The International Journal of Oral & Maxillofacial Implants, 01/2008

Purpose: The aim of this study was to investigate the deviations of the implant positions of both impressions and casts using different impression materials and techniques. Furthermore, the existence of a correlation between the deviations of the impression and those of the cast was investigated. Materials and Methods: A reference model was fabricated with 5 Frialit-2 implants parallel to each other. In a standardized experimental setting, 5 stone casts were produced with 5 different techniques using polyether (A) or polyvinyl siloxane (B through E). In 3 groups, a direct technique was used with a medium-viscosity material or a putty-tray material in combination with a light-viscosity syringe material (A to C). In 2 groups, an indirect technique (either 1-step [group D] or 2-step [group E] was used with a putty-tray material in combination with a light-viscosity syringe material. The center-to-center distances were measured for impressions and casts in the horizontal plane using a computer-aided microscope, and the relative and absolute deviations compared to the reference model were calculated. Analysis of variance followed by the post-hoc Scheffé test (parametric data) or the Kruskal-Wallis test followed by pair-wise Mann-Whitney tests (nonparametric data) were used for statistical analyses. Deviations of impressions were compared with their respective casts using paired t tests and the Pearson correlation coefficient. Results: No significant differences for the relative deviations were found for impressions (-5 to -8 µm) or casts (+7 to +16 µm). Group E produced significantly higher absolute deviations for impressions (38 µm) and casts (39 µm) compared to the other groups (11 to 18 µm and 17 to 23 µm, respectively). A significant correlation between deviation of the impression and its respective cast was found for every group (r = 0.40 to 0.80) except group D. Conclusions: The distortions in the horizontal plane of the casts obtained from the impression techniques of groups A to D would probably not affect the clinical fit of implant-retained superstructures. Because of the high variation of deviations (-113 to +124 µm), the 2-step technique cannot be recommended. The method to measure both impression and cast provided a better understanding of how inaccuracies are caused. Keywords: dental implants, impression materials, impression technique, transfer coping

Purpose: The aim of this study was to identify and measure postextraction maxillary sinus pneumatization using fixed reference lines on panoramic radiographs. Materials and Methods: One hundred fifty-two panoramic radiographs, each of a different subject, were used to measure superoinferior differences of the sinus floor position in dentate sites in comparison with contralateral edentulous sites. Fifty-eight pairs of panoramic radiographs, each pair of the same subject, were used to measure superoinferior differences of the sinus floor position in the same site before and 6 to 67 months after extraction. All measurements were performed using an interorbital line and 2 zygomatic process lines as reference lines. Statistical correlations between the amount of expansion of the sinus and the root classification, projection length, duration after extraction, type, and number of the extracted teeth were examined. Results: Postextraction expansion of the sinus in an inferior direction occurred in both comparisons (2.18 ± 2.89 mm for dentate versus contralateral sites and 1.83 ± 2.46 mm for the same site pre- and postextraction). A considerable amount of expansion occurred after the extraction of teeth surrounded by a superiorly curving sinus floor (5.27 ± 1.59 mm). A larger expansion was also measured after second molar extractions in comparison to first molars and in cases of extractions of 2 or more adjacent posterior teeth. Discussion: Posterior maxillary tooth extraction caused an inferior expansion of the maxillary sinus in relation to fixed anatomic landmarks, thus proving the pneumatization phenomenon after tooth loss. Conclusions: Sinus pneumatization was identified after extraction of maxillary posterior teeth. The expansion of the sinus was larger following extraction of teeth enveloped by a superiorly curving sinus floor, extraction of several adjacent posterior teeth, and extraction of second molars (in comparison with first molars). If dental implant placement is planned in these cases, immediate implantation and/or immediate bone grafting should be considered to assist in preserving the 3-dimensional bony architecture of the sinus floor at the extraction site. Keywords: extraction, maxillary sinus, panoramic radiograph, pneumatization, sinus floor topography

Purpose: The aim of this study was to determine the relative contribution of changes in implant system, position, bone type, and loading condition on the biomechanical response of a single-unit implant-supported restoration using nonlinear 3-dimensional finite element analysis (3D FEA). Materials and Methods: FEA models of a single-unit (crown) restoration supported by the Frialit-2 implant and MH-6 abutment or the Straumann standard implant with the Straumann solid abutment were used. Each system was analyzed by FEA with both straight and 20-degree angled abutments. Simulated implant placement was performed in the maxillary premolar area with 3 variations in implant orientation relative to the residual ridge. Analysis of each orientation was conducted for each of 4 bone quality types described by Lekholm and Zarb, with lateral and axial loading conditions imposed. The effect of each variable was expressed as a percentage of the total sum of squares as computed using analysis of variance. Results: Larger strain values were noted in cortical bone with lateral force and the Frialit-2 system. Bone strain increased with decreasing bone density and was affected primarily by bone quality. Implant stress was influenced mainly by implant position. Conclusions: Better stress/strain distribution is possible when implants are placed along the axis of loading with multiple areas of cortical contact. The Straumann solid abutment performed better as a force-transmission mechanism. Keywords: abutment-implant connection, biomechanics, bone type, finite element analysis, implant placement

Purpose: To evaluate continuous and simultaneous variations of thread height and width for an experimental screw-type implant. Materials and Methods: A finite element model of an implant with a V-shaped thread was created. The range of thread height was set at 0.20 to 0.60 mm, and the range of thread width was set at 0.10 to 0.40 mm. Forces of 100 N and 50 N were applied along the implant axis (AX) and an angle of 45 degrees in a buccolingual direction (45-degree BL), respectively. The maximum von Mises stresses in jawbone were evaluated, and the sensitivity of the stress in jawbone to the variables was also evaluated. Results: Under AX load, the maximum von Mises stresses in cortical and cancellous bones increased by 4.3% and 63.0%, respectively, as thread parameters changed. Under 45-degree BL load, maximum von Mises stresses in cortical and cancellous bones increased by 19.3% and 118.0%, respectively. When thread height was from 0.34 to 0.50 mm and thread width was 0.18 to 0.30 mm, the tangent slope of the maximum von Mises stress response curve ranged from -1 to 1. The variation of the maximum von Mises stresses in jawbone was more sensitive to thread height than to thread width. Conclusions: Stress in cancellous bone is more likely to be influenced by thread parameters than stress in cortical bone. A 45-degree BL force is more likely to be influenced by thread parameters than an axial force. A thread height of 0.34 to 0.50 mm and a thread width of 0.18 to 0.30 mm is optimal from a biomechanical point of view. In the design of a screw-type implant, thread height is more important than thread width for the reduction of stress within the bone. Keywords: 3-dimensional finite element analysis, dental implant, optimized thread design, stress

Purpose: The aim of the present investigation was to review and evaluate the current literature on skeletal bone anchorage in orthodontics with regard to success rates of the various systems. Materials and Methods: MEDLINE, PubMed, and Cochrane searches (period January 1966 to January 2006, English language) of animal and human studies using skeletal anchorage during orthodontic treatment were scrutinized. A total of 50 relevant articles were identified which investigated various types of implants. Results: Two types of anchorage systems are used in orthodontics: (1) osseointegrated dental implants, including temporary mid-palatal implants. These systems were associated with a wide variety of success rates in animal studies. In human studies, the systems were shown to be reliable, with success rates between 85% and 100% (ie, systems still functioning at the end of the orthodontic treatment). (2) Nonosseointegrated mini-plates and mini-screw anchorage systems. Titanium mini-plates were associated with 100% success in animals, and hardly any loss of these mini-plates (bone anchors) were lost due to infection in human studies, with success rates between 91% and 100%. Few long-term studies on nonosseointegrated mini-screws were found, but in animal studies, success rates ranged from 90% to 100%. A success rate of more than 75% in human studies is considered favorable for these orthodontic implants, which confirms the clinical applicability of this type of immediate loading anchor support in orthodontics. Conclusions: Both animal and human studies revealed that mesiodistal and intrusion movements can be reliably carried out by means of skeletal anchorage devices. A drawback is that animal studies do not reflect the real orthodontic clinical situation; thus, the outcome of these studies should be interpreted with caution. Human studies, however, show that orthodontic forces between 100 and 400 grams can be applied successfully to skeletal anchorage devices. Appropriate treatment strategies need to be confirmed by randomized prospective clinical trials. (More than 50 references.) Keywords: bone anchors, micro-screws, mid-palatal implants, mini-screws, skeletal anchorage

Purpose: To assess the need for surgical and prosthetic aftercare of craniofacial prostheses supported by endosseous implants. Materials and Methods: A retrospective clinical study assessing the surgical and prosthetic aftercare from implant placement to last visit of follow-up was performed in consecutively treated patients with implant-retained craniofacial prostheses in a department of oral and maxillofacial surgery between 1988 and 2003. Results: Ninety-five patients were rehabilitated with implant-retained craniofacial prostheses. Mean follow-up was 88 months (median, 79 months). Two hundred seventy implants were placed; 153 implants in the mastoid region, 99 in the orbital region, and 18 in the nasal region. The craniofacial defects were due to genetic disorders (24 patients), trauma (12 patients), and ablative tumor surgery (59 patients). In the latter group, 104 implants (33 patients) were placed in irradiated bone. Thirty implants were lost; 8 implants in nonirradiated bone (95.2% overall implant survival rate; mastoid, 95.7%; orbit, 94.1%; nose, 87.5%) and 22 implants in irradiated bone (78.8% overall implant survival rate; mastoid, 86.2%; orbit, 73.8%; nose, 90.0%). Irrespective of the craniofacial defect, on average every 1.5 to 2 years a new facial prosthesis was made, mostly for reasons because of discoloration (31.2%), problems with attachment of the acrylic resin clip carrier to the silicone (25.3%), rupture of the silicone (13.3%), or bad fit (10.9%). Severe skin reactions around implants or beneath prostheses were only observed in the orbital region. Conclusion: Implant-retained craniofacial prostheses are a reliable treatment option for the restoration of craniofacial defects. The need for surgical aftercare was minor, and prosthetic aftercare predominantly consisted of making new prostheses. Keywords: aftercare, craniofacial prostheses, extraoral implants, implant survival, radiotherapy

Purpose: Implant osseointegration has been well described, but coronal osseous healing continues to be investigated because of its impact on esthetic results and long-term maintenance. Although numerous implant diameters and designs exist, little is known about the role of these parameters on surrounding bone. Therefore, this study aimed at elucidating the influence of implant dimensions on crestal bone morphology. Materials and Methods: Sixty Biomet/3i implants (20 standard, 20 wide, and 20 expanded platform [XP]) were randomly placed in posterior quadrants of 5 mongrel dogs. After healing, exposure of the implants to the oral cavity, and euthanasia of the animals, samples were harvested. Histomorphometric measurements were performed to determine the bone cuff height, width, and angle, and analysis of variance was applied to compare groups. Results: Formation of a peri-implant cuff was noticed in all implant sites. Mean cuff height was 0.8 mm, 1 mm, and 1.4 mm for standard, wide, and XP implants, respectively. Mean cuff width was 1.9 mm, 2.1 mm, and 2.8 mm for standard, wide, and XP implants, respectively. These differences were statistically significant between wide and XP implants (P = .035), as well as between standard and XP implants (P = .001). Angle did not differ significantly between implants of different platform widths. Conclusions: Craterization after placement of healing abutments and a healing period was observed around all implants. Width and height of the cuff varied significantly with implant diameter and platform design, but the angle formed with the implant did not vary significantly. Keywords: animal study, bone healing, dental implants, implant diameter, osseointegration

Purpose: The purpose of this study was to estimate the 1-year survival rate of immediate vertical-load splinted locking-taper implants and to identify risk factors for implant failure. Materials and Methods: To address the research aim, the investigators implemented a retrospective cohort study design and enrolled a sample derived from the population of patients who had received immediate vertical-load splinted implants (Bicon, Boston, MA). The predictor variables were the sets of exposures associated with implant failure and classified as demographic, health status, anatomic, implant specific, prosthetic, and surgical. The primary outcome variable was implant failure, which was defined as implant removal. Descriptive, univariate, and multivariate analyses using clustered marginal approach of the Cox proportional hazards models were computed. The level of statistical significance was set at P .05. Results: The study cohort was composed of 209 patients who received 477 implants. The overall 1-year Kaplan-Meier survival estimate was 90.3% (95% CI: 86.9%, 93.7%). In the multivariate model, implant placement in a delayed manner versus implantation the same day as extraction (hazard ratio = 3.7, P = .002), uncoated implants versus coated implants (hazard ratio = 22.1, P .001), and an increased per-unit number of pontics involved in the temporary prosthesis (hazard ratio = 1.8, P .001) were statistically associated with an increased risk of implant failure. Conclusions: An overall 1-year survival estimate of 90.3% (95% CI: 86.9%, 93.7%) was calculated for immediately loaded splinted implants. After controlling for other variables, 3 variables-timing of implant placement relative to extraction (delayed implant placement after tooth extraction), coating of implant (uncoated), and increased number of pontics-were associated with an increased risk for implant failure. Keywords: dental implants, immediate loading, multivariate models, retrospective cohort study, risk factors

Scientific literature describes autogenous bone as the gold standard among graft materials for alveolar reconstructive procedures. Alveolar ridge augmentation has been clinically achieved with different forms of autogenous bone, including autogenous cortical bone particulate (ACBP). However, few histologic studies demonstrating the biologic potential and healing dynamics following the use of ACBP are currently available. This case report presents 2 patients in whom atrophic edentulous alveolar crests were submitted to a vertical/lateral ridge augmentation prior to implant placement. The technique was performed through the use of a titanium-reinforced expanded polytetrafluoroethylene (e-PTFE) membrane with an ACBP graft obtained from the retromolar region with a specially designed bone scraper. Bone biopsy specimens were harvested at 9 months after graft placement. Analysis of the reconstructed bone revealed bone with a lamellar quality characterized by a mature osteonic structure. Sparse particles of grafted bone were evident in direct contact with the regenerated bone. Marrow spaces showed a normal stromal component with limited grafted particles. Keywords: alveolar ridge augmentation, autogenous cortical bone particulate, guided bone regeneration

This clinical article describes a case of dental rehabilitation using an implant-carrying plate system (EPITEC) for a patient with severely resorbed edentulous maxilla and microstomia. In this case, the presence of microstomia prevented bone augmentation procedures through an intraoral approach. Treatment using 2 endosseous implants inserted in the canine regions and an implant-supported overdenture was planned. However, endosseous implants were not feasible on the right side because of insufficient available bone volume. An implant-carrying plate system was then utilized on the right side. Four months later, an implant-supported ball-attachment overdenture was fabricated. At the 2-year follow-up, the clinical course remained uneventful, and the patient remained satisfied with the treatment. Keywords: dental implant, edentulous maxilla, implant-carrying plate system, implant-supported overdenture, resorbed maxilla

In anterior maxillary extraction sockets, immediate implants are usually positioned along the palatal slope of the extraction socket. However, this positioning frequently causes unintentional slipping of dental implant toward thin labial plate, leading to its fracture or perforation. To prevent this, the present authors have created a simple apico-palatal guiding slot in the extraction socket following atraumatic extraction. Guided by this slot, sequential drilling up to implant placement can be easily accomplished while maintaining ideal axial orientation of the dental implant. Keywords: anterior maxilla, extraction socket, immediate implant placement

A bovine-bone mineral block was used to treat a severe horizontal and vertical anterior ridge deficiency. Such a block can be shaped to conform to the defect, and it avoids the need for harvesting autogenous bone or fixation of the block with screws. After a 6-month integration period, an implant was placed. Six months later the implant was restored with a single crown. The case has been followed for 3 years. Slow bone resorption has been observed at the interface between the block and the surrounding bone, but the interproximal bone peaks, important for soft tissue support and esthetics, have been maintained over time. The 3-year follow-up results suggest that bovine-bone mineral blocks may be a suitable bone-replacement material for augmentation of extensive alveolar ridge defects in the anterior region. Keywords: bone grafting, bovine bone mineral block, vertical augmentation

The osteotome method is an often-used technique of great utility in certain patients with maxillary bone atrophy. However, it has been associated with the provocation of benign paroxysmal positional vertigo (BPPV), which has been described as a consequence of working the implant bed with osteotomes. During the placement of maxillary dental implants using the osteotome technique, the trauma induced by percussion with the surgical hammer, along with hyperextension of the neck during the operation, can displace otoliths and induce BPPV. Four cases of BPPV occurring after the preparation of maxillary implant beds are presented. Treatment consists fundamentally of maneuvers to move the calcium carbonate crystals from their anomalous location in the semicircular canal to their correct place in the utricle. Keywords: benign paroxysmal positional vertigo, dental implants, osteotomes

Inferior alveolar nerve transposition and placement of endosseous implants is one of the treatment options for patients with an edentulous posterior mandible with inadequate bone height superior to the inferior alveolar canal. The possible complications associated with this technique include prolonged neurosensory disturbances, infection, and pathologic fracture. This report presents the surgical management of a patient who sustained a mandibular fracture after inferior alveolar nerve transposition for the placement of 3 endosseous implants. Keywords: complications, endosseous implants, inferior alveolar nerve, mandibular fracture

Risk factors and complications in immediate implant placement are widely discussed. The present report describes a case of severe osteomyelitis as a serious complication after the immediate placement of a dental implant into an extraction socket of a 61-year-old woman. The course leads from initial treatment of recurrent perimandibular abscesses with surgical drainage and high-dose intravenous antibiotics to a refractory osteomyelitis. Hemimandibulectomy and partial mandibular reconstruction with a free fibular flap followed. Keywords: free fibular flap, immediate dental implantation, infection, osteomyelitis

The scientific literature has demonstrated the use of the buccal fat pad (BFP) flap to cover bone grafts in the correction of maxillary osseous defects and in the closure of oroantral communications. The use of the pedicled BFP flap to provide an immediate blood supply to a recipient site is recommended to provide closure of oroantral communications. The author presents a case report of zygomatic implant surgery in which the BFP flap technique was used in the closure of an oroantral communication caused by maxillofacial surgery. Keywords: buccal fat pad, oroantral communication, zygomatic implants

Intraoral distraction osteogenesis (DO) has been widely used for the reconstruction of various dentoalveolar defects. However, its use in the management of alveolar clefts is relatively new. This method allows the closure of the cleft via the regeneration of new alveolar bone and attached gingiva through the distraction of a dento-osseous segment. It eliminates the need for a donor site for autogenous bone grafting and possible graft failure. However, the relatively long consolidation period required for the use of intraoral DO devices may result in soft tissue irritation that would compromise patient cooperation, especially in children. In the case presented, the intraoral DO technique was used for the treatment of a unilateral residual alveolar cleft and an implant was subsequently placed in the regenerated bone. A miniplate was also placed to serve as a skeletal anchor to enable the early removal of the distractor device. The distractor was removed before the beginning of the consolidation phase. Keywords: alveolar cleft, dental implant, distraction osteogenesis, skeletal anchorage

The purpose of this case report is to demonstrate the relation between occlusal overload and peri-implant bone loss and the reversal of the situation after removal of the offending forces. The placement of an unstable removable prosthesis on 3 well-integrated implants that had been stable for 9 years caused noticeable bone loss after 6 months. The elimination of the traumatic occlusion reversed the situation, and a remarkable healing of the peri-implant tissue occurred until the pretrauma condition was nearly restored. The condition has been stable for the past 4 years. Keywords: occlusal overload, osseointegration, peri-implant bone loss