About the issue of over-eruption, not much is known. A survey made in Sweden last year revealed that 85% of dentists belive that over-eruption is a common occurence when teeth lack antagonists in the opposite jaw, in spite of the fact that very little is known about this:

It is strange that this general belief that permanent teeth without antagonists overerupt, creating when very few studies in the literature support this. A recent study in Switzerland showed that after 10 years only a minority of teeth did in fact overerupt. That is when the teeth had been unopposed for a period of at least TEN YEARS !

In Scandinavia a combined orthodontic/prosthetic treatment of patients with advanced localized attrition has been used, a so called Dahl splint, which is a device used 24/7 that never allows tooth contact. Continuous
wearing of this partial bite raising splint for several months has been recorded with regards to overeruption. And it was really really small.

So the NTI, that will not come near that sort of use, is of no risk for teeth withot antagonists (teeth in opposing jaw) except in dentists' perception.

Bye for now,
Hans Lennros DDS  
hans@dentistry.se

PS: Some additional facts:

There are two types of supereruption: a quick one and a slow one. Extensive research has been done on this by
Prof BL Dahl in Oslo, Norway who started by cementing an anterior partial bite-raising splint on the lingual portion
of the upper front teeth as a treatment of patients with advanced localized attrition or low vertical dimension.
Professor Zackrisson, also in Norway, has later refined the technique which now is performed with clinical excellence.

Supraeruption of a molar due to the absence of oppsosing tooth contacts is mainly due to growth of the periodontium
(even if a raise of the dentoalveolar ridge cannot be detected by the naked eye). Later tooth movement beyond the plane
of occlusion is due principally to active eruption. The process takes a least a years. In the following early years after the
tooth loss, supraeruption is due mainly to periodontal growth. Such growth, however, does not occur when a tooth is in
even the slightest function.

Active eruption, with root exposure due to supereruption, is in fact, when comparing results, clinically similar to bone
loss due to periodontitis but should not be confused with that type of bone loss that has occurred around a former
periodontally compromised tooth.

There is one study from Kinoshita et al. that demonstrates that it will take 8 days of hypofunction (i.e., no occlusal
contact at all) of the molars before eruption of the unopposed molars occurred.  But the specimens in this study were
rats and not human beings. Rats are monophyodont, which means that they have one set of teeth during their lifetime.
In comparison, humans are polyphyodont, because we lose one set, then grow another. So the rat teeth need to grow
continously all the rat's life which menas that the "eruption- power" of a rat-tooth is far greaterh than that in humans.