Study On The Effect Of Polyamidoamine Pretreatment On The Durability Of Resin-dentin Bonds

Objective:Secondary caries at the bonded interface and hybrid layer degradation are two important contributors to the poor resin–dentin bond durability.Pretretment with long-term antimicrobial and anti-proteolytic activities are in demand for eliminating bacteria-induced secondary caries and preventing hybrid layers from degradation.The objectives of the present study were to examine the long-term antimicrobial effect and anti-proteolytic potential of poly（amidoamine）dendrimers with amino terminal groups（PAMAM-NH₂）cavity cleanser,which providing new insights into improving the durability of resinous dentin bonding method.Methods:The cytotoxicity of PAMAM-NH₂ was evaluated by the Cell Counting Kit-8（CCK-8）assay.Micro-tensile bond strength and adhesive permeability of bonded interface were employed to assess whether the PAMAM-NH₂ cavity cleanser adversely affected resin–dentin bonding.Adsorption tests by attenuated total reflectance–infrared（ATR-IR）spectroscopy and confocal laser scanning microscopy（CLSM）were first performed to evaluate whether the PAMAM-NH₂ cavity cleanser had binding capacity to dentin surface to fulfill its relatively long-term antimicrobial and anti-proteolytic effects.For antibacterial testing,Streptococcus mutans,Actinomyces naeslundii,and Enterococcus faecalis were grown on dentin surfaces,prior to the application of cavity cleanser.Colony-forming unit（CFU）counts and live/dead bacterial staining were performed to assess antibacterial effects.Gelatinolytic activity within the hybrid layers was directly detected by in situ zymography.Results:CCK-8 assay showed that PAMAM-NH₂ had low cytotoxicity on human dental pulp cells（HDPCs）and L929.Furthermore,PAMAM-NH₂ pretreatment did not adversely affect resin–dentin bonding because it did not decrease micro-tensile strength and adhesive permeability.Adsorption tests demonstrated that the binding capacity of PAMAM-NH₂ on dentin surface was much stronger than that of 2%chlorhexidine（CHX）because its binding was strong enough to resist phosphate-buffered saline（PBS）washing.Antibacterial testing indicated that PAMAM-NH₂ significantly inhibited bacteria grown on the dentin discs as compared with the control group（p<0.05）,which was comparable with the antibacterial activity of 2%CHX（p>0.05）.Hybrid layers conditioned with PAMAM-NH₂ showed significant decrease in gelatin activity as compared with the control group.Conclusions:PAMAM-NH₂ cavity cleanser could provide simultaneous long-term antimicrobial and anti-proteolytic activities for eliminating secondary caries that caused by bacteria and degradation of hybris layers naked collagen by MMPs,which are crucial for the maintenance of resin–dentin bond durability.