Constructing cast crowns to fit existing removable partial denture clasps

A step-by-step procedure has been presented for fabrication of a cast crown to fit an existing partial denture clasp. The procedure can be accomplished in two appointments, and the patient need not be subjected to the incovenience of being without the partial denture between office visits. It is an accurate and easy technique which gives uniform results and eliminates the need for remaking an adequate removable partial denture.     

Laser welding in the dental laboratory: an alternative to soldering

Only recently has laser welding been applied to dental technology, primarily as an alternative to soldering. This article addresses how the laser is used for welding, the effect welding has on metals as the energy is converted into heat and reacts with the alloy's surface and the practicality of laser welding in the dental laboratory. A step-by-step procedure for accomplishing laser-welded connections in a fixed partial denture is included. A laser-welded clasp repair using wrought wire and the addition of custom cast parts welded to an existing removable partial denture framework on the master model are also shown.     

Fabricating abutment crowns for existing removable partial dentures using custom resin clasp analogs

A universal approach for fabricating abutment crowns for existing removable partial dentures is described. A replica (analog) of the clasp assembly is generated and transferred to a traditional working cast, which includes the abutment die. The analog is incorporated into the working cast as a removable component to allow the formation of the crown contours. The article reviews in detail the procedures required to transfer accurately all the essential components and information from the mouth to the working cast while allowing the patient uninterrupted use of the removable partial denture. Prestabilizing the removable partial denture, creating the analog impression, avoiding errors due to soft tissue components, forming a precise analog base, selecting materials, generating a rigid resin analog, and prescribing a path of insertion and withdrawal to the analog are described. The method replicates all types of clasps and can generate all types of fixed prosthodontic retainers to function harmoniously with the existing partial denture.     

Removable partial overdentures

A technique for applying the overdenture concept to removable partial denture construction has been presented. Endodontically treated abutments are prepared with cast gold posts and copings over which removable partial dentures with conventional components are fabricated. No special materials or complicated laboratory techniques are required, and the maintenance and repair problems of precision attachments are avoided. A variety of potential uses and advantages of the technique are discussed.     

Surface charges on membranes

The mesial rest-I-bar concept is the most important contribution to clasp partial denture design in the last 30 to 40 years. When used with discernment in situations where it is not contraindicated, it constitutes an excellent design for extension-base removable partial dentures. It has become the design of choice for an increasing number of dentists. Use of the three elements that make up the clasp assembly does not necessarily insure that the clasp will function as intended. There are situations for which it should not be used. Unless adequately adjusted after framework construction as well as during the maintenance program, the beneficial effects may be more imaginary than actual. Strict adherence to the mesial position for the rest is not rational for toothsupported dentures and may be questioned for some extension-base prostheses. I-bars have several advantages as direct retainers. However, no single type of retainer is applicable for all retentive situations, and other types should be selected where conditions are unfavorable for I-bar use. A framework which permits a slight amount of movement toward the edentulous residual ridge is an important consideration in design of extension-base removable partial dentures, particularly for those of the mandibular arch. However, compromise of this principle is sometimes necessary to satisfy other design requirements. Design of the framework is only one of the factors that contribute to a successful removable partial denture. Of at least equal importance is the adequacy of support provided by the denture base and the nature of the occlusion. If meticulous attention is directed to these two factors, the forces transmitted to the teeth through the framework can be kept to a minimum and within physiologic tolerance. Conversely, neglect of these considerations may cause a framework of any design to become destructive.     

Effect of water and artificial saliva on the low cycle fatigue resistance of cobalt-chromium dental alloy

STATEMENT OF PROBLEM: Fatigue of denture clasp alloys causes clasp failures and decreases the retention of removable partial dentures. Little information is available on how the environment (dry, water, artificial saliva) effects the fatigue behavior of cast cobalt-chromium alloy clasps. PURPOSE: This study determined the effect of water and the artificial saliva on the resistance of cast cobalt-chromium alloy to the deflection fatigue. MATERIAL AND METHODS: Test bars (n = 10) were tested either dry, in water, or in artificial saliva (Fusayama type) with a constant deflection fatigue test. The number of loading cycles before fracture was registered as resistance to fatigue. To establish whether there were indications of alloy corrosion occurring during the fatigue test, the testing liquid was analyzed retrospectively with an atomic absorbance spectroscopy. To determine elemental composition of the fracture surface, fracture surfaces of the test bars were analyzed with a scanning electron microscope and energy dispersive spectroscopy. RESULTS: The bars that were tested dry had a mean fatigue resistance of 78,000 loading cycles, whereas test specimens tested in artificial saliva had a resistance of 59,000 loading cycles and 36, 000 for those tested in water. Atomic absorbance spectroscopy revealed small amounts of cobalt (Co) in testing water and in artificial saliva. Energy dispersive spectroscopy analysis revealed differences in elemental composition of a fatigue fracture surface compared with that of a 1-bend fracture. CONCLUSIONS: The results suggest that both water and artificial saliva reduce the fatigue strength of cobalt-chromium alloy, explained by corrosion of the alloy in the wet environment.     

A secondary lingual casting for removable partial dentures

This article describes a technique for constructing a nickel chromium alloy lingual casting that reinforces a removable partial denture against heavy anterior occlusion. The metal can be cast into a thin secondary casting, and it is easily etched and bonded to the resin anterior teeth and associated base. This type of lingual casting has the potential to provide a simple and effective solution to the problem of repeated fracture or displacement of anterior teeth in many restorations.     

Bend testing of wrought wire removable partial denture alloys

The flexibility of the wrought wire clasp is related to a number of factors, including the type and gauge of the alloy. The purpose of this study was to compare the bend behavior of five wrought wire alloys used in removable partial dentures. The alloys and their gauge diameters (in millimeters) were Ticonium (18, 19, 20), platinum-gold-palladium (18, 19), Wironium (18, 20), Jelenko Standard (18, 19, 20), and Denture Clasp (18, 19, 20). A total of 12 to 15 samples of each dental alloy were tested. Three-point bending was performed on a servohydraulic testing system controlled by a computer at 1.00 mm/sec until fracture or actuator contact occurred. Maximum stress and elastic modulus in bending were determined for each gauge diameter. Analysis of variance and post hoc Scheffe statistical analyses revealed significant maximum stress and elastic modulus in bending differences for different alloys of the same gauge and for different gauges of the same alloy. The choice of material and the gauge diameter significantly influenced the mechanical property of bending for wrought wire removable partial denture alloys. The Ticonium alloy had the greatest elastic modulus (stiffest) at all levels and the Denture Clasp and the Jelenko Standard alloys had the lowest elastic modulus (most flexible). These data indicate that knowledge of the bending properties of an alloy is equally as important as the gauge size when selecting a wire clasp.     

Detection of K-ras mutations in stools of patients with colorectal cancer by mutant-enriched PCR

This study determined the effect of various durations of induction melting of a cobalt-chromium alloy on resistance to deflection fatigue. Commercial cobalt-chromium alloy was melted by high-frequency induction for various lengths of time before it was cast into the shape of a denture clasp. The test method used was a constant-deflection fatigue test. The fatigue fracture surface of the clasp was examined with a scanning electron microscope, and the surface hardness (Vickers hardness) of the clasps was measured. In clasps with greater fatigue resistance scanning electron microscope photomicrographs revealed a coarse grain structure. The surface hardness of the alloy was least in the group with the lowest fatigue resistance and was higher in groups with greater fatigue resistance. This study suggests that, although some porosities are formed in the middle of the clasps after the alloy is overheated, the fatigue resistance of cobalt-chromium alloy denture clasps can be increased by lengthening the induction melting period of the alloy.     

The effect of removable partial denture framework design on gingival inflammation: a clinical model

A clinical trial using the experimental gingivitis model developed for periodontal clinical research was performed to evaluate the effect of a removable partial denture mandibular major connector design on the surrounding gingival tissues. A comparison of the state of health of adjacent gingival tissues was made between the linguoplate (control) and cingulum bar (test) major connectors. Clinical parameters were recorded in a single-blind crossover experimental gingivitis trial. Subjects were brought to a level of optimal gingival health and then randomly assigned to use one framework design while refraining from any oral hygiene. Measurements were made at 7-day intervals for 21 days. The subjects were returned to optimal oral health and repeated the experimental period with the alternate design. Results showed a greater increase in mean gingival inflammation with the control than with the test removable partial denture, suggesting that the cingulum bar has fewer detrimental effects on gingival tissues than the linguoplate major connector. Results of this study suggest that the experimental gingivitis model can be a useful and valid system for studying the potential effects of a removable partial denture design on surrounding oral tissues.     

The component partial: a new RPD construction system

Most removable partial denture frameworks constructed today are one-piece castings. This article presents the Component Partial, a removable partial denture in which the framework is constructed in pieces. Such construction ensures a more accurate fit of the RPD.     

Fimbrial-mediated colonization of murine teeth by Actinomyces naeslundii

PURPOSE: The hardness, porosity, and adaptation of removable partial dentures fabricated with one heat-polymerized denture base resin and two resins designed for microwave polymerization were evaluated. MATERIALS AND METHODS: Five prostheses were evaluated for each resin. Adaptation of the denture bases to the master cast was evaluated by spatial orientation and mean weight of residual impression material. The prostheses were than embedded in epoxy resin and sectioned for evaluation of resin hardness (Knoop hardness) and microporosity. RESULTS: There were no significant differences in the adaptation of the acrylic resin bases for Acron MC and Ch Lucitone. There was no significant difference in the mean Knoop hardness values for any of the resin bases near and away from the metal. None of the denture bases showed porosity greater than 100 microns. CONCLUSIONS: Both resin bases formulated for microwave polymerization were effectively polymerized around metal frameworks without adverse effects on resin hardness or porosity. Justi Denture Base material had poorer base adaptation than the other two resins.     

Comparative clinical evaluation of removable partial dentures made from impressions with different materials

Impressions for removable partial dentures (RPDs) should provide an accurate and detailed record of the teeth and soft tissues. Removable partial denture casts should be exact replicas of the mouth to ensure that RPD frameworks fit accurately and are fully adjusted to oral structures. A comparative clinical evaluation was performed on the oral fit of RPDs made from impressions with either irreversible hydrocolloid (alginate) or condensation silicone. The difference between the two groups was found to be statistically significant.     

A procedure for relining a complete or removable partial denture without the use of wax

Various procedures are used to reline removable dentures. Some of these involve the use of wax to seal the denture to the cast for flasking and processing. This necessitates the use of high temperatures for an extended period and involves the risk of warpage of the denture. It is also relatively time-consuming. This article describes a procedure that uses polyvinyl siloxane instead of wax. The procedure is more time efficient and decreases the risk of warpage of the denture.     

Crystal structure of a murine alpha-class glutathione S-transferase involved in cellular defense against oxidative stress

STATEMENT OF PROBLEM: The electric alloy brazed joints of removable partial denture alloys have failed frequently after routine usage. PURPOSE: A technique providing higher joint strengths was investigated. This investigation compared the tensile strengths of electric-brazed and laser-welded joints for a cobalt-chromium removable partial denture alloy. MATERIAL AND METHODS: Twenty-four cobalt-chromium standard tensile testing rods were prepared and divided into three groups of eight. All specimens in the control group (group 1) were left in the as-cast condition. Groups 2 and 3 were the test specimens, which were sectioned at the center of the rod. Eight specimens were joined by using electric brazing, and the remaining specimens were joined by using laser welding. After joining, each joint was ground to a uniform diameter, then tested to tensile failure on an Instron universal testing machine. Failure loads were recorded and fracture stress calculated. Statistical analysis was applied. RESULTS: The student-Newman-Keuls test showed a highly significant difference between the joint strengths of the as-cast control specimens, the electric-brazed and laser-welded joints. CONCLUSIONS: The tensile strengths of the as-cast joints were higher than those for the laser-welded joints, and both were higher than the electric-brazed joint strengths.     

Allosteric nicotinic receptors, human pathologies

The purpose of this study was to investigate the biomechanical significance of major connectors and base mucosal contacts on the mechanical behaviour of maxillary removable partial dentures in vivo. Six subjects wearing maxillary dentures retained by conical crowns were selected for the study. Reflective photoelasticity and strain gauges were used to monitor the development of strain/stress during functional loading. Loading tests were performed initially with a denture design including a palatal major connector and denture bases and then repeated after removal of the major connectors and denture base alveolar muccosa contacts. The palatal major connector and the denture bases mucosal contacts contribute significantly to the rigidity and stability of removable partial dentures retained by conical crowns.     

A follow-up study on changes in mastication after insertion of mandibular bilateral free end saddle denture by EMG]

The purpose of this study was to investigate changes in the mandibular shortened arch, whose occlusal deficit had been reconstructed by removable partial denture, during mastication by using the EMG analyzing system. A total of 5 shortened dental arch patients was provided with RPDs, and observed by a sophisticated masticatory analyzing system using EMG, before and one day, about 2 weeks, 3 months, after denture insertion. The conclusions were as follows: i) The elements of the shortened arch during mastication, that is, the duration, interval, and cycletime, were prolonged at the time of insertion of RPD, but 3 months after denture insertion, they were shortened to almost the same state as before treatment. ii) Prosthetic treatment for shortened dental arch improved revitalization of functional musculatures, and their rhythmicity of functional procedure. iii) The functional tongue room for optimal bolus position in mastication was provided by insertion of mandibular bilateral free end saddle removable partial denture.     

Placement of multiple and different stent types for very long dissections during coronary angioplasty

A coordinate measurement machine with laser probe was used to measure the vertical distortion of the casts produced by use of three types of impression materials (irreversible hydrocolloid, condensation silicone, and addition silicone) and two types of trays (stock and custom trays). Results indicated that all impression groups showed positive vertical distortion (ranging from 0.00566 to 0.30299 mm) at the edentulous ridges and palatal area. The amount of the vertical distortion was greatest at the palatal area and was followed by the high edentulous ridge and the low edentulous ridge. Addition silicone, with either custom tray or stock tray, was the most accurate impression material. Condensation silicone was more accurate than irreversible hydrocolloid in custom tray impression. However, in stock tray impression the irreversible hydrocolloid was more accurate than the condensation silicone. The results suggest that, with careful manipulation, irreversible hydrocolloid with stock tray impression may provide a satisfactory cast for fabricating the framework of a distal extension removable partial denture.     

An indirect procedure for making a crown under an existing partial denture

Direct procedures to make a crown under an existing partial denture are inconvenient for the patient. A process is described that uses an irreversible impression of both the crown preparation and the removable prosthesis to fabricate a crown indirectly. The process is efficient and inexpensive.     

Fatigue Life of Cast Titanium Alloys Under Simulated Denture Framework Displacements

The objective of the study was to evaluate the hypothesis that the mechanical properties and fatigue behavior of removable partial dentures (RPD) made from cast titanium alloys can be improved by alloying with low-cost, low-melting elements such as Cu, Al, and Fe using commercially pure Ti (CP-Ti) and Ti-6Al-4V as controls. RPD specimens in the form of rest-shaped, clasp, rectangular-shaped specimens and round-bar tensile specimens were cast using an experimental Ti-5Al-5Cu alloy, Ti-5Al-1Fe, and Ti-1Fe in an Al₂O₃-based investment with a centrifugal-casting machine. The mechanical properties of the alloys were determined by performing tensile tests under a controlled displacement rate. The fatigue life of the RPD specimens was tested by the three-point bending in an MTS testing machine under a cyclic displacement of 0.5 mm. Fatigue tests were performed at 10 Hz at ambient temperature until the specimens failed into two pieces. The tensile data were statistically analyzed using one-way ANOVA (α = 0.05) and the fatigue life data were analyzed using the Kaplan-Meier survival analysis (α = 0.05). The experimental Ti-5Al-5Cu alloy showed a significantly higher average fatigue life than that of either CP-Ti or Ti-5Al-1Fe alloy (p < 0.05). SEM fractography showed that the fatigue cracks initiated from surface grains, surface pores, or hard particles in surface grains instead of the internal casting pores. Among the alloys tested, the Ti-5Al-5Cu alloy exhibited favorable results in fabricating dental appliances with an excellent fatigue behavior compared with other commercial alloys.