Intracoronal stress transfer through enamel following RBC photopolymerisation: A synchrotron X-ray study

Maisoon Al-Jawad; Owen Addison; Slobodan Sirovica; Samera Siddiqui; Richard A Martin; David J Wood; David C Watts

doi:10.1016/j.dental.2018.07.005

Intracoronal stress transfer through enamel following RBC photopolymerisation: A synchrotron X-ray study

Dent Mater. 2018 Oct;34(10):1426-1439. doi: 10.1016/j.dental.2018.07.005. Epub 2018 Aug 14.

Authors

Maisoon Al-Jawad¹, Owen Addison², Slobodan Sirovica³, Samera Siddiqui⁴, Richard A Martin⁵, David J Wood⁶, David C Watts⁷

Affiliations

¹ Institute of Dentistry, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, UK. Electronic address: m.al-jawad@qmul.ac.uk.
² Biomaterials Unit, University of Birmingham School of Dentistry, Birmingham, UK; University of Alberta, School of Dentistry, Edmonton, AB, Canada. Electronic address: oaddison@ualberta.ca.
³ University of Alberta, School of Dentistry, Edmonton, AB, Canada; Aston Institute of Materials Research, Aston University, Birmingham, UK.
⁴ Institute of Dentistry, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, UK.
⁵ Aston Institute of Materials Research, Aston University, Birmingham, UK.
⁶ Biomaterials and Tissue Engineering Research Group, School of Dentistry, University of Leeds, Leeds, UK.
⁷ School of Medical Sciences and Photon Science Institute, University of Manchester, UK.

PMID: 30119841
DOI: 10.1016/j.dental.2018.07.005

Abstract

Objectives: To measure the spatial distribution of crystallographic strain in tooth enamel induced by the photo-polymerisation of a dimethacrylate resin based composite cavity restoration.

Methods: Six sound first premolar teeth, allocated into two groups (n=3), were prepared with mesio-occlusal distal cavities. The enamel was machined at the point of maximum convexity on the outer tooth to create a vertical fin of thickness 100μm and 0.5mm depth to allow for synchrotron X-ray diffraction measurements. 2D diffraction patterns were used to determine crystallite orientation and quantify changes in the hydroxyapatite crystal lattice parameters, before and after photo-polymerisation of a composite material placed in the cavity, to calculate strain in the respective axis. The composite was photo-polymerised with either relatively high (1200mWcm^-2, group 1) or low (480mWcm^-2, group 2) irradiances using LED or quartz halogen light sources, respectively. A paired t-test was used to determine significant differences in strain between irradiance protocols at ɑ=0.001.

Results: Photo-polymerisation of the composite in the adjacent cavity induced significant changes in both the crystallographic c and a axes of the enamel measurement area. However the magnitude of strain was low with ∼0.1% difference before and after composite photo-polymerisation. Strain in enamel was not uniformly distributed and varied spatially as a function of crystallite orientation. Increased alignment of crystallites perpendicular to the cavity wall was associated with higher c axis strain. Additionally, strain was significantly greater in the c (p<0.001) and a axis (p<0.001) when using a high irradiance photo-polymerisation protocol.

Significance: Although cuspal deflection is routinely measured to indirectly assess the 'global' effect of composite shrinkage on the tooth-restoration complex, here we show that absolute strains generated in enamel are low, indicating strain relief mechanisms may be operative. The use of low irradiance protocols for photo-polymerisation resulted in reduced strain.

Keywords: Enamel; Photo-polymerisation; Resin based composite; Shrinkage; Strain; Stress; Synchrotron X-ray micro-focussed diffraction.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Bicuspid
Composite Resins / chemistry*
Composite Resins / radiation effects
Crystallography, X-Ray
Dental Cavity Preparation / methods*
Dental Enamel / chemistry*
Dental Enamel / radiation effects
Dental Leakage
Durapatite / chemistry*
Durapatite / radiation effects
Humans
Image Processing, Computer-Assisted
In Vitro Techniques
Polymerization
Stress, Mechanical
Synchrotrons*
X-Ray Diffraction

Substances

Composite Resins
Durapatite