[Study of the mucosal morphological difference of distal-extension of mandibular dentition defect impressions taken by intra-oral digital scanning and selective pressure impression technique].

PURPOSE: To compare the mucosal morphological difference in distal-extension area of mandibular dentition defect taken by intra-oral digital scanning and selective pressure impression techniques. METHODS: Seventeen patients with Kennedy Class I and Class II dentition defect in lower jaw were included, including twenty-two distal-extensions. Intraoral digital scanning and functional impression technique were taken in each patients, respectively. Laboratory cast scanner was used to scan the plaster casts made from the selective pressure impression to obtain the three-dimensional data. All the data were stored in STL format. The 3D data collecting from intra-oral digital scanning and selective pressure impression from the same patient were compared by Geomagic Control 2014 software. Root mean square of 2.5mm diameter area was calculated in 5,10,15 mm from terminal tooth. Pearson's correlation test was used to analyze the correlation of the distance and morphological difference with SPSS 20.0 software package. RESULTS: Mean mucosal morphological difference of jaw distal-extension edentulous area taken by intra-oral digital scanning and selective pressure impression techniques was (0.37±0.12) mm. There was positive correlation between distance from terminal tooth and mucosal morphological difference(P＜0.05). Morphological differences in 5, 10, 15 mm from terminal tooth were (0.14±0.11) mm, (0.22±0.13) mm and (0.39±0.16) mm, respectively. CONCLUSIONS: In this study, there was positive correlation between the length of distal-extension edentulous area and mucosal morphological difference, while the kind of ridge defect and mucosal thickness may also affect the morphological difference quantity.

[Study of the morphological difference of upper jaw impressions taken by intra-oral digital scanning and functional impression technique].

PURPOSE: To compare the difference in distal-extension models taken by intra-oral digital scanning and functional impression technique. METHODS: Twenty patients with dentition defect in upper jaw, including 10 Kennedy Ⅰ defect and another 10 Kennedy Ⅱ defect, were chosen to treat with intraoral digital scanning and functional impression technique respectively. Laboratory cast scanner was used to scan the plaster casts made from the functional impression to obtain the three-dimensional data. All the data were stored in STL format. The 3D data collecting from intra-oral digital scanning and functional impression from the same patient were compared by Geomagic Qualify 12 software, and the trueness of the difference on free end morphology were analyzed. Paired t test was used to analyze the difference of the alveolar mucosa variable with SPSS 20.0 software package. RESULTS: There was no significant difference between the group of Kennedy I defect and Kennedy Ⅱ defect(P>0.05） regarding the two methods of impression. All the cases presented the tendency that with distance from distal teeth increasing, the average RMS also increased. CONCLUSIONS: Whether using intra-oral digital scanning or functional impression technique, the type of dentition defect was not obviously related to the difference of RMS in distal-extension tissues. In addition, there is positive correlation between the length of distal-extension edentulous area and difference of RMS, which needs further studies with more cases.

[A comparative study on the effect of glass fiber post and metal post in restoration of anterior tooth defect].

PURPOSE: To analyze the effect and long-term success rate of using glass fiber post or metal post in restoration of anterior tooth defect. METHODS: One hundred and fifty cases with anterior tooth defects were chosen after root canal therapy in our hospital. According to different material being chosen, the patients were divided into fiber post group and metal post group with 75 cases in each group. Local gingival sulcus fluid (GCF) levels and alkaline phosphatase (ALP) level in gingival sulcus liquid were measured and compared 4 weeks, 6 months, 1 year, 2 years and 3 years after restoration. Restoration integrity, edge fitness and color matching of two groups were compared after follow-up for 3 years. The data were analyzed with SPSS 19.0 software package. RESULTS: Four weeks, 6 months, and 1 year after restoration, local GCF, ALP levels significantly elevated in both groups. The fiber post group showed more significant elevated levels of GCF and ALP than the metal post group (P<0.05). After 2 and 3 years, the difference between the two groups was not significant. The gingival color matching degrees were significantly better in the glass fiber post group after 1 year compared with that in the metal post group(P<0.05). The success rate of metal post group was significantly higher than that of fiber post group 3 years after restoration(P<0.05). CONCLUSIONS: Fiber post and metal post both have satisfactory restoration result for tooth defect in anterior teeth area. However, the use of precious metal alloy post may reduce the possibility of microleakage between tooth-prosthesis surfaces.

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

PURPOSE: To analyze the retention of 3 different Co-Cr-Mo alloy clasps on premolars, and provide information for clinical design of aesthetic clasps. METHODS: An EZ20 force measuring instrument was used to record the retention of Co-Cr-Mo alloy casting aesthetic clasps when they were dislodged from undercuts of different depths (0.25, 0.50, 0.75 mm) on premolars. The data were analyzed with SPSS 22.0 software passage. RESULTS: The clasp retention in groups of 0.25 and 0.5 mm undercut was three-arm clasp > varied Y-shaped clasp > modified RPI clasp. In the group of 0.75 mm undercut, the clasp retention was varied Y-shaped clasp>three-arm clasp>modified RPI clasp after circulations. CONCLUSIONS: A varied Y-shaped bar clasp of 0.75 mm undercut depth is suitable for premolar both for its adequate retention and aesthetic effect.

[Effects of repeated firing on microleakage of selective laser melting ceramic crowns].

PURPOSE: To investigate the effects of repeated firing on microleakage of selective laser melting ceramic crowns. METHODS: Fifty molars were randomly divided into 2 groups (25 teeth in each group). Teeth in group A received a chamfer finish line preparation, whereas teeth in group B received a shoulder finish line. After SLM metal crowns were fabricated, all the crowns received initial oxidation step, opaque firing, dentin firing and glaze firing, then crowns in each group were randomly divided into 5 sub-groups according to different time of clinical firings. Glass ionomer was applied for bonding. After 5000 thermocycles ranging from 5degrees centigrade to 55degrees centigrade, all the specimens was evaluated by dye penetration and then microleakage was examined under light microscopy. The data were analyzed with SPSS 20.0 software package. RESULTS: Microleakage between all specimens of group A were not statistically significant (P>0.05) whereas that of group B were statistically significant (P<0.05); After the fifth time of clinical firing, microleakage of specimens in group B(B5) were significantly higher than that of group A(A5). CONCLUSIONS: Repeated firings had no significant influence on marginal microleakage of SLM ceramic crowns whereas the crowns of chamfer finish lines result in better clinical performance after repeated firings.

[Comparative study of microleakage by using different finished lines in selective laser melting metal crowns].

PURPOSE: To evaluate microleakage of SLM Co -Cr alloy metal crown with two types finished line (chamfer and shoulder), compared with conventional fabrication of Co -Cr alloy metal crowns. METHODS: Thirty healthy non-carious human molars were selected and randomly assigned to 3 groups, 10 in each. Teeth in group A and C received a chamfer finish line preparation, whereas teeth in group C received a shoulder finish line. Conventional Co -Cr alloy metal crowns were fabricated for group A when SLM metal crowns were made for group B and group C. Glass ionomer was applied for bonding. After 5000 thermocycles ranging from 5degrees centigrade to 55degrees centigrade,all the specimens were evaluated by dye penetration and then microleakage was examined under light microscope. The data were analyzed statistically with SPSS 20.0 software package. RESULTS: Microleakage in group A was significantly higher than the other two groups, group B and group C showed no significant difference in microleakage while microleakage in group B was higher than that in group C. CONCLUSIONS: Microleakage of SLM metal crowns was significantly less than that of conventional Co-Cr alloy metal crowns; chamfer finish line designs was recommended for SLM metal crowns in consideration of reducing microleakage and protecting tooth.

[Evaluation of fiber reinforcement composites in restoring lower dentition defect and fixing loose teeth for chronic periodontitis].

PURPOSE: To evaluate the effect of fiber reinforcement composites (FRC) in treating chronic periodontitis with dentition defect. METHODS: Thirty patients who had chronic periodontitis and missed less than 2 lower anterior teeth were chosen. After appropriate periodontal treatment, EverStick fibers were used to fabricate splint with the missing teeth repaired. One month, 6 months, 1 year and 2 years after treatment, periodontal indexes such as plaque index (PLI), gingival index (GI) and probe depth (PD) were recorded and the patients' satisfaction was evaluated. SPSS 17.0 software package was used for statistical analysis. RESULTS: The results showed that no significant difference was found in PLI and GI during observation period (P>0.05). PD decreased significantly after 6 months of observation (P<0.05). Patients' satisfaction degree for aesthetics, pronunciation, comfort and function was beyond 80%. CONCLUSIONS: Using FRC technique in chronic periodontitis with dentition defect can effectively fix the loosen teeth and maintain physical function. Appropriate periodontal treatment every 6 months is the key factor for satisfactory results.

[Photoelastic analysis of mandibular edentulous alveolar bone with denture adhesives].

PURPOSE: To compare the stress distribution of supporting tissues in Atwood level 3 alveolar bones under the mandibular complete dentures with and without denture adhesives. METHODS: Photoelastic models of epoxy were fabricated according to the standard Atwood level 3 edentulous model. 1.5 kg force was vertically applied on the bite force loading device. After stress frozen, photoelastic model slices in posterior teeth area were observed and analyzed. RESULTS: When using denture adhesives, stresses distributed more adequately in the buccal and lingual side and the force of alveolar crest increased remarkably. CONCLUSIONS: To those with Atwood level 3 alveolar ridge and complete denture, denture adhesives can not only increase stability but also prevent local pressure under uneven stress distribution.

[Effect of different surface treatments on the shear bond of zirconia substructure and veneering ceramic].

PURPOSE: To investigate the effect of different surface treatments on the shear bond strength of zirconia substructure and veneering ceramic. METHODS: Kavo zirconia specimens were divided into 4 groups (each group contains 8 specimens) according to different surface treatments: Group A was pigmented by dipping presintered blocks in the coloring solution VITA LL5, and not treated with abrasion after firing; Group B was pigmented with the same solution and then dealt with abrasion; Group C was not treated by any methods and Group D was only dealt with abrasion. All the veneering ceramics were fired on the zirconia substructure by slip-casting technique and the shear bond strength of zirconia substructure and veneering ceramic were tested. The data was analyzed statistically with SPSS 10.0 software package. RESULTS: The shear bond strength of the abrasive-treated groups (group B and group D) was significantly higher than the other two groups, but no significant difference was found between pigmented-treated groups (group A and group C) and non-pigmented-treated groups (group B and group D). CONCLUSIONS: Abrasion can increase the shear bond between Kavo zirconia substructure and veneering ceramics while pigmentation has no significant effect on the bonding strength.

[The stress distribution of mandibular alveolar mucosa under functional impressive complete denture studied by 3-D finite element analysis].

PURPOSE: To analyze the stress distribution and displacement of the mandibular alveolar mucosa under functional impressive complete denture. METHODS: CT images were processed by Mimics and Geomagic studio, and the solid models and 3-D finite element models were established by Unigraphics NX. 3-D finite element analysis (3-D FEA) was used to study the stress distribution and displacement on the mandibular alveolar mucosa under functional impressive complete denture and anatomic impressive complete denture. RESULTS: The stress distribution on the mandibular alveolar mucosa under two types of complete denture were consistent, and arranged from large to small order as follow: alveolar process crest of molar area, alveolar process crest of anterior area, external oblique ridge and internal oblique ridge. At alveolar process crest and internal oblique ridge, the stress and Z-axis displacement of functional impressive complete denture were less than those of anatomic impressive complete denture. CONCLUSIONS: During masticatory period, the stress distribution on the mandibular alveolar mucosa under functional impressive complete denture is more even and more comprehensive than that under anatomic one.

[Comparative adaptation of crowns of selective laser melting and wax-lost-casting method].

OBJECTIVE: To investigate the marginal adaptation of crowns fabricated by selective laser melting (SLM) and wax-lost-casting method, so as to provide an experimental basis for clinic. METHODS: Co-Cr alloy full crown were fabricated by SLM and wax-lost-casting for 24 samples in each group. All crowns were cemented with zinc phosphate cement and cut along longitudinal axis by line cutting machine. The gap between crown tissue surface and die was measured by 6-point measuring method with scanning electron microscope (SEM). The marginal adaptation of crowns fabricated by SLM and wax-lost-casting were compared statistically. RESULTS: The gap between SLM crowns were (36.51 ± 2.94), (49.36 ± 3.31), (56.48 ± 3.35), (42.20 ± 3.60) µm, and wax-lost-casting crowns were (68.86 ± 5.41), (58.86 ± 6.10), (70.62 ± 5.79), (69.90 ± 6.00) µm. There were significant difference between two groups (P < 0.05). CONCLUSIONS: Co-Cr alloy full crown fabricated by wax-lost-casting method and SLM method provide acceptable marginal adaptation in clinic, and the marginal adaptation of SLM is better than that of wax-lost-casting method.

[Clinical analysis of laser welding on porcelain bonded metal surface].

PURPOSE: To evaluate the clinical effect of laser-welded crowns and bridges. METHODS: Two hundred defective crowns and bridges were welded by using Heraplus laser welding machine, and then restored by porcelain. RESULTS: After being welded ,those defective crowns and bridges of different materials fit well and their marginal areas were also satisfactory. During the follow up period of one year, no fractured porcelain and crack were found at welding spots. CONCLUSIONS: The technology of laser welding has no direct effect on welding spots between metal and porcelain and could be used to deal with the usual problems of the crowns and bridges.