This article is about the click and clatter of teeth.

There was a time in my professional career, that I tried to assess the condition of the bite of my patients by listening to the sound of maxillary and mandibular teeth occluding. At those times, I had the habit to grab the jaw of my patients at my hands and carefully guide my patients to close their jaw “right”. Sometimes I could feel with my hands the uninterrupted relaxed jaw movement and the sharp click-sound produced by simultaneous contact of the maxillary teeth opposing with the teeth of the mandible. I often wondered – that can’t be bad. On the other hand, I very often realized that the muscles of my patients were tense and did not allow relaxed closing. A dull, crash-landing noise is characteristic for the unrelaxed and tense bites. Normally, these patients did not complain so much, they seemed to be happy with their bites. Yes, they had the habit of biting a little bit more to the more comfortable side of dentition, but they could live with it. I sometimes tried to change the way they bite. I reasoned that there must be premature occlusal contacts that prevent them from closing their jaw in a relaxed manner. To my dismay, it was very difficult to decide, where in the dentition of my patients the problematic occlusal prematurities happened. However carefully I tried to guide the closing path of the mandible, the ink from the occlusal foil did not always reliably mark the prematurities of occlusion in repeated measurements.

In my previous articles I have presented a hypothesis, the “Philosophiae Naturalis Principia Masticatoria”. It is a novel approach to explain the function of the masticatory system. In my thinking, the afferent information from occlusal contacts from different teeth are guiding different groups of masticatory muscles. The front teeth are inducing an opening reflex, whereas the premolar and molar teeth induce a closing reflex by triggering activity of masseter and temporalis muscles. When the front teeth feel pressure different things happen with the muscles as compared to when most of the occlusion contact point force pressure is felt by the back teeth. I intend to demonstrate my point by making you listen carefully to the sounds of bites.

Don’t I love to hear the perfect click-sound when the patient bites with a perfectly equilibrated dentition. The undisturbed, relaxed closing of the jaws brings simultaneously all the contact points together between the upper and lower jaw. It is a soundbite that makes the clinician dentist immediately  feel rewarded. The filling he/she just made, fits perfectly.

The click-sound – is it a hallmark of quality of occlusion?

How many times did you hear the happy clatter of your patient’s teeth, but nevertheless, the same patient came to you six months later with a fractured cusp of a molar tooth. Should I rely on the sound of occlusion only, or is there something else I should know about the jaw-closing business?

Normally in my office, when I ask a person to open and close his/hers jaws, he/she closes the jaw with a vertical down-up movement. Unlike when chewing a piece of food, there is no lateral excursion of the mandible. Ideally, the closing path of the mandible follows an uninterrupted arch form, at the end point of which all the teeth occlude simultaneously.

modified from www.pocketdentistry.com

You can test the sound of your own bite. Should you happen to be one of the fortunate ones that can make a click sound with your jaw-closing, then try tilting your head a little to the left or right, you’ll probably hear the sound of your bite changing – the gravity pulls your mandible out of the maximum intercuspal position (MIP).

The Tscan is a tool to investigate the sequence of events that happen when the mandibular teeth occlude with the teeth of maxilla. The force/time graph, which is shown below the 2- and 3-D occlusal charts in a Tscan movie, indicates the first occlusal contact with a mark “A”. Mark “B” appears when all the points of occlusal contacts have been met.The video shows the points of occlusal contacts accumulating from the earliest initial contact in point A, and followed little past point B.

The A to B part of the Force/time graph is an important parameter. It is a tool of what the previous generations of dentists and occlusion -scientists could only dream of. A long time elapsing between the time points A to B is indicative of prematurities of occlusion. The “normal and physiologic” closing time from the earliest first tooth contact to the MIP is generally agreed to vary between 0,1-0,2 seconds. Would there be a premature occluding contact, we can assume that the closing path of the mandible should have to be altered. Adjustment would take more time. It would take miniature zig-zag-movements and muscle work for the mandible to find its way to the MIP. A microsecond after the first tooth contact a second contact would follow, after a few microseconds later a third one, and up to the umpteenth tooth-to-tooth contacts before the mandible would lay securely in MIP. There can’t be a click sound there, it rather sounds like a soft, jumpy crash-landing of the mandible against maxilla. The duration of the time that it takes from the first occlusal contact, to the full amount of all occluding contacts in MIP is directly related to the sound of jaw-closing. The more evenly the occluding points meet, the faster is the closing time, the sharper and louder is the click-sound and the less there is need for muscles to adjust the position of the mandible to match that of the maxilla.

To find out what my patient’s occlusion time is, it would not make sense to assist my patients by guiding their jaw-closing with my hands. For a Tscan user it is obvious that the occlusion is a finely tuned neuro-muscular event and it is our mission to try to understand the dynamics of occlusion undisturbed, in vivo. The repeated Tscan movies reveal to me, where the premature contact points are. The beauty of the Tscan is that I can be assured that I know where the trouble lies in my patient’s dentition. Grinding off a forceful contact point of a tooth, of course, should be kept to minimum. It is always with a heavy heart that I proceed to shorten an elongated cusp tip of an otherwise healthy tooth. I normally run a low-speed flame-shaped red grit diamond at 40 000 rpm. A few gentle sweeps of the surface of enamel (or hopefully of filling material) can’t take more than micrometers off the load-bearing points. I routinely perform the equilibration with repeated Tscan measurements between the grindings. The “Force Outliers” feature of the Tscan software points out which teeth are subject to rapid increase of relative occlusal force during the A to B phase of closing.

On a Tscan movie the distribution of occlusal forces in the dentition can often be severely skewed. The forceful contacts may be totally asymmetric in the different parts of dental arch. However, even the highest force outliers in the molar and premolar area can very often go unnoticed by the patients. The closing time from A to B, however, can be very short despite there are markedly forceful contacts here and there. I often ask the patient does he/she feel that there would be a point in his/her occlusion that feels more forceful than elsewhere. If I get an answer “Yes”, the patient most often points to some tooth in the anterior area. The force outliers in the back teeth do not seem to disturb the patients. The high forces hitting the back teeth do not seem to slow down the occlusion time either.

Then what about the sound of bite? Did I not just earlier say that I love to hear the click of unison? Yes, despite unevenly distributed high forces in the molar and premolar area, the sound of closing can be a sharp and loud click….

Grinding down an obvious spot of excess occlusal force in the back teeth very often goes unnoticed by the patient. In my practice, I have chosen not to start the equilibration with the forceful contacts of the back teeth. Instead, I always start from the anterior contacts. I have found that it is almost always after I have leveled down the forceful contacts of the anterior area, that the patients report any relief of jaw-closing. The leveling down the anterior force outlier contacts is the easiest way to shorten the A to B time. Time after time I have been surprised to find how little it takes of enamel grinding of the anterior teeth to produce the desired relief in occlusion. Shortening of the occlusion time follows, and yes, the initially murky sound of the bite changes into a sharp click. The data from the Tscan movies supports this phenomenon. Leveling down the excessive force outliers of the anterior teeth effectively reduces the occlusion time.

To sum it up, the click-sound of occluding teeth in itself is not necessarily a sign of  healthy occlusion, but the absence of a click is always a sign of tense and slowed-down closing reflex. The sensory organs of the front teeth react to force outliers in microseconds. A very rapid muscle reflex ensues to slow down the momentum of up-surging mandible. In contrast, should the force outlier contact point happen in the premolar and molar region, no such slow-down of mandible happens. This is because the back teeth must produce a qualitatively opposite reaction to force outliers as compared to anterior teeth.

The soundbites of sound bites corroborate the basic tenet of Philosophiae Naturalis Principia Masticatoria. The front teeth are different from the back teeth. To make the dentition occlude with evenly distributed occlusal forces, it takes little more than just listening to the clatter of teeth. A Tscan is indispensable for the work…