Cuspal movement and microleakage in premolar teeth restored with posterior filling materials of varying reported volumetric shrinkage values

Objectives To investigate the effect of polymerisation shrinkage stress of various aesthetic posterior filling materials on cuspal movement and cervical gingival microleakage of mesio-occlusal-distal (MOD) restorations placed in increments in extracted maxillary premolar teeth. Methods Forty sound extracted upper premolar teeth were subjected to standardised preparation of a large MOD cavity. One curing regimen was used and each posterior filling material was placed in eight increments with the appropriate bonding system. A twin channel deflection-measuring gauge allowed a measurement of individual cusp deflections at each stage of polymerisation. Restored teeth were thermocycled before immersion in 0.2% basic fuchsin dye for 24 h. After sagittal sectioning of the restored teeth in a mesio-distal plane, the sectioned restorations were examined to assess cervical gingival microleakage. Results In general, cuspal deflection measurements were dependent upon the constituent monomers and the associated shrinkage on curing, with significantly increased cuspal movement (P<0.05) being recorded for Z100 (20.03±2.92 μm) compared with Filtek Z250™ (12.34±2.18 μm), P60 (13.41±4.43 μm) and Admira (11.2±2.58 μm). No significant differences were identified between the posterior filling materials when the cervical gingival microleakage scores were examined. Conclusions It would appear that a reduction in the manufacturersʹ reported volumetric polymerisation shrinkage for Z100 (4.0%) to below 3% for Filtek Z250™, P60 and Admira, resulted in a significant reduction in the associated cuspal strain on the MOD cavity. The diluent triethyleneglycol dimethacrylate (TEGDMA) increases the polymerisation shrinkage of Z100 resin-based composite due to an increased concentration of carbon-to-carbon double bonds (C6-point double bond; length half of m-dashC). The replacement of TEGDMA with urethane dimethacrylate (UDMA) and Bis-EMA in Filtek Z250™ and P60, decreases the polymerisation shrinkage stress by increasing the cross-linking of polymer networks. However, no group was identified as producing less gingival microleakage at the cervical dentine cavosurface margin when the cavities were sectioned and examined, regardless of the reported variations in cuspal strain and the associated volumetric polymerisation shrinkage values.