title: Effect of restoration volume on stresses in a mandibular molar: a finite element study.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  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.
authors.affiliation: Professor, Department of Biomedical Engineering, School of Engineering, Virginia Commonwealth University, Richmond, Va. Electronic address: jwayne@vcu.edu.
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Wayne
authors.affiliation: Graduate student, Department of Biomedical Engineering, School of Engineering, Virginia Commonwealth University, Richmond, Va.
authors.forename: Ruchi
authors.initials: R
authors.lastname: Chande
authors.affiliation: Graduate student, Department of Biomedical Engineering, School of Engineering, Virginia Commonwealth University, Richmond, Va.
authors.forename: H Christian
authors.initials: HC
authors.lastname: Porter
authors.affiliation: Associate Professor, Department of Prosthodontics, School of Dentistry, Virginia Commonwealth University, Richmond, Va.
authors.forename: Charles
authors.initials: C
authors.lastname: Janus
mesh_terms: D001696:Biomechanical Phenomena; D001732:Bite Force; D003198:Computer Simulation; D003723:Dental Amalgam / Q000737:chemistry*; D003743:Dental Enamel / Q000473:pathology; D003782:Dental Pulp / Q000473:pathology; D003793:Dental Restoration, Permanent / Q000145:classification*; D003804:Dentin / Q000473:pathology; D055119:Elastic Modulus; D020342:Finite Element Analysis; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008954:Models, Biological; D008963:Molar / Q000473:pathology*; D013314:Stress, Mechanical; D013499:Surface Properties; D014057:Tomography, X-Ray Computed / Q000379:methods; D019237:Tooth Cervix / Q000473:pathology; D019228:Tooth Crown / Q000473:pathology
chemical_list: D003723:Dental Amalgam