Assessment of the internal fit and marginal integrity of interim crowns made by different manufacturing methods.

STATEMENT OF PROBLEM: The adaptation of interim crowns made by subtractive and additive manufacturing has not been well investigated. PURPOSE: The purpose of this in vitro study was to evaluate the internal fit and marginal discrepancy of interim crowns made by different manufacturing methods. MATERIAL AND METHODS: A dentoform mandibular left first molar was prepared for a ceramic crown and scanned for the fabrication of 48 stereolithical resin dies and interim crowns. Group CAM included 16 ZCAD interim crowns made by computer-aided design and computer-aided manufacturing (CAD-CAM) technology; group 3DP, 16 NextDent MFH interim crowns made by digital light processing technology; and group APP, 16 Jet interim crowns manually made by using autopolymerizing acrylic resin and used as controls. The silicone replica technique was used to determine the internal discrepancy volume before definitive cementation. All crowns were cemented with Temp-Bond NE under a 50-N load and bench set for 10 minutes before microcomputed tomographic (µCT) scan assessment. The volume of cement space was measured by using the µCT scan 3-dimensional (3D) images, and gap distance at assigned locations was recorded by using the µCT scan 2-dimensional (2D) images. The marginal discrepancy was measured by the polyvinyl siloxane (PVS) impression technique and using a stereomicroscope. Data were analyzed by ANOVA and the Tukey honestly significant difference tests (α=.05). The association between different measuring techniques was analyzed by the Pearson correlation test. RESULTS: The gap distance between interim crowns and dies from all 3 groups measured by using the µCT scan 2D images ranged from 0.13 mm to 0.55 mm, with the highest value found at the central occlusal location in group APP. The total average gap distance values recorded for group APP were significantly higher than those for group CAM and group 3DP (P<.05). No significant differences were found in internal discrepancy and cement space volume between group CAM and group 3DP (P>.05). The Pearson correlation test showed a moderate correlation (r=0.69) between the silicone replica technique and the µCT scan technique in determining cement space volume. When the PVS impression technique was used to measure the marginal discrepancy, the mean values obtained from group APP were statistically significantly higher than those from group CAM and group 3DP (P<.05). No statistically significant difference in marginal discrepancy was found between group CAM and group 3DP (P=.70). CONCLUSIONS: Digitally fabricated interim crowns had better internal fit and smaller marginal discrepancy than manually constructed interim crowns. The silicone replica technique and µCT scan technique measurements had a moderate correlation in assessing the adaptation of cemented interim crowns.

Experience-based virtual training system for knee arthroscopic inspection.

BACKGROUND: Arthroscopic surgical training is inherently difficult due to limited visibility, reduced motion freedom and non-intuitive hand-eye coordination. Traditional training methods as well as virtual reality approach lack the direct guidance of an experienced physician. METHODS: This paper presents an experience-based arthroscopic training simulator that integrates motion tracking with a haptic device to record and reproduce the complex trajectory of an arthroscopic inspection procedure. Optimal arthroscopic operations depend on much practice because the knee joint space is narrow and the anatomic structures are complex. The trajectory of the arthroscope from the experienced surgeon can be captured during the clinical treatment. Then a haptic device is used to guide the trainees in the virtual environment to follow the trajectory. RESULTS: In this paper, an experiment for the eight subjects' performance of arthroscopic inspection on the same simulator was done with and without the force guidance. The experiment reveals that most subjects' performances are better after they repeated the same inspection five times. Furthermore, most subjects' performances with the force guidance are better than those without the force guidance. In the experiment, the average error with the force guidance is 33.01% lower than that without the force guidance. The operation time with the force guidance is 14.95% less than that without the force guidance. CONCLUSIONS: We develop a novel virtual knee arthroscopic training system with virtual and haptic guidance. Compared to traditional VR training system that only has a single play-script based on a virtual model, the proposed system can track and reproduce real-life arthroscopic procedures and create a useful training database. From our experiment, the force guidance can efficiently shorten the learning curve of novice trainees. Through such system, novice trainees can efficiently develop required surgical skills by the virtual and haptic guidance from an experienced surgeon.

Virtual Dental Articulation Using Computed Tomography Data and Motion Tracking.

Dental articulation holds crucial and fundamental importance in the design of dental restorations and analysis of prosthetic or orthodontic occlusions. However, common traditional and digital articulators are difficult and cumbersome in use to effectively translate the dental cast model to the articulator workspace when using traditional facebows. In this study, we have developed a personalized virtual dental articulator that directly utilizes computed tomography (CT) data to mathematically model the complex jaw movement, providing a more efficient and accurate way of analyzing and designing dental restorations. By utilizing CT data, Frankfurt's horizontal plane was established for the mathematical modeling of virtual articulation, eliminating tedious facebow transfers. After capturing the patients' CT images and tracking their jaw movements prior to dental treatment, the jaw-tracking information was incorporated into the articulation mathematical model. The validation and analysis of the personalized articulation approach were conducted by comparing the jaw movement between simulation data (virtual articulator) and real measurement data. As a result, the proposed virtual articulator achieves two important functions. Firstly, it replaces the traditional facebow transfer process by transferring the digital dental model to the virtual articulator through the anatomical relationship derived from the cranial CT data. Secondly, the jaw movement trajectory provided by optical tracking was incorporated into the mathematical articulation model to create a personalized virtual articulation with a small Fréchet distance of 1.7 mm. This virtual articulator provides a valuable tool that enables dentists to obtain diagnostic information about the temporomandibular joint (TMJ) and configure personalized settings of occlusal analysis for patients.

Modeling of digital dental articulator and its accuracy verification using optical measurement.

BACKGROUND AND OBJECTIVES: Temporomandibular joint has been considered one of the most complex joints in human body. Dental articulation hinged upon temporomandibular joint is essential and fundamentally important for dental restoration design and prosthetic/orthodontic occlusion analysis. As digital dentistry rapidly grows, a complete digital work flow requires the use of a digital articulator for occlusion analysis. However, commercial CAD/CAM systems do not provide any method to verify the modeling accuracy of a digital articulator. There is also a lack of detail and generalized mathematical modeling of the digital articulator for simulating the jaw movement. METHODS: This paper presents the development of a digital articulator by mathematically modeling a general dental articulator which simulates the relative jaw motion between the maxilla and mandible. As the digital articulator moves, the digital upper teeth move relatively to the digital lower teeth, thus simulating the occlusal path with teeth collision detection function. To verify the accuracy of our modeled digital articulator, an improved optical tracking method is proposed to measure the pose of a mechanical articulator with 6 degrees of freedom and compare that with the digital articulator. RESULTS: The digital articulator system proposed in this paper achieves the following functions: 1. Digitalize the dental articulator with verified precision. Combined with dental design software, restorations can be designed with more efficiency and accuracy. 2. Provide an improved optical tracking method which can compare the movement error between the mechanical articulator and digital articulator. Thus the accuracy of the digital articulation can be verified. The result shows the error of our system is controlled under sub-millimeter which provides sufficient accuracy for the design of restoration under static and dynamic occlusion conditions. CONCLUSIONS: We develop a general digital articulator which can simulate jaw movement between opposing teeth and an improved optical tracking method to verify the accuracy of the digital articulator. The modeling and accuracy verification of the digital articulator shows that there is a systematic and reliable way to replace traditional mechanical articulator and can close the gap for digital restoration fabrication.

A new combinatorial approach to surface reconstruction with sharp features.

This paper presents a new combinatorial approach to surface reconstruction with sharp features. Different from other postprocessing methods, the proposed method provides a systematic way to identify and reconstruct sharp features from unorganized sample points in one integrated reconstruction process. In addition, unlike other approximation methods, the reconstructed triangulated surface is guaranteed to pass through the original sample points. In this paper, the sample points in the sharp regions are defined as characteristic vertices (c-vertices), and their associated poles (c-poles) are used as a "sculptor" to extract triangles from a Delaunay structure for the sharp features. But, for smooth surface regions, an efficient region-growing scheme is used for triangle extraction and connection. Since only the c-poles associated with the sharp regions are used to participate in the Delaunay computation with the sample points, the proposed algorithm is adaptive in the sense that, given a sampled object with less sharp features, the triangulation becomes more efficient. To validate the proposed algorithm, some detailed illustrations are given. Experimental results show that it is robust and highly efficient.

A novel dental implant guided surgery based on integration of surgical template and augmented reality.

BACKGROUND: Stereoscopic visualization concept combined with head-mounted displays may increase the accuracy of computer-aided implant surgery. PURPOSE: The aim of this study was to develop an augmented reality-based dental implant placement system and evaluate the accuracy of the virtually planned versus the actual prepared implant site created in vitro. MATERIALS AND METHODS: Four fully edentulous mandibular and four partially edentulous maxillary duplicated casts were used. Six implants were planned in the mandibular and four in the maxillary casts. A total of 40 osteotomy sites were prepared in the casts using stereolithographic template integrated with augmented reality-based surgical simulation. During the surgery, the dentist could be guided accurately through a head-mounted display by superimposing the virtual auxiliary line and the drill stop. The deviation between planned and prepared positions of the implants was measured via postoperative computer tomography generated scan images. RESULTS: Mean and standard deviation of the discrepancy between planned and prepared sites at the entry point, apex, angle, depth, and lateral locations were 0.50 ± 0.33 mm, 0.96 ± 0.36 mm, 2.70 ± 1.55°, 0.33 ± 0.27 mm, and 0.86 ± 0.34 mm, respectively, for the fully edentulous mandible, and 0.46 ± 0.20 mm, 1.23 ± 0.42 mm, 3.33 ± 1.42°, 0.48 ± 0.37 mm, and 1.1 ± 0.39 mm, respectively, for the partially edentulous maxilla. There was a statistically significant difference in the apical deviation between maxilla and mandible in this surgical simulation (p < .05). CONCLUSIONS: Deviation of implant placement from planned position was significantly reduced by integrating surgical template and augmented reality technology.

Tooth model reconstruction based upon data fusion for orthodontic treatment simulation.

This paper proposes a full tooth reconstruction method by integrating 3D scanner data and computed tomography (CT) image sets. In traditional dental treatment, plaster models are used to record patient׳s oral information and assist dentists for diagnoses. However, plaster models only save surface information, and are therefore unable to provide further information for clinical treatment. With the rapid development of medical imaging technology, computed tomography images have become very popular in dental treatment. Computed tomography images with complete internal information can assist the clinical diagnosis for dental implants or orthodontic treatment, and a digital dental model can be used to simulate and predict results before treatment. However, a method of producing a high quality and precise dental model has yet to be developed. To this end, this paper presents a tooth reconstruction method based on the data fusion concept via integrating external scanned data and CT-based medical images. First, a plaster model is digitized with a 3D scanner. Then, each crown can be separated from the base according to the characteristics of tooth. CT images must be processed for feature enhancement and noise reduction, and to define the tooth axis direction which will be used for root slicing. The outline of each slice of dental root can then be determined by the level set algorithm, and converted to point cloud data. Finally, the crown and root data can be registered by the iterative closest point (ICP) algorithm. With this information, a complete digital dental model can be reconstructed by the Delaunay-based region-growing (DBRG) algorithm. The main contribution of this paper is to reconstruct a high quality customized dental model with root information that can offer significant help to the planning of dental implant and orthodontic treatment.