Dental Hypotheses

: 2020  |  Volume : 11  |  Issue : 3  |  Page : 91--94

Clear Twin Block: A Step Forward in Functional Appliances

Ahmad Behroozian1, Les Kalman2,  
1 Department of orthodontics, Dental School, Tabriz University of Medical Sciences, Tabriz, Iran, Iran
2 Schulich School of Medicine & Dentistry, Western University, Ontario, Canada

Correspondence Address:
Ahmad Behroozian
Department of orthodontics, Dental School, Tabriz University of Medical Sciences, Tabriz, Iran,


Introduction: Functional appliances have been used for treatment of skeletal class II patients. Clark’s twin block appliance is a commonly used functional appliance, but it has some shortcomings like compromised appearance and lack of patient cooperation. Therefore we introduced the present modification to enhance patient cooperation and increase the efficiency of the appliance. Clinical innovation: The present innovation describes a new functional appliance. The clear twin block is a modification of the traditional twin block that is made by thermoplastic clear sheets without using any wire. The unique features of this device include improved appearance and patients’ acceptance. Discussion: This appliance is relatively easy to make as wire bending is not required. Patient cooperation may also be improved as compared to traditional twin block, as there are no wire clasps to irritate the soft tissue and it is more inconspicuous. This manuscript summarizes the properties of the device and the method of fabrication.

How to cite this article:
Behroozian A, Kalman L. Clear Twin Block: A Step Forward in Functional Appliances.Dent Hypotheses 2020;11:91-94

How to cite this URL:
Behroozian A, Kalman L. Clear Twin Block: A Step Forward in Functional Appliances. Dent Hypotheses [serial online] 2020 [cited 2022 Jan 26 ];11:91-94
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Full Text


Functional appliances have been widely used for treatment of skeletal class II malocclusion[1] and can be defined as the devices that change the posturing forward the lower jaw.[2]

The main objective of therapy with functional appliances is to promote the growth of the mandible.[3]

The twin block appliance was developed by Clark[4] and it is the commonly used functional appliance.[5] Several studies have shown the positive skeletal effects of the twin block in class II patients.[6],[7]

However, proclination of the lower incisors that happens during the treatment with twin block reduces the potential of achieving maximum skeletal effects[8] Furthermore, wire clasps can cause tissue irritation and require repeated adjustments. Wire elements on the labial surface of the teeth may also jeopardize esthetics.

This study aimed to propose a proof-of-concept modification of the traditional twin block, with a review of the method of fabrication.

 Clinical Innovation

Following are the impressions and fabrication of the stone models by dental technician:A thermoformable sheet is molded on the maxillary and mandibular stone models using standard vacuum-forming procedures, similar to clear retainer fabrication. The upper plate should be extended to the most posterior tooth of the arch. At the lower arch the plate usually extends up to the second primary molar or second premolar. The extension of the appliance can be determined by the clinician and the patient-specific anatomy [Figure 1] and [Figure 2].{Figure 1}{Figure 2}Clear retainers are removed from the casts and the casts are mounted with the use of construction bite, similar to the traditional twin block procedure. The exact nature of the construction wax bite depends on the three-dimensional skeletal properties of the patient and their customized treatment plan. The sagittal and transverse position of the mandible should be predetermined according to the correction of the skeletal discrepancy.After mounting the stone models with construction wax, the articulator is locked. Clear plates and added on the cast [Figure 3]. And a pair of self-cured acrylic bite ramps added on the retainers similar to the process of twin block fabrication [Figure 4]. The upper bite block extends from the most posterior tooth to about second premolar or second primary molar and the lower bite block is located anteriorly and covers the lower premolars and canine [Figure 5]. The inclined planes of the upper and lower blocks are usually 70 degrees, to facilitate forward positioning of the patient’s mandible [Figure 6].{Figure 3}{Figure 4}{Figure 5}{Figure 6}Upper and lower retainers are removed from the casts and polished [Movie 1] ([MULTIMEDIA:1]). The appliance is ready to be delivered to the patient [Figure 7].{Figure 7}


The use of clear aligners is associated with an improved esthetics and a reduced fabrication time.[9]

The present modified appliance, called “clear twin block”, maintains all of the positive properties of the “traditional twin block” as well as several additional advantages.

The clear twin block has no wire elements on the labial surface of the teeth; therefore, its appearance is improved over the traditional twin block [Figure 8]. Esthetics and comfort represent key aspects, as they can influence the growth modification by influencing patient’s cooperation and wear time of the appliance [10].{Figure 8}

Moreover, wire elements of traditional twin block-like “arrowheads of Adams’ clasp” and ”the loop of the labial bow” can irritate the soft tissue of the patient and cause painful ulcers that inhibit the child to wear the appliance.[11],[12] The clear twin block has no wires to damage the soft tissue of the patients and should provide more comfort young patients.

Additionally, the chairside adaptation of clear twin block could be shortened, as there is no need to adjust the wire clasps at each session. Furthermore, this technique is also time-saving for laboratory technician as wire bending process is eliminated.For achieving maximum response, skeletal changes without dental movement are desired. One of the main drawbacks of the traditional twin block and other functional appliances is that they have no control over the lower anterior teeth tipping. With the present appliance, full coverage of the clinical crowns can control the anterior teeth.[13]

This appliance provides full coverage of all of the teeth as for retention of the appliance. The engagement of an increased number of teeth provides adequate retention as teeth are missing, exfoliated, and/or extracted.

Further researches are required to validate the novel appliance in terms of effectiveness and efficiency.

 Suggestion for Further Assessment

We propose to design a multicenter randomized clinical trial to compare the clear twin block to the traditional twin block.


We would like to acknowledge Milad Hemmatian who prepared the 3-D virtual models and Amir Faturechi, the technician of dental laboratory who warmly helped us in making the models.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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