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

Clear Twin Block: A Step Forward in Functional Appliances

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

Date of Submission07-Feb-2020
Date of Decision09-Apr-2020
Date of Acceptance17-May-2020
Date of Web Publication23-Jul-2020

Correspondence Address:
Ahmad Behroozian
Department of orthodontics, Dental School, Tabriz University of Medical Sciences, Tabriz, Iran,
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/denthyp.denthyp_14_20

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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.

Keywords: Clear, functional appliance, growth modification, twin block

How to cite this article:
Behroozian A, Kalman L. Clear Twin Block: A Step Forward in Functional Appliances. Dent Hypotheses 2020;11:91-4

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 Nov 30];11:91-4. Available from:

  Introduction Top

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 Top

Following are the impressions and fabrication of the stone models by dental technician:
  1. 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 Schematic drawing of clear retainers.

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    Figure 2 Clear retainer of upper jaw is made on the stone model.

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  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.
  3. 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 Position of clear plates after removal of the wax.

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    Figure 4 Schematic view of the acrylic plates.

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    Figure 5 The virtual relationship of the bite blocks.

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    Figure 6 Three-dimensional model of the appliance.

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  4. Upper and lower retainers are removed from the casts and polished [Movie 1] (

    ). The appliance is ready to be delivered to the patient [Figure 7].
    Figure 7 Completed appliance.

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  Discussion Top

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 Clear twin block is delivered to the patient.

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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 Top

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.

  References Top

Chen JY, Will LA, Niederman R. Analysis of efficacy of functional appliances on mandibular growth. Am J Orthod Dentofac Orthop 2002;122:470-6.  Back to cited text no. 1
Jiang YY, Sun L, Wang H, Zhao CY, Zhang WB. Three-dimensional cone beam computed tomography analysis of temporomandibular joint response to the Twin-block functional appliance. Korean J Orthod 2020;50:86-97.  Back to cited text no. 2
Staderini E, Meuli S, Gallenzi P. Orthodontic treatment of class three malocclusion using clear aligners: a case report. J Oral Biol Craniofac Res 2019;9:60-2.  Back to cited text no. 3
Clark WJ. The Twin Block technique. A functional orthopedic appliance system. Am J Orthod Dentofac Orthop 1988;93:1-18.  Back to cited text no. 4
Chadwick SM, Banks P, Wright JL. The use of myofunctional appliances in the UK: a survey of British orthodontists. Dent Update 1988;25:302-8.  Back to cited text no. 5
Lund DI, Sandler PJ. The effects of Twin Blocks: a prospective controlled study. Am J Orthod Dentofac Orthod 1998;113:104-10.  Back to cited text no. 6
Mills CM, McCulloch KJ. Treatment effects of the Twin Block appliance: a cephalometric study. Am J Orthod Dentofac Orthop 1998;114:15-24.  Back to cited text no. 7
Tripathi T, Singh N, Rai P, Gupta P. Mini-implant-supported twin-block appliance: an innovative modification. Niger J Clin Pract 2019;22:432-8.  Back to cited text no. 8
[PUBMED]  [Full text]  
Patini R, Gallenzi P, Meuli S, Paoloni V, Cordaro M. Clear aligners’ effects on aesthetics: evaluation of facial wrinkles. J Clin Exp Dent 2018;10:696-701.  Back to cited text no. 9
Aggarwal P, Kharbanda OP, Mathur R, Duggal R, Parkash H. Muscle response to the twin-block appliance: an electromyographic study of the masseter and anterior temporal muscles. Am J Orthod Dentofac Orthop 1999;116:405-14  Back to cited text no. 10
Baricevic M, Mravak-Stipetic M, Majstorovic M, Baranovic M, Baricevic D, Loncar B. Oral mucosal lesions during orthodontic treatment. Int J Paediatr Dent 2011;21:96-102.  Back to cited text no. 11
Gursoy UK, Sokucu O, Uitto VJ, Aydin A, Demirer S, Toker H et al. The role of nickel accumulation and epithelial cell proliferation in orthodontic treatment-induced gingival overgrowth. Eur J Orthod 2007;29:555-8.  Back to cited text no. 12
Tepedino M, Franchi L, Fabbro O, Chimenti C. Post-orthodontic lower incisor inclination and gingival recession-a systematic review. Prog Orthod 2018;19:17.  Back to cited text no. 13


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]


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