Assessing the Accuracy of Casting and Additive Manufacturing Techniques for Fabrication of a Complete Palatal Coverage Metal Framework.

PURPOSE: To provide information regarding the accuracy of additive manufacturing in comparison to conventional casting, specifically for fabrication of complete palatal coverage metal frameworks. MATERIALS AND METHODS: Three additive manufacturing techniques were tested: selective laser melting (SLM), electron beam melting (EBM), and computer-aided design/cast (CADcast), with conventional casting as the control. Both the SLM and EBM groups were tested pre- and post-finishing, for a total of six test groups (n = 10/group). A digital master design was used as the standard to which all frameworks were digitally compared by best-fit analysis, which generated root mean square values using proprietary software. A one-way ANOVA was conducted to test for statistical differences among materials, followed by a post-hoc multiple comparison test (Tukey's test HSD). Surface roughness for one framework arbitrarily selected from each group was analyzed using a profilometer. RESULTS: There was a significant difference in accuracy among the materials (F = 99.79, p < 0.0001). A post-hoc Tukey test indicated that CADcast differed significantly from the other five materials (i.e., most accurate, p < 0.01). EBM prefinished and EBM finished were both significantly different from the other materials (i.e., least accurate). Color mapping images help visualize the differences between each framework compared to the master design. The surface roughness values ranged from 22 to 63.5 µm, with CADcast being the smoothest, and EBM prefinished the roughest. CONCLUSIONS: CADcast and SLM techniques were as or more accurate than the conventional technique for producing an uncomplicated framework design. Further investigation is recommended regarding the surface roughness of additive manufacturing products and potential biological complications.

The Development of Lingualized Occlusion.

This article is a historical review of the development of the lingualized occlusion concept over the past century. It focuses on the pioneers of lingualized occlusion and their designs rather than on techniques for achieving a lingualized complete denture occlusion.

The Contributions of Dr. Alfred Gysi.

This article is a historical overview of Dr. Alfred Gysi's contributions to the profession in the areas of denture tooth and articulator design. His understanding of occlusion and mandibular movement resulted in denture tooth designs and occlusal concepts still in widespread use.

Lingualized occlusion revisited.

Lingualized occlusion represents an established method for the development of functional and esthetic complete denture articulation. Since its introduction, the lingualized technique has undergone many changes. This article provides an overview of the history and development of lingualized occlusion, and addresses common misconceptions associated with the lingualized technique. In addition, a practical method for the development of lingualized denture occlusion is presented.

The effects of primers and surface bonding characteristics on the adhesion of polyurethane to two commonly used silicone elastomers.

PURPOSE: When restoring facial defects, maxillofacial prosthodontists and anaplastologists are often limited by material deficiencies. Silicone elastomers bonded to a polyurethane liner best satisfy the functional and esthetic requirements necessary for facial prostheses; however, patients using silicone prostheses with polyurethane liners often experience varying degrees of debonding at the polyurethane-silicone interfaces. This may result in failure of such prostheses. The purpose of this investigation was to evaluate the effects of five primers on bonding between polyurethane and two commonly used silicone elastomers. MATERIAL AND METHODS: Six bonding regimens were used to join polyurethane and silicone materials. Each treatment group consisted of 12 specimens. Bonding regimens included (1) a 40:60 mixture of MDX4-4210 and Silastic Medical Adhesive Type A, in conjunction with Dow Corning 1205 primer (Udagama's technique); (2) silicone A-2000 with Dow Corning 1205 primer; (3) silicone A-2000 with A-330-G primer; (4) silicone A-2000 with Mucopren primer; (5) silicone A-2000 with Sofreliner T primer; and (6) silicone A-2000 with Sofreliner MS primer. Following fabrication, specimens were attached to a universal testing machine and separated in tension at a crosshead speed of 25.4 mm/min. One examiner performed the assessment of T-peel strength (N/mm), peak load (N), and peel distance (mm) for all specimens. Mean data were analyzed using one-way ANOVA followed by Fisher's protected significant difference multiple comparison of the means (alpha= 0.05). RESULTS: A statistically significant difference (p < 0.05) in T-peel strength was found among specimen groups. Post hoc analysis indicated that Sofreliner MS primer (1.32 +/- 0.13 N/mm) and Sofreliner T primer (1.25 +/- 0.11 N/mm) increased the bond strengths significantly compared to A-330-G primer (0.91 +/- 0.10 N/mm) and Udagama's technique (0.13 +/- 0.02 N/mm). Cohesive failure between silicone A-2000 and polyurethane liner was observed when Sofreliner MS primer and Sofreliner T were used. CONCLUSION: Within the limitations of this study, the use of Sofreliner MS primer and Sofreliner T primer produced significant increases in the bond strength of silicone elastomer to polyurethane liner material. Based on T-peel strength, peel distance, and peak load data, the combination of silicone A-2000 and Sofreliner MS primer resulted in the greatest mean bond strength for silicone-to-polyurethane applications.

Microabrasion of cast metal margins--a warning.

Plastic test patterns were milled to simulate casting margins and were cast in a variety of dental alloys. The cast specimens were exposed to horizontal and vertical streams of low-pressure microabrasion with 50 microm aluminum oxide particles. Post-exposure measurements show all specimens were affected by microabrasion. Dentists and laboratory technicians who use microabrasion must be aware of the potential damage to casting margins.

Evaluation of mechanical and thermal properties of commonly used denture base resins.

PURPOSE: The purpose of this investigation was to evaluate and compare the mechanical and thermal properties of 6 commonly used polymethyl methacrylate denture base resins. MATERIALS AND METHODS: Sorption, solubility, color stability, adaptation, flexural stiffness, and hardness were assessed to determine compliance with ADA Specification No. 12. Thermal assessments were performed using differential scanning calorimetry and dynamic mechanical analysis. Results were assessed using statistical and observational analyses. RESULTS: All materials satisfied ADA requirements for sorption, solubility, and color stability. Adaptation testing indicated that microwave-activated systems provided better adaptation to associated casts than conventional heat-activated resins. According to flexural testing results, microwaveable resins were relatively stiff, while rubber-modified resins were more flexible. Differential scanning calorimetry indicated that microwave-activated systems were more completely polymerized than conventional heat-activated materials. CONCLUSION: The microwaveable resins displayed better adaptation, greater stiffness, and greater surface hardness than other denture base resins included in this investigation. Elastomeric toughening agents yielded decreased stiffness, decreased surface hardness, and decreased glass transition temperatures.

Casting titanium partial denture frameworks: a radiographic evaluation.

STATEMENT OF PROBLEM: Titanium is the most biocompatible metal available for dental castings. However, there is some concern about the castability of titanium used on a daily basis. PURPOSE: A radiographic evaluation of titanium partial denture frameworks was undertaken to ascertain whether these castings were technically acceptable for clinical use. MATERIAL AND METHODS: Three hundred Grade II titanium removable partial denture frameworks were cast in a Titec 205M casting machine. All materials were used as directed by the manufacturer, and all castings were made by an experienced titanium specialist. Each casting was evaluated by radiograph. Based on the number, location, and size of argon inclusions, the frameworks were rated as follows: technically acceptable for clinical use as cast; technically acceptable after laser welding modifications; or unacceptable as cast, with remake necessary. RESULTS: Of the 300 titanium frameworks cast, 97% were rated technically acceptable for clinical use in terms of castability. SUMMARY: Within the limitations of this radiographic evaluation, it was determined that the castability of titanium was such that technically acceptable castings could be made on a daily basis.