Table 1. Characteristic of the included studies.

NO.	Authors/Country	Sample	RNA extraction	Study (sample for case and control)	Technique	miRNAs studied	Fold Change\Log Value
1.	Zhong et al., 2012, United States	pulp tissue	miRNeasy Mini kit (Qiagen, Valencia, CA)	Healthy Pulp (n = 12); Inflammed Pulp (n = 18)	Human miRNA Microarrays	36 were differentially expressed: 3 (miR-150*, miR-584, miR-766) ↑ and 33 ↓. The most significantly repressed expression were miR-664, miR-214, and miR-152.	miR-150* fold change: 2.71, miR-584 fold change: 4.54, miR-766 fold change: 2.17
2.	Huang et al., 2019, China	pulp tissue	kit: TRIzol reagent (Invitrogen, Grand Island, NY, USA)	Healthy Pulp (n = 10); Inflammed Pulp (n = 10)	quantitative reverse transcription–poly- merase chain reaction (qRT-PCR)	hsa-miR-223-3p ↑ , hsa-miR-148a ↓, hsa-miR-146a-5p ↓ and hsa-miR-98-3p ↓.	hsa-miR-223-3p, hsa-miR-148a , hsa-miR-146a-5p and hsa-miR-98-3p fold change >2.0
3.	Lei, Zhang & Xie, 2019, China	pulp tissue	TRIzol reagent (Thermo Fisher, Waltham, MA, USA).	Healthy Pulp (n = 4); Inflammed Pulp (n = 4)	quantitative reverse transcription–poly- merase chain reaction (qRT-PCR)	miR-455-5p ↓	Fold Change >1.0.
4.	Zhang et al., 2019, china	pulp tissues, blood and saliva	phenol chloroform method	Healthy Pulp (n = 16); Inflammed Pulp (n = 28)	Reverse transcription-quantitative polymerase chain reaction (RT-qPCR)	miR-30b ↓	ND
5.	Brodzikowska et al., 2019, Poland	pulp tissue	RecoverALL Total Nucleic Acid Isolation Kit (Ambion™, Life Technologies, USA).	Healthy Pulp (n = 3); Inflammed Pulp (n = 3)	quantitative reverse transcription–poly- merase chain reaction (qRT-PCR)	miR-410 ↓	miR-410 fold change >4
6.	Zhou & Li, 2021 China	serum & pulp tissue	kit: TRIzol kit (Invitrogen, Carlsbad, CA, USA)	Healthy Pulp (n = 34); Inflammed Pulp (n = 66)	SYBR Green qRT- PCR	miR-27a-3p ↓	ND
7.	Liu et al., 2021, China	pulp tissue	TRIzol Reagent (Thermo Fisher Scientific, Waltham, MA, USA)	Healthy Pulp (n = 7); Inflammed Pulp (n = 7)	quantitative reverse transcription–poly- merase chain reaction (qRT-PCR)	hsa-mir-30a-5p ↓; hsa-miR-128-3p ↓	hsa-miR-128-3p: fold change is–1.47; hsa-miR-30a-5p: fold change is–1.22
8.	Chan et al., 2013, United States	periapical tissues and periodental tissue	miRNeasy Mini kit (Qiagen, Valencia, CA)	Apical periodontitis (n = 8); normal periodental tissue (n = 8)	quantitative reverse transcription–poly- merase chain reaction (qRT-PCR)	miR-95 ↓, miR-181a ↓, miR-181b ↓, miR-181c ↓, miR-455-3p ↓, miR-24-1 ↓ and miR-149 ↓	Log values: miR-95 <−20; miR-181a <−30; miR-181b <−50; miR-181c <−30; miR-455-3p <−20; miR-24-1 <−40; miR-149 <−40
9.	Lina et al., 2019, China	periapical tissue	kit: RNAiso Plus (TaKaRa Bio, Tokyo, Japan)	Apical periodontitis (n = 20), normal periodental tissue (n = 13)	ABI 7500 real time PCR system with a SYBR® Premix Ex TaqTM II kit (TaKaRa)	miR-146a ↑	ND
10.	Yue et al., 2016, China	periodental tissue	Trizol (Life Technologies, Carlsbad, CA) lysis methods	Apical periodontitis (n = 10), normal periodental tissue (n = 6)	Real-time polymerase chain reaction (PCR)	miR-29b ↑, miR-106b ↑, miR-125b ↑, miR-143 ↑, miR-155 ↑, and miR-198 ↑	ND
11.	Yue et al., 2017, China	periodental tissue	Trizol (Life Technologies, Carlsbad, CA) lysis methods	Apical periodontitis (n = 10), normal periodental tissue (n = 6)	Real-time polymerase chain reaction (PCR)	miR-335-5p ↓	ND
12.	Shen et al., 2021, United States	periapical tissues and periodental tissue	TRIzol (Invitrogen, Thermo Fisher Scientific, Waltham, MA)	Apical periodontitis (n = 10), normal periodental tissue (n = 2)	next-generation miRNA-seq analysis (miRNA-seq)	miR-10a-5p ↑, miR-155-5p ↑, miR-7-5p ↑, miR-142-5p ↑, miR-625-3p ↑. miR-891a-5p ↓, miR-514a-3p ↓, miR-128-3p ↓, miR-509-3-5p ↓, miR-199a-5p ↓.	Fold change:miR-10a-5p = 8.44; miR-155-5p =: 4.54; miR-7-5p = 3.67; miR-142-5p = 3.64 = miR-625-3p = 3.50; miR-891a-5p = 0.14; ,miR-514a-3p = 0.19; miR-128-3p =: 0.19; miR-509-3-5p = 0.21; miR-199a-5p = 0.22

Notes.

^*activated miR150.

ND

Not determined