Predicting fatigue damage in intact and restored teeth
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Predicting fatigue damage in intact and restored teeth. Sam Evans Sam Smith School of Engineering, Cardiff University PO Box 925, The Parade, Cardiff CF24 0YF. Introduction. Tooth fracture or cracking is a common cause of clinical failure The cause of this problem is not well understood

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Predicting fatigue damage in intact and restored teeth

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Predicting fatigue damage in intact and restored teeth

Predicting fatigue damage in intact and restored teeth

Sam Evans

Sam Smith

School of Engineering, Cardiff University

PO Box 925, The Parade, Cardiff CF24 0YF


Introduction

Introduction

  • Tooth fracture or cracking is a common cause of clinical failure

  • The cause of this problem is not well understood

  • Cracks occur in the tooth due to cavity preparation

  • Abfraction may involve fatigue


Typical tooth damage

Typical tooth damage

Reproduced from:-

http://www.umbc.edu/engineering/

me/bsms/dental.html


Abfraction

Abfraction

Typical non- carious cervical lesions (Rees 1998)


Introduction1

Introduction

  • The aim of this study was to model fatigue crack growth using computational fracture mechanics models

  • This could provide insights into the mechanisms of abfraction and post- restoration cracking


The problem

The problem

  • A typical molar with an amalgam restoration was modelled

  • A 114m crack was introduced at the region of maximum stress, as found by Xu et al after preparation with a diamond burr1.

    1. Xu, H. H. K., Kelly, J. R., Jahanmir, S., Thompson, V. P., Enamel subsurface damage due to tooth preparation with diamonds. J. Dent. Res. 76(10) (1997):1698-706.


Finite element model

Finite element model

  • A 2D finite element model was developed, based on Arola et al2.

  • Modelled in plane strain, using Franc2D (Cornell Fracture Group, www.cfg.cornell edu)

  • Linear interface elements were used- mostly in compression

2. Arola, D., Huang, M. P. and Sultan, M. B., The failure of

amalgam dental restorations due to cyclic fatigue crack growth

J. Mat. Sci.: Materials in Medicine10(1999): 319-327.


Predicting fatigue damage in intact and restored teeth

Initial mesh, showing dentine, enamel and restoration


Predicting fatigue damage in intact and restored teeth

Initial 114m

crack


Predicting fatigue damage in intact and restored teeth

Crack region

remeshed


Predicting fatigue damage in intact and restored teeth

Crack propagated in 50m steps up to 1.6mm


Fatigue life prediction

Fatigue life prediction

  • Preliminary fatigue crack growth data by Arola et al3 was used to predict the crack growth rate

  • A simple Paris Law model fits the data well

  • Variable amplitude loading etc will affect crack growth in practice

    3. www.enduratec.com/pdf/Appbrief-UMBC.PDF


Predicting fatigue damage in intact and restored teeth

Stiffness of

side much

reduced


Crack length vs time

Crack length vs time

Crack length (mm)

Time (years)


Discussion

Discussion

  • Stresses in the tooth are in the right range to cause clinical fractures in a typical clinical timescale

  • Crack may become dormant due to load redistribution

  • Tooth is then left vulnerable to unusual loads, decay etc


Abfraction1

Abfraction


Crack propagation

Crack propagation


Crack length

Crack length

Crack length (mm)

50N load

20Nload

Figure The number of cycles for the crack to grow to a given length under a 10N load for the first and final models

Cycles


Discussion1

Discussion

  • Propagation of cracks is likely at typical physiological loads

  • Crack growth likely from small (50µm) initial cracks

  • Possible formation of deep rounded lesions inside the PDL

  • Interaction with erosion during initiation and propagation


Conclusions

Conclusions

  • These models predict crack propagation at relevant rates under typical physiological loads

  • Fatigue seems likely to be a factor in abfraction damage

  • Possible to avoid fatigue damage through improved restorations?


Acknowledgements

Acknowledgements

  • The abfraction model was developed by Sam Smith

  • The Franc software is provided by the Cornell Fracture Group http://www.cfg.cornell.edu


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