Biointegrated hydroxylapatite-coated dental implants: 5-year clinical observations

Survival rates of hybrid rough surface implants and their alveolar bone level alterations

BACKGROUND

The design of hybrid surface implants takes advantage of characteristics of two different textures to improve clinical outcomes. To date, there are limited numbers of studies reporting the clinical results of hybrid surface implants. This study aimed to assess hybrid surface implants with two different rough textures in regard to survival, marginal bone level change, and biological complications.

METHODS

Retrospective review of dental records was conducted for 161 patients who had 460 hybrid surface implants to analyze survival rate. These implants had the dual sandblasted and anode oxidized surface. Sixty patients with 192 implants who had consecutive radiographs taken at specific time points and complete clinical examinations were included in the comprehensive analysis. The associations between patient- and implant-related characteristics, and clinical results were analyzed by log-rank test, Cox regression, and linear regression analysis.

RESULTS

Cumulative survival at 12, 36, and 60 months after placement was 97.4%, 96.4%, and 95.8%, respectively. The average marginal bone level change from baseline to the last visit was 0.31 ± 0.68 mm and 0.34 ± 0.77 mm at the mesial and distal sites, respectively. Prevalence of peri-implantitis was 0.5% at the implant level and 1.7% at the patient level. Implant site was associated with implant failure (P = 0.03). Smoking habit, history of periodontitis, and implant site were significantly associated with marginal bone level change (P = 0.001, < 0.001, 0.01, respectively).

CONCLUSIONS

Hybrid rough surface implants had high survival rate, stable bone level, and low prevalence of biological complications. This surface design demonstrated promising clinical outcomes. More studies are needed to further support the clinical advantages of hybrid surface implants.

Fabrication of strongly attached hydroxyapatite coating on titanium by hydrothermal treatment of Ti-Zn-PO4 coated titanium in CaCl 2 solution

Hydroxyapatite (HAp) coating was formed on zinc phosphate (Ti-Zn-PO4) coated Ti plates by hydrothermal treatment in CaCl2 solution at 200 °C for 12 h. Uniform surface coverage of the fabricated HAp coating was obtained by this method. SEM-EDX analysis of the adhesion test area showed that the presence of fractures only occurred in HAp crystals. On the other words cohesive fracture was seen in HAp coating layer formed on the Ti-Zn-PO4. The measured strength was around 42.3 ± 17 MPa. Rat bone marrow (RBM) mesenchymal stem cells were cultured and differentiation-induced on each sample (Ti plate, Ti-Zn-PO4 coated and HAp coated), and cell calcification properties were examined. Apparent differences in morphology and extension of the RBM cells were obtained, while the Ti-Zn-PO4 coated samples showed the highest cell number among all samples. After differentiation-induction, HAp coated samples showed the highest amount of alkaline phosphatase activity, and the highest level of cell calcification. Therefore, the hard tissue compatibility of Ti is improved by hydrothermally HAp coating of samples.

Chitosan fibers modified with HAp/β-TCP nanoparticles

This paper describes a method for preparing chitosan fibers modified with hydroxyapatite (HAp), tricalcium phosphate (β-TCP), and HAp/β-TCP nanoparticles. Fiber-grade chitosan derived from the northern shrimp (Pandalus borealis) and nanoparticles of tricalcium phosphate (β-TCP) and hydroxyapatite (HAp) suspended in a diluted chitosan solution were used in the investigation. Diluted chitosan solution containing nanoparticles of Hap/β-TCP was introduced to a 5.16 wt% solution of chitosan in 3.0 wt% acetic acid. The properties of the spinning solutions were examined. Chitosan fibers modified with nanoparticles of HAp/β-TCP were characterized by a level of tenacity and calcium content one hundred times higher than that of regular chitosan fibers.

Five-year prospective clinical evaluation of highly crystalline HA MP-1-coated dental implants

Contemporary plasma-sprayed hydroxylapatite (HA) coatings with high crystalline content are much more resistant to in vivo degradation than HA coatings of a decade ago but reportedly exhibit reduced wettability, which could potentially negatively affect tissue adhesion and long-term clinical outcome. The present prospective study was undertaken to determine if highly crystalline HA MP-1-coated implants could meet a minimum 5-year implant success rate standard of 85% in view of their previously reported decreased wettability. Study subjects were consecutive patients with 1 or more missing teeth in the maxillary and/or mandibular jaw who presented in 3 university dental clinics and 1 private dental practice. A total of 120 patients were treated per protocol and successfully restored with implant-supported prostheses. Four implants failed in 3 patients and were withdrawn from the study. There were no other irresolvable adverse events. Cumulative implant success at 5 years was 97% (n = 184 implants in 88 patients), which exceeded the 85% standard for implant success after 5 years of clinical function.

Cylindrical Dental Implants With Hydroxyapatite- and Titanium Plasma Spray–coated Surfaces: 5-year Results

Clinical follow-up was conducted on 127 cylindrical implants placed in 21 patients after 5 years of function: 75 implants were coated with titanium plasma spray (TPS) and 52 implants were coated with hydroxyapatite (HA). The aim of the study was to assess possible differences in clinical function and success rates for each implant type. Clinical and radiographic evaluations were conducted, and the periodontal indices of gingival bleeding, plaque, and calculus were measured. Cumulative data were analyzed for differences by implant type and jaw location. No significant differences were found between the 2 implant systems according to the periodontal parameters studied; however, 5-year success rates were 86.7% for TPS-coated implants and 94.3% for HA-coated implants. The periodontal probe index presented abnormal values in the patients with systemic disease and those who were provisionally restored with single-tooth restorations, complete screw-retained dentures, and fixed partial dentures. There were no differences regarding implant placement when mandibles and maxillae were compared. Long-term success rates were outstanding for HA-coated implants and acceptable for TPS-coated implants after 5 years of function. No significant differences were found between the 2 surfaces.

Hydroxyapatite film coating by thermally induced liquid-phase deposition method for titanium implants

Thermally induced liquid-phase deposition method was employed to produce a thin hydroxyapatite (HA) film on a titanium substrate in a metastable calcium phosphate solution. Titanium foil of 100x10x0.02 mm3 was used as a substrate. Prior to HA coating, the substrate was immersed in 5 M NaOH solution at 60 degrees C for 24 hours. Substrate temperature was kept constant at 60 degrees C for 0.5-3 hours by electrical heating with a DC power source in the metastable calcium phosphate solution. An X-ray diffractogram indicated that the film deposited on the titanium substrate was composed of HA. The amount of HA deposited increased with increase in heating time. These results suggested that a uniform HA film can be formed by simple chemical and thermal treatments. Based on the results of this study, this technique seemed to be useful for producing uniform HA coatings on complex-shaped and porous dental implants.

A distinguishable observation between survival and success rate outcome of hydroxyapatite-coated implants in 5-10 years in function

PURPOSE

To differentiate between the survival and success definitions of functional hydroxyapatite (HA)-coated implant prosthesis.

METHODS

A total of 248 implants (62 patients), 5-10 years in function, were evaluated. The implant distribution length was 8 mm (6.5%), 10 mm (29.4%), 13 mm (30.2%) and 15 mm (33.9%). The diameter was 3.25 mm (60.1%) and 4 mm (39.9%). Probing depth (PD), gingival index (GI), height of keratinized mucosa (KM) and recession (REC) were measured. Periapical radiographs were taken to estimate the amount of crestal bone resorption (BL), mesially and distally, with the aid of a millimetric-scaled magnifying glass (x 8). Only implants that fulfilled the success rate criteria were considered as successful. All other functional implants were assigned to the non-successful group. All functional implant prostheses were defined as survival ones.

RESULTS

The accumulative survival rate after 5 and 10 years was 94.4% and 92.8%, respectively. Accumulative success rates were 89.9% and 54%, respectively. Implants 13 and 15 mm in length (97.9% and 96.4%, respectively) had the highest survival rate, which was higher over implants 8 and 10 mm in length (75%, P<0.01 and 88.2%, respectively). The survival rate of 4 mm diameter implants compared with 3.25 mm was 96.5% and 90.3%, respectively (P=0.019). The average BL was 1.7, 0.92 and 2.79 mm for the survival, successful and non-successful defined implant groups. PD was 3.26, 2.79 and 4 mm and GI was 0.96, 0.75 and 1.57, respectively. These measurements were statistically different between implant groups. KM and REC measurements showed similar scoring for all groups. A correlation was shown between successful and non-successful implants on the score of GI and PD (P<0.001 in both).

CONCLUSION

A distinguishable observation between survival and success rate was noted particularly in long-term observations. Implant length and diameter have an influence on the survival rate. Clinical parameter scores expressed an influence on the defined implant status.

Finite Element Analyses of Two Antirotational Designs of Implant Fixtures

The purpose of this study was to compare the effect of cyclic compressive forces on loosening of the abutment retaining screw of dental implant fixtures with two different antirotational designs using the finite element analysis. A three-dimensional model of externally hexed and trichannel dental implant fixtures with their corresponding abutments and retaining screws was developed. Comparison between the two designs was carried out using finite element analysis. The results revealed that the externally hexed design has significantly higher overall stress, contact stress, and deflection compared with the trichannel design. The trichannel antirotational design has the least potential for fracture of the implant/abutment assembly in addition to its capability for preventing rotation of the prosthesis and loosening of the screw.

A study of the initial attachment and subsequent behavior of rat oral epithelial cells cultured on titanium

BACKGROUND

The seal between an implant and the oral epithelium is an important factor for successful implant therapy. The purpose of this study was to evaluate the initial attachment and subsequent behavior of rat oral epithelial (OE) cells on pure titanium (Ti) used for dental implants.

METHODS

OE cells derived from 4-day-old rats were cultured on Ti, polystyrene culture dishes, and glass coverslips. The number of attached cells, cell areas, number of colonies, and proliferation rates were measured. Additionally, immunostaining of vinculin and laminin-5 (LN5) was performed, and LN5-immunoreactive areas were measured.

RESULTS

After 24 hours of culture, there were fewer cells attached to the Ti than to the polystyrene dishes or glass coverslips, and the area of cells was greater on the polystyrene than on the Ti or glass. OE cells reached their maximum proliferation rate after 48 hours of culture on the polystyrene and glass, and after 72 hours on Ti. LN5 was deposited behind cells as they migrated, and the LN5-immunoreactive area was smaller on Ti than on polystyrene after 96 hours of culture.

CONCLUSIONS

The initial attachment of OE cells to Ti was inferior to that on polystyrene or glass, and the OE cell migration area indicated by the deposition of LN5 was smaller on Ti than on the other materials. Therefore, this study suggests that further improvement of Ti surface properties is needed for rapid attachment and spreading of oral epithelium to dental implants.

Development of calcium phosphate cement using chitosan and citric acid for bone substitute materials

We developed a calcium phosphate cement that could be molded into any desired shape due to its chewing-gum-like consistency after mixing. The powder component of the cement consists of alpha-tricalcium phosphate and tetracalcium phosphate, which were made by decomposition of hydroxyapatite ceramic blocks. The liquid component consists of citric acid, chitosan and glucose solution. In this study, we used 20% citric acid (group 20) and 45% citric acid (group 45). The mechanical properties and biocompatibility of this new cement were investigated. The setting times of cements were 5.5 min, in group 20 and 6.4 min, in group 45. When incubated in physiological saline, the cements were transformed to hydroxyapatite at 3, and 6 weeks, the compressive strengths were 15.6 and 20.7 MPa, in group 45 and group 20, respectively. The inflammatory response around the cement implanted on the bone and in the subcutaneous tissue in rats was more prominent in group 45 than in group 20 at 1 week after surgery. After 4 weeks, the inflammation disappeared and the cement had bound to bone in both groups. These results indicate that this new calcium phosphate cement is a suitable bone substitute material and that the concentration of citric acid in the liquid component affects its mechanical properties and biocompatibility.

Material fundamentals and clinical performance of plasma-sprayed hydroxyapatite coatings: a review

The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has aroused as many controversies as interests over the last decade. Although faster and stronger fixation and more bone growth have been revealed, the performance of HA-coated implants has been doubted. This article will initially address the fundamentals of the material selection, design, and processing of the HA coating and show how the coating microstructure and properties can be a good predictor of the expected behavior in the body. Further discussion will clarify the major concerns with the clinical use of HA coatings and introduce a comprehensive review concerning the outcomes experienced with respect to clinical practice over the past 5 years. A reflection on the results indicates that HA coatings can promote earlier and stronger fixation but exhibit a durability that can be related to the coating quality. Specific relationships between coating quality and clinical performance are being established as characterization methods disclose more information about the coating.

A comparison of hydroxylapatite coated implant retained fixed and removable mandibular prostheses over 4 to 6 years

In a 6-year prospective clinical study, 181 hydroxylapatite coated endosseous dental implants were placed into the anterior mandible of 48 patients. Twenty-one patients were treated with fixed prostheses and 27 patients with an overdenture. When the implants were exposed all 181 had integrated. To date, there is 100% survival of all implants and they all retain a functioning prostheses. The initial results were very promising, in both groups the interval success was over 95% in the first 4 years of the study. However, by year 6, the interval success rates had fallen to 83% for both the fixed and removable groups. This study also compares the construction and maintenance complications for the two types of restorations. The clinical time taken, after implant exposure, to construct the prostheses was similar whether the fixed (mean of 8 visits) or removable option (mean of 7 visits) was chosen. However, the removable restoration cost less than half the price of the fixed when both technical time and implant component costs were evaluated. Maintenance for both groups was higher than expected, but patients required more appointments in the removable group both in the first year and beyond. Regarding the prostheses itself, the incidence of remakes, relines and general adjustments was higher in the removable group. This study has shown that the overdenture offers an effective and initially a more economical alternative to the fixed prostheses, in the treatment of the edentulous mandible. However, long-term maintenance of such a prosthesis can be significant.

Simplified radiographic-surgical template for placement of multiple, parallel implants

A radiographic-surgical template can facilitate consultation with a surgeon and patient when implant-supported restorations are planned. A template that provides radiographic evaluation of the implant site and precise or modified surgical placement is presented.

Implant surface coating and bone quality-related survival outcomes through 36 months post-placement of root-form endosseous dental implants

Survival rates from placement to 36 months were reported for the ongoing Dental Implant Clinical Research Group studies of root-form endosseous dental implants. Failure rates for all implants were similar in bone qualities 1 and 2 (6.2% and 6.7%, respectively) and slightly higher in bone qualities 3 and 4 (8.5% and 8.7%, respectively). Hydroxyapatite (HA)-coated implants had an overall failure rate of 3.9% over 36 months in all bone qualities combined, while non-coated implants had a 13.4% failure rate for the same parameters. For each bone quality, there was a significant difference in implant survival for the non-coated implants (P < 0.01). The highest failure rates for non-coated implants were in bone qualities 3 and 4 (19.1% and 25.5%, respectively). No major difference in survival was found for HA-coated implants placed in each bone quality. Possible reasons for the differences in survival are discussed.

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.

In vitro stability of a highly crystalline hydroxylapatite coating in a saturated citric acid solution

A novel pressurized hydrothermal post-plasma-spray process has been developed to convert the crystalline non-HA and amorphous components of plasma-sprayed hydroxylapatite coatings back into crystalline HA. The process, known commercially as MP-1, was used to produce coatings comprising approximately 96% crystalline HA. The in vitro solubility of the coating in saturated citric acid solution has been measured to simulate the effect of implant detoxification procedures, which use citric acid as a cleaning medium. The MP-1 coating solubility in saturated citric acid solution (pH = 1) was compared to that of coatings with crystalline HA contents ranging from 37.5-82%. All coatings showed an initial sharp rise in coating dissolution, which correlated with crystalline HA content, followed by a steady state dissolution rate. After 60 s at 25 degrees C, the MP-1 coating showed a 65% decrease in solubility compared to a highly amorphous coating (AM-2). All coatings showed very similar steady state dissolution rates, except for AM-2, which was significantly higher. SEM analysis showed that the AM-2 coating surface was degraded substantially more than the other coatings, resulting in partial coating exfoliation. A mechanism of coating dissolution is proposed, in which the initial rapid leaching of soluble phases from the coating leaves behind a porous layer of highly crystalline HA at the coating surface. The stability of this porous crystalline layer leads to steady state, diffusion-limited dissolution of the remainder of the coating. The observed two-regime dissolution profile can be accurately represented by a 2-parameter model, which predicts the initial sharp rise in coating dissolution followed by a slower, steady state loss in coating mass. Model parameters were determined from experimental solubility data, and were shown to correlate with the percentage of crystalline HA in the coatings. The present data suggest that the treated coating is significantly more resistant to degradation from aggressive detoxification procedures such as citric acid burnishing.

A comparison of endosseous dental implant surfaces

Endosseous dental implants are available with various surface characteristics ranging from relatively smooth machined surfaces to more roughened surfaces created by coatings, blasting by various substances, by acid treatments, or by combinations of the treatments. Studies characterizing these implants and surfaces include in vitro experimentation, animal studies, and human clinical trials. Both descriptive and functional testing of the bone-implant interface includes histomorphometrics and biomechanical testing such as torque removal values and push out/pull out strength. Using these assays to evaluate and compare different surfaces, the data demonstrate that rough implant surfaces have increased bone-to-implant contact and require greater forces to break the bone-implant interface compared to more smooth surfaces. The objective of this report was to evaluate publications of human clinical experiences evaluating implant use in patients and to determine if differences existed in success rates of implants with relatively smooth surfaces compared to implants having roughened implant surfaces. Human trials were reviewed to determine the clinical efficacy of implants under various clinical indications. Synopsis tables were constructed and the experiences segregated by implant surface characteristics. Meta-analyses were performed on all implants in all locations, on implants placed only in the maxilla or the mandible, and, finally, on implants placed in the maxilla compared to implants placed in the mandible. Evaluation of the data revealed that predictably high success rates can be achieved for implants with both rough and smooth titanium surfaces and for hydroxyapatite-coated implants. When studies were clustered by specific indications or patient populations, rough surfaced implants had significantly higher success rates compared to implants with more smooth surfaces except in the case of single tooth replacements where the success rates were comparable. In general, implants placed in the mandible had significantly higher success rates than implants placed in the maxilla. However, in the partially edentulous patient group, titanium implants with a rough surface had significantly higher success rates in the maxilla compared to the mandible and, in cases of single tooth replacement, success rates were similar in the maxilla and in the mandible as was the case for hydroxyapatite-coated implants. The documented advantage of implants with a roughened surface in animal and in vitro experiments has been demonstrated in clinical cases when studies were compared in which specific indications or patients were treated. Additionally, implants placed in the mandible have, in general, higher success rates than implants placed in the maxilla, with only a few exceptions noted. These data from human clinical experiences support the documented advantage of implants with a roughened surface in animal and in vitro experimentation and indicate that the magnitude of the advantage is significant for patient care.

A survey of U.K. centres on implant failures

This study investigated the experience of endossoseus implants in the U.K. - how success rates compare with other countries; the common causes of failure; early detection, definition and treatment of the failing implant. Information was gathered by means of a questionnaire sent to 120 centres in the U.K. Thirty-nine centres responded to the survey, reporting on a total of 5328 implants which had been placed over an average time period of 6.5 years. A mean failure rate of 4.3% was reported in the mandible with 16% in the maxilla. The survey showed that 11 different implant systems were in use and that implants were used to support an overdenture in 56% of cases, and bridgework in 26%. The definition of the failing implant and the causes of failure were unclear, with a wide range of opinions given. A combination of methods were used to treat the failing implant including surgical techniques and chemotherapeutic agents, but the long-term success of these treatments was uncertain. Failure rates especially in the maxilla at some of the centres appear higher than have been previously suggested in the U.K. or abroad. Universal agreement on the criteria for 'success' and 'failure' of fixtures is needed along with agreed treatment protocols for the failing implant.

Differences in microstructural characteristics of dense HA and HA coating

Two implant types of hydroxyapatite (HA) currently are available for dental implants: dense HA-cemented titanium (Ti) and HA-coated. It has been shown in previous reports that there are differences in the chemical and mechanical stabilities between the dense HA and HA coated. The differences are thought to be due to structural differences between the two ceramic types. The aim of this study was to investigate the differences in microstructural characteristics of currently available dense HA and HA coated implants before implantation and at periods of 3 weeks and 10 months after implantation in canine bone. X-ray diffractometry, infrared analysis, transmission electron microscopy, and energy dispersive X-ray analysis were used. The dense HA is composed of crystal grains, with a well crystallized structure of HA, closely bound to each other and approximately 0.4-0.6 micron in size. Implantation did not change the original sintered structure of the dense HA. The HA coating was composed of an amorphous phase with a Ca/P ratio of 1.46 and a crystal phase consisting of oxyhydroxyapatite, tricalcium phosphate, tetracalcium phosphate, and CaO, with a Ca/P ratio of 1.57. In the amorphous phase, compared to other portions in the amorphous phase, there were some layers with lower atomic density and with no significant difference in Ca/P ratio. After implantation, the crystallization of super fine crystals of approximately 4-5 nm in thickness occurred in the amorphous phase, and with time it progressed and spread from the surface to the deeper portion of the HA coating. A Ca/P ratio of 1.58 in the crystallized portion was close to the ratio (1.60) in the dense HA, suggesting that the super fine crystals were HA. This crystallization cannot significantly decrease the solubility of the amorphous phase portion and poses risks of stress accumulation within the coating and a decrease of binding strength between the HA coating and the substrate.

The process of physical weakening and dissolution of the HA-coated implant in bone and soft tissue

Hydroxyapatite (HA)-coated implants were developed to promote osseointegration of titanium implants and to overcome the mechanical drawbacks of solid HA implants. Although many clinical reports on the prognosis of HA-coated implants have reported high success rates, the risks of dissolution and weakening of the coating have been noted. We hypothesized that the chemical and mechanical stability of HA coating are affected by its microstructural characteristics. The present study investigates differences in the microstructures of available HA-coated implants, before and after implantation into the coxal bones of dogs for periods ranging from 3 weeks to 10 months and under the coxal periosteum of dogs for 10 months. The results of transmission electron microscopy and energy-dispersive x-ray analysis revealed that crystallization of super-fine HA crystals occurred in the amorphous phase of the HA coating and progressed over time. This crystallization weakens HA-coated implants by making the amorphous phase brittle, causing stress accumulation within the coating, and causing a decrease in the binding strength between the coating and the substrate. Furthermore, the HA coating dissolved in soft tissue. Dissolution started with the super-fine HA crystals in the crystallized portion that was originally part of the amorphous phase.

Splinting osseointegrated implants and natural teeth in rehabilitation of partially edentulous patients. Part II: principles and applications

Lone standing splinted implant segments are accepted as optimal. However, in the treatment of partial edentulism, clinical reality often predicates the consideration of splinting teeth and implants due to variables of tooth/implant location and available bone support. This article presents a review on biomechanical aspects of splinting teeth and some considerations of splinting teeth and implants. A proposed classification of splinting applicable to both teeth and implants is presented as well as a discussion of the clinical aspects of splinting illustrated with clinical cases.

Prosthodontic problems and limitations associated with osseointegration

When compared with any other surgical or prosthodontic procedure, osseointegration has offered the greatest improvement in quality of life for patients who suffer with the effects of an edentulous condition. Results have been dramatic both functionally and from the aspect of patient satisfaction. However, a level of complication and compromise remains that limits overall patient and practitioner satisfaction. This article critically analyzes the existing literature relative to prosthodontic problems and complications of osseointegration for the edentulous patient. An attempt is made to compare the documented frequency of complication versus the perceived potential for complications, including implant failure, prosthesis misfit, component fracture, and screw loosening.

Clinical application of short hydroxylapatite-coated dental implants to the posterior mandible: a five-year survival study

STATEMENT OF PROBLEM

The surgical and restorative procedures at the posterior region of the maxilla and the mandible present a complex task in the treatment of partially edentulous patients.

PURPOSE

The purpose of this study was to investigate the applicability of short hydroxylapatite-coated dental implants to the posterior mandible of partially edentulous patients.

MATERIAL AND METHODS

Eight and 11 mm implants were evaluated as to their cumulative survival rate, clinical status (plaque index, gingival index, probing depth), and marginal bone loss over a 5-year period.

RESULTS AND CONCLUSIONS

The verified overall cumulative survival rate was 94% for implants and 91% for prostheses. These results suggest predictable success for the application of short implants to the posterior mandible.

Abscess formation around a hydroxyapatite-coated implant placed into the extraction socket with autogenous bone graft. A histological study using light microscopy, image processing, and confocal laser scanning microscopy

The purpose of this study was to evaluate the radiologic, histologic, and histometric findings for a retrieved hydroxyapatite (HA)-coated implant which had been placed into a fresh extraction socket with autogenous bone graft 3 months previously. A periapical radiography disclosed a vertical bone loss around the implant cervix. Examination of histologic section disclosed that granulation tissue including bone chips around the cervix, and newly-formed bone tissue around the grafted bone tissue on the HA coated surface. In the confocal laser scanning microscopic findings toluidine blue-negative bone tissue showed autofluorescence. Histometric analysis indicated that the average percent bone contact was 29.2% (ranged 26.4% to 34.1%). Suspected reasons for failure were an early exposure of the barrier membrane, its early removal, the implant placement into an infected site, inadequate antibiotic premedication, and/or poor control of infections around teeth prior to implant surgery and around implants before and after placement of barrier membrane.

Validation of dental implant systems through a review of literature supplied by system manufacturers

STATEMENT OF PROBLEM

The use of endosseous implants to support and retain dental prostheses has become a routine treatment option in many dental practices. Although physical, mechanical, and chemical differences exist among implant systems, survival claims are similar.

PURPOSE OF STUDY

This review solicited literature from six implant manufacturers that was thought, by their standards, to be pertinent to the validation of their implant system.

METHODS

The literature was reviewed and categorized.

CONCLUSION

On the basis of the literature supplied by the manufacturers, only one implant system demonstrated scientifically valid long-term success.

Experimental peri-implant tissue breakdown around hydroxyapatite-coated implants

This study monitored experimental peri-implant tissue breakdown around hydroxyapatite (HA)-coated titanium dental implants. Thirty-two HA-coated cylindrical implants, in groups of two, were bilaterally inserted in the posterior maxilla and mandible in 4 Macaca mulatta monkeys. Two months after healing-abutment connection, a 2-month plaque control program was initiated. Clinical and radiographic recordings and peri-implant submucosal microbial samples were then obtained (baseline). Cotton ligatures were next placed around the healing-abutments and plaque control measures were abandoned. Clinical and radiographic recordings were repeated at 5 and 10 months post-baseline. Microbial samples were repeated at 10 months post-baseline, and ligatures were removed. Clinical, radiographic, and microbial examinations were again repeated at 11 months post-baseline. Mean modified plaque index (mPI; P < 0.01), gingival index (G]; P < 0.01), and bleeding on probing (BOP; P < 0.05) scores increased over the plaque accumulation period. The mPI, and GI scores decreased after ligature removal (P < 0.001). Mean probing depth (PD) and clinical attachment level (AL) increased between baseline and the 5- and 10-month examinations (delta PD 3.0 mm; delta AL 2.7 mm; P < 0.05). PD values were reduced following ligature removal (P < 0.05). AL values and BP scores remained unchanged. A significant negative correlation was found between induced defect depth and width of keratinized mucosa at baseline (P = 0.03). At baseline, the submucosal microbiota was dominated by coccoid cells. Following ligature placement, the microbiota included a large proportion of Gram-negative anaerobic rods, predominantly Porphyromonas gingivalis, Bacteroides forsythus, and Fusobacterium species as well as beta-hemolytic streptococci. Ligature removal had a limited effect on the composition of the submucosal microbiota. This non-human primate study indicates that ligature-enhanced plaque accumulation is a precursor of progressive peri-implant tissue breakdown around HA-coated implants. The associated microbiota resembles that of peri-implantitis and destructive periodontal disease in humans. This preclinical model may be useful to study modalities aimed at arresting peri-implant tissue breakdown and at regeneration of bone in peri-implantitis defects.

The response of bone in primates around unloaded dental implants supporting prostheses with different levels of fit

Implant failure as a consequence of prosthetic loading following clinical determination of successful stage I healing is poorly understood. A basic premise of accepted prosthetic protocol is passive connection of multiunit prostheses to the implant support. To better understand mechanical factors related to implant failure, this basic passivity premise was experimentally tested prior to study of functional loading research. The purpose of this preliminary study was to measure the bone response around implants placed in the mandible of baboons that supported prostheses exhibiting two levels of fit and not loaded occlusally. Screw-retained prostheses that exhibited a mean linear distortion of 38 microns and 345 microns made up the fit and misfit groups respectively. The results failed to distinguish a difference in bone response between the two levels of prosthetic fit. Although the finding can be argued as a sample size limitation, the data strongly suggest an opposite response than is clinically expected and, consequently, does not warrant the use of additional animals in this initial study. Because the design of this study does not mimic the clinical application of misfitting prostheses (where dynamic functional loads are superimposed with misfit loads), it cannot be inferred that, in clinical application, fit does not alter the osseointegrated interface. Ongoing investigation of failure due to nonpassive connections under dynamic loading conditions of mastication will help clarify the clinical significance of passivity.

The effect of electrical perturbation on osseointegration of titanium dental implants: a preliminary study

PURPOSE

Successful osseointegration of titanium dental implants is decreased in areas of poor bone volume and density. Low amperage direct current (LADC) has been shown to perturb bone cells, which in turn promotes bone growth. The purpose of this experiment was to evaluate the effect of LADC on the osseointegration of endosseous titanium dental implants.

MATERIALS AND METHODS

Two implant sites were prepared in the body of the mandible of five rabbits by an extraoral approach. An LADC-stimulated 3.75 x 7 mm-titanium implant was placed in one site and an identical control implant was inserted on the contralateral side. A sterilized silicone-encased power pack producing 7.5 +/- 0.2 uA and 1.35 +/- 0.01 V was placed in a submandibular pouch. The active cathode lead was attached to the LADC implant and the anode was placed in the mandible 5 mm distal to the implant. Nonactive leads were similarly connected to the control implant. Twenty-eight days after placement, the implants were removed using a torque wrench, and the bone surrounding the implants was examined both microscopically and radiographically.

RESULTS

The average force to initial rotation was 1,320 +/- 880 g/cm for the LADC-stimulated implants and 1,290 +/- 238 g/cm for the control implants. This was significantly different by t test (P = .94). Light microscopic evaluation demonstrated a mixture of compact and woven bone and fibrous tissue adjacent to both groups of implants. Histomorphometric analysis demonstrated an average percent of bone in relation to the total tissue adjacent to the control implants of 33.5 +/- 15.4 and 40.2 +/- 4.8 for the LADC-stimulated implants (not significantly different, t test, P = .39). CONCLUSION. It was concluded that LADC as used in this study does not positively affect the healing of bone. Its ability to enhance bone growth around titanium dental implants needs further investigation.

Histological and mechanical comparison of hydroxyapatite-coated cobalt-chrome and titanium implants in the rabbit femur

The purpose of this study was to compare hydroxyapatite (HA)-coated titanium (Ti) and HA-coated cobalt-chrome (CoCr) implants in the distal femur of the rabbit by evaluating bone apposition and interfacial shear strength. Bilateral cylindrical implants with a plasma sprayed 50-microns thick HA coating were press-fit into the metaphyseal cancellous bone of the lateral femoral condyles in a transverse fashion, and the animals were sacrificed at 2, 4, and 8 weeks postimplantation. Mechanical strength of the interface between HA and bone was measured using the pushout method. For histologic analysis, the fractional linear extent of bone apposition was quantitated. No differences were found in the interfacial shear strength between the Ti and CoCr at any time period. The amount of bone apposition increased significantly at each time interval for both substrate metals, but there were no significant differences between the two substrates at any of the time periods studied. The HA-coated CoCr implants performed in a similar manner to the HA-coated Ti implants, both mechanically and histologically, suggesting that HA-coated CoCr implants deserve further study as a viable alternative to Ti for the biological fixation of total joint components in orthopaedic surgery.

Long-term follow-up on hydroxylapatite-coated cylindrical dental implants: a comparison between developmental and recent periods

PURPOSE

To compare success rates for dental implants placed from 1985 through 1988 and from 1989 through 1991, and to investigate the factors associated with success or failure.

PATIENTS AND METHODS

All hydroxylapatite-coated cylindrical implants placed from 1985 through 1991 were followed yearly. Lifetable survival analyses compared implant success for a "developmental period" from 1985 through 1988 (4 to 8 years follow-up) and a "recent period" from 1989 through 1991 (1 to 4 years follow-up). Reasons for success or failure, time from implant placement to removal related to failure reason, outcome after implant removal, and a morbidity analysis are included.

RESULTS

The 7 to 8-year cumulative success rate for all implants placed in the developmental period (maxilla and mandible combined) was 86.5%; it was 84.2% for all maxillary implants and 87.5% for all mandibular implants. The cumulative success rate for all implants placed in the recent period was 97.5%; it was 97.5% for all maxillary implants and 97.6% for all mandibular implants. The difference between the two periods was statistically significant only for the anterior maxilla. Regression analysis on the interval success rates indicates that interval failure did not follow a linear relationship with time. The most common reasons associated with failure were lack of keratinized gingiva, poor oral hygiene, mechanical overload, and malposition.

CONCLUSION

Comparison with previously reported cumulative success rates indicated learning curve experiences comparable with other implant systems. Improvements in hardware, surgical and prosthetic techniques, and patient selection have led to an improvement in success rates with the recent period implants.

Morphologic variation in plasma-sprayed hydroxyapatite-bioactive glass composite coatings in Hank's solution

Pure hydroxyapatite (HA), pure bioactive glass (BG), and a new series of (HA/BG) composite coatings were plasma-sprayed onto a commercial Ti6A14V substrate. Changes in morphology and phases of these coatings after immersion in Hank's physiologic solution were investigated using XRD and SEM. Results indicated that the as-sprayed BG coating has an essentially amorphous structure with a very rough surface. After 7 days of immersion, the BG surface started to dissolve, and weak XRD peaks of apatite started to develop. Small amounts of CaO, beta-TCP, Ca4P2O5, as well as a glassy film, were found on the as-sprayed pure HA surface, most of which dissolved in 7 days. The XRD intensity of apatite in pure HA slowly increased with immersion time until, on the 10th day, the intensity started to drop, and 10 days later, the intensity rose again. This undiscovered "drop and rise" phenomenon was observed for the HA/BG composite coatings in an even more dramatic way. The presence of HA accelerates the dissolution of bioactive glass.

Hydroxyapatite ceramic coating for bone implant fixation. Mechanical and histological studies in dogs

The success of bone ingrowth into porous coated implants depends on several factors which can be separated into five main groups: implant related factors, such as design of implant, surface structure and pore characteristics. status of host bone bed, such as underlying disease (rheumatoid arthritis, osteoporosis), available bone stock, use of drugs and surgical technique. mechanical stabilization and loading conditions applied on the implant. adjuvant therapies such as bone grafting and HA coating which might enhance the amount of bone ingrowth. remodeling of periprosthetic bone. Once bone ingrowth has occurred, maintenance of bony anchorage depends on bone remodeling at the interface. The present series of studies were performed in order to investigate the effect of some of these factors on bone ingrowth in relation to hydroxyapatite (HA) and titanium alloy (Ti) coating when subjected to pathological and mechanical conditions mimicking the clinical situation. HA- and Ti-coated implants were inserted into the femoral condyles of mature dogs. The observation period ranged from 4 to 16 weeks, and the results were evaluated by mechanical push-out testing, histomorphometric analysis, polarized light microscopy, UV fluorescence microscopy, collagen analysis and transmission electron microscopy (microanalysis). There were no complications related to the operative procedures and all dogs were terminated according to the original time schedule. Host bone related factors were studied in the initial experiments. First, the effect of a gap between bone and implant was studied and compared with press-fit insertion. The HA-coating yielded superior effect on bone ingrowth compared to Ti in situations where the implant was surrounded by a gap and also where the implants were inserted in press-fit. Gaps of 1 mm and 2 mm around the implant were bridged by bone around HA implants whereas significantly less amounts of bone filled the gap around Ti implants. The gap-healing capacity of bone was increased even at a relatively great distance (400 microns) from the HA surface. This finding indicates that the osteoconductive effect of HA is not limited to the bone forming capacity on the surface of the implant. A positive gradient of newly formed bone was found towards the HA-coating, this gradient not being found towards the Ti-coating. In order to investigate the significance of arthritic bone changes (osteopenia) on fixation of porous coated implants we adopted the Carragheenin-induced gonarthritis model resulting in substantial bone loss as determined by CT-scanning.(ABSTRACT TRUNCATED AT 400 WORDS)

Current trends in implant reconstruction

Significant advances have occurred in preprosthetic surgery in the past decade. Patients whose problems range from the loss of a single tooth to extreme conditions involving acquired or congenital defects now have options for reconstruction previously not possible. Optimal care most often requires a team approach with careful planning and execution. Ongoing basic research and strict clinical documentation involving current and future areas of treatment will provide an even greater degree of safety and effectiveness for our patients.

Dental implants: a review

The present article is a review presenting an update on the field of dental implants since the World Workshop in Clinical Periodontics in July 1989. Areas that are discussed include following: 1. Biomaterials and the implant interface, and the interaction of these with the environment. 2. Periodontal considerations including data supporting a perimucosal seal of implant to soft tissue and discussion of the endosseous interface between the bone and the implant. 3. Newer techniques of diagnostic imaging and their determination of bone types are related to the future practice of dental implants. 4. Implant selection and the surgical techniques involved in implant placement. 5. Current ideas of implant prosthodontics, implant maintenance, and the treatment of implant failures. 6. Finally, the use of dental implants in the United States and Sweden.

Placement of endosseous implants into tooth extraction sites

This study reports 4-year experiences with placement of hydroxylapatite-coated dental implants into extraction sites immediately after tooth extraction. Small defects present after implant placement were treated with dense, nonresorbable hydroxylapatite. Larger defects present after implant placement were treated with demineralized bone. Indications and contraindications for placement, as well as surgical techniques, are discussed.

Clinical comparison of hydroxyapatite-coated titanium dental implants placed in fresh extraction sockets and healed sites

The placement of hydroxyapatite-coated dental implants in fresh extraction sockets was compared to placement in adjacent healed sites in 14 patients. Systematic sequential documentation was obtained regarding periodontal health, radiographic bone levels, and implant stability at the time of implant placement, at uncovering, and from 8 to 24 months (mean 16 months) after loading and restoration delivery. There were no significant differences in any clinical parameter between those implants placed in fresh extraction sockets and those placed in healed areas. Periodontal health, maintenance of crestal bone levels, and implant stability were excellent for implants placed in both types of recipient sites. The results of this study suggest that hydroxyapatite-coated dental implants can be successfully placed in fresh extraction sockets utilizing otherwise standard implant placement techniques, and that they appear to clinically perform equally well in fresh sockets and healed sites.

Factors associated with soft- and hard-tissue compromise of endosseous implants

This prospective analysis identifies factors associated with endosseous implant removal as well as factors associated with implant morbidity resulting in nonscheduled patient visits. Treatment of the latter conditions is discussed. The most important factors identified for implant success were surgery without compromise in technique, placing implants into sound bone, avoiding thin bone or implant dehiscence at the time of implant placement, avoiding premature implant exposure during the healing period, establishing a balanced restoration, and insuring appropriate follow-up hygiene care. In the posterior mandible, the presence of keratinized gingiva was strongly correlated with optimal soft- and hard-tissue health.