Study of masking ability of laminate veneers for discolored teeth / 北京大学学报(医学版)

OBJECTIVE@#To select the most effective method among different masking treatments, such as different thickness and transparence, tissue surface's opaque coating, and opaque resin cement to restore discolored teeth esthetically by porcelain veneer.@*METHODS@#Four extracted intact maxillary central incisors were prepared for porcelain veneer restoration and each three heat pressed porcelain veneers from three thicknesses (0.8 mm, 1.0 mm, 1.2 mm) and two transparency(high transparence, HT and low transparence, LT))in Vita shade A2 were fabricated for each tooth, in total of 72 pieces. The surfaces of three prepared teeth were then painted to mimic situations of severe dental fluorosis, severe tetracycline teeth, and necrotic teeth. Each of the veneers was temporarily cemented to the corresponding tooth surface using try-in cements with three different colors (transparent, opaque, and yellow), then used the shade guide (3D master) and electronic colorimeter (easy shade) to record the shade of each porcelain veneer through hue, lightness, and chroma reading. After that, high-transparence porcelain veneers in thickness of 0.8 mm was fused with a layer of opaque porcelain in tissue surface, and were shade matched again after cementation. Statistic treatments were performed to analyze the difference in each masking method.@*RESULTS@#For each 0.2 mm increase in the veneer thickness of porcelain, the average lightness was reduced by 1 unit, while the chroma was not changed which was independent of the type of the resin cements. When the thickness of the porcelain veneer was decreased to 0.8 mm, the opacity effect was not remarkable even if a low-transparence porcelain veneer was used. Transparent and yellow resin cements had poor opaque performance, while opaque resin cement could reduce the lightness by 2 units and the chroma was also reduced. The opaque layer of the tissue surface could be applied uniformly, and the lightness and chroma could be reduced to Vita 2M1 to 2M1.5 levels regardless of the color of resin cements, which suggested a stable opacity effect for different discolored teeth in this study.@*CONCLUSION@#For porcelain veneer restoration of discolored teeth, thickened veneers are the most effective means to display a natural transmittance and color. Tissue surface's opacity coatings and opaque resin cements can also be used to reduce grayscale and increase lightness.

Influence of autoclave sterilization on dimensional stability and detail reproduction of 5 additional silicone impression materials / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the dimensional stability and detail reproduction of five additional silicone impression materials after autoclave sterilization.</p><p><b>METHODS</b>Impressions were made on the ISO 4823 standard mold containing several marking lines, in five kinds of additional silicone. All the impressions were sterilized by high temperature and pressure (135 °C, 212.8 kPa) for 25 min. Linear measurements of pre-sterilization and post-sterilization were made with a measuring microscope. Statistical analysis utilized single-factor analysis with pair-wise comparison of mean values when appropriate. Hypothesis testing was conducted at alpha = 0.05.</p><p><b>RESULTS</b>No significant difference was found between the pre-sterilization and post-sterilization conditions for all locations, and all the absolute valuse of linear rate of change less than 8%. All the sterilization by the autoclave did not affect the surfuce detail reproduction of the 5 impression materials.</p><p><b>CONCLUSIONS</b>The dimensional stability and detail reproduction of the five additional silicone impression materials in the study was unaffected by autoclave sterilization.</p>

In vivo model to evaluate the accuracy of complete-tooth spectrophotometer for dental clinics / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To test ΔE between measured value and right value from the Crystaleye complete-tooth spectrophotometer, and to evaluate the accuracy rate of the spectrophotometer.</p><p><b>METHODS</b>Twenty prosthodontists participated in the study. Each of them used Vita 3D-Master shadeguide to do the shade matching, and used Crystaleye complete-tooth spectrophotometer (before and after the test training) tested the middle of eight fixed tabs from shadeguide in the dark box. The results of shade matching and spectrophotometer were recorded. The accuracy rate of shade matching and the spectrophotometer before and after training were calculated.</p><p><b>RESULTS</b>The average accuracy rate of shade matching was 49%. The average accuracy rate of the spectrophotometer before and after training was 83% and 99%.</p><p><b>CONCLUSIONS</b>The accuracy of the spectrophotometer was significant higher than that in shade matching, and training can improve the accuracy rate.</p>

Comparison of shade matching accuracy of tabs of shadeguide and tabs out of shadeguide / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To compare the shade matching accuracy between tabs of shade guide and tabs out of shade guide by prosthodontists.</p><p><b>METHODS</b>Sixty-two graduate students who had 1 to 5 years clinical experience without color blindness were included in this study. Twenty-nine tabs from Vita 3D-Master shadeguide and 7 tabs out of Vita 3D-Master shade guide but from Vita Bleachedguide 3D-Master were taken as the targets of shade matching and observed under the standard light. Subjects' shade matching accuracy on tabs of shadeguide and tabs out of shadeguide was recorded. Frequency of right match was analyzed using Monte Carlo exact probability-test. Wilcoxin test was used to analyze the difference between each group on ranked data of value, chroma and hue.</p><p><b>RESULTS</b>The shade matching accuracy of tabs of shade guide [45.9% (199/434)] was significantly higher than that of tabs out of shade guide [9.0% (39/434)]. There was significant difference between the two kinds of tabs of ranked data of value [0.2 (0.1 - 0.3), 0.4 (0.4 - 0.5)] and chroma [0.2 (0.1 - 0.4), 0.5 (0.4 - 0.6), P < 0.01, but there was no significant difference in hue data [0.3 (0.1 - 0.4), 0.3 (0.1 - 0.4)].</p><p><b>CONCLUSIONS</b>The shade matching ability of prosthodontists on tabs out of shade guide is lower than that on tabs of shadeguide. To fulfill clinical need, more training is necessary.</p>

Application and comparison of two shade guide training systems / 中华口腔医学杂志

<p><b>OBJECTIVES</b>To evaluate the effect of shade guide training box and shade guide training software on shade matching ability of observers when used separately. To find out the difference between two training plans when the two training methods were used in combination, and to provide information on shade matching training system.</p><p><b>METHODS</b>Sixty-two postgraduate dental students who specialized in prosthodontics with 1 to 5 year clinical experience were enrolled in this study. At base line, each participant were asked to match 7 standard shade tabs which have been randomly chosen from Vita 3D-Master shade guide and 7 intermediate shade tabs from Vita bleached guide 3D-Master. Then the subjects were allocated to 2 groups [Toothguide Training Box (TTB) group and Toothguide Training (TT) group] according to the baseline data. Participants in group TTB received training session once a week for 3 weeks, while those in group TT received TT training session once a week for 3 weeks. All participants took a middle term shade-matching test. Then the two groups exchange the training methods and repeat the whole process, a final test was given to each participant. The elapsed time and number of accurate shade matching were recorded for each training session. Wilcoxon signed ranks test and ANOVA were used in data analysis.</p><p><b>RESULTS</b>There were no significant differences in the number of accurate shade matching (standard shade tab and the sum) between group TTB (4.4 +/- 1.3 and 5.3 +/- 1.6) and TT (4.0 +/- 1.4 and 4.9 +/- 1.5) in the middle term test with higher value found in group TTB. In the final test, the number of accurate shade matching (standard shade tab and the sum) in group TT (4.9 +/- 0.8 and 6.4 +/- 0.8) was higher than that in group TTB (4.7 +/- 1.1 and 5.8 +/- 0.9), but significant difference was found only when the sum number of accurate shade matching was compared between the two groups (P < 0.05). There was no significant difference between data from middle term test and from final test in group TTB; while in group TT, the number of accurate shade matching in the final test was significantly increased compared with that in the middle term test (P < 0.05).</p><p><b>CONCLUSIONS</b>When used in combination, TT training followed by TTB training is recommended.</p>

Evaluation and comparison of various renal function tests in elderly patients with chronic kidney disease / 中华老年医学杂志

Objective To find out whether the levels of serum creatinine and urea,creatinine clearance rate and GFR estimated by using different equations correlate with the exact measurement of GFR with ~(99m)Tc-DTPA in elderly patients with chronic kidney disease.Methods Renal function was determined by using ~(99m)Tc-DTPA technique in 83 elderly patients aged 65—96 years.Blood and urine tests were done at the same time.Estimated clearance was determined by using the equations of Cockcroft-Gauh,MDRD(modification of diet in renal disease)predigestion and MDRD seventh,and the correlation coefficients between the above parameters and ~(99m)Tc-GFR were determined.Veracity for the diagnosis of renal dysfunction was calculated by using receiver operating characteristic(ROC) curves.Results Cockcroft-Gault formula(r=0.833),MDRD predigestion formula(r=0.811), MDRD seventh formula(r=0.803),creatinine(r=-0.672),Ccr(r=0.632),urea(r=-0.612), and albumin(r=0.444)were correlated significantly with ~(99m)Tc-GFR in this sequence.If GFR 30, 40,50,60ml/min were defined respectively as renal impairment thresholds and areas under the curve (AUC)were compared,the best parameter for estimation of GFR was the Cockcroft-Gault formula. Then MDRD predigestion formula and MDRD seventh formula,creatinine and Ccr were less accurate in all different renal dysfunction thresholds.Conclusions The Cockcroft-Gault equation seems to be the best formula available for GFR estimation,the two equations of MDRD are the second,creatinine is the third,Ccr and urea are the last.