[Study on the bending strength of cast porcelain material of different linker sizes].

PURPOSE: To investigate the relationship between size of different connectors and bending strength of cast porcelain materials. METHODS: The samples were divided into 5 groups according to the area of all-porcelain materials and simulated connector. In group A, simulated connector with cast porcelain material with a cross-section of 2 mm×3 mm was selected; In group B, simulated connector with cast porcelain material with a cross-section of 2 mm×4 mm was selected; In group C, simulated connector with cast porcelain material with a cross-section of 3 mm×3 mm was selected; In group D, simulated connector with cast porcelain material with a cross-section of 3 mm×4 mm was selected; In group E, simulated connector with zirconium oxide material with a cross-section of 2 mm×3 mm was selected. The fracture load was tested using classical three-point bending experiment, statistical analysis was performed using SPSS 18.0 software package. RESULTS: For lithium disilicate cast porcelain, the fracture load increased with increasing cross section area, but both below the shear zirconia fracture load with a cross section of 2 mm×3 mm(P＜0.05).The increase in width increased the fracture load of porcelain samples compared to the length. CONCLUSIONS: It is suitable to increase linker area when cast porcelain is applied to single-end bridge, which is especially achieved by increasing the width at the linker.

[Fracture resistance of endodontically treated maxillary premolars restored with different CAD/CAM all-ceramic restorations].

PURPOSE: This study was to evaluate the fracture resistance of endodontically treated maxillary premolars restored with different CAD/CAM all-ceramic restorations in vitro. METHODS: Mesio-occluso-function tip(MOF) cavities were prepared in 21 extracted human maxillary premolars due to endodontic treatment. The teeth were divided into 3 groups. G1:conventional composite resin; G2: cavities；G3: conventional composite resin with a horizontal glass fiber post inserted palatal walls. Restorations were fabricated from a pressable lithium disilicate glass-ceramic and adhesively cemented (Rely X U200). Then, the specimens were subjected to a compressive load at a crosshead speed of 0.5 mm/min until fracture. The fractured specimens were analyzed to determine the fracture pattern using a stereomicroscope. SPSS 15.0 software package was used to analyse the data. RESULTS: G3（1570.7±108.7） had higher failure load than G1(1214.6±95.8) and G2(1285.9±87.6)(P<0.05). G1 was similar to G2.The crown was lost in G1 and G2. There was a fracture of the crown and tooth in G3. CONCLUSIONS: CAD/CAM all-ceramic crown with fiberglass posts might be an effective method for restoration of endodontically treated premolars with MOF cavity defect.

[Electrochemical impedance spectroscopic study of titanium in physiological environment with blood-serum protein].

PURPOSE: Electrochemical impedance spectroscopy (EIS) was employed to study the corrosion behaviour of titanium in dummy environment with blood-serum protein. METHODS: EIS of titanium in PBS and cell culture fluid was acquired by advanced electrochemical system. The characteristic of EIS-Nyquist and EIS-Bode were investigated and the equivalent circuit was used to analyze the EIS results. The data was analyzed using SPSS 11.0 software package. RESULTS: The corrosion resistance of the titanium in cell culture fluid was significantly higher than that in PBS (P<0.05). The phase angle of TiO2-based passive film at low frequency decreased to 55° when titanium was in PBS, but 75° when in cell culture fluid. CONCLUSIONS: The blood-serum protein plays an important role in the corrosion behaviour of titanium in physiological environment.

[Evaluation of bond strength of three resin cements on CAD/CAM ceramic-dentin].

PURPOSE: To evaluate the bond strength of 3 resin cements on ceramic-dentin. METHODS: Thirty sound human posterior tooth were selected for this study and the flat dentin surfaces were prepared. The specimens were divided into 3 groups(n=10) randomly, which were bonded to the CAD/CAM ceramics with RelyX ARC(etch-and-rinse adhesive), Clearfil DC Bond(self-etching resin cement) and RelyX Unicem(self-adhesive resin cement). The bond strengths were tested and the bond surfaces were observed under stereoscopic microscope.SPSS 11.0 software package was used for statistical analysis. RESULTS: The shear bond strength of RelyX ARC and Clearfil DC Bond was (15.90±6.15)MPa and (14.41±5.07)MPa, respectively. The shear strength of RelyX Unicem was(23.29±7.39)MPa, significantly higher than the others.The shear strength between the three resin cements was significantly different (P<0.05). CONCLUSION: Clearfil DC Bond and RelyX Unicem can achieve a successful bond on CAD/CAM ceramic crowns.

[The influence of heat treatment on retention force of magnetic attachments].

PURPOSE: To study the influence of heat treatment on retention force of magnetic attachments. METHODS: Three groups of magnetic attachments (including 10 Magfit EX 400W, 10 Magfit EX 600W, 10 Magfit EX 800W) were fixed on universal test machine respectively. The retention force of each attachment was measured. After heat treatment, their retention force was measured again. The difference of retention force before and after heat treatment was compared using SPSS11.0 software package. RESULTS: The average retention force of magnetic attachments (Magfit EX 400W) was (1.58±0.12)N before heat treatment and (1.64±0.11)N after heat treatment. The average retention force of magnetic attachments (Magfit EX 600W) was (2.67±0.19)N before heat treatment and (2.65±0.14)N after heat treatment.The average retention force of magnetic attachments (Magfit EX 800W) was (3.02±0.25)N before heat treatment and (3.02±0.24)N after heat treatment. The retention force of magnetic attachments had no significant change after heat treatment (P>0.05). CONCLUSION: The magnetic attachments can be treated by waterbath heart treatment in the clinic without significant change of their retention force.

[Corrosion resistance and wear resistance of Ni-Cr alloy after coating titanium nitride (TiN) in oral containing fluorine environment].

PURPOSE: The aim of this study was to evaluate the corrosion resistance and wear resistance of Ni-Cr alloy after coating titanium nitride (TiN) in oral containing fluorine environment. METHODS: Physical vapor deposition was established to coat titanium nitride (TiN) on the surface of dental cast Ni-Cr alloy to form TiN/Ni-Cr compound. Both Ni-Cr alloy and TiN/Ni-Cr compound were exposed to 37 degrees centigrade, artificial saliva containing 0.24% NaF. The polarization curves of the specimens were measured by PARSTAT 2273 electrochemical station to investigate its corrosion resistance. Vicker's hardness was measured by HXD-1000TMC/LCD micro-hardness tester to investigate its wear resistance. Statistical analysis was performed by SAS 8.2 software package for Student's t methods. RESULTS: The corrosion potential of Ni-Cr alloy was -362.407 mV, the corrosion current density was 1.568µAcm(-2),the blunt-breaking potential was 426 mV bofor TiN coating. The corrosion potential of TiN/Ni-Cr compound was -268.638 mV, the corrosion current density was 0.114µAcm(-2),the blunt-breaking potential was 1142 mV after TiN coating. Polarization curves showed TiN/Ni-Cr compound improved the corrosion potential and blunt-breaking potential, decreased the corrosion current density. The Vicker's hardness of Ni-Cr alloy was 519.75±27.27 before TiN coating, the Vicker's hardness of TiN/Ni-Cr compound was 803.24±24.64, the D-value between them was 283.49±39.34. The difference of Vicker's harnesses between Ni-Cr alloy and TiN/Ni-Cr compound had significant (P<0.01). CONCLUSION: The results demonstrate that the TiN coating can improve the corrosion resistant to F-and the surface hardness of Ni-Cr alloy. Supported by Research Fund of Science and Technology Commission of Shanghai Municipality (Grant No.08DZ2271100), Shanghai Leading Academic Discipline Project (Grant No.S30206 ) and Research Fund of Health Bureau of Shanghai Municipality (Grant No.2009074).

[Microleakage of various cementing agents for casting ceramics].

PURPOSE: To observe and compare the microleakage of different composite resin cement systems for IPS Empress 2 ceramics base. METHODS: Sixteen healthy non-carious human molars were selected in the study. Class V ceramic inlay was prepared by IPS Empress 2 ceramics. The samples were divided into two groups, eight in each group. RelyX Unicem and Variolink 2 were used for bonding respectively in 2 groups. All specimens were stored in water at 37 degrees centigrade for 24 hours, then the specimens were subjected to 500 thermocycles ranging from 5 degrees centigrade to 55 degrees centigrade. Eight specimens in each group were evaluated by dye penetration. The microleakage was examined with light microscope. Statistical analysis was performed with SPSS11.0 software package. RESULTS: Enamel margins exhibited lower leakage than dentin margins by using two cementing agents for casting ceramics (P<0.05). The depth of dye for Variolink 2 and RelyX Unicem at enamel and dentin was not significantly different (P>0.05). CONCLUSIONS: The microleakage of Variolink 2 and RelyX Unicem for IPS Empress 2 ceramics base has similar sealing abilities.

[The effect of tooth preparation design on the CEREC all-ceramic crown's marginal adaptation].

PURPOSE: To study the effect of tooth preparation on marginal adaptation of all-ceramic crown designed by the Cerec system. METHODS: Lower first molar in the standard model was prepared into four types, two occlusal convergences (6 degrees and 12 degrees ) and two marginal shapes (chamfer and shoulder), and then divided into four groups correspondingly with 8 copies of abutment preparation test piece in each group. All-ceramic crown was designed by the Cerec 3 system and inserted with corresponding test piece. Marginal silicon rubber thickness of each axis surface was measured by stereo microscope after dissection. The data were analyzed with SPSS11.0 software package. RESULTS: No significant difference was observed between edge silicon rubber thickness of 4 groups of test pieces (Group A: 172.8 microm+/-42.6 microm,Group B: 181.9 microm+/-46.6 microm,Group C: 187.1 microm+/-46.5 microm,Group D: 191.7 microm+/-46.4 microm,P>0.05). Significant difference was observed between mesial surface and distal surface, mesial surface and buccal surface, mesial surface and lingual surface, distal surface and buccal surface, distal surface and lingual surface (P<0.05). No significant difference was observed between buccal surface and lingual surface. Silicon rubber thickness was in the range of 278.1 microm+/-28.8 microm and 135.8 microm+/-14.6 microm, with that of distal surface the largest (278.1 microm+/-28.8 microm) and that of buccal surface the smallest (135.8 microm+/-14.6 microm). CONCLUSIONS: All the restorations appear to have acceptable marginal adaptability,which suggests that the marginal adaptation of occlusal convergence with 12 degrees is better than 6 degrees , while the marginal design with chamfer is better than shoulder. Supported by Shanghai Leading Academic Discipline Project (Grant No.T0202).

[Influence of time on shear strength using resin cements].

PURPOSE: To compare the shear bond strength of different composite resin cement systems at different time intervals. METHODS: 48 healthy non-carious human molars were selected in the study. The samples were divided into two groups, 24 in each group. (1) RelyX unicem was used on bonding, (2) Variolink 2 was used on bonding. All specimens were stored in water at 37 degrees C for 2 hours, 24 hours and 1 week. 8 specimens in each group were stressed in shear until failure. Statistical analysis was performed with SPSS11.0 software package. Debonged surface was examined under light microscope. RESULTS: Shear bond strengths of two resin cements showed a significant increase as time went (P<0.05). The failure involved the adhesive/dentin interfaces. CONCLUSIONS: Time can influence the shear bond strength using different composite resin cement systems. Supported by Shanghai Leading Academic Discipline Project (Grant No.T0202).

[Long-term observation of 920 porcelain fused to metal prostheses].

PURPOSE: To evaluate the long-term clinical results of porcelain fused to metal prostheses. METHODS: Since January 1995, 920 porcelain fused to metal prostheses were fabricated. The long-term outcome were evaluated according to the condition of the prosthese, abutment and the periodontal tissue in the respects of successful rate and causes of failure. RESULTS: 74 patients were found to be during the follow up period, including 36 anterior crowns (46 units), 18 posterior crowns (22 units), 12 percentage of anterior bridges and 8 posterior bridges. The overall failure rate was 8.04%, 4.84% for crown, 8.77% for bridge. The failed prostheses was 5.39%. CONCLUSIONS: Porcelain fused to metal prostheses is an ideal method for restoration. The standard process both for the clinician and the technician must be obeyed to improve the success rate.

[Stress analysis of the post and core system under loading].

PURPOSE: To analyze the stress of the post and core system by using finite element analysis and study the influence of the "crown materials" on the analytic results. METHODS: Three groups of 3D finite element models of maxillary incisors were established according to the fabricating standard of the post and core system by using I-DEAS finite element analysis software. Group A was consisted of the cast metal post and core, the tooth structure after preparation and the periodontal structure. Group B was composed of the PFM, the cast metal post and core, the tooth structure after preparation and the periodontal structure. Group C was composed of the resin crown, the cast metal post and core, the tooth structure after preparation and the periodontal structure. The three groups were loaded and analyzed under the same loading according to the mean value of the bite force of incisors. RESULTS: (1)The maximum stress of dentin in group A was twice higher than that in group B. The maximum primary stress, minimum primary stress and maximum shear stress of group A were respectively 236.35, 228.83 and 218.05 percent of those in group B. The difference of maximum stress values of group B and group C was neglectable. (2) The maximum stress distribution of dentin in group A and group B was quite different (the stress was concentrated in labial and lingual side of the cervical dentin in group A, otherwise in group B it was concentrated in the area around the alveolar and the labial and lingual side of the dentin which was opposite to the tip of the cast metal post and core). The maximum stress distribution of dentin in group A and group B was almost the same. CONCLUSIONS: Different materials of the crown did not influence the result of 3D finite element stress analysis of the post and core system.

[The use of computer-aided colorimeter in porcelain-fused-to-metal (PFM) crowns among patients with special colored teeth].

PURPOSE: To evaluate the roll of ShadeEye-NCC, a computer-aided colorimeter, in Porcelain-Fused-to-Metal crowns among patients with special colored Teeth. METHODS: The first step was to choose the proper patients. The next was to use the colorimeter to measure the base shade of tooth and fabricate the PFM crowns according to the recipe given by the colorimeter. At last, the effects of the PFM crowns were evaluated subjectively by patients and doctor. RESULTS: The satisfaction rates of patients and doctor were 83.7% and 81.4% respectively, there was no significant difference between the two rates. CONCLUSIONS: The computer-aided colorimeter can offer good base shade recipe for fabricating PFM crowns of patients with special colored teeth.