2.  What are Orthodontic Forces ? Orthodontic forces are usually small forces used to move crowded or un- erupted teeth into place

3. Bone resorption in direction of force & bone apposition on the other side Force transmit to Bone & PDL Orthodontic forces on teeth crowns

4.  What is periodontal ligament (PDL) ?  It is a soft ligamentous tissue enclosed between 2 hard tissues (alveolar bone and tooth cementum). PDL acts as a shock absorbent in response to orthodontic forces.  What is periodontal ligament (PDL) ?  It is a soft ligamentous tissue enclosed between 2 hard tissues (alveolar bone and tooth cementum). PDL acts as a shock absorbent in response to orthodontic forces. Periodontal ligament

5.  The molecular mechanism that underlies this phenomenon(bone resorption and formation) is not fully understood.  Current in vitro models fall short of simulating the tooth attachment apparatus (periodontium) with both of its components : hard tissue (bone) and soft tissue (PDL).  Hence there is a demand for a multilayered tissue engineered model to simulate tooth periodontium under orthodontic forces  The molecular mechanism that underlies this phenomenon(bone resorption and formation) is not fully understood.  Current in vitro models fall short of simulating the tooth attachment apparatus (periodontium) with both of its components : hard tissue (bone) and soft tissue (PDL).  Hence there is a demand for a multilayered tissue engineered model to simulate tooth periodontium under orthodontic forces

6.  Characterizing 2 scaffolds to be used in our proposed multilayered model :one representing the hard tissue component of periodontium : Sol-Gel scaffolds.  In addition a membrane representing the soft tissue component of periodontium : Geistlich Bio-Gide®  Biological Characterization : investigating the following: cells’ viability, adhesion, proliferation, and matrix formation (Confocal and SEM imaging).  Mechanical Characterization : properties were evaluated before and after cell seeding.  Characterizing 2 scaffolds to be used in our proposed multilayered model :one representing the hard tissue component of periodontium : Sol-Gel scaffolds.  In addition a membrane representing the soft tissue component of periodontium : Geistlich Bio-Gide®  Biological Characterization : investigating the following: cells’ viability, adhesion, proliferation, and matrix formation (Confocal and SEM imaging).  Mechanical Characterization : properties were evaluated before and after cell seeding.

7.  Biologically :  scaffolds tested in this study were all biocompatible with human periodontal ligament cells individually and in combined culture  Gene expression studies qRT PCR:  Gen expression for the BGC and SGC were different in most of the genes studied  Gene expression profile was in accordance with the previous literature which is an indication of a suitable model for studying OTM  Biologically :  scaffolds tested in this study were all biocompatible with human periodontal ligament cells individually and in combined culture  Gene expression studies qRT PCR:  Gen expression for the BGC and SGC were different in most of the genes studied  Gene expression profile was in accordance with the previous literature which is an indication of a suitable model for studying OTM

8. SolGel Scaffold Live/Dead imaging Sol-Gel Scaffold SEM

9. Bio-Gide Live/Dead imaging Bio-Gide membrane SEM

10. Bio-Gide membrane Sol-Gel Scaffold

11. SEM image SEM showing cells grown at the interface Bio-Gide Sol-Gel

13.  SolGel was considered to be suitable in representative for the hard tissue component.  Bio-Gide® membrane was considered more suitable to represent the soft tissue component.  A bi-layered construct with the above materials can be considered a suitable model for studying OTM  SolGel was considered to be suitable in representative for the hard tissue component.  Bio-Gide® membrane was considered more suitable to represent the soft tissue component.  A bi-layered construct with the above materials can be considered a suitable model for studying OTM

14.  In-Vivo implantation of the bi-layered construct in mice  Cell-cell interaction studies

15.  El-Gendy R, Raif E Leeds Uni UK  Goudouri OM, Boccaccini A, Erlangen Uni Germany  Refaat W, Ramadan A, SCU Egypt