The International Journal of Prosthodontics 784 FUNDAMENTAL RESEARCH A dditive manufacturing (AM) was originally introduced in the 1980s as rapid prototyping and has developed dramatically over the past decades. It has found its way into a variety of industrial branches, including the medical sector. 1 In dentistry, computer-aided manufacturing (CAM) is a well-established technology. It is often equated with subtractive manufacturing methods, 2 but AM is said to yield many advantages compared to subtractive methods: several objects can be printed simultaneously, there is less waste of material, and even the fnest details can be re- produced. In addition, production takes place passively without application of force, unlike the subtractive method, in which burs suffer from wear. 3 AM is being used for a wide range of different applications in dentistry, including surgical 4 as well as end- odontic 5 guides, occlusal devices, 6,7 dental models, 8 replicas for educational use, 9,10 and even maxillofacial prostheses. 11 There are also restorative materials certifed for temporary intraoral use available on the market. 12 Correspondence to: Johannes Mayer Department of Prosthetic Dentistry, University Hospital, LMU Munich Goethestrasse 70 80336 Munich, Germany +4917634496272 Email: johannes_mayer@live.de Submitted April 3, 2020; accepted February 3, 2021. ©2021 by Quintessence Publishing Co Inc. Purpose: To investigate the infuence of different cleaning methods for additively manufactured fxed dental prostheses (FDPs) for long-term temporary use on the degree of conversion (DC), surface roughness, Martens parameters, and biaxial fexural strength. Materials and Methods: A total of 180 specimens per material (3Delta Etemp; Freeprint; Temp PRINT; C&B; and C&B Micro Filled Hybrid) were additively manufactured (D20II) and subsequently cleaned by different methods: by rinsing for 5 minutes in 99.5% acetone; 100% butyl glycol; 96% ethanol; 100% isopropanol; Yellow Magic 7; or by applying centrifugal force for 4 minutes (n = 30 per subgroup). After postpolymerization (Otofash G171, NK-Optik), the DC was measured using Raman spectroscopy, and the surface roughness, as well as the Martens parameters, were recorded. Biaxial fexural strength was investigated after artifcial aging (thermocycling for 10,000 cycles). Data were statistically analyzed (Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests, and Pearson correlation coeffcient). Results: The highest DC was recorded after the use of butyl glycol or isopropyl (P < .001 to P = .047). The highest surface roughness was measured after the use of butyl glycol (P < .001 to P = .024). The use of centrifugal force or Yellow Magic resulted in the highest Martens parameter values (P < .001 to P = .036) and the highest biaxial fexural strength (P < .001 to P = .013), while acetone and butyl glycol led to the lowest values. Conclusion: The use of centrifugal force and Yellow Magic resulted in the highest Martens parameter values and the highest biaxial fexural strength. Concerning Yellow Magic, no negative effect on the mechanical properties was observed. The 3Delta Etemp material especially was prone to degradation after chemical cleaning. Int J Prosthodont 2021;34:784–795. doi: 10.11607/ijp.7048 Temporary 3D-Printed Fixed Dental Prosthesis Materials: Impact of Postprinting Cleaning Methods on Degree of Conversion and Surface and Mechanical Properties Johannes Mayer, DDS Department of Prosthetic Dentistry, University Hospital, Ludwig Maximilian University of Munich, Munich, Germany. Marcel Reymus, PD Dr Department of Conservative Dentistry and Periodontology, University Hospital, Ludwig Maximilian University of Munich, Munich, Germany. Felicitas Mayinger, PD Dr Daniel Edelhoff, Prof Dr Reinhard Hickel, Prof Dr Bogna Stawarczyk, Prof Dr Dipl Ing (FH), MSc Department of Prosthetic Dentistry, University Hospital, Ludwig Maximilian University of Munich, Munich, Germany. © 2021 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART M AY BE REPRODUCED OR TRANSM ITTED IN ANY FORM WITHOUT WRITTEN PERM ISSION FROM THE PUBLISHER.