Eleven-year study of hydroxyapatite implants

SECTION EDITORS

Eleven-year study of hydroxyapatite implants H. W. D e n i s s e n , D . D . S . , Ph.D.,* W. K a l k , D . D . S . , Ph.D.,** A. A. H. V e l d h u i s , D . D . S . , Ph.D.,*** a n d A. v a n d e n H o o f f , M.D., Ph.D.****

University of N~megen, Dental School, N~megen, The Netherlands An l l - y e a r clinical r e s e a r c h study w a s conducted w i t h both u n l o a d e d bulk h y d r o x y a p a t i t e i m p l a n t s and loaded h y d r o x y a p a t i t e - c o a t e d titanium implants. A total of 102 s u b m e r g e d bulk h y d r o x y a p a t i t e i m p l a n t s w e r e placed after extraction of teeth to m a i n t a i n the v o l u m e of the r e s i d u a l a l v e o l a r ridge by their p h y s i c a l presence. All 21 i m p l a n t s under fixed partial d e n t u r e s and 51 of 81 i m p l a n t s under l o w e r c o m p l e t e d e n t u r e s r e m a i n e d submucosal. A total of 71 h y d r o x y a p a t i t e - c o a t e d titanium i m p l a n t s w e r e connected w i t h p e r m u c o s a l s u p e r s t r u c t u r e s by use of a t w o - s t a g e method. Modifications in d e s i g n and in i m p l a n t a t i o n technique w e r e required. This l o n g - t e r m r e s e a r c h indicates that cylindrical h y d r o x y a p a t i t e i m p l a n t s are reliable d e v i c e s as natural tooth root s u b s t i t u t e s that bond directly to bone i n s t e a d of s i m p l y being o s s e o i n t e g r a t e d . (J PROSTHET DENT 1989;61:706-12.)

H y d r o x y a p a t i t e implants have been used both as submerged implants and as endosteal implants with a transmucosal superstructure. 1-3 The submerged hydroxyapatite implant consists of bulk hydroxyapatite (bulk HA) ceramic only (Fig. 1). Bulk HA implants were placed as supports for the cortical plates after extraction of teeth to preserve the volume of the ridge by acting as space maintainers. It has become evident t h a t they do not prevent resorption of the cortical plates. Histologic findings suggest t h a t a direct and intimate contact develops between crystals of the hydroxyapatite ceramic and the newly formed bone matrix t h a t completely fills the space between the i m p l a n t and the cortical plate. 4 The question remains as to whether the bonding at the interface is the result of physicochemical interaction between collagen of the bone and hydroxyapatite crystals of the implant. Clinically, bonding occurs at the interface, allowing an intimate contact between the synthetic ceramic material and the living alveolar bone. The hydroxyapatite implant destined as a substructure for a future transmucosal superstructure is made of hydroxyapatite ceramic reinforced with a titanium core. H y d r o x y a p a t i t e / t i t a n i u m (HA/TI) implants were used as abutments for splints under overdentures and as abutments for crowns (Fig. 2). Contrary to other implant

*Associate Professor, Department of Prosthodontics and Maxillofacial Prosthetics. **Professor and Head, Department of Prosthodontics and Maxillofacial Prosthetics. ***Chief Resident, Clinic for Dentally Handicapped Patients, Amsterdam Public Health Service. ****Professor, Department of Histology and Bone Biology, University of Amsterdam. 706

F i g . 1. Implantation of bulk HA implants in mandible of patient immediately after extraction of teeth. Note inverted cone shape of implants with sharp cervical edges.

designs, the H A / T I implant has a smooth cylindrical design, which is considered a definite advantage. To date, the fixation of implants in alveolar bone has always been achieved with some type of purely mechanical retention; t h a t is, the device is kept in place as a result of its shape. 5 Implants are secured to the bone by screws, pins, or spirals. Alternatively, bone is p e r m i t t e d to grow into porous surfaces or holes of specially designed blades. 6 Bone is a living tissue and tends to respond to fixation devices by actively changing its structure, particularly by undergoing resorption. When this occurs, the implant can become unstable and will sooner or JUNE 1989

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IMPLANTS

F i g 2. Radiograph of mandible of patient with four HA/T1 implants. Hydroxyapatite coaling interfaces with alveolar bone, and l itanium core lends strength and serves as anchoring site for future superstructure.

later be lost. Williams and R~af~ stated, "Would it not be better, m fact, to devi~-e an artificial system that could be intrinsically incorporated into tl',e h u m a n system, without resorting to an intermediate fastening device, wherein many of the problems arise?" It would be advisahle to avoid mechanical fixation in the bone by complicated designs. An alveolar bone implant should preferably have a simple shape, a smooth surface, and be bonded strongly t(, living b,me. The H A / T I implant ridfills these requiremen,'s because the bone-contacting surface of the implant eonsisls of hydroxyapatite. The implant can also be small and sm,ng because of the titanium core. This article discusses results, obtained over a period of l 1 years of clinical use ~:f hydrox~'apatite implants.

MATERIAL AND METHODS B u l k HA i m p l a n t s Bulk HA implants were produced from hydroxyapatite ceramic powder as described earlier by Denissen et al. s Two categories of patients were treated with bulk HA implants. Category I: Patienls with six or more teeth remaining in the mandible that needed extraction because of a poor periodontal condition as shown by mobility of the teeth in three directions_ The patients required mandibular complete immediate dentures_ Immediately after tooth extraction, the implants were placed into the empty sockets and the gingiva was sutured, submerging the implants. The bulk HA implants were placed between the vestibular and the lingual cortical bone plates of the ridge, which still was high and well rounded_ The underly ing principle is to maintain the volume THE JOURNAL

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of the edentulous ridge by introducing a physical barrier against horizontal movement of the cortical plates toward each other (Fig. 3). Categ~Jry 2: Patients who had one or two teeth in the anterior region of the mouth that had to Le extracted because of draining fistula.? after endodontic treatment. Immediately after tooth extraction, bulk HA implants were inserted in the sockets of the extracted teeth to maintain the vestibular curvature of the ridge. Thereafter a three- or four-unit fixed partial denture was placed.

HA/TI i m p l a n t s The HA/TI implants consisted of a cemented core of titanium with a coating of hydroxyapatite ceramic_ Two categories of patients received HA/TI implants: Catego13' I: Patients who for a long period of time experienced problems with the mandibular denture because of an atrophic ridge. Some patients, in an earlier phase, had experienced vestibuloplasty with a skin graft to achieve augmentation of the alw~olar process. All of Lhese patients were treated under local anesthesia. In the vestibulum of the remaining alveolar process, an incision was; made in the mucosa and the residual ridge was exposed. F, mr implant sockets were prepared by a standardized technique. 9 The axes of the implants were placed 6 mm from each other in the region between the mental foramen of the atrophic mandible. The cylindrical implants were carefully inserted into the prepared sockets witlhout screwing or tapp:ng. The flap was repositioned and the incision was sutured. After 4 to 6 months the implants were provided with posts {hat were connected 707

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F i g . 3. A, Principle of ridge maintenance demonstrated 10-year subject after exposure of part of lower anterior ridge with bulk HA implant. At site of implant, lingual and vestibular cortical bone plates are physically kept apart by HA implant, while at site where no implant is present, cortical plates have collapsed. B, Smooth HA implant is maintained in bone without mechanical retention. I m p l an t is not simply osseointegrated but chemically bonded to bone. Forceful removal gives same clinical sensation as removal of ankylosed natural tooth root.

Table I. Bulk HA after 11 years Position

Placed

Under full lower dentures Under fixed partial dentures

81 21

Submucosal

Permucosal

51 21

Lost

10 --

20 --

Tab l e II. H A / T I implants after 8 years With

Position

Placed

Under overdentures Freestanding implant crown Implant crown splinted

56 3 12

super-structure

52 3 12

with a splint (Figs. 4 and 5). T h e t r e a t m e n t was completed with the placement of an overdenture. Early in this research project, retention of the denture was achieved by means of a Dolder or a Rider construction. Later, preference was given to a ferromagnetic splint with magnets (Dyna Dental Engineering BV, Bergen, The Netherlands) in the mandibular denture (Fig. 6). Category 2: Patients with one or two teeth missing. Instead of a three- or four-unit fixed partial denture, an alternative t r e a t m e n t was suggested to these patients. Th e

708

Without super-structure

4 ---

Ti-cere lost

Fracture post

15 1 --

-1 --

t r e a t m e n t included the implantation of one or two submerged H A / T A implants. After 6 months, a transmucosal post and core and crown were placed, and a choice was made whether to leave the crown freestanding or to splint it to one adjacent tooth.

Evaluation Every 3 months a clinical examination was performed, and every 6 months intraoral radiographs were made by using the short cone technique.

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Fig. 4. Mandible of patient with four transmucosal posts connected to HA/TI implants. Not~: healthy mucosal cuffs around cervical portions of posts. Fig. 5. Removable splint connected to posts, 5 years after placement in mandible ~f patient_ Overdenture is retained with Rider system to splint. Fig. 6. Ferr,~magnetic splint in mandible ol patient with skin transplant. Splint ~'orr,~.sponds with ~nagnets in overdenture_ Fig. 7. P a t i e n t with six permucosal bulk HA implants in mandible_ Implants were placed Tl0 years ago and have been permucosal for past 4 years. Implants lay m a "basket" of mHcop~riosteal tissue while ankylosed to bone. It was not possible to remove implants, l!pper surfaces of ir~plants are worn hy denture base. However, implam~s still m a i n t a i n bulk ~f ridg~ by their physical presence.

RESULTS Bulk HA implants under mandibular complete dentures During the first observation period of 5 years, 16 of 81 ira plants placed in 11 palients had become permucosal but were ankylosed to the bone and therefore could not be removed. A cuff of mucosal tissue had formed around the neck of these implants. Of these 16 implants, four became loose and were lost. In the second observation period (5 to 11 years after im plantation) 16 implants of the remaining 77 were lost. Ten

T i l E J O U R N A L OF P R O S T H E T I C D E N T I S T R Y

of the implants that were still present were h)und to be permucosal and strongly attached to the bone (Fig. 7). Table I summarizes the results. It should be noted that 28 implants were lost during the observation period of l 1 years because of the death of three of the elderly patients with the implants still in the mouth. Some patients stated that the loss . f implants left a ternporary feeling similar to that of a sore spot caused by the pressure of the denture. After implant loss, healing occurred without further problems. Other patients were totally unaware that implants had become permucosal or were lost.

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Fig. 8. Radiograph of bulk HA implant inserted directly after extraction of mandibular incisor. Implant was made to fit socket in vestibulolingual direction. Nevertheless there is a large radiolucency present around implant (arrows).

B u l k HA i m p l a n t s u n d e r f i x e d p a r t i a l dentures All 21 bulk HA implants placed under fixed partial dentures remained submucosal, thus maintaining the vestibular curvature of the ridge under the pontics (Figs. 8 and 9) (Table I).

HA/TI i m p l a n t s u n d e r o v e r d e n t u r e s The group with the HA/TI implants was followed up during a period of approximately 8 years. One of the 14 patients refused to have a splint placed on the implants. The implants in this patient remained under the mucosa in the jaw. The splints were placed in the other 13 patients. Nine of the splints that had a Dolder or Rider retentive attachment were replaced by a ferromagnetic splint. A total of three splints with corresponding 12 posts and 12 titanium cores from the HA/TI implants had to be removed because of loosening of the cement layer between the titanium and the hydroxyapatite coating. The HA coatings appeared to be attached firmly to the bone, comparable to the bulk HA implants. The splint had to be shortened in three patients because the same problem with the cement occurred in one of the four HA/TI implants. These patients had no problems because the overdenture functioned satisfactory with a splint on only three of the four HA/TI implants (Fig. 10). Table II summarizes these results.

HA/TI implants with a freestanding crown or a s p l i n t e d i m p l a n t c r o w n A total of 15 HA/TI implants have been inserted for single tooth replacement. All of these implants received posts, cores, and crowns. Only three implant crowns have been left 710

Fig. 9. Same patient as in Fig. 8 approximately 10 years after implantation. Implant is surrounded by bone and is stable part of ridge.

freestanding. In other patients it was safer to splint the implant crown to the crown on the adjacent tooth. All splinted implant crowns remained intact. Two of the freestanding crowns gave complications. In one patient, the Ti-core became loose because of cement failure. Another implant crown fractured at the cervical margin of the post (Table II). DISCUSSION The underlying concept of this type of implant, as compared with the other implant systems, was to achieve an attachment to the bone without mechanical retention. The concept was to use a nonvital hydroxyapatite ceramic in living bone as a natural tooth-root substitute and to allow function. There is no ideal artificial tooth-root attachment to periodontium. However, the principle of an ankylotic root can be simulated by using the hydroxyapatite implant. Bulk HA implants maintain the volume of the denture-bearing region of the mandible because of their physical presence, whether they are submucosal or permucosal. Hygienic care by the patient of the mucosal tissue around the permucosal implant is essential to maintain the ankyloJUNE 1989

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F i g . 11. Modified implants now in use. Lc/t, H A / T I implant with plasma-sprayed coating of hydi oxyapatite. Right, Cylindrical bulk HA implant that has rounded off upper surface.

F i g . 10. Radiograph ~,f part of mandible of patient with H A / T I implants and splint con~struction. Titanium core of implant on let~ side became loose because of cement failure. H y d r o x y a p a t i t e coating is still present in jaw (arrows). This radiograph was taken 4 years after shortening of splint.

tic binding of the implant to the bone. When oral hygiene is not adequate, the implant becomes periodontally involved, and it will loosen and exfoliate_ These problems do not arise under fixed partial dentures since all of the implants remain submucosal because this type of prosthesis does not run the risk of the mucosa overlying the implants being displaced. H A / T I implants can be used as abutments for a post and core and crown. It is necessary to splint the implant crown to the crown on or adjacent to a tooth. The introduction of resin-bonded retainers has made the use of H A / T I implants as single tooth replacement desirable. It is apparent t h a t H A / T I implants can f, mction satisfactorily under overdenlures. CONCLUSIONS The results indicate t h a t the design of the bulk HA implant and the time of implantation had to be changed. In design, the shape of the present bulk HA implant is like a bullet, with a rounded top (Fig. 11). The sharp cervical edges of the inverted cone implant used caused dehiscence and subsequent permneosal exlcosure of the implant because the mucosa became displaced between the implant edges and the base of the denture. Implantation of the bulk HA immediately after extraction of the teeth is complicated because of the difficulty in closing the extraction wounds over the implants. Therefore it is TIlE JOURNAl_ OF PROS'] HETIC DENTISTRY

desirable to wait until the mucoperiosteum has covered the extraction wounds in the course of wound healing, to avoid mobilization of mucosal tissue with consequent loss of vestibular depth. From a practical view, it is advisable to perform implantation just before placing the fixed partial denture and with mandibular complete dentures, before the denture must be rebased or remade, u~ually 3 to 4 months after extractions. An additional advantage of delayed implantation under mandibular complete dentures is that the initial vertical resorption has already (.ceurred, thus avoiding permucosal exposure of the implant. Both the design and the implantation technique of the HA/T]I implant is considered satisfactory. However, since cement fractures occasionally occurred, we now prefer plasma-sprayed coatings of hydroxyapatite on the titanium cores, t~) thus avoiding the cement layer (Fig. 11). In view of this long-term research, loaded and unloaded hydroxyapatite implants have introduced to dentistry reliable natural tooth-root substitutes. REFERENCES 1. Denissen HW, de Grnot K Immediate dent~al root implants from synlhetic dense calcium hydroxylapatite ,1 Pm)STH>:T DENT 1979;42: F,51-6 2. l)enissen HW, Veldhuis HA. Relda BV. Dense apatite ceramic implant systems: a pre|iminary report. ,J PROSTIqET DENT 1983;49:229 33. :L Quinn JH, blent JN. Alveolar ridge maintenance with stolid nonporous hydroxylapatite roet impIanls. Oral Surg 1984:85:5i 1-21. 4. Denissen HW, Veldhuis AAH. Jansen HBW, van den HooffA. The interface of permucosal dense apatite ceramic implants in humans. J Bimned Mater Res 1984:18:147 54. 5. Branemark PI, Zarb GA. Albrektsson T. Fissue-integrated prostheses, osseointe~ralion in clinical dentist, ry. Chicago,: Qtfintessenee Pub| Co, lne, t985. 6. Linknw I I . The blade vent. A new dimenslol~ in endesseous implantolo Ky Dent (?~nc I913S,:11::/.

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7. Williams DF, Roaf R. Implants in surgery. WB Saunders Co, Ltd 1973. 8. Denissen HW, van Dijk HJA, Gehring AP, de Groot K. Preparation of densely sintered calcium hydroxylapatite. J Dent Res 1979;42:551-6. 9. Denissen HW, Veldhuis AAH, van Faassen F. Implant placement in the atrophic mandible: an anatomical study. J PROSTHET DENT 1984;52: 260-3_ 10_ Dneheyne P., van Raemdonk W., de Meester P. Physical and material properties of hydroxylapatite coatings sintered on titanium. Biomaterials Transactions 1984;7:350.

Reprint requests to: DR_ HARRY W. DENISSEN UNIVERSITY OF N'~CMEGEN DENTAL SCHOOL P.O. BOX9101 6500 HB N~MEGEN THE NETHERLANDS

Fabrication of facial p r o s t h e s e s by applying the o s s e o i n t e g r a t i o n concept for retention R i c h a r d R. S e a l s , Jr., D.D.S., M.Ed., M.S.,* A q u i l e o L. C o r t e s , B.S., M.A.,** a n d S t e p h e n M. P a r e l , D.D.S.***

The University of Texas Health Science Center at San Antonio, Dental School, San Antonio, Tex. Initial clinical studies applying the o s s e o i n t e g r a t i o n concept for retention of facial p r o s t h e s e s h a v e been encouraging. The results of these preliminary i n v e s t i g a t i o n s indicate n e w treatment possibilities with facial p r o s t h e s e s anchored to the cranial s k e l e t o n by o s s e o i n t e g r a t e d implants. O s s e o i n t e g r a t e d rehabilitation of the m a x i l l o f a c i a l prosthetic patient presents the potential for o v e r c o m i n g many of the d i s a d v a n t a g e s associated with conventional r e t e n t i v e methods. Fabrication and support for facial prostheses by using o s s e o i n t e g r a t e d implants for retention are described. (J PROSTHET DENT 1989;61:712-16.)

T h e history of osseointegrated implants, with carefully documented animal experiments 1-3 and corresponding clinical studies 4-1° has documented favorable results using commercially pure titanium implants. The achievements of osseointegrated implantology are based on an atraumatic surgical procedure, a specific metallurgic response, an initial implant healing period without loading, and a passive stress-distributed prosthetic technique. 11 Together these factors contribute to a predictably high degree of implant longevity and long-term prosthesis use. Clinicians providing facial prostheses have been searching for improved retentive media. In some clinical situations mechanical retention, such as tissue undercuts.or conformers, can be used, but most patients have to rely on aromatic ostomy cements, two-sided tapes, and water soluble or silicone base adhesives. Each of the retentive media, whether cements, tapes, or adhesives, have significant drawbacks.12,13 Osseointegrated implant rehabilitation offered the first real promise for overcoming many of the disadvantages associated with conventional retentive media. If stable, bone-anchored implants could permanently pene-

Supported by an American Cancer Society Clinical OncologyCareer Development Award_ *Assistant Professor, Department of Prosthodontics. **Assistant Professor, Dental Laboratory Technology Program; Certified Dental Technician. ***Professor, Department of Prosthodonties712

Fig. 1. A, Osseointegrated implants with bar-splint assembly and magnetic retainers. B, Nasal prosthesis in place. JUNE 1988 VOLUME 61 NUMBER e