The International Journal of Oral & Maxillofacial Implants, 02/2007

Purpose: The purpose of this study was to evaluate radiographic bone levels adjacent to implants placed in fresh extraction sockets (ESs) and immediately loaded with a fixed full-arch provisional restoration compared to bone levels adjacent to implants placed in native bone (NB) under the same restorative conditions. Materials and Methods: Patients with a hopeless maxillary and/or mandibular dentition had their remaining teeth extracted and 6 to 8 implants placed and restored within 72 hours. Radiographs were obtained at time 0, 3 to 6 months, and annually for 5 years. The radiographs were digitized, and the bone level changes were measured using a computer-assisted method. Results: A total of 139 implants, 42 ES and 97 NB, placed in 17 patients were evaluated. The overall results indicated that for all implants (ES + NB), 0.60 ± 0.71 mm of bone was lost after 6 months; 1.17 ± 0.59 mm of bone was lost after 18 months; 0.87 ± 0.76 mm bone was lost after 36 months; and 1.35 ± 0.42 mm of bone was lost after 60 months. When stratifying for NB versus ES implants, it was found that for NB implants, 0.75 ± 0.21 mm of bone was lost after 6 months; 1.31 ± 0.91 mm of bone was lost after 12 months; 1.07 ± 0.21 mm of bone was lost after 36 months; and 1.45 ± 0.49 mm of bone was lost after 54 months. For ES implants, 0.14 ± 0.33 mm of bone was lost after 6 months; 1.02 ± 0.27 mm of bone was lost after 12 months; 0.86 ± 0.42 mm of bone was lost after 36 months; and 1.30 ± 0.48 mm of bone was lost after 54 months. Conclusion: The combination of ES and NB implants can be immediately loaded with a fixed full-arch prosthesis and remain stable for greater than 5 years. The bone loss adjacent to these implants is similar to that seen surrounding those placed and restored using traditional protocols. Keywords: bone loss, dental implants, extraction sockets, immediate loading, immediate placement, radiographic analysis, radiographic bone levels

Purpose: To present the long-term results for screw-type implants consecutively placed in the pterygomaxillary-pyramidal region in the treatment of patients with posterior maxillary edentulism. Materials and Methods: One hundred fifty-two implants were inserted in 92 partially edentulous patients using cylindric osteotomes as bone-site formers, thus minimizing the use of drills in the bone preparation. Results: The 152 implants placed were loaded for an average of 89.7 ± 30.7 months. There were a total of 8 failures; 6 took place between implant placement and prosthesis delivery (early failures), and 2 failed in following functional loading. The overall survival rate was 94.7%. Discussion: Cylindric osteotomes allow the surgeon to accurately place implants. The use of surgical drilling was minimized, resulting in lowered surgical risk and diminished bone loss. Conclusion: Implant placement in the posterior pterygomaxillary region using cylindric osteotomes for osteotomy preparation resulted in an implant survival rate of 94.7%. Keywords: low-risk surgical techniques, pterygomaxillary-pyramidal region, screw-type implants, sinus grafting

Purpose: The aim of this study was to evaluate bone regeneration in bone cavities filled with particulate autogenous bone either harvest in blocks and subjected to milling procedures or collected during osteotomy with implant burs. Materials and Methods: In 12 rabbits, 3 noncritical unicortical cavities 7 mm in diameter were prepared with a trephine drill on the right tibia. The cavities were filled respectively with particulate autogenous bone achieved with a manual bone crusher (particulate group), with particulate autogenous bone obtained using bone collector during osteotomy (collected group), and with blood clot (control group). Animals were sacrificed at 7, 15, and 30 days after surgery (4 animals for each time period). The sections were examined by histologic and histomorphometric analysis. Results: At 7 days, the samples were filled by coagulum, and bone particles were observed only in the collected (24%) and particulate groups (44.75%). At 15 days, there was connective differentiation in all groups, with presence of grafted bone particles and onset of newly formed bone in the collected (38.88%) and particulate groups (46.0%). At 30 days, there was bone fill (immature trabecular bone) of the cavities in the control (50%), collected (64.63%) and particulate groups (66%). Conclusion: No significant difference was demonstrated between noncritical unicortical bone defects in rabbit tibiae filled with particulate bone harvested as a block and subjected to milling and those filled with bone collected during osteotomy with implant drills when the defects were observed up to 30 days following their creation. Keywords: bone regeneration, bone remodeling, bone transplantation, particle size, revascularization

Purpose: In previous publications of this series of studies on human cadaver jaws, bone densities were assessed and compared using subjective evaluation, conventional computed tomography (CT), and cone-beam computed tomography (CBCT). The aim of this study was to compare subjective bone quality during osteotomy and implant insertion resistance torque to noninvasive subjective and objective radiographic bone density assessments. Materials and Methods: Forty-two designated implant sites were selected. Self-tapping implants were inserted into these sites. The operator subjectively rated the bone density during the osteotomy procedure. Resistance torque was recorded during insertion of the implants. Results: Subjective drilling resistance was modestly correlated to subjective radiographic density evaluation (Lekholm and Zarb; Spearman's rho of 0.53, P .001). Subjective drilling resistance compared to the bone density in Hounsfield units (HU) obtained using CT and CBCT showed correlation coefficients of 0.61 and 0.59, respectively (P .001). Significant overlap of density values was found for adjacent drilling ratings. On average, a difference in bone density of 180 HU was required to identify differences between drilling resistance groups. Comparisons of 2 implant insertion resistance torque variables (highest reading and regression slope of available readings) with CT and CBCT HU showed correlation coefficients of 0.61 to 0.63 (P .01). Conclusion: Insertion torque resistance was modestly correlated with objective CT and CBCT measurements of bone density. The merit of these assessments of cadavers awaits clinical study. Keywords: bone quality, dental implants, implant placement, radiographic bone density, resistance torque

Purpose: The aim of this study was to describe the stress and strain fields around orthodontically loaded dental implants using the finite element method and to evaluate the relationship between the generated strain and the biologic reaction expressed through histomorphometric parameters. Finally, this study aimed to evaluate the interaction between the orthodontic loading and the deformation generated by normal occlusal function. Materials and Methods: Sixteen titanium dental implants were inserted in extraction sockets after the removal of the second premolars and first molars of 4 adult Macaca fascicularis monkeys. After 17 weeks of healing, the implants were loaded by a pair of Sentalloy springs (50 cN) for 16 weeks. After sacrifice, tissue blocks including the implants and surrounding bone were excised. Five tissue blocks were scanned with a synchrotron radiation-based microtomography (µCT) scanner and sample-specific finite element models were generated. Subsequently all samples were prepared for histomorphometric analysis. Results: All implants were osseointegrated, although the surrounding alveolar bone differed from sample to sample. As a consequence the finite element analyses showed that the stresses and strains in the peri-implant alveolar bone greatly varied among the samples. A high level of remodeling activity was found close to the implants. Discussion: Individual differences between the receptors (in this case, the monkeys) have a large effect on both the biologic and morphologic parameters. These variations were indeed found to have a substantial impact on the (re)modeling dynamics and the load transfer mechanisms around the implants. Conclusions: By integrating different analysis techniques to evaluate bone (re)modeling around orthodontically loaded implants, this study has demonstrated the complexity and case-specific character of alveolar adaptation to orthodontic loading. Furthermore, stresses generated by combined functional and orthodontic forces should not be neglected. (More than 50 references) Keywords: biomechanics, dental implants, finite element analysis, histomorphometry, osseointegration

Purpose: The aim of the present investigation was to evaluate the marginal bone level after 1 year of follow-up of 1-piece implants after immediate provisional restoration fabrication. Materials and Methods: Patients received NobelDirect and NobelPerfect 1-piece implants (Nobel Biocare, Göteborg, Sweden) that were immediately restored and placed into function as part of a 3-year, multicenter investigation. Life table analysis was used for evaluation of implant cumulative survival rates. The Student t test (for dichotomous variables) and Pearson correlation (for continuous and ordered categorical variables) were used to estimate the influence of separate parameters on marginal bone. Results: Eighty-seven patients received 152 NobelDirect or NobelPerfect 1-piece implants. Of these, 81 patients returned for the 1-year follow-up and 21 for the 2-year follow-up. Three implants were lost, resulting in a cumulative survival rate of 97.9% after up to 2 years. The average marginal bone level at implant placement was 0.33 mm (SD 1.20, n = 141) superior to the reference point (lower edge of the implant collar). Marginal bone level was -0.77 mm (SD 1.33, n = 138) at 6 months and -0.98 mm (SD 1.38, n = 123) at 1 year. Average bone level at the 2-year follow-up was 0.17 mm (SD 1.20, n = 26). After 1 year of loading, bone level in the maxilla was more apical compared to that in the mandible (P = .05), and a positive correlation was found between bone level at placement and bone level at 12 months (P = .008). Shallow implant positioning resulted in less marginal bone remodeling compared to deep implant positioning. Conclusion: On the basis of this prospective multicenter study, stable marginal bone level and soft tissue support the hypothesis that the 1-piece implant has the capacity to preserve both hard and soft tissue. Keywords: bone level, immediate function, 1-piece dental implants, radiologic evaluation

Purpose: The objectives of this study were (1) to compare the stability, evaluated by means of resonance frequency analysis (RFA), of implants placed posterior mandibles augmented with autogenous bone harvested from the mandibular symphysis with that of implants placed in nongrafted edentulous posterior mandibles and (2) to compare peri-implant marginal bone height changes and implant failure for the 2 groups. Materials and Methods: Eight patients with thin posterior mandibular ridges (buccolingual crestal width less than 4 mm) underwent labial onlay alveolar grafting with symphyseal bone blocks 4 months prior to placement of 17 implants. Seven nongrafted patients received 18 implants in the edentulous posterior mandible; these patients served as a control group. RFA was performed the day of implant placement (baseline), 1 month postplacement, 4 months postplacement (after prosthesis delivery), and 12 months postloading. Peri-implant bone height changes at a level of 0.01 mm were assessed using periapical radiographs at baseline, the 1-month follow-up, and the 4-month follow-up. Analysis of variance was used to evaluate statistical differences within the groups, and t test was used to make comparisons between groups. Results: None of the patients presented postoperative complications or implant failure. Mean implant stability quotient (ISQ) was 63.0 ± 6.0 to 70.2 ± 3.5 for the grafted group and 64.1 ± 4.1 ISQ to 70.1 ± 3.9 for the nongrafted group. No significant difference was found in mean ISQ between the grafted and nongrafted groups at baseline, the 1-month follow-up, 4 months postplacement, or 12 months postloading (P = .211, P = .873, P = .925, P = .735, respectively). Mean peri-implant bone loss was 0.16 ± 0.04 mm mesially and 0.16 ± 0.05 mm distally. Conclusion: RFA revealed no difference in implant stability between mandibular ridges augmented with autologous bone grafts at baseline or after loading. Keywords: autogenous bone graft, edentulous posterior mandible, implant stability, resonance frequency analysis, symphysis

Purpose: Mandibular deformation during function in patients with implant-supported prostheses is associated with increased strain at the bone-implant interface when dental implants are connected by a relatively rigid superstructure. Whilst there is a body of evidence concerning deformation as measured between the corpora, there are little data on its effects in the midline. This study measured 3 types of midline mandibular deformation during nonmasticatory functional mandibular movements in edentulous subjects with dental implants. Materials and Methods: A range of custom displacement transducers was fabricated for 5 edentulous subjects who had been treated with dental implants in the anterior mandible. These transducers were mounted on contralateral implant abutments adjacent to the midline to measure medial convergence, corporal rotation, and anteroposterior shear. Their output was recorded for offline analysis by a personal computer. Results: The values of medial convergence ranged from 15 to 42 µm during opening, from 10 to 21 µm during lateral excursions, and from 18 to 53 µm during protrusion. Corporal rotation varied from 0.05 to 0.11 degrees during opening, from 0.03 to 0.08 degrees during lateral excursions, and from 0.03 to 0.15 degrees during protrusion. Anteroposterior shear varied from 38 to 93 µm during opening, from 28 to 56 µm during lateral excursions, and from 52 to 103 µm during protrusion. Discussion and Conclusions: Nonmasticatory physiological mandibular movements cause the jaw to deform about the midline in at least 3 directions. It is important for the clinician to be aware of the phenomenon of mandibular deformation, which should be taken into consideration in the design and monitoring of mandibular prostheses. Keywords: dental implants, edentulous subjects, mandibular deformation

Purpose: To aid in developing mechanically optimized implant-abutment connectors, the fatigue resistance of 5 connector configurations of the Replace Select system (Easy abutment, Easy abutment without antirotational mechanism, Multi-unit abutment, Esthetic Alumina abutment, Esthetic Zirconia abutment) was investigated. Other purposes of the study were to determine whether the connector's antirotational mechanism participates in fatigue resistance and to compare the results with previous data on Straumann connectors. Materials and Methods: The repetitive, alternating, and multivectorial intraoral force pattern was reproduced by subjecting the test specimens to the rotating cantilever beam test. To this end, the samples were spun around their long axis while clamped into a revolving collet on one end and loaded normal to their long axis on the other end. The aim was to determine the load level at which 50% of the specimens survived and 50% fractured before 106 cycles. Means were determined using the staircase procedure. They were fitted with 95% confidence intervals for intergroup comparisons. Results: In the chosen testing configuration, 2 statistical groups emerged. The Easy abutments with and without antirotational mechanism were statistically similar, with mean failure loads in the 70 to 72 N range. Both ceramic and the Multi-unit abutments belonged to the second group, with mean failure loads in the 53 to 58 N range. Conclusions: (1) The fatigue resistance of ceramic and the Multi-unit abutments was approximately 20% less than that of the Easy Abutments. (2) The antirotational mechanism did not participate in mechanical resistance. (3) The fatigue strength of the Easy abutment connectors was approximately 20% greater than the equivalent abutments in the Straumann system. Keywords: connectors, dental implants, failure, fatigue

Purpose: The aim of the present study was to test whether a newly developed synthetic matrix made of polyethylene-glycol (PEG) containing a covalently bound peptide of the parathyroid hormone (PTH1-34) enhances bone regeneration compared to grafting procedures and to spontaneous healing. Materials and Methods: In each of 16 rabbits used, 4 titanium cylinders were screwed into perforated slits made in the cortical bone of the calvaria. The cylinders were either left empty (control) or filled with 1 of the following: (1) PEG matrix and hydroxyapatite/tricalcium phosphate (HA/TCP) granules, (2) PEG matrix containing 100µg/mL of PTH1-34 and HA/TCP granules, or (3) PEG matrix containing 20µg/mL of PTH1-34 and HA/TCP granules. After 8 weeks, the animals were sacrificed, and ground sections were obtained for histology. Results: Quantitative histomorphometry demonstrated a significantly increased amount of newly formed bone for PTH1-34 compared to sites treated with PEG and HA/TCP and to empty control sites (P .01; analysis of variance and subsequent pairwise Student t test). The mean percentages of mineralized bone were 19.6% ± 6.0% for 100µg/mL PTH, 18.0% ± 6.2% for 20µg/mL PTH, 12.0% ± 6.5% for PEG and HA/TCP without PTH, and 10.5% ± 3.7% for the empty control. The mean areas of bone regenerated within the cylinders were 53.5% ± 22.7% for 100 µg/mL PTH, 51.1% ± 22.6% for 20 µg/mL PTH, 34.3% ± 22.5% for PEG and HA/TCP without PTH, and 23.2% ± 10.1% for the empty control. Discussion: Human and animal trials have demonstrated that daily systemic injection of PTH increases bone mineral density. The present study showed that local administration of PTH was also effective in stimulating bone formation. Conclusion: It is concluded that this synthetic PEG hydrogel containing a covalently bound peptide of the PTH combined with HA/TCP granules significantly stimulated in situ bone augmentation in rabbits. Keywords: bone regeneration, calcium phosphates, graft material, hydroxyapatite, parathyroid hormone, polyethylene glycols

Purpose: The goal of this study was to evaluate retrospectively the efficacy of a treatment modality for a lesion at the apical portion of a nonmobile dental implant. Materials and Methods: All patients were treated with an intraoral treatment approach. A flap was elevated facial to the effected implant site, exposing the bone. A carbide bur was used to open a window in the bone. The bur was then used to cut the implant and completely remove the affected portion of the implant. The surgical site was then closed with interrupted vicryl sutures, and patients were prescribed. Results: Thirty-nine implants in 35 patients with a mean age of 58.3 years were identified clinically and radiographically with the presence of a periapical lesion. These 39 implants, which constituted 9.9% of implants (39 of 395) placed in these 35 patients, were consecutively treated using the intraoral apicoectomy procedure. Thirty-eight of the 39 implants (97.4%) treated with this technique remained stable and continued in function with no further complication. Follow-up time averaged 4.54 years; the longest follow-up time exceeded 15 years. Conclusion: Based upon the results of this retrospective study, lesions in the apical region of implants can be treated successfully using an intraoral apicoectomy procedure. Keywords: complications, machined implants, osseointegration, overheating, periapical abscesses

Purpose: Improvements in the bone-implant interface can provide clinical benefits, such as increasing the amount of bone in contact with the implant and shortening the time required to achieve sufficient bone appositioning to allow early prosthetic loading. The present study describes the results obtained with 2 new surface treatments: (a) CO ion implantation; and (b) diamond-like carbon (DLC) coating. Materials and Methods: Each group (ion implantation, DLC, and the control group, turned titanium) consisted of 12 samples. Beagle dogs subjected to previous partial edentulation were used. Dual histologic evaluation was made of percentage bone-implant contact (% BIC) of all samples based on conventional histomorphometric analysis and environmental scanning electron microscopy (ESEM). Results: The results obtained after 3 and 6 months of dental implant placement showed greater and faster bone integration in the CO ion implantation group (61% and 62% BIC, respectively) compared with the DLC group (47% and 50%); the data corresponding to the ion implanted samples were statistically significant compared with the control group (33% and 49% BIC after 3 and 6 months, respectively). Conclusions: The results showed improved % BIC for implants with ion-implanted surfaces in comparison to DLC coating and machined controls. Furthermore, bone integration appeared to be accelerated in the ion implantation group, since high % BIC values were recorded in the early stages after in vivo implantation. Keywords: bone integration, dental implants, diamond-like carbon, histomorphometry, ion implantation, osseointegration, periodontology, surface treatments

Purpose: To evaluate a new method to treat the posterior atrophic edentulous maxilla: dental implants placed in the ulna and transplanted with their surrounding bone blocks as inlays into the sinus. Conventional sinus augmentation with particulated autogenous bone grafts served as a control procedure. Materials and Methods: Fifty-two implants were placed in the ulnas of 20 patients. After 6 weeks, bone blocks containing 1 to 3 implants were harvested and transplanted into the sinuses protruding 3 to 4 mm. Implants were left to heal for 6 weeks. Twenty patients with similar treatment indications treated with particulated bone grafts from the mental symphysis, tibia, or iliac crest acted as controls. Grafts were allowed to heal for 6 months in the control group. Fifty-two control-group implants were allowed to heal for 4 months. The main outcome measures were prosthetic and implant success. Stability of individual implants was assessed with Osstell and Periotest at baseline and after 6 and 12 months of loading. Independent sample chi-square tests, t tests, and paired t tests were used with a significance level of .05. Results: No patient dropped out or withdrew; no prosthesis or implant failed. No major surgical complications were occurred. There were no differences between the 2 groups at any time point in implant stability. Both modalities resulted in a significant increase of implant stability at 6 and 12 months. The mean change (SD) from baseline to 1 year in Periotest measurements was 1.44 (0.48) in the test and 1.29 (0.58) in the control (paired t tests; P .001). For the Osstell, these values were -5.88 (4.18) and -5.48 (3.93) for the test and control groups, respectively (paired t tests: P .001). Conclusions: Ulna implant block grafting represents an alternative to conventional sinus augmentation, particularly when vertical augmentation is desirable or large iliac crest grafts are needed. Keywords: bone grafting, dental implants, sinus augmentation, ulna

Purpose: To evaluate the evidence for the diagnostic accuracy of clinical methods to assess bone density, quantity, or quality prior to and during dental implant placement. Materials and Methods: A PubMed literature search with specific indexing terms and a hand search were made. From the retrieved titles and abstracts, 3 reviewers selected publications on the basis of predetermined inclusion and exclusion criteria. Data were extracted from the selected publications using a protocol. Original studies were interpreted with the aid of the Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool. Results: The literature search yielded 145 titles and abstracts, of which 71 were selected and read in full text. Seven studies were judged relevant. In 1 study, no method was presented as the test method. In 6 studies, the results of the test method were compared to those of a reference method. However, only 1 study presented the results in terms of percentage of correct diagnoses. In that study, the use of periapical radiography together with reference images yielded correct assessment of the trabecular pattern of the mandible in 3 categories in 58% of the sites. The kappa index of interobserver agreement was 0.35 and intraobserver agreement was 0.67. Corresponding kappa values for 4 classes of bone quality presented by Lekholm and Zarb were 0.33 and 0.43, respectively. No study examined the accuracy of the method originally described by Lekholm and Zarb. Conclusion: The evidence for the efficacy of clinical methods to assess jawbone tissue prior to and during endosseous dental implant placement is sparse. This emphasizes the need for studies that incorporate accepted methodologic criteria for diagnostic efficacy. Keywords: bone, bone density, dental implants, diagnostic accuracy

Purpose: To evaluate the influence of the stress/strain distribution in bone around an anterior maxillary implant using 2 types of bone and under 3 different loads. Materials and Methods: A premaxillary finite element model featuring an implant and its superstructure was created. Six different testing conditions incorporating 2 types of cancellous bone (high density and low density) under 3 different loading angles (0, 30, and 60 degrees) relative to the long axis of the implant were applied in order to investigate resultant stress/strain distribution. Results: The maximum equivalent stress/strain increased linearly with the increase of loading angle. For each 30-degree increase in loading angle, the maximum equivalent stress in cortical bone increased, on average, 3 to 4 times compared with that of the applied axial load. In addition to loading angle, bone quality also influenced resultant stress distribution. For the low-density bone model, a substantial strain in the cancellous bone was found not only near the implant neck but also at the implant apex. Conclusion: To achieve a favorable prognosis under off-axis loading of an anterior maxillary implant, careful case selection for appropriate bone quality and precise occlusal adjustment should be attempted to optimally direct occlusal force toward the long axis of the implant. Keywords: biomechanics, bone quality, dental implants, finite element analysis, off-axis load, premaxilla