Statement of problem Marginal adaptation is important for the long-term success of dental restorations. Data on the marginal discrepancy of zirconia-based fixed dental prostheses made with different computer-aided design/computer-aided manufacturing technology is needed. Purpose The purpose of this study was to evaluate the marginal adaptation of different zirconia 3-unit fixed dental prostheses at different fabrication stages and after artificial aging. Material and methods Twenty-four zirconia 3-unit fixed dental prostheses (DCS, Procera, and VITA YZ-Cerec; n=8) were fabricated using different manufacturing systems and conventionally cemented with glass ionomer cement on human teeth. Each group was aged in a masticatory simulator with thermal cycling. The marginal gaps were examined on epoxy replicas for frameworks and for restorations before and after cementation, and after masticatory simulation, at ×250 magnification. Marginal adaptation was assessed using geometric means of the marginal gap values with 95% confidence intervals. Differences between the manufacturing systems and the effect of artificial aging were tested using repeated-measures ANOVA and post hoc paired and unpaired t tests with Bonferroni-Holm correction (α=.05). Results The geometric mean (95% confidence limits) marginal gap values (μm) for frameworks and for restorations before cementation, after cementation, and after masticatory simulation were, respectively: DCS: 86 (80-93), 86 (83-90), 86 (78-94), and 84 (79-90); Procera: 82 (74-89), 89 (81-97), 89 (84-95), and 88 (82-94); and VITA YZ-Cerec: 64 (57-72), 67 (61-77), 76 (71-82), and 78 (76-80). The repeated-measures ANOVA showed significant group and stage effects ( P P P P P >.05). Conclusions The marginal accuracy of zirconia fixed dental prostheses is influenced by manufacturing technique. (J Prosthet Dent 2009;101:239-247)

Marginal adaptation of three different zirconium dioxide three-unit fixed dental prostheses.

Purpose The aim of this study was to review the published literature on in vitro articles investigating the retentive force or wear features of different attachment systems, specifically for mandibular two-implant overdentures using an unsplinted prosthodontic design. Materials and methods An electronic search was performed through PubMed, Embase, and Medline databases using Boolean operators to combine the following key words: "retention," "wear," "overdenture attachments," "attachment systems," "implant-retained overdentures," and "implant-supported overdentures." The search was limited to articles written in English published up to October 2008. In addition, a hand search through articles and reference lists retrieved from the electronic search and peer-reviewed journals was also conducted. Results From a total of 193 articles, only 15 met the specified inclusion criteria for the review. These articles provided evidence that the majority of attachment systems for mandibular two-implant overdentures demonstrate a reduction in their retentive force under in vitro conditions. Wear was unquestionably implicated as the etiologic factor for the loss of retention; however, the specific mechanisms involved in the wear process have not been researched adequately. Findings from the literature have also implicated several factors that influence the retentive force of the attachment system and its wear features; compelling evidence on its precise role however, is still lacking. Conclusions Further in vitro investigations of the factors involved in the retention and wear of attachment systems for mandibular two-implant overdentures are still needed. These factors must be investigated separately under well-controlled conditions to limit the influence of confounding variables on their outcome.

Attachment systems for mandibular two-implant overdentures: a review of in vitro investigations on retention and wear features.

UNLABELLED The aims of this study were: (i) to evaluate and compare retention of two-teeth (implant) supported mandibular overdenture with either stud or magnetic attachments during linear (axial) and rotational (paraxial) dislodgements; (ii) to compare retentive properties before and after wear simulation. The test group consisted of five magnetic and four stud overdenture attachments (n = 12 specimens for each attachment type). Retention in axial direction was evaluated on one-tooth (implant) model by measuring maximum retentive force (N) and range of retention (mm) during the linear dislodgement. Retention in the paraxial direction was evaluated on mandibular-overdenture model by measuring the maximum retentive force (N) during three types of rotational dislodgements - anterior, lateral and posterior. The minimum number of cycles required to simulate wear was determined by special wear test. Afterwards, the wear was simulated in the test group, and retention in axial and paraxial directions was measured again. STATISTICAL ANALYSIS one-way anova, Scheffe post hoc and paired-samples t-tests (P < 0.05). Initially, studs had higher retention (4-11 N) than magnets (4.5-6 N) in axial direction. After the wear simulation, it had decreased from 76% to 48% for some of the studs and had become similar to the retention of magnetic attachments. Magnets had lower retention range (0.2-0.3 mm) than studs (0.5-1.1 mm). Studs provided similar or higher retention in paraxial directions than magnetic attachments both before and after wear simulation. Retentive properties of magnets decreased mostly with posterior rotational dislodgement. Retentive properties of stud overdenture attachments were less constant.

Influence of attachment wear on retention of mandibular overdenture.

This study aimed to compare the trueness of one type of CAD/CAM milled complete removable dental prostheses (CRDPs) with injection-molding and conventionally manufactured CRDPs. Thirty-three CRDPs were fabricated by three different manufacturing techniques (group CAD/CAM (AvaDent™): n = 11; group injection molding (Ivocap™): n = 11; group flask-pack-press: n = 11) using a single master reference model and incubated in artificial saliva for 21 days. The trueness of the entire intaglio surface along with five specific regions of interest (vestibular-flange, palate, tuberosities, alveolar crest, and post-dam areas) was compared. Non-parametric tests were used with a level of significance set at p < 0.05. At baseline, there was no difference in the trueness of the total intaglio surfaces between the groups. After incubation, only the conventional CRDPs showed a significant improvement in trueness of the entire intaglio surface (p = 0.0044), but improved trueness was confirmed for all three techniques in most individual regions of interest. The 80–20 % /2 median quantile of the CAD/CAM group demonstrated the highest variability of individual readings, probably due to the size of the milling instrument. However, for all three techniques, 80 % of all deviations of the complete intaglio surface after incubation in saliva were below 0.1 mm. In this in vitro study, the trueness of the intaglio surface of all three investigated techniques seems to remain within a clinically acceptable range. Additional research is warranted on material-related aspects, cost-effectiveness, clinical performance, patient-centered outcomes, as well as other CAD/CAM techniques for CRDP fabrication. The intaglio surface trueness is an essential aspect in the clinical performance of CRDPs.

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CAD/CAM milled removable complete dentures: an in vitro evaluation of trueness.

Objective: To evaluate the retentive force and lateral force of an implant with various types of attachments for overdentures in relation to implant inclination.

Material and methods: An implant (3.75 × 13 mm) was embedded into an acrylic resin block, simulating the edentulous ridge. Four different attachment systems were used, including: (1) Locator black and blue, (2) a ball attachment, (3) a flat-type magnetic attachment and (4) a self-adjusting magnetic attachment, which has vertical and rotational movement. All of the attachments were under a constant dislodging force with an angle of the implant at 0°, 15°, 30° and 45°, and the experiments were repeated 10 times using a universal testing machine to measure the retentive force. The lateral force to the implant was measured by strain gauges attached on the implant surface. Statistical analysis was performed by multiple comparisons with Bonferroni's correction. P<0.05 was considered statistically significant.

Results: At 0°, the significantly highest retentive force was observed in the Locator blue, followed by the Locator black, ball, flat-type and self-adjusting magnetic attachments. The Locator blue and ball attachment maintained the retentive force until a 30° inclination; however, the lateral force increased significantly, especially with the ball attachment. The retentive force of the magnetic attachment was significantly lower at 0°, as well as the lateral force in the self-adjusting magnetic attachment.

Conclusion: Within the limitations of this study, we conclude that the retentive force decreases with an increase in implant inclination, whereas the lateral force increases, except for in magnetic attachments.

To cite this article:
Yang T-C, Maeda Y, Gonda T, Kotecha S. Attachment systems for implant overdenture: influence of implant inclination on retentive and lateral forces.
Clin. Oral Impl. Res. 22, 2011; 1315–1319.
doi: 10.1111/j.1600-0501.2010.02137.x

Attachment systems for implant overdenture: influence of implant inclination on retentive and lateral forces.

This study evaluated retention force and fatigue resistance of two overdenture attachment systems Twenty samples (O-ring and Bar-Clip) from two manufacturers (Conexao Sistemas de Protese and Lifecore Biomedical) were prepared and divided into four groups: (i) Conexao/O-ring; (ii) Conexao/Bar-Clip; (iii) Lifecore/O-ring and (iv) Lifecore/Bar-Clip, with five samples in each group They were submitted to mechanical fatigue test using a servohydraulic machine performing 5500 cycles of insertion and removal (f=08 Hz), immersed in artificial saliva Retention force values were obtained three times (0, 3000 and after 5500 cycles) simulating the clinical service, using a tensile strength at 1 mm min(-1) and load cell of 1 kN Data were analysed with analysis of variance and Tukey's test at 5% level Results showed that Conexao/Bar-Clip specimens had significantly higher retention values than Lifecore/Bar-Clip (4461 and 1844 N, respectively), Conexao/O-ring specimens had significantly lower values than Lifecore/O-ring (1391 and 1975 N, respectively) Conexao/Bar-Clip values were always significantly higher than those of Conexao/O-ring group (4461 and 1391 N, respectively) Lifecore (O-ring and Bar-Clip) presented similar values (1975 and 1844 N, respectively) The systems evaluated showed satisfactory retention force values, before and after fatigue testing Conexao/Bar-Clip specimens presented the highest values A 5-year simulation of insertion and removal did not decrease retention values or fracture components

D. M. Botega

Papers

Retention force and fatigue strength of overdenture attachment systems.