title: The effect of mechanical loading on the cusp defection of premolars restored with direct and indirect techniques.
abstract: OBJECTIVE
  This study assessed the effect of fatigue load cycling on human premolars restored with MOD restorations (direct and indirect approaches) on cuspal defection, compared to intact teeth (unprepared) and unrestored teeth with an inlay preparation.
  
  
  METHODS
  MOD inlay preparations were performed on sixty premolars with their roots embedded in acrylic resin. These teeth were divided into six groups (n = 10): (1) intact teeth; (2) unrestored and prepared teeth; (3) teeth restored with direct composite resin; (4) teeth restored with an indirect composite resin; (5) teeth restored with injected ceramic inlays (IPS Empress 2 (Ivoclar); (6) teeth restored with CAD/CAM inlays made of feldspathic ceramic (Vita Mark II). All of the indirect restorations were adhesively cemented. Strain-gauges were bonded to the buccal and lingual surfaces of the specimens. Compressive axial loading of 100N was applied on the occlusal face of the specimens to measure the cuspal deflection (microstrain) under compressive loading. These measurements were obtained before and after mechanical cycling (1 Hz, 37°C, 100,000x).
  
  
  RESULTS
  Comparing the results obtained before and after fatiguing, the cuspal defection increased only in the CAD/CAM approach. The prepared tooth group had the highest cuspal defection, before and after mechanical cycling.
  
  
  CONCLUSIONS
  The evaluated restoring approaches decrease the cuspal defection, consequently appear to improve the cuspal reinforcement.
authors.affiliation: PhD Graduate Student, PhD Graduate Program, Prosthodontic unit, Science and Technology Institute, Sao Paulo State University, S P, Brazil.
authors.forename: Sandra Costa
authors.initials: SC
authors.lastname: Zamboni
authors.affiliation: Adjunct Professor,, Department of Dental Materials and Prosthodontics, Sao Paulo State University, SP, Brazil.
authors.forename: Lafayette
authors.initials: L
authors.lastname: Nogueira
authors.affiliation: Professor, Department of Dental Materials and Prosthodontics, Sao Paulo State University, SP, Brazil.
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Bottino
authors.affiliation: Professor, Department of Dental Materials, Piracicaba Dental School, University of Campinas, SP, Brazil.
authors.forename: Lourenço Correr
authors.initials: LC
authors.lastname: Sobrinho
authors.affiliation: Associate Professor, MSD/PhD Graduate Program, Prosthodontic Unit, Federal University of Santa Maria, RS, Brazil.
authors.forename: Luiz Felipe
authors.initials: LF
authors.lastname: Valandro
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D000538:Aluminum Silicates / Q000737:chemistry; D001641:Bicuspid / Q000473:pathology*; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D017076:Computer-Aided Design; D003737:Dental Cavity Preparation / Q000145:classification; D003764:Dental Materials / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry; D003793:Dental Restoration, Permanent / Q000145:classification*; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D007284:Inlays; D055115:Light-Curing of Dental Adhesives / Q000295:instrumentation; D018020:Lithium Compounds / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D017680:Potassium Compounds / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013696:Temperature; D019228:Tooth Crown / Q000473:pathology*
chemical_list: D000538:Aluminum Silicates; D003188:Composite Resins; D003764:Dental Materials; C118557:Empress 2; D018020:Lithium Compounds; D011109:Polymethacrylic Acids; D017680:Potassium Compounds; C462240:RelyX ARC; D019279:Resin Cements; C084018:Scotchbond Multi-Purpose; C477352:Sinfony composite resin; C533204:filtek Z350; D003776:Dental Porcelain; C016447:feldspar; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C023506:Glass ceramics