J. BIOMED. MATER. RES. SYMPOSIUM
No. 6 , pp. 9- 16 (1 975)
Biomaterials Science Protocols for Clinical Investigations on Porous Alumina Ceramic and Vitreous Carbon Implants J . E . LEMONS, Departments of Engineering Biophysics and Biomaterials, University of Alabama in Birmingham, Birmingham, Alabama
Summary A written protocol for the investigation of candidate surgical implant materials is quite important. Biomaterials science sections of clinical protocols have been developed for porous alumina ceramic and nonporous vitreous carbon biomaterials. Published data on the properties of the biomaterials were evaluated as related to bone replacement and augmentation. Where necessary, limited laboratory studies were conducted. If decisions could not be reached with respect to a given application, animal studies were initiated. The surgeons worked with biomaterials in the laboratory and the biomaterials scientist attended the experimental surgery procedures. Biomaterials Science Laboratory nondestructive investigations including stereomicroscopic and x-ray inspections were conducted on the vitreous carbon dental implant systems. The investigations elucidated a number of unexpected features for both implant biomaterials and the overall interaction between the different disciplines resulted in a more complete protocol for the study of these biomaterials at our Medical and Dental Center.
INTRODUCTION Inorganic biomaterials for the replacement or reconstruction of tissues are quite important to the practice of medicine and dentistry. The experience gained over many years of applications has resulted in numerous metallic, polymeric and ceramic biomaterials [ 11, [ 2 ] . Although many acceptable implant biomaterials are available, a need for new biomaterials remains, especially where solutions to clinical situations are not presently available. Porous alumina ceramic and nonporous vitreous carbon have recently been introduced as surgical implant biomaterials. The porous alumina ceramic is suggested as a bone substitute or supplement biomaterial at sites of relatively low mechanical stress while vitreous carbon has been selected as a bone interface material for a dental root replacement system [3], [4]. The initial laboratory and clinical studies indicate considerable potential for the application of these biomaterials to 9 @ 1975 by John Wiley & Sons, Inc.
10
LEMONS
selected clinical situations. This potential, at least in part, is related to the inertness of the oxide ceramic and carbon biomaterial surfaces. This property may prove to be a very important factor in the long term SUCcess of these biomaterials. Members of the Medical and Dental faculty at the University of Alabama in Birmingham Medical Center are presently evaluating the porous alumina ceramic and vitreous carbon biomaterials for clinical applications. The development of an overall clinical protocol for these candidate biomaterials resulted in a direct interaction between the clinical programs and the Biomaterials Science Laboratory. The Medical and Dental surgeons worked with the candidate biomaterials in the laboratory and the biomaterials scientist attended the experimental surgery procedures. This interaction, along with the combined previous experiences of both groups, has resulted in the development of more complete protocols for the study of these biomaterials at our Medical Center. TECHNIQUES, RESULTS, AND DISCUSSION
Since the biomaterials science and clinical considerations are different for the porous alumina ceramic and the vitreous carbon implant biomaterials, they will be considered separately. Porous Alumina Ceramic
The biomaterials science protocol for the porous alumina ceramic included: 1) the engineering properties of the material; 2) a history of biocompatibility studies related to biomaterial-tissue interaction; 3) possible sources of the biomaterial and the quality control procedures of the producer; 4) the final (immediate presurgery) preparation of the materials including shaping, cleaning, and sterilizing; 5 ) limited animal testing to evaluate selected designs and procedural difficulties; and 6 ) the initial considerations for the clinical trials. Engineering Properties. The physical, mechanical, chemical and electrical properties of candidate biomaterials should be available. Testing procedures should, where possible, follow standard A S T M procedures. I n vitro testing under simulated biological conditions is also desirable. More specifically in outline form, data should be provided on the following properties. A. Physical and Mechanical Properties 1. Uniaxial tensile stress-strain properties including modulus of elasticity, yield, ultimate and fracture stress, elongation or reduction in area, and area under the stress-strain curve.
CERAMIC A N D VITREOUS CARBON IMPLANTS
I1
2.
B.
Fatigue strength including the stress versus number of cycles to failure for smooth and notched specimens. For porous specimens such as the oxide ceramics, the collection of this type data is experimentally difficult. 3. Fracture and impact properties for smooth and notched specimens. 4. Microstructure and surface topography including quantitative microscopy determinations of specific features such as porosity, interconnectivity of porosity, grain size, secondary phases or impurities, and surface cracks or roughness. 5. Bulk and surface hardness. 6 . Abrasion and wear characteristics. Chemical and Electrochemical Properties 1. Bulk chemistry. 2. Surface impurities for “as received” material. 3. Electrometric evaluation of surface as specified by the ASTM F4 committee on surgical implants. 4. Standard engineering evaluations of corrosion or degradation potentials. 5. Electrochemical evaluation under implant conditions simulated by mechanical testing.
The preimplantation testing of the material should, where applicable, include combined evaluations such as stress corrosion, combined stresschemical-electrical testing and simulated implantation site characterization of the implant design. This testing should be limited to tests that are specifically applicable to the implant and implant design. Such testing should be expanded where certain property related design limitations are indicated. If more than one material or a composite material is to be used for a given implant, certain interrelated properties such as relative electrochemical potential differences, possible abrasion and wear, local stress concentration, etc., should be considered. All implants considered for an experimental research program should be photographed prior to implantation so that the initial design and surface conditions are made a part of a permanent record. From the engineering data it should be possible to make decisions on the best possible test for routine quality control on the “as received” implants. Additionally, the data should provide ideas on the most critical implant conditions to be considered during the postimplantation evaluation period. If material or design related failures are experienced, the preimplantation characterization would provide direct methods for failure analysis and a rapid feedback for subsequent improvements in the material, the design, the surgical procedure or postsurgical care.
12
LEMONS
The microstructure of the porous alumina ceramic was considered in detail. Insufficient data were available on the three dimensional characteristics of the pore structure and an investigation into the microstructural properties was initiated. These studies are to be presented elsewhere [5]. Biocompatibility. Information on the biocompatibility of the porous oxide ceramics has been accumulating for the past several years [6-111. Previous investigations provide a basis for the tentative acceptance of the alumina ceramic as far as histological and toxological considerations are concerned. This information is somewhat confused by the inability to accurately define the chemistry of all samples; however, a relatively high purity alumina ceramic was used in several instances. It is realized that biomaterial evaluations are always subject to design considerations and specific design criteria and directed studies should always be included in any experimental program. The specific appliances to be studied in our program have been included in an animal study using canines and rabbits. Biomaterials Supply and Quality Control. A controlled porosity alumina ceramic is not routinely available. Therefore, a decision was made to go with a single source and to extensively characterize the selected biomaterial. It is intended to use this biomaterial as a model system for comparison with other porous ceramics available in the future. The source of the porous alumina ceramic used in our program is Dr. Stig Lyng.* These biomaterials were supplied in block form, 5 cm x 5 cm x 1 cm. Similar porous alumina ceramic has been investigated previously and showed good promise for porous biomaterial applications [ 121. The quality control on this material has been maintained under the directions of Dr. Lyng. Within the samples provided for our studies, the structure was relatively reproducible sample to sample throughout the material available. In our opinion, routine quality control from the supplier is fundamental to the future use of a biomaterial of this type. Biomaterials Final Shaping, Cleaning, and Sterilization. The fired alumina oxide ceramic is extremely hard. The shaping of appliance-like forms from the bulk material requires the use of diamond surfaced cutting tools. We found that the cutting and shaping of the material can be done with acceptable accuracy using standard dental equipment. When shaping the alumina ceramic, some debris from the metal back cutting disc was transferred to the ceramic. The debris was present along the surface and in some cases the debris migrated into the internal porosity of the highly porous biomaterial. Ultrasonic cleaning and washing did not completely remove the metallic deposits, especially at sites within the Dr. S. Lyng is Head of the Division of Inorganic Materials, Central Institute for Industrial Research, Oslo, Norway.
C E R A M I C A N D VITREOUS CARBON IMPLANTS
13
sample. A sequence of mineral acid treatments followed by a firing procedure resulted in a clean material. A thorough cleaning treatment is quite important to the subsequent application of this type biomaterial because toxic substances within the pores could adversely influence the biomaterial tissue interface and the long term stability of the associated tissues. After cleaning, the biomaterial was packaged and sterilized in a steam autoclave sterilizer. Packaging in sterile envelopes prevented the possible deposition of autoclave related debris onto the candidate implants. Animal Testing. The previous history of use of the porous ceramics in laboratory studies, animal testing studies, and clinical investigations provides a basis for tentative acceptance of this particular material. However, since our biomaterial porosity and designs were slightly different from previous experiments, it was decided to initiate a limited animal testing program. The main objectives of the animal studies were to evaluate simulated functional sites for our future clinical programs and to discover possible difficulties in handling this material at the surgery table. The applications tested were ridge augmentation in edentulous canines, segmental defects in canine mandibles, small hole defects in rabbit long bones and segmental defects along ribbit tibias. A number of procedural difficulties were encountered at the surgery table. The sterility of the surgical environment is fundamental to the long term success of these porous biomaterials. The basic problems in handling the biomaterial and maintaining sterility is complicated by the difficulties in placing the porous biomaterial into sites within the oral cavity. The placement of porous ceramic along the mandibular ridge of canines using both flap and tunnel techniques were investigated. Difficulties in avoiding unclean regions of the oral environment, and preventing the implant from touching the gingival tissues proved to be quite difficult for the larger implants.* Procedures were developed to avoid contamination of the porous implants. Additionally, the implant shape never seems to be perfect. There is a great desire to shape the implant at the time of surgery by breaking pieces from the structure. Although a clean break might be acceptable, other hazards exist with respect to partial fractures of this type biomaterial. Therefore, several implant shapes need to be available at the time of surgery. Another difficulty relates to the placement of the implant. In many cases, it is desirable to set the implant into the surgical site several times before final placement. In a wet environment the porous implant ma-
* The implants were shaped as 1 to 3 cm long one-half cyclinders. The inside of the cylinders were contoured to fit the mandibular ridge and the porous ceramic thickness varied from I to 3 m m
14
LEMONS
terials, if not infiltrated with blood in advance, tend to rapidly fill with the blood and other debris. This solution, if allowed to dry when the implant is subsequently removed from the surgical site, could possibly produce problems with respect to the filling of the pore network with ossified tissues. In some cases, the implant was placed several times and the blood mass within the porosity could have dried quite completely before final implantation. This difficulty should be avoided. Suggested solutions are to provide several of each implant size or to prefill the porosity of the implant with anticoagulated blood from the host [13]. Initial Clinical Studies. The initial clinical studies using the porous alumina ceramic as a ridge augmentation material are presently being considered. The porous biomaterials are under consideration for augmentation of mandibular ridges for the stabilization of standard dentures. Other investigators have conducted such programs using the porous ceramic and have found this to be a clinically acceptable procedure [ 141. The complete clinical protocol for this type application is a prerequisite to the subsequent use of this material for ridge augmentation. The preclinical trials, in the laboratory and in animal testing, provide a basis for limited and controlled clinical study. We feel that a multidisciplinary approach to this type of application is quite important to insure its future success. Vitreous Carbon
Many of the engineering properties and the biocompatibility criteria specifications have been developed for the vitreous carbon root replacement system currently available from a manufacturer [ 151. The engineering properties and biocompatibility data were reviewed for this candidate biomaterial prior to establishing a clinical protocol [16-181. Since this material is available for general clinical use, the engineering and biocompatibility criteria were tentatively accepted. It was decided however to conduct a limited laboratory program on this material associated with the quality control on this particular implant material. An investigation of the surface of the vitreous carbon root replacement systems, during the early stages of the availability of this material,* showed that some of the “as received” implants contained surface irregularities or small cracks along the carbon surface. Cross and longitudinal polished sections made at the location of several of these particular features showed open pathways or cracks that extended from the carbon surface to the inner metallic core. * These materials were received in early 1973 prior to the release of the Vitredent Root Replacement System for general dental applications.
CERAMIC AND VITREOUS CARBON IMPLANTS
15
The statistical information related to the incidence of visable surface features from the initially received vitreous carbon endosseous root replacement systems is listed in Table I . This data was immediately reported to the company and subsequent quality control procedures were initiated to eliminate this kind of feature from the materials available to the practicing dentist. A series of nondestructive examinations intended to uncover possible internal irregularities in the materials using standard industrial x-ray examination procedures was initiated. The x-ray micrographs of the specimens were taken along the three principle directions of each sample. The thickness, width, and length films were examined using a limited field light source and a stereo microscope. The results of the x-ray nondestructive of these implants are summarized in Table 11. The surface evaluation and the nondestructive x-ray examination of the vitreous carbon root replacement system showed a number of the early “as received” implants t o contain irregularities that might jeopardize the future success of this implant for clinical use. The biomaterials science protocol for the vitreous carbon implant thus includes an initial screening nondestructive type examination before these particular implants are provided to the dental clinic. A complete protocol for the prescreening, placement and post evaluation of these particular implants has been developed within the Dental School. At this time, a series of about 40 vitreous carbon dental root replacement systems are available for the clinical programs within our School of Dentistry. The biomaterials science protocol for all of the materials provided for experimental surgical use included the characterization of the implants and photography of the surface of the implants prior to making the implants available to the surgical disciplines. The photographs of these implant specimens provides a permanent record of the materials and surface conditions prior to clinical implantation. If any of these implants were unsuccessful for some reason, the preevaluation would provide a closed loop system for the postimplantation evaluation and hopefully a
TABLE I Stereomicroscopic Examination of Vitreous Carbon Root Replacement Systems.
Group 1
2 3
Number of samples Number of surface examined (1-7x) “crack-like” features 85 71 48
5 7 10
Comments Early design-no large grooves Early design-no large grooves New design-with large grooves
LEMONS
16
TABLE I1 Industrial Type X-ray Examination of Vitreous Carbon Implant Systems
Group
Number of samples examined
Number of internal irregularities found
1-3
47
8
Comments New design-with large grooves Samples selected by size from previously stereomicroscopically examined groups.
meaningful failure analysis. We always hope that such analyses will not be necessary. References [ l ] P. G. Laing, Orthoped. Clin. No. Amer., 4 , (2) 249 (1973). [2] D. F. Williams, Eiomed. Eng. 260 (June, 1971). [3] S. F. Hulbert, J . Eiomed. Muter. Res. Symp. No. 4 , 1 (1973). [4] D. E. Grenoble and R. L. Kim. Ariz. State DentulJ., (1973). [ 5 ] J. E. Lemons and W. C . Richardson. ZADR Abstr.. (March, 1974), in press. [6] L. Smith, Arch. Surg., 87, 653, (1963). [7] Use of Ceramics in Surgery, S. F. Hulbert and F. A. Young, Eds., Gordon and Breach, New York, 1970. [8] G. A. Graves, R. L. Hentrich, H. G . Stein, and P. K. Pajpai, J . Eiomed. Muter. Res. Symp. No. 2 (part I), 161 (1971). [9] J . Autian and J . E. Hamner, III., J . Dent. Res., 51, 880 (1972). [lo] J . J . Klawitter, and S. F. Hulbert, J . Biomed. Muter. Res. Symp. No. 2, (part l), 161 (1971). [ l l ] P. Predecki, A. Auslaender, J . E. Stephan, V . L. Mooney, and C. Stanitski, J . Eiomed. Mater. Res. 6 ( 9 , 375 (1972). [12] S. Lyng, Research Program Report, Clemson University, Clemson, S. Car., 1973. [I31 C. A. Homsy, J . N. Kent, and E. C. Hinds,J. Amer. Dent. Ass., 86, 817 (1973). [14] R. G. Topazian, W. B. Hammer, C. D. Talbert, and S. F. Hulbert, J . Eiomed. Muter. Res. Symp. No. 2 (part 2), 31 1 (1972). [ 151 The Vitredent Tooth Root Replacement System, Prosthetic and Surgical Consideration, Vitredent Corporation, 1973. [I61 J . Bensen,J. Eiomed. Muter. Res. Syrnp. No. 2 (part 1). 41 (1972). [17] V. Mooney, P. K. Predecki, J. Renning, and J. Gray, J . Eiomed. Muter. Res. Symp. No. 2 (part I ) , 143 (1972). [I81 K. L. Stewart and R. M. Meffert, Continuing Education Course, “Vitreous Carbon Implants-A Simple Technique,” Birmingham, Alabama (Sept., 1973).
No. 6 , pp. 9- 16 (1 975)
Biomaterials Science Protocols for Clinical Investigations on Porous Alumina Ceramic and Vitreous Carbon Implants J . E . LEMONS, Departments of Engineering Biophysics and Biomaterials, University of Alabama in Birmingham, Birmingham, Alabama
Summary A written protocol for the investigation of candidate surgical implant materials is quite important. Biomaterials science sections of clinical protocols have been developed for porous alumina ceramic and nonporous vitreous carbon biomaterials. Published data on the properties of the biomaterials were evaluated as related to bone replacement and augmentation. Where necessary, limited laboratory studies were conducted. If decisions could not be reached with respect to a given application, animal studies were initiated. The surgeons worked with biomaterials in the laboratory and the biomaterials scientist attended the experimental surgery procedures. Biomaterials Science Laboratory nondestructive investigations including stereomicroscopic and x-ray inspections were conducted on the vitreous carbon dental implant systems. The investigations elucidated a number of unexpected features for both implant biomaterials and the overall interaction between the different disciplines resulted in a more complete protocol for the study of these biomaterials at our Medical and Dental Center.
INTRODUCTION Inorganic biomaterials for the replacement or reconstruction of tissues are quite important to the practice of medicine and dentistry. The experience gained over many years of applications has resulted in numerous metallic, polymeric and ceramic biomaterials [ 11, [ 2 ] . Although many acceptable implant biomaterials are available, a need for new biomaterials remains, especially where solutions to clinical situations are not presently available. Porous alumina ceramic and nonporous vitreous carbon have recently been introduced as surgical implant biomaterials. The porous alumina ceramic is suggested as a bone substitute or supplement biomaterial at sites of relatively low mechanical stress while vitreous carbon has been selected as a bone interface material for a dental root replacement system [3], [4]. The initial laboratory and clinical studies indicate considerable potential for the application of these biomaterials to 9 @ 1975 by John Wiley & Sons, Inc.
10
LEMONS
selected clinical situations. This potential, at least in part, is related to the inertness of the oxide ceramic and carbon biomaterial surfaces. This property may prove to be a very important factor in the long term SUCcess of these biomaterials. Members of the Medical and Dental faculty at the University of Alabama in Birmingham Medical Center are presently evaluating the porous alumina ceramic and vitreous carbon biomaterials for clinical applications. The development of an overall clinical protocol for these candidate biomaterials resulted in a direct interaction between the clinical programs and the Biomaterials Science Laboratory. The Medical and Dental surgeons worked with the candidate biomaterials in the laboratory and the biomaterials scientist attended the experimental surgery procedures. This interaction, along with the combined previous experiences of both groups, has resulted in the development of more complete protocols for the study of these biomaterials at our Medical Center. TECHNIQUES, RESULTS, AND DISCUSSION
Since the biomaterials science and clinical considerations are different for the porous alumina ceramic and the vitreous carbon implant biomaterials, they will be considered separately. Porous Alumina Ceramic
The biomaterials science protocol for the porous alumina ceramic included: 1) the engineering properties of the material; 2) a history of biocompatibility studies related to biomaterial-tissue interaction; 3) possible sources of the biomaterial and the quality control procedures of the producer; 4) the final (immediate presurgery) preparation of the materials including shaping, cleaning, and sterilizing; 5 ) limited animal testing to evaluate selected designs and procedural difficulties; and 6 ) the initial considerations for the clinical trials. Engineering Properties. The physical, mechanical, chemical and electrical properties of candidate biomaterials should be available. Testing procedures should, where possible, follow standard A S T M procedures. I n vitro testing under simulated biological conditions is also desirable. More specifically in outline form, data should be provided on the following properties. A. Physical and Mechanical Properties 1. Uniaxial tensile stress-strain properties including modulus of elasticity, yield, ultimate and fracture stress, elongation or reduction in area, and area under the stress-strain curve.
CERAMIC A N D VITREOUS CARBON IMPLANTS
I1
2.
B.
Fatigue strength including the stress versus number of cycles to failure for smooth and notched specimens. For porous specimens such as the oxide ceramics, the collection of this type data is experimentally difficult. 3. Fracture and impact properties for smooth and notched specimens. 4. Microstructure and surface topography including quantitative microscopy determinations of specific features such as porosity, interconnectivity of porosity, grain size, secondary phases or impurities, and surface cracks or roughness. 5. Bulk and surface hardness. 6 . Abrasion and wear characteristics. Chemical and Electrochemical Properties 1. Bulk chemistry. 2. Surface impurities for “as received” material. 3. Electrometric evaluation of surface as specified by the ASTM F4 committee on surgical implants. 4. Standard engineering evaluations of corrosion or degradation potentials. 5. Electrochemical evaluation under implant conditions simulated by mechanical testing.
The preimplantation testing of the material should, where applicable, include combined evaluations such as stress corrosion, combined stresschemical-electrical testing and simulated implantation site characterization of the implant design. This testing should be limited to tests that are specifically applicable to the implant and implant design. Such testing should be expanded where certain property related design limitations are indicated. If more than one material or a composite material is to be used for a given implant, certain interrelated properties such as relative electrochemical potential differences, possible abrasion and wear, local stress concentration, etc., should be considered. All implants considered for an experimental research program should be photographed prior to implantation so that the initial design and surface conditions are made a part of a permanent record. From the engineering data it should be possible to make decisions on the best possible test for routine quality control on the “as received” implants. Additionally, the data should provide ideas on the most critical implant conditions to be considered during the postimplantation evaluation period. If material or design related failures are experienced, the preimplantation characterization would provide direct methods for failure analysis and a rapid feedback for subsequent improvements in the material, the design, the surgical procedure or postsurgical care.
12
LEMONS
The microstructure of the porous alumina ceramic was considered in detail. Insufficient data were available on the three dimensional characteristics of the pore structure and an investigation into the microstructural properties was initiated. These studies are to be presented elsewhere [5]. Biocompatibility. Information on the biocompatibility of the porous oxide ceramics has been accumulating for the past several years [6-111. Previous investigations provide a basis for the tentative acceptance of the alumina ceramic as far as histological and toxological considerations are concerned. This information is somewhat confused by the inability to accurately define the chemistry of all samples; however, a relatively high purity alumina ceramic was used in several instances. It is realized that biomaterial evaluations are always subject to design considerations and specific design criteria and directed studies should always be included in any experimental program. The specific appliances to be studied in our program have been included in an animal study using canines and rabbits. Biomaterials Supply and Quality Control. A controlled porosity alumina ceramic is not routinely available. Therefore, a decision was made to go with a single source and to extensively characterize the selected biomaterial. It is intended to use this biomaterial as a model system for comparison with other porous ceramics available in the future. The source of the porous alumina ceramic used in our program is Dr. Stig Lyng.* These biomaterials were supplied in block form, 5 cm x 5 cm x 1 cm. Similar porous alumina ceramic has been investigated previously and showed good promise for porous biomaterial applications [ 121. The quality control on this material has been maintained under the directions of Dr. Lyng. Within the samples provided for our studies, the structure was relatively reproducible sample to sample throughout the material available. In our opinion, routine quality control from the supplier is fundamental to the future use of a biomaterial of this type. Biomaterials Final Shaping, Cleaning, and Sterilization. The fired alumina oxide ceramic is extremely hard. The shaping of appliance-like forms from the bulk material requires the use of diamond surfaced cutting tools. We found that the cutting and shaping of the material can be done with acceptable accuracy using standard dental equipment. When shaping the alumina ceramic, some debris from the metal back cutting disc was transferred to the ceramic. The debris was present along the surface and in some cases the debris migrated into the internal porosity of the highly porous biomaterial. Ultrasonic cleaning and washing did not completely remove the metallic deposits, especially at sites within the Dr. S. Lyng is Head of the Division of Inorganic Materials, Central Institute for Industrial Research, Oslo, Norway.
C E R A M I C A N D VITREOUS CARBON IMPLANTS
13
sample. A sequence of mineral acid treatments followed by a firing procedure resulted in a clean material. A thorough cleaning treatment is quite important to the subsequent application of this type biomaterial because toxic substances within the pores could adversely influence the biomaterial tissue interface and the long term stability of the associated tissues. After cleaning, the biomaterial was packaged and sterilized in a steam autoclave sterilizer. Packaging in sterile envelopes prevented the possible deposition of autoclave related debris onto the candidate implants. Animal Testing. The previous history of use of the porous ceramics in laboratory studies, animal testing studies, and clinical investigations provides a basis for tentative acceptance of this particular material. However, since our biomaterial porosity and designs were slightly different from previous experiments, it was decided to initiate a limited animal testing program. The main objectives of the animal studies were to evaluate simulated functional sites for our future clinical programs and to discover possible difficulties in handling this material at the surgery table. The applications tested were ridge augmentation in edentulous canines, segmental defects in canine mandibles, small hole defects in rabbit long bones and segmental defects along ribbit tibias. A number of procedural difficulties were encountered at the surgery table. The sterility of the surgical environment is fundamental to the long term success of these porous biomaterials. The basic problems in handling the biomaterial and maintaining sterility is complicated by the difficulties in placing the porous biomaterial into sites within the oral cavity. The placement of porous ceramic along the mandibular ridge of canines using both flap and tunnel techniques were investigated. Difficulties in avoiding unclean regions of the oral environment, and preventing the implant from touching the gingival tissues proved to be quite difficult for the larger implants.* Procedures were developed to avoid contamination of the porous implants. Additionally, the implant shape never seems to be perfect. There is a great desire to shape the implant at the time of surgery by breaking pieces from the structure. Although a clean break might be acceptable, other hazards exist with respect to partial fractures of this type biomaterial. Therefore, several implant shapes need to be available at the time of surgery. Another difficulty relates to the placement of the implant. In many cases, it is desirable to set the implant into the surgical site several times before final placement. In a wet environment the porous implant ma-
* The implants were shaped as 1 to 3 cm long one-half cyclinders. The inside of the cylinders were contoured to fit the mandibular ridge and the porous ceramic thickness varied from I to 3 m m
14
LEMONS
terials, if not infiltrated with blood in advance, tend to rapidly fill with the blood and other debris. This solution, if allowed to dry when the implant is subsequently removed from the surgical site, could possibly produce problems with respect to the filling of the pore network with ossified tissues. In some cases, the implant was placed several times and the blood mass within the porosity could have dried quite completely before final implantation. This difficulty should be avoided. Suggested solutions are to provide several of each implant size or to prefill the porosity of the implant with anticoagulated blood from the host [13]. Initial Clinical Studies. The initial clinical studies using the porous alumina ceramic as a ridge augmentation material are presently being considered. The porous biomaterials are under consideration for augmentation of mandibular ridges for the stabilization of standard dentures. Other investigators have conducted such programs using the porous ceramic and have found this to be a clinically acceptable procedure [ 141. The complete clinical protocol for this type application is a prerequisite to the subsequent use of this material for ridge augmentation. The preclinical trials, in the laboratory and in animal testing, provide a basis for limited and controlled clinical study. We feel that a multidisciplinary approach to this type of application is quite important to insure its future success. Vitreous Carbon
Many of the engineering properties and the biocompatibility criteria specifications have been developed for the vitreous carbon root replacement system currently available from a manufacturer [ 151. The engineering properties and biocompatibility data were reviewed for this candidate biomaterial prior to establishing a clinical protocol [16-181. Since this material is available for general clinical use, the engineering and biocompatibility criteria were tentatively accepted. It was decided however to conduct a limited laboratory program on this material associated with the quality control on this particular implant material. An investigation of the surface of the vitreous carbon root replacement systems, during the early stages of the availability of this material,* showed that some of the “as received” implants contained surface irregularities or small cracks along the carbon surface. Cross and longitudinal polished sections made at the location of several of these particular features showed open pathways or cracks that extended from the carbon surface to the inner metallic core. * These materials were received in early 1973 prior to the release of the Vitredent Root Replacement System for general dental applications.
CERAMIC AND VITREOUS CARBON IMPLANTS
15
The statistical information related to the incidence of visable surface features from the initially received vitreous carbon endosseous root replacement systems is listed in Table I . This data was immediately reported to the company and subsequent quality control procedures were initiated to eliminate this kind of feature from the materials available to the practicing dentist. A series of nondestructive examinations intended to uncover possible internal irregularities in the materials using standard industrial x-ray examination procedures was initiated. The x-ray micrographs of the specimens were taken along the three principle directions of each sample. The thickness, width, and length films were examined using a limited field light source and a stereo microscope. The results of the x-ray nondestructive of these implants are summarized in Table 11. The surface evaluation and the nondestructive x-ray examination of the vitreous carbon root replacement system showed a number of the early “as received” implants t o contain irregularities that might jeopardize the future success of this implant for clinical use. The biomaterials science protocol for the vitreous carbon implant thus includes an initial screening nondestructive type examination before these particular implants are provided to the dental clinic. A complete protocol for the prescreening, placement and post evaluation of these particular implants has been developed within the Dental School. At this time, a series of about 40 vitreous carbon dental root replacement systems are available for the clinical programs within our School of Dentistry. The biomaterials science protocol for all of the materials provided for experimental surgical use included the characterization of the implants and photography of the surface of the implants prior to making the implants available to the surgical disciplines. The photographs of these implant specimens provides a permanent record of the materials and surface conditions prior to clinical implantation. If any of these implants were unsuccessful for some reason, the preevaluation would provide a closed loop system for the postimplantation evaluation and hopefully a
TABLE I Stereomicroscopic Examination of Vitreous Carbon Root Replacement Systems.
Group 1
2 3
Number of samples Number of surface examined (1-7x) “crack-like” features 85 71 48
5 7 10
Comments Early design-no large grooves Early design-no large grooves New design-with large grooves
LEMONS
16
TABLE I1 Industrial Type X-ray Examination of Vitreous Carbon Implant Systems
Group
Number of samples examined
Number of internal irregularities found
1-3
47
8
Comments New design-with large grooves Samples selected by size from previously stereomicroscopically examined groups.
meaningful failure analysis. We always hope that such analyses will not be necessary. References [ l ] P. G. Laing, Orthoped. Clin. No. Amer., 4 , (2) 249 (1973). [2] D. F. Williams, Eiomed. Eng. 260 (June, 1971). [3] S. F. Hulbert, J . Eiomed. Muter. Res. Symp. No. 4 , 1 (1973). [4] D. E. Grenoble and R. L. Kim. Ariz. State DentulJ., (1973). [ 5 ] J. E. Lemons and W. C . Richardson. ZADR Abstr.. (March, 1974), in press. [6] L. Smith, Arch. Surg., 87, 653, (1963). [7] Use of Ceramics in Surgery, S. F. Hulbert and F. A. Young, Eds., Gordon and Breach, New York, 1970. [8] G. A. Graves, R. L. Hentrich, H. G . Stein, and P. K. Pajpai, J . Eiomed. Muter. Res. Symp. No. 2 (part I), 161 (1971). [9] J . Autian and J . E. Hamner, III., J . Dent. Res., 51, 880 (1972). [lo] J . J . Klawitter, and S. F. Hulbert, J . Biomed. Muter. Res. Symp. No. 2, (part l), 161 (1971). [ l l ] P. Predecki, A. Auslaender, J . E. Stephan, V . L. Mooney, and C. Stanitski, J . Eiomed. Mater. Res. 6 ( 9 , 375 (1972). [12] S. Lyng, Research Program Report, Clemson University, Clemson, S. Car., 1973. [I31 C. A. Homsy, J . N. Kent, and E. C. Hinds,J. Amer. Dent. Ass., 86, 817 (1973). [14] R. G. Topazian, W. B. Hammer, C. D. Talbert, and S. F. Hulbert, J . Eiomed. Muter. Res. Symp. No. 2 (part 2), 31 1 (1972). [ 151 The Vitredent Tooth Root Replacement System, Prosthetic and Surgical Consideration, Vitredent Corporation, 1973. [I61 J . Bensen,J. Eiomed. Muter. Res. Syrnp. No. 2 (part 1). 41 (1972). [17] V. Mooney, P. K. Predecki, J. Renning, and J. Gray, J . Eiomed. Muter. Res. Symp. No. 2 (part I ) , 143 (1972). [I81 K. L. Stewart and R. M. Meffert, Continuing Education Course, “Vitreous Carbon Implants-A Simple Technique,” Birmingham, Alabama (Sept., 1973).
