Clear Aligners are designed to deliver a balance between rigidity and flexibility in order to move teeth, while also being thin, transparent and comfortable. Bruxism can exert significant forces on these devices, so it is important to think about clear aligner suitability, material choice and impact bruxism can have on the orthodontic treatment as well as the aligner itself.
Clear aligners are not indestructible; they are carefully designed, thin plastic devices which can be damaged by incorrect removal as well as more sustained forces such as grinding. Very little evidence exists around the impact of bruxism specifically but the intraoral environment certainly has a detrimental impact on the mechanical properties of the aligner.
A recent study (link) showed that despite no detectable chemical changes, the elastic index and hardness reduced after wear. A second study (link) showed that there was no difference in wear indices between 1 and 2 week wear schedules.
In a sense, yes they can be. Regardless of the plastic type used, severe bruxism can cause wear and structural weakness at key points, increasing the chance of breakage.
Tooth morphology can also impact the thickness of aligners at various points, studies (link) have shown that aligners are generally thinner anteriorly regardless of plastic type. The aligner will therefore be thinner around ‘pointy’ areas, and this is where breakages can occur.
If your patient is a severe bruxer, we suggest potentially requesting your treatment plan is adjusted so that the patient can switch aligners more often. This will prevent the likelihood of an aligner breaking.
Clear aligner plastics range from 0.5mm-1mm, and 0.75-0.8mm is the thickness most commonly used, regardless of the plastic type. Part of the appeal of clear aligners is their subtle, comfortable nature; therefore, a balance must be struck between multiple factors from patient comfort, durability and the orthodontic forces applied. The thicker the material the higher the forces (link), the less comfortable the appliance will be for the patient and the more retentive the aligners will be.
At times, the thicker 1mm aligner material may be chosen if wear due to bruxism is occurring, but this will be less comfortable for the patient, which may impact compliance. Additionally, factors that can further increase retention should be taken into account, such as recession or edentulous spaces.
In short, no. The majority of published literature shows no significant impact on bruxism, although there may be an increase in masticatory muscle activity at the start of treatment which settles over time.
One study (link) looked at patients with existing sleep bruxism (SB) and treated them with occlusal splints, clear aligners and a placebo splint for 6 months. They found no decrease in the sleep bruxism index for the patients wearing clear aligners overall. However, it was observed that in the earlier stages of treatment (month 1 and 3) there was a slight increase in phasic contractions related to SB in clear aligner wearers compared to placebo. Another study (link) looked at healthy subjects wearing clear aligners over a 5 day period and found no evidence that clear aligners caused an increase in SB or masticatory muscle activity, although there could be a short term increase in masticatory muscle soreness during the first 4 weeks of treatment (study (link)).
There are very few high quality studies on clear aligners and bruxism, and it is important to be honest with patients about this. Based on the available evidence it seems that clear aligners seem to neither cause nor reduce SB - baseline activity appears to remain the same on average over the course of treatment.
However, given the lack of robust evidence and given an individual’s perception of jaw pain/tension varies, it is probably sensible to consent for a potential increase or no change in jaw discomfort, particularly at the start of treatment.
The one aspect that aligners can help when it comes to bruxism is protection of the occlusal surfaces of the teeth, as long as the plastic has not been worn down. Many times patients are appreciative of this throughout treatment and can get a thicker night guard fabricated following active orthodontic treatment.
Bruxism is not an absolute contraindication to clear aligner therapy, but severe bruxism may increase the chance of breakage. To mitigate this, you may choose to prescribe a slightly thicker plastic, programme in less movement per aligner to allow for a shorter wear schedule, or prescribe an alternative orthodontic device. This will need to be accompanied by additional patient education to align expectations.
Much more research is needed into the effects the intraoral environment on clear aligner efficacy, as most research is carried out in-vitro.