Ultrasound Treatment Of Mandibular Osteoradionecrosis Of The Animal Experimental Study

Osteoradionecrosis of the jaws(ORNJ) is a serious complication of radiation therapy to the head and neck. More than 90% of all osteos arise in the mandible. Osteoradionecrosis (ORN) of the mandible can arise following therapeutic radiotherapy for head and neck cancer. Mandibular osteoradionecrosis is the most serious long-term complication of radiotherapy, with a variable incidence, ranging from 2 to 44.2%. With adequate prevention, the incidence is still around 2-5%. Its machnism is still not completely clear. the cause and pathogenesis of osteoradionecrosis are far more complex than originally believed. Osteoradionecrosis is a process of dysvascular bone necrosis and the poorly vascularized necrotic tissue may cause pain and/or instability, and it cannot resist infection well, which may result in secondary osteomyelitis. Ongoing research is also being conducted to clarify the role of osteoclasts in the pathogenesis of osteoradionecrosis. Restoration of blood supply or vascularized tissue to the affected area continues to be of primary importance in the resolution of osteoradionecrosis.Conservative and surgical therapies used for ORN have included vascularized osteocutaneous flap transfers, hyperbaric oxygen and ultrasound therapy. Given the increased use of radiation therapy and combined chemotherapy-radiation therapy regimens in treatment of head and neck malignancies, it is anticipated that osteoradionecrosis will continue to be an important clinical problem.Once ORNJ occurs, operation should be made actively.Osteotomy plays a major role and assistant hyperbaric oxygen can enhance the effect ulteriorly. Simultaneous anterior mandibulotomy and marginal mandibulectomy results in a high morbidity rate of avascular necrosis of the mandible and therefore should be avoided. To avoid a disastrous complication, segmental mandibulectomy and a composite free fibular osteoseptocutaneous flap reconstruction would be a preferred surgical alternative. The results of HBO in treating established ORN are not convincing. Higher levels of oxygen tension was found in tissues affected by ORN based on transcutaneous partial oxygen pressure (TCPO2) after treatment with HBO, which suggested that these tissues were hypoxic before they were treated. Once ORN is recognised, it is irreversible and extremely difficult to treat. When osteoradionecrosis occurs, removal of necrotic bone under antibiotic treatment is indicated. Also, treatment can be supported by hyperbaric oxygen, which is of value in establishing revascularization. But the high price of HBO limited its application on ORN treatment, in which the regular and long term management is necessary.Very little information is available concerning the treatment of osteoradionecrosis by means of ultrasound. Therapeutic angiogenesis is the controlled induction or stimulation of new blood vessel formation to reduce unfavourable tissue effects caused by local hypoxia and to enhance tissue repair. The effects of ultrasound on wound healing, chronic ulcers, fracture healing and osteoradionecrosis may be explained by the enhancement of angiogenesis.If blood flow can be re-established or increased, cell delivery and tissue oxygenation will improve, and so should healing. It seems that ultrasound can heal osteoradionecrotic bone by countering the negative effects of hypocellularity, hypoxia, and hypovascularity. When ultrasound is compared with the other forms of treatment, such as surgical intervention or hyperbaric oxygen treatment, adjunct ultrasound treatment of osteoradionecrotic bone seems to be more patient-friendly and economically viable (Harris, 1992)The purpose of this study was to evaluate in vivo the effect of ultrasound in revascularisation of mandibular osteoradionecrosis. We have established animal model of ORNJ and examined the pathological change between before and after ultrasound treatment. The mandible with dental implant was also evaluated in our study by means of micro-CT, confocal microscopy and biomechanics. The parameters evaluated were microvessel density and microarchitecture in mandible, and metabolism in osteoblasts.The ultrasounic effect on the implant in mandible was also investigated. With the 30mW/cm2 , 1 MHz, 1:4 pulse ultrasound treatment of 20 days, the parameters such as microvessel density, bone trabecula thickness, the ratio of bone surface area vs volume, were all higher than the parameters of the control animals. The cofocal microscopy results showed Bone morphogenetic protein (BMP) also rised after the ultrosonic treatment.In the mandible around implants, the ultrasonic treatment produced much higher increases in bone volume fraction (BVF), trabecular thickness, the bone surface/volume ratio, the maxilum implant pull-out forces than those untreated by ultrasound. These results suggested that the ultrasound could raise microvessle to improve the metabolism in mandible. The clinical observation coincided the results in the experiment, in which a woman recoverd the degree of mouth openning after 40 days treatment. Our study proved that the ultrasound treatment as a novle method might be a potential way to cure ORNJ.