3D analysis of occlusal registration through geometry embedded library matching between quadrant and full-arch digital impression.

OBJECTIVE: This study aimed to compare the accuracy of occlusal registration for single-unit restorations in the posterior area of the jaw using the complete-arch or quadrant scan techniques. MATERIALS AND METHODS: A master cast was prepared and articulated on a nonadjustable articulator, and the maxillary left first molar was prepared for a full-coverage crown. The master cast was digitized as the reference data using a laboratory scanner (E3 scanner, 3Shape, Copenhagen, Denmark). It was scanned 10 times in the complete arch and 10 times in the quadrant, with an occlusal registration in each, using four intraoral scanners (i500, Primescan, TRIOS 3, and TRIOS 4). The scanned data were aligned to the reference data using GOM Inspect software. A three-dimensional analysis of the surface-based occlusal clearance and angular deviation, focusing on the prepared tooth, was performed. RESULTS: The mean surface-based occlusal clearance in the quadrant and complete-arch scans was 1.622 ± 0.032 mm and 1.642 ± 0.043 mm, respectively. Angular deviations compared to the reference cast showed a difference of 0.10° distally and 0.09° buccally for the quadrant scan and 0.12° distally and buccally for the complete-arch scan. Statistical analysis was performed using one-way analysis of variance and post hoc Scheffe's test. No significant differences were observed between the test groups. CONCLUSIONS: No significant differences were found between occlusal registrations of the complete-arch and quadrant scans. Therefore, a quadrant scan can achieve the same outcome as a complete-arch scan for single-unit restoration in the posterior area of the jaw. CLINICAL RELEVANCE: Quadrant scanning for single-unit restoration showed similar outcomes as complete-arch scans.

Evaluation of different registration methods and dental restorations on the registration duration and accuracy of cone beam computed tomography data and intraoral scans: a retrospective clinical study.

OBJECTIVES: To evaluate whether the accuracy and duration of registration for cone beam computed tomography (CBCT) and intraoral scans differ according to the method of registration and ratio of dental restorations to natural teeth. MATERIALS AND METHODS: CBCT data and intraoral scans of eligible patients were grouped as follows according to the ratio of the number of dental restorations to the number of natural teeth (N): group 1, N = 0%; group 2, 0% < N < 50%; group 3, 50% ≤ N < 100%; and group 4, 100% ≤ N. Marker-free registration was performed with a deep learning-based platform and four implant planning software with different registration methods (two point-based, one surface-based, and one manual registration software) by a single operator, and the time consumption was recorded. Registration accuracy was evaluated by measuring the distances between the three-dimensional models of CBCT data and intraoral scans. RESULTS: A total of 36 patients, one jaw per patient, were enrolled. Although registration accuracy was similar, the time consumed for registration significantly differed for the different methods. The deep learning-based registration method consumed the least time. Greater proportions of dental restorations significantly reduced the registration accuracy for semi-automatic and deep learning-based methods and reduced the time consumed for semi-automatic registration. CONCLUSIONS: No superiority in registration accuracy was found. The proportion of dental restorations significantly affects the accuracy and duration of registration for CBCT data and intraoral scans. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov Identifier: KCT0006710 CLINICAL RELEVANCE: Registration accuracy for virtual implant planning decreases when the proportion of dental restorations increases regardless of registration methods.

Application of additive and subtractive manufacturing technology for a digitally fabricated removable partial denture after a partial maxillectomy: A clinical report.

This clinical report describes the treatment of a patient with a large defect area in the maxillary central incisor, left lateral incisor, canine, and first premolar area after a partial maxillectomy. Computer-aided design and computer-aided manufacturing (CAD-CAM) techniques including rapid prototyping and milling were applied together to fabricate a removable partial denture.

Effects of postpolymerization conditions on the physical properties, cytotoxicity, and dimensional accuracy of a 3D-printed dental restorative material.

STATEMENT OF PROBLEM: Although the introduction of high-speed 3-dimensional (3D) printing technology has significantly reduced printing time, the time required for postpolymerization is a speed-determining step because of the long wait time. How postpolymerization conditions affect material properties is unclear. PURPOSE: The purpose of this in vitro study was to assess the physical properties, accuracy, and biosafety of a 3D-printed dental restorative material according to postpolymerization conditions. MATERIAL AND METHODS: Specimens were prepared by 3D printing with a digital light processing 3D printer with 1 interim dental material (C&B MFH). All printed specimens underwent a postpolymerization process with 5 different postpolymerization devices and were designated as groups D1 (D102H), FO (Form Cure), LC (LC-3DPrintBox), ME (Medusa), and MP (MP100). The light intensity and temperature of each device were measured, and the Vickers hardness, flexural strength and modulus, degree of conversion (DC), cytotoxicity, and polymerization shrinkage were analyzed. Statistical analyses were conducted with 1-way analysis of variance, the Tukey post hoc test, and regression testing (α=.05). Scanning electron microscopy was used to assess the fracture surface characteristics of the specimens. RESULTS: Light intensity was strongest with the ME device, and the temperature inside the device during postpolymerization showed the highest increase with the LC device and the lowest increase with the D1 device. The LC group specimens showed the highest mean Vickers hardness, and the MP group showed the lowest. The flexural strength was ≥100 MPa in all groups, with a flexural modulus ranging from 1.17 to 1.5 GPa. The DC results were similar to the physical properties test results. The D1, FO, LC, and ME groups all showed ≥70% cell viability, indicating no toxicity. The FO group showed the highest shrinkage rate of 0.52%. CONCLUSIONS: When the light intensity was strong, the surface was sufficiently hard, and toxic substances were not eluted even after a short postpolymerization time, suggesting that light intensity modulation and time management can be used to improve the postpolymerization process.

Sleeve insert scan body to predict implant placement position by using implant surgical guides: A dental technique.

In studies that assessed the accuracy of implant surgical guides, evaluations were based on the placement position of the implant by using a manufactured surgical guide. However, such assessments could involve errors that may occur during implant placement. Therefore, evaluating the 3-dimensional accuracy of the fabrication of the implant surgical guide itself is not enough. In the evaluation method described in this article, location-related information is obtained by connecting a scan body to the sleeve of the surgical guide instead of directly placing the implant. This helps to evaluate the accuracy of the surgical guide without errors in the placement of an implant.

Dental students' perceptions on a simulated practice using patient-based customised typodonts during the transition from preclinical to clinical education.

PURPOSE/OBJECTIVES: Dental students experience difficulties during the transition from preclinical to clinical curriculum. In order to help the students to adapt to the clinical education programme, a simulated practice using patient-based customised models was introduced in this study to prepare for their first clinical practice. METHODS: This study included 45 third-year predoctoral students (D3 students) who were about to perform the preparation of a single crown abutment on their first patient. After practicing abutment preparation using simulated models and providing the actual treatment to their own patient, the students were surveyed to investigate their perceptions on the simulated practice using the 3D-printed customised typodont model. The statistical analysis of the quantitative data and the thematic analysis of the qualitative data were conducted. RESULTS: Regarding this simulation, more than 80% of the students gave positive feedback on their practice of (a) operative positions and postures, (b) finger rest, (c) occlusal reduction, (d) axial reduction and (e) proximal reduction. Student responses on the open-ended questions about how they perceived the usefulness of this simulation were categorised as "First clinical case," "Patient-based model" and "Realistic simulation environment." In addition, a number of improvements of the simulation were also suggested by the students including the typodont and the manikin. CONCLUSIONS: This study gives insights into the significance of simulated practice using patient-based customised typodonts as a transitional education tool and its direction of development in the field of restorative treatments accompanied by irreversible tooth preparations.

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.

Digital approach for production of interim implant-supported fixed restoration with a prefabricated implant component library.

During production of an immediate interim implant-supported fixed restoration with interim cylinders, the formation of an access hole in the dentures is critical. Traditional access hole formation involves repeated prosthesis insertion and removal in the oral cavity, primarily through trial and error, to adjust the hole position and size. The presented technique simulates the interim cylinder position based on the healing abutment position, enabling confirmation of the access hole position and ensuring more precise seating of the interim implant-supported fixed restoration.

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.

Digital workflow to provide an immediate interim restoration after single-implant placement by using a surgical guide and a matrix-positioning device.

This article describes a workflow based on a top-down approach to provide a fixed-type immediate interim restoration after placing a single implant using a digitally driven surgical guide and a matrix-positioning device. A characteristic of the technique is that both the surgical guide and the matrix-positioning device are fabricated from a single diagnostic virtual trial restoration designed on computer-aided design (CAD) software. This workflow may shorten the time required for chairside placement of an interim restoration and enhance esthetics when rehabilitating anterior teeth.

Integration of intraoral digital scans with a 3D facial scan for anterior tooth rehabilitation.

This article describes a digital technique that combines intraoral digital scans with a 3-dimensional facial scan to predict the outcome of prosthodontic treatment of anterior teeth at the treatment planning phase. This approach may increase patient acceptance of the definitive treatment, as the altered facial appearance is visualized with definitive prosthodontic restorations, thereby improving communication before treatment begins.

Computer-based implant planning involving a prefabricated custom tray with alumina landmark structures.

The purpose of this technical report was to describe a method for the fabrication of a custom tray with landmark structures to coordinate cone beam computed tomography and scan data for use in guided implant surgery in patients with numerous artifact-causing metal prostheses. The fabricated custom tray can be used to coordinate cone beam computed tomography data and scan data from the dentition, as well as to fabricate the prostheses.

Enamel wear and aging of translucent zirconias: In vitro and clinical studies.

STATEMENT OF PROBLEM: Zirconia is a widely used restorative material. However, phase transformation on clinical application of zirconia has not yet been studied. PURPOSE: The purpose of this study was to evaluate the wear, surface roughness, and aging associated with polished translucent zirconia in both in vitro and clinical experiments. MATERIAL AND METHODS: In vitro experiments were performed with Rainbow and Katana zirconia blocks and natural tooth enamel as the control. They were subjected to 100 000 loading cycles with a maxillary premolar antagonist. All specimens were analyzed for wear, and the zirconia specimens were evaluated for surface roughness and monoclinic phase (m-phase) transformation by X-ray diffractometry before and after cyclic loading. The clinical study included participants who required single-crown implant-supported restorations replacing the first or second molar. The participants received Rainbow or Katana zirconia prostheses (n=15, each). For wear analysis, impressions of each prosthesis, antagonist, and adjacent tooth were made at 1 week and 6 months after crown delivery. The occlusal relationship of the crowns in maximum intercuspation was evaluated by using the T-Scan 8 occlusal diagnostic system. The degree of transformation of zirconia to the m-phase was measured by using X-ray diffractometry of the crowns after 6 months of use. RESULTS: Zirconia induced significantly greater enamel wear than the natural tooth control. Katana specimens exhibited significantly greater wear and surface roughness than the Rainbow specimens. The degrees of antagonistic wear and zirconia phase transformation in the clinical experiment were significantly greater than those in the in vitro experiment. The Katana groups showed significantly higher m-phase levels than the Rainbow groups. CONCLUSIONS: Phase transformation of zirconia occurs within 6 months of clinical use, and the wear and degrees of phase transformation varied according to the zirconia product used.

A digital implant custom tray fabrication method using the design process for simulating the position of the impression copings and 3D printing technology.

The technique described allowed an implant custom tray to be fabricated referencing the location of connected impression copings. The technique uses dental computer-aided design (CAD) software and 3D printing technology. The method controls the thickness of the impression material around the impression copings, improving the impression-making process.

Accuracy of Scanned Stock Abutments Using Different Intraoral Scanners: An In Vitro Study.

PURPOSE: To determine the accuracy of a digital manufacturing method for dental implant restorations on stock abutments using intraoral scanners and prefabricated stock-abutment libraries. MATERIALS AND METHODS: Two dental implants with internal hexagonal connections were placed in the mandibular second premolar and second molar areas of a partially edentulous dentoform model; stock abutments with a diameter of 5 mm, abutment height of 5.5 mm, and gingival cuff height of 2 mm were connected. The study model was scanned 10 times using a reference tabletop scanner and 5 types of intraoral scanners (IOSs). The data collected by 5 types of IOSs were divided into 3 groups, based on the type and matching of stock abutment library data: no library, optical library, and contact library groups. A total of 160 data files were analyzed, including reference data. The resulting data were used to evaluate trueness and precision. RESULTS: Trueness and precision values in the group in which library data of the stock abutment were not used were 42.0 to 76.3 µm and 30.5 to 99.7 µm; corresponding values when the library data using an optical scanner were matched were 51.2 to 73.4 µm and 26.3 to 62.8 µm, and those when contact scanner library data were used were 30.1 to 62.4 µm and 15.5 to 55.9 µm. Thus, the accuracy of the contact library group was significantly higher than the accuracies of the no library (p < 0.001) and optical library groups (p < 0.001). CONCLUSION: The application of prefabricated library data of stock abutments using a contact scanner improved the accuracy of scan data. Scan accuracy of the stock abutments differed significantly based on the type of scanner.

Effect of the number of splinted abutments on the accuracy of zirconia copings.

STATEMENT OF PROBLEM: Splinting periodontally or structurally compromised abutments is a common procedure. However, studies that investigated the effect of splinting on the accuracy of zirconia copings are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the magnitude of marginal and internal gaps of zirconia copings based on the number of splinted abutments and digital scan technique. MATERIAL AND METHODS: Four maxillary acrylic resin incisors were prepared for ceramic restorations. Epoxy resin master models were fabricated by duplicating the acrylic resin model. An intraoral scanner was used to build 40 digital models (direct digital scan group [DD]); an additional 40 digital models were constructed by scanning 40 maxillary definitive casts using a laboratory scanner (indirect digital scan group [ID]). During computer-aided design, the DD and ID groups were subdivided into 4 groups; single unit (group SU); 2-unit splinted (group 2S); 3-unit splinted (group 3S), and 4-unit splinted (group 4S). Zirconia copings were then fabricated. Using the replica technique, marginal, axial, and occlusal gaps were measured and statistically evaluated (α=.05). RESULTS: In DD, group 4S exhibited larger marginal gaps than groups SU, 2S, and 3S (P<.001). In ID, group SU exhibited smaller marginal and occlusal gaps than group 4S (P<.001). Group 4S exhibited significantly greater axial gaps than groups SU, 2S, and 3S (P<.001). CONCLUSIONS: As the number of splinting units increased, the magnitude of the marginal gap tended to increase; however, the differences were less than 5 µm, which is clinically insignificant. Axial gaps in the ID group demonstrated a significant difference (>35 µm) among the groups.

Accuracy of 9 intraoral scanners for complete-arch image acquisition: A qualitative and quantitative evaluation.

STATEMENT OF PROBLEM: Different intraoral scanners (IOSs) are available for digital dentistry. However, information on the accuracy of various IOSs for complete-arch digital scans is limited. PURPOSE: The purpose of this in vitro study was to evaluate the trueness and precision of complete-arch digital scans produced by 9 IOSs, using the superimposition method, and to compare them based on characteristics including the data capture principle and mode and the need for powder coating. MATERIAL AND METHODS: Nine IOSs were used to obtain standard tessellation language (STL) data for a bimaxillary complete-arch model with various cavity preparations (N=10). The scanning performance was evaluated quantitatively and qualitatively. For quantitative evaluation, the images were processed and analyzed using 3-dimensional (3D) analysis software. After we superimposed the datasets, trueness was obtained by comparing it with the reference scan, and precision was obtained from intragroup comparisons. The IOSs were compared based on the data capture principle and mode and the need for powder coating. Statistical analyses were conducted using a Kruskal-Wallis test, followed by multiple Mann-Whitney U tests for pairwise comparisons among groups (α=.05). For qualitative evaluation, surface smoothness and sharp edge reproducibility of the digital images were compared. RESULTS: The median precision values were lowest in the TRIOS model (average, 34.70 µm; maximum, 263.55 µm) and highest in the E4D model (average, 357.05 µm; maximum 2309.45 µm). Median average trueness values were lowest in the TRIOS model (42.30 µm) and highest in the Zfx IntraScan model (153.80 µm). The CS 3500 model had the lowest median maximum trueness values (450.75 µm); the E4D model had the highest values (2680.55 µm). Individual image and video sequence data captures showed similar median average trueness values (P>.05); the median maximum values of individual images were higher than those of the video sequence (P<.05). Swept source optical coherence tomography (SS-OCT) exhibited higher trueness values than those of other scanning principles (P<.05). The FastScan and True Definition, which require powder coating, showed significantly better trueness than other IOSs that did not require powdering (P<.05). The E4D, PlanScan, and Zfx IntraScan models had an increased tendency to produce images with imperfect surface features and to round off sharp edges. CONCLUSIONS: The E4D and Zfx IntraScan models did not perform as accurately as the other IOSs. The data capture principle of SS-OCT and the mode of individual image acquisition exhibited inferior trueness. The FastScan and True Definition, which require powder coating, exhibited better trueness. The qualitative aspects of the IOSs varied in terms of polygon shapes, sharp edge reproducibility, and surface smoothness.

Computer-guided implant planning using a preexisting removable partial dental prosthesis.

Converting a conventional removable partial dental prosthesis (RPDP) into an implant-assisted removable partial dental prosthesis (IARPDP) may be facilitated by using data from the intaglio surface of the RPDP for proper implant placement. This procedure can be done by connecting the data from the intaglio surface of the RPDP to the residual ridge data of the cone beam computed tomography scan with implant planning software. However, although a misplaced implant under an RPDP can cause various complications, as yet, no technique has connected the information on a patient's existing RPDP to the implant planning software. This article presents computer-guided implant planning, using a patient's existing RPDP.

Accuracy of intraoral digital impressions using an artificial landmark.

STATEMENT OF PROBLEM: Intraoral scanners have been reported to have limited accuracy in edentulous areas. Large amounts of mobile tissue and the lack of obvious anatomic landmarks make it difficult to acquire a precise digital impression of an edentulous area with an intraoral scanner. PURPOSE: The purpose of this in vitro study was to determine the effect of an artificial landmark on a long edentulous space on the accuracy outcomes of intraoral digital impressions. MATERIAL AND METHODS: A mandibular model containing 4 prepared teeth and an edentulous space of 26 mm in length was used. A blue-light light-emitting diode tabletop scanner was used as a control scanner, and 3 intraoral scanners were used as experimental groups. Five scans were made using each intraoral scanner without an artificial landmark, and another 5 scans were performed after application of an artificial landmark (a 4×3 mm alumina material) on the edentulous area. The obtained datasets were used to evaluate trueness and precision. RESULTS: Without an artificial landmark on the edentulous area, the mean trueness for the intraoral scanner ranged from 36.1 to 38.8 µm and the mean precision ranged from 13.0 to 43.6 µm. With an artificial landmark on the edentulous area, accuracy was improved significantly: the mean trueness was 26.7 to 31.8 µm, and the mean precision was 9.2 to 12.4 µm. CONCLUSIONS: The use of an alumina artificial landmark in an edentulous space improved the trueness and precision of the intraoral scanners tested.

Fabrication of a complete, removable dental prosthesis from a digital intraoral impression for a patient with an excessively tight reconstructed lip after oral cancer treatment: A clinical report.

This clinical report describes the management of a patient who had an excessively tight reconstructed lip because of oral cancer surgery and postoperative radiotherapy. The presented technique used an intraoral scanner for a preliminary impression and computer-aided design and computer-aided manufacturing (CAD-CAM) technology for preliminary laboratory procedures. This digital impression technique may reduce patient discomfort.