title: Laboratory mechanical parameters of composite resins and their relation to fractures and wear in clinical trials-A systematic review.
abstract: To evaluate a range of mechanical parameters of composite resins and compare the data to the frequency of fractures and wear in clinical studies.
  
  
  
  Based on a search of PubMed and SCOPUS, clinical studies on posterior composite restorations were investigated with regard to bias by two independent reviewers using Cochrane Collaboration's tool for assessing risk of bias in randomized trials. The target variables were chipping and/or fracture, loss of anatomical form (wear) and a combination of both (summary clinical index). These outcomes were modelled by time and material in a linear mixed effect model including random study and experiment effects. The laboratory data from one test institute were used: flexural strength, flexural modulus, compressive strength, and fracture toughness (all after 24-h storage in distilled water). For some materials flexural strength data after aging in water/saliva/ethanol were available. Besides calculating correlations between clinical and laboratory outcomes, we explored whether a model including a laboratory predictor dichotomized at a cut-off value better predicted a clinical outcome than a linear model.
  
  
  
  A total of 74 clinical experiments from 45 studies were included involving 31 materials for which laboratory data were also available. A weak positive correlation between fracture toughness and clinical fractures was found (Spearman rho=0.34, p=0.11) in addition to a moderate and statistically significant correlation between flexural strength and clinical wear (Spearman rho=0.46, p=0.01). When excluding those studies with "high" risk of bias (n=18), the correlations were generally weaker with no statistically significant correlation. For aging in ethanol, a very strong correlation was found between flexural strength decrease and clinical index, but this finding was based on only 7 materials (Spearman rho=0.96, p=0.0001). Prediction was not consistently improved with cutoff values.
  
  
  
  Correlations between clinical and laboratory outcomes were moderately positive with few significant results, fracture toughness being correlated with clinical fractures and flexural strength with clinical wear. Whether artificial aging enhances the prognostic value needs further investigations.
authors.affiliation: R&D, Ivoclar Vivadent AG, Preclinical Research, Schaan, Liechtenstein. Electronic address: siegward.heintze@ivoclarvivadent.com.
authors.forename: Siegward D
authors.initials: SD
authors.lastname: Heintze
authors.affiliation: Department of Operative Dentistry and Periodontology, University Hospital, Ludwig-Maximilian-University, Munich, Germany.
authors.forename: Nicoleta
authors.initials: N
authors.lastname: Ilie
authors.affiliation: Department of Operative Dentistry and Periodontology, University Hospital, Ludwig-Maximilian-University, Munich, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Hickel
authors.affiliation: Department of Restorative Dentistry, State University of Ponta Grossa, Brazil.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Reis
authors.affiliation: Department of Restorative Dentistry, State University of Ponta Grossa, Brazil.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Loguercio
authors.affiliation: Division of Biostatistics, Institute for Social and Preventive Medicine, University Hospital Lausanne, Switzerland.
authors.forename: Valentin
authors.initials: V
authors.lastname: Rousson
mesh_terms: D002986:Clinical Trials as Topic; D003188:Composite Resins; D019245:Compressive Strength; D019232:Dental Restoration Failure; D008422:Materials Testing; D018583:Pliability; D013314:Stress, Mechanical; D057085:Tooth Wear
chemical_list: D003188:Composite Resins
keywords: Artificial aging; Chipping; Clinical; Composite resin; Compressive strength; Diametric tensile strength; Flexural modulus; Flexural strength; Fracture toughness; Material fracture