Combination Therapy: Hyperbaric Oxygen and PENTOCLO for Treatment of Osteoradionecrosis of the Mandible

Inclusion Criteria: * Diagnosis of mandibular ORN after completion of radiotherapy * ORN will be defined as "an area of exposed devitalized irradiated bone (\> 20 mm2)"; minor bone spicules (MBS) (\< 20 mm2) in the absence of radiographic abnormality, will be considered clinically insignificant * Has no contraindications for undergoing hyperbaric oxygen therapy as assessed by a Hyperbaric Physician, and is willing to commit the time to undergo 60 sessions * Negative Human Chronic Gonadotropin (hCG) screening test at baseline (for female patients of reproductive age not practicing medically acceptable methods of birth control (e.g., hormonal contraceptives, implants, injectables, intrauterine device (IUD), intrauterine system (IUS), vasectomy and bilateral tubal ligation) * Baseline in-date ECG (within 60 days prior to enrolment) * Age ≥ 18 Exclusion Criteria: * Inability to give informed consent * Previous treatment for ORN (PENTOCLO, HBOT or surgery) * Major surgical procedure planned (more extensive than sequestrectomy) * Severe trismus and inability to obtain intraoral photographs * Contraindications for HBOT: pneumothorax, bullous disease, uncontrolled hypertension, uncontrolled epilepsy, claustrophobia * Contraindications to mPENTOCLO (inability to swallow medication; pregnancy or lactating; allergy to any study drug; currently on oral anticoagulants; hemorrhagic/coagulation disorder; Vitamin K deficiency; active unresolved cardiac disease; severe liver or kidney disease (CrCl\<30 mL/min)) * Known QT prolongation as documented on an in-date ECG (within 60 days prior to enrolment) are excluded. Patients with the QTc prolongation associated with a correctable cause (e.g., electrolyte imbalance or drug-induced), and corrected QTc prior to enrolment into the study as documented on 12 lead ECG will be eligible for inclusion * Patients requiring concurrent use of medications known to significantly prolong the QT interval with a high risk of clinical impact (e.g., erythromycin, cisapride, astemizole, pimozide or quinidine) are excluded unless safe discontinuation or substitution of these medications is feasible prior to initiation of the study * Patients on medication with a potential but low risk of QTc prolongation (e.g., ondansetron, SSRIs) may be included if a post-initiation ECG conducted within 24-48 hours of starting ciprofloxacin or fluconazole confirms that there is no significant QTc prolongation * History of cholestatic jaundice/hepatic dysfunction associated with amoxicillin-clavulanate * Moderate to severe active liver disease (class B or C Pugh-Child Score) or active liver disease with significant acute elevation of LFT values * History of myasthenia gravis * Patients with a history of nontraumatic tendon disorders with severe functional impairment (i.e., significant swelling of the affected tendon, or partial tendon tear documented on clinical examination or imaging) * Patients who have previously experienced peripheral neuropathy due to exposure to antibiotics * Smokers, high alcohol intake (average of \>2 standard drinks per day), sepsis, severe undernourishment and severe immunodeficiency conditions (e.g. HIV, autoimmune disease, immune-compromised) * Persistent or recurrent cancer and active neoplastic pathology will be excluded * Patients with documented Vitamin K deficiency * Patients taking additional Vitamin E * Patients with concomitant prescription of anti-resorptive or anti-angiogenic medications (e.g. risedronate, alendronate, aIbandronate, zoledronic acid, pamidronate, etidronate or prescription of denosusamab, etc.) * Patients diagnosed with retinitis pigmentosa * Patients diagnosed with clinically significant anemia