Clinical performance and physical properties of twelve amalgam alloys

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.

Effect of heat treatment on structure and properties of dispersed-type dental amalgam

Effect of heat treatment of Ag-Cu-Pd dispersant particles on the structure, mechanical properties and mercury vapor release rate of an Ag-Cu-Sn/Ag-Cu-Pd-based dental amalgam has been investigated. Experimental results indicate that crystallinity of dispersant Ag-Cu-Pd alloy increases with increasing HTT, with most notable increase occurring between 100 and 200 degrees C. Increasing HTT of Ag-Cu-Pd alloy does not change much of the mercury/alloy ratio for amalgamation, but largely reduces working/setting time of the amalgam. The Ag-Cu-Pd particles in 7 d-aged amalgam are comprised primarily of an outer Sn/Cu/Pd-rich zone and an inner Ag/Cu/Pd-rich zone with eutectic-type morphology and chemical distribution. The annealing-enhanced Pd segregation effect is most significantly observed in the amalgam derived from 300 degrees C-annealed Ag-Cu-Pd dispersant. This amalgam also has the highest compressive strength, highest DTS, and lowest creep rate. Higher annealing temperature causes mechanical property of the amalgam to deteriorate. The initial mercury vapor release rates of amalgams derived from 100, 200 and 300 degrees C-annealed Ag-Cu-Pd dispersant are significantly lower than that derived from 400 degrees C-annealed dispersant.

Creep as a Mechanism for Sealing Amalgams

Creep may be a major factor in amalgam sealing from microleakage. Creep expansion causes amalgam to fill in the tooth/amalgam interface gap and causes the restoration to extrude out of the preparation.

A comparison of the mechanical properties of a gallium-based alloy with a spherical high-copper amalgam

OBJECTIVES

The aim of the present study was to investigate how the mechanical properties of a palladium free gallium-based alloy (Galloy) compare with a leading spherical high-copper amalgam (Tytin).

METHODS

Cylindrical specimens were mechanically condensed, according to the ISO 1559:1986 standard, to measure compressive strength, Vickers hardness, static creep and dimensional change on setting. Disc and beam shaped specimens were manually prepared to assess the diametral tensile and flexural strengths of the investigated alloys.

RESULTS

The mean hardness, 1h compressive fracture strength, 24 h diametral tensile and 24h flexural strengths of Galloy were significantly lower (P<0.001) than Tytin. No significant differences in modulus of elasticity, creep, dimensional change on setting, 24 and 168 h compressive fracture strength for the two alloys were identified.

SIGNIFICANCE

The significant reduction in the 1 h mean compressive fracture strength and hardness identified for Galloy compared with Tytin possibly indicate a slower setting reaction in the gallium-based alloy. Manual condensation of the gallium-based alloy produced specimens with inferior mechanical properties possibly due to the increased likelihood of introducing voids within the test specimens. Previous reports indicating poor corrosion resistance and moisture sensitivity of gallium-based alloys highlight the need for further research to investigate the effect of the oral environment on the gallium-based alloy.

Effect of zinc on strength and fatigue resistance of amalgam

OBJECTIVES

This study was conducted to determine the effect of zinc in amalgam on the static mechanical properties and resistance to fatigue-crack propagation of amalgams.

METHODS

Fatigue, creep, compressive and flexure tests were performed on high-Cu Dispersalloy (Johnson and Johnson Dental Products Co., East Windsor, NJ, USA) and low-Cu Velvalloy (S.S. White Dental Products Int., Philadelphia, PA, USA) in both Zn-containing and Zn-free formulations. Linear Elastic Fracture Mechanics principles were used to characterize the fatigue behavior (crack lengths were monitored).

RESULTS

The incorporation of Zn into these amalgams significantly improved their fatigue and creep resistance, while the effect of Zn on the static compressive and flexure strengths was not consistent. Zn significantly increased (p < 0.05) the resistance to fatigue crack propagation during Stage II crack growth for both amalgams, and increased the variations in crack velocity for a given stress intensity difference, without visibly altering the path or nature of the fatigue cracks. Possible influences on fatigue behavior were the mixed microstructure (particles and matrix), the nature of the crack tip, and creep.

SIGNIFICANCE

The superior resistance to tensile fatigue crack propagation of amalgams containing small amounts of Zn (approximately 1 wt%) in vitro compared with amalgams with no Zn correlated with the superior resistance to marginal breakdown in vivo of Zn-containing amalgams. The range of stress intensities over which stable cracks could propagate was small, while the large variations observed in fatigue crack growth rates for individual materials invalidate predicting a unique fatigue life from the empirical equations obtained.

Long-term evaluation and rerestoration of amalgam restorations

In this study, 1544 class-II amalgam restorations were made and evaluated for 10 yr and the reasons for rerestoration were registered. Two categories of failure could be established: failures due to poor restorative technique (true failures) and those not due to poor restorative technique (false failures). After 10 yr, 1415 restorations were evaluated. Only 120 restorations (8.5%) had been replaced, most of these replacements being true failures (105 = 87.5%), which could be divided into: isthmus fracture (37), fracture of the enamel cusp (25), recurrent caries (16), partial fracture of the restoration (9), severe marginal breakdown (5), pulpal pathology (7) and others (6). The false failures (15) could only be classified into: caries elsewhere in the tooth (15). Origins of the true failures were the operator, the material (amalgam) and the type and size of the restoration. In this study, there were significantly more replacements of larger restorations than of smaller ones and more replacements in molars than in premolars. There is also a significant difference among the replacements by the various operators but not between the various types of amalgam. Origins of the false failures seem to be more related to patient factors like caries activity, caries susceptibility and oral hygiene, but chewing habits (bruxism) may also play a role.

Dental materials for posterior restorations

Assessment of the quality of dental restorations by the Ryge system is described. Generally, the quality of dental restorations is shown to be dependent on the technique sensitivity of the restorative material as well as the skill and experience of the dentist. Concerning biocompatibility, adverse reactions related to amalgam restorations are unlikely or scarce, due to small amounts of released mercury. Resin based restorative materials contain a large number of organic compounds and, as such, the toxic and allergenic potentials are unknown. Gold and ceramics turn out to be the most biotolerable dental materials. Based on studies on longevity, data indicate that the median age of amalgam restorations is 10-12 years, of gold castings 13-14 years and more, and of composite restorations 4 years. Data on longevity of ceramic restorations are sparse. Secondary caries appears to be the most frequent cause for replacement of the different restorations, followed by marginal degradation. Secondary caries account for more failures among the resin based restorations than among amalgam. Reviewing the literature, it appears that amalgam is the best and most economic dental material for routine posterior restorations with reasonable durability. Gold is recommended for complex restorations. Resin based composites may be limited to small restorations where cosmetics is the main aspect, as wear and recurrent caries are main problems. Ceramic restorations comprise aesthetic restorations with excellent biocompatibility, however, data on longevity and marginal adaptation are not encouraging.

Microstructures of admixed amalgams produced from Pd-containing dispersants

Blended Pd-containing dental amalgams were developed by substituting Pd for up to 20 w/o Ag or Cu in the Ag-Cu eutectic alloy. Melted ingots were lathe-comminuted to a particle size distribution of 1-45 microns. Alloy blends were created from two parts of a traditional amalgam and one part of experimental Ag-Cu-Pd particles. Amalgams with from 0.42 to 1.67 w/o Pd were fabricated by trituration of alloys and mercury at a Hg/alloy ratio of 1:1 with a mechanical triturator at 5000 rpm for 10 s and hand-condensed. XRD studies of these amalgams revealed the suppression of eta' (Cu6Sn5) phase with Pd addition and no gamma 2 (Sn8Hg) phase found. At 3.3 w/o Pd, the eta' (Cu6Sn5) concentration of the amalgam was below the detection limit of the instrumentation (1%). SEM micrographs revealed that reaction zones around eutectic particles decreased with increased Pd concentration.

Changes in compressive strength of glass ionomer restorative materials with respect to time periods of 24 h to 4 months

This study investigated whether long-term changes occur in the compressive strength of a number of glass ionomer restorative materials, in view of the fact that little information is available from the manufacturers, and any variations with time might affect suitability for clinical use. It was found that, over the period of 24 h to 4 months, some materials, namely those based on polyacrylic acid, maintained or even showed a slight increase in their strength, whereas others based on copolymers of acrylic acid first increased in strength, but thereafter showed deterioration. In one case the strength decreased by nearly 50% compared to that at 24 h.

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.

Marginal microhardness of corroded amalgams: a comparative in vitro study

One conventional and two high-Cu amalgams were tested for marginal microhardness after 2 months' corrosion in an 85 mM NaCl solution. Amalgams immersed in 200 mM phosphate buffer solution were used as controls. The microhardness tests were conducted on cross-sections of the amalgams 50 microns from the surface edges. The microstructure of the amalgams was studied in SEM and the amounts of Sn, Cu, Zn, Ag, and Hg dissolved in the solutions were analyzed with an atomic absorption spectrophotometer. For the amalgams immersed in the NaCl solution the depth of corrosion after 2 months was between 50 and 400 microns. The specimens immersed in the phosphate solution showed no signs of subsurface corrosion. The marginal microhardness of all the amalgams was reduced after corrosion in the NaCl solution. The greatest microhardness in both the uncorroded and corroded states was shown in the two high-Cu amalgams. The reduction in marginal microhardness after corrosion can probably be attributed mainly to degradation of the gamma-2 phase for the conventional amalgam and to degradation of the eta' phase for the two high-Cu amalgams.

Dynamic mechanical properties of dental amalgams

The dynamic mechanical properties of two high-copper amalgams (Tytin and Dispersalloy) and two traditional amalgams (Aristalloy and Aristalloy with Zn) were measured over a temperature range of 0-70 degrees C and at frequencies of 0.1, 1, and 10 Hz by means of a DuPont DMA. Values of storage modulus (E') for the amalgams were equivalent to the Young's modulus (E) measured from static mechanical test methods, with Dispersalloy demonstrating the highest moduli. Values of E' decreased with increased temperature. E' of traditional amalgams decreased more rapidly than did those of the Cu-rich amalgams. Values of loss modulus (E") for Tytin were smaller than those of Dispersalloy and the two types of Aristalloy. High values of E" for the traditional amalgams correspond to a greater viscous behavior. Marked differences between the magnitude of tan delta and its temperature coefficients for traditional and high-copper amalgams were observed, which is indicative of differences in visco-elastic behavior between these two amalgam systems.

The effect of trituration time on the mechanical properties of four high-copper amalgam alloys

Several manipulative variables have been shown to influence the physical properties of dental amalgam. Variation in trituration time has been reported to affect creep, compressive strength, and diametral tensile strength in various amalgams. Recent classification of amalgam alloys by particle microstructure reveals four categories: single-composition lathe-cut; single-composition spherical; lathe-cut and eutectic admixture; and lathe-cut and single-composition spherical admixture. The effect of variation of trituration times has not been studied for these newer high-copper alloys. A representative from each classification was selected and physical properties tested, with varied times for trituration utilized. Results showed little compromise in laboratory values for the properties tested. Additional laboratory and clinical trials are warranted, but this study supports the premise that clinicians may vary trituration time to improve handling characteristics without significantly affecting mechanical properties.

Evaluation of an indirect method for assessing the quality of amalgam restorations in epidemiological studies

The purpose of the present study was to compare an indirect method with direct clinical observations for its ability to assess the clinical quality of amalgam restorations. Two evaluators examined independently the quality of 290 amalgam restorations in 25 patients. All restorations were examined directly as well as indirectly using seven well-defined characteristics. Direct assessment consisted of visual examination utilizing mirror and explorer. Indirect observations were made with the aid of color transparencies and bite-wing radiographs. The results showed a high interexaminer agreement for the indirect method which was even higher than for the direct method. No statistically significant differences existed between the two examiners in both methods. When using color transparencies for the indirect method, there is a high degree of agreement between both methods. Only one characteristic, the "anatomic form", showed significant differences in the sense that an unsatisfactory "anatomic form" is diagnosed more often by direct evaluation. Therefore, the indirect method, using color transparencies, is reliable in assessing quality of amalgam restorations except for "anatomic form". When using bite-wing radiographs for the indirect method, unsatisfactory characteristics were diagnosed more frequently indirectly than directly. On the basis of the results, it was concluded that bite-wing radiographs are indispensable in examining amalgam restorations.

Marginal degradation and corrosion of a dispersed high copper amalgam

The marginal degradation and corrosion of restorations made of a high copper dispersed amalgam were studied as a function of time for up to 5-yr observation periods. The effect of minor defects present after finishing the restorations was included in the assessment of the initial marginal degradation. A slow progressive marginal degradation was noted and it was enhanced by initial defects. Subsurface corrosion including attacks of the phase and grain boundaries, corrosion within the bulk, and layers of corrosion products along the tooth/restoration interfaces were observed in restorations after some years in clinical service. The subsurface corrosion is considered to weaken the amalgam and it might enhance the marginal degradation, i.e. a stress corrosion type of degradation.

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.

Restorative treatment pattern and longevity of amalgam restorations in Denmark

A survey has been made of the reasons for placement and replacement of 6052 amalgam restorations in Denmark. In patients more than 16 years of age 48% of all restorations were made because of primary caries, and 52% were replacements of failed restorations. In primary teeth 64% and in permanent teeth of children 83% of the restorations were made because of primary caries. The reasons for replacement of restorations were dependent on dentition, age of the patient, and type of restoration. Secondary caries was the most frequent reason for replacement of failed restorations in permanent teeth, comprising a third of all replacements. Marginal discrepancies and bulk fracture of fillings were the other two major reasons. In primary teeth fracture and loss of fillings were the two major reasons for replacement of amalgam restorations, whereas secondary caries caused less than a quarter of all restorations to be replaced. The age of the restorations replaced ranged from 0 to 38 years, and half of the restorations replaced in permanent teeth of adults were less than 7 years old. A shorter longevity of failed restorations was noted in primary teeth and permanent teeth of children.

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.

Creep versus marginal fracture of amalgam restorations

In the literature there is controversy over the existence of a correlation between creep and marginal deterioration of amalgam restorations. It was the aim of this study to re-investigate this correlation. In five clinical trials, 2068 amalgam restorations were made of six conventional alloys and ten high copper systems. The results show a correlation between creep and marginal fracture in the conventional, low copper amalgams. No correlation could be found for the group of high copper, non-gamma-2, amalgams. It is emphasized that dental practitioners should not buy their amalgam alloy on the basis of creep data, because wrong decisions might be taken. Evidence from a controlled clinical study is a more reliable criterion.

Clinical evaluation of marginal fracture of amalgam restorations: one-year report

Fourteen dental amalgam alloys were used in this study. After 1 year, amalgam restorations were evaluated for fracture at the margins. The clinical results indicated that Dispersalloy, Indiloy, a high-copper blend by Syntex, Cluster, and Unison had the least marginal failure. This was followed by Premalloy, Cupralloy, Tytin, Cupralloy ESP, and Contour. Velvalloy and Sybraloy and Orosphere II were the third major grouping with Summalloy having the most fracture at the margins. Different batches of the same alloy performed similarly. The correlation between creep and ridit means (fracture at the margins) was not found to be statistically significant.

Strength and creep of dental amalgam: the effects of deviation from recommended preparation procedure

The effects of deviations from recommended preparation procedures on the compressive strength, modulus of elasticity, plastic deformation, toughness, and creep of four commercial amalgam alloys have been investigated. Deviations included changes in trituration time, mercury/alloy ratio, and condensation pressure. With regard to both compressive strength and creep, there were great differences in the susceptibility of different amalgam alloys to variations in manipulation. One conventional alloy showed almost no variation in compressive strength as a result of the deviations from the recommended preparation procedure. This material also showed much greater plastic deformation and fracture toughness than the other materials, making it less brittle and probably more resistant to bending forces. Dispersalloy exhibited both increased and decreased strength as a result of the deviations, while ANA 2000 and Revalloy only showed decreased strength. Some of the alterations for ANA 2000 and Revalloy resulted in a decrease in strength below an acceptable clinical level. Regarding the modulus of elasticity, only the conventional alloys were affected by the alterations in the preparation procedure. However, for the plastic deformation, the results were reversed; only the high-copper alloys were affected. The toughness of the specimens was decreased for all the alloys with the exception of one, which was insensitive to changes in the preparation procedure as far as compressive strength was concerned. One of the high-copper alloys showed the least change in creep relative to deviations in preparation procedures. Lowered condensation pressure increased the creep value for all the amalgams; and for the conventional alloys a lowered mercury/alloy ratio also resulted in increased creep.(ABSTRACT TRUNCATED AT 250 WORDS)

Creep-fatigue as a possible cause of dental amalgam margin failure

Fracture of the margins is the most common cause of failure of dental amalgam restorations. Both corrosion and creep have been identified as possible contributors to this type of failure. The stresses that induce creep may arise from the continued setting expansion of the amalgam, the formation of corrosion products, mastication, or from the thermal expansion of the amalgam during ingestion of hot foods. The latter two are low-frequency cyclic stresses. The amalgams used in dentistry have fusion temperatures only about 40 degrees C above mouth temperature, and they experience grain boundary sliding during creep deformation. Since grain boundary sliding, low-frequency cyclic stresses, and a temperature near the fusion temperature of the alloy are prerequisites for so-called "creep-fatigue fracture", this type of fracture may contribute to amalgam margin failure. Amalgam made from seven different alloys was condensed into stainless steel dies. After being allowed to set for seven days, the specimens were thermally cycled between 4 degrees C and 50 degrees C for 500 and 1000 cycles. Amalgam margin integrity was evaluated by scanning electron microscopy both before and after each cycling period. The amount of margin fracture was calculated after 1000 cycles. Thermal cycling of amalgam restorations placed in stainless steel dies resulted in predominantly intergranular fracturing of the amalgam margins, indicating that creep-fatigue failure may be a significant contributor to in vivo margin fracturing.

Corrosion product formation sequence on Cu-rich amalgams in various solutions

A single particle and four blended Cu-rich amalgam systems were immersed in 37 degrees C solutions for 1-20 months in order to determine the characterization and sequence of corrosion product formation. X-ray diffraction and SEM/EDS were used to characterize the products. The same sequence of formation occurred in all systems in Ringer's and 0.1% Ringer's solutions. The times at which each product formed varied with the brand of the amalgam and the concentration of the solution. The initial products were ZnSn(OH)6 in Zn-containing systems and SnO2 in most other systems. Cu2O formed next, followed by CuCl2 X 3Cu(OH)2. Immersion in 1% Na2S yielded only HgS on all brands. A combination of 1% Na2S and Ringer's solution yielded CaSn(OH)6 after 2 months and Cu2O at later periods. Artificial saliva resulted in a retardation of corrosion product formation and only limited amounts of a Sn-rich product could be found after 20 months. Interactions of the various components appear to alter the nature and rate of corrosion product formation on these systems and additional systematic investigations are necessary to understand the influence of these interactions on corrosion.

Corrosion of amalgams with special regard to zinc

Five dental amalgams were studied in an in vitro corrosion test. Cylindrical test specimens were stored in weak lactic acid solutions at different pH for 1 month. The solutions were analyzed for zinc, the specimens were inspected and examined in SEM. The results showed that zinc was dissolved rather quickly from the amalgams and the amount was highest for the conventional one. Some amalgams had a low tendency for corrosion products to adhere to the surfaces. The presence of zinc did not seem to reduce their corrosion resistance.

In vitro corrosion and in vivo marginal fracture of dental amalgams

The relationship between in vitro corrosion and in vivo marginal fracture of dental amalgams has been studied. The potentiodynamic cyclic polarization technique has been used to determine the in vitro corrosion index. The marginal fracture data have been obtained from previous clinical studies reported by three independent research groups. A linear regression analysis has been employed to determine the degree of correlation between in vitro and in vivo data. Depending on the method of corrosion index measurement and the source of clinical data, correlation coefficients (r) ranging from 0.82 to 0.94 (p less than .01) have been obtained.

Fracture at the margins of amalgam as predicted by creep, zinc content, and gamma-2 content

Fracture at the margins of amalgams as predicted by an equation suggested by Mahler using creep, zinc content, and gamma-2 content was tested on the three-year clinical results of 12 alloys. The results tend to agree with Mahler's results when gamma-2 and non-gamma-2 alloys are used in the same equation. This appears, however, to be an effect of combining two distinctly different types of alloys. It is suggested that, when non-gamma-2, low creep alloys are evaluated, the equation suggested by Mahler would be inappropriate. In addition, for non-gamma-2 alloys, the prediction using creep values does not appear to be appropriate.

A 30-month clinical evaluation of the influence of finishing and size of restoration on the margin performance of five amalgam alloys

The influence of finishing and size of the restorations using five amalgam alloys (Aristaloy, Dispersalloy, Oraloy, Sybraloy, and Tytin) was evaluated at 30 mo. when size of the restoration was considered, Dispersalloy displayed the best margin performance. Oraloy, Sybraloy, and Tytin were inferior to Dispersalloy and were grouped together. Aristaloy was inferior to all other alloys in the study. When the aspect of finishing was considered, Dispersalloy and Sybraloy evidenced excellent margin performance when unfinished. Aristaloy showed the worst margin performance of all the alloys in the study when unfinished, but showed remarkable improvement in margin performance when finished.

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.

Failure at the margin of amalgams as affected by cavity width, tooth position, and alloy selection

The effects of alloy, cavity width, and tooth position on failure rate at the margins of 429 two-year-old Class II amalgams were analyzed. Interpretation of the results from a factorial design indicated that: (1) There were significant differences among alloys; (2) conservative preparations exhibit less breakdown than wider preparations; and (3) there was less failure in lower premolars than in other posterior teeth.

Dynamic mechanical properties of amalgams

A recently developed dynamic mechanical analysis technique was utilized to determine the setting rates of dental amalgams. Via a compound parallel beam apparatus the dynamic mechanical properties of five amalgam materials were continuously measured at 37 degrees C within ca. 7 min after the start of trituration. Over a 15 hr period results showed that the modulus of elasticity (Ea) increased from 1.2 X 10(10) Pa to 6.5 X 10(10) Pa--the latter generally approaching those values reported via ultrasonic techniques. Moduli results via compression tests on microspecimens (3 X 2 X 1 mm) paralleled previous reliable literature data, nominally yielding values for Ea of 2-3 X 10(10) Pa. The extent of Ea scatter from both inter- and intrapreparer experiments appeared similar, although superior technique generally could be recognized by a systematic shift of the mean results to higher Ea's. In addition to modulus studies both compressive strengths (sigma max) and their corresponding strains (epsilon) were measured on microspecimens at a strain rate (epsilon) of 0.031 min-1, with a significant increase being noted in sigma max for the one material tested at over an order of magnitude increase in epsilon.

Influence of variation in contact stress on the sliding-wear behaviour of a dental amalgam

The influence of variation in contact stress on the sliding-water behaviour of a dispersed amalgam has been investigated. The results demonstrate that: (1) the rate of wear of the amalgam in sliding contact with pins fashioned from human enamel remains virtually constant (0.39 +/- 0.06 micrometer/h-1) throughout the range of stresses encountered in vivo; and (2) the wear process involves adhesive transfer of amalgam to the contacting face of the enamel pin during sliding.

Assessment of variables in clinical studies of amalgam restorations

Marginal degradation of two amalgams with different creep properties was studied as a function of clinical variables. The amalgam with the highest creep values showed the most marked marginal degradation, irrespective of operator, doubling of the trituration time, and the use of contralateral, opposing, or unrelated teeth for comparison.

A predictive model for the clinical marginal fracture of amalgam

The relationship of clinical marginal fracture to creep and zinc content of amalgam alloys was examined. Using multiple regression analysis, a predictive equation was found which produced an excellent fit to the experimental data (R2 = .944).

Two independent evaluations of ten amalgam alloys

Two independent research groups evaluated marginal failure and conducted creep tests on 10 commercial amalgam alloys. Correlation data determined that both laboratory tests and clinical results were essentially the same between the two studies. The 2-year clinical results indicate that five alloys, Cupralloy, Dispersalloy, Indiloy, Phasealloy, and Tytin give best results. Creep correlated with the rate of marginal failure within a study when all alloys were assessed; however, for the seven gamma-2-free alloys, there was no significant relationship between in vivo and in vitro data. Since creep tests did not predict marginal failure of the gamma-2-free alloys, the results of clinical studies should be the guide to selection of the better amalgam alloys.