The International Journal of Prosthodontics, 04/2010

Purpose: The focus of this systematic review was to assess the published data concerning zirconia dental implant abutments from various aspects. Materials and Methods: To identify suitable literature, an electronic search was performed using PubMed. The keywords "zirconia," "zirconium," "ceramic," "dental abutments," "dental implants," "plaque," and "bacteria" were included. Titles and abstracts were screened, and literature that fulfilled the inclusion criteria was selected for a full-text reading. Articles were divided into four groups: (1) studies on the mechanical properties of zirconia abutments, (2) studies on the peri-implant soft tissues around zirconia abutments, (3) studies on plaque accumulation on zirconia, and (4) clinical studies on the survival of zirconia abutments. Results: The initial literature search resulted in 380 articles. For groups 1 to 4, 11, 4, 7, and 3 articles satisfied the inclusion and exclusion criteria, respectively. Only 1 randomized clinical study was identified. Review of the selected articles showed that zirconia abutments were reliable in the anterior region from both biologic and mechanical points of view. Furthermore, zirconia abutments may represent a material surface less attractive for early plaque retention compared to titanium. Three clinical follow-up studies indicated that zirconia abutments could function without fracture and peri-implant lesions. Conclusions: Based on the reviewed literature, zirconia has the potential to be used as a dental abutment material, although some issues have to be studied further.

Purpose: The aim of this study was to evaluate patient satisfaction and clinical and prosthetic outcomes of two-implant mandibular overdenture treatment with different attachment types after 10 years of function. Materials and Methods: In a crossover clinical trial, 18 edentulous subjects with complaints regarding their mandibular dentures received two implants and a new denture with magnet, ball-socket, or bar-clip attachments that were applied in a random order. At the end of the experiment, the attachment type of their choosing was fitted in the overdenture. After 10 years, 7 subjects with a ball-socket and 7 subjects with a bar-clip attachment were available for evaluation. The same questionnaire from 10 years before was completed, and subjects were asked to express their overall appreciation of their dentures on a visual analog scale (VAS). Six scales of denture complaints were constructed. Mean scale and VAS scores between initial evaluation and after 10 years were compared. In addition, marginal probing depths, Bleeding Index, and radiographic marginal bone loss were assessed. Results: There was no marked difference in satisfaction between subjects with ball-socket- and bar-clip-retained two-implant mandibular overdentures at initial evaluation and after 10 years of function. Conclusion: Patients' appreciation of their implant-retained denture was and remained high over time. Clinical parameters revealed healthy mucosal conditions and stable marginal bone levels, determined radiographically. Probing depths around implants provided with ball-socket attachments were slightly shallower than those with bar-clip attachments after 10 years of function (P .05).

This clinical study evaluated the effect of two microwave disinfection protocols at 650 W for 3 minutes (group 1, once a week; group 2, three times a week) on the linear dimensional stability of complete dentures. Measurements were taken across four reference points: before the first microwave disinfection (baseline) and after each week of disinfection. Furthermore, the dentures were monitored clinically. Group 2 showed significantly greater shrinkage than group 1 in all evaluated weeks. During clinical monitoring, no significant findings were observed. Even though dimensional changes occurred, the clinical evaluation did not yield any changes in either group.

Purpose: The aim of this study was to evaluate long-term marginal bone levels for two unsplinted implants supporting mandibular overdentures using conventional and early loading protocols with different implant surfaces and attachment systems. Materials and Methods: A cohort of 106 edentulous participants (mean age: 65 years) was treated with mandibular two-implant overdentures opposing complete maxillary dentures. Participants were randomly allocated into three loading protocol groups using four implant systems; single-stage surgery was performed for all participants, followed by an unsplinted prosthesis using six different attachment systems. Standardized intraoral radiographs taken at baseline (loading) and over 10 years appraised marginal bone levels mesially and distally from reference points under magnification. Three calibrated examiners repeated measurements, diminishing intra- and interobserver variability. Progressive attrition of participants occurred as a result of deaths, dropouts, and emigration. Seventy-nine participants (74.5%, mean age: 72 years) were available at the 10-year recall. Differences in bone loss among different loading protocols, implant surfaces, and attachment systems were tested using chi-square and one-way analysis of variance tests. Results: Minimal, time-dependent, long-term marginal bone loss occurred with all loading protocols. Annual marginal bone loss progressed at low levels after the first year with episodes of bone loss and gain. There was stability in marginal bone levels over the long term, with the majority of remodeling occurring during the first year of function. Roughened implant surfaces may be beneficial during the early remodeling period. The amount of marginal bone loss in the first year of loading differed significantly by loading protocol and implant surface, whereas attachment system had a minor influence. Differences were not reflected in the success rates calculated using standard criteria. The remaining participants at 10 years were classified as successful related to the criterion of marginal bone loss, irrespective of the determining criteria for success. Conclusions: Either a 2- , 6-, or 12-week loading protocol for mandibular two-implant overdentures is possible in the long term, irrespective of the attachment system used. Minimal marginal bone loss may be attributed primarily to mandibular basal bone remaining from long-term edentulism. Revision of the current implant success criteria to offer a stricter limit is desirable.

Purpose: The aim of this study was to investigate the biomechanical role of trabecular bone around dental implants in the mandible. Materials and Methods: The model in this study was made using micro-computed tomography data taken from a cadaver in whom endosseous implants had been in place for 15 years prior to death. Morphologic analysis and three-dimensional (3D) finite element analysis were performed to calculate the peri-implant loading path of the model in which the trabecular structure was accurately simulated. Results: As seen through multiscale analysis using the homogenization method, the trabecular bone architecture around implants was isotropic for the most part. Also, 3D finite element analysis showed that compressive stresses oblique to the implant axis were transmitted to the lower constrained surface; tensile stresses oblique to the implant axis were transmitted to the upper constrained surface, and they intersected each other with vertical loading. The highest stress in cancellous bone was observed on perpendicular loading, and stress produced in trabeculae decreased approaching horizontal loading. Conclusion: Cancellous bone architecture around the implant was generally isotropic. 3D finite element analysis showed that cancellous bone trabeculae around implants dispersed stress by forming load transfer paths. The results suggest that trabecular bone plays a major role in supporting functional pressure exerted via the implant.

Swallowed prostheses have been described in the literature, and in some cases, the diagnosis can be challenging, especially if the partial or complete denture is metal-free. This article presents a case of a swallowed partial denture and points to the importance of early diagnosis. A man was admitted to the emergency room complaining of progressive breathing difficulty while presenting with an extra volume in his neck. After inconclusive image examinations, endoscopy under sedation was used to identify and retrieve the foreign object, which was a metal-free acrylic partial denture. Early diagnosis and the correct treatment can avoid serious sequelae, such as edematous reactions, mucosal infection, and necrosis. Patients should be scheduled for regular recall visits for evaluation of prosthesis fit and retention, condition of the abutments, and nocturnal wear.

Purpose: Injuries to the trigeminal nerve are a common postoperative complication of dental implant surgery. Usually, the altered sensation and neuropathic pain caused by the nerve injury is temporary, but a permanent neurosensory disorder can sometimes occur. Surgery is commonly used to treat this condition, but the treatment is associated with some complications and a relatively low success rate. This study analyzed the characteristics of pharmacologic management of trigeminal nerve injury pain after dental implant surgery. Materials and Methods: Eighty-five patients who visited a temporomandibular joint and orofacial pain clinic with a history of trigeminal nerve injury pain after dental implant surgery were enrolled in this study. The pharmacologic management for trigeminal nerve injury pain was evaluated by prescribing a variety of medications for 12 weeks according to the prescription protocol of the study. The patients' pain characteristics, average percentage of pain reduction, and pain relieving factors were investigated prospectively. Results: Patients who took anticonvulsants and antidepressants for at least 12 weeks reported a mean reduction in pain of 24.8%. Interestingly, patients who experienced an altered sensation and neuropathic pain for more than 1 year also reported a reduction in pain and discomfort, with an average decrease of 17.1%. In addition, it was found that early treatment using medications had a significant effect on reducing the level of pain and discomfort. Conclusion: These results suggest that pharmacologic management can be used for treating trigeminal nerve injury pain after dental implant surgery.

The effect of guidance elements on the rotation of crowns was analyzed. Resin molars were prepared with curved or horizontal preparation lines. Further groups were formed with a groove or one or two boxes. Teeth were duplicated eightfold; crowns were produced and cemented with a rotational torque of 0.5 Ncm. The width of the cement gap was measured at 11 reference points. Having either one or two guidance boxes had a significant centering effect. No differences were found between both types of preparation lines. The use of a proximal guidance box may be considered to reduce torsion of a single crown during cementation.

This study evaluated the effect of framework design on the fracture resistance of metal-ceramic implant-supported crowns. Screw-retained molar crowns with a screw access hole composed of metal or porcelain were compared to a cement-retained crown (control). For each group (n = 10), five crowns were subjected to dynamic loading (1,200,000 3 100 N 3 2 Hz at 37°C). Afterward, all specimens were loaded to failure using a universal testing machine. Significant differences could be established between the cement- and screw-retained groups (P = .05), but no difference was found between the screw-retained groups and the specimens subjected to dynamic loading. Occlusal discontinuity of screw-retained crowns affects their resistance, and the metallic support on the screw access hole did not reinforce the crowns.

Purpose: The aim of this study was to evaluate the survival rate of three-unit surface-retained, resin-bonded, metal-ceramic fixed dental prostheses (RBFDP) using two adhesive cements and two surface conditioning methods. Materials and Methods: Between 2005 and 2009, a total of 58 patients (34 women, 24 men; mean age: 42.1 years) received 58 three-unit RBFDPs made of a nonprecious alloy (Wirocast Co-Cr). Restorations were cemented employing the following combinations: (1) alumina air abrasion-silane + Panavia F 2.0 (group A1), (2) tribochemical silica coating (CoJet)-silane + Panavia F 2.0 (group A2), (3) alumina air abrasion-silane + Super-Bond C&B (group B1), and (4) CoJet-silane + Super-Bond C&B (group B2). Teeth were conditioned using the adhesives of the cements accordingly. Adaptation, debonding, fracture, and crack and caries formation were considered for clinical evaluation. Data were collected at baseline, 6 months, and annually thereafter. Forty-eight RBFDPs were available for follow-up (mean: 20.3 months, minimum: 6 months, maximum: 42 months). Results: The effect of cement type on the survival rate of RBFDPs was not significant (P > .05). The survival rate was also not significantly affected by the location (maxilla: 93.2%, mandible: 92.9%; P = .928). All experienced failures were observed within the first year after cementation. In total, four complete debondings were encountered (two in group A1, one in group A2, and one in group B1 at months 1, 3, 7, and 3, respectively). Group B2 did not result in any failures during the observation period. The failures were adhesive debondings between the metal surface and the cement. Conclusion: Early findings did not show significant differences between the cement and conditioning type combinations, with group B2 presenting no failures.

This study compared the fracture load and failure types of implant-supported zirconia all-ceramic crowns cemented with various luting agents. The ceramic frameworks were fabricated from a presintered yttria-stabilized zirconium dioxide block using computer-aided design/computer-assisted manufacturing technology, and were then veneered with feldspathic porcelain. Three luting agents were used. Composite resin cement (1,560.78 ± 39.43 N) showed the highest mean fracture load, followed by acrylic/urethane cement (1,116.20 ± 77.32 N) and zinc oxide eugenol cement (741.21 ± 41.95 N) (P .05). The types of failure varied between groups.

Purpose: The development of high-strength oxide ceramic materials has led to increased interest in all-ceramic fixed dental prostheses (FDPs). Success rates reported in clinical studies for all-ceramic FDPs based on high-strength oxide ceramic materials reportedly approach those of porcelain-fused-to-metal FDPs. These reconstructions, however, are still of limited size and have mainly concerned FDPs supported by natural teeth. The purpose of this study was to evaluate the clinical performance of multiunit all-ceramic FDPs supported by dental implants. Materials and Methods: Ten patients received mandibular yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) FDPs manufactured according to the Cercon technique and supported by four Astra Tech implants. Nine patients received 10-unit FDPs and one patient received a 9-unit FDP. The FDPs were cemented with Panavia F 2.0 onto individually prepared titanium abutments. The FDPs were evaluated at baseline and after 12, 24, and 36 months. Results: At the 3-year follow-up, all FDPs were in use, and all patients were fully satisfied with their treatment. None of the reconstructions had fractured. Superficial chip-off fractures of the veneering porcelain were, however, observed in nine patients (34 of 99 units, 34%). Conclusion: Results from this 3-year study suggest that implant-supported full-arch Y-TZP FDPs manufactured according to the Cercon technique should be viewed as a treatment alternative cautiously. A better understanding of the factors resulting in chip-off fractures is needed, together with longer follow-up studies involving larger numbers of patients, before the material and technique can be recommended for general use.

This article reports on a method to digitally survey and build virtual patterns for removable partial denture (RPD) frameworks using a new three-dimensional (3D) computer-aided design/computer-assisted manufacturing (CAD/CAM) software package developed specifically for RPD design. The procedure included obtaining 3D data from partially dentate casts, deciding on the path of insertion, and modeling the shape of the components of the frameworks digitally. The completed model data were stored as stereolithography (STL) files, which are commonly used in transferring CAD/CAM models to rapid prototyping technologies. Finally, metal RPD frameworks were fabricated using a selective laser melting technique.