Master Cast Research Articles

Trueness of Extraoral Digital Impressions for Full-Arch Implant Impressions-In Vitro Study.

Direct scanning of silicone impressions is a valid technique. However, studies in implant-supported rehabilitations are lacking. This in vitro study aims to compare the trueness of impressions obtained with two types of silicone and their corresponding stone casts, using two laboratory scanners in a full-arch implant rehabilitation. A master cast with six dental implants was scanned with a 12-megapixel scanner to obtain a digital master cast. Ten implant impressions were made using two silicones (Zhermack and Coltene) with the open-tray technique. The impressions and stone casts were scanned by two extraoral scanners (Identica T500, Medit; and S600 ARTI, Zirkonzhan). Trueness was assessed by comparing linear and angular distances in digital casts with the master cast. A p < 0.05 significance level was considered. The results showed that for the linear measurements, 72% were higher than the master cast measurements, and no consistent pattern was observed in the angular measurements. The greatest deviations were detected between the most posterior implants, with mean values ranging between 173 and 314 µm. No significant differences were found between scanners. However, differences were observed in the distances between silicones (46.7%) and between impressions and stone casts (73.3%). This work demonstrates that the direct scanning of silicone impressions yields results comparable to those obtained from scanning gypsum casts in full-arch implant-supported rehabilitation.

Evaluation of the Stability of Open-Tray Impression Coping Using Two Different Impression Materials at Three Different Subgingival Implant Placement Depths.

Objective To evaluate and compare the stability of the open trayimpression coping within the set impression while attaching the lab analog when polyether (PE) heavy body and polyvinyl siloxane (PVS) putty impression materials were used and the implant platform was placed sub-gingivally at three different depths. Methods Two impression materials, PE and PVS, and custom-made plexiglass models with embedded single implants to simulate implant positioning depths of 0 mm, 2 mm, and 4 mm, sub-gingivally, were used in the study. Open tray impressions were made after attaching impression coping to theimplant embedded in themodel. Implant lab analog was attached to the impression coping in the set impression, and its stability was measured using a universal testing machine. Forty-two open tray impressions were madein six groups, with seven impressions in each group. Descriptive statistics such as mean and standard deviation were calculated. A comparison of the meanstability between the two impression materials at each depth was done using an independent t-test.Comparison of the mean stability between the three different subgingival implant depths in each material was done by one-way ANOVA with the Scheffe multiple comparison test (post-hoc analysis). The level of significance was set at p<0.05. Results The stability of the impression coping was measured as the force in Newtons required for the displacement of the analog attached to the impression coping embedded in the set impression. PEwith the embedded impression coping at a depth of 0 mm gave the highest mean stability value (4.37+/-0.41), and the least mean stability was offered by PVS with the embedded impression coping at 4 mm depth (1.88+/-0.37). When an independent t-test was done to compare the mean stability values of PE and PVS,there was a statistically significant difference at0 mm, 2 mm, and 4 mm. On doing one-way ANOVA to compare the mean stability between the different depth groups, there was a statistically significant difference between the three depth groups in PE and PVS. Scheffe multiple comparison tests (post-hoc analysis) revealed a statistically significant difference between 0 mm, 2 mm, and 4 mm subgingival depths of the impression coping placement in bothPE and PVS. Conclusion The accuracy of the master cast is an important determinant for the precise fit and long life of the final prosthesis. In the case of maxillary anterior implant placements where deep subgingival placement of the implant platform is needed for aesthetic and functional reasons, the impression material should be selected carefully to ensure the stability of the impression coping. Among the materials included in the present study, the PE impression material offered the maximum stability for impression coping compared to PVS.

Dimensional Stability of Additively Manufactured Dentate Maxillary Diagnostic Casts in Biobased Model Resin.

This study aimed to evaluate the dimensional stability of maxillary diagnostic casts fabricated from a biobased model resin, which consists of 50% renewable raw materials for sustainable production, a model resin, and stone, over one month. A master maxillary stone cast was digitized with a laboratory scanner to generate a reference file. This master cast was also scanned with an intraoral scanner to additively manufacture casts with a biobased model resin (BAM) and a model resin (AM). Polyvinylsiloxane impressions of the master cast were also made and poured in type III stone (CV) (n = 8). The same laboratory scanner was used to digitize each model one day (T0), 1 week (T1), 2 weeks (T2), 3 weeks (T3), and 4 weeks (T4) after fabrication. Deviations from the reference file were calculated with an analysis software and analyzed with generalized linear model analysis (α = 0.05). The interaction between the material and the time point affected measured deviations (p < 0.001). Regardless of the time point, CV had the lowest and AM had the highest deviations (p < 0.001). BAM mostly had lower deviations at T0 and mostly had higher deviations at T4 (p ≤ 0.011). AM had the highest deviations at T4 and then at T3, whereas it had the lowest deviations at T0 (p ≤ 0.002). The measured deviations of CV increased after each time point (p < 0.001). BAM casts had deviations within the previously reported clinically acceptable thresholds over one month and had acceptable dimensional stability. Therefore, tested biobased resin may be a viable alternative for the sustainable manufacturing of maxillary diagnostic casts that are to be used clinically.

Fiber-Reinforced Composites for Full-Arch Implant-Supported Rehabilitations: An In Vitro Study.

Background: Fiber-reinforced composites (FRCs) have been proposed as an alternative to traditional metal alloys for the realization of frameworks in full-arch implant-supported prostheses. The aim of the present in vitro study was to evaluate the deflection under load of seven prostheses endowed with frameworks made of different materials, including different types of fiber-reinforced composites (FRCs). Methods: A master cast with four implant analogues in correspondence with the two lateral incisors and the two first molars was used to create full-arch fixed prostheses with the same shape and different materials. Prostheses were made of the following different materials (framework+veneering material): gold alloy+resin (Au+R), titanium+resin (Ti+R), FRC with multidirectional carbon fibers+resin (ICFRC+AR), FRC with unidirectional carbon fibers+composite (UCFRC+C), FRC with glass fibers+resin (GFRC+AR), FRC with glass fibers+composite (GFRC+C), and resin (R, fully acrylic prosthesis). Flexural tests were conducted using a Zwick/Roell Z 0.5 machine, and the deflection of the lower surface of the prosthesis was measured in order to obtain load/deflection graphs. Results: Greater rigidity and less deflection were recorded for UCFRC+C and GFRC+C, followed by Ti+R and Au+R. The greatest deformations were observed for resin alone, ICFRC+R, and GFRC+R. The results were slightly different in the incisal region, probably due to the greater amount of veneering material in this area. Conclusions: When used to realize full-arch frameworks, Au and Ti allow for predictable mechanical behavior with gradual deformations with increasing load. UCFRC also demonstrated good outcomes and less deflection than ICFRCs when loaded. The GFRC full-arch framework may be a valid alternative, although it showed greater deflections. Further studies are needed in order to evaluate how different prosthesis designs and material thicknesses might affect the outcomes.

Accuracy of impression methods through the comparison of 3D deviation between implant fixtures.

To compare the accuracy of three impression methods by comparing the distance between the reference points of the implant fixture, especially in curved maxillary anterior teeth. Implant fixtures were placed in the maxillary central incisor and canine regions. A maxillary master cast was made using a model scanner and 3D printer. Ten impressions were taken from the three experimental groups constructed (group P: pick-up impression coping; group I: scan body with an intraoral scanner; group B: bite impression coping). The distance between the reference points, the angle between the scan bodies, and displacement of the 3D surface area were measured. The distances between the reference points were significantly different between groups I and B in the maxillary incisors, and between group P and the other two groups in the maxillary canines. Group P had the least amount of displacement in both fixtures. Both fixtures showed the highest displacement in group B. Displacement of the 3D surface area in the maxillary incisors showed no significant difference between the groups. There was a significant difference in the maxillary canines between groups P and I. In the present study, all three implant impression methods showed changes in the position and angle of the fixture compared with the master cast. The highest accuracy was shown by the impression method using the pick-up impression coping, but the impression method using the intraoral scanner also showed clinically acceptable accuracy. It should be noted that errors may occur when taking impressions using a bite impression coping.

Evaluation of Dimensional Change in Different Elastomeric Impression Materials Used in Implants: An Original Research

ABSTRACT Aim: The study’s objective was to assess the dimensional accuracy of hybrid polyether and polyvinyl siloxane materials for implant impressions. Materials and Methods: Nine groups were created from 45 samples of various building materials and construction techniques from the study. Five samples were tested, and 45 impressions were recorded. Results: The hybrid non-splinted technique has improved implant site replication, accuracy, and low interimplant distance alterations. Conclusion: The finest possible reproduction of implant sites on the master cast was made feasible by the use of an open, non-splinted method and a hybrid polyvinyl siloxane–polyether impression material.

Evaluation with a Coordinate-Measuring Machine of Dimensional Accuracy of the Abutment Duplication Technique in Cement- Retained Implant Restoration.

To evaluate the effectiveness and accuracy of a proposed duplication technique in terms of one- and three-dimensional discrepancies between an original abutment and polyurethane duplicates obtained through a conventional workflow in single-implant rehabilitation. A titanium, shoulderless abutment was chosen for a single-implant cemented rehabilitation. The master cast was made using a plastic-based die system, and the implant portion was separated. The implant section was consecutively duplicated eight times using a manual technique with polyvinyl siloxane and unfilled polyurethane resin as impression and die materials. The duplicates were analyzed with a coordinate-measuring machine (SmartScope Flash 200, Optical Gaging Products): one- and three- dimensional discrepancies were determined for each duplicate on 20 analysis points (A to T) located on the abutment surface. Changes in the abutment radius were also calculated to estimate the effects on cement thicknesses. One-dimensional discrepancies were -0.5 Å} 61.2 μm, -6.6 Å} 39.7 μm, and -19.4 Å} 47.8 μm on the X, Y, and Z axes, respectively; three-dimensional variation was -66.4 Å} 60.1 μm. Friedman test showed no significant difference between duplicates' one-dimensional variations on X (P = .059), Y (P = .156), or Z (P = .223) axes; a significant difference was found regarding three-dimensional changes (P < .001). Dunn test showed higher discrepancies on the X axis and on the abutment head. Mean variation of the abutment radius was -12.09 μm. The abutment duplication technique was shown to be an accurate and repeatable procedure for single cementable restorations.

Accuracy of merging scans of definitive fixed prosthodontic impressions to obtain single, accurate digitized master casts.

Many elastomeric impressions sent to commercial laboratory dental technicians may include marginal defects. To fabricate accurate restorations, digital technology may be used to merge digital files of defective impressions into a single standard tessellation language (STL) file free of errors. This would save clinicians and patients time and may improve clinical care. The purpose of this study was to compare the accuracy of digital master casts reconstructed from merged STL files of defective impressions with the file of the original defect-free preparations. Ivorine teeth on a dentoform were prepared to receive a posterior fixed dental prosthesis (FDP) with complete coverage preparations. An impression was made in a stock tray using polyvinyl siloxane (PVS) impression material and an extraoral scanner (E3, 3Shape, Denmark) was used to digitize the impression; this was the reference cast. Wax was used to create defects on the buccal and lingual margins of the preparations. Fifteen PVS impressions were made of the FDP preparations with defects in the mesial and distal margins; another set of 15 PVS impressions was made of FDP preparations with defects in the buccal and palatal margins for a total of 30 impressions. All impressions were digitized using the same extraoral scanner (E3, 3Shape, Denmark). Corresponding STL files were paired and merged, and a master cast was created by eliminating the defects using the scanned data. This master cast was compared to the reference cast using reverse engineering software (Geomagic, Morrisville, NC, USA). The results were expressed as average errors and standard deviations in the master casts relative to the reference cast. To account for the presence of positive and negative values in the data set, in terms of errors, the root mean square (RMS) value was calculated for each sample. The mean average error in the sample was -0.4 μm. The average upper limit of 95% confidence interval was +36.5 μm, while the average lower limit of 95% confidence interval was -37.3 μm. The mean RMS of the errors found was 18.9 μm. The results of this study indicated that merging digitized definitive impressions to correct marginal defects resulted in master casts with a high level of accuracy relative to the reference cast.

An Evaluation of Retention of Complete Denture Bases Made with a “Modified Single-stage Impression” Technique Using a Heat-moldable Tray

Abstract Aim: Although most dental schools teach complete denture definitive impression techniques consisting of secondary impressions in border-molded custom impression trays, it has been found that later, graduates in clinical practice abandon this step because of its complexity and attempts to seek easier alternatives. To simplify two-stage techniques, single-step border molding with elastomeric impression materials and light-cured resin materials has gathered acceptance among clinicians. The study aims to evaluate the retention of record bases made with a modified single-stage impression technique that uses elastomeric impression material in a heat moldable tray with modeling compound as material for border molding. Settings and Design: This was an in vivo preliminary cohort study. Materials and Methods: Thirteen completely edentulous patients requiring complete dentures were included in the study. A traditional two-stage impression was made using custom trays fabricated over diagnostic casts and further border molding done with a modeling compound, and the final impression was made to use zinc oxide–eugenol impression material. Additionally, a modified single-stage impression technique using heat moldable impression trays was made. Master casts from each technique were made, and further record bases were made on each master cast. Wire loops were adapted on the palatal aspect of record bases. The retention of each record base was evaluated using a force gauge. Statistical Analysis: The Kolmogorov–Smirnov test was used to analyze the normality of variables and later Wilcoxon signed-rank test was applied. Results: The double-stage technique exhibited retention values in the range of 0.6–66.7 units, whereas the single-stage technique showed a range of 0.15–78.55. The tests showed no significant difference between double-stage and single-stage techniques (P &gt; 0.05). Conclusions: The single-stage technique using heat moldable trays with elastomeric impression material and modeling compound as a material for border molding can produce denture retention compared to the conventional technique that uses a two-step impression technique. The use of the modified single-stage technique can additionally save an extra appointment for patients, although it is better to use such a technique as an advanced impression technique and not as a training technique for beginners or students, as the material cost is substantially higher than the conventional two-stage technique.

Mounting and utilization of provisional prostheses on master cast for the fabrication of fixed implant-supported prostheses: a case report

Mounting and utilization of provisional prostheses on master cast for the fabrication of fixed implant-supported prostheses: a case report

Complete mouth rehabilitation case with reconstructed master cast using pattern resin transfer copings after partial dental arch impression taking: A case report

Complete mouth rehabilitation case with reconstructed master cast using pattern resin transfer copings after partial dental arch impression taking: A case report

Improvement of Clay Soil Using a Plaster Mortar Additive

This study examines possibility of improving clayey soils in the Handere Formation exposed in the vicinity of Adana (S. Turkey), one of the largest cities in southern Turkey. The Handere Formation, from where the samples for this study are taken, is stratigraphically at the upper most part of the marine sediments of the Adana Basin. The unit is located at the northern part of Adana city. The samples were examined in the geotechnical laboratory to determine the effect of plaster mortar (Master Cast) on the geotechnical properties of the soil and its ability to improve the soil. shear box, consolidation, unconfined compressive strength tests were applied on the samples. It has been shown that the master cast used can improve soil properties geometrically and can be used as a soil stabilizer. The plasticity values of the soils were reduced by master cast addition. Besides, it was determined that the highest maximum dry unit weight and the lowest optimum moisture content were obtained by 15% master cast addition. The soil strength properties were reached to the top values in case of 15% master cast added into the mixtures. Besides, it is determined that the coefficient of volume compressibility (Mv) and the pre-consolidation pressure values are ideal when the master cast ratio in the mixtures are 10% and 5% respectively.

A Preliminary Study on the Accuracy of Cast Metal Removable Partial Denture Frameworks Produced from Wax, Printed, and Milled Patterns

To compare the accuracy of two digital workflows for producing resin patterns to be cast into metal frameworks compared to an identical framework manufactured conventionally from a wax pattern. Nine casts were duplicated from a maxillary master cast of a partially edentulous arch. Their accuracy was determined by measuring the same points in two and three dimensions using a reflex microscope, which was also used to measure all frameworks to an accuracy of 4 μm. The same design was used throughout. Three casts were used to make a framework conventionally from an invested wax pattern. Six casts were scanned, and a digital pattern created. Three patterns were milled from a resin block, and three were 3D printed with resin. Then each pattern was cast. The sample size precluded direct statistical conclusions, but no significant differences were found. Duplicate models showed minimal differences compared to the master cast. All patterns and all frameworks showed some level of difference compared to the master cast, but no differences were greater than those reported in the literature as being clinically acceptable. The maximum overall discrepancy between the cast frameworks was 0.64 mm, and at the rest seats was 0.262 mm. Within the limitations of this study, given the very small actual differences both within and between the groups of the three different workflows, the use of digitally produced resin patterns prior to their being cast as metal frameworks is both feasible and well within the accepted limits for clinical acceptability.

Influence of Implant ScanBody Material and Intraoral Scanners on the Accuracy of Complete-Arch Digital Implant Impressions.

To evaluate the accuracy of complete-arch digital implant impressions using different intraoral scan body (ISB) materials and intraoral scanners (IOSs). The mandibular dental cast of an edentulous patient with six tissue-level dental implants was used as the master cast. Two types of ISBs-polyether ether ketone (PEEK) and plasma-coated medical titanium-were used with five IOSs: TRIOS 4 (T4), Virtuo Vivo (VV), Medit i700 (Mi700), iTero 5D (i5D), and Primescan (PS). To assess accuracy, digital impressions (n &#61; 10) with each IOS and ISB were compared to two reference models obtained by digitizing the master cast with each ISB type using a desktop scanner (IScan4D LS3i) and importing the scan data into metrology software (Geomagic Control X). Root mean square (RMS) error was employed to evaluate overall deviation values (trueness), while precision was determined using the SD of RMS values. Statistical significance was set at P < .05. Kruskal-Wallis test was used, followed by the pairwise comparison method with Bonferroni correction (α &#61; .05). An interaction between ISB material and IOS was found (P &#61; .001). Plasma-coated medical titanium ISBs demonstrated significantly higher trueness and precision compared to PEEK ISBs with T4 (P &#61; .001), Mi700 (P &#61; .001; P &#61; .004), and i5D (P &#61; .001). Conversely, VV exhibited higher trueness and precision values with PEEK ISBs (P &#61; .005; P &#61; .003). PS provided the highest trueness and precision regardless of the ISB material (P &#61; .912). T4 showed the lowest accuracy for PEEK ISBs, and VV showed the lowest accuracy for plasma-coated medical titanium ISBs. Except for PS, all IOSs showed significant differences between ISB materials. PS demonstrated the highest accuracy with both ISB materials, whereas T4 had the lowest accuracy for PEEK ISBs, and VV showed the lowest accuracy for plasma-coated medical titanium ISBs.

A technique to convert a 3D printed cast used in the fabrication of an interim implant-supported crown into a definitive cast capturing the acquired emergence profile.

An esthetic peri-implant soft tissue contour is a critical element of the success of implant restorations in the esthetic zone. Once the optimal transmucosal soft tissue profile is formed, it needs to be accurately replicated on the master cast. This clinical technique involves the utilization of a silicone putty positioning index placed in the patient's mouth to accurately duplicate the external contour of teeth and soft tissue. By combining this positioning index with the implant-supported interim crown, the 3D-printed initial cast, which was used to fabricate the interim crown, can be conveniently and efficiently transformed into a definitive master cast.

Accuracy of different digital acquisition methods in complete arch implant-supported prostheses: An in vitro study

Statement of problemDigital methods such as intraoral scanners for recording the location of implants supporting complete arch prostheses have limitations. Photogrammetry devices should be able to digitize implant positions accurately, but standardized comparisons between different digital acquisition methods are lacking. PurposeThe purpose of this in vitro study was to compare the repeatability of different digital acquisition methods for complete arch prostheses supported by 6 and 4 implants. Material and methodsA master cast was created with 6 and 4 dental implants with multiunit abutments to obtain the master digital casts. The evaluated devices were the industrial high-resolution 12-megapixel scanner (reference) Atos Compact Scan 12M (GOM), the laboratory scanners D2000 (3Shape A/S) and S900 Arti (Zirkonzahn), the photogrammetry devices iCam (iMetric4D) and PIC (PIC Dental), and the intraoral scanners TRIOS 3 (3Shape A/S) and iTero Element 5D (Align Technology). The resulting files were imported to a computer-aided design software program (exocad GmbH) to obtain the implant replicas as standard tessellation language (STL) files. These files were imported into a software program (Geomagic Control X) and superimposed per group through the best-fit algorithm to determine repeatability, defined as the closeness of agreement between each group’s scanned results as root mean square (RMS) values. The normality of distribution was tested by the Shapiro-Wilk normality test, and the Kruskal-Wallis test with adjustment with the Bonferroni correction method was used accordingly (α=.05). ResultsThe repeatability means and 95% confidence intervals for the 4 implant scans were: 1.07 µm (0.86; 1.29) for GOM, 2.05 µm (1.89; 2.21) for D2000, 3.61 µm (3.23; 3.99) for S900, 7.01 µm (6.11; 7.91) for iCam, 5.18 µm (4.6; 5.76) for PIC, 20.52 µm (18.33; 22.72) for TRIOS 3, and 20.5 µm (17.37; 23.63) for iTero. Statistically significant differences were found between devices, except for iCam versus PIC, GOM versus S900, iCam versus D2000, PIC versus D2000, and TRIOS 3 versus iTero. The repeatability means and 95% confidence intervals for the 6 implant groups were: 1.36 µm (1.08; 1.65) for GOM, 3.17 µm (3.01; 3.33) for D2000, 2.15 µm (2.04; 2.25) for S900, 8.67 µm (8.06; 9.28) for iCam, 13.88 µm (12.62; 15.14) for PIC, 40.32 µm (36.29; 44.36) for TRIOS 3, and 38.86 µm (34.01; 43.71) for iTero. Statistically significant differences were detected between devices, except for S900 versus GOM, PIC versus iCam, and iTero versus TRIOS 3. ConclusionsThe results suggest that photogrammetry could be a suitable alternative for recording implant locations of complete arch prostheses supported by 4 or 6 implants, with better repeatability than intraoral scanners. Increasing the number of implants decreased the repeatability of every device tested except the laboratory scanners.

A simplified technique of mandibular complete denture fabrication for a condition of ankyloglossia – A case report

ABSTRACT Rationale: During the construction of a complete denture, obtaining adequate retention is always a problem in the mandibular denture. In the case of ankyloglossia, the retention of mandibular denture is severely compromised due to a decrease in neutral zone space and thick musculature of the tongue web attached to the mouth’s anatomical floor. Diagnosis: The patient was diagnosed as completely edentulous with ankyloglossia. Intervention: The intervention that was done to this condition was a modification of the master cast before the final wax-up and processing of the denture. Outcomes: Through the modification that was done to the master cast, an acceptable level of retention was attained. Lessons: This case report describes a simple modification that is done to achieve optimal retention for a patient with ankyloglossia and to maintain that retention during function.

Customized implant impression copings: provisional cast technique

Dental UpdateVol. 50, No. 6 Technique TipsCustomized implant impression copings: provisional cast techniqueHannah Bradley, William Keys, Andrew MacInnesHannah Bradleyemail: E-mail Address: [email protected]StR in Restorative Dentistry, Glasgow Dental Hospital and SchoolSearch for more papers by this author, William KeysConsultant in Restorative Dentistry, Edinburgh Dental InstituteSearch for more papers by this author, Andrew MacInnesConsultant in Restorative Dentistry, Glasgow Dental Hospital and SchoolSearch for more papers by this authorHannah Bradley; William Keys; Andrew MacInnesPublished Online:13 Jun 2023https://doi.org/10.12968/denu.2023.50.6.538AboutSectionsView articleView Full TextPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail View article References Furze D, Byrne A, Alam S, Wittneben JG. Esthetic outcome of implant supported crowns with and without peri-implant conditioning using provisional fixed prosthesis: a randomized controlled clinical trial. Clin Implant Dent Relat Res 2016 Dec; 18(6):1153-1162. https://doi.org/10.1111/cid.12416 Medline, Google ScholarPolack MA. Simple method of fabricating an impression coping to reproduce peri-implant gingiva on the master cast. J Prosthet Dent 2002; 88: 221–223. https://doi.org/10.1067/mpr.2002.127895 Medline, Google ScholarHinds KF. Custom impression coping for an exact registration of the healed tissue in the esthetic implant restoration. Int J Periodontics Restorative Dent 1997; 17: 584–591. Medline, Google ScholarBreeding LC, Dixon DL. Transfer of gingival contours to a master cast. J Prosthet Dent 1996; 75: 341–33. https://doi.org/10.1016/s0022-3913(96)90497-7 Medline, Google Scholar FiguresReferencesRelatedDetails 2 June 2023Volume 50Issue 6ISSN (print): 0305-5000ISSN (online): 2515-589X Metrics History Published online 13 June 2023 Published in print 2 June 2023 Information© MA Dentistry Media LimitedAcknowledgementsWe thank Sharon Weir, Dental Technician, at Glasgow Dental Hospital and School for her prosthodontic work.PDF download

Self-assessment skills of undergraduate dental students in the preclinical course of complete removable prosthodontics at Tehran University of Medical Sciences.

This study evaluated the self-assessment skills of third-year dental students regarding their performance in complete removable prosthodontics (CRP) preclinical course. This cross-sectional study was conducted on all third-year dental students attending the International Dental College of Tehran University of Medical Sciences. The students were requested to self-assess their performance in primary impression making, custom tray fabrication, border moulding, final impression making, master cast fabrication, record-base fabrication and tooth arrangement in CRP preclinical course. The performance of dental students in each step was scored by themselves and their mentors. Data were analysed by the Mann-Whitney U, Pearson's correlation and t-tests (α = 0.05). Totally 25 male (55.6%) and 20 female (44.4%) dental students were evaluated. Significant differences were noted between male and female dental students in self-assessment scores regarding adequate extension of the custom tray (p = .027), the correct position of tray handle (p = .020), visibility of vestibular width and depth on the cast (p = .011), the coincidence of upper and lower midlines (p = .005) and correct orientation of maxillary and mandibular planes in the articulator (p = .036). The mean self-assessment score of female students was significantly higher than that of male students (p = .01). The scores given by the mentors were not significantly different for male and female students (p = .975). The difference between the self-assessment score of students and the mentor score was not significant (p = .067) either in males or in females (p > .05). Undergraduate dental students favourably self-assessed their performance in all steps of the preclinical course of CRP, comparable with their mentor assessment.

Effect of relative humidity on the accuracy, scanning time, and number of photograms of dentate complete arch intraoral digital scans

Statement of problemIntraoral scanners (IOSs) have been used in dentistry for diagnostic and treatment purposes; however, the influence of environmental factors such as humidity or temperature on the accuracy of intraoral scanning is uncertain. PurposeThe purpose of this in vitro study was to evaluate the influence of relative humidity and ambient temperature on the accuracy, scanning time, and number of photograms of dentate complete arch intraoral digital scans. Material and methodsA completely dentate mandibular typodont was digitized by using a dental laboratory scanner. Four calibrated spheres were attached following the International Organization for Standardization (ISO) standard 20 896. A watertight box was designed to simulate 4 different relative humidity conditions (50%, 70%, 80%, and 90%) (n = 30). An IOS (TRIOS 3) was used to obtain a total of 120 complete arch digital scans (n = 120). Scanning time and number of photograms of each specimen were recorded. All the scans were exported and compared with the master cast by using a reverse engineering software program. The linear distances among the reference spheres were used to calculate trueness and precision. A unifactorial analysis of variance (ANOVA) and Levene tests followed by the post hoc Bonferroni test were used to analyze trueness and precision data, respectively. A unifactorial ANOVA followed by a post hoc Bonferroni test was also conducted to analyze scanning time and the number of photogram data. ResultsStatistically significant differences were found in trueness, precision, number of photograms, and scanning time (P<.05). Regarding trueness and precision, significant differences were found between the 50% and 70% relative humidity groups and the 80% and 90% relative humidity groups (P<.01). Regarding scanning time and number of photograms, significant differences were obtained among all groups, except between the 80% and 90% relative humidity groups (P<.01). ConclusionsThe relative humidity conditions tested influenced accuracy, scanning time, and number of photograms in complete arch intraoral digital scans. High relative humidity conditions resulted in the decreased scanning accuracy, longer scanning time, and greater number of photograms of complete arch intraoral digital scans.