Evaluation of microleakage in class-II bulk-fill composite restorations

Abstract

Background/purpose: Despite the clinical appeal of restoring deep class II cavities in single increment using bulk-fill resin composite, sealing of bulk-filled composite restorations is a concern. This study evaluated interfacial adaptation of bulk-fill composite restoration to axial wall and gingival floor of class II cavities using cross-polarization optical coherence tomography (CP-OCT).

Materials and methods: Box-shaped class II cavities were prepared in extracted molars and divided into three groups (n = 7) according to adhesive used; Clearfil SE Bond 2 (SE2), Tetric-N Bond Self-Etch (TSE) or Tetric-N Bond Universal (TNU). All adhesives were applied in self-etch mode and according to manufacturers' recommendation. Then, preparations were bulk-filled with Filtek Bulk Fill Posterior Restorative resin composite and immersed in a contrast agent. Tomographic images of axial wall and gingival floor of each restoration were obtained by CP-OCT (IVS-300, Santec) with a central wavelength of 1330 nm and were imported to an image analysis software to quantify microleakage.

Results: Mann-Whitney U test showed statistically significant difference in microleakage percentage between the groups at both axial wall and gingival floor (p < 0.05). SE2 group had the lowest percentage of microleakage (p < 0.05), as only few cross-sections showed areas of reflections from contrast agent penetrating into axial wall (8.23 ± 6.8) and gingival floor (7.07 ± 4.1), followed by TNU group (18.13 ± 12.9 axially and 30.61 ± 11.9 gingivally). Microleakage was frequently observed at the axial wall and gingival floor of TSE group, showing the highest percentages of 25.50 ± 12.5 and 36.97 ± 10.2, respectively (p < 0.05).

Conclusion: All tested groups exhibited different extent of interfacial microleakage, however, two-step self-etch adhesive yielded superior adaptation in comparison to one-step self-etch adhesive and universal adhesive.

Keywords: Adhesive; Bulk-filled; Composite-resins; Microleakage; Optical coherence tomography.

Figure 1

Schematic diagram of study methodology. (a) Cavity preparation and matrix placement. (b) Restoration and specimens grouping according to the applied adhesive (c) Water storage for 24 h. (d) Silver nitrate infiltration. (e) CP-OCT imaging of axial wall and gingival floor.

Figure 2

Representative optical coherence tomography (OCT) images and binary images of the axial wall obtained from all groups (a) The axial wall (dotted box) of this cross-section from SE2 group demonstrated no increase in signal intensity with no bright cluster formations, indicating good interfacial sealing. Applying the binarization process to the cropped axial wall in the same cross-section did not detect any target pixels. Scattered pixels in the corresponding binary image (solid line box) indicate absence of penetrating silver nitrate particles in this cross-section. (b) B-scan of a selected interface from TNU specimen showing some areas of silver nitrate uptake at the axial wall appearing as bright scatters in CP-OCT image and black pixels in the binary image (arrows), which indicate interfacial microleakage. (c) The axial wall in this B-scan of the TSE specimen is showing diffuse clusters of bright pixels extending throughout the wall, indicating loss of seal as correlated with target pixels in binarized image of the cropped interface (solid line box). C: Composite; D: Dentin.

Figure 3

Cross sectional optical coherence tomography (OCT) images of the gingival floor for selected specimens with corresponding binary images of the interface (solid line boxes). (a) Cross-sectional B-scan of a SE2 specimen showing sealed gingival floor with binary image devoid of dark pixels representing microleakage. Entrapped voids in composite could be observed in this OCT image as pointed by the bold arrow. (b) Interfacial area from TNU specimen without high signal intensity at gingival floor or marked target pixels during the binarization process. (c) OCT image of TSE specimen with high reflection from silver particles detected at the interface. Blank arrows point toward the same location in OCT image and cropped interfacial area after applying binarization process to mark the target pixels. Bold arrow points at defect introduced into composite. C: Composite; D: Dentin.