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Ceramic-coated subperiosteal implants. Part I. A pilot study
Ceramic-coated A pilot
subperiosteal
implants.
Part I.
study
and David Benson, D.D.S., M.S.** M. H. Reisbick, D.M.D., MS.,* School of Dentistry, University of California, Los Angeles, Calif.
S
ubperiosteal implants provide a practical treatment approach for the patient who has little or no remaining alveolar bone and cannot tolerate a mandibular (conventional) complete denture. The indications for implant dentures and the favorable and unfavorable aspects of this type of treatment have been discussed in the literature.‘-* The subperiosteal implant is attached directly to the body of the mandible. The stresses of mastication are transmitted to the underlying connective tissue and bone. Because the implant is securely fixed and the pressure placed on the soft tissue is minimal, patients with implant dentures can exert higher masticatory forces than patients with conventional dentures.’ The enthusiastic patient acceptance of implant dentures suggests a continuing increase in patient demand.:’ Permanent fixation of subperiosteal implants occurs by dense, collaginous, fibrous tissue encapsulation around the framework.” An epithelial cuff may form around the post of the substructure that penetrates the oral mucosa. This cuff has been compared to the epithelial cuff around a natural tooth.’ Although the reported success of subperiosteal implants is high, the criteria for determining success are poorly defined. Certain problems are frequently encountered with the mandibular subperiosteal denture implant that are not necessarily the immediate cause of failure but may lead to the eventual removal of the implant. The most common problem is breakdown of the oral mucosa over the metal substructure.” This exposes the metal framework and establishes a route for oral fluids to penetrate below the mucosa. Exposure of the substructure also presents a pathway for the downgrowth of epithelium which may result in bone resorption8 Accumulation of plaque and calculus on the substructure post may cause inflammation and loss of a *Assistant Professor and Chairman, Biomaterials Section, Division of Restorative Dental Sciences. **Assistant Professor, Fixed Prosthodontics Section, Division of Restorative Dental Sciences. 204
Volume 3 1 Number 2
Ceramic-coated
subperiosteal
implants
205
Fig. 1. Pre-extraction site. Fig. 2. Postextraction site. Fig. 3. Postsurgical site after eight weeks of healing.
firm epithelial cuff. Oral fluids and debris may then pass between the post and epithelium causing an infection of the underlying tissue. There is a need to investigate dental implants which will allow tissue ingrowth and attachment directly into the substructure. Ingrowth directly into the substructure would : (a) enhance the permanent fixation of the substructure beneath the mucosa, (b) minimize exposure of the substructure framework, (c) minimize pathways for epithelial downgrowth, and (d) encourage the formation of a tight connective tissue seal around the substructure post at the point of oral penetration thus minimizing seepage of oral fluids into the underlying tissue bed. To prevent the formation of encapsulating tissues and to aid in attachment, titanium implants covered with a porous surface were placed in dogs. This surface was found to allow ingrowth and prevent the encapsulation reported by other investigators.” In 1963, a porous ceramic material was found to be well tolerated by rabbit bone.” Porosity in ceramic materials has been found to allow ingrowth in soft tissues, while impervious ceramics implanted in soft tissue were found to be encased by fibers.‘l
206
Reisbick
Fig. 4. Bilateral
impression
Fig. 5, Cast chrome-cobalt Fig. 6. (Left)
J. Prosthet. Dent. February. 1974
and Benson
Ceramic-coated
of exposed alveolar
ridges.
implants. implant.
(Right)
Control
chrome-cobalt
implant.
Hulbert and associates’2 investigated the growth of tissue into porous ceramic pellets and concluded that the minimum interconnective pore size necessary for tissue ingrowth into calcium aluminate was 5 to 15 p for fibrous tissue, 20 to 50 p for osteoid tissue, and about 100 p for mineralized bone. Porous metals and ceramics that have been experimentally studied are fashioned into specific geometric shapes, usually cylinders or disks. Porous metals, produced by the powder process (compressing and sintering), and porous ceramics cannot be conveniently fabricated into the complicated shapes necessary to satisfy the requirements of a subperiosteal implant. By coating a cast structure, complicated shapes containing porous surfaces may be produced. Since there is evidence to demonstrate tissue compatibility of ceramic materials, the feasibility of using ceramic-coated Vitallium implants became worthy of investigation. Metals have been used traditionally to replace or mend different body parts where the predominant requirement is one of strength. Ceramics have been largely disregarded in the past for use in the body due to the characteristic brittleness and low flexural strength they exhibit.‘,: Therefore, the possibility of fracture of ceramic coatings when the implant is subjected to stress is a serious question. However, the stress level required to crack the coating increases in proportion to the yield point of the metal used. It has been observed in a low-carbon steel that the stress necessary for a ceramic coating to crack is only about 25,000 p.s.i., but in steel with a high yield point, a stress approaching 100,000 p.s.i. is required.14 Porous ceramic implant materials should be of sufficient porosity to permit tissue invasion to achieve proper mechanical attachment and yet meet the following requirements: ” (a i must be inert, (b) must not be modified by the body, (c) must b e noninflammatory, (d) must be noncarcinogenic, (c) must not produce allergy or sensitivity, (f) must be capable of resisting mechanical strains, (g) must have a reasonable cost for fabrication, and (h) must be capable of being sterilized. Ceramiccoated metals seem to meet these requirements. PURPOSE OF THIS STUDY Most materials
studies to date have investigated the use of porous ceramics for implant by placing these implants in surgically sterile sites-either in long bones
Ceramic-coated subperiosteal implants
Fig. 7. Low-power
magnification
of chrome-cobalt
Fig. 8. Low-power
magnification
of alumina
207
surface.
surface on a chrome-cobalt
casting.
or subcutaneous tissue. Since porous materials might readily gather dental plaque, which could be destructive to surrounding tissue, orthotopic placement of the implants is necessary for practical evaluation. There is no reported work investigating the feasibility of using subperiosteal implants with porous surfaces. Therefore, the objective of this study was to evaluate the response of monkey tissue to coatings of porous alumina (A120R) that were applied to chrome-cobalt subperiosteal denture implants.
MATERIALS AND METHODS Three adult stump-tail monkeys were prepared to receive bilateral subperiosteal implants by removal of their mandibular molars along with the alveolar bone surrounding these teeth (Figs. 1 and 2). Healing was allowed to progress for eight weeks (Fig. 3). The edentulous areas were then surgically reopened, and impressions were made of the mandible (Fig. 4). Chrome-cobalt implants were then fabricated (Fig. 5). It has been recognized clinically that the substructure framework should not encroach into the thin lingual tissue. However, for this project, the implants were designed to extend over the lingual ridge crest to provide the severest test conditions.
208
Reisbick
Fig. 9. Surgical
J. I’rosthet. Dent. Februaq, 1974
and Benson
insertion
and temporary
Fig. 10. The tissue is appositioned Fig. 11. A control
implant
Fig. 12. An experimental
fixation
with retaining
screw.
and sutured over the implant.
removed after three months. implant
removed after three months.
Three of the irnplants rereivcd a coating of alumina. Each animal received a control (CrCo‘I and an experimental (Al,O,+--CrCoj implant (Fig. 6). The surface of each material is shown (Figs. 7 and 8) The implants kvere inserted and held in place by a retaining scre\\’ (Fig. 9). The soft tissue was sutured to bring the \\,ound edges into close apposition (Fig. 10). The clinical success of each implant was recorded by evaluating mobility of the implant along with general tissue health. Photographs were made at two-week intervals. No attempt was made to make dentures for the animals being studied. The intent of the investigation was to elraluate only the tissue reaction to Vitailium and alurnina-coated Vitallium. After three months, thr implants in monkey No. 1 were mobile and appeared to be failing. ‘This ~vas due to traumatic occlusion caused by extrusion of the maxillary molars opposing the implant posts. The implants were removed and examined microscopically.
RESULTS The tissue surrounding the removed alumina implant was tenaciously attached. Adherence of tissue fibers was pronounced on the experimental implant but not on the control implant as shown in (Figs. 11 and 12). Fig. 13 shows the site three months after insertion of one experimental implant.
;o,lkd~~T:,
Ceramic-coated
Fig. 13. An experimental
implant
subperiosteal
implants
209
after three months.
DISCUSSION
The animals used in this study will be sacrificed and histologic evaluations made of the tissues surrounding the implants. At this time, no definite conclusion can be formed. The histologic evidence will yield additional knowledge on the nature of the attachment. SUMMARY A pilot study to investigate the effect of alumina-coated subperiosteal implants is reported. Initial clinical results are encouraging; there is evidence to indicate that a direct attachment occurs to the alumina surface. Histologic evidence will be reported at a later date. Further investigation studying the effect of other coatings, as well as different pore sizes, on the success of subperiosteal implants is planned. References DENT. 10: 1118 1. Doner, A. G.: Implant Dentures: Surgical-Favorable, J. PROSTHET. 1126, 1960. 2. Archer, W. H.: Implant Dentures: Surgical-Unfavorable-Qualified, J. PROSTHET. DENT. 10: 1127-1131, 1960. 3. Bodine, R. L.: Implant Dentures: Prosthodontic-Favorable, J. PROSTHET. DENT. 10: 1132-l 142, 1960. 4. Boucher, C. 0.: Implant Dentures: Prosthodontic-Unfavorable, J. PROSTHET. DENT. 10: 1143-1148, 1960. 5. Knowlton, J. P.: Masticatory Pressures Exerted With Implant Dentures as Compared With Soft-Tissue-Borne Dentures, J. PROSTHET. DENT. 3: 721-726, 1953. 6. Bodine, R. L., and Mohammed, C. I.: Histologic Studies of a Human Mandible Supporting an Implant Denture, J. PROSTHET. DENT. 21: 203-214, 1969. 7. Ponitz, D. P., Gershkoff, A., and Wells, N.: Passage of Orally Administered Tetracycline Into the Gingival Crevice Around Natural Teeth and Around Protruding Subperiosteal Implant Abutments in Man, Dent. Clin. North Am. 14: 125-136, 1970. 8. Bodine, R. L.: Implant Dentures: Follow-up after 7-10 Years, J. Am. Dent. Assoc. 67: 352-363, 1963.
210
Reisbick
and Benson
J. Prosthet. Dent. February, 1974
9. Beder, 0. E., and Eade, G.: An Investigation of Tissue Tolerance to Titanium Metal Implants in Dogs, Surgery 39: 470-473, 1956. 10. Smith, L.: Ceramic-Plastic Material as a Bone Substitute, Arch. Surg. 87: 653-661, 1963. 11. Morrison, S. J.: Tissue Reaction to Three Ceramics of Porous and Non-porous Structures, M.S. thesis, Clemson University, Clemson, S. C.. 1971. J. J., Talbert, C. D., and 12. Hulbert, S. F., Young, F. H., Mathews, R. S., Klawitter, Stelling, F. H.: Potential of Ceramic Materials as Permanently Skeletal Prosthesis, J. Biomed. Mater. Res. 4: 433-456, 1970. 13. Hulbert, S. F., Skinner, H. B., Leonard, R. B., and Klawitter, J. J.: Attachment of Prosthesis to the Musculo-skeletal System by Tissue Ingrowth and Mechanical Interlocking, Clemson University Symposium, Clemson, S. C., April 3-7, 1972. 14. Deringer, W. A.: Investigation of Tensile Properties of Various Steels After Enameling, Proc. Porcelain Enamel Inst. 13: 60-72, 1950. 15. Roberts, A. C.: Modern Materials: Their Contribution and Use in the Human Body, Dent. Techn. 21: 95-100, 1968. SCHOOL OF DENTISTRV UNIVERSITY OP CALIFORSIA Los ANGELES. CALIF. 90024
subperiosteal
implants.
Part I.
study
and David Benson, D.D.S., M.S.** M. H. Reisbick, D.M.D., MS.,* School of Dentistry, University of California, Los Angeles, Calif.
S
ubperiosteal implants provide a practical treatment approach for the patient who has little or no remaining alveolar bone and cannot tolerate a mandibular (conventional) complete denture. The indications for implant dentures and the favorable and unfavorable aspects of this type of treatment have been discussed in the literature.‘-* The subperiosteal implant is attached directly to the body of the mandible. The stresses of mastication are transmitted to the underlying connective tissue and bone. Because the implant is securely fixed and the pressure placed on the soft tissue is minimal, patients with implant dentures can exert higher masticatory forces than patients with conventional dentures.’ The enthusiastic patient acceptance of implant dentures suggests a continuing increase in patient demand.:’ Permanent fixation of subperiosteal implants occurs by dense, collaginous, fibrous tissue encapsulation around the framework.” An epithelial cuff may form around the post of the substructure that penetrates the oral mucosa. This cuff has been compared to the epithelial cuff around a natural tooth.’ Although the reported success of subperiosteal implants is high, the criteria for determining success are poorly defined. Certain problems are frequently encountered with the mandibular subperiosteal denture implant that are not necessarily the immediate cause of failure but may lead to the eventual removal of the implant. The most common problem is breakdown of the oral mucosa over the metal substructure.” This exposes the metal framework and establishes a route for oral fluids to penetrate below the mucosa. Exposure of the substructure also presents a pathway for the downgrowth of epithelium which may result in bone resorption8 Accumulation of plaque and calculus on the substructure post may cause inflammation and loss of a *Assistant Professor and Chairman, Biomaterials Section, Division of Restorative Dental Sciences. **Assistant Professor, Fixed Prosthodontics Section, Division of Restorative Dental Sciences. 204
Volume 3 1 Number 2
Ceramic-coated
subperiosteal
implants
205
Fig. 1. Pre-extraction site. Fig. 2. Postextraction site. Fig. 3. Postsurgical site after eight weeks of healing.
firm epithelial cuff. Oral fluids and debris may then pass between the post and epithelium causing an infection of the underlying tissue. There is a need to investigate dental implants which will allow tissue ingrowth and attachment directly into the substructure. Ingrowth directly into the substructure would : (a) enhance the permanent fixation of the substructure beneath the mucosa, (b) minimize exposure of the substructure framework, (c) minimize pathways for epithelial downgrowth, and (d) encourage the formation of a tight connective tissue seal around the substructure post at the point of oral penetration thus minimizing seepage of oral fluids into the underlying tissue bed. To prevent the formation of encapsulating tissues and to aid in attachment, titanium implants covered with a porous surface were placed in dogs. This surface was found to allow ingrowth and prevent the encapsulation reported by other investigators.” In 1963, a porous ceramic material was found to be well tolerated by rabbit bone.” Porosity in ceramic materials has been found to allow ingrowth in soft tissues, while impervious ceramics implanted in soft tissue were found to be encased by fibers.‘l
206
Reisbick
Fig. 4. Bilateral
impression
Fig. 5, Cast chrome-cobalt Fig. 6. (Left)
J. Prosthet. Dent. February. 1974
and Benson
Ceramic-coated
of exposed alveolar
ridges.
implants. implant.
(Right)
Control
chrome-cobalt
implant.
Hulbert and associates’2 investigated the growth of tissue into porous ceramic pellets and concluded that the minimum interconnective pore size necessary for tissue ingrowth into calcium aluminate was 5 to 15 p for fibrous tissue, 20 to 50 p for osteoid tissue, and about 100 p for mineralized bone. Porous metals and ceramics that have been experimentally studied are fashioned into specific geometric shapes, usually cylinders or disks. Porous metals, produced by the powder process (compressing and sintering), and porous ceramics cannot be conveniently fabricated into the complicated shapes necessary to satisfy the requirements of a subperiosteal implant. By coating a cast structure, complicated shapes containing porous surfaces may be produced. Since there is evidence to demonstrate tissue compatibility of ceramic materials, the feasibility of using ceramic-coated Vitallium implants became worthy of investigation. Metals have been used traditionally to replace or mend different body parts where the predominant requirement is one of strength. Ceramics have been largely disregarded in the past for use in the body due to the characteristic brittleness and low flexural strength they exhibit.‘,: Therefore, the possibility of fracture of ceramic coatings when the implant is subjected to stress is a serious question. However, the stress level required to crack the coating increases in proportion to the yield point of the metal used. It has been observed in a low-carbon steel that the stress necessary for a ceramic coating to crack is only about 25,000 p.s.i., but in steel with a high yield point, a stress approaching 100,000 p.s.i. is required.14 Porous ceramic implant materials should be of sufficient porosity to permit tissue invasion to achieve proper mechanical attachment and yet meet the following requirements: ” (a i must be inert, (b) must not be modified by the body, (c) must b e noninflammatory, (d) must be noncarcinogenic, (c) must not produce allergy or sensitivity, (f) must be capable of resisting mechanical strains, (g) must have a reasonable cost for fabrication, and (h) must be capable of being sterilized. Ceramiccoated metals seem to meet these requirements. PURPOSE OF THIS STUDY Most materials
studies to date have investigated the use of porous ceramics for implant by placing these implants in surgically sterile sites-either in long bones
Ceramic-coated subperiosteal implants
Fig. 7. Low-power
magnification
of chrome-cobalt
Fig. 8. Low-power
magnification
of alumina
207
surface.
surface on a chrome-cobalt
casting.
or subcutaneous tissue. Since porous materials might readily gather dental plaque, which could be destructive to surrounding tissue, orthotopic placement of the implants is necessary for practical evaluation. There is no reported work investigating the feasibility of using subperiosteal implants with porous surfaces. Therefore, the objective of this study was to evaluate the response of monkey tissue to coatings of porous alumina (A120R) that were applied to chrome-cobalt subperiosteal denture implants.
MATERIALS AND METHODS Three adult stump-tail monkeys were prepared to receive bilateral subperiosteal implants by removal of their mandibular molars along with the alveolar bone surrounding these teeth (Figs. 1 and 2). Healing was allowed to progress for eight weeks (Fig. 3). The edentulous areas were then surgically reopened, and impressions were made of the mandible (Fig. 4). Chrome-cobalt implants were then fabricated (Fig. 5). It has been recognized clinically that the substructure framework should not encroach into the thin lingual tissue. However, for this project, the implants were designed to extend over the lingual ridge crest to provide the severest test conditions.
208
Reisbick
Fig. 9. Surgical
J. I’rosthet. Dent. Februaq, 1974
and Benson
insertion
and temporary
Fig. 10. The tissue is appositioned Fig. 11. A control
implant
Fig. 12. An experimental
fixation
with retaining
screw.
and sutured over the implant.
removed after three months. implant
removed after three months.
Three of the irnplants rereivcd a coating of alumina. Each animal received a control (CrCo‘I and an experimental (Al,O,+--CrCoj implant (Fig. 6). The surface of each material is shown (Figs. 7 and 8) The implants kvere inserted and held in place by a retaining scre\\’ (Fig. 9). The soft tissue was sutured to bring the \\,ound edges into close apposition (Fig. 10). The clinical success of each implant was recorded by evaluating mobility of the implant along with general tissue health. Photographs were made at two-week intervals. No attempt was made to make dentures for the animals being studied. The intent of the investigation was to elraluate only the tissue reaction to Vitailium and alurnina-coated Vitallium. After three months, thr implants in monkey No. 1 were mobile and appeared to be failing. ‘This ~vas due to traumatic occlusion caused by extrusion of the maxillary molars opposing the implant posts. The implants were removed and examined microscopically.
RESULTS The tissue surrounding the removed alumina implant was tenaciously attached. Adherence of tissue fibers was pronounced on the experimental implant but not on the control implant as shown in (Figs. 11 and 12). Fig. 13 shows the site three months after insertion of one experimental implant.
;o,lkd~~T:,
Ceramic-coated
Fig. 13. An experimental
implant
subperiosteal
implants
209
after three months.
DISCUSSION
The animals used in this study will be sacrificed and histologic evaluations made of the tissues surrounding the implants. At this time, no definite conclusion can be formed. The histologic evidence will yield additional knowledge on the nature of the attachment. SUMMARY A pilot study to investigate the effect of alumina-coated subperiosteal implants is reported. Initial clinical results are encouraging; there is evidence to indicate that a direct attachment occurs to the alumina surface. Histologic evidence will be reported at a later date. Further investigation studying the effect of other coatings, as well as different pore sizes, on the success of subperiosteal implants is planned. References DENT. 10: 1118 1. Doner, A. G.: Implant Dentures: Surgical-Favorable, J. PROSTHET. 1126, 1960. 2. Archer, W. H.: Implant Dentures: Surgical-Unfavorable-Qualified, J. PROSTHET. DENT. 10: 1127-1131, 1960. 3. Bodine, R. L.: Implant Dentures: Prosthodontic-Favorable, J. PROSTHET. DENT. 10: 1132-l 142, 1960. 4. Boucher, C. 0.: Implant Dentures: Prosthodontic-Unfavorable, J. PROSTHET. DENT. 10: 1143-1148, 1960. 5. Knowlton, J. P.: Masticatory Pressures Exerted With Implant Dentures as Compared With Soft-Tissue-Borne Dentures, J. PROSTHET. DENT. 3: 721-726, 1953. 6. Bodine, R. L., and Mohammed, C. I.: Histologic Studies of a Human Mandible Supporting an Implant Denture, J. PROSTHET. DENT. 21: 203-214, 1969. 7. Ponitz, D. P., Gershkoff, A., and Wells, N.: Passage of Orally Administered Tetracycline Into the Gingival Crevice Around Natural Teeth and Around Protruding Subperiosteal Implant Abutments in Man, Dent. Clin. North Am. 14: 125-136, 1970. 8. Bodine, R. L.: Implant Dentures: Follow-up after 7-10 Years, J. Am. Dent. Assoc. 67: 352-363, 1963.
210
Reisbick
and Benson
J. Prosthet. Dent. February, 1974
9. Beder, 0. E., and Eade, G.: An Investigation of Tissue Tolerance to Titanium Metal Implants in Dogs, Surgery 39: 470-473, 1956. 10. Smith, L.: Ceramic-Plastic Material as a Bone Substitute, Arch. Surg. 87: 653-661, 1963. 11. Morrison, S. J.: Tissue Reaction to Three Ceramics of Porous and Non-porous Structures, M.S. thesis, Clemson University, Clemson, S. C.. 1971. J. J., Talbert, C. D., and 12. Hulbert, S. F., Young, F. H., Mathews, R. S., Klawitter, Stelling, F. H.: Potential of Ceramic Materials as Permanently Skeletal Prosthesis, J. Biomed. Mater. Res. 4: 433-456, 1970. 13. Hulbert, S. F., Skinner, H. B., Leonard, R. B., and Klawitter, J. J.: Attachment of Prosthesis to the Musculo-skeletal System by Tissue Ingrowth and Mechanical Interlocking, Clemson University Symposium, Clemson, S. C., April 3-7, 1972. 14. Deringer, W. A.: Investigation of Tensile Properties of Various Steels After Enameling, Proc. Porcelain Enamel Inst. 13: 60-72, 1950. 15. Roberts, A. C.: Modern Materials: Their Contribution and Use in the Human Body, Dent. Techn. 21: 95-100, 1968. SCHOOL OF DENTISTRV UNIVERSITY OP CALIFORSIA Los ANGELES. CALIF. 90024