A simple method to estimate restoration volume as a possible predictor for tooth fracture☆

Abstract 

Statement of problem

Many dentists cite the fracture risk posed by a large existing restoration as a primary reason for their decision to place a full-coverage restoration. However, there is poor agreement among dentists as to when restoration placement is necessary because of the inability to make objective measurements of restoration size.

Purpose

The purpose of this study was to compare a new method to estimate restoration volumes in posterior teeth with analytically determined volumes.

Material and methods

True restoration volume proportion (RVP) was determined for 96 melamine typodont teeth: 24 each of maxillary second premolar, mandibular second premolar, maxillary first molar, and mandibular first molar. Each group of 24 was subdivided into 3 groups to receive an O, MO, or MOD amalgam preparation design. Each preparation design was further subdivided into 4 groups of increasingly larger size. The density of amalgam used was calculated according to ANSI/ADA Specification 1. The teeth were weighed before and after restoration with amalgam. Restoration weight was calculated, and the density of amalgam was used to calculate restoration volume. A liquid pycnometer was used to calculate coronal volume after sectioning the anatomic crown from the root horizontally at the cementoenamel junction. True RVP was calculated by dividing restoration volume by coronal volume. An occlusal photograph and a bitewing radiograph were made of each restored tooth to provide 2 perpendicular views. Each image was digitized, and software was used to measure the percentage of the anatomic crown restored with amalgam. Estimated RVP was calculated by multiplying the percentage of the anatomic crown restored from the 2 views together. Pearson correlation coefficients were used to compare estimated RVP with true RVP.

Results

The Pearson correlation coefficient of true RVP with estimated RVP was 0.97 overall (P≤.0001). Coefficients for comparisons stratified by tooth type, restoration type, and restoration size groups were all greater than 0.90 (P≤.0001).

Conclusion

Within the limitations of this study, the high correlation between estimated RVP and true RVP indicated that estimated RVP was an accurate method to quantify the relative volume of restorative material in coronal tooth structure. The fact that it can be done in a nondestructive manner makes it attractive for clinical situations.