Relevant Degree Programs
Graduate Student Supervision
Master's Student Supervision (2010 - 2018)
Purpose: To evaluate and compare the mechanical properties of various commercially available pigmented polydimethylsiloxane elastomers (silicone elastomers) utilized in the fabricationof maxillofacial prostheses.Materials & Methods: Three commonly used silicone elastomers were evaluated: A-2000 (Factor II), A-2186 (Factor II), A-103 (Factor II). The silicones was combined with opacifier: Titanium White (Factor II), and pigment: Intrinsic Pigment in Naturelle (Factor II). Specimens were fabricated through the use of aluminum and stone moulds to form trouser- and dumbbell- shaped specimens. From each material 20 specimens were prepared, 10 dumbbell-shaped and 10 trouser-shaped (n=10) for a total of 60 specimens. Mechanical properties evaluated included: Shore-A hardness, tear strength, tensile strength, and percent elongation. These properties were tested according to ASTM protocols. Data was statistically-analyzed with one-way ANOVA of each property at the 95% level of confidence as well as Tukey’s post-hoc tests for specific identification of significant differences between materials.Results: ANOVA indicated statistically-significant differences among the three materials for each of the four outcomes tested. Further statistical analysis with Tukey’s post-hoc tests showed significantly lower tensile strength and tear strength and higher % elongation for A-103 when compared to both A-2000 and A-2186. No statistically significant differences were found between A-2000 and A-2186 with respect to tensile strength, percent elongation or tear strength. All three groups were found to be significantly different from each other in terms of Shore-A hardness. A-103 exhibited the lowest hardness values, whereas A-2186 was found to have the highest hardness.iiiConclusions: Material A-103 exhibited the lowest tensile and tear strengths as well as hardness, however, it displayed the greatest percent elongation. Material A-2000 and A-2186 displayed similar characteristics with regard to tensile and tear strengths, but differed in terms of Shore-A hardness with A-2186 exhibiting the greatest hardness.
Statement of problem: The use of digital impressions for implants are limited to single and short span bridges due to the few available studies supporting their usage in more complex cases. Therefore, its essential to evaluate their accuracy in full arch cases to benefit from their great advantages. Purpose: Evaluate and compare the accuracy of digital and conventional impressions for multiple straight and angulated implants of full arch implant supported fixed prosthesis. Also, assess the effect of implant angulation of 45° and increased length on the accuracy of both methods.Materials and methods: A stereolithographic (SLA) model of edentulous mandibular cast was fabricated and used to produce the master stone cast with four Nobel CC RC implants placed at tooth positions 3.4, 3.2, 4.2 and 4.4. Implants at #32 and 42 were perpendicular to the occlusal plane and parallel to each other while implants at #34 and 44 were distally angulated with 45°.Three impression methods were made from the master stone cast. Digital impressions were made with Trios (3Shape, Copenhagen, Denmark) intraoral scanner (IOS) (n=10). Conventional splinted open-tray implant–level impressions were made with Polyvinyl (PVS) (n=10) and Polyether (PE) (n=10). All stone casts were digitized using a 3shape D800 lab scanner to obtain STL (standard tessellation language) files, which then were imported into Rhino5 3D software. Six linear measurements were obtained for each cast to evaluate their discrepancies from the master cast. Absolute values of the linear deviation of each line among the three groups were compared using Kruskal-Wallis test and Dunn's post hoc test.Results: Significant difference (P