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.