Understanding Masticatory Function in Unilateral Crossbites

Maria Grazia Piancino, Stephanos Kyrkanides

• Publisher: Wiley-Blackwell
• Year: 2016
• ISBN:
  9781118971895
• Edition: 1
• Topic: Medicine
• Subtopic: Orthodontics

Unilateral posterior crossbite is a problem often seen in orthodontic practice, and properly understanding chewing patterns will lead to the most effective treatment program. Drawing on their research and available literature, Drs. Piancino and Kyrkanides present a fascinating look at chewing cycles and their role in the functional treatment of unilateral posterior crossbite.

• Describes the physiology and pathology of chewing patterns and muscular activation in humans
• Explains chewing patterns and muscular coordination, and their influence on the growth and harmony of the stomatognathic system
• Clinical instruction for checking and correcting masticatory function and functional asymmetry in order to prevent the relapse of the malocclusion
• Clinical cases walk readers through the treatment of seven crossbites

CHAPTER 1
Introductory Explanation of Masticatory Function

Contents

1. 1.1 Introduction
2. 1.2 The study of masticatory function
   1. 1.2.1 The case gnathic replicator
   2. 1.2.2 The Sirognathograph
3. 1.3 The evolution of electrognathography and electromyography
   1. 1.3.1 Plotted masticatory cycles
   2. 1.3.2 1983: Early computer processing of plotted data on chewing cycles
   3. 1.3.3 1986: First recording of chewing cycles in alignment with electromyography of the masseter and anterior temporalis muscles – customization of software
   4. 1.3.4 1992: Replacement of the Sirognathograph with a customized K6-I kinesiograph instrument – rewriting of the software
   5. 1.3.5 2002: From K6-I to a customized and portable K7-I – the software is rewritten again
4. 1.4 From the 1980s to today
   1. 1.4.1 The bolus
   2. 1.4.2 The protocol
5. 1.5 Ready to start
6. References

1.1 Introduction

Mastication is one of the most important functions of the stomatognathic system. It is a highly coordinated neuromuscular operation and features rapid mandibular movements that demand continual modulation and adaptation to load. The nervous system, peripheral receptors (which determine sensory input), and the masticatory muscles (which produce the response from the brain and adaptation of movement) are continually involved during mastication. This is a complex process and plays a fundamental role in the quality of life for patients during childhood, maturity, and old age.

Mastication is a rhythmic and phylogenetically ancient movement. The best-known players in this process are the teeth; these are no longer a vital organ for humans (as they are for animals, for example), but they are still of fundamental importance both in terms of healthy functioning of the stomatognathic system and for social relationships. In fact, the peripheral input arriving from the periodontal receptors of teeth is numerically concentrated, sensitive, highly specialized, and extremely fast in reaching the neural centers allocated to masticatory control. Experimental studies on the topic have identified the mechanisms in animals during phylogenetic development that maintain and control the chewing cycles, mechanisms that are extremely precise in humans too. However, it is the cerebral cortex – which is so developed in human beings that it takes up half of the brain area – that controls the chewing pattern.

At this point, the “clinical physiopathology of masticatory function” becomes of specific interest, particularly the search to link masticatory function with dental occlusion, structural and neuromuscular structures, and the whole brain (Figure 1.1). This scientific interest emerged and was developed during the 1980s at the School of Orthognathic Studies in the University of Turin under the leadership of Professor P. Bracco. From the very outset, he focused on a functional, multidisciplinary, and especially gnathological approach to the diagnosis and therapy of malocclusions. The study and comprehension of masticatory function was supported by this underlying methodology, without which the research carried out would have been limited to the simple publication of statistical results without any true contribution being made to the improvement of diagnostic and therapeutic procedures. Such contribution is, however, the true objective of all research.

Figure 1.1 Linking masticatory function with dental occlusion, cranial structure, and neuromuscular activity.

In the fields of orthognathics and prosthetics, the study of occlusion is extremely important, particularly as the correlation between “occlusion” (involving the teeth of upper and lower dental arches), function, aesthetics, and social relationships becomes increasingly acknowledged. An understanding of the relationships between dental occlusion and neural control has been improved beyond question by gnathological knowledge of occlusion (Figure 1.2). It was also clear from very early on that, in order to understand and establish a meaningful clinical study, the gnathological base would have to be supported by an understanding of neurology. The concepts of functional occlusion and neuromuscular control are very close to the question of medical treatment of the psychophysical aspect of humans. This concept is clearly expressed in Springer’s International Journal of Stomatology and Occlusion Medicine, a title created by Professor R. Slavicek, one of the most important and dedicated modern-day gnathologists. Dentistry deals with one of the most refined anatomical areas of the body from a neuromuscular point of view – it has an incredible ability to adapt, which, instead of being abused, should be studied and understood in all its physiological aspects in order to allow treatments, “cures” even, that improve its functioning and, consequently, the general psychophysical health of the patient. We hope, then, that the study of mastication can help achieve this objective.

Figure 1.2 The stomatognathic system: relationships between dental occlusion, temporomandibular joint (TMJ) and neuromuscular control. Source for the muscles: redrawn from Neff (1999). Source for the brain: Purves et al. (2000). Reproduced with the permission of Sinauer Associates

The information gathered from chewing patterns is important in diagnosing the functional condition of the patient; for example, the repetition and variability of mandibular movement, neuromuscular coordination between the two sides, or the ability to adapt to load while chewing a hard bolus. As the brain is entirely engaged during chewing, the importance of this study from a clinical point of view is clear, but the technical, statistical–mathematical, and numeric difficulties have meant that only professionals working specifically in this field have been involved in the research so far. One aspect of evolution is to simplify complex processes, and this is the aim of this book, a first step in this direction. The fine-tuning of functional magnetic resonance imaging (fMRI) has allowed the study of neural control in humans, which we hope will permit us to better understand the functioning of the central nervous system.

The study of masticatory function began at the University of Turin in the 1980s, when the first devices for recording human chewing patterns were produced and sold. The necessary hardware and software were developed and fine-tuned over many years, thanks to the fundamental and collaborative work of the bioengineers Professor D. Farina and Dr A. Merlo. We will later look at the intrinsic difficulties encountered in the study of functional movement from a statistical–mathematical point of view, which were overcome thanks to the skill and effort of these professionals – without their contribution, none of the results later achieved would have been possible. Not only the bioengineers, but also many research...