Long-term survival of endodontically treated molars without crown coverage: a retrospective cohort study

Teeth are weakened after endodontic treatment and should, ideally, be crowned, especially posterior teeth. However, this is not always possible. Information about the longevity of endodontically treated teeth without crown coverage may assist in selecting appropriate treatment modalities.

The aims of this cohort study were to evaluate the survival rate for endodontically treated molars without crown coverage and to identify possible related factors.

A total of 220 endodontically treated permanent molar teeth in 203 subjects on a waiting list for fixed prosthodontic treatment at the Faculty of Dentistry-Mahidol University, Thailand, were included. Follow-up data were derived from a clinical examination and review of the dental record and radiographs. Subjects were not included in the study if teeth had provisional crowns, definitive restorations with cuspal coverage, or with dowel and core and/or crown restorations. The outcome evaluated was defined as a failure if there were negative findings in the condition of a tooth that required a restoration, tooth repair, or extraction. Tooth loss due to endodontic and periodontal reasons was excluded. The independent variables assessed were patient age, gender, location (maxilla or mandible), the existence of an opposing dentition and adjacent teeth, remaining tooth structure, and types of restorative material. Kaplan-Meier analysis with a 95% confidence level was used to calculate the survival probability, and a log-rank test was used to determine whether significant differences existed.

Overall survival rates of endodontically treated molars without crowns at 1, 2, and 5 years were 96%, 88%, and 36%, respectively. With greater amounts of coronal tooth structure remaining, the survival probability increased. Molar teeth with maximum tooth structure remaining after endodontic treatment had a survival rate of 78% at 5 years. Restorations with direct composite had a better survival rate than conventional amalgam and reinforced zinc oxide and eugenol with polymethacrylate restorations.

Within the limitations of this study, the amount of remaining tooth structure and types of restorative material have significant association with the longevity of endodontically treated molars without crown coverage.