The International Journal of Oral & Maxillofacial Implants, 02/1998

In this review, the appropriate use of cell culture to evaluate substrate effects on osteoblast behavior during the process of osseointegration has been considered in the context of existing reports. The interactions of osteoblasts with different substrates can be measured in terms of cytotoxicity, attachment, proliferation, and differentiation. The osteoblast culture systems that produce an osteoblast matrix opposing implant material substrates provide one model for evaluating the implant-bone interface. Alterations in osteoblast behavior at different culture substrates may reflect clinical determinants of bone formation at these substrates in vivo; however, cell responses in vitro have not been compared or correlated with in vivo outcomes. Legitimate interpretations of in vitro experiments are discussed in terms of practical, technical, and biologic limitations presented by the cell culture approach. Cell culture provides access to molecular and cellular information that fosters nanostructural engineering approaches to implant design and significant hypotheses to be tested in vivo. In this way, cell culture offers unique insights into the process and phenomenon of osseointegration. Keywords: biomaterials, cell culture, interface, osteoblast, review, surface topography

A variety of materials and procedures are used to create adequate bone volume in the maxillary sinus for placement of endosseous implants in the posterior atrophic maxilla. This review used the structured method of meta-analysis to evaluate the survival of the implants placed into various materials that have been used in the maxillary sinus with the sinus lift procedure. A MEDLINE computer search of the English literature yielded 28 studies that reported using the maxillary sinus augmentation procedure to increase bone volume for placement of endosseous implants; only 10 of these met the inclusion criteria for meta-analysis. Data regarding immediate or delayed placement of implants were combined to simplify analysis. Implant survival was 90% for autogenous bone (484 implants in 130 patients followed for 6 to 60 months), 94% for the combination of hydroxyapatite (HA) and autogenous bone (363 implants in 104 patients followed for 18 months), 98% for the combination of demineralized freeze-dried bone (DFDB) and HA (215 implants in 50 patients followed for 7 to 60 months), and 87% for HA alone (30 implants in 11 patients followed for 18 months). The results for autogenous bone were based on six reports, for the combination of autogenous bone and HA on three reports, and for DFDB/HA and HA alone on one study each. The results of single studies cannot be weighted as heavily as the results combining several studies; however, the analysis of these studies suggests that implant survival rates were similar for autogenous bone, HA/autogenous bone mix, HA/DFDB, and HA alone. Keywords: implants, maxillary sinus augmentation, meta-analysis, review, sinus lift

The purpose of this study was to clarify the effects of steroid administration on the osseointegration of pure titanium implants. Twelve female New Zealand white rabbits, 8 weeks of age, were divided into two groups: a prednisolone-treated group (Group P) and a control group (Group C). In each rabbit, two implants were placed into the mandible and two into the tibial metaphyses with bone tapping. The six steroid-treated rabbits received three courses of 4 days of prednisolone injections (10 mg/kg per day) before implant placement, 1 month and 2 months after implant placement. The six control rabbits received no administration of prednisolone. Three months after implant placement, all rabbits were sacrificed. Bone density of the femur and removal torque of the implants placed in the tibia were significantly lower in Group P than in Group C. In addition, there were significant correlations between the bone density of the femur and the removal torque of the implants placed in the tibia. There was no significant difference in removal torque of the implants placed in the mandible between Group P and Group C, and there was no significant correlation between the bone density of the femur and the removal torque of the implants placed in the mandible. These results suggest that steroid administration could have less effect on the osseointegration of titanium implants in the mandible than in the skeletal bone. Keywords: microdensitometry, rabbit, removal torque, steroid-induced osteoporosis, titanium implant

Because osseointegrated implants have no resilience in bone, passive fit between dental implants and prosthetic superstructures has been identified, both from biologic and mechanical perspectives, as a potential discriminating prognostic factor. Distortion of the metal framework during the casting procedure has been cited as a main cause of misfit. The objectives of the present article were to describe a recently presented method (CrescoTi Precision method) intended to correct for distortion in cast titanium frameworks, and to elucidate and evaluate the method by photoelastic and strain gauge techniques. The method appears to be an efficient and accurate procedure for correcting for distortion in cast titanium frameworks. Keywords: cast framework, dental implants, distortion, laser welding, misfit, passive fit, photoelastic analysis, precision of fit, strain gauge analysis, titanium

The purpose of this study was to examine the dose enhancement at bone-implant interfaces from scattered radiation during simulated head and neck radiotherapy. Three cylindric implant systems with different compositions (pure titanium, titanium-aluminum-vanadium alloy, titanium coated with hydroxyapatite) and a high gold content transmandibular implant system (gold-copper-silver alloy) were studied. Extruded lithium fluoride single crystal chips were used as thermoluminescent material to measure radiation dose enhancement at 0, 1, and 2 mm from the bone-implant interface. The relative doses in buccal, lingual, mesial, and distal directions were also recorded and compared. The results indicated that the highest dose enhancement occurred at a distance of 0 mm from the bone-implant interface for all the implant systems studied. The transmandibular implants had higher scattered radiation than other groups at 0 mm and at 1 mm from the bone-implant interface. There was no significant difference of dose enhancement between buccal, lingual, mesial, and distal directions. Titanium implants coated with hydroxyapatite demonstrated the best results under the simulated irradiation. Keywords: bone-implant interface, head and neck radiotherapy, scattered radiation, thermoluminescent dosimetry (TLD), titanium implant, transmandibular implant system

Implant and prosthesis success for 77 partially edentulous patients, provided with 97 fixed prostheses, supported by 230 Brånemark implants, in place for up to 12 years (mean 5.41 years), were documented in this study. Implant losses per location mirrored their placement, with no difference between zones I and II or between the maxilla and mandible. The implant success rate was 94%, and continuous prosthesis stability was 97%. These results indicate that the Brånemark implant-supported fixed partial prosthesis is a highly efficacious treatment. Keywords: Brånemark implants, osseointegration, partial edentulism, success/failure

In this multicenter prospective study, the results achieved with the use of Brånemark implants for single tooth replacement were evaluated. The overall cumulative success rate was 95.9% for implants and 91.1% for crowns. Two of the 99 implants placed had to be removed before the prosthodontic stage of treatment; thus, 97 were restored with CeraOne crowns. Seventy-seven implants were evaluated radiographically at the 1-year follow-up, 57 at 3 years, and 47 at 5 years. Mean marginal bone resorption was well within the limits set by Albrektsson et al in 1986. The status of the soft tissue around crowns and adjacent teeth remained stable over the evaluation period. The gold abutment screw in the CeraOne system seems to have eliminated the problem of loosening abutment screws in single tooth replacements. The results suggest that the Brånemark system can be safely used for tissue-integrated replacement of single teeth. Keywords: CeraOne, full ceramic crown, osseointegrated Brånemark implant, prospective follow-up study, single tooth replacement

Localized management of sinus floor (LMSF) achieves implant placement and sinus lifting simultaneously. LMSF is a further application of the principles of the edentulous ridge expansion (ERE) technique. It comprises the dissection of a partial-thickness flap, the buccal expansion of the residual alveolar bone, and the fracture and elevation of the sinus floor with simultaneous implant placement. Three hundred three patients were treated with 499 implants placed using the LMSF between April 1988 and December 1993. The selected patients, who showed no signs of sinus pathology, exhibited insufficient vertical alveolar bone dimensions for the placement of dental implants with the traditional technique. The minimal residual alveolar bone height was between 5 and 7 mm. Based on the criteria established by Albrektsson and his coworkers in 1986, the success rate of the 499 implants placed with the LMSF was 97.5%. Keywords: edentulous ridge expansion, osseointegration, sinus elevation

A common assumption when planning for treatment for a fixed partial denture potentially involving an osseointegrated implant is to avoid connection between the implant and natural tooth abutment because of the differences in mobility and potential long-term effects. A large population was surveyed to measure the incidence of natural tooth intrusion in implant-assisted fixed partial dentures (IAFPD) and to try to identify a correlation between type of implant and/or type of connector. Natural tooth intrusion occurred in 3.5% of the patient population specifically treated with IAFPD. No correlation could be made between incidence of intrusion and the type of implant or type of connector used. Keywords: implant, natural tooth intrusion, survey

To date, transverse and vertical forces applied eccentrically to the axis of dental implants in the molar area during oral function have not been quantified. A specially designed load cell placed directly in the implant allowed for measurements of bending moments. Results of both load directions were compared to each other and to the loads applied vertically along the implant axis. The stress in the bone-implant interface area caused by these three different types of loads was calculated by finite element analysis. The transverse loads during chewing resulted in the highest bending moments (170 Nmm mean maximum) and the highest stress in the bone (smax Å 6.2 MPa) at the crest to the buccal side. Mesial implant moment was significantly less (52 Nmm mean maximum moment; smax Å 1.3 MPa). Clenching in centric occlusion caused a bending moment either to the lingual or to the buccal side, depending on the occlusal contour (140 Nmm maximum). Keywords: bending moments, chewing forces, clenching, implant loading, interface, measuring device, occlusion, premature contact

Retention of implant-supported facial prostheses presents challenges in design that may lead to use of freestanding abutments. This is particularly so in the midface and orbit. Individual implant success rates are lower in these regions, and bone remodeling capacity may be compromised by combined modality cancer therapy. The present study was undertaken to determine the variations in load delivery so as to compare the use of long cantilevers and offset abutments with freestanding axially loaded abutments. The study revealed not only that the loads delivered are not trivial, but also that the highest loads generated are frequently delivered at the cervix of the implant. The long cantilevers produced the highest laterally acting cervical loads, whereas the 30-degree and 60-degree Console abutments delivered the highest laterally acting cervical loads of all the Console abutments. The potential of long cantilevers and offset abutments to deliver significant loads should be considered when designing retention for a facial prosthesis. Keywords: console abutments, craniofacial osseointegrated implants, facial prostheses, finite element analysis, loading, lone-standing abutments

The aim of this study was to evaluate the clinical function and long-term prognosis of overdentures retained by a small number of implants in the maxilla and mandible using one of two different attachment systems. Included in the study were all patients referred to specialty clinics in Jönköping and Linköping, Sweden, during the treatment period who needed an overdenture and could be provided with a minimum number of two bilaterally-placed implants. Excluded were patients with bone-grafted jaws, irradiated cancer patients, heavy bruxers, and patients who had lost a fixed prosthesis because of implant losses. The patients were randomly assigned to receive one retentive system, either a round 2-mm-diameter bar with clips or ball attachments (Nobel Biocare). Eighteen overdentures were placed in maxillae and 32 in mandibles, supported by a total of 115 Brånemark implants. Of the implants placed, 86.1% were continuously osseointegrated. The cumulative implant survival rates after 7 years of loading were 75.4% in the maxillae and 100% in the mandibles. There was no difference in implant survival rate between the attachment systems. Patients with implant losses were characterized by severely resorbed maxillary ridges and inferior bone quality, together with unfavorable loading circumstances such as short implants combined with long leverages. Complications and prosthetic adjustments were mostly resolved early and easily. Keywords: Brånemark implants, oral implants, overdenture

This report outlines the experimental, surgical, and prosthodontic protocols for a prospective clinical trial using the Endopore dental implant to replace single maxillary teeth. Twenty patients (10 male, 10 female) ranging in age from 30 to 60 years each received one implant (mean length 10.1 mm), which, after an initial healing period of 4 months, was restored with a single crown. Records collected included radiographs, Periotest mobility measurements, supragingival Plaque Index, and an assessment of peri-implant soft tissue health using pocket probing depths, sulcular bleeding following probing, and probing attachment levels. Radiographs were exposed at predetermined intervals following crown placement (1 and 6 months, and then yearly) in a standardized procedure using a specialized filmholder that attaches to each implant after removal of the crown. At the time of this preliminary report, all of the 20 implants placed had been uncovered and were in function; 16 of the implants had been in function for 6 months or more, 14 had passed 1 year of function, and 3 had passed the 2-year function point. There have been no failures to date. Keywords: early results, Endopore implants, maxilla, single

The authors report on the clinical and histologic features of a single implant replacing a mandibular molar, which fractured after a 1-year loading period. Because of anatomic factors, the implant had been placed in an angulated position. The histologic examination showed a very high percentage of bone-implant contact. The bone located at the interface with the implant was mature, compact, and had few marrow spaces. No resorption areas were present, and no connective tissue was seen at the interface. Most likely, the lateral nonaxial forces exerted on the implant created very high bending moments. These forces produced a fracture of the implant, although no loss of osseointegration was observed at the interface. Keywords: axial loading, bending moments, commercially pure titanium, implant failure, implant fracture, overloading