Highly crystalline MP‐1 hydroxylapatite coating Part II: In vivo performance on endosseous root implants in dogs

The in vivo integration strength and degree of bone apposition were compared for oral endosseous implants with different plasma-sprayed hydroxylapatite (HA) coatings. Pullout strength measurements and histological analysis were used to compare two different commercially available coating from the same manufacturer. One coating does not receive a post-plasma-spray treatment and contains about 75% crystalline HA. The other coating is treated with the MP-1 process, a pressurized hydrothermal post-plasma-spray process, which increases the coating composition to approximately 95% crystalline HA without changing the coating's adhesive or cohesive strength. Comparisons were made in dogs after healing times of 3 and 15 weeks in the mandible. No significant differences were found in either case between the two coatings. Two different methods were used to determine the degree of bone apposition at 15 weeks. Both methods confirmed that the MP-1 process does not affect the osseointegration rate of plasma-sprayed HA coatings. Qualitative histology data suggest that the treated coating is more stable than the control coating, especially in cases of direct soft tissue attachment to the implant. The present data suggest that extensive dissolution of calcium phosphate components into surrounding tissue is not a necessary precursor for direct apposition of bone to HA-coated implants.     

Human histologic and histomorphometric analyses of hydroxyapatite-coated implants after 10 years of function: a case report

PURPOSE: No consensus exists on the long-term performance of hydroxyapatite (HA) coatings on dental implants. The aim of this study was to evaluate the long-term stability of the HA coating in a human autopsy specimen. MATERIALS AND METHODS: Two mandibular HA-coated implants were retrieved postmortem from a woman after 10 years of functional loading with an implant/tooth-supported fixed partial denture. After ground sectioning, the specimens were histomorphometrically analyzed. RESULTS: Direct bone-implant contact was found at 78.48% of the implant surface. HA coating disappearance had occurred in a few areas (22.75%), but bone was in direct apposition to the titanium surface. Bone volume measured 27.66%, and expected bone-implant contact was 37.55%. No inflammatory reaction was seen in the supracrestal soft tissues or the bone compartment. DISCUSSION: Most of the HA coating was maintained on the implants, and areas lacking HA were directly apposed by bone. This observation suggests that the underlying titanium surface should have a macro-texture to promote the adaptation of bone to the titanium surface in case of HA disappearance, as well as to decrease failure at the HA-titanium interface. CONCLUSIONS: In a patient in whom prosthetic treatment was appropriately performed and proper plaque control was maintained, the HA coating was not damaged and contributed to the success of the implant over 10 years of clinical functioning.     

Two human hydroxyapatite-coated dental implants retrieved after a 14-year loading period: a histologic and histomorphometric case report

BACKGROUND: Controversy over the long-term clinical effectiveness of hydroxyapatite (HA)-coated dental implants still persists, despite numerous clinical studies documenting high survival rates. Concerns about the degradation of the coating over the years have been raised; it has been speculated that resorption of the HA could produce a space between the implant and the bone with a resultant mechanical instability. METHODS: Two HA-coated implants were retrieved due to a fracture of the abutment screws after a loading period of 14 years and were treated to obtain thin ground sections for histologic evaluation. RESULTS: At low-power magnification, it was possible to observe that the HA coating was in contact with mature bone. No gaps or connective fibrous tissue was found at the implant-bone interface. No epithelial downgrowth was present. No acute or chronic inflammatory cell infiltrate was present at the implant-bone interface. No foreign body reaction was present in the peri-implant tissues. Some osteocytes were in direct contact with the coating. For implant 1, the percentage of bone-titanium contact was 25% +/- 2.1%, and the percentage of bone-HA contact was 35% +/- 1.4%. The total bone-implant contact was approximately 60%. The HA coating appeared to be resorbed in 46% +/- 3.2% of the implant perimeter, especially in the coronal portions of the implant. For implant 2, the mean percentage of bone-HA contact was 13% +/- 1.8%, and the mean percentage of bone-titanium contact was 15% +/- 2.3%. The total bone-implant contact was approximately 28%. The HA coating appeared to be resorbed for a mean of 68% +/- 4.1% of the implant perimeter, especially in the coronal portion of the implant. CONCLUSIONS: No acute or chronic inflammatory cell infiltrate was present in the peri-implant tissues. No signs of coating infection, fatigue, or failure were observed in two specimens. The HA coating may not be susceptible to degradation or dissolution under long-term function.     

正畸支抗种植体骨整合与稳定性的实验研究

目的　考察正畸支抗种植体的骨整合与稳定性以及二者之间的关系。方法　将HA涂层钛种植体、钛浆喷涂钛种植体、未涂层钛种植体植入狗股骨 ,愈合期后施加 1 96N正畸力 2个月。测量施力后种植体的位置变化和种植体—骨界面的剪切结合强度 ,用扫描电镜观察界面。结果　 3种种植体位移分别为 (- 0 5 0± 1 78)mm、(- 0 0 5± 1 76 )mm、(0 2 9± 1 77)mm ,统计学分析结果显示 ,还不能认为 3种种植体出现移动。 3种种植体—骨界面的剪切结合强度分别是 (2 88± 0 5 5 )MPa、(1 89± 0 81)MPa和 (2 14± 0 49)MPa。HA涂层种植体与骨紧密结合 ,其界面结合强度最高 ;另外 2种种植体与骨的结合强度差异无显著性。结论　虽然HA涂层种植体与骨结合最牢固 ,但 3种种植体—骨界面均可形成骨整合 ,在常规正畸力作用下不会发生明显移动。本项研究结果表明 ,种植体可用作短期的正畸支抗。     

Histological and clinical comparisons of guided tissue regeneration on dehisced hydroxylapatite-coated and titanium endosseous implant surfaces: a pilot study.

Fifty-six endosseous cylindrical implants were placed in dog mandibles 12 weeks after the extraction of all mandibular premolars and first molars. Eight implants, four coated with 50 microns of hydroxylapatite (HA) and four grit-blasted and titanium-surfaced, were placed in each dog. Ideal implant placement sites were modified by creating standardized 3 x 5-mm facial dehiscence defects. Half the dehiscences were treated with a modified expanded polytetrafluoroethylene (PTFE) membrane; the remainder served as controls. After 8 weeks of healing, the animals were sacrificed and measurements made to determine the percentage of dehiscence repair. The HA-coated implants had a mean defect fill of 95.17% and the grit-blasted implants had a percent fill of 82.8% in the guided tissue regeneration (GTR) test group; the control implants demonstrated a mean fill of 55% and 39% in the HA-coated and grit-blasted implants, respectively. Significant differences (P less than .05) were noted between both test groups and the titanium control group, and between the HA test and HA control groups. Histologic evaluation showed significantly greater repair associated with HA-coated implants, as well as significant bone loss associated with clinically exposed membranes. It was concluded that within the limitations of this study, guided tissue regeneration is a viable option in treating defects associated with dental implants.     

Histologic evaluation of a 9-year-old hydroxyapatite-coated cylindric implant placed in conjunction with a subantral augmentation procedure: a case report.

The histologic examination of dental implants retrieved from humans provides a unique opportunity to evaluate the bone-implant interface. This case report presents a clinical, radiographic, and histologic evaluation of a cylindrical hydroxyapatite- (HA) coated implant retrieved from the posterior maxillary area of a patient after 9 years after placement. The implant had been placed in conjunction with a subantral augmentation procedure with HA as the graft material. Clinical examination revealed an immobile implant with no sign of pathosis. Radiographic examination indicated close proximity of the bone to the implant surface without evidence of radiolucency. Histologically, because of tissue destruction during implant retrieval, only the apical portion of the implant was available for examination under light microscopy, and it appeared to be integrated with the surrounding bone; 45.9% of the surface of the implant had close bone apposition at the interface. There was no evidence of dissolution of the HA coating and the bone appeared to be in immediate contact with the coating. Residual graft particles were present and in close proximity with the implant surface. These observations suggest that the subantral augmentation procedure performed simultaneously with the placement of an HA-coated implant with HA as the graft material apparently resulted in osseointegration between the implant and the surrounding bone. The implant was maintained without complication for 9 years.     

Clinical and radiographic experience with a hydroxyapatite-coated titanium plasma-sprayed porous implant.

Recent efforts to improve the interface between implant and bone have involved the use of bioactive materials, specifically hydroxyapatite (HA). HA coatings applied to implants have shown excellent clinical results at 2 years. There have been no radiolucent lines around the HA-coated implants. The long-term strength of the HA coating-substrate bone interface remains a concern as osseointegration of the HA appears to be a consistent phenomenon. This can lead potentially to an interruption between the substrate itself and the osseointegrated coating.     

Osseous healing characteristics of three different implant types

The macroscopic and especially microscopic properties of implant surfaces play a major role in the osseous healing of dental implants. The aim of this study was to perform a histologic and histomorphometric comparison of the healing characteristics of anodically modified, machined and hydroxyapatite (HA)-coated implant types. A total of 24 machined surface implants (MSI), 24 HA-coated implants (HCI) and 24 anodized titanium surface implants (ASI) were inserted into the mandibles of 12 adult mini-pigs after extracting all mandibular premolars. Four animals each were killed after covered healing for 3, 6 and 12 weeks. Undecalcified ground sections were subjected to histologic and histomorphometric examinations. Primary effects and interactions were statistically evaluated and least square means (Tukey test) were compared. Histologic evaluations showed broad-based bone apposition to HA-coated and anodically roughened surfaces as well as narrow bone contacts to the machined surface. Localized resorption was only observed with the HA-coated implants. Overall, histomorphometric evaluation of bone-to-implant contact percentages for all observation periods showed significant differences between MSI (19.39% +/- 4.53) and HCI (39.05% +/- 4.53; P = 0.0092) and between MSI and ASI (42.72% +/- 4.20; P = 0.0011). In conclusion, the results of this study show that an anodically roughened implant may provide a similar rate of bone-to-implant contact as a HA-coated implant. In the presence of bone quality II to IV, according to Lekholm & Zarb (1985, in: Tissue-Integrated Prostheses: Osseointegration in Clinical Dentistry. Chicago: Quintessence Publishing), this may be of particular benefit, possibly because of higher stability, in maintaining pre-implantation functional strength after implant healing.     

Postmortem histologic evaluation of mandibular titanium and maxillary hydroxyapatite-coated implants from 1 patient.

Postmortem examination of human specimens is an extremely important aspect of evaluating the relative compatibility and long-term success of endosseous implant surfaces. The bone-implant interface of 5 commercially pure titanium screw-type mandibular implants after 85 months of service and 2 hydroxyapatite- (HA) coated maxillary implants after 38 months of service were examined. All implants were stable at the time of the patient's death. The mandibular implants had an average of 65% contact with bone and the maxillary implants had an average of 47% contact. The HA coating had separated from the maxillary implants in some areas and was free within surrounding connective tissue or surrounded by invaginating sulcular epithelium. The arrangement and pattern of bone contact appeared different between HA-coated and titanium implant surfaces.     

Bone response to plasma-sprayed hydroxyapatite and radiofrequency-sputtered calcium phosphate implants in vivo

PURPOSE: The objective of this study was to evaluate the effect of radiofrequency- (RF) sputtered calcium phosphate (CaP) coating of titanium implants on bond strength at the bone-implant interface and percent bone contact length. MATERIALS AND METHODS: Cylindric sputtered CaP-coated and plasma-sprayed hydroxyapatite- (HA) coated implants (4.0 mm diameter and 8 mm length) were implanted in dog mandibles. Half the sputtered CaP-coated implants were heat-treated. RESULTS: Twelve weeks after implant placement, no statistical differences in the mean ultimate interfacial strengths were observed between as-sputtered CaP-coated, sputtered CaP-coated heat-treated, and control plasma-sprayed HA-coated implants. Histomorphometric evaluation indicated that the percent bone contact lengths for the plasma-sprayed HA-coated implants and the as-sputtered CaP-coated implants were similar and significantly greater than that for the sputtered CaP-coated heat-treated implants. Differences in the ultimate interfacial strength and percent bone contact length between different implant sites in the mandible were not observed. DISCUSSION: The results of this study, considered together with the results of previous studies, suggest that once early osseointegration is achieved, biodegradation of the thin CaP coatings is not detrimental to bone-coating-implant fixation, and does not compromise bone responses to the coated implant surfaces. CONCLUSION: The interfacial strength and histomorphometric data suggest that the CaP coatings applied using the sputtering process produce bone responses similar to those of HA coatings applied using plasma spraying.     

Marginal bone loss pattern around hydroxyapatite-coated versus commercially pure titanium implants after up to 12 years of follow-up

PURPOSE: The purpose of this study was to compare the marginal bone loss (MBL), complications, and 12-year survival rates of commercially pure titanium (cpTi) and hydroxyapatite (HA)-coated implants placed in the maxilla. MATERIALS AND METHODS: The study group consisted of 120 patients (77 women, 43 men) treated from 1988 to 1997. A total of 388 implants (156 cpTi and 232 HA-coated) were placed in the maxilla. There were 126 immediate (32.5%) and 262 (67.5%) nonimmediate implants. Patients were evaluated annually. Mean follow-up was 60 +/- 32.3 months. MBL was measured on radiographs using the implant threads as the dimensional reference. MBL, complications, and 12-year survival and success rates were correlated with implant coating, time of implantation, implant dimensions, and position in arch. RESULTS: Total mean MBL was 1.07 +/- 2.16 mm. MBL was significantly lower with cpTi implants (0.55 +/- 1.04 mm) compared to HA-coated implants (1.51 +/- 2.71 mm) (P < .001). No statistical difference in regard to MBL was found between immediate and nonimmediate implants (0.86 +/- 1.8 mm vs 1.16 +/- 2.3 mm). The total 12-year survival rate was 91.4%. HA-coated implants had a significantly higher 12-year survival rate than cpTi implants (93.2% vs 89%; P < .03). Nonimmediate implants had a significantly higher failure rate (8.2%) than the immediate implants (1.3%) (P < .009). No correlation was found between type of implant coating and late implant failure. DISCUSSION: Immediate implants can serve as a predictable option, providing higher survival and success rates. HA-coated implants tended to fail less during the surgical phase, but had higher mean MBL compared to cpTi implants. CONCLUSIONS: HA-coated implants had greater MBL than cpTi implants but a higher 12-year survival rate. Immediate implants had a lower failure rate than the nonimmediate implants in this study population.     

The effects of ion beam-assisted deposition of hydroxyapatite on the grit-blasted surface of endosseous implants in rabbit tibiae

PURPOSE: This study was undertaken to evaluate ion beam-assisted deposition (IBAD) of hydroxyapatite (HA) on the grit-blasted surface of endosseous dental implants 6 weeks postplacement. MATERIALS AND METHODS: A total of 40 implants was placed in the tibiae of 10 New Zealand white rabbits. Twenty implants were grit-blasted only and the other 20 were grit-blasted and coated with HA by the IBAD method. After 6 weeks of healing, the rabbits were sacrificed and removal torque tests, histomorphometry, and morphometric analysis of microtomographic images were performed. RESULTS: The HA-coated group showed significantly higher removal torque, bone-to-implant contact, and bone volume than the other group. DISCUSSION AND CONCLUSION: In a previous study, the authors suggested that HA coating deposited on a machined surface by the IBAD method showed results comparable to or more favorable than the results obtained with a blasted surface. This study indicated that the HA coating produced by the IBAD method was also very effective on the aluminum oxide-blasted surface, as demonstrated by the early formation of osseointegration. Morphometric analysis by microtomography showed some promise in measuring the osseointegration rate. (More than 50 references.)     

In vivo evaluation of hydroxyapatite coatings of different crystallinities

PURPOSE: The influence of calcium phosphate (CaP) and hydroxyapatite (HA) crystallinity on bone-implant osseointegration is not well established. In this study, the effect of HA crystallinity and coating method on bone-implant osseointegration was investigated using a rat tibia model. MATERIALS AND METHODS: HA coatings 1 to 5 microm thick were produced using a supersonic particle acceleration (SPA) technology. The HA crystallinities used for this study were weight ratios of 30%, 50%, 70%, and 90%. A total of 128 HA-coated implants were placed into the tibiae of 64 male Sprague-Dawley rats. Bone-implant interfaces were evaluated using histology and push-out strength testing at 3 and 9 weeks after implantation. RESULTS: The 70% crystalline coatings exhibited significantly greater interfacial strength (5 implants/time point/treatment) than the 30%, 50%, and 90% crystalline coatings at 3 and 9 weeks following implantation. The implants with coatings of 70% crystallinity also had the greatest bone contact length. In addition, the HA coatings produced with SPA demonstrated greater interfacial strength and bone contact length than plasma-sprayed HA coatings (except for the HA coating with 30% crystallinity). DISCUSSION: HA coatings of different crystallinities exhibited different dissolution and re-precipitation properties which may enhance early bone formation and bone bonding. CONCLUSIONS: This study suggested that coating crystallinity and coating methods can influence the bone-implant interface.     

Histological evidence of osseointegration in human retrieved fractured hydroxyapatite-coated screw-type implants: a case report

Histological evidence of clinically successful dental implants is very rare. This case report presents histological evidence of osseointegration in human implants retrieved because of fractures at the connected portion between the abutments and fixtures due to a car accident. The duration of functional loading of the implants was 18 months. Two hydroxyapatite (HA)-coated screw-type implants were removed with part of the healthy bone from the mandibular left molar region. A block was prepared using cutting and grinding equipment to obtain a central section approximately 50 microm thick, which was stained with basic fuchsin and methylene blue. Histological examination revealed that the bone was dense and in close relation with the HA coating of the implants. The interspaces of each thread of the implant were filled with mineralized bone. Peri-implant soft tissue was not observed in the section. A high degree of osseointegration was noted, with a bone-to-implant contact of 87.5% (implant corresponding to tooth 36) and 97.4% (implant corresponding to tooth 37). The connection between the 30 and 50 microm HA coating and the metal was uniformly tight and constant. In conclusion, the histological evidence showed a high degree of osseointegration in two HA-coated screw-type dental implants retrieved after functional loading for 18 months.     

Hydroxyapatite-coated total hip replacement.

Biologic attachment of load-bearing orthopedic implants has developed as a response to long-term problems associated with polymethylmethacrylate cement fixation. Although early clinical results of uncemented hip and knee implants have been encouraging, histologic studies of retrieved implants have shown a distinct lack of bone apposition and ingrowth. Hydroxyapatite (HA) coatings applied to metallic implant substrates have been shown to enhance biologic fixation. These results have led to the clinical investigation of the use of HA-coated total hip replacements.     

Effect of hydroxyapatite on bone formation around exposed heads of titanium implants in rabbits

Dense hydroxyapatite (HA)--collagen was placed around the protruding heads of titanium and titanium alloy implants in the femurs of 38 rabbits. After 6 months, bone apposition was evaluated by gross examination and scanning electron microscopy. Although bone was observed in direct contact with the implant heads, the extremities of the implant heads were surrounded by connective tissue. Compared with the control animals, packing dense HA-collagen around the implant heads did not increase the area of osteogenesis. When the implants penetrated into bone through previously placed HA-collagen blocks, there was a decrease in the amount of bone attached to the body of the implants compared with the controls. The results of this study suggest that the use of dense HA does not increase the amount of bone tissue formed around titanium implants.     

Survival of hydroxyapatite-coated implants: A meta-analytic review

PURPOSE: Some reports show a benefit of coating dental implants with hydroxyapatite (HA), and others assert that resorption of the HA coating compromises long-term implant survival. This study examined this controversy by systematically reviewing all the current literature that reports the outcomes of HA-coated implants in human clinical trials. MATERIALS AND METHODS: A systematic Medline computer search of the English literature yielded 45 human clinical trials that reported on the outcome of HA-coated implants. Eleven studies that met specific inclusion criteria were selected for detailed analysis. The studies were divided into 2 groups. One group of 5 studies reported implant survival using overall percentage, and another group of 6 studies reported implant survival using life-table analysis. RESULTS: The overall percentage survival rates ranged from 93.2% to 98.5%, with 4 to 8 years of follow-up. The cumulative survival rates for studies that used life-table analysis ranged from 79.2% to 98.5%, with 5 to 8 years of follow-up. The yearly interval survival rates reported for the studies using life-tables were variable but remained above 90% and did not show a progressive or precipitous decrease with increasing years of follow-up. CONCLUSIONS: The survival rates reported for HA-coated implants were similar to the survival rates reported for uncoated titanium implants. If resorption of the HA coating causes late failure of implants, the yearly interval survival rates should have decreased with increased years of follow-up. This decrease was not observed in the longitudinal human clinical trials that met the selection criteria for this study. Detailed analysis of these clinical trials did not show that HA-coating compromises the long-term survival of dental implants.     

Tissue regeneration in bone defects adjacent to endosseous implants: an experimental pilot study

Extraction socket defects or alveolar ridge defects may limit or restrict placement of implants. The present study assessed the efficacy of inducing bone formation with demineralized freeze-dried bone (DFDB), osteoinduction with hydroxyapatite (HA), and guided bone regeneration with expanded polytetrafluoroethylene (e-PTFE) in bone defects adjacent to endosseous implants in an animal model. Twenty-four implants were placed in the long bones of 3 pigs. After preparation of 24 cylindric acute defects adjacent to the coronal 5 mm of each implant, 18 of the defects were treated by DFDB, HA, or e-PTFE. The 6 remaining defects healed spontaneously with no treatment (controls). In each pig, one tibia received 4 commercially pure titanium screw implants (3.75 mm x 15 mm), while the contralateral tibia received 4 HA-coated cylindric implants (3.25 mm x 15 mm). Bone formation in response to the 3 treatments and control cases was evaluated using computer-assisted densitometric image analysis. The results showed that a higher density of tissue formed under e-PTFE membranes. A significantly greater increase in bone density was noticed in bone defects treated with an e-PTFE membrane vs DFDB (P = 0.04), in e-PTFE vs control sites (P = 0.04), and in defects treated with HA vs DFDB (P = 0.04) in HA-coated implants. In titanium implants the differences observed were not significant. It was also observed that bone regeneration in defects treated with HA differs with the type of implant used (titanium vs HA-coated implants), but such differences were not significant.     

Influence of implant geometry and surface characteristics on progressive osseointegration

PURPOSE: Although no currently available technique for the measurement of osseointegration is entirely satisfactory, 3 clinical variables can be reasonably associated with the process: probing depth, micromobility, and crestal bone height. Micromobility can be quantified to some extent with the use of the Periotest, a commercially available instrument In this investigation, the influence of surface characteristics and geometry upon Periotest value (PTV) and probing depth measurements was studied. MATERIALS AND METHODS: In a multicenter trial, 120 healthy edentulous patients received 5 or 6 implants in the anterior mandible and were followed for 3 years. A total of 634 implants were placed. Every patient received at least 1 implant of each of 3 types: threaded titanium plasma-sprayed (TPS), threaded hydroxyapatite-coated (HA), and cylindric HA-coated. A randomization schedule assured that approximately equal numbers of each type of implant were placed and that they were uniformly distributed over the arch. RESULTS: Of the 4 tested combinations of dependent and independent variables, the only statistically significant (P < .05) effect was that of coating on PTV. At 1 year after prosthetic restoration, the mean PTV for HA-coated threaded implants was -5.36 +/- 1.24, compared with -4.86 +/- 1.70 for TPS implants. This difference steadily declined in magnitude and significance, until, after 3 years, the groups were indistinguishable. DISCUSSION: This study agrees with the previous observations that HA coating tends to accelerate the initial rate of osseointegration. The absence of a difference between threaded and cylindric implants confirms that the PTV responds to micromobility near the surface, on a scale much smaller than such gross geometric features. CONCLUSION: On the basis of these results, one may conclude that HA-coated implants exhibit a more rapid decrease in micromobility than do TPS implants of identical geometry.     

Comparative study of hydroxyapatite and titanium dental implants in dogs

This study compares the clinical performances and histologic response in dogs to a cylindrical implant with a surface consisting of dense hydroxyapatite (HA) and a threaded titanium implant in functionally loaded and unloaded conditions. Implantation was performed in five dogs, which were killed at 2 or 4 months postfunctional condition (4 or 6 months after implantation). Clinical evaluation showed that neither implant demonstrated significant movement, and assessment of gingival inflammation and sulcus depth showed no significant differences between them. After axial sectioning, the titanium implants were easily removed from the bone, whereas the HA-coated implants were adherent to the bone. Histologically, both implants showed osteogenic ingrowth to the surface in functional and nonfunctional conditions. High-magnification scanning electron micrographs of plastic sections showed that a portion of the interface between the HA-coated implant and the bone showed no gap, whereas gaps were observed at all interfaces with the titanium implant. Histomorphometric analysis by light microscopy indicated that there was no significant difference in the percent bone contact length. Clinically, the two implants behaved similarly.