Ludger Keilig

University of Bonn, Bonn, North Rhine-Westphalia, Germany

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Publications (81)111.94 Total impact

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    ABSTRACT: Analysing the influence of implant splinting and its relation to different framework materials is a complex issue. The stiffness of framework materials and the overload of the implant system directly affect the final transferred load of the bone around implants.
    Annals of Anatomy - Anatomischer Anzeiger. 01/2015;
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    ABSTRACT: Self-ligating brackets are widely believed to be more effective in clinical use and to involve less friction and force. Thus, the goal of this in vitro investigation was to experimentally assess the effectiveness of different bracket-archwire combinations and the force levels exerted in two-dimensional direction during correction of tooth malalignment. An important aspect of this objective was to determine whether the behaviors of conventional bracket systems with an elastic or steel ligature differ from that of self-ligating brackets.
    11/2014; 75(6):459-470.
  • 11/2014; 146(5):546.
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    11/2014; 146(5):547-8.
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    ABSTRACT: Objectives Nickel (Ni) is one of the main metal elements in orthodontic and prosthetic devices. Different effects of Ni are described ranging from an induction of local inflammation to allergy and cancerous/mutagenic properties. Inflammatory reactions are frequently observed in the oral cavity, but the interrelationship of Ni with those events is still unknown. Therefore, we focused on the impact of Ni on inflammation in vitro. Methods In accordance to previous immersion tests of our lab, human gingival fibroblasts (HGFs) (n = 6) were exposed to a pro-inflammatory environment using interleukin-1 beta (IL-1β) and additionally stimulated with different Ni(II) concentrations (400 and 4000 ng/ml). At varying time points the expression of pro- and anti-inflammatory as well as matrix degeneration proteins, i.e. MMPs, were analyzed. Furthermore, proliferation assays, wound healing tests and the detection of NF-κB activation were conducted. Unstimulated HGFs served as control. Results Our experiments showed that low clinical average Ni(II) levels did not alter pro-inflammatory cytokines significantly compared to control (p > 0.05). Instead, a 10-fold higher dose up-regulated these mediators significantly in a time-dependent manner (p < 0.01). This was even more pronounced combining both Ni(II) concentrations with an inflammatory condition (p < 0.001), MMP expressions were in line with our findings (p < 0.001). The mRNA data were supported by proliferation and wound closure assays (p < 0.001). However, the combination of both stimuli induced contradictory results. Analyzing NF-κB activation revealed that our results may be in part attributed to NF-κB. Significance Our in vitro study implicated that Ni(II) has various modifying effects on IL-1β-induced inflammatory processes depending on the concentration.
    Dental Materials 10/2014; · 4.16 Impact Factor
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    ABSTRACT: Structured AbstractObjective To evaluate the efficacy of tooth alignment achieved by various small cross-section archwire/bracket combinations using the orthodontic measurement and simulation system.Materials and Methods The study comprised three types of orthodontic brackets 1) conventional ligating (Victory Series and Mini-Taurus), 2) self-ligating (SmartClip a passive self-ligating bracket and Time3 an active self-ligating bracket), and 3) a conventional low-friction bracket (Synergy). All brackets had a nominal 0.022″ slot size. Brackets were combined with 1) 0.012″ stainless steel, 2) 0.012″ Orthonol, 3) 0.012″ Thermalloy, and 4) 0.0155″ coaxial archwires. Archwires were tied to the conventional brackets with stainless steel ligatures and elastomeric rings. The malocclusion simulated represented a central upper incisor displaced 2 mm gingivally (x-axis) and 2 mm labially (z-axis).ResultsThe inciso-gingival correction achieved by the different archwire/bracket combinations ranged from 15 to 95%, while the labio-lingual correction ranged from 10 to 95%. The smallest correction was achieved by coaxial, Orthonol, and thermally archwires when ligated with the elastomeric rings to conventional brackets. Stainless steel archwires achieved from 65 to 90% of inciso-gingival correction and from 60 to 90% of labio-lingual correction.Conclusion The resultant tooth alignment was the product of interaction between the archwire type, bracket type, and bracket design including ligature type. Small cross-sectional archwires might produce up to 95% correction if combined properly with the bracket system. Elastomeric rings when used with conventional brackets limit the efficacy of malalignment correction.
    Orthodontics and Craniofacial Research 09/2014; 18(1). · 1.29 Impact Factor
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    ABSTRACT: The aim of this work was to investigate whether electrochemical surface treatment of nickel-titanium (NiTi) and titanium-molybdenum (TiMo) archwires (OptoTherm™ and BetaTitan™; Ortho-Dent Specials, Kisdorf, Germany) reduces friction inside the bracket-archwire complex. We also evaluated further material properties and compared these to untreated wires.
    Journal of Orofacial Orthopedics / Fortschritte der Kieferorthopädie 07/2014; 75(4). · 0.82 Impact Factor
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    ABSTRACT: BackgroundThe aim of this study was to investigate the efficacy of orthodontic treatment using the Invisalign® system. Particularly, we analyzed the influence of auxiliaries (Attachment/Power Ridge) as well as the staging (movement per aligner) on treatment efficacy.MethodsWe reviewed the tooth movements of 30 consecutive patients who required orthodontic treatment with Invisalign®. In all patients, one of the following tooth movements was performed: (1) Incisor Torque >10°, (2) Premolar derotation >10° (3) Molar distalization >1.5 mm. The groups (1)-(3) were subdivided: in the first subgroup (a) the movements were supported with the use of an attachment, while in the subgroup (b) no auxiliaries were used (except incisor torque, in which Power Ridges were used). All tooth movements were performed in a split-mouth design. To analyze the clinical efficacy, pre-treatment and final plaster cast models were laser-scanned and the achieved tooth movement was determined by way of a surface/surface matching algorithm. The results were compared with the amount of tooth movement predicted by ClinCheck®.ResultsThe overall mean efficacy was 59% (SD = 0.2). The mean accuracy for upper incisor torque was 42% (SD = 0.2). Premolar derotation showed the lowest accuracy with approximately 40% (SD = 0.3). Distalization of an upper molar was the most effective movement, with efficacy approximately 87% (SD = 0.2).ConclusionIncisor torque, premolar derotation and molar distalization can be performed using Invisalign® aligners. The staging (movement/aligner) and the total amount of planned movement have an significant impact on treatment efficacy.
    BMC Oral Health 06/2014; 14(1):68. · 1.15 Impact Factor
    This article is viewable in ResearchGate's enriched format
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    ABSTRACT: Introduction The exact force systems as well as their progressions generated by removable thermoplastic appliances have not been investigated. Thus, the purposes of this experimental study were to quantify the forces and moments delivered by a single aligner and a series of aligners (Invisalign; Align Technology, Santa Clara, Calif) and to investigate the influence of attachments and power ridges on the force transfer. Methods We studied 970 aligners of the Invisalign system (60 series of aligners). The aligners came from 30 consecutive patients, of which 3 tooth movements (incisor torque, premolar derotation, molar distalization) with 20 movements each were analyzed. The 3 movement groups were subdivided so that 10 movements were supported with an attachment and 10 were not. The patients' ClinCheck (Align Technology, Santa Clara, Calif) was planned so that the movements to be investigated were performed in isolation in the respective quadrant. Resin replicas of the patients' intraoral situation before the start of the investigated movement were taken and mounted in a biomechanical measurement system. An aligner was put on the model, the force systems were measured, and the calculated movements were experimentally performed until no further forces or moments were generated. Subsequently, the next aligners were installed, and the measurements were repeated. Results The initial mean moments were about 7.3 N·mm for maxillary incisor torque and about 1.0 N for distalization. Significant differences in the generated moments were measured in the premolar derotation group, whether they were supported with an attachment (8.8 N·mm) or not (1.2 N·mm). All measurements showed an exponential force change. Conclusions Apart from a few maximal initial force systems, the forces and moments generated by aligners of the Invisalign system are within the range of orthodontic forces. The force change is exponential while a patient is wearing removable thermoplastic appliances.
    American Journal of Orthodontics and Dentofacial Orthopedics 06/2014; 145(6):728–736. · 1.44 Impact Factor
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    ABSTRACT: The rigidity of framework materials and overload of the implant system directly affect the final transferred load of the bone around implants. The aim of the present study has been to analyse the influence of framework materials on the transferred load to the implant system and the surrounding bone. A finite element model of a long-span cementable implant-supported fixed prosthesis was created with two coping layers (gold and hybrid composite) to optimise the fitting of the prosthesis to the abutments. Three framework materials were analysed: Titanium, gold alloy, and zirconia. The connection screws were first preloaded with 200 N. The framework was then loaded with 500 N vertically and at 30° to the framework long axis. Two loading conditions were considered: At the mesial and distal boundaries of the framework and at the centre of the framework. The stresses and strains within the framework materials and bone bed around the supporting implants were analysed. The region and angle of load applications showed an obvious effect on the values of the stresses and strains within the framework itself and, consequently, their distribution in the implant system and surrounding bone. A correlation of the framework material and stresses of the coping materials was observed as well. The gold framework showed acceptable values of stress within the cortical bone (92 MPa and 89 MPa with 30° loading at two points and at the centre, respectively) in comparison to titanium (92 MPa and 113 MPa) and zirconia (88 MPa and 115 MPa).
    Annals of Anatomy - Anatomischer Anzeiger 05/2014; · 2.08 Impact Factor
  • Zahnmedizin up2date 01/2014; 8(01):87-107.
  • Biomedizinische Technik/Biomedical Engineering 01/2014; · 1.16 Impact Factor
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    ABSTRACT: Once periodontitis has been completely resolved, one common follow-up method is to carry out orthodontic treatment to take advantage of the residual bone, i.e., via tooth intrusion. In this study, the biomechanical behavior of teeth in a reduced periodontium was studied by numerically simulating upper-incisor intrusion accomplished with various orthodontic mechanics. Using the finite element method, a patient-customized 3D model of a periodontally reduced dentition was generated in order to simulate tooth movement. The morphology of this upper-jaw model was derived from cone-beam computed tomography (CBCT) datasets of four patients. Material parameters were adopted from previous investigations, including teeth (E=20 GPa), periodontal ligament (PDL) (bilinear elastic; E1=0.05 MPa; E2=0.20 MPa; ε12=7%), and bone (homogeneous, isotropic; E=2 GPa). Two intrusion scenarios were used, the first drawing from Burstone's segmented-arch technique to intrude four splinted incisors at a time, and the second one using cantilevers to intrude single incisors. The aforementioned PDL material parameters were varied in several ways to simulate different biological and biomechanical states of PDL. All simulations were recalculated with an idealized, periodontally intact model to assess the effect of bone loss by way of comparison. Single-tooth intrusion via cantilever mechanics was accompanied by less rotation than the segmented-arch approach. Both intrusion systems involved significantly greater degrees of tooth displacement and PDL load in the periodontally reduced model. Periodontally reduced dentitions are associated with an increased load on periodontal tissue. This can be counteracted by reducing orthodontic force levels and by selecting mechanics that do not harm the tissue. In so doing, the use of numerical methods may greatly facilitate individualized computer-aided treatment-planning strategies.
    Fortschritte der Kieferorthopädie 11/2013; 74(6). · 0.89 Impact Factor
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    ABSTRACT: The force applied to the teeth is a variable of orthodontic treatment that can be controlled. Poor control of the applied force can lead to adverse biologic effects as well as undesirable tooth movements. The selected archwire-bracket combination is a primary determining factor in the force level applied to a tooth during orthodontic treatment. The aim of this research was to use an experimental biomechanical setup to measure forces generated during complex orthodontic tooth movements with various archwire-bracket combinations. The materials consisted of 3 types of 0.022-in slot orthodontic brackets: (1) conventional brackets (Victory Series [3M Unitek, Monrovia, Calif] and Mini-Taurus [Rocky Mountain Orthodontics, Denver, Colo]), (2) self-ligating brackets (SmartClip [3M Unitek] and Time3 [American Orthodontics, Shegoygan, Wis]), and (3) a conventional low-friction bracket (Synergy [Rocky Mountain Orthodontics]); and 4 archwire types: (1) 0.012-in stainless steel (3M Unitek), (2) 0.0155-in coaxial (Advanced Orthodontics [Näpflein, Düsseldorf, Germany]), (3) 0.012-in Orthonol (Rocky Mountain Orthodontics), and (4) 0.012-in Thermalloy (Rocky Mountain Orthodontics). Stainless steel ligatures and elastomeric rings were used. The materials were used in different combinations in a simulated malocclusion that represented a maxillary central incisor displaced 2 mm gingivally (x-axis) and 2 mm labially (z-axis). The lowest forces were measured when the brackets were combined with either the coaxial or the Thermalloy archwires; the forces ranged from 3.4 ± 0.2 to 0.7 ± 0.1 N in the x-axis direction, and from 4.5 ± 0.3 to 0.5 ± 0.1 N in the z-axis direction. The highest forces were measured in combination with stainless steel archwires; the forces ranged from 6.3 ± 0.3 to 3.0 ± 0.1 N in the x-axis direction, and from 6.3 ± 0.3 to 1.7 ± 0.1 N in the z-axis direction. We recommend 0.0155-in coaxial and 0.012-in Thermalloy archwires for leveling and alignment. Elastomeric rings, when used with conventional brackets, increased the force applied to the teeth.
    American journal of orthodontics and dentofacial orthopedics: official publication of the American Association of Orthodontists, its constituent societies, and the American Board of Orthodontics 04/2013; 143(4):507-14. · 1.33 Impact Factor
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    ABSTRACT: OBJECTIVES: To develop an in vitro assay for quantitative analysis of the degradation to which a bone substitute is exposed by osteoclasts. The aim of establishing this method was to improve the predictability of carrying out tooth movements via bone substitutes and to provide a basis for verification in exemplary clinical cases. METHODS: After populating a bone substitute (NanoBone®; ArtOss, Germany) with osteoclastic cells, inductively-coupled mass spectrometry was used to evaluate changing calcium levels in the culture medium as a marker of resorption activity. RESULTS: It was observed that calcium levels increased substantially in the culture medium with the cells populating the bone substitute. CONCLUSIONS: This in vitro assay is a valid method that can assist clinicians in selecting the appropriate materials for certain patients. While tooth movements occurring through this material were successful, uncertainty about the approach will remain as long-term results are not available.
    Fortschritte der Kieferorthopädie 03/2013; · 0.89 Impact Factor
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    ABSTRACT: OBJECTIVE: The significance of friction inside the bracket-wire-ligature interface remains controversial despite having been investigated for four decades. Numerous approaches have been proposed to reduce friction via any of the elements of the interface, key among them being recently developed bracket modifications and the introduction of surface-modified wires. The present study explored whether archwires treated by a novel electrochemical process of surface refinement influence first-order couples generated inside self-ligating and conventionally ligated brackets during tooth rotation. MATERIALS AND METHODS: A surface-refined nickel-titanium archwire (OptoTherm/LoFrix™) was compared ex vivo to a non-refined archwire of the same production lot (OptoTherm™), the nominal dimensions being 0.014×0.025'' in both cases. Three bracket designs were included to assess the role of the ligation mechanism: (1) Carrière SLB™ passive self-ligating brackets, (2) BioQuick® active self-ligating brackets, and (3) Classic Series® conventionally ligated brackets. The brackets were bonded to leveled tooth elements on a resin mandibular arch. To simulate rotation, the lower left first premolar was removed and connected to a biomechanical measuring system. The simulation procedures were performed at 37°C. RESULTS: The various bracket designs yielded characteristic torque curves mainly reflecting the play of the archwire specimens inside their slots. While the passive self-ligating brackets exhibited 2-3° of play in either direction, both the active self-ligating brackets and the conventional brackets with elastic ligatures did not reveal any play. Torque levels ranged from 8 Nmm inside the conventional brackets to 13 Nmm inside the passive self-ligating brackets. The surface-refined archwires induced significantly (up to 35%) lower torque levels and were slightly reduced in cross-section. CONCLUSION: Electrochemical surface refinement can significantly reduce first order couples induced by archwires. This effect is caused by less friction, but also by the slightly reduced cross-section of these wires.
    Fortschritte der Kieferorthopädie 03/2013; · 0.89 Impact Factor
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    ABSTRACT: This study aimed to investigate the differences in the force loss during simulated archwire-guided canine retraction between various conventional and self-ligating brackets. Three types of orthodontic brackets have been investigated experimentally using a biomechanical set-up: 1. conventional ligating brackets (Victory Series and Mini-Taurus), 2. self-ligating brackets (SmartClip: passive self-ligating bracket, and Time3 and SPEED: active self-ligating brackets), and 3. a conventional low-friction bracket (Synergy). All brackets had a nominal 0.022″ slot size. The brackets were combined with three rectangular 0.019×0.025″ archwires: 1. Remanium (stainless steel), 2. Nitinol SE (nickel-titanium alloy, NiTi), and 3. Beta III Titanium (titanium-molybdenum alloy). Stainless steel ligatures were used with the conventional brackets. Archwire-guided tooth movement was simulated over a retraction path of up to 4mm using a superelastic NiTi coil spring (force: 1 N). Force loss was lowest for the Victory Series and SmartClip brackets in combination with the steel guiding archwire (35 and 37.6 per cent, respectively) and highest for the SPEED and Mini-Taurus brackets in combination with the titanium wire (73.7 and 64.4 per cent, respectively). Force loss gradually increased by 10 per cent for each bracket type in combination with the different wires in the following sequence: stainless steel, Nitinol, and beta-titanium. Self-ligating brackets did not show improved performance compared with conventional brackets. There was no consistent pattern of force loss when comparing conventional and self-ligating brackets or passive and active self-ligating brackets.
    The European Journal of Orthodontics 02/2013; · 1.53 Impact Factor
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    ABSTRACT: The analysis of the non-linear and time-dependent viscoelasticity of the periodontal ligament (PDL) enables a better understanding of the biomechanical features of the key regulator tissue for tooth movement. This is of great significance in the field of orthodontics as targeted tooth movement remains still one of the main goals to accomplish. The investigation of biomechanical aspects of the PDL function, a difficult area of research, helps towards this direction. After analysing the time-dependent biomechanical properties of pig PDL specimens in an in vitro experimental study, it was possible to confirm that PDL has a viscoelastic anisotropic behaviour. Three-dimensional finite element models of mini-pig mandibular premolars with surrounding tissues were developed, based on micro-computed tomography (μCT) data of the experimental specimens. Tooth mobility was numerically analysed under the same force systems as used in the experiment. A bilinear material parameter set was assumed to simulate tooth displacements. The numerical force/displacement curves were fitted to the experimental curves by repeatedly calculating tooth displacements of 0.2mm varying the loading velocities and the parameters, which describe the nonlinearity. The experimental results showed a good agreement with the numerical calculations. Mean values of Young's moduli E(1), E(2) and ultimate strain ε(12) were derived for the elastic behaviour of the PDL for all loading velocities. E(1) and E(2) values increased with increasing the velocity, while ε(12) remained relatively stable. A bilinear approximation of material properties of the PDL is a suitable description of measured force/displacement diagrams. The numerical results can be used to describe mechanical processes, especially stress-strain distributions in the PDL, accurately. Further development of suitable modelling assumptions for the response of PDL under load would be instrumental to orthodontists and engineers for designing more predictable orthodontic force systems and appliances.
    The European Journal of Orthodontics 01/2013; · 1.53 Impact Factor
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    ABSTRACT: The aim of this study was to determine the material composition and cell-mediated remodelling of different calcium phosphate-based bone substitutes. Osteoclasts were cultivated on bone substitutes (Cerabone, Maxresorb, and NanoBone) for up to 5 days. Bafilomycin A1 addition served as the control. To determine cellular activity, the supernatant content of calcium and phosphate was measured by inductively coupled plasma optical emission spectrometry. Cells were visualized on the materials by scanning electron microscopy. Material composition and surface characteristics were assessed by energy-dispersive X-ray spectroscopy. Osteoclast-induced calcium and phosphate release was material-specific. Maxresorb exhibited the highest ion release to the medium (P = 0.034; calcium 40.25 mg/l day 5, phosphate 102.08 mg/l day 5) and NanoBone the lowest (P = 0.021; calcium 8.43 mg/l day 5, phosphate 15.15 mg/l day 5); Cerabone was intermediate (P = 0.034; calcium 16.34 mg/l day 5, phosphate 30.6 mg/l day 5). All investigated materials showed unique resorption behaviours. The presented methodology provides a new perspective on the investigation of bone substitute biodegradation, maintaining the material-specific micro- and macrostructure.
    International Journal of Oral and Maxillofacial Surgery 01/2013; · 1.52 Impact Factor
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    ABSTRACT: Huang Y., Keilig L., Rahimi A., Reimann S., Bourauel C: Torque capabilities of self-ligating and conventional brackets under the effect of bracket width and free wire length Orthod Craniofac Res 2012;15:255-262. © John Wiley & Sons A/S STRUCTURED ABSTRACT: Objectives -  To numerically investigate the torque capacity of conventional and self-ligating brackets under the effect of varying bracket width and free wire length. Material and Methods -  Finite element models of three kinds of orthodontic brackets in the 0.022-inch slot size were investigated: Discovery, Damon 3MX, Speed. Additionally, finite element (FE) models of Speed and Damon brackets were generated with the same width as the Discovery. From the left upper incisor to the right upper canine, four brackets each were modelled. The total wire length at the upper right incisor was kept constant at 12 mm for all brackets types. For the Discovery brackets, the wire length was increased from 12 to 16 mm in 2-mm steps. A torque of 20° was applied to the upper right incisor with 0.46 × 0.64 mm(2) (0.018″ × 0.025″) and 0.48 × 0.64 mm(2) (0.019″ × 0.025″) wires. Wires made of stainless steel, titanium molybdenum and nickel titanium were studied. Torque angle/moment characteristics were recorded. Results -  Wider brackets showed more torque control capability (e.g. Discovery: 10.6 Nmm, Damon: 9.2 Nmm, Speed: 4.0 Nmm for the NiTi wire). Even with the same width as the Discovery bracket, Damon and Speed brackets showed lower torque capability than the Discovery bracket. Increasing the free wire length decreased the torsional stiffness of the wire and thus decreased the torque capability. Conclusion -  The results showed that the bracket design has less influence on the torquing moment than other parameters, such as bracket width, free wire length, wire/slot play or misalignment.
    Orthodontics and Craniofacial Research 11/2012; 15(4):255-62. · 1.29 Impact Factor

Publication Stats

327 Citations
111.94 Total Impact Points


  • 1999–2014
    • University of Bonn
      • Poliklinik für Kieferorthopädie
      Bonn, North Rhine-Westphalia, Germany
  • 2013
    • Mansoura University
      • Faculty of Dentistry
      Al Manşūrah, Muhafazat ad Daqahliyah, Egypt
  • 2007
    • University of Padova
      • Center of Mechanics of Biological Materials
      Padova, Veneto, Italy