Volumetric contraction in some tooth-coloured restorative materials.

BACKGROUND: Much of the concern about the setting contraction of tooth-coloured restorative materials has been focused on the composite resins. This study investigated setting contraction of a range of glassionomer materials and included, for comparison, products from other groups of restorative materials. METHODS: A deflecting disk method was used to determine the volumetric contraction of three conventional (non-light cured) glass-ionomer cements (GICs), two restorative, one "lining" consistency and one adhesive/lining consistency resin-modified glass-ionomers (RMGIs), two resin adhesives, three restorative composite resins and two compomers. The influence of powder:liquid ratio on two hand-mixed materials was also examined. RESULTS: The light-cured materials (including RMGIs) showed substantially greater per cent contraction at 5 minutes than did the three conventional GICs (not light cured) and a substantially greater proportion of the 30-minute contraction had occurred at 5 minutes for these light-cured materials. Their further contraction after 1 hour was generally less than 5 per cent of the 1 hour contraction. CONCLUSION: Although the conventional GICs contract more slowly in the first 5 minutes, by 30 minutes the current restorative GICs and RMGIs exhibit a volumetric setting contraction that is comparable with the composite resins and compomers and is generally in the range of 2-3 per cent.

Clinical evaluation and microstructural analysis of a direct placement gallium restorative alloy.

OBJECTIVES: The objective of this study was to assess the clinical performance of a direct placement gallium alloy sealed with an established dentine adhesive system. In addition, microanalysis of a few gallium restorations that failed in clinical service was performed. Clinical factors such as pulpal sensitivity, fracture of the restoration and of the tooth, marginal deterioration, and tarnish were assessed. METHODS: Sixty-five restorations of Galloy and 62 of Tytin (49 and 51 Class II restorations, respectively) were placed according to a predetermined scheme for randomisation in 37 patients by two operators using rubber dam isolation. For the Galloy restorations, the enamel and dentine were etched, and then sealed with PAAMA 2 dentine adhesive according to the manufacturer's instructions. After carving, PAAMA 2 was applied to the Galloy and light-cured. Cavity preparations for Tytin received no adhesive sealer. All restorations were polished at least 24 h post-operatively. Microstructural analysis of retrieved fragments of failed restorations was conducted using electron probe microanalysis. RESULTS: At 1 year, only one Tytin restoration was found to have failed due to an isthmus fracture. The remaining restorations of Tytin were intact with no reported sensitivity. Of the 65 Galloy restorations placed, 28 had to be removed, including restorations in teeth, which were symptomatic, non-vital and/or fractured, and teeth with fractured restorations. Tarnish was present on many of the Galloy restorations. Retrieved fragments of failed Galloy restorations exhibited a dark surface at the pulpal wall interface and small cracks were observed in that surface. Internal cracks and extensive corrosion was observed using the microprobe. Gallium oxides and chlorides were identified as the predominant corrosion products. CONCLUSIONS: The gallium alloy, Galloy, sealed with PAAMA 2 dentine adhesive system demonstrated a high clinical failure rate.

Clinical evaluation of amalgam bonding in Class I and II restorations.

BACKGROUND: Many dental practitioners are bonding amalgam to tooth structure. Although in vitro studies support this procedure, its efficacy has not been adequately confirmed in the clinical environment. METHODS: The authors placed traditional Class I and Class II bonded and unbonded amalgam restorations in 76 patients. Panavia 21 (J. Morita USA Inc.) was the bonding agent selected, and Aristaloy CR (Englehard Dental) and Tytin (Kerr Corp.) were the amalgam alloys used. Postoperative sensitivity and marginal fracture were evaluated at yearly intervals, for up to three years of clinical service. RESULTS: At the patients' appointment for polishing one to two weeks after restoration placement, and at each yearly recall appointment, the authors found no significant difference in postoperative sensitivity between bonded and unbonded restorations for either amalgam alloy (chi 2 analysis, alpha = .05). In addition, there was no significant difference between bonded and unbonded restorations for either amalgam alloy with respect to marginal fracture (analysis of variance and Tukey's contrasts at alpha = .05). Moreover, no cusp fractures were observed for either bonded or unbonded restorations. CONCLUSIONS: After three years of clinical service, amalgam bonding for traditional Class I and Class II restorations had no effect on postoperative sensitivity or marginal integrity. CLINICAL IMPLICATIONS: The merit of using adhesive bonding agents for traditional Class I and Class II amalgam restorations was not demonstrated in this three-year clinical study.

The high-copper dental amalgam alloys.

For many years, the amalgamation of silver with mercury to produce a condensable mixture which could be used to restore carious defects in teeth followed a tortuous path of negative results. However, at the turn of the century, amalgam alloys having acceptable characteristics for successful clinical use emerged. From that point on, silver amalgam was widely accepted as the material of choice for low-cost, easily placed, and durable restorations. About 60 years later, a major discovery occurred that resulted in a most significant improvement in the clinical performance of this material. The key to this improvement was an increase in the Cu content of the amalgam alloy which previously had been considered to be inappropriate. This paper describes the history of this discovery, which produced what has come to be known as high-copper dental amalgam alloys.

Microleakage of amalgam alloys: an update.

Using an in vitro air pressure test, the authors found a wide variation in the microleakage characteristics of amalgam restorations made from 33 recently manufactured precapsulated alloys. Spherical particle alloys as a group exhibited the highest microleakage values. When the authors changed the mercury/alloy ratios to produce 1 percent more mercury in the capsules by weight, microleakage decreased significantly. Because extensive microleakage of amalgam restorations has been related to increased postoperative sensitivity, the authors suggest that practitioners should be alert to this potential problem.

One-year clinical evaluation of bonded amalgam restorations.

Using one selected amalgam bonding agent, the authors evaluated bonded and unbonded restorations in clinical service. Based on postoperative sensitivity one to two weeks after placement and marginal fracture at one year, no difference was found between the bonded and unbonded restorations. Furthermore, some technical difficulties were experienced with use of the bonding agent.

Hg emission from dental amalgam as related to the amount of Sn in the Ag-Hg (gamma 1) phase.

Previous studies have shown that: (1) different dental amalgams emit different amounts of Hg vapor after surface films have been removed by abrasion (Boyer, 1988); (2) Sn oxide may be the predominant factor in these surface films that inhibit Hg vapor loss (Okabe et al., 1989); and (3) Sn in the Ag-Hg (gamma 1) phase may influence the vapor pressure of gamma 1 (Reynolds, 1974). The purpose of this study was to explore the relationship between Hg vapor emission and the Sn content of the Ag-Hg (gamma 1) phase in dental amalgam. Eleven commercial amalgams were selected whose gamma 1 phases contain different amounts of Sn. Amalgam specimens were ground on 600-grit carborundum paper and immediately placed into an apparatus designed around a gold film Hg vapor detector. Hg vapor loss in air over a 30-minute period was determined, and the log10 Hg loss/volume fraction gamma 1 was plotted vs. the Sn content of the gamma 1 phase for the 11 test amalgams. A linear regression of these data, showing that of the higher the Sn content in gamma 1, the lower the Hg vapor loss, produced a highly significant R2 = 0.94 (p < 0.001). To examine for differences in vapor pressure among alloys, we eliminated the oxidation effect by conducting these same tests in an argon atmosphere. Although the Hg loss was significantly greater in argon than in air, the same differences among alloys were observed. Thus, from the standpoint of both vapor pressure and oxidation, the amount of Sn in the gamma 1 phase of dental amalgam has a significant and specific influence on the potential for Hg vapor emission.

Sensitivity answers sought in amalgam alloy microleakage study.

Sensitivity often occurs shortly after an amalgam restoration is placed. This phenomenon has been related in part to microleakage at the amalgam/tooth interface. When microleakage characteristics of a large number of commercially available dental amalgams were examined, results showed wide variation in the amount of microleakage.

The interval nature of an ordinal scale for measuring the marginal fracture of amalgam.

The clinical performance of amalgam alloys over time has been assessed by measuring the extent of marginal fracture of restorations made from these alloys. Scales of photographs of restorations exhibiting varying degrees of marginal fracture have been used to make these assessments. The purpose of this study was to determine the relationship between the ordinal scale numbers of five photographs composing a commonly used scale (Mahler and Marantz, 1979) and the average width in micrometers of marginal fracture of the restorations in the photographs of this scale. In addition, a comparison was made between parametric and non-parametric statistical methods when applied to marginal fracture data. The results showed that four of the five photographs of this scale demonstrated a significant linear regression with marginal fracture width (R2 = 0.997; p = 0.002). The last photograph of the scale, which proved to be an outlier, was not used in the regression and was accommodated by an extrapolation procedure. Using previously gathered clinical data on the marginal fracture behavior of five amalgam alloys, the use of parametric statistical procedures (ANOVA and Scheffé's multiple comparison test) proved to be more discriminatory than the use of nonparametric procedures (Kruskal-Wallis and Dunn's Multiple comparison test) when tested at the same overall confidence level. Thus, having a photographic scale of an interval nature removes any doubt about using the more powerful technique of parametric statistics to evaluate the marginal fracture behavior of dental amalgams.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors influencing the creep of dental amalgam.

The purpose of this study was to investigate the influence of relevant microstructural and compositional factors on the creep of 12 representative dental amalgams by means of stepwise multiple linear regression. The independent variables accepted by the regression were volume percent of the eta' (Cu6Sn5) phase, grain size of the gamma 1 (Ag2Hg3) phase, volume percent of the gamma (Ag3Sn) plus epsilon (Cu3Sn) phases, number of very small eta' crystals (less than 1.5 microns) per mm, and weight percent of Hg. The results of this regression showed an adjusted R2 of 0.949, significant at p = 0.002.

Bonding of dentin adhesives in clinically-simulated occlusal resin composite restorations.

The purpose of this study was to measure the bond strength of resin dentin bonding agents under clinically-simulated conditions. Using extracted human teeth subjected to physiologic-pulpal fluid pressure, occlusal cavity preparations were restored with three dentin bonding agent/resin composite combinations. The teeth were sectioned to remove the occlusal enamel and upper part of the restoration. The force required to remove the remainder of the restoration was converted to a dentin bond strength value. The effect of incremental placement of the resin composite also was investigated. Scotchbond 2 showed better bonding than Gluma or Scotchbond Dual Cure, and Gluma showed better bonding than Scotchbond Dual Cure. Although all materials showed better bonding with the use of three increments of resin composite versus one, only in the case of Scotchbond 2 was there a statistically-verified difference.

Effect of Pd on the clinical performance of amalgam.

The purpose of this study was to determine the effect of a small amount of Pd on the clinical performance of a high-copper spherical-particle dental amalgam. Two identical alloys, with and without 0.5% Pd, were investigated. The marginal fracture, surface texture, and surface luster of 193 clinical restorations were evaluated at one year, those of 182 at two years, and those of 144 at three years of service. In vitro corrosion tests of anodic polarization and constant potential coulometry were also conducted. Over the three-year period, the results showed no differences in marginal fracture or surface texture between the two alloys. However, the alloy with Pd showed a significant superiority in surface luster over this time period. Both corrosion tests showed less electrochemical activity on the part of the alloy containing Pd.

Factors influencing the sealing behavior of retrograde amalgam fillings.

In this study, the sealing behavior of apical (retrograde) amalgam fillings was evaluated with particular regard to the nature of the amalgam and the manipulative procedures used. With the use of an in vitro air pressure test, four high-copper alloys and one traditional composition low-copper alloy were selected for determination of their microleakage characteristics. Measurements were made on both normal and water-contaminated mixes, and the effect of mix plasticity was evaluated. In addition, both setting and postsetting dimensional changes of these alloys were determined. The results showed that amalgams differ in their ability to provide a complete seal and that low plasticity mixes result in greater microleakage. All zinc-containing alloys that were contaminated with water exhibited a postsetting or delayed expansion. However, only the low-copper alloy exhibited a delayed expansion of a magnitude that might induce root fracture.

Sn in the Ag-Hg phase of dental amalgam.

In a recent study, Sarkar and Eyer (1986) studied an amalgam which was formed using a unique procedure. Based on their results, they concluded that the solubility of Sn in the Ag-Hg (gamma 1) phase of dental amalgam was virtually nil (less than 0.25 wt%). This finding is contrary to the published results of other investigations. The purpose of the present study was to clarify these disparate findings. A low-copper dental amalgam was examined by electron probe microanalysis. This amalgam was selected because it exhibits unusually large gamma 1 grains (10 microns). Because the influence of the electron-analyzing beam can be completely contained within these large grains, grain boundaries or peripheral phases would not be excited, and a valid analysis of the gamma 1 grains themselves could be made. The analyses showed significant Sn contents of 2.0-3.0 wt%. Analyses of areas which contained grain boundaries showed slight or no differences in Sn content compared with that for the grains alone. Furthermore, secondary electron scans of this dental amalgam failed to reveal the intergranular precipitates of Sn-Hg observed by Sarkar and Eyer (1986) in their amalgam. These different results can be explained by the fact that the unique amalgam investigated by Sarkar and Eyer does not exhibit the same diffusional patterns as does dental amalgam, and that the composition of the gamma 1 in the two amalgams is not the same. The final conclusion is that the Ag-Hg (gamma 1) phase in dental amalgam does indeed contain a significant amount of Sn.

Assessing composite resin wear in primary molars: four-year findings.

Many investigators have reported minimal wear of resin restorations in primary molars. Until recently, quantitative wear assessments have not been reported. The purpose of this investigation was (1) to present and contrast data from two 48-month clinical trials wherein quantitative wear assessments were used to evaluate wear of resin restorations in primary molars, and (2) to compare these results with those using the USPHS method of wear assessment. The data were collected from two different clinical trials. One was conducted at the University of California in San Francisco by Tonn and Ryge (TR Trial). The other was conducted at the University of North Carolina at Chapel Hill by Oldenburg, Vann, and Dilley (OVD Trial). The OVD Trial had a sample size of 45 patients with 106 restorations; the TR Trial had 44 patients with 96 restorations. The restorations in both trials were Class I and II restorations in occlusion. They were placed with the experimental light-cured posterior composite resin F-70, later marketed as Ful-Fill. At baseline, six, 12, 24, 36, and 48 months, restorations were evaluated by two evaluators trained in USPHS criteria as well as by a quantitative method of wear assessment, the standard cast technique as described by Leinfelder. Interstudy comparisons were made by Chi-square tests (USPHS evaluations) and ANOVA (quantitative assessments). The results showed that resin restorations in primary molars exhibited progressive wear with time in service. The rate and quantity of wear were very similar to those seen in permanent posterior teeth over 36 months. Findings agree with previous reports that the USPHS evaluation criteria are insensitive in detecting early wear in primary molars.