Evaluation of Streptococcus Mutans on Dental Composite Resins

Objective:   Over the past decade, the clinical placement of dental composites for posterior restorations has dramatically increased as amalgam use has declined.  Dental composites have evolved both chemically and physically; however, they still have some drawbacks, including polymerization shrinkage, potential failure at resin-dentin interfaces leading to secondary caries, and relatively high coefficient of thermal expansion.  Recently, attention has shifted towards deleterious effects of dental biofilms on the potential accelerated degradation of resin-based composites

Methods: Composite discs were formed in Teflon molds and light-activated according to the manufacturers' recommended procedures. Cured specimens were then wet-polished with 3 mm diamond paste to replicate clinical polishing procedures.  Specimens were then exposed to Streptococcus mutans (biofilm-forming strain of this organism (UA159-BS480)) and bacterial adhesion was quantified using confocal scanning laser microscopy (CLSM) after period of 1, 4, 7, 11, 13, and 15 days.  Additionally, stylus profilometry, AFM, and SEM were used to analysis composite degradation.

Dental Composite	AFM Initial Ra (nm)	AFM Final Ra (nm)	Profilometry Initial Ra (nm)	Profilometry Final Ra (nm)
Filtek Supreme Ultra	10.5	29.5	10.0	47.3
Premise	22.3	37.9	22.0	58.9
Kalore	35.1	74.9	37.9	214.8
Esthet-X	77.0	276.9	44.5	368.5

 Results: CLSM revealed that surfaces exhibited an increase in biofilm thickness (from 2-4 µm at 1 day to 5-30 µm at 13 days) and the onset of concavities indicating foci of microbial attack and potential sites of material degradation.  Surface roughness analysis showed that all composite surfaces increased in R_a indicating biofilm-driven degradation.   Conclusions: Dental composites provide a novel substrate in the oral environment that is colonized by complex microbial communities which can further accelerate degradation and promote secondary caries.  By characterizing biofilm-enhanced degradation may lead to the development of new composites with increased restoration lifetime.  This research was supported through NIH/NIDCR Grant NIH - R56 DE021387-01.