[The effect of fluoride on adhesion of Streptococcus mutans and Streptococcus sanguis on the dental pure titanium surface].

PURPOSE: This study was to investigate the effect of fluoride on adhesion of Streptococcus mutans and Streptococcus sanguis on the dental pure titanium surface. METHODS: The adhesion of Streptococcus mutans and Streptococcus sanguis on the dental pure titanium surface were examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay after soaked in artificial saliva containing different concentrations of sodium fluoride for 24 h. Then the surface roughness and surface morphology of the pure titanium were analyzed by atomic force microscope after bacterial adhesion experiments. The data was statistically analyzed by analysis of variance(ANOVA) with SPSS11.0 software package. RESULTS: After soaked in artificial saliva containing different concentrations of sodium fluoride for 24 h, the sequence of OD values showed the adhesion of Streptococcus mutans and Streptococcus sanguis on dental pure titanium surface was 0 g/L < 0.5 g/L < 1.0g/L < 2.0 g/L (P<0.05). In addition, the sequence of Ra values showed the surface roughness of pure titanium after bacterial adhesion experiments was 0 g/L < 0.5 g/L < 1.0g/L < 2.0 g/L (P<0.05). And the surface morphology of pure titanium was consistent with the changes of OD value and Ra value. CONCLUSIONS: The results of adhesion of Streptococcus mutans and Streptococcus sanguis, surface roughness and surface morphology reveal that fluoride aggravates the corrosion of pure titanium, increases the surface roughness, and thus promots the adhesion of Streptococcus mutans and Streptococcus sanguis on the titanium surface.

[The effect of epigallocatechin gallate (EGCG) on the surface properties of nickel-chromium dental casting alloys after electrochemical corrosion].

PURPOSE: To investigate the effect of epigallocatechin gallate (EGCG) on the surface properties of nickel-chromium dental alloys after electrochemical corrosion. METHODS: The surface morphology and surface structure of nickel-chromium dental alloys were examined by stereomicroscope and scanning electron microscopy before and after electrochemical tests in 0 g/L and 1.0 g/L EGCG artificial saliva. The surface element component and chemical states of nickel-chromium dental alloys were analyzed by X-ray photoelectron spectrograph after electrochemical tests in 0 g/L and 1.0 g/L EGCG artificial saliva. RESULTS: More serious corrosion happened on the surface of nickel-chromium alloy in 1.0 g/L EGCG artificial saliva than in 0 g/L EGCG. The diameters of corrosion pits were smaller, and the dendrite structure of the alloy surface was not affected in 0 g/L EGCG. While the diameters of corrosion pits were larger, the dendritic interval of the alloy surface began to merge, and the dendrite structure was fuzzy in 1.0 g/L EGCG. In addition, the O, Ni, Cr, Be, C and Mo elements were detected on the surface of nickel-chromium alloys after sputtered for 120 s in 0 g/L EGCG and 1.0 g/L EGCG artificial saliva after electrochemical corrosion, and the surface oxides were mainly NiO and Cr(2)O(3). Compared with 0 g/L EGCG artificial saliva, the content of O, NiO and Cr(2)O(3) were lower in 1.0 g/L EGCG. CONCLUSIONS: The results of surface morphology and the corrosion products both show that the corrosion resistance of nickel-chromium alloys become worse and the oxide content of corrosion products on the surface reduce in 1.0 g/L EGCG artificial saliva.

[Evaluation of masticatory efficiency of lingualized occlusal complete denture].

PURPOSE: To compare the masticatory efficiency of lingualized occlusal complete denture with that of semi-anatomical occlusal complete denture. METHODS: Sixty cases with flat or depressed residual ridges were selected from 2009 to 2011. After randomly divided into two groups, the patients were treated with lingualized and semi-anatomical occlusal complete dentures, respectively. A comparative study of masticatory efficiency was carried out on patients wearing lingualized occlusal complete dentures with those wearing semi-anatomical occlusal complete dentures in different period (1st, 2nd, 3rd, 6th month) after wearing. SAS6.16 software package was used for data analysis. RESULTS: Once masticatory time or masticatory times were fixed, there was no significant difference between lingualized occlusal dentures and semi-anatomical occlusal complete dentures (P>0.05). CONCLUSION: Lingualized occlusal complete denture can achieve good masticatory efficiency for edentulous patients with flat or depressed residual ridges.

[Study of the appearance difference of lower complete denture between functional and anatomic impression techniques].

PURPOSE: To compare the difference in oblique external ridge, oblique internal ridge and alveolar process crest of lower complete denture base made through functional impression and anatomic impression techniques. METHODS: Fifteen patients were chosen to treat with two kinds of complete dentures through functional impression and anatomic impression technique respectively. 3D laser scanner was used to scan the three-dimensional model of the denture base and the differences of the surface structural between two techniques in alveolar process crest, external and internal oblique ridges were analyzed, using paired t test with SPSS 12.0 software package. RESULTS: Between the two techniques, there were significant differences in the areas of internal and external oblique ridge(P<0.01); there was no significant difference in the main support areas(P>0.05). CONCLUSIONS: The results explain why there is less tenderness when functional impression technique is applied. The differences measured also indicate that sufficient buffering should be made in external and internal oblique ridge areas in clinic.

[Study on cytotoxicity of three kinds of dental ceramic alloys on L929 mouse fibroblasts in vitro].

PURPOSE: To investigate the cytotoxicity in vitro of three kinds of dental ceramic alloys on L929 mouse fibroblasts. METHODS: CCK-8 assay was a quick method to study the cell relative proliferation rate or cytotoxicity. L929 mouse fibroblasts were used to detect the cell relative proliferation rate of the three kinds of dental ceramic alloys(NiCr,CoCr and golden alloys containing 58% of gold) by CCK-8 assay. The DNA damage of L929 mouse fibroblasts was determined by single cell gel electrophoresis(SCGE). The data was statistically analyzed with SAS 9.0 software package. RESULTS: The relative growth rate induced by NiCr, CoCr and golden dental ceramic alloys was (75.9510+/-7.6244)%, (84.8920+/-8.2660)% and (88.5420+/-12.3611)%, respectively. NiCr ceramic alloys caused the most marked cytotoxicity(P<0.05), and there was no difference between CoCr ceramic alloys and 58% golden ceramic alloys(P>0.05). The cytotoxicity of the three kinds of metal ceramic alloys was all grade 1, i.e. mild cytotoxicity. The DNA damage of L929 mouse fibroblasts induced by NiCr ceramic alloys was most serious(P<0.05). There was no difference in the DNA damage between CoCr ceramic alloys and 58% golden ceramic alloys(P>0.05). CONCLUSIONS: NiCr ceramic alloys can suppress the proliferation of the L929 mouse fibroblasts and promote DNA damage. While CoCr ceramic alloys which are similar to 58% golden ceramic alloys show less cytotoxicity than NiCr ceramic alloys. CoCr or 58% golden ceramic alloys should be used as crown and bridge for patients instead of NiCr ceramic alloy clinically.

[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 dental caries prevalence of primary teeth in 789 five-year-old children in Shanghai].

OBJECTIVE: The aim of this study was to observe the change of the prevalence of five-year-old children's dental caries for 10 years in Shanghai and to establish a related policy to provide a basis for the government. METHODS: The sampling method was multi-stage, stratified, adqulis capacity and whole flock in this study. The method of third national survey for oral health was used. The data of prevalence of dental caries, dmft and relative component were collected and were compared with the data of the second survey in 1995. RESULTS: The prevalence of dental caries, dmft, caries filling constitutent ratio of 5-year-old children in 2005 was 71.74%, 4.17, 7.70%, respectively, and denscend 6.54%, 0.59, 1.12% compare with the data in 1995. There was significant difference between them (P<0.01). CONCLUSION: The results showed the descend trend of prevalence of dental caries in 5-year-old children in Shanghai and the oral health condition had an obvious improvement. However, caries filling constitutent ratio was decreases. Therefore, it is very important to strengthen the public oral health care service for children.

[Cytotoxicity of three kinds of temporary crown and bridge materials on mouse fibroblasts in vitro].

PURPOSE: This study was to investigate the cytotoxicity in vitro of three kinds of common temporary crown and bridge materials, i.e.,self-curing resin, heat-curing resin, and DMG-TEMP bi-acrylic composite. METHODS: L-929 mouse fibroblasts were used to evaluate the cytotoxicity of three kinds of temporary crown and bridge materials by agar overlay assay to test the cell death rate through trypan blue dyeing. RESULTS: The agar overlay assay showed that the value of Zone/Lysis of self-curing resin was 2/3, heat-curing resin was 1/0, and DMG-TEMP bi-acrylic composite was 1/2. Self-curing resin caused the most significant cytotoxicity (P<0.05), followed by heat-curing resin and DMG-TEMP composite, and the latter two showed no significant difference(P>0.05). The results of trypan blue dyeing were in accordance with the above. CONCLUSIONS: Self-curing resin, heat-curing resin, and DMG-TEMP bi-acrylic composite could decrease L-929 fibroblasts proliferation. Of all, self-curing resin caused most marked cytotoxicity, so we should avoid using self-curing resin as temporary crown and bridge to protect pulp.