Rodney D. Phoenix

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.

Effect of Varying Fixture Width on Stress and Strain Distribution Associated with an Implant Stack System

&NA; The purpose of this investigation was to evaluate the dissipation of a force applied to an assembled stack of implant components. The stack consisted of a 10‐mm threaded implant, a screw‐retained abutment and a screw‐retained gold crown. The dissipation of force was analyzed in relation to varying the implant diameter with and without a concomitant change in abutment diameter. Two experimental groups were evaluated. The first group consisted of 25 titanium screw‐form implants (Implant Innovations, Inc.). These implants measured 10 mm in length and 3.25 mm, 3.75 mm, 4.0 mm, 5.0 mm, and 6.0 mm in diameter. The second group included 15 titanium screw‐form implants (Nobel Biocare, Inc.) measuring 10 mm in length and 3.75 mm, 4.0 mm, and 5.0 mm in diameter. All implants were embedded in standardized photoelastic resin blocks. Points of interest were marked on each block using standardized templates to ensure consistency. Implants were restored using system‐specific conical abutments and standardized single‐unit restorations. A strain gauge was affixed to each abut ment, and an eccentric load of 176 N was applied to the restoration. Periimplant stresses were measured using photoelastic analysis. Abutment strain was determined using an electronic strain indicator. Data were collated and compared using ANOVA and the Duncan multiple range statistical tests. When stress was analyzed at points on the resin‐implant interface or a fixed distance from the interface, stress tended to decrease from the 5‐mm‐wide implant to the 6‐mm‐wide implant. Stress in relation to the 3.25‐mm, 3.75‐mm, and 4.0‐mm implant was not as well defined, indicating the possibility that some deformation of implants was occurring. Increased abutment width resulted in decreased abutment strain. Therefore, using a wider abutment may be helpful in preventing preload reduction in clinical applications. This may reduce the incidence of loosening and fracture of abutment and restoration screws. (Implant Dent 2000;9: 310‐320)

An investigation of new metal framework design for metal ceramic restorations

STATEMENT OF PROBLEM Metal ceramic restorations have been implicated in the discoloration of associated gingival tissues. Attempts to remedy this by altering the design of the metal frameworks for such restorations may lead to unacceptable decreases in fracture resistance. PURPOSE This study evaluated a new metal framework design for metal-ceramic restorations. MATERIAL AND METHODS Twenty artificial crowns were fabricated with various degrees of facial metal reduction; 0, 1, 2, and 3 mm. The study was conducted in two parts. The first part evaluated changes in light transmission into adjacent root tissue. A light box was fabricated so sample crowns could be illuminated on a mounted natural tooth. The root of the tooth remained outside the light box, and the light transmitted through the crowns into root tissue was measured with a light meter. The second part of the study evaluated changes in fracture strength. The sample crowns were subjected to a vertical load until fracture with use of an Instron machine at a crosshead speed of 1 mm per minute. The load at fracture was recorded. RESULTS Results indicated a statistically significant increase in light transmission with 1 mm framework reduction or greater, and fracture strengths did not decrease with up to 1 mm of framework reduction. A 1 mm facial axial reduction of the metal framework may be indicated for anterior metal-ceramic restorations.

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 (Udagamas 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 Fishers 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 Udagamas 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.

A precise design and fabrication method for metal base maxillary complete dentures

Metal bases sometimes are used to enhance the physical properties of complete dentures. Unfortunately, improper positioning of metal-resin finish lines may adversely affect phonetics. In the past, placement of these finish lines has been somewhat arbitrary. This article describes a precise method for the placement and contour of metal-resin finish lines. The resultant prostheses should exhibit surfaces that reestablish proper anatomic, physiologic, and phonetic contours.

Gold alloy cast to base metal removable partial denture frameworks

For many years, gold and base metal alloys have been used in the construction of cast removable partial dentures. Each alloy has desirable properties, yet neither is ideally suited for all portions of a framework. A method has been developed to fabricate prostheses by casting gold alloy against a base metal alloy. This procedure allows the practitioner to combine the favorable characteristics of both alloys within a single framework. Consequently, the practitioner may create frameworks that more effectively meet the biomechanical demands of the oral environment.

The Contributions of Dr. Alfred Gysi: Contributions of Alfred Gysi

This article is a historical overview of Dr. Alfred Gysis 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.

The Development of Lingualized Occlusion: Lingualized Occlusion Development

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 Gysis 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.