J Oral Maxlllofac
Surg
49:151-156.1991
Bone Replacement With Porous Hydroxyapatite Blocks and Titanium Screw Implants: An Experimental H. SCHLIEPHAKE,
Study
DDS, MD,* AND F.W. NEUKAM, DDS, MDt
The aim of this experimental study was to examine whether porous hydroxyapatite (HA) blocks, fixed with titanium screw implants, could be used as a bone graft substitute. Twenty minipigs received coralline HA blocks for augmentation of surgically created defects in edentulous mandibles. Each block was fixed with two titanium screw implants. Two types of porous HA blocks that differed in pore diameter were used. A high rate of HA loss occurred in the group of animals that had received the HA block with small pore sizes, and fractures of the block occurred in the vicinity of the titanium implants in 12 of the remaining 13 cases. Histologic examination showed that the HA blocks with larger pore size were homogenously penetrated by bone that extended into the central pores and even incorporated the dislocated block fragments. The titanium implants were in close contact with the newly formed bone in these blocks. Little contact between bone and implants was seen in the HA blocks with the smaller pore size. The results indicate that, with improved mechanical properties, a combined augmentation with porous HA blocks and screw implants may be useful in primary reconstruction of bone defects.
Introduction
tation with either free’ or microvascular bone grafts.’ Furthermore, it has been shown that the potential of ridge augmentation and screw implant fixation of dentures can be combined by simultaneous transplantation of free autogenous bone grafts.’ Experimental studies on animals have shown that coralline porous hydroxyapatite (HA) blocks that have been inserted as onlay grafts or for defect augmentation in the jaw bones can be penetrated by ingrowing bone to a considerable extenL4” Replacing the autogenous bone grafts with HA blocks could eliminate the need for second surgical site and bone procurement. Furthermore, the high rate of dehiscence and necrosis of the alveolar mucosa related to denture load associated with HA block implantatiot+’ could be minimized, as the screw implants would bear the load during mastication. The aim of this experimental study was twofold. First, to examine whether bone ingrowth into porous HA blocks is sufficient for the simultaneous
The restoration of bone defects after tumor resection is a frequent problem in maxillofacial surgery. The fixation of a prosthetic device to restore masticatory function can be difficult to achieve because of defects related to corrective surgery. The insertion of screw implants for stabilization of dentures has often proved to be advantageous after augmenReceived from the Department of Oral and Maxillofacial Surgery, University Medical School (Medizinische Hochscule Hannever), Hannover, Germany. * Resident. t Consultant. Address correspondence and reprint requests to Dr Schliephake: Department of Oral and Maxillofacial Surgery, University Medical School (Medizinische Hochschule Hannever), Konstanty-Gutschow-Str 8. D-3000 Hannover 61, Germany. 0 1991 American geons
Association
of Oral and Maxillofacial
Sur-
0278-2391/91/4902-0009$3.00/0
151
152
HYDROXYAPATITE
FIGURE 1.
Diagram of the surgical procedure.
AND TITANIUM IMPLANTS
FIGURE 2. Diagram showing preparation of specimens for histologic workup.
use of osteointegrated titanium screw implants, and, second, to determine if fixation of the blocks and subsequent stabilization of a prosthesis can be achieved by the screw implants.
created defects: Interpore 200 and Interpore 500 (Interpore International, Irvine, CA). For Interpore 200, the given pore diameter was 140 to 160 km*; for Interpore 500, it was 260 pm.’ Each surgical defect was filled with one block. The block was carved and adapted to the defect and then fixed in place with two titanium screw implants of I3 or 15 mm length (Nobelpharma, Gothenburg, Sweden) (Fig 1). Ten animals received Interpore 200 implants, and the other 10 received Interpore 500 blocks. With both types of blocks, a postoperative implantation time of 3 months was scheduled for five of the blocks, and a 5-month period was scheduled for the other five. A high rate of postoperative implant loss occurred in the group of animals that had received Interpore 200 implants, and one animal in this group died of pneumonia. Due to this loss, an evaluation after 3 months was abandoned in this group and the
Materials and Methods The experiments were performed on 20 Gottingen minipigs (average weight, 29.3 kg). The deciduous and permanent teeth of the canine-premolar region of the mandible were removed unilaterally. Three months later, a block-shaped portion of bone (7 x 10 X 25 mm) was resected from the edentulous jaws. An extraoral submandibular incision was used, and great care was taken not to perforate the lingual soft-tissue layers during exposure and resection of the ridge. Two types of coralline porous HA blocks (10 x 10 x 25 mm) that differed in mean interconnecting pore diameter were then inserted through this incision for restoration of the surgically Table 1. Results Animal No. (Time [mo])
1 (5) 2 3 (5) 4 (5) 5 6 7 8 9 10 (5) 11 (5) 12 (5)
13 (5) 14 (5) 15 (5) 16 (3) 17 (3) 18 (3) 19 (3) 20 (3)
Implant IP 200 IP 200 IP 200 IP 200 IP 200 IP 200 IP 200 IP 200 IP 200 IP 200 IP 500 IP 500 IP 500 IP 500 IP 500 IP 500 IP 500 IP 500 IP 500 IP 500
Block Fracture
Dislocation
Dehiscence
Infection
t
0
0
0
-
_
_
-
Loss 0
Total
t
0
0
0
0
+ _ _ + + +
+ _ _ _ _
+ _ _
0 _ _ _
+
0
0
0 Total Total Pneumonia Total Total Partial
t
t
0
0 t 0
0 0 0
0 + + + + +
0 0 0 0 0 0
0 0 _ 0 0 0 0
0 0 0 0 0 0
+
_
0 0
Partial 0 Partial Total Partial Partial 0 Partial
153
SCHLIEPHAKE AND NEUKAM remaining blocks (n = 4) were analyzed after 5 months. One loss of Interpore 500 implant occurred in the 3-month group. Thus, only 13 of the initial 20 cases remained. Group I (n = 4) had Interpore 200 implanted for 5 months, group 2 (n = 4) had Interpore 500 implanted for 3 months, and group 3 had Interpore 500 (n = 5) implanted for 5 months. At the end of the scheduled postoperative intervals, the implantation sites were examined for implant stability and signs of infection. The animals were killed and the mandibles removed in toto, radiographed, and fixed immediately in 10% formalin. After thorough fixation, the implanted blocks were removed from the jaws together with the implants and the surrounding bone and cut into four sections, two of them containing one screw implant each (Fig 2). The resulting pieces were embedded into methylmethacrylate and thick sections (70 pm) were prepared from these blocks perpendicular to the long axis of the screw implants. The sections were used for microradiograms (W-anode, 15 kV, 3.5 mA; FaxitronR, Rhode & Schwartz, Cologne, Germany) and subsequently stained with methylene blue/ alizarin. ” Results CLINICAL EVALUATION Although the blocks had been properly adapted to the bone cavity, fractures occurred in 12 cases near the vicinity of the titanium screws during insertion and fixation (Table 1). This led to a splitting off of small portions of the block during surgery (nos. 13, IS, 17). In one case (no. 20) there was a massive loss of over 50% of the block volume. In four cases (nos. 4, 10, II, 12) postoperative dislocation of block fragments occurred; in one case (no. IO), loss of a large fragment occurred. At the time of death, all remaining implants were stable and firmly fixed to the jaws. There was no sign of acute infection. Figure 3 shows a linear sec-
FIGURE 3. Section through implant showing lack of contact with the HA block.
FIGURE 4. Radiograph showing osteolysis around HA block and titanium implants (Interpore 200R. 5 months postoperatively).
tion through the implant device. Small dehiscences through which the upper anterior buccal corner of the blocks was exposed were found in two animals (nos. 4, 12), although no infection was seen in these sites. RADIOGRAPHS The Interpore 200 implants showed extensive osteolysis (no. 1) (Fig 4) or massive bone apposition with an increased density around the implanted blocks (nos. 3, 4, 10). Considerable dislocation of blocks and screw implants was evident (Fig 5). Clinically, no signs of infection were observed in these animals. In the groups of animals with Interpore 500 implants, comparable radiographic findings in the surrounding bone were observed in only two of nine cases. Major dislocation of the implant occurred in one animal (no. 11). HISTOLOGIC
FINDINGS
Group 1
Histologic findings in the group of Interpore 200 implants varied considerably. Some portions of the
FIGURE 5. Radiograph of displaced HA block showing massive bone apposition (Interpore 200R, 5 months postoperatively).
154
FIGURE 6. Photomicrograph of Interpore 200R block 5 months postoperatively showing regular bone ingrowth (original magnification X25).
block showed uneventful integration by ingrowth of bone tissue (Fig 6). Bone had invaded the block in a lateral direction, although there was often only a small area of contact with the surrounding bone (Fig 7). Haversian systems could be found in places of massive bone ingrowth. Other portions of the blocks showed areas of isolated osteogenesis within highly cellular connective tissue. Bone tissue appeared limited to the block boundaries and almost completely filled the implant pores in these areas (Fig 8). Newly formed bone was deposited directly on the implant surface (Fig 9). Areas where osteogenesis had just commenced, however, were rarely seen. Large portions of the Interpore 200 blocks only showed ingrowth of connective tissue and often contained amorphous material in the central parts of the blocks (Fig 10). There was very little contact between the ingrowing bone and the titanium screw implant. Group 2 The Interpore 500 blocks exhibited much more uniform patterns of bone ingrowth. Integration of
FIGURE 7. Photomicrograph of Interpore 200R block 5 months postoperatively showing bone invasion from a small contact area (alizarinlmethylene blue, original magnification x25).
HYDROXYAPATITE
AND TITANIUM IMPLANTS
FIGURE 8. Photomicrograph of Interpore 200R block 5 months postoperatively showing an island of osteogenesis within the highly cellular connective tissue (alizarin/methylene blue, original magnification x 25).
the implant into bone tissue was nearly complete after 3 months. In the outer parts of the block, the bone tissue was nearly undisturbed compared to the surrounding bone (Fig 11). There were extended zones of lamellar bone structure with Haversian systems (Fig 12). In the central part of the block, more cancellous bone structure, with osteoblast seams, could be observed (Fig 13). No bone was found in those parts of the implants that extended beyond the contours of the mandible (Fig 14). Bone tissue had invaded the central parts of the blocks and was in close contact to the screw implants (Fig 15). Group 3 Histologic findings in the Interpore 500 implants after 5 months were very similar to those of group 2. Uneventful healing, with complete integration of the implant material, was observed. Occurrence of Haversian systems in areas of dense bone ingrowth
FIGURE 9. Photomicrograph of Interpore 200R block 5 months postoperatively showing bone apposition on the HA surface and one isolated osteocyte (alizarin/methylene blue, original magnification X 160).
SCHLIEPHAKE
AND NEUKAM
155
FIGURE 10. Photomicrograph of lnterpore 200R block 5 months postoperatively showing soft tissue and amphorous material in the central part of the block (alizarin/methylene blue, original magnification x40).
FIGURE 12. Photomicrograph of Interpore 500R block 3 months postoperatively showing Haversean systems inside the HA block talizarin/methylene blue, original magnification x40).
and portions resembling cancellous bone structure with fatty marrow in the central block portions were the characteristic histologic features (Fig 16). As in group 2, intimate contact between bone tissue and the titanium screw implants was observed. Histologic examination of the contact zones between the HA and the titanium screw implants showed that the threads that were cut into the implanted blocks were too wide for the HA to be fixed rigidly by the inserted implants. The implants were mainly surrounded by HA debris without close contact to the block.
One of the main problems during the surgical procedure was the brittleness of the implanted HA material. Fractures of the HA block during the insertion of the titanium implants often made rigid fixation impossible. Histologic examination furthermore showed that primary fixation even of the unbroken blocks could only rarely be achieved, as
there was very little contact between the screws and the implanted blocks. Subsequent problems with unstable or dislocated implant material led to different clinical and histologic results with the two different types of HA implants. In the group of Interpore 200 implants, a high rate of loss occurred and in the remaining cases extensive osteolysis or massive apposition of sclerotic bone was observed. In contrast, both the rate of implant loss and the number of complications were considerably lower in the groups with Interpore 500 blocks. On the microscopic level, bone ingrowth into the Interpore 200 blocks after 5 months was very irregular and was found mainly in the outer parts of the blocks, so that the titanium implants were not osseointegrated and would therefore have been useless for the subsequent stabilization of a prosthetic device. The Interpore 500 implants, on the other hand, were completely penetrated by ingrowing bone that integrated the screw implants after only 3 months. Dislocation of HA material resulting from frac-
FIGURE Il. Microradiograph of Interpore SOOR block 3 months postoperatively showing the bone structure in the vicinity of the HA block (original magnification x7.5).
FIGURE 13. Photomicrograph of Interpore 5OOR block 3 months postoperatively showing osteoblast seams in the central part talizarin/methylene blue, original magnification x 100).
Discussion
156
HYDROXYAPATITE
AND TITANIUM IMPLANTS
FIGURE 14. Microradiograph of Interpore SOOR block 3 months postoperatively showing empty parts of the block that extended above the bone level (original magnification x 100).
FIGURE 16. Photomicrograph of Interpore 500R block 5 months postoperatively showing fatty marrow in central parts (alizarin/methylene blue, original magnification x25).
tures of the implanted blocks proved disadvantageous, particularly in the group of Interpore 200 implants. These fragments were not penetrated by bone, whereas in the case of Interpore 500 blocks, the fractured, dislocated HA material was completely integrated. The failure of the Interpore 200 HA block implants observed in this experimental study also has been previously reported after clinical use for augmentation of atrophic alveolar ridges.6*7,‘0 The present results suggest that a porous structure with larger pore size, such as that of Interpore 500, is more suitable for use in mandibular augmentation and may allow complete integration of the block and even of dislocated fragments within shorter periods. The mechanical properties of the implanted blocks are, however, still a serious problem. Fabrication of a less brittle material through the replamineform process,‘* which preserves the origi-
nal advantageous pore structure, may help to avoid possible complications arising from block fractures. With an improved material, the suggested combined augmentation with screw implants and HA blocks could be useful in cases of primary reconstruction after resection of benign bone tumors of the jaws.
FIGURE 15. Photomicrograph of Interpore SOOR block 3 months postoperatively showing intimate contact between titanium implant and ingrowing bone (alizarimmethylene blue, original magnification x 25).
References 1. Dodson TB, Smith RA: Mandibular reconstruction with autogenous and alloplastic materials following resection of an odontogenic myxoma. Int .I Oral Maxillofac Implants 41227, 1989 2. Riediger D, D’Hoedt B, Pielsticker W: Implantate nach mikrochirurgischer Beckenkammtransplantation. Z Zahnarztl Implant01 2:97, 1986 3. Neukam FW, Scheller H, Hausamen J-E: Functional and esthetic rehabilitation with B&emark implants following oncologic surgery, in Albrektsson T, Zarb GA (eds): The Brinemark Osseointegrated Implant. Chicago. IL, Quintessence, 1989, pp 147-162 4. Holmes RE: Bone regeneration within a coralline hydroxyapatite implant. Plast Reconstr Surg 63:626, 1979 5. Holmes RE, Hagler HK: Porous hydroxylapatite as a bone graft substitute in mandibular augmentation. J Oral Maxillofac Surg 45:421, 1987 6. Hupp JR, McKenna SJ: Use of porous hydroxylapatite blocks for augmentation of atrophic mandibles. J Oral Maxillofac Surg 46:538, 1988 7. Rooney T, Berman S, Indresano AT: Evaluation of porous block hydroxylapatite for augmentation of alveolar ridges. J Oral Maxillofac Surg 46:15, 1988 8. Chiroff RT, White EW, Weber JN, Roy DM: Tissue ingrowth of replamineform implants. J Biomed Mater Res 6:29, 1975 9. Holmes RE, Buchholz RW, Mooney V: Porous hydroxylapatite as a bone-graft substitute in meta physeal defects. J Bone Joint Surg 68A:904, 1986 10. Smith LG, Karagianes MT: Histological preparation of bone to study ingrowth into implanted materials. Calc Tissue Res 14:333, 1974 11. Chao SY, Poon CK: Histological study of tissue response to implanted hydroxylapatite in two patients. J Oral Maxillofac Surg 45:359, 1987 12. Weber JN, White EW: Carbonate materials as precursors of new ceramic, metal and polymer materials for biomedical applications. Miner Sci Eng 5: 151, 1973
Surg
49:151-156.1991
Bone Replacement With Porous Hydroxyapatite Blocks and Titanium Screw Implants: An Experimental H. SCHLIEPHAKE,
Study
DDS, MD,* AND F.W. NEUKAM, DDS, MDt
The aim of this experimental study was to examine whether porous hydroxyapatite (HA) blocks, fixed with titanium screw implants, could be used as a bone graft substitute. Twenty minipigs received coralline HA blocks for augmentation of surgically created defects in edentulous mandibles. Each block was fixed with two titanium screw implants. Two types of porous HA blocks that differed in pore diameter were used. A high rate of HA loss occurred in the group of animals that had received the HA block with small pore sizes, and fractures of the block occurred in the vicinity of the titanium implants in 12 of the remaining 13 cases. Histologic examination showed that the HA blocks with larger pore size were homogenously penetrated by bone that extended into the central pores and even incorporated the dislocated block fragments. The titanium implants were in close contact with the newly formed bone in these blocks. Little contact between bone and implants was seen in the HA blocks with the smaller pore size. The results indicate that, with improved mechanical properties, a combined augmentation with porous HA blocks and screw implants may be useful in primary reconstruction of bone defects.
Introduction
tation with either free’ or microvascular bone grafts.’ Furthermore, it has been shown that the potential of ridge augmentation and screw implant fixation of dentures can be combined by simultaneous transplantation of free autogenous bone grafts.’ Experimental studies on animals have shown that coralline porous hydroxyapatite (HA) blocks that have been inserted as onlay grafts or for defect augmentation in the jaw bones can be penetrated by ingrowing bone to a considerable extenL4” Replacing the autogenous bone grafts with HA blocks could eliminate the need for second surgical site and bone procurement. Furthermore, the high rate of dehiscence and necrosis of the alveolar mucosa related to denture load associated with HA block implantatiot+’ could be minimized, as the screw implants would bear the load during mastication. The aim of this experimental study was twofold. First, to examine whether bone ingrowth into porous HA blocks is sufficient for the simultaneous
The restoration of bone defects after tumor resection is a frequent problem in maxillofacial surgery. The fixation of a prosthetic device to restore masticatory function can be difficult to achieve because of defects related to corrective surgery. The insertion of screw implants for stabilization of dentures has often proved to be advantageous after augmenReceived from the Department of Oral and Maxillofacial Surgery, University Medical School (Medizinische Hochscule Hannever), Hannover, Germany. * Resident. t Consultant. Address correspondence and reprint requests to Dr Schliephake: Department of Oral and Maxillofacial Surgery, University Medical School (Medizinische Hochschule Hannever), Konstanty-Gutschow-Str 8. D-3000 Hannover 61, Germany. 0 1991 American geons
Association
of Oral and Maxillofacial
Sur-
0278-2391/91/4902-0009$3.00/0
151
152
HYDROXYAPATITE
FIGURE 1.
Diagram of the surgical procedure.
AND TITANIUM IMPLANTS
FIGURE 2. Diagram showing preparation of specimens for histologic workup.
use of osteointegrated titanium screw implants, and, second, to determine if fixation of the blocks and subsequent stabilization of a prosthesis can be achieved by the screw implants.
created defects: Interpore 200 and Interpore 500 (Interpore International, Irvine, CA). For Interpore 200, the given pore diameter was 140 to 160 km*; for Interpore 500, it was 260 pm.’ Each surgical defect was filled with one block. The block was carved and adapted to the defect and then fixed in place with two titanium screw implants of I3 or 15 mm length (Nobelpharma, Gothenburg, Sweden) (Fig 1). Ten animals received Interpore 200 implants, and the other 10 received Interpore 500 blocks. With both types of blocks, a postoperative implantation time of 3 months was scheduled for five of the blocks, and a 5-month period was scheduled for the other five. A high rate of postoperative implant loss occurred in the group of animals that had received Interpore 200 implants, and one animal in this group died of pneumonia. Due to this loss, an evaluation after 3 months was abandoned in this group and the
Materials and Methods The experiments were performed on 20 Gottingen minipigs (average weight, 29.3 kg). The deciduous and permanent teeth of the canine-premolar region of the mandible were removed unilaterally. Three months later, a block-shaped portion of bone (7 x 10 X 25 mm) was resected from the edentulous jaws. An extraoral submandibular incision was used, and great care was taken not to perforate the lingual soft-tissue layers during exposure and resection of the ridge. Two types of coralline porous HA blocks (10 x 10 x 25 mm) that differed in mean interconnecting pore diameter were then inserted through this incision for restoration of the surgically Table 1. Results Animal No. (Time [mo])
1 (5) 2 3 (5) 4 (5) 5 6 7 8 9 10 (5) 11 (5) 12 (5)
13 (5) 14 (5) 15 (5) 16 (3) 17 (3) 18 (3) 19 (3) 20 (3)
Implant IP 200 IP 200 IP 200 IP 200 IP 200 IP 200 IP 200 IP 200 IP 200 IP 200 IP 500 IP 500 IP 500 IP 500 IP 500 IP 500 IP 500 IP 500 IP 500 IP 500
Block Fracture
Dislocation
Dehiscence
Infection
t
0
0
0
-
_
_
-
Loss 0
Total
t
0
0
0
0
+ _ _ + + +
+ _ _ _ _
+ _ _
0 _ _ _
+
0
0
0 Total Total Pneumonia Total Total Partial
t
t
0
0 t 0
0 0 0
0 + + + + +
0 0 0 0 0 0
0 0 _ 0 0 0 0
0 0 0 0 0 0
+
_
0 0
Partial 0 Partial Total Partial Partial 0 Partial
153
SCHLIEPHAKE AND NEUKAM remaining blocks (n = 4) were analyzed after 5 months. One loss of Interpore 500 implant occurred in the 3-month group. Thus, only 13 of the initial 20 cases remained. Group I (n = 4) had Interpore 200 implanted for 5 months, group 2 (n = 4) had Interpore 500 implanted for 3 months, and group 3 had Interpore 500 (n = 5) implanted for 5 months. At the end of the scheduled postoperative intervals, the implantation sites were examined for implant stability and signs of infection. The animals were killed and the mandibles removed in toto, radiographed, and fixed immediately in 10% formalin. After thorough fixation, the implanted blocks were removed from the jaws together with the implants and the surrounding bone and cut into four sections, two of them containing one screw implant each (Fig 2). The resulting pieces were embedded into methylmethacrylate and thick sections (70 pm) were prepared from these blocks perpendicular to the long axis of the screw implants. The sections were used for microradiograms (W-anode, 15 kV, 3.5 mA; FaxitronR, Rhode & Schwartz, Cologne, Germany) and subsequently stained with methylene blue/ alizarin. ” Results CLINICAL EVALUATION Although the blocks had been properly adapted to the bone cavity, fractures occurred in 12 cases near the vicinity of the titanium screws during insertion and fixation (Table 1). This led to a splitting off of small portions of the block during surgery (nos. 13, IS, 17). In one case (no. 20) there was a massive loss of over 50% of the block volume. In four cases (nos. 4, 10, II, 12) postoperative dislocation of block fragments occurred; in one case (no. IO), loss of a large fragment occurred. At the time of death, all remaining implants were stable and firmly fixed to the jaws. There was no sign of acute infection. Figure 3 shows a linear sec-
FIGURE 3. Section through implant showing lack of contact with the HA block.
FIGURE 4. Radiograph showing osteolysis around HA block and titanium implants (Interpore 200R. 5 months postoperatively).
tion through the implant device. Small dehiscences through which the upper anterior buccal corner of the blocks was exposed were found in two animals (nos. 4, 12), although no infection was seen in these sites. RADIOGRAPHS The Interpore 200 implants showed extensive osteolysis (no. 1) (Fig 4) or massive bone apposition with an increased density around the implanted blocks (nos. 3, 4, 10). Considerable dislocation of blocks and screw implants was evident (Fig 5). Clinically, no signs of infection were observed in these animals. In the groups of animals with Interpore 500 implants, comparable radiographic findings in the surrounding bone were observed in only two of nine cases. Major dislocation of the implant occurred in one animal (no. 11). HISTOLOGIC
FINDINGS
Group 1
Histologic findings in the group of Interpore 200 implants varied considerably. Some portions of the
FIGURE 5. Radiograph of displaced HA block showing massive bone apposition (Interpore 200R, 5 months postoperatively).
154
FIGURE 6. Photomicrograph of Interpore 200R block 5 months postoperatively showing regular bone ingrowth (original magnification X25).
block showed uneventful integration by ingrowth of bone tissue (Fig 6). Bone had invaded the block in a lateral direction, although there was often only a small area of contact with the surrounding bone (Fig 7). Haversian systems could be found in places of massive bone ingrowth. Other portions of the blocks showed areas of isolated osteogenesis within highly cellular connective tissue. Bone tissue appeared limited to the block boundaries and almost completely filled the implant pores in these areas (Fig 8). Newly formed bone was deposited directly on the implant surface (Fig 9). Areas where osteogenesis had just commenced, however, were rarely seen. Large portions of the Interpore 200 blocks only showed ingrowth of connective tissue and often contained amorphous material in the central parts of the blocks (Fig 10). There was very little contact between the ingrowing bone and the titanium screw implant. Group 2 The Interpore 500 blocks exhibited much more uniform patterns of bone ingrowth. Integration of
FIGURE 7. Photomicrograph of Interpore 200R block 5 months postoperatively showing bone invasion from a small contact area (alizarinlmethylene blue, original magnification x25).
HYDROXYAPATITE
AND TITANIUM IMPLANTS
FIGURE 8. Photomicrograph of Interpore 200R block 5 months postoperatively showing an island of osteogenesis within the highly cellular connective tissue (alizarin/methylene blue, original magnification x 25).
the implant into bone tissue was nearly complete after 3 months. In the outer parts of the block, the bone tissue was nearly undisturbed compared to the surrounding bone (Fig 11). There were extended zones of lamellar bone structure with Haversian systems (Fig 12). In the central part of the block, more cancellous bone structure, with osteoblast seams, could be observed (Fig 13). No bone was found in those parts of the implants that extended beyond the contours of the mandible (Fig 14). Bone tissue had invaded the central parts of the blocks and was in close contact to the screw implants (Fig 15). Group 3 Histologic findings in the Interpore 500 implants after 5 months were very similar to those of group 2. Uneventful healing, with complete integration of the implant material, was observed. Occurrence of Haversian systems in areas of dense bone ingrowth
FIGURE 9. Photomicrograph of Interpore 200R block 5 months postoperatively showing bone apposition on the HA surface and one isolated osteocyte (alizarin/methylene blue, original magnification X 160).
SCHLIEPHAKE
AND NEUKAM
155
FIGURE 10. Photomicrograph of lnterpore 200R block 5 months postoperatively showing soft tissue and amphorous material in the central part of the block (alizarin/methylene blue, original magnification x40).
FIGURE 12. Photomicrograph of Interpore 500R block 3 months postoperatively showing Haversean systems inside the HA block talizarin/methylene blue, original magnification x40).
and portions resembling cancellous bone structure with fatty marrow in the central block portions were the characteristic histologic features (Fig 16). As in group 2, intimate contact between bone tissue and the titanium screw implants was observed. Histologic examination of the contact zones between the HA and the titanium screw implants showed that the threads that were cut into the implanted blocks were too wide for the HA to be fixed rigidly by the inserted implants. The implants were mainly surrounded by HA debris without close contact to the block.
One of the main problems during the surgical procedure was the brittleness of the implanted HA material. Fractures of the HA block during the insertion of the titanium implants often made rigid fixation impossible. Histologic examination furthermore showed that primary fixation even of the unbroken blocks could only rarely be achieved, as
there was very little contact between the screws and the implanted blocks. Subsequent problems with unstable or dislocated implant material led to different clinical and histologic results with the two different types of HA implants. In the group of Interpore 200 implants, a high rate of loss occurred and in the remaining cases extensive osteolysis or massive apposition of sclerotic bone was observed. In contrast, both the rate of implant loss and the number of complications were considerably lower in the groups with Interpore 500 blocks. On the microscopic level, bone ingrowth into the Interpore 200 blocks after 5 months was very irregular and was found mainly in the outer parts of the blocks, so that the titanium implants were not osseointegrated and would therefore have been useless for the subsequent stabilization of a prosthetic device. The Interpore 500 implants, on the other hand, were completely penetrated by ingrowing bone that integrated the screw implants after only 3 months. Dislocation of HA material resulting from frac-
FIGURE Il. Microradiograph of Interpore SOOR block 3 months postoperatively showing the bone structure in the vicinity of the HA block (original magnification x7.5).
FIGURE 13. Photomicrograph of Interpore 5OOR block 3 months postoperatively showing osteoblast seams in the central part talizarin/methylene blue, original magnification x 100).
Discussion
156
HYDROXYAPATITE
AND TITANIUM IMPLANTS
FIGURE 14. Microradiograph of Interpore SOOR block 3 months postoperatively showing empty parts of the block that extended above the bone level (original magnification x 100).
FIGURE 16. Photomicrograph of Interpore 500R block 5 months postoperatively showing fatty marrow in central parts (alizarin/methylene blue, original magnification x25).
tures of the implanted blocks proved disadvantageous, particularly in the group of Interpore 200 implants. These fragments were not penetrated by bone, whereas in the case of Interpore 500 blocks, the fractured, dislocated HA material was completely integrated. The failure of the Interpore 200 HA block implants observed in this experimental study also has been previously reported after clinical use for augmentation of atrophic alveolar ridges.6*7,‘0 The present results suggest that a porous structure with larger pore size, such as that of Interpore 500, is more suitable for use in mandibular augmentation and may allow complete integration of the block and even of dislocated fragments within shorter periods. The mechanical properties of the implanted blocks are, however, still a serious problem. Fabrication of a less brittle material through the replamineform process,‘* which preserves the origi-
nal advantageous pore structure, may help to avoid possible complications arising from block fractures. With an improved material, the suggested combined augmentation with screw implants and HA blocks could be useful in cases of primary reconstruction after resection of benign bone tumors of the jaws.
FIGURE 15. Photomicrograph of Interpore SOOR block 3 months postoperatively showing intimate contact between titanium implant and ingrowing bone (alizarimmethylene blue, original magnification x 25).
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