The International Journal of Oral & Maxillofacial Implants, 01/1998

The clinical success of endosseous implants is associated with the formation and maintenance of bone at implant surfaces. Histologic analyses have indicated that bone formation at a variety of implant surfaces is a continuous process that supports long-term functional integration. Based on in vivo observations, several generalizations have been derived regarding the nature of the interface. Experimental descriptions indicate that the implant-bone interface may be characterized in spatial and temporal terms as discontinuous. Biomechanical tests of the bone associations with implants demonstrate that the chemical composition and the surface topography of the implant influence the rate and extent of bone formation at implant surfaces. The precise character and functional attributes of this interface are the focus of this investigation. Many technical difficulties are associated with its structural and chemical characterization in vivo. Despite the technically difficult nature of this type of analysis and the limitations of current histologic examinations and biomechanical tests, in vivo models of osseointegration are necessary experimental tools for the continued empirical development of clinical implant applications. Keywords: dental implant, histology, interface, osseointegration, osteoblast, review

The purpose of this study was to compare bone regeneration within a surgically created defect using three different resorbable membranes (polyglactin 910 knitted mesh/Vicryl, freeze-dried fascia lata, and crosslinked bovine type I collagen/BioMend) and two nonresorbable membranes (expanded polytetrafluoroethylene/Gore Tex, and polytetrafluoroethylene/Millipore). Each of three adult male dogs underwent surgical preparation of six bicortical defects of the calvarium, each 1.5 cm in diameter. The experimental barrier membranes were placed on both sides of the defects (inner and outer cranial tables). Five of the six defects were covered randomly by one of the five membrane materials, and one was left uncovered to serve as a negative control. The animals were sacrificed 10 weeks after membrane placement. Bone response was measured clinically, as well as radiographically, via densitometric examination. All surgical sites healed uneventfully. Variable degrees of new bone growth were present at all sites when evaluated by both clinical and radiographic examination. The general trend of observed osseous response indicates a greater, although not statistically significant, degree of bone growth using nonresorbable membranes. The animal model employed appears to be an efficient and reliable means of evaluating guided bone regeneration membranes. Keywords: bone regeneration, canine calvarium, guided tissue regeneration, resorbable membranes

The purpose of this in vivo study was to determine maximum and functional forces simultaneously in three dimensions on mandibular implants supporting overdentures. The anchorage system for overdenture connection was the ball-shaped retentive anchor. Five edentulous patients, each with two mandibular ITI implants, were selected as test subjects. A novel miniaturized piezo-electric force transducer was developed for specific use with ITI implants. Force magnitudes and directions were registered under various test conditions by means of electrostatic plotter records. The test modalities were maximum biting in centric occlusion, maximum biting on a bite plate, grinding, and chewing bread. Maximum forces measured in centric occlusion and on the ipsilateral implant when using a bite plate were slightly increased in vertical and backward-forward dimension (z-, y-axis) compared to the lateral-medial direction (x-axis). On the contralateral implant, equally low values were found in all three dimensions. This may be the effect of a nonsplinted anchorage device. With the use of a bite plate, force magnitudes on the ipsilateral implant were significantly higher on the z- and y-axis than mean maximum forces in centric occlusion (P .001). Chewing and grinding resulted in lower forces compared to maximum biting, particularly in the vertical direction. The transverse force component in backward-forward direction, however, reached magnitudes that exceeded the vertical component by 100% to 300% during chewing function. This chewing pattern had not been observed in previous investigations with bars and telescopes, and therefore appears to be specific for retentive ball anchors. The prevalent or exclusive force direction registered on both implants in the vertical direction was downward under all test conditions. In the transverse direction during maximum biting the forward direction was more frequently registered, while no obvious prevalence of transverse force direction was observed during chewing and grinding. Keywords: mandibular implants, overdentures, retentive ball anchors, three-dimensional force measurements

The healing of standardized bone defects grafted with either particulate ionomeric or hydroxyapatite bone substitutes was compared in the mandibular ramus of 30 Sprague-Dawley rats. The possible additional response achieved when combining these materials with a guided bone regeneration (GBR) technique was also evaluated. Three groups of 10 animals received either no implant material or ionomeric or hydroxyapatite bone substitute in defects in the right ramus. The left mandibular defects received the same treatment, except that the operation site was covered by a membrane (GBR technique). Half of the animals were sacrificed at 4 and 10 weeks following surgery, and the inflammatory response at the implant site and the amount of new bone formed in the defects were determined histomorphometrically. Defects implanted with ionomeric bone substitute exhibited more bone formation (4 weeks = 3.19 ± 0.38 mm2, 10 weeks = 5.35 ± 0.26 mm 2) than both defects that received no treatment (4 weeks = 0.88 ± 0.35 mm 2, 10 weeks = 2.1 ± 0.49 mm 2), membrane alone (4 weeks = 1.21 ± 0.05 mm 2) or hydroxyapatite bone substitute (4 weeks = 1.41 ± 0.46 mm 2, 10 weeks = 3.34 ± 0.41 mm 2) at 4 weeks (P .01) and at 10 weeks (P .05). The use of a GBR technique did not increase the amount of bone formed, compared to the use of bone substitutes alone. Hydroxyapatite and ionomeric bone substitutes used alone were more effective in inducing repair of the defects than was GBR membrane alone. The use of hydroxyapatite was associated with a greater inflammatory reaction (P .01) than was ionomer in this model. Keywords: bone regeneration, glass-ionomer cement, hydroxyapatite, ionomeric

Two hundred twenty-two sinus augmentation procedures were performed using one of three techniques: crestal approach; lateral approach; or lateral approach with simultaneous implant placement. Forty-one of these sinus augmentation procedures were performed in conjunction with buccolingual ridge augmentation. Of the 222 procedures, 217 (97.7%) were successful. Of 510 implants placed in augmented sinus areas, 495 (97.0%) were deemed successful by the criteria of Albrektsson et al for up to 73 months in function. Clinical considerations in the execution of such therapy are discussed. Keywords: buccolingual ridge augmentation, crestal approach, grafting materials, guided bone regeneration, simultaneous implant placement, sinus augmentation procedures

The purpose of this study was to evaluate experimental peri-implant breakdown microbiologically, radiographically and histologically. Hydroxyapatite-coated, titanium plasma-sprayed, and titanium alloy surfaces were investigated. Eighty-four implants were placed in 14 beagle dogs. Standardized radiographs and microbiologic samples (DNA) were obtained. Dogs were sacrificed at 3 and 6 months. Undecalcified histologic sections were prepared. Thickness of hydroxyapatite coating, changes in crestal bone height, and marginal changes in osseointegration were measured. Vertical bone loss was computed. Radiographs were analyzed using computer-assisted densitometric image analysis (CADIA). Microbial analysis (DNA) did not clearly favor any of the examined surfaces. CADIA did not show differences among implant surfaces. No significant differences among the three implants were noted for histometry, except the experimental titanium plasma-sprayed surface showed an increase in vertical bone loss 6 months (P .05). Thickness of hydroxyapatite was decreased in active peri-implantitis sites (P .05). Clinical attachment level was shown to be the most sensitive clinical parameter for detecting histologic changes. All implants were equally susceptible to peri-implantitis. Keywords: beagle dog, endosseous, hydroxyapatite, implant, machined titanium alloy, peri-implantitis, surface, titanium plasma-sprayed

Thirteen patients were treated for elevation of the maxillary sinus floor with autogenous or composite (autogenous bone + hydroxyapatite granules) bone grafts and endosseous implants. Bone biopsies were taken both at graft positioning and at implant placement. Histologic and histomorphometric results suggest that graft architecture, conformation, and composition may influence the mean bone content at the end of the healing. Iliac bone grafts contained 53% bone, while chin bone grafts contained 66% bone. Composite bone grafts had the smallest percentage of bone: 44.3%. Chin block bone grafts had the largest percentage of bone content (69.3%), while chin particulate bone graft conformation had 62.6%. Although particulate grafts healed in only 4 months, bone quality and quantity allowed earlier implant placement. Keywords: atrophic maxillae, autogenous bone graft, bone graft, composite graft, sinus lift

This investigation was concerned with the resorption of the posterior mandibular residual ridge in patients wearing mandibular overdentures supported by either parallel-sided bars (rigid joint) or oval straight bars (resilient joint) on two activated implants. Rotational tomographs were taken shortly after implant placement and up to 8 years later. Using proportional measurement, the area of residual ridge was measured in bilateral posterior areas. Patients rehabilitated with implant-stabilized mandibular overdentures demonstrated posterior mandibular residual ridge resorption at low rates, which were not significantly influenced by the design of the prefabricated bar. Keywords: bone resorption, dental implants, mandible, overdentures, residual ridge

The three-dimensional finite element analysis method was used to assess stress in bone around titanium implants using three treatment designs for a partially edentulous mandible, under axial (AX), buccolingual (BL), or mesiodistal (MD) loads. For each of these loads, highest stress was calculated in the model with a cantilever prosthesis supported by two implants (M2). Less stress was found in the model with a conventional fixed partial denture on two implants (M3), and lowest stress was calculated in the model with three connected crowns supported by three implants (M1). When BL load was applied to M3, cortical bone stress was high, comparable to that calculated for M2 under the same load. When AX or MD load was applied to M3, the cortical bone stress was low, similar to that found in M1 under each of these loads. Keywords: bone stress, dental implants, fixed partial prosthesis, three-dimensional finite element analysis

The aim of this in vitro study using implants and abutments was to examine traces left by various cleaning instruments and to determine the quantity of substance removal. The implants and relevant abutments were Screw-Vent implants (Dentsply), titanium plasma-coated full-screw implants (Straumann), and standard Brånemark implants (Nobel Biocare). The instruments used were titanium curettes, Gracey curettes, plastic curettes, rubber cups with Zircate prophy paste, the Cavitron Jet ultrasonic scaler with universal inserts and airpolishing nozzles with Prophy-Jet cleaning powder, and the Densonic sonic scaler with SofTip disposable prophy tips and universal tips. Two test fields (2 x 2 mm) on the respective implant head and abutment underwent standard treatment with each instrument. With the full-screw implants, an additional two test fields were examined from the transition of the titanium plasma coating to the implant head. Untreated implants and abutment surfaces served as controls. The treated and untreated surfaces were examined by scanning electron microscopy for work traces and by optical laser profilometry for substance removal. The results showed that the Cavitron Jet ultrasonic unit, the Densonic sonic scaler with universal tips, and the Gracey curette left pronounced traces and induced high substance removal. The titanium curette and the Densonic sonic scaler with SofTip disposable prophy tips left virtually no traces and removed very little substance. The rubber cup, the plastic curette, and the Cavitron Jet airpolishing system left the implant surfaces unchanged. All instruments apart from the rubber cup and Cavitron Jet airpolishing system left pronounced traces at the transition of the implant head to the titanium plasma coating of the full-screw implants. The Cavitron Jet airpolishing system, the rubber cup, the plastic curette, and, with some reservations, the Densonic sonic scaler with SofTip plastic fittings and the titanium curette, appear to be suitable for cleaning implant surfaces. Keywords: implant surface, profilometry, scanning electron microscopy

he Periotest percussion force acting on a dental implant was estimated by assuming a mass-spring-dashpot model of the implant-bone system constructed on the basis of a clinical experiment. A theoretical value of about 10 N, comparable to hitherto reported experimental values, was obtained for an osseointegrated implant of about 1 g. The percussion force would probably be smaller for a heavier implant. Keywords: dental implant, percussion force

This clinical report presents rationale and clinical procedures involved in the use of ceramometal implant-supported titanium-cast prostheses for the rehabilitation of patients with atrophic maxillae requiring iliac crest grafting procedures. Favorable clinical results have been obtained, although clinical observation periods have been limited. The present observations suggest that osseointegrated ceramometal titanium prostheses could form a valuable part of restorative therapy following augmentation procedures. Furthermore, these titanium prostheses may be a meaningful contribution to implant prosthodontics, facilitating restorations of optimum biocompatibility. Keywords: atrophic maxilla, ceramometal titanium restorations, dental implants, iliac crest grafts, implant-supported prosthesis, Le Fort I osteotomy, sinus lift procedure

The precise placement of dental implants is essential to designing a prosthesis that fulfills the esthetic and functional requirements of the patient, and simultaneously allows clear phonetics and facilitates oral hygiene. To achieve this, an effective surgical template is essential: it must provide good orientation, be comfortable, have adequate intraoral fixation, allow freedom of choice to the surgeon, and be capable of use during image-diagnostic procedures. In accordance with this criteria, the profile surgical template, based on utilization of the buccal contour of missing teeth, has been designed. Keywords: sthetics, implants, osseointegration, profile surgical template

Several procedures have been used to regenerate localized bone defects around dental implants or to increase bone volume at an implant site, including bone grafting, placement of barrier membranes, and use of bone graft substitutes. This study sought to determine whether the bone graft substitute natural coral skeleton (NCS), with or without a protective polymer mesh, enhances bone formation in rat critical size craniotomy defects. The control group (1) had unfilled defects, while the defects in the four experimental groups (six rats each) were treated with: (2) an NCS disc of the size of the defect; (3) NCS granules; (4) NCS granules covered by a polyglactin 910 mesh; and (5) polyglactin 910 mesh alone. Undecalcified histologic sections were assessed by histomorphometric measurements 28 days later. The three NCS groups showed improved bone formation, which was statistically significant in groups (2) (NCS disc) and (4) (NCS granules covered by polyglactin 910 mesh). Group 4 had more bone formation than all the other groups. Polyglactin 910 mesh alone (group 5) produced no greater bone formation than the unfilled control. It is concluded that the bone formation obtained with NCS granules is enhanced when the particles are retained at the site of the defect with a protective mesh. Keywords: bone graft substitute, bone regeneration, natural coral, critical size defects, polymer mesh

This retrospective study evaluated the use of percutaneous craniofacial implants for the prosthetic rehabilitation of patients with a history of orbital exenteration and irradiation for oncologic tumors of the head and neck. A total of 24 implants were placed in six patients. All implants were determined to be osseointegrated at the time of uncovering. Three implants were subsequently resubmerged beneath the soft tissue because of positional interferences with prosthesis fabrication. The remaining 21 implants were ultimately used to retain six orbital prostheses. Two implants failed to maintain osseointegration during the follow-up period and were subsequently removed without complications. This represents an overall integration success rate of 90.5% over a mean follow-up period of 32.8 months (range = 11 to 68 months). The significance of these findings and their relationship to comparable reports in the literature are discussed. Keywords: craniofacial implants, orbital defect, osseointegration, radiation therapy