Resin/Dentin Interface Degradation is Dependent on Restorative Material and MMP-Inhibition

Huang, Bo (1. Faculty of Dentistry, University of Toronto; 2. IBBME, University of Toronto)
Cvitkovitch, Dennis G (1. Faculty of Dentistry, University of Toronto; 2. IBBME, University of Toronto)
Santerre, Paul J (1. Faculty of Dentistry, University of Toronto; 2. IBBME, University of Toronto)
Finer, Yoav (1. Faculty of Dentistry, University of Toronto; 2. IBBME, University of Toronto)

Introduction

Resin-based restorations are the most popular restorative materials in dentistry. However, the invasion of cariogenic bacteria (Streptococcus mutans) into tooth/restoration interface leads to the development of secondary caries which limits restoration's longevity.1 This biological interface is characterized as a 3-D interlocking network created by resin polymer penetration and entanglement of exposed collagen fibrils in the tooth structure (dentin).2 Resin-based adhesive systems are applied in between of dentin/resin to facilitate the polymer penetration. A completely sealed interface is considered to be the first defense for preventing secondary caries. To date, however, no commercial dentin bonding system is capable of achieving a hermetic seal between the tooth/resin margins. In addition, host-derived matrix metalloproteinase (MMPs) caused tooth collagen collapse2 and human salivary esterase catalyzed degradation of resin monomers crack the interfacial margin and allows bacteria penetration subsequently.3 So, in this study, MMPs inhibitor (Galardin), different dental materials and adhesive systems are investigated to study the stability of the tooth-restoration interface.

Materials and Methods

Standardized resin-dentin specimens (3x3x6mm) were prepared from traditional composite (Z250, 3M) or PMCR (Dyract-eXtra, DENTSPLY), bonded to human dentin using total-etch (TE, Scotchbond MP) or self-etch (SE, Easybond) adhesives. TE was prepared with or without the application of 0.2mM galardin (G) for 30 sec at the dentinal-interface.4 In total, there are 6 groups: TE/G-Z (total-etch with galardin +Z250), TE-Z (total-etch+Z250 ), SE-Z (self etch +Z250), TE/G-D (total-etch with galardin +Dyract), TE-D (total-etch+Dyract) and SE-D (self-etch+Dyract). Specimens (N=3/group) were incubated in phosphate-buffer (PBS) or simulated human salivary esterases (SHSE) media (37oC, pH=7.0) for up to 180 days, then suspended in continuous media biofilm fermenter cultivating biofilms of Streptococcus mutans UA159 for 3- days (1/4-THYE+10mM sucrose, 37oC, pH=7.0, D=0.6). Bacterial penetration and viability along interfaces was assessed by confocal laser scanning microscopy with biomarkers (Live/Dead, Life technology), reconstructed by software (Imaris, Bitplane) and statistically analyzed using an ANOVA and Scheffe multiple comparison analysis (p<0.05).

Results

Regardless of incubation media, MMP inhibition, restorative material, and mode of adhesion, longer incubation periods resulted in increased interfacial penetration and bacterial cell count (p<0.05). Bacterial penetration was increased with SHSE incubation vs. PBS with both traditional composite and PMCR boned interfaces (p<0.05), confirming the contribution of salivary esterases activities on the degradation of resin-dentin interfaces, regardless of adhesion mode. The application of MMP-inhibitor (galardin) to TE interfacial dentin after the etching step in total-etch adhesive application enhanced marginal biostability, as indicated by the reduced interfacial bacterial ingress and reduced bacterial biofilm cell-count (p<0.05), providing evidence to the contributing role of MMPs in marginal degradation. And, in the current study, SE interfaces bonded to traditional composites (SE-Z) showed an increased in interfacial bacterial cell-count vs. their TE counterparts (TE-Z) and their PMCR counterparts (SE-D) (p<0.05). TE interfaces bonded to traditional composite (TE-Z) showed reduced bacterial biofilm cell-count vs. their PMCR counterparts (TE-D) (p<0.05). Further, only SE interfaces bonded to traditional composites showed an increase in interfacial bacterial biofilms after incubation in SHSE vs. PBS after 180-days (p<0.05).

Discussion and Conclusion

These observations indicate that the degradation of the restoration-tooth interface is a continuous multi-factorial dependent process that could ultimately result in the restoration’s failure. However, different combination of restorative materials and adhesive systems create various stability of tooth-restoration interface. The optimal combination may slow down the bacterial penetration. In addition, inhibiting MMPs activity along the tooth-restoration interface has promising effect on reducing bacterial invasion, further, preventing secondary caries formation.

Figure 1. Merged image of 3 days S. mutans biofilm along dentin/composite interface (Cyto 9 stained live cell green

Figure 2. The bars mean significant difference, each color represents the different comparison group. All groups show increased bacterial penetration for longer incubation periods in both PBS and SHSE (P<0.05). Galardin-treated group showed reduced interfacial bacterial ingression (P<0.05).

Figure 3. The bars mean significant difference, each color represents the different comparison group. PMCR groups showed reduced bacterial ingress vs. composite after 90 days in PBS and 180 days in PBS

Acknowledgements

Grant: NIH R01DE021385; CIHR MOP115113

References

1. Borges MAP, Matos IC, Mendes LC, Gomes AS, Miranda MS. Degradation of polymeric restorative materials subjected to a high caries challenge. Dental Materials 2010, 27:244-252 2. Spencer, P.; Singh, V.; Sene, F.: Adhesive/dentin interface: the weak link in the composite restoration. Annals of biomedical engineering 2010, 38, 1989-2003 3. Finer, Y.; Santerre, J.: Salivary esterase activity and its association with the biodegradation of dental composites. Journal of Dental Research 2004, 83, 22 4. Breschi, L.; Martin, P; Pashley, D. H.: Use of a specific MMP-inhibitor (galardin) for preservation of hybrid layer. Dent Mater 2010, 26, 571-8

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