Rikardo Minguez

Direct transfer of the position of digitized casts to a virtual articulator

This article describes a digital technique to transfer the location of digitized casts obtained directly from the patient to a virtual articulator (digital/virtual facebow transfer). The primary advantage of this technique is that it allows the dentist and the dental laboratory technician to work in a fully digital environment without having to mount stone casts on a physical articulator. This results in a significant time reduction and a higher degree of accuracy in the cast location.

Comparison of the accuracy of a 3-dimensional virtual method and the conventional method for transferring the maxillary cast to a virtual articulator

STATEMENT OF PROBLEM The currently available virtual articulators fail to locate the digitized maxillary cast at the exact position in the virtual environment. Some locate the casts on a mechanical articulator with a facebow, and this position is then digitized for the virtual environment. PURPOSE The purpose of this study was to compare the location of the maxillary cast on an articulator by using 2 different procedures: the conventional method and a virtual method. MATERIAL AND METHODS With the conventional procedure, the kinematic axis of the participant was determined with an axiograph. The location of the maxillary cast in reference to this axis was then physically transferred to a Panadent mechanical articulator. By a virtual procedure, the same kinematic axis and the maxillary cast were transferred directly from the participant to the Panadent virtual articulator by means of reverse engineering devices. The locations obtained with both procedures were compared in a virtual environment with an optical scanner. By calculating the deviation at every point of the occlusal surface, the results obtained with this procedure were then compared with those of the conventional method. RESULTS The mean deviation on the occlusal surface was 0.752 mm, and the standard deviation was 0.456 mm. CONCLUSIONS The deviation between the procedures was sufficiently small to allow the methodology for orthodontic purposes. However, the accuracy of the virtual procedure should be improved so as to extend its use to other fields, such as orthognathic surgery or dental restorations, in which the clinical technique requires an articulator.

Improved digital transfer of the maxillary cast to a virtual articulator

The clinical procedure described provides a quantifiable, repeatable, and reliable method of transferring the location of the maxillary dental arch from the patient directly to a virtual articulator (virtual facebow transfer) by means of reverse engineering devices to design a customized dental restoration. This procedure allows the dentist and the dental laboratory technician to work in a fully digital environment without having to mount stone casts on a mechanical articulator. In addition, specific suggestions are provided for designing the transfer device to enhance patient comfort during the data transfer process and reduce deviation.

Virtual facebow technique.

This article describes a virtual technique for transferring the location of a digitized cast from the patient to a virtual articulator (virtual facebow transfer). Using a virtual procedure, the maxillary digital cast is transferred to a virtual articulator by means of reverse engineering devices. The following devices necessary to carry out this protocol are available in many contemporary practices: an intraoral scanner, a digital camera, and specific software. Results prove the viability of integrating different tools and software and of completely integrating this procedure into a dental digital workflow.

Computer-aided dental prostheses construction using reverse engineering.

The implementation of computer-aided design/computer-aided manufacturing (CAD/CAM) systems with virtual articulators, which take into account the kinematics, constitutes a breakthrough in the construction of customised dental prostheses. This paper presents a multidisciplinary protocol involving CAM techniques to produce dental prostheses. This protocol includes a step-by-step procedure using innovative reverse engineering technologies to transform completely virtual design processes into customised prostheses. A special emphasis is placed on a novel method that permits a virtual location of the models. The complete workflow includes the optical scanning of the patient, the use of reverse engineering software and, if necessary, the use of rapid prototyping to produce CAD temporary prostheses.

Close Range Photogrammetry for Direct Multiple Feature Positioning Measurement without Targets

The main objective of this study is to present a new method to carry out measurements so as to improve the positioning verification step in the wind hub part dimensional validation process. This enhancement will speed up the measuring procedures for these types of parts. An industrial photogrammetry based system was applied to take advantage of its results, and new functions were added to existing capabilities. In addition to a new development based on photogrammetry modelling and image processing, a measuring procedure was defined based on optical and vision system considerations. A validation against a certified procedure by means of a laser-tracker has also been established obtaining deviations of ±0.125 μm/m.

Retrieval of unfiltered digitized cylindrical surfaces based on spin-images

In current design and manufacturing processes, the verification of tolerances is mainly focused on dimensional tolerances. As a general rule, manufacturing instructions specify dimensional tolerances and surface qualities. However, geometric tolerances are hardly ever specified, and this often leads to a lack of adequacy of the design. A better adequacy of this design would certainly produce a significant reduction in manufacturing costs. The lack of trained engineers, as well as the non-availability of the appropriate software, has relegated geometric tolerances, at the very best, to a second place. One of the greatest difficulties when using the current software solutions is the partition and identification of the meshes obtained from a scanning process on specific features. These processes can hardly be carried out via automation because they are subject to the accuracy of the tool and the skill of the technician in charge of processing the meshes. This paper presents a semi-automatic process to detect non-ideal, cylindrical features in point clouds. Its aim is to identify and extract the points from these features in order to implement them into the verification algorithms of possible associated geometric tolerances. In this process, spin-images, usually developed in the detection of shapes, are used as a graphic tool.

Accuracy Evaluation of Dense Matching Techniques for Casting Part Dimensional Verification

Product optimization for casting and post-casting manufacturing processes is becoming compulsory to compete in the current global manufacturing scenario. Casting design, simulation and verification tools are becoming crucial for eliminating oversized dimensions without affecting the casting component functionality. Thus, material and production costs decrease to maintain the foundry process profitable on the large-scale component supplier market. New measurement methods, such as dense matching techniques, rely on surface texture of casting parts to enable the 3D dense reconstruction of surface points without the need of an active light source as usually applied with 3D scanning optical sensors. This paper presents the accuracy evaluation of dense matching based approaches for casting part verification. It compares the accuracy obtained by dense matching technique with already certified and validated optical measuring methods. This uncertainty evaluation exercise considers both artificial targets and key natural points to quantify the possibilities and scope of each approximation. Obtained results, for both lab and workshop conditions, show that this image data processing procedure is fit for purpose to fulfill the required measurement tolerances for casting part manufacturing processes.

Obtaining reliable intraoral digital scans for an implant-supported complete-arch prosthesis: A dental technique

This article describes a technique for obtaining an accurate complete-arch digital scan for an edentulous patient. To achieve this, an auxiliary polymeric device that simulates a denture is designed, fabricated, and placed in the mouth. This device, having the geometry of a typical dental arch, facilitates the digitalization of the edentulous complete arch. This is because the change in radius of the curvature (change of geometry) enables the scanner to perform a more accurate alignment. Initially, the necessary location of the implants is acquired, and then the soft tissue is added. This technique can achieve accurate complete-arch digital scans. Distances between implants are closer to the gold standard when using this auxiliary geometry piece than those obtained without using it.

Evaluation of the Accuracy of a System to Align Occlusal Dynamic Data on 3D Digital Casts

In recent years the T-Scan system has introduced the possibility of importing digitization of dental arches to its registrations. This is a remarkable advance, which allows an intuitive display of the location of the gathered dynamic data on the denture. Nevertheless, todays usual method of manually positioning the arch in relation to the T-Scans force registration gives rise to the possibility of human error. In order to guarantee a good alignment between the dynamic registration and 3D digital casts, a specific method was developed. The aim of this study is to evaluate the accuracy of this alignment method. For this purpose, it was compared with the most common procedure for detecting occlusal contacts, the articulating paper method. The comparison comprised overlapping digital models of both methods. Contacts of casts of 11 adults were registered, both with articulating paper and the T-Scan system. For one method, articulating paper marks were scanned in color; for the second method, the previously mentioned alignment was carried out with the T-Scan registrations. The results of both methods were overlapped in 3D digital casts, quantifying occlusal data matches. Statistical analyses were made to measure the quality of this alignment method. The study revealed a mean matching percentage of 79.02%, confirming the high reliability of the method.