Three-year clinical comparison of three amalgam alloy types emphasizing an appraisal of the evaluation methods used

Resin-based composite performance: are there some things we can't predict?

OBJECTIVE

The objective of this manuscript is to address the following questions: Why do direct dental composite restorative materials fail clinically? What tests may be appropriate for predicting clinical performance? Does in vitro testing correlate with clinical performance?

METHODS

The literature relating to the clinical and laboratory performance of dental composite restorative materials was reviewed. The main reasons for failure and replacement of dental composite restorations provided the guidance for identifying specific material's properties that were likely to have the greatest impact on clinical outcomes.

RESULTS

There are few examples of studies showing correlation between laboratory tests of physical or mechanical properties and clinical performance of dental composites. Evidence does exist to relate clinical wear to flexure strength, fracture toughness and degree of conversion of the polymer matrix. There is evidence relating marginal breakdown to fracture toughness. Despite the fact that little confirmatory evidence exists, there is the expectation that clinical fracture and wear relates to resistance to fatigue. Only minimal evidence exists to correlate marginal quality and bond strength in the laboratory with clinical performance of bonded dental composites.

SIGNIFICANCE

The use of clinical trials to evaluate new dental composite formulations for their performance is expensive and time consuming, and it would be ideal to be able to predict clinical outcomes based on a single or multiple laboratory tests. However, though certain correlations exist, the overall clinical success of dental composites is multi-factorial and therefore is unlikely to be predicted accurately by even a battery of in vitro test methods.

Corrosion sealing of amalgam restorations in vitro

Amalgam restorations, when first placed, have been shown to exhibit a gap at the amalgam/tooth interface. With time in service, this gap fills with corrosion products that have the potential to "seal" the restoration. With the advent of high-copper, more corrosion-resistant amalgams, there has been concern that the time required to create this seal would be increased significantly when compared with low-copper traditional amalgams. The current study was designed to address this concern. Amalgam was condensed into a MACOR mold, simulating a Class I cavity form and then immersed into a 1.0% NaCl solution to simulate oral conditions. Using an air pressure test, the sealing was monitored over time. The results showed that the sealing was influenced by the size of the initial gap prior to immersion as well as corrosion resistance of the amalgam and that a corrosion-resistant amalgam with a small initial gap size can seal as quickly as a corrosion-prone amalgam. Therefore, it is not possible to predict sealing behavior based on corrosion resistance, alone. Furthermore, the presence of zinc in the amalgam alloy has been shown to result in the formation of zinc corrosion products in the amalgam/mold margin, which contributes to more rapid sealing. Analysis of a tooth extracted after 16 years of clinical service that had been restored with an amalgam-containing zinc was also shown to contain zinc corrosion products in the occlusal marginal area. This could explain the reported reduction in marginal fracture of clinically placed amalgam restorations made from zinc-containing alloys.

Wear of teeth due to occupational exposure to airborne olivine dust

OBJECTIVES

To clarify whether high tooth wear of employees in a mining industry that extracts the mineral olivine could be associated with airborne dust exposure in their working environment.

METHOD

The cumulative exposure to airborne mineral dust for the workers in the company was calculated on the basis of their period of employment multiplied by the airborne olivine-dust concentrations, which have been monitored continuously during the past 20 years for all divisions of the company. After invitation, 85% of the employees (n = 191) were examined clinically and their dentitions were photographed and duplicated in plaster casts. Four clinicians, working independently, examined the sets of casts/photographs for tooth wear and ranked these from most to least. Two groups of employees were compared with regard to tooth wear, i.e. the 30% with the highest (case) and the lowest (control) estimated dust exposure levels. Tooth wear in the case and control groups was compared using a non-parametric test based on rankings (Mann-Whitney test).

RESULTS

Tooth wear differed significantly between the workers in the low and the high mineral dust exposure groups (p < 0.001). The differences were also apparent within three age subsets, although statistical significance was reached only in the 34-44 years subset (p = 0.002). Considerable individual variation was noted within the three exposure groups.

CONCLUSION

Workers with high exposure to airborne olivine dust may contract considerable tooth wear.

Effect of restorative materials and in vitro carious challenge on amalgam margin quality

The surface margin of a restoration is where the restored tooth is subjected to aggressive oral attack. Any resistance to this attack will have favorable consequences on the clinical performance and longevity of the restoration. In this study, Black's class I classic cavity preparations were completed in 120 extracted intact human premolars that were restored with one of two silver amalgams, six different base conditions, and with or without cavity varnish, resulting in 20 different restoration combinations. The cavities were aged for 3 months and 1 year in 1% NaCl at 20 degrees C. A resin cast impression was made of the restoration margin for each specimen. Thereafter 80 restored teeth were subjected to an in vitro bacterial challenge for 36 days. The other 40 specimens were placed in an acidified (pH = 4.0) broth for the same length of time. A second cast impression was then made of the margin of each specimen. The casts were examined with a scanning electron microscope and the widest gap of the margin opening and the length of margin showing a discrepancy were measured. Specimens were ranked first on the basis of the gap size and then on percent of margin discrepancy length. Results were evaluated with one-way ANOVA and Turkey's Student range test with a critical level of statistical significance (p < 0.05). Base type significantly affected aged margin quality. Cariogenic challenge caused a significant breakdown of the amalgam margin although the type of challenge was not significant. A shorter aging time, varnish, and high copper amalgam exacerbated the breakdown. Margin breakdown can be reduced by judicious selection of restoration material combinations.

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)

Measurement of oral status and treatment need among subjects with dental prostheses: are the measures less reliable than the prostheses? Part III: Fixed prosthodontics and restorative dentistry

Poor quality measures of oral status and treatment need have adversely affected clinical and epidemiologic research in prosthodontics. The failure to create reliable and valid indices prevents comparing and pooling data from different studies and obscures meaningful variation within individual studies. Part III of this literature review is focused on problems of measurement of restoration quality and need for treatment in the areas of fixed prosthodontics and restorative dentistry.

Assessment of marginal degradation of restorations on impressions

The study aimed to validate the scoring of the degree of marginal degradation of amalgam restorations by using impressions, as an alternative to other indirect scoring methods using photographs or casts. Ten-year-old condensation silicone elastomer impressions and epoxy replicas made in 1979 were compared in a scanning electron microscope at 5 kV with different magnifications up to x200. The impression material was not distorted or degraded, and the dimensional stability was good after 10 years of storage in a dry environment. The inter-examiner agreement of the scorings of impressions and a six-point scale reference set was satisfactory as evaluated by kappa statistics, demonstrating that degrees of marginal degradation can be distinguished on impressions with relatively high accuracy. The rating distribution of the scorings of impressions showed good correlation to the rating distributions obtained with the clinical USPHS rating method and with photographs for recording marginal degradation. A slight difference between the photographic and impression ratings at the upper and lower levels of the six-point rating scale was observed. The difference varied with the type of alloy, possibly due to a bias depending on the surface quality--that is, whether the restoration kept the glossiness of high polishing or became heavily tarnished.

Relationship of restoration width, tooth position, and alloy to fracture at the margins of 13- to 14-year-old amalgams

The effect of width of the restoration, tooth position, and amalgam type on the fracture of the margins of 13- to 14-year-old, high-copper, amalgam restorations was evaluated. The evaluation assessed 193 photographs of restorations by use of ridit analysis and a rank-ordering test. The results indicated that the width of the restoration was the predominant factor and that tooth position and the different high-copper alloys were less significant. Interactions between tooth position and width indicated that lower premolars with conservative restorations exhibited the least fracture at the margins, and upper premolars with a wide preparation exhibited the most. It is postulated that tooth deflection under mastication may play a role in long-term fracture at the margins of amalgams.

13-year clinical assessment of 10 amalgam alloys

The first commercial high-copper amalgam was developed in the mid-1960's. In 1975, a study to evaluate in vivo/in vitro performance of nine of these new alloys was initiated at Indiana University. These nine high-copper amalgams plus a traditional amalgam were tested for four laboratory properties and their gamma-2 content, and were clinically assessed for fracture at the margins. Originally, 60 restorations of each material were placed in patients and then recalled at six, 12, and 24 months. Recently, 13 years post-operatively, approximately one-third of the original patients were located. These patients were given a clinical exam, and photographs were taken of their restorations. From these recall data, the mean loss of all restorations at 13 years was 11.3%. The alloys Cupralloy, Tytin, and Dispersalloy had the lowest loss rates. The evaluation of the fracture at the margins (ridit means) indicates that there are five groups of alloys with some overlap between groups. The alloys Cupralloy, Indiloy, Dispersalloy, and Phasealloy exhibited the least fracture at the margins. The gamma-2-containing alloys--Optaloy II, Micro II, Velvalloy, and Aristaloy CR--showed the greatest rate of fracture at the margins. A correlation matrix of the ridit means at different years, the loss of restorations at 13 years, and the mechanical properties indicate that the early (one- and two-year) fracture at the margins predicts the 13-year results. Mechanical properties, however, do not predict the clinical performance of the materials at 13 years.

Clinical behaviour of high-copper amalgams with time, site, size and class of cavity preparation

In this study 767 amalgam restorations placed in the posterior permanent teeth of 122 patients were evaluated at 6-monthly intervals up to 2 years. Six commercially available high-copper alloy amalgams were assessed for surface roughness, surface tarnish, marginal staining and marginal fracture and the results were related to product, restoration age, restoration cavity class type, restoration size (normal or large Class II preparations) and tooth type (premolar or permanent molar). Dispersalloy (Johnson and Johnson, East Windsor, USA) gave restorations which were overall superior for the clinical characteristics examined. Large restorations on the occlusal surfaces of molar teeth showed more signs of deterioration over the study than did other restoration types. However, all restorations remained clinically satisfactory throughout the study.

A controlled clinical study of amalgam restorations: survival, failures, and causes of failure

The survival and modes of failure of amalgam restorations were investigated retrospectively. 2660 Class I or II lesions were restored and evaluated yearly or half-yearly for failures during the 30- to 84-month follow-up. Restorations with unacceptable margins were not counted as failures if no traces of secondary caries could be seen. 8% of the restorations were lost because of patient drop-out. Of the remaining restorations, 1% was replaced due to primary caries. Of the remaining number (2431), 9% failed because of all other reasons. The leading mode of failure was bulk fracture (4.6%), followed by tooth fracture (1.9%), and marginal ridge fracture (1.3%). For all other reasons, 0.8% of the restorations failed. Only two restorations were replaced because of secondary caries. The alloy selection in both conventional and high-copper categories significantly influenced the survival of the restorations for reasons directly related to the restoration.

Ranking of histologic tissue responses in the biologic evaluation of dental materials

Implantation tests are frequently used to evaluate biological properties of dental materials. The tissue reactions have been rated as no, slight, moderate and severe responses, mainly based on a quantitative assessment of the cellular response. The distinction between categories is subject to discussion, and interexaminer calibration is necessary to obtain reproducible results. This paper presents a statistical method of evaluating tissue reaction by ranking photographic prints representing histologic sections. Polyethylene tubes, carrying the materials, were implanted subcutaneously in guinea pigs. The tissue reactions at the tube ends, where the material was exposed to the tissue, were evaluated. Photographs of 20 histologic sections were selected. Five investigators from a scientific staff and five from a group of assisting personnel with minimal instruction ranked the reactions on the prints in increasing order of severity. Assisting personnel received 1 h of instruction before the ranking. Generally, the rank ordering of the different examiners showed good agreement. Qualitative histopathologic examination of the sections indicated a marked variation in the cellular response, which limits the value of the quantitative assessment.

An evaluation of a lathe-cut high-copper amalgam alloy

Modification of an amalgam alloy may give rise to improved physical properties. The physical properties of a newly formulated, single-composition lathe-cut amalgam alloy were studied and found to be superior to those of a conventional lathe-cut amalgam alloy. However, such modification in formulation may result in changes in the clinical handling properties of the material. The high-copper amalgam alloy was assessed by a panel of general practitioners who found that the general handling properties of the material were similar to those of conventional lathe-cut amalgam alloys. The longer term performance of the high-copper alloy was assessed by means of a blind, controlled clinical trial carried out by two operators. A 1-year assessment of the resulting restorations and tooth replicas could not distinguish between the high-copper alloy and a conventional alloy. The two alloys had both given good clinical results.

Dynamic creep of dental amalgam as a function of stress and number of applied stress cycles

Dynamic creep tests on specimens of dental amalgam gave a relationship between creep (epsilon), applied dynamic stress (sigma), and number of applied stress cycles (N) as epsilon = AN (m sigma + c) where A, m, and c are constants. This equation can be used to predict creep of amalgam at low levels of stress and extended times. The pattern of results produced for different types of amalgam indicates that the creep process is multifactorial in nature.

Veterans Administration Cooperative Studies Project No. 147. Part II: A new assessment system for rating metal-ceramic crowns

The rating system developed for this study combined ordinal and numerical scoring. The method involved the following: defining the critical criteria, defining the ordinal rating criteria for the assignment, assigning numerical scores for each individual criterion and totalling the scores for each restoration, adding an adjustment number, and scaling the results to the 0-to-10 range and rounding off to the nearest tenth. When tested on sample data gathered at the 12-month followup appointment, the new system elicited a finer discrimination of differences in the quality of the restorations. Although the system fully meets the needs of the specific project, it should not be considered an answer to the needs of all clinical investigations. It should be viewed as a different approach in the development of an acceptable clinical rating system.

Clinical evaluation of four amalgam alloys: a five-year report

In this study 96 teeth of 12 patients were restored with either the conventional alloy Premix, the blended non-gamma 2 amalgam Dispersalloy, or one of the spherical alloys Sybraloy and Tytin. To ascertain an objective comparison of the clinical performance of these alloys, two different alloys were used in each of at least two dental arch quadrants in the same patient and consequently were placed in the same oral environment. Clinical performance of the restorations was evaluated by macrophotography and scanning electron microphotography of replicas made after placement and 2, 3, and 5 years thereafter. Standard criteria were used for the evaluation of anatomic form, surface condition, and marginal adaptation of the fillings. In addition, the filling-enamel interface was assessed from the microphotographs. The three high-copper alloys performed better clinically than the conventional alloy, and the spherical alloys had the best qualifications. In addition to visual examination and photographic evaluation of restorations, the micrometric assessment of replica photographs from the scanning electron microscope may render clinical trials of amalgam alloys measurable and less subjective.

Standardizing evaluations of the clinical marginal fracture of amalgam

In this study, we investigated both inter-examiner and intra-examiner differences in the evaluation of the marginal fracture characteristics of dental amalgam restorations. Evaluations were made by matching intra-oral photographs of the occlusal surfaces of clinical restorations to a reference set of clinical photographs illustrating increasing amounts of marginal fracture. Four amalgam alloys and five examiners provided the data base. Differences in marginal fracture indices were found among examiners and between evaluation times for the same examiners. However, these differences were reduced significantly after application of a standardization procedure.

Clinical assessment of a fluoride-containing amalgam

The aim of this study was to compare the marginal breakdown as a measure of clinical behavior of fillings made with two conventional amalgam alloys, one of which contained 1% stannous fluoride. Children requiring class II restorations in both mandibular molars received conventional amalgam (New True Dentalloy (R] in one molar and a fluoride-containing amalgam (Fluor Alloy (R)) in the other. Impressions of the filled teeth were taken just after polishing and at 1-yr intervals up to a 2-yr period. Plastic models were made and evaluated under a stereomicroscope. The results showed that the fluoride-containing amalgam presented slightly better margins than the conventional amalgam after 2 yr.

Quality assessment of amalgam and inlay restorations on posterior teeth: a retrospective study

This study was designed to assess and compare the quality of posterior proximo-occlusal amalgam and inlay restorations relative to type of restoration (material, surfaces involved, and cusp protection) and length of service of the restorations. A clinical evaluation system based on operationally defined and clinically important criteria was used. Clinically and statistically significant differences were found between overall ratings for amalgam and inlay restorations and between small (two-surface) amalgam and inlay restorations, as well as between larger (three-surface) amalgam and inlay restorations. In all cases, inlay restorations were of higher quality. A not acceptable rating for marginal integrity was the most frequent reason for not acceptable overall ratings. There was no difference in satisfactory/not acceptable ratings for inlay restorations with or without protected cusps (p = .95).

Early prediction of long-term margin adaptation of dental amalgam restorations

The present study assessed the predictive value of an indirect metric method for the early detection of margin defects of amalgam restorations, relative to results using a direct clinical method. The material consisted of plaster casts of amalgam restorations taken at 1- and 2-yr examinations of four different amalgam-treatment combinations. The widest margin defect of each restoration was measured in a dissection microscope equipped with a metric scale in the ocular. The ranking order obtained from the metric measurements of the different amalgam-treatment combinations after 1 and 2 yr was compared with that obtained from the direct clinical evaluation after 2 yr. Finally, the rank order of those restorations rated Alfa (no visible evidence, along the margin, of a crevice (ditch) into which an explorer will penetrate) at the 2-yr clinical examination was studied in relation to the 1-yr metric measurements. For the total material, the rank order based on the metric measurements of the margin defects of the four amalgam-treatment combinations agreed with that obtained with the clinical rating. In the 1-yr data, where the metric technique was applied only on the restorations rated Alfa at the 2-yr clinical evaluation, the order of two neighboring combinations was reversed; otherwise the same rank order was obtained. It is recommended that the clinical performance of new brands of amalgam alloy are tested in short-term, small-scale studies using the metric evaluation technique, before more extensive field studies over longer periods are instituted, in order to sort out unsatisfactory materials and treatment techniques at an early stage.

Enamel surface evaluations after clinical treatment and removal of orthodontic brackets

Methods for the removal of resins attached to acid-etched enamel are receiving increased attention. An evaluation method which permitted convenient statistical comparisons of the effectiveness of various removal procedures was used. The method was based on ranking of SEM photomicrographs of epoxy replicas of teeth from clinical cases. Forty-five orthodontically treated teeth were evaluated after removal of brackets and a heavily filled bonding resin, using three basic procedures. Eleven raters ranked photomicrographs on the basis of the apparent smoothness of the replicated enamel surface. There was no significant difference in the judgment of smoothness by the raters. Significant differences were found between the three removal techniques. Enamel roughness decreased with removal technique in the following order: (1) hand scaler, (2) twelve-fluted carbide bur, and (3) ultrafine bur. A final pumicing treatment was also found to be beneficial, although it did not remove any deep scratches.

Clinical evaluation of high copper amalgam restorations

A comprehensive clinical investigation of amalgam restorations was undertaken to evaluate the performance of "high copper' amalgams and the methods used to examine the marginal integrity of restorations. Six alloys, Aristaloy CR (A), Dispersalloy (D), Indiloy (I), an experimental "high copper' amalgam (E), Tytin (T), and New True Dentalloy (N) as a control, were randomly placed by four operators in 435 Class 1 and Class II restorations. Black and white 1 x photographs were taken at baseline, 6, 12 and 18 months and evaluated using the method described by Mahler & Marantz (1979). In addition, the U.S. Public Health Service system (Cvar & Ryge, 1971) was used at each recall. An analysis of variance based on photographic scoring indicated significant differences (P less than 0.05) among alloys at each recall. The use of Duncan's multiple range test resulted in two homogeneous subsets at 18 months: D, I, E and T, N, A. Six and 12 months recall data showed a close similarity in the rank order of the six alloys. The U.S.P.H.S. system showed no statistically significant differences between the alloys using the chi-square test, however, at each recall the rank order was comparable to that obtained with the photographic method.

The effect of time on the marginal fracture behaviour of amalgam

In this study the effect of time on the marginal fracture behaviour of amalgam was determined. Six alloys in clinical service for up to 6 years were used as a data base and occlusal photographs were categorized according to a standard set of photographs depicting varying degrees of marginal fracture. The standard set of photographs was assigned a linear numerical scale, and the index of extent of fracture was considered to be an arithmetic mean based on this linear scale. An observed patient effect and unequal sample size were considered in the determination of both the mean and variance. The results of applying these procedures to the data of this study showed that marginal fracture increased with time for all alloys; that the relative ranking of alloys did not change with time; and that, with certain limitations, early time evaluations can predict long-term behaviour.

Evaluation of clinical methods for assessing the surface roughness of restorations

Using four different clinical methods to assess the surface roughness of Concise and Spheraloy samples finished with four different treatments, two dentists untrained as evaluators found the following: 1. Although the control profile measurements showed significant differences both between the two materials and the four surface treatments (p less than .001), no clinical assessment method differentiated clearly between all treatments, especially for Concise. 2. Differentiation between the surface treatments was shown best for Spheraloy by the clinical criteria, abraded glass blocks, and ranked photographic negatives. For Concise the best results were shown by the clinical criteria and abraded glass blocks. However, evaluator agreements were highest for Spheraloy with the ranked replica profiles and photographic negatives. For Concise the highest agreements were with the ranked replica profiles. 3. Differentiation between pairs of each material finished with the same surface treatment was shown best by the ranked replica profiles and photographic negatives. These two methods also gave the highest evaluator agreements. 4. Where possible, the use of suitable visual ranking assessment methods rather than clinical ratings or scores to assess surface roughness is preferred for dentists untrained as evaluators.

Clinical performance and physical properties of twelve amalgam alloys

An assessment of the marginal failure rate of 1,041 restorations of twelve alloys was made at one year. In addition, physical property tests were conducted. A correlation was found between the clinical performance and creep (.79), flow (.62) and 24-hour compressive strength (.60).

Reasons for replacement of amalgam dental restorations

Recurrent caries appears to be the most frequently occurring reason for replacement of amalgam dental restorations. Recent developments of amalgam alloys have improved the clinical appearance of such fillings but the possible influence on their durability is uncertain.