One problem with orthodontic-orthognathic surgery combination therapy is that we do not know the actual problem too well. What are we mainly dealing with? Is it Angle Class II or Angle Class III problems? Is it deep bite or open bite problems? Is it crossbite problems? To our understanding the basic question of epidemiology in this specific treatment approach was too seldom addressed in the past. However, a sound knowledge about this aspect would help to better meet our patients’ demands and educate the postgraduate students in both specialities.

In the first part of this lecture we will report on an investigation we did concerning the above described topic. Of course, the results of such studies depend very much on the population evaluated. To facilitate an international comparison we like to encourage other researcher to repeat such a study.

Another problem is that whenever an individual patient is treated with a combination therapy the oro-maxillo-facial surgeon and the orthodontist have to find out about the best surgical procedure. For this reason they have to simulate the operation on models of the patient. Hereby the problem is that in average operation simulation systems one (pair of) model(s) is needed for every different approach. Also one cannot be absolutely sure how much material was lost during sawing the model(s).

The alternative is to use an operation simulation system which was developed in our department. Apart from unimaxillary segmental osteotomies it works without destroying a patient’s models and all displacements in the three dimensions of space can be exactly and reproducibly registered. Therefore with respective care all necessary splints for one patient can be fabricated with one pair of models. Another advantage is that the system is very low priced.

One more severe problem in all patients with fixed appliances is restricted oral hygiene. The problem is aggravated in surgically treated patients with intermaxillary fixation. One possible solution of this problem could be the extensive use of air polishing devices. However, the questions which subsequently arise are:

Do these devices harm the enamel by roughening it or do they cause intolerable substance loss? How if dentine or cement is exposed? How are adhesives affected if they are air polished? Does air polishing have a negative effect (increased friction) on brackets and orthodontic wires? How valuable are air polishing units in general for an improvement of oral hygiene. Due to a thorough evaluation of different air polishing devices all these questions can now be answered satisfactorily.