Working Cast Research Articles

Effect of the Inter-Tooth Distance and Proximal Axial Wall Height of Prepared Teeth on the Scanning Accuracy of Intraoral Scanners.

This study aimed to analyze the effect of the height of the proximal axial wall of the prepared tooth and the distance between the adjacent tooth and the prepared tooth on the scan accuracy of intraoral scanners. Ten working casts with maxillary first molars prepared to receive zirconia crowns were randomly obtained from a dental clinic. Each of the 10 casts was scanned using two intraoral scanners (i700; MEDIT and CS3600; Carestream; computer-aided design [CAD] test model, CTM; N = 15 per working cast) 15 times per scanner. Individual dies of the prepared teeth were fabricated, and high-precision scan data were acquired using a laboratory scanner (CAD reference model, CRM; N = 1). CTMs were aligned relative to the prepared tooth of CRMs by using three-dimensional inspection software (Ver 2018.1.0; Control X; 3D Systems). Data were statistically analyzed using an independent t-test and one-way analysis of variance for between-group comparisons (α = 0.05). The inaccuracy in the proximal regions (mesial or distal) of the prepared tooth was higher than that in the buccal and lingual regions (p < 0.05). The scan accuracy was not correlated with the variables when the distance between the adjacent tooth and the prepared tooth was ≥2.0 mm and the height of the proximal axial wall of the prepared tooth was <3.0 mm (p > 0.05). Therefore, an excellent scan accuracy can be obtained using an intraoral scanner when the distance between the adjacent tooth and the prepared tooth is ≥2.0 mm and the proximal axial wall height of the prepared tooth is <3.0 mm.

Accuracy and Retention of Molding Plates Used for Infants with Cleft Lip and Palate Fabricated from Different Materials: A Cross-Sectional Clinical Study.

The study aimed to comparatively assess the accuracy and retention of molding plates made of polyethylene terephthalate modified with glycol (PET-G) and polymethyl methacrylate (PMMA) materials, while also investigating the effect of adhesive addition on retention. A cross-sectional clinical study. The study included 30 infants diagnosed with non-syndromic cleft lip and palate (16 unilateral, 14 bilateral). Two molding plates were fabricated for each infant, and their accuracy and retention were evaluated. The data were analyzed using independent t-tests, Mann-Whitney U tests, and Wilcoxon rank tests. Accuracy: The accuracy of the molding plates was assessed by measuring the virtual gap between the inner surface of the plates and their working cast using Exocad software. The accuracy was evaluated in different regions (anterior, middle, and posterior) and compared between PET-G and PMMA materials. Retention: The retention of the molding plates was measured using a digital force gauge, which recorded the force required to dislodge the plates from the infant's mouth. The retention was compared between PET-G and PMMA materials, as well as the effect of adhesive addition on retention. Overall adaptation; PET-G plates showed a significantly smaller gap (mean= 0.264 ±0.106) compared to PMMA (mean= 0.362 ±0.130). Region-specific adaptation: PET-G plates demonstrated better accuracy in all regions (means of anterior =0.246, middle =0.262, posterior =0.282 µm). Significant differences in accuracy were observed in the middle and posterior regions compared to PMMA. Retention assessment revealed that the PET-G groups (with or without adhesive) exhibited significantly higher retention compared to the PMMA groups (P<0.01). PET-G plates demonstrated superior accuracy and retention compared to PMMA, with a significant difference observed in both accuracy and retention. Furthermore, the addition of denture adhesive had a positive effect on retention for both materials.

Occlusal contact and clearance of posterior implant-supported single crowns designed by two different methods: a self-controlled study

BackgroundPrecise occlusal design of implant-supported fixed prostheses is difficult to achieve by the conventional wax-up method, often requiring chairside adjustments. The computer-aided design (CAD) method is promising. This study aims to compare the occlusal contacts and clearance of posterior implant-supported single crowns designed by the CAD and conventional methods.MethodsSample size calculation indicated fourteen samples per group. Two sets of type-IV plaster casts with a single implant analog inserted in the posterior teeth region were mounted as master casts in a mechanical articulator in maximal intercuspal position (MIP). Seven working cast sets were obtained from each master cast by a closed tray technique, and mounted in MIP. Two implant-supported single crowns were designed with an occlusal clearance to achieve light occlusal contact in each working cast set by CAD and conventional method, separately. For the CAD group, the crown was designed in digital models obtained by scanning the working casts. For the conventional group, wax-up of the crown was prepared on the working casts and scanned to generate a STL file. In the working and master casts, mean and minimum occlusal clearances in the designed occlusal contact area of the both finished prostheses were calculated using the occlusal clearance (OC) and occlusal record (OR) method. The prostheses’ occlusion was evaluated in master casts.ResultsFor the evaluation in the working casts, both design methods had similar mean occlusal clearances by the OC method (195.4 ± 43.8 vs. 179.8 ± 41.8 μm; P = 0.300), while CAD group resulted in a significantly larger minimum occlusal clearance in the designed occlusal contact area (139.5 ± 52.3 vs. 99.8 ± 43.8 μm; P = 0.043). Both design methods had similar mean and minimum occlusal clearances by the OR method (P > 0.05). For the evaluation in the master casts, both design techniques had similar mean and minimum occlusal clearances, number and distribution of occlusal contacts, and lateral interference ratios (P > 0.05).ConclusionOcclusal contact and clearance of posterior implant-supported single crowns designed by the CAD method can be at least as good as those designed by the conventional wax-up method.

HIP effect on microporosity value of large-sized working cast blades sections of IN-92-5A alloy

The formation of a dense cast billet is a basic requirement for products made of heat-resistant alloys. Based on the comparison of research results, the use of hot isostatic pressing (hereinafter – HIP) for castings made of IN-792-5A alloy. Work on selection of technological regimes to reduce the microporosity content in the body of cast billet has been carried out. The object of the research was a cast billet of the working blade of the fourth stage of a high-power gas turbine unit.

Evaluation of The Processing Discrepancies Between Dental and Nondental CAD Software Using The Smoothing Design Tool

Statement of the problem: The advancing computer-aided design/com-puter-aided manufacturing (CAD/CAM) technology has changed the fabrica-tion protocols of fixed prosthodontic restorations dramatically in the last 25 ye-ars. Beside the dental CAD programs open source nondental software have been utilized for prosthodontic purposes. Despite the progress in technology, varying accuracy and precision rates, and lack of standardized workflows are still challenging issues. Objective: No study to the authors' knowledge evaluated the precision of the manually used processing tools of CAD softwares despite the necessity of utilizing multiple tools to design a restoration, thus it was aimed to evaluate the processing discrepancies of smoothing procedures. Materials &amp; Methods: A virtual working cast of a maxilla with six teeth prepared with shoulder finish lines containing irregularities up to 50μm were composed. The irregularities were smoothed manually using the 'brush' tools in the 'sculpt' mode of the DWOS, Blender and Meshmixer softwares. Smoothed virtual working casts were superimposed with the reference virtual working cast. Results: The results of Tukey HSD test revealed significant differences between Meshmixer and Blender (P=0.000), and Meshmixer and DWOS (P=0.000), no significance was found between DWOS and Blender values (P=0.987). Conclusion: The results of the study pointed out that smoothing proce-dure may lead to significant differences in discrepancy values, nondental CAD software can perform smoothing with less discrepancy thus, commencing furt-her studies including multiple users and softwares for the evaluation of diffe-rent design tools seems imperative.

Prosthetic Rehabilitation With Immediate Denture for Periodontally Hopeless Teeth: A Case Report

Background: Patient with poor oral hygiene may have periodontally diseased teeth with hopeless prognosis. The treatment is usually teeth extraction, which may be unpleasant to the patient because it can affect their appearance, speech and stomatognathic systems. It can be prevented by prosthetic rehabilitations with immediate denture. Immediate denture is a prosthodontic appliance to replace teeth and its subsequent structures which is inserted after tooth extractions.&#x0D; Objectives: To observe immediate denture as a prosthetic rehabilitation treatment to replace periodontally hopeless teeth.&#x0D; Case Report: We report a case of a 48-year-old woman with poor oral hygiene and elongated and mobile teeth which affected her chewing, speaking and appearance. The patient denied edentulous period. Patient management included subjective and objective examinations, preprosthetic treatment, impressions taking, diagnostic cast and working cast fabrications. Since try-in was impossible, midline position, tooth size and shade were taken in the early visit. Maxillomandibular relationship was determined and transferred to articulators. Cast modification with spatial modeling method, tooth set-up, wax modelling and insertion was done. Immediate denture was inserted right after the teeth extraction. Post-insertion control was done after one day, one week and one month.&#x0D; Results: The results were esthetically satisfactory with acceptable occlusion, speech, retention and stabilization.&#x0D; Conclusion: Immediate denture can be considered as a predictable treatment to replace hopeless teeth, which will restore esthetics, occlusions and speech with satisfactory retention and stabilization.&#x0D; Keywords: immediate denture, periodontally hopeless teeth, prosthetic rehabilitation

In Vivo Complete-Arch Implant Digital Impressions: Comparison of the Precision of Three Optical Impression Systems.

(1) Multiple in vitro studies reported insufficient accuracy of intraoral scanners (IOSs) for complete-arch multiple implant impression. The aim of the study is to analyze the precision of three IOSs, PIC dental (Pic dental, Iditec North West SL), TRIOS 3 (3Shape), and True Definition (Midmark Corporation) and the influence of several factors in the edentulous complete maxillary and mandibular arch. (2) A fully edentulous patient with eight implants in the maxillary and in the mandibular jaw was selected. Five impressions were taken per system and arch. A suprastructure was designed on each digital working cast. The precision was analyzed comparing each of the 28 distances and seven relative angulations of the abutments of all the designed suprastructures. The descriptive statistics, the Student’s t-test, and the ANOVA test were used to analyze the data (α = 0.05). (3) Significant differences were observed when comparing the IOSs in some of the distances and angulations. (4) The increase in the distance between implants affected the precision of T and TD but not the PIC system. The type of arch did not affect the PIC precision, but the T and TD systems performed worse in the mandibular arch. The system with the best precision was the PIC, followed by TD, and then T.

Study of 3D scanning technologies and scanners in orthodontics

Digital dental scanners are devices which are used to capture optical impression of intra and extra oral structures of the patient’s mouth. The basic principle of digital scanning is based upon optical phenomena like optical triangulation, coherence tomography, parallel confocal imaging and three-dimensional motion videos capturing technique. In orthodontic practice, digital scanners can be successfully used in efficient treatment planning, custom appliance fabrication, clear aligner technology and orthognathic surgical simulation. From digital record keeping, digital cast models, occlusogram, extra oral and intra oral scanners to software for cephalometric analysis, etc. have taken the orthodontic practice to newer heights. Intraoral digital scanner that utilizes the parallel-confocal imaging technology and point and stitch reconstruction to generate digital impressions which are accurate and powder free. Digitization has revolutionized the conventional orthodontics completely. In modern day orthodontic dental practice digital extra-oral and intra-oral scans are used to fabricate working and study cast models that facilitates construction of fixed orthodontic appliances, retainers and custom trays for lingual orthodontic procedures. Digital scanners are the new face of impression making and digital cast fabrication in dentistry. This review aims to identify advantages of utilising digitally scanned impressions over the conventional impression making techniques and application of digital scanning technology pertaining to the speciality of orthodontics in dental practice.

Clinical Study of the Influence of Ambient Light Scanning Conditions on the Accuracy (Trueness and Precision) of an Intraoral Scanner.

To quantify the impact of ambient lighting conditions on the accuracy (trueness and precision) of an intraoral scanner (IOS) when maxillary complete-arch and maxillary right quadrant digital scans were performed in a patient. One complete dentate patient was selected. A complete maxillary arch vinyl polysiloxane impression was obtained and poured using Type IV dental stone. The working cast was digitized using a laboratory scanner (E4 Dental Scanner; 3Shape) and the reference standard tessellation language (STL file) was obtained. Two groups were created based on the extension of the maxillary digital scans performed namely complete-arch (CA group) and right quadrant (RQ) groups. The CA and RQ digital scans of the patient were performed using an IOS (TRIOS 3; 3Shape) with 4 lighting conditions chair light (CL), 10000lux, room light (RL), 1003lux, natural light (NL), 500lux, and no light (ZL), 0lux. Ten digital scans per group at each ambient light settings (CL, RL, NL, and ZL) were consecutively obtained (n = 10). The STLR file was used to analyze the discrepancy between the digitized working cast and digital scans using MeshLab software. Kruskal-Wallis, one-way ANOVA, and pair-wise comparison were used to analyze the data. Significant difference in the trueness and precision values were found across different lighting conditions where RL condition obtained the lowest absolute error compared with the other lighting conditions tested followed by CL, NL, and ZL. On the CA group, RL condition also obtained the best accuracy values, CL and NL conditions performed closely and under ZL condition the mean error presented the highest values. On the RQ group, CL condition presented the lowest absolute error when compared with the other lighting conditions evaluated. A pair-wise multicomparison showed no significant difference between NL and ZL conditions. In all groups, the standard deviation was higher than the mean errors from the control mesh, indicating that the relative precision was low. Light conditions significantly influenced on the scanning accuracy of the IOS evaluated. RL condition obtained the lowest absolute error value of the digital scans performed. The extension of the digital scan was a scanning accuracy influencing factor. The higher the extension of the digital scan performed, the lower the accuracy values obtained. Furthermore, ambient light scanning conditions influenced differently depending on the extension of the digital scans made.

An impression technique to accurately register peri-implant soft tissue in single- and multi-unit implant restorations

Tooth replacement in the esthetic zone presents a challenging situation for the clinician. Contouring the soft-tissues around single- and multi-unit unit implant restoration is critical to achieving an esthetically pleasing final restoration. Duplicating the emergence profile is equally important for effective communication between the clinician and laboratory technician. This article presents a simple, quick, and convenient impression technique for easy and accurate transfer of the tissue contours to the working cast. This precludes the step of doing the jig trial resulting in a decrease in overall treatment time.

MOLDAGEM COM CASQUETE: UMA VARIAÇÃO NA TÉCNICA

Introdução: A obtenção de um modelo de trabalho preciso em prótese parcial fixa é fundamental para se atingir o sucesso e está relacionada, principalmente, às técnicas e material de moldagem. Há várias técnicas para obtenção do modelo de trabalho e troquéis para confecção de prótese parcial fixa, dentre elas está a técnica do casquete. Objetivo: Este trabalho tem o objetivo de apresentar uma variação na técnica de reembasamento do casquete confeccionado previamente com resina acrílica convencional. Material e Métodos: Nesta técnica, o casquete é completamente preenchido com resina acrílica (Duralay) em uma única mistura, a qual é manuseada até a fase plástica e então, o conjunto casquete/resina duralay é inserido no dente preparado para copiar a linha de término do preparo. Resultados: A vantagem é que a fase plástica da resina acrílica possui baixa quantidade de monômero livre e adequada consistência para promover o afastamento gengival provocando desconforto mínimo ao paciente e possui adequada consistência para promover o afastamento gengival. Não é necessária a troquelização do modelo. Conclusão: Conclui-se que essa variação técnica tem aplicação clínica simples e eficaz e produz troquéis de gesso muito precisos.

Customized Soft Tissue Model for Implant Working Cast

The objective of this technique was to fabricate a customized soft tissue gingival mask with vinyl poly siloxane impression materials. Microsoft paint software was used to obtain the concentration of color on the patient images and matched for the color differences of impression materials. This color concentration is transferred to the Vinyl Siloxane Impression (VPS) material. The colors were added by addition technique to the catalyst paste of VPS impression materials. Disposable syringe is used to inject the material around the implant analogue of the implant impression and soft cast obtained simulates the gingival color and tissue of the patient around the implant. The patient gingival color on the cast is obtained with this customized technique of gingival mask.

CAD/CAM-Fabricated Nonmetal Clasp Denture: In Vitro Pilot Study

The purpose of this study was to fabricate a prototype nonmetal clasp denture using computer-aided design/computer-assisted manufacture (CAD/CAM) technology. A partially edentulous mandibular working cast was scanned using an optical scanner. A sectional denture separated by two parts was designed on the scanned cast. These parts were milled and combined, and adhered using an adhesive luting agent. The completed denture was delivered on the working cast and provided an excellent level of fitness. A prototype nonmetal clasp denture could be fabricated using CAD/CAM technology.

Measurement of the accuracy of dental working casts using a coordinate measuring machine.

Dental impressions present a negative imprint of intraoral tissues of a patient which is, by pouring in gypsum, transferred extraorally on the working cast. Casting an accurate and precise working cast presents the first and very important step, since each of the following stages contributes to the overall error of the production process, which can lead to inadequately fitting dental restorations. The aim of this study was to promote and test a new model and technique for in vitro evaluation of the dental impression accuracy, as well as to asses the dimensional stability of impression material depending on the material bulk, and its effect on the accuracy of working casts. Impressions were made by the monophasic technique using the experimental master model. Custom trays with spacing of 1, 2 and 3 mm were constructed by rapid prototyping. The overall of 10 impressions were made with each custom tray. Working casts were made with gypsum type IV. Measurement of working casts was done 24 h later using a co-ordinate measuring machine. The obtained results show that the working casts of all the three custom trays were in most cases significantly different in the transversal and sagittal planes in relation to the master model. The height of abutments was mainly unaffected. The degree of convergence showed certain significance in all the three custom trays, most pronounced in the tray with 3 mm spacing. The impression material bulk of 1–3 mm could provide accurate working casts when using the monophasic impression technique. The increase of the distance between abutment teeth influences the accuracy of working casts depending on the material bulk. [Projekat Ministarstva nauke Republike Srbije, br. TR 35020: Research and development of modelling methods and approaches in manufacturing of dental recoveries with the application of modern technologies and computer aided systems]

Modified Technique for Making Auto-polymerized Polymethylmethacrylate Resin Custom Tray.

Custom made tray for dental impression is designed to provide a uniform space for the impression material and thereby improve the accuracy of the resultant working cast. Auto-polymerized acrylic resins have been the most commonly used material for the fabrication of these trays. The custom tray produces more accurate and reliable results for inter-abutment distance at the occlusal and gingival level than stock trays. This article describes a modified technique for fabrication of auto-polymerized Polymethylmethacrylate (PMMA) resin trays.

부산, 경남지역 치과기공사의 직무분석

Purpose: This study intends to set standard for organizing the curriculum of short-term dental technicians and the change of job environment, as well as the knowledge & training, by identifying the importance and actual job performance of dental technicians following job analysis in the university education of Dept. of Dental Laboratory Technology, and furthermore to foster junior executives to cope with modernization and globalization. Methods: The tools used in this study are based on the job analysis of research report suggested by National Health Personnel Licensing Examination Board(Lee Gyu-seon, 2011), and it consists of general characteristic 7 items. Every competence duty was measured through Likert 5 point gauging, and internal consistency through Cronbach’s Alpha. The competence importance of entire questionnaire was .984 and its performance was .874, reflecting considerably high level, and in terms of each competence duty, high credibility was proved and high internal consistency was verified with competence importance ranging from the minimum .655 to the maximum .966 and its performance ranging from the minimum .677 to the maximum .993. Results: Competence importance and its performance in each duty on the job analysis of dental technicians were measured. In competence importance in each duty, the highest was “checking design order form”(average, 4.52), followed by “selling dental prosthesis°”(average 4.49), “making removable orthodontic appliance”(average, 4.48), “open managing dental laboratory”(average, 4.46) in order. However, “making complete denture” was found the lowest(average, 4.23), with importance of all competence dutys was considerably high level. In the performance of its competence duty, “checking design order form”(average, 4.04) was found to be the most importance competence, followed by “making conservative restoration”(average, 4.00), “making porcelain”(average 3.98), “checking working cast”(average, 3.90) in order. However it was found out that “making fixed orthodontic appliance”(average, 3.12) was the lowest, and the importance of all competence dutys was quite high level. [Abstract]

Comparative evaluation of the accuracy of pick up transfer impressions performed with two different types of trays

The success of implant-supported prostheses is related to the passive union between the prostheses’ connections and the implants, so it is necessary to obtain an accurate working cast. Objective: To evaluate the accuracy of the transfer impressions of implants performed with individual acrylic resin trays and conventional trays using polyvinyl siloxane. Material and methods: To carry out the transfer impressions, a master cast with four external hexagon implants parallel to each other was used. Five impressions were made with individual acrylic resin trays and five other impressions with modified conventional trays, opened in the region of the implants. The linear measurements between the implants were made with a digital caliper with an accuracy of 0.01 mm and the results were statistically evaluated �(alpha = 5%)�. Results: For the points AB and BC, the measurements obtained with the individual trays were statistically similar to the master cast. For the points CD and DA no statistical differences among the three groups were observed. Conclusion: Given the obtained results and the methodology used, it can be concluded that the impressions performed with individual trays presented higher accuracy compared to the ones obtained with conventional trays.

Effect of digitizing techniques on the fit of implant-retained crowns with different antirotational abutment features

The development of computer-aided design/computer-aided manufacturing technology has enabled the fabrication of implant-retained restorations. However, information on the marginal and axial accuracy of restorations fabricated by different digitizing techniques with different antirotational abutment features is not sufficient. The purpose of this invitro study was to evaluate the influence of digitizing techniques on the fit of implant-retained crowns with 2 antirotational features. An experimental working cast housing a tissue-level dental implant was created. Resin-retained abutments with different antirotational features were connected to the implant. Optical impressions of 2 abutment types were obtained separately with 1 chairside and 2 laboratory approaches. Alumina silicate restorations were milled from chairside optical impressions, and ceramic oxide cores were milled from laboratory optical impressions. Restoration fit was evaluated from axial sections of restorations with silicone materials representing the marginal and axial gaps. Axial and marginal fits were measured on digital photographs of the sectioned specimens with a computer program. Two-way ANOVA was used to compare differences between abutments with 2 different antirotational features and digitizing techniques separately for the marginal and axial fits of single implant-retained crowns. A post hoc least significant difference test was used to compare digitizing techniques (α=.05). Significant differences in the marginal fit of single-implant-retained crowns were found among digitizing techniques (P=.011) and between antirotational features (P<.001). No significant difference in the axial fit of single-implant-retained crowns was found among digitizing techniques (P=.905) or between antirotational features (P=.075). Within the limitations of this invitro study, the marginal fit of single-implant-retained crowns was affected by antirotational abutment features. Furthermore, digitizing techniques were found to play an important role in the marginal fit of single-implant-retained restorations.

Comparison of the accuracy for three dental impression techniques and index: An in vitro study

ObjectivesThis in vitro study compared the dimensional accuracy of stone index (I) and three impression techniques: tapered impression copings (T), squared impression copings (S) and modified squared impression copings (MS) for implant-supported prostheses. MethodsA master cast, with four parallel implant abutment analogs and a passive framework, were fabricated. Vinyl polysiloxane impression material was used for all impressions with two metal stock trays (open and closed tray). Four groups (I, T, S and MS) were tested (n=5). A metallic framework was seated on each of the casts, one abutment screw was tightened, and the gap between the analog of implant and the framework was measured with a stereomicroscope. The groups’ measurements (80 gap values) were analyzed using software (LeicaQWin – Leica Imaging Systems Ltd.) that received the images of a video camera coupled to a Leica stereomicroscope at 100× magnification. The results were statistically analyzed with Kruskal–Wallis One Way ANOVA on Ranks test followed by Dunn's Method, 0.05. ResultsThe mean values of abutment/framework interface gaps were: Master Cast=32μm (SD 2); Group I=45μm (SD 3); Group T=78μm (SD 25); Group S=134μm (SD 30); Group MS=143μm (SD 27). No significant difference was detected among Index and Master Cast (P=.05). ConclusionUnder the limitations of this study, it could be suggested that a more accurate working cast is possible using tapered impression copings techniques and stone index.

Failure Analysis of an Abutment Fracture on Single Implant Restoration

This study evaluated the mechanism of an abutment fracture by means of a case-based finite element (FE) stress analysis. A patient presented with a complaint of fracture of an implant-retained single posterior restoration that had been in place for 6 years. The retrieved restoration was examined on the original working cast and subjected to microscopic observation for fracture surface analysis. A case-based FE analysis was conducted to detect the location and magnitude of stress concentration in the implant structures. The fracture occurred at the concave neck of the abutment, with an evidence of fatigue fracture on the titanium surface. Ratchet marks were shown at the distal lingual edge, indicating that the crack proceeded from distolingual to mesial direction. The highest maximum tensile stress at the distolingual concave neck of the abutment was shown when the load was directed on the internal and external surfaces of the mesial buccal cusp. It is suggested that an offset loading because of the cantilever structure caused a high tensile stress on the distolingual edge, resulting in the fatigue fracture of the abutment.