Effects of etchants and primers on shear bond strength of a self-ligating esthetic orthodontic bracket.

INTRODUCTION: Damon 3 orthodontic brackets (Ormco, Orange, Calif), combining a self-ligating bracket with a composite bracket pad were the subject of an in-vitro bonding study to determine the shear bond strength to enamel and adhesive remaining on the teeth with various enamel and bracket preparation procedures. METHODS: A 3 x 2 factorial design was selected with the following factors as variations of the enamel preparation: liquid phosphoric acid etchant followed by primer (Ortho Solo; Ormco), gel phosphoric acid etchant followed by primer, and self-etching primer (Transbond Plus; 3M Unitek, Monrovia, Calif). The second factor was a primer (Ortho Solo) either applied to the bracket pad or absent as a control. RESULTS: No statistically significant differences were observed in shear bond strengths, with group average estimates ranging from 14.5 to 16.6 MPa. Debonding predominantly occurred at the bracket-pad interface with no significant differences in adhesive remaining on the teeth. CONCLUSIONS: This in-vitro study indicated that self-etching primer, gel etchant, and liquid etchant produce equal and sufficient bond strengths. Furthermore, application of primer to the bracket pad does not improve bond strength.

The wetting of surface-treated silicone impression materials by gypsum mixes containing disinfectants and modifiers.

PURPOSE: This work evaluated wettability of silicone impression surfaces by gypsum mixes containing disinfectants. MATERIALS AND METHODS: Two types of dental stone were modified by mixing with aqueous solutions of either sodium hypochlorite or povidone iodine. These materials were subjected to further modification by adding a mixture of 1% gum arabic and 0.132% calcium hydroxide to reduce the water requirement of the hemihydrate. Mix consistency tests were carried out to determine the effect of the disinfectants and the modifying additives on the mix fluidity. Contact angles of the mixed materials were measured when they were poured against a polyvinylsiloxane impression material that had undergone the following treatments (1) no treatment (control), (2) surfactant treated, (3) disinfectant treated, and (4) treated with both surfactant and disinfectant. One-way analysis of variance (ANOVA) was carried out using Dunnett's method to determine if experimental groups were significantly different from the control. RESULTS: Gypsum mix consistency was reduced by the presence of combined gum arabic and calcium hydroxide additives. Contact angle data showed that the additives and disinfectants incorporated into the gypsum had, in general, no beneficial effect on the wetting of an untreated silicone surface, or a surface treated with surfactant. In some instances, better wetting was obtained with disinfectant-treated surfaces, and surfaces that had been disinfected and treated with surfactant. CONCLUSIONS: Fluidity of the mixed gypsum was affected by the modifying additives. Chemical disinfectants incorporated in gypsum have little effect on the wetting behavior of dental gypsum. Modifying dental stone powders with gum arabic and calcium hydroxide additives (before mixing at the manufacturers' recommended liquid/powder ratios), improved the wetting behavior of the mixed materials in some cases, but results were not consistent.

The surface free energy of dental gold-based materials.

OBJECTIVE: A gold composite material (Captek) has been developed which is claimed to resist plaque deposition. This study's aim was to compare the surface free energy (SFE) of this composite material with that of a type III casting gold. METHODS: Contact angle measurements, using the Wilhelmy technique, were made on four bar-shaped samples of each material, using five test liquids (diiodomethane, ethylene glycol, formamide, glycerol and water) and four measurements per sample per liquid. For each material, the dispersive, Lewis acid and Lewis base components of SFE (gamma(S)D, gamma(S)+, gamma(S)-, respectively) were estimated by least squares analysis and also by a Bayesian method. RESULTS: The gold composite material and the type III casting gold did not differ significantly in their gamma(S)D values (95% confidence interval for gold composite minus type III gold, -5.0 to +2.7). Both materials had low gamma(S)+ values in common with most solids. The gold composite had a significantly lower Lewis base component of SFE than the type III gold-8.4 mN/m for the former material compared to 19.1 mN/m for the latter (95% confidence interval for gold composite minus type III gold, -16.4 to -4.9). The difference between materials could be related to the lack of non-precious metals and the structure of the gold composite material. CONCLUSIONS: It is hypothesized that difference in gamma(S)- components of SFE may be an important parameter in predicting bacterial adhesion and plaque resistance. Methods that only determine SFE as a single parameter may be unable to differentiate adequately between dental restorative materials.

Evaluation of disinfected casts poured in gypsum with gum arabic and calcium hydroxide additives.

STATEMENT OF PROBLEM: Disinfection of stone casts is an important measure for the control of cross-contamination. Many approaches have been used to disinfect stone casts, but information regarding the accuracy of the resultant casts is limited. PURPOSE: The purpose of this in vitro study was to evaluate the dimensional accuracy, incidence of abutment fracture, and the abutment reproduction of disinfected stone casts made from elastomeric impressions and to determine the effect of gum arabic and calcium hydroxide additives on these properties. MATERIAL AND METHODS: Two aqueous solutions of chemical disinfectants (0.525% sodium hypochlorite and 0.1% povidone iodine) were used as mixing water substitutes for 3 types of dental stone: Types III (Lab Stone), IV (Mile Stone), and V (Die Keen). These stone powders were subjected to further modification by adding 1% gum arabic and 0.132% calcium hydroxide before mixing at the manufacturer-recommended liquid/powder ratios (0.30 for Type III, 0.21 for Types IV and V, respectively). As these additives increased the fluidity of the mix, reduced liquid/powder ratios (0.26 for Type III, 0.19 for Types IV and V, respectively) were also evaluated. Unmodified stone powder mixed with water served as the control. These modifications resulted in 7 test groups for each type of stone. Mixed stones of these groups were poured into 10 putty/wash vinyl polysiloxane impressions made of a customized definitive cast. The percentage of abutments fractured at the time of releasing the resultant casts, as well as the percentages of incompletely reproduced abutments, abutments with air bubbles, and abutments with defective finish lines were compared statistically among the tested groups using the chi-square test (alpha=.05). The average dimensional deviations of the resultant cast from the definitive cast measured in mm were statistically analyzed using 1-way ANOVA (alpha=.05) followed by the Dunnett test to detect any differences among the tested groups. RESULTS: No significant difference was found in abutment fracture or abutment defects for the different formulations of each type of stone used. The resultant casts showed no significant dimensional changes except for Type III and IV stones modified by gum arabic and calcium hydroxide additives and mixed at the recommended liquid/powder ratios. CONCLUSION: Both 0.525% sodium hypochlorite and 0.1% povidone iodine can be used to disinfect dental gypsum with no significant effect on the dimensional accuracy and reproducibility of the resultant casts. Addition of gum arabic and calcium hydroxide to the hemihydrate powders before mixing does not aid in reducing the incidence of defective abutment reproduction.

A protocol for determining the surface free energy of dental materials.

OBJECTIVE: The purpose of this study was to develop a standard methodology for measuring the surface free energy (SFE), and its component parts, of dental biomaterials. METHODS: The contact angle of each of four samples of two materials--low density polyethylene and poly(methyl methacrylate)--was measured three times in each of six liquids (1-bromonaphthalene, diiodomethane, ethylene glycol, formamide, glycerol and distilled water). Critical surface tension estimates were obtained from Zisman plots. Data were then analyzed by the least-squares method to estimate the components of SFE. Estimates were also made for each of 12 liquid triplets, and by maximum likelihood and Bayesian analyses. RESULTS: The use of liquid triplets could yield misleading estimates of the components of SFE. A testing protocol is suggested in which multiple test liquids are used, and multiple methods of statistical analyses employed. SIGNIFICANCE: SFE is important, in that high SFE is desirable when adhesion is required, but undesirable if plaque resistance is needed. Methodology that avoids some of the limitations of existing studies has been proposed.

Polymerization of orthodontic adhesives using modern high-intensity visible curing lights.

This study was undertaken to assess the efficacy of 3 visible curing lights: a conventional halogen light and 2 high-intensity halogen lights in the polymerization of a polymer-based and resin-modified glass ionomer orthodontic cement. Degree of polymerization was measured by Fourier transform infrared spectroscopy and the development of mechanical properties by Barcol hardness. The results were analyzed with either 2- or 3-way analysis of variance. It was shown that, for the polymer-based material, there was a significant increase in degree of cure and hardness with time of application of the light for each light source. For chemical conversion, there was no significant difference between the lights. However, there was a difference in hardness: the higher intensity lights produced greater hardness in shorter time. Thus, there was poor correlation between degree of polymerization and hardness. For the resin-modified glass ionomer, similar trends were found, but there was a difference in hardness between the top and the bottom of the specimens. It was concluded that the higher intensity lights could aid in the more rapid development of mechanical properties of the tested adhesives.

Calcium hypochlorite as a disinfecting additive for dental stone.

STATEMENT OF PROBLEM: Dental casts come into direct contact with impression materials and other items that are contaminated by saliva and blood from a patient's mouth, leaving the casts susceptible to cross-contamination. Topical methods of disinfecting casts are difficult to control, while immersion methods are potentially destructive. Thus, an additional method to control cross-contamination between patients and laboratory personnel is needed. PURPOSE: This study was undertaken in an attempt to develop a dental stone with disinfecting properties and adequate compressive and tensile strengths. MATERIAL AND METHODS: Calcium hypochlorite [Ca(OCl)(2)] in aqueous solution in concentrations from 0 to 1.5% was tested as a disinfecting additive to type V dental stone. The compressive and tensile strength properties of the modified stone were measured (MPa) using a universal testing machine at a consistency similar to unmodified stone. Strength data were analyzed by 1-way ANOVA and post hoc Tukey-Kramer procedure (alpha < or =.05). To measure the disinfecting ability, the effect on Bacillis subtilis bacteriophage phi29 was tested in triplicate to find the minimum concentration at which no phage was detected. Additionally, 3 impressions were disinfected with CaviCide, and 3 impressions rinsed in water served as controls. RESULTS: In general, the effect of adding the disinfectant to the stone was a decrease in strength. Exceptions were the dry compressive strength, for which there was a significant increase in strength (P=.048) at 0.5%, and the wet compressive and wet tensile strength, which showed no significant difference between the 1.5% and the control. When Ca(OCl)(2) was added at the concentration 0.5% (2765 ppm available chlorine), the gypsum had acceptable mechanical properties; dry compressive strength was 78.86 +/- 4.12 MPa, and dry tensile strength was 10.64 +/- 1.27 MPa, compared to control values of 67.85 +/- 6.28 and 13.41 +/- 1.24 MPa, respectively. At concentrations of 0.3% and higher (36 1650 ppm of available chlorine), calcium hypochlorite was able to completely inactivate phi29. CONCLUSION: It is possible to prepare a type V dental stone that contains a disinfectant, has adequate mechanical properties, and will reduce numbers of residual microorganisms. For example, stone mixed with water containing 0.5% Ca(OCl)(2) meets these criteria.

The effect of disinfectants on the properties of dental gypsum, part 2: surface properties.

PURPOSE: This study is part of an ongoing investigation to evaluate the surface properties of dental stones mixed with disinfection solutions, and to determine the effect of adding gum arabic and calcium hydroxide on the same properties. MATERIALS AND METHODS: Aqueous solutions of 2 chemical disinfectants were used in mixing 2 types of dental stones (type III and type V). These dental stones were modified further by adding 1% gum arabic and 0.132% calcium hydroxide to their hemihydrate powders before mixing. Five specimens prepared from each type of dental stone were classified into 7 groups according to the hemihydrate powder modification and mixing liquid/powder ratio. Surface roughness was tested by 2-dimensional profilometery and scanning electron microscopy (SEM). Knoop hardness testing was carried out, and detail reproduction was assessed using ADA specification 25 in addition to SEM and 3-dimensional profilometer studies. RESULTS: Dental stones mixed with chemical disinfectants showed higher average roughness (R(a)) values than those of the controls. However, adding gum arabic and calcium hydroxide to the hemihydrate powders before mixing restored values to the level of the control. The additives seemed to have a role in the improvement of surface hardness. There was no significant difference between the experimental and the control group in the terms of detail reproduction. CONCLUSIONS: Using SEM, 3-dimensional profilometry, and ADA testing methods, we found that the surface roughness of stone casts was adversely affected by using the disinfectant solutions as mixing water substitutes. Gum arabic and calcium hydroxide additives can yield a harder stone surface without compromising other surface properties.

The effect of disinfectants on the properties of dental gypsum: 1. Mechanical properties.

PURPOSE: This study was conducted to evaluate the effect of selected disinfectants incorporated in the liquid of dental stones on material strength properties with the aim of developing a material with acceptable mechanical properties. MATERIALS AND METHODS: Two types of dental stone (types III and V) were mixed with aqueous solutions of 0.525% sodium hypochlorite, 0.1% and 10% povidone-iodine, and 2% glutaraldehyde, and with water as a control. The liquid/powder ratios recommended by the manufacturer were used. These materials were subjected to further modification by adding a mixture of 1.0% gum arabic and 0.132% calcium hydroxide to the hemihydrate powders before mixing with the disinfectant solutions at 2 different liquid/powder ratios for each. Both the regular and the modified materials were tested for compressive and diametral tensile strength after 1 hour and 1 week from the start of the mix. The structure of set materials was determined by scanning electron microscopy examination of fracture surfaces. RESULTS: The disinfectants often reduced the strength of both types of dental stone. However, using either 0.1% povidone-iodine or 0.525% sodium hypochlorite resulted in strength values comparable with that of the control. The addition of gum arabic and calcium hydroxide helped reduce the mixing liquid/powder ratios, improving the strength properties of the disinfected materials. CONCLUSIONS: Chemical disinfectants reduce the strength of dental gypsum when used as mixing water substitutes. Gum arabic and calcium hydroxide additives permit a lower liquid/powder ratio and can help offset this weakening.

Bonding of stainless steel brackets to enamel with a new self-etching primer.

The purpose of this study was to measure the shear bond strength of stainless steel brackets bonded to enamel in vitro with a recently developed self-etching primer (Transbond Plus Self Etching Primer, 3M Unitek, Monrovia, Calif). Forty-eight extracted human teeth were obtained and randomly divided into 4 groups of 12: (1) control group with a conventional etchant and separate primer, (2) experimental group with the self-etching primer, left for 15 seconds before bonding, (3) same as group 2, but with the primer left for 2 minutes before bonding, (4) same as group 2, but with the primer left for 10 minutes before bonding. For each group, stainless steel brackets were mounted onto the prepared enamel, stored for 24 hours at 37 degrees C, and tested in a testing machine with a crosshead speed of 1 mm/min. There was no significant difference in the bond strength between the 4 groups as determined by analysis of variance (ANOVA) (P <.05). Under the conditions of these experiments, a 10-minute delay in bonding after application of the self-etching primer might not be deleterious to adhesion.

Effect of water quality on the bonding of resin to moist dentin.

PURPOSE: To test the effect of different water samples, used for rinsing the dentin, following acid conditioning, on the bond strength of a resin-based composite (RBC) restorative material (Z100), to dentin using a one-bottle dentin adhesive (Single Bond). MATERIALS AND METHODS: In preliminary experiments two experimental shear bond strength methods were compared, and one was selected which was deemed to permit more uniform application of the adhesive and better light curing. In the definitive experiments there were five experimental groups, according to rinsing water used (1) distilled water as control, (2) water with 3.5 ppm iodine, (3) water 3.0 ppm sodium hypochlorite, (4) water with 2% ethanol, (5) water contaminated with 6 x 10(4) cfu/mL of E. coli BH5V. For each experimental group the shear bond strength to moist dentin from 10 human intact impacted third molars was measured. The dentin samples were etched, washed and gently blotted to leave the dentin moist. Following application of the adhesive and resin, specimens were stored at 37 degrees C for 24 hours prior to testing in an Instron testing machine at a rate of 0.5 mm/minute. RESULTS: Data (in MPa +/- standard deviation) were: Group 1: 21.2 +/- 4.1; Group 2: 20.8 +/- 5.6; Group 3: 21.8 +/- 6.2; Group 4: 22.9 +/- 5.9; Group 5: 19.6 +/- 5.5. These data support the null hypothesis that the water types used in this work had no significant effect on the bonding of a resin composite to dentin (P= 0.74, ANOVA).

New core and sealer materials for root canal obturation and retrofilling.

A new endodontic obturation and retrofilling material has been invented to satisfy Grossman's requirements for an ideal material. Methylene blue dye leakage studies were carried out to compare the new material with conventional products, for both obturation and retrofilling. The experimental material when used in root canal obturation had a mean apical leakage of 0.49+/-0.27 mm, compared with 3.75+/-2.81 mm for the conventional material (p < 0.01, t test). Retrofilling leakage was not significantly different from that of a glass-ionomer (p < 0.01, t test) but was substantially lower than that of MTA and Super EBA (p < 0.01, Chi-square test). It was concluded that leakage in root canal obturation was reduced by an order of magnitude and in retrofilling was significantly better than clinically advocated materials. It was inferred that the adhesion mechanism used has contributed to the reduction in leakage.