15 1 Thesis outline As described above, mastication, swallowing and salivary flow are important functions which can deteriorate due to head and neck cancer itself, or because of its treatment. Therefore, the aim of this thesis is to further optimize the understanding of mastication, swallowing, and salivary flow in patients with head and neck cancer and investigate associated factors possibly affecting these functions, up to two years after treatment. Chapter 2 consists of a review that was written about masticatory ability, to provide an overview of the existing literature about oral health related quality of life (QoL) as measured with the University of Washington Quality of Life (UW-QoL) questionnaire. This questionnaire is often used in oral cancer, in which patients have to state whether they can chew normally, can only chew soft food, or cannot chew soft (nor hard) food. In order to predict the burden of masticatory and swallowing dysfunction, the first important step was to determine the reliability of the tests used to measure objective masticatory and swallowing function, and to determine the measurement error of these tests. Chapter 3 was written to assess the reliability of the Mixing Ability Test (MAT), which measures masticatory performance. The reliability of the 100 mL Water Swallow Test (WST) to assess swallowing was described in chapter 4. The next step was to determine the correlation between objective function outcomes and patient-reported outcomes, to investigate whether objective tests measure the same construct as patient-reported outcomes. Chapter 5 therefore assesses this correlation between objective tests and questionnaires. Based on chapter 5, associative models were created to investigate masticatory performance and swallowing function in relation to demographic and clinical factors, and to describe the course in time of these tests. In chapter 6, the associative model for masticatory performance was described, and in chapter 7 the associative model for swallowing function was described. Chapter 8 describes the course in time of the SWALQOL questionnaire, in which the whole food process from eating to swallowing, as well as mental problems caused by food processing difficulties, are taken into account. In addition, an associative model was created which describes patients that are most likely to experience problems after HNC treatment.