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Biomedical subjects

J Wolfaardt

Publications and source records attributed to J Wolfaardt.

11 recordsLinked to original sources
PubMed2006

Simulation of impact test for determining "health" of percutaneous bone anchored implants.

There is an ongoing requirement for a clinically relevant, noninvasive technique to monitor the integrity of percutaneous implants used for dental restorations, bone-anchored hearing aids, and to retain extra-oral prostheses (ear, eye, nose, etc). Because of the limitations of conventional diagnostic techniques (CT, MRI), mechanical techniques that measure the dynamic response of the implant-abutment system are being developed. This paper documents a finite element analysis that simulates a transient response to mechanical impact testing using contact elements. The detailed model allows for a specific interface between the implant and bone and characterizes potential clinical situations including loss of bone margin height, loss of osseointegration, and development of a soft connective tissue layer at the bone-implant interface. The results also show that the expected difference in interface stiffness between soft connective tissue and osseointegrated bone will cause easily measurable changes in the response of the implant/abutment system. With respect to the loss of bone margin height, changes in the order of 0.2 mm should be detectable, suggesting that this technique is at least as sensitive as radiography. A partial loss of osseointegration, while not being as readily evident as a bone margin loss, would still be detectable for losses as small as 0.5 mm.

Computer Simulation↗
PubMed2005

Implications of radiation dosimetry of the mandible in patients with carcinomas of the oral cavity and nasopharynx treated with intensity modulated radiation therapy.

Intensity modulated radiation therapy (IMRT) is a newer method of delivering highly conformal, salivary gland sparing radiation treatment that is finding increasing applications in head and neck malignancies. However, the radiation dose distribution to the mandible is rarely considered with IMRT, and the potential risks of osteoradionecrosis or osseointegrated implant failure are not well characterized for this modality. In a series of 10 patients with oral cavity and nasopharyngeal cancers who previously underwent IMRT, examination of the three-dimensional mandibular dose distribution was undertaken. The findings indicate a modest potential risk of osteoradionecrosis and osseointegrated implant failure in cases where IMRT optimization constraints are not specifically aimed at sparing the mandibular bone. Significantly higher mandibular doses (P < 0.04) were received in cases of oral cavity as opposed to nasopharyngeal cancers with IMRT. Efforts to optimize IMRT to further reduce doses to the mandible should be considered, and development of software tools to integrate three-dimensional dose distributions into planning of post-radiotherapy osseointegration would be beneficial.

Carcinoma↗
PubMed2003

Indications and methods of care for aspects of extraoral osseointegration.

The introduction of percutaneous osseointegration biotechnology in 1979 to head and neck reconstruction permanently revised the long held view that a facial prosthesis was a last resort for the patient and surgeon alike. Since that time, the use of extraoral osseointegration has expanded considerably. The present review of the literature considers indications and methods of care for aspects of extraoral osseointegration as it relates to facial prosthetics. The clinical literature reviewed was graded for hierarchy of strength of evidence according to the Bandolier system. Almost all literature reviewed was of the lowest level of strength of evidence. Consequently, clinicians are advised to be cautious in applying the evidence to patients.

Ear, External↗
PubMed1985

An experimental comparison of vertical tooth movement of 33 degrees and 0 degree teeth after denture processing procedures.

Movement of teeth during denture processing is an unsolved problem. This study investigates the amount of vertical tooth movement during controlled processing of acrylic, using 33 degrees and 0 degree teeth invested in specific mixes of plaster of Paris or dental stone. Forty sample set-ups each containing four posterior teeth were processed under strictly controlled laboratory conditions. Twenty of these samples carried 33 degrees teeth and the other twenty carried 0 degree teeth. Each group of twenty samples was randomly divided on a factorial design into batches of ten for investment in plaster of Paris or stone. The vertical movements were measured with a greater degree of accuracy than is required for clinical application. All results were analysed statistically. Significantly greater movement occurred with teeth invested in stone than those invested in plaster of Paris. Whereas, for teeth invested in stone, significantly greater movement occurred with 33 degrees than with 0 degree teeth, no such effect was found with teeth invested in plaster of Paris.

Calcium Sulfate↗
PubMedDate not supplied

Mechanical evaluation of craniofacial osseointegration retention systems.

This study evaluates mechanical behavior of retention systems that have been used in craniofacial osseointegration. A loading/measuring apparatus was custom designed and constructed. Test bases that represented a typical auricular situation were constructed. These bases allowed for three points of retention. Jigs that could be reproducibly positioned carried the reciprocal portion of the retentive components. The test apparatus provided vertical and horizontal loads in five locations. The system was used to test two ball-and-socket attachments (Dalla Bona; Nobelpharma), cast and preformed bar and clips (Nobelpharma), and three magnet systems (Dynamag; Neomag; Technovent). The loading/measuring apparatus was also used to evaluate the performance of two facial prosthetic adhesives. Retention systems employed in craniofacial osseointegration offer more predictable retention than the facial prosthetic adhesives. The mechanical retention systems are best suited to situations where tensile and shear forces will operate. Magnet systems are best used where only tensile forces are anticipated or where horizontal forces on the implants are to be avoided.

Adhesives↗
PubMedDate not supplied

Craniofacial osseointegrated implant-induced strain distribution: a numerical study.

Strain distributions that occur in the hard tissue in the region surrounding craniofacial osseointegrated implants are compared. Three commercially available implant designs were evaluated under both axial loading and axial loading with a moment in three bone configurations typical of the craniofacial region. The evaluations that used the finite element method indicated that for axial loading, the implant designs produced similar strain levels in each bone configuration. When moments as well as vertical loads were applied, the strains were three to seven times higher and variations among the designs were greater. The variations found were related to the amount of bone present in each situation, as well as the neck diameter of the implant involved.

Bone and Bones↗
PubMedDate not supplied

Console abutment loading in craniofacial osseointegration.

Retention of implant-supported facial prostheses presents challenges in design that may lead to use of freestanding abutments. This is particularly so in the midface and orbit. Individual implant success rates are lower in these regions, and bone remodeling capacity may be compromised by combined modality cancer therapy. The present study was undertaken to determine the variations in load delivery so as to compare the use of long cantilevers and offset abutments with freestanding axially loaded abutments. The study revealed not only that the loads delivered are not trivial, but also that the highest loads generated are frequently delivered at the cervix of the implant. The long cantilevers produced the highest laterally acting cervical loads, whereas the 30-degree and 60-degree Console abutments delivered the highest laterally acting cervical loads of all the Console abutments. The potential of long cantilevers and offset abutments to deliver significant loads should be considered when designing retention for a facial prosthesis.

Bone Remodeling↗