The International Journal of Oral & Maxillofacial Implants, 05/2001

Previous studies to compare the influence of surface characteristics of dental implants on cell behavior have used model systems to simulate the implant surface. In this study, bone cell interactions with smooth titanium, titanium dioxide-blasted, titanium plasma-sprayed, and hydroxyapatite plasmasprayed implants, as manufactured for clinical use, were compared. Implants were exposed to neonatal rat osteoblast cells in suspension for a 20-minute period and, by means of scanning electron microscopy, attached cells were classified according to stage of attachment. Quantitative analysis showed that cells spread most quickly on the titanium plasma-sprayed implants. Fully spread cells on the smooth titanium implants were closely adherent to the surface, while on the titanium dioxide -blasted surface they showed no adaptation to surface irregularities. On the hydroxyapatitecoated implants, cells adhered closely only to smooth areas. To avoid the use of proteolytic enzymes for cell derivation, the authors developed a novel organ culture system in which the implant was contained in a nylon pocket surrounded by bone fragments, permitting cells to migrate onto the implant surface. Cultures were maintained for up to 4 weeks, allowing comparison of cell migration, proliferation, and differentiation on the implant surfaces.

Research into the formation, destruction, and adaptation of bone around implants would benefit from a sensitive, nondestructive, noninvasive, and quantitative technique to assess the bone-implant interface. It is hypothesized that osseointegration can be quantified by sensing the mechanical impedance (or micromobility) of the implant when it is subjected to minute vibratory forces superimposed upon a quasi-static preload. To test this hypothesis, a total of 24 identical threaded, titanium root-form implants (103.75 mm, Osteo-Implant, New Castle, PA) were placed in the mandibles of 4 Walker hounds and allowed to heal submerged for 3 months. The implants were exposed and characterized for osseointegration using clinical observations, quantitative radiography, and a custom-designed impedance instrument. Subsequently, arbitrarily selected implants were ligated to induce bone loss and examined monthly over a 6-month study period. Following the terminal examination and euthanasia, quantitative histologic measurements were made of bone adjacent to the implant, including estimates of both crestal bone height and the percent bone (bone fraction). Linearized dynamic parameters (effective stiffness and effective damping) correlated well with radiographic and histologic measures of bony support (r2 values ranged from 0.70 to 0.89). Moreover, the presence of nonlinear stiffness was clearly associated with a bimodal "clinical impression" of osseointegration (P .0003, 1- way analysis of variance). These results confirm that, in this animal model, mechanical impedance can be used as a measure of implant osseointegration. Keywords: animal model, dynamics, histomorphometry, impedance, implant, instrumentation, mobility, osseointegration, stiffness

The purpose of this study was to histometrically evaluate an absorbable collagen membrane (Bio- Gide) and a nonabsorbable polytetrafluoroethylene membrane (PTFE), associated with or without bone grafts, regarding "re-osseointegration" after treating ligature-induced peri-implantitis defects in dogs. All mandibular premolars were removed from five 2-year-old mongrel dogs. After 3 months of healing, 3 titanium implants were placed on each side of the mandible. Experimental peri-implantitis was induced with ligatures after abutment connection. Ligatures and abutments were removed after 1 month and the bone defects were randomly assigned to one of the following treatments: debridement alone (DB), debridement plus PTFE membrane associated with mineralized bone graft (Bio-Oss) (GBR+BG-I), debridement plus collagen membrane (Bio-Gide) associated with mineralized bone graft (GBR+BG-II), debridement plus PTFE membrane (GBR-I), debridement plus collagen membrane (GBRII), or debridement plus mineralized-bone graft (BG). The dogs were sacrificed after 5 months. Data analysis did not reveal significant differences among the treatments regarding the percentage of bone-to-implant contact ("re-osseointegration") within the limits of the threads of the implant (P = .997). Thus, in the treatment of peri-implantitis, debridement alone as well as grafting alone had the same effect as did either membrane. Keywords: absorbable/nonabsorbable membrane, bone graft, guided tissue regeneration, peri-implantitis

Forty-eight Endopore dental implants were placed in the posterior mandibles of 24 partially edentulous patients. Seventeen of these implants replaced premolar teeth, while 31 replaced molars. Only 7- mm and 9-mm implants were used, and the majority of prosthetic restorations (83%) were single crowns. After a mean functional time of 32.6 months (range, 8.2 to 50.3 months), the implant survival rate was 100% and assessment of available radiographic data showed minimal to no crestal bone loss. Keywords: clinical trial, porous-surfaced dental implant, posterior mandible, surface treatments

One of the many applications for which lasers have been proposed in implant dentistry is for the decontamination process. The purposes of this study were to assess possible alterations in titanium implants in vitro and in vivo by use of the carbon dioxide (CO2) laser and to determine whether new bone formation can occur on previously contaminated implants. In vitro, temperature changes at the bone-titanium implant interface were recorded during use of a CO2 laser-scanning system (Swiftlase). Additionally, the effects of laser irradiation on titanium implants at various power settings were examined. In 6 beagle dogs, a total of 60 implants and bony defects resulting from plaque accumulation were treated by air-powder abrasive (the conventional treatment), laser irradiation, or both. Depending on the parameters chosen, melting and other surface alterations were seen in vitro, especially in the superpulse mode. Otherwise, no alterations were found, even at high power settings in the continuous mode. In vivo, corresponding histologic examination of 4-month sections showed evidence of new direct bone-to-implant contact after laser-assisted therapy, especially when the implants had been treated concomitantly with submerged membranes. These results support the hypothesis that periimplant defects can be treated successfully by laser decontamination without damaging the surrounding tissues in the dog model. Nevertheless, further investigations will be required to determine the clinical efficacy of the treatment. Keywords: dental implants, lasers, peri-implantitis

The aim of this 3-year prospective study was to evaluate the prosthetic treatment in 2 groups of maxillary edentulous patients with similar age and gender distribution: a study group of 39 patients treated with intra-sinus block bone grafts and implants in a 1-stage procedure, and a control (reference) group of 37 patients treated with implants and no grafting. In the study group, bone volumes were regarded as insufficient for implant treatment unless a bone grafting procedure was performed (posterior alveolar bone height was less than 5 mm). Self-tapping Nobel Biocare implants were used in both groups of patients. In the study group, 35 fixed partial dentures and 4 overdentures were placed, and in the control group 34 fixed partial dentures and 3 overdentures were placed. All patients were followed for at least 3 years. The 3-year follow-up examination included examination of a number of clinical parameters as well as the type of abutment and evaluation of stability of prosthesis retention screws and abutment screws. During the follow-up period, 2 patients were lost from the study group and 4 patients from the control group, giving a total of 70 patients available for examination after 3 years (8% dropout rate). Both the amount of plaque and gingival bleeding were significantly lower in the study group than in the control group. The presence of attached gingiva was 25% in the study group and 35% in the control group. The number of angulated abutments was significantly higher in the study group than in the control group. There was no significant difference in the number of prosthetic complications in the 2 groups of patients. Neither was there any significant difference in prosthesis screw or abutment screw stability between the 2 groups. The type of abutment did not significantly influence the stability of prosthesis retention screws or abutment screws in either of the groups. However, prosthesis screw stability was significantly greater than abutment screw stability in both groups of patients. It can be concluded that the prosthetic outcome was similar in the 2 groups of patients, regardless of whether or not a bone grafting procedure was used. Keywords: bone grafts, complications, dental implants, maxillary prosthesis

The goal of this study was to provide data relative to the use of a new implant system (Mac System, Cabon, Milan, Italy) with a Morse taper implant-abutment connection for single implant restorations. The implant system is composed of an endosseous screw made of commercially pure titanium grade 2, while the abutment is titanium alloy (Ti-6Al-4V). A total of 80 single implants were placed in 69 patients (36 women and 33 men, mean age 42 years, range 16 to 61). All patients gave their informed consent and received a thorough clinical and radiographic examination. Smokers and diabetics were excluded from the study. Three implants were placed in areas of previous tooth impaction, 5 were placed in posttraumatic edentulous areas, 2 were used in situations involving tooth agenesis, and 60 replaced teeth lost because of caries or periodontal disease. All patients were edentulous for at least 1 year prior to treatment. The implants received a definitive prosthesis and had been in function for a mean period of 3.5 years. At second-stage surgery, 2 implants were removed because of lack of osseointegration. After 2 years of loading, 1 implant showed evidence of peri-implantitis and was removed. In addition, 2 fractured abutments and 1 loosened abutment were observed. Few mechanical or infectious complications were seen, and this may have been the result of high stability of the conical connection. Keywords: biomechanics, dental abutments, dental implants, single-tooth implants

The aim of this research was to compare 2 different graft materials, -tricalcium phosphate (Cerasorb) and autogenous bone, used in the same patient. Bilateral sinus grafting was performed on 4 selected patients; Cerasorb only was used on the experimental side, and autogenous bone only was used on the control side. In all 4 patients, the maxilla was atrophied to such an extent that the reconstruction included not only sinus grafting but also onlay plasty. The procedure was followed by implant placement 6 months later. In addition to routine panoramic radiographs, 2- and 3-dimensional computed tomographic (CT) examinations were performed pre- and postoperatively and after implantation. Information from CTs is necessary when alveolar bone atrophy is extensive, complications appear probable, and in difficult cases, when exact documentation is important. A total of 16 bone biopsies were taken at the time of implant placement. The histologic and histomorphometric results indicated that when the formation of new bone was slow, it was slow on both sides; when it was fast, then it was fast on both sides. Individual patient factors strongly influenced the fates of the various graft materials in the organism. Comparisons of the present results with the findings of other investigators demonstrated that -tricalcium phosphate is a satisfactory graft material, even without autogenous bone. Keywords: autogenous bone, bone grafting, calcium phosphates, computed tomography, histology, histomorphometry, maxillary sinus

An important reason to improve methods of isolating platelet-rich plasma (PRP) is the potential use of autologous platelet growth factors. In addition to discontinuous plasma separation, a second method for extraction of PRP has now become available, which can be performed directly by the surgeon. In this study, the suitability of the 2 methods of producing PRP was compared. Whole blood was drawn from 158 healthy donors (112 men, 46 women) aged 20 to 62 years (mean 34, SD 10). The PRP was separated by the discontinuous plasma separation method (by the blood bank) or by the so-called "buffy coat" method (the "self-concentration" method, analogous to the PRP Kit, Curasan, Kleinostheim, Germany). Platelet counts differed significantly according to donor blood (median men 237,500/µL, women 272,000/µL), blood bank PRP preparation (median men 1,302,000/µL, women 1,548,500/µL), and self-concentrated PRP (median men 944,000/µL, women 1,026,000/µL). The platelet concentration of the blood bank PRP correlated with the platelet count in the donor whole blood (Spearman's correlation coefficient rS = 0.73). However, there was no significant correlation between the platelet count of self-concentrated PRP and donor whole blood (rS = 0.22). Significant but irrelevant influences of sex on platelet concentration were found, but no influence of age was detected. Keywords: growth factors, plasmapheresis, plateletpheresis, platelet count

This cohort study (n = 83) investigated whether patients with implant-stabilized overdentures would demonstrate less impact on daily life, would have less difficulty in the mastication of different types of food, and would generally be more satisfied than patients with conventional complete dentures. The groups were comparable for gender, age of dentures, and duration of edentulism. The patients were interviewed using a questionnaire, which included the Oral Impacts on Daily Performances (OIDP) sociodental indicator. Patients with implant-stabilized overdentures were more satisfied with the comfort of their dentures, could eat a wide range of food items with less difficulty, and experienced less impact on daily life than patients with conventional complete dentures. The findings of this study support the need to consider implant-stabilized overdentures in the treatment of edentulous patients. Keywords: complete denture, endosseous dental implantation, oral health, overdenture, patient satisfaction

Xenografts have been used extensively, either alone or in combination with autogenous bone, in sinus floor elevation techniques. However, controversy exists regarding the need to cover the lateral osteotomy site with a membrane. Also, the healing period before loading remains undefined when machined-surface implants are placed. Twenty-nine patients showing reduced bone volume in the posterior maxilla had 61 Brånemark System implants placed in 30 sinuses augmented with a lateral osteotomy approach. Sinuses grafted with Bio-Oss and covered with a collagen membrane Bio-Gide (M+) received 29 implants, while grafted but uncovered sites (M-) received 32 implants. An immediate procedure was followed to place 41 implants and a staged procedure was used for 20 implants. Abutment connection was made in 2 distinct postoperative periods: 6 to 9 months and over 9 months. The patients were followed for an average of 22.4 months. The survival rate of the implants was dependent on the postoperative healing time and membrane presence. In case of the immediate procedure and in M- sites, when residual bone height was less than 5 mm, more failures occurred when the loading was done at 6 to 9 months than after 9 months. No failures occurred in the M- series when a staged approach was followed. The overall survival rate was 78.1% for the M- sites and 93.1% for the M+ sites. No failures occurred (0/35) in the control implants placed in adjacent native bone. Implant survival rate was related to the quality of the reconstructed cortical plate and to implant length. The concomitant use of a collagen barrier to cover the osteotomy site, when machined-surface implants were used in sinus grafting, seemed to improve the quality of the graft healing and survival rate of the implants loaded between 6 and 9 months after placement. Keywords: bone grafting, endosseous dental implants, maxillary sinus, membranes

Bending moments resulting from non-axial overloading of dental implants may cause stress concentrations exceeding the physiologic supporting capacity of cortical bone, leading to various kinds of failures. The aim of this study was to evaluate the effect of staggered (offset, tripodization) implant placement configuration and placement of wider-diameter implants in a straight-line configuration in mandibular posterior edentulism. A mandibular Kennedy Class II partially edentulous finite element model was constructed. Seven different partial fixed prostheses supported by 3 implants were designed according to 2 main configurations: straight-line or staggered implant placement. In 5 of the designs, implants with various diameters and length were placed along a straight line. In the other 2 models, offset placement of the middle implant buccally and lingually was simulated. A 400 N static load was applied perpendicular to the buccal inclination of the buccal cusps on each unit. Tensile and compressive stress values on cortical bone in the cervical region of the implants were evaluated. Lower stress values were recorded for the configuration with wider implants placed in a straight line. Other configurations, including staggered implant placement, produced similar stress values. Despite the offset implant placement, the stresses were not decreased; however, straight placement of wider implants may decrease bending moments. Keywords: finite element stress analysis, posterior edentulism, staggered implant placement

The aim of the present study was to evaluate the use of reduced-diameter implants as an alternative to bone grafting for treatment of patients with severely resorbed maxillae. Forty patients (25 females, 15 males, mean age of 57 years, range 19 to 86) with insufficient bone volume for placement of standard- size implants in the maxilla (31 totally edentulous) were treated with 3.3-mm-diameter implants (ITI, titanium plasma-sprayed solid screws). Augmentation was considered for all patients because of lack of sufficient bone volume. Preoperative radiographic examination showed that in all cases, the height of the alveolar crest with a width of 4 mm was less than 10 mm. A total of 182 implants with a length of 8 to 12 mm were placed. All but 3 patients planned for overdenture treatment received fixed prostheses or single crowns (n = 3). One implant (8 mm long) was lost 1 month after placement, providing a survival rate of 99.4% after 1 year of loading. Since 4 implants with peri-implantitis were sucessfully treated and 1 implant left as a "sleeper" because of malposition, the cumulative success rate was 96.4%. The mean marginal bone resorption at baseline was 0.14 ± 0.67 mm (range 0 to 6 mm). After 1 year of loading the mean resorption was 0.35 ± 1.05 mm (range 0 to 7 mm); 4.8% of the implants had marginal bone resorption of more than 2 mm. Keywords: bone resorption, clinical study, dental implants, maxilla

The histologic examination of dental implants retrieved from humans provides a unique opportunity to evaluate the bone-implant interface. This case report presents a clinical, radiographic, and histologic evaluation of a cylindrical hydroxyapatite- (HA) coated implant retrieved from the posterior maxillary area of a patient after 9 years after placement. The implant had been placed in conjunction with a subantral augmentation procedure with HA as the graft material. Clinical examination revealed an immobile implant with no sign of pathosis. Radiographic examination indicated close proximity of the bone to the implant surface without evidence of radiolucency. Histologically, because of tissue destruction during implant retrieval, only the apical portion of the implant was available for examination under light microscopy, and it appeared to be integrated with the surrounding bone; 45.9% of the surface of the implant had close bone apposition at the interface. There was no evidence of dissolution of the HA coating and the bone appeared to be in immediate contact with the coating. Residual graft particles were present and in close proximity with the implant surface. These observations suggest that the subantral augmentation procedure performed simultaneously with the placement of an HA-coated implant with HA as the graft material apparently resulted in osseointegration between the implant and the surrounding bone. The implant was maintained without complication for 9 years. Keywords: dental implants, hydroxyapatites, osseointegration, sinus augmentation