors related to both the patient and the dentist. The aim of this paper is to look at factors, exclusive of clinical data, that may explain why there is so much variation in the practice of dentistry, and specifically pertaining to replacement of restorations. Due to the paucity of studies related specifically to dentists, findings from physician studies will be presented. No studies are available that compare variation in medical and dental practices, but since both professions deal with the provision of health care and function in similar circumstances, comparisons are arguably generalizable between the two groups. Development of clinical judgment will be explored based on dental training experiences, and two explanatory models of practice pattern variation will be discussed--the dentist as a self-fulfilling practitioner and the dentist as the patient's agent. Along with these models, the matter of uncertainty in clinical practice and the development of routines will also be discussed in light of explaining variations.