“…The remaining samples were used for quantitative reverse transcription polymerase chain reaction (qRT-PCR). Periapical tissues surrounding the mesial and distal root apices of the first molars were carefully extracted in accordance with previous reports [24,25], rinsed in cold phosphate-buffered saline, freed of clots, and immediately placed in RNAlater TM Storage Solution (SigmaeAldrich, St. Louis, MO, USA).…”