Purpose: to evaluate the effect of the number and distribution of dental implants on the occlusal pressure transmitted to the palate. Material and Methods: eight implant analogs were placed in a replica of maxilla in the areas of teeth number 3, 4, 5, 6, 11, 12, 13 and 14. Locator attachments were attached to the implant analogs. The distances between the centers of implant analogs on each side were 8 mm. Fifteen denture bases with occlusal rims were fabricated to fit on the maxillary replica. Under a load of 245 N, pressure on the palate was measured under each denture base in six different designs of Locator insertions: No Locators, 2 Locators, 4 Locators with distances of 8, 16, and 24 mm and 8 Locators. Data was analyzed using One-Way ANOVA and Tukey's HSD test. A p value of ≤0.05 was considered significant. Results: Pressure transmitted to the palate ranged from 20.67 +/- 16.06 N (mean +/- SD) for overdentures supported by 8 Locators to 85.61 +/- 27.94 N for a conventional denture (control). The amount of pressure transmitted to the palate when the overdentures were supported by 4 Locator attachments, was significantly lower than when no, or when two Locator attachments were used. However, they were not significantly different from each other. When the overdentures were supported by 8 locator attachments, the pressure transmitted to the palate was significantly lower than that of conventional dentures, overdentures supported by 2 Locator attachments and overdentures supported by 4 Locator attachments when the distance between the anterior and posterior implants was 8 mm. Conclusion: Using 4 Locator attachments produced significantly less pressure on the palate, compared to when zero or two Locators were used. When the distance between the 4 Locators was 16 or more mm, the pressure was not significantly lower than 8 Locator design, suggesting that the palate of a 4 implant-retained overdenture with a distance of 16 mm or more, does not contribute significantly to the pressure distribution under the overdenture. Considering the static nature of the load, the results of this study should be interpreted clinically with caution.
Purpose: To measure the accuracy of implant impression techniques in vitro, using open and closed tray techniques with internal and external connection implants at various angulations. Materials and Methods: Three internal connection implants and three external connection implants were placed in an acrylic master cast as follows from posterior to anterior: 90, 15 and 30 degrees. Twenty-four open tray and closed tray impressions were made and the resulting casts were analyzed using digital photography. The following measurements were performed (1) horizontal displacement; (2) vertical displacement; (3) angulation displacement in the lateral view; (4) angulation displacement in the frontal view. Statistical analysis was completed by using a factorial analysis of variance (three-way ANOVA). A p value ≤0.05 was considered significant. Tukey's HSD test was used to analyze significant differences for the angulation variable. Results: (1) The results show that there was no difference in the impression accuracy when open vs. closed tray impression techniques were used except in the horizontal plane where the closed tray produced more accurate impressions than the open tray. (2) External connection implants produced a significantly larger horizontal displacement compared to the internal connection implants. (3) The results did not follow a particular pattern for the effect of implant angulation on impression accuracy. (4) The interactions observed between connection type, implant angulation and tray type and the resulting discrepancy in the horizontal plane showed that implants placed at 90 degrees produced the largest horizontal displacement. In the vertical plane, internal connection implants placed at 15 degrees when an open tray technique was used produced the largest vertical displacement. Conclusion: Clinically, the results from this study suggest that when encountering full arch implant restorations it is most beneficial to have the implants as parallel to each other as possible and to remove the custom tray along the same path as the implant angulation. The splinted open tray technique is time consuming and it might not result in a more accurate master cast. Open or closed tray techniques can be used, however, the master cast should always be verified before fabricating the final prosthesis.
Purpose: This study examined the retentive values of Locator attachments (Zest Anchors, Escondido, CA) with initially placed nylon-inserts, as compared to Locator attachments with replacement nylon-inserts. Materials and Methods: Five test samples simulated implant retained overdentures utilizing Locator attachments. Each attachment was tested with the initially placed pink nylon-insert (Group 1, n=5), and with a replacement nylon-insert (Group 2, n=5). Both groups were tested for 2920 cycles. The results were used to compare Group 1 with Group 2 at three time intervals. A one-way analysis of variance (ANOVA) with a p value of ≤0.05 was considered significant. Results: No significant differences were found between the retentive values of both groups (initial p=0.70, middle p = 0.41, and final p=0.09). The retentive values at the three time intervals were plotted in terms of cycles. A best-fit linear regression showed the rate of degradation. The slope of Group 2 was double that of Group 1. Conclusions: No significant differences in retentive values were found between the attachments with the initial nylon-inserts, and the attachments with replacement nylon-inserts for the time intervals studied. However, the attachments with replacement nylon-inserts lost retention at twice the rate of the attachments with initially placed nylon-inserts.
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