Effect of hydroxyapatite based agents on the bonding properties of universal adhesives / 中华口腔医学杂志

Objective: To study the effect of hydroxyapatite (HA) based agents on the bonding properties of universal adhesive with different application modes, and to provide evidence for the use of adhesives after desensitization treatment. Methods: Sixty impacted third molars were extracted and selected (acquired from Department of Oral and Maxillofacial Surgery, College of Stomatology, Xi'an Jiaotong University). Four third molars were used to prepare 1 mm thick dentin disks and treated with 1% citric acid to simulate sensitive tooth models. The dentin surfaces were observed by scanning electron microscope (SEM) after treating with no desensitization (control group), desensitized by HA based toothpaste Biorepair and Dontodent Sensitive respectively (desensitizing toothpaste A group and B group), or HA paste treatment (desensitizing paste group ) (n=2 per group). The remaining teeth were selected to expose the mid-coronal dentin and establish dentin sensitivity models. Then, the specimens were divided into 4 former groups and received corresponding treatment. Each group was randomly divided into 2 subgroups, and intermediately strong universal adhesive (G-Premio Bond) was applied on the desensitized dentin by either etch-and-rinse mode or self-etch mode. Resin-dentin slice specimens (n=4 per subgroup), microtensile specimens (n=20 per subgroup) and slice specimens (n=6 per subgroup) were prepared. The microstructure and nanoleakage of the adhesive interfaces were observed by scanning electron microscopy (SEM). The microtensile strength (bond strength) and fracture mode were tested and recorded. The water permeability of the adhesive interface was observed by laser scanning confocal microscopy (LSCM). Results: SEM showed that desensitizing toothpaste and desensitizing paste could partially or entirely occlude most of the dentin tubules. For the etch-and-rinse mode, the bond strength of specimens treated with toothpaste A [(40.98±4.60) MPa], toothpaste B [(40.89±4.64) MPa] and HA paste [(41.48±3.65) MPa] was significantly higher than that of the control group [(38.58±4.28) MPa] (F=3.89,P<0.05). There was no statistically significant difference in bond strength among the 4 subgroups for self-etch modes (F=0.48,P>0.05). After desensitization, the bond strength of the control group and desensitizing groups in the self-etch mode was significantly higher than that in the etch-and-rinse mode (P<0.05). The overall fracture modes were mixed failure and interfacial failure in the control group and desensitizing groups. SEM showed speckled silver-stained particles deposited along the bottom of the hybrid layer on the bond interface of etch-and-rinse mode, and there were few silver-stained particles deposited on the bond interface of self-etch mode. LSCM showed continuous linear penetration in the hybrid layer of etch-and-rinse mode subgroups and discontinuous linear penetration in the hybrid layer of self-etch mode subgroups. Conclusions: HA based desensitizers have no adverse effect on the bond strength of intermediately strong universal adhesive and show good bonding performance accompanied with the self-etch mode.

Influence of preparation height and cement space on the fit and retention of computer aided design/computer aided manufacturing zirconia crown / 华西口腔医学杂志

OBJECTIVE@#To investigate the effects of preparation height and cement space on the fit and retention of computer aided design (CAD)/computer aided manufacturing (CAM) zirconia crown, and to provide reference for the clinical design and fabrication of CAD/CAM crowns.@*METHODS@#3D printing system was used to fabricate resin abutment teeth with convergence angle of 2° and height of 1-3 mm. The models' optical impressions were collected by the three-shape scanner. Then, the cement spaces were set by Cradle CAD/CAM system at 10-50 μm to create an all-ceramic zirconia crown. The fit of the crowns was measured by using silicone rubber interstitial impression method. The retention of the crowns was measured by pull-off test with uniaxial tensile force after the crown was bonded. The data were analyzed by SPSS 22.0 soft-ware.@*RESULTS@#When the preparation height was fixed, the fitness values of different cement space groups have statistical difference (P0.05). The fitness values of different preparation height groups have no statistical difference (P>0.05), and the retention values of different preparation height groups have statistical difference (P0.05).@*CONCLUSIONS@#When cradle CAD/CAM system is used to create a full crown in the clinic, the preparation height should be set to more than 3 mm, and the cement space should be set at 30 μm.

Effect of a desensitizing polishing paste on bonding strength of two self-etching adhesives to dentin / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the effect of an 8% arginine-CaCO3 containing desensitizing polishing paste on bonding strength of two self-etching adhesives to dentin.</p><p><b>METHODS</b>Thirty-six intact human premolars extracted for orthodontic reasons were collected within 1 month after extraction and randomly assigned into three groups using a table of random numbers (n = 12): specimens without any treatment served as control. In the polishing powder group specimens were polished with a slurry of pumice, and in the desensitizing polishing paste group dentin surfaces of the sample teeth were treated with 8% arginine-CaCO3 containing desensitizing polishing paste. Then each group was divided into two sub-groups using a table of random numbers in order to evaluate the bonding strength of two self-etching adhesive agents (G-Bond, GC; Fl-Bond II, Shofu). Microtensile bond strength test was conducted immediately and after 5000 thermocycling (n = 15). Scanning electron microscope (SEM) was used to evaluate the occluding effect of the desensitizing polishing paste.</p><p><b>RESULTS</b>In the pre-thermocycling stage, there were no significant differences in Fl-Bond II bonding strength among the three groups [control: (30.34 ± 5.42) MPa, polishing powder group: (29.72 ± 5.16) MPa, desensitizing polishing paste group: (31.53 ± 4.86) MPa] (P > 0.05). However there were significant differences among the three groups in G-Bond bonding strength [control: (38.19 ± 4.42) MPa, polishing powder group: (36.47 ± 4.72) MPa, desensitizing polishing paste group: (46.88 ± 7.83) MPa] (P < 0.05). After thermocycling process, there were no significant differences in bonding strength among the three groups in both G-Bond groups and Fl-Bond II groups. SEM observation showed that the desensitizing polishing paste could occlude open dentinal tubules effectively, and the application of self-etching adhesives could re-open the dentinal tubular orifices. An even layer can be seen on the dentin surface treated with self-etching adhesive containing functional monomers.</p><p><b>CONCLUSIONS</b>The 8% arginine-CaCO3 containing desensitizing polishing paste could effectively occlude dentinal tubules, thus may have potential benefits in preventing post-operative sensitivity. Additionally, it had no adverse effect on bonding strength of self-etching adhesives to dentin.</p>

Study on the micropermeability of resin-dentin bonding interfaces with ethanol-wet bonding technique / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the micropermeability on bonding hydrophobic adhesive to dentin with ethanol-wet bonding under simulated pulp pressure.</p><p><b>METHODS</b>Twenty-four intact human third molars were used in the study. After the enamel of occlusal surfaces was removed, the molars were randomly divided into six groups. Adper Scotchbond Multi-Purpose was used in the control group; in the experimental groups, the dentin surfaces were saturated with ethanol for 20 s (group 1), 1 min (group 2), 2 min (group 3), 3 min (group 4) or with a series of increasing ethanol concentrations before application of hydrophobic adhesive (group 5). All the bonding procedures were done under simulated pulp pressure. After 24 hours, micro-tensile bond strength test were performed on the specimens. Bonding interfaces were observed under laser scanning confocal microscope (LSCM) after the pulp chamber were filled with a water-soluble fluoroprobe rhodamine B for 3 hours.</p><p><b>RESULTS</b>Compared with the control group [(38.14 ± 4.97) MPa], bond strengths in group 1 [(21.02 ± 7.23) MPa] and group 2 [(29.64 ± 3.81) MPa] were statistically lower (P > 0.05), while bond strength in group 3 [(38.40 ± 5.03) MPa], group 4 [(37.26 ± 4.68) MPa] and group 5 [(40.12 ± 5.95) MPa] were similar to the control group (P < 0.05). The images taken by LSCM showed that with extension of ethanol-wet time, the deposition of fluorescent dye in hybrid layer and along the dentinal tubules decreased gradually. Especially in group 5, only spare fluorescent dye deposition could be detected in the hybrid layer.</p><p><b>CONCLUSIONS</b>Dentin saturated with ethanol for more than 2 min before bonding hydrophobic adhesive to dentin could provide favorable bond strength and decreased the micropermeability of bonding interfaces under simulated pulp pressure.</p>