Interest of rheological studies on dental resin composites

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Interest of rheological studies on dental resin
composites

• Sébastien BEUN
• April 2005

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PLAN

• Introduction - Context
• Results
• Perspectives

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INTRODUCTION

• Over years dental amalgams
• Nowadays resin composites

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COMPOSITION

• ORGANIC FRACTION
• Methacrylated monomers (Bis-GMA, TEGDMA, UDMA)
• Photoinitiators, inhibitors, stabilisers,
  pigments

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• INORGANIC FRACTION
• Silanated filler particles
• Quartz, barium, strontium, zirconium oxides,
  SILICON DIOXIDE (Aerosil)

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CLASSIFICATIONS

• Numerous
• Based on the inorganic fraction (filler type,
  filler load or size distribution)
• Based on handling properties (depending on the
  viscosity)
• Pits and fissures sealants
• Flowable
• Universal
• Packable

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CLINICAL HANDLING

• Restoration of a right-lower premolar

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• Isolation of the tooth
• Elimination of the old material
• Elimination of the carious lesion

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• Placement of pulpal protection

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• Positionning of the matrix
• Etching

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• Thorough rinsing
• Drying

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• Application of an adhesive resin
• Photopolymerization

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• Application of the first layer of composite

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• Application of the following layers

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• Control of occlusal contacts
• Polishing

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COMPOSITES RHEOLOGY

• What do we want?
• No flow without stress
• Easy flow of the material under low stresses
• High viscosity fluid but shear-thinning
• Yield stress fluid
• Thixotropic fluid

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Admira Flow

• Frequency sweep 100 0.01 rad/s 23C

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Admira Flow

• Yield stress determination

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Admira Flow
Thixotropy
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PURPOSE OF THE WORK

• To understand and to control the rheological
  behaviour of dental resin composites
• To make models by varying their different
  components
• To modify their rheological behaviour using
  special additives (nanofillers, new monomers)

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ORGANIC FRACTION

• Composition
• Bis-GMA, TEGDMA, UDMA, Bis-EMA
• Photoinitiators, inhibitors, stabilisers,
  pigments
• Materials methods
• Bis-GMA/TEGDMA mixtures
• Measurement of the rheological behaviour
  depending to the Bis-GMA/TEGDMA ratio
• Measurement of Tg of each mixture

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Bis-GMA

• Viscosity (25C) 628 Pa.s

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TEGDMA

• Viscosity (25C) 0.008 Pa.s

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Bis-GMA / TEGDMA
70/30
60/40
Viscosity 1,77 Pa.s
Viscosity O,51 Pa.s
50/50
Viscosity 0,20 Pa.s
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Bis-GMA / TEGDMA
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Bis-GMA / TEGDMA Tg
TEGDMA
Bis-GMA
Tg -4,19C
Tg -84,32C
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70/30
Tg -46,61C
80/20
Tg -31,79C
60/40
Tg -56,38C
50/50
Tg -62,79C
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Bis-GMA / TEGDMA Tg
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Composition / Tg
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Organic fraction

• The organic fraction of dental resin composites
  has a strictly Newtonian behaviour
• Bis-GMA has to be mixed with thinning monomers (?
  intensive research activity on development of new
  monomers)

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• The rheological behaviour of composites is due to
  
• Filler particles
• Filler-matrix interface

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PERSPECTIVESFilled flowable systems

• Experimental resins
• Made by Voco GmbH
• Bis-GMA/TEGDMA 50/50
• 60 wt of fillers
• Varying micro-/macrofillers ratio
• Macrofiller silanated dental glass (av.
  diameter 1 µm)
• Microfiller partially hydrophobic silica (av.
  diameter 0.1 µm)
• Commercially available systems

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Then

• Filled universal packable systems, both
  experimental and commercially available
• Dental bonding systems
• Gutta-percha
• Tooth bleaching materials

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Aknowledgements

• Supervisors, scientific committee
• Prof. G. Leloup
• Prof. J. Devaux
• Prof. Ch. Bailly

• Technical staff
• Th. Glorieux
• A.-M. Dos Santos

• Additional help
• M. Dewaele
• G. Vermeersch