To evaluate the chemical, mechanical, and biological properties of modern composite surface sealers (CSS) having different compositions.
The CSS products tested were Biscover LV (BC), Durafinish (DF), G-Coat Plus (GC), and Permaseal (PS). The tests performed were: (A): degree of conversion (DC%) by ATR-FTIR spectroscopy; (B): thickness of O 2 -inhibition layer by transmission optical microscopy; (C): surface hardness, 10 min after irradiation and following 1 week water storage, employing a Vickers indenter (VHN); (D): color (Δ E *) and gloss changes (ΔGU) after toothbrush abrasion, using L * a * b * colorimetry and glossimetry; (E): accelerated wear (GC,PS only) by an OHSU wear simulator plus 3D profilometric analysis, and (F): cytotoxicity testing of aqueous CSS eluents on human gingival fibroblast cultures employing the methyl- 3 H thymidine DNA labeling method. Statistical analyses included 1-way (A, B, Δ E *, ΔGU) and 2-way (C, F) ANOVAs, plus Tukey post hoc tests. Student’s t -test was used to evaluate the results of the accelerated wear test ( α = 0.05 for all).
The rankings of the statistical significant differences were: (A) PS (64.9) > DF,BC,GC (56.1–53.9) DC%; (B) DF,PS (12.3,9.8) > GC,BC (5.2,4.8) μm; (C): GC (37.6) > BC,DF (32.6,31.1) > PS (26.6) VHN (10 min/dry) and BC,DF (29.3,28.7) > GC(26.5) > PS(21.6) VHN (1w/water), with no significant material/storage condition interaction; (D): no differences were found among GC,DF,BC,PS (0.67–1.11) Δ E *, with all values within the visually acceptable range and PS,BC (32.8,29.4) > GC,DF (19.4,12.9) ΔGU; (E): no differences were found between GC and PS in volume loss (0.10,0.11 mm 3 ), maximum (113.9,130.5 μm) and mean wear depths (30.3,27.5 μm); (F): at 1% v/v concentration, DF showed toxicity (23% vital cells vs 95–102% for others). However, at 5% v/v concentration DF (0%) and BC (9%) were the most toxic, whereas GC (58%) and PS (56%) showed moderate toxicity.
Important chemical, mechanical, and biological properties exist among the CSS tested, which may affect their clinical performance.
Although significant developments have been made in the field of direct restorative materials, there are still problems related to their clinical performance over time. The most frequently encountered problems are marginal debonding, abrasion, wear, and surface defects (roughness, porosity, etc.) that lead to loss of gloss, marginal discoloration, and staining . To overcome these problems, composite surface sealers (CSS) were introduced in the mid-70s, to preserve surface quality of traditional resin composites, which contained quartz filler particles.
The first generation of CSS was comprised of unfilled, transparent light-cured liquid resins, placed on cured resin composite surfaces. Use of resinous coatings improved surface gloss, color stability, wear resistance, and marginal leakage . However, important problems were associated with use of these products, such as formation of a non-uniform layer, film thinning, cracking, and debonding, thus creating a rough texture, vulnerable to staining and discoloration . The CSS materials reappeared in early 90s, as protective coatings for glass-ionomer restorations, until completion of the slow acid–base setting reaction. Resinous coatings significantly improved the mechanical properties of glass-ionomers being more efficient than protective varnishes containing polar solvents . This efficiency was even greater when applied to resin modified glass-ionomer materials, because of the copolymerization capacity through the resinous phase .
A new generation of CSS has been introduced in order to improve marginal and surface defects of contemporary light-cured materials, which possess increased free-radical yield when polymerized using high-intensity curing units . According to manufacturer-supplied data, modern CSSs are unfilled or low-filled resin composites containing cross-linkable monomers, with a minimum extent of oxygen inhibition and color stable catalysts. These products are recommended for application on direct or indirect resin composite and glass-ionomer restorations . However, there is a lack of data regarding mechanical, chemical, and biological properties of these materials to support their clinical use.
The purpose of the present study was to evaluate the extent of monomer conversion, thickness of oxygen inhibition, hardness, changes in color and gloss, wear, and cytotoxicity of a variety of commercially available CSS products. The null hypothesis was that no statistically significant differences exist among the CSS in the properties tested.
Materials and methods
The CSS products tested are presented in Table 1 . Selection included the most representative products, according to the composition given by their manufacturers: BC is based on a pentacrylate monomer, DF on methyl methacrylate and acrylate monomers, GC on methyl methacrylate and phosphate-functionalized methacrylate monomers, and PS on conventional dimethacrylate monomers. Two of the products with different monomer composition (DF, GC) are filled with silica nanofillers, whereas the rest are unfilled.
|Biscover LV (0700001300)||BC||Dipentaerythritol pentaarylate ester, Ethanol, Initiators||Bisco, Inc., Schaumburg, IL, USA|
|DuraFinish (07206)||DF||Acrylates, Methyl methacrylate, Nanofillers, Initiators||Parkell, Inc., Edgewood, NY, USA|
|G-Coat Plus (0019241)||GC||Methyl methacrylate, Methacryloyloxydecyl dihydrogen phosphate, Silanated colloidal SiO 2 , Initiators, Stabilizers||GC Corporation, Tokyo, Japan|
|PermaSeal (B86P7)||PS||Bisphenol-A glycidyl ether dimethacrylate, Triethyleneglycol dimethacrylate, Initiators||Ultradent Products, Inc., S. Jordan, UT, USA|
Degree of conversion
The degree of conversion (DC%) of the products was evaluated using micro-attenuated total reflectance Fourier transform infrared spectroscopy (micro-ATR FTIR). Spectra acquisition were performed on an FTIR spectrometer (Spectrum GX, Perkin-Elmer, Beaconsfield, UK) equipped with a micro-ATR cell (Golden Gate MK II, Specac, Smyrna, GA, USA), operated under the following conditions: 4000–600 cm −1 range, 4 cm −1 resolution, 20 scans co-addition, 2 mm type IIIa diamond minicrystal of a single internal reflection, ZnSe lenses and 2 μm depth of analysis at 1000 cm −1 . Disk-shape specimens (8 mm diameter, 1.5 mm height, n = 5 per material) were fabricated using opaque rubber molds after being exposed for 20 s to a halogen light-curing unit (Elipar Trilight, ESPE, Seefeld, Germany), operated in standard irradiation mode (750 mW/cm 2 irradiance) as measured with the curing radiometer of the device. The specimens were polymerized between transparent matrix strips and 100-μm thick microscopic cover slips, to avoid oxygen inhibition. Uncured specimens from each CSS were used as individual controls. The directly irradiated surfaces of each specimen were pressed against the diamond reflective element using a flat metal anvil (10 mm in diameter), and spectra were acquired 10 min after setting. The DC% of the directly irradiated surfaces was calculated employing the two band technique, by using the net peak absorbance areas of C C stretching vibrations at 1638 cm −1 as analytical band and the aromatic C⋯C stretching vibrations at 1605 cm −1 as reference band according to the equation:
DC % = 100 × 1 − AM ( C ⋯ C ) × AP ( C C ) AM ( C C ) × AP ( C ⋯ C )