Defining challenging areas of the preparation finish line by using an open-source 3D modeling computer program: A tip to simplify margin identification by the dental laboratory technician

Abstract

Intraoral data acquisition and computer-aided design and computer-aided manufacturing (CAD-CAM) systems have simplified and expedited the fabrication of dental prostheses. 1 Van Noort R. The future of dental devices is digital. Dent Mater. 2012; 28: 3-12 Crossref PubMed Scopus (801) Google Scholar ,2 Giuliodori G. Rappelli G. Aquilanti L. Intraoral scans of full dental arches: an in vitro measurement study of the accuracy of different intraoral scanners. Int J Environ Res Public Health. 2023; 20: 4776 Crossref Scopus (0) Google Scholar Contemporary dental CAD-CAM provides the freedom to design and fabricate diverse dental devices, including custom impression trays, surgical templates, and removable and fixed dental prostheses. 1 Van Noort R. The future of dental devices is digital. Dent Mater. 2012; 28: 3-12 Crossref PubMed Scopus (801) Google Scholar ,3 Revilla-León M. Özcan M. Additive manufacturing technologies used for processing polymers: current status and potential application in prosthetic dentistry. J Prosthodont. 2019; 28: 146-158 Crossref PubMed Scopus (217) Google Scholar ,4 Turkyilmaz I. Wilkins G.N. Varvara G. Tooth preparation, digital design and milling process considerations for CAD/CAM crowns: understanding the transition from analog to digital workflow. J Dent Sci. 2021; 16: 1312-1314 Crossref Scopus (8) Google Scholar These dental appliances are created from a digital file that recreates the surface geometry of the target object, typically a standard tessellation language (STL) file. 5 Grant G.T. Campbell S.D. Masri R.M. Andersen M.R. The American college of prosthodontist digital dentistry glossary development task force. Glossary of digital terms. J Prosthodont. 2016; 25: S2-S9 Crossref PubMed Scopus (27) Google Scholar A prerequisite for accurate manufacture is the exact capture and identification of the fine details in the target intraoral structures. An accurate capture can be challenging when the preparation finish line is subgingival, when abundant bleeding or salivation occurs, or when operator scanning skills and speed are still developing. 6 Mangano F. Gandolfi A. Luongo G. Logozzo S. Intraoral scanners in dentistry: a review of the current literature. BMC Oral Health. 2017; 17: 149 Crossref PubMed Scopus (308) Google Scholar Additionally, the location of fine details can be challenging for the dental laboratory technician to visualize when the CAD file is outsourced for the manufacture of the definitive restoration, since STL files lack attributes such as color and texture. 5 Grant G.T. Campbell S.D. Masri R.M. Andersen M.R. The American college of prosthodontist digital dentistry glossary development task force. Glossary of digital terms. J Prosthodont. 2016; 25: S2-S9 Crossref PubMed Scopus (27) Google Scholar These features help differentiate the tooth from its surrounding tissues when finish lines are subgingival or when displacement is limited. The present article presents a straightforward workflow that defines challenging areas of the preparation finish line by using an open-source 3D modeling computer program. This procedure can be used to communicate the finish line observed to the dental laboratory technician when STL files are used to design the definitive restoration and stops the technician guessing the finish line, since the hard-to-see areas are defined by the clinician. Additionally, this approach has advantages over the margin tracing and sculpting tools available in most 3-dimensional (3D) CAD computer programs since it allows selecting the critical areas around the finish line considering the mesh geometry of the 3D file. Visualizing the 3D mesh permits a more precise selection, which can minimize distortion as even the smallest changes in the mesh surface can be observed if transformation or sculpting procedures are used.