Contemporary relevance of occlusion and mastication.

411 Editorial T he evolution of new dental technologies, such as three-dimensional (3D) image manipulation, computer-aided design/computer-assisted manufacture (CAD/CAM), and new ceramics, are having a profound impact on treatment planning in oral rehabilitation. Yet the fundamentals of mastication, which are crucial determinants of optimizing treatment outcomes, are often overlooked. The importance of an optimal dentition for mastication is undergoing renewed recognition of its clinical significance beyond the commonly accepted importance of the arrangement of the teeth for esthetics and function. It is accepted that the dentition is a key feature for enhanced mastication, swallowing, diet, nutrition, and speech clarity. Indeed, anterior tooth arrangement, form, color, and character improve esthetics and individual social interaction, confidence, and quality of life. However, in addition, data are emerging that suggest that enhancing mastication may support maintenance of higher-level cognitive skills. 1–4 This research represents a paradigm shift for all aspects of oral rehabilitation and emphasizes an additional dimension of clinical responsibility. It adds to the significance of maintaining teeth for function and esthetics and acknowledges the importance of prosthodontic rehabilitation as a requirement for general health. Animal and human studies have shown associations with mastication and cognitive function through the hippocampus and its role in individual learning and memory. 1–4 Decreased mastication has been shown to be an epidemiologic risk factor for dementia and decreased spatial memory associated with decreased hippocampal neurons. The question of whether this is reversible is of particular importance and there is some evidence for this: (1) Data suggest that masti-cation influences memory processes by reducing en-docrinologic and autonomic stress responses, leading to increased activity of the hippocampus and prefron-tal cortex, thereby increasing cognitive processing. (2) So-called " abnormal " mastication (eg, caused by experimentally altering the occlusion through tooth extraction or reducing the height of natural crowns) induces chronic stress, decreases learning capacity, and reduces spatial memory and hippocampal neurons in animals. 4,5 Interestingly, restoring masticatory function with artificial crowns in aged mice counteracted the reduction in spatial memory and hippocampal neuron function. 5 This outcome cannot be directly linked with humans, but raises important issues. (3) In an older Swedish population sample, a robust association was found between cognition and self-reported chewing ability. 6 Whether the participants chewed with natural teeth or prostheses did not contribute significantly to cognitive impairment as long as they had no chewing difficulty. This was also recognized as a significant association by Paganini-Hill …