The altered cast impression technique revisited

BACKGROUND: The altered cast impression technique of fabricating removable partial dentures, originally described more than 60 years ago, improves the residual-ridge-to-dentition relationship of the prosthesis. This potentially increases patient satisfaction while preserving the remaining supporting structures. LITERATURE REVIEWED: This article reviews research that evaluated abutment tooth movement as a result of the relationship of the denture base to the residual ridge, revealing that improved fit reduced tooth movement. Load distribution studies have shown that a well-fitting denture base distributes stresses favorably to the supporting bone and abutment teeth. Other studies showing that increased residual ridge coverage coupled with a well-fitting denture base reduces stress per unit area, potentially preserving the remaining supporting structures. CASE DESCRIPTION: The article describes a patient who had a unilateral distal extension removable partial denture that was fabricated after the failure of a 20-year-old partial denture due to extensive dental decay. The prosthesis was fabricated over the course of four appointments, and the prosthesis was delivered on the fifth appointment. The patient, who wears the prosthesis daily, expressed comfort and ease of use at a one-year recall examination. CLINICAL IMPLICATIONS: Distal extension edentulism can affect a patient's ability to function as a dentate person. A well-made removable partial denture that has appropriate extensions, borders and ridge-to-dentition relationship will benefit the partially edentulous patient by providing increased comfort and improved dental function.     

Overcoming the unstable mandibular complete denture: the neutral zone impression technique

This article describes a technique for improving the stability of mandibular complete dentures for patients who have a diminished mandibular neutral zone.The technique involves making an impression which is shaped by the patient's oral musculature, and which defines the shape and contour of the patient's neutral zone. A case report is presented in which the use of this technique is described. It is hoped that this article will increase the awareness of dental practitioners to the use of this technique. Clinical Relevance: The neutral zone impression technique is a useful technique when providing mandibular complete dentures. Its use can overcome some of the denture stability difficulties caused in some patients by a more powerful oral musculature, or in patients who have poor or altered neuromuscular control.     

两种流动性硅橡胶组合应用于Piezography中性区印模法初探

目的探讨2种流动性硅橡胶印模材组合应用于Piezography中性区印模法并初步分析印模形态稳定性。方法选择牙槽嵴严重吸收的无牙颌患者1例,组合中流动性和高流动性2种硅橡胶印模材,利用Piezography发音法制取下颌中性区印模,测量分析其咬合面不同部位水平位置稳定性。结果制取的下颌中性区印模抛光面形态光滑完整。两侧后牙区咬合面不同位置的间距最大变异系数(C.V)为2.49%,颊侧缘间距C.V较舌侧缘小。双尖牙区各间距C.V较磨牙区小,稳定性高。前牙区正中部唇舌向中点的水平位置稳定性较唇侧和舌侧高。结论将2种流动性硅橡胶印模材组合应用于Piezography中性区印模的方法可提高临床效率,印模抛光面光滑,后牙区颊侧形态和位置稳定。     

The neutral zone in complete dentures

The neutral-zone philosophy is based upon the concept that for each individual patient, there exists within the denture space a specific area where the function of the musculature will not unseat the denture and where forces generated by the tongue are neutralized by the forces generated by the lips and cheeks.The influence of tooth position and flange contour on denture stability is equal to or greater than that of any other factor. We should not be dogmatic and insist that teeth be placed over the crest of the ridge, buccal or lingual to the ridge. Teeth should be placed as dictated by the musculature, and this will vary for different patients. Positioning artificial teeth in the neutral zone achieves two objectives.First, the teeth will not interfere with the normal muscle function, and second, the forces exerted by the musculature against the dentures are more favorable for stability and retention.     

Using tissue conditioner material in neutral zone technique

The looseand unstable lower complete denture is a common problem faced by denture patients. One method used to solve this problem is the neutral zone technique. The neutral zone is the area where the displacing forces of the lips, cheeks and tongue are in balance. In the clinical report presented here, a severely resorbed lower alveolar ridge was treated by determining the neutral zone with tissue conditioner material (Visco-gel, Dentsply Ltd., Weybridge, U.K.). The neutral zone approach with Visco-gel is a more practical and economically feasible treatment for patients having atrophic mandibular ridge.     

中性区技术在义齿制作中的应用

中性区技术能帮助提高全口义齿,特别是下颌义齿的稳定性,尤其适用于牙槽嵴严重吸收患者全口义齿的制作,但国内尚未广泛应用。本文通过报道1例采用此种技术制作义齿的病例,介绍中性区技术,并改良了利用发音塑形的方法,结合文献对中性区技术在国内临床的应用进行讨论。     

The impression tray--an important factor in impression precision.

The flow behaviour of impression materials during impression taking was first investigated, and reference made to the pressure which occurs in the compound. Individual trays of plastic and shellac-bases which could be softened by heating, and a cold-curing tray material were then also examined: (1) for their distortion by slight loads upon the tray walls; (2) for their ability to retain their shape when stored, and (3) their distortion when temporarily warmed to body temperature. It was found that no tray materials, although graded according to type and thickness, can be considered rigid under experimental conditions, since distortions which were in some cases considerable could be measured. In laboratory experiments, the behaviour of the tray was then measured while taking impressions of models and the precision of the impression was examined at the same time. This confirmed the suspicion that the precision of an impression is to a considerable extent related to the tray material used. The smallest alterations were found when using cold-curing plastic material of a sufficient thickness (greater than 2 mm).     

中立区与齿槽嵴顶关系的深入研究

通过测量１０名上下无牙颌患者（双颌组）和１０名上颌无牙颌患者（单颌组）的齿槽弓和中立区堤弓的宽度，以及堤平面与堤长轴的夹角，深入研究中立区与齿槽嵴顶的关系。结果发现，单颌组尖牙及前磨牙区齿槽弓明显窄于双颌组；单颌组中立区较双颌组接近齿槽嵴顶；中立区位置与齿槽嵴顶在尖牙区差异较大，在磨牙区差异较小，在前磨牙区基本一致。该结果可为双颌和单颌总义齿排牙提供有益的借鉴。     

The position of the neutral zone in relation to the alveolar ridge.

Included in this study are 21 edentulous patients. They were classified according to their period of edentulousness into two groups. One group was edentulous from 1/2 to 2 years. The other group was edentulous for more than 2 years. The neutral zone (NZ) was located for each patient by using record bases, and an impression compound as the occlusion rim. A 30-gauge stainless steel wire was adapted along the center of the alveolar ridge on the final cast. A 24-gauge stainless steel wire was adapted and stabilized over the center of each occlusion rim. An occlusal view radiograph was obtained of each recording base and its cast. Each film was placed in a viewing box and the relationship between the images of the two wires in the buccolingual direction was studied in the anterior, premolar, and molar regions on the left and right sides. Where the two images coincided a zero score was given. In the case of buccal location a plus scores was given, and where there was a lingual location of the (NZ), a minus score was given. All measures were taken in millimeters. Statistical analysis was performed between the two groups. The longer the period of edentulousness, the more buccally/lingually located was the NZ.