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

• Main Authors: Addison, O. (Author), Al-Jawad, M. (Author), Martin, R.A (Author), Siddiqui, S. (Author), Sirovica, S. (Author), Watts, D.C (Author), Wood, D.J (Author)
• Format: Article
• Language: English
• Published: Elsevier Inc. 2018
• Subjects: Bicuspid; chemistry; Composite Resins; Crystal orientation; Crystallite orientation; Crystallites; Crystallographic strain; Crystallography, X-Ray; Dental Cavity Preparation; Dental Enamel; Dental Leakage; dental surgery; Durapatite; enamel; Enamel; Enameling; Enamels; Halogen light sources; human; Humans; hydroxyapatite; Hydroxyapatite; Hydroxyapatite crystals; image processing; Image Processing, Computer-Assisted; in vitro study; In Vitro Techniques; Light sources; mechanical stress; Photo-polymerisation; Photopolymerization; polymerization; Polymerization; premolar tooth; procedures; radiation response; resin; Resin based composite; Resin-based composite; Resins; Restoration; Shrinkage; Strain; Stress; Stress, Mechanical; Stresses; synchrotron; Synchrotron x ray diffraction; Synchrotron x rays; Synchrotron X-ray micro-focussed diffraction; Synchrotrons; tooth disease; Tooth enamel; X ray crystallography; X ray diffraction; X-Ray Diffraction
• Online Access: View Fulltext in Publisher

 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 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 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 (1200 mW cm−2, group 1) or low (480 mW cm−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. © 2018 The Academy of Dental Materials