title: Comparison of Internal Adaptation in Class II Bulk-fill Composite Restorations Using Micro-CT.
abstract: OBJECTIVE
  This study compared the internal adaptation of bulk-fill composite restorations in class II cavities and explored the relationship between internal adaptation and polymerization shrinkage or stress.
  
  
  METHODS
  Standardized mesio-occluso-distal cavities were prepared in 40 extracted human third molars and randomly divided into five groups (n=8). After having been applied by total-etch XP bond (Dentsply Caulk, Milford, DE, USA) and light curing, the teeth were restored with the following resin composites: group 1, Filtek Z350 (3M ESPE, St. Paul, MN, USA); group 2, SDR (Dentsply Caulk, Milford, DE, USA) + Z350; group 3, Venus Bulk Fill (Heraeus Kulzer, Dormagen, Germany) + Z350; group 4, Tetric N-Ceram Bulk Fill (Ivoclar Vivadent, Schaan, Liechtenstein); and group 5, SonicFill (Kerr, West Collins, Orange, CA, USA). After thermo-mechanical load cycling, cross-sectional microcomputerized tomography (micro-CT) images were taken. Internal adaptation was measured as imperfect margin percentage (IM%), which was the percentage of defective margin length relative to whole margin length. On the micro-CT images, IM% was measured at five interfaces. Linear polymerization shrinkage (LS) and polymerization shrinkage stress (PS) were measured on each composite with a custom linometer and universal testing machine. To explore the correlation of IM% and LS or PS, the Pearson correlation test was used.
  
  
  RESULTS
  The IM% of the gingival and pulpal cavity floors were inferior to those of the cavity walls. The IM% values of the groups were found to be as follows: group 5 ≤ groups 1 and 4 ≤ group 2 ≤ group 3. The correlation analysis showed that the p value was 0.006 between LS and IM% and 0.003 between PS and IM%, indicating significant correlations (p<0.05).
  
  
  CONCLUSIONS
  Flowable bulk-fill composites had a higher IM% and polymerization shrinkage stress than did packable bulk-fill and hybrid composites. In class II composite restoration, the gingival floor of the proximal box and pulpal floor of the cavity had higher IM% than did the buccal and lingual walls of the proximal box. LS and PS, which were measured under compliance-allowed conditions, were significantly related to internal adaptation.
authors.forename: S H
authors.initials: SH
authors.lastname: Han
authors.forename: S H
authors.initials: SH
authors.lastname: Park
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000379:methods*; D017220:Dentin-Bonding Agents; D006801:Humans; D066298:In Vitro Techniques; D055115:Light-Curing of Dental Adhesives; D008964:Molar, Third; D058105:Polymerization; D011897:Random Allocation; D013499:Surface Properties; D055114:X-Ray Microtomography
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; C000614714:SDR composite; C000613185:SonicFill; C121818:Tetric ceram; C532387:XP-Bond; C533204:filtek Z350