Practicability of modified functionally generated path Technique for CAD/CAM Restorations

Objectives: 　The purpose of this present study was to design a CAD/CAM crown with a functional occlusal surface by modifying the Functionally Generated Path (FGP) Technique and subsequently verify crown precision. Methods: The Modified FGP Technique: Adding the abutment impression to functional occlusal surface by conventional methods. Our CAD/CAM system procedures composed of the 4 following steps: Step 1: A virtual dentition model (VDM) was reconstructed through laser surface scanning data of dental casts, scanned with a 3D scanner via 3D mesh modeling software VRMesh 4.1. Step2: Scanned VDMs have an independent coordinate value. The relative position between upper and lower VDMs was decided via labial-buccal surface data from upper and lower casts placed at the intercuspal position. Step3: The Virtual Reality crown (VR crown) was designed via Freeform and Phantom Omni. VDM data from functional occlusal surface was removed from crown data, and occlusal contact points were set and masked. The occlusal surface was shaped without modifying the occlusal contact. Abatement teeth data was removed from crown data. Step4: The dental crown wax pattern was modeled from VR crown data via 3D printer (thickness=25.4µm). The cast was realized via a traditional approach. Occlusal contacts were assessed at the whole dentition, with/without CAD/CAM crown via an articulator, using silicone.　They were subsequently put on a film viewer and scanned via digital camera at a specific setting. Results: The vertical gap between the finish line on the abutment teeth and the margin on the dental crown was 28±5µm in the conventional crown, 35±13µm in the CAD/CAM crown. The real crown's occlusal contacts almost corresponded with its VR crown. Conclusion: We developed a novel CAD/CAM system which can design functional occlusal surfaces via a modified FGP technique and haptic device. The marginal fit in our CAD/CAM crown was sufficient for clinical application.