The Experimental Study On Enamel Bonding Interface Following Application Of The Nd: YAG Laser

Objectives:The aim of this study was to investigate the effects of Nd:YAG laser etching on enamel bonding interface,by comparing the thickness of hybrid layer and the length of resin tags after acid etching and laser etching under different conditions.Methods:36 adolescent healthy permanent premolars were collected,and their buccal faces were made flat,prior to polishing,then randomly divided them into seven groups from A to F.Groups A,B,C were conditioned respectively with 35%phosphoric acid for 30s,45s and 60s;groups D,E,F were exposed to 0.75W,1.00W and 1.25W power with a pulsed Nd:YAG laser energy for 20s.And then,the specimens were immediately followed by application of the 1g/L Rhodamine B/Single Bond adhesive with a brush to enamel surface for 30s,blow 5s with light wind and light-cured for 20s.A 2-mm layer of P60 composite resin was applied over the adhesive system layers,light-cured for 40s. Subsequently,each specimen was sliced transversally with a slow speed diamond disk with water coolant,producing approximately 1-mm thick samples then polished them.After that,observe and measure the thickness of hybrid layer and the length of resin tags on enamel bonding interface with LSCM.Collect data for statistical analysis.Results:1.Enamel bonding interface with laser etching achieved thicker hybrid layer than that with phosphoric acid etching(P＜0.05).And the maximum hybridization formation was achieved when the enamel surface was conditioned with 1.25w,15Hz Nd:YAG laser,it was about 29μm, twice of that in groups with phosphoric acid etching(15μm). 2.Enamel bonding interface with laser etching achieved longer resin tags than that with phosphoric acid etching(P＜0.05).And the maximum length formation was achieved when the enamel surface was conditioned with 1.25w,15Hz Nd:YAG laser,it was about 77μm,2.5 times of that in groups with phosphoric acid etching(32μm).Conclusions:1.Compared with 35%phosphoric acid etching,the bonding system can infiltrate well into enamel bonding interface to achieve thicker hybrid layer and longer resin tags in groups with pulsed Nd:YAG laser etching.2.The bonding system can infiltrate effectively into enamel bonding surface in groups with 1.25w,15Hz pulsed Nd:YAG laser etching.