• The Effect of Bar Design and Repetitive Loading on the Reverse Torque Values of Lateral Set Screws

      Yahya, Jenin Hilmi; Masri, Radi, 1975- (2015)
      Statement of problem: Utilizing set screws allows easy retrieval of the prostheses with minimum cost and satisfies esthetic requirements. Set screws use is mostly governed by retrospective, anecdotal and clinical reports. The purpose was to investigate the difference in reverse torque values of fatigued one set screw or two set screws used to retain straight or curved implant prostheses in vitro. Materials and methods: Milled substructures (straight and curved) and cast superstructures retained by one or two set screws were used. There were four groups (n=8). Set screws were tested for changes in reverse torque values after simulated chewing of six months. Data (Ncm) was analyzed using 2-way ANOVA (p≤0.05). Results: No statistically significant difference in the reverse torque values between prostheses retained by one set screw and two set screws (F = 0.18, p = 0.67) or between prosthesis retained on curved bars and straight bars (F = 0.42, p = 0.52). No significant interaction was found in the reverse torque values between the number of set screws and substructure design (F = 0.32, p = 0.58). Conclusions: Under functional loading the reverse torque values are not affected by the design of the prosthesis or the number of set screws used to retain the prosthesis.
    • The Effect Of Locator Abutment Height On The Retentive Values Of Pink Locator Attachments: An In Vitro Study.

      Sia, Priscilla Kia Suan; Masri, Radi, 1975-; 0000-0002-4799-8707 (2015)
      Purpose of this study was to evaluate the effect of different Locator abutment heights on the retention of overdentures. This study was conducted using four sets of edentulous mandible analogs with implants positioned at different depths relative to each other (N=40). Two implant-retained overdenture set-ups with Locator attachments at different vertical levels of 0, 2, 4, 6 mm to each other were tested for changes in peak load-to-dislodgement after simulated chewing of six months. Varying heights of Locator abutments had a significant effect on the retentive values of the pink Locator attachments. The results of ANOVA and Tukey HSD showed that the retention of Groups 0 mm and 2 mm was significantly lower than Group 6 mm. In conclusion, a difference in Locator abutment heights between the two implants did not adversely affect retention, therefore clinicians should choose Locator abutments according to the tissue thickness for implants at different levels.
    • Polymicrobial Colonization of Athletic Mouth Guards Following Mechanical Chew Simulation.

      Richards, Samuel Ian; Masri, Radi, 1975- (2015)
      Mouth guard material is used for athletic mouth guards, temporary dental splints, whitening trays, medicinal depositories and catheter tubing. This study evaluated biofilm formation on mouth guard materials after simulated use to ascertain the propensity of mouth guards to harbor bacteria. Three different mouth guards were evaluated (n=18/group): two boil-and-bite guards, Shock Doctor® (SD) Nano 3D and The Wrightguard™ (TWG) and one custom 100% EVA Buffalo guard (EVA). In vitro wear of the fabricated guards were simulated via a chewing simulator for 120,000 cycles per guard. The most visibly worn 8x10mm section of each guard was determined and cut to standardize specimen size. All guard specimens were incubated with equal cell densities of both S. aureus (SA) and Candida albicans (CA) strains and colony-forming units (cells/ml) were measured as a quantification of biofilm growth. A one-way ANOVA with Tukey's-HSD test was used to analyze biofilm retention (CFU/ml) on non-simulated and simulated EVA, SD, and TWG guards. Neither EVA (2.89±1.09 - 3.28±0.74; p=.486) nor TWG (10.22±3.31 - 11.17±5.46; p=.725) groups exhibited a significant increase in CFUs after 6 months of simulated use. In contrast, SD guards (3.33±1.55 - 9.72±5.37; p=.019) exhibited a significant increase in mean CFUs of CA when non-simulated guards were compared to simulated guards. Like with CA, neither EVA (3.11±1.90 - 3.50±1.63; p=.712) nor TWG (9.83±4.09 - 12.56±5.58; p=.358) groups exhibited significant increases in adherent SA following 6 months of simulated use. However, Shock Doctor (5.11±2.20 - 9.67±4.77; p=.06) guards had a significant increase in adherent SA CFUs when non-simulated guards were compared to simulated guards. With chewing simulation parameters remaining constant for all guard types, significantly greater adherence could indicate a greater change in surface topography/roughness from simulated use. While EVA guards exhibited the lowest measured adherence of CA and SA, and TWG exhibited the highest CA and SA levels of adherence, neither of their respective material compositions undergo surface changes as readily as SD guards.The increased propensity of both fungal and bacterial species to adhere to mouth guards after continuous use indicates a potential concern for regular mouth guard users.