title: Fracture resistance of endodontically treated maxillary premolars restored with CAD/CAM ceramic inlays.
abstract: BACKGROUND
  Endodontically treated posterior teeth are more likely to fracture compared to posterior teeth with vital pulps. Reinforcement with an extracoronal restoration that covers the cusps is the most commonly recommended method for reducing the risk of fracture. It is not known whether bonded intracoronal restorations without cuspal coverage will reduce the risk of fracture.
  
  
  OBJECTIVE
  The aim of this in vitro study was to investigate whether reinforcement of endodontically treated premolars with MOD preparations could be achieved by insertion of bonded CAD/CAM ceramic inlays.
  
  
  METHODS
  Forty-five extracted maxillary premolars were equally distributed among 3 groups (END, CER, CTR). In group END (n=15), root canals were enlarged with a rotary NiTi system and obturated with heat-softened gutta-percha around a plastic carrier (Thermafil). After filling of the endodontic access cavities with autopolymerizing composite resin (Luxacore), standardized MOD cavity preparations were made and CAD/CAM ceramic inlays (CEREC) were fabricated and then bonded to the teeth with composite resin (Tetric) and an adhesive system (Syntac Classic). In group CER (n=15), teeth without endodontic treatment were restored with bonded inlays (CEREC). Sound premolars served as controls (group CTR, n=15). Teeth were then thermal cycled (1445 cycles, dwell time: 30 seconds, 5 degrees /55 degrees C). An eccentric load was applied on the buccal incline of the palatal cusp in a universal testing machine until cusp fracture (N). Fracture load was evaluated with the Mann-Whitney test, and type of fracture, with a chi-square analysis (alpha=.05). The type of fracture was determined by visual inspection: type I - supragingival fracture within the palatal cusp; type II - fracture below cemento-enamel junction of palatal cusp; and type III - fracture of palatal cusp and central portion of the tooth exposing the root canal cavity.
  
  
  RESULTS
  No significant difference was found among the 3 groups with respect to load required for fracture. Mean fracture load +/- SD was recorded as follows: 291.6 +/- 113.7 N for group END, 363.2 +/- 140.3 N for group CER, and 296.5 +/- 170.5 N for group CTR. Regarding fracture modes, significantly more teeth from group END exhibited fractures of type III and II compared with control specimens.
  
  
  CONCLUSIONS
  Teeth restored with bonded CAD/CAM ceramic inlays (CEREC) fractured with a significantly higher number of severe fractures compared to the control group.
authors.affiliation: Department of Operative Dentistry, PreventiveDentistry and Periodontology, University of Gottingen, Robert-Koch-Strasse 40, 37075 Gottingen, Germany. christian.hannig@med.uni-goettingen.de
authors.forename: Christian
authors.initials: C
authors.lastname: Hannig
authors.forename: Christoph
authors.initials: C
authors.lastname: Westphal
authors.forename: Klaus
authors.initials: K
authors.lastname: Becker
authors.forename: Thomas
authors.initials: T
authors.lastname: Attin
mesh_terms: D001641:Bicuspid / Q000503:physiopathology*; D002516:Ceramics / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry; D017076:Computer-Aided Design; D001840:Dental Bonding; D003737:Dental Cavity Preparation / Q000379:methods; D003743:Dental Enamel / Q000293:injuries; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis; D017220:Dentin-Bonding Agents / Q000737:chemistry; D006171:Gutta-Percha / Q000737:chemistry; D006801:Humans; D007284:Inlays; D019279:Resin Cements / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation; D012390:Root Canal Therapy; D013314:Stress, Mechanical; D019237:Tooth Cervix / Q000293:injuries; D019228:Tooth Crown / Q000293:injuries; D014082:Tooth Fractures / Q000503:physiopathology*; D019553:Tooth, Nonvital / Q000503:physiopathology*
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; D019279:Resin Cements; D003776:Dental Porcelain; D006171:Gutta-Percha