12 Chapter 1 with oral intake and often lead to weight loss and dehydration during and immediately after CRT [34]. Unintentional weight loss and low muscle mass, the clinical features of cachexia [35], negatively impact treatment-related toxicity and oncologic outcome. Patients with HNC and unintentional weight loss and/ or low muscle mass experience higher toxicity, more unplanned hospitalizations, and poorer overall survival [36-38]. Worldwide, patients with HNC cite fear of the cancer relapse as by far the greatest concern after cancer treatment [39, 40]. However, this main concern is closely followed by the side effects of cancer treatment, with the most important side effects being: Dry mouth, chewing/eating, swallowing, speech/voice/being understood, and dental health/teeth [40]. Young age at diagnosis combined with a better prognosis for HPV-positive HNC and thus a longer life expectancy has increased awareness of late treatment-related toxicity [41]. Consequences of the loss of dental functions Teeth may be lost due to surgical resection of an oral cavity tumor, but also due to the removal of potential oral sources of infection prior to RT, CRT or BRT to prevent ORN [42, 43]. Tooth extractions result in a reduced number of functional units and impair the ability to chew and swallow [44, 45]. The implications of disrupting our masticatory system are great. Qualitative studies have shown that this multiple tooth loss negatively affects patients’ ability to chew and eat, and thus their quality of life [46-48]. Specifically, a greater number of missing teeth is associated with a reduced maximum bite force (MBF), decreased masticatory performance, and self-perceived oral health status [44, 49, 50]. Compared to the non-cancer general dental practitioners group, patients with HNC rated oral function issues as more important than other domains. Other issues such as pain, appearance, activity, recreation, mood, and anxiety were considered less important [51]. Despite the fact that masticatory performance can often return to pre-treatment levels after surgery, even in patients who survive for five years, some degree of masticatory impairment persists and may affect the ability to eat [17, 44]. RT and its side effects on the quantity and quality of saliva, oral mucosa, and masticatory muscles, exacerbate masticatory problems [17]. The masticatory performance of patients with oral cavity cancer is positively affected by having full dentures or better, a higher number of occlusal units (OU), an increased MMO, and an increased maximum bite force (MBF). The location of the tumor also plays an important role [44].
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