One-yer and two-year clinical evaluation of a composite resin vs. amalgam

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.

An abrasion test for composite resins

An abrasive wear test for composite resins was proposed. A slurry of glass pearls and abrasive particles were used. The abrasive effect was examined for different particle sizes. Particle sizes were found which gave the same order of wear as found clinically for an amalgam, a composite resin, and unfilled resin.

A long-term evaluation of abrasion of dental composite resins

A long-term study was performed on the abrasion of dental composites stored in different solutions for six months. No difference in wear resistancewas noticeable between the water and lactic acid group. But the composite with regular filler showed reduced wear resistance when compared with a microfiller composite.

Abrasion of class 1 restorative resins

Studies have been made on the abrasion by food of different restorative resins in standard Class 1 cavities in mandibular first molars of schoolchildren. The abrasion was recorded by measuring the increasing height of the exposed cavity walls. It was found that Sevriton Simplified was abraded more than Adaptic, that no difference in abrasion between Adaptic and Adaptic without filler could be demonstrated, and that Adaptic was abraded more than an experimental composite containing 30% by weight Aerosil, an ultra-fine SiO2 filler with a grain size of the order of 25-50 nm. The results are in accord with the findings in an initial study by one of the present authors, in which the fillings were placed in denture porcelain teeth. It is stressed that the conclusions of the present work are pertinent only to the type of abrasion studied, i.e. chewing of food without the possibility of direct contact between the fillings involved and the corresponding antagonists.

Compressive fatigue limits of composite restorative materials

Compressive fatigue limits at 5,000 stress cycles have been measured for seven commercial composite restorative materials. The average of the ratios between fatigue limit and compressive strengths is 0.64.

Finished surface texture, abrasion resistance, and porosity of Aspa glass-ionomer cement

1. With the finishing agents tested Concise had a smoother surface texture than Aspa. 2. The smoothest surface was on Concise polymerized against a Mylar matrix strip. The smoothest surface for Aspa was obtained with a silicon carbide disk. 3. Aspa abraded about three times as rapidly by volume as Concise when tested by a two-body abrasion method. 4. Significantly more air bubbles were entrapped by hand mixing within Aspa than within Concise. 5. Controlled clinical studies of the glass-ionomer cements are needed before they can be fully evaluated as restorative materials.

Relationship between abrasive wear and microstructure of composite resins

The in vitro abrasion resistance of seven commercial composite resin restorative materials has been measured. Analysis of the composite microstructures shows that abrasion rates are dependent upon the size, hardness, and volume fraction of particles in the material. The most abrasion-resistant composites contain a high volume fraction of large, hard particles.

Remaining methacrylate groups in composite restorative materials

The quantity of the remaining unreacted methacrylate groups in polymerized composite materials has been determined. Six proprietary composites were investigated by infrared multiple internal reflection spectroscopy. Infrared reflectance measurements were made before polymerization and repeated after the composites were subjected to polymerization at 37 degrees C for 24 hours. The quantities of remaining unreacted methacrylate groups were determined and the data expressed as percentages of the total amount of methacrylate groups in the unpolymerized materials. The specimens were specially prepared to ensure that the surface properties simulated the bulk properties of the polymerized composites. The quantities of remaining methacrylate groups in the six composites determined by this surface measuring technique ranged from 25 to 48%. The results demonstrate that commercially available composite materials exhibit different degrees of conversion 24 hours after the start of polymerization. These differences can be correlated to the different monomer compositions of the composite restorative resins.

Assessment of the quality of restorations. A literature review

Most assessments of the quality of restorations are entirely subjective and involve standard clinical diagnostic equipment. However in recent years there has been an increasing demand for more accurate and reliable methods. Attempts to achieve these have been directed mainly towards the standardization of clinical judgements by the provision of various systems of guidelines of criteria upon which to base them. While these have improved the usefulness of the assessments, they have remained largely subjective. Furthermore, the efficacy of using the particular criteria selected are themselves open to questioning. By the use of more complex methods of examination, often in the field of restorative materials research, assessments have been made of various features of restorations and a body of knowledge concerning factors that might influence or manifest their quality has been build up. However the true significance of much of this knowledge in terms of the clinical behaviour, and thus the finite quality of restorations in service, has yet to be established, for many of the studies have been undertaken in isolation from the dynamic conditions of function in the mouth. Notably, however, a few objective clinical studies have been carried out and objective measurements of some factors affecting the quality of restorations have been reported.

Abrasive wear, tensile strength, and hardness of dental composite resins--is there a relationship?

The in vitro abrasive wear resistance, tensile strength, and hardness of seven widely used composite restorative resins have been measured. Findings indicate that the values of tensile strength and hardness are not related to the measured abrasion rates. It is apparent that abrasive wear is a complex phenomenon and that materials which have high values for strength and/or hardness do not necessarily have high resistance to abrasive wear.

Semiporous reinforcing fillers for composite resins: I. Preparation of provisional glass formulations

A conceptual means of obtaining improved bonding between filler particles and the polymeric binders of composites is presented. It involves preparing glass particles that separate into two interconnected vitreous phases when heated to an appropriate temperature, and then etching these to produce a porous surface layer. Candidate glass compositions were prepared and subjected to heat treatment in a gradient furnace. Compositions susceptible to phase separations were delineated.

Six-month and one-year clinical evaluation of a composite resin for class II restorations

This clinical study was undertaken to compare a composite resin, containing a modified filler, with a dental amalgam alloy in Class II restorations. Eight senior dental students placed 98 pairs of restoration in 69 patients. After six months and one-year, 69 pairs of restorations in 49 patients were evaluated by two examiners. No significant differences were found between baseline and one-year evaluations for ratings of anatomic form and marginal adaptation. Color match was found to decrease in time, and marginal discoloration was found to increase in time. Failures of restoration were not attributed to the materials, but more probably were caused by faulty cavity preparations. Although the results for each patient analysis indicated no significant differences in anatomic form and marginal adaptation at one year, the B ratings for these two criteria for both types of restorations in this study indicate the need for continued clinical evaluation. The decreased number of composite restorations with good color match is not unexpected and indicates the need for judgment when selecting composite resin as the restorative material in Class II preparations for esthetic purposes. The significant number of composite restoration in this study with increasing marginal discoloration is reason for concern and continued evaluation of these restorations. Marginal discoloration and poor marginal adaptation are factors related to recurrent caries and replacement of restorations. Thus, continued research and clinical evaluation of new restorative materials is a necessity.

Long term follow-up of clinical evaluations of lathe-cute versus spherical amalgam

A spherical alloy was tested against a conventional lathe-cut amalgam in clinical trials. Results indicated that both alloys had comparable marginal breakdown rates. However, the three dentists who placed the restorations showed decided differences in marginal breakdown rates for their patients. Operator variable was the most significant finding.