ROBERT W. CHRISTENSEN, D.D.S.
PRESIDENT OF TMJ IMPEANTS, INC.
GOLDEN, COLORADO
ADJUNCT PROFESSOR OF BIOENGINEERING
COLLEGE OF ENGINEERING AND SCIENCE,
CLEMSON UNIVERSITY
CLEMSON, SC

In the long-term performance of the temporomandibular joint (TMJ) = implant, wear must be considered. Thus retrieved and laboratory test implants were examined both optically = and in a scanning electron microscope (SEM). In laboratory testing, the volumetric wear of = metal-on-metal was about an order of=20 magnitude less than that ofacrylic-on-metal TMJ implants. This = metal-on-metal wear was also about half of that reported in the literature for a laboratory test of = polyethylene-on-metal TMJ implants. The retrieved TMJ implants shelved some abrasive wear occurred during = multi-directional articulation with smaller wear zones for the metal-on-metal compared to the acrylic-on-metal = configuration. Further efforts to characterize=20 and minimize wear were recommended as prudent in the continuing = development of TMJ arthroplasty. The metal-on-metal temporomandibular=20 joint (TMJ) implant is not a new concept to the oral maxillofacial surgeon. In the early 1970s, Kiehn et al.¹ reported on the clinical use of a Christensen Fossa-Eminence component mated with a Cargill-Hahn condyle component both of which were made of a cast cobalt-chromium-molybdenum (Co-Cr-Mo) metal alloy = (Vitallium®). They reported a short-term follow-up of 27 cases, = which were rated as successful through reduction of pain and increase in the range of motion of jaw opening.² Later, Kummoona reported a short-term clinical = trial of a similar Co-Cr-Mo metal-on-metal TMJ implant³ and an animal study using the same TMJ implant system. In the animal study, the microradiographic = examination=20 of histiologic ground sections demonstrated, in the author's terms, "biological acceptance of the metal implants by the natural tissue." However, neither Kiehn et al. or = Kummoona studied the long-term performance of metal-on-metal TMJ implants.

Kummoona also reported³ the formation of a fibrous tissue = layer approximately 2 mm thick, that was interposed between the two metal surfaces and seemed to function as a meniscus. The development of this "pseudo-meniscus" was noted by other research groups, ^4,5 but the extent of the load bearing by this structure was not ascertained. Consequently, it was not clear = whether this fibrous tissue would protect the implant surfaces from wear.

The acrylic-on-metal TMJ implant also has a long history of application in oral maxillofacial surgery.^5,6 In addition, acrylic (PMMA or polymethylmethacrylate)=20 was used for the articular surface of a femoral head implant for hip hemiarthroplasty by Judet and Judet^7,8 in the early 1950s. Mechanical failure of the Judet hip prosthesis forced discontinuance of the device after a = decade of use.^9,10 However, some recent publications^11-13 = reported that the long-term performance of a few remaining Judet implants seemed to be well tolerated by the surrounding tissues despite evidence of wear. For acrylic-on-metal TMJ implants, the relevant issues in long term performance are the wear and tissue response to wear particles.

Other polymeric materials have been used for TMJ implants with very poor results. Oral maxillofacial surgeons are familiar with the pain, foreign body reaction and bone loss caused by particles generated from = Proplast-Teflon and Silastic materials that were used in TMJ implants.^14-20

In orthopaedics, the cause of smaller-scale but somewhat similar = problems has been identified as wear particle induced osteolysis.^21-27 Because of the small particle sizes, this osteolysis is not easy to identify and early orthopedic papers incorrectly attributed the granulomas sac and/or radiolucent line = that developed around implants as the onset of late infection or inadequate stress transfer through the implant-bone interface.^28,29 Wear particle-induced osteolysis is now considered the leading problem in orthopaedic surgery.³⁰ It is likely that the bone loss and/or development of granulomas sacs of = tissue observed in the Proplast-Teflon implants are caused by this same particle-induced osteolysis.

Because of the problem of wear particle-induced osteolysis in = orthopaedic joint replacement, wear phenomena have been studied with some rigor with joint simulator devices.^31-34 However, very little wear test data has been published on TMJ implant systems. = The testing of the Proplast-Teflon TMJ Interpositional implant by Fontenot and Kent³⁵ ended suddenly at 21,786 cycles when the implant itself fell apart and they concluded it would have a "very short in situ service life." A premarket notification report³⁶ (51Ok) to the Federal Drug = Administration (FDA) by Anspach, Inc. describes wear testing of a polyethylene-on-metal TMJ implant system(original Techmedica, Inc. Custom TMJ System). An average wear rate 0.389 mm³/million cycles was reported for the polyethylene of the fossa component. Unfortunately, the "Anspach report" described wear testing=20 with a uniaxial motion based on the protocols in the F732 test ofthe American Society for Testing and = Materials (ASTM). This test (Standard Practice for Reciprocating Pin-on-Flat Evaluation of Friction and Wear Properties = of Polymeric Materials for Use in Total Joint Prostheses) was subsequently withdrawn by ASTM in 1997 because it was recognized that unrealistically low wear rates occurred when uniaxial rather than biaxial motion was employed. Support for this sensitivity to motion was provided by Bragdon et al³¹ who showed that the wear of polyethylene hip sockets in = a simulator apparatus changed from a undetectable level with uniaxial motion to about 27 mm³/million cycles with biaxial motion. Thus the wear of a polyethylene-on-metal TMJ implant in = vivo might be much higher than the wear measured in the simulator apparatus of the Anspach report.³⁶

The purpose of the present study is to examine the wear of both metal-on-metal and acrylic-on-metal = Christensen TMJ Implants. This study is part of an overall development program described previously³⁷ and includes the comparison of retrieval = implants (up to 11=20 years) with laboratory wear test implants. The assessment includes the measurement of changes in the macrogeometry=20 with a three dimensional profiling=20 system and the examination of the microgeometry with a SEM. The focus of the present study is to begin to characterize wear behavior of these = two implant systems and thus eventually evaluate the risk of clinical complications associated with wear = particle release into the surrounding tissues. The scope of the work is not yet com prehensive but complements other wide-range development work.^38-51 The aim of the overall development program is to provide a well-engineered TMJ implant system with minimal risk of either short- or long-term complications.

Laboratory wear tests were conducted for 2 million cycles on = commercial TMJ implants (5 metal-on-metal and 5 acrylic-on-metal) by an independent laboratory (Rose Musculoskeletal Research Laboratory, Denver, CO).⁵¹ A custom apparatus was designed and built to provide conditions in the laboratory that were close to those = in vivo (Figure 1). Only two previous studies involved wear testing of TMJ implants (Table 1).=20

In the laboratory wear test, the implant specimens were fixed in a position similar to that encountered in vivo by screws in an epoxy material which was an analogue for bone. However,=20 the fossa component oscillated (rather than the condyle component as in vivo) through an arc of 30=B0 at a frequency of 2 Hz. Both the range = of motion and the frequency were some what higher than the previous laboratory wear testing of TMJ implants = (Table 1). Also, previous wear tests (Table 1) had used a constant load of 20 Ibs (9.1 kg) based on predictions of various investigators.³⁶ However, in the laboratory wear test, the = forces found by Brehnan et al.⁵² and Bovd et al.,⁵³ who performed direct measurements by interposing a piezoelectric foil transducer on the condyle of TMJ in = primates, were adjusted to human levels following the work by Smith.⁵⁴ This approach resulted in the application of a cyclic "saw tooth" load pattern varying from 10 lb to 35 lb (4.5 kg to 15.9 kg). In a separate study,³⁸ a load of 35 Ib. (15.9 kg) gave an average contact stress of 7,01 Ipsi (48.34MPa) with a standard deviation of 812 psi (5.6MPa) for 5 Christensen metal-on-metal implants. The same load gave an average contact stress of 5,562 psi (38.35 MPa) with a standard deviation of 580 psi (4.0 MPa) for five Christensen acrylic-on-metal implants. It was interesting to note that the average contact stress for the metal- on-metal hip implants at the beginning of the wear test was about the same as that found at the beginning of the simulator tests of metal-on-metal as = reported in the orthopaedic literature.⁵⁵ This average contact stress was much less than the yield strength of the cast Co- Cr-Mo metal alloy. On the other hand, the average contact stress for the acrylic-on-metal implants was about one-half of the tensile strength (of about 10,000 psi or 69 MPa), ³⁹ which means that some local plastic deformation might have accelerated the = wear at the beginning of the testing.

The lubricant that was employed in the laboratory wear test was a mixture of 90% by volume filtered sterilized bovine calf serum (HyClone Laboratories, Logan, UT), ethylene diamine tetraacetic acid (EDTA) in distilled water (9%) making a 20 mM solution and streptomycin (1%).⁵¹ The bovine serum was selected because it had been used as an analogue for synovial fluid wear testing in orthopedics.^55,56 The EDTA was intended to suppress excessive calcium and phosphorus rich deposits. ⁵⁷ The streptomycin was used as an antibacterial agent.⁵⁵ The acrylic condyle components were soaked in the bovine scrum mixture for 5 days prior to testing to ensure an equilibrium fluid absorption level.

The volumetric wear was evaluated by converting mass loss measurement (weight), taken every 0.25 million cycles using an analytical balance, to volume estimates assuming a density of 8.28 mg/mm³ for the Co-Cr-Mo alloy. In addition, volumetric wear was determined using surface profile = measurements^58,59 taken before testing and after 2 million cycles. This profiling system (MTS Systems Corp., Minneapolis, MN) had been developed in conjunction with the University of Minnesota Dental Research for Biomaterials and Biomechanics Laboratory for dental research (Figure 2).⁵⁹

The wear zones on a typical metal- on-metal implant showed oriented surface scratches in the direction of = motion that were visible to the naked eye (Fig ure 3). The wear zone of an acrylic condylar head was larger (Figure 2) and oriented surface scratches were not clear to the naked eye. The metal fossa had no detectable wear when tested against the acrylic condylar head. The volumetric wear of the fossa components in the metal-on-metal implants was calculated from mass loss measurements conducted every 0.25 million cycles and showed essentially a linear variation over the 2 million cycle duration. After 2 million cycles the = mass loss measurement procedure gave about the same volumetric wear as the profiling system procedure (Figure 4). = However,=20 both the metal and acrylic heads seemed to gain mass during the wear testing and thus some unknown error must have been present in the measure ment procedure. Consequently, the mass loss procedure was not reported further in the present study.

The profiling system procedure was used to provide volumetric wear data corresponding to 2 million cycles. For the metal-on-metal implants (Figure 5a), there was usually more wear on the fossa compared with the condyle component. Furthermore, there was = considerable scatter in the results, which all had the same nominal conditions. For the acrylic condyle components (Figure 5b), there was a similar scatter and about an order of magnitude more wear. Such scatter in wear test data was not considered unusual.^32,55,56,60 However, one of the = metal-on-metal and one of the acrylic-on-metal implants showed no detectable signs of wear (Figures 5a and 5b).

This suggested that load was not applied properly to these two implants in the wear test. If these two implants that did not wear were eliminated as erroneous data, the average wear rate was 0.197 mm³/million cycles for the metal-on-metal implants and 1.64 mm³/million cycles for the acrylic-on- metal implants.

Interestingly, the wear of the metal-on-metal=20 TMJ implants was about the same level as that reported in the orthopedic literature for some metal-on-metal=20 hip implants.³² In general, the metal-on-metal TMJ implants experi enced lower wear than the acrylic-on-metal=20 implants, but the large scatter in the wear results for each material pairing=20 introduced some overall imprecision into this observation. The average wear of the metal-on-metal was about half ot the average wear of 0.389 mm³/million cycles reported for the polyethylene fossa components in the Anspach report.³⁶ However, the previously mentioned = application of uniaxial motion in the wear tests of the Anspach report might have suppressed the wear compared with that likely to occur in vivo and thus the wear of metal-on-metal=20 implants might be much less than half the polyethylene-on-metal wear for the TMJ implants in vivo.

The wear of the acrylic-on-metal TMJ implants was measurable on the condylar head alone and was about 8 times higher than the total wear of the metal-on-metal TMJ implants. While the body seems to tolerate the acrylic wear debris,^11-13 the lower wearing metal-on-metal TMJ implant may be advantageous in the long term.

In the retrieval group, 4 metal-on-metal=20 implants, 3 acrylic-on-metal implants, 2 metal condyle components and I metal tossa-eminence component were examined both optically and in a SEM (JSM-840, JEOL, Tokyo, Japan). In addition, 3 acrylic-on-metal implants and I acrviic condyle component were examined opticallv. The period of use in the body ranked from 3 to 5 years for the metal-on-metal implants and from 1 to 11 years for the acrylic-on-metal implants.

The group of laboratory wear test implants included 5 metal-on-metal and 5 acrylic-on-metal configurations.⁵¹ All implants were examined optically but only two of each type were examined in the SEM. To examine the acrylic condylar heads, it was necessary to = sputter coat them with gold.

For the metal-on-metal retrievals, distinct wear zones were present on both the condyle head and fossa components. The wear zones were oval in shape with an average size of 3 x 2 mm. On the condylar heads, separate wear zones were on the anterior and posterior=20 sides of the dome with the long axis aligned in the superior-inferior (S-1) direction.

Separate wear zones were also found on the anterior and posterior walls ot the sulcus (or valley) of the fossa with the long axis in the medial-lateral (M-L) direction. The wear zones were shiny and smooth and had a distinct edge (Figure 6a).

At higher magnifications, fine randomly oriented scratches and small = pits (I to 10 \im across) were observed in the wear zone (Figure 6b), while away from the wear zone carbides ( 1 to 10 [µm in size) were present as well as pits and scratches (Figure 6c).

The shape and position of the wear zones on the retrieved metal-on-metal implants suggested that much of the sliding motion was in the M-L direction. However, the sliding motion was not uniaxial. If that were the case, the scratches on the wear zone would be straight and aligned in the direction of motion. Therefore, it was concluded that a reciprocating sliding action occurred in both the M-L direction and the vertical plane to produce a multi directional motion. The presence of scratches in the wear zone indicated that the surfaces were subjected to abrasive wear, the abrasive agent being the hard carbides in the surface of the metal. The similar size of pits and carbides suggested the pits were = sites where carbides had been detached from the surface. Thus, free carbides would also abrade the metal surfaces through a process known as "third-body" abrasive wear.

On the retrieved acrylic condylar heads, the wear zones tended to be saddle-shaped,=20 extending from the anterior side, over the apex, and down the posterior side of the dome. The wear = was visible to the naked eye (Figure 7). Considering all the acrylic condylar heads, the average size of the wear zone was 10 x 7 mm, with the long axes extending down both sides in the S-1 direction. At higher magnifications, the surfaces were covered with randomly oriented scratches and some pits (Figures=20 8a and 8b). No wear zones were observed on the mating fossa, except for the 11 year implant, and none were expected because the acrylic polymer was much softer than the Co-Cr-Mo alloy of the fossa. In the case of the 11=20 year fossa, the observed wear zones resulted not from the contact with the acrylic polymer, but rather with the central metal post around which the acrylic had been molded. Wear of the acrylic head had exposed the metal post which had then rubbed against the metal fossa.

The presence of randomly oriented scratches in the wear zone of the retrieved acrylic heads (Figure 8a) showed that abrasive wear had occurred, the abrasive agent being the carbides in the mating fossa (Figure 8b). Once again, random orientation of the scratches implied a multidirectional sliding action. The shape of the wear zone, although different from those on the metal-on-metal implants, was

formed essentially by the same wear mechanism. Initially, contact on the acrylic head was on the anterior and posterior aspects of the dome. Because the polymer was softer and therefore wore faster than the Co-Cr-Mo alloy, the dome was worn away rapidly on its anterior and posterior sides and thus penetrated more deeply into the sulcus of the fossa, resulting in contact between the dome and the bottom of the sulcus, and hence wear of the apex of the dome.

The metal-on-metal implants from the laboratory wear tests⁵¹ had wear zones that were very different from the retrieved metal-on-metal implants. The wear zones tended to be saddle-shaped and straddled the apex of the condylar head and the sulcus of the fossa with the long axis in the A-P direction (Figure 3). The average size of these wear zones was 5 x 2 mm. At higher magnifications, parallel scratches were clearly visible, oriented in the A-P direction (Figure 9). In contrast, the retrieved implants had two separate smaller wear zones (each averaging 3 x 2 mm in size) on both the condylar head and the fossa with fine scratches of random orientation and a highly polished = appearance (Figures 6a and 6b). On the acrylic-on-metal implants from the laboratory wear tests,⁵¹ similar wear zones, although slightly larger when compared with the metal-on- metal implants, were found with an average size of 7 x 2 mm. The wear zone was smooth but large pits and some surface cracks were visible at low magnification (Figure lOa). At higher magnification, there were parallel scratches predominantly in the A-P direction together with pits (Figure 10b).=20

These scratches did not seem to be as deep or as numerous as those on the metal-on-metal implants. In contrast, the retrieved acrylic condylar heads had larger wear zones (10 x 7 mm) with randomly oriented scratches (Figure 8a) and smaller pits (Figure 8b). No wear zones were found on the mating=20 fossa of the implants from the laboratory wear tests,^{51 =} although a few parallel scratches were observed in the anticipated contact zone.

In both the metal-on-metal and acrylic-on-metal implants from the laboratory=20 wear tests,⁵¹ the shape of the wear zones reflected the simple sliding action of the testing, in which the fossa rotated through a 30º arc about the M-L axis. Contact occurred over the dome and sulcus apexes because the largest fossa were chosen for the wear tests such that each sulcus was wider than the dome of the contacting condylar head. Abrasion was again the dominant wear mechanism, the scratches being parallel because of the uniaxial reciprocating motion. The absence of = wear zones on the mating fossa for the acrylic heads was to be expected. However, some abrasion of the fossa did occur as demonstrated by the presence of parallel scratches in the contact zone. = Presumably, these scratches were made by the abrasive action of carbides detached from the metal fossa surfaces, the carbides either moving freely within = the joint space or embedding in the softer acrylic head.

The comparison between the retrieved and the laboratory wear test implants revealed some differences in the wear test kinematics. Although both the metal-on-metal and the acrylic-on-metal=20 implants were subject to abrasive wear in vivo and in the wear tests, the wear test kinematics did not fully represent the multi-directional = sliding actions occurring in vivo. Examination of the retrievals showed that movement of the condylar head within the fossa was restricted in the A-P direction by the walls of the sulcus. The head moved from side-to-side in the M-L direction with an additional vertical movement. As a result, the in vivo kinematic inter action involved cross-shear and this motion was not reproduced in the laboratory wear tests,⁵¹ = where the head was stationary and the mating fossa rotated about a M-L axis. While this kinematic difference was significant, Tipper et al ⁶¹ recently showed in pin-on-plate wear testing of high carbon Co-Cr-Mo (a wrought rather than a cast alloy as used in Christensen TMJ implants but with similar carbon content) that metal-on-metal=20 wear was not influenced much by changing the motion from uniaxial to biaxial. Thus the wear in the laboratory tests of the metal-on-metal implants might be similar to wear in vivo.

On the other hand, wear tests should strive to represent in vivo conditions as closely as possible to improve the likelihood=20 of producing wear similar to that found in vivo and, therefore, some uncertainty was introduced by the different kinematics of the laboratory = wear tests,⁵¹ particularly for the acrylic-metal implants.

Furthermore, the use of the large fossa in the laboratory wear tests⁵¹ gave a single contact area on both mating components rather than two smaller ones observed in the retrievals of the present study. These larger fossa could have been used in clinical practice and were chosen to reduce geometric con formity, in an attempt to give a worst case scenario. In retrospect, however, a closer representation ot the in vivo conditions of the retrievals = would have occurred by selecting smaller fossa components.

The average wear of Co-Cr-Mo metal-on-metal TMJ implants in laboratory tests for 2 million cycles was = 0.197 mm³/million cycles. When compared with wear in laboratory testing of other TMJ implants with different material combinations, the metal-on-metal had the lowest wear.

The average wear of acrylic-on-metal=20 TMJ implants in laboratory tests for 2 million cycles in a simulator apparatus was 1.64 = mm³/million cycles, occurring almost exclusively on the acrylic condylar head.

Examination of the wear tested acrylic and metal components optically and in the SEM showed single wear zones with parallel surface scratches oriented in the uniaxial direction of motion imposed by the wear test apparatus. These scratches seemed deeper and more numerous on the metal-on-metal=20 implant surfaces. In both types of implants, the mechanism of wear appeared to be abrasion with additional "third body" abrasion by carbides detached from the metal surfaces. Examination of retrieved metal-on- metal TMJ implants optically and in the SEM showed evidence of abrasive wear, in particular, "third body" abrasion by detached surface carbides. Each component=20 had two wear zones with randomly oriented scratches.

Examination of retrieved acrylic-on-metal=20 TMJ implants optically and in the SEM showed almost zero wear of the metal fossa and a single large saddle shaped wear zone on the acrylic condylar head with randomly oriented scratches. Evidence was found for abrasive wear with additional "third = body" abrasion by carbides detached from the metal fossa surface.

The randomly oriented surface scratches of the retrieved implants indicated that multidirectional = motion occurs in the articulation of TMJ implants in vivo.

The laboratory wear test apparatus did not represent all of the features of the TMJ implants in vivo with regards to the kinematic detail and contact mechanics, but the results could still provide useful information on TMJ implant performance. For example, the abrasive wear occurring in both material combinations and the amount of = wear in the metal-on-metal TMJ implants was comparable to that reported for laboratory testing metal-on-metal hip implants in the orthopaedic literature.³² Furthermore, the lowest wear in laboratory testing occurred tor the = metal- on-metal implants compared with acrylic-on-metal or polyethylene-on-metal³⁶=20 implants. This same ranking of wear performance is expected to occur in vivo.

Use of metal-on-metal as an articulating=20 surface for load bearing joints has been criticized in the literature.^5,35 It was stated that a metal-on-metal combination=20 of materials would produce "galling" and lead to catastrophic failures. While galling may occur in = some softer metal materials such as the stain less steel or titanium alloys, harder cobalt-based alloys arc known to be very wear resistant materials in their industrial applications. It is true that the wear test in this study produced a rough, dull surface with parallel scratches over the wear zone due to uniaxial reciprocating motion, but the surface profile measurements indicated that low material loss occurred - leading one to believe that minimal = wear debris was produced. The retrieval implants exhibited a "smooth and shiny" wear zone surface to the naked eye, much different in appearance from the laboratory wear test surfaces. The multi-directional motions of the mating Co-Cr-Mo components in vivo along with an abrasive slurry of small carbides must be the mechanism to produce these "lapped and highly polished" wear zone surfaces.

The wear was not sufficient to suggest any risk of device failures in = either the laboratory tested or retrieved implants. Thus, the statements predicting catastrophic failure of = metal-on- metal implants made of Co-Cr-Mo arc not justified.

Retrieved and laboratory tested acrylic-on-metal implants have shown higher wear than metal-on-metal implants in both the laboratory wear tests as well as implant retrievals. Although a correspondingly larger volume of acrylic wear in particulate = form is generated in vivo, no report of deleterious foreign body = reaction in sur rounding tissue has been found in the oral maxillofacial literature. Some long term retrievals (20 to 40 years) of orthopaedic Judet hip implants showed high acrylic wear yet no significant adverse tissue reaction.^11-13

Wear particle-induced osteolysis is a new issue that must be considered in the development of implants for load bearing joints. Osteolysis development is dependent on (1) volume of particles accumulated, (2) particle size and shape, and (3) threshold levels of particles that surrounding tissues of = an individual patient can tolerate.³⁷ The influence of these factors on osteolysis involving cell phagocytosis of particles through the release of tissue destructive biological substances, is the focus of current implant research.^62-65 New designs are being explored to reduce the volume of particles.

This research includes improving the material composition and manufacturing methods of the Co-Cr-Mo alloys to reduce wear. Research centers have looked at various heat treatments,^66-68 the alloy composition in the generation of microstructure carbides,^69,70 and the "sliding contact" microstructure deformation processes with twinning and stacking fault energies,^71-73 as an explanation for the = superior wear resistance of Co-Cr-Mo. New methods of decreasing wear such as coating Co-Cr- Mo with diamond-like-carbon (DLC) coatings,^74,75 have demonstrated improved wear resistance with effective corrosion resistance and biocompatability. Adhesion of the coating to = the substrate is critical and is the subject of on-going research. Both laboratory testing and retrieval analysis of the = metal- on-metal and acrylic-on-metal Christensen TMJ System (s) show that the use of these implant devices for combating temporomandibular joint disease is a viable option for the oral maxillofacial surgeon.

In TMJ laboratory wear testing, the protocol for mass loss rncasurements must be improved to yield realistic and repeatable mass loss values. In the labo ratory wear testing, multi-directional motion should be imposed in the surface articulations.

Further examination of retrieved TMJ implants is required, particularly those in situ (or more than 10 years. The retrieval process should include study of tissue samples collected from surrounding tissues so that both the wear particles and the response to wear particles can be studied. New approaches in design and materials should be explored to further reduce wear.

This paper was supported by TMJ Implants, Inc. (Golden, CO), manufacturer ot the TMJ implant devices. = All testing as reported was conducted by independent laboratory research facilities as referenced in the = publication. The authors would like to thank Eric J. Northcut of Rose Musuloskelctal Research Lahoratorv, Denver, CO, for his assistance in supplying information and performing the wear testing ofthe TMJ devices. Appreciation is also expressed to Dr. Maria R. Pintado from the Minnesota Dental Research Center for Biornatcrials and Biomechanics, University of Minnesota, Minneapolis, MN, for preparing the surface profile measurements on the wear test implants. And finally, we would like to thank Dr. Subrata Saha, Professor, Department of Bioengineering, College of Engineering and Science, Clernson University, Clemson, SC. for his detailed testing and study of TMJ implants in contact mechanics through the Robert W. Christensen Biomechanics Laboratory. STI

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WE ARE ANGELS UNITED TOGETHER ON TMJ! TMJD_SAFE_HAVEN_4_LIFE_ISSUES · TMJ SUPPORT GROUP This TMJD Support Group is intended to be a Safe Haven and provide a place where people with TMJ pain can come and offer and receive support from people who know what they are going through. This is not a medical group and we do not have medical degrees or medical backgrounds. However, with the variety of members in here, there is bound to be someone who has been there and done that and can answer your questions. This group is in memory of Debbie Ward whom suffered from TMJD & died of unknown causes. There are many types of members with TMJD. Some have been treated medically, some treated with various splint therapies and physical therapies as well as some with surgical treatments ranging from Arthroscopy to full jaw joint replacements. Everyone with any degree of TMJD or has a family member that deals with it is welcome to join and offer and receive support that we all so badly need to get through each day with the pain we have to live with. It is YOUR place to cry, scream or vent on the pain you are dealing with and how it is affecting your life and the lives of your loved ones. The group is MODERATED to avoid the unsolicited advertisements and spam. We are all in pain and do not need to have to deal with that too. TMJ SURGERY FAMILY!. A Great Place to Share Information! This site is for sharing and is not a substitute for the advise of your physician/oral surgeon. Please consult with your health care professional.

The owners and creators of this website will not be held liable for telling it like it is. What we offer here is a collection and display of documented information. Our intention in building and maintaining this web site is to make all information available for others to access and view. The information provided on this site is for educational purposes and to encourage sharing and communication among interested persons. It is not the intention of this site to violate trademark or copyright laws so it is hoped that all contributors will do their best to identify sources and or avoid copyright infringement when submitting information. And there is no intention to profit for any money for any reason. This site is designed to provide a safe place for persons to communicate with the hope that all information is presented in good faith and with accuracy. Together we can make a difference....

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