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Biomedical subjects

J F McCabe

Publications and source records attributed to J F McCabe.

At least 91 records · Page 5Linked to original sources
PubMed1994

Wear characteristics in a two-body wear test.

OBJECTIVES: A previous report compared spherical steatite (ceramic enamel substitute) abraders with those of natural enamel in a two-body wear test. The wear rates and coefficients of friction of the two abraders against various composites and an amalgam were well correlated although the wear rates were slightly higher with steatite. This report investigates the characteristics of the worn abrader and specimen surfaces. METHODS: Scanning electron microscopy and laser profilometry were used. RESULTS: Similar wear characteristics were found for the two types of abraders. Adhesive wear was evident for the amalgam, Dispersalloy (Johnson & Johnson), and the heat/pressure-cured microfill composite, Isosit (Ivoclar-Vivadent). Abrasion was seen with the hybrid composite, Occlusin (ICI), and, to a lesser extent, the microfill composite, Heliomolar (Ivoclar-Vivadent). The appearance of the worn small particle hybrid composite, Brilliant Dentin (Coltène), suggested that fatigue and delamination were involved. Laser profilometry showed that the hybrid composites caused much greater wear to the abraders than either the microfill composites or amalgam. The Ra values of the worn abraders and specimens were similar, suggesting conformal contact between them and endorsing the well controlled conditions of the wear test. SIGNIFICANCE: The results of this and other publications suggest that steatite can be used as an alternative to enamel in performing two-body wear tests on dental composites. This should help significantly in materials evaluation and development.

Acrylic Resins↗
PubMed1994

Adhesion of composite resin to bone--a pilot study.

This pilot study investigated the adhesion of composite resin to pig calvarium using All-bond 2 dentine bonding agent in an in vitro model. The bone was subjected to different methods of preparation. Acid-etching decreased the bond strength between bone and composite. Roughening the bone with a surgical bur prior to application of the adhesive produced bond strengths in the range 11.1-16.1 MPa.

Animals↗
PubMed1994

Bond strength to dentine of two light-activated glass polyalkenoate (ionomer) cements.

The effects of sample thickness on the in vitro bond strength of two light-activated glass polyalkenoate cements to dentine have been investigated. The buccal and/or lingual surfaces of non-carious human third molar teeth were used for bonding. The tensile bond strengths to dentine of samples of the cements of 0.5 mm, 1.0 mm, 1.5 mm and 2.0 mm were measured 10 min after bonding. For one of the materials bond strength and reliability were found to decrease as the sample thickness increased. The bond strength to dentine of the second material was also affected by changes in the thickness of the cement but as the bond strengths were all very low for this material, any differences are probably of little clinical relevance.

Dental Bonding↗
PubMed1994

Factors that influence the setting characteristics of encapsulated glass ionomer cements.

The slow rate of the setting reaction of glass ionomer cements (GICs) is one of the problems associated with their clinical use. The manufacturers of these materials suggest that increasing the mixing time will increase the rate of reaction and it was the purpose of this study to investigate the limits of this relationship. The method used to monitor the setting reaction with Differential Thermal Analysis (DTA). The results obtained using DTA were compared with those obtained using the ISO penetrometer method as defined in the ISO standard for water-based cements, ISO 9917:1991E. It was shown that increasing the mixing time of cements did not significantly reduce the setting time (P > 0.05). Under the conditions of the study it was only possible to measure a working time for the Chemfil II (and then only if it was mixed for less than 12 s). Storing the capsules at 4 degrees C did enable a working time to be measured using the DTA for all the materials, however these storage conditions also produced a significant increase in the setting time which would be undesirable to the clinician. The penetrometer method underestimated the duration of the setting reaction by up to 32% compared with the DTA method. However it was a quick and reproducible method of measuring setting time and as such may still be an appropriate method for use in the ISO standards.

Cermet Cements↗
PubMed1994

Incorporation of bacterial inhibitor into resin composite.

Attempts to produce resin composite with antibacterial properties by incorporation of an antibacterial agent such as chlorhexidine have been reported, but problems can arise due to release of the inhibitory agent from the composite. Such problems may include toxic effects, influence on mechanical properties, and loss of effectiveness. A new monomer, methacryloyloxydodecylpyridinium bromide (MDPB), was synthesized by combining an antibacterial agent and methacryloyl group. The monomer was incorporated into resin composite to develop a non-releasing antibacterial composite. The ability of composite incorporating MDPB to inhibit growth and plaque accumulation by Streptococcus mutans in vitro was assayed, elution of antibacterial components from the material was investigated, and the influence of incorporation of MDPB on the mechanical properties of composite was studied. Uncured MDPB revealed antibacterial activity against S. mutans and six other species of oral streptococci, with the minimum inhibitory concentration for S. mutans being comparable with that of triclosan. After composite incorporating MDPB was cured, no elution of the antibacterial components was observed from the material, even after 90 days' immersion in water or other solvents. Growth of S. mutans on agar under specimens of MDPB-containing composite was inhibited compared with controls. In a bacterial accumulation study, S. mutans accumulated to a lesser degree on the surface of composite incorporating MDPB (p < 0.05) than on control. Incorporation of MDPB had no significant influence on the mechanical properties of the composite.

Analysis of Variance↗
PubMed1994

A two-body frictional wear test.

Enamel abraders used in two-body wear tests suffer the disadvantage that standardization is difficult or impossible to obtain. The aim of this study was to test whether steatite (a ceramic material with a Vickers Hardness similar to that of enamel) could be used as a satisfactory human enamel analogue. The friction and wear characteristics of 'spherical' abraders made from these two materials against composite and amalgam specimens were therefore compared. A two-body wear test for restorative materials was devised which could be carried out in a Universal Testing Machine and which allowed for continuous monitoring of the frictional forces during wear. The results showed that steatite and enamel abraders produced similar coefficients of friction (correlation coefficient, r = 0.98). A linear relationship was found between depth (and volume) of wear and number of cycles (r = 0.98 to 0.99). Wear rate was not affected by the increase in abrader facet area. The wear rate against the steatite abrader was slightly greater than that against enamel, but the two abraders were reasonably correlated (r = 0.94). Friction and wear were correlated for the steatite abrader (P < 0.05, r = 0.88) but not the enamel abrader. The hybrid composites had a high wear rate and wore both the abraders more than did the microfilled composites or amalgam. These findings suggest that steatite is a suitable substitute for enamel in this type of test.

Acrylic Resins↗
PubMed1994

Influence of incorporation of antibacterial monomer on curing behavior of a dental composite.

A newly developed monomer, methacryloyloxdodecylpyridinium bromide (MDPB), has an antibacterial activity against oral streptococci, and this monomer can be active even after being immobilized as one component of a cured composite. The purpose of this study was to investigate the influence of incorporation of MDPB on the curing behavior of Bis-GMA-based composites. Depth of cure, degree of cure, light-attenuating effect, and surface hardness of composites incorporating 0.4 or 0.5% MDPB were measured and compared with those of a control material without MDPB. Depth of cure of composites with MDPB, measured by means of a penetrometer, was greater than for the control (p < 0.05). Differential thermal analysis showed that composites with MDPB had a significantly greater degree of cure than the control (p < 0.05). The light-attenuating effect of MDPB composites was less than for the control (p < 0.05). No significant difference between experimental and control was obtained with respect to Vickers hardness after both one day's and seven days' storage in water. These results indicate that the incorporation of small quantities of MDPB into Bis-GMA-based composites did not adversely affect the cure performance. On the contrary, a significant, though small, improvement was observed.

Analysis of Variance↗
PubMed1994

A laboratory investigation into cements used to retain orthodontic bands.

A laboratory study is presented where a technique of band retention testing is characterized. A glass polyalkenoate and a zinc phosphate cement were evaluated for band retention under simulated conditions of mechanical stress. In the absence of mechanical and other stresses there was no difference in the two cements for band retention. However, after mechanical stress was applied the glass polyalkenoate cement proved superior to the zinc polyalkenoate cement for band retention (P < 0.05). Weibull analysis is presented and described as a useful adjunct to statistical handling of band retention data.

Dental Bonding↗
PubMed1994

A critique of bond strength testing in orthodontics.

The literature contains a large number of publications on in vitro bond strength testing of materials used in orthodontics. The results are often quoted by manufacturers to support their products. Little attention has been paid to the detail of the test procedures used. However, a review of the literature revealed a large variation in the methods used for bond strength testing in orthodontics making comparison of papers difficult and often impossible. The case for a possible standard technique is suggested. It is hoped that this will lead to more meaningful testing of new products, which will produce more reliable guidance for the clinical orthodontist.

Animals↗
PubMed1993

Impact strength of acrylic resin denture base materials with surface defects.

The first part of this study involved the development of a method for evaluating the effect of small surface defects (3.0 microns-80.0 microns) on the impact strength of acrylic denture base materials. The method was used to compare the properties of 12 denture base materials, some of which are described as "high-impact strength" products. The defects were introduced by drawing the specimens over abrasive papers of varying grit sizes or by notching with a craft knife. Flexural toughness tests were also carried out in order to evaluate the materials under both rapid (impact) and slow (flexural) rate test conditions. The impact resistance of acrylic resins was significantly reduced by the presence of very small surface defects (e.g., < 16 microns), and this was particularly noticeable for so-called high-impact resins. The latter have values of impact strength only slightly higher than standard acrylic products when defects are present. Testing "notched" specimens with small surface defects was a simple method of obtaining reproducible results. This test was sensitive enough to differentiate among several types of currently available denture base resins.

Acrylic Resins↗
PubMed1993

Fluoride release from light-activated glass ionomer restorative cements.

Fluoride release from four light-activated glass ionomer cements, including newly developed restorative cements, was evaluated and compared with four conventional acid-base glass ionomer cements. There was no significant difference between the group of light-activated cements and the group of conventional cements, and light-activated cements were found to have a potential for releasing fluoride equivalent to that of conventional cements. The amount and rate of release varied among cements. It may be affected not only by the formation of complex fluoride compounds and their interaction with polyacrylic acid but also by the type and amount of resin used for the photochemical polymerization reaction.

Acrylic Resins↗
PubMed1993

Displacement Rheometer: a method of measuring working time and setting time of elastic impression materials.

A new method of measuring both working time and setting time of elastomeric impression materials has been developed. A Displacement Rheometer was used to monitor the development of elasticity in setting elastomers. The results obtained with the Displacement Rheometer were compared to the results of the ISO test as well as those of the Controlled Stress Rheometer. Working time using the ISO method was calculated according to the standard method described in the specification, while for both the Controlled Stress Rheometer and the Displacement Rheometer working times were the times when initial elastic recovery was observed at 23 degrees C. With the Displacement Rheometer the setting time is the time when the mixed material reaches optimal elastic recovery at 37 degrees C. Statistical analysis with ANOVA showed that for five of the test materials there were no differences between the three methods. For three of the materials the working time determined by the ISO method was significantly longer than that determined by the other two methods. The advantages and disadvantages of each method are discussed and the Displacement Rheometer is recommended as a supplement to the standard specification method.

Alginates↗
PubMed1993

Evaluation of the viscoelastic properties of denture soft lining materials.

Denture soft lining materials are widely used in prosthetic dentistry. Their success has been attributed to their softness and resilience, properties described by their viscoelasticity. Though these properties have been extensively investigated in laboratory studies, clinical studies have been limited. The viscoelastic properties of the temporary soft lining material Coe Soft and the permanent soft lining materials Palasiv 62 and Molloplast-B have been studied using a force/distance probe whereby penetration was measured against time under constant stress. Derived values of an initial and time-dependent compliance has allowed a quantitative in vivo and in vitro assessment of freshly prepared samples of each test material and comparison between materials. The baseline behaviour of each test material in response to the test regimen was similar for both clinical and laboratory specimens. Three types of behaviour could be identified: (i) constant strain in which penetration was clearly less than specimen thickness--elastic behaviour (Molloplast-B); (ii) constant strain in which the penetration was equal or nearly equal to specimen thickness--apparent elastic behaviour (Coe Soft); (iii) strain which increased with time of load application--viscoelastic behaviour (Palasiv 62). The mean and range of baseline clinical thickness for Coe Soft was approximately half that seen for the permanent soft lining materials. There was a much smaller range in the baseline compliance of all materials than might have been anticipated from a knowledge of their relative softness.

Acrylic Resins↗
PubMed1993

Age changes in the viscoelasticity of permanent soft lining materials.

Age-related changes in the viscoelasticity of an acrylic-based (Palasiv 62) and silicone (Molloplast-B) permanent soft lining material were evaluated in parallel clinical and laboratory longitudinal studies using a force/distance probe. Changes in the viscoelastic properties of Palasiv 62 in clinical use were characterized by a significant and continued reduction in both initial and delayed compliance. That is, the material became harder whilst still retaining the underlying pattern of viscoelasticity seen at baseline. Laboratory immersion in distilled water resulted in significant reductions in compliance values. These reductions were cumulatively similar to those seen clinically but did not occur as rapidly. There was evidence of small, continued reductions in the measured thickness of clinical linings of Palasiv 62. The clinical and laboratory compliance of Molloplast-B remained stable over time. Ageing did not affect the essential elasticity of this material.

Acrylic Resins↗
PubMed1993

Age changes in the viscoelasticity of a temporary soft lining material.

The viscoelastic properties of a widely used temporary soft lining material have been monitored in vivo and in vitro using a force distance probe. Over a period of 8 weeks' clinical use, Coe Soft demonstrated a significant and continued reduction in compliance with time, the reduction being particularly rapid over the first week. These changes were not associated with a reduction in measured lining thickness for which significant changes were not found. In vitro immersion in water, saline or artificial saliva was characterized by a rapid and significant reduction in compliance values over the first week. Further continued reductions in compliance values were only observed in artificial saliva over 8 weeks, and on prolonged immersion in distilled water over 96 weeks. All reductions in compliance were significantly less than those seen clinically.

Acrylic Resins↗
PubMed1993

The role of sandblasting on the retention of metallic brackets applied with glass ionomer cement.

A laboratory investigation of the shear bond strength of stainless steel brackets applied with glass ionomer cement (Ketac-Cem) and a conventional adhesive (Right-on) is described. Sandblasting of the bracket base was undertaken in half of the sample bonded with Ketac-Cem and produced a significant reduction in the probability of failure relative to the unsandblasted sample. Brackets with sandblasted and unsandblasted bases, bonded with Ketac-Cem were subjected to mechanical fatigue in a ball mill for a total of 20 hours. Mean survival time (MST) was then calculated for each group and was found to be significantly improved by sandblasting of the bracket base (P < 0.01).

Adhesives↗