MTBS-Analysis of Class-II Bulk Versus Incremental Fill Resin Composite Restorations

To assess MTBS and failure-mode at cervical interfaces of bulk versus incremental-fill and open-sandwich class-II aged resin-composite restorations.

Method:

Box-only class-II  cavities were prepared in 91 maxillary premolars with gingival-margin placed on each side (1mm above and below CEJ).

84 maxillary premolars were divided according to bonding-technique into total-etch (TE) and self-etch (SE) groups, furtherly subdivided into 6 restorative subgroups (n=7):

Tetric Ceram HB, Ivoclar-Vivadent, used incrementally (group1-TC) and in open-sandwich-technique combined with Tetric Evoflow, Ivoclar-Vivadent, (group2-TC+EF) or Smart Dentin Replacement, Dentsply, (group3-TC+SDR).

Bulk-fill restoratives were SonicFill, Kerr, (group4-SF), Tetric N-Ceram Bulk Fill, Ivoclar-Vivadent (group5-TNC-BF) and Tetric EvoCeram Bulk Fill, Ivoclar-Vivadent (group6-TEC-BF).

In subgroups1-5 Tetric N-Bond, Ivoclar-Vivadent, (TE), and Tetric N-Bond Self-Etch, Ivoclar-Vivadent, (SE) and in subgroup6 Excite F, Ivoclar-Vivadent, (TE) and AdheSE, Ivoclar-Vivadent, (SE) were used.  An additional group (n=7), Filtek P90 Low Shrink Posterior Restorative, 3M ESPE (group7-P90), was used only with its self-etch-bond.

Materials were manipulated according to manufacturers’ instructions, light-cured (20sec, 1600mW/cm²), artificially aged (thermal and occlusal load-cycling), sectioned (two microrods/side) and tested for microtensile bond strength (crosshead-speed=0.5mm/min, Instron-testing-machine). Fracture loads were recorded (Newton) and MTBS-values calculated (MPa). Fractured ends were examined for failure mode.

Result:

Mean MTBS-values were statistically analyzed (Kruskal-Wallis-test and post-hoc Mann-Whitney-U-test, p<0.05) with signifant differences between highest MTBS-value groups at enamel-margins and lowest MTBS-value groups at cementum-margins. In all groups, mean MTBS-values were higher at enamel-margins than at cementum-margins. At enamel-margins, highest MTBS-values were group3-TC+SDR/TE (24.2±SD=9.5), followed by group4-SF/TE (23.8±SD=5.2) and group7-P90 (23.5±SD=4.1), while group6-TEC-BF/TE (10.3±SD=6.6) had lowest. At cementum-margins, highest values were group3-TC+SDR/TE (21.6±SD 16.0), group7-P90 (17.3±SD 9.0) and group4-SF/TE (13.1±SD=4.1), while lowest were group1-TC/SE (6.5±SD=4.4) and group1-TC/TE (7.0±SD=3.2). Most failures were mixed.

Conclusion:

Bulk-fill can provide better cervical interfacial quality than incremental-fill composite-restorations in class-II cavities. When margins are inevitably located in cementum, bulk-fill restorative-materials might be preferable.