| Objective: The objective of this study is to investigate theinfluence of the pulsed Nd:YAG laser on the bond strength ofenamel-resin and dentin-resin . The clinical use of Nd:YAGlaser in operative dentistry was evaluated.Methods: Part one: The influence of the pulsed Nd:YAGlaser on the bond strength of enamel-resin: Thirty-two recentlyextracted human normal bicuspid teeth were randomly dividedinto A,B,C and D groups according to substrate and the type oftreatment performed, eight teeth in every group. Those teeththat were caries-, crunch-, and fracture-free, were stored in NSat 4℃. The buccal surface was flattened by a water-cooleddiamond disc . Then the teeth were embedded in acrylic resinwith the buccal surface exposed. A standard smear layer wasprepared according to the routine technique, using 240-grit,400-grit and 600 -grit abrasive paper orderly.Group A: The adhesive system (Prime & Bond NT, Dentsply)was applied after the procedure of being etched by 35%phosphoric acid for 30 seconds, washed for 10 seconds anddried. A layer of the adhesive was applied as indicated bymanufacture and photocured for 20 seconds.Group B: The enamel surface was irradiated with Nd: YAG(50mj,15pps) laser and the same procedure followed as groupA except etching enamel with phosphoric acid .Group C: AdperTM promptTM (3M,USA) was applied asindicated by manufacture.Group D: Irradiation of enamel surface with Nd: YAG laser(50mj,15pps) was followed by the use of the adhesive as ingroup C.Samples were mounted in an appropriate mold composed ofstainless , with a shape of an inverted truncated cuboid 3×3×6mm. Incremental insertion of composite resin was performedby using a spatula in several increments, with each onephotocured for 40 s . Specimens were immersed in NS at 37℃for 24 hours. Subsequently, share bond strength tests wereperformed in a universal testing machine under 1mm/minconstant speed. The result of SBS were recorded. All statisticsof SBS was analysed with one-way ANOVA and q-test byusing SPSS11.5 software package.Part two:The influence of the pulsed Nd:YAG laser on thebond strength of dentin-resin: Forty-eight human bicuspid teeth,which had been recently extracted for orthodontic reasons,were selected. Those teeth that were caries-, crunch-, andfracture-free, were stored in NS at 4℃. The buccal surface wasflattened by a water-cooled diamond disc . So the dentinsurface was exposed. A standard smear layer was prepared ,according to the routine technique, by using 240-grit, 400-gritand 600-grit abrasive paper orderly. Samples were divided intosix groups of eight teeth each, according to the substrate andthe type of treatment performed:Group E: Prime & Bond NT (Dentsply) as indicated bymanufacture was applied.Group F: Irradiation of dentin surface with pulsed Nd: YAGlaser(50mj,15pps) was followed by the use of Prime & BondNT ( Dentsply ) as in group E.Group G: The same procedure as in group B, without thefinal photocuring procedure after adhesive system, wasfollowed by irradiation with Nd:YAG laser(50mj,15pps).Group H: Prime & Bond NT( Dentsply) was applied asindicated by manufacture.Group I: Irradiation of dentin surface with pulsed Nd:YAGlaser(50mj,15pps) was followed by the use of Prime & BondNT( Dentsply) as in group H.Group J: The same procedure as in group H, without thefinal photocuring procedure after adhesive system, wasfollowed by irradiation with Nd:YAG laser(50mj,15pps).Samples were mounted in an appropriate mold as describedbefore. Incremental insertion of composite resin was performedusing a spatula in several increments, each one was photocuredfor 40 seconds with a photocuring apparatus. Specimens wereimmersed in NS for 24 hours at 37℃. Subsequently, sharebond strength test were performed in a universal testingmachine under 1mm/min constant speed. The result of SBSwere recorded. All statistics of SBS was analysed with one-wayANOVA and q-test by using SPSS11.5 software package.Results: 1.Part one: The mean values of share bondstrength of groups were as follows: group A 14.59±1.68Mpa, group B 4.10±0.68Mpa, group C 12.39±2.15 Mpa,group D 10.62±1.14Mpa. The mean value of group A wasstatistically higher than group B, C and D (p<0.05). The meanvalue of group C was statistically higher than group B and D(p<0.05). And the mean value of group D was statisticallyhigher than group B (p<0.05).2.Part two: The mean values of share bond strength ofgroups was as follows: group E 6.47±0.82Mpa, group F 6.00±1.10Mpa, group G 5.86±0.92Mpa, group H 6.73±1.11Mpa,group I 9.64±2.08Mpa, group J 6.63±0.90Mpa. The meanvalue of group I is significantly higher than group E, F, G, Hand J (p<0.05). But significant differences were not foundamong any of tested group E, F, G, H and J (p>0.05).3.SEM examination of interface cross section: Sectionof group A showed that resin tags, which were resulted fromthe penetration of adhesive into spaces left by selectivedissolution of hydroxyapatite crystals among enamelrods ,were about 20μm long. The composite resin of A wasbonded closely to the enamel. Section of group B showed thatthe resin tags was short. The composite resin of B was notclosely bonded to the enamel. Section of group C showed thatthe resin tags was short. However, the resin was closely bondedto the enamel. Section of group D showed that there was fusionof surface enamel ,which was about 20~25μm thick, and resinwas closely bonded to the enamel. Section of group E showedthat resin tags was not found and the dentinal tubules lined upin order. Section of group F and I showed that the fusion ofdentin and the closing of dentinal tubules. The resin of group Iwas closely bonded to dentin. Section of group G, H and Jshowed that resin wasn't closely bonded to the dentin and therewas a chink between them. The resin tags of 5μm long wasfound in group J.Conclusion: 1.When Prime & Bond NT (Dentsply) wasapplied after the use of 35% phosphoric acid, the highest sharebond strength of resin-enamel was achieved.2.In this study, when the adhesive system of Prime & BondNT (Dentsply) was applied to the human enamel, the pulsedNd:YAG laser's irradiation couldn't get a higher share bondstrength of enamel-resin. So the laser's irradiation couldn't takethe place of phosphoric acid and still needed to be followed bythe etching of phosphoric acid.3. When the adhesive system of AdperTM promptTM(3M,USA) was applied to the human enamel, a share bondstrength, which was higher than the groups of dentin, wasachieved.4. In this study, when the adhesive system of AdperTMpromptTM (3M,USA) was applied to the human enamel, thepulsed Nd:YAG laser's irradiation could decrease the sharebond strength of resin-enamel.
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