[Comparison of fracture strength of two chairside CAD/CAM ceramic blocs with different thickness].

PURPOSE: To provide theoretical basis for clinical CAD/CAM restorations with a comparison of the fracture strength between two chairside CAD/CAM immediate restorative materials (IPS e.max CAD and Vita Enamic) with different occlusal thickness in vitro. METHODS: IPS e.max CAD and Vita Enamic full-crowns with occlusal thicknesses 1.5/2.0/2.5 mm were fabricated with CEREC and adhesively seated to dies customized by manufacturer (n=42). All specimens were stored in distilled water at 37 ℃ for 24 h. Later, static fractural loading was performed. The fracture surface was observed through scanning electron microscope (SEM) and energy dispersive spectrum (EDS). The composites of two materials were detected by X-Ray diffraction (XRD) techniques. The results of fracture strength were analyzed by one-way ANOVA and t-test via SPSS 20.0 software package. RESULTS: With the increase of occlusal thickness, the fracture strength of IPS e.max CAD increased remarkably. However, the Vita Enamic's fracture strength remained the same with no significant difference. With the occlusal thickness increased from 1.5 to 2.0 mm, there was no significant difference in the fracture strength between IPS e.max CAD group and Vita Enamic group. As the thickness increased from 1.5 to 2.0 mm, the fracture strength of IPS e.max CAD group was significantly higher than that of Vita Enamic group. The results of SEM showed that the filler particles of IPS e.max CAD were smaller compared to that of Vita Enamic. Cone cracks were mainly found in the fracture surface of IPS e.max CAD, while radical cracks appeared in Vita Enamic. EDS showed the metal oxide and SiO2 in Vita Enmic was significantly higher than that in IPS e.max CAD. XRD showed that the primary crystal phase of IPS e.max CAD was lithium silicate, while Vita Enamic was amorphous. CONCLUSIONS: Both IPS e.max CAD and Vita Enamic can meet the standard of clinical application as the occlusal thickness reaches 1.5 mm. IPS e.max CAD showed better fracture resistance when the thickness was greater than 2.0 mm.

[Evaluation of the filling quality of different root canal obturation techniques using micro-CT].

PURPOSE: The aim of this study was to evaluate the quality of different root canal obturation techniques by micro-CT. METHODS: Forty single-canal upper incisors were collected and decoronated to obtain 12 mm root segments. The root canals were prepared by using ProTaper rotary files and allocated into 4 groups randomly（n=10）, then obturated with gutta-percha and(or) iRoot SP by cold lateral compaction (CLC), continuous wave condensation (CWC), single core (SC), sealer-only buckfill (SoB) techniques, respectively. Each tooth was then scanned with micro-CT, and the percentage of 3D volume and 2D slices of voids and gaps were calculated 1 week later. The data were analyzed using SPSS 22.0 software package. RESULTS: Percentage of cross-sections with voids and gaps in CWC group was significantly less than others (P<0.05) , and it had a significantly greater filling area in 3D volume in whole root canal, middle third and coronal third levels (P<0.05), while SOB group had the largest filling quality in apical third levels (P<0.05). CONCLUSIONS: No filling technology can avoid voids. CWC technology provides the best filling performance.

[The effect of glass fiber volume content on the flexural property of fiber-reinforced composite].

PURPOSE: To investigate the effect of glass fiber volume content on the flexural property of fiber-reinforced composite． METHODS： The specimens of composite were fabricated with 4 different glass fiber volume contents by changing roving winded number of strands dipped in resin matrix, and the mechanical properties were tested by 3-point flexural test in order to determine the optimal fiber volume content. The data was analyzed statistically with SPSS20.0 software package. RESULTS: Self-made fiber-reinforced composites with the glass fiber volume content percentage of 60.4% achieved the maximal flexural strength and the maximal elastic modulus. CONCLUSIONS: As the glass fiber content in matrix of composite material is increased in certain range, the flexural strength and the elastic modulus can be improved，then reaches the peak. However, the flexural property decreases rather than rises when the fiber content is more than 60.4%.

[The effect of core veneer thickness ratio on the flexural strength of diatomite-based dental ceramic].

PURPOSE: To evaluate the effect of different core veneer thickness ratios on the flexural strength and failure mode of bilayered diatomite-based dental ceramics. METHODS: Diatomite-based dental ceramics blocks (16 mm×5.4 mm×1 mm) were sintered with different thickness of veneer porcelains: 0 mm (group A), 0.6 mm (group B), 0.8 mm (group C) and 1.0 mm (group D). Flexural strength was detected and scanning electron microscope was used to observe the interface microstructure. Statistical analysis was performed using SPSS 17.0 software package. RESULTS: With the increase of the thickness of the veneer porcelain, flexural strength of group C showed highest flexural strength up to (277.24±5.47) MPa. CONCLUSIONS: Different core veneer thickness ratios can significantly influence the flexural strength of bilayered diatomite-based dental ceramics. Supported by Science and Technology Projects of Nantong City (HS2013010).

[Preliminary study of bonding strength between diatomite-based dental ceramic and veneering porcelains].

PURPOSE: In order to choose the best veneering porcelain for diatomite-based dental ceramic substrate, the bonding strength between diatomite-based dental ceramics and veneering porcelains was measured, and the microstructure and elements distribution of interface were analyzed. METHODS: The coefficient of thermal expansion (CTE) of diatomite-based dental ceramics was detected by dilatometry. Three veneering porcelain materials were selected with the best CTE matching including alumina veneering porcelain (group A), titanium porcelain veneering porcelain (group B), and E-max veneering porcelain (group C). Shear bonding strength was detected. SEM and EDS were used to observe the interface microstructure and element distribution. Statistical analysis was performed using SPSS 17.0 software package. RESULTS: The CTE of diatomite-based dental ceramics at 25-500 degrees centigrade was 8.85×10-6K-1. The diatomite-based substrate ceramics combined best with group C. Shear bonding strength between group A and C and group B and C both showed significant differences(P<0.05). SEM and EDS showed that the interface of group C sintered tightly and elements permeated on both sides of the interface. CONCLUSIONS: The diatomite-based substrate ceramics combines better with E-max porcelain veneer.

A novel combination of nano-scaffolds with micro-scaffolds to mimic extracellularmatrices improve osteogenesis.

To improve bone engineering for clinical applications, we coupled nanofiber-peptide hydrogel to nano-hydroxyapatite/collagen to form a bioactive scaffold (cnHAC) that mimics extracellular matrices. In comparison to nano-hydroxyapatite/collagen, we found that cnHAC promoted cell adhesion and spreading, and DNA content measurements, alkaline phosphatase activity assays, and reverse transcriptase-polymerase chain reaction analyses of osteogenic gene expression showed that cnHAC significantly improved cellular attachment, proliferation, and osteogenic differentiation in vitro (P < 0.05). In vivo models based on rat calvarial implants showed that cnHAC significantly enhanced bone regeneration (P < 0.05). In conclusion, we demonstrated that novel cnHAC scaffolds could potentially facilitate future bone regenerative medicine.

[Preliminary study of wireless biofeedback therapy for treatment of bruxism].

OBJECTIVE: To access the effect of wireless biofeedback therapy on bruxism. METHODS: Ten voluntary bruxers (seven female and three male, mean age 26.1 years) were invited to participate in this clinical research. An electric resistance strain gauge was embedded in the position of canine of a maxillary splint for monitoring the abnormal clenching or grinding movement of teeth during sleep. The relevant details of bruxism events, including value of relative force, occurring time and duration were recorded and analyzed by the receiver device and monitoring program respectively. Meanwhile, for the purpose of nerve system and muscle relaxation, a watch-style device around the patient's wrist will vibrate to alert the patient of teeth grinding or clenching if the value of biting force and duration exceed the threshold. Total average episodes of bruxism and duration was observed during eight hours sleep, and was analyzed with one-way analysis of variance in SPSS 19.0 by the end of 6th week and three months following biofeedback therapy. RESULTS: The average episodes of bruxism has declined dramatically from (9.8 ± 2.2) times to (3.0 ± 1.2) times during one night (P < 0.05), and the average duration of bruxism events was reduced from (20.7 ± 12.2) s to (10.0 ± 3.4) s (P < 0.05) after six weeks biofeedback therapy. By the end of three months, the average episodes declined to (2.9 ± 1.2) times (P < 0.05), and the average duration decline to (9.2 ± 2.9) s (P < 0.05) with contrast to preliminary night. CONCLUSIONS: The pressure-based wireless biofeedback device is able to monitoring clenching and grinding of bruxism. The results suggest that biofeedback therapy may be an effective, novel and convenient measure for treatment of bruxism according to several months therapy.

[Improving bonding of zirconia through deposition of silica layer via collosol-gelatin process, the roles of NaHCO3].

OBJECTIVE: To evaluate the effects of NaHCO3 on gelation of silica sols and shear bond strength of silica coated zirconia via collosol-gelatin (Sol-Gel) process. METHODS: The gelation time of silica sols after being mixed with 1%, 3%, 5%, 7%, 10% concentrations of NaHCO3 was recorded. The one got the shortest gelation time was used for the following tests. Zirconia blocks were prepared and divided into five experimental groups according to surface conditioning methods: group A, alumina sandblasting; group B, sandblasting + tribochemical silica coating + silane; group C, sandblasting + silica coating via Sol-Gel process + silane; group D, sandblasting + silica coating via Sol-Gel process (NaHCO3 was used) + silane; group E, sandblasting + zirconia primer. A composite resin column was bonded on the treated zirconia surface with Bis-GMA based composite resin cement. All specimens were subjected to shear bond strength (SBS) tests. RESULTS: The shortest gelation time of silica sols were found when silica sols was mixed with 10% NaHCO3. Group A showed the lowest SBS values of (4.12 ± 0.52) MPa, which was significant different from SBS of group B [(10.24 ± 2.78) MPa], C [(7.36 ± 1.59) MPa], D [(9.79 ± 2.07) MPa], D [(8.39 ± 0.49) MPa], and no statistical difference was found between group C and D. CONCLUSIONS: The silica coating via Sol-Gel process can significantly improve the bond strength of zirconia, and NaHCO3 would not exert influences to bonding.

[Induction of apoptosis and related genes by five kinds of dental materials on L929 cell].

OBJECTIVE: To evaluate a new type of diatomite-based machinable ceramic biocompatibility by studying its induced apoptosis on L929 cell in contrasted with other prosthodontics materials. METHODS: Cell line was treated with extracting liquid containing different concentrations of diatomite-based machinable ceramic and other materials. Flow cytometry tested cell cycle progression and induced cell apoptosis. Annexin V-FITC/PI apoptosis staining kit quantitative detected cell death patterns. The expression of Bcl-2 and Bax mRNA were determined by reverse transcription-polymerase chain reaction. RESULTS: The experimental groups had no special influence on cell cycle. Apoptosis rates of the new ceramic closed to the negative group (P > 0.05). The apoptosis rate of resin was the highest, and the cell necrosis level of resin was increased, which had significant difference to the new ceramic (P < 0.05). The Bcl-2 and Bax mRNA levels of the new ceramic and the negative group were closed to each other, which had no statistical significance (P > 0.05). CONCLUSION: The new diatomite-based machinable ceramic has no apparent cytotoxicity, which is consistent with the clinical application of the basic requirements of biocompatibility.

[Effect of niobium nitride on the bonding strength of titanium porcelain by magnetron sputtering].

OBJECTIVES: To investigate the effect of magnetron sputtered niobium nitride (NbN) on the bonding strength of commercially pure cast titanium (Ti) and low-fusing porcelain (Ti/Vita titankeramik system). METHODS: Sixty Ti specimens were randomly divided into four groups, group T1, T2, T3 and T4. All specimens of group T1 and T2 were first treated with 120 microm blasted Al2O3 particles, and then only specimens of group T2 were treated with magnetron sputtered NbN film. All specimens of group T3 and T4 were first treated with magnetron sputtered NbN film and then only specimens of group T4 were treated with 120 microm blasted Al2O3 particles. The composition of the deposits were analyzed by X-ray diffraction (XRD). A universal testing machine was used to perform the three-point bending test to evaluate the bonding strength of Ti and porcelain. The microstructure of NbN, the interface of Ti-porcelain and the fractured Ti surface were observed with scanning electron microscopy (SEM) and energy depressive spectrum (EDS), and the results were compared. RESULTS: The XRD results showed that the NbN deposits were cubic crystalline phases. The bonding strength of Ti and porcelain in T1 to T4 group were (27.2+/-0.8), (43.1+/-0.6), (31.4+/-1.0) and (44.9+/-0.6) MPa. These results were analyzed by one-way analysis of variance and differences between groups were compared using least significant difference test. Significant inter-group differences were found among all groups (P<0.05). The results of SEM showed that with treatment of Al2O3 or NbN, alone, pre-cracks were found in the interface of Ti-porcelain, while samples treated with both Al2O3 and NbN had better bond. EDS of Ti-porcelain interface showed oxidation occurred in T1, T2 and T3, but was well controlled in T4. CONCLUSIONS: Magnetron sputtered NbN can prevent Ti from being oxidized, and can improve the bonding strength of Ti/Vita titankeramik system. Al2O3 blast can also improve the bonding strength of Ti/Vita titankeramik system.

[Color property evaluation of 7 kinds of resin-based composite products].

OBJECTIVE: To investigate the color stability and opacity of seven resin-based composite products after ultraviolet irradiation. METHODS: Seven kinds of light-cured resin-based composite products (Aelite Flo, Filtek Z350 Flowable, Clearfil AP-X, Dyract AP, Z100, Durafill VS, Filtek Z350 Universal) were tested in the study (five for each group). Changes in color and opacity of test samples were determined before and after 8, 16 and 24 h ultraviolet irradiation using the CIE 1976 L*a*b* system and CIE 1931 XYZ system by a colorimeter. RESULTS: The color of resin disks suffering ultraviolet irradiation was different in different irradiating time. Color difference values ranged from 1.85-3.21 for 8 h ultraviolet irradiation to 2.88-4.55 for 24 h ultraviolet irradiation. Opacity values ranged from 0.75-0.82 before ultraviolet irradiation to 0.80-0.98 after 24 h ultraviolet irradiation. Among all the groups, Z100 and Filtek Z350 Flowable showed the biggest color change, while Filtek Z350 Universal showed the highest opacity. CONCLUSION: It can be concluded that for some products, ultraviolet irradiation leads to color instability and opacity variation.

[Effect of silicon coating on bonding strength of ceramics and titanium].

OBJECTIVE: This study investigated the effect of silicon coating (SiO2) by solution-gelatin (Sol-Gel) technology on bonding strength of titanium and ceramics. METHODS: Sixteen pure titanium specimens with the size of 25 mm x 3 mm x 0.5 mm were divided into two groups (n=8), test group was silicon coated by Sol-Gel technology, the other one was control group. The middle area of the samples were veneered with Vita Titankeramik system, the phase composition of two specimens were characterized by X-ray diffraction (XRD). The bonding strength of titanium/porcelain was evaluated using three-point bending test. The interface of titanium and porcelain and fractured titanium surface were investigated by scanning electron microscope (SEM) with energy depressive spectrum (EDS). RESULTS: Contents of surface silicon increased after modification with silicon coated by Sol-Gel technology. The mean bonding strength of test group and control group were (37.768 +/- 0.777) MPa and (29.483 +/- 1.007) MPa. There was a statistically significant difference (P=0.000) between them. The bonded ceramic boundary of test group was wider than control group. CONCLUSION: Silicon coating by Sol-Gel technology was significant in improving bonding strength of titanium/Vita Titankeramik system.

[Effects of magnetron sputtered ZrN on the bonding strength of titanium porcelain].

OBJECTIVE: To investigate the effect of magnetron sputtered ZrN on the bonding strength between a low-fusing porcelain (Ti/Vita titankeramik system) and commercially pure cast titanium. METHODS: Sixteen specimens were randomly assigned to test group and control group (n=8). The control group received no surface treated. Magnetron sputtered ZrN film was deposited on the surface of specimens in the test group. Then the sixteen titanium-porcelain specimens were prepared in a rectangular shape and went through three-point bending test on a universal test machine. The bond strength of Ti/porcelain was recorded. The phase composition of the specimens was analyzed using X-ray diffraction (XRD). The interface at titanium and porcelain and the titanium surface after debonding were observed with a scanning electron microscopy (SEM) and analyzed using energy depressive spectrum (EDS). RESULTS: New phase of ZrN was found with XRD in the test group. Statistical analysis showed higher bond strength following ZrN surface treatment in the test group [(45.991+/-0.648) MPa] than that in the control group [(29.483+/-1.007) MPa] (P=0.000). Bonded ceramic could be observed in test group, the amount of bonded ceramic was more than that in the control group. No obvious bonded ceramic in control group was found. CONCLUSIONS: Magnetron sputtered ZrN can improve bond strength of Ti/Vita titankeramik system significantly.

[Effects of ultraviolet aging on color and translucency of composite resin cements].

OBJECTIVE: To investigate the color stability and translucency of four composite resin cements after ultraviolet (UV) aging. METHODS: 20 composite resin cement disks for four groups (Group A, dual cured, Biscem; Group B, light cured, Choice; Group C, self cured, PermaCem; Group D, self cured, RelyX Aplicap) were prepared according to their manufacture recommendation. Changes in color and translucency of test samples were determined before and after UV aging for 8, 16 and 24 hour using the CIE L* a* b* system by a colorimeter. The results were analyzed by LSD multi-compare tests. RESULTS: The color changes of composite resin cement disks suffering UV aging were significantly different when irradiated different time. For the same irradiated time, Group C had the highest delta E, and Group B and D had the smaller ones. Translucency was found no difference among different irradiated time for group A, B and D. Translucency of group C decreased after UV aging. CONCLUSION: Translucency of composite resin cement kept stable after UV aging, and color coordinate changed after UV aging.

[Cytotoxicity of several materials of full crowns on human gingival fibroblast cells in vitro].

PURPOSE: To evaluate the cytotoxicity of Ni-Cr base metal alloy, gold casting alloy and castable dental ceramic on human gingival fibroblast cells (HGFC)ain vitro. METHODS: HGFC were cultured with extractions of Ni-Cr base metal alloy, gold casting alloy and castable dental ceramic. Relative growth rate (RGR) was analyzed with a methyl thiazolyl tetrazolium (MTT) assay. The shape of HGFCs was observed when HGFCs were directly contacted with three prosthodontic materials. Factor analysis was performed using Stata 9.1 software. RESULTS: The relative growth rates of HGFCs cultured with gold casting alloy were 1.016,1.014,0.824 and 0.796,respectively. The relative growth rates of HGFCs cultured with Ni-Cr base metal alloy were 1.028,1.079,0.903 and 0.809,respectively. The relative growth rates of HGFCs cultured with castable dental ceramic were 1.018,1.030,0.924 and 0.818, respectively. There was significant difference of RGR between the gold casting alloy and the Ni-Cr base metal alloy groups(P=0.021). No significant difference of RGR was observed between the gold casting alloy and castable dental ceramic groups (P>0.05).No significant difference of RGR was observed between the Ni-Cr base metal alloy and castable dental ceramic groups (P>0.05). Cytotoxical grades of Ni-Cr base metal alloy, gold casting alloy and castable dental ceramic were 0 to 1. HGFC could grow around the three prosthodontic materials. CONCLUSIONS: Ni-Cr base metal alloy has more cytotoxic effect in direct contact test than in extraction test on HGFC. Gold casting alloy and castable dental ceramic have good biocompatibility. Supported by Medical PI Project for Provincial Advancement through Science and Education of Jiangsu Province (RC2007099).

[Effect of nano-silica coating prepared by different concentration silica sol on shear bond strength of alumina ceramic].

OBJECTIVE: To evaluate the effect of nano-silica coating prepared by different concentration silica sol on shear bond strength between alumina ceramic and resin cement. METHODS: Silica coating was prepared with colloidal silica sol on alumina ceramic surface that was treated with air particle abrasion. Infrared spectrum (IR), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) were used to analyze the silica coating. A total of 32 alumina ceramic discs were randomly divided into 4 groups with 8 discs per group, which received different surface treatments as silane couple agent (control group), 20% silica sol + silane (group A), 30% silica sol + silane (group B), 40% silica sol + silane (group C). Each ceramic disc was bonded to composite with resin cement, and then shear bond strength of these samples was tested. RESULTS: It was observed from the IR pictures that symmetrically flexible vibration absorption kurtosis, anti-symmetrically flexible vibration absorption kurtosis, and bending vibration absorption kurtosis of Si-O-Si enhanced after heat treatment. SEM pictures showed that nanoparticles in coating gel were well distributed and some of them conglomerated after heat treatment. There was a little conglomeration in 20% coating, more in 30%, and the most in 40%. Contents of surface silicon increased after modification with silica coating prepared by sol-gel method. Bond strength of three groups with silica coating was significantly higher than that of the group with only silane couple agent [(1.881 +/- 0.156) MPa] (P < 0.05). Group B gained the highest strength [(4.852 +/- 0.178) MPa] compared with group A [(3.196 +/- 0.171) MPa] and group C [(3.576 +/- 0.671) MPa] (P < 0.05). CONCLUSIONS: Surface silicon contents all increased after surface modification with different concentration silica sol. Silica coating followed with silane couple agent could significantly enforce bond strength of alumina ceramic, with 30% silica sol group gaining the highest bond strength.

[Surface modification of dental alumina ceramic with silica coating].

OBJECTIVE: To make silica coating through sol-gel process, and to evaluate the wettability of dental alumina ceramic with or without coating. METHODS: Silica coating was prepared with colloidal silica sol on In-Ceram alumina ceramic surface which had been treated with air particle abrasion. Coating gel after heat treatment was observed with atomic force microscope (AFM), and was analyzed by infrared spectrum (IR) with gel without sintered as control. Contact angles of oleic acid to be finished, sandblasted and coated ceramic surface of were measured. RESULTS: AFM pictures showed that some parts of nano-particles in coating gel conglomerated after heat treatment. It can be seen from the IR picture that bending vibration absorption kurtosis of Si-OH also vanished after heat treatment. Among contact angles of three treated surface, the ones on polished surface were the biggest (P = 0.000, P = 0.000), and sandblasting+silica coating surface the smallest (P = 0.000, P = 0.003). CONCLUSION: Silica coating can be made with sol-gel process successfully. Heat treatment may reinforce Si-O-Si net structure of coating gel. Wettability of dental alumina ceramic with silica coating is higher than with sandblasting and polishing.

[The effect of disinfection on dimension stability of impressions].

PURPOSE: To measure the effect of disinfection on dimension stability of alginate, hydrocolloid, and Express putty impressions which were separately immersed in 2% glutaraldehyde solution and 1% 84 disinfector. METHODS: Alginate, hydrocolloid, and Express putty impressions were made by 20 mm x 20 mm x 40 mm standards test wares. There were 45 in each kind of test wares. They were divided into 9 groups and 5 pieces in every group. Among them, one group using clear water to flush acted as the matched control, the other groups received respectively 2% glutaraldehyde solution and 1% 84 disinfector immersed in 10 minutes, 20 minutes, 30 minutes. After two hours, the spiral instrument was used to measure the model. The experiment data were analyzed by using the SPSS 11.0 statistic software package. RESULTS: There was no significant difference in pure water flush and spraying treatment respectively. There was significant difference for alginate and hydrocolloid impression was immersed before and after. There was no significant difference for Express putty silicon rubber impression materials before and after immersion. There was no significant difference in 2% glutaraldehyde solution and 1% 84 disinfector when impressions were immersed in. CONCLUSION: Alginate, hydrocolloid and Express putty impressions immersed in 2% glutaraldehyde solution and 1% 84 disinfector separately for 20 minutes does not affect the accuracy, and can be used clinically.

[Study on the occlusal surface design methods of CAD/CAM all-ceramic coping crown].

OBJECTIVE: To evaluate the accuracy of occlusal surface design methods for Cerec2 CAD/CAM all-ceramic coping crown. METHODS: Ten first molar all-ceramic crown preparations were made. Five were normal occlusion, and five were abnormal. The crown was designed by Cerec 2 CAD/CAM using three methods, namely Extrapolation, Correlation and Function, for every preparation. The Z values of mesiobuccal, mesiolingual, distobuccal, distolingual angle in marginal ridge were recorded. RESULTS: In the normal occlusion group, there was no statistical difference among the three occlusal surface design methods (P > 0.05). In the abnormal occlusion group, there were statistical differences between the occlusal surface design methods (P < 0.05); the function method was noted to be more accurate than the others. CONCLUSION: The results indicate that the extrapolation method can be applied to patients with normal occlusion and the function method can be applied to patients with abnormal occlusion.