Ludger Keilig’s research while affiliated with University of Bonn and other places

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Publications (190)


Wear investigation of implant-supported upper removable prothesis with electroplated gold or PEKK secondary crowns
  • Article

January 2025

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13 Reads

Annika Holtz

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Manfred Grüner

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Ludger Keilig

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[...]

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Istabrak Dörsam

Objectives The aim of the present study was to investigate, whether polyetherketoneketone (PEKK) secondary crowns could be considered as alternative to gold standard in terms of their physical properties and manufacturing costs. Methods An upper jaw model with six implants was used. Frameworks with either 6 PEKK- or 6 electroplated secondary crowns were cemented in a wear simulator. A total of 20 specimens (10 PEKK, 10 gold) run 10,000 cycles in the wear simulator with a lubricant. Additionally, 10,000 cycles in the thermocycling baths with 5 °C and 55 °C have gone through, before running extra 10,000 cycles in the wear simulator again. Finally, the abutments were analysed for signs of wear under the electron microscope. Results The mean pulling out force value for PEKK was 21 N. For the electroplated gold secondary crowns an average of 19 N was measured. Multiple fluctuations were observed in the gold series of tests. After 20,000 cycles in the wear simulator and 10,000 cycles in the thermocycling machine, there were no major losses to be measured in terms of wear for both materials. In the microscopic analysis of the abutments, traces of wear could be seen in pull-out direction, mainly in the gold samples. Conclusions PEKK secondary crowns have lower costs, more stable retention force values and are easier to produce than the gold standard. On average, the pull-out force values were 11 N higher than recommended.


From model validation to biomechanical analysis: In silico study of multirooted root analogue implants using 3D finite element analysis
  • Article
  • Full-text available

January 2025

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44 Reads

Journal of the Mechanical Behavior of Biomedical Materials

Objectives: To create a validated 3D finite element model and employ it to examine the biomechanical behaviour of multirooted root analogue implants (RAIs). Methods: A validated finite element model comprising either an RAI or a threaded implant (TI) and an idealized bone block was developed based on a previously conducted in vitro study. All the experimental boundary conditions and material properties were reproduced. Force/displacement curves were plotted to ensure complete alignment with the in vitro findings. Following the validation of the FE model, the material properties were adjusted to align with those reported in the literature. Two contact scenarios were then examined: immediate placement with touching contact and osseointegration with glued contact. The bone block was constrained in all directions, and a 300 N point load was applied along the long axis of the implant, and with an angulation of 30°. The resulting values for equivalent stress, maximum principal stress, microstrain, and displacement were evaluated. Results: The numerical model demonstrated a high degree of agreement with the experimental results, particularly regarding displacement in the loading direction (Z). The findings of the applied FEA indicated that RAIs generally outperformed TIs. The RAI exhibited lower equivalent stress, with values of 3.3 MPa for axial loading and 13.1 MPa for oblique loading, compared to 5.4 MPa and 29.5 MPa for the TI, respectively. Furthermore, microstrain was observed to be lower in the RAI, with a value of 4,000 με compared to 13,000 με in the TI under oblique loading. Additionally, the RAI exhibited superior primary and secondary stability, with lower micromotion values compared to the TI. Conclusions: The root analogue implant showed superior biomechanical performance, with more uniform stress distribution and greater stability compared to the conventional threaded implant, positioning it as a promising alternative.

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Customized 3D Allogenic Bone Blocks for Mandibular Buccal-Bone Reconstruction Increase Resistance to Tongue-Protrusion Forces: A Finite Element Analysis

December 2024

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39 Reads

Journal of Functional Biomaterials

Background. The impact of tongue protrusion forces on the formation of malocclusions is well documented in academic literature. In the case of bone dehiscence of the buccal wall in front of the lower frontal teeth, this process may be even more pronounced. Augmentation with 3D customized allogenic bone blocks (CABB) has been proposed as a potential solution for treating such defects. The objective was to assess the impact of bone block adjustment accuracy on the resistance of teeth to protrusion forces at various stages of alveolar bone loss. Methods: A finite element analysis (FEM) was conducted to ascertain whether augmentation with a CABB will result in increased resilience to tongue protrusion forces. Three-dimensional models of the mandible with dehiscenses were created, based on the dehiscences classification and modification proposed in the journal by the authors of regenerative method. The models feature a CABB positioned at three different distances: 0.1 mm, 0.4 mm, and 1.0 mm. The material parameters were as follows: bone (homogenous, isotropic, E = 2 GPa), teeth (E = 20 GPa), periodontal ligament (E = 0.44 MPa), and membrane between bones (E = 3.4 MPa). A tongue protrusion force within the range of 0–5 N was applied to each individual frontal tooth. Results: The use of an CABB has been shown to positively impact the stability of the teeth. The closer the bone block was placed to the alveolar bone, the more stable was the result. The best results were obtained with a ¼ dehiscence and 0.1 mm distance. Conclusions: The protrusive forces produced by the tongue might not be the biggest one, but in a presence of the bone loss they might have serious results. Even shortly after the surgery, CABB has a positive impact on the incisor resilience.



Fig. 1 High-resolution image of the new screw design and schematic representation of the optimal positioning in the bone using an artificial bone block: a: connection area with internal thread, b: mucosa, c: cortical bone, d: cancellous bone Abb. 1 Hochauflösende Aufnahme des neuen Schraubendesigns und schematische Darstellung der optimalen Positionierung im Knochen anhand eines künstlichen Knochenblocks: a: Verbindungsbereich mit Innengewinde, b: Schleimhaut, c: Kortikalis, d: Spongiosa
Fig. 3 Measuring device with test holder and predrilled hole. a Measuring device with fixed predrill and test holder, with embedded artificial bone block. b Red predrill, diameter 1.4 mm, PSM Medical GmbH. c Finished predrilling in the embedded artificial bone block Abb. 3 Messgerät mit Probenhalter und vorgebohrtem Loch. a Messgerät mit festem Vorbohrer und Probenhalter, mit eingebettetem künstlichem Knochenblock. b Roter Vorbohrer, Ø 1,4 mm, PSM Medical GmbH. c Fertige Vorbohrung im eingebetteten künstlichen Knochenblock
Fig. 4 Testing of a temporary anchorage device (TAD) on primary stability. a TAD attachment with MIRA screw, which is attached to the measuring device and has already been inserted into the artificial bone block. b Completely inserted thread of the MIRA screw in the artificial bone block. No thread is visible from the outside Abb. 4 Primärstabilitätsprüfung eines temporären Verankerungselements (TAD). a TAD-Aufsatz mit MIRA-Schraube, die am Messgerät befestigt ist und bereits in den künstlichen Knochenblock eingesetzt wurde. b Vollständig eingesetztes Gewinde der MIRA-Schraube im künstlichen Knochenblock. Von außen ist kein Gewinde sichtbar
Fig. 6 Evaluation of the maximum insertion torques. Illustration of the analyzed maximum insertion torques in Ncm for each temporary anchorage device (TAD) group examined in a box-and-whisker plot (A = Aarhus ® , B = BENEfit ® , C = MIRA screw). The asterisks illustrate the significant differences between the marked groups (p < 0.05) according to Kruskal-Wallis tests and post hoc Dunn-Bonferroni tests Abb. 6 Auswertung der maximalen Eindrehmomente. Darstellung der analysierten maximalen Eindrehmomente in Ncm für jede untersuchte TAD(temporäres Verankerungselement)-Gruppe in einem Box-and-Whisker-Diagramm (A = Aarhus ® , B = BENEfit ® , C = MIRA-Schraube). Die Sternchen zeigen die signifikanten Unterschiede zwischen den markierten Gruppen (p < 0,05) gemäß Kruskal-Wallis-Test und Post-hoc-DunnBonferroni-Test
Fig. 7 Evaluation of the maximum fracture torques. Illustration of the analyzed maximum fracture torques in Ncm for each tested screw group in a box-and-whisker plot (A = Aarhus ® , B = BENEfit ® , C = MIRA). The asterisks illustrate the significant differences between the marked groups (p < 0.05) according to Kruskal-Wallis tests and post hoc Dunn-Bonferroni tests Abb. 7 Auswertung der maximalen Bruchdrehmomente. Darstellung der analysierten maximalen Bruchdrehmomente in Ncm für jede getestete Schraubengruppe in einem Box-and-Whisker-Diagramm (A = Aarhus ® , B = BENEfit ® , C = MIRA). Die Sternchen zeigen die signifikanten Unterschiede zwischen den markierten Gruppen (p < 0,05) gemäß Kruskal-Wallis-Test und Post-hoc-Dunn-Bonferroni-Test

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Development and in vitro testing of an orthodontic miniscrew for use in the mandible

November 2024

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43 Reads

Journal of Orofacial Orthopedics / Fortschritte der Kieferorthopädie

Objective Temporary anchorage devices (TADs) have been successfully used in the maxilla. However, in the mandible, lower success rates present a challenge in everyday clinical practice. A new TAD design will be presented that is intended to demonstrate optimization of the coupling structure as well as in the thread area for use in the mandible. Methods Three TADs were examined: (A) Aarhus® system (68.99.33 A, Medicon, Tuttlingen, Germany), (B) BENEfit® orthodontic screw (ST-33-54209; PSM Medical, Gunningen, Germany) and (C) a new design with a two-part screw thread. The TADs were inserted into artificial bone blocks after predrilling to test primary stability. To test the fracture stability, the TADs were embedded in Technovit® 4004 (Heraeus Kulzer, Wehrheim, Germany) and torsional loaded at an angle of 90° until fracture. The threshold torque values occurring were recorded digitally. The statistical evaluation was carried out using the Kruskal–Wallis test with a post hoc test according to Bonferroni ( p < 0.05). Results The following values were measured for the insertion torque: A: 33.7 ± 3.3 Ncm; B: 57.1 ± 8.4 Ncm; C: 34.2 ± 1.4 Ncm. There were significant differences between A–B and B–C. The measured values for the fracture strength were as follows: A: 46.7 ± 3.5 Ncm; B: 64.2 ± 5.1 Ncm; C: 55.4 ± 5.1 Ncm. Significant differences were found between all groups. Conclusion The adapted screw design has no negative influence on primary and fracture stability. Whether the design has a positive effect on the success rates in the mandible must be clarified in further clinical studies.


Comparative Experimental Evaluation of Orthodontic Appliances for Maxillary Arch Expansion

October 2024

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48 Reads

Background/Objectives: The orthodontic treatment of posterior crossbite using appliances for gradual maxillary expansion is crucial to ensure proper transversal jaw relationships as much as occlusal functionality. The aim of this study was to analyze forces and torques generated by different appliances for maxillary expansion. Methods: Measurements were conducted for the Wilson® 3D® Quadhelix (WQH) and Wilson® 3D® Multi-Action Palatal Appliance (WPA) across various sizes and compared to the Remanium® Quadhelix (RQH). Activations were set to 8 mm for the WQH and RQH and 6 and 8 mm for the WPA. Rotations and root torque were simulated via an activation of 10° for arches. A total of eight test series were conducted. Results: The WPA displayed the highest force and torque values for all movements, far surpassing recommended guideline values (expansion 8.5–>15.0 N/46.3–86.5 Nmm, rotation 3.1–6.1 N/40.7–61.4 Nmm, torque 3.9–5.1 N/22.4–29.7 Nmm), and the WQH displayed the lowest values (expansion 2.7–12.6 N/11.1–39.6 Nmm, rotation 0.1–1.7 N/23.0–32.2 Nmm, torque 0.9–2.9 N/3.4–10.5 Nmm). Appliances with the smallest transverse dimensions exhibited the highest force and torque maxima. Conclusions: This study underscores the importance of understanding biomechanical principles in orthodontics for minimizing unintended tooth movements, providing detailed insights into the force systems of appliances acting in the transverse plane, and establishing a foundation for future clinical investigations to validate these in vitro findings.


Figure 7. Cont.
Material parameters of the model structures utilized in the investigation.
Example results from the simulation with retraction forces.
Numerical Simulation of Maxillary Anterior Teeth Retraction Utilizing Power Arms in Lingual Orthodontic Technique

September 2024

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28 Reads

Journal of Personalized Medicine

Aims: It was the scope of this study to explore the biomechanical implications of retraction force application point modifications in lingual orthodontics, aiming to mitigate the bowing effect and enhance anchorage stability in the anterior teeth. Methods: Using the FE method on an idealized maxillary model, en masse retraction was simulated using a modified lingual fixed appliance including edgewise lingual brackets, a 0.017″ × 0.025″ mushroom-shaped archwire, and power arms between lateral incisors and canines, with a transpalatal arch (TPA) connecting the first molars. Applying bilateral retraction forces of 1.5 N at twelve positions, initial tooth displacements during space closure were evaluated. Results: Shifting power arms gingivally did not effectively counteract palatal tipping of incisors but reduced posterior and palatal tipping of canines with a power arm length of 11.3 mm preventing posterior tipping. Apically displacing the TPA retraction force increased mesiobuccal rotation while preventing mesial molar tipping for retraction forces applied 12.6 mm from the archwire. Conclusions: Apically shifting retraction forces can mitigate vertical bowing effects in lingual orthodontics, yet it also highlights the challenges in maintaining torque in the anterior teeth. Further research and clinical validation are essential in order to confirm these results, emphasizing the complexity and need for advanced biomechanical strategies in personalized lingual orthodontic treatments.


The Role of Bone and Root Resorption on the Biomechanical Behavior of Mandibular Anterior Teeth Subjected to Orthodontic Forces: A Finite Element Approach

August 2024

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70 Reads

Aims: This study was conducted to systematically evaluate the biomechanical impact of varying degrees of root and bone resorption resulting from periodontitis and orthodontic tooth movement (OTM) on the mandibular anterior teeth. The objective was to determine whether these distinct resorption patterns exert a specific influence on tooth displacement and strain patterns. Methods: A finite element (FE) model of an idealized anterior mandible from the first premolar in the third to the fourth quadrant was developed without bone or root resorption and a constant periodontal ligament (PDL) thickness of 0.2 mm. Variations included three root resorption levels (0%, 20%, 50%) and three bone resorption types (circular 50%, circular 80%, vestibular 80%). Models ranged from 200,000 to 440,000 elements and 55,000 to 130,000 nodes. Orthodontic forces, namely root torque (5 Nmm), intrusion (0.2 N), and distalization (0.5 N) were applied for subsequent crown displacement and PDL strain analysis. Results: A total of 180 simulations were performed. Simulations showed that displacement was similar across different bone resorption conditions, irrespective of modeled root resorptions. Circumferential bone resorption increased tooth displacement, regardless of root resorption status. Vestibular bone resorption exhibited less increase in tooth displacement. However, when accompanied by root resorption, the combination exacerbated tooth displacement. Strains in the PDL clearly increased with a circumferential bone resorption of 80%. Conclusions: This study highlights the critical role of bone resorption in tooth displacement during OTM, particularly the challenges associated with circumferential resorption. Clinicians must consider both bone and root resorption for personalized medicine treatment of patients with severe periodontitis, in favor of low-force application strategies to optimize outcomes and minimize complications linked to excessive tooth displacement.




Citations (67)


... These factors, together with other intraoral conditions such as salivation and humidity, were not comprehensively considered in the present study. Although these conditions have been reported to impact force generation over time with thermoformed materials [46,55], their effects on 3D-printed materials have not yet been documented. ...

Reference:

Force system of 3D-printed orthodontic aligners made of shape memory polymers: an in vitro study
Effect of thermomechanical aging on force system of orthodontic aligners made of different thermoformed materialsAuswirkung thermomechanischer Alterung auf das Kräftesystem von kieferorthopädischen Alignern aus verschiedenen tiefgezogenen Materialien: An in vitro studyEine In-vitro-Studie

Journal of Orofacial Orthopedics / Fortschritte der Kieferorthopädie

... In the past, these guides were manually crafted based on the traditional plaster model, but with the advent of digital technology, the production of guides using digital CAD/CAM has become predominant [5,[7][8][9][10]. These advancements have significantly enhanced the accuracy and efficiency of implant placements, reducing the potential for errors and improving patient outcomes [4,[11][12][13][14][15]. ...

Accuracy of template-based guided dental implant placement-An in vitro comparison of different manufacturing methods
  • Citing Article
  • April 2024

Clinical Oral Implants Research

... The success of this approach hinges on several factors, including implant distribution and prosthetic design. These must work in tandem to evenly distribute occlusal forces and prevent excessive stress on the implants and surrounding biological structures, as excessive stress can lead to bone resorption and adversely affect implant survival (Aboelfadl et al., 2024;Amaral et al., 2018). Studies (Yu et al., 2022;Zhong et al., 2020) suggested that a wider implant distribution with a fixed-fixed framework offers reliable outcomes. ...

Biomechanical behavior of implant retained prostheses in the posterior maxilla using different materials: a finite element study

BMC Oral Health

... Of twelve included articles, six studies utilized Finite Element Method (FEM), with three focusing on single tooth movements of the upper maxillary central incisor [23,34,35] and three examining multiple-tooth movements, including en-masse retraction of upper anterior teeth [33], upper arch expansion [36], and utilization of Class II elastic traction [37]. The remaining six studies employed laboratory techniques, in which three used force measuring devices/sensors on single teeth [38,39] and adjacent teeth [33], two conducted retentive tests on upper dental models [22,41], and one utilized pressure-sensitive films to visualize force, pressure, and stress distribution on the dental crown surface during palatal translation of the upper central incisor [24]. ...

Effect of attachment configuration and trim line design on the force system of orthodontic aligners: A finite element study on the upper central incisor

Orthodontics and Craniofacial Research

... The morphology of the aligner trimline may influence the biomechanical performance of CAT. The gingival margin design of aligners, commonly known as the trimline, is an important determinant of both aligner retention and biomechanical force delivery [22][23][24]. These trimlines can be straight or scalloped, following the cervical margin of teeth, and may extend over varying areas of the attached gingiva. ...

Numerical biomechanical finite element analysis of different trimming line designs of orthodontic aligners: An in silico study

Journal of the World Federation of Orthodontists

... It has been seen that this new technique offers a convenient, accurate, and risk-free assessment of tooth wear. Similarly, Keilig et al. [26] evaluated the efficiency of teeth alignment with clear aligners (CAs) using the 3D overlap, considering the different variability. They deduced that CAs can implement tooth movements effectively through the inclination of clinical crowns. ...

Treatment Efficiency of Maxillary and Mandibular Orovestibular Tooth Expansion and Compression Movements with the Invisalign® System in Adolescents and Adults

... While the latter is an assessment of the overall treatment outcome, it does not specifically address the amount of tooth movement. Measuring of tooth movement on digital models provides a more comprehensive understanding of the actual tooth movement in three dimensions by superimposing the digital dental casts [22][23][24][25][26]. A dental cast study on tooth movement after extraction of the maxillary first or second premolars in patients with fixed appliances using model superimposition showed that mesial movement of the first molars was comparable in both treatment modalities, at 4.7 mm (SD 1.6 mm) and 4.6 mm (SD 1.6 mm), respectively [26]. ...

Superimposition of dental models to determine orthodontic tooth movements : Comparison of different superimposition methods in vitro and in vivo
  • Citing Article
  • February 2024

Journal of Orofacial Orthopedics / Fortschritte der Kieferorthopädie

... The aim of this study was to develop a validated 3D numerical finite element model based on previous in vitro research (Aldesoki et al., 2024), and to use this model to investigate the biomechanical behaviour of multirooted RAIs. The research hypothesis postulated that there is no difference in terms of biomechanical behaviour between the multirooted RAI and the conventional TI. ...

Evaluation of micromotion in multirooted root analogue implants embedded in synthetic bone blocks: an in vitro study

BMC Oral Health

... Thermomechanical loading was performed in a chewing simulator (Chewing Simulator 4; SD Mechatronik, Westerham, Germany) using a stainless-steel ball with 8 mm diameter as an antagonist (1.2 Hz frequency, 50 N, 1.2 million cycles), corresponding to approximately 5 years of clinical function in the oral cavity [43]. Additionally, specimens underwent 6,000 thermal cycles between 5 and 55 °C, simulating 5 years of temperature fluctuations encountered daily in the oral environment [44]. ...

The effect of cyclic loading on the fracture resistance of 3D-printed and CAD/CAM milled zirconia crowns-an in vitro study

... To address this gap, our research team is undertaking an extensive project on orthodontic aligners, investigating various aspects at multiple levels. This includes providing insights into how the mechanical properties of aligners, made of different materials, are affected by ageing over different durations, using various ageing agents, 15 ageing techniques, 16 and measurement methods. 16,17 As a part of the project, the aim of the current research is to report the changes in forces generated by different thermoformed aligner materials after undergoing a 2-days ageing protocol involving both thermal and mechanical loading, with a specific focus on comparing the mechanical behaviour of multi-layer and single-layer materials before and after ageing. ...

Effect of thermomechanical aging of orthodontic aligners on force and torque generation: An in vitro study
  • Citing Article
  • May 2023

Journal of the Mechanical Behavior of Biomedical Materials