Comparison of the accuracy of a cone beam computed tomography-based virtual mounting technique with that of the conventional mounting technique using a facebow.

STATEMENT OF PROBLEM: The introduction of digital technology in dentistry has resulted in a shift from conventional methods to digital techniques. However, mounting a digitized dental cast on a virtual articulator is challenging. Several techniques have been suggested to resolve this problem, but in the absence of a standardized method, digitized dental casts are often mounted arbitrarily on a virtual articulator. PURPOSE: The purpose of this clinical study was to compare the accuracy of a novel virtual facebow transfer (VM) technique based on cone beam computed tomography (CBCT) with that of the conventional mounting (CM) technique using a facebow. MATERIAL AND METHODS: Five repeated mountings were performed with each technique for 15 participants. In the CM group, dental casts were mounted using a facebow record and scanned for transmission to the virtual dental space. In the VM group, digital dental casts were mounted on the standard tessellation language file of a reference articulator by reconstructing a file of the participant's skull from CBCT data. In this group, a virtual facebow, prepared by scanning the articulator and facebow complex, was used. After the CM and VM casts had been aligned, the coordinates of target points set on the maxillary right central incisor, maxillary right first molar, and maxillary left first molar were determined, and the mean ±standard deviation distance between the target points was calculated to compare the precision of the techniques. Additionally, vectors of the target point on the maxillary right central incisor were compared to analyze the spatial difference between the techniques. Finally, the occlusal plane angle was calculated. For the correlation analysis of repeated measured data, a 1-way repeated measures analysis of variance (ANOVA) was first performed. The Kolmogorov-Smirnov test was performed to determine normality, and a paired t test and the Wilcoxon signed rank test were performed for normally and nonnormally distributed variables, respectively (α=.05). RESULTS: The mean distance between target points was significantly greater in the CM group (4.72 ±1.45 to 5.17 ±1.54 mm) than in the VM group (2.14 ±0.58 to 2.35 ±0.60 mm) (P<.05). The standard deviation between target points was significantly greater in the CM group (1.60 ±0.64 to 2.30 ±0.87 mm) than in the VM group (0.74 ±0.23 to 1.12 ±0.45 mm) (P<.05). The maxillary right central incisor was located more anteriorly in the VM group than in the CM (100%, P<.05) group. The occlusal plane angle was significantly steeper in the CM group than in the VM group (8.14 degrees versus 2.13 degrees, P<.05). CONCLUSIONS: The VM technique was more precise than the CM technique. VM casts were positioned ahead of CM casts. Further, the occlusal plane angle tended to be steeper with the CM technique than with the VM technique.

A comprehensive study on the mechanical effects of implant-supported prostheses under multi-directional loading and different occlusal contact points.

AIMS: To evaluate screw loosening and fracture load and angular deviation of a single implant-supported prosthesis under multi-directional loading condition at three different occlusal contact points. METHODS: A total of 40 metal crowns were cemented to external connection implants and were embedded vertically and obliquely. The occlusal surface of the crown was designed with three flat surfaces, contact a, b, and c, representing outer and inner 20-degree inclination for buccal and lingual cusps. The angular deviations of implant crown under static 50N of loading were measured. And screw removal torque was evaluated before and after 57,600 load cycles. Then, fracture load was measured for each specimen. Data analysis was performed using one-way analysis of variance test of significance followed by Tukey honest significant difference (HSD) test(p < 0.05). RESULTS: Angular deviation results showed statistical significance between all contact points in vertically embedded group compared to obliquely embedded group, which showed similar results between contact A and B compared to C. In the other hand, screw loosening evaluation did not show statistical significance among the tested groups. And for the fracture load evaluation the maximum values reached twice the yield values in all contact areas. CONCLUSIONS: Mechanical effects were different regarding to diverse loading direction and contact points. The results of this study suggest that the stress concentration might increase in unfavorable vector direction.

Effect of airborne particle abrasion treatment of two types of 3D-printing resin materials for permanent restoration materials on flexural strength.

OBJECTIVES: This study aimed to assess the effects of airborne-particle abrasion (APA) on the flexural strength of two types of 3D-printing resins for permanent restoration. METHODS: Two types of 3D printing resins (urethane dimethacrylate oligomer; UDMA, ethoxylated bisphenol-A dimethacrylate; BEMA) constituting different components were printed. The specimen surfaces were subjected to APA using 50 and 110 µm alumina particles under different pressures. The three-point flexural strength was measured for each surface treatment group, and a Weibull analysis was performed. Surface characteristics were analyzed via surface roughness measurements and scanning electron microscopy. Dynamic mechanical analysis and nano-indentation measurements were limited to the control group. RESULTS: The three-point flexural strength according to the surface treatment was significantly lower in the UDMA group for large particle sizes and at high pressures; the BEMA group demonstrated low flexural strength for large particle sizes regardless of the pressure. After thermocycling, the flexural strengths of UDMA and BEMA significantly decreased in the group subjected to surface treatment. The Weibull modulus and characteristic strength of UDMA were higher than those of BEMA under different APA and thermocycling conditions. As the abrasion pressure and particle size increased, a porous surface formed, and the surface roughness increased. Compared with BEMA, UDMA featured a lower strain, greater strain recovery, and a negligible increase in modulus according to strain. SIGNIFICANCE: Thus, surface roughness increased with the sandblasting particle size and pressure of the 3D-printing resin. Hence, a suitable surface treatment method to improve adhesion can be determined by considering physical property changes.

Effect of cement space settings on the marginal and internal fit of 3D-printed definitive resin crowns.

STATEMENT OF PROBLEM: The cement gap setting affects the marginal and internal fits depending on the crown material and manufacturing method (subtractive or additive manufacturing). However, information on the effects of cement space settings in the computer-aided design (CAD) software program, which is used to aid the manufacturing with 3-dimensional (3D) printing-type resin material, is lacking, and recommendations for optimal marginal and internal fit are needed. PURPOSE: The purpose of this in vitro study was to evaluate how cement gap settings affect the marginal and internal fit of a 3D-printed definitive resin crown. MATERIAL AND METHODS: After scanning a prepared typodont left maxillary first molar, a crown was designed with cement spaces of 35, 50, 70, and 100 µm by using a CAD software program. A total of 14 specimens per group were 3D printed from definitive 3D-printing resin. By using the replica technique, the intaglio surface of the crown was duplicated, and the duplicated specimen was sectioned in the buccolingual and mesiodistal directions. Statistical analyses were performed using the Kruskal-Wallis and the Mann-Whitney post hoc tests (α=.05). RESULTS: Although the median values of the marginal gaps were within the clinically acceptable limit (<120 µm) for all the groups, the smallest marginal gaps were obtained with the 70-µm setting. For the axial gaps, there was no observed difference in the 35-, 50-, and 70-µm groups, and the 100-µm group showed the largest gap. The smallest axio-occlusal and occlusal gaps were obtained with the 70-µm setting. CONCLUSIONS: Based on the findings of this in vitro study, a 70-µm cement gap setting is recommended for optimal marginal and internal fit of 3D-printed resin crowns.

Effect of Adhesion Conditions on the Shear Bond Strength of 3D Printing Resins after Thermocycling Used for Definitive Prosthesis.

Three-dimensional (3D) printing polymers such as urethane dimethacrylate (UDMA) and ethoxylated bisphenol A dimethacrylate (Bis-EMA) are typically used in definitive prosthesis and require surface treatments before bonding. However, surface treatment and adhesion conditions often affect long-term use. Herein, polymers were divided into Groups 1 and 2 for the UDMA and Bis-EMA components, respectively. The shear bond strength (SBS) between two types of 3D printing resins and resin cements was measured using Rely X Ultimate Cement and Rely X U200, according to adhesion conditions such as single bond universal (SBU) and airborne-particle abrasion (APA) treatments. Thermocycling was performed to evaluate the long-term stability. Sample surface changes were observed using a scanning electron microscope and surface roughness measuring instrument. The effect of interaction between the resin material and adhesion conditions on the SBS was analyzed via a two-way analysis of variance. The optimal adhesion condition for Group 1 was achieved when U200 was used after APA and SBU, whereas Group 2 was not significantly affected by the adhesion conditions. After thermocycling, the SBS significantly decreased in Group 1 without APA treatment and in the entire Group 2. Additionally, porosity, along with increased roughness, was observed on both material surfaces after APA.

Top-down design and fabrication with digital technology of removable partial dentures incorporating custom abutments: A dental technique.

A novel design of removable partial dentures (RPDs) is described wherein custom abutments are incorporated into the RPD framework. The artificial teeth and custom abutments are designed by using a computer-aided design (CAD) software program. Subsequently, the RPD framework is designed and merged to the custom abutments in the CAD software program to form a single unit. This modified framework is additively manufactured in metal by using a 3D printer. Thereafter, the framework is adapted to the definitive cast and scanned by using a laboratory scanner. The scanned file is imported into the CAD software program, and the artificial teeth are redesigned. After fabricating each artificial tooth from a polymethylmethacrylate disk and artificial tooth and denture-base assemblies from a wax disk, the RPD is injection molded. This RPD design and fabrication workflow enables a top-down approach by prioritizing the shape and arrangement of the artificial teeth and facilitates their replacement.

Changes in masticatory performance during the retention period following 4-premolar extraction and non-extraction orthodontic treatment.

OBJECTIVES: To evaluate changes in masticatory performance (MP) during the retention period after extraction and non-extraction treatment and compare it with MP in individuals with normal occlusion. MATERIALS AND METHODS: Adult patients who had completed orthodontic fixed appliance treatment comprised the extraction and non-extraction treatment groups, and those with normal occlusion comprised the control group. Their mixing ability (MA), maximum bite force (MBF), and occlusal contact area (OCA) were recorded immediately after the fixed appliance was removed and at 1 month, 6 months, and 1 year post-treatment. The MA was measured via the two-color chewing gum MA test using ViewGum software, and the MBF and OCA were measured using Dental Prescale II system. RESULTS: MA immediately after orthodontic treatment was lower than that in the normal group but showed a time-dependent gradual increase during a 1-year retention period (P < 0.01). The MA at 1 month post-treatment was not significantly different between the three groups (P > 0.05). The MA revealed a significant correlation with the MBF and OCA (P < 0.01). CONCLUSIONS: The MP immediately after orthodontic treatment was lower than that in the normal group but increased gradually, with levels comparable to those of the normal occlusion group at 1 month post-treatment. Further, extraction did not affect the recovery of the MP after orthodontic treatment. CLINICAL RELEVANCE: No other study has evaluated the changes in MP during the retention period after orthodontic treatment. The findings show that compared with MBF and OCA, the patients' MP improved faster to levels found in normal occlusion.

Novel 3D Printed Resin Crowns for Primary Molars: In Vitro Study of Fracture Resistance, Biaxial Flexural Strength, and Dynamic Mechanical Analysis.

This study evaluated the fracture resistance, biaxial flexural strength (BFS), and dynamic mechanical analysis (DMA) of three-dimensional (3D) printing resins for the esthetic restoration of primary molars. Two 3D printing resins, Graphy (GP) and NextDent (NXT), and a prefabricated zirconia crown, NuSmile (NS), were tested. GP and NXT samples were 3D printed using the workflow recommended by each manufacturer. Data were collected and statistically analyzed. As a result of the fracture resistance test of 0.7-mm-thick 3D printed resin crowns with a thickness similar to that of the NS crown, there was no statistically significant difference among GP (1491.6 ± 394.6 N), NXT (1634.4 ± 289.3 N), and NS (1622.8 ± 323.9 N). The BFS of GP was higher for all thicknesses than that of NXT. Both resins showed high survival probabilities (more than 90%) when subjected to 50 and 150 MPa. Through DMA, the glass transition temperatures of GP and NXT were above 120 °C and the rheological behavior of GP and NXT according to temperature and frequency were analyzed. In conclusion, GP and NXT showed optimum strength to withstand bite forces in children, and 3D printed resin crowns could be an acceptable option for fixed prostheses of primary teeth.

Accuracy of metal 3D printed frameworks for removable partial dentures evaluated by digital superimposition.

OBJECTIVES: To evaluate the accuracy of metal 3D printed frameworks (MEP group) for removable partial dentures (RPDs) by digital superimposition, in comparison to that of frameworks produced by the conventional (CON group) and resin printing/casting (RPC group) workflows. METHODS: A partially edentulous maxillary dentiform was prepared with rest seats and guiding planes on the right canine, left first premolar, and left second molar. Thirty master casts were prepared via repeated impressions of the dentiform. Frameworks were fabricated by three different workflows (n = 10 for each group). The internal discrepancies of the frameworks were assessed at 12 points by digital scanning with an optical triangulation principle-based tabletop scanner and superimposition using a reference best-fit alignment method. First, the master cast was scanned alone. Subsequently, a thin silicone material was applied to the framework and fitted onto the master cast, after which the framework was removed. Finally, the master cast with the silicone material attached was rescanned. The data from the two scans were matched, with the reference being the area not occupied by the silicone. RESULTS: For the CON, MEP, and RPC groups, respectively, the mean overall internal discrepancies (279.72 µm, 241.02 µm, and 331.70 µm), and the mean internal discrepancies on palate areas (292.92 µm, 250.72 µm, and 355.84 µm) and rest seat areas (240.12 µm, 211.91 µm, and 259.26 µm) did not significantly differ among the three fabrication methods (p = 0.558, 0.542, and 0.774). SIGNIFICANCE: The reference best-fit alignment of scan datasets is a useful approach to evaluate the internal discrepancy of frameworks. Metal 3D printing produces RPD frameworks that are comparable to conventional frameworks and meet clinical standards.

Accuracy of impression-making methods in edentulous arches: An in vitro study encompassing conventional and digital methods.

STATEMENT OF PROBLEM: Studies evaluating the accuracy of edentulous arch impressions encompassing conventional and digital methods are lacking. PURPOSE: The purpose of this in vitro study was to evaluate 8 impression-making methods for edentulous arches and to determine the effects of using a 3-dimensionally printed polyetheretherketone (PEEK) scanning aid on the accuracy of intraoral scanners. MATERIAL AND METHODS: Three sets of edentulous arch typodonts were scanned with an industrial scanner as a reference. Subsequently, a scanning aid for the edentulous arch was individually designed on each reference scan dataset by using a 3-dimensional modeling software program and fabricated in PEEK with a 3-dimensional printer. Each typodont was scanned with 2 intraoral scanners 12 times, with and without the assistance of a scanning aid for the edentulous arch. Impressions were made with 4 different conventional impression materials (irreversible hydrocolloid, polysulfide, polyether, and polyvinyl siloxane)-12 times for each typodont-the casts were poured and digitized with a tabletop scanner. Each scan data set was superimposed over the corresponding scan data set, and the original and absolute distance values from the paired surface points were obtained to measure the trueness and precision. These were expressed by using the mean, median, root mean square, and (90 percentile-10 percentile)/2 of the absolute distance value (NMT) concepts, based on the raw data extraction protocol. A repeated-measures ANOVA followed by a post hoc Bonferroni test was conducted (α=.05). RESULTS: The impression-making methods did not show statistically significant differences (P>.05) for either trueness or precision, particularly when the median values of the original and absolute distance values from the paired surface points were chosen as the standard values. One of the intraoral scanners used exhibited significantly superior outcomes to conventional impression materials when scanned with the scanning aid for the edentulous arch for both trueness and precision when the mean, root mean square, and NMT concepts were applied (P<.05). CONCLUSIONS: Intraoral scanners demonstrated accuracy comparable with that of conventional impression materials for making edentulous arch impressions, regardless of the concepts used to express the trueness and precision. The PEEK-based scanning aid for the edentulous arch did not improve the accuracy of the intraoral scanners; however, its application resulted in higher accuracy compared with that of conventional impression materials.

Immediate loading of fixed partial prostheses reconstructed using either tapered or straight implants in the posterior area: A randomized clinical trial.

BACKGROUND: In immediately loaded implants within 72 h after the implant placement in the unilaterally and partially edentulous ridge, primary stability is considered critical, which can be influenced by the design of the implant fixture. PURPOSE: To determine the outcomes at 1 year after the immediate loading of multiunit fixed partial prostheses over either tapered implants (TIs) or straight implants (SIs) in the posterior region. MATERIALS AND METHODS: Forty-eight patients (24 patients, 52 implants in TI group; 24 patients, 50 implants in SI group) were included for the study. Except for the one SI group patient whose two implants showed the insertion torque less than 30 Ncm, provisional prostheses designed and fabricated from intraoral scan data obtained immediately after implant surgery were delivered to rest of the 47 subjects at 3-7 days. After a year, the survival rate was estimated by intention-to-treat (ITT) and per-protocol (PP) analyses, and marginal bone loss (MBL) and implant stability were also analyzed statistically (p < 0.05). RESULTS: Survival rate at implant level in TI group was 96.2%, and that of SI group in the ITT analysis was 86.0%. Intergroup difference, however, was not statistically significant (p > 0.05). Insertion torque was significantly higher in TI group than SI group (47.12 ± 6.37 Ncm vs. 41.60 ± 9.77 Ncm; p < 0.05). MBLs of both groups were less than 0.1 mm at 1-year follow-up and was similar between two groups (p > 0.05). CONCLUSIONS: Immediate loading of fixed partial prostheses after TI and SI placement showed reliable outcomes in the partially edentulous posterior ridge. In terms of the initial mechanical stability, the performance was superior for TIs than for SIs.

Influence of shoulder coverage difference of abutment on stress distribution and screw stability in tissue-level internal connection implants: A finite element analysis and in vitro study.

STATEMENT OF PROBLEM: Tissue-level internal connection implants are widely used, but the difference in abutment screw stability because of the shoulder coverage formed by the contact between the shoulder of the implant collar and the abutment remains unclear. PURPOSE: The purpose of this finite element analysis (FEA) and in vitro study was to investigate stress distribution and abutment screw stability as per the difference in shoulder coverage of the abutment in tissue-level internal connection implants. MATERIAL AND METHODS: Abutments were designed in 3 groups as per the shoulder coverage of the implant collar, yielding complete coverage (complete group), half coverage (half group), no coverage (no group) groups. In the FEA, a tightening torque of 30.0 Ncm was applied to the abutment screw, a force of 250 N was applied to the crown at a 30-degree angle, and the von Mises stresses and the stress distribution patterns were evaluated. In the in vitro study, the groups were tested (n=12). A total of 200 000 cyclic loads were applied at 250 N, 14 Hz, and at a 30-degree angle. Removal torque values and scanning electron microscopy (SEM) images were assessed. Removal torque values were analyzed by ANOVA and paired t tests. RESULTS: The maximum von Mises stress of the abutment screw was the lowest in the complete group, slightly higher in the half group, and highest in the no group. High stresses were concentrated in 1 location in the implant abutment connection area of the no group. The removal torque values after loading were significantly lower in the no group than in the complete group (P=.047). The SEM images revealed concentrated structural loss and wear in 1 location of the no group. CONCLUSIONS: FEA and in vitro studies confirmed that the shoulder coverage of the abutment in the tissue-level internal connection implant helped improve screw stability. Cyclic loading reduced the removal torque of the abutment screw.

Mounting casts on a mechanical articulator by using digital multisource data: A dental technique.

A facebow transfer is typically used for mounting a maxillary gypsum cast in an ideal location in a mechanical articulator. However, the facebow transfer procedure is difficult and may cause the patient discomfort. This proposed technique uses a patient's cone beam computed tomography (CBCT) data to reproduce the occlusal plane in relation to digital articulator scan data, align the patient's gypsum cast or intraoral scan data on the reproduced plane, and then transfer the data to a mechanical articulator.

Fabrication of a removable partial denture combining conventional and digital techniques.

This article describes a combined conventional and digital workflow for fabricating removable partial dentures (RPDs). After scanning the dental cast and RPD framework assembly, artificial teeth and denture base regions were designed using computer-aided design software. The artificial teeth and denture base assembly was milled as a single structure by using a wax disk and then placed on the RPD framework. The artificial teeth were additionally milled from a polymethyl methacrylate disk. Conventional procedures were followed for denture investment until the wax elimination procedure, after which the assembly was replaced with the artificial teeth in the cope of the flasks, and the denture resin material was injected to process the RPD. This technique enabled the RPD to be fabricated in the same form as the design state.

Evaluation of the 3D Printing Accuracy of a Dental Model According to Its Internal Structure and Cross-Arch Plate Design: An In Vitro Study.

The amount of photopolymer material consumed during the three-dimensional (3D) printing of a dental model varies with the volume and internal structure of the modeling data. This study analyzed how the internal structure and the presence of a cross-arch plate influence the accuracy of a 3D printed dental model. The model was designed with a U-shaped arch and the palate removed (Group U) or a cross-arch plate attached to the palate area (Group P), and the internal structure was divided into five types. The trueness and precision were analyzed for accuracy comparisons of the 3D printed models. Two-way ANOVA of the trueness revealed that the accuracy was 135.2 ± 26.3 µm (mean ± SD) in Group U and 85.6 ± 13.1 µm in Group P. Regarding the internal structure, the accuracy was 143.1 ± 46.8 µm in the 1.5 mm-thick shell group, which improved to 111.1 ± 31.9 µm and 106.7 ± 26.3 µm in the roughly filled and fully filled models, respectively. The precision was 70.3 ± 19.1 µm in Group U and 65.0 ± 8.8 µm in Group P. The results of this study suggest that a cross-arch plate is necessary for the accurate production of a model using 3D printing regardless of its internal structure. In Group U, the error during the printing process was higher for the hollowed models.

Assessment of Compatibility between Various Intraoral Scanners and 3D Printers through an Accuracy Analysis of 3D Printed Models.

To assess the accuracy of various intraoral scanners (IOSs) and to investigate the existence of mutual compatibility that affects the accuracy between IOS and 3-dimensional (3D) printing using a scan quadrant model. For clinical implication, crown preparations and cavity design according to prosthetic diagnosis and treatment considerations must be acquired by a digital scanner. The selected typodont model was scanned using a reference scanner, from which reference (Ref) standard tessellation language (STL) data were created. Data obtained by scanning the typodont model with IOSs based on three different technologies were divided into three groups (CS3600, i500, and Trios3). Scanned data from the groups were divided into sub-groups of digital light processing (DLP), fused deposition modeling (FDM), and stereolithography apparatus (SLA), based on which 3D printed models (3DP) were fabricated. The 3DP dental models were scanned to obtain a total of 90 3DP STL datasets. The best-fit algorithm of 3D analysis software was used for teeth and arch measurements, while trueness was analyzed by calculating the average deviation among measured values based on superimposition of Ref and IOS and 3DP data. The differences between Ref and IOS (Ref-IOS), Ref and 3DP (Ref-IOS/3DP), and IOS and 3DP data (IOS-3DP) were compared and analyzed, while accuracy within each of the three main groups was assessed. For statistical analysis, the Kruskal-Wallis, Mann-Whitney U, and repeated measures ANOVA test were used (p < 0.05). The major finding is that the mutual relationships between IOSs and 3D printers vary depending on the combination. However, i500 intraoral scanner and DLP 3D printer was the combination that showed the best trueness value.

Effect of Pressure and Particle Size During Aluminum Oxide Air Abrasion on the Flexural Strength of Disperse-Filled Composite and Polymer-Infiltrated Ceramic Network Materials.

Esthetic dental computer-aided design/computer-aided manufacturing (CAD/CAM) polymers such as disperse-filled composites (DFC) and polymer-infiltrated ceramic networks (PICN) should be subjected to surface treatment before bonding. However, such treatment can lead to defect formation and a decrease in strength. Therefore, in this study, we compared the flexural strengths of DFC and PICN materials air-abraded with alumina particles of different sizes at different pressures. In addition to Weibull analysis, the samples (untreated and treated) were characterized by scanning electron microscopy and atomic force microscopy. Both DFC and PICN exhibited the lowest flexural strength at large particle sizes and high pressures. Therefore, we optimized the air abrasion parameters to maintain the flexural strength and significantly increase surface roughness. In the case of DFC, the optimal particle size and pressure conditions were 50 µm at 2 bar and 110 µm at 1 bar, while for PICN, the best performance was obtained using Al2O3 particles with a size of 50 µm at 1 bar. This study reveals that optimization of the surface treatment process is crucial in the fabrication of high-performance clinical materials for dental restorations.

Effect of Low-Concentration Hydrofluoric Acid Etching on Shear Bond Strength and Biaxial Flexural Strength after Thermocycling.

This study evaluated the shear bond strength (SBS) and biaxial flexural strength (BFS) of resin cements according to the surface treatment method using low-temperature hot etching with hydrofluoric acid (HF) on a yttrium-stabilized tetragonal zirconia (Y-TZP) surface; 96 discs and 72 cubes for BFS and SBS tests for Y-TZP were randomly divided into four groups of BFS and three groups of SBS. Specimens were subjected to the following surface treatments: (1) no treatment (C), (2) air abrasion with 50 µm Al2O3 particles (A), (3) hot etching with HF at 100 °C for 10 min (E), and (4) air abrasion + hot etching (AE). After treatments, the specimens were coated with primer, and resin cement was applied with molds. The specimens were evaluated for roughness (Ra) via scanning electron microscopy and x-ray diffraction, and the data were analyzed by an analysis of variance (ANOVA) and Kruskal-Wallis tests. Group E produced significantly higher SBS compared to group A and AE before and after thermocycling. The BFSs of all groups showed no significant differences before thermocycling; however, after thermocycling, C and E treatment groups were significantly higher compared to group A and AE. All groups showed phase transformation. Group E was observed lower monoclinic phase transformation compared to other groups.

A generation process for a three-dimensional digital cast that simulates the oral cavity by using an existing maxillary obturator.

To simulate the current oral status of patients, including maxillofacial defects, the digital method described uses a method based on multisource data. These include data recorded from scans made with and without wearing an obturator and data obtained by scanning the surgical or interim obturator. This method eliminates the need for preliminary impressions and complex border-molding steps during the process of creating a definitive obturator, thereby greatly simplifying the fabrication process.