The International Journal of Oral & Maxillofacial Implants, 04/2000

Formation of a calcium phosphate layer was studied on the surfaces of plasma-sprayed hydroxyapatite (PSHA) and sandblasted commercially pure (cp) titanium in simulated body fluid with ion concentrations similar to those of human blood plasma. The PSHA surface induced the formation of calcium phosphate surface layers, while the precipitation of calcium phosphate on sandblasted cp titanium was not detected. Histologic evaluation of in vivo tests demonstrated that implants with a PSHA coating enabled the growth of bone tissue into gaps with a depth of up to 1 mm without significant formation of intermediate fibrous tissue. In comparison to sandblasted cp titanium, implants with PSHA coating exhibited greater tolerance to unfavorable conditions during healing, such as gaps at the interface or primary instability of the implant. In the case of good primary stability of the implant, filling of the gap with fibrous tissue was observed for sandblasted cp titanium implants over the greater part of the surface of gaps with a depth of 0.3 mm. Direct contact of cp titanium implants with bone was achieved only when the press-fit implantation model was used. Keywords: calcium phosphates, hydroxyapatite, osteoconduction, titanium, wound healing

With the technique of maxillary ridge expansion, 449 implants were placed in 150 patients and observed over a period of up to 93 months. Thin maxillary ridges of adequate height and comprising 2 separate cortical plates with intervening cancellous bone were selected for maxillary ridge expansion and simultaneous implant placement. Two-stage implants were used and allowed to heal in a closed environment for 6 months prior to loading. Single and multiple teeth were replaced using this technique, and an estimated mean survival rate better than 97% after a 5-year observation period was calculated (95% confidence interval of the mean survival estimation: 98% ± 1%). Good esthetic and functional outcomes were observed. Keywords: alveolar ridge augmentation, dental implants, endosseous dental implantation, osteotomes, ridge expansion

t present, there are no diagnostic tools that permit early detection of peri-implantitis. The purpose of this cross-sectional study was to evaluate the correlation of aspartate aminotransferase (AST) levels with traditional periodontal clinical parameters around dental implants, since AST has been associated with destruction of cardiac, hepatic, and periodontal tissues. Twenty healthy volunteers with 59 implants were recruited from the Harvard School of Dental Medicine clinics. Clinical parameters evaluated included: AST level, probing depth (mm), Gingival Index (0, 1, 2, or 3), and bleeding on probing (0 or 1). Utilizing the site or implant as the unit of measure, the authors found a statistically significant association of increased AST activity with positive bleeding on probing, increased probing depth, and increased Gingival Index. No statistical correlations were found between clinical indices and increased AST levels when the results were examined on an individual patient basis. This cross-sectional study was able to demonstrate a statistical correlation between diseased clinical periodontal parameters and elevated AST levels. Keywords: aspartate aminotransferase, dental implants, diagnosis, gingival crevicular fluid, peri-implantitis

This study examined whether it is possible to restore an edentulous mandible with a complete-arch fixed prosthesis retained by only 4 implants without decreasing the survival rate. One hundred nineteen patients received complete-arch mandibular prostheses retained by 4 implants. Most patients were followed for 3 years or more. All patients followed a routine protocol, including annual check-ups and regular radiographic examinations. Twenty-one patients dropped out. Radiographic measurements used the threads of the implants as a basis for comparison. No indication was found that the number of supporting implants could have influenced the observed frequency of technical and surgical complications. Three implants were lost, 2 after 1 year and 1 after 5 years. A statistically significant difference in bone loss between the mesial and distal implants was found. The number of fractured resin teeth in mandibular prostheses was higher when patients had an implant-supported prosthesis in the maxilla. The present study revealed an implant survival rate of 98.6% after 5 years. Therefore, it was concluded that there may not be a need for more than 4 implants to support a fixed mandibular prosthesis, when implants at least 10 mm long can be used. Keywords: dental implants, implant-supported dental prosthesis, mandible

The objective of this research was to evaluate the influence of radiotherapy on the osseointegration of oral implants in a canine model. After the extraction of all mandibular premolars and first and second molars, 11 male beagles were divided into 3 groups. The control group (3 dogs) received no radiation. The second group (4 dogs) was irradiated 4 weeks after implantation. The third group (4 dogs) was irradiated 8 weeks before implantation. Eight implants were placed in each dog, in an alternating pattern: 4 non-submerged ITI Bonefit titanium plasma spray-coated and 4 submerged Steri-Oss hydroxyapatite-coated. The irradiated dogs received 4.3 Gy daily for 10 days. After 6 months of osseointegration, the dogs were sacrificed and each hemimandible was dissected to isolate the implants. Quantification of the extent of the direct bone-implant contact was carried out by scanning electron microscopy backscattered electron images that reproduced each implant in its entirety, using a digitizing table connected to a computer. The results were expressed as a percentage of direct bone-implant contact versus total perimeter accessible to bone. The bone contact percentage for the control group was 87% for Steri-Oss implants and 69% for the ITI Bonefit implants; for the animals irradiated after implantation, the percentages were 82 for Steri-Oss implants and 58 for ITI Bonefit implants; and for the animals irradiated before implantation, the percentages were 62 for Steri-Oss implants and 28 for ITI Bonefit implants. A statistically significant difference appeared between the 2 types of implants (P .001). A statistically significant difference was also seen between the 3 groups for both types of implants, except between the control group and the group irradiated after implantation (P = .14). This indicates that, overall, the timing of irradiation influences osseointegration. Osseointegration is possible before and after radiotherapy; however, the direct bone-implant contact increased when the implants were placed before irradiation. Keywords: dental implants, dogs, endosseous dental implantation, irradiation

This paper presents a comparison between the 8-degree Morse Taper and the butt joint as connections between an implant and an abutment. Three-dimensional, non-linear finite element models were created to compare the 2 connection principles under equal conditions. The loading configuration was thereby modeled according to a test setup actually used for the dynamic long-term testing of dental implants as required for regulatory purposes. The results give insight into the mechanics involved in each type of connection and are compared to actual findings with the testing machine. The comparison indicates the superior mechanics of conical abutment connections and helps to explain their significantly better long-term stability in the clinical application. Keywords: dental implants, finite element analysis, mechanical stress

A longitudinal study was performed, which measured the soft tissue around implants following surgery, to determine if a predictable pattern of soft tissue changes could be identified. This study evaluated 63 implants in 11 patients. Baseline measurements were recorded at stage 2 surgery in 2-stage implant systems, and at stage 1 surgery in the 1-stage system. Subsequent measurements were recorded at 1 week, 1 month, 3 months, 6 months, 9 months, and 1 year after baseline measurements. The majority of the recession occurred within the first 3 months, and 80% of all sites exhibited recession on the buccal. It is therefore recommended that one wait 3 months for the tissue to stabilize before either selecting a final abutment or making a final impression. As a general rule, one can anticipate approximately 1 mm of recession from the time of abutment connection surgery. A comparison of this studys results with data recorded in previously reported studies reveals clinically significant trends in the nature of soft tissue healing. Keywords: dental abutment, dental implantation, endosseous dental implants, gingival recession, mouth mucosa

The aim of this article was to present the experimental peri-implantitis models described in the literature and to provide a review of currently used treatment methods. For this purpose, 29 English- and German-language studies published in internationally reviewed journals were examined for similarities and differences regarding animal models, types of implants, and methods used for inducing peri-implantitis. In almost all studies, the implants were located in the mandible, which suggests that peri-implantitis of the maxilla has been researched very little. While in most studies, peri-implantitis was induced by means of ligature and plaque accumulation, only 3 studies have been published that attempted to induce peri-implantitis by means of mechanical overload. Of the latter, only one author observed peri-implant bone resorption. Eleven studies reporting on ligature-induced peri-implantitis presented enough data to be subjected to further statistical data analyses. Meta-analysis revealed that the period of ligature application, and thus the duration of plaque accumulation, generally had no influence on the resultant depth of the bone defect. However, when screw-type and cylindric implants were analyzed separately, a weakly significant positive effect of the duration of ligature application on the resultant defect depth was determined for cylindric implants (P = .092). This could imply that smooth screw-type implants were less susceptible to ligature-induced peri-implant inflammation. Regenerative treatment methods included the membrane technique using non-resorbable membranes (guided bone regeneration), augmentation with autogenous bone, augmentation with bone substitute materials (hydroxyapatite or demineralized freeze-dried bone) or with recombinant human bone morphogenetic protein-2, and a combination of membrane and augmentation procedures. While all described methods resulted in acceptable bone gain, it seems to be difficult to achieve new osseointegration (reosseointegration) of treated implants. Of all tested treatment methods, the combination of guided bone regeneration and augmentation with demineralized freeze-dried bone resulted in the most favorable results regarding bone gain and reosseointegration. Keywords: peri-implantitis, review literature, treatment outcome

The major disadvantage of cement-retained implant-supported fixed partial dentures (FPDs) is difficulty in retrievability. The retentive strengths of the provisional luting agents usually employed in these cases are therefore an important consideration. This study evaluated the cement failure loads of 4 provisional luting agents used for the cementation of FPDs supported by 2 implants or 4 implants. Nogenol luting agent exhibited the lowest retentive values in both types of FPD. ImProv proved to be the most retentive cement of all tested. Temp Bond NE and Temp Bond presented significantly different values (P .05) for the 2-implant FPD, but not for the 4-implant model. On the basis of the study results, it may be concluded that Nogenol appears to be more appropriate for cementation of both 2- and 4-implant-supported FPDs when removal of the provisionally cemented superstructure is anticipated. Keywords: dental cements, denture retention, implant-supported dental prosthesis

In 21 patients, 28 maxillary teeth were extracted because of periapical or periodontal infection, root fracture, or untreatable caries. A rotated palatal flap procedure was used to achieve primary soft tissue closure over extraction sites. At 5 to 7 weeks postextraction, 28 implants were placed. Buccal dehiscence-type defects were treated with guided bone regeneration procedures using bovine bone mineral and resorbable collagen membranes. Mean defect area at the time of implant placement (23.7 mm2, SD 11.49) was significantly reduced at uncovering (0.7 mm2, SD 0.99). The mean percentage of defect reduction (clinical bone fill) was 97% (SD 4.26). Implants placed in compromised sites shortly postextraction according to the presented 2-stage protocol gave good short-term clinical results. Keywords: alveolar bone loss, dental implants, endosseous dental implantation, guided tissue regeneration

This study investigated various designs of stress breakers incorporated into the dental implant using 3-D finite element analysis. These designs employed hydroxyapatite-reinforced polyethylene (HRP), a material capable of inducing osseointegration. The most successful design was that of a dental implant with a peripheral HRP component that was in direct contact with the bone surrounding the neck of the implant. This design lowered the compressive stress values in bone around the neck of the implant. Attempts were also made to optimize this design. Keywords: dental implants, dental models, dental stress analysis, finite element analysis, polyethylenes

To study the influence of bed preparation on the incorporation of autogenous bone grafts in mandibles, 6 dogs with 3 different types of receptor bed were used: cortical, perforated, and decorticated. After 45 and 90 days, the animals were sacrificed and block sections of grafted and adjacent bone were removed. The specimens were prepared and stained with hematoxylin and eosin and Massons trichromic. The autogenous bone grafts were integrated with the receptor bed, mainly in the perforated and decorticated groups. The poorest results were found in the cortical group. Keywords: alveolar ridge augmentation, bone transplantation

In this study, the effect of various materials used in fabricating superstructures for implant-retained fixed partial dentures on stress distribution around implant tissues was investigated. Five different mathematical models consisting of 11,361 nodes and 54,598 elements were constructed to study porcelain, gold alloy, composite resin, reinforced composite resin, and acrylic resin veneering materials using the 3-dimensional finite element analysis method. MARC K7.2/Mentat 3.2 software was used for the analysis. Reference points were determined on the cortical bone, where perpendicular, oblique, and horizontal forces were applied. Stress values created by oblique and horizontal forces appeared to be higher than those created by vertical forces. Stress seemed to be concentrated at the cortical bone around the cervical region of the implant. Gold alloy and porcelain produced the highest stress values in this region. Stresses created by acrylic resin and reinforced composite resin were 25% and 15% less, respectively, than porcelain or gold alloy. Porcelain and gold alloy produced stress values at the lingual implant sites that reached the ultimate strength values of the cortical bone. Keywords: dental implant, dental materials, dental stress analysis, finite element analysis, fixed partial denture

Sinus bone grafting with autogenous bone is routinely performed to allow placement of endosseous dental implants. Although numerous maxillary sinuses have been successfully grafted, some complications of this procedure have been reported. These include maxillary sinusitis, resorption, infection and possible failure of grafts, loss of implants after 1-stage surgery, and oroantral fistulae. Only one case of postoperative maxillary cyst developing in the graft has been reported in the literature. Here, the authors report a similar case that necessitated grafting of the cyst with autologous iliac bone. Keywords: bone transplantation, cysts, endosseous dental implants, maxillary sinus