In vitro evaluation of basal shapes and offset values of artificial teeth for CAD/CAM complete dentures Shinta Yamamoto, Manabu Kanazawa n , Daisuke Hirayama, Toshinari Nakamura, Toshio Arakida, Shunsuke Minakuchi Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Japan article info Article history: Received 27 May 2015 Accepted 10 November 2015 Keywords: Complete dentures Accuracy CAD/CAM Artificial teeth Offset Basal shapes abstract Statement of Problem. Artificial teeth are bonded onto the recesses of a milled denture base in a com- plete denture prepared using computer-aided design/computer-aided manufacturing (CAD/CAM). Little is known, however, about the effects of basal shapes and offset values on the accuracy of positions of the bonded artificial teeth. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction Recently, computer-aided design/computer-aided manufacture (CAD/CAM) technologies were applied to the field of complete denture prosthodontics [1,2]. Several fabrication methods for CAD/ CAM fabricated complete dentures have been reported [3]. Among these methods, the laboratory procedures are subdivided broadly into 2 categories. One involves fabrication of denture bases using computerized-numerical-control milling [1,4], and the other is a hybrid of rapid prototyping (RP) and conventional laboratory procedures [5]. The abovementioned reports, however, described the fabrication methods and did not mention the accuracy of the finished dentures. The development of the system for fabricating CAD/CAM fab- ricated complete dentures was reported previously [6,7]. In this system, artificial teeth are bonded onto the recesses of a milled denture base. The authors previously reported that the polished surface of dentures shows high accuracy, whereas the occlusal surface shows low accuracy [8]. This is because artificial teeth are occasionally not returned to the specified positions during the bonding process, when there is no space between artificial teeth and the recesses. The authors also reported previously that in CAD/ CAM fabricated complete dentures, recesses require an offset for precise positioning of teeth [9]. However, in the abovementioned study [9], the displacement of bonded artificial teeth to the buccal surface was observed. This problem is because of the horizontal movement of artificial teeth during the bonding process. Furthermore, the study results showed a wide range of offset values of .10–.25 mm and did not specify the optimal offset value. In addition, cone-beam computed tomography (CBCT) was used for analysis of bonded artificial teeth. In a previous report, Yamashina stated that CBCT is inaccurate [10]. In order to solve these problems, in the present study, basal shapes of artificial teeth were developed from scratch; these shapes are intended to prevent the horizontal movement. Three offset values that were specified in a previous study were selected. A 3-dimensional (3D) laser scanner was used for accurate scanning of the prototype [11]. Thus, our null hypothesis was that, in this preliminary study, among 3 types of basal shape and 3 offset values, there are no differences in positioning of the artificial teeth. 2. Material and methods 2.1. Master data acquisition The flow chart used in this study is described in Fig. 1. The denture base model was designed in CAD software (FreeForm; Geomagic, Morrisville, NC, USA; Fig. 1a). The standard triangulated language data on artificial teeth (SURPASS G; GC Corp., Tokyo, Japan) were obtained using a non-contact optical 3D scanner (ATOS Triple Scan; GOM, Braunschweig, Germany; Fig. 1b) based on the principle of triangulation. The mandibular left first Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/cbm Computers in Biology and Medicine http://dx.doi.org/10.1016/j.compbiomed.2015.11.004 0010-4825/& 2015 Elsevier Ltd. All rights reserved. n Correspondence to: 1-5-45, Yushima, Bunkyo, Tokyo 113-8549, Japan. Tel.: þ81 3 5803 5563; fax: þ81 3 5803 0214. E-mail address: m.kanazawa.gerd@tmd.ac.jp (M. Kanazawa). Computers in Biology and Medicine 68 (2016) 84–89