title: Influence of proximal box elevation on the marginal quality and fracture behavior of root-filled molars restored with CAD/CAM ceramic or composite onlays.
abstract: OBJECTIVE
  This study investigated the influence of proximal box elevation (PBE) with composite resin when applied to deep proximal defects in root-filled molars with mesio-occluso-distal (MOD) cavities, which were subsequently restored with computer-aided designed/computer-aided manufacturing (CAD/CAM) ceramic or composite restorations.
  
  
  METHODS
  Root canal treatment was performed on 48 human mandibular molars. Standardized MOD cavities were prepared with the distal box located 2 mm below the cemento-enamel junction (CEJ). The teeth were randomly assigned to one of four experimental groups (n = 12). In groups G1 and G2, the distal proximal box was elevated up to the level of the CEJ with composite resin (PBE). No elevation was performed in the remaining two groups (G3, G4). CAD/CAM restorations were fabricated with feldspathic ceramic (Vita Mark II, CER) in groups G1 (PBE-CER) and G3 (CER) or with resin nano-ceramic blocks (Lava Ultimate, LAV) in groups G2 (PBE-LAV) and G4 (LAV). Replicas were taken before and after thermomechanical loading (TML; 1.2 Mio cycles; 49 N; 3,000 thermocycles between 50 °C and 5 °C). Following TML, load was applied until failure. Fracture analysis was performed under a stereomicroscope (×16). Marginal quality before and after TML (tooth restoration, composite restoration) was evaluated using scanning electron microscopy (×200).
  
  
  RESULTS
  After TML, lower percentages of continuous margins were observed in groups G1-G3 compared with pre-TML assessments; however, the differences were not statistically significant. For group G4-LAV, the marginal quality after TML was significantly better than in any other group. The highest mean fracture value was recorded for group G4. No significant difference was found for this value between the groups with PBE compared with the groups without PBE, regardless of the material used. The specimens restored with ceramic onlays exhibited fractures that were mainly restricted to the restoration while, in teeth restored with composite onlays, the percentage of catastrophic failures (fractures beyond bone level) was increased.
  
  
  CONCLUSIONS
  PBE had no impact on either the marginal integrity or the fracture behavior of root canal-treated mandibular molars restored with feldspathic ceramic onlays. CAD/CAM-fabricated composite onlays were more favorable than ceramic onlays in terms of both marginal quality and fracture resistance, particularly in specimens without PBE.
  
  
  CONCLUSIONS
  Composite onlays with or without PBE may be a viable approach for the restoration of root-filled molars with subgingival MOD cavities.
authors.affiliation: Department of Periodontology, Endodontology, and Cariology, University of Basel, Hebelstrasse 3, 4056, Basel, Switzerland, Irina.Ilgenstein@unibas.ch.
authors.forename: Irina
authors.initials: I
authors.lastname: Ilgenstein
authors.forename: Nicola U
authors.initials: NU
authors.lastname: Zitzmann
authors.forename: Julia
authors.initials: J
authors.lastname: Bühler
authors.forename: Florian J
authors.initials: FJ
authors.lastname: Wegehaupt
authors.forename: Thomas
authors.initials: T
authors.lastname: Attin
authors.forename: Roland
authors.initials: R
authors.lastname: Weiger
authors.forename: Gabriel
authors.initials: G
authors.lastname: Krastl
mesh_terms: D000134:Acid Etching, Dental; D002516:Ceramics / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry*; D017076:Computer-Aided Design; D003731:Dental Caries / Q000628:therapy*; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D006801:Humans; D066298:In Vitro Techniques; D007284:Inlays; D008334:Mandible; D008963:Molar / Q000601:surgery*; D012387:Root Canal Filling Materials; D012390:Root Canal Therapy
chemical_list: D003188:Composite Resins; D012387:Root Canal Filling Materials