[The factors influencing the flexural strength of zirconia ceramic restorations].

Zirconia material has a very broad application prospect in prosthodontics,and restorations made of zirconia through CAD/CAM technology have been applied widely in recent years. In this paper we summarized the features of zirconia material which used for all ceramic restorations and the factors which affected its flexural property. We also sated the relevant indicators and methods used for evaluation of flexural property of zirconia material in order to lay a basis for its clinical use.

[The experimental research of the influence of cervical settling method on marginal accuracy of wax patter].

OBJECTIVE: To study the influence of cervical settling method on marginal accuracy of wax patters. METHODS: 24 wax patterns were made on the standard cast specimens and round capsules of which twelve patters were made with the method of cervical settling (experiment group), twelve patters were made with the method of wax dripping (control group). Marginal accuracy of patterns were measured before sublation, sublation half an hour and twenty-four hours. RESULTS: The results revealed that marginal accuracy had significant difference between the cervical settling methods and wax dripping methods (P < 0.05). There was significant difference between the cervical settling methods measured after half an hour and twenty-four hours (P < 0.01). There was also significant difference between the wax dripping methods measured after half an hour and twenty-four hours (P < 0.01). CONCLUSION: Wax patterns with the method of cervical settling can improve marginal accuracy of patterns. The marginal accuracy of wax patters are influenced by the existing time.

[Research advances of adult stem cells and dental stem cells].

Human stem cells have a major effect in the development of human bodies. Acting as an in vitro model, human stem cells have a great value in the study of the mechanism of individual development and in the cell-replacement treatments and gene therapy of tissue deficiency diseases. The study of stem cells has been given rise to a keen interests in the bio-medical area at present. This paper reviews the present status and progress of adult stem cells and dental stem cells.

[The test of metal-ceramic bonding strength among three ceramic alloies].

PURPOSE: To compare the metal-ceramic bonding strength of different ceramic alloies. METHODS: 30 wax sheets were divided into 6 groups at random. Each group included 5 sheets. After being invested conventionally with Bellaves SH,the samples were casted and fused with porcelain.The metal-ceramic bonding strength was evaluated. RESULTS: The highest bonding strength was found in Bio Herador N alloy, and then in TILITE alloy and Heraenium S alloy respectively. Bio Herador N alloy and TILITE alloy all had significant differences of the bonding strength before and after treatment (P<0.05). There was no significant differences in the bonding strength of the Heraenium S alloy after treatment (P>0.05). CONCLUSION: The bonding strength of precious metal-ceramic was higher than that of non-precious metal-ceramic.Pre-oxygen treatment can improve the metal-ceramic bonding strength of Bio Herador N alloy and TILITE alloy,but it had no effect on the metal-ceramic bonding strength of the Heraenium S alloy.

[Clinical effects of three systems of dental implants].

OBJECTIVE: To evaluate the clinical value of dental implants including Brånemark, Steri-oss and BLB systems. METHODS: The total 384 implants of different materials and shapes were inserted normally. According to the Chinese standard of dental implantation, the success rates of three types were compared. RESULTS: By following-up from one year to five years, the success rates of all implants were above 97%. CONCLUSION: The success rates of routine implants were mainly associated with indication, case selection, operation, rehabilitation and patients maintenance.

[Experimental study of the effect on marginal seating of the castings by different investing methods].

OBJECTIVE: The purpose of this study was to observe the effect on marginal seating of the castings with and without ring investments. METHODS: Standarded as-cast specimens and round capsules simulated post tooth crowns were made. 12 wax pattern were prepared on the as-cast specimens. The 12 specimens were divided into two groups with 6 wax pattern in each group. Two different investing methods with the same investing material were tested. The marginal seating of the castings was measured under travelling microscope. RESULTS: The marginal seating of the casting without ring investment had significant difference compared with the castings with ring investment (P<0.05). CONCLUSION: Casting without ring can improve the marginal seating of the castings.

[A study on the rate of collagenase in the degradation of human root dentin in vitro].

OBJECTIVE: The purpose of this study was to evaluate the effect of degradation of human root dentin collagen treated with collagenase after demineralization. METHODS: The root dentin samples were demineralized by incubating with PH5.0 lactate acid at 37 degrees C. The incubation solutions were taken on days 1, 7, 14, 21 and 28, and centrifuged 10,000r/min at 4 degrees C. The supernature solutions were analyzed for Ca(2+) and hydroxyproline. The demineralized root samples were incubated with PH7.4 collagenase solution for 7 days at 37 degrees C. The incubation solutions were centrifuged 10,000r/min at 4 degrees C and analyzed for hydroxyproline. RESULTS: The release of Ca(2+) increased and had significant differences at all observation periods within 28 days (P<0.05). There were no significant differences of the amount of degradable collagen during the nonenzymatic procedure (P>0.05). The amount of collagenase-degradable collagen was proportional to the calcium released until a plateau value at a calcium loss of about 80.01 micromol/cm(2) was reached. CONCLUSION: The degradability of collagenase is in close association with calcium released. The retention of mineral is of relevance for lesion arrestment or remineralization of early root caries.