Biomedical subjects

R M Pilliar

Publications and source records attributed to R M Pilliar.

At least 37 records · Page 2Linked to original sources

PubMed1998

The Endopore implant-enhanced osseointegration with a sintered porous-surfaced design.

The Endopore implant provides a novel method for reliable fixation of endosseous dental implants within the bone. Through the use of a porous-surfaced zone formed by sintering Ti alloy particles of the appropriate size and under appropriate processing conditions to a sold Ti alloy core of desired shape (tapered truncated cone), an implant is now available that can be placed using a relatively simple surgical procedure using either surgical burs or hand osteotomes. Of even greater value is the suitability of this implant design for treatment of cases that because of minimal bone height cannot be treated routinely using other currently-available implants. The high success rates experienced with significantly shorter implant lengths compared with other designs indicate the appropriateness of this system for difficult-to-treat cases. The Endopore system represents the next generation of endosseous dental implants characterized by uncomplicated and reliable treatment for a wider range of dentally-compromised patients. Its history is founded on extensive and fully-documented research at the human preclinical stage as well as human use experiences. The results during the past nine years have confirmed the high expectations that those early studies suggested.

Dental Implantation, Endosseous↗

PubMed1996

Evaluating sol-gel ceramic thin films for metal implant applications. I. Processing and structure of zirconia films on Ti-6AI-4V.

Thin ceramic films or coatings over metallic bone-interfacing implant surfaces have the potential to improve implant performance with respect to implant fixation, wear, or corrosion. In this study, zirconia (ZrO2) thin films formed on Ti-6AI-4V using a polymeric alkoxide-based solgel process were investigated. ZrO2 films of uniform thickness on the order of 100 nm were obtained by dip coating Ti-6AI-4V samples into a zirconium propoxide containing solution using a substrate withdrawal speed ranging from 2 to 8 cm/min and a sol of nominal viscosity approximately 6 cps. These films were essentially free of surface macrodefects but had random submicron "pinholes." X-ray diffraction studies suggested that the films were at least partially crystalline, with some "metastable" cubic and/or tetragonal phases after annealing for 1 h at 500 degrees C. The demonstrated reproducibility of this approach for producing good quality ZrO2 films on Ti-6AI-4V warrants further studies to optimize processing conditions for implant applications.

Alloys↗

PubMed1996

Evaluating sol-gel ceramic thin films for metal implant applications. II. Adhesion and fatigue properties of zirconia films on Ti-6AI-4V.

The degree to which ceramic coatings or thin films applied to bone-interfacing metallic implants can improve the overall performance of these implants with respect to implant fixation, wear, or corrosion relies especially on the response of these films to loading. In this study, the adhesion and fatigue properties of sol-gel zirconia films that could be reproducibly deposited onto polished Ti-6AI-4V substrates was investigated. For zirconia films on the order of 100 nm thick, a shear lag-based strain approach indicated a shear adhesion strength of approximately 275 MPa. Small variations in film thickness and substrate surface preparation had little effect on this adhesion, which was believed to be due to alkoxide molecule interactions with free hydroxyl groups on the substrate surface as well as some limited interfacial diffusion following the 500 degrees C anneal. Subsequent fatigue testing of these films in air using novel tapered rotating beam fatigue samples demonstrated their excellent fatigue characteristics, with films surviving up to 10(7) cycles, the endurance limit of the Ti-6AI-4V (approximately 635 MPa). Overall, the exceptional mechanical properties of this ZrO2/Ti-6AI-4V system along with the inherent advantages of sol-gel processing support continued studies to utilize this technology for implant surface modification.

Alloys↗

PubMed1996

Titanemia from total knee arthroplasty. A case resulting from a failed patellar component.

The subject of this case report is a patient with elevated serum levels of titanium (77 parts/billion [ppb]; normal, 3.3 ppb) and vanadium (0.38 ppb; normal, 0.17 ppb) resulting from excessive wear of a metal-backed patellar component in a total knee arthroplasty. The patellar component was worn through both its polyethylene and metal backing as a result of abnormal contact between the patellar and femoral components. Scanning electron microscopic examination of the ingrowth surface of the patellar component indicated that particle debonding occurred as a result of overloading of the sintered neck regions at the particle-substrate interface, suggesting a possible damage during initial insertion of the device, which may have predisposed it to loosening and abnormal contact with the femoral component. Wear particles resulted in staining of the tissues within the knee and an inflammatory and immune response in the synovium consisting of giant cells and T lymphocytes. The serum metal levels were reduced 22 weeks after replacing the patellar component; however, the titanium level was still slightly elevated (8 ppb).

Aged↗

PubMed1996

Initial healing in the dog of submerged versus non-submerged porous-coated endosseous dental implants.

It has previously been reported that porous-coated root form endosseous dental implants, became well integrated when used in the traditional 2-stage surgical approach. In this study, the placement of the implant in a 1-stage (non-submerged) technique was to be explored. Implants were placed in the mandibles of dogs, and 2 designs were used differing only in that one (experimental) had a 3-mm transgingival extension, permitting it to be exposed to the oral cavity from the outset. 12 (3 per animal) non-submerged implants were placed on 1 side of 4 beagle dogs and 12 control (submerged) implants were placed contralaterally. All implants were allowed to heal for 6 weeks, after which histological preparations were made. 2 of 12 non-submerged implants were lost due to post-operative complications; otherwise, all implants healed uneventfully. Histomorphometric analysis revealed bone-implant contact, as assessed by absolute bone contact (ABC) and contact length fraction (CLF), to be greater for the submerged design, suggesting that bone healing may be delayed with the non-submerged approach. As well, at this early stage of healing, for both implant designs, ABC and CLF were significantly greater on proximal than on buccal and lingual aspects.

Alloys↗

PubMed1996

Periodontal parameters around porous-coated dental implants after 3 to 4 years supporting overdentures.

In this study, an assessment using modified periodontal indices was done on a group of 48 fully edentulous patients who had each been treated with 3 porous-coated (EndoPore) dental implants and a mandibular overdenture. Parameters assessed included plaque index (PI), sulcular bleeding index (SBI), pocket probing depth (PD), probing attachment level (PAL) and mobility (M) using a Periotest device. At the time of the assessment, all of the patients had passed 3 years of continuous function while 26 had passed 4 years. Approximately 50% of implant surfaces were plaque-free while 79% of surfaces showed no bleeding upon probing. There was no correlation between PI and SBI. The mean PD was 3.1 mm with 64% of sites < or = 3.5 mm. Mobility measurements taken with the Periotest device gave a mean PTV of (-4.35) with 96% of measurements (-0.5). No significant correlations were found between mobility and either PAL or implant length.

Analysis of Variance↗

PubMed1995

Finite element analysis of crestal bone loss around porous-coated dental implants.

Crestal bone loss is observed around various designs of dental implants. A possible cause of this bone loss is related to the stresses acting on periimplant bone. To investigate the relationship between stress state and bone loss, two-dimensional finite element models corresponding to bucco-lingual and mesio-distal sections of canine mandibles with one of two designs of porous-coated dental implants were analyzed. A fully porous-coated design consisting of a solid Ti6A14V core had a porous coating over the entire outer surface of the implant component, while a partially porous-coated design had the porous coating over the apical two-thirds of the implant surface only. Occlusal forces with axial and transverse components were assumed to act on the implant with interface bonding and effective force transfer at all porous coat-bone interfaces and no bonding for the non-porous-coated regions. The results of the analysis indicated that at most implant aspects (buccal, lingual, mesial, and distal), the equivalent stresses in crestal bone adjacent to the coronal-most, non-porous-coated zone of the partially porous-coated implants were lower than around the most coronal region of the fully porous-coated implants. The region of lower stress around the partially porous-coated implants corresponded to observed areas of crestal bone loss in animal studies, suggesting that crestal bone loss in this case was due to bone disuse atrophy. A number of parameters of the finite element models were varied to determine the effect on the resulting stress fields and, therefore, possible long-term bone remodeling. Based on differences in observed bone structures by histological examination and results of finite element analyses with fully and partially porous-coated implants, an equivalent stress equal to 1.6 MPa was determined to be sufficient to avoid bone loss due to disuse atrophy in the canine mandibular premolar region.

Alloys↗

PubMed1994

Predictable crestal bone remodelling around two porous-coated titanium alloy dental implant designs. A radiographic study in dogs.

We have previously suggested that altering the height of the porous-coat segment of a partially porous-coated TiAl6V4 endosseous dental implant would affect the degree of crestal bone loss occurring during implant function by changing the patterns of stress transfer. This conclusion arose from the analysis of data from several different experiments and lacked a direct intra-animal comparison. In the present study we have compared two implant designs varying only in the extent to which they were porous-coated. With one design (type A) the coronal 1.8 mm of the implant root had a machined surface while the remainder of its length was porous-coated with TiAl6V4 beads. The other design (type B) had all but the coronal-most 0.75 mm porous-coated. Two implants of each type were placed in each of 4 dogs and the sites allowed to heal for 4 weeks before re-entry and prosthesis attachment. Monthly the implant-supported bridges were removed and radiographs exposed of each implant using a special film holder connected separately to each implant. These radiographs were analyzed for crestal bone loss using both direct visual and computer-assisted techniques. The results showed that bone remodelled to the machined surface-to-porous coat junction for type B implants and achieved a steady state by 12 weeks of function, whereas a longer time was required to achieve this state with type A implants. Significantly more bone loss occurred with the type A design, and this difference was detectable as early as after the first month of function.

Aluminum↗

PubMed1994

Fracture surface characterization of dentin-bonded interfacial fracture toughness specimens.

Although the current trend in dentin bonding favors the development of a hybrid layer interdiffusion zone for micromechanical bonding, the exact nature of the dentin-composite bond is still unclear. The objective of this study was to characterize the fracture surfaces of specimens used to measure interfacial fracture toughness. Morphological (SEM) and chemical (EDS and XPS) surface analyses were used for characterization. Fracture toughness specimens generally failed along the dentin-bonded interface in agreement with observed clinical failure modes. Four sites of bond failure were identified within the dentin-composite interfaces when All-Bond 2, Scotchbond Multi-Purpose, and Scotchbond 2 were used as the dentinal adhesives. These were located within (1) the smear layer, (2) a resin-modified layer between the interdiffusion zone and the adhesive resin, (3) a well-infiltrated hybrid interdiffusion zone, and (4) a non-infiltrated unsupported collagen layer. The interfacial region had a complex architecture which varied with the nature of the dentin, the dentin surface treatment, and the dentin bonding system. The sites of bond failure appeared to correlate with the interfacial fracture toughness and the extent to which polymerized resin infiltrated and acted to support the organic dentinal structures.

Animals↗

PubMed1994

Effects of dentin surface treatments on the fracture toughness and tensile bond strength of a dentin-composite adhesive interface.

It has been proposed that the fracture toughness test provides an appropriate method for assessing the fracture resistance of the dentin-composite interface. The plane-strain fracture toughness test was therefore applied to a dentin-composite interface, with use of a specific dentinal adhesive, so that the effects of various dentin surface treatments on dentin-bond integrity could be studied. Interfacial fracture toughness (KIC) values were determined following 24h and 180 days of specimen aging in distilled water at 37 degrees C. Tensile bond strength (TBS) results following 24-hour aging were also obtained for comparison with the 24-hour KIC results. In general, the fracture resistance of the dentin-composite interface was highest when the dentin surface was conditioned with acid but not air-dried, intermediate when the dentin surface was conditioned with acid and subsequently air-dried, and lowest when the dentin was not conditioned with acid. The tensile bond strength results differed from the fracture toughness results in indicating differences in surface preparation effects and the type of interfacial failure observed.

Acid Etching, Dental↗

PubMed1993

Post-plasma-spraying heat treatment of the HA coating/Ti-6A1-4V implant system.

The metal/ceramic interface that constitutes an important part of the plasma-sprayed HA-coated Ti-6A1-4V system may, in fact, represent the "weak link" in the implant design. A post-plasma-spray heat treatment to enhance chemical bonding at the metal/ceramic interface and, hence, improve the mechanical properties (interface fracture toughness and tensile coating adhesion strength) of the plasma-sprayed implant system does show promise. In preliminary heat treatment studies, however, any improvements realized were lost due to the chemical instability of the coating in a moisture-laden environment, with a concomitant loss in bonding properties. This deterioration in properties appears to be related to environmentally assisted crack growth as influenced by processing conditions. Still, an ability to improve HA/Ti-6A1-4V bonding through enhanced diffusion bonding was demonstrated, warranting further heat treatment studies involving atmosphere control during processing.

Alloys↗

PubMed1993

Fracture toughness of dentin/resin-composite adhesive interfaces.

The reliability and validity of tensile and shear bond strength determinations of dentin-bonded interfaces have been questioned. The fracture toughness value (KIC) reflects the ability of a material to resist crack initiation and unstable propagation. When applied to an adhesive interface, it should account for both interfacial bond strength and inherent defects at or near the interface, and should therefore be more appropriate for characterization of interface fracture resistance. This study introduced a fracture toughness test for the assessment of dentin/resin-composite bonded interfaces. The miniature short-rod specimen geometry was used for fracture toughness testing. Each specimen contained a tooth slice, sectioned from a bovine incisor, to form the bonded interface. The fracture toughness of an enamel-bonded interface was assessed in addition to the dentin-bonded interfaces. Tensile bond strength specimens were also prepared from the dentin surfaces of the cut bovine incisors. A minimum of ten specimens was fabricated for each group of materials tested. After the specimens were aged for 24 h in distilled water at 37 degrees C, the specimens were loaded to failure in an Instron universal testing machine. There were significant differences (p < 0.05) between the dental adhesives tested. Generally, both the fracture toughness and tensile bond strength measurements were highest for AllBond 2, intermediate for 3M MultiPurpose, and lowest for Scotchbond 2. Scanning electron microscopy of the fractured specimen halves confirmed that crack propagation occurred along the bond interface during the fracture toughness test. It was therefore concluded that the mini-short-rod fracture toughness test provided a valid method for characterization of the fracture resistance of the dentin-resin composite interface.

Analysis of Variance↗

PubMed1993

Fractures of the fixture component of an osseointegrated implant.

The cause of mechanical failure of the fixture component of an osseointegrated dental implant was investigated. The surfaces of five clinical specimens that had fractured were compared to those of new specimens fractured in the laboratory under monotonic and cyclic loads. Scanning electron microscopy revealed striations on the fractured surfaces of the clinical specimens, similar to striations on the laboratory-fatigued specimens and in contrast to the dimpled surfaces on the overloaded specimens. The investigation demonstrated that fractures of the fixture component of this dental implant occurred by fatigue under physiologic loads, with marginal alveolar bone loss around the fixture.

Alveolar Bone Loss↗

PubMed1991

Dental implant design--effect on bone remodeling.

Bone remodeling around three different endosseous dental implant designs placed in dog mandibles was studied using radiography during lengthy periods of function and by histology after animal sacrifice. The three designs investigated were (a) threaded (c.p. titanium), (b) fully porous-coated (titanium alloy), and (c) partially porous-coated (titanium alloy). The implants were kept in function for either 32 weeks (fully porous-coated) or 73 to 77 weeks (partially porous-coated and threaded). The studies indicated that some crestal bone loss occurred for both the threaded and partially porous-coated implants while no significant bone loss was seen with fully porous-coated implants in the absence of plaque-associated infection. It is suggested that these observed differences are a result of the different stress states that develop in bone surrounding the three designs underlying the importance of implant design on bone remodeling.

Alveolar Process↗

PubMed1991

Dental implant materials. I. Some effects of preparative procedures on surface topography.

The effect of different treatments for preparing implant materials was examined by scanning electron microscopy and by contact angle measurements. The materials examined were Ti6A14V alloy, Co-Cr-Mo alloy, A12O3, and synthetic hydroxyapatite. Samples were prepared with solid or porous surfaces of these materials. These were detergent-cleaned and then either autoclaved (steam sterilization), radiation-sterilized, nitric acid-etched, or plasma-cleaned. The results of wettability studies indicated marked changes in surface energy corresponding to the different preparation methods, and differences in surface morphology were also observed. These differences could have significant consequences on in vivo implant behaviour as mediated by tissue-implant interactions.

Alloys↗

PubMed1991

Dental implant materials. II. Preparative procedures and surface spectroscopic studies.

The tissue response to an implant may involve both physical and chemical factors. There is little reliable information on the effects of these parameters and the associated ionic release on the cell-material interaction because the majority of studies have not fully characterized the implant material. In this work surface spectroscopy using ISS, ESCA, and SIMS was carried out on Ti6A14V, Co-Cr-Mo, A12O3, and hydroxyapatite dental implant materials that had been subjected to six commonly used preparative procedures. The results showed that each procedure generated an individualistic composition for the outermost surface of each material. These differences could be significant in cellular and tissue response. Improved understanding of these factors requires defined and reproducible surfaces.

Alloys↗

PubMed1991

Characterization of the interface in the plasma-sprayed HA coating/Ti-6Al-4V implant system.

The successful use of plasma-sprayed hydroxyapatite (HA) coatings on Ti-alloy implants for implant-to-bone fixation requires strong adherence of the ceramic coating to the underlying metal substrate. In this study, the metal-ceramic interface was evaluated using mechanical, chemical, and structural characterization methods. Evaluations of an HA-coated Ti-6Al-4V implant system using a modified short bar technique for interfacial fracture toughness determination revealed relatively low fracture toughness values. Additionally, conventional tensile bond strength testing indicated much lower values than previously reported. Using high resolution electron spectroscopic imaging, evidence of chemical bonding was revealed at the plasma-sprayed HA/Ti-6Al-4V interface, though bonding was primarily due to mechanical interlock at the interface. This study illustrates the benefits of, and the need for, a multilevel approach to evaluate and improve these plasma-sprayed ceramic-metal substrate interfaces.

Alloys↗

PubMed1991

Modern metal processing for improved load-bearing surgical implants.

A review of modern methods for preparing metallic alloys that could be useful for the fabrication of load-bearing metallic biomaterials is presented. The use of rapid solidification processing and surface modification of metals by ion implantation or surface coatings and variations thereof is used currently for the formation of novel metallic alloys in other high-tech fields, notably the optoelectronics industry. Further studies to explore potential benefits for surgical implant fabrication through the application of these technologies is recommended.

Alloys↗