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

Maisoon Al-Jawad, Owen Addison, Slobodan Sirovica, Samira Siddiqui, Richard Martin, David Wood, D.C. WATTS

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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 mesioocclusal distal cavities. The enamel was machined at the point of maximum convexity on the outer tooth to create a vertical fin of thickness 100 μm and 0.5 mm 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 photopolymerisation of a composite material placed in the cavity, to calculate strain in the respective axis. The composite was photo-polymerised with either relatively high (1200 mWcm-2, group 1) or low (480 mWcm-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.
Original languageEnglish
Pages (from-to)1426-1439
Number of pages14
JournalDental Materials
Issue number10
Early online date14 Aug 2018
Publication statusPublished - Oct 2018


  • Synchrotron X-ray micro-focussed diffraction, Resin based composite, Photo-polymerisation, Enamel, Stress, Strain, Shrinkage

Research Beacons, Institutes and Platforms

  • Advanced Materials in Medicine


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