Prof. Dr. Karl-Friedrich Krey & Dr. Anja Ratzman & Benjamin Hanel

Abstract

Prof. Dr. Karl-Friedrich Krey

Germany

  • 1993-1998: Degree in Dentistry
  • 1999-2003: postgraduate education "Fachzahnarzt für Kieferorthopädie" University Leipzig and Doctoral thesis
  • 2005-2007: "Master of Medical Education", University Heidelberg
  • 2010: Habilitation deputy Head of Department of Orthodontics at University Leipzig
  • 2013: Head of Department of Orthodontics, University Medicine Greifswald
  • Memberships in various national and international scientific societies as well as reviewer of internationally recognized journals.


Focus of research and clinical work

  • Mathematical modeling/multivariate statistics in Orthodontics and related Anthropology
  • Epidemiology, health services research
  • Cold Atmospheric Plasma (CAP) research
  • Treatment of children and adults with craniofacial anomalies, cleft-lip and palate
  • Digital orthodontics, CAD/CAM, Aligners


Dr. Anja Ratzmann

Germany

  • October 2024 – May 2025 Certification in “Myofunctional Orthodontics – Mykie®” 
  • 17 July 2024 Habilitation and award of the venia legendi for dentistry 
  • 2024  Established and headed the division “Orthodontic Prevention and Early Treatment” 
  • January 2023 Appointed Deputy Director of the Department of Orthodontics at University Medicine Greifswald (UMG) 
  • 27 February 2013 Authorisation to provide specialist training in orthodontics by the Dental Association of Mecklenburg-Western Pomerania 
  • Since February 2008 Specialist in orthodontics at the ZZMK of the University of Greifswald 
  • February 2008 Specialist examination in orthodontics 
  • 10 December 2007 Completion of the postgraduate degree “Dental Functional Diagnostics and Therapy with Computer Support” (MSc) with the grade: “Excellent” 
  • 28 May 2004 Awarded the degree of Dr med dent 
  • September 2003 – February 2008 Specialist training assistant in the Department of Orthodontics at the ZZMK of the University of Greifswald (now UMG) 
  • Since November 2000 Research associate in the Department of Prosthodontics and Dental Materials at the ZZMK of the University of Greifswald (now UMG) 
  • 13 December 1999 Granted licence to practise dentistry 
  • 1993–1999 Studied dentistry at the Free University of Berlin and Humboldt University of Berlin 

Areas of work 

  • Community Dentistry (research and teaching network of UMG Greifswald) 
  • Educational research and the development of new teaching and examination formats for preclinical training and orthodontic education 
  • Postgraduate education: Development of the postgraduate Master’s programmes “Dental Functional Diagnostics and Therapy with Computer Support” and “Dental Aesthetics and Function” 
  • Craniomandibular dysfunction 
  • Diabetes and oral health 
  • Digital orthodontics (digital planning and manufacturing) 
  • Digital therapy monitoring (methods of digital axiography, digital tooth shade determination, digital caries diagnostics) 
  • Orthodontic prevention and early treatment 

 

Memberships in professional societies 

  • DGZMK – German Society of Dental, Oral and Maxillofacial Medicine 
  • GMA – German Society for Medical Education 
  • DGKFO – German Society of Orthodontics 


Benjamin Hanel

Germany

University Medicine Greifswald, since October 2021 Degree in Dentistry


  • Second State Examination (Z2) September 2024
  • First State Examination (Z1) September 2023 


Research 

  • Force and torque development of shape memory aligners – Department of Orthodontics, Greifswald, Prof. Krey 


Training courses 

  • Canadian Association of Orthodontists - Annual Scientific Session, September 2025 
  • Young Dental Experts – Theory and practice of implantology and augmentation, March 2025
  • DGÄZ 2nd International Symposium – Theory and practice of aesthetic and reconstructive therapies, October 2022



  • Abstract

    Comparison of the in vitro force generation of aligner systems  


    Objective: The development of directly 3D-printed aligners made from shape-memory polymers has led to recommendations for larger step sizes in staging; however, evidence on the force development of these aligners in relation to the thickness of the material and the magnitude of tooth movement remains limited. The aim of this in vitro study was to determine the forces and torques generated on moved teeth as a function of step size and material thickness.  


    Materials and methods: A modular 3D-printable orthodontic measurement apparatus (M3DOMA) based on ATI sensors was used. The dental arch was captured with an intraoral scanner (Aoral Scan 3 Wireless, Shining 3D Dental Inc., Hangzhou, China) and imported into OnyxCeph³™ (Image Instruments GmbH, Chemnitz). After base creation and segmentation, movements of a first molar were simulated in steps of 0.1 mm/1°. From this, both 3D models for 3D printing and STL files for direct aligner printing with material thicknesses ranging from 0.4 to 1.0 mm were exported. The aligners were printed with Tera resin (Graphy, Seoul, Korea) using an Asiga Max (Scheu-Dental GmbH, Iserlohn). Thermoformed aligners (CA-Pro) were produced as a control group. Post-processing was carried out strictly according to the manufacturer’s instructions. Forces and torques were measured using the measuring apparatus in a shielded enclosure at a constant temperature of 37°C.  


    Results: The aligners were successfully 3D printed. However, in this configuration, reproducible printing was possible only from a material thickness of 0.5 mm. Aligners with a material thickness greater than 0.8 mm were usable only to a limited extent on the measuring apparatus. The measurements yielded forces ranging from 0.3 to 0.8 N. Force increased with material thickness; however the effect was inconsistent. A relationship between displacement and force and torque generation was apparent but not strictly linear.   


    Discussion/conclusion: 3D-printed aligners generate relatively low forces that are largely within the ideal range of biological effectiveness. However, within the production workflow and materials tested here, force and torque development was not consistent. 

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