Effects of rotary instrumentation and different etchants on removal of smear layer on human dentin.

STATEMENT OF PROBLEM: Various methods of rotary preparation and conditioning of teeth affect surface topography and may affect the retention of dental restorations. PURPOSE: This study microscopically evaluated dentin surfaces prepared by different rotary instruments and etched using several types of acid etchants that have been deemed suitable dentin conditioners. MATERIAL AND METHODS: Occlusal surfaces of 35 extracted human molars were ground wet with 320-grit silicon carbide paper to the depth of the central groove and then prepared with diamond (n = 5) and finishing burs (n = 30). Five specimens from each group were used for SEM evaluation of mechanical preparation effects. Dentin specimens (n = 5) prepared with finishing burs were then etched with 1 of 5 etchants (25% polyacrylic acid, 10% phosphoric acid, 10% citric acid, 20% lactic acid, or 32% phosphoric acid) for 10 seconds. Specimens were critical-point dried and freeze fractured for SEM analysis. RESULTS: Diamond rotary instruments created more undulating surfaces than finishing burs. Fine grooves were observed running perpendicular to undulations and parallel to the direction of instrument rotation. Specimens prepared with finishing burs exhibited a smooth surface interrupted by only a slight granularity. The amorphous smear layer was partially removed after the application of 25% polyacrylic acid (pH 1.53), but all dentinal tubules contained plugs. The number of dentin tubules containing plug material and the amount of material in the tubules decreased noticeably with 10% phosphoric acid (pH 0.86), and the dentin surface had an appearance similar to the specimen etched with 10% citric acid (pH 1.70). The surfaces treated with 20% lactic acid (pH 1.40) produced a clearly etched surface with minimal demineralization. Etching of dentin with 32% phosphoric acid (pH 0.16) revealed significant changes in dentin with the evidence of increased tubule diameter. CONCLUSION: Differences related to the method of instrumentation were found in the surface characteristics of dentin. The degree of smear layer removal was related to the pH of the acid etchant.

The effect of recementation on crown retention.

PURPOSE: The object of this study was to evaluate retention of complete cast crowns cemented with different luting cements and to determine whether recemented castings are as retentive as when initially placed. MATERIALS AND METHODS: Thirty standardized Rexillium III complete crowns were made on extracted human molar teeth prepared with a modified milling machine using conventional laboratory techniques. The crowns were randomly assigned into three groups according to the luting cement used: zinc phosphate (Fleck's, Mizzy), adhesive resin (Panavia-EX, J. Morita), and glassionomer (Ketac-Cem, Aplicap, ESPE-Premier Sales). Retention was evaluated by measuring the tensile force required to dislodge the crowns from tooth preparations with an Instron testing machine after thermocycling (1,500 cycles between 5 degrees C and 55 degrees C with 1-minute dwell times). Subsequently, the tooth preparations were scraped clean and polished with flour of pumice (prophylaxis paste), and the fitting surfaces of the artificial crowns were ultrasonically cleaned and air abraded using 50-micron aluminum oxide powder prior to recementation. Results were subjected to two-way analysis of variance and Tukey's Studentized Range test. RESULTS: The analysis showed the highest mean retention for cast crowns cemented with Panavia-EX cement (314 N), but the difference was not statistically significantly different from crowns cemented with glass-ionomer cement (307 N). However, crowns cemented with zinc phosphate cement (233 N) had significantly lower values (P < 0.05). Restorations recemented with zinc phosphate had significantly lower retention (190 N) than their initial cementation (P < 0.05). CONCLUSIONS: Panavia-EX and glass-ionomer cements yielded the highest initial and recementation retentive strength, with values almost 32% higher than those obtained with zinc phosphate cement during the initial cementation and 59% higher than zinc phosphate for recementation. Zinc phosphate cement exhibited significantly lower retention for the initial and second trial of cementation.

Preliminary evaluation of tin plating for extracoronal restorations: evaluation of marginal quality and retention.

PURPOSE: The influence of tin plating on marginal seating and retention of complete cast crowns was evaluated. MATERIALS AND METHODS: Thirty-six standardized gold-alloy complete crowns were made on extracted human molar teeth prepared with a modified milling machine using conventional laboratory techniques. The crowns were randomly assigned to two groups according to the treatment of the fitting surface (air abraded with 50-micron aluminum oxide for 10 seconds, or tin plated with a microtin system for 3 seconds), and luted with adhesive resin cement (Panavia-EX, J. Morita). Scanning electron microscopy was used to evaluate the variables for the cast alloy. Retention was measured with an instron testing machine after thermocycling (1,500 cycles between 5 degrees C and 55 degrees C with 1 minute dwell times). Marginal adaptation was measured with a Nikon microscope before and after cementation. Results were subjected to one-way analysis of variance and Student's t test. RESULTS: Retention was significantly different (P < 0.001); the highest retention (367 N) was reported in tin-plated crowns. Differences for marginal seating were not statistically significant. CONCLUSION: Tin plating after air abrasion was found to be a predictable and simple technique to roughen the casting surface, increase the surface area for bonding, and significantly improve the retention of cast crowns in vivo.

Insulin sensitivity and intake of vitamins E and C in African American, Hispanic, and non-Hispanic white men and women: the Insulin Resistance and Atherosclerosis Study (IRAS).

Elevated fasting insulin concentrations and insulin resistance have been associated with non-insulin-dependent diabetes mellitus (NIDDM), obesity, atherosclerosis, and hypertension. Vitamin E supplementation in persons with and without NIDDM may be related to greater insulin sensitivity (SI). The cross-sectional associations of the intake of vitamins E and C with SI and insulin concentrations were evaluated among African American, Hispanic, and non-Hispanic white men and women with a wide spectrum of glucose tolerance included in the Insulin Resistance and Atherosclerosis Study (IRAS) (n = 1151). Insulin sensitivity was measured by minimal model analysis of a 12-sample, insulin-modified, frequently sampled intravenous glucose tolerance test. Nutrient intake (including vitamin supplement use) was assessed with a food-frequency questionnaire modified to include foods consumed by the three ethnic groups. Linear-regression models were used, including rank of SI and the log of fasting insulin as the outcome variables. Pearson correlation coefficients for vitamins E and C in relation to rank SI were r = 0.07 (P = 0.01) and r = 0.07 (P = 0.02), respectively. After adjustment for total energy and BMI these associations were no longer statistically significant and did not differ between ethnic groups. Results were similar when vitamins E and C were combined in categories of low and high antioxidant intake. Models replicated with log of fasting insulin as the outcome variable also did not produce significant associations with vitamins E or C. Thus, these cross-sectional analyses do not support the hypothesis of improved SI with increased intake of vitamins E and C.

Differences between the tolbutamide-boosted and the insulin-modified minimal model protocols.

The insulin-modified frequently sampled intravenous glucose tolerance test (FSIGTT) with minimal model analysis (MINMOD) was compared with the tolbutamide protocol and the glucose clamp in 35 nondiabetic subjects (age 38 +/- 2 years [mean +/- SE], BMI 27.2 +/- 0.9 kg/m2). Each subject underwent two FSIGTTs, one with tolbutamide (300 mg) and the other with insulin (0.03 U/kg) and a euglycemic hyperinsulinemic clamp (40 mU x m(-2) x min(-1)). Insulin sensitivity was determined from each FSIGTT with MINMOD and from the clamp. Insulin sensitivity indexes (S(I)) from the two FSIGTTs were significantly correlated (r = 0.77, P < 0.001), but S(I(insulin)) was 29 +/- 4% lower than S(I(tolbutamide)). Both S(I(insulin)) and S(I(tolbutamide)) correlated significantly with S(I(clamp)) (r = 0.70 and 0.71, P < 0.001 for each). Expressed in the same units (dl/min per pU/ml), S(I(tolbutamide)) was on average 13 +/- 6% lower than S(I(clamp)) (4.51 +/- 0.40 vs. 5.36 +/- 0.36 x 10(-2), P = 0.009), whereas S(I(insulin)) was 44 +/- 4% lower. S(G(tolbutamide)) and S(G(insulin)) were not different (1.88 +/- 0.10 vs. 2.01 +/- 0.09 x 10(-2) min(-1), P = 0.167) and were significantly correlated (r = 0.50, P = 0.002). Thus, insulin sensitivity estimates from both protocols correlate significantly with each other and with the clamp. They are quantitatively discrepant, however, possibly due to differences in the route of insulin delivery, saturation of insulin action, and/or tolbutamide-induced proinsulin release. Data obtained from these two MINMOD protocols are not directly comparable, and the same protocol must be used in any single cross-sectional or longitudinal study.

Influence of tooth surface roughness and type of cement on retention of complete cast crowns.

STATEMENT OF PROBLEM: Bond strength of luting cements to dentin is a critical consideration for success of cast restorations. PURPOSE OF STUDY: This study determined the relationship between surface characteristics of teeth prepared for complete cast crowns and retention of respective cemented restorations. MATERIAL AND METHODS: Ninety artificial crowns were cast for standardized complete crown tooth preparations accomplished with the use of a milling machine on extracted human teeth. Diamond, tungsten carbide finishing, and cross-cut carbide burs of similar shape were used. The crowns in each group were randomly subdivided into three subgroups of 10 for the three luting cements selected for this study: zinc phosphate cement (Fleck's), glass ionomer cement (Ketac-Cem), and adhesive resin cement (Panavia-EX). Retention was evaluated by measuring the tensile load required to dislodge the artificial crowns from tooth preparations with an Instron testing machine. RESULTS: Analysis of forces with parametric analysis of variance and Tukey's Studentized Range (HSD) disclosed a statistically significant difference for both luting cement and finishing burs (p < 0.001). A statistically significant interaction effect (p < 0.001) was also found. The greatest retention value (372.9 N) was for tooth preparations refined with carbide burs and cemented with Panavia-EX cement. However, the least retention value (201.6 N) was for tooth preparations completed with finishing burs and luted with zinc phosphate cement. CONCLUSIONS: Significant differences were found among all three cements for finishing burs. However, there was a difference only between Panavia-EX cement and the other two cements for tungsten carbide burs. For diamond rotary instruments, zinc phosphate cement was significantly different from glass ionomer and Panavia-EX cements.

Dietary fat and insulin sensitivity in a triethnic population: the role of obesity. The Insulin Resistance Atherosclerosis Study (IRAS)

From the Insulin Resistance Atherosclerosis Study (IRAS), 1173 men and women of African-American, non-Hispanic white, and Hispanic ethnicity with no history of diabetes were included in an evaluation of the cross-sectional relation of habitual dietary fat intake with insulin sensitivity (SI) as assessed by minimal-model analysis of a 12-sample, insulin-modified frequently sampled intravenous-glucose-tolerance test. Dietary intake was measured by a food-frequency interview modified to enhance sensitivity to food choices within the three ethnic groups. Percentage of energy from total fat was associated with rank of SI (SI(rank); r = -0.06, P = 0.03), with log fasting insulin (r = 0.10, P < 0.001), and with BMI (r = 0.10, P < 0.001). Multiple-linear-regression models included SI(rank) as the dependent variable, dietary fat (g/d) as the primary independent variable adjusted sequentially for total energy, other covariates, body mass index, and waist-hip circumference ratio (WHR). For all subjects combined, total fat intake was inversely related to SI(rank), but this association was not significant (P = 0.14) and was attenuated by adjustment for body mass index and WHR (P = 0.44). The association of total fat (g/d) with SI(rank) differed significantly (P < 0.01) for obese compared with nonobese individuals. Higher fat intake was associated with lower SI(rank) among obese (beta = -1.40, P = 0.03) but not among nonobese persons (beta = 0.16, P = 0.80). Among the obese (body mass index < or = 63), adjustment for body mass index largely accounted for the observed association of dietary fat with SI(rank). These findings were generally consistent for monounsaturated, polyunsaturated, and saturated fats. Among individuals already at increased risk for non-insulin-dependent diabetes mellitus because of obesity, high intake of dietary fat may worsen insulin sensitivity. This effect may be mediated by the relation of dietary fat to obesity.

A pilot study of lactic acid as an enamel and dentin conditioner for dentin-bonding agent development.

The purpose of this pilot study was to determine how lactic acid solution at various concentrations and etching times affected prepared human enamel and dentin surfaces and to assess whether it could be used in place of phosphoric or maleic acid as an etchant. The occlusal surfaces of extracted molar teeth were ground wet with 600-grit silicon carbide paper and treated with various aqueous solutions of lactic acid. Random samples were prepared for observation by scanning electron microscopy. The rest were used to determine shear bond strength of bonded dental composite cylinders. The micrographs revealed that lactic acid dissolved the smear layer with various degrees of etching and demineralization. The degree of smear layer and matrix removal was proportional to the concentration of the acid and the length of application time. A 20% lactic acid concentration applied for 10 seconds produced a clearly etched surface with minimal demineralization. A 30% concentration not only removed the smear layer and enlarged the dentin tubule orifices but also appeared to affect the collagen matrix. The shear bond strength to enamel treated with 50% lactic acid (17.5 +/- 1.5 MPa) and All-Bond 2 etchant (18.9 +/- 1.3 MPa) were not significantly different (p > 0.05). However, mean dentin bond strengths for all groups of lactic acid etchant and All-Etch etchant (10% phosphoric acid) were statistically similar.

Surface roughness of dentin after tooth preparation with different rotary instrumentation.

Although surface finish can be a critical variable in clinical performance, there is a dearth of information regarding surface characteristics of teeth prepared for artificial crowns. This study characterized teeth prepared for complete cast restorations using three representative types of rotary instruments. One hundred and five standardized tooth preparations for complete crowns were performed using a modified milling machine on extracted human teeth with diamond, tungsten carbide, and tungsten carbide finishing burs of similar shape (n = 35). The prepared dentin was analyzed with a surface profilometer and a scanning electron microscope (SEM). Differences between rotary instrument groups were determined with parametric ANOVA and Tukey's Studentized Range (HSD). Statistically significant differences in the surface topography of prepared teeth were open. Mean surface roughnesses (Ra) were 8.6 and 6.8 mum for teeth prepared with diamond and tungsten carbide burs. Teeth completed with finishing burs appeared to result in a smoother surface (1.2 mum).