1
|
Elshazly TM, Bourauel C, Ismail A, Ghoraba O, Aldesoki M, Salvatori D, Elattar H, Alhotan A, Alkabani Y. Effect of material composition and thickness of orthodontic aligners on the transmission and distribution of forces: an in vitro study. Clin Oral Investig 2024; 28:258. [PMID: 38637429 PMCID: PMC11026231 DOI: 10.1007/s00784-024-05662-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2024] [Accepted: 04/12/2024] [Indexed: 04/20/2024]
Abstract
OBJECTIVES To investigate the effects of material type and thickness on force generation and distribution by aligners. MATERIALS AND METHODS Sixty aligners were divided into six groups (n = 10): one group with a thickness of 0.89 mm using Zendura Viva (Multi-layer), four groups with a thickness of 0.75 mm using Zendura FLX (Multi-layer), CA Pro (Multi-layer), Zendura (Single-layer), and Duran (Single-layer) sheets, and one group with a thickness of 0.50 mm using Duran sheets. Force measurements were conducted using Fuji® pressure-sensitive films. RESULTS The lowest force values, both active and passive, were recorded for the multi-layered sheets: CA Pro (83.1 N, 50.5 N), Zendura FLX (88.9 N, 60.7 N), and Zendura Viva (92.5 N, 68.5 N). Conversely, the highest values were recorded for the single-layered sheets: Duran (131.9 N, 71.8 N) and Zendura (149.7 N, 89.8 N). The highest force was recorded at the middle third of the aligner, followed by the incisal third, and then the cervical third. The net force between the incisal and cervical thirds (FI-FC) showed insignificant difference across different materials. However, when comparing the incisal and middle thirds, the net force (FI-FM) was higher with single-layered materials. Both overall force and net force (FI-FM) were significantly higher with 0.75 mm compared to those with a thickness of 0.50 mm. CONCLUSIONS Multi-layered aligner materials exert lower forces compared to their single-layered counterparts. Additionally, increased thickness in aligners results in enhanced retention and greater force generation. For effective bodily tooth movement, thicker and single-layered rigid materials are preferred. CLINICAL RELEVANCE This research provides valuable insights into the biomechanics of orthodontic aligners, which could have significant clinical implications for orthodontists. Orthodontists might use this information to more effectively tailor aligner treatments, considering the specific tooth movement required for each individual patient. In light of these findings, an exchangeable protocol for aligner treatment is suggested, which however needs to be proven clinically. This protocol proposes alternating between multi-layered and single-layered materials within the same treatment phase. This strategy is suggested to optimize treatment outcomes, particularly when planning for a bodily tooth movement.
Collapse
Affiliation(s)
- Tarek M Elshazly
- Oral Technology, Dental School, University Hospital Bonn, Welschnonnenstr. 17, Bonn, 53111, Germany.
| | - Christoph Bourauel
- Oral Technology, Dental School, University Hospital Bonn, Welschnonnenstr. 17, Bonn, 53111, Germany
| | - Ahmed Ismail
- Oral Technology, Dental School, University Hospital Bonn, Welschnonnenstr. 17, Bonn, 53111, Germany
- Biomaterials Department, Faculty of Dentistry, Ain Shams University, Cairo, Egypt
| | - Omar Ghoraba
- Oral Technology, Dental School, University Hospital Bonn, Welschnonnenstr. 17, Bonn, 53111, Germany
| | - Mostafa Aldesoki
- Oral Technology, Dental School, University Hospital Bonn, Welschnonnenstr. 17, Bonn, 53111, Germany
| | | | - Hanaa Elattar
- Orthodontic Department, Faculty of Dentistry, Suez Canal University, Ismailia, Egypt
| | - Abdulaziz Alhotan
- Department of Dental Health, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia
| | - Yasmine Alkabani
- Oral and Dental Research Institute, National Research Centre, Giza, Egypt
| |
Collapse
|
2
|
Nayak AS, H C KK. A comparative study on tensile strength of various thermoplastic polymers sheets following thermoforming on a pre-treatment and post-treatment maxillary model of a patient: an in vitro study. Clin Oral Investig 2024; 28:240. [PMID: 38570397 DOI: 10.1007/s00784-024-05640-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2023] [Accepted: 03/30/2024] [Indexed: 04/05/2024]
Abstract
OBJECTIVES Thermoplastic polymers show alteration in their mechanical properties after thermoforming on a dental model. The purpose of this in-vitro study was to evaluate the tensile strength of different thermoplastic polymer sheets thermoformed on a pre-treatment (moderate crowding) and post-treatment (well-aligned) maxillary model of a patient. MATERIALS AND METHODS Forty maxillary models (Twenty Pre-treatment & twenty Post-treatment of uniform dimension) were made by duplicating them using alginate Hydrogum 5 (Zhermack). Samples were then divided into eight groups of 5 samples each. The thermoplastic sheets Imprelon® (Scheu-Dent), AVAC R® (Jaypee), Placa Crystal® (BioART), EZ-VAC® (3A Medes)-1.0 mm thick were thermoformed on these models respectively. The sample was retrieved using ceramic bur mounted on a straight hand-piece and subjected for testing using TINIUS Olsen 10ST micro universal testing machine and recorded. RESULTS There was no statistically significant difference (P > .05) in tensile strength of thermoformed thermoplastic polymer sheets between pre-treatment and post-treatment maxillary model. Tensile strength of EZ-VAC (3A Medes) showed higher variation between pre-treatment and post-treatment maxillary model though it was found to be statistically insignificant (P > .05). Significant difference (P < .05) was seen between groups when they were compared separately among pre-treatment and post-treatment models. CONCLUSION Placa Crystal (BioART) among the pre-treatment group, EZ - VAC (3A Medes) among the post-treatment group, showed highest tensile strength. CLINICAL RELEVANCE Results of the study highlights the necessity to test materials in conditions which stands in accordance with the clinical scenario to a considerable extent and also emphasizes the need for further study in aligner.
Collapse
Affiliation(s)
- Ashwath S Nayak
- Department of Orthodontics and Dentofacial Orthopedics, Bapuji Dental College and Hospital, Davangere, Karnataka, India, 577004.
| | - Kiran Kumar H C
- Department of Orthodontics and Dentofacial Orthopedics, Bapuji Dental College and Hospital, Davangere, Karnataka, India, 577004
| |
Collapse
|
3
|
Staderini E, Chiusolo G, Guglielmi F, Papi M, Perini G, Tepedino M, Gallenzi P. Effects of Thermoforming on the Mechanical, Optical, Chemical, and Morphological Properties of PET-G: In Vitro Study. Polymers (Basel) 2024; 16:203. [PMID: 38257002 PMCID: PMC10820839 DOI: 10.3390/polym16020203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2023] [Revised: 12/30/2023] [Accepted: 12/30/2023] [Indexed: 01/24/2024] Open
Abstract
The effectiveness of clear aligners in correcting malocclusions is closely linked to the properties of the materials used to make them. The polymers used in the manufacture of clear aligners have well-established properties. However, the process of manufacturing clear aligners, known as thermoforming, involves thermal and mechanical shocks that may alter these properties. The objective of this study was to evaluate the effects of thermoforming on the mechanical, optical, chemical, and morphological properties of sixty PET-G specimens. The study compared the thickness, weight, absorbance, chemical structure, surface roughness, elastic modulus, yield strength, and breaking load of thirty thermoformed specimens with thirty non-thermoformed specimens. The study introduces a new approach by using standardized samples to analyze both chemical and physical properties. The results showed statistically significant differences in thickness (-15%), weight (-11%), and surface roughness (+1233% in roughness average; +1129% in RMS roughness) of the material. Additionally, a correlation was found between reduction in thickness and increase in opalescence. There was no significant change in the functionality of the aligners after thermoforming, as no significant mechanical changes were found. However, the increase in surface roughness may lead to plaque and fluid accumulation and worsen the fit of the aligners.
Collapse
Affiliation(s)
- Edoardo Staderini
- School of Dentistry, Dean: Prof. Massimo Cordaro, Catholic University of the Sacred Heart, IRCCS “A. Gemelli” University Polyclinic Foundation, Largo Agostino Gemelli 8, 00168 Rome, Italy; (E.S.); (G.C.); (P.G.)
- Postgraduate School of Orthodontics–Director: Prof. Massimo Cordaro, Catholic University of the Sacred Heart, Largo Agostino Gemelli 8, 00168 Rome, Italy
| | - Giuseppe Chiusolo
- School of Dentistry, Dean: Prof. Massimo Cordaro, Catholic University of the Sacred Heart, IRCCS “A. Gemelli” University Polyclinic Foundation, Largo Agostino Gemelli 8, 00168 Rome, Italy; (E.S.); (G.C.); (P.G.)
| | - Federica Guglielmi
- School of Dentistry, Dean: Prof. Massimo Cordaro, Catholic University of the Sacred Heart, IRCCS “A. Gemelli” University Polyclinic Foundation, Largo Agostino Gemelli 8, 00168 Rome, Italy; (E.S.); (G.C.); (P.G.)
- Postgraduate School of Orthodontics–Director: Prof. Massimo Cordaro, Catholic University of the Sacred Heart, Largo Agostino Gemelli 8, 00168 Rome, Italy
| | - Massimiliano Papi
- Department of Neurosciences, Catholic University of the Sacred Heart, Largo Francesco Vito 1, 00168 Rome, Italy; (M.P.); (G.P.)
- IRCCS “A. Gemelli” University Polyclinic Foundation, Largo Agostino Gemelli 8, 00168 Rome, Italy
| | - Giordano Perini
- Department of Neurosciences, Catholic University of the Sacred Heart, Largo Francesco Vito 1, 00168 Rome, Italy; (M.P.); (G.P.)
- IRCCS “A. Gemelli” University Polyclinic Foundation, Largo Agostino Gemelli 8, 00168 Rome, Italy
| | - Michele Tepedino
- Department of Biotechnological and Applied Clinical Sciences, University of L’Aquila, Piazza Santa Margherita 2, 67100 L’Aquila, Italy
| | - Patrizia Gallenzi
- School of Dentistry, Dean: Prof. Massimo Cordaro, Catholic University of the Sacred Heart, IRCCS “A. Gemelli” University Polyclinic Foundation, Largo Agostino Gemelli 8, 00168 Rome, Italy; (E.S.); (G.C.); (P.G.)
- Postgraduate School of Orthodontics–Director: Prof. Massimo Cordaro, Catholic University of the Sacred Heart, Largo Agostino Gemelli 8, 00168 Rome, Italy
| |
Collapse
|
4
|
Chen SM, Ho CT, Huang TH, Kao CT. An in vitro evaluation of aligner force decay in artificial saliva. J Dent Sci 2023; 18:1347-1353. [PMID: 37404637 PMCID: PMC10316483 DOI: 10.1016/j.jds.2023.04.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Revised: 04/18/2023] [Indexed: 07/06/2023] Open
Abstract
Background/purpose The present study aimed to compare the force decay of invisible aligners for maxillary anterior teeth with 0.1 mm (D1), 0.2 mm (D2), and 0.3 mm (D3) labial movement within a simulated oral environment over 7 days. Materials and methods The prepared invisible aligners were immersed in saliva (S) and subjected to applied force (F) for 7 days. The aligners were set and placed on the maxillary right central incisor with 0.1 mm (D1), 0.2 mm (D2), and 0.3 mm (D3) labial movement. Thin-film pressure sensors were used to measure the aligner force changes. The data were collected and analyzed by statistical methods. Results Significant differences were observed in the initial and first-day force between the D2 and D3 groups under simulated oral environment force (SF) (P < 0.05). There was a significant difference in force decay between Day 1 and Day 7 for all groups (P < 0.05). The SFD1 group showed a significant decrease in force on Day 5 (P < 0.05), while the SFD2 and SFD3 groups showed significant force decay on Day 4 (P < 0.05). The force decay ratio on Day 7 was higher in the SFD3 group than in the SFD1 and SFD2 groups, but no significant difference was observed. Conclusion Larger labial movement of the aligners resulted in higher force decay under artificial saliva environments, and the force decay of invisible aligners was increased by immersion time in artificial saliva.
Collapse
Affiliation(s)
- Shou-Min Chen
- School of Dentistry, College of Oral Medicine, Chung Shan Medical University, Taichung, Taiwan
- Orthodontic Department, Chung Shan Medical University Hospital, Taichung, Taiwan
| | - Chun-Te Ho
- School of Dentistry, College of Oral Medicine, Chung Shan Medical University, Taichung, Taiwan
- Orthodontic Department, Chung Shan Medical University Hospital, Taichung, Taiwan
| | - Tsui-Hsein Huang
- School of Dentistry, College of Oral Medicine, Chung Shan Medical University, Taichung, Taiwan
- Dental Department, Chung Shan Medical University Hospital, Taichung, Taiwan
| | - Chia-Tze Kao
- Orthodontic Department, Chung Shan Medical University Hospital, Taichung, Taiwan
- Dental Department, Chung Shan Medical University Hospital, Taichung, Taiwan
| |
Collapse
|
5
|
Elshazly TM, Salvatori D, Elattar H, Bourauel C, Keilig L. Effect of trimming line design and edge extension of orthodontic aligners on force transmission: A 3D finite element study. J Mech Behav Biomed Mater 2023; 140:105741. [PMID: 36857974 DOI: 10.1016/j.jmbbm.2023.105741] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Revised: 02/20/2023] [Accepted: 02/21/2023] [Indexed: 02/27/2023]
Abstract
OBJECTIVES To investigate in a numerical study the effect of the geometry and the extension of orthodontic aligner edges and the aligner thickness on force transmission to upper right central incisor tooth (Tooth 11). METHODS A three-dimensional (3D) digital model, obtained from a 3D data set of a complete dentulous maxilla, was imported into 3-matic software. Aligners with four different trimming line designs (scalloped, straight, scalloped extended, straight extended) were designed, each with four different thicknesses (0.3, 0.4, 0.5, and 0.6 mm). The models were exported to a finite element (FE) software (Marc/Mentat). A facial 0.2 mm bodily malposition of tooth 11 was simulated. RESULTS The maximum resultant force was in the range of (7.5 - 55.2) N. The straight trimming designs had higher resultant force than the scalloped designs. The resultant force increases with increasing the edge extension of the aligner. The normal contact forces were unevenly distributed over the entire surface and were concentrated in six areas: Incisal, Mesio-Incisal, Disto-Incisal, Middle, Mesio-Cervical, and Disto-Cervical. The resultant force increases super linearly with increasing thickness. CONCLUSIONS The design of the trimming line, the edge extension, and the thickness of the aligner affect significantly the magnitude of the resultant force and the distribution of normal contact force. The straight extended trimming design exhibited better force distribution that may favor a bodily tooth movement. CLINICAL RELEVANCE A straight extended trimming design of an orthodontic aligner may improve the clinical outcomes. In addition, the manufacturing procedures of the straight design are much simpler compared to the scalloped design.
Collapse
Affiliation(s)
- Tarek M Elshazly
- Oral Technology, Dental School, University Hospital Bonn, Bonn, Germany.
| | | | - Hanaa Elattar
- Orthodontic Department, Faculty of Dentistry, Umm Al-Qura University, Makkah, Saudi Arabia; Orthodontic Department, Faculty of Dentistry, Suez Canal University, Ismailia, Egypt
| | | | - Ludger Keilig
- Oral Technology, Dental School, University Hospital Bonn, Bonn, Germany; Department of Dental Prosthetics, Propaedeutics and Materials Science, Dental School, University Hospital Bonn, Bonn, Germany
| |
Collapse
|
6
|
Elshazly TM, Bourauel C, Aldesoki M, Ghoneima A, Abuzayda M, Talaat W, Talaat S, Keilig L. Computer-aided finite element model for biomechanical analysis of orthodontic aligners. Clin Oral Investig 2023; 27:115-124. [PMID: 35989373 DOI: 10.1007/s00784-022-04692-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Accepted: 08/15/2022] [Indexed: 02/01/2023]
Abstract
OBJECTIVES To design a finite element (FE) model that might facilitate understanding of the complex mechanical behavior of orthodontic aligners. The designed model was validated by comparing the generated forces - during 0.2-mm facio-lingual translation of upper left central incisor (Tooth 21) - with the values reported by experimental studies in literature. MATERIALS AND METHODS A 3D digital model, obtained from scanning of a typodont of upper jaw, was imported into 3-matic software for designing of aligners with different thicknesses: 0.4, 0.5, 0.6, 0.7 mm. The model was exported to Marc/Mentat FE software. Suitable parameters for FE simulation were selected after a series of sensitivity analyses. Different element classes of the model and different rigidity values of the aligner were also investigated. RESULTS The resultant maximum forces generated on facio-lingual translation of Tooth 21 were within the range of 1.3-18.3 N. The force was direction-dependent, where lingual translation transmitted higher forces than facial translation. The force increases with increasing the thickness of the aligner, but not linearly. We found that the generated forces were almost directly proportional to the rigidity of the aligner. The contact normal stress map showed an uneven but almost repeatable distribution of stresses all over the facial surface and concentration of stresses at specific points. CONCLUSIONS A validated FE model could reveal a lot about mechanical behavior of orthodontic aligners. CLINICAL RELEVANCE Understanding the force systems of clear aligner by means of FE will facilitate better treatment planning and getting optimal outcomes.
Collapse
Affiliation(s)
- Tarek M Elshazly
- Oral Technology Department, Dental School, University Hospital Bonn, Welschnonnenstr. 17, 53111, Bonn, Germany.
| | - Christoph Bourauel
- Oral Technology Department, Dental School, University Hospital Bonn, Welschnonnenstr. 17, 53111, Bonn, Germany
| | - Mostafa Aldesoki
- Oral Technology Department, Dental School, University Hospital Bonn, Welschnonnenstr. 17, 53111, Bonn, Germany
| | - Ahmed Ghoneima
- Department of Orthodontics, College of Dental Medicine, MBRU, Dubai, United Arab Emirates
| | - Moosa Abuzayda
- Department of Prosthodontics, College of Dental Medicine, MBRU, Dubai, United Arab Emirates
| | - Wael Talaat
- Department of Oral and Craniofacial Health Sciences, College of Dental Medicine, University of Sharjah, Sharjah, United Arab Emirates.,Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Suez Canal University, Ismailia, Egypt
| | - Sameh Talaat
- Oral Technology Department, Dental School, University Hospital Bonn, Welschnonnenstr. 17, 53111, Bonn, Germany.,Department of Orthodontics, Future University in Egypt, Cairo, Egypt
| | - Ludger Keilig
- Oral Technology Department, Dental School, University Hospital Bonn, Welschnonnenstr. 17, 53111, Bonn, Germany.,Department of Dental Prosthetics, Propaedeutics and Materials Science, Dental School, University Hospital Bonn, Bonn, Germany
| |
Collapse
|
7
|
Lee S, Lee C, Bosio JA, Melo MAS. Smart Flexible 3D Sensor for Monitoring Orthodontics Forces: Prototype Design and Proof of Principle Experiment. Bioengineering (Basel) 2022; 9:570. [PMID: 36290538 PMCID: PMC9598351 DOI: 10.3390/bioengineering9100570] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 10/09/2022] [Accepted: 10/13/2022] [Indexed: 11/16/2022] Open
Abstract
There is a critical need for an accurate device for orthodontists to know the magnitude of forces exerted on the tooth by the orthodontic brackets. Here, we propose a new orthodontic force measurement principle to detect the deformation of the elastic semi-sphere sensor. Specifically, we aimed to detail technical issues and the feasibility of the sensor performance attached to the inner surface of the orthodontic aligner or on the tooth surface. Accurate force tracking is important for the optimal decision of aligner replacement and cost reduction. A finite element (FE) model of the semi-sphere sensor was developed, and the relationship between the force and the contact area change was investigated. The prototype was manufactured, and the force detection performance was experimentally verified. In the experiment, the semi-sphere sensor was manufactured using thermoplastic polymer, and a high-precision mold sized 3 mm in diameter. The change in the contact area in the semi-sphere sensor was captured using a portable microscope. Further development is justified, and future implementation of the proposed sensor would be an array of multiple semi-sphere sensors in different locations for directional orthodontic force detection.
Collapse
Affiliation(s)
- Soobum Lee
- Department of Mechanical Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
| | - Chabum Lee
- J. Mike Walker’ 66 Department of Mechanical Engineering, Texas A&M University, 3123 TAMU, College Station, TX 77843, USA
| | - Jose A. Bosio
- Division of Orthodontics, Department of Orthodontics & Pediatric Dentistry, University of Maryland School of Dentistry, Baltimore, MD 21201, USA
| | - Mary Anne S. Melo
- Division of Operative Dentistry, Department of General Dentistry, University of Maryland School of Dentistry, Baltimore, MD 21201, USA
| |
Collapse
|
8
|
Elshazly TM, Keilig L, Salvatori D, Chavanne P, Aldesoki M, Bourauel C. Effect of Trimming Line Design and Edge Extension of Orthodontic Aligners on Force Transmission: An in vitro Study. J Dent 2022; 125:104276. [PMID: 36055460 DOI: 10.1016/j.jdent.2022.104276] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 08/26/2022] [Accepted: 08/29/2022] [Indexed: 11/29/2022] Open
Abstract
OBJECTIVES To investigate how the stress distribution and forces transmitted from orthodontic aligners to the tooth surface are affected by the geometry and extension of the trimming line. MATERIALS AND METHODS Thirty-six aligners were thermoformed from Zendura FLX sheets (0.75 mm thick) and divided into four groups based on the design of the trimming line: Scalloped, Scalloped extended, Straight and Straight extended. Fuji pressure-sensitive films were used for pressure measurement. The pressurized films were scanned and evaluated. Pressures and forces were measured over the entire facial surface of an upper right central incisor (Tooth 11) and at 7 different locations [cervical, middle, incisal, mesio-incisal, mesio-cervical, disto-cervical, and disto-cervical]. In addition, the thickness of the aligners at these 7 sites was measured with a digital caliper. RESULTS The active force ranged from (2.2 - 6.9) N, and the average pressure was (1.6 - 2.7) MPa. The highest values were recorded for the (straight extended) design, while the lowest values were recorded for the scalloped design. The forces and stresses were not uniformly distributed over the surface. When the values in each area were compared separately, significant differences were found between the different designs in the cervical area, with the scalloped design transmitting the lowest cervical forces. Aligner thickness was drastically reduced (60-75% thinning) over the entire tooth surface after thermoforming. CONCLUSIONS The straight extended design of aligner's trimming line exhibited more uniform force transfer and stress distribution across the surface than the other designs. CLINICAL RELEVANCE The trimming line design could have a significant impact on the clinical outcome of orthodontic aligner treatment.
Collapse
Affiliation(s)
- Tarek M Elshazly
- Oral Technology, Dental School, University Hospital Bonn, Bonn, Germany.
| | - Ludger Keilig
- Oral Technology, Dental School, University Hospital Bonn, Bonn, Germany; Department of Dental Prosthetics, Propaedeutics and Materials Science, Dental School, University Hospital Bonn, Bonn, Germany
| | | | | | - Mostafa Aldesoki
- Oral Technology, Dental School, University Hospital Bonn, Bonn, Germany
| | | |
Collapse
|