One-piece Cast Research Articles

インプラント上部構造作製方法と適合精度

The accuracy of implant superstructure (three units fixed partial denture) was evaluated for four different fabrication methods : one-piece casting (OC), soldering after tacking (TS), conventional soldering (CS), and laser welding (LW). Ceramo metal (Herador H, Panasonic Heraeus) was cast onto the gold cylinder (DCB 141, Nobel Biocare), and then soldered or welded for three units fixed partial denture for implant superstructure frame work with three different methods except for one piece casting. After fabricating implant superstructure framework, porcelain (Super Porcelain AAA, Noritake) was fused to the framework. The degree of unfit was evaluated by measuring the vertical gap with one screw test between the margin of the gold cylinder of the each unit and the conical abutment replica (DCA 176, Nobel Biocare) on the clinical stone model during the fabricating procedure and after the porcelain firing. One-piece castings (OS) were in mesio-distally warped shape, when screwed at intermediate units. When they were screwed at the end, moment arm effect appeared with large gap at the opposite end. There was the tendency for TS and CS group to show better fit than OC group with no moment arm effect and resulting small standard deviation. When compared among four groups before porcelain firing, there was the tendency for CS to show least gap and for LW to show largest gap. Because of porcelain firing there was the tendency for one-piece casting (OC) to show improving the fit with distorting from mesio-distally warped to straight as original shape, After porcelain firing, soldering groups (TS, CS) were distorted to decrease the soldering space, resulting in increasing the gap. Overall the gap of soldering groups (TS, CS) increased in same as one-piece casting (OC). Average gap of both ends was 10μm when frameworks were screwed at intermediate units, and average gap of other two units was 20μm when screwed at the one end. Laser welding showed the increased gap after porcelain firing. It was 20μm and 70μm when frameworks were screwed at the intermediate unit and the one end, respectively.

Fit of implant frameworks fabricated by different techniques

Purpose. This study evaluated the precision of fit between an implant framework and a patient simulation model that consisted of five implant abutments located in the mandibular symphysis area. One-piece cast frameworks were compared with Procera machined and laser-welded frameworks with laser videography. Material and methods. Five frameworks of each type were measured with a laser digitizer and a graphics computer program to determine a single point represented as the “Centroid” for each framework component and each implant abutment. Differences between the paired centroids for each framework/abutment interface are reported as x- and y-axis displacements, and z-axis gaps. The direction of the x- and y-axis displacements was determined. Results. There were significant differences ( p < 0.05) in the precision of fit between both the one-piece cast frameworks and the Procera frameworks, when compared with the abutments in the patient simulation model. The laser-welded framework exhibited a more precise fit than the one-piece casting, with significant differences at four of the five prosthodontic interfaces, when evaluated by the mean z-axis gap at the centroid points. (J Prosthet Dent 1997;78:596-604.)

The Periotest method: implant-supported framework precision of fit evaluation.

In this study, the Periotest instrument was used to measure the precision of fit between cast high noble-metal frameworks and the supporting implants in a patient-simulation model. Three framework conditions and three implant-location variables were used to evaluate the rigidity of the assembly as measured by the Periotest method. The framework variables were (1) one-piece castings (OPC); (2) sectioned-soldered inaccurate castings (SSIC); and (3) sectioned-soldered accurate castings (SSAC). The implant-location variables were right anterior (RA), center (C), and left anterior (LA). The patient simulation model used consisted of three self-tapping Branemark implants in a reasonable arch curvature in bovine bone. Three working casts were fabricated from the patient-simulation model using polyvinyl siloxane and tapered impression copings. From the working casts, three sets of three frameworks were fabricated as OPCs, SSICs, and SSACs using type 3 high noble alloy. The SSICs were fabricated with a quantitative misfit of 101.6 microns at the facial surface, between the abutment-to-gold cylinder interface at the C implant location. Periotest value (PTV) measurements were made at the midfacial surface of the frameworks directly above each abutment-to-gold cylinder interface. Three measurements were made for each test condition. The data were analyzed to compare framework condition(s) and implant location(s) using ANOVA and Fisher's Protected Least Significant Difference Comparison Test. The ANOVA showed that significant differences exist between the mean PTV data for framework condition and for implant location (p < .01). Significant differences were shown between the mean PTV data for the SSAC assemblies and the OPC and SSIC assemblies. The SSICs displayed a more positive (+) mean PTV than the OPCs. The OPC assemblies had a more positive mean PTV than the SSAC assemblies. The mean PTV data for the SSAC assemblies had a significantly different PTV (p < .01) than the other two framework condition assemblies. The OPC and the SSIC assemblies had PTVs that were not significantly different. The C implant location was significantly different from the RA and the LA implant locations (p < .01). The RA and the LA implant locations were not significantly different from each other. The C implant location always demonstrated the most positive mean PTV regardless of the framework condition being tested. The Periotest instrument quantified differences in the precision of fit between three framework conditions. The SSAC assemblies were significantly more rigid than the OPC and SSIC assemblies. The OPC and SSIC assemblies' mean PTVs were not significantly different. The mean PTVs for the C implant location and the RA and LA implant locations were significantly different (p < .01). The mean PTVs of the RA and LA implant locations were not significantly different. The implant-location PTVs followed the same rank order for all three framework conditions. The procedures used to fabricate a more precise fit between the framework and the supporting implants is influenced by the skill of the clinician and technician.

Passive adaptation of the prosthesis-implant interface by soldering gold cylinders to the framework casting

Difficulties associated with accuracy of conventional long-span one-piece castings for fixed partial dentures are also observed in the fabrication of implant-supported prostheses. A technique is proposed whereby direct intraoral verification of cylinder-abutment relationship, master cast accuracy, possible corrected cast procedures, and soldering of gold cylinders to the framework ensure an accurate, passive adaptation of the prosthesis to all supporting implants.

Alternatives to posterior complete crowns: Integrating foundations with cuspal protection

A common approach for restoring compromised posterior teeth is to reconstruct the missing anatomic crown with a dental restorative material and prepare the remaining tooth structure for an artificial veneer. Because this procedure is also compounded by designing subgingival finish lines for tooth preparations, a conservative approach for the fabrication of one-piece castings is suggested that incorporates both foundations and cuspal protection, with finish lines prepared above the gingival crest. Patient selection, advantages, disadvantages, and armamentarium are discussed.

The fit of fixed partial dentures joined by infrared soldering

This study determined the accuracy of fit of three-unit fixed partial dentures joined by an infrared soldering technique compared with one-piece fixed partial denture castings and individually cast crowns. Wax patterns of prepared Ivorine teeth, maxillary left central incisor and maxillary left canine, were injection molded; a plastic rod was used as a pontic. One group of patterns was cast as one-piece dentures; the other group was sectioned in the connector area, cast individually, and then joined by infrared soldering. Castings were seated on their respective dies, embedded in epoxy resin, and sectioned. Gap distances between the casting and the die were measured at specified marginal sites with a profile projector. Results showed that the fit of infrared-soldered fixed partial dentures was significantly better than that of one-piece castings and was comparable with the fit of single crowns. The gap openings measured in all castings were within the range of clinical acceptability.

Impulse Responses to Connection Forms of Experimental One-Piece Cast Bridge Prosthetics

Impulse Responses to Connection Forms of Experimental One-Piece Cast Bridge Prosthetics

The seating of one-piece and soldered fixed partial dentures

This laboratory study compared the seating of one-piece castings with that of soldered fixed partial dentures. Two investments were investigated, five American Dental Association type III and five metal ceramic alloy fixed partial dentures were made by using the conventional indirect technique. The investing and casting protocol was designed to produce an ideal fit of the individual complete crown abutments, not the fixed partial denture. Independent seating of each retainer provided a baseline measurement for complete seating and was compared with fixed partial denture seating. Fixed partial dentures were then sectioned and reassembled by soldering twice, using a low- and high-expansion investment. Statistical evaluation identified significant differences between the metals and the techniques. Marginal discrepancies with one-piece casting and lower (0.6%) thermal-expansion soldering were clinically unacceptable. A clinically acceptable fit was obtained with the higher (1%) thermal-expansion soldering investment.

Evaluation of a two-piece post and core fabrication technique

Casting a core to a prefit post reduces the need for adjustments at cementation. This study compared two-piece post and core castings to one-piece castings of the same geometric configuration. The specimens were made with 0.070-inch Whaledent laboratory burnout posts invested in a phosphate investment and cast with Midas, Sturdicast, or Rexillium III alloys. Three groups (n = 10) with two-piece castings had the post cast followed by a second casting of a 1 mm thick core to the post head. Three groups (n = 5) were cast in one piece. The specimens were tested for tension at a head speed of 1 cm/min. One Midas alloy two-piece casting was dislodged at the post head-to-core interface whereas the other specimens failed within the post. There was no significant difference between the two techniques using a generalized linear model ( p < 0.05).

Flexion characteristics of fixed partial denture frameworks tested by using elapsed-time holographic interferometry

lh fl e exion of a ceramometal fixed partial denture framework under functional loading may cause fracture of the porcelain superstructure.’ The framework must be rigid without compromising biologic and esthetic acceptance. Fixed partial denture frameworks may be made as a one-piece casting (unit-cast) or as two or more units soldered together. The method to be used is usually left to the discretion of the dentist. Some design variables include the type of metal used, the geometry, and location of the solder joint. Although one-piece castings can fit more accurately* or fit as accurately as soldered individual units,) one-piece castings offer no opportunity to verify the fit of individual retainers.’ Because inaccuracy increases as casting length increases,5s6 frameworks larger than three units should be cast in two pieces and soldered.’ Previous testing of the strength of soldered joints was done under tensile loading with the assumption that there is a correlation with the compressive loads experienced in the oral cavity.‘-‘* In this study, using a compressive load, deformation was detected by elapsedtime holographic interferometry,13-‘5 an extremely sensitive tool for identifying stress-induced distortions and nondistorted displacements in the nanometer range. In addition, this method provides a permanent photographic record of the observed results. All results are based on the recorded responses of the prostheses to the same static load exceeding the calculated biting force in the human dentition in the first molar region.16 The properties of laser light allow the optical phenomenon of the interference of two beams of light to produce visible fringe patterns on objects. A hologram captures the interference patterns of two beams of light on photographic film, one beam is reflected from an object and the other functions as a steady “reference” beam coming directly from the laser. If the object is very

Dental soldering part VIII. Distortion of non-precious ceramometal fixed bridge during the soldering

The purpose of this study is to mesure the three dimentional distotions and displacements in the Non-precious (Ni-Cr) ceramometal fixed bridge using the pre-soldered method.Following conclusions were obtained as a results.1. During the Pre-soldering stage, the distotion of soldered bridge frame (the potion was made with one-piece cast method) are minimal.2. During the Pre-soldering stage, the curve of fixed bridge frame was slight opened on horizontal plane, but on the vertical displacement was larger than others.

Tensile strength analysis of midpontic soldering

A total of 120 three-unit fixed partial dentures were made by using a latex mold to produce uniform wax patterns. Four groups were used to compare the tensile strength of connectors with interproximal solder, midpontic vertical solder, midpontic diagonal solder, and a control of one-piece castings. Three different metals were tested and the tensile load required to fracture the samples as well as the fracture sites were recorded. The following was found: Soldering the interproximal connector area produced the weakest solder joints, regardless of metal tested, at p less than .001. There was no significant difference in the fracture loads between midpontic vertical soldering and midpontic diagonal soldering with all three metals at p less than .01. There was no significant difference in fracture loads between midpontic soldering and unit casting with all three metals at p less than .01. The extreme variations in fracture loads when soldering nickel-chrome-beryllium confirms the technique sensitivity of presoldering this alloy.

Accuracy of one-piece castings, preceramic and postceramic soldering

An investigation was conducted to evaluate the relative accuracy of one-piece castings of FPDs of three, four, and five units with those assembled by preceramic soldering and postceramic soldering. The preceramic soldered FPDs were subjected to six simulated porcelain firing cycles to assure a homogeneous sample. A total of 15 FPDs, five of each length, were evaluated for each test condition. A three-piece aluminum mold with stainless steel dies, which allowed for varying the length of the prosthesis, was used to fabricate the FPDs in 52% gold-palladium alloy. Marginal discrepancies of the castings on the dies were compared for the three test techniques. The mesiodistal length of the FPDs that were pre- and postsoldered were also measured at the occlusal and at the gingival margins and compared with the restorations before soldering.

Comparison of accuracy of multiunit one-piece castings

An investigation was conducted to evaluate the accuracy of one-piece castings of FPDs consisting of three, four, and five units with a ceramometal alloy cast in a large circular ring. A three-piece aluminum mold with stainless steel dies simulating the various lengths of the FPDs was used. A total of 18 castings, six castings for each FPD, were fabricated. Marginal discrepancies of the castings on the dies and the length of the castings were compared before and after sectioning the castings at the connectors. The following conclusions were drawn from the study. Seating of the castings improved approximately 50% after sectioning, which indicates that the castings were distorted. The distortion was a three-dimensional phenomenon, with the greatest discrepancy on the mesiogingival surface of the anterior retainer and on the distolingual surface of the posterior retainer. The distortion was least for the three-unit FPDs and greatest for the five-unit FPDs. The lingual-facial diameter of the castings at the gingival axial line angle was significantly larger than the dies in most cases. The mesiodistal diameter of the castings at the gingival axial line angle was smaller than that of the dies but was only significant with the three-unit FPDs. Although the castings were slightly oversized or undersized, the primary reason the castings did not seat was warpage.

前ろう着法による陶材焼付金属冠ブリッジの技工操作過程における変位

The author, conducted the following studies in order to clarify the causes of displacements and distortions in the ceramometal fixed partial prosthodontics (bridge) using the pre-solderd joint that occur during the laboratory procedure. In conducting these studies, the author assembled a ceramometal fixed bridge consisting of 8 units with a canine and a first premolar on either side in the maxillaserving as the abutment, for the portion in which four teeth-the central incisors and lateral incisors on both sides-were missing. Then, in order to find out when the framework of the fixed bridge was displaced or distorted and what the extent and direction of such displacements or distortions were, three-dimentional deviations of the framework were measured. As a result of these studies, the following conclusions were reached;1. Throughout the laboratory procedure, it was at the time of pre-soldering and degassing that a substantial displacement ofthe fixed bridge was noted. Some displacement, although a minor one, was found at the time of the firing of body-incisor porcelain and that of glazing, too. However, no significant displacement was noted at the time of surface-grinding and that of the firing of opaque porcelain.2. As to the displacement at the time of pre-soldering, the distortion of the soldered body (the portion made with one-piece cast method) itself was minimal; a kind of displacement was seen where the curve of the fixed bridge closed mainly as a result of two soldered bodies coming close to each other.3. At the time of degassing, the curve of the fixed bridge opend wide as a result of the distortion in the portion made with one-piece cast method and the displacement at the soldered portion.

歯科ろう着に関する研究 埋没材と予備加熱法との相違が適合精度に及ぼす三次元的検討

In the clinical practices of the Crown and Bridge Prosthetics, the developments and improvements achieved in the instruments have made the adoption of the indirect method a day-to-day affair and have enabled the making of fixed restorations with adequate accuracy. It has now become possible to easily make a bridge for the portion where 1 or 2 teeth are missing with the one-piece cast technique and this technique is now beginning to be applied also to the making of a bridge for the portion where 3 or more teeth are missing. However, in the cases where there are restrictions due to the abutment tooth contour or where there are many units, the assembly operation is done, even today when the indirect method is already well established, with the soldering method which is employed in parallel with the checking of fitness accuracy. Also, as in the cases where different kinds of metals are joined together or where the prosthetic techniques are employed using attachments or telescope system, there are many instances in which the reliance on the soldering method is either absolutely necessary or its adoption is preferable.This soldering method not only uses many kinds of materials and requires complex assembling process but also necessitates a high level of technique. Hence, there are many factors that affect the fitness accuracy of the bridge assembled with the soldering method. For this reason, many a study has been made on the soldering method itself but, so far, we can hardly say as yet that a systematic soldering method has been established.So, the author has taken up, from among the various factors that affect the fitness accuracy of the soldering method, the following two factors, viz., (1) soldering investment and (2) preheating procedure, and, with the purpose of clarifying the effects that these two factors give to the fitness accuracy, measured the three dimen sional distortions of the retainers. Following are the conclusions obtained as a result of the measurements and examinatios done by the author:1. With respect to the linear distortion and rotational distortion, the effects resulting from the differences in the types of soldering investments and the preheating procedures used were particularly large in terms of the volume of mesiodistal distortion (ΔX).2. As to the effects given to the fitness accuracy by the soldering investment and the preheating procedure used, the largest effect was given by the soldering inve stment, which was followed in the intensity of effects by the interacation of soldering investment and preheating procedure, and then by the preheating procedure.3. It was found that, among the various kinds of soldering investments used at the time of the soldering, the Deguvest L (manufactured by the Degussa, Inc.) with the highest thermal expansion ratio produced good fitness accuracy regardless of the type of the preheating proce dures used.4. It was found that, regardless of the type of the soldering investments used, the preheating at the tem perature of 150°C was a most important factor in obtain ing good fitness accuracy.

Spatial changes occurring in fixed partial dentures made as one-piece castings

U se of base metal alloys to make the metal framework of ceramic veneered crowns and fixed partial dentures has created the need for technical modification in procedures previously applied to gold base ceramic alloys. Making one-piece metal castings for multipleunit fixed partial dentures is one of the more notable technical modifications, since in preand postsoldering procedures it has been difficult to achieve a strong, dependable solder joint in the base metal framework. Thus, one specific problem is assessing the degree of dimensional accuracy in casting a one-piece base metal fixed partial denture. Studies on casting accuracy for single crowns1-4 and multiple-unit fixed partial dentures5-* reported marginal discrepancies after cast specimens were returned to dies of origin. In general, these investigations determined casting accuracy by observing the closeness by which the margin(s) of castings and margin(s) of dies could be brought into apposition. Suffert and Mahler’ suggested that inherent surface roughness of the casting influenced fit and that this variable could create confusion in making an assessment of casting fit. This study was designed to establish a method of assessing the dimensional changes occurring at the margins of a multiple-unit fixed partial denture. The distances between specific precast (wax stage) and postcast (metal stage) points on abutment crown margins were recorded in conjunction with alterations in the expansion of investment material. Comparisons of these measurements provided an evaluation of the accuracies of the castings.

One-piece cast impellers for axial pumps

One-piece cast impellers for axial pumps

A one-piece cast permanent splint

With the use of the findings of many fundamental investigations, a system was established to make not only individual inlays or crowns but also extensive fixed partial dentures or splints by the indirect method and one-piece castings. A procedure for making a permanent splint for mobile teeth by this system has been described. This technique provides favorable and accurate results, and requires far less labor, time, and skill than other techniques.

Three-dimensional Photoelastic Investigations of Bite Stresses on the Abutment Tooth, the Alveolar Socket and Plate-supporting Alveolar Ridge Bones Part.2

The present study is concerned with a consolidated analysis through the photoelastic method of mechanical properties of physical stresses which are responsible for pathohystological changes on the abutment tooth, alveolar socket and plate-supporting alveolar ridge bones due to bite stresses when a partial denture is inserted in a patient. By the use of Epoxy resin B hardener 901 product of Ciba Company, Switzerland, the author constructed through a casting method of his own design study models which would fit intercalary denture (56 missing), one-side free-end denture (76 missing), as well as both side free-end denture (76 67 missing). On these models there were constructed one-piece cast denture bases and clasps of platinum-gold having an elastic coefficient of 12, 300Kg/mm2, on which dentures were completed with artificial porcelain teeth and resin gingiva. On the other hand, the upper jaws were made of hard plaster on which were planted artificial teeth made of cobalt-chrome alloy having an elastic coefficient of 12, 000Kg/mm2. When the upper and lower jaws were firmly mounted on the articulator in the position of centric and lateral occlusion, bite load was administered to them while they were placed in the stress freezing apparatus. Then, sections were prepared of the jaws and a three dimensional photoelastic analysis was conducted on them by means of photographic fringe method. As a result of these experiments, the following findings came to light.1) As regards bite load working on the abutment teeth, a stress concentration on a load point on the tooth crown, and a stress distribution on the tooth surface except the load point were observed. With reference to the roots and alveolar socket bones, stresses were dispersed by the stress braking action of the periodontium. Therefore, under these conditions the uniform load was obtained which gave little fatigue on the abutment teeth.2) When bite load was exerted on the single-rooted abutment teeth in the axial direction, there was produced an equilibrium between a load point on the crown and the root apex, and thus stresses were uniformly distributed all over the surface of root and alveolar socket bone. In case more than two stresses in different directions acted on one another and consequently in balance, the working center of force took place inside the dental substance of the root portion. The posion of the working center of force varied in terms of the direction, angle and size of stresses. As the working center of force acted as a fulcrum of inclination of the abutment tooth, a compression stress was distributed locally on the surface of the abutment tooth as well as on the alveolar socket bone surface in the inclined direction of the tooth.3) When bite load was exerted on the multirooted abutment teeth in the axial direction of the one root, an equilibrium was produced between a load point on the crown and the apex of the root. Moreover, when more than two loads were experted in different directions and they were in balance, the working center of force was produced inside the dental substance of the crown center portion. On the other hand, when more than two loads working in different directions were out of balance, the working center of force tended to be located inside the dental substance of the side portion of the crown on which a stronger stress acted, a compression stress being distributed locally on the surface of multiroots in the direction of that stress and the opposing surfaces of alveolar sockets and the inter-alveolar septum.4) As compared with the single-rooted abutment teeth, the multirooted abutment teeth had a larger surface to bear a stress because of inter-alveolar septum and, for this reason, a load on the alveolar socket bone becomes less. Also the resistance against torsion was correspondingly large.