Typodont Model Research Articles

Marginal accuracy and internal fit of copings by the digital impression and CAD‐CAM systems

Background Digital impression systems have been developed to overcome the disadvantages associated with conventional impression methods while, the computer-aided design computer-aided manufacturing (CAD CAM) technology in dentistry have been replaced error-prone manual laboratory steps with aligned industrial manufacturing processes. Therefore, the combination of them can be time-saving, comfortable, and cost-effective compared to conventional impression and casting technology. Aim/Hypothesis The purpose of this study was to compare the marginal fit and internal fit of metal and zirconia copings obtained with the use of an iTero digital impression and two different CAD-CAM systems in the anterior, premolar and molar teeth with chamfer or shoulder margin. Material and Methods A typodont model with prepared metal tooth was used as the master model. For the conventional impression group, base metal dies were replicated as stone dies by means of a conventional impression technique with polyvinyl siloxane material. For the digital impression, base metal dies were replicated as polyurethane dies with the iTero system. For the zirconia copings by Cercon® and Arum® CAD-CAM systems, stone and polyurethane dies were scanned and CAD-CAM milled. For gold and Empress copings, wax-up and casting procedures were performed based on the stone and polyurethane dies. The marginal gap and internal fit of each specimen were measured after manual refinement with a light microscope and silicone weight technique. One-way ANOVA and the Scheffe's test were used for statistical analysis (P < 0.05). Results There was no significant difference in the marginal gap among four different groups of copings between digital and conventional impression regardless of the tooth location and type of finish line (P > 0.05). However, statistically significant differences in the silicone weight for internal fit were found between the casting groups and CAD-CAM groups (P < 0.05). Conclusions and Clinical Implications The internal fit between the copings and definitive base metal die was greater in the groups that used the digital impression method and CAD-CAM systems in the group that used the conventional impression and casting method. However, the marginal discrepancies of all of the groups were no difference and clinically acceptable.

Comparative evaluation of the fit of ceramic inlay restorations fabricated with heat-press technique and CAD/CAM systems: A preliminary study

Objective: The objective of this in-vitro study was to evaluate the marginal and internal fit of a lithium disilicate inlays fabricated by two CAD/CAM systems (extra-oral and intra-oral scanning), and conventional heat-press technique. Materials and methods: Mandibular first molars were used for inlay restorations in a typodont model. Three groups (n=12 each) of inlays were fabricated by Computer Aided Design/ Computer Aided Manufacturing (CAD/CAM) technology using intraoral and extraoral scanning devices, and conventional heat-press method. Replica technique was used to assess the discrepancies. Internal and marginal gaps were measured at 4 points on each side with stereomicroscope at 200x magnification. One-way variance analysis test (ANOVA) and paired-samples t-test were used for analyzing the results. Results: The fit values were statistically significantly influenced by the production method in total discrepancy comparisons (p= .000). Intraoral scanner group demonstrated the lowest marginal and internal gap values whereas conventional heat-press group showed the highest results. Statistically significant differences were found for fit values with respect to the groups (p&lt;.001). Conclusion: Within the limitations of the study, restorations fabricated via complete digital workflow demonstrated better marginal and internal accuracy than silicone impressions with conventional heat-press technique.?

Thermo-Mechanical Properties of Glass Fiber Reinforced Shape Memory Polyurethane for Orthodontic Application.

Glass fiber reinforced shape memory polyurethane (GFRSMPU) has great potential to be an alternative kind of material for orthodontic archwires for overcoming the disadvantages of metal wires in terms of esthetic and allergy and deficiency of pure shape memory polyurethane (SMPU) wires in mechanical properties. The objective of this study was to investigate the thermo-mechanical properties and shape recovery functions of GFRSMPU and evaluate the feasibility of using this composite for orthodontic archwires. GFRSMPU were made from short cut glass fibers and SMPU by mixing extrusion. Scanning electron microscope (SEM) and differential scanning calorimetry (DSC) were performed to investigate the distribution of glass fibers in the mixture and glass transition temperature (Tg). Then the thermo-mechanical properties, including tensile modulus, flexural modulus and stress relaxation effects, were measured. Furthermore, shape recovery functions of GFRSMPU characterized by the shape recovery ratio and force were investigated through shape recovery tests, typodont models and finite element analysis (FEA). SEM images indicated that an excellent dispersity of glass fibers was obtained after double-extrusion. DSC experiments showed Tg was not enormously affected with the existence of glass fibers, but the mechanical properties of GFRSMPU were greatly improved. Shape recovery tests showed reduction of shape recovery ratio of the GFRSMPU material with the addition of glass fibers, but dentition aligning time was reduced by 50% in the simulation performed on identical typodont models with GFRSMPU archwires filled with 30 wt.% glass fibers. The FEA results illustrated that the reacting forces of GFRSMPU archwires with 30 wt.% glass fiber was increased by 96.36% compared with pure SMPU archwires. The mechanical properties of GFRSMPU can be considerably improved by adding glass fibers, and the shape memory function would be well preserved too. Enhanced SMPU owns a good application prospect in orthodontics for dentation aligning on the preliminary stage, as well as other medical fields.

Accuracy and Reproducibility of 3D Printed Dies versus Stone Dies

Statement of the problem: researches studying the accuracy of the 3D printed dies were very rare.Aim: The aim of the current study was to assess the difference in accuracy and reproducibility of the three dimensionally printed dies versus the stone dies.Materials& Methods: A maxillary typodont (D13PP-TR.1; Nissan, Kyoto, Japan) model with missing upper 1st molar was prepared as master model. Two types of dies were obtained from the master model (n=6). Group 1 was the conventional stone dies using type IV stone (GC FujiRock EP; GC) while group 2 representing the 3D printed dies (Dent2 Mogassam LLC Co. Egypt, Cairo) using resin (industrial blended resin, Funtodo Co. Netherlands). All working models were scanned (Open Technologies 3D scanner, Brescia, Italy) and STL file was superimposed on the STL file of the master model with the best-fit alignment method to analyze the volumetric changes and color maps were provided using 3Shape 3D software software. The mean average distance between the master dies and the working dies in all groups was recorded. Data were fed to the computer and analyzed using IBM SPSS software package version 20.0. Quantitative data were explored for normality using Kolmogorov-Smirnov and Shapiro-Wilk tests. Results: There were no statistically significant differences in volumetric discrepancies between stone model (0.186±0.231) mm3 as a (mean±SD) and 3D printed model (0.176±0.211) mm3 as a mean±SD. Conclusion: Digital work flow can eventually replace the conventional techniques with minimal volumetric discrepancies in 3D printed dies.

Marginal and internal fit of pre-sintered Co-Cr and zirconia 3-unit fixed dental prostheses as measured using microcomputed tomography

Statement of problemLimited information is available on the precision of new metal processing technologies. PurposeThe purpose of this in vitro study was to evaluate the marginal and internal fit of pre-sintered cobalt-chromium (Co-Cr) and zirconia 3-unit fixed dental prostheses using x-ray microcomputed tomography. Material and methodsThree-unit fixed dental prostheses were prepared on metal dies (N=12) using a typodont model from the maxillary first premolar to the first molar. A standardized preparation with a 1.2-mm chamfer (360 degrees) and a 2-mm occlusal reduction was prepared on abutment teeth. The dies were scanned and divided into 2 groups to receive the fixed dental prostheses (n=6) made of pre-sintered Co-Cr and pre-sintered zirconia. Each framework was seated on its cast, and marginal and internal discrepancies were measured at 9 points, starting from the most distal point from the pontic for the maxillary first premolar and the first molar (points 1-4, mesial; point 5, occlusal; points 6-9, distal) of each abutment tooth using microcomputed tomography. The data were analyzed using the Levene test, t test, and ANOVA (α=.05). ResultsWhen overall mean discrepancy values were compared, no significant difference was observed between pre-sintered Co-Cr and pre-sintered zirconia (P=.085). Discrepancy values for points 1, 2, and 3 were significantly different for pre-sintered Co-Cr and pre-sintered zirconia, with the lowest mean values for point 1 and the highest for point 5. On the abutment tooth basis, for the maxillary first premolar and the first molar, a significant difference was found only in points 6 (P<.001) and 8 (P<.003) for both materials. When the discrepancies for the maxillary first premolar were considered for pre-sintered Co-Cr and pre-sintered zirconia, the mean values were significantly different only at points 1 (P<.001), 2 (P=.007), and 3 (P=.003) and were smaller for pre-sintered zirconia. For the tooth the first molar, a significant difference was observed at point 2 (P=.002) and point 3 (P=.008) for both materials, where the mean values were higher for pre-sintered Co-Cr than for pre-sintered zirconia. The pairwise comparison between points showed a significant difference between measurement points within each material (P<.05). The increase in values between points 1 and 5 was evident for both pre-sintered Co-Cr and pre-sintered zirconia materials. ConclusionsThree-unit fixed dental prostheses made of pre-sintered Co-Cr or zirconia showed similar marginal and internal discrepancy values, with the highest discrepancy values at the occlusal region in both the first premolar and first molar.

Influence of repeated firings on marginal, axial, axio-occlusal, and occlusal fit of metal-ceramic restorations fabricated with different techniques

Statement of problemIll-fitting restorations can jeopardize dental, periodontal, and systemic health. Repeated ceramic firing may influence the fitting accuracy of restorations, but scientific information regarding this issue is lacking. PurposeThe purpose of this in vitro study was to assess and compare the influence of repeated firings on the marginal, axial, axio-occlusal, and occlusal fit of metal-ceramic 3-unit fixed partial dentures (FPDs) manufactured with different framework methods, including casting, fully sintered hard alloy milling (FHAM), presintered soft alloy milling (PSAM), and selective laser sintering (SLS). Material and methodsA total of 60 Co-Cr metal frameworks for 3-unit FPDs were fabricated with 3 different computer-aided design and computer-aided manufacturing (CAD-CAM) techniques and conventional casting for a typodont model. The discrepancy values for premolar and molar abutments were measured by using the silicone replica technique after fabrication of the framework, second firing, fourth firing, and seventh firing. The replicas were separated into mesiodistal and buccolingual cross-sections, and digital images of the cross-sections were obtained with a stereomicroscope at ×80 magnification. The measurement points were examined to record the discrepancy values (μm) with in-built measuring software. The recorded data were subjected to repeated-measures 4-way ANOVA and the Bonferroni post hoc test (α=.05). ResultsFor all measurement periods, the marginal, axial, axio-occlusal, and occlusal discrepancy values differed significantly among the manufacturing groups (P<.001). Moreover, the repeated firings had a statistically significant influence on the discrepancy values of PSAM, FHAM, and SLS groups (P<.05). The cast group was not significantly affected by repeated firings (P>.05). The PSAM group revealed the lowest discrepancy values at all measurement periods (P<.05), except after the second firing in the marginal and axial locations. ConclusionsThe PSAM-fabricated restorations demonstrated superior fitting accuracy. All manufacturing groups were influenced by repeated firings, except the cast group. The marginal discrepancy values of all manufacturing groups were within the range of clinical acceptability (<120 μm).

Marginal discrepancy of CAD-CAM complete-arch fixed implant-supported frameworks

Statement of problemComputer-aided design and computer-aided manufacturing (CAD-CAM) high-density polymers (HDPs) have recently been marketed for the fabrication of long-term interim implant-supported fixed prostheses. However, information regarding the precision of fit of CAD-CAM HDP implant-supported complete-arch screw-retained prostheses is scarce. PurposeThe purpose of this in vitro study was to evaluate the marginal discrepancy of CAD-CAM HDP complete-arch implant-supported screw-retained fixed prosthesis frameworks and compare them with conventional titanium (Ti) and zirconia (Zir) frameworks. Material and methodsA screw-retained complete-arch acrylic resin prototype with multiunit abutments was fabricated on a typodont model with 2 straight implants in the anterior region and 2 implants with a 30-degree distal tilt in the posterior region. A 3-dimensional (3D) laboratory laser scanner was used to digitize the typodont model with scan bodies and the resin prototype to generate a virtual 3D CAD framework. A CAM milling unit was used to fabricate 5 frameworks from HDP, Ti, and Zir blocks. The 1-screw test was performed by tightening the prosthetic screw in the maxillary left first molar abutment (terminal location) when the frameworks were on the typodont model, and the marginal discrepancy of frameworks was evaluated using an industrial computed tomographic scanner and a 3D volumetric software. The 3D marginal discrepancy at the abutment-framework interface of the maxillary left canine (L1), right canine (L2), and right first molar (L3) sites was measured. The mean values for 3D marginal discrepancy were calculated for each location in a group with 95% confidence limits. The results were analyzed by repeated-measures 2-way ANOVA using the restricted maximum likelihood estimation and the Satterthwaite degrees of freedom methods, which do not require normality and homoscedasticity in the data. The between-subjects factor was material, the within-subjects factor was location, and the interaction was included in the model. Tukey tests were applied to resolve any statistically significant source of variation (overall α=.05). ResultsThe 3D marginal discrepancy measurement was possible only for L2 and L3 because the L1 values were too small to detect. The mean discrepancy values at L2 were 60 μm for HDP, 74 μm for Ti, and 84 μm for Zir. At the L3 location, the mean discrepancy values were 55 μm for HDP, 102 μm for Ti, and 94 μm for Zir. The ANOVA did not find a statistically significant overall effect for implant location (P=.072) or a statistically significant interaction of location and material (P=.078), but it did find a statistically significant overall effect of material (P=.019). Statistical differences were found overall between HDP and the other 2 materials (P≤.037). ConclusionsWhen the tested materials were used with the CAD-CAM system, the 3D marginal discrepancy of CAD-CAM HDP frameworks was smaller than that of titanium or zirconia frameworks.

Three-dimensional evaluation of marginal and internal fit of 3D-printed interim restorations fabricated on different finish line designs

PurposeTo evaluate the influence of fabrication method and finish line design on marginal and internal fit of full-coverage interim restorations.MethodsFour typodont models of maxillary central-incisor were prepared for full-coverage restorations. Four groups were defined; knife-edge (KE), chamfer (C), rounded-shoulder (RS), rounded-shoulder with bevel (RSB). All preparations were digitally scanned. A total of 80 restorations were fabricated; 20 per group (SLA/3D-printed n=10, milled n=10). All restorations were positioned on the master die and scanned using micro-computed tomography. The mean gaps were measured digitally (ImageJ). The results were compared using MANOVA (α=.05).ResultsInternal and marginal gaps were significantly influenced by fabrication method (P=.000) and finish-line design (P=.000). 3D-Printed restorations showed statistically significant lower mean gap compared to milled restorations at all points (P=.000). The mean internal gap for 3D-printed restorations were 66, 149, 130, 95μm and for milled restorations were 89, 177, 185, 154μm for KE, C, RS, RSB respectively. The mean absolute marginal discrepancy in 3D-printed restorations were (30, 41, 30, 28μm) and in milled restorations were (56, 54, 52, 38μm) for KE, C, RS, RSB respectively.ConclusionsThe fabrication methods showed more of an influence on the fit compared to the effect of the finish-line design in both milled and printed restorations. SLA-printed interim restorations exhibit lower marginal and internal gap than milled restorations. Nonetheless, for both techniques, all values were within the reported values for CAD/CAM restorations.Significance3D-printing can offer an alternative fabrication method comparable to those of milled restorations.

Evaluation of die trim morphology made by CAD-CAM technology

Statement of problemThe die contour can affect the emergence profile of prosthetic restorations. However, little information is available regarding the congruency between a stereolithographic (SLA) die and its corresponding natural tooth. PurposeThe purpose of this vitro study was to evaluate the shapes of SLA die in comparison with the subgingival contour of a prepared tooth to be restored with a ceramic crown. Material and methodsTwenty extracted human teeth, 10 incisors, and 10 molars, were disinfected and mounted in a typodont model. The teeth were prepared for a ceramic restoration. Definitive impressions were made using an intraoral scanner from which 20 SLA casts with removable dies were fabricated. The removable dies and corresponding human teeth were digitized using a 3-dimensional desktop scanner and evaluated with computer-aided design software. The subgingival morphology with regard to angle, length, and volume at the buccolingual and mesiodistal surfaces and at zones A, B, C, and D were compared. Data were first analyzed with repeated measures analysis of variance (ANOVA), using locations (buccolingual and mesiodistal), zones (A, B, C, and D), and model type (SLA and Natural) as within-subject factors and tooth type (molar and incisor) as the between-subject factor. Post hoc analyses were performed to investigate the difference between natural teeth and corresponding SLA models, depending upon the interaction effect from the repeated measures ANOVA (α=.05). ResultsFor angle analysis, the incisor group demonstrated a significant difference between the natural tooth and SLA die on the buccolingual surfaces (P<.05), whereas the molar group demonstrated a significant difference at the mesiodistal surfaces (P<.05). For the evaluation of length and volume, the incisor group showed significant differences in zone D on both the buccolingual (P<.05) and the mesiodistal (P<.05) surfaces. However, significant differences in zones C (P<.05) and D (P<.05) on the buccolingual surfaces and in all zones on the mesiodistal surfaces were observed in the molar group. ConclusionsFor the comparison of angles, SLA dies did not replicate the subgingival contour of natural teeth on the buccolingual surfaces of the incisal groups. For the comparison of length and volume, SLA dies were more concave and did not replicate the subgingival contour of natural teeth in the incisal and molar groups.

The effects of glass fiber-reinforced plastic for orthodontic wire on the malocclusion of mild anterior crowding during the initial leveling stage: A typodont experimental study

PurposeRecently, we developed glass fiber-reinforced plastic (GFRP) orthodontic wire made from polycarbonate and E-glass fiber. The purpose of this study was to investigate the utility of GFRP wire in a clinical orthodontic treatment setting, the typodont model was simulated with a Class I malocclusion and mild crowding (arch length discrepancy: 4.5mm). Materials and methodsGFRP round wire with a diameter of 0.45mm (0.018 in.) was prepared using 7μm glass fibers. As control, nickeltitanium (Ni–Ti: 0.018 inch) alloy was also evaluated. For both wire groups, we examined the difference the arch widh and the arch length in the maxillary and mandibular using superimposition of 3D virtual models before and after immersion in typodont model. We also examined the strain force and permanent deformation. ResultsThe inclination toward the labial aspect and the major axis of the upper and lower incisors increased, respectively, after the experiment. No significant differences before and after treatment were noted between the wires. On comparing the strain force of both wires after ligating the wire (4 weeks) in the strain test, the force of the GFRP wire was slightly lower than that of the Ni–Ti wires. In addition, there was more permanent deformation in the GFRP wire than in the Ni–Ti wire (P<0.05). ConclusionGFRP wire showed equivalent efficiency to that of commercial Ni–Ti wire in improving mild anterior crowding in a typodont experiment. Therefore, GFRP wire can be used in place of Ni–Ti wire during the initial leveling stage.

Ceramic molar crown reproducibility by digital workflow manufacturing: An in vitro study.

PURPOSEThis in vitro study aimed to analyze and compare the reproducibility of zirconia and lithium disilicate crowns manufactured by digital workflow.MATERIALS AND METHODSA typodont model with a prepped upper first molar was set in a phantom head, and a digital impression was obtained with a video intraoral scanner (CEREC Omnicam; Sirona GmbH), from which a single crown was designed and manufactured with CAD/CAM into a zirconia crown and lithium disilicate crown (n=12). Reproducibility of each crown was quantitatively retrieved by superimposing the digitized data of the crown in 3D inspection software, and differences were graphically mapped in color. Areas with large differences were analyzed with digital microscopy. Mean quadratic deviations (RMS) quantitatively obtained from each ceramic group were statistically analyzed with Student's t-test (α=.05).RESULTSThe RMS value of lithium disilicate crown was 29.2 (4.1) µm and 17.6 (5.5) µm on the outer and inner surfaces, respectively, whereas these values were 18.6 (2.0) µm and 20.6 (5.1) µm for the zirconia crown. Reproducibility of zirconia and lithium disilicate crowns had a statistically significant difference only on the outer surface (P<.001). The outer surface of lithium disilicate crown showed over-contouring on the buccal surface and under-contouring on the inner occlusal surface. The outer surface of zirconia crown showed both over- and under-contouring on the buccal surface, and the inner surface showed under-contouring in the marginal areas.CONCLUSIONRestoration manufacturing by digital workflow will enhance the reproducibility of zirconia single crowns more than that of lithium disilicate single crowns.

Tooth width measurement using the Lythos digital scanner

Abstract Introduction Digital models have become more widely accepted for orthodontic diagnostic purposes. Intraoral scanners have the advantage of eliminating the need for conventional impressions. The aim of the present study was to assess the reliability and reproducibility of the Lythos intraoral scanner and to determine if a significant advantage is delivered over stone model and caliper measurements in tooth width and Bolton ratio accuracy. Methods The study comprised 30 typodont models for which conventional alginate impressions and digital scans were obtained to generate stone and digital models, respectively. Mesiodistal tooth width measurements and Bolton ratios were obtained with either calipers and stone models or with Digicast (Ormco Lythos digital model software, Ormco, CA, USA) software using digital models. Pearson’s correlation coefficients tested intra-examiner reliability. Interclass correlation coefficients were used to assess agreement between examiners (reproducibility). The differences in the mean tooth width measurements and Bolton ratios from the typodont values and either the digital or conventional method were used to assess validity by applying two tailed t-tests. Results The measurements obtained from the Lythos and stone models had near perfect intra-examiner agreement (Pearson ≥ 0.98). The inter-examiner reproducibility for tooth widths, anterior Bolton and overall Bolton ratio was high and similar for both methods (Lythos scanner Interclass correlation coefficient (ICC) above 0.89, stone models ICC above 0.92). Stone model measurements were statistically twice as accurate as those derived from the digital system (0.032 mm versus 0.074 mm). There were no significant differences in accuracy between the methods for Bolton calculations. Clinically, there was no difference between the methods for tooth width measurements and Bolton calculations. Conclusions The Lythos system is as reliable and reproducible as conventional calipers and stone models in tooth width measurements and Bolton calculations. The caliper method presents a statistically more valid tooth width measurement technique but the clinical significance of this is questionable.

Influence of preparation design on the quality of tooth preparation in preclinical dental education

Background/purposeOne of the major educational goals in preclinical dental education is to learn tooth preparation techniques. The purpose of this study was to evaluate the influence of different preparation designs on the development of the manual dexterity of students, in order to perform a state-of-the-art tooth preparation. Material and methodsSeventy-two 1st semester students were divided into two groups and educated in tooth preparation for a ceramic anterior single crown. One group received cylindrical burs with a rounded edge to prepare a typodont model with a shoulder finishing line, while the other group had cylindrical burs with round noses to prepare a chamfer finishing line. All preparations were digitized and evaluated using special software focusing on the parameters of preparation depth and preparation angle. In addition, violation of the adjacent teeth was estimated. Data was statistically evaluated at a level of significance of 5%. ResultsThe preparation design used did not show a statistically significant influence on the preparation depth or on the preparation angle. A trend to a higher tooth structure removal as required was detected. Furthermore, no influence of the type of preparation design on the number of violated adjacent teeth was found. ConclusionIn preclinical dental education, the type of preparation design was found to have no influence on the measured parameters representing the quality of the preparation.

Micro-CT analysis of in-office computer-aided designed/computer-aided manufactured dental restorations

Purpose: The current study evaluated two different materials, using micro-CT to compare the marginal gap of feldspathic ceramic (V) and resin nano-ceramic (L) crowns obtained by two different computer-aided design/computer-aided manufacturing (CAD/CAM) systems, CEREC CAD/CAM system and E4D Technologies. Methods: A human lower left first premolar was mounted on a typodont model and prepared for an all-ceramic crown. Two groups (n = 5) were divided based on the system for obtaining the crowns and the material used for it (V and L). Micro-CT images were obtained for marginal gap measurements of each crown, and the data were statistically analysed by one-way analysis of variance followed by Tukey’s post hoc test for pairwise comparisons (α¼ 0.05). Results: There were no statistically significant differences between marginal gap of groups V and L (p = 0.473). The mean and standard deviation for the vertical misfit was V = 62.6 (65.2) and L = 66.5 (59.0). For the horizontal misfit, the values were divided into three groups: underextension (L = 20.8%) and (V = 54.6%), equally extended (L = 16.9%) and (V = 36.9%) and overextension (L = 62.3%) and (V = 8.5%). Conclusion: The results revealed no difference in the marginal fit of crowns produced by different materials and different chairside CAD/CAM systems. Both are considered clinically acceptable according to all cited classifications.

Evaluation of fit accuracy of computer-aided design/computer-aided manufacturing crowns fabricated by three different digital impression techniques using cone-beam computerized tomography

Purpose: The aim of this in vitro study was to evaluate the fit accuracy of computer-aided design (CAD)/computer-aided manufacturing lithium disilicate full contour crowns fabricated by three different digital impression techniques. Materials and Methods: An acrylic upper first molar was prepared to receive a full ceramic crown and used to fabricate ten ceramic master dies using lost wax and heat press techniques. Each ceramic die was seated in a typodont model and ten polyvinyl siloxane impressions were made for the dies and neighboring teeth to fabricate ten stone casts. Three groups of lithium disilicate crowns ( n = 10) were fabricated; Group E: Crowns were fabricated by scanning the ten stone casts with in Eos X5 extraoral scanner. Group O: Crowns were fabricated by powder-free scanning of the ten ceramic dies in their typodont models with CEREC Omnicam. Group B: Crowns were fabricated by CEREC Bluecam optical impressions of the ceramic dies in their typodont models after titanium dioxide powder application. All the specimens were milled from IPS e-max CAD blanks. Each crown was evaluated on its die for fit accuracy using computerized cone-beam tomography at seventy measuring points. The variability among the three groups was evaluated using one-way ANOVA test at P Results: No statistically significant difference was found among the three groups for overall results at ( P = 0.658), whereas Group E showed significantly better marginal fit with a mean value of 76 ± 39.0 μm at P = 0.047. Conclusions: All tested digital impression techniques showed clinically acceptable accuracy and extraoral scanning significantly enhanced the marginal fit.

Accuracy and reproducibility of linear measurements of resin, plaster, digital and printed study-models.

To compare the accuracy and reproducibility of measurements of on-screen three-dimensional (3D) digital surface models captured by a 3Shape R700™ laser-scanner, with measurements made using a digital caliper on acrylic, plaster models or model replicas. Four sets of typodont models were used. Acrylic models, alginate impressions, plaster models and physical replicas were measured. The 3Shape R700™ laser-scanning device with 3Shape™ software was used for scans and measurements. Linear measurements were recorded for selected landmarks, on each of the physical models and on the 3D digital surface models on ten separate occasions by a single examiner. Comparing measurements taken on the physical models the mean difference of the measurements was 0.32 mm (SD 0.15 mm). For the different methods (physical versus digital) the mean difference was 0.112 mm (SD 0.15 mm). None of the values showed a statistically significant difference (p < 0.05) on the Objet Eden 250™ 3D prints, alginate impressions, plaster and acrylic models. The comparison of measurements on the physical models showed no significant difference. The 3Shape R700™ is a reliable device for capturing surface details of models in a digital format. When comparing measurements taken manually and digitally there was no statistically significant difference. The Objet Eden 250™ 3D prints proved to be as accurate as the original acrylic, plaster, or alginate impressions as was shown by the accuracy of the measurements taken. This confirms that using virtual study models can be a reliable method, replacing traditional plaster models.

Dental image replacement on cone beam computed tomography with three-dimensional optical scanning of a dental cast, occlusal bite, or bite tray impression

The goal of the present study was to compare the accuracy of dental image replacement on a cone beam computed tomography (CBCT) image using digital image data from three-dimensional (3D) optical scanning of a dental cast, occlusal bite, and bite tray impression. A Bracket Typodont dental model was used. CBCT of the dental model was performed and the data were converted to stereolithography (STL) format. Three experimental materials, a dental cast, occlusal bite, and bite tray impression, were optically scanned in 3D. STL files converted from the CBCT of the Typodont model and the 3D optical-scanned STL files of the study materials were image-registered. The error range of each methodology was measured and compared with a 3D optical scan of the Typodont. For the three materials, the smallest error observed was 0.099±0.114mm (mean error±standard deviation) for registering the 3D optical scan image of the dental cast onto the CBCT dental image. Although producing a dental cast can be laborious, the study results indicate that it is the preferred method. In addition, an occlusal bite is recommended when bite impression materials are used.

Monitoring of typodont root movement via crown superimposition of single cone-beam computed tomography and consecutive intraoral scans

The purpose of this study was to develop a new methodology to visualize in 3 dimensions whole teeth, including the roots, at any moment during orthodontic treatment without the need for multiple cone-beam computed tomography (CBCT) scans. An extraoral typodont model was created using extracted teeth placed in a wax base. These teeth were arranged to represent a typical malocclusion. Initial records of the malocclusion, including CBCT and intraoral surface scans, were taken. Threshold segmentation of the CBCT was performed to generate a 3-dimensional virtual model. This model and the intraoral surface scan model were superimposed to generate a complete set of digital composite teeth composed of high-resolution surface scan crowns sutured to the CBCT roots. These composite teeth were individually isolated from their respective arches for single-tooth manipulations. Orthodontic treatment for the malocclusion typodont model was performed, and posttreatment intraoral surface scans before and after bracket removal were taken. A CBCT scan after bracket removal was also obtained. The isolated composite teeth were individually superimposed onto the posttreatment surface scan, creating the expected root position setup. To validate this setup, it was compared with the posttreatment CBCT scan, which showed the true positions of the roots. Color displacement maps were generated to confirm accurate crown superimpositions and to measure the discrepancies between the expected and the true root positions. Color displacement maps through crown superimpositions showed differences between the expected and true root positions of 0.1678 ± 0.3178 mm for the maxillary teeth and 0.1140 ± 0.1587 mm for the mandibular teeth with brackets. Once the brackets were removed, differences of 0.1634 ± 0.3204 mm for the maxillary teeth and 0.0902 ± 0.2505 mm for the mandibular teeth were found. A new reliable approach was demonstrated in an ex-vivo typdont model to have the potential to track the 3-dimensional positions of whole teeth including the roots, with only the initial CBCT scan and consecutive intraoral scans. Since the presence of brackets in the intraoral scan had a minimal influence in the analysis, this method can be applied at any stage of orthodontic treatment.

Application of Typodont-based table clinic competition in undergraduate orthodontic education

Objective To evaluate the effectiveness of Typodont-based table clinic competition （ TCC ） on undergraduate orthodontic education. Methods Students who have finished basic orthodon- tic courses made diagnosis, treatment strategy and performed orthodontic treatment for malocclusion cases on Typodonts. A self-design questionnaire was employed to investigate their perception to this pedagogy. Results The majority of participants （ 82.2%-92.9% ） highly evaluated Typodont-based TCC. Conclu- sions Typodont-based TCC course is conducive to arousing students＇ study internets and to promoting association between theory and practice. Key words: Orthodontics; Typodont model; Table clinic competition; Orthodontic education

An initial assessment of haptics in preclinical operative dentistry training

The purpose of this study was to assess novice student perception of haptic-based manual dexterity training. The short-term impact of haptic training in the early phase of preclinical operative dentistry education was also investigated. Dental students performed a class II amalgam and a class III resin tooth preparation in a typodont model at baseline. The experimental group performed exercises on the manual dexterity module of the IDEA™ software using a haptic device. The exercises required removing the maximum amount of three-dimensional geometric shapes within a predetermined width and depth. Tooth preparations were repeated 2weeks later. A questionnaire survey was given to assess the subjective evaluation of the haptic simulation exercise. Tooth preparations were scored regarding external outline, internal form, and integrity of adjacent tooth. Improvement of overall tooth preparation scores post-haptic use was not statistically significant compared to controls (P>0.05). However, students found the game-feature of the haptic device made the learning experience more fun and interesting. The haptic exercises with the manual dexterity module software were not superior in improving the dexterity of students for tooth cavity preparations in short-term. Benefits of ease of use and fun learning experience can be further investigated in future studies.