Van P. Thompson

Etched castings: An improved retentive mechanism for resin-bonded retainers

Summary A technique was described for a retentive mechanism that etches the inner side of cast fixed partial denture frameworks. The etched metal ceramometal restoration was then bonded to the enamel surface utilizing the technique for acid etching enamel. Improved resin-bonded retainers provide innovative, conservative, and viable alternatives to traditional fixed prosthodontics.

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.

Sandblasting and silica coating of a glass-infiltrated alumina ceramic: Volume loss, morphology, and changes in the surface composition

Silica coating can improve bonding of resin to glass-infiltrated aluminum oxide ceramic (In-Ceram), and sandblasting is a pretreatment to thermal silica coating (Silicoater MD system) or a tribochemical coating process (Rocatec system). This study evaluated the effects of sandblasting and coating techniques on volume loss, surface morphology, and surface composition of In-Ceram ceramic. Volume loss through sandblasting was 36 times less for In-Ceram ceramic compared with a feldspathic glass ceramic (IPS-Empress), and sandblasting of In-Ceram ceramic did not change its surface composition. After tribochemical coating with the Rocatec system, a layer of small silica particles remained that elevated the silica content to 19.7 weight percentage (energy-dispersive spectroscopy). Ultrasonic cleaning removed loose silica particles from the surface and decreased the silica content to 15.8 weight percentage, which suggested firm attachment of most of the silica layer to the surface. After treatment with the Silicoater MD system, the silica content increased only slightly from that of the sandblasted specimen. The silica layer created by these systems differs greatly in both morphology and thickness, which could result in different bond strengths. Sandblasting of all ceramic clinical restorations with feldspathic glass materials should be avoided, but for In-Ceram ceramic the volume loss was within an acceptable range and similar to that of noble metals.

Sandblasting and silica-coating of dental alloys: volume loss, morphology and changes in the surface composition.

Silica-coating alloys improves chemo-mechanical bonding. Sandblasting is recommended as pretreatment to thermal silica-coating or as part of a tribochemical silica-coating process. This study evaluated the effects of sandblasting and coating techniques on volume loss, surface morphology and compositional changes in noble (AuAgCu) and base alloys (NiCr and CoCr). Volume loss was statistically significantly higher in the noble as compared to the base alloys but does not seem to be critical for the clinical fit of restorations. Embedded alumina particles were found in all alloys after sandblasting and the alumina content increased to a range of 14 to 37 wt% as measured by EDS. Following tribochemical silica-coating, a layer of small silica particles remained on the surface, increasing the silica content to between 12 and 20 wt%. Ultrasonic cleaning removed loose alumina or silica particles from the surface, resulting in only slight decreases in alumina or silica contents, thus suggesting firm attachment of the major part of alumina and silica to the alloy surface. Clinically, ultrasonic cleaning of sandblasted and tribochemically silica-coated alloys might improve resin bonding as loose surface particles are removed without relevant changes in composition. Silica content following thermal silica-coating treatment increased only slightly from the sandblasted specimen. The silica layer employed by these silica-coating methods differs widely in both morphology and thickness. These results provide a basis for explanation of adhesive failure modes in bond strength tests which will possibly optimize resin bonding. Further research is needed to characterize the outermost surface layers after these treatments and the exact location of adhesive failures.

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 μm 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.

Resin-bonded retainers. Part I: Resin bond to electrolytically etched nonprecious alloys

Nonprecious Ni-Cr casting alloys can be electrolytically etched to yield a highly retentive surface for micromechanical bonding of dental resins. The acid, current density, and etching time to achieve the retentive features are specific for each alloy. Conditions for etching one beryllium-containing and one non-beryllium-containing alloy are described. The tensile strength of a resin system to these alloys has been determined to be over two times the accepted value of the resin bond to acid-etched enamel.

In vitro Effect of APF Gel on Three Composite Resins

A laboratory study was conducted to determine effects of 1.23% APF gel on three composite resins. All composite resins immersed in APF gel lost significantly more weight than did their controls with significantly different weight losses among the APF-treated composites. Surfaces of all resins exposed to APF gel, as viewed in SEMs, exhibited degradation of filler particles.

Influence of prolonged thermal cycling and water storage on the tensile bond strength of composite to NiCr alloy

OBJECTIVES The purpose of this study was to evaluate the bond strength and bond durability of new adhesive systems (both micromechanical and chemo-mechanical) to a beryllium-free nickel-chromium alloy (NiCr). METHODS Plexiglass tubes filled with composite were bonded to NiCr 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 d, 30 d or 150 d. In addition, the 30 and 150 d samples were thermal cycled for 7,500 or 37,500 cycles, respectively. RESULTS The bond strength of a conventional BisGMA composite to sandblasted NiCr was statistically significantly lower than that of chemo-mechanical bonding systems and decreased continuously during the storage time of 150 d. The additional use of a silane on the sandblasted alloy resulted only in a slight, statistically insignificant increase in bond strength. Statistically significantly higher and more durable bonds to NiCr alloy were achieved either with the combination of silica coating and use of a conventional BisGMA composite or with the combination of sandblasting and the use of a composite modified with a phosphate monomer. In these systems, the bond strengths were limited by the cohesive strength of the resin composites. However, a newly developed composite containing the same active phosphate monomer showed a statistically significant decrease in bond strength (cohesive strength) over storage time. SIGNIFICANCE Longer-term storage times in a wet environment are needed in laboratory tests to examine the durability of bonding systems.

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.

Linear dimensional accuracy of epoxy resin and stone dies

1 Ideally, d ie material for fixed restorations should be dimensionally accurate, durable, consistent, and of reasonable cost. It should also be simple to manipulate, compatible with currently used impression materials, able to reproduce fine details, and have a stable shelf life. Toreskog et al.’ tested eight different classes of die materials and concluded that no one material was superior. Newman and Williams’ also concluded that “an ideal universal die material is yet to be produced.” There have been several reports on epoxy resin dies.‘.’ Although they have been shown to have superior compressive strength and abrasion resistance,3 their dimensional accuracy has been poor due to shrinkage.” Stone dies are still considered the standard for most fixed partial denture construction. The relative accuracy of stone dies is well documented in clinical and bench studies.’ However, lack of durability during the increased handling that is inherent in extensive reconstructive dentistry often creates problems in the laboratory. The newer formulations and techniques for epoxy resin are said to produce dies that are comparable to stone dies in dimensional accuracy.” If a resin die is as dimensionally accurate as a stone die, its use would be justified because of superior resistance to fracture and abrasion. The purpose of this study was to compare the linear dimensional accuracy of epoxy resin dies to stone dies.