Monday, 17 May 2010

Class II div 2 Deep Bite, Where is the Limit

Patient is 46 years old with a severe Skeletal class II div 2, with extremelly retroclined incisors as you can see from the above pictures.

With patients like this a question arises as to where is the limit is biomechanic and biologically wise. The aim in this case is to intrude and torque those four front teeth with the minimum overjet-proclination possible, unlocking the bite and giving room to the patient to protrude her dorsally forced mandible to a more relaxed position.

The mechanics that would be the most consistent to the movement needed would be a controlled tiping movement with center of rotation close to the tip of the crowns, moving-retracting the roots back while keeping the crowns, thus correcting the torque of the four incisors. To apply that force system one would have to consolidate the four front teeth and with long power arms higher than the center of resistance of the complex apply the force palatally, to a TPA (transpalatal bar)

In this case a quadhelix was used to expand on the sides, gaining space from the transverse expansion to retract later the front, diminishing the overjet, and a CuNiTi (0.016) with a 17x25 TMA overlay arch as you can see on the following picture:

In 5 months the situation in the mouth is the following, with some spaces created due to not figure-eight legating the segment (which was figurated at that point).

Up to this point, no bite raising was used, and the vertical overlap, even though the incisors inclination was corrected, it was reduced. Removable bite plateau was given to the patient and start of Class II elastics.
Before and after is  shown on those two pictures:

and intra-oral on that phase (with two vector mechanics to intrude slight and tip back the four front closing the space between laterals and canines):

The mandible unlocked and came forward, in this case however there is always a risk of dual bite on those patients: In that case, 
1)you can accept the dual bite if patient is not bothered, 
2)you can extract 2 premolars on the upper and finish distal, if the face allows it, 
3)you can refer to surgery,BSSO and mandibular advancement, 
4)you can reconstruct prosthetically the occlusion to the protruded position.

In this case none was needed as the mandible came forward.
  • The question however of the limits in those severely retro-clined incisor cases remains un-answered
There are cases that even with the correct mechanics applied, the incisors inclination cannot be corrected or as it is said clinically "they are not coming".

The only thing that could perhaps give an idea to the clinician as to where the limit is of his patient, would be:
1)the palatal cortical bone and the distance from the roots, as to how much the teeth can be retracted, and
2)the distance of the apexes to the floor of the nasal cavity, as to how much they can be intruded.

The optimal way to measure the above is the lateral cephalogram of the patient.

This is another case with sever Class II div 2, that the result although correct mechanics were applied is not optimal, the incisors could not be retracted and intruded more, and in this case 2 premolar extraction might have been an option. These are initial and final pictures after orthodontic and prosthetics:

You can see that this is a compromise both on the vertical as the bite is still deep and on the torque as the front is still steep.

If you take a closer look on the initial cephalograms of the first case and this last one:

successful case


You can clearly observe that the nasal floor on the lower X-Ray is much closer to the appex of the root of the four incisors, giving less room for intrusion in this case, when compared with the anteriorly inclined maxilla and the room for intrusion on the first X-Ray.
  • This observation might give the clinician in those difficult cases, an extra "tip"towards what treatment protocol to follow.
This is of course in no way scientifically based as there are no studies in the literature for the matter, as it is this is simply a case report, with some clinical observations, and can only be taken as such.

p.s. Case is in treatment at the OR Department of the Aarhus dental school, by Dimitris Galaktopoulos, DDS, under the supervision of prof. Dr odont, B. Melsen.

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