The Course on Functional Diagnosis in Prosthetic Rehabilitation, given by Dr. Mas on 29th September 2016, placed special emphasis on analysing the respiratory, masticatory and deglutory functions when proceeding with Dental Prosthetic Rehabilitation.

Said Rehabilitation should be carried out when:

  • Fitting porcelain veneers or crowns from one side of the mouth to the other.
  • Fitting crowns on implants from left to right.
  • There is an upper and/or lower overdenture on the implants
  • Fitting classic full upper or lower dentures.

In the event of respiratory, deglutory or masticatory pathology, the prosthesis may suffer a number of problems when adapting due to movement, fractures or wear.

Prior to implementing a prosthetic rehabilitation, we must look at the following aspects, which can reveal a pathological function:

Buccal exploration

  • If pieces are missing, the teeth move, are tilted, broken or extruded, the mouth will adapt to the new situation by changing position and altering the bite. As the jaw tries to move into a more balanced position, the teeth may suffer wear or bruxism. Also, on changing contact with the cranium, a TMD pathology may occur, such as pain when chewing, headaches or clicking.
  • Worn teeth: bruxism occurs when wearing of the top teeth corresponds to an issue with the bottom teeth. Otherwise, it could be due to chemical corrosion caused by vomiting (anorexia or bulimia), acid reflux or the excessive intake of acid drinks.
  • We must establish which teeth are most worn: front, back, those on one side or the other, since this will tell us what kind of bruxism we are dealing with.

Facial exploration

  • Tense, thick cheeks could be due to masseter muscle hypertrophy and, therefore, to bruxism.
  • Labial incompetence, where the lips fail to contact while in repose; this may mean breathing through the mouth, which entails a narrow palate and occlusion or insufficient bite. The causes for not breathing through the nose must be studied and a solution found, such as correction of nasal septum deviation, or extraction of the adenoids obstructing the nostrils.
  • Furthermore, the patient must receive functional re-education from a speech or physiotherapist so that they learn to breathe through the nose instead of through the mouth. Once completed, we can proceed with a prosthetic rehabilitation. Often preliminary orthodontic treatment is required.

Neuromuscular exploration

We must learn to recognise functional alterations when inspecting and palpating the patient.

Poor jaw position can affect the way a patient breathes and swallows, the shape of their face and the position of their head in respect to the trunk.

  • If the face is elongated, with separated lips while in repose, the patient breathes through the mouth.
  • If the patient’s head is tilted forward, it is to enable said breathing through the mouth. In cases such as these the cervical vertebrae may be affected with pain, muscle strain or dizziness.
  • The dentist must palpate the neck muscles, the masseter muscle in the jaw and the temporal muscles in the cranium to check whether or not the patient has bruxism, and to find out whether they are in pain. Pain is a symptom of muscular hyperactivity.
  • Remember that if the relationship between the cranium and the cervical vertebrae is not correct, it will affect the relationship between the cranium and the jaw. In other words, the pathology of the cervical spine can have an effect on the cranium-jaw relationship and, therefore, on the bite.

Mechanisms which produce bruxism

  • The nerve ends inside the tooth, as well as detecting heat or cold in food, transmit the pressure of one against the other to the brain. This means that, when they are in occlusion, i.e. with the bite closed, the brain detects whether or not the teeth fit properly against one another and that they are in the correct position.
  • The central nervous system processes these contacts and instructs the lateral pterygoid muscles to align and centre the jaw with the superior maxilla. The elevating and depressing muscles then take action and maximum intercuspation occurs, i.e. maximum contact between the masticatory surfaces. This means that the jaw position is registered by the brain.
  • Different changes in tooth position, due to extractions or inappropriate reconstructions, can cause changes in the jaw position. Thus, during mastication, the teeth look for a comfortable position to go about their function and sometimes those that get in the way of maximum intercuspation or contact suffer grinding, causing bruxism.
  • Furthermore, if the jaw articulates in an inappropriate position with the cranium, it can cause pain in the TMD, particularly in the case of bruxism.
  • On the other hand, when the patient cannot breath through the nose and instead uses buccal respiration, they sometimes suffer vibration of the soft palate, otherwise known as snoring, caused by a lack of oxygenation or intermittent hypoxia. This leads to hyperactivity of the Sympathetic Nervous System, with increased activity of the masticatory muscles, causing bruxism and tooth wear.

Mandibular and dental position in the new rehabilitation

  • This must be well balanced, and the mandible well positioned. It must be done in the so-called Centric Relation, which is a stable skeletal muscle position. This is when the muscles are relaxed, not in tension.
  • The dental cusps (elevations between the crests) must be well marked for good contact and in their correct place, with the lower teeth matching the upper ones. If the premolars and molars are flat, they meet in different positions, and the brain is confused as to where to place the jaw.
  • In the case of a rehabilitation on implants, it is better for the teeth to be screwed to the implants than to apply a cemented prosthesis. If the prosthesis is screwed on and occlusal overload occurs, the screw should be loosened rather than overloading the implant, which would break or lead to high bone loss.
  • The objective of a good prosthetic rehabilitation, as well as aesthetics and proper masticatory function, is to ensure that no muscular activity (bruxism) occurs while sleeping or in repose.