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Biomedical subjects

V P Thompson

Publications and source records attributed to V P Thompson.

At least 19 recordsLinked to original sources
PubMed2006

Evaluation of a self-limiting concept in dentinal caries removal.

The mechanical removal of dentinal caries traditionally involves the use of tactile sensation and/or caries-indicating dyes. This study tested the hypothesis that self-limiting polymer burs are as effective as conventional carbide burs in creating substrates for dentin bonding. Carious dentin from extracted human molars was removed with carbide or polymer burs, with dental explorer hardness as the end-point for caries removal. Dentin substrates were bonded with etch-and-rinse or self-etch adhesives and prepared for microtensile bond testing and transmission electron microscopy. For each bur type, there was no difference in bond strength between adhesives. However, the polymer bur surface exhibited significantly lower bond strengths than the carbide bur, and both were lower than flat, non-carious dentin controls. TEM revealed areas of incompletely removed, denatured caries-infected dentin in the polymer bur specimens. These first-generation polymer burs might best be utilized for deep caries removal where pulpal exposure is a concern.

Analysis of Variance↗
PubMed2005

Near-surface damage--a persistent problem in crowns obtained by computer-aided design and manufacturing.

Robust dental systems obtained by computer-aided design and manufacture (CAD/CAM) have been introduced and, in parallel, the strength of the ceramic materials used in fabricating dental crowns has improved. Yet all-ceramic crowns suffer from near-surface damage, limiting their clinical success, especially on posterior teeth. Factors directly associated with CAD/CAM fabrication that contribute to the degree of damage include material selection and machining parameters and strategies. However, a number of additional factors also either create new damage modes or exacerbate subcritical damage, potentially leading to catastrophic failure of the crown. Such factors include post-fabrication manipulations in the laboratory or by the clinician, fatigue associated with natural occlusal function, and stress fields created by compliance or distortion within the supporting tooth structure and/or adhesive material holding the crown to the tooth. Any damage reduces the strength of a crown, increasing the probability of catastrophic failure. The challenge is to understand and manage the combination of competing damage initiation sites and mechanisms, limitations imposed by the demand for aesthetics, and biologically related constraints.

Ceramics↗
PubMed2002

Materials design of ceramic-based layer structures for crowns.

Radial cracking has been identified as the primary mode of failure in all-ceramic crowns. This study investigates the hypothesis that critical loads for radial cracking in crown-like layers vary explicitly as the square of ceramic layer thickness. Experimental data from tests with spherical indenters on model flat laminates of selected dental ceramics bonded to clear polycarbonate bases (simulating crown/dentin structures) are presented. Damage initiation events are video-recorded in situ during applied loading, and critical loads are measured. The results demonstrate an increase in the resistance to radial cracking for zirconia relative to alumina and for alumina relative to porcelain. The study provides simple a priori predictions of failure in prospective ceramic/substrate bilayers and ranks ceramic materials for best clinical performance.

Aluminum Oxide↗
PubMed2001

Use of contact testing in the characterization and design of all-ceramic crownlike layer structures: a review.

Ceramic-based crowns, particularly molar crowns, can fail prematurely from accumulation of fracture and other damage in continual occlusal contact. Damage modes depend on ceramic types (especially microstructures), flaw states, loading conditions, and geometric factors. These damage modes can be simulated and characterized in the laboratory with the use of Hertzian contact testing on monolayer, bilayer, and trilayer structures to represent important aspects of crown response in oral function. This article reviews the current dental materials knowledge base of clinically relevant contact-induced damage in ceramic-based layer structures in the context of all-ceramic crown lifetimes. It is proposed that simple contact testing protocols that make use of sphere indenters on model flat, ceramic-based layer structures-ceramic/polymer bilayers (simulating monolithic ceramic crowns on dentin) and ceramic/ceramic/polymer trilayers (simulating veneer/core all-ceramic crowns on dentin)-can provide useful relations for predicting critical occlusal loads to induce lifetime-threatening fracture. It is demonstrated that radial cracking from the lower core layer surface is the dominant failure mode for ceramic layer thicknesses much below 1 mm. Such an approach may be used to establish a scientific, materials-based foundation for designing next-generation crown layer structures.

Bite Force↗
PubMed1999

The seal slighted?

Explore the source record for details and available documents.

American Dental Association↗
PubMed1998

Indentation damage and mechanical properties of human enamel and dentin.

Understanding the mechanical properties of human teeth is important to clinical tooth preparation and to the development of "tooth-like" restorative materials. Previous studies have focused on the macroscopic fracture behavior of enamel and dentin. In the present study, we performed indentation studies to understand the microfracture and deformation and the microcrack-microstructure interactions of teeth. It was hypothesized that crack propagation would be influenced by enamel rods and the dentino-enamel junction (DEJ), and the mechanical properties would be influenced by enamel rod orientation and tooth-to-tooth variation. Twenty-eight human third molars were used for the measurement of hardness, fracture toughness, elastic modulus, and energy absorbed during indentation. We examined the effect of enamel rod orientation by propagating cracks in the occlusal surface, and in the axial section in directions parallel and perpendicular to the occlusal surface. The results showed that the cracks in the enamel axial section were significantly longer in the direction perpendicular to the occlusal surface than parallel. The cracks propagating toward the DEJ were always arrested and unable to penetrate dentin. The fracture toughness of enamel was not single-valued but varied by a factor of three as a function of enamel rod orientation. The elastic modulus of enamel showed a significant difference between the occlusal surface and the axial section. It is concluded that the cracks strongly interact with the DEJ and the enamel rods, and that the mechanical properties of teeth are functions of microstructural orientations; hence, single values of properties (e.g., a single toughness value or a single modulus value) should not be used without information on microstructural orientation.

Analysis of Variance↗
PubMed1998

Mechanical characterization of dental ceramics by hertzian contacts.

Hertzian indentation testing is proposed as a protocol for evaluating the role of microstructure in the mechanical response of dental ceramics. A major advantage of Hertzian indentation over more traditional fracture-testing methodologies is that it emulates the loading conditions experienced by dental restorations: Clinical variables (masticatory force and cuspal curvature) identify closely with Hertzian variables (contact load and sphere radius). In this paper, Hertzian responses on four generic dental ceramics systems-micaceous glass-ceramics, glass-infiltrated alumina, feldspathic porcelain, and transformable zirconiaare presented as case studies. Ceramographic sectioning by means of a "bonded-interface" technique provides new information on the contact damage modes. Two distinct modes are observed: "brittle" mode, classic macroscopic fracture outside the contact (ring, or cone cracks), driven by tensile stresses; and "quasi-plastic" mode, a relatively new kind of deformation below the contact (diffuse microdamage), driven by shear stresses. A progressive transition from the first to the second mode with increasing microstructural heterogeneity is observed. The degree of quasi-plasticity is readily apparent as deviations from ideal linear elastic responses on indentation stress-strain curves. Plots of threshold loads for the initiation of both fracture and deformation modes as a function of indenter radius constitute "damage maps" for the evaluation of prospective restoration damage under typical masticatory conditions. The degree of damage in both modes evolves progressively with load above the thresholds. Strength tests on indented specimens quantify sustainable stress levels on restoration materials after damage. The most brittle responses are observed in the fine glass-ceramics and porcelain; conversely, the most quasi-plastic responses are observed in the coarse glass-ceramics and zirconia; the medium glass-ceramics and alumina exhibit intermediate responses. Implications of the results in relation to future materials characterization, selection, and design are considered in the clinical context.

Aluminum Oxide↗
PubMed1997

Enamel subsurface damage due to tooth preparation with diamonds.

In clinical tooth preparation with diamond burs, sharp diamond particles indent and scratch the enamel, causing material removal. Such operations may produce subsurface damage in enamel. However, little information is available on the mechanisms and the extent of subsurface damage in enamel produced during clinical tooth preparation. The aim of this study, therefore, was to investigate the mechanisms of subsurface damage produced in enamel during tooth preparation by means of diamond burs, and to examine the dependence of such damage on enamel rod orientation, diamond particle size, and removal rate. Subsurface damage was evaluated by a bonded-interface technique. Tooth preparation was carried out on two enamel rod orientations, with four clinical diamond burs (coarse, medium, fine, and superfine) used in a dental handpiece. The results of this study showed that subsurface damage in enamel took the form of median-type cracks and distributed microcracks, extending preferentially along the boundaries between the enamel rods. Microcracks within individual enamel rods were also observed. The median-type cracks were significantly longer in the direction parallel to the enamel rods than perpendicular to the rods. Preparation with the coarse diamond bur produced cracks as deep as 84 +/- 30 microns in enamel. Finishing with fine diamond burs was effective in crack removal. The crack lengths in enamel were not significantly different when the removal rate was varied. Based on these results, it is concluded that subsurface damage in enamel induced by tooth preparation takes the form of median-type cracks as well as inter- and intra-rod microcracks, and that the lengths of these cracks are sensitive to diamond particle size and enamel rod orientation, but insensitive to removal rate.

Dental Enamel↗
PubMed1996

Resin-bonded fixed partial dentures. I. Proposed standardized criteria for evaluation.

Since etched cast resin-bonded prostheses were introduced in 1980, many articles have been written about them. Most state that the reported clinical success of these bonded restorations has been based primarily on the longevity of the bonding. For a comprehensive evaluation, however, it is important not only to examine the bonding but also to evaluate the periodontal response. The proposed standard method provides a consistent and comprehensive evaluation of resin-bonded prostheses that is applicable for researchers and clinicians alike.

Dental Plaque Index↗
PubMed1996

Resin-bonded fixed partial dentures. II. Clinical findings related to prosthodontic characteristics after approximately 10 years.

A clinical study was conducted for patients who were functioning with resin-bonded fixed partial dentures for approximately 10 years. The purpose of this study was to evaluate the periodontal health and determine the prosthodontic characteristics of the fixed partial dentures. Results indicated that plaque indexes, probing, recession, and loss of attachment were greater for abutments than for control teeth. The differences were statistically significant but clinically small. The bonded restorations were generally well adapted and contoured for case of cleaning.

Chi-Square Distribution↗
PubMed1996

Maximum likelihood estimates for the lifetime of bonded dental prostheses.

Clinical studies measuring the lifetime of dental prostheses produce censored data when not all specimens have failed during the course of the study. Such clinical data can be analyzed by the Weibull probability distribution function. Algorithms are presented that provide the maximum likelihood estimates of the distribution's parameters. These parameters are the characteristic lifetime (time to failure for 63% of the specimens of the total sample) and the Weibull or shape parameter. Two iterative methods for solving the maximum likelihood equations are given. These mathematical methods have been applied to the results from a retrospective clinical investigation into the lifetime assessment of resin-bonded prostheses. This study evaluated 164 resin-bonded prostheses (for 146 patients) placed between January, 1980, and May, 1985. To date (April, 1995), 47 prostheses (29%) have failed with a median time in service of 74 months (6.2 yr). For the surviving prostheses, the median time in service is 123 months (10.3 yr) and still increasing. The maximum likelihood estimate of the characteristic lifetime for these restorations is 255 months (21.3 yr). Differences in the characteristic lifetime were observed between prostheses placed anteriorly, 338 months (28 yr), and posteriorly, 207 months (17 yr). Since there are no rigorous confidence intervals for deeply censored samples, only provisional confidence bounds could be determined, which substantiated the observed differences. The Weibull modulus value of 1.5 indicates that the probability of failure for resin-bonded prostheses begins to decrease after 10 years in service.

Algorithms↗
PubMed1996

Ten-year clinical and microscopic evaluation of resin-bonded restorations.

A clinical recall was conducted for 103 patients who were functioning with resin-bonded restorations for approximately 10 years. The purpose of this study was to evaluate marginal adaptation of the cast metal retainers. Following clinical evaluations, replicas of incisal and occlusal margins were examined in the scanning electron microscope to determine marginal separation and microscopic patterns of the resin composite interface between metal and tooth. Anterior abutments exhibited better clinical adaptation and fewer voids and debonds than did posterior abutments. Larger microscopic marginal separations were associated with those retainers that had clinically detectable voids or defects.

Chi-Square Distribution↗
PubMed1995

Durability of resin bonds to a cobalt-chromium alloy.

Common nickel-chromium-beryllium alloys used for resin-bonded fixed partial dentures have possible health hazards due to leaching of nickel and beryllium. For resin-bonded restorations corrosion resistant cobalt-chromium alloys (CoCr) are a suitable alternative material without sacrificing physical properties. This study evaluated the bond strength and bond durability of new adhesive systems to a CoCr alloy. Plexiglas (acrylic) tubes filled with composite were bonded to CoCr alloy discs. Groups of 24 samples were bonded using six different bonding systems. Subgroups of eight bonded samples were stored in an isotonic artificial saliva solution (37 degrees C) either for 1 day, 30 days or 150 days. In addition the 30- and 150-days samples were subjected to 7500 or 37,500 thermal cycles, respectively. The bond strength of a conventional BisGMA composite (Twinlook) to sandblasted CoCr was significant lower than when using chemomechanical bonding systems and decreased continuously during the storage time of 150 days. The additional use of silane on the sandblasted alloy resulted in an insignificant increase in bond strength. Statistically significant higher and more durable bonds to CoCr alloy were achieved either with the combination of silica coating and use of the conventional BisGMA composite or with the combination of sandblasting and the use of a composite modified with a phosphate monomer (Panavia EX). In the latter systems, the bond strengths were mainly limited by the cohesive strength of the resin composites: partial adhesive failures were only observed for a tribochemical silica coating system. A new composite also containing the active phosphate monomer (Panavia TPN-S) exhibited a significant decrease in cohesive strength over time.

Adhesiveness↗
PubMed1995

Bonding to glass infiltrated alumina ceramic: adhesive methods and their durability.

Resin bonding to a glass-infiltrated aluminum oxide ceramic (In-Ceram) cannot be achieved by the methods commonly used for conventional silica-based dental ceramics. This study evaluated the durability of alternative methods of adhesive bonding to In-Ceram ceramic. The tensile bond strength of six bonding systems to In-Ceram ceramic was tested after up to 150 days of storage in isotonic artificial saliva solution and thermal cycling. Sandblasting alone or additional use of a silane did not result in a durable bond of a conventional BIS-GMA composite resin to In-Ceram ceramic. A durable bond to In-Ceram ceramic was achieved with a combination of tribochemical silica coating and conventional BIS-GMA composite resin or with the combination of sandblasting and a composite resin modified with a phosphate monomer. These two chemomechanical bonding methods appeared suitable for clinical bonding of In-Ceram ceramic restorations. A delayed degradation in bond strength was recorded for the combination of thermal silica coating and a conventional BIS-GMA composite resin; no reduction was found after 30 days, but there was a pronounced decrease after 150 days. This degradation indicated that extended storage in a wet environment was needed in laboratory tests to evaluate the durability of chemical bonds.

Aluminum Oxide↗
PubMed1995

Durability of resin bonds to pure titanium.

PURPOSE: This study evaluated the bond strength and bond durability of new adhesive systems to pure titanium. MATERIALS AND METHODS: Plexiglass tubes filled with composite were bonded to titanium discs. Groups of 24 samples were bonded using six different bonding systems. Subgroups of eight bonded samples were stored in an isotonic artificial saliva solution (37 degrees C) for 1, 30, or 150 days. In addition, the 30- and 150-day samples were thermal cycled for 7,500 or 37,500 cycles between 5 degrees C and 55 degrees C, respectively. After these storage conditions, all samples were debonded in tension. RESULTS: The bond strength of a conventional bisphenol-A glycidyl methacrylate composite to sandblasted titanium was significantly lower than using chemomechanical bonding systems and decreased slightly during the storage time of 150 days. The additional use of a silane on sandblasted titanium resulted in an insignificant increase in bond strength and decreased over storage time to the same level as on sandblasted-only titanium. Statistically significant higher bond strengths were achieved either with the combination of silica coating and use of a conventional bisphenol-A glycidyl methacrylate composite or with the combination of sandblasting and the use of composites modified with a phosphate monomer. In the latter systems, the bond strengths were only limited by the cohesive strength of the composite resins. A new phosphate monomer containing composite showed a tendency to lose cohesive strength over time (statistically not significant). CONCLUSIONS: Using chemomechanical bonding systems, ie, silica-coating systems or modified composites with adhesive monomers, resulted in 2 to 2.5 times increased bond strength to titanium compared with the bond strength of a conventional bisphenol-A glycidyl methacrylate composite. With chemomechanical bonding systems, the resin bond to titanium was durable over 150 days, even after being stored in water and thermal cycled.

Adhesiveness↗
PubMed1995

10-year periodontal response to resin bonded bridges.

The purpose of this study was to evaluate the long-term (10 years +/- 15 months) periodontal response to resin bonded bridges (RBRs). A total of 103 patients who had RBRs bonded between 1980 and 1984 were recalled. Periodontal evaluations were made by two clinicians for all abutment teeth and for selected control teeth with intact, non-restored lingual surfaces. Periodontal indices consisted of: plaque index (PI), gingival index (GI), gingival recession, probing depth, and loss of attachment. Paired t tests indicated no significant difference in overall GI between experimental and control sites, but a significant difference in PI and probing depth with experimental sites (abutment teeth) showing higher PI and greater probing depths. Significant differences were found in overall recession and attachment loss, again with more recession and attachment loss observed on the abutment teeth as compared to the controls. Site specific analyses for PI, probing, and loss of attachment showed small but significant differences between experimental and control teeth in 15 of 21 sites. Although these findings may be statistically significant, the clinical impact for resin bonded restorations functioning for over 10 years is minimal and is comparable to periodontal response to other types of restorations.

Analysis of Variance↗
PubMed1994

Tensile bond strength of dental adhesives bonded to simulated caries-exposed dentin.

This study investigated the possibility of resin bonding to carious dentin. The study was divided into two parts, to determine first whether an in vitro model for caries could be developed for testing bond strength and second whether chemical modification of the caries model dentin surface, instead of mechanical removal of the carious layer, would enhance resin bond strengths. Dentin samples were exposed to an artificial caries decalcification solution (lactic acid+nitrocellulose) for 7 days. The depth of the decalcified surface was determined by microhardness and the nature of the surfaces analyzed by use of the scanning electron microscope. After bur removal of the decalcified dentin, samples were bonded with three different dentin bonding systems and the tensile bond strengths were determined. Control specimens were prepared and bonded with no decalcification or bur preparation. These values were compared with specimens prepared by decalcification but with no mechanical removal of the decalcified surface layer before bonding. Additional decalcified samples were treated with phosphoric acid to modify the decalcified surface before dentin bond testing. Bond strengths were significantly higher (p < 0.05) for the decalcified and mechanically prepared dentin as compared with either the unmodified or the phosphoric acid modified decalcified dentin. The highest bond strengths for all systems were found for the undecalcified control group. These results suggest that it may be possible to bond to the collagenous structures remaining in carious dentin. This could lead to conservation of tooth structure and rethinking of cavity preparation design.

Collagen↗