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A Novel Layer-by-Layer Biomimetic Structure

Structural Design, Mechanical Properties, and Failure Mechanism

Adelina TJOKRONEGORO

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Background

• Oral health is a window to general health show health signs and infections

• Oral problems can affect the overall health

• Cavities is the most prevalent oral problem affecting both adult and child

• Filling is a way to restore back a tooth damage to its normal function and shape

• By closing off the spaces, enter of bacteria and further decay can be prevented

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Background• Common dental fillings used:

Porcelain fillings: http://www.webmd.com/oral-health/guide/dental-health-fillings#1

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Background• Metals:

- Tooth pain and sensitivity contact between metal of adjacent tooth

- Expensive- Immunoreactive mercury in amalgram may

induce allergies• Deteriorating fillings

- Composite fillings are cheap and safe, but have low mechanical properties

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Aim• To design new structure that aim to improve

mechanical properties and decrease failure rate of dental filling composites

• To compare the mechanical properties values of different structural design and determine the significance of structural design differences

• Provide alternative dental fillings with better structure and mechanical properties for commercial application

• Substitute the current dental fillings that are commonly used in the market

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Methodology

Materials Fabrication Testing

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Materials: Matrix

Function Quantity MassBisGMA Monomer Weight ratio:

1:1~ 20 gram

TEGDMA Monomer (Dilute)

~ 20 gram

Camphoquinone (CQ)

Photoinitiator 2 mole% ~ 0.4 gram

2-(dimethylamino)ethyl methacrylate (DMAEMA)

Coinitiator 2mole% ~ 0.4 gram

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Fabrication Process

Matrix

Composite

Sample Fabrication

- BisGMA- TEGDMA- Camphoquinone (CQ)- 2-(dimethylamino)ethyl methacrylate (DMAEMA)

Adding Zirconia (ZrO2) filler particles- 10.7vol%- 21.4vol%

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Fabrication Process: Matrix

Vacuum Twister ProcessThe final mixture is put in the vacuum for 1 hour and ready to be

used

Triple Roller MillsMatrix mixture is even out to have uniform particles distribution within the mixture

Matrix MixtureBisGMA is diluted with TEGDMA and photoinitiator CQ, coinitiator DMAEMA are added based on weight calculation

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Zirconia (ZrO2) Filler Particles

• High purity (~99%)• Have favorable influence on mechanical properties of

materials• Transformation toughening property: tetragonal form

into monoclinic symmetry stable and high toughness

Citation:Zych, L. (2009, September 27). The effect of nanometric zirconia particle additives on microstructure and mechanical properties of dense alumina. Processing and Application of Ceramics, 131- 135. Retrieved October 27, 2016, from http://www.tf.uns.ac.rs/publikacije/PAC/pdf/PAC 05 04.pdf

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Zirconia (ZrO2) Filler Particles

• Comparable mechanical properties to metals• Similar color to tooth color• Biocompatible inert material, no oncogenic or mutagenic

effects• Small radioactivity • Optical characteristics natural-looking teeth

Citation:Ali, S. A., Karthigeyan, S., Deivanai, M., & Mani, R. (2014, March). ZIRCONIA: PROPERTIES AND APPLICATION — A REVIEW. Pakistan Oral & Dental Journal, 34, 1st ser., 178-183. Retrieved October 28, 2016, from http://www.podj.com.pk/March_2014/PODJ-40.pdf Bavbek, A. B., Özcan, M., & Eskitascioglu, G. (2014, December 6). Radioactive potential of zirconium-dioxide used for dental applications. Journal of Applied Biomaterials and Functional Materials, 12(1), 35-40. Retrieved November 1, 2016.

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Zirconia Alumina Silica

Mechanical Stability ++ ++ +

High Surface Area ++ ++ ++

Control of Average Pore Diameter ++ ++ +Control of Average Particle Diameter ++ ++ ++

Chemically Flexible + ++ +

Energetically Homogeneous - - +

Swelling ++ ++ -Chemical Stability (to acid and base) ++ - ++

Thermal Stability ++ + -

++ = Very good; + = good performance; - = fair performance

In general, zirconia has a similar performance with alumina and silica. The significant advantage of zirconia over either silica or alumina is its chemical and thermal stability.Unlike alumina, Zirconia is completely stable over the entire pH range, which is an important aspect for dental application and unlike silica, zirconia is stable at elevated temperatures and does not shrink or swell as an organic content.

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Fabrication Process: 10.7vol%

Layer-by-layer assembling

Repeating the same structural design up to 10 layers

SolidificationUV exposure to fix each layer structure

Create structural designUsing cover glass as reference of height (~2mm) and

transparency as the support the structure

TransparencyCover Glass

Microscope Slide

~2mm

~2mm~30mm

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Fabrication Process: Stepped (0 & 21.4vol%)

Layer-by-layer assemblingCreate second layer with 21.4vol% and repeat the same

steps to create 10 layers of stepped design

SolidificationUV exposure to fix each layer structure

Create structural designUsing cover glass as reference of height (~2mm) and transparency as the support the pure resin structure

Pure Resin (0vol%)

21vol%

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Testing: Three-Point Flexural Test• For polymers, wood and composites, brittle materials• Obtain failure from tension and compression stress

and avoid shear stress• Full control of span and depth ratio• Ease of specimen preparation and testing procedure

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Three-Point Flexural Test

• Measures bending force (F) and bending displacement (D) simultaneously

• Helps in determining modulus of elasticity (Ef), flexural stress (), flexural strain ()

• Above neutral axis will experience compression, below neutral axis will experience tension

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Three-Point Flexural Test

Calculation:• Flexural strength: = • Flexural strain: = • Modulus of elasticity: Ef =

F = load at a given point on the load deflection curve (N)L = Support span (mm)b = Width of test beam (mm)d = Height of tested beam (mm)D = maximum deflection of the center of the beam (mm)m = Slope of the initial straight-line portion of the load deflection

Notes:The modulus of elasticity tension is equal to modulus of elasticity compression when the beam material is isotropic and homogeneoushttp://www.dtic.mil/dtic/tr/fulltext/u2/a113937.pdf

Testing Result: 10.7vol%

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949698

100102104106

Mean: 97.89

Mean: 103.80

ADELINA JI

Flex

ure

Stre

ngth

(MPa

)

STD: 17.65

STD: 6.11

0.0440.0450.0460.0470.0480.049

0.050.0510.052

Mean: 0.047

Mean: 0.051

ADELINA JI

Flex

ure

Stra

in STD: 0.010

STD: 0.006

2.85

2.9

2.95

3

3.05

3.1

Mean: 2.95

Mean: 3.085

ADELINA JI

Mod

ulus

(GPa

) STD: 0.36

STD: 0.31

1.941.961.98

22.022.042.062.08

2.12.12

Mean: 2.007

Mean: 2.106

WIDTH HEIGHT

Sam

ple

Size

(mm

)STD: 0.113

STD: 0.366

Testing Result: Stepped (0 & 21.4vol%)

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2.85

2.9

2.95

3

3.05

3.1

3.15

3.2

3.25

Mean: 2.97

Mean: 3.18

ADELINA JI

Mod

ulus

(GPa

) STD: 0.41 STD: 0.35

84.4

84.6

84.8

85

85.2

85.4

85.6

85.8

86

86.2

Mean: 85.97

Mean: 84.96

ADELINA JI

Flex

ure

Stre

ngth

(MPa

)

STD: 12.66 STD: 13.47

0.028

0.029

0.03

0.031

0.032

0.033

0.034

0.035

Mean: 0.03

Mean: 0.034

ADELINA JI

Flex

ure

Stra

in

STD: 0.0048 STD: 0.0098

0

0.5

1

1.5

2

2.5

3

3.5 Mean: 2.065 Mean: 2.97

WIDTH HEIGHT

Sam

ple

Size

(mm

) STD: 0.042 STD: 0.19

Discussion• Based on the overall 3-point bending test results, 10.7vol% has

higher flexure strength and strain in comparison to stepped composite– Fracture characteristics of 2 dissimilar materials can be

significantly influenced by interaction between the concentrated strain at the crack tip possibly has negative interaction which results in weakening the structure

Citation:Landes, J. D. (1988). Nonlinear Fracture Mechanics: Elastic-Plastic Fracture. ASTM International.

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Conclusion• Fabrication, measurement, and testing method might

influence the final results, however the overall estimation is acceptable and lead to conclusion that:– Singular 10.7vol% has better mechanical properties

comparing to stepped 0 & 21.4vol%– Singular 10.7vol% can be said to have more desirable

structure comparing to stepped 0 & 21.4vol%

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Reference• J. Nawrocki, M.P. Rigney, A. McCormick, and P.W. Carr, Review,

"Chemistry of Zirconia and Its Use in Chromatography," J. Chromatogr. A 657, 229-82 (1993)

• Vizcarra, C. (n.d.). Biocompatible Dental Material. Retrieved October 26, 2016, from http://www.biodentistrydrvizcarra.com/?

s=8&sub=1