Prediction and diagnosis of clinical outcomes affecting restoration margins.

The longevity of dental restorations is largely dependent on the continuity at the interface between the restorative material and adjacent tooth structure (the restoration margin). Clinical decisions on restoration repair or replacement are usually based upon the weakest point along that margin interface. Physical properties of a restorative material, such as polymerisation shrinkage, water sorption, solubility, elastic modulus and shear strength, all have an effect on stress distribution and can significantly affect margin integrity. This review will focus on two aspects of margin deterioration in the oral environment: the in vitro testing of margin seal using emersion techniques to simulate the oral environment and to predict clinical margin failure and the relationship between clinically observable microleakage and secondary caries. The many variables associated with in vitro testing of marginal leakage and the interpretation of the data are presented in detail. The most recent studies of marginal leakage mirror earlier methodology and lack validity and reliability. The lack of standardised testing procedures makes it impossible to compare studies or to predict the clinical performance of adhesive materials. Continual repeated in vitro studies contribute little to the science in this area. Clinical evidence is cited to refute earlier conclusions that clinical microleakage (penetrating margin discoloration) leads to caries development and is an indication for restoration replacement. Margin defects, without visible evidence of soft dentin on the wall or base of the defect, should be monitored, repaired or resealed, in lieu of total restoration replacement.

Clinical wear performance of eight experimental dental composites over three years determined by two measuring methods.

The effect of matrix selection, filler composition, filler silanization, operator variations, and test site (dental clinic) on the wear rate of eight composites were evaluated. The wear was measured on replicas using both a microscopic and a laser scanning measuring method. The average wear rate on contact-free surfaces was 9.2 +/- 4.2 microm/month with the microscopic measurement and 8.5 +/- 3.7 microm/ month with the laser scanner over the 36-month period. The urethane-based composites performed significantly better than those which were bisGMA-based. Restorations placed at one dental clinic showed significantly lower initial wear. There was also a significant difference between the operators that was most pronounced during the first 6 months. The other variable (filler composition and silane treatment) did not affect the wear rate significantly.

Salivary mucin as related to oral Streptococcus mutans in elderly people.

MG1 (MUC5b and MUC4) and MG2 (MUC7), predominant mucins in human whole saliva, provide lubrication and antimicrobial protection for oral tissues. This study examines potential relationships between Streptococcus mutans titers in the oral cavity and the following: mucin concentrations; unstimulated and stimulated whole saliva flow rates; decayed, missing, and filled tooth surfaces; and age of 24 elderly patients. S. mutans titers were determined using Denticult SM. Mucin concentrations were determined using Stains-all, sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Logistic regression was used to identify potential relationships between the above variables. S. mutans classification served as the dependent variable. The remaining variables were possible predictor variables. The best model for predicting S. mutans category contained log MG2 as a predictor variable for all of its parameter estimates. No other set of parameter estimates were statistically significant. These results suggest that elevated S. mutans titers are significantly associated with diminished concentrations of MG2 in unstimulated whole saliva, as quantified in mucin-dye binding units.

The effects of alcoholic beverages on composite wear.

OBJECTIVES: In vivo wear of composite restorative materials appears to be, in part, dependent on various patient factors. Specifically, consumption of alcoholic beverages has the potential for increasing the degradation rate. The hypothesis tested in this experiment was that composite wear is dependent on the type of alcohol-containing liquid the materials are exposed to during three-body abrasive wear. METHODS: To test this hypothesis, composite wear experiments were performed using the ACTA three-body wear machine. Abrasive slurries containing either beer, wine, 9 vol% ethanol or water were used during the wear experiments. The data were analyzed using ANOVA and Tukey's test. RESULTS: The wine and ethanol solutions caused significantly more wear compared to the beer and water. There was no significant differences in the wear between the wine and 9 vol% ethanol groups, and the beer groups were not significantly different from the water groups. Furthermore, there was no significant interaction between the composite type and the various abrasive slurries. SIGNIFICANCE: These results indicate that alcoholic beverages with at least 9 vol% ethanol will increase the wear of composite. The observed increase in wear of composite by the wine was caused primarily by the ethanol content of the wine. Other constituents in the wine do not appear to have an effect on composite wear. The ethanol effect was consistent among different composite types.

Effect of home bleaching products on mercury release from an admixed amalgam.

PURPOSE: To test the effect of three carbamide peroxide bleaching products, Opalescence (O), Nite White (N), and Platinum (P) on mercury release from amalgam (Valiant PhD). MATERIALS AND METHODS: Sixty uniform amalgam specimens were prepared in Acrylite clear acrylic blocks. After aging for 1 week at 37 degrees C, the specimens were placed in individual polystyrene jars containing 20 mL of sterile saline, and divided into three groups A, B, and C. Specimens were bleached in cycles by removing them from the jars, blotting to remove excess moisture, and covering with either O, N, P, or saline control (SC). After 8 hours, the specimens were cleaned with a toothbrush, rinsed with deionized water, and returned to the saline. Group A was tested for mercury release after 8 hours of bleaching, Group B after 40 total hours of bleaching, and Group C after 80 total hours of bleaching. Mercury testing was performed by first reducing the mercury in solution in each jar with 1 mL of SnCl2, and then testing the remaining headspace with a Gold Film Mercury Vapor Analyzer. RESULTS: ANOVA indicated there was no significant difference between the bleaches and controls at 8 and 40 hours, however at 80 hours, O caused significantly more mercury release (P < 0.05). Means at 80 hours in mg/m3 were: O = 0.98 +/- 0.36; N = 0.58 +/- 0.20; P = 0.47 +/- 0.11; SC = 0.52 +/- 0.14.

Wear resistance of dual-cured resin luting agents.

PURPOSE: To evaluate the three-body wear resistance of five commercially available dual-cured resin-based composite luting agents compared both in a dry state and after water storage. MATERIALS AND METHODS: Six specimens of each material were prepared and tested for three-body wear resistance in the ACTA wear machine for 250,000 cycles and the loss of material was measured with a profilometer. Material wear was measured under three conditions: dry storage, 6-month water storage, and 12-month water storage. RESULTS: One-way and two-way ANOVA and Tukey's HSD test of multiple comparisons revealed significant differences in wear resistance. Water storage did not significantly affect the wear resistance of four of the five materials. The order of wear resistance was: Cosmedent Insure > Vivadent Dual-Cement > Kerr Porcelite Dual Cure > Jeneric/Pentron Optec Luting Cement > Chameleon Mirage FLC (P < or = 0.0001). The rank order of wear resistance could not be readily predicted when based solely on the manufacturers' reported physical specification data.

System for the pH-dependent release of a dye in model dental restorations.

We are developing a system for detecting recurrent caries under dental restorations. The controlled release of dyes under conditions of likely demineralization will alert the dentist to potential secondary caries. Production of acidic species is a characteristic of caries activity; hence, the system uses pH-sensitive polymers to release markers when the pH at the cavity wall of the restored tooth is below 6.5. The objectives of this investigation were to test the hypotheses that (1) the proposed system can be designed to release detectable marker continuously for at least six months in a simulated carious environment, and (2) the transient pH changes in the oral cavity caused by simulated dietary intake will not induce premature marker release from the pH-sensitive polymer placed beneath restorations. Two types of dye-loaded microspheres based on styrene, vinylpyridine, and divinylbenzene were prepared and placed on the floor of model cavity preparations made from an acrylic rod. Each model cavity was restored with a hybrid dental composite, placed in a vial with 5 mL of sodium-lactate/lactic-acid base buffer solution, and stored at 37 degrees C. Solutions of three different pH values were used: 2.86, 4.73, and 6.39. The dye release into storage media was monitored periodically with a UV/VIS spectrophotometer. Results showed that the duration could extend beyond six months for pH > 4.73, and that transient oral pH changes are not likely to result in premature dye release. The data indicate that it would take approximately 21 days for the acidic agent external to the restoration to initiate dye release from restored sites.

The effect of water on polymer matrix and composite wear.

OBJECTIVES: Previous studies have demonstrated increased in vitro wear of composite after long-term water exposure. The increased wear effect was not clearly related to debonding of the filler from the matrix, resulting in accelerated loss of filler particles. The hypothesis tested in this experiment was that the changes in in vitro three-body wear of a composite following water storage are caused by changes in the wear resistance of the polymer matrix. METHODS: In the in vitro wear test used, a specimen wheel was rotated against an antagonist wheel in a slurry of millet seed and water. Specimens were fabricated of composite and polymer matrix only. Specimens were wear tested after 1 wk of ambient temperature dry storage and after 14, 20, and 26 mon of water storage at 37 degrees C. RESULTS: The wear of the composite significantly increased (23%) during the 26 mon of water storage. The wear of the polymer specimens increased slightly; however, the increase was not statistically significant. SIGNIFICANCE: Analyses of the data using a series model for the wear of a composite indicated that the increase in wear of the composite was not due to changes in the wear resistance of the polymer matrix. Instead, the increased composite wear was more likely due to increases in the dislodgment rate of filler particles and the wear rate of the filler itself.

Modeling the relationship between clinical, microbiologic, and immunologic parameters and alveolar bone levels in an elderly population.

A cross-sectional periodontal study of 74 subjects aged 65 to 75 years was performed. Clinical data were collected and related to microbiological and immunological data. A statistical model (step-wise multiple regression) of factors related to bone loss was created initially using clinical data only; then by adding either the microbiologic or immunologic data; and then by using clinical, microbiologic, and immunologic data together. When only clinical data were considered, three factors were found to have significant positive correlations with bone loss. Tooth mobility accounted for 17% of the variability in the alveolar bone level measurements, probing depth for 12%(r2), and plaque index for 3%, for a total of 32% of the variability explained by these clinical factors. Tooth mobility and probing depth were clinical factors which remained significant in the model when the microbiological data were also considered. As percentages of the total cultivable microbiota, E. corrodens (r2 = 14%) and black-pigmenting Prevotella intermedia (r2 = 4%) correlated positively with alveolar bone loss. The addition of the microbiologic data only increased the r2 to 33%. When immunological data were considered with the clinical data, pocket depth and tooth mobility were the clinical parameters which remained in the model. IgG antibody levels to P. gingivalis W83 and/or 381 (r2 = 24%) A. actinomycetemcomitans 627 (r2 = 2%) were the significant immunologic measures having a positive correlation with bone loss. Anti-F. nucleatum levels had a significant negative correlation. A total of 50% of the variability in alveolar bone level was accounted for in the model by the addition of specific serum antibody levels to subgingival plaque microorganisms. When clinical, microbiological, and immunological measurements were all considered together, antibody to P. gingivalis W83 and/or 381 (r2 = 42%), percentage of B-lymphocytes (r2 = 3%), probing depth (r2 = 4%), anti-E. corrodens levels (r2 = 2%), and anti-P. gingivalis 33277 levels (r2 = 4%) all had significant positive correlation with loss of alveolar bone. The number of enteric bacteria, anti-F. nucleatum levels, and anti-P. intermedia levels each had a significant negative correlation with alveolar bone heights. The r2 for this model was 75%. These results indicated that antibody levels to subgingival plaque microorganisms and tooth mobility were the best predictors of bone loss in the elderly patients tested in this study.

Visual and profilometric wear measurements.

Wear of composites can be estimated by the degree of marginal discrepancy between the prepared cavity wall and the occlusal margins of composites. Such evaluations are done on casts by comparing and rating the marginal discrepancy with those on standard casts. We analyzed the reliability of this technique on metal and stone specimens. These specimens contained grooves of different width and depth. For the visual comparison we used stone casts of machined standards of known groove depth. We measured the depths of the metal specimens with a profilometer and made stone casts of these original specimens. Using the stone casts of the standards, five dentists estimated the unknown groove depths on the remaining stone casts. These estimates were done under standardized conditions and repeated by each dentist on five different occasions. The results showed that visual depth evaluations of die stone specimens underestimated the depths when compared with the values measured with a profilometer on the original metal models. One investigator gave significantly different (p less than 0.05) groove depth estimates at different occasions.

Water and abrasive effects on three-body wear of composites.

The degrees of in vitro three-body wear resistance of a hybrid, a small-particle, and a microfilled composite were determined after water storage for up to 24 months. The hybrid composite was the most wear-resistant, while the microfilled composite showed the most wear. The hybrid composite showed no loss of wear resistance as a result of water storage. The small-particle composite showed a decrease in wear resistance after water storage only when tested with silicon carbide abrasive. The wear resistance of the microfilled composite decreased following water storage when tested with either a soft (CaCO3) or a hard (SiC) abrasive. For all composites, the soft abrasive was not capable of causing preferential wear of the polymer matrix, as observed on in vivo specimens. Instead, the filler particles became flattened, with minimal loss of interparticle substance. The hard abrasive did cause preferential wear of the matrix. All composites absorbed water and leached silicon during water storage, indicating that the filler-polymer bond was attacked by hydrolytic degradation. Scanning electron microscopic evaluation of the three-body wear specimens indicated that the in vitro wear method did not duplicate in vivo wear conditions (e.g., the hard abrasive caused excessive wear and chipping of the filler particles in vitro, a pattern that was not usually observed in vivo). Filler-polymer de-bonding was observed on in vivo specimens of all the composites, while it was found only on the in vitro microfilled composite specimens. These findings suggest that filler dislodging is a complex process that cannot be simulated with the in vitro wear method used in this study, not even after prolonged water storage.

Heat generated when threaded pins are cut: a comparison of techniques.

The temperature rise of threaded pins was measured when cut under various conditions and with different instruments. The air-water coolant and intermittent cutting produced significantly lower temperature rises than the air coolant and constant cutting, respectively. No particular carbide bur or diamond stone is recommended since little difference existed among them with respect to heat generation.