Development of a custom-fit mouthstick appliance.

Quadriplegics rely on mouth-controlled devices to perform a variety of tasks and to establish some degree of self-sufficiency. The most functional mouthstick appliances have custom-fitted mouthpieces which are fabricated by dental professionals, and in some cases are cost-prohibitive. An inexpensive lightweight mouthstick which incorporates a new thermoplastic mouthpiece and can be custom-fitted by the user is described.

Fracture of porous polyethylene-bone composite.

Porous high-density polyethylene specimens were implanted in the femurs of mongrel canines. At the end of the residency period (3 or 6 months), the animals were sacrificed and the implants were retrieved. The work-of-fracture of the implant specimens was then determined using the technique of Tattersall and Tappin. The work required to fracture a specimen in three-point bending by controlled crack propagation through a triangular cross section was obtained directly from the load-deflection curve. The area of the resulting fracture surface was measured by macrophotographic techniques, and the work-of-fracture was calculated as work per unit area. The implants were subsequently sectioned and examined microradiographically to determine the extent of bone ingrowth. Bone specimens adjacent to the implants and porous high-density polyethylene controls (no ingrowth) were also tested to determine their work-of-fracture. The results showed that bone adjacent to the implant specimens had a higher work-of-fracture than normal medial, canine femoral bone and was not appreciably different from the composite. The work-of-fracture of porous high-density polyethylene was not significantly increased by an increase in bone infiltration, and this anomalous behavior was attributed to a degradation of the polyethylene during implant residence. Control studies supported this hypothesis.

Porous high density polyethylene (PHDPE) - autogenous tissue tracheal prosthesis.

This study has demonstrated the feasibility of using PHDPE/autogenous tissue tracheal prostheses to repair defects in the cervical trachea. The PHDPE rings have proven to be an efficacious method of providing a noncollapsing, yet flexible airway. The problems encountered were of a technical nature relating to blood supply in types I and II prostheses and airway leakage and dislodgment in type III prostheses. Future efforts will be directed toward solving these problems.

Dental implant fixation by electrically mediated process. I. Interfacial strength.

In order to determine the effect of electrical stimulation on canine alveolar bone, porous PMMA dental implants with a solid core (on which a Pt-13% Rh electrode was wound) were implanted in the mesial socket of the canine mandibular fourth premolars bilaterally. The positive electrode was implanted into the distal socket. The power pack was placed over the masseteric fossa. The implants, wires and power packs were all implanted subcutaneously. Each animal had an experimental and control implant. Mechanical push-out samples were prepared by sectioning a 2mm thick section of the mandible with the implant in the middle. The samples were tested immediately and the load-deflection curves were obtained.

The effect of high pressure insertion and antibiotic inclusions upon the mechanical properties of polymethylmethacrylate.

The properties of self-curing polymethylmethacrylate as affected by the admixing of an antibiotic to the powder-liquid mixture and as affected by insertion technique demonstrated that the antibiotic agent may leach from the surface of the acrylic, but not necessarily from the interior. The compressive and tensile strength, determined on two different commercial formulations, suggests that the antibiotic additive is not detrimental to the mechanical properties. A high pressure insertion technique produces a significant improvement in the mechanical properties of the self-curing acrylic material.

An intraluminal transducer/telemetry system for oviductal motility studies.

A method for measurement of changes in lumen diameter of the oviduct has been developed. Miniature intraluminal "doughnut-shaped" transducers, 1.0-1.2 mm in diameter, constructed from conductive silicone rubber are implanted in the rabbit isthmus and respond to localized changes--increases or decreases--in lumen diameter. Multiple transducer implants in the same tube permit rate as well as direction of contractions to be determined. A custom-designed, micropower dual-channel telemetry system was fabricated to record motility from unrestrained animals. Typical data collected using this system to determine the effects of induced ovulation on instantaneous changes in lumen diameter are presented.

An evaluation of bone growth into porous high density polyethylene.

The purpose of this investigation was to study bone growth into porous polyethylene rods as a function of time and pore structure. Previous studies have indicated the biocompatibility of solid polyethylene materials which are currently being used clinically. Porous polyethylene rods were implanted in the femurs of mongrel dogs which are sacrificed four, eight, and 16 weeks postoperatively. The implants were then sectioned and examined histologically and microadiographically. Quantitative techniques were employed to determine the amount of bone ingrowth as a function of time and pore size. The pore structures of the materials were evaluated using optical microscopy and mercury intrusion porosimetry. The results of this investigation have demonstrated that porous polyethylene is capable of accepting bone growth into pores as small as 40 mum. The optimum rate of bone ingrowth was observed in pore sizes of approximately 100 to 135 mum, with no increase in the rate of bone ingrowth observed in samples possessing larger pore sizes. No adverse tissue response was found at implant times up to 16 weeks in pore sizes of 100 mum or larger.

Early tissue infiltrate in porous polyethylene implants into bone: a scanning electron microscope study.

The results of the present study demonstrate the utility of the scanning electron microscope for characterizing the ultrastructure of the initial tissue infiltrate in porous polyethylene implants. Shortly after implantation a thin noncellular fibrous-like coating was observed to form on the pore surface. The cells observed in the polyethylene pellets 3 days after implantation were generally consistent with what one would expect to see in a hematoma. As early as 14 days after implantation much of the blood clot was replaced by newly formed bone spicules. Tissue shrinkage accompanying dehydration of the specimen for scanning electron microscope study although a disadvantage occasionally proved useful in that it provided the opportunity to study the internal surface of the fibrous coating when separated from the surface of the implant. Less shrinkage was observed in implants whose pores were filled with bone spicules.

Soft tissue response to four dense ceramic materials and two clinically used biomaterials.

Disk-shaped implants of spinel, alumina, mullite, zircon, a cast Co-Cr-Mo alloy, and ultra-high molecular weight polyethylene (UHMWPE), were implanted in the paraspinalis muscle of 12 adult, male, white New Zealand rabbits. Prior to implantation the implants were characterized with respect to size and shape, weight and surface roughness. After periods of 1 month, 2 months, and 4 months, the rabbits were sacrificed and the tissue specimens were retrieved with the implants still intact. Histological examination of the tissues surrounding the implants along with changes in the size and shape, weight, and surface roughness of the implants were used as criteria for evaluating these materials for implant purposes. No surfaces degradation of any of the materials was detected using scanning electron microscopy. Fibrous tissue seemed to adhere to the UHMWPE implants more than any other material used in this study. Large amounts of fibrous tissue were also found to adhere to the cast Co-Cr-Mo alloy implants. The histological results indicated that within the limits of this investigation, the biocompatibility of the ceramic materials used in this study compared favorably with the clinically used Co-Cr-Mo alloy implants and the UHMWPE implants.

Evaluation of a metal-ceramic composite hip prosthesis.

This investigation attempts to apply the concept of direct skeletal attachment via tissue ingrowth to the attachment of femoral head prostheses to the femur. Stainless steel (316L) canine femoral head prostheses with a ceramic coated stem were implanted into the femora of dogs and their results compared to those obtained by the impaction of stainless steel prostheses and acrylic-stabilized prostheses. The implants were tested in vivo for time periods ranging from 2 to 13 months, after which time the animals were sacrificed and the femora excised. The femora were sectioned with the implants in place and prepared for examination by light microscopy. Bone was in closer approximation to the ceramic coated implants than to the other two types of implantations. The uncoated and acrylic-stabilized implants were usually characterized by the presence of a relatively thick fibrous sequestering membrane.