Cast Frameworks Research Articles

Passive fit of implant-retained prosthetic superstructures improved by electric discharge machining.

An absolutely passive fit at the interface with the superstructure and the abutment cylinders is needed for implant longevity. In this study, a method of cast framework correction using electric discharge machining (EDM) was evaluated. An original research model incorporating strain gages was devised to measure the fit of implant superstructures in three dimensions as cast and to compare this relationship with the fit following framework machining with EDM. Visually, the fit of the frameworks was excellent, and the results of ANOVA demonstrated that the mean fit of the frameworks significantly improved (P > .04) after machining with EDM. The EDM process offers a rapid, accurate, and simple technique to correct for casting inaccuracies in the fabrication of hybrid implant prostheses.

The shear strength of polymethyl methacrylate bonded to titanium partial denture framework material

Premachined titanium frameworks are used in implant-supported fixed completearch prostheses. Traditionally, retentive mechanisms are incorporated in the wax patterns to provide retention between polymethyl methacrylate and the cast framework. Nontraditional forms of retention are needed with machined frameworks. This study determined whether three different surface characteristics of titanium improve the bond shear strength of polymethyl methacrylate. Thirty rod shaped specimens of titanium were divided into three equal groups: group 1 received no pretreatment; group 2 was pretreated with 110 μm alumina air abrasive; and group 3 was pretreated with 110 μm alumina air abrasive plus silane (clear). Denture resin was processed around each specimen. A Shell-Nielsen shear test was then performed at a crosshead speed of 0.5 mm/minute to determine the bond shear strength in kilograms per square centimeter. The bond shear strength of group 3 was 63% greater than group 1 (significant, p < 0.01; ANOVA-Scheffe´interval 63 kg/cm 2). The results of this study indicated that surface pretreatment of titanium with 110 μm alumina air abrasive plus silane coating significantly enhances the bond shear strength of polymethyl methacrylate.

Direct assembly of implant suprastructures

The technique described uses innovative technology and conventional prosthodontic techniques to directly assemble a cast framework to implant abutments with a resin luting agent. This technique has been used to restore multiple implants with a fixed restoration and for implant connecting bars to support overdentures. Brånemark and Calcitek implant systems have been used successfully.

Radiographic and metallographic evaluation of porosity defects and grain structure of cast chromium cobalt removable partial dentures

A study was undertaken to determine the defects in the internal microstructure of clasps of cast chromium cobalt removable partial denture frameworks. Ninety cast frameworks were radiographically evaluated for porosity with an industrial radiographic machine. The grain structure of the clasps was analyzed with an optical photomicroscope before and after various heat treatments. The radiographic study showed a large number of internal defects in various parts of removable partial denture frameworks. The grain structure study revealed microporosities randomly distributed within the matrix. Various heat treatments were performed and resulted in no change in the grain structure of the original castings.

Adhesive abutment cylinder luting

The connection between dental implants must be passive so that stress is not introduced between bone, implant, and prosthesis. To achieve this passivity clinically is difficult if not impossible with current procedures. A technique is presented in which premachined titanium abutment cylinders are clinically luted to a cast framework to create a stress-free connection. Possible advantages and disadvantages are discussed.

A comparison of impression techniques for a five-implant mandibular model

Production of an accurate dental cast framework that meets the implant objective of passive fit demands an understanding of potential processing errors. Working casts fabricated from impressions using two different transfer copings, as provided by a leading implant manufacturer, were investigated for differences in accuracy. A five-implant mandibular model was used to produce seven casts by both the indirect and direct transfer coping techniques. Comparison was made by using a dental cast framework fitted to the master cast. Differences in distances measured between each group and the master cast were analyzed to establish differences between methods. For the model used, the direct technique produced more accurate working casts. A concern for potential impression distortion given the specific clinical situation underscores the method of choice.

アーク融解・加圧吸引鋳造機の試作 ＶＩＩ 純チタン鋳造床の製作

The pure titanium cast frameworks were made using an arc-melting pressure and vacuum casting apparatus invented by Sato, and an experimental investment material. The salient features of the method and the cast frameworks were as follows: 1. The casting apparatus used was capable of making both complete and partial denture frameworks with pure titanium. It reduced casting errors and the interaction between titanium and the casting mold, producing less porous casted frameworks with a smooth surface. 2. The experimental investment material made a firm heat-resistant investment model with a smooth surface. It showed appropriate expansion and also excellent strength at room temperature after the burn out of the wax pattern. 3. The titanium casted frameworks fitted to the model and the oral cavity closely, and yielded satisfactory clinical results in more than 15 patients.

Use of a modified reversible hydrocolloid syringe for stick modeling compound

The technique should (1) be easily performed in the laboratory on a routine basis, (2) significantly enhance the rigidity of the removable partial denture framework, and (3) increase the strength of the attachment of the acrylic resin portion containing the denture teeth and the denture base retention to the cast framework. These goals are achieved by use of an added metal cingulum that increases the rigidity of the cast framework and by use of labial loops that provide additional rigidity to the lingual bar and strong mechanical anchorage for the acrylic resin part of the removable partial denture. 1. During the design procedure, decide whether to use open lattice retention or bead retention and note this on the diagnostic cast and work authorization form. Either form of acrylic resin retention may be used. In the absence of factors such as recent extractions or ongoing periodontal disease of abutment teeth, beaded retention is recommended. 2. Make a vertical cingulum continuous with the approximate height and location of the cingulums of the anterior incisors being replaced. The cingulum can be either smooth or scalloped along its superior border and should follow the anterior-posterior curvature of the ridge (Fig. 4). A useful guideline that allows for ridge resorption is to make the wall of the vertical cingulum approximately three fourths as high as the length of the replacement denture teeth. The horizontal denture base retention portion of the framework may be relieved or fit directly against the cast (Fig. 5). 3. When waxing the framework, place retention loops on the labial surface of the vertical cingulum (Fig. 6). The loops are made from small l&gauge round wax forms. Angle the loops in a cervical and labial direction (Fig. 7). Keep the loops small so they will not interfere with the arrangement of the denture teeth. When the denture teeth are set and processed, the loops provide secure retention and the vertical cingulum wall and loops add a great amount of rigidity to the framework (Fig. 8).

鋳造床フレームワーク研磨作業で飛散する粉塵に関する産業衛生学的研究

Dental laboratory work includes frequent cutting and polishing, which are always accompanied by scattering of dust. It is well known that microscopic particles are deposited in lung alveoli when inhalated for long periods, so that dentists and dental technicians may have their health affected by inhalation of dust.In a preliminary measurement of cutting dust from various laboratory procedures, I found that polishing cast framework for dentures caused the highest concentration of dust.Chromium-cobalt alloy is commonly used in denture framework. Cobalt exposure can cause interstitial pulmonary fibrosis, and chromium has cell toxicity and exerts corrosive action on mucous membranes.Therefore, I investigated dust from framework polishing from the viewpoint of occupational hygiene.Air samplings during work were performed with a low volume air sampler (flow rate 15 l/min.) at 7 dental laboratories in the Tokyo area, and personal exposure was measured with a size-selective personal dust sampler (flow rate 1.4-1.5 l/min.) which sorted dust particles 7 μm increments.Dust collected by both atmospheric air sampling and personal sampling was measured as dust concentration, and cobalt and chromium concentrations were measured with atomic absoption analysis and neutron activation analysis.The free silica and chromium content of the polishing materials were also analyzed.The following results were obtained:1. The atmospheric dust concentration in polishing workplaces was 0.07-0.26 mg/m3.2. Although a low atmospheric dust concentration was maintained in the workplaces, personaldust exposure was several times higher than the atmospheric dust concentration. The average dust exposure of dental technicians differed greatly according to working conditions, such as the type of work, working posture of the technician, and the use of a local exauster. In 13 cases of dental technicians who polished framework under the condition using local exaust systems, the average concentration of dust did not exceed the threshold limit value (JAIH) in any case, but 8 of 11 cases without local exaust systems exceeded the threshold limit value.3. The atmospheric cobalt concentration in polishing workplaces was from 0.001 to 0.016 mg/m3. Chromium concentration was from 0.001 to 0.008mg/m3.4. The average cobalt exposure of dental technicians was 0.1mg/m3, which ACGIH indicated as the TLV·TWA for cobalt, in 1 of 14 cases with local exaust systems, and more than 0.1mg/m3 in 3 of 10 cases without local exaust systems. Therefore, I suggest that cobalt exposure is hazardous to the health of dental technicians under some polishing conditions.5. The average chromium exposure of dental technicians was less than 0.5mg/m3, which ACGIH indicated as the TLV·TWA for chromium, independently of the use of a local exaust system.6. Free silica content was 11.3% in abrasive for sandblasting, and less than 5% in the other polishimg materials for cast framework.7. Cr2O3 was confirmed as a main component of“green polishing agents”by X-ray diffraction analysis, and buffing with“green polishing agents”caused a high degree of chromium exposure.

Metal framework design for an onlay removable partial denture

R eestahlishing the occlusal plane and surface of one or both arches is often the goal of treatment planning.‘,’ Alteration of the occlusal morphology is also desired for specific treatment needs. 3 Technically, the dentist has various methods available to accomplish this modification, dependent on diagnostic information and case evaluation. Use of a cast framework onlay for construction of removable partial dentures has been described in the dental literature and standard dental textbooks.“6 This article discusses a mandibular partial denture design for individual clinical situations.

Laboratory accuracy in casting removable partial denture frameworks

An attempt was made to compare the clinical accuracy of two types of cast metals used in the fabrication of removable partial dentures as they were prepared by commercial laboratories. No comparison of the metals could be made, because the discrepancies that were found were too gross and were related to technical error. Suprabulge clasps were placed in less undercut than prescribed. Infrabulge clasps were placed in more undercut than prescribed. The laboratories produced better accuracy when they were informed of the purpose of the cast frameworks than when the frameworks were made without the knowledge that their work would be tested. One laboratory produced better results than the other under similar conditions.

Abrasion resistant casts for removable partial dentures

Stone casts used for fabrication of cast frameworks for removable partial dentures can be distorted or mechanically abraded in the duplication process. As a result the framework produced may not accurately fit the cast and the patient’s mouth, and it may require major adjustment. Surface trealment of gypsum casts with cyanoacrylate resins significantly increases abrasion resistance without loss of surface detail.‘bz The dimensional increase in size of the casts has been found to be in the range of 2 to 4 pm, which is not a clinically significant amount. To reduce the mechanical abrasion and/or distortion of casts made for the fabrication of removable prostheses, the following procedure is recommended. 1. Make a slone cast, trim, and thoroughly dry it. 2. Apply cyanoacrylate resin (Aron Alpha adhesive, Howmedica, Inc., Clifton, N.J.; or Permabond 910 Adhesive, Permabond Int,ernational Corp., Inglewood, N. J.) liberally to the cast with a cotton-tipped applicator. Excess resin is

An improved split-denture technique

A technique for the construction of split dentures with a cast framework to hold the denture segments together has been described. The advantages of this technique to the patient were noted. Patients are carefully instructed first on how to insert the sections and then on how to insert the casting after the individual segments of each arch are in place (Fig. 16).

The upper anterior sectional denture

An upper anterior sectional denture is described which consists of (1) a cast cobalt-chromium framework with two passive clasps that contact undercuts on the distal surfaces of the most posterior remaining teeth and (2) a labial flange that carries the replaced tooth or teeth and engages the labiointerproximal gingival undercuts of the anterior teeth adjacent to the edentulous ridge. The cast framework is inserted occlusogingivally, and the labial flange is inserted labiolingually. Both sections are held together by the frictional resistance of the split post of the framework that fits into a tube on the labial flange and hollowed-out artificial tooth. With this type of prosthesis, certain clinical problems can be handled without abutment tooth preparation and with a minimal amount of chair time.

Repairing chrome-cobalt castings

<h2>Summary</h2> This method of repairing with the spot welder and the band material is applicable in various locations on a casting. Frequently, the casting of a bicuspid on a cast framework will present a hole on the lingual surface usually in the area of greatest bulk. These voids can be welded full and to excess the same as on any flat surface. If a lingual bar or a strut has a weak area due to underwaxing or overfinishing, the band material is wrapped around the thin portion and welded to place. Any amount necessary to produce the required strength may be added. The finishing and polishing is accomplished, and the repaired areas will retain their surface and luster indefinitely.