Discussion
Anterior extrusion, surgical impaction of the maxilla in adult patients,
or molar eruption control in growing patients can all be used to address
an AOB.10 There is currently no agreement on whether
surgery or non-surgical treatment is the most stable strategy for adult
patients with AOB.7,11 Several factors, particularly
those AOB etiological factors, influence the related stability (or lack
thereof). Tongue position and size, a persisting thumb sucking habit,
occlusal determinants, respiratory problems, and/or adverse hereditary
factors are just a few of them.1,12
In correcting this type of malocclusion aligners may be more effective
than traditional braces, because they have less of an extrusive effect
on the back teeth. Laura Talens-Cogollos et.al, recently in a
retrospective descriptive analytical study concluded that 74.2 % of the
subjects presented some degree of molar intrusion after
CAT.13 Straight wire mechanics tend to have an
extruding effect on the posterior teeth, which favors to aggravate the
AOB.14, 15 Anecdotal evidence suggests, that the
covering plastic on the posterior teeth help to intrude the posterior
teeth using the natural functional stomatognathic forces. Some also
believe, that a covering of anterior teeth with the aligners may aid in
the restraining of habits such as tongue thrusting. Despite the lack of
data to support these claims, several cases ranging from mild to severe
AOB have been treated successfully with the mentioned benefits of
CAT.6,11
A relative open bite / dental open bite usually presents itself
clinically by excessive incisor proclination.16 Among
dental components, Sabri17 claimed that proclination
of maxillary incisors can significantly reduce MIDR. This can be
corrected by reducing incisor proclination, resulting in a relative
extrusion of anterior teeth (drawbridge effect).11Additional intermaxillary elastics or optimized attachments are not
necessary for these maneuvers.
Arch expansion and/or interproximal reduction can help gain space in
both arches.
The arch shape, teeth size and of course the periodontal condition all
play a role in the screening of such cases.12 In case
of a mild open bite (eg. case 1), it is feasible to get enough relative
extrusion in order to fix the problem by CAT alone.14
The most demanding movements to replicate with aligners is clearly
dental extrusion. Tooth extrusion in CAT is greatly influenced by the
presence or absence of attachments. When pure extrusion of 0.5mm or more
is recognized, the software automatically places extrusive and
anchorage-optimized attachments.15 Conventional
attachments (with a beveled edge toward the gingiva) allow for
appropriate pressure from the aligner in order to extrude teeth. If
aesthetics are a priority, these attachments might be placed on the
palatal surface, too. In cases wherein greater aligner fit is required,
the attachments may be placed both on the labial and palatal
surfaces.18
Relative and absolute extrusion of the incisors are effectively
controlled by using large rectangular-shaped attachments with beveled
edges toward the gingiva - placed as incisally as
possible.19,20 Use of additional intermaxillary
elastics may aid with their extrusive movements in AOB cases of moderate
severity (as seen in case 2).
Often a clockwise (downward) rotation of the maxilla is associated with
an excessive lower anterior facial height (LAFH) going hand in hand with
a hyperdivergent pattern, resulting in increased gingival show when
smiling.21 The clinician’s task is to avoid any
posterior extrusion during leveling and alignment, as well as any
anterior extrusion that might exacerbate a gummy smile.
While treating a severe AOB, vertical control of the posterior teeth is
crucial. To resolve class II malocclusions with associated AOB, the
biomechanical technique using IZC screws allows posterior intrusion
generating a counterclockwise rotation of the jaw (shown in the case 3)
resulting in a reduced mandibular plane angle and an increase in chin
projection.22,23
Simulated rotation of the mandible in the ClinCheckTM analysis can be
helpful, if intrusion of the posterior segments is planned in such
cases.