An In Vitro Study Of Er:YAG Laser Debonding Of All-ceramic Veneers

Objective:The aim of this study was to compare the debonding time of IPS e.max CAD lithium disilicate glass-ceramic veneers and cubic stabilized zirconia veneers in different thickness using erbium:yttrium-aluminum-garnet?Er:YAG?laser and evaluate the effect of Er:YAG laser on the surface topography of the veneers,the underlying tooth and the functional groups of resin cement.Materials and Methods:A total of eighteen maxillary first premolar teeth were collected and veneer prepared,then made seventy-two veneers of A₂-colour by Computer aided design and manufacture?CAD/CAM?System.The veneers were divided into six groups according to different thicknesses and materials of the restoration?n=3?:e.max HT with 0.5 mm thickness,e.max HT with 1.0 mm thickness,e.max LT with 0.5 mm thickness,e.max LT with 1.0 mm thickness,cubic stabilized zirconia with 0.5 mm thickness,and cubic stabilized zirconia with 1.0 mm thickness.Three veneers of each group were cemented to prepared premolar with RelyX?Veneer cement and then stored in saline solution at room temperature for 7 days.All veneers were debonded with Er:YAG laser.The Er:YAG laser parameters were:a pulse duration of 50?s at 100 mJ/pulse,10 Hz repetition rate pulse,water-air ratio of 6:2,H14 handpiece,1.1 mm diameter fiber tip irradiation with contact application mode.The debonding time of all-ceramic veneers of all groups was recorded.Six veneers of each group without Er:YAG laser irradiation used as control groups.The remaining three veneers irradiated with Er:YAG laser and the three veneers debonded in experiment one were together used as experimental groups.The laser parameters and irradiation time were the same as experiment one.In addition,three tooth surfaces after Er:YAG laser debonding in experiment one were randomly selected as the experimental group,and three tooth surfaces without Er:YAG laser irradiation served as the control group.The scanning electron microscopy?SEM?observation and X-ray diffraction?XRD?analysis were performed on the veneers of the experimental group and the control group.The tooth surfaces of the experimental group and the control group were observed by SEM.The influence of Er:YAG laser on surface topography of all-ceramic veneers and tooth was analyzed.The resin cement not irradiated with Er:YAG laser was used as control group?n=3?.The residual resin cement on the tooth surfaces of the experiment one was used as an experimental group?n=3?.Both groups were detected by fourier transform infrared spectroscopy and the effect of the Er:YAG laser irradiation on the functional group of resin cement was analyzed.Results:When the veneer thickness was 0.5 mm,the average debonding time of e.max LT group was the longest?21.00±3.00 s??P<0.05?,e.max HT group?15.33±2.08 s?and CSZ group?12.00±1.00s?was no significant difference?P>0.05?.When the veneer thickness was 1.0mm,the longest debonding time was71.00±3.61 s in e.max LT group?P<0.05?,CSZ group?51.00±3.60 s?and e.max HT group?47.33±2.51 s?with the similar time?P>0.05?.The debonding time of 1.0 mm-thick groups were longer than 0.5 mm-thick groups?P<0.05?.No cracks and crater structure were found in SEM observation of veneers after Er:YAG laser irradiation.Teeth surface was covered with bonding cement with no signs of ablation or damage of the enamel.XRD of veneers showed that the crystal phase of Er:YAG laser irradiation group and the control group are basically the same.The FTIR of the resin cement showed that the debonding of veneers by the Er:YAG laser reduced the functional groups such as-OH,-CH₃,-CH₂ and C=O in the resin cement,and C-O-C increase.Conclusion:Er:YAG laser can completely debond lithium disilicate glass-ceramic veneers and cubic stabilized zirconia veneers.The debonding time depends on the materials and thickness of the veneer itself.The lower translucent porcelain veneers?e.max LT?had a longer debonding time.The longer time required for the thicker veneers.Er:YAG laser does not damage the morphology and topography of the veneer surface or change the crystal of the veneer,nor does it damage the morphology and topography of the tooth.According to the FTIR results,the reduction of the functional groups of-OH,-CH₃,-CH₂ and C=O,which may be related to the influence of Er:YAG laser debonding of all-ceramic veneers.Therefore,Er:YAG laser debonding of all-ceramic veneers is a safe and effective clinical method.