the study.

Author contributions
====================

**Conceptualization:** Jun Asai, Junko Yamaguchi, Taku Tsukamoto, Norito Katoh, Junya Kuroda.

**Data curation:** Jun Asai, Junko Yamaguchi, Taku Tsukamoto, Yoshiaki Chinen, Yuji Shimura, Tsutomu Kobayashi, Junya Kuroda.

**Formal analysis:** Jun Asai, Junko Yamaguchi, Taku Tsukamoto, Yoshiaki Chinen, Yuji Shimura, Tsutomu Kobayashi, Junya Kuroda.

**Funding acquisition:** Norito Katoh, Junya Kuroda.

**Investigation:** Jun Asai, Junko Yamaguchi, Taku Tsukamoto, Yoshiaki Chinen, Yuji Shimura, Tsutomu Kobayashi, Norito Katoh, Junya Kuroda.

**Methodology:** Jun Asai, Junko Yamaguchi, Norito Katoh, Junya Kuroda.

**Project administration:** Jun Asai, Norito Katoh, Junya Kuroda.

**Resources:** Norito Katoh, Junya Kuroda.

**Software:** Norito Katoh, Junya Kuroda.

**Supervision:** Norito Katoh, Junya Kuroda.

**Validation:** Norito Katoh, Junya Kuroda.

**Visualization:** Norito Katoh, Junya Kuroda.

**Writing -- original draft:** Jun Asai, Junko Yamaguchi.

**Writing -- review & editing:** Norito Katoh, Junya Kuroda.

Junya Kuroda orcid: 0000-0001-6130-1550.

Abbreviations: aGVHD = acute graft-vs-host disease, allo-HSCT = allogenic hematopoietic stem-cell transplantation, ATG = antithymocyte globulin, CR = complete response, NB-UVB = narrowband ultraviolet B, ORR = overall response rate, PD = progressive disease, PR = partial response, SD = stable disease.

JA and JY contributed equally to this work.

This study is supported by the education and research expenses provided by our university those are not associated with any treatment or measurements for this research.

The authors have no conflicts of interest to disclose.


INTRODUCTION {#sec1-1}
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During nonsurgical retreatment, all existing root canal filling materials should be removed because they might contain microorganisms that can interfere with the effective distribution of irrigants and prevent adaptation of new root canal filling materials. Nickel-titanium (NiTi) rotary instruments have 