active vertical corrector cannot achieve effective molar intrusion in adult patients

http://www.slu.edu/Documents/cade/thesis/Thesis%20-%20Shuka%20Moshiri.pdf

Skeletal anchorage systems

Many investigators contend that maxillary incisor
extrusion in adult patients may compromise the periodontal
structures, lead to root resorption and ultimately
jeopardize smile esthetics.54 Other authors have shown
extruded teeth to be less stable than intruded teeth55 and
have, instead, turned their efforts towards posterior
intrusion.
Molar intrusion is often needed if a skeletal open
bite is to be corrected non-surgically.
56 The use of
skeletal anchorage systems, such as mini-implants and
miniplates, has been promoted for closure of anterior open
bites via molar intrusion. The studies conducted have
shown promise, with true maxillary and mandibular molar
intrusion leading to counterclockwise rotation of the
mandible and, consequently, closure of the bite.54, 56
Concomitant reduction of the mandibular plane angle and
anterior face height usually follow.
Other advocated treatment alternatives such as highpull
headgear, vertical chin cup, vertical holding
30
appliance, or an active vertical corrector cannot achieve
effective molar intrusion in adult patients due to lack of
rigid anchorage.56 Presumably, open bite closure through
posterior intrusion and little to no anterior extrusion
leads to more stable outcomes.
55 Baek et al.57 investigated
the long term stability of anterior open bite correction
after intrusion of maxillary posterior teeth; they observed
22.88% relapse of the maxillary molars and 17% relapse of
the incisal overbite after a three year follow up period.
Unfortunately, the majority of literature involving
skeletal anchorage and open bites are case reports lacking
long-term follow up studies examining stability.20

Fixed appliance therapy
Most of the literature evaluating the dento-skeletal
effects of open bite therapy is centered on early treatment
of growing patients. With the exception of case reports,
there is a lack of sound data examining the effects of
fixed appliance therapy in adult anterior open bite
patients. When Remmers et al.58 evaluated treatment results
and stability in a large group of anterior open bite
adolescent patients, they discovered mean overbite
increased from -3.2 mm pre-treatment to .4 mm posttreatment,
with 71% of the sample obtaining a positive
31
overbite. Mean values for MP-PP and SN-MP decreased
insignificantly, while the mean value for SN-PP increased
insignificantly post-treatment. There were no appreciable
differences in these angular measurements over five years
post-treatment. The relapse rate was 27% five years posttreatment
and, overall, 44% of the sample had an open bite
at five years follow-up. The authors admit, “The poor
treatment response between Ts and T0 in the present study
raises the question whether conventional edgewise treatment
can adequately control the vertical dimension.”58
One variation of the MEAW technique uses upper
accentuated-curve and lower reverse-curve NiTi arch wires
with intermaxillary elastics; this theoretically offsets
the anterior intrusive forces of the wire and allows the
posterior intrusive forces to take effect while extruding
the anterior teeth. Once incisal overlap is achieved,
stainless steel wires are placed and patients are directed
to wear box elastics. Kucukkeles et al.59 observed the
dentofacial effects of this method on adult anterior open
bite patients and found that LAFH increased significantly
by 2.5 mm (p < .001) post-treatment, which the authors
believed to be a consequence of molar extrusion.
Interestingly, the mandibular plane angle was maintained
throughout treatment. SN to the functional occlusal plane
32
(FOP) decreased by 2.09˚ (p <.01) and the FOP-MP increased
by 2.38˚ (p <.001). The counterclockwise rotation of the
FOP can be accounted for by the extrusion of the lower
premolars and uprighting of the lower molars. Upper and
lower incisors and first molars were all extruded while
being uprighted. As compared to the MEAW technique, this
method proves to be more efficient, hygienic and
comfortable for the patient. However, bite-closure is
primarily achieved through extrusion of the incisors which
is not always ideal, particularly in those individuals
already presenting with excess gingival display at the
outset of treatment.

Surgery
If patients present with a true skeletal open bite, a
combined surgical-orthodontic approach is often encouraged
to attain an esthetic and stable treatment result. A common
surgical technique utilized for skeletal open bites is
posterior maxillary impaction. Superior repositioning of
the maxilla allows for autorotation of the mandible,
closure of the bite, and a decreased LAFH.
60 If the open
bite it not severe, however, it is hard to justify the
risks and trauma involved with surgery to achieve a
correction with no guaranteed stability.