Learn Orthodontics

Impressions for Functional Appliances

Usually you are taking impressions for study models at the same time as designing the patients removable appliance. In this case it is not normally necessary to take separate impressions for the appliance.

However, if you are taking an impression only for the construction (or repair) of a functional appliance. You must take an impression of both arches.

Bite registration for Functional appliances

There are two techniques for taking the registration for a function, try both before deciding which you prefer

Method 1

  1. Explain to the patient what is required, ie that they posture forward to the required occlusion. NB Do not over posture the patient or place them into a class III relationship.
  2. Soften 2-3 sheets of pink modeling wax in hot water, folding them into a horseshoe shape.
  3. Place them into the patient's mouth and get them to close into the postured position. You must ensure that the centre lines are correct.
  4. bite 9
  5. Remove the wax registration and chill the wax under cold running water, cut away the wax as shown in the canine/premolar region
  6. bite 1
    bite 7
  7. Place back into the mouth to check the registration is correct - the lateral opening and that the centre lines are correct.
  8. bite 6

Method 2

  1. Use either a thick or thin 'bite fork'. The 'ProJet' bite forks are available in thick for when an overbite needs reducing and thin for normal or reduced overbites. In the photograph below the thick one is yellow and the thin is blue
  2. bite 5
  3. Explain to the patient what is required, ie that they posture forward to the required occlusion.
  4. Place the bite fork into the mouth and ask the patient to practice biting into the required position NB Do not over posture the patient or place them into a class III relationship. Place the single notch down and the middle notch to locate the upper teeth (this is opposite to the ProJet instructions, but is much easier for patient and operator)
  5. bite 8
  6. Remove the bite fork and chill the wax under cold running water.
  7. bite 4
    bite 2
  8. Place back into the mouth to check the registration is correct.
  9. bite 3