Hot isostatic pressing-processed hydroxyapatite-coated titanium implants: light microscopic and scanning electron microscopy investigations.

Hot isostatic pressing (HIP) was used in a new procedure to produce hydroxyapatite (HA) coatings on a commercially pure titanium (cpTi) substrate for osseous implantation. Eighteen HIP-processed HA-coated implants were placed in the inferior border of the mandibles in 2 Labrador retriever dogs and left submerged for 3 months. As control specimens, 12 sandblasted cpTi implants were placed in the same mandibles and, to compare the bone reaction, 2 additional plasma-sprayed HA-coated implants (Integral) were placed. Tissue reactions at the bony interfaces of the implants were studied in ground sections with the implants in situ, using ordinary, fluorescent, and polarized light microscopy and scanning electron microscopy (SEM). The HIP-processed HA coatings displayed an increased density in light microscopy and SEM as compared to plasma-sprayed coatings. Direct bone-implant contact was found in all 3 types of surfaces. However, the production of new bone was far more abundant for the HA-coated implants than for sandblasted cpTi implants. The presence of bone-forming and bone-resorbing cells indicated active bone remodeling in the interface area at 3 months after implant placement. The present results support the view that epitaxial bone growth may occur from the HA-coated implant surface. It was concluded that the increased density of the present HIP-processed HA material does not reduce the bioactive properties of the coatings.

Registration of localization, occlusion and occluding materials for failing screw joints in the Brånemark implant system.

This study is based on data from routine follow-up registration following functional loading of a consecutive number of osseointegrated prostheses at the Dental School, University of Oslo. Fifty-six patients with 240 Brånemark implants were examined 2-4 months after the implants were loaded, and a protocol form for collecting information about the status of the treatment was completed. The examinations included registration of oral hygiene, pathological alterations in soft and hard tissues, type of material used in contacting occlusal surfaces, occlusal design and technical and mechanical failures. All superstructures, except CeraOne single-tooth prostheses, were unscrewed for inspection of implant and screw joint mobility. Eighty-three per cent of the implants were found in the upper and lower frontal segments of the jaws. The survival rate for individual implants in this study was 94%, which is well within the generally accepted level for osseointegrated implant systems. Plaque and soft tissue complications were low and could not be associated with the early losses of implants. Group function was the preferred design of the occlusal contact pattern (53.4%), followed by 37% for canine guidance and about 9% for balanced articulation. Fourteen abutment screws and 7 gold screws loosened during the period between permanent loading and the first follow-up registration. A majority of the failures occurred in osseointegrated bridges occluding with complete dentures in the opposite jaw. The failing screw joints were found in 25% of the patients, which means that one fourth of the patients needed extra mending appointments. The failures are assumed to be iatrogenic, and measures to avoid them are discussed.

[What happens to patients referred for implant evaluation? Treatment choice and patient response]. / Hva skjer med pasienter som henvises for implantatutredning? Terapivalg og pasientreaksjoner.

Case histories of patients referred to a university clinic for evaluation/treatment with implants were studied, regarding recommended and actually performed treatment. Patient reactions after treatment with conventional methods were also recorded. Three main groups attended: 1) Elderly, unsatisfied complete denture wearers. 2) Patients with few remaining teeth and an aversion against removable dentures. 3) Young patients with single teeth missing in an otherwise healthy dentition. Fifty-seven per cent of edentulous patients were recommended correction/replacement of their conventional full denture. Three out of four followed the recommendation. For jaws with a severely reduced dentition conventional prosthetic alternatives were advocated in 80 per cent of the cases. Corresponding treatment was carried out in 57 per cent of the cases, prosthetic appliances differing substantially from the suggested alternative in 26 per cent, and 17 per cent received no prosthetic treatment. Only few jaws required single tooth replacements. Every second patient who had this complete denture corrected or remade, considered implant therapy then superfluous. All complicated cases with extensive tooth loss were treated to the patients satisfaction, without using implant support, provided the treatment was referred to a colleague with specialist training. Forty per cent of similar cases remitted to their general practitioner did not receive any prosthetic treatment at all.

Effects of cyclophosphamide on open, granulating skin wounds in rats.

The effect of cyclophosphamide on the healing of open cutaneous wounds was studied in rats. Following intraperitoneal injections of 25 mg/kg body weight every second day for 9 days, only about 7% of the wounds were completely covered by epithelium after 15 days, whereas in the control animals 60% of the wounds were completely epithelialized. Measurements of wound diameters in circular skin wounds revealed unhealed wound areas in the drug treated animals which were significantly larger than those of the control animals. Cyclophosphamide was found to reduce the occurrence of H3-labelled cells in the granulation tissue when evaluated after 11 days. At 15 days there was no difference in the labelling frequency between treated and control animals, indicating reversal of the drug effect.

Mechanical properties and hydroxyproline content of connective tissue in porous ceramic implants.

The present study describes a model applying ceramic implants (A1203) for in vivo studies of connective tissue regeneration. Two types of implants have been developed: a one-piece model for histological examination and chemical analyses, and a two-piece implant which can also be used for mechanical testing of connective tissue. When these were implanted subcutaneoulsly on the back of rats, a correlation was found between the mechanical strength and the hydroxyproline content of connective tissue in the implants. The peak synthesis occurred between the 7th and the 14th day after implantation, and a plateau was reached for both strength-increases and hydroxyproline-formation between the 14th and the 21st days. For histological examination, the implants were embedded in plastic materials and prepared as hard tissue specimens. The model presented can be applied to study connective tissue regeneration in normal and pathological conditions, including studies of the effects of various drugs on the connective tissue.

Corrosion of gallium alloys in vivo.

The aim of this work was to study the corrosion of gallium alloys in vivo. Three gallium alloys were tested: GF alloy, Galloy and an experimental GaIn alloy. An amalgam was applied as a control. After ageing for a minimum of two weeks, one disc of each of these alloys was mounted with the polished side up in the buccal surfaces of 17 acrylic dentures. Eight sets of the specimens were retrieved after exposure to the oral cavity for 2-4 months, and another seven were retrieved after 6-9 months. Corrosion of the polished cross-sections of the specimens was studied using scanning electron microscopy (SEM). Only the CuGa2 phase was found to corrode substantially in all three of the alloys investigated, leaving behind holes up to 20 microm deep. This is consistent with the corrosion reported after immersion tests in a solution of 0.1 mol lactic acid and 0.1 mol NaCl for 7 days. Such in vitro tests are also reported to cause distinct corrosion of the Sn phase in the gallium alloys. However, a salient feature of the corrosion in vivo was the lack of detectable dissolution of this phase. Thus, for gallium alloys, the accelerated in vitro immersion method produced results which did not agree with clinical observations. Large variations in the corrosion of the CuGa2 were observed from patient to patient. The amount of corrosion on the Galloy specimens appeared to be less and on a finer scale than on specimens of the two other alloys. The depth of corrosion was thus shallower than for this alloy. This finding indicates that there is room for further improvement of the corrosion resistance by modifying the microstructures. Less overall corrosion was found for the amalgam control than for the gallium alloys.

Effects of cyclophosphamide on the formation and solubility of collagen.

The effects of low (5 mg/kg X 7) and high (20 or 30 mg/kg X 7) doses of cyclophosphamide on the formation an solubility of collagen in subcutaneous, porous implants, bones and incisional skin wounds were studied in young, male rats. At the 5 mg/kg schedule, effects from the drug were only detected as an increased solubility of collagen in implant connective tissue. At the 20 mg/kg schedule, there was a significant reduction of the synthesis and solubility of collagen in bones and in skin wounds. The 30 mg/kg schedule significantly depressed all the parameters studied except the specific activity of hydroxyproline in implants. Collagen stability seems to be impaired at low dose levels, whereas one of the main effects of high doses appears to be inhibition of collagen synthesis.

Synthesis and solubility of collagen in rats during recovery after high-dose cyclophosphamide administration.

The metabolism of collagen and mineral was studied during a nine-day postmedicational period in young, male rats receiving high-dose intraperitoneal cyclophosphamide treatment every second day for 12 days. Two days after ending medication the white blood cell counts (WBC) were reduced by about 70%. Both synthesis and solubility of collagen were suppressed by the present medication 2 days after termination of treatment. This suppression continued throughout the 9-day postmedicational period in bones, whereas in connective tissue of porous, ceramic implants both total collagen and the amount of salt soluble collagen regained normal values 9 days after cessation of treatment. Increased mineralization was found 2 days after ending medication and this high degree of mineralization persisted during the postmedicational period studied. Serum albumin levels were reduced and no increases were detected during the postmedicational period. The suggestion is made that the general protein synthesis is affected by high-dose cyclophosphamide administration.

Effects of cyclophosphamide on mechanical properties of bone and skin in rats.

The effects of several different doses of cyclophosphamide on weight increase, longitudinal bone growth and mechanical properties of bone, intact skin and skin wounds, were studied in 30 young, male rats. The cystostatic effect was evaluated by counting white blood cells (WBC) in arterial blood at the end of the medication period. Compared with the control animals, the longitudinal bond growth, the mechanical properties of the distal femoral metaphysis and the skin wounds were most noticeably affected by the drug. Diaphyseal torsional strength of the femoral bone and tensile strength of intact skin were less affected.

Methylmethacrylate screw implants--radiographic, histological and fluorescence microscopic investigations in dogs.

Twenty-one methylmethacrylate screw implants were inserted in the jaws of three Labrador dogs. Clinical, radiographic, microscopic and fluorescence microscopic examinations were performed. Direct bone-implant contact was found in all firm implants, and the density of the alveolar bone increased towards the screw surface. In these areas no fibrous tissue was found between bone and implant. Horizontal fibres at the junction between the head and the neck of the implant seem to have impeded downgrowth of subepithelial granulation tissue.

Evaluation of endosseous implant abutments as a base for fixed prosthetic appliances. A preliminary clinical study.

In the present 2-year report nineteen Linkow blade implants with a total of twenty-seven perforating posts were assessed. All implants included were considered functionally successful and served as abutments for fixed prosthetic appliances. Periodontal probe and radiographic measurements of bone loss around the perforating implant posts, and registration of plaque and gingival index scores were performed every 6 months. During the first 4-6 weeks after implantation a vertical bone loss approximating an average of 1-2 mm occurred in the neck area of the implants. After this initial resorption, bone loss proceeded at a slower rate. The mean annual crest reduction was approximately 0.1 mm from the first to the fourth examination, as assessed from radiographic measurements. Periodontal probe measurements, showing a mean annual crest reduction of 0.2 mm, usually exhibited higher values than corresponding radiographic measurements at both implants and abutment teeth. At implants there was a significant positive correlation between plaque and gingivitis after 18 and 24 months, but not before that time. No correlation was seen between gingival index scores and the degree of bone resorption.

Method for radiographic assessment of alveolar bone level at endosseous implants and abutment teeth.

A radiographic method expressing the alveolar bone level in absolute figures is presented. By means of a calibrated measuring radiographic film fixed to a magnifying viewer, alveolar bone levels were determined directly on intraoral periodic "identical" radiographs. A polyether impression was made for fixation of the filmholder in order to obtain reproducible radiographs. The method was applied to assess changes in the alveolar bone level at endosseous implants and abutment teeth. Radiographs of 23 endosseous implants and 21 abutment teeth from nine patients were examined and measurements of the alveolar bone level were performed. The mean difference between double observations on the same exposure as well as on repeated exposures was about 0.2 mm (s.d. 0.17-0.32 mm). The uncertainty of the present radiographic method was mainly due to the measurement procedure, as the radiographic technique showed a high degree of reproducibility. The method is a simple and reliable technique for longitudinal investigations of changes in the alveolar bone level at endosseous implant and tooth abutments.

Bonding capacity in bone of HIP-processed HA-coated titanium: mechanical and histological investigations.

The main problems using plasma-sprayed hydroxyapatite (HA) as a coating material on metallic implants are its porosity, low fatigue strength, and weak adherence to the metallic substrate. To overcome these problems a new technique using hot isostatic pressing (HIP) has been developed for producing HA-coated titanium (Ti) implants. Specimens produced at a maximum temperature of 850 degrees C and a maximum pressure of 720 bar displayed a dense, glassy, 25-microns thick coating with small amounts of porosity and a mean surface roughness of 0.7 microns, as compared with 1.6 microns for sandblasted Ti. Twenty conical HA-coated (720 and 100 bar pressure) and 10 noncoated Ti implants were inserted through the cortex of the lower margin of the mandibles of sheep and allowed to heal for 60 days. Push-out tests for implants processed at 720 bar pressure showed substantially higher bone/implant bonding values than for sandblasted Ti implants. Histological studies indicated a direct contact and probably chemical bonding between bone tissue and the HA coatings. The area of contact was almost 3 times as large as for the Ti implants. The adherence of the 100-bar coating to the Ti surface was inferior to the 720-bar coating, as shown by the loosening of the coatings in several areas.

Hydroxyapatite coatings on Ti produced by hot isostatic pressing.

Plasma spraying is a technique currently used in the production of HA-coated titanium implants. These coatings have been shown to be porous; they dissolve and have a weak bond to the substrate. The long-term interface strength has been questioned in particular. The aim of the present work was to produce HA coatings without the shortcomings of those produced by plasma spraying. Hot isostatic pressing (HIP) at 850 degrees C and 1000 bar with no holding time was applied for this purpose. Initially, the HA powder was mixed with water and air sprayed on the Ti substrate. The Ti specimens were then cold-pressed, enclosed by a protective Pt foil, and encapsulated in an evacuated glass ampulla. Subsequent to HIP, the glass and the Pt foil were removed. These coatings were denser than those produced by plasma spraying. The bonding was measured to be > 62 MPa, which is considered to be satisfactory. The structure of the coating was checked by X-ray diffraction and IR spectroscopy, and was found to correspond to that of HA. Some cracks were observed in the coating running predominantly vertical to the surface. Whether these are acceptable has to be verified by in vivo experiments.

Mechanical properties of bone and skin during recovery after cyclophosphamide administration.

The effects of cyclophosphamide were studied 2, 5 and 9 days after terminating a two-week every-second-day intraperitoneal medication in young, male rats. The cytostatic effect was assessed by counting white blood cells (WBC) in arterial blood. WBC counts were reduced by 72% of control values at 2 days and regained normal values at 9 days after an overshooting leucocytosis at 5 days. Compared to control animals, the treated rats had significantly reduced body weights, metaphyseal bending strength and longitudinal growth of the femur at all time intervals observed. The torsional strength of the femur diaphysis and the strength of wounded skin were not affected at 2 days, but significantly reduced at 5 and 9 days. The tensile strength of intact skin was not found to be affected by the drug. From the 5th to the 9th day after ending medication, the curves for control and treated animals were assuming parallel slopes regarding metaphyseal bone strength, longitudinal bone growth and tensile strength of wounds. This may indicate reversion of the drug effects approximately one week after terminating medication.

Comparison of bone reactions to coated tricalcium phosphate and pure titanium dental implants in the canine iliac crest.

Titanium and TCP-coated implants were compared after insertion in the canine iliac crest. Observation time was 14 wk. Evaluation included pull-out tests, energy dispersive X-ray analysis, and histologic examination of in situ, undemineralized implants. The TCP-coated implants were more firmly attached to bone than were the titanium implants. The calcium/phosphorus ratios around the titanium implants were higher than around the TCP-coated implants. Both types of implants were closely surrounded by bone after a 14-wk implantation.

Comparison of bone resorption at one-step and two-step mandibular endosseous implants in dogs.

Endosseous dental implants have been inserted into dog jaw bone following two different implantation principles. Using the two-step procedure, the implant is left submerged, covered by the mucoperiosteum for a healing period, before communication with the oral cavity is established. According to the one-step procedure, this communication is established peroperatively. In order to estimate radiographically the degree of bone resorption following the two-step as compared to the one-step procedure, the former was used on the right and the latter on the left side of the mandible in two dogs. Periodic identical intraoral radiographs revealed bone resorption in the neck area of all implants. After a 1-yr period with bilateral bridges, the vertical resorption varied between 3 and 5 mm. No difference was found between the two methods concerning this bone resorption. The observation seems to be contrary to the general opinion on the matter, and pertinent investigations with the present model will be performed in a human material.

Implant-tissue interface of endosseous dental implants in dogs. validity of clinical evaluation methods.

Plaque and gingival bleeding were scored and probing, radiography, and histologic methods were used to evaluate clinical methods for estimating alterations of supporting structures at functioning endosseous dental implants. Twelve implant abutment posts in three Labrador retriever dogs were assessed. The observation period was 3 months of submerged healing followed by 6 months in function. In the presence of daily gingival cleaning, both plaque and gingival bleeding scores were reduced on implant abutments. No correlation was found between gingival scores and the degree of bone resorption. The correlation between probing and radiographic measurements was studied by comparing 136 parallel measurements. The average difference was 0.4 mm. Discrepancies were observed when evaluating bone loss that reached the shoulder area. Better accordance was obtained when moderate (2 to 4 mm) or extensive (6 to 8 mm) resorption was assessed. Histologic evaluation indicated alternating regions of implant-bone contact and fibrous encapsulation. Progressive infiltrates were observed in the permucosal area, sometimes extending into the deeper parts of the supporting bone. A combination of probing and radiographic measurements seems to give the most reliable information about the level of bone support and is recommended to be included in routine control of implant abutments.