Ulf Lekholm

A 15-year study of osseointegrated implants in the treatment of the edentulous jaw.

Osseointegration implies a firm, direct and lasting connection between vital bone and screw-shaped titanium implants of defined finish and geometry-fixtures. Thus, there is no interposed tissue between fixture and bone. Osseointegration can only be achieved and maintained by a gentle surgical installation technique, a long healing time and a proper stress distribution when in function. During a 15-year period (1965-1980), 2768 fixtures were installed in 410 edentulous jaws of 371 consecutive patients. All patients were provided with facultatively removable bridges and were examined at continuous yearly controls. The surgical and prosthetic technique was developed and evaluated over a pilot period of 5 years. The results of standardized procedures applied on a consecutive clinical material with an observation time of 5-9 years were thought to properly reflect the potential of the method. In this group, 130 jaws were provided with 895 fixtures, and of these 81% of the maxillary and 91% of the mandibular fixtures remained stable, supporting bridges. In 89% of the maxillary and 100% of the mandibular cases, the bridges were continuously stable. During healing and the first year after connection of the bridge, the mean value for marginal bone loss was 1.5 mm. Thereafter only 0.1 mm was lost annually. The clinical results achieved with bridges on osseointegrated fixtures fulfill and exceed the demands set by the 1978 Harvard Conference on successful dental implantation procedures.

Marginal tissue reactions at osseointegrated titanium fixtures (I). A 3-year longitudinal prospective study.

16 consecutive totally edentulous patients were provided with 95 osseointegrated titanium fixtures in 7 upper and 9 lower jaws. Facultatively removable bridges were later connected to abutments, attached to the fixtures. The marginal soft and hard tissue reactions were investigated at a baseline examination and after 6, 12, 21, 30 and 39 months by standardized clinical and radiographical methods. At the last examination, microbiological samples and gingival biopsies were also analysed. The % ratios of abutments without plaque, 70-75%, and without any gingivitis, 80-85%, were almost constant throughout the study. The mean probing depth was 2.9 mm at the final examination. About 75% of all probing depths were 3 mm or less and none exceeded 5 mm. The bridge-gingiva distances increased during the investigation. Attached gingiva surrounded 65% of the buccal and lingual abutment surfaces. Only 0.9 mm marginal bone was lost as a mean during the first year and not more than 0.05 mm annually for the next 2 years. After 6 months, no significant changes in marginal bone levels occurred. The perifixtural bone gradually became more radiopaque, especially marginally in upper jaws, indicating a successive load-related remodelling. The microbiotia comprised coccoid cells and non-motile rods to 93% in 32 samples. Healthy tissues were present in 35% of the 14 soft tissue biopsies. In a further 29%, only a slight inflammation was observed. No constant correlations could be established for any of the investigation parameters used. It is concluded that the marginal soft tissue reactions were mild and not significant for a progressive periodontitis. Mobility tests of separate fixtures combined with quantitative and qualitative standardized radiological examinations of the surrounding bone appear to provide a truer comprehension of longitudinal events at osseointegrated implants than conventional clinical soft tissue observations. The prognosis for the osseointegrated implants appears excellent, especially with regard to the microbiotia, the small marginal bone height changes, and the radiological indications of remodelling in the perifixtural bone.

Marginal tissue reactions at osseointegrated titanium fixtures. (II) A cross-sectional retrospective study.

20 totally edentulous patients, provided with 24 facultatively removable fixed bridges (13 upper and 11 lower jaws) were recalled. The material consisted of 125 osseointegrated titanium fixtures with a mean observation time of 7.6 years (range 6 months to 15 years). The marginal tissues were examined by conventional periodontal clinical methods and standardised radiography. Microbiological samples and biopsies of the soft marginal barrier tissues were retrieved for dark-field and histological analysis, respectively. The percental ratios of abutment surfaces devoid of plaque and without signs of gingivitis, were 46% and 20%, respectively. In contrast to earlier studies, the presence of plaque and gingivitis was significantly correlated. This relationship was probably due to more plaque being present. The mean probing depth was 3.8 mm. In 40% of the measurements, the probing depths were 3 mm or less, and in 45% between 4 and 5 mm, whereas they only in 15% were 6 mm or more. They were greater in upper than in lower jaws and were found to be significantly correlated with gingivitis. Attached gingiva surrounded about 51% of the buccal and lingual abutment surfaces. The marginal bone height changes were very small during the follow-up period (0.07 mm annually). Coccoid cells and non-motile rods dominated the microflora to 94% in the 48 samples taken. Out of the 19 biopsies, 58% showed healthy mucosa and a further 37% had the lowest inflammation score. The indications of gingivitis and deep pockets at the clinical examination were not found accompanied by an accelerated marginal bone loss, nor by a microflora or histological changes indicative of periodontitis.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison between cutting torque and resonance frequency measurements of maxillary implants. A 20-month clinical study.

Abstract Oral implant treatment ad modum Branemark was undertaken in nine patients with edentulous maxillae. Cutting torque measurements and resonance frequency analyses (RFA) were conducted at implant placement and the corresponding values were subjected to correlation analyses. The implants were also evaluated with RFA at abutment connection and at one-year follow-up in order to identify possible changes in implant stability. A total of 61 implants were inserted, of which 49 were of the Mk II self-tapping type. Two implants were lost during the study period. The cumulative torque was presented as a mean value for the upper/crestal, the middle and the lower/apical third of the implant site respectively, as well as an overall value for the whole site. The highest correlation ( r =0.84, P P =0.047) and between groups 1 and 3 ( P =0.002). When repeating the resonance frequency analyses at second stage surgery and at one-year follow-up, no significant differences were detected between any of the groups. It was shown that the stability of implants placed in softer bone seemed to “catch up” over time with more dense bone sites.

Stability measurements of one-stage Brånemark implants during healing in mandibles: A clinical resonance frequency analysis study

Using a one-stage surgical protocol, 75 implants ad modum Brånemark of three different designs were inserted in 15 edentulous mandibles of high bone density. All implants were followed with repeated stability measurements by means of resonance frequency analysis (RFA) from implant placement to connection of the fixed prostheses (3-4 months), in order to evaluate possible stability changes during healing. It was shown that the resonance frequency (RF) values slightly decreased for the majority of the implants during the study period independent of design. Consequently, the results of the present study indicated that the implants were as stable at time of placement as when measured at 3-4 months post-surgery, i.e. when the prostheses were attached. The available data support the concept of direct loading of implants when inserted between the mental interforaminal regions. One implant failed during healing and the corresponding RF measurement disclosed, at six weeks post-surgery, a value being far below the one registered at implant placement. The lowered RF value indicated the failure several weeks before the mobility was clinically diagnosed. The presence or absence of a fixture/abutment junction did not exert any influence on the marginal bone level, as determined radiographically at the end of the short investigation period.

An experimental and clinical study of osseointegrated implants penetrating the nasal cavity and maxillary sinus

Implants were inserted in the upper jaw of three dogs in such a way that they penetrated the bone wall of the nasal cavity. The dogs were killed one year later, and the hard and soft tissues around the penetrating implants were analyzed. Radiographic and histologic examinations did not show any signs of adverse tissue reaction. The implants were all integrated in bone without fibrous tissue formation in the interface. A total of 139 implants, which pierced the bone of the sinus or nasal cavity, were inserted in the upper jaws of 101 patients. Forty-four sinus- and 47 nasal-penetrating implants were observed for five to ten years. The success rates were 70% and 72%, respectively. For 25 sinus- and 23 nasal-penetrating implants that were observed for two to five years, the success rates were 88% and 96%, respectively. The implant losses in nearly all clinical cases occurred during the first two years of function.

Osseointegrated titanium fixtures in the treatment of edentulousness

A 91 per cent positive 5-9 year result has been reported when using titanium implants and gold bridges to restore edentulous jaws. About 400 consecutive patients have been operated. The reasons for the good results are believed to depend on the anchorage of the implants in the living bone without interposing soft tissue layers. Repeated X-rays ensuring a strict parallelism are used to indicate direct bone integration. Some implants had to be removed in spite of still being anchored in the bone. In these cases SEM and TEM provided direct evidence of an osseointegration.

Influence of implant diameters on the integration of screw implants: An experimental study in rabbits

The influence of diameter on the integration of titanium screw-shaped implants was studied in the rabbit tibia by means of removal torque measurements and histomorphometry. Implants 3.0, 3.75, 5.0, and 6.0 mm in diameter and 6.0 mm long were inserted through one cortical layer in the tibial metaphyses of nine rabbits and allowed to heal for 12 weeks. The implants were then unscrewed with a torque gauge, and the peak torque required to shear off the implants was recorded. The histologic analysis in undemineralized ground sections comprised (1) a gross description of the implant sites and assessments of (2) the total implant length in bone and (3) in the cortical passage, as well as (4) the thickness of the cortical bone adjacent to the implants. From the removal torque values obtained and morphometric measurements, a mean shear stress value was calculated for each implant type. The biomechanical tests showed a statistically significant increase of removal torque with increasing implant diameter. The resistance to shear seemed to be determined by the implant surface in supportive cortical bone, whereas the newly formed bone at the periosteal and endosteal surfaces did not seem to have any supportive properties after 12 weeks. It is suggested that wide diameter implants may be used clinically to increase implant stability.

Influence of mono- and bicortical anchorage on the integration of titanium implants: A study in the rabbit tibia

The study aimed to evaluate the removal torque and bone tissue response to titanium implants supported by one or two cortical layers. A total of 72 screw titanium implants, either 10 or 16 mm in length and 3.75 mm in diameter, were inserted in right and left tibiae of 18 adult New Zealand rabbits. The implants engaged either one or two cortical layers, and the animals were allowed a healing period of 6 or 12 weeks. The degree of integration was assessed by measuring the removal torque with a torque gauge manometer. Histomorphometric calculations were also performed in 10-microns-thick ground sections. All implants were clinically stable at the end of the experiment. The removal torque was two times higher for the bicortical implants after 6 weeks, and three times higher after 12 weeks, than for the monocortical ones. The 16-mm implants also showed a statistically higher amount of bone contact and bone area after 6 and 12 weeks, respectively, than the short ones. The results support bicortical anchorage of implants also in the clinical situation.

Histologic investigations on 33 retrieved Nobelpharma implants.

Thirty Nobelpharma implants were retrieved from 17 patients despite a remaining clinical stability, after between 1 and 16 years of clinical function. The reasons for implant removal were bone resorption in combination with soft tissue disorders, psychological causes, implant fracture and post mortem cases. When measured at the cortical passage, there was an average of 84.9% direct bone-to-implant contact and 81.8% average surface bone area in individual threads as evaluated in a computerized morphometric system at the light microscopic level.