J. BIOMED. MATER. RES.

VOL. 11, PP. 893-901 (1977)

A Polymethacrylate-Silica Composite Material for Dental Implants M. HODOSH and G. SHKLAR, Department of Oral Medicine and Oral Pathology, Harvard School of Dental Medicine, Boston, Massachusetts, and M. POVAR, Division of Life Sciences, Brown University, Providence, Rhode Island

Summary A study has been carried out on the structure and surface texture of a new dental implant material composed of silica microspheres (3 or 5 wt yo) and poly(methy1 methacrylate). A recently developed composite material composed of vitreous carbon microballoons and poly(methy1 methacrylate) has proven highly successful in clinical use, but the black color presents aesthetic problems at the gingival margin. The new material was developed in order to reproduce the many desirable qualities of the vitreous carbon-polymethacrylate composite, while omitting the black color. Square wafers (10 mm X 10 inm X 1mm) were studied, with the surface sandblasted in half of the specimens. Light microscopy revealed an even spacing of spherical configurations throughout the material. Scanning electron microscope studies revealed a finely porous surface with many large craters in the sandblasted specimens.

INTRODUCTION The validity of the polymer tooth implant concept has been demonstrated by extensive investigations in baboons and other experimental anirnals.'-'j Clinical studies'6-z0 have provided further information on the successful use of dental polymer implants. The importance of porosity at the implant surfacez1was demonstrated by more rapid acceptance of the implant by the surrounding periodontal (periimplant) tissues, as evidenced by implant stability and restoration of the lamina dura of alveolar bone. Self-support of polymer tooth implants in a difficult experimental animal such as the baboon was facilitated by the development of a polymer with considerable porosity so that the surface of the material resembled the structure of 893 @ 1977 by John Wiley & Sons, Inc.

894

HODOSH, SHKLAR, AND POVAR

natural cementum covering the roots of teeth.22 This polymer material was composed of polymethacrylate, ground inorganic bone, N-tributylphosphate, and a blowing agent (dinitrosopentamethylene tetramine). The degree of porosity proved somewhat difficult to control in this complex mixture, and the use of a biologic material in the mixture presented the problem of the ready availability of the inorganic bone chips for widespread use of the material. A significant improvement in polymer dental implant materials was a composite composed of vitreous carbon balloons (3 w t yo)and poly(methy1 methacrylate). Tooth replica implants using this material had been successfully placed in baboons, and the implants were firm when the retaining splints had been removed after 5 months. Histologic study after 4 months of scllf-support revealed normal alveolar bone conforming to the outline of the roots of the implants. There was an obvious attachment of both gingiva and periodontal membrane t o the implant, and the periodontal (peri-implant) fibers had a horizontal of diagonal orientation similar t o that of periodontal fibers in relation to the natural tooth.23 Histologic studies of the periodontal attachment to dental implants composed of other polymer materials had rcvealed more of a vertical orientation of the periodontal (peri-implant) fibtrs. The vitreous carbon microballoons added t o the polymethacrylatt offered porosity by rupture of the hollow carbon spheres a t the implant surface, as the composite material was heat-treated a t 300°F for 30 min. Scanning electron microscopy revealed a finely porous surface with multiple large craters where the microballoons had fract~red.~~ Vitreous carbon is a n inert material, not easily degraded in the oral environment, and produces no obvious adverse reactions within thc surrounding tissues. It combines strength with chemical inertness, and is light, hard, and has a low coefficient of linear thermal expanDental implants fashioned entirely of vitreous carbon have been used with some success,2132*but their major disadvantages include brittleness, the necessity of construction prior t o use by the dentist so that they cannot be made t o conform to a natural tooth socket, and the difficulty of processing the material on metal strengtheners. The mixture of vitreous carbon and polymethacrylate solves these problems, and this composite has now been used clinically in a variety of mandibular and maxillary siteszg The major disadvantage of the vitreous carbon-polymethacrylate

POLYRIETHACRYLATE-SILICA COMPOSITE MATERIAL

895

composite material is its black color. The dental implant material is visible through the marginal gingiva and the grey color is aesthetically objectionable. The black implant material cannot be completely covered with a gold crown in all cases, and a discolored gingival margin may be apparent, or may become apparent as some gingival recession occurs in response t o the placement of the crown. The pure vitreous carbon type of implant presents the same aesthetic problem. Since the vitreous carbon-polymethacrylate composite was found t o be the most successful and most convenient tooth implant material used by us, an attempt was made to find a material that could replace the vitreous carbon, so that its advantages of inertness and strength would be retained without the black color. Silica appeared t o be an ideal replacement for carbon, and we found that thin-walled, hollow silica microspheres were produce,d commercially as “Eccospheres S1” by Emerson and Cuming, Inc., Canton, Massachusetts. It was decided t o study composites of various proportions of silica microspheres and polymethacrylate, and then use the best material for the fashioning of replica tooth implants t o be placed in baboons. The material was tested for toxicity using routine tissue culture and direct mouse fibroblast monolayer inhibition assay. The material was found t o cause no apparent inhibition of monolayer cells, and there was no significant cytotoxicity detected in the agar overlay tissue culture assay.3o

MATERIALS AND METHODS Square wafers (10mm x 10mm x Imm) of silica-polymethacrylate were fashioned. Three percentages of weight of silica microspheres were evaluated; 1) 3% silica, 970/, clear poly(methy1 methacrylate) ; 2) 5% silica, 95% clear poly(methy1 methacrylate); 3) 10% silica, 90% clear poly(methy1 methacrylate). The microspheres were 30180 /* in size. Samples were prepared by adding 0.6 cc monomer t o 1 g of dry ingredients. The material was mixed and packed into the plaster molds. The molds, held in flasks under pressure, were processed at 400°F for 45 min. The processed samples were then water-cooled, removed from the flasks, and sandblasted for 1 min at 120 psig with a fine quartz (Jelenko sand). The silica microspheres are produced by Emerson and Cuming, Inc., Canton, Massachusetts, as “Eccospheres S1.”

896

HODOSH, SHKLAR, AND POVAR TABLE I Properties of Silica Microspheres Physical Form

Free-Flowing Powder

True particle density (liquid displacement) Bulk density (tamped) Packing factor Particle size range, p (yoby wt)

g/cc (lb/ft3) g/cc (lb/ft3)

Average particle diameter, p (weight basis) Average wall thickness, p (weight basis) Thermal conductivity of loosely packed material BTU/hr/f tZ/OF/ft Softening temperature, O F Dielectric constant (dry) 11 MHz-8.6 GHz Dissipation factor (dry)

so

0.254 (15.8) 0.152 (9.5) 0.559 >175 (0) 100-125 (12) 149-175 (14) 62-100 (40) 125-149 (10) 44-62 (15)

A polymethacrylate-silica composite material for dental implants.

J. BIOMED. MATER. RES. VOL. 11, PP. 893-901 (1977) A Polymethacrylate-Silica Composite Material for Dental Implants M. HODOSH and G. SHKLAR, Departm...
767KB Sizes 0 Downloads 0 Views