Читать книгу Practical Procedures in Dental Occlusion - Ziad Al-Ani - Страница 22

 Mucosal and periosteal – these receptors are more important when teeth are lost, i.e. when wearing a complete denture or an implant‐supported prostheses (Jacobs and Van Steenberge 1991).

 Cutaneous – the skin contains cutaneous receptors which provide kinaesthetic perceptions, and this has been shown in other parts of the body such as the hand. It is thought that the skin overlying the TMJ may also respond to stretch and therefore provide additional input information regarding condylar movement. There is no direct evidence for this, but we can surmise this during phonetics where the somatosensory input from the facial skin and muscle mechanoreceptors is consistently activated (McClean et al. 1990).

The masticatory system is therefore an all‐encompassing, information‐gathering and communicative neuromuscular system. The term ‘neuromuscular dentistry’ was introduced by Dr Bernard Jankelson in 1967 which helps us understand that the masticatory system is a three‐dimensional system composed of the TMJ, muscles and teeth with a focus on using transcutaneous electrical nerve stimulators (TENS) to stimulate and relax the muscles, thus providing a physiological rest position and the occlusion was then built around this position. There are many other schools of occlusion and they all recognise that we must assess the TMJ and muscles before rebuilding the teeth because an unhealthy joint does not function in the same way as a healthy one.

So, we are chewing our food happily but when are the teeth touching? Jankelson (1953) stated that ‘contact of teeth seldom occurs during the act’. Wassell et al. (2008) state that the time teeth actually touch in total over a 24‐hour period is 17.5 minutes.

 8 minutes empty swallowing contacts – equating to 500 swallowing contacts.

 9.5 minutes of chewing contacts – the chewing contacts start to occur at the end phase of chewing providing the necessary information that the food is ready to be swallowed – equating to 1800 chewing contacts.

This means that teeth are designed for minimal contact and low forces so when we increase contact time and force, as in parafunction or hypernormal function (nail biting, chewing gum), the teeth can wear, crack or become inflamed (pulpitis), the muscles become inflamed or enlarged, the TMJ becomes inflamed and cartilage can become displaced.

So when do we know when to swallow? When the food is broken down to a size that is small enough for us not to choke and there is variability amongst individuals with regard to size. It was Parmeijer et al. (1970) who showed that the majority of swallowing contacts are in a habitual occlusal position, also called intercuspal position (ICP) or maximum intercuspation (MIP), using intraoral occlusal telemetry devices (a multifrequency transmitter) and less so in centric relation.