Drill a bit,  not too far.

In the tooth is a nerve:

do not disturb it

It would not have been fair to my patients if I had written what follows before I had retired from practising dentistry. If I had been one of my patients, I might have lost confidence in my dentist after reading this.

Before dental students are allowed to drill teeth on living patients, much training is required. A great deal of this is done using plastic teeth mounted in the jaws of the heads of a mannequin, known as a ‘phantom head’. The plastic teeth are held in the artificial jaws with metal screws. The screws fit into holes on the undersides of the teeth so that the crowns of the teeth appear intact. As a dental student, I spent many hours each week practicing cutting standardised cavities. The cavities had to be cut to very precise dimensions, which were neither to be exceeded nor the opposite. I recall that certain parts of the plastic teeth had to be cut to exactly two millimetres deep and much the same width. At first, I found this extremely difficult. Not only was I not yet used to using dental drills, but also the plastic cuts in an awkward way.

Eventually, the time arrived for a practical test. Unsupervised, we were required to cut one of the several cavities that we had been learning to prepare. Disaster struck. Within a few seconds of starting my tooth, I had cut too deep. The metal of the screw retaining the plastic tooth in the phantom head was staring me in the face. I called over the examiners. They studied the tooth carefully, and then one of them said to me:

“I think you have exposed the nerve, Mr Yamey.”

“We might be looking at a root treatment, here, don’t you think?” asked the other examiner.

I could not believe what I was hearing.

“I think we’re looking at a failure here,” I replied.

They agreed.

I spent another few weeks in the phantom head room, and retook the exam, which I passed with flying colours, you will be relieved to learn. Now, I was deemed ready to treat dental cavities on real teeth in real patients – under supervision, of course.

The first tooth that I had to work on had only a little decay. Nevertheless, after the intense training, which emphasised cutting teeth should be done as conservatively as possible, cutting only as little of healthy tooth tissue as was strictly necessary to retain the restoration (‘filling’), I approached my first ‘real’ tooth with much trepidation. After boring down to the two-millimetre depth that was ingrained in my mind, I could see nothing but healthy tooth – no sign of decay. I summoned the clinical teacher (the ‘demonstrator’). He looked at the tiny hole I had created with great care and laughed.

“You have not yet cut through the enamel. Keep going,” he said.

The enamel, for those who are uncertain about dental anatomy, is the outer covering of the part of the tooth that is visible in the mouth. Beneath it, is the dentine, and below that the dental pulp chamber, which contains nerves and blood vessels. Decay spreads much more rapidly through dentine than through enamel.

I looked at the demonstrator, and said:

“But in the phantom head room we were told never to go deeper than two millimetres.”

“Those were just plastic teeth,” the demonstrator replied, “forget all that.”

[Picture from “Der Zahnarzt in der Karikatur” by E Henrich]