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

Effect of restoration volume on stresses in a mandibular molar: a finite element study

STATEMENT OF PROBLEM

There can be significant disagreement among dentists when planning treatment for a tooth with a failing medium-to-large--sized restoration. The clinician must determine whether the restoration should be replaced or treated with a crown, which covers and protects the remaining weakened tooth structure during function.

PURPOSE

The purpose of this study was to evaluate the stresses generated in different sized amalgam restorations via a computational modeling approach and reveal whether a predictable pattern emerges.

MATERIAL AND METHODS

A computer tomography scan was performed of an extracted mandibular first molar, and the resulting images were imported into a medical imaging software package for tissue segmentation. The software was used to separate the enamel, dentin, and pulp cavity through density thresholding and surface rendering. These tissue structures then were imported into 3-dimensional computer-aided design software in which material properties appropriate to the tissues in the model were assigned. A static finite element analysis was conducted to investigate the stresses that result from normal occlusal forces. Five models were analyzed, 1 with no restoration and 4 with increasingly larger restoration volume proportions: a normal-sized tooth, a small-sized restoration, 2 medium-sized restorations, and 1 large restoration as determined from bitewing radiographs and occlusal surface digital photographs.

RESULTS

The resulting von Mises stresses for dentin-enamel of the loaded portion of the tooth grew progressively greater as the size of the restoration increased. The average stress in the normal, unrestored tooth was 4.13 MPa, whereas the smallest restoration size increased this stress to 5.52 MPa. The largest restoration had a dentin-enamel stress of 6.47 MPa. A linear correlation existed between restoration size and dentin-enamel stress, with an R(2) of 0.97.

CONCLUSIONS

A larger restoration volume proportion resulted in higher dentin-enamel stresses under static loading. A comparison of the von Mises stresses to the yield strengths of the materials revealed a relationship between a tooth's restoration volume proportion and the potential for failure, although factors other than restoration volume proportion may also impact the stresses generated in moderate-sized restorations.

Restoration of noncarious tooth defects by dentists in The Dental Practice-Based Research Network

BACKGROUND

The authors conducted a study to quantify the reasons for restoring noncarious tooth defects (NCTDs) by dentists in The Dental Practice-Based Research Network (DPBRN) and to assess the tooth, patient and dentist characteristics associated with those reasons.

METHODS

Data were collected by 178 DPBRN dentists regarding the placement of 1,301 consecutive restorations owing to NCTDs. Information gathered included the main clinical reason, other than dental caries, for restoration of previously unrestored permanent tooth surfaces; characteristics of patients who received treatment; dentists' and dental practices' characteristics; teeth and surfaces restored; and restorative materials used.

RESULTS

Dentists most often placed restorations to treat lesions caused by abrasion, abfraction or erosion (AAE) (46 percent) and tooth fracture (31 percent). Patients 41 years or older received restorations mainly because of AAE (P < .001). Premolars and anterior teeth were restored mostly owing to AAE; molars were restored mostly owing to tooth fracture (P < .001). Dentists used directly placed resin-based composite (RBC) largely to restore AAE lesions and fractured teeth (P < .001).

CONCLUSIONS

Among DPBRN practices, AAE and tooth fracture were the main reasons for restoring noncarious tooth surfaces. Pre-molars and anterior teeth of patients 41 years and older are most likely to receive restorations owing to AAE; molars are most likely to receive restorations owing to tooth fracture. Dentists restored both types of NCTDs most often with RBC.