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Biomedical subjects

R M Pilliar

Publications and source records attributed to R M Pilliar.

At least 55 records · Page 3Linked to original sources
PubMed1991

The effect of partial coating with hydroxyapatite on bone remodeling in relation to porous-coated titanium-alloy dental implants in the dog.

For inhibition of crestal bone resorption due to stress shielding and disuse atrophy, an hydroxyapatite (HA) plasma coating was added to the coronal portion of partially porous-coated endosseous dental implants. These implants, as well as control non-HA-coated implants were placed in healed mandibular premolar extraction sites in dogs for a 72-week period of function. Histological examination showed that both implant designs became securely fixed by bone ingrowth into the porous-coated apical region of the implants. The plasma-sprayed HA coating resulted in significantly greater bone height formation and maintenance next to the coronal portion of the implant compared with non-HA-coated implants of similar design. In addition, significant resorption of the 20-to-50-microns-thick plasma-sprayed HA coating occurred over the 18-month period of function.

Alloys↗
PubMed1990

A histological comparison in the dog of porous-coated vs. threaded dental implants.

The histological findings of an 18-month trial, in the dog of a partially porous-coated endosseous dental implant made of Ti-6Al-4V, with a truncated conical shape, are described and compared with those for a cylindrical, threaded, endosseous implant made of commercially pure Ti. Six beagle dogs each received two porous-coated implants on one side of the mandible and two threaded implants on the contralateral side. Each set of two implants supported a two-unit fixed bridge for an 18-month functional period. Methylmethacrylate sections of both the buccolingual and mesiodistal aspects of each implant were examined qualitatively and by computer-assisted morphometry. The morphometric measurements were used for determination of the length of implant surface in direct contact with bone on each aspect of each implant. The data were expressed both as an absolute length and as a fraction of the maximum length available for contact (contact length fraction or CLF). On the buccal and lingual aspects of the implants, both the absolute lengths and CLF were significantly smaller for the porous-coated design. For the mesial and distal aspects, the absolute lengths and CLF were less for the porous-coated design, but the differences were not significant. However, when the absolute contact length was related to the corresponding vertical bone height, significant differences were observed, the absolute contact length being greater for any given bone height for the porous-coated design. Taken together, the data suggest that shorter implants may be used with the porous-coated design.

Alloys↗
PubMed1990

Dental implants: materials and design.

The use of endosseous dental implants represents one of the most rapidly expanding areas of dentistry. This article attempts to summarize the current understanding of factors affecting dental implant success. The need continues for further fundamental studies to provide a base for future improvements in the design and use of dental implants.

Aluminum Oxide↗
PubMed1988

Evaluation of the retention of endodontic implants.

The study investigated the retentive strength of endodontic implants measured by forced removal (pull-out or push-out tests) as a function of implant design and cement type. Smooth-tapered, threaded, and an innovative porous-surfaced implant were evaluated. Specimens were cemented in single-rooted human teeth with five different cements: zinc phosphate, polycarboxylate, glass ionomer, silicophosphate, or AH-26. The results indicated superior retention for the threaded and porous-surfaced implants, and stronger retention with glass-ionomer and AH-26 cements.

Bismuth↗
PubMed1988

Evaluation of shear strength at the cement-endodontic post interface.

The strength characteristics of the cement-implant interface were evaluated for smooth-tapered, threaded, and porous-surfaced endodontic implants with the use of different cements. Specifically, tensile and torsional shear strengths were measured for zinc phosphate, polycarboxylate, glass-ionomer, silicophosphate, and AH-26 cements. The results indicated superior shear strength characteristics for threaded endodontic implants on axial loading. However, this strength was diminished when torsional forces were applied. Porous-surfaced endodontic implants showed strong resistance to both axial and torsional loading.

Bismuth↗
PubMed1988

Cell attachment of human gingival fibroblasts in vitro to porous-surfaced titanium alloy discs coated with collagen and platelet-derived growth factor.

The influence of biological coating, with or without the incorporation of growth factor, on the migration, attachment and orientation of human gingival fibroblasts in relation to porous-surfaced titanium alloy (Ti6AI4V) discs, was measured. Comparison was made between coating the discs with collagen and with collagen incorporating platelet-derived growth factor (PDGF); controls comprised porous-surfaced discs coated with agar or collagen containing bovine serum albumin (used as a carrier for the PDGF), uncoated porous-surfaced Ti6AI4V discs (with or without additional protein additives) exhibited significantly higher attachment indices (AI) and orientation indices (OI) compared with naked control discs (p less than 0.01); OI was also significantly higher than that of surface-demineralized root slices (p less than 0.001) on days 1, 2 and 3. Addition of PDGF to the collagen resulted in a further enhancement in OI on days 1 and 2 (p less than 0.01) over that shown by discs coated with collagen incorporating the bovine serum albumin vehicle. There was no cell attachment and consequently, no cell orientation, in relation to Ti alloy discs that had been coated with agar. These data suggest that attachment and orientation of cells following migration in relation to porous-surfaced Ti6AI4V discs can be modified by the application of biological molecules to the surface of the disc. This may have a useful application in clinical implantology.

Alloys↗
PubMed1988

A histological evaluation of a functional endosseous, porous-surfaced, titanium alloy dental implant system in the dog.

We have previously reported the clinical and radiographic findings of a trial in dogs of a new dental implant system after a functional period of eight months. The present report consists of the corresponding qualitative and quantitative histological data. The implant system was fabricated from Ti-6A1-4V and employed a porous-surfaced configuration to achieve implant fixation by bone ingrowth. A similar porous surface was used on the apical 1/3 of the transgingival collar in an attempt to gain ingrowth and attachment of gingival connective tissue. The qualitative histological data confirmed that while such attachment to the collar did occur for some implants, in the majority of implants (22 of 32) the porous region of the collar became contaminated with bacterial plaque, resulting in implant failure (four implants) or suggesting future implant failure (18 implants). Statistical analyses of the quantitative histological data indicated that there were no significant differences in surface contact of bone with the middle third of the porous implant surface (CLF) when initial healing interval (four or eight weeks), implant location, or aspect of implant (buccal vs. lingual vs. mesial vs. distal) were compared. However, comparison of the current group of functional implants with an earlier group of similarly implanted non-functional implants indicated that function produced a highly significant increase in CLF.

Alloys↗
PubMed1987

Effect of the surface geometry of smooth and porous-coated titanium alloy on the orientation of fibroblasts in vitro.

The migration and orientation of human gingival fibroblasts in relation to the rim of smooth-surfaced and porous-coated titanium discs placed on multilayers in vitro was investigated. Samples were examined after 6 h, 24 h, 3 days, and 7 days of culture using phase-contrast and scanning electron microscopy. The cells migrated from the multilayer onto the smooth-surfaced discs forming bridges between them, and orientated along parallel circumferential grooves in the rim of the discs. This resulted in the cellular bridges orientating at an acute angle to the rim of the disc, and adjacent cells in the multilayer orientating parallel to the rim. Cellular bridges were also formed between the porous-coated discs and the multilayer but, because the cells that migrated onto, and between, the spheres of the porous-coat showed no preferred orientation, the bridges retained their orientation at right angles to the surface of the rim. This in turn resulted in the cells of the adjacent multilayer becoming similarly orientated. These observations suggest that the geometrical configuration of the surface of implants could influence whether a capsule or an orientated fibrous attachment is developed in relation to implants in vivo.

Alloys↗
PubMed1987

The effect of proximally and fully porous-coated canine hip stem design on bone modeling.

Porous coated canine femoral hip replacement implants were evaluated for biological fixation by bone ingrowth and the effect of the extent of porous coating on bone modeling. The Co-Cr alloy implants were either fully porous coated or coated only on the proximal 40% of the stem. Two implants of each type were studied 9, 16, and 36 months after surgery. Implant fixation and bone modeling were assessed radiographically throughout the implant periods and histologically after the test animals were killed. All 12 implants appeared stably fixed within the femur and were bone-ingrown in the porous region. Radiographic features such as proximal medial and anterior cortical thinning, proximal cancellous bone hypertrophy, and new endosteal bone formation near the stem tip were noted within the first postoperative year, with no appreciable change thereafter. The extent of proximal cortical thinning varied from virtually none to as much as 40%, being more prominent with the proximally coated implants at 16 months and with the fully coated implants at 36 months. Of consistent note was cancellous hypertrophy at the junction of porous and smooth implant surfaces with proximally coated implants and new endosteal bone formation and ingrowth at the stem tip of fully coated implants. These results indicate that the proximally porous-coated implant design causes increased proximal stress transfer, but this does not necessarily preclude proximal cortical resorption.

Adaptation, Physiological↗
PubMed1987

The effect of environmental aging on the fracture toughness of dental composites.

The effect of aging four commercially-available dental composites in water or ethanol at 37 degrees C for periods of up to 28 days was assessed by measuring changes in the materials' plane-strain fracture toughness (KIC). The results, obtained by means of a mini Short Rod Fracture Toughness Test specimen design, suggest that while water aging does not produce significant changes in KIC, aging in ethanol does cause significant increases in fracture toughness for three of the four dental composites studied. In view of previously-reported loss of wear resistance for dental composites aged in ethanol solutions, the present study emphasizes the difficulties in using fracture toughness to predict wear properties.

Air↗
PubMed1987

Migration, attachment, and orientation of human gingival fibroblasts to root slices, naked and porous-surfaced titanium alloy discs, and Zircalloy 2 discs in vitro.

Cell migration, attachment, and orientation of cultured human gingival fibroblasts (HGF) were measured in relation to four types of specimens: Ti-6Al-4V alloy discs with either ground surfaces or porous structured surfaces, and Zr alloy discs (Zircalloy 2) with either ground surfaces or surfaces modified by being heated to form a thicker oxide cover. Surface-demineralized and non-demineralized root slices were used as controls. Initial cell attachment was measured by means of a 51Cr assay, and cell attachment and orientation following migration by an assay that measures development of the resulting refractile material in relation to the specimen. No significant difference between initial cell attachment to Ti alloy and control demineralized root slices could be detected after one hr using the 51Cr assay. However, with the second assay, cell attachment and orientation at three, seven, 10, and 14 days were significantly higher in relation to surface-demineralized root slices than to all of the metal discs and the non-demineralized root slices. While cell attachment to the surface-ground Ti alloy discs appeared to be higher than that to the porous-surfaced Ti alloy discs at three days and seven days, cell orientation to the porous-surfaced Ti alloy discs and the non-demineralized root slices at days 7, 10, and 14 was greater than that to all of the other metal discs. These data suggest that surface geometry could affect attachment and orientation of cells in vitro.

Alloys↗
PubMed1987

Porous-surfaced metallic implants for orthopedic applications.

The fixation of orthopedic implants in bone by tissue ingrowth presents a possible solution to the problem of long-term implant loosening. To achieve this objective, metallic implants formed with porous surface coatings have been developed. This article reviews the methods proposed for fabricating such implants. Some possible problems related to loss of mechanical properties due to the processing to form the porous surface zone are described. For some of the porous-surfaced implant systems, processes have been developed to avoid the occurrence of such changes. It is particularly important at this stage of the evaluation of porous-surfaced implants in clinical situations that manufacturers are fully cognizant of the effects of processing on mechanical properties of these devices.

Animals↗
PubMed1986

A histological assessment of the initial healing response adjacent to porous-surfaced, titanium alloy dental implants in dogs.

We report here the results of a histological assessment of the initial healing response following implantation into the dog mandible of a porous-surfaced, titanium alloy endosseous dental implant. Two implants were placed in edentulous areas on each side of the mandible of each dog and covered with a full-thickness mucoperiosteal flap. The implant sites on one side of the mandible were allowed to head for four weeks, while those on the other side were allowed to head for eight weeks before the animals were killed. Histological specimens were obtained and assessed both qualitatively and by computer-assisted morphometry. All but one of the 24 implants were well-tolerated and healed with a variable ingrowth of bone into the porous-surface geometry. The histomorphometric measurements revealed that bone ingrowth had reached a plateau by four weeks of initial healing.

Alloys↗
PubMed1986

A clinical and radiographic assessment of a porous-surfaced, titanium alloy dental implant system in dogs.

A new endosseous dental implant system incorporating a porous-surface geometry with a tapered, truncated-cone shape was placed bilaterally in edentulous areas of dog mandibles in a two-stage procedure. All implants had been stabilized by bone ingrowth by the time of the second procedure (insertion of a transgingival collar and implant-supported bridge). The transgingival collar had a porous-surface geometry on its apical one-third, and was meant to encourage gingival connective tissue ingrowth and attachment, but in fact provided an excellent milieu for bacterial contamination. As a consequence, many of the implants showed clinical and radiographic signs of impending failure by eight months. Only those implants for which the porous coat, including that of the transgingival collar, was completely submerged in bone were observed to be successful. This study reports on the radiographic and clinical assessment of this implant system in dogs during the period of function.

Alloys↗