title: Influence of restorative technique on the biomechanical behavior of endodontically treated maxillary premolars. Part II: strain measurement and stress distribution.
abstract: BACKGROUND
  Unresolved controversy exists concerning the preferred cavity design and restorative technique used to restore endodontically treated maxillary premolars to minimize strain and improve stress distribution under occlusal load.
  
  
  OBJECTIVE
  The purpose of this study was to analyze the influence of cavity design and restorative material on strain measurement and stress distribution in maxillary premolars under occlusal loading conditions, and correlate these influences with the failure modes analyzed in Part I.
  
  
  METHODS
  For the strain gauge test, 21 additional specimens were prepared as described in Part 1 of this study (n=3). Two strain gauges were fixed on the buccal (B) and palatal (P) cusps of each specimen with cyanoacrylate adhesive. The specimens were submitted to continuous axial compression loading at a speed of 0.5 mm/min, using a 6-mm sphere, to a maximum limit of 150 N in a universal testing machine. Total strain values were obtained by combining the B and P cusp strain values. These values were submitted to 2-way ANOVA and the Dunnet test (alpha=.05). For finite element analyses, 7 numerical 2-D models were generated: MODd, direct mesio-occlusal-distal preparation; MODi, indirect mesio-occlusal-distal preparation; AM, MODd restored with amalgam; CR, MODd restored with composite resin; LPR, MODi restored with laboratory-processed composite resin; and LGC, MODi restored with leucite-reinforced glass ceramic; each corresponding to 1 of the experimental groups tested in Part I of this study. The models were analyzed with finite element software, using the von Mises criteria for stress distribution analysis.
  
  
  RESULTS
  With the strain gauge test, MODd, MODi, and AM groups showed significantly higher strain values than the CR, LPR, and LGC. Finite element analyses revealed that tooth structure removal and the type of restorative material altered the stress distribution pattern. The MODd, MODi, AM, and LPR models showed higher stress concentration within the tooth structure.
  
  
  CONCLUSIONS
  The specimens with adhesive restorations were shown to behave in a manner similar to the biomechanical behavior of healthy teeth, while the behavior of those restored with amalgam restorations was more like that observed for teeth with nonrestored cavity preparations. These results directly correlate with the fracture mode results obtained in Part I of this study.
authors.affiliation: Biomechanical Group, Dentistry and Dental Materials, School of Dentistry, Federal University of Uberlandia, Minas Gerais, Brazil.
authors.forename: Paulo Vinicius
authors.initials: PV
authors.lastname: Soares
authors.forename: Paulo Cesar Freitas
authors.initials: PC
authors.lastname: Santos-Filho
authors.forename: Henner Alberto
authors.initials: HA
authors.lastname: Gomide
authors.forename: Cleudmar Amaral
authors.initials: CA
authors.lastname: Araujo
authors.forename: Luis Roberto Marcondes
authors.initials: LR
authors.lastname: Martins
authors.forename: Carlos Jose
authors.initials: CJ
authors.lastname: Soares
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D001641:Bicuspid / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D001732:Bite Force; D003188:Composite Resins / Q000737:chemistry; D003300:Copper / Q000737:chemistry; D003723:Dental Amalgam / Q000737:chemistry; D003737:Dental Cavity Preparation / Q000379:methods*; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000379:methods*; D020342:Finite Element Analysis; D005898:Glass / Q000737:chemistry; D006801:Humans; D008437:Maxilla; D012834:Silver / Q000737:chemistry; D013314:Stress, Mechanical; D014082:Tooth Fractures / Q000503:physiopathology; D019553:Tooth, Nonvital / Q000503:physiopathology*
chemical_list: D000538:Aluminum Silicates; D003188:Composite Resins; D003764:Dental Materials; C474035:Filtek Supreme; C075815:IPS-Empress ceramic; D003776:Dental Porcelain; C078519:leucite; D012834:Silver; D003300:Copper; D003723:Dental Amalgam; C092423:Permite C