I remember the first time I dived into the world of aligners. In those first trainings, they showed us the strengths and weaknesses of invisible orthodontics. For example, an open bite case could be easier to treat with aligners than with braces, thanks to the intrusion produced by the forces exerted by the patient on the aligners in the posterior area. However, these forces, which are so useful for closing bites, can work against us in cases of augmented overbite.
We should not generalize, but the majority of patients with deepbite have an increased muscle tone and tend to grind. In these patients it is easy to see how an unwanted intrusion occurs. This effect is difficult to avoid, even with bite ramps, as the bite ramps that are on the aligners are not as effective as the bite ramps that we place with fixed orthodontics for two reasons:
- Bite ramps are removable, they are part of the structure of the aligner. As they are not fixed to the teeth, when the patient removes the aligners, they have no effect.
- Usually, they have less contact than bite ramps placed with brackets. They can even be useless in cases with large overjet, as they have a limited length and in these situations they will not make contact with the lower incisors.
To overcome these shortcomings, other strategies are available, such as making "hand-made" bite ramps and scanning the patient so that they can be manufactured in the aligner. We will discuss this topic in another article.
In the first studies published about the effectiveness of aligners and brackets in correcting deepbites, they found that brackets were far superior to aligners (approximately 50% more effective). Years later, the performance of aligners in cases of deepbite has been re-analysed and surprisingly they have found similar efficacy to brackets. It is true that there are always differences in the methodology of the studies, but it is interesting to see how, since the appearance of G5, the results have improved. The advent of bite ramps, optimised attachments and Smart Forces designed specifically for this malocclusion, together with the increased understanding of aligner biomechanics, have made it possible to treat these patients and achieve acceptable results.
In the study by Fujiyama et al. we see how the overbite correction with braces produces a greater posterior extrusion compared to aligner treatment and, when correcting an overbite with aligners, it will be resolved mainly by anterior intrusion (1 mm of intrusion of upper incisors and 2 mm of intrusion in lower incisors). Depending on the vertical dimension of the patient, the extrusion produced with braces may or may not be favourable, as it will increase the vertical dimension and, in adult patients, this may cause a clockwise rotation of the lower jaw. With aligners we can achieve better control of the vertical dimension, but we will be very limited if we want to correct the overbite with posterior extrusion.
However, there are other factors beyond the aligner system that are essential to understand the difficulty of the overbite to be treated:
- Pure intrusion vs. relative intrusion: pure intrusion is a less predictable movement than relative intrusion produced by proinclination of the incisors. Depending on the anterior inclination of the case, the correction of the overbite will be more or less predictable. In a case with negative torque, we will plan more proinclination and, therefore, it will be easier to correct the overbite.
- Crowding: the greater the amount of crowding, the easier it will also be to resolve the overbite, as the correction of crowding is always associated with a certain amount of proinclination, even when stripping is planned. For this reason, when we face a case with all the anterior teeth aligned, we should be aware that it will be more difficult to achieve their intrusion.
- Amount of teeth to intrude: when measuring the overbite, we look at the number of millimetres that cover the upper incisors to the lower incisors, but not all overbites are the same. A 100% overbite on lower incisors with relatively well positioned canines is not the same as an overbite where both canines and incisors are equally extruded. The intrusion of the incisors will be more predictable than the intrusion of the whole anterior group (canines and incisors).
For the same value of overbite, each case will present a different degree of difficulty, which is why we cannot rely only on numerical diagnosis. It is advisable to analyse the patient's clinical conditions in detail and determine the viability of the case with invisible orthodontics on the basis of these conditions. Once the complexity of the malocclusion has been discerned, we can decide whether auxiliary tools, such as micro-screws, are necessary or whether aligners are sufficient to resolve the deepbite.
Krieger E et al. Invisalign treatment in the anterior region: were the predicted tooth movements achieved? J Orofac Orthop 2012;73:365-76.
Fujiyama K et al. Comparison of clinical outcomes between Invisalign and conventional fixed appliance therapies in adult patients with severe deep overbite treated with nonextraction. Am J Orthod Dentofacial Orthop 2022;161:542-7.