William R. Lacefield

Structure, solubility and bond strength of thin calcium phosphate coatings produced by ion beam sputter deposition

Ion beam sputter deposition was used to produce thin calcium phosphate coatings on titanium substrates. Structure, solubility and bond strength of the as-sputtered and heat treated coatings were evaluated. X-ray diffraction (XRD) analysis of the heat treated coatings revealed a hydroxyapatite-type structure. The heat treated coatings were found to have significantly lower solubility as compared to the amorphous as-sputtered coatings. Although the crystalline coatings exhibited the lowest solubility, in general, the bond strengths were lower for the heat treated coatings.

Analysis of bovine serum albumin adsorption on calcium phosphate and titanium surfaces.

The protein adsorption behavior of thin films of calcium phosphate (CaP) bioceramic and titanium (Ti) was studied in this research. The thin films were produced with an ion beam sputter deposition technique using targets of hydroxyapatite (HA), fluorapatite (FA) and titanium (Ti). Fourier transform infrared spectroscopy (FTIR) with attenuated total internal reflectance (ATR) was used to evaluate protein adsorption on these surfaces. This study showed that surface composition and structure influenced the kinetics of protein adsorption and the structure of adsorbed protein. CaP surfaces adsorbed greater amount of protein than the Ti surface, and caused more alteration of the structure of adsorbed BSA than did the Ti surface. The differences in protein adsorption behavior could result in very different initial cellular behavior on CaP and Ti implant surfaces.

Interaction between topography and coating in the formation of bone nodules in culture for hydroxyapatite- and titanium-coated micromachined surfaces

Rat osteoblast cultures were maintained from 24 h to 6 weeks on hydroxyapatite (HA)- or titanium (Ti)-coated smooth and micromachined grooved substrata in medium supplemented with L-ascorbic acid-2-phosphate and beta-glycerophosphate to promote mineralization. The HA coatings, approximately 1 microm thick, were characterized using X-ray diffraction, surface roughness, and scanning electron microscopy (SEM). Osteoblasts elongated, aligned, and moved in the direction of the grooves on both Ti and HA grooved surfaces. HA surfaces produced significantly more bone-like nodules than Ti surfaces. All grooved substrata produced significantly more nodules than smooth surfaces. These results are consistent with the hypothesis that substrata can increase osteogenesis by formation of an appropriate microenvironment. There was also a statistically significant interaction between topography and chemistry in the formation of mineralized nodules. A strong correlation (r = 0.958) between alkaline phosphatase (Alk-P) at 2 weeks and nodule counts at 6 weeks was observed, suggesting that Alk-P may possibly be used as a leading indicator of osteogenesis on microfabricated surfaces. The results of this study indicate that surface topography and chemistry can affect osteogenesis, and that interactions between chemistry and topography can occur.

Orthodontic In Vivo Bond Strength: Comparison with In Vitro Results

The purpose of the present study was to test a new in vivo debonding device and compare in vivo bond strengths recorded by this device with in vitro bond strengths recorded by a universal testing machine such as the Instron. For the in vitro part of the study, 60 extracted premolar teeth were divided into 2 groups of 30 each. Both groups of 30 teeth had 3M Unitek Victory Twin brackets, precoated with Transbond XT composite resin, bonded to them. Shear bond strength tests were carried out in vitro using the universal testing machine on one group of 30 teeth while the debonding device was used on the other group of 30 teeth. The mean shear bond strength of the group debonded using the universal machine was 11.02 MPa and that of the group debonded with the debonding device was 12.82 MPa. For the in vivo part of the study, 8 patients randomly assigned to the research clinician from patients in The University of Alabama School of Dentistry, Department of Orthodontics, had a total of 60 premolar teeth bonded with 3M Unitek Victory Twin brackets. Following comprehensive orthodontic treatment (average time of 23 months), shear bond strength tests were carried out using the debonding device, which can measure debonding forces in vivo. The mean shear bond strength recorded in vivo was 5.47 MPa. Statistically significant differences were found between all 3 groups tested. The results appear to indicate that mean bond strengths recorded in vivo following comprehensive orthodontic treatment are significantly lower than bond strengths recorded in vitro.

Tensile bond strength of a glass-ionomer cement

The tensile load strength of a glass-ionomer cement to untreated, etched, and citric acid-cleansed enamel, dentin, and cementum was measured. This study also tested one material for which neither conditioning nor etching was recommended by the manufacturer.

Materials Characteristics of Uncoated/Ceramic-Coated Implant Materials

In this paper, the biocompatibility of dental implant materials is discussed in the context of both the mechanical characteristics of the materials and the type of surface presented to the surrounding tissues. The proper functioning of the implant depends on whether it possesses the strength necessary to withstand loading within the expected range, with other properties such as elongation being of importance in some instances. A suitable modulus of elasticity may be of major importance in situations when optimum load transmission from the implant into the surrounding bone is key to the successful functioning of the device. Dental implants present a wide range of surfaces to the surrounding tissues based on surface composition, texture, charge energy, and cleanliness (sterility). Metallic implants are characterized by protective oxide layers, but ion release is still common with these materials, and is a function of passivation state, composition, and corrosion potential. An effective surface treatment for titanium appears to be passivation or anodization in a suitable solution prior to implantation. Inert ceramic surfaces exhibit minimal ion release, but are similar to metals in that they do not form a high energy bond to the surrounding bone. Some of the newly developed dental implant alloys such as titanium alloys, which contain zirconium and niobium, and high-strength ceramics such as zirconia may offer some advantages (such as lower modulus of elasticity) over the conventional materials. Calcium phosphate ceramic coatings are commonly used to convert metallic surfaces into a more bioactive state and typically cause faster bone apposition. There is a wide range of ceramic coatings containing calcium and phosphorus, with the primary difference in many of these materials being in the rate of ion release. Although their long-term success rate is unknown, the calcium phosphate surfaces seem to have a higher potential for attachment of osteoinductive agents than do uncoated titanium and other more inert implant materials.

Effect of denture thickness and curing cycle on the dimensional stability of acrylic resin denture bases.

Abstract This study evaluated the relationship between denture thickness and the dimensional stability of acrylic resin denture bases as a result of the compression molding process. Forty-eight maxillary complete dentures were fabricated in 3 different thicknesses using 4 curing and cooling cycle combinations. After processing, the dentures were replaced on the original cast and both the molar-to-molar linear shrinkage and the dimensional change in the posterior palatal area were measured using an optical comparator. The different curing cycles tested (e.g., 165°F for 9 h as opposed to 165°F for 1 h followed by 212°F for 30 min) had little effect on the processing shrinkage. However, significantly more distortion (p=0.05) was observed for the dentures quenched in water as compared to those specimens which were benced cooled. The thicker dentures had less molar-to-molar linear shrinkage, but more dimensional change in the posterior palatal area as compared to the thinner dentures.

Evaluation of wear: Enamel opposing three ceramic materials and a gold alloy

STATEMENT OF PROBLEM The wear of human enamel and of the restorative material is often a critical concern when selecting a restorative material for any given clinical restorative treatment. PURPOSE This in vitro wear investigation evaluated three ceramic restorative materials and one type III gold (the control) opposing enamel. MATERIAL AND METHODS The area of enamel lost at specified time intervals, the stylus area lost, and the combined stylus and enamel vertical height lost were evaluated. RESULTS Enamel wear opposing one type III gold was statistically similar to that of Dicor MGC, which was lower than that of Vita Mark II and IPS Empress, which were also statistically similar in value. CONCLUSIONS The total vertical height lost from the type III gold specimens and opposing enamel was statistically lower than that of Dicor MGC and IPS Empress (alpha < 0.05).

Calcium phosphate coatings for medical and dental implants

Abstract Long-term fixation of metallic dental and medical implants in bony tissues continues to be a problem. One possible solution involves the application of calcium phosphate (Ca-P) ceramic coatings such as hydroxyapatite (HA) onto the metallic devices. Two methods being investigated for producing the coatings include plasma spraying, a commercially available process, and ion-beam sputter deposition, a technique being experimentally investigated. The plasma spraying process produces coatings on the order of 40–60 μm thick. The chemistry and structure of the coatings are similar to those of HA; however, the plasma spraying process will result in the formation of amorphous and other Ca-P phases in the resulting coatings. One concern with respect to these coatings is their relatively low bond strength. The ion-beam sputtering process produces thin (0.6–1 μm) Ca-P coatings that have a significantly higher bond strength than the plasma-sprayed coatings. One concern with the sputtered coatings relates to the amorphous structure obtained after sputtering. These amorphous coatings have high dissolution rates, and a post-deposition heat treatment is required to form more stable crystalline phases in the coatings. The chemistry and structure of the heat-treated coatings are again similar to those of HA; however, other phases can result from this process as well. Both deposition processes result in the formation of HA-type coatings; however, optimization of various coating properties such as stability and bond strength remain a challenge which must be addressed before an optimal tissue response can be attained.

Effectiveness of a method used in bonding resins to metal

Currently, several methods are available for bonding resin veneers to dental casting alloys. Recently a new system (Silicoater) has been developed that involves the chemical bonding of polymers to dental substrates. This study determined bond strengths of several proprietary composite resin luting agents to three different types of casting alloys. The results were compared with those obtained using electrolytic etching techniques. The pyrogenically silica-treated specimens generated the highest bond strengths.