The International Journal of Oral & Maxillofacial Implants, 02/1996

The objective of this study was to measure and compare the precision of fit of implant-supported prostheses in the edentulous jaw by using both the master cast replicas and the intraoral implants as references. Seven maxillary and 10 mandibular prostheses were randomly selected and measured by means of a three-dimensional (3-D) photogrammetric technique. The results indicated that prostheses routinely connected to osseointegrated implants could demonstrate distortion between the framework and individual implants of up to several hundred microns. When master casts were used as a reference, the mean 3-D distortion of the center point of gold cylinders was 37 µm (SD 18) and 75 µm (SD 40) for mandibular and maxillary prostheses, respectively. The corresponding mean displacement was 90 µm (SD 51) and 111 µm (SD 59), respectively, when the intraoral implants were used as references. The mean 3-D distortion was significantly higher for the intraoral measurements in both arches (P .001 and P .05). Furthermore, the overall distortion was significantly higher for the maxillary prostheses when the master casts were used as the reference (P .05). However, for the intraoral measurements, no statistically significant difference of fit between the arches was possible to observe (P .05). This could possibly be explained by the finding that intraoral measurements of the mandibular prostheses indicated a deformation and rotation of the mandible that was not observed in the maxillary prostheses. A further factor in the lack of statistical significance could be the relatively small sample size. Keywords: framework, implant, precision

A prospective study involving 24 centers and 145 patients was conducted to evaluate the long-term osseointegration survival rate for titanium implants anchoring a craniofacial prosthesis (auricular, orbital, or nasal) and to evaluate the long-term retention and stability of the prosthesis. Of 452 implants placed, 19 were lost (overall survival rate of 96%). Of the 145 patients, 115 were evaluated (remained active) throughout the study period and were followed-up for at least 30 months. The results of the study suggest that the bone-anchored craniofacial prosthesis system is a viable alternative to conventional reconstructive surgery and offers significant improvement in the quality of life when compared with the support systems previously available for these types of prostheses. Keywords: bone anchored, craniofacial, prosthesis

The roughness of intraoral hard surfaces plays an important role in bacterial adhesion and colonization. Earlier studies have shown that rough surfaces accumulate up to 25 times more subgingival plaque than do smooth sites. In the present study, the influence of surface smoothing was studied. In six partially edentulous patients waiting for a fixed prosthesis supported by endosseous titanium implants, four titanium abutments with different surface roughness were randomly placed. After 1 month of intraoral exposure, subgingival plaque samples from each abutment were compared within each patient by means of differential phase-contrast microscopy. After 3 months, supragingival and subgingival plaque samples were taken from all abutments for differential phase-microscopy and culturing. Probing depth, recession, and bleeding upon probing were scored at the same visit. Differential phase-contrast microscopy showed that subgingivally, only the two roughest abutments harbored spirochetes after 1 month. After 3 months, subgingivally, the composition of the flora showed little variation on the different abutment types, although spirochetes were only noticed around the roughest abutments. Anaerobic culturing resulted in comparable amounts of colony-forming units for all abutment types, both supragingivally and subgingivally. Subgingivally, the microbiologic composition did not show major interabutment differences. Clinically, small differences in probing depth were observed. The roughest abutment showed some attachment gain (0.2 mm) during 3 months, whereas all other abutments had an attachment loss ranging from 0.8 to greater than 1 mm. The results indicate that a reduction in surface roughness (less than a roughness of 0.2 µm) had no major effect on the microbiologic composition, supragingivally or subgingivally. These observations indicate the existence of a threshold roughness below which no further impact on the bacterial adhesion and/or colonization should be expected. However, clinical evaluation seems to indicate that a certain surface roughness is necessary for increased resistance to clinical probing. Keywords: bacterial adhesion, implants, microbiology, plaque, surface roughness

Reverse torque to failure on implants has been studied in animals. Three implants were reverse torqued to failure in a human volunteer, with failure rates between 45 and 58 Ncm. Clinical data are presented on 404 implants examined after reverse-torque testing and loading, with no increase in failure rates. Reverse-torque testing at 20 Ncm appears to be a safe, reliable method for verifying osseointegration with pure titanium screw-shaped implants. Keywords: human trial, reverse torque, surface area, verification

Mandibular lengthening by distraction osteogenesis is a new method for use in treating congenital deformities or postsurgical bone defects. However, the use of extraoral transcutaneous pins in the mandible has disadvantages, such as facial scars and facial nerve or inferior alveolar nerve injury. The purpose of this study was to establish a new approach to distraction osteogenesis in the mandible by using osseointegrated implants and an intraoral device. Ten adult canines were used for this experiment. After extraction of the teeth and placement of two titanium implants in the left mandible, connection of the intraoral distraction device to the abutments, and corticotomy in the medial portion between implants were performed. Distraction was done at the rate of 1 mm per day to elongate 10 mm in length. Radiographic and histologic examinations showed that successful mandibular lengthening was achieved. New bone was primarily formed by intramembranous ossification and partial endochondral ossification. Titanium implants placed for anchorage of the device remained stable during the course of mandibular lengthening. Study results suggest that the intraoral device using osseointegrated dental implants can be used as a mechanism for distraction osteogenesis in the mandible. Keywords: distraction osteogenesis, intraoral device, mandibular lengthening, osseointegrated implant

This study compared the experiences with surgical procedures and treatment effects of a mainly implant-supported overdenture retained by a transmandibular implant with those of an implant tissue-supported overdenture retained by two cylindrical endosseous implants. Treatment had been assigned according to a balanced allocation method to 95 patients, including a control group who received only conventional complete dentures. Since some of the patients refused the allocated treatment, the "intention to treat" analysis was applied. The results show that the experiences with surgical procedures were significantly more positive for the transmandibular implant group than the endosseous implant group. The differences with respect to satisfaction, complaints, and subjective chewing ability were not statistically significant. These results were unexpected because the overdentures retained by the transmandibular implants were, to a much larger extent, supported by the implant than were the overdentures retained by two endosseous implants. Keywords: clinical trial, dental implants, denture satisfaction, overdentures

With single-tooth implant restorations, a divergence between implant and crown axes, a lack of interocclusal space, and supracrestal implant placement may result in fabrication problems for the prosthetic crown. It was found that the CeraOne abutment can be modified in three ways: (1) height reduction is possible; (2) a 15-degree taper can be applied; and (3) the cervical shoulder can be reduced in height with a chamfer remaining. For these modified abutments, the Celay-InCeram system was used to create individual, all-ceramic crowns for these modified abutments with improved esthetics. Keywords: all-ceramic restorations, Celay-InCeram system, CeraOne abutment

In 51 patients (21 males and 30 females) aged 16 to 72 years, a total of 109 Nobelpharma implants were placed into extraction sockets immediately following extraction. The follow-up period varied between 1 and 67 months with a mean of 30.5 months. Osseointegration was determined by clinical stability, lack of symptoms, and lack of peri-implant pathology based on radiographic examination. The implant survival rate was 93.6%. Six implants were mobile at the abutment connection stage, and one was lost when function commenced. The success rate was 92.0% for implants replacing teeth extracted because of periodontitis and 95.8% for implants replacing teeth extracted for other reasons. Two other complications occurred: 12 cover screws perforated the gingiva during healing; and infection developed in five cases. The incidence of infection was higher in the periodontitis group. It was found that immediate placement of implants into extraction sockets is a safe and predictable procedure if certain guidelines are followed. Keywords: extraction socket, immediate implant, osseointegration, stability

Bacterial colonies split implanted membranes that are exposed to oral biologic fluids as a consequence of dehiscence. The clinical and histologic behavior of 14 implanted polyurethane membranes was observed during the period of exposure to oral fluids for 2, 3, 4, and 6 weeks and without dehiscence (after 8 weeks). Statistical analysis indicated that the decrease in the number of neutrophils after 5 weeks, associated with the increase in the number of activated fibroblasts, cellular debris, giant cells, and aggression of bacteria, was statistically significant (from P .05 and P .01 for activated fibroblasts to P .005 and P .001 for neutrophilic cells). The increase in bacterial passage through the polyurethane membranes and in the number of giant cells and cellular debris after 8 weeks represents late dissolution of the membranes; the progressive increase of activated fibroblasts is significant because the longer the membrane resists, the better the cells can grow and give way to the process of tissue regeneration. Keywords: nonresorbable membranes, oral microbiology, oral pathology

Three impression techniques were assessed for accuracy in a laboratory cast that simulated clinical practice. The first technique used autopolymerizing acrylic resin to splint the transfer copings. The second involved splinting of the transfer copings directly to an acrylic resin custom tray. In the third, only impression material was used to orient the transfer copings. The accuracy of stone casts with implant analogs was measured against a master framework. The fit of the framework on the casts was tested using strain gauges. The technique using acrylic resin to splint transfer copings in the impression material was significantly more accurate than the two other techniques. Stresses observed in the framework are described and discussed with suggestions to improve clinical and laboratory techniques. Keywords: abutment, autopolymerizing acrylic resin, implant, transfer copings

The issue of changes in marginal bone levels around maxillary implants supporting overdentures has been studied very little because of radiographic difficulties when using conventional intraoral techniques. The present study used detailed narrow-beam radiography, which offers excellent opportunities to depict implants and the surrounding bone in severely resorbed maxillae. Marginal bone levels around implants in patients with overdentures were compared to corresponding bone levels in a group of matched control patients with fixed prostheses supported by osseointegrated implants. No statistically significant difference in marginal bone height was noted between the groups. This finding is not in accordance with an earlier report on continuous loss of marginal bone around many maxillary implants supporting overdentures. Keywords: implants, marginal bone, maxilla, overdenture, radiography

To evaluate tissue reaction to cobalt 60 irradiation around implant materials used in maxillofacial surgery, 2.0-mm titanium alloy bone screws and 2.0-mm cylindrical solid hydroxyapatite implants were placed in mandibular bone of rabbits and irradiated with a single 15-Gy dose on the fifth postoperative day. Tissue reaction around the implants was examined histologically and histomorphometrically at 7, 14, 28, and 56 days after irradiation. Mature bone was relatively radioresistant, but newly formed bone around both implants was damaged by irradiation in several places. After irradiation, the beginning of bone formation was delayed and the amount of new bone formed was less. Bone-implant contact measured histomorphometrically was less in the irradiated group than in the nonirradiated group. All titanium alloy screws showed bone contact, but two of eight hydroxyapatite implants failed after irradiation, probably the result of loss of primary stability of the cylindrical implants caused by radiation damage to newly formed bone. Keywords: animal study, hydroxyapatite, implants, irradiation, titanium

Demineralized laminar bone sheets were utilized as membranes to affect guided bone regeneration around five implants in two patients and to perform a ridge augmentation procedure in one patient. In all cases, significant regeneration of hard tissues occurred, and no complications were encountered. The regenerated hard tissues have been in function for up to 32 months with no clinical signs of breakdown. Keywords: guided bone regeneration, laminar bone sheet, implant

Nine hollow dental implants that were removed from patients were examined histologically to determine whether there was a common mechanism of failure with this implant design. When a hollow implant showed saucerized bone loss at the neck portion radiologically, the hollow portion was divided histologically into soft tissue and bone tissue. In advanced cases, stratified flattened epithelium that had invaded the hollow and the dead space at the top was observed. The condition of bone tissue located in the bottom of the basket can be adversely affected by an unfavorable crown-root ratio. The presence of an empty basket may cause fracture of the basket portion. The hollow portion can foster the growth of pathogenic bacteria. The hollow-type implant may not be suitable for immediate placement because surrounding soft tissues can invade the basket immediately. Keywords: dental implant, failing implant, full body implant, histology, hollow implant