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Purpose: To compare the debonding time of IPS e.max CAD lithium disilicate glass-ceramic veneers in different thickness and transparency using Er:YAG laser, and evaluate the effect of Er:YAG laser on the surface topography of the veneers and the underlying tooth., Methods: A total of twelve maxillary first premolar teeth were collected and prepared, then veneers were made by computer aided design and computer aided manufacture(CAD/CAM) system. The veneers were divided into four groups according to different thicknesses and transparency: e.max HT with 0.5 mm and 1.0 mm thickness, e.max LT with 0.5 mm and 1.0 mm thickness. Three veneers of each group were cemented to prepared premolar with resin cement and then stored in normal saline solution at room temperature for 7 days. All veneers were debonded with Er:YAG laser and the debonding time of all-ceramic veneers of all groups was recorded. Scanning electron microscopy(SEM) observation was performed to detect the surface topography of the veneers and the underlying tooth. SPSS 19.0 software package was used for statistical analysis., Results: The debonding time of 1.0 mm-thick groups were longer than 0.5 mm-thick groups. When the veneer thickness was 0.5 mm, the average debonding time of e.max LT group was longer than e.max HT. Consistent with the finding of 0.5 mm, the longer debonding time was found in the e.max LT group of 1.0mm. 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., Conclusions: Er:YAG laser can completely debond lithium disilicate glass-ceramic veneers, and the debonding time depends on the transparency and thickness of the veneers. The lower translucent porcelain veneers (e.max LT) and thicker ones (1.0 mm-thick) had a longer debonding time. Moreover, Er:YAG laser does not damage the morphology and topography of the veneer and the teeth surface.

Purpose: To compare enamel surface state and operating time following debonding by using 5 different resin removal methods., Methods: Forty healthy human premolars extracted for orthodontic purpose were selected and then divided into 5 groups randomly based on different resin-removal methods, 8 in each group. After regular bonding brackets and debonding, tungsten carbide bur (group A), tungsten carbide bur+silicon particles(group B), corundum bur(group C), corundum bur+silicon particles (group D) and silicon particles (group E) were used respectively to deal with the enamel surfaces. The operating time(T) of each group was recorded. The samples were observed under scanning electron microscope (SEM), and enamel damage index(EDI) was recorded. The scores of EDI were analysed using SPSS 20.0 software package ., Results: The order of EDI was group C>group D>group A >group B>group E, significant difference was found between 5 groups (P<0.05). The order of operating time was group E>group D>group B>group A>group C, significant difference was found between 5 groups (P<0.05)., Conclusions: Using tungsten carbide bur followed by silicon particles to remove residual resin on enamel surface causes less damage to the enamel surface, and requires reasonable time.

Purpose: The aim of this study was to compare if there was any difference in the enamel discoloration after staining when three orthodontic adhesives and 4 enamel clean-up methods were tested., Methods: Three types of orthodontic adhesives were used: chemically cured resin, light-cured resin and resin-modified glass-ionomer cement. A total of 120 human extracted premolars were included. Ten teeth of each orthodontic adhesive were randomly cleaned-up with 1 of 4 different procedures and stained in coffee for 7 days: carbide bur (TC), carbide bur and Sof-Lex polishers (TC＋SL), carbide bur and One Gloss polishers (TC＋OG), carbide bur and PoGo polishers (TC＋PG). Colour measurements were made with Crystaleye dental spectrophotometer at baseline and after storage in a coffee solution for 1 week. Two way ANOVA and Bonferroni test were used for statistical analysis with SPSS 13.0 software package., Results: The colour change values of adhesive materials in the TC group were the greatest. The lowest ΔE* values were obtained from the TC＋SL group. However, there was no significant difference between the TC＋SL and TC＋PG group (P>0.05). The resin-modified glass-ionomer cement group showed the lowest colour differences and chemically cured resin group showed the highest ΔE* values among all orthodontic adhesives (P<0.05)., Conclusions: The colour change of enamel surface is affected by the type of adhesive materials and clean-up procedures.

Purpose: To investigate effects of acid etching, adhesives, brackets and debonding process on tooth color during direct bonding technique., Methods: One hundred freshly extracted premolars were divided into blank control, acid etching, adhesive, acid etching+adhesive and acid etching+adhesive+bracket group. Computerized colorimeter was utilized to evaluate L*, a* and b* of tooth color parameters before treatment, 7 days and 30 days after treatment. SPSS 16.0 software package was utilized for statistical analysis., Results: At 7 day, ΔE** value in all experimental groups were significantly higher than blank control group. ΔE* values of acid etching+adhesive+bracket group, and acid etching group were greater than 3.3, showing that recognizable clinic change was observed, but no significant difference was observed between the 2 groups. At 30 d, for ΔE* value, acid etching+adhesive+bracket group > acid etching group, and acid etching+adhesive group > adhesive group > blank control group. Recognizable clinic change was observed in all experimental groups (ΔE*>3.3)., Conclusions: In fixed orthodontic procedures, acid etching and metal erosion resulting from long time wearing braces are two important factors leading to enamel discoloration, and adhesives removing procedures may also affect tooth discoloration.

Objective: To investigate the bond strengths of customized titanium bracket manufactured by selective laser melting., Methods: Eighty human premolars which had been extracted for orthodontic purpose were collected and divided randomly (by random table) into two groups (customized bracket group and 3M bracket group, 40 molars in each group). The 35% phosphoric acid was used for etching and the brackets were bonded with 3M Unitek bonding adhesive. All bonded specimens were placed in saline for 24 hours at room temperature and were tested on DWD3050 electronic testing machine to determine the shear bond strength and tensile bond strength. After debonding, the adhesive remnant indexes (ARI) were recorded., Results: The shear bond strengths of customized brackets was 6.80 (6.20, 8.32) MPa, which was significantly lower than that of the 3M brackets [10.46 (9.72, 11.48) MPa] (Z = -3.463, P < 0.05). And the tensile bond strengths of customized brackets was (6.93 ± 1.21) MPa, which was significantly higher than that of the 3M brackets [(5.88 ± 1.23) MPa] (t = 2.81, P < 0.05). No significant difference was found in the ARI between two different kinds of the brackets., Conclusions: The shear bond strength and tensile bond strength of both kinds of brackets were enough for clinic application.

Objective: Ceramic brackets debonding by Nd:YAG laser is based on the thermal effect of laser, which may cause injury of the pulp tissue. In this study, the histological changes of pulp tissue that subjected to Nd: YAG laser irradiation with different power and time were observed., Methods: 20 New Zealand rabbits were included in this study. Ceramic brackets were bonded to the 4 incisors as routine. The ceramic brackets of left upper teeth that debonded mechanically were used as control group, while the brackets of right upper, left lower and right lower incisors were debonded by laser with 3 W 3 s (group A), 2 W 5 s (group B) and 5 W 2 s (group C) energies, respectively. The teeth were pulled out at 5 minutes, 1 day, 3 days, 1 week and 1 month after the debonding operations. Slides prepared from the pulp tissues of the debonded teeth were used to evaluate the injury of laser., Results: In comparison with the control group, pulp tissue of teeth that exposed to laser with different energy for 5 minutes showed mild capillary dilation. One day later, group A, B and C showed moderate capillary dilation, and group C also showed moderate infiltration. At 3 days, inflammation was disappeared in group B, whereas capillary dilation was found in group A. Hemorrhage and inflammation cells infiltration were found in group C. At 1 week, alleviation of capillary dilation was found in group A but not in group C. One month later, inflammation disappeared in group A, while pulp tissue in group C showed mild edema and capillary dilation., Conclusion: Nd:YAG laser of high energy may cause injury of the pulp tissue during debonding. Laser energy of 3 W 3 s could effectively debond ceramic brackets without irreversible pulp injury.

Due to the significantly increasing demand of aesthetics during orthodontic treatments, aesthetic brackets have gained popularity in clinic. In general, the current aesthetic brackets are either ceramic brackets or plastic brackets. This article provided a review of the latest information about the aesthetic brackets' materials, designs, and their clinical applications. Although significant improvements have been made in recent years on aesthetic brackets, more laboratory studies and clinical trials are needed to further demonstrate the critical issues of bonding, debonding and recycling to meet their optimal uses in orthodontics.

Purpose: To observe the tooth surface after acid etching and removing of bonding adhesive by two means for polishing., Methods: Thirty extracted premolars for orthodontic purpose were used in this experiment. The brackets were adhered and debonded. Then the premolars were randomly divided into two groups. They were treated by traditional method and silicone particles, and observed by roughness instrument and scanning electronic microscope. The polishing-time and surface roughness value(Ra) were recorded. SPSS13.0 software package was used for paired t test., Results: There was no significant difference in Ra and polishing-time between the two groups (P>0.05). Under SEM, the scratches on tooth surface polished by silicone particles were shallower and thinner., Conclusion: The silicone particles could provide good requirement for tooth polishing after bracket debonding clinically.

Objective: The aim of this study was to investigate the effect of short enamel etching time on bonding strength., Methods: 80 healthy premolars were randomly divided into two equal groups, one was etched for 15 seconds, the other for 60 seconds, after normally bonding Edgewise brackets, the tooth specimen was stored in water at room temperature for 24 hours. An MTS NEW810 100KN testing machine was used to examine the shear force., Results: Although the bonding strength for 15 seconds etching time was weaker than that for 60 seconds, the means of the bonding strength in 15 seconds group reached 5.8625 MPa., Conclusion: Etching for 15 seconds could provide enough bond strength for orthodontic practice. Furthermore, the adhesive remained on tooth after debonding was less by comparison with 60 seconds etching group, therefore brackets could be removed easily and the work efficiency could be increased in clinic by means of 15 seconds etching time.