Gerodontology. 2019;00:1–6. wileyonlinelibrary.com/journal/ger | 1 © 2019 Gerodontology Association and John Wiley & Sons Ltd 1 | INTRODUCTION Dentin is a complex hard tissue that comprises the bulk of the tooth and covers the dental pulp. 1 Microtubules filled with dentinal fluid, odontoblastic process, mineralised intertubular dentin and highly min‐ eralised peritubular dentin constitute the microstructure of dentin. 1,2 With ageing, the thickness of the peritubular linings increase and re‐ duction in the tubule lumen diameter begins. 2,3 These changes appear to continue at a constant rate until the lumens have been completely occluded. 3,4 Once the majority of the tubule lumens are mineralised and translucent, sclerotic tissue becomes visible. 4,5 Besides the mi‐ crostructural alterations, changes in mechanical properties, such as Received: 8 February 2019 | Revised: 26 August 2019 | Accepted: 18 October 2019 DOI: 10.1111/ger.12444 ORIGINAL ARTICLE Influence of different irrigation protocols on microhardness and flexural strength values of young and aged crown dentin Nurab Deniz Pedersen | Emel Uzunoglu‐Özyürek | Hatice Dogan Buzoglu Department of Endodontics, Faculty of Dentistry, Hacettepe University, Ankara, Turkey Correspondence Emel Uzunoğlu Özyürek, Department of Endodontics, Faculty of Dentistry, Hacettepe University, Sihhiye, Ankara/ Turkey. Email: emel_dt@hotmail.com Abstract Objective: To investigate the effect of different irrigation protocols on microhard‐ ness (MH) and flexural strength (FS) values of young and aged crown dentin. Background: In addition to ageing, root canal irrigation might also affect the me‐ chanical properties of coronal dentin walls. Materials and Methods: One hundred and twenty dentin bars (2 mm × 2 mm × 8 mm) were obtained from the crowns of extracted, non‐caries, human molars of young and older patients (n = 60 bars; average patient ages: 16.7 and 65.4, respectively). Subgroups were formed as follows: 2.5%NaOCl(sodium hypochlorite)+5%EDTA(ethylen ediaminetetraacetic acid), 2.5%NaOCl + 15%EDTA, 2.5%NaOCl, 5%EDTA, 15%EDTA and Saline. NaOCl and saline were used for 20 minutes and EDTA solutions for 1 minute. MH values of each sample were measured before and after the irrigation protocols. The same samples were also submitted for FS analysis. The data were statistically analysed. Results: Young samples had lower MH values at pre‐ and post‐treatment compared to aged samples (P < .05). A significant decrease was observed in MH values of aged samples exposed to 2.5%NaOCl and both NaOCl + EDTA combinations (P < .05). FS values of the young saline‐treated group were statistically higher than aged ones (P < .05). Both NaOCl + EDTA combinations caused a significant decrease in FS values of young samples compared to saline (P < .05). Conclusion: Ageing has a significant effect on the MH and FS values of crown dentin samples. 5% EDTA solutions revealed similar results to 15%EDTA regarding MH and FS values of crown dentin in both age groups. The NaOCl + EDTA combination had a prominent effect than EDTA alone, on MH values of young‐, and FS values of aged dentin samples. KEYWORDS age, biomechanics, chelating agents, endodontics, root canal irrigation