A biofilm-based aging model for testing degradation of dental adhesive microtensile bond strength

Abstract

The objective of this work was to develop a short-term, clinically simulative, biofilm-based aging/storage model for lab testing of newer dental adhesives in order to predict their long-term performance. To do this we tested the hypothesis that 15 days of biofilm challenge with cariogenic bacterial species, Streptococcus mutans (SM) and Streptococcus sobrinus (SS), would produce similar or a greater reduction in microtensile bond strength (μTBS) of dental adhesives as compared to a standard 6 months of water storage (WS). Thirty-one molars were flattened to dentin, restored using Optibond-FL adhesive and Z-100 dental composite, sectioned and trimmed into four dumbbell-shaped specimens and randomly distributed according to aging conditions (n=31): A) Water storage for 6 months, B) Water storage for 5.5 months + S. mutans-biofilm challenge for 15 days, C) S. mutans-biofilm challenge for 15 days and D) S. sobrinus-biofilm challenge for 15 days. Specimens were gripped centrally with respect to the test axis with a nongluing passive gripping device. Microtensile bond strength testing was performed using a Zwick Material Testing Machine at a crosshead speed of 1 mm/min and failure modes were classified using light microscopy. Mixed model ANOVA and Weibull regression analysis revealed that the type of storage condition significantly affected the microtensile bond strength (p<0.0001). Mean microtensile bond strength observed within group A (49.69 ± 15.53MPa) was significantly higher than those in groups B (19.26 ± 6.26MPa), C (19.92 ± 5.86MPa) and D (23.58 ± 7.88MPa). Also, microtensile bond strength obtained with group D was significantly greater than that with groups B and C, while no difference was seen between vi the latter two groups. Chi-square statistical analysis indicated that specimens from groups B (74.2%), C (83.9%) and D (80.6%) were more likely to have cohesive failures in dentin than specimens from group A (54.8%). Within the limitations of the study, it can be concluded that 15 days of Streptococcus mutans-and Streptococcus sobrinus-based biofilm challenge produced more reduction in microtensile bond strength of dental adhesive than 6 months of water storage and appear to be a promising in vitro accelerated aging model.

The effect of aging methods on the fracture toughness and physical stability of an oxirane/acrylate, ormocer, and Bis-GMA-based resin composites

“…After that, they were placed in a six wells tissue culture plate (Falcon 353046, Corning Inc.) and kept at 37 o C. This BHI medium was then added and supplemented with 0.5% sucrose to promote the establishment of a biofilm on the composite sticks within each well for 24 hours. The (BHI) growth medium was changed every day for the 15 days [39] resulting in a thick adapted biofilm layer [ Figure 4]. Three additional specimens from each composite material were fabricated and immersed in BHI for 15 days.…”

“…The type of solvent and storage medium affect the rate of penetration of the solvent through the material. Water storage is considered the standard and recommended type of solvent by the International Organization for Standardization (ISO 37]) for aging simulation (Indrani, Cook [38], Jain [39]). Ferracane et al (1990) found that a solution of 75% of ethanol/ 25% water significantly improved the uptake of the solvent compared to water alone and this finding was verified in another study (Ferracane and Condon [19], Ferracane [15]).…”

“…mutans. However, other species such as S. subrinus and Actinomyces viscosus were tested and showed similar metabolic activity (Jain [39], Beyth, Domb [49], Hahnel, Muhlbauer Furthermore, monomers leach out from resin composite materials, affecting the expression and growth of cariogenic bacteria (Ferracane and Condon [19]). Hensel et al…”

“…In this study, a single species Streptococcus mutans biofilm was used due to its known effect on the resin composite materials and for the simplicity of this aging method composite adhesives compared to 6 months of water storage ( Jain [39]).…”

“…Jain[39], Beyth, Bahir[21]). Nedeljkovic et al 2017, has looked into the effect of a single species Streptococcus mutans vs multi-species biofilm on surface roughness and topography of two different resin composite materials.…”