[Effect of full crown preparation with ultrasound instrument on marginal adaption: a randomized controlled trial].

PURPOSE: To study the effect of full crown ultrasound preparation on crown margin. METHODS: Thirty-two patients with 35 units of full crown were randomly divided into 2 groups. Teeth in the experimental group were prepared with ultrasound diamond instrument while teeth in the control group were prepared with a high-speed hand piece with regular diamond burs. Teeth in both groups were restored using Zirconia full ceramic crowns. Then all patients were evaluated for morphology of finishing line, marginal adaptation and marginal gingival coloration in the proximal side after 6-month of follow-up, respectively. SPSS17.0 software package was used for statistical analysis. RESULTS: Marginal adaptation did not show significant difference between the experimental and control group (P>0.05). Morphology of finishing line and marginal gingival coloration in the proximal side showed significant difference (P<0.05). CONCLUSIONS: It is recommended to perform tooth preparations with ultrasound diamond instruments, which may produce significantly less marginal gingival coloration in the proximal margin after 6-month of follow-up.

[Analysis of retention of 3 different aesthetic Co-Cr-Mo alloy clasps on premolars].

PURPOSE: To evaluate the 3-D surface topography of ultrasonically prepared tooth. METHODS: Ten extracted human maxillary premolars were prepared for crowns. A split-tooth model was used to refine the margins: half of the margin was finished with traditional rotary instruments, the other with ultrasonic instruments. The 3-D profiles of the prepared surface were observed under scanning electron microscopy and Talysurf CCI 3000 non-contact 3D profiler, and a quantitative comparison of 3-D surface roughness average(SA) and the surface of skewness(SSK) was conducted with Talymap Gold software. The data were analyzed by independent sample t test using SPSS13.0 software package. RESULTS: The surface finished with ultrasonic instruments exhibited a smoother surface. 3-D surface roughness analysis showed that the SA and SSK of surfaces made by ultrasonic instruments were significantly lower, compared with surfaces produced using conventional rotary instruments. CONCLUSIONS: The ultrasonic instruments produce surface in better condition than the conventional rotary instruments.

[Evaluation of the clinical effect of the teeth with subgingivally involved defect conserved by crown lengthening surgery].

PURPOSE: To evaluate the clinical effect of the teeth with subgingivally involved defect which were conserved by crown lengthening surgery. METHODS: 62 teeth, with defect subgingivally from 1.5 mm to 4 mm, mobility degree(MD)0.05), but a significant increase about MD occurred in the major defect group one year after restoration (P<0.01), and there was significant correlation between MD of each stage after operation and PD of pre-operation in anterior teeth (r=0.489, 0.526, 0.531, P<0.01). CONCLUSIONS: According to the biological width principle, crown lengthening surgery may conserve these teeth with subgingivally involved defect, and has a good, long-time clinical effect. But MD showed an increasing trend after operation and significant cor.