## 2 Materials and Methods  
A case-control study was carried out in patients undergoing aHST in the Department of Cellular Biotechnologies and Hematology at Sapienza University of Rome with the cooperation of the Department of Oral Sciences and Maxillofacial Surgery at Sapienza University of Rome. The study is part of a project called \"MoMax\" (Oral Medicine and Maxillofacial Surgeons), a task force designed to provide cancer patients and high-risk patients with multidisciplinary team care, through cooperationbetween different health providers. All subjects gave their informed consent for inclusion in the study. The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Local Ethical Committee of Sapienza University of Rome (Prot. N.264, 13 March 2017).  
All patients receiving conditioning regimens for aHST in the age range of 6 to 80 years, were considered eligible in the study. Uncooperative patients, patients with systemic diseases that hinder wound healing (e.g., uncontrolled diabetes mellitus, etc.), patients with an oxygen mask, or orogastric catheters that might hinder the PBM application, and patients with suspicious lesions within the oral cavity were excluded from the study.  
A total of 40 patients (17 females and 23 males) with a median age of 46 years, were included in the study. Twenty-three patients received HST from a matched unrelated donor (MUD) and 17 patients received HST from a matched related donor (MRD). The patient characteristics of both groups are presented in Table 1.  
This case-control study analyzed two groups of patients:  
The preventive group (PG): 20 patients (7 females and 13 males) were recruited prospectively and were subjected to intra-oral PBM for prevention purposes.  
\begin{table}
\begin{tabular}{l c c} \hline \hline \multicolumn{1}{c}{**Characteristics**} & **Preventive Group (PG)** & **Control Group (CG)** \\ \hline
**Mean age (range)** & 46.5 (7–66) & 45.6 (19–65) \\ \hline
**Gender** & n (\%) & n (\%) \\ \hline Male & 13 (65) & 10 (50) \\ Female & 7 (35) & 10 (50) \\ \hline
**Type of aHST** & & \\ \hline Matched Unrelated Donor (MUD) & 14 (70) & 9 (45) \\ Matched Related Donor (MRD) & 6 (30) & 11 (55) \\ \hline
**Underlying Pathology** & & \\ \hline Acute Lymphocytic Leukemia & 3 (15) & 4 (20) \\ Acute Myelogenous Leukemia (AML) & 3 (15) & 7 (35) \\ Myelofibrosis & 3 (15) & 3 (15) \\ Myeloblastic Syndrome & 3 (15) & 1 (5) \\ Chronic Myelogenous Leukemia & 2 (10) & - \\ Non-Hodgkin’s Lymphoma & - & 2 (10) \\ Multiple Myeloma & 1 (5) & - \\ Myeloid Sarcoma (MS) & 1 (5) & - \\ Mixed Phenotype Acute Leukemia & 1 (5) & - \\ Chronic Lymphocytic Leukemia & - & 1 (5) \\ T-cell polymorphocytic leukemia & - & 1 (5) \\ Aplastic Anemia & - & 1 (5) \\ MS and AML & 1 (5) & - \\ Others & 2 (10) & - \\ \hline
**aHST Conditioning Regimen** & & \\ \hline Thio, BUS, FLU, Meth & 14 (70) & 11 (55) \\ Thio, BUS, FLU, Cyclo & 4 (20) & 5 (25) \\ TBI, Thio, FLU, Meth & 1 (5) & - \\ Thio, FLU, and Meth & 1 (5) & - \\ Treo, FLU & - & 1 (5) \\ Rituximab, Cyclo, Thio, Cyclosporine & - & 1 (5) \\ Cyclo, Meth & - & 1 (5) \\ Cyclosporine, Thio, FLU, Cyclo & - & 1 (5) \\ \hline Thiotepa (Thio); Busulphan (BUS); Fludarabine (FLU); Methotrexate (Meth); Total Body Irradiation (TBI); Treosulfan (Treo); Cyclophosphamide (Cyclo). & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Clinical characteristics and patients preview.  
The retrospective control group (CG): 20 patients (10 females and 10 males) receiving aHSCT between December 2014 and October 2016, and not subjected to PBM were selected retrospectively to compare the obtained results. The aim of the study was to compare OM incidence and severity between the two groups.