Removable Partial Denture Education in U.S. Dental Schools

PURPOSE: A survey of U.S. dental schools was conducted in 2001 to determine the curricular structure, techniques, and materials used in predoctoral clinical removable partial denture (RPD) programs. MATERIALS AND METHODS: The questionnaire was mailed to the chairperson of the prosthodontic/restorative departments of 54 U.S. dental schools. Of these, 44 schools returned the completed survey, resulting in a response rate of 82%. RESULTS: Results from this survey show that a large majority of schools are using similar materials in clinical RPDs; for instance, using modeling compound for border molding final impression trays (61%) and using a semi-adjustable articulator for mounting preliminary casts (90%) and final casts (98%). In addition, a large majority of schools are using similar techniques in clinical RPDs, such as border molding the edentulous areas of the final impression tray (80%) and using the altered cast impression technique (59%). A set post-insertion protocol is present for patients who receive partial dentures in the majority of the schools (93%). Only 25% of schools reported incorporating new educational materials such as the use of Portrait artificial teeth at the predoctoral level. Eighteen percent of schools are allowing students to graduate without a set number of RPD clinical requirements as has been traditionally the case. CONCLUSIONS: Predoctoral clinical RPD programs vary from school to school, yet a large percentage of schools agree on many topics.     

A Survey of U.S. Prosthodontists and Dental Schools on the Current Materials and Methods for Final Impressions for Complete Denture Prosthodontics

PURPOSE: The purpose of this study was to survey members of The American College of Prosthodontists (ACP) to evaluate current materials and methods for final impressions for complete denture prosthodontics in the United States. In addition, those methods were compared with methods and materials taught in U.S. dental schools via a second survey sent to the chairpersons of prosthodontic/restorative departments. MATERIALS AND METHODS: An anonymous questionnaire was mailed to all 1762 active ACP members in the United States in 2003. A slightly modified questionnaire was also distributed to chairpersons of prosthodontic/restorative departments in the 54 U.S. dental schools. Data analysis was performed via frequency distribution and chi-square statistics. RESULTS: Nine hundred and forty-five questionnaires were returned by members of the ACP (54% return rate) and 42 questionnaires were returned by the U.S. dental schools (78% return rate). The majority of the reporting prosthodontists (88%) and dental schools (98%) use a border-molded custom tray for final impressions for complete denture prosthodontics. The most popular material for border molding was plastic modeling compound (67% of reporting ACP members, and 95% of the responding dental schools). Variability of the materials used for final impressions was observed, with the most popular materials being polyvinylsiloxane for the ACP members (36%) and polysulfide for the dental schools (64%). Statistically significant differences were found in the materials used for border molding by prosthodontists based on the time elapsed since completion of prosthodontic training. No differences were found in the materials used for impression of edentulous arches based on years of experience. Geographic location did not influence the materials and methods used by prosthodontists for complete denture final impressions. CONCLUSIONS: There was variability of the materials and techniques used for final impressions by ACP members and dental schools; however, overall there was an agreement on the materials and techniques used by prosthodontists and dental schools. Distinct trends for increasing use of polyvinylsiloxane and polyether for border molding procedures and impressions of edentulous arches were observed both in members of the ACP and in the U.S. dental schools.     

The Results of a Brief Survey of Complete Denture Prosthodontic Techniques in Predoctoral Programs in North American Dental Schools

A brief mail survey of North American dental schools was undertaken to ascertain the current techniques in complete denture prosthodontics regarding preliminary and final impressions, record bases, and denture teeth. Of the 64 schools surveyed, 54 responded (84%). Seventy-four percent of the respondents used only irreversible hydrocolloid (alginate) for their preliminary impressions; 15% used only modeling plastic impression compound. Eighty-one percent used only modeling plastic impression compound for border molding of the final impression tray; 7% used only polyether impression material. Forty-eight percent used only polysulfide rubber (PR) impression material for their final impression material; 4% used only polyether impression material. Only 1 school still used shellac as one of its materials for record bases. Thirty-five percent used only Triad; 35% used only acrylic resin; 24% used both of these materials. Thirteen percent of responding schools used only nonanatomic teeth. The majority (54%) used all three options (nonanatomic, semianatomic, and anatomic). Eleven percent used lingualized occlusion. As compared with a survey performed in 1985, the use of irreversible hydrocolloid as a preliminary impression material, the use of visible light-cured resins for record bases, and the use of anatomic teeth have increased. The use of plastic impression compound for border molding and PR as the final impression material has largely remained the same.     

Effect of different labio-lingual spaces in tray designs on the displacement of and pressure against a mobile tooth

Summary  The present study aimed to examine the effect of custom tray designs on the displacement of mobile tooth and local impression pressures during the impression procedure, using partially edentulous simulation models with six anterior teeth containing a mobile tooth prepared in previous studies. The custom trays were designed by altering the thickness of the respective spaces on the labial and lingual sides of the remaining tooth arch. In previous studies, the mobile tooth was displaced in the labial direction and local impression pressures of the mobile tooth were greater against the lingual side than the labial side for all custom tray designs. Furthermore, the custom trays perforated with holes on the lingual side were effective to reduce mobile tooth displacement, labial and lingual impression pressures against the mobile tooth, and the differences between them. Therefore, the present study was performed focusing on the labial and lingual thickness of spaces in custom tray designs. It was found that mobile tooth displacement, labial and lingual impression pressures against the mobile teeth and their differences were less in trays with spaces >3·0 mm thick on both the labial and lingual sides, but markedly greater in trays with a 1·5 mm-thick space on the labial side. These results indicate that the thickness of spaces on the labial side in the tray should not be reduced to prevent mobile tooth displacement.     

Complete Denture Education in U.S. Dental Schools

PURPOSE: In 2001, a survey of U.S. dental schools was conducted to determine curricular content, teaching philosophies, and techniques used in clinical complete denture programs. MATERIALS AND METHODS: The questionnaire was mailed to the chairperson of the prosthodontic/restorative department of 54 U.S. dental schools. Of these, 44 schools returned the completed survey, resulting in a response rate of 82%. The mean, median, and range of responses were computed where applicable. RESULTS: Results from this survey show that a large majority of schools are using similar materials in clinical complete denture treatment: irreversible hydrocolloid for preliminary impression (87%); light-cured composite resin for record base fabrication (70%); a semiadjustable articulator (98%); and semianatomic posterior tooth form used exclusively or in combination with other tooth forms (75%). In addition, a large majority of schools are using similar techniques in clinical complete denture treatment: use of a protrusive record (80%); use of extra-oral measurements, speech, and esthetics for establishing the occlusal vertical dimension (59%); use of the conventional compression molding method for processing complete dentures (82%); occlusal equilibration and face-bow preservation (75%); and the clinical remount procedure (91%). A quality control program is present for cases sent to and returned from the laboratory in 73% and 84% of responding schools, respectively. CONCLUSIONS: Clinical complete denture predoctoral programs vary from school to school, yet a large percentage of schools agree on many topics. Only 55% of schools reported incorporating new educational materials such as the use of dental implants and treatment of patients with implant-retained overdentures at the predoctoral level. Sixteen percent are allowing students to graduate without a set number of required complete dentures as has traditionally been the case. Sixteen percent are using newer techniques such as injection molding and microwave processing technique in addition to the conventional processing technique.     

A retrospective comparison of two definitive impression techniques and their associated postinsertion adjustments in complete denture prosthodontics

PURPOSE: To compare the number of postinsertion adjustment visits required by edentulous patients whose dentures were made from border-molded definitive impressions using modeling plastic impression compound (traditional technique) with patients whose dentures were made from border-molded definitive impressions using heavy-body vinyl polysiloxane impression material. MATERIALS AND METHODS: In this retrospective clinical study, 78 patients were treated with the traditional technique (custom impression trays border molded with gray modeling plastic impression compound) and 78 were treated with the modified technique (custom impression trays border molded with heavy-body vinyl polysiloxane impression material). In both techniques, definitive wash impressions were made with light-body vinyl polysiloxane impression material. Postinsertion visits were quantified for 1 year after the dentures were inserted. RESULTS: The average number of adjustment visits for patients treated with the traditional technique was 2.68. The average number of adjustment visits for patients treated with the modified technique was 2.68. The data were compared using Student t tests. There was no significant difference in the number of adjustments required for patients whose dentures were made with either technique (t = 0.000, p = 1.00). There was no significant difference in the number of post-insertion visits required by patients from either population. CONCLUSIONS: Within the limitations of this clinical study, border-molding custom denture impression trays with vinyl polysiloxane impression material provided similar results in terms of postinsertion visits for one year as compared to dentures made from impressions border molded with modeling plastic impression compound.     

Modified functional impression technique for complete dentures

This report describes the use of a removable acrylic resin tray handle that can be easily attached to custom impression trays to produce an improved peripheral sealing zone. This device can be indicated to develop functional impressions for complete dentures using the patient-conducted muscular motion technique. In upper trays, the handle is fixed in the midline with acrylic resin, while in lower trays the centrally positioned handle is removed before border molding. This removable handle allows patient's suction and free tongue movements. Final impression is carried out in two stages: peripheral sealing (low fusion compound) and recording of the main supporting region of the denture (zinc oxide and eugenol paste). All border records are obtained from the patient's own movements (handle suction and tongue motion). The removable handle is simple to use, is reusable, can be adapted to any individual acrylic resin trays and allows accurate registration of the peripheral sealing zone (border tissues).     

A Technique for Border Molding Edentulous Impressions Using Vinyl Polysioxane Material

A technique for making selective tissue placement final impressions for complete dentures using vinyl polysiloxane and custom trays with peripheral relief is presented. This technique is an alternative to the conventional method of border molding using modeling plastic impression compound.     

Linear dimensional accuracy of a polyvinyl siloxane of varying viscosities using different impression techniques

Abstract Aim: The present study is an in vitro study to evaluate the linear dimensional accuracy of commercially available polyvinyl siloxanes of varying viscosities using different impression techniques. Methods: Different impression techniques used were: (a) putty wash, with a two‐step technique with polyethylene spacer, using a stock tray; (b) putty wash, with a one‐step technique, using a stock tray; (c) single‐mix technique, utilizing medium viscosity in a custom tray; and (d) multiple‐mix technique, utilizing a heavy‐ and low‐viscosity combination in a custom tray. For each technique, 10 impressions were made of a metallic maxillary dentulous master model. Results: The result of this study dictates that a heavy‐ and low‐viscosity combination, double‐mix technique in a custom tray produced an accurate result in all dimensions, followed by the single‐mix technique, utilizing medium viscosity in a custom tray, and the putty wash two‐step technique with polyethylene spacer, using a stock tray. Group 2 putty wash, one‐step, simultaneous technique produced the least accurate result in all dimensions. Conclusion: The putty wash two‐step techniques were found to be as accurate as the multiple‐mix technique, utilizing a heavy‐ and low‐viscosity combination in a custom tray, and the single‐mix technique, utilizing medium viscosity in a custom tray. Making custom trays is time consuming and costly.     

Accuracy of open tray implant impressions: an in vitro comparison of stock versus custom trays

STATEMENT OF PROBLEM: The accuracy of an implant fixture-level impression is affected by the type of impression tray used. PURPOSE: The purpose of this in vitro study was to investigate the accuracy of open tray implant impressions comparing polycarbonate stock impression trays and rigid custom-made impression trays to make implant fixture-level impressions. MATERIAL AND METHODS: Gold cylinder pairs, splinted by gold bars (reference frameworks) were constructed on an aluminum typodont. Polyether impressions were made of 2 pairs of Br?nemark 3.75-mm diameter fixtures mounted in an aluminium typodont, with 3 stock impression trays, 3 close-fit custom trays, and 3 spaced custom impression trays, by use of an open tray technique. The casts produced were assessed for accuracy by attaching the reference frameworks with alternate single screws and measuring the vertical fit discrepancy of these reference frameworks to the analogs within the working cast using a traveling microscope. Comparison of gap dimensions by tray type was performed with a nonparametric Kruskal-Wallis analysis of variance (ANOVA) followed by pair-wise Mann-Whitney U tests. To adjust for multiple comparisons in the post-ANOVA contrasts (P<.02). Comparison of gap dimensions between anterior and posterior regions were performed with Mann-Whitney U tests (P <.05). RESULTS: The results showed that the mean fit accuracy, as measured by vertical fit discrepancy, of casts from the stock trays (23 +/- 20 microm) were statistically significantly less (P<.001) than the spaced custom trays (12 +/- 10 microm) or close fit custom trays (11 +/- 10 microm). The difference in median gap size for analogs with a 20-mm separation was 10 microm. CONCLUSION: Within the limits of this in vitro study, rigid custom trays produced significantly more accurate impressions than the polycarbonate stock trays. The stock trays used in this study could not produce accurate impressions consistently. For analogs with a 20-mm separation, there was a difference in medians of 10 microm in accuracy between the stock and custom trays.     

Retention of alginate impression material using a polyester fiber-mat textile

To ensure accuracy, alginate, impression materials must be firmly retained in the impression tray. This short report compares the effectiveness of perforated trays with a newly developed self-adhesive polyester fibre mat material which can be used to line the inner surface of stock and custom made impression trays. In all cases, the fibre mat was much more effective as a retention medium when compared with perforations. Also, small perforations proved more effective than larger ones for alginate retention.     

The use of light-cured acrylic resin for custom trays by undergraduate dental students: a survey

INTRODUCTION: It is unknown how the use of a light-cured acrylic resin is appreciated over the traditional chemically cured resins for the construction of custom trays in a teaching environment. OBJECTIVE: To evaluate the acceptance of light-cured acrylic resin for custom trays by dental students. METHOD: A questionnaire addressing the use and handling properties of both light-cured (Megatray, Megadent, Germany) and chemically-cured (Excel, Wright Health Group, UK) custom tray materials was distributed amongst undergraduate dental students of the University of the Western Cape. RESULTS: Of a total of 196 dental students, 38 were absent on the day of the survey. Of the 158 questionnaires that were distributed and returned, 18 did not meet the inclusion criteria and 1 person chose not to participate. Of the 139 participating students, 98 were in 4th year, 41 in 5th year. With regards to the light-cured acrylic custom tray material, 77% used it most often, 64% said it saved time and 62 % said that it was easier to handle. Fifty two percent indicated that both types of materials should be taught in undergraduate training, 26% preferred the light-cured acrylic resin custom tray material, 20% suggested that only the light-cured resin be used and no one suggested the chemically-cured resin exclusively. CONCLUSIONS: Most undergraduate students positively accepted the light-cured resin, but training in the use of both materials was recommended.     

Implant overdenture impressions using a dynamic impression concept

A dynamic impression is a functional impression that records the functional movement of the patient''s own muscle and muscle attachment. This process reduces the number of random factors. This article describes a method for making a special tray using a dynamic impression concept that was made from provisional dentures used for implant healing. The individual tray is used to make a wash-impression to record the features of the mucosa in detail. The main advantage of this technique is that it provides a functional relationship of the implant components to the supporting tissues without overextension because provisional denture had been used for 2 months and the border length of individual tray was nearly the same as that of provisional denture. The delivery of the prosthesis constructed using this impression technique is time-saving because there is no need for border molding and there are fewer post-insertion appliance adjustments.     

数字化设计个别托盘在研究生临床实习中的应用评价

目的： 以全口义齿个别托盘为例,探讨在口腔医学专业研究生临床实习中应用数字化辅助设计（CAD）的教学效果。方法： 选取2019年1月—2019年5月于同济大学附属口腔医院修复科实习的27名研究生作为研究对象,获得知情同意后,进行传统手工方法及数字化方法设计制作个别托盘的理论教学和操作示范,然后分别对其进行操作考核,记录完成个别托盘所需的操作时间,并对托盘边缘延伸位置做出评价。操作完成后填写问卷调查表。采用 SPSS 22.0 软件包对数据进行统计学分析。结果： CAD在操作时间、托盘边缘位置及学生使用偏好上均显著优于传统手工方法（P<0.05）。结论： CAD有助于学生掌握个别托盘制作的理论知识和数字化操作流程,建议在现有口腔医学教育中加入数字化相关内容。     

Evaluation of a rubber-base impression material.

A laboratory experiment has been described that utilized materials found in most dental offices and that was designed to evaluate a distinctly different polysulfide impression material. In this experiment the largest duplicating errors were produced with use of the stock tray and single-mix technique recommended by the manufacturer. This study therefore supports the use of the custom tray and double-mix technique for dental duplication procedures utilizing Neo-Plex impression material. Further investigation is necessary before stock trays and single-mix techniques can be recommended for routine use in fixed prosthodontics.     

Dimensional accuracy of dental casts: Influence of tray material, impression material, and time

PURPOSE: This study evaluated the influence on dimensional accuracy of dental casts made with different types of trays and impression materials and poured at different and multiple times. MATERIALS AND METHODS: Two types of stock trays (plastic stock tray, perforated metal stock tray) and 4 types of custom tray materials (autopolymerizing acrylic resin, thermoplastic resin, and 2 types of light-polymerized acrylic resins) were used with 2 types of impression materials (addition polymerizing silicone and polyether), to make impressions of a metal master model. Each tray and impression material was used to make 5 impressions. Casts were made by multiple pourings at 30 minutes, 6 hours, 24 hours, and 30 days after impression making. Using a measuring microscope, 12 distances were calculated based on measurements of 8 reference points. The absolute value of the difference of each measurement was calculated, as was the corresponding measurement on the master model. A Bayesian model using a simple noninformative prior was used to analyze these data. RESULTS: Statistical differences within 6 microm were found only with thermoplastic resin tray material for addition silicone, and for thermoplastic resin tray material and 1 type of light-polymerized acrylic resin for polyether. Neither stock trays nor custom trays contributed to the differences in accuracy of the casts. All deviations in casts made with silicone impression material were within a clinically acceptable range. For the polyether, distortions occurred that were clinically unacceptable. Impressions made from polyether distorted over time. Silicone impression material has dimensional stability up to 30 days. CONCLUSION: Accurate casts can be made with either stock trays or custom trays. An impression made from polyether should be poured only once and within 24 hours after impression making, because of the distortion of the material over time. Silicone impression material has better dimensional stability than polyether. .     

Pressure Generated on a Simulated Mandibular Oral Analog by Impression Materials in Custom Trays of Different Design

PURPOSE: The purpose was to measure the pressure exerted under a simulated mandibular edentulous impression at different locations using commonly used impression materials and four impression tray configurations. MATERIALS AND METHODS: This study was performed using an oral analog that simulated an edentulous mandibular arch. Three pressure transducers were embedded in the oral analog-one pressure transducer in the anterior ridge area, and the other two in the right and left buccal shelves. Four configurations of custom trays were fabricated: trays with no relief, with and without holes; and trays with relief, with and without holes. The impression materials tested were light body polysulfide, light body vinyl polysiloxane, medium body vinyl polysiloxane, and irreversible hydrocolloid. The custom tray and the oral analog were mounted using a reline jig, and a Satec universal testing machine was used to apply a constant pressure of 1 kg/cm(2) over a period of 5 minutes on the loaded custom tray. Eighty impressions for the 16 groups (n = 5) were made, and pressures were recorded every 10 seconds. Factorial ANOVA and Tukey Multiple Comparison Test were used to analyze the results (p < 0.05). RESULTS: A significant difference was found in the pressure produced using different impression materials. Irreversible hydrocolloid and medium body vinyl polysiloxane produced significantly higher pressure than light body polysulfide and light body vinyl polysiloxane impression materials. The presence of holes and/or relief significantly altered the magnitude of pressure produced by irreversible hydrocolloid and medium body vinyl polysiloxane but not light body polysulfide and light body vinyl polysiloxane. CONCLUSION: All impression materials produced pressure during simulated mandibular edentulous impression making. For making mandibular edentulous impressions, low-viscosity impression materials-light body polysulfide and light body vinyl polysiloxane-are recommended. Tray modification was not important in changing the amount of pressure produced for the low-viscosity impression materials.     

Duplication of interim speech aid for definitive impression tray fabrication.

A wax tray is stable and easily relieved if overextended. Unusual tray undercuts or angles needed for the partial resection patient need not be eliminated before the impression procedure. Relief of these undercuts is necessary with acrylic resin trays to ensure separation from the final stone cast. Because the wax tray is separated easily from the prosthesis during the boil-out, it is not necessary to "burn" or grind acrylic resin from the framework. The tray shape is duplicated from the existing interim prosthesis on the nasopharyngeal and oropharyngeal side. An arbitrarily shaped acrylic resin tray may be grossly overextended and require time-consuming clinical adjustments. An underextended tray on the nasopharyngeal side will not carry or support the impression material around or through the residual soft palate remnant. A tray that closely approximates the final prosthesis will allow use of a tissue conditioner final impression without need for border molding (Fig. 2). Duplicating the oropharyngeal side of the interim speech aid duplicates the previously established plane that is compatible with the tongue. The author has used this technique successfully for eight total and five partial soft palate resections. A cleft palate speech aid prosthesis has also been made with this technique.     

A laboratory study of dimensional changes for three elastomeric impression materials using custom and stock trays

Clinical success of fixed prosthodontic procedures is dependent in part upon the dimensional accuracy of elastomeric impression materials and impression procedures. Three elastomeric impression materials were used in custom and stock trays to determine the accuracy of impressions taken from an experimental stainless steel model representing premolar and molar bridge abutment preparations. Horizontal and vertical individual abutment and interabutment dimensions were measured on die stone replicas, and the measurements compared with those obtained from stainless steel master models. The results of this study demonstrate polysulphide is the least accurate impression material for both vertical and horizontal individual abutment dimensions. However, for interabutment horizontal dimensions, no statistical differences were noted between impression material types when using a custom tray. Stock trays produced unreliable results for all the materials tested.     

Use of Implant‐Supported Custom Milled Impression Copings to Capture Soft‐Tissue Contours and Incisal Guidance

A technique is presented where a custom milled impression coping is used to replicate the clinically established anterior incisal guidance to the definitive prosthesis when multiple implants are restored in the esthetic zone. A conventional impression is initially made, then the stone cast is scanned, and a digitally designed custom screw‐retained, implant‐supported interim prosthesis is milled from a polymethylmethacrylate (PMMA) billet. This is aimed to digitally design the pontic areas, contour the gingival soft tissue, and establish an anterior incisal guidance. A custom milled impression coping (CMIC) is then fabricated. The CMIC has contours similar to the contours of the interim prosthesis and is fabricated from a PMMA billet. Titanium inserts are placed in the interim prosthesis and the CMIC. The CMIC is inserted intraorally and used for the final impression by using a custom tray and by following the open tray impression protocol. With the proposed technique, the exact contours of the digitally designed and clinically verified interim prosthesis are used to fabricate the definitive restoration.