There are many procedures encountered where the drilling of holes to specified depths is required. This is especially true in dental procedures. For example, when a dentist is involved in a procedure in which a hole or channel must be drilled in bone or in the canal of a root, several major hurdles and obstacles are encountered. Since the depth of the hole to be drilled is not visible to the naked eye as drilling proceeds, ancillary diagnostic equipment must be used to give an indication as to when the proper depth has been reached. This, in some cases, involves using x-rays to locate a probe in the canal or the hole in the bone. In some cases it involves the use of an electronic device in which the patient is grounded and a circuit completed between the patient and the metal instrument which is inserted into the canal.
The problem is especially acute in dealing with drilling into bone in dental implant procedures. In these cases, it is extremely important that a precisely constructed depth of drilling be obtained because the internal structures in the jawbones are filled with areas that could be seriously damaged were they to be struck with the drill. Such structures as nerves, muscles, and sinuses are especially vulnerable because the dentist cannot see these structures as drilling proceeds.
In practice, once the length of the canal or the location of sensitive structure is accurately determined, the dentist is then faced with the problem of fixing that length in a manner in which the depth can be accurately measured. Current techniques for performing this depth measurement as, for example, by holding the canal probe with forceps at the level at which it exits the canal, removing the probe and measuring the distance between the tip of the probe and the forceps, are cumbersome. The dentist can only estimate when the appropriate drilling depth has been reached. This technique gives rise to error and is fraught with the possibility of mishandling.
For determining the location of critical structures, measurements must be taken from x-rays and transferred to the drilling instrument. Yet there is no reliable way to transfer these measurements to the drill and maintain the same during drilling. The dental profession is constantly seeking new and alternative means for fixing the drilling depth of a drill in a simple way so that when drills of different lengths and diameter are used to drill a hole in bone or in a canal, the dentist will know that the appropriate depth has been obtained when a predetermined part of the drill has been reached.