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Twin Block



Can the Twin Block appliance be used on my 13.5-year-old son who has a bone age that matches his chronological age and who presents a 9-mm discrepancy (overjet) in a Class II molar relationship?
In France, the only treatment suggested to me was the use of bands with elastics. I was even told that a discrepancy between his upper and lower jaws will remain.
How can I find an orthodontist who will accept to use the Twin Block appliance?

I would like to try something efficient to prevent him from having to undergo a surgery later.

Thank you for your answer.




For the internet users’ benefit, I will first describe was is a Twin Block appliance and provide one or two articles in the literature about the subject. We will also answer the following question: Is it the best appliance to correct your son’s problem?


Twin Block

Twin Block-Dr Chamberland orthodontist in Quebec City

Upper bite block with an expansion screw, headgear tube, inclined plane and labial bow. Lower bite block with a labial bow and inclined plane.

Twin Block is a removable functional appliance composed of 2 elements. The upper bite block covers the posterior teeth and ends with an inclined plane. The lower bite block covers the primary molars and first premolars. When the teeth close together, the inclined planes articulate and force the lower jaw to posture forward.

Twin-Block-Dr Chamberland orthodontist in Quebec City

1- Headgear tube. 2- Area where the inclined planes meet. 3- Anterior lower bite block. 4- Posterior upper bite block.

The front and profile views show that the lower jaw is postured forward when the inclined planes interlock. The acrylic pads create an anterior open bite and the upper teeth cannot touch the lower teeth.

Literature review

Two comprehensive articles were published on the use and efficiency of the Twin Block appliance compared to the other functional appliances.

O’Brien et coll. published in 2009 a study that spanned over 10 years. Its purpose was to study the efficiency of an early treatment to correct a Class II division 1 malocclusion. 89 children from 8 to 10 years of age got a treatment using a Twin Block appliance and 85 children of the same age did not get any treatment and served as the control group. The control group then received a treatment using a Twin Block appliance. The control group started their treatment at 12.1 years of age in average. The “early treatment” group started a second phase of their orthodontic treatment at 12.4 years of age in average.

The conclusion of this study is:

1- The results from the early treatment group with a Twin Block appliance followed by a second phase of treatment with fixed appliances in adolescence were no significantly different compared to the control group who got the treatment in a single phase that started later (12 years of age).

2- A 2-phase treatment has significant disadvantages in terms of the number of appointments, the cost of the orthodontic treatment, a longer treatment duration (duration of phase 1 + duration of phase 2) and the occlusal results are not as good.

3- This study reinforced the conclusions of previous studies that indicated that an early treatment of Class II malocclusions is not justified.

The second article is nothing less than an article from the Cochrane library.

In this article, which is a meta-analysis, the Twin Block appliance is compared to the other functional appliances (headgear, bionator, Frankell).

Twin Block versus other functional appliances final ANB-Dr Chamberland orthodontist in Quebec City

Results show that the Twin Block appliance has a small significant advantage of 0.68° in the reduction of the ANB angle measuring the difference between both jaws compared to the other functional appliances. Two-thirds (2/3) of a degree is small. It is statistically significant, but clinically, it does not make a big difference.

Twin Block versus other functional applianes final overjet-Dr Chamberland orthodontist in Quebec City

Results also show that the Twin Block appliance is not more efficient than the other appliances in reducing the overjet, which is the distance between the upper and lower teeth. 9 mm in your son’s case.

O’Brien KD et coll. Early treatment for Class II Division 1 malocclusion with the Twin-block appliance: A multi-center, randomized, controlled trial, Am J Orthod Dentofacial Orthop 2009;135:573-9.

Harrison JE, O’Brien KD, Worthington HV. Orthodontic treatment for prominent upper front teeth in children (Review), Cochrane Database Syst Reve. 2007; 3 CD003452.

Getting back to your son

I do not know where you picked up the idea that a Twin-Block appliance would be more efficient than another appliance to treat your son’s Class II malocclusion, but literature does not support your impression. The efficiency of all functional appliances is similar.

I admit that the use of intermaxillary elastics is not the most efficient and fastest method to correct a Class II malocclusion, but it works.

Nowadays, fixed functional appliances are the ones that are mostly used to correct Class II malocclusions. Bionator, headgear, Frankell, Twin-Block and activator are good appliances that used to provide good results, but they are obsolete.

These days, orthodontists use Forsus™ Class II correctors, Twin Force® Bite Corrector™ devices, Sabbagh Universal Spring (SUS2) correctors and even anchorage miniscrews in certain cases.

Your son has a 9-mm discrepancy between his upper and lower teeth. You are probably referring to the overjet. The molar relationship is probably off by 5 mm rather than 9.

A treatment with any of the fixed functional appliances enumerated above should allow the correction of this discrepancy. If the worst comes to worst, a camouflage treatment with the extraction of 2 upper premolars could be possible. This should be taken with caution though.

An orthosurgery treatment is not a bad treatment either, but at his age, it would not be my first choice.

Therefore, I wish that you find an orthodontist in France who will know which treatment is most efficient for your son.


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