Improved digital transfer of the maxillary cast to a virtual articulator Eneko Solaberrieta, PhD,a Jose Ramon Otegi, PhD,b Rikardo Mínguez, PhD,c and Olatz Etxaniz, PhDd Faculty of Engineering at Bilbao, University of the Basque Country (UPV/EHU), Bilbao, Spain 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. (J Prosthet Dent 2014;-:---) After George Snow introduced his innovative version of the facebow in 1899, and for more than 100 years, the complementary device of the mechanical articulator has been the facebow.1-3 Over this period, many types of facebows have been invented with the same objective: to position the casts in the articulator. A good example of this is the Walker facial clinometer. In dentistry, the location of the maxillary cast is transferred from the patient onto the dental mechanical articulator by means of a facebow. This transfer is critical for extensive rehabilitation such as multiple crowns, complex fixed dental prostheses, or complete dentures.4 Facebow transfer is also important in maxillofacial orthognathic surgery.5,6 Dentistry, however, has undergone many significant changes in the recent past. Some concepts and techniques traditionally considered indisputable are now undergoing intensive review. In prosthodontic laboratory procedures, conventional casting, a process that has remained unchanged for decades, is now being replaced by the technologic advances such as computer-aided design and computera

aided manufacturing (CAD/CAM) techniques. In the late 1980s, Duret et al7 were the first to describe computer-assisted crowns. However, the occlusal surface of these crowns was not functionally shaped. The second breakthrough in this field was made and published by Mörmann et al,8 the developers of the Cerec system. They succeeded in implementing CAD/CAM in a dental office and developed a chairside method of producing dental crowns. Several aspects of CAD/CAM systems have recently improved significantly, including the application of new materials,9-11 the introduction of virtual articulator software,12-14 the development of new intraoral scanners,15-17 and the availability of more efficient CAM machines.18-20 These improvements, among others, have led to a significant workload reduction and to greater control over the definitive product. However, one problem still to be solved is the transfer of digitized casts onto the virtual articulator. This article describes a step-by-step improved technique for the transfer of a maxillary cast to a virtual articulator

Associate Professor, Department of Graphic Design and Engineering Projects. Assistant Professor, Department of Graphic Design and Engineering Projects. c Associate Professor, Department of Graphic Design and Engineering Projects. d Associate Professor, Department of Graphic Design and Engineering Projects. b

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with a novel methodology based on reverse engineering. The purpose of this treatment step was to generate a customized restoration, taking into account the actual position of the maxillary and mandibular casts.

CLINICAL REPORT A 27-year-old man was referred to the Department of Prosthodontics of the University of the Basque Country (UPV/EHU) for a restoration. The participant agreed to this new technique for the location of the maxillary cast in a virtual environment, and it was used to locate his maxillary cast on a virtual articulator. First, to obtain digital casts, the dental arches of the patient were scanned with an optical scanner (ATOS Compact Scan 5M; GOM GmbH). Subsequently, 3 skin-adhesive targets (provided with the scanner) were placed at 3 given points on the patient’s head: 2 temporomandibular points and 1 infraorbital point. Then, articulating paper was placed on a flat metal facebow fork, which was introduced into the patient’s mouth

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1 Process to determine intraoral points. A, Placing metal facebow fork with articulating paper. B, Three marks on occlusal plane.

(Fig. 1A). The facebow fork was pushed by the dentist against the maxillary cast, and the 3 most prominent cusps on the occlusal surface were determined (see Fig. 1B). These 3 marked points determined the occlusal plane. With a 3D optical scanner and the touch probe (provided with the scanner), 3 intraoral points and 3 points on the patient’s head were located. To achieve this, the 3 points on the patient were scanned directly as reference points, and the intraoral ones were registered by pointing each time at one of the intraoral points with the touch probe (Fig. 2). Once the 6 points had been located in the space, the patient’s cranial coordinate system was created with different reverse engineering software (GOM Inspect; GOM GmbH, and Solid Edge ST; Siemens PLM Software, Inc) by using the first 3 points. The 3 most prominent cusps on the virtual maxillary cast were then identified to generate the occlusal plane. Applying the method of least squares, the maxillary cast was transferred to the cranial coordinate system (Fig. 3A). Finally, the maxillary cast was transferred to the virtual articulator

software, bringing the cranial coordinate system to coincidence with the virtual articulator’s coordinate system (see Fig. 3B).

DISCUSSION This technique consists of 3 key elements. First, the use of the touch probe enables the fast location of an intraoral point. Second, by following this procedure, the clinician can work in a fully digital environment without having to mount stone casts on a mechanical articulator. Third, in comparison with the use of a conventional facebow, the use of this technique may increase patient comfort; the procedure is also friendlier for the dentist. Several reports have emphasized the importance of the facebow in prosthodontics,21,22 orthognathic surgery,4,5 and orthodontics.23,24 The location of the maxillary cast on the articulator is essential in 3 situations: first, when there is a vertical dimension change on the articulator; second, when the movement of the casts is essential for the restoration; and third, when orthognathic surgery must be planned on the maxilla.

The Journal of Prosthetic Dentistry

Up to the present, 2 methods have been applied to orient the maxillary cast to the articulator digitally. One of them consists of using the measurements of the Bonwill triangle (arbitrary method), and the other consists of scanning the articulator with mounted casts. For this second method, a mechanical facebow must be used.25 Because the introduction of virtual environments is still very recent, most dentists are working with mechanical facebows and articulators. The art of occlusal rehabilitation requires more accurate, more reproducible, easier, and quicker procedures to reduce unnecessary technical failures. This proposed novel technique constitutes a second25 step in terms of virtualizing the facebow transfer step.

SUMMARY The exact position of the maxillary and mandibular cast on the mechanism of the dental articulator is essential, because this starting point determines the path and the occlusion of the simulation in both virtual and mechanical environments. Therefore, this improved technique significantly

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2 Process of scanning intraoral points. A, Scanning pointer at occlusal point. B, Location of 3 most prominent cusps on digitized maxillary cast. C, Location of maxillary cast on cranial coordinate system with 3 positions of touch probe.

3 Transfer of digitized casts onto virtual articulator software, bringing coordinate systems to coincidence. A, Maxillary cast. B, Mandibular cast.

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REFERENCES 1. Starcke EN. The history of articulators: from facebows to the gnathograph, a brief history of early devices developed for recording condylar movement, part I. J Prosthodont 2001;10:241-8. 2. Starcke EN. The history of articulators: from facebows to the gnathograph, a brief history of early devices developed for recording condylar movement, part II. J Prosthodont 2002;11:53-62. 3. Starcke EN. The history of articulators: the appearance and early history of facebows. J Prosthodont 2000;9:161-5. 4. Infante L, Yilmaz B, McGlumphy E, Finger I. Fabricating complete dentures with CAD/ CAM technology [published online January 23, 2014]. J Prosthet Dent. doi:10.1016/j. prosdent.2013.10.014. 5. Walker F, Ayoub AF, Moos KF, Barbenel J. Face bow and articulator for planning orthognathic surgery: 1 face bow. Brit J Oral Max Surg 2008;46:567-72. 6. Sharifi A, Jones R, Ayoub A, Moos KF, Walker F, Khambay B, et al. How accurate is model planning for orthognathic surgery? Int J Oral Maxillofac Surg 2008;37:1089-93. 7. Duret F, Blouin JL, Duret B. CAD/CAM in dentistry. J Am Dent Assoc 1988;117:715-20. 8. Mörmann WH, Brandestini M, Lutz F, Barbakow F. Chairside computer-aided direct ceramic inlays. Quintessence Int 1989;20: 329-39.

9. Tyas MJ, Burrow MF. New materials in dentistry. Aust Dent J 2011;56(suppl 1):1. 10. Sadhasivam S, Chen JC, Savitha S, MingXiang H, Chung-King H, Chun-Pin L, et al. Synthesis of partial stabilized cement-gypsum as new dental retrograde filling material. Mat Sci Eng 2012;32:1859-67. 11. Vichi A, Louca C, Corciolani G, Ferrari M. Color related to ceramic and zirconia restorations: a review. Dent Mater 2011;27: 97-108. 12. Szentpétery A. Computer aided dynamic correction of digitized occlusal surfaces. J Gnathol 1997;16:53-60. 13. Kordass B, Gärtner C, Söhnel A, Bisler A, Voss G, Bockholt U, et al. The virtual articulator in dentistry: concept and development. Dent Clin North Am 2002;46: 493-506. 14. Gaertner C, Kordass B. The virtual articulator: development and evaluation. Int J Comput Dent 2003;6:11-24. 15. Mehl A, Ender A, Mörmann W, Attin T. Accuracy testing of a new intraoral 3D camera. Int J Comput Dent 2009;12:11-28. 16. Garino F, Garino B. The iOC intraoral scanner and Invisalign: a new paradigm. J Clin Orthod 2012;46:115-21. 17. Kurbad A. Impression-free production techniques. Int J Comput Dent 2011;14: 59-66. 18. Yau HT, Chen HC, Yu PJ. A customized smart CAM system for digital dentistry. Comput Aided Des Appl 2011;8: 395-405. 19. Uzun G. An overview of dental CAD/CAM systems. Biotechnol Biotec Eq 2008;22: 530-5.

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20. Fuster-Torres MA, Albalat-Estela S, AlcañizRaya M, Peñarrocha-Diago M. CAD/CAM dental systems in implant dentistry: update. Med Oral Patol Oral Cir Bucal 2009;14: 141-5. 21. Ferrario VF, Sforza C, Serrao G, Schmitz JH. Three-dimensional assessment of the reliability of a postural face-bow transfer. J Prosthet Dent 2002;87:210-5. 22. Wang MQ, Xue F, Chen J, Fu K, Cao Y, Raustia A. Evaluation of the use of and attitudes towards a face-bow in complete denture fabrication: a pilot questionnaire investigation in Chinese prosthodontists. J Oral Rehabil 2008;35:677-81. 23. Clark JR, Hutchinson I, Sandy JR. Functional occlusion, II. The role of articulators in orthodontics. J Orthod 2001;28:173-7. 24. Samuels RHA, Brezniak N. Orthodontic facebows: safety issues and current management. J Prosthet Dent 2002;87:210-5. 25. Solaberrieta E, Mínguez R, Barrenetxea L, Etxaniz O. Direct transfer of the position of digitized casts to a virtual articulator. J Prosthet Dent 2013;109:411-4. Corresponding author: Dr Eneko Solaberrieta University of the Basque Country (UPV/EHU) Alameda Urquijo s/n Bilbao 48013 SPAIN E-mail: [email protected] Copyright ª 2014 by the Editorial Council for The Journal of Prosthetic Dentistry.

Solaberrieta et al

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 fr...
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