The influence of approximal restoration extension on the development of secondary caries

To evaluate whether occlusoproximal restorations with cervical margins apical to the cemento-enamel junction (CEJ) are more prone to failure than restorations with margins coronal to the CEJ, in particular failure due to secondary caries.

A method was developed for scoring cervical margin extension on bitewings, and validated in vitro. Records from patients with at least one occlusoproximal restoration replaced due to secondary caries were selected from an existing database. Cervical margins of approximal restoration sites were scored on bitewings in relation to the CEJ (supra vs. sub CEJ). For all restorations dates of placement, replacement and reason for failure were recorded. Survival times were calculated and Cox-regression analysis was applied to assess influence of selected variables on survival of restorations: extension of cervical margins, number of restored surfaces, restoration material and age of the patient.

Records of 84 patients with 1912 restoration sites were examined, 655 failed; 399 supra CEJ and 256 sub CEJ. 257 restorations failed because of secondary caries. Restorations ending below the CEJ showed significantly increased risk for failure (HR=1.28, p=0.020), however, no relation with secondary caries was found (p=0.130). Amalgam restorations showed decreased risk for secondary caries (HR=0.51, p<0.001).

Occlusoproximal restorations with cervical margins apical to the CEJ do not fail more often due to secondary caries. However, those restorations did show larger risk of failure overall compared to restorations with margins coronal to the CEJ. Resin composite restorations showed increased risk for secondary caries compared to amalgam restorations.

Within the limitations of this study, no association was found clinically between extension of restoration margins below the CEJ and the occurrence of secondary caries.