The International Journal of Oral & Maxillofacial Implants, 03/1996

This report presents the results of a 5-year prospective multicenter study including nine centers worldwide. A total of 30 patients received 117 Brånemark implants in the maxillae, and 103 patients received 393 implants in the mandibles. According to the protocol, all integrated maxillary implants were to be loaded; however, only two of four mandibular implants were planned for support of the overdentures, leaving the remaining implants covered by mucosa as backup for possible implant failures. Thirty-five patients (26.3%) who were provided with 127 implants (24.9%) were withdrawn from the study. Six patients treated in the maxilla lost all their implants and resumed wearing complete dentures. The cumulative success rates for implants and for overdentures supported by two implants in the edentulous mandible were 94.5% and 100%, respectively. The corresponding cumulative success rates for implants and for overdentures supported by an optimal number of implants in the maxilla were 72.4% and 77.9%, respectively. Significantly better jawbone characteristics at the time of implant surgery were considered to contribute to the better cumulative success rates in the mandibles. Mean marginal bone loss was 0.8 mm (SD 0.8) and 0.5 mm (SD 0.8) for loaded implants during a 5-year period of time in the maxillae and mandibles, respectively. Measurements of the clinical height of the abutment cylinders indicated a mean recession (0.2 mm) of peri-implant mucosa during the follow-up period in the mandibles. Conversely, hyperplasia was observed in the maxillae. Keywords: Brånemark System, long term, osseointegration, overdentures, titanium implants

Immediate implants have the advantages of few surgical exposures, short treatment time, and maintenance of alveolar bone height and width. The purpose of this study was to compare immediate implants with conventional implants (implants placed into ossified extraction sites) in adult monkeys. Forty-eight implants were placed and allowed to heal for a 6-month period. Following a 7-month loading period, the monkeys were sacrificed, and implant sections were evaluated histologically. Clinical and radiographic measurements showed few significant differences between immediate and control implants. Keywords: animal, clinical parameters, endosseous dental implants, immediate implantation, osseointegration, radiography, titanium, tooth extraction

Forty-one patients received 49 single-tooth implants placed in different jaw locations. One implant was not osseointegrated at stage 2 surgery. Three successfully osseointegrated implants were not available for follow-up. Forty-five implants were monitored for 1 to 8 years after loading. Each one of the implants met all of the traditionally accepted success criteria, except for nine individual implants that did not meet the proposed bone level criterion. No success criteria exist for natural teeth adjacent to implants. Although preliminary results are favorable, extensive long-term studies are needed to determine which specific criteria comprise optimal functional and esthetic results with minimal risk of morbidity. Keywords: clinical study, dental implants, effectiveness, single-tooth implant

The maximum cantilever length-anterior-posterior spread (CL-AP) ratio is often used as an indication of the ability to cantilever in completely implant-supported prostheses. The CL-AP ratios were determined assuming that failure occurs when the prosthesis retaining screw-prosthesis joint was compromised by either compressive (exceeding the pretorque value) or tensile (opening of the joint via plastic deformation) vertical forces using the Skalak model. Geometric arrangements of three, four, five, and six implants were analyzed. Force variables were 143, 200, and 400 N for the applied force, the pretorque value, and the joint tensile yield strength, respectively. The pretorque value was always exceeded before the yield strength. Allowable CL-AP ratios were (1) lower than those previously reported and (2) found to be 0.5 to 1.8, 0.7 to 1.6, 1.1 to 1.7, and 1.8 for three, four, five, and six implants, respectively. Although implant distributions with the highest AP often provide adequate occlusion, the results of this study indicate that the use of a single CL-AP ratio alone is not necessarily a good indicator of the ability to cantilever. Keywords: biomechanics, dental implant, pretorque value, prosthesis retaining screw, Skalak model

A total of 1,202 press-fit cylinder implants were placed in 479 patients from March 1986 to March 1994. The patients' ages ranged from 14 to 88 years. The implants included 889 titanium plasma-sprayed implants and 313 hydroxyapatite-coated implants. There were no statistically significant differences in the distribution of hydroxy apatite-coated and titanium plasma-sprayed implants based on implant location, type of restoration, age, and sex. Although differences in long-term success rates based on simple percentages were also not statistically significant, cumulative survival rates based on life table analysis up to 96 months were 92.7% for titanium plasma-sprayed systems and 77.8% for hydroxyapatite-coated systems. Graphical interpretations of these data revealed interesting contrasts, including the timing and results of implant failure, which are discussed in detail. Keywords: hydroxyapatite coating, life table analysis, press-fit cylinder implants, spreadsheet analysis, titanium plasma-spray coating

Limited crestal bone loss has been observed around dental implants partially covered with a porous coating. The results of a two-dimensional finite element analysis suggested that for this implant design, the observed crestal bone loss is the result of low stresses acting on bone around the uncoated superior region of the implant, causing disuse atrophy of bone. This finite element study investigated the effect on crestal bone loss of varying the design of the prosthesis connecting pairs of implants, the length of the uncoated region of the implant, and the friction at the noncoated coronal portion of the implant and adjacent host bone. Keywords: biomechanics, bone remodeling, dental implant, finite element analysis

A commercially pure titanium threaded implant was compared to a hydroxyapatite-coated threaded implant of similar geometric design and dimensions in the canine model. Bilateral posterior implants supported fixed prostheses, and some implants in the same mandibles served as unloaded control implants. Implants were evaluated clinically, radiographically, and histomorphometrically at the light microscope level to detect any differences in bone response to loaded conditions. No statistically significant differences were found between the two implant designs under loaded or nonloaded conditions with regard to mobility, probing depth, percentage of osseointegration, and crestal bone position. Keywords: implants, loaded, mobility, osseointegration, Periotest

A comparative study between one and two Brånemark implants replacing a single molar was conducted. Forty-seven individuals comprised two groups of 22 patients treated with one implant and 25 with two implants. A total of 72 implants were placed, 66 (92%) in the mandible and six (8%) in the maxilla. After the first year of function, the success rate was 99%, with only one implant lost. Between the second- and third-year follow-ups, 100% of the implants continued to function in the remaining 46 patients, giving a 3-year cumulative success rate of 99%. The marginal bone loss between 1 and 3 years of function was 0.10 mm (SD 0.20) for the group with one implant and 0.24 mm (SD 0.20) for the group with two implants. No changes were observed in the Sulcus Bleeding Index during the 3-year follow-up. Prosthesis mobility or screw loosening was the most frequent complication and was predominant in the group using one implant (48%), but was substantially reduced in the group using two implants (8%). These mechanical problems, using one implant only, seem to be preventable using a stronger screw joint (CeraOne abutment). Precise centric occlusal contact was established and maintained over the study period, which was thought to contribute to the very high success rate for the single-implant-supported molars, despite their high degree of mechanical problems. This study suggests that implant-supported molars can be effective therapy, and the results confirm the biomechanical analysis that two implants provide more advantageous support than does one. Keywords: biomechanical analysis, comparative study, complications, marginal bone loss, single-molar implant

As experience with osseointegrated implants has grown, greater use has been made of placement in the posterior jaw. To reduce the risk of implant failure and increase the ability of posterior implants to tolerate the occlusal forces, it is beneficial to create a wider base either by using wider (eg, 5-mm) implants or by placing two or even three standard implants at one site. In the present series, unpaired 5-mm Nobelpharma implants were placed in 38 sites in the mandible and 21 sites in the maxilla. All implants were uncovered and restored with ceramometal crowns, with follow-up ranging from 3 to 26 months (mean 16 months) postloading. Two implants in one patient failed and were replaced successfully at 14 months. At 20 sites, pairs of 5-mm implants were placed and restored, and with a loading period of 3 to 26 months (mean 14 months), all of these implants were successful. At 34 sites, a 5-mm implant was paired with a 3.75-mm or 4-mm implant. With a loading period of 3 to 24 months (mean 13 months), one implant 5 mm wide and 8 mm long failed and was replaced successfully at 13 months, and an implant 4 mm wide and 10 mm long failed and was not replaced. The failure rate for this group of implants therefore was 3%. Double 3.75-mm or 4-mm implants were placed at 149 sites in the mandible and 13 sites in the maxilla. All of these double-root implants were uncovered and restored with ceramometal crowns. With follow-up ranging from 4 to 78 months (mean 37 months) postloading, there were five implant failures in four patients, for a failure rate of 1.2%. The failure rate for all 5-mm implants was 2.3%, and that for all double implants was 1.6%. The use of either 5-mm or double implants necessitates changes in surgical technique, and both are highly dependent for their success on proper surgical execution. Keywords: endosseous dental restoration, dental implantation

Sufficient bone volume is still considered the most important prerequisite for the osseointegration of dental implants. The TIME technique (autogenous bone grafting combined with stabilization using a titanium mesh) for localized alveolar ridge augmentation was evaluated in 20 patients who had insufficient bone volumes for the primary placement of dental implants. Different clinical recordings were evaluated at TIME stage 1 (augmentation surgery) and at TIME stage 2 (reentry surgery with mesh removal and simultaneous dental implant placement). In most patients, single- or extended-tooth gaps (up to four units) were augmented with autogenous bone harvested from the chin or retromolar area. With the exception of temporary disturbances of tooth sensibility, no morbidity at the donor sites was observed. In one patient, the stabilizing titanium micromesh had to be removed prematurely because of graft infection. At the reentry surgery, the bone grafts were found to be completely incorporated in 75% of the patients. In 15% of the patients, only minimal graft resorption was observed (less than 10% of the graft volume). Subsequently, 28 implants could be placed in 19 patients. The stabilizing titanium mesh was best suited for vertical ridge augmentations. Another feature of the mesh was the excellent tissue compatibility, with little clinical or histologic inflammation, even when the mesh had become exposed. Keywords: autogenous bone grafting, clinical study, localized alveolar ridge augmentation, titanium micromesh

Provisional restorations in implant dentistry have rarely been considered an important stage in treatment. The definitive restoration is commonly fabricated in the laboratory with very little clinical input. The potential for error in the selection of abutments, framework design, appropriate vertical dimension of occlusion, occlusal profile, and finally the esthetic interpretation is significant. These static and dynamic variables can be identified clinically and communicated to the laboratory. It is suggested that all fixed detachable implant procedures incorporate a provisional phase to allow the diagnosis of static and dynamic clinical variables that determine the final design of the prosthesis. Implant restorations should be designed with a clinical basis that can be confirmed from a functional provisional restoration. Keywords: fixed detachable, laboratory communication, osseointegration, provisional implant restoration

This case report describes the design process for engineering an implant-retained bar to support maxillary dental and facial prostheses for a patient missing his midface, including the maxilla, bilaterally. A computer-driven finite element analysis program was used to anticipate the forces and moments on each implant to distribute occlusal forces as evenly as possible. The implants, and later the prosthesis, were used to support the upper lip in the absence of bony support. The completed restorations greatly improved the patient's speech, eating, and appearance. Keywords: design, engineer, implant, midface