The dimensional accuracy of four impression techniques with the use of addition silicone impression materials

OBJECTIVE: The aim of this study was to assess the influence of impression technique selection on the dimensional accuracy of the produced casts. METHODOLOGY: Four impression techniques (single-stage, two-stage, monophase, and heavy/wash technique) were used to make addition silicone impressions of a phantom head maxillary jaw. The impression materials used were Aquasil, Extrude, and Imprint. Measurements on casts were made for the inter-abutment distances to assess dimensional accuracy. RESULTS: There was a significant difference (p < 0.05) for the anteroposterior distances with the single-stage technique. The crossarch distances were slightly increased compared with the master model for all techniques, but significant statistical differences were only recorded for the single-stage technique and the monophase technique. The monophase technique demonstrated irregular results. The heavy/wash technique showed no significant differences for all the measurements compared with the standard model. CONCLUSION: The results suggest that the selection of impression technique is an important factor that can affect the dimensional accuracy of the subsequent models which are used for indirect restorations.     

The use of polydimethylsiloxane as a custom impression tray

A technique for fabrication and use of a flexible polydimethylsiloxane impression tray for final impressions of maxillectomy patients has been described.     

Distortion of disposable plastic stock trays when used with putty vinyl polysiloxane impression materials

STATEMENT OF PROBLEM: Impressions are made using high-viscosity putty vinyl polysiloxane impression materials in conjunction with disposable plastic stock trays. The impression materials have been shown to be dimensionally stable. However, it remains unclear if the disposable plastic stock trays are rigid enough to resist deformation thus yielding potentially unreliable results. PURPOSE: This study evaluated the rigidity and ability to resist deformation of 6 commercially available disposable plastic stock trays and 1 metal stock tray when used in conjunction with a high-viscosity vinyl polysiloxane impression material. MATERIAL AND METHODS: Ten impressions were made with 1 putty vinyl polysiloxane material (Reprosil Putty) using each of the 6 tested disposable plastic stock trays, Sani-Trays (perforated), Sani-Trays (nonperforated), COE Disposable Spacer Tray (perforated), COE Disposable Spacer Tray (nonperforated), Bosworth Tray-Aways (perforated), Track-it Trays (perforated), and 1 metal stock tray (nonperforated), Cadco Dental Products, as a control on a mandibular plastic model. The dimensions of the tray in cross section at the mandibular right first molar area were measured before, during, and after the impression procedures with an electronic digital caliper. The cross-arch dimensions of the tray were measured at similar intervals. One examiner made all measurements and each measurement was repeatable within +/-0.01 mm. A split plot repeated measures analysis of variance (ANOVA) was performed and 2-sided P -values were calculated (alpha=.05). RESULTS: The results indicated that the disposable plastic trays tested were not sufficiently rigid to resist deformation when used with very high-viscosity putty material. Metal stock trays showed significantly less change in cross-arch dimension than plastic trays (F(1.68)=11.25, P =.001). Metal stock trays also showed significantly less change in cross-sectional arch dimension than plastic trays (F(1.68)=15.15, P<.001). CONCLUSION: When disposable plastic stock trays were tested in conjunction with very high-viscosity impression materials there was distortion of the tray both across the arch and in cross section.     

Clinical outcome of the altered cast impression procedure compared with use of a one-piece cast

STATEMENT OF THE PROBLEM: An altered cast impression procedure to improve the support of distal extension removable partial dentures is widely taught, but not often used in dental practice. PURPOSE: The purpose of this study was to determine the efficacy of an altered cast compared to a one-piece cast with regard to base support, abutment health, and patient comfort over time. MATERIAL AND METHODS: Seventy-two patients receiving a mandibular bilateral distal extension removable partial denture were assigned randomly for treatment using either a one-piece or an altered cast. All impressions and associated laboratory procedures were made by one investigator. A second investigator evaluated extension, support, and adaptation of the denture bases by observation of border length and lifting of the indirect retainer from its seat. The space between the soft tissues and the base when the framework was related to the teeth was measured cross-sectionally at half the length of the denture base. Mobility, gingival index, and sulcus depths at 6 locations around each abutment tooth were recorded at insertion and again 1 year later. Chi-square tests were used to evaluate differences between the treatment groups (alpha=.05). RESULTS: There was 0.15 mm less space between the ridge crest and base in the altered cast group (P<.01), and underextension of the base occurred only in the one-piece cast group (P=.01). At insertion, no tissue-ward movement was observed in 85% of the prostheses when anterior-posterior rotation was attempted. Fifteen subjects (21%) were lost to recall at 1 year, but they were distributed equally between the 2 groups. Of the remaining 57 prostheses, 42% exhibited decreased base support and 33% had increased gingival inflammation; the deepest probing depth decreased in 61%, mobility decreased or remained the same in 80% of the direct abutments, and 88% of the subjects were satisfied. None of these findings were related to the impression procedure. CONCLUSION: The altered cast impression procedure does not offer significant advantages over the one-piece cast, provided the standards used in this study are met. These include a completely extended impression, use of magnification to adjust and ensure complete seating of the framework, and coverage of the retromolar pad and buccal shelf by the base.     

Sterilization of impression materials for use in the surgical operating room

In this study, 30 samples of one type of irreversible hydrocolloid powder and 30 samples of one type of plaster material were effectively sterilized using gaseous ethylene oxide. The procedure did not adversely affect the setting time or the dimensional accuracy of the hydrocolloid material.     

一种复方消毒喷雾剂对印模及石膏的消毒效果观察

目的观察一种以三氯羟基二苯醚为主要杀菌成分的复方消毒喷雾剂对染菌藻酸盐印模及超硬石膏模型的消毒效果。方法在藻酸盐印模和超硬石膏模型表面分别均匀涂布金黄色葡萄球菌、大肠杆菌、白假丝酵母菌、变异链球菌和枯草杆菌黑色变种芽孢悬液后,采用以三氯羟基二苯醚为主要成分的不同质量浓度的复方消毒喷雾剂（实验组）和碘伏消毒液（对照组）喷涂消毒5、10和15 min,然后进行取样、接种、培养后进行菌落形成单位计数,以杀灭对数值对消毒效果进行评价。结果3 000 mg·L-1复方消毒喷雾剂作用10 min以上可以有效杀灭印模和石膏表面的所有微生物。在作用时间相同情况下,同质量浓度消毒液对印模和石膏表面的消毒效果有统计学差异（P＝0.000）,对印模表面的消毒效果要优于石膏表面。结论以三氯羟基二苯醚为主要成分的复方消毒喷雾剂是有效的印模及模型消毒剂。     

Secondary softening of modeling compound for copper band impressions

A technique for secondary softening compound when making copper band/compound impressions was presented. The advantages of the technique include (1) increased working time; (2) greater precision, especially at the cervical part of the preparation; and (3) better temperature control.