FDI World Oral Health Forum:Are you ready for amalgam phase-down?

How the Minamata Convention impacts your Dental Practice.

New materials for a post-Minamata era

September 9, 2016

Jirun Sun, MS, PhDVolpe Research Center

American Dental Association Foundationjsun@nist.gov

Dental restorative materials other than amalgam

• Glass ionomer cements (GIC)• Resin composites• Hybrid of GIC and Resin composite

• Resin modified GIC• Poly acid modified resin composite (compomer)

StrongerWeaker GICResin modified GIC

CompomerResin composite

Advantages and limitations of existing dental composites

• Advantages• Aesthetics: can match the tooth color• Strong bonding to tooth • No mercury• Versatile for large and small restorations• Anterior and posterior restorations

• Compared to Amalgam: short service life (~8 years)• Suboptimal clinical placement• Secondary caries

Break down of materials by bacteria and enzymesMicroleakage

• Stress-induced micro-fractures

Inventor Dr. Bowen in dental practice

Longer-lasting dental materialsare needed!

Resin composites

Resins: continuous phase

Tooth/Restoration interface

Com

posi

te

Toot

h

Adh

esiv

eFillers: for better mechanical performance

Coupling agents: bond resin and fillers togetherRestoration

Dental Materials Innovation Workshop (London, Dec 2012, Adv Dent Res 2013)

5

Desired properties for new dental composites• Resist degradation• Stronger materials for posterior restoration• Clinically applicable• Self-healing• Antimicrobial

http://estheticdentist.in/Treatments/posterior-restorations/

Novel

Traditional

O OO OOHOH

OO

OO

OO

O

O

OO

OO

HOO

OOHO OHO OH

OHOH

OH

O

BisHPPP TEG

Methacrylic Acid(MA)

BisGMA TEGDMA

TEG-DVBE

No Hydrolysis Product

6

Fundamental change in chemistry improved performance: structure determines performance

acid, base, or esterase

New resin systems

An esterase is a hydrolase enzyme that splits esters into an alcohol in a chemical reaction with water called hydrolysis.

Resistance to enzymatic and hydrolytic challenges

Two major esteraseenzymes in human saliva:Cholesterol Esterase (CE) Pseudocholine Esterase (PCE)

Gonzalez-Bonet Biomacromolecules 2015Finer JDR 2004, Biomaterials 2004; Delaviz Dent Mat 2014.

New materials resist enzymatic challenges

• Traditional monomers degrade at different rates• Our novel monomer resists degradation

0

25

50

75

100

125

150

Enzyme 2Enzyme 1

Rel

ativ

e de

grad

atio

n (%

)

Traditional-Bis-GMA Traditional-TEGDMA Novel monomer

in Saline

Gonzalez-Bonet Biomacromolecules 2015Finer JDR 2004, Biomaterials 2004; Delaviz Dent Mat 2014.

Resins after incubation with enzyme• Traditional resin:

~2% mass loss; ~15% hardness drop in 16 days

• Novel resin: No mass loss; no hardness change

Scientific recognition of our work

Gonzalez-Bonet Biomacromolecules 2015.

Other new resins and new concepts

• The click chemistry was introduced into dentistry to provide smart, reconfigurable and responsive network (Xi Advanced Functional Materials 2014)

• Thiol-ene (Bowman Dental Materials 2015) dental composites• Adding thio-urethane oligomers improved the performance of

resin composites (Bacchi JDR 2014) • And many more…

Clinically practical photo-copolymerization

• Using handheld curing devices• Fully cured in seconds• Well defined polymer composition• Extremely high monomer conversion• Expect significantly reduced leachables (no toxicity)

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Stronger and tougher composites

Composition

elastic modulus (Gpa)

flexural strength (Mpa)

fracture toughness (MPa·m1/2)

BisGMA/TEGDMA 70/30 9.4/10.1 97/11.4 1.19/0.05New composite 1 9.4/0.6 123/14 1.52/0.04

• Similar or better mechanical performance than amalgam• Strong and easy to handle for anterior and posterior

restoration

Self-healing dental composites (SHDC)

• To significantly extend the life span of the restorations by autonomic self-healing of micro-cracks

• Two new components added:- Silica-based healing powder (HP)- Polyacid healing liquid (HL) in

microcapsules• HP + HL glass ionomer cements• Autonomous healing procedure:

- Cracking (A)- Releasing of HL (B)- Healing (C)

20 µm 20 µm

Initial Healed

2) New material formed by reaction HP + HL

Energy dispersive X-ray spectroscopy (EDS)

Confirmation of healing reaction1) Morphology changed after healing

Huyang JMAD 2016

Scanning Electron Microscopy (SEM)

Initial Healed

0 4 8

0

4

8

Dis

plac

emen

t [m

]

Force [N]

With healing liquid No healing liquid

Increased Healing

SHDC heals autonomously

Dynamic mechanical analysis

Fatigue study: Fatigue life time was extended 5 times.

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Advantage of SHDC

• To autonomously repair micro-cracks • It may increase fatigue life more than 5 times• Using materials clinically tested• To deliver drugs• Prevent caries through F release

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Prevent secondary caries- antibacterial dental composites

Dental composites

Tooth/Restoration interface

Com

posi

te

Toot

h

Adh

esiv

e

Resins

Filler

Coupling agentsRestoration

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Antibacterial dental composites-examplesAdhesives: • Kill bacteria without diminishing bonding strength (Hirose JDR 2016)Resins: • Rechargeable antibacterial polymers (Sun Acta Biomat 2012)• Quaternary ammonium polymers (Antonucci Dent Mat 2012) Fillers: • Strong composites with antibacterial properties (Imazato Biomaterials

2003)Coupling agents: • pH sensitive antibacterial compounds (Sun in development)

New technologies to improve dental materialsNanotechnology,• In-situ formation of antibacterial nanoparticles showed very

promising results (Fan Dental Materials 2011) • Biosensor in oral cavities for disease diagnosis and screening

3D printing Precision medicine

Challenges in developing new dental materials• New materials new challenges

• Unknown limitation of new materials• Unknown toxicity to human beings in the long term• Lack of standard evaluation methods• Make the new materials affordable

• Adapting existing tools and guidance for dental practice• Make materials that can avoid suboptimal clinical placement

Thanks and questions