模型置换印模技术修复下颌游离端牙列缺损的临床研究

目的：探讨模型置换印模技术对双侧下颌游离端缺牙患者的修复效果。方法：在解剖式印模上常规制作铸造支架,在铸造支架上制作自凝暂时基板,经口内肌功能修整并制取咬合记录后于口内取功能性印模。经模型置换后常规完成义齿。结果：90.2%的患者用模型置换印模技术制作的义齿疗效良好。结论：模型置换印模作为游离端可摘部分义齿的重要功能印模方法,可以有效改善义齿修复质量。     

Technique for achieving a passive framework fit: a clinical case report

The clinical application of a 4-step technique for achieving the passive fit of an implant-supported cast bar or framework is reported. Implant-level transfers were attached, splinted intraorally with pattern resin, picked up in an open-tray elastomeric impression, and used to fabricate a working cast containing implant analogs. A light-cured template was used to verify master cast accuracy. A ceramometal fixed partial denture restoration was fabricated on the working cast with a preliminary try-in of the cast metal framework. A passive prosthesis fit was achieved. Failure to create an accurate working cast can distort the intended fit of a cast framework on the abutments in the patient's mouth. Optimal positioning of the implant analog in the master cast depends on (1) the transfer technique and (2) the ability of the system to maintain precise rotational orientation of the transfer components. The splinted transfer technique developed 20 years ago has sometimes been effective in improving the accuracy of framework fit with external hexagon implant-abutment connections, but it has not been documented with newer implant-abutment connections. Techniques for reestablishing master cast accuracy and correcting the superstructure are presented. The use of the presented technique resulted in a passive-fitting framework.     

An impression technique to make a new master cast for an existing removable partial denture.

When the master cast for a removable partial denture is lost and a well-fitting framework remains, it may be necessary to replace the master cast. A two-step impression procedure is described that combines the altered-cast technique and the use of a modified disposable tray. Finger pressure is maintained on the major connector throughout the making of both impressions, to prevent framework movement and loss of contact with prepared rest seats.     

Adapting fixed prosthodontics principles to screw-retained restorations

Implant restorations may be visualized clinically using a provisional fixed partial denture and in the laboratory with a fully contoured waxing on the master cast. The benefits of eggshell restorations for provisional restorations are as valid in implant prostheses as in conventional restorations. A technique is presented using the plastic laboratory sleeves to provide reliable anchorage as well as protection and preservation of the abutments. A fully contoured waxing on the master cast predictably determines the most appropriate design for screw-retained restorations. When unfavorable implant placement would create compromised morphology, a retrievable auxiliary substructure is indicated.     

Index to reposition the metal framework accurately on the altered cast.

The relieved portion of a master cast below the major connector of a cast removable partial denture framework can be filled with dental stone to act as a third point of reference when the framework is reseated in an altered cast procedure. With this simple procedure, an index is formed that will allow accurate repositioning of the metal framework on the altered cast.     

Fabricating Crowns to Fit Existing Removable Partial Dentures: An Illustration of Two Techniques

The prosthetic treatment of a structurally compromised abutment tooth supporting a removable partial denture may present a variety of restorative modalities. Ideally, a surveyed crown is made for the individual tooth, which is later followed by a new removable partial denture fit to the contours of the crown. Frequently, however, the removable partial denture is clinically acceptable, and remaking the prosthesis is not indicated. In these cases, the crown can be made to fit the existing removable partial denture. Fabricating crowns to fit existing removable partial dentures can be accomplished using a direct method, an indirect method, or combinations of these techniques. Direct techniques traditionally use acrylic resin and inlay wax intraorally to develop a custom pattern that captures the contours of the clasp assembly. Indirect techniques use a pick-up impression to allow the crown pattern to be waxed against the denture framework on a cast in the laboratory. Combination methods use either a direct-indirect or indirect-direct approach. The direct-indirect method develops the preliminary resin pattern directly on the tooth and finalizes the contours in wax on a master cast. The indirect-direct technique initiates a crown pattern on a die and completes it either intraorally or on the die after the intraoral refinements. This article reviews the literature for methods of fabricating surveyed crowns under existing removable partial dentures. Additionally, two cases are presented that illustrate an indirect and combination direct-indirect technique for making the restorations.     

A technique for fabricating patterns for removable partial denture frameworks using digitized casts and electronic surveying

Although computer-aided design and manufacture techniques have shown some promising applications in the fabrication of crowns, inlays, and maxillofacial and oral surgery, the field of removable prosthodontics has not embraced these technologies so far. This article describes the development and investigation of computer-aided techniques that may eventually enable prosthodontic procedures such as surveying and the production of sacrificial patterns to be performed digitally. A 3-dimensional computer model of a conventional cast from a patient was obtained using an optical surface capture device (a scanner). The shape of a number of components of a removable partial denture framework was modeled on the 3-dimensional scan electronically, using computer-aided design software. A physical plastic shape of the components was produced using a Rapid Prototyping machine and used as a sacrificial pattern. Techniques to allow digital cast surveying before the production of sacrificial patterns were also developed. The results show that digital dental surveying and machine-produced sacrificial patterns can be accomplished. This article forms a basis for further developments leading to a fully integrated approach to the computer-aided design and fabrication of removable partial denture frameworks.     

Laboratory procedures for fitting removable partial denture frameworks.

A technique has been described for fitting a removable partial denture framework to the master cast prior to adapting it in the mouth. Emphasis should be placed on maintaining the original contour of the framework throughout the procedure. The amount of metal removed should be only that necessary to seat the casting on the master cast without abrading the stone. When finishing the tooth-contacting surfaces on the casting, very light pressure should be used to burnish the rough surfaces, not reduce them. If these steps are accomplished carefully in the laboratory, the dentist should be able to fit the framework in the mouth in a minimum of time (Fig. 7).     

A method of stabilizing removable partial denture castings during clinical and laboratory procedures.

The use of a temporary incisal rest at the most anterior point of a removable partial denture framework is advocated. This rest provides stabilization during intraoral and laboratory procedures when the corrected master cast technique is used.     

Fabrication of a New Crown and Provisional to an Existing Removable Partial Denture

A method of fabricating a new crown to an existing removable partial denture is described. A press-form plastic shell made from the diagnostic cast provides the outer contours for the abutment tooth, while an acrylic resin coping is fabricated on a die to provide accurate internal adaptation. The acrylic resin coping is seated on the prepared abutment. Autopolymerizing acrylic resin is mixed and placed in the plastic shell that is then placed in the mouth over the coping, forming the acrylic resin crown pattern. The removable partial prosthesis is fitted over the crown pattern intraorally. The pattern is transferred back to the die, the margins are refined, and the casting is completed and finished, avoiding reduction of the established contours. The same plastic shell is used with tooth-shaded acrylic resin to construct a provisional crown directly in the mouth. This technique allows the patient to wear the removable partial denture while the laboratory procedures are completed.     

Incorporation of a cast,embossed identification plate into a partial denture framework

This article presents a technique for the fabrication and incorporation of a stable and fireproof identification plate into a cast partial denture framework. Embossing tape is embedded in the wax pattern of the major connector. The resulting casting reproduces the embossed lettering, which is identifiable through the tissue-colored acrylic denture base resin.     

A denture tooth position index fabricated with light-polymerized acrylic resin

A denture tooth position index transfers the position of the denture teeth to the master cast during metal framework and bar-substructure fabrication stage. This article describes the use of light-polymerizing acrylic resin to fabricate a tooth position index.     

光栅投影技术在获取牙列缺损三维数据中的应用

目的 介绍一种采集牙列缺损石膏模型三维数据的方法,为重建牙列缺损三维数字模型及研究可摘局部义齿支架的计算机辅助设计奠定基础。方法 利用计算机控制投影系统在0.4 s的时间内连续将间隔∏/2正弦周期4幅光栅,投射在牙列缺损石膏模型表面,数码相机采集由于受到模型表面高度的调制而变形的条纹图像,通过相移法解调得到包含高度信息的相位变化, 去包裹后的位相值通过三角测量法实现相位-高度的转换,计算机自动完成多视数据拼合,从而得到整个石膏模型外形轮廓的三维数据,重建牙列缺损的三维数字模型。结果 获得了密集完整的牙列缺损点云模型,基本上未见扫描盲区。重建的牙列缺损三维模型牙颌解剖结构清晰。结论 采用光栅投影和相移法获取牙列缺损的三维数据,具有精度高速度快的特点,可以满足后续的可摘局部义齿支架三维设计的需要。     

A comparison of impression materials for complete-arch fixed partial dentures

This study compared the marginal fit of complete-arch fixed prostheses under simulated clinical conditions. Prostheses were made on casts constructed from three commonly used impression materials; polyether, polyvinyl siloxane (medium-viscosity and putty-wash), and reversible hydrocolloid. A maxillary dentoform with four abutment teeth was used as the master cast and six impressions were made with each material. Individual castings for each abutment were made on the stone casts. The abutment castings were luted together on the casts to provide a complete-arch fixed partial denture using a ticonium framework and acrylic resin. The marginal fit of the abutment castings was measured on the master cast before and after the prostheses were luted together. The polyether and both addition silicone impression materials were significantly more accurate than the reversible hydrocolloid in both situations. All of the single castings were clinically acceptable, but the luted restorations made from reversible hydrocolloids were not.     

A two-pour technique for investing interim partial dentures

A technique for the use of two stone layers to invest an interim partial denture has been presented. Holding all components on the master cast ensures accuracy.     

International telephone code used for citizenship identification in a denture

This case report describes a simple method for identifying the citizenship of a denture wearer by marking the telephone country code number inside the denture base. A wax pattern for the denture framework was prepared on the refractory cast. A piece of embossing tape, containing the country code (81, Japan), Japanese prefectural code, and abbreviation of the dental clinic where the denture was fabricated, was placed on the metal framework. A titanium-aluminum-niobium (Ti-6Al-7Nb) alloy was cast in the mold, and the denture was then fabricated by the conventional method. The casting satisfactorily reproduced the embossed letters, and the plate was identifiable through the gingiva-colored acrylic denture base resin. Since an embossed metal plate integrated with the skeleton is embedded in the denture base resin material, the current denture marking technique serves as a simple procedure for insertion of an undegradable denture identification mark which makes it possible to identify the nationality of the denture wearer.     

An altered cast procedure to improve tissue support for removable partial denture

Free-end saddles are liable to be displaced under occlusal pressure. This is as a result of the displaceability of the mucosa. The altered cast technique is employed to try and prevent this by making an impression of the mucosa under controlled pressure. The metal framework was constructed on a cast produced by a mucostatic impression material. Base plates were then constructed in self-cured acrylics on the framework in the saddle areas, and these are close fitting. Border molding was carried out; impression was made with zinc oxide eugenol impression paste.In the laboratory, the free-end saddle areas on the master cast are sectioned off. The denture is then positioned on the model and the new saddle areas are poured. The resulting model represents the free-end saddle areas under conditions, which mimic functional load. Denture construction then continues as normal. The distribution of loading of the free-end saddles is improved and denture is more stable.     

Cast connectors as cores for ceramometal pontics on removable partial dentures and for splinting anterior crowns

A cast connector is a solderless union between two metal components, an alternative to soldering. Cast connectors depend upon mechanical retention for their strength and integrity and are mostly used in repairing or adding to prostheses cast in base metal alloys. Two techniques using cast connectors are described. One is for a removable partial denture that requires the replacement of an anterior tooth or teeth incorporating diastemas or unusual surface anatomy and color variations. Stock denture teeth may not adequately replicate such teeth. A solution to the problem is to extend a porcelain-compatible base metal cast connector from the removable partial denture framework onto the pontic site. A ceramometal pontic reproducing the unusual characteristics of the natural teeth may then be placed by vacuum-firing porcelain directly onto the framework. A second technique is described whereby multiple ceramometal anterior crowns may be splinted together by creating interproximal retentive zones in the frameworks, casting connectors into the retentive zones, and proceeding with porcelain application.     

Comparison of the Dimensional Accuracy of Injection-Molded Denture Base Materials to that of Conventional Pressure-Pack Acrylic Resin

Purpose : This study compared the linear dimensional changes of 3 injection-molded denture base materials to that of conventionally processed polymethylmethacrylate (PMMA) resin.
Materials and Methods : An impression of an aluminum maxillary edentulous arch was made with a condensation silicone impression material (Denture Elasticon) to fabricate a gypsum master cast that was replicated as a silicone mold. A maxillary complete denture with acrylic teeth was waxed to full contour on the master cast and replicated to make 40 wax dentures. ERA attachments cast in metal (Rexillium) with indices milled into the centers were waxed into 3 positions in each denture for recording dimensional measurements of the wax denture. Ten dentures were allocated to each of 4 groups; Group 1 was processed using conventionally processed PMMA (Microlon), Group 2 used injection-molded PMMA (SR-lvocap), Group 3 employed injection-molded nylon (Valplast), and Group 4 used injection-molded styrene (Northern). All processed specimens were stored at room temperature (25°C, ambient humidity) for 1 week (while still on the master cast) before anteroposterior and cross-arch measurements were made using the ERA reference points with a digital caliper. After separation from the master cast and following water storage at 37°C for 7 days additional measurements were made.
Results : An analysis of the results showed that the effect of processing was not the same for the 3 dimensions studied, regardless of which dimension was considered ( p < 0.0001). The pattern of dimensional changes associated with the material type was not the same between the wax and processing stages as it was for the change between the processing and decasting stages ( p < 0.0001).
Conclusions : Processing the denture base materials produced unequal deformation in different dimensions (anterior-posterior and cross-arch). Each material tested also responded differently to the processing stages.     

Achieving an even thickness in heat-polymerized permanent acrylic resin denture bases for complete dentures.

Permanent denture bases form the fitting surface of a denture and are constructed on a master cast, in heat-polymerized acrylic resin. These bases are strong and rigid and demonstrate both the fit and retention of the final prosthesis. General recommendations suggests a thickness of between 1.5 to 3 mm for these bases. The normal procedure for producing such a denture base is to manually adapt materials to the cast, in their plastic state, before processing. Such procedures are liable to distortion and variation in the thickness of the resultant denture base and may be unreliable. This article describes a method for achieving a consistent thickness in a heat-polymerized, permanent, acrylic resin denture base through the use of a vacuum-formed, thermoplastic blank as a template. The method is simple, and results in a denture base with a consistent even thickness.