Prevention of demineralisation by addition of chlorhexidine in the adhesive procedure of composite resins assessed with an artificial mouth model

Objective
Aim of the study was to investigate the antibacterial and antiproteolytic effect of chlorhexidine (CHX) when added in the adhesive procedure, at baseline, after biological loading and after 6- or 12-month storage in distilled water or in artificial saliva.
Materials & Methods
The study consisted of two parts: biological loading of restorations in a bacterial caries model (n=60 teeth) and μTBS at baseline, after biological loading and after storage (n=2979 sticks). Following groups were formed: i) Control group (CTRL), 3-step adhesive Adper Scotchbond™ Multipurpose, 3M ESPE, ii) 2% CHX as dentine pre-treatment (DENT), iii) 0.1% CHX in primer (PRIM), iv) 0.1% CHX in bonding (BOND), v) 2-step adhesive Peak® Universal Bond with 0.2% CHX (PEAK). PRIM and BOND were fabricated on the basis of the 3-step adhesive used. Class V composite restorations were loaded in caries model with S. mutans according to a 10-day biological protocol. Demineralisation was evaluated with fluorescence microscopy and marginal analysis was performed with SEM. For μTBS (Syndicad TC-550), dentine-composite sticks with 0.46 mm2 adhesive interface were fabricated and tested at baseline, after 2-day caries model, after 6- and 12-month storage in distilled water or artificial saliva. Fracture mode analysis followed and exemplary sticks were evaluated under SEM.
Results
None of the CHX adhesives inhibited secondary caries formation but 2% CHX dentine pre-treatment (DENT) managed to limit marginal gap formation in enamel (p<0.05). Bond strength of CHX adhesives at baseline was worse compared to the CTRL (p<0.05) and decreased significantly after caries model (p<0.05). Only PRIM exhibited same μTBS values after 12-month storage in saliva, compared to baseline.

Conclusions
2% as dentine pre-treatment inhibited marginal degradation at enamel margins, but no CHX adhesive protected composite restorations against secondary caries. 0.1% CHX in primer protected bond strength degradation after 12 months in artificial saliva, exhibiting a potential antiproteolytic effect.