A Twin-Block or Bionator is a removable appliance to treat Class 2 patients.

Twin Block Appliance  is a removable, orthodontic functional appliance that is used to help correct jaw alignment, particularly an underdeveloped lower jaw. They work by influencing the growth and development of both upper and lower jaws.

Class 2 correction appliances have been around for many years. From a laboratory perspective, an orthodontist would request a Twin Block as opposed to a fixed Herbst appliance in the 1980’s.  Fast forward to 2017, the request seems to be favoured more towards a fixed appliance, such as the AO Hanks Fixed Herbst Appliance.

In fact, the ratio of choice between the Herbst appliances to Twin Block appliance in our laboratory for a Class 2 correction is over 100:1 in favour of the former.

Twin-Block and Intra-oral Scanners

Now, with the growing popularity of intra-oral scanners, it is critical to scan the patient with the mandible advanced in Class 2 cases. In the early orthodontic digital days, an orthodontist would intra-orally scan a patient and then send the protrusive registration bite by mail or courier.

Having a non-protrusive bite on a Herbst appliance in not as critical as the AO Hanks, as this appliance has universal hinges and also cripple shims of varying thickness to allow much more flexibility and the ability to fine-tune the mandible advancement chair-side.

This is not the case with a Twin-Block. It is impossible to ensure that you have the correct angle of the space between the arches without canting an arch left to right or even antro-posteriorly when advancing the mandible (manually or digitally) by hand and eye.

If the patient has been intra-orally scanned with the mandible advanced (Fig1), we can create a virtual registration bite to ensure we mimic the exact scan (Fig 2).





This registration bite is then 3D printed and used as the advanced registration bite prior to the fabrication of Twin-Block no different to a wax or silicon bite given on the day.

Digital Orthodontics Victoria

If you would like to know more about Digital Twin Block Registration and how it can help your patients, contact us today.

Digital Ortho

Ari Sciacca – Director of Digital Orthodontics

With a proven track record, Ari has strong digital orthodontic laboratory experience. And using strategic thinking skills, Ari crafts solutions that meet clients’ business needs and add value. Specialties: lingual orthodontics appliance set-ups, digital advancements in both lingual and labial indirect bonding as well as Herbst appliances. Learn more

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