[Comparative study of 4 types of luting cements on shear bond strength of Zirconia ceramics to dentin].

PURPOSE: To investigate the adequate luting cements for zirconia ceramics to dentin. METHODS: Blocks of sintered zirconia ceramics were randomly divided into 4 groups with 8 slices in each. After saliva immersion,airborne-particle abraded ceramic specimens were cleaned with phosphoric acid gel(containing 35% phosphoric acid) and then bonded to dentin with these four kinds of luting cements. After preserved in 37 degrees centigrade distilled water for 24 hours, the shear bonding strength of these specimens was tested and the data was analyzed with SPSS12.0 software package. RESULTS: The Multilink Automix could attain the highest shear bonding strength and the 3M RelyXTM Unicem AplicapTM could attain higher shear bonding strength, which were both significantly higher than in the Tokuso Ionomer and Shofu Polycarboxylate Cement groups(P<0.05). CONCLUSION: Total etching resin luting cement is an ideal option to the bonding of zirconia ceramics and can provide a strong bonding.

[Effect of self-made colloid paste on gingival retraction in dogs].

PURPOSE: To evaluate the efficiency of self-made paste on gingival retraction in dogs as well as its potential clinical application. METHODS: Forty teeth from two mature dogs were prepared with 0.5 mm wide shoulder in the lip and buccal sides of the teeth, and then divided into four groups randomly. The gingival grooves of the four groups were filled with self-made colloid paste, Expasyl gingival retraction paste, gingival retraction cord, and medicated (15.5% Fe2SO4 solution) gingival retraction cord, respectively. The gingival grooves models before and after gingival retraction were analyzed using the image precise mapper instrument; the gingival width and height of the gingival groove were compared using SAS6.12 software package. RESULTS: The changes of gingival width of the gingival groove before and after gingival retraction were not significant between the four groups. However, the gingival height of the gingival groove in the medicated gingival retraction cord group increased significantly [(0.423 + or - 0.348) mm before gingival retraction and (0.623 + or - 0.278) mm after gingival retraction] compared with the other three groups. CONCLUSIONS: The self-made colloid paste for gingival retraction is efficient like Expasyl gingival retraction paste and gingival retraction cord with potential clinical application, while the medicated gingival retraction cord can induce gingival shrinkage. Supported by Research Fund of Science and Technology Bureau of Huangpu District,Shanghai.

[Effect of nano-silica coating on bonding strength of zirconia ceramics to dentin].

PURPOSE: To investigate the effect of silica coating by sol-gel process on bonding strength of zirconia ceramics to dentin. METHODS: Blocks of sintered zirconia ceramics were cut and randomly divided into 4 groups,16 slices in each group. Each group was subject to one of the 4 kinds of surface treatment (control group, sandblasting, sandblasting +silicone, sandblasting + silica coating + silicone) and then bonded to dentin with resin cement. After preservation in 37 degrees centigrade distilled water for 24 hours, the shear bonding strength of these specimens was tested and the data was analyzed with SAS6.12 software package for analysis of variance. The surface modality of the ceramics was observed under scanning electron microscopy (SEM). RESULTS: The group of sandblasting+ silica coating + silicone attained the highest shear bonding strength, which was significantly different from the other groups(P=0.000);There was no significant difference between the sandblasting and sandblasting + silicone group (P=0.827), which was significantly different from the control group(P=0.001). CONCLUSION: Silica coating by sol-gel process, coupled with silicone, can significantly increase the bonding strength of zirconia ceramics to dentin.

[Stress analysis of mandibular second premolar restored with fiber post-core with different shapes and diameters].

PURPOSE: To evaluate the stress distribution of mandibular second premolar restored with different shapes and diameters fiber post-core. METHODS: A load of 200N was distributed to the finite element model of mandibular second premolar restored with three different shapes (column post, cone post and trapezium post) and three different diameters(1/2,1/3 and 1/4 of root diameter) fiber post-core in vertical and lateral ( 45 degrees ) direction, and software of "Nastran" was applied to analyze the three-dimensional finite element distribution of stress respectively. RESULTS: Irrespective of the shapes, there was no significant change of stress distribution with the increase of post diameter. Under lateral load, the cone post and trapezium post created the least increased range of maximum stress than that under the vertical load. CONCLUSION: Cone and trapezium fiber posts are the more ideal designs to restore the residual crowns and roots.

[The influence of Streptococcus sanguis on corrosion resistance of magnetic retainer].

PURPOSE: To study the effect of Streptococcus sanguis on corrosion resistance of magnetic retainers in which are encapsulated with stainless steel artificial saliva. METHODS: A magnetic retainer was put in one culture flask,which was filled with artificial saliva.Ten of them were added Streptococcus sanguis suspension,the others were added PBS as control.The culture flasks were cultivated in incubator(36 degrees centigrade). 5 ml suspension was dislodged from each flask at the 3rd, 10th and 20th day. The quantity of Fe(3+) and Mn(2+) was detected.Statistical analysis of paired t test was performed with SPSS10.0 software package. RESULTS: When Streptococcus sanguis existed, the quantity of Fe(3+) and Mn(2+) was significantly higher than that in the control (P<0.01). CONCLUSION: The existence of Streptococcus sanguis destroys the corrosion resistance of magnetic retainers remarkably.

[Three dimensional finite element analysis of stress distribution of bone tissues around abutments in telescope fixed bridge supported by tooth-implant].

PURPOSE: To study the stress distribution of bone tissues around the abutments in telescope fixed bridge supported by tooth-implant. METHODS: A patient with loss of the left first mandibular molar was used as the subject. Two partial fixed denture models were established. One model (model I) was supported by the second premolar and implant in the second molar, the other model (model II) was supported by the second premolar and implant other than the second molar. Under decentralized vertical and oblique loads, the stress distribution of bone tissues around the tooth and implant was evaluated by three dimensional finite element analysis. RESULTS: Under decentralized vertical load, the max EQVs of the bone tissues around the tooth and implant in model I were 2.58MPa and 43.92MPa, and 2.17MPa and 20.23MPa in model II. Under decentralized oblique load, the max EQVs of the bone tissues around the tooth and implant in model I were 2.23MPa and 46.37MPa, and 1.91MPa and 21.19MPa in model II. CONCLUSIONS: The stress surrounding the implant is declined by the buffer of telescope retainer, and the decline is not different under the two loads. In designing the fixed bridge supported by tooth-implant, we can design telescope retainer on implant to reduce the stress of bone tissues around the implant and to prevent damages to bone tissues.

[Comparative study of bond strength between zirconia ceramics and 4 luting cements].

PURPOSE: To study the bonding strength of zirconia ceramics with 4 kinds of luting cement materials. METHODS: Blocks of sintered zirconia ceramics were cut and randomly divided into 4 groups with 16 slices in each group. They were treated with sandblasting and bonded with 4 kinds of luting cements respectively. After preserved in 37 degrees C distilled-water for 24 hours and 30 days, the shear bonding strength of these specimens was tested and the data were analyzed by SAS6.12 software package and bond section were observed by scanning electron microscope. RESULTS: Two-way ANOVA revealed that the group of PanaviaF could attain the highest shear bonding strength: (34.7+/-3.44) MPa (after 24 hours), (31.5+/-3.44) MPa (after 1 month), which was significantly different from other treatment methods (P<0.01). The initial shear bonding strength of the groups of resin-reinforced glass ionomer was (15.5+/-2.71) MPa, (16.0+/-1.77) MPa (after 24 hours) but dropped markedly to (6.80+/-1.24) MPa, (3.38+/-2.32) MPa after 30 days (P<0.05). CONCLUSIONS: Resin luting cement containing phosphate monomer (MDP) can provide zirconia ceramics a strong and long-lasting bonding. Resin-reinforced glass ionomer can get good bonding strength too, but can't last long.

[Study on abutment movement of distal removable dentures retained by attachments].

PURPOSE: To study the influence on the abutment movement with three kinds of precision attachments designed for distal-extension removable partial dentures (RPDs). METHODS: Snap attachment, Ceka attachment, Mini-SG attachment were used to retain RPDs. Then food chip was masticated between the upper and lower dentitions on the attachments side. Placement of abutment was measured by LB-72 high-sensitive-laser-traneferring-detector and the data were statistically analyzed for random block analysis of variance. RESULTS: The displacement, inclination, and torsion of the abutment movements in the mesial-distal, bucco-lingual and occluso-gingival directions all had statistical significance (P<0.05). The largest mesial-distal inclination occurred with the Mini-SG attachment. The Ceka attachment produced more abutment displacement in mesial distal and apical directions. Occlusal displacement and anti-clockwise rotation were the least with the Snap attachment. CONCLUSION: The most equitable distribution of stresses on the supporting structures was achieved by Snap attachment with its resilent assemble, Ceka attachment transfers most of the loading forces to the abutments, Mini-SG attachment can not reduce the excessive torque applied to the abutments effectively.

[Study on the stress distribution of different superstructures for tooth-implant supported denture].

PURPOSE: To compare the stress distributions of fixed bridge, cement-retained telescopic prostheses and extracoronal precision attachment (CEKA attachment) when connect the implants to the natural teeth, in order to find a more suitable design for it. METHODS: 3-D finite element models of tooth-implant partial fixed dentures were constructed by using the ANSYS software. The partial fixed denture was supported by the second premolar and an implant (substitute the second molar). A total load of 200N was distributed to the three units of the denture in vertical and lateral (45 degree) directions. RESULTS: Both of the cement-retained telescopic and the CEKA attachment made the stress of the osseous tissues surrounding the implant and the tooth declined obviously under the loads of the two directions. The stress of the cement-retained telescopic was lower under vertical load,the stress of Ceka attachment was lower under lateral load while it caused the stress of the natural tooth increasing slightly. The stress under the lateral load was higher than that under the vertical load. CONCLUSION: Both of the cement-retained telescopic and the CEKA attachment can improve the stress distribution of tooth-implant support denture. The CEKA attachment is better under lateral loads.