1. School of Clinical Dentistry, University of Sheffield, UK
A New Photoelastic Dental Model for 3D Photoelasticity Abdurraouf Ziglam, Antony Johnson, Duncan Wood, David Patrick and Rachel Tomlinson Department of Adult Dental Care, School of Clinical Dentistry, University of Sheffield, UK.
INTRODUCTION
Photoelasticity is one of the most important experimental stress analysis techniques, that utilises polarized light to obtain the stress state in a loaded transparent model. It is the only whole-field technique which can study the interior of a 3D model. Recently, it is use has once again become more wide spread due to the development of digital methods of fringe analysis and the development of stereolithography in model production. It was first introduced into Dentistry by Noonan in 1949, since that time it has been extensively used in different dental fields and nowadays specially in Implantology. Resin Model making is a fundamental step for accuracy of the technique. Since not all factors related to the oral cavity can be reproduced, similarity in mechanical properties between the model and the real object is mandatory. Modulus of elasticity is of upmost important in material selection.
AIM and OBJECTIVES
Figure 3: Tg and E of Araldite 2020
The aim of this study is to fabricate dental model using two photoelastic resins with different properties. One for the abutment teeth, while the other one for the rest of the model, and have modulus of elasticity of the same ratio as that of tooth to bone in order to carry out photoelastic experiments. Moreover, most of the studies highlighted the use of integrated 3D photoelasticity at room temperature where little can be concluded regarding the state of stress at any point. This study aims to use stress freezing technique to allow accurate analysis of interior stresses at specific points.
1. Determine the Glass transition temperature(Tg) and Modulus of elasticity(E) at Tg of suitable polymeric materials.
2. Produce a resin model composed of two materials that has mechanical properties mimic those of tooth and bone.
properties
PL2
PL1
PMMA
Araldite 2020
Tg°C 40
62.6
73.9
60.2
(E)atTg
0.167
0.214
0.624
0.043
(E)atTg PL2 (40)
2.422
2.498
1.472
(E)atTgPL1 (62) -
1.458
0.027
(E)atAraldite 2020 (60.2)
0.597
1.613
MATERIALS & METHOD
Figure 4: E (Gpa) of materials VS temperature
1. Four materials 3 Epoxy resins PL1,PL2,(Vishay precision group, USA) and Araldite 2020 (Huntsman advanced materials, Swiss) and PMMA ( Candulor AG, Germany)
2. Dynamic Mechanical Analyser (Perkin Elmer DMA 8000) was used to measure the temperature dependant elastic moduli of the materials selected.
3. The test was conducted with 3 point bending mode. The support span was 30mm, a temperature scanning from low to high was performed with a heating rate of 2°C/min at an oscillation frequency of 0.05mm (Figure 1).
School of Clinical Dentistry, University of Sheffield, UK
Figure 5: The fabricated models.
Figure 1: The sample in DMA machine.
DISCUSSION and CONCLUSIONS
RESULTS
Modulus of elasticity (E):
E tooth material = E tooth
E bone material at Tg E bone
E tooth material = E tooth X Bone material at Tg
E bone
= 18 X = Gpa
1.3
Finding from this experiment showed that:
1/ Araldite 2020 to be used as bone material, and the material to simulate tooth should has (E) at Tg of Araldite 2020
2/ PL1 has (E ) of 0.595GPa at Tg of Araldite 2020
This study concluded that PL1/Araldite ratio could mimic the tooth/bone modulus of elasticity ratio. Therefore this combination will be used as a dental model to evaluate the load distribution of the dental prosthesis.
Figure 2: Tg and E of PL1,PL2, and PMMA.