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 Table of Contents  
Year : 2022  |  Volume : 16  |  Issue : 2  |  Page : 174-178

Modification of Twin-block appliance using an innovative approach

1 CO, 1 AFDC, New Delhi, India
2 DO & Classified Spl, 3 Corps Dental Unit, New Delhi, India

Date of Submission21-Sep-2020
Date of Decision07-Dec-2021
Date of Acceptance19-Jul-2022
Date of Web Publication21-Dec-2022

Correspondence Address:
Harihara Naik
CO, 1 AFDC, New Delhi
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jodd.jodd_58_20

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Successful correction of skeletal malocclusion using commonly used standard Twin-block design is a challenging task which can further become difficult to manage with noncompliant patients. Literatures have reported various modifications of commonly used Twin-block appliance to overcome the limitations of the design, to make it more patient-friendly with reproducible results. In the attempt of increasing comfort, retention, and acceptability to the existing design, the present article is reporting an innovative modification of Twin-block with a successful outcome and reproducible results.

Keywords: Case report, Class II, Twin block

How to cite this article:
Naik H, Maurya RK. Modification of Twin-block appliance using an innovative approach. J Dent Def Sect. 2022;16:174-8

How to cite this URL:
Naik H, Maurya RK. Modification of Twin-block appliance using an innovative approach. J Dent Def Sect. [serial online] 2022 [cited 2023 Jan 31];16:174-8. Available from: http://www.journaldds.org/text.asp?2022/16/2/174/364524

  Introduction Top

Management of skeletal Class II due to retrognathic mandible using myofunctional appliance is one of the noninvasive, successful, and reliable treatment methods. Although various myofunctional appliances have been reported in the literature, the Twin-block appliance can be claimed to be the most commonly used device. The standard Twin block can be called the successor of the Swartz plate, introduced by Williams J Clark in 1977.[1],[2] The versatile design of the appliance increased the compliance of the patients and due to two separate components, allowed the users to use the appliance while masticating. Although the appliance has been modified and customized by various researchers depending on their needs and treatment planning, the standard design of upper acrylic plate with expansion screw and Delta clasp in the molar region and lower acrylic plate with Delta clasp on the first permanent premolar as well as ball end clasp in anterior is still most commonly practiced. Literatures have reported that the nonwearing of the appliance while eating, unable to close the appliance in sagittal advancement and frequent mouth opening are few of the limiting factors in the successful management of the standard design.[3],[4] The present article reports an innovative modification of Twin block for increased compliance, comfort and retention, and successful treatment of a skeletal Class II patient. The case is being reported as per the CARE (Case Report) reporting guidelines.[4]

  Case Report Top

A 12-year-old adolescent boy had reported with chief complaints of protruding upper teeth and an ugly smile. The patient as well as his parents reported the existence of problems for the past 3–4 years which have increased concerning the patient as it was affecting his social interaction and trauma prone. Parents reported no relevant present and past medical or dental history. The patient as well as parents were motivated and keen for treatment as early as possible.

[Figure 1],[Figure 2],[Figure 3],[Figure 4] and [Table 1]">  Clinical Findings [Figure 1],[Figure 2],[Figure 3],[Figure 4] and [Table 1] Top
Figure 1: Pretreatment extraoral photographs

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Figure 2: Pretreatment Intraoral Photographs

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Figure 3: Pretreatment orthopantomogram

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Figure 4: Pretreatment lateral cephalogram

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Table 1: Comparative cephalometric value

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The patient had mesomorphic appearance, euryprosopic face, and average body mass index. The extraoral examination revealed a convex facial profile, potentially incompetent lips, and reduced lower one-third and symmetrical face. The intraoral examination revealed permanent dentition with permanent second molars erupted, Angle Class II Division 1 malocclusion with mild upper incisors proclination, and upright lower incisors. The palate, tongue, and buccal mucosa were normal with mild encrustation of the lower lip. The tongue was low lying in position but of normal size. The modified Malampatti score was revealed to be two. The Visual Treatment Objective (VTO) of the patient was acceptable. The temporomandibular joint (TMJ) had symmetrical unrestricted movement with no pain or sound of click, crepitus, or grit while intra-auricular/extra-auricular palpation. The study model represented mild constriction in the upper arch, 2.5 mm curve of Spee, and well-aligned arches. The radiographic orthopantomogram feature reveals a well-developed condyle, permanent dentition with 28 erupted teeth, and 28 and 38 in Nolla stage II. The lateral cephalogram revealed an average growth pattern with proclined upper incisors and upright lower incisors, adequate soft-tissue drape, and Cervical Vertebra Maturation Index (CVMI) stage III.

Diagnostic assessment

Based on the patient's chief complaint, clinical, study model, and radiographic analysis, the patient was diagnosed as a prepubertal male, skeletal Class II due to retrognathic mandible with convex profile and mild proclination of upper incisors.

Therapeutic plan

Single-phase therapy for the treatment of skeletal Class II using myofunctional appliance for correction of mandibular position was planned followed by orthodontic correction of dentoalveolar structures if required.

The alternative treatment plan was devised based on orthodontically assisted fixed functional or dentoalveolar camouflage if required. Informed and written consent was given by parents for the first treatment plan.

Therapeutic intervention

The standard Twin-block appliance with upper expansion screw was given to the patient with 5 mm sagittal and 4 mm vertical prescription inbuilt. The patient was followed initially after 2 weeks to check for the pterygoid response which was found to be negative. Subsequent follow-ups at every 3 weeks for the next 4 months found no positive result. Upon further exploration, it was found that the patient was not regular in wearing the appliance and had frequent complaints of inability to masticate along and constant forwarding. After discussion with parents and further consent, the appliance was modified by providing occlusal inter digitation using dentulous blocks in the upper and lower acrylic plates with the assumption of better mastication and retention. The patient was requested for follow-up after every 2–3 weeks [Figure 5] and [Figure 6]. The pterygoid treatment response was found positive after 6 weeks with increased compliance and better retention as well as comfort history from the patient. The appliance was continued for the next 6 months and switched over to the support phase for the next 7 more months. Continuous careful occlusal guidance using selective trimming was performed which led to adequate inter digitation of occlusion in Angle Class I with satisfactory Andrew's keys of occlusion. The patient was kept on a long-term retention phase since then till the time of reporting of the article [Figure 7],[Figure 8],[Figure 9],[Figure 10] and [Table 1].
Figure 5: Modification of appliance

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Figure 6: Appliance in situ

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Figure 7: Posttreatment extraoral photographs

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Figure 8: Posttreatment intraoral photographs

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Figure 9: Posttreatment orthopantomogram

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Figure 10: Posttreatment lateral cephalogram

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  Discussion Top

The present article reported the successful correction of skeletal Class II malocclusion using a modified Twin block in an innovative way. Although modification of the original Twin-block design has been reported since its inception in 1970s such as removal of a labial bow by originator himself, addition of acrylic capping, variation in the number of ball end clasp, addition of Delta clasp in place of Adam clasp and vice versa, modification of angulation of bite blocks, Banded block addition of magnets in blocks, torque control spurs and different extensions of blocks.[5],[6],[7],[8],[9] These modifications reported in the literature had the sole aim that is to correct the malocclusion as early, as permanent, and as skeletally as possible within the comfort of patients.

Chintakanon et al. and Chavan et al. have reported that the immediate advancement of the mandible with Twin block inclines does not have any significant temporomandibular disorder risk. The occlusal indentation provided in the present study facilitates the chewing and improved compliance however the long-term prospective study in a controlled environment on a larger sample size needs to be carried out to rule out further TMJ impact.[10]

The recommended height of the block depends on the freeway space of the patient. The number of the blocks depends on the permissible occlusal coverage as per the standard design recommended by Clark for the blocks, i.e., upper molars in the upper arch and lower premolars and canine in the lower arch.[11],[12]

The present modification reported in this article is an innovative way and has never been reported so far and was intended to provide a dentulous platform to bite blocks to not only provide retention and increased compliance but also make appliances look more lifelike. The studies have reported more predictable success with the appliance when it is encouraged to be used while chewing and mastication which is an inherent advantage of the appliance in comparison to other monobloc designs.[9] The standard designs had flat half coverage of functional cusp which make it difficult for patients to masticate efficiently, leading to discouraging the continuous wearing. The present modification instantly brought changes in patient behavior in the form of increased confidence, comfort, and motivation in wearing the appliance.

Since this is the one unique case being reported, further modification is being tried at a larger sample size in a controlled manner prospective study to assess its internal and external validity and generalizability.

  Conclusion Top

The present article reported the successful modification of conventional standard Twin-block design which was helpful not only in the correction of malocclusion but also had better acceptability, retention, and positive feedback from patients.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Clark WJ. The twin block technique. A functional orthopedic appliance system. Am J Orthod Dentofacial Orthop 1988;93:1-18.  Back to cited text no. 1
Clark W. The twin block technique. Funct Orthod 1991;8:24-5, 27-8.  Back to cited text no. 2
Lund DI, Sandler PJ. The effects of Twin Blocks: A prospective controlled study. Am J Orthod Dentofacial Orthop 1998;113:104-10.  Back to cited text no. 3
Gagnier JJ, Kienle G, Altman DG, Moher D, Sox H, Riley D, et al. The CARE guidelines: Consensus-based clinical case reporting guideline development. BMJ Case Rep 2013;2013:bcr2013201554.  Back to cited text no. 4
Trenouth MJ, Desmond S. A randomized clinical trial of two alternative designs of Twin-block appliance. J Orthod 2012;39:17-24.  Back to cited text no. 5
Harradine NW, Gale D. The effects of torque control spurs in twin-block appliances. Clin Orthod Res 2000;3:202-9.  Back to cited text no. 6
El Kattan E, El-Yazeed A, Aya E. A new design of twin block appliance for treatment of mandibular deficiency in mixed dentition stage. Aust J Basic Appl Sci 2012;6:701-7.  Back to cited text no. 7
Gerber JW. Banded block. Funct Orthod 1999;16:16-20.  Back to cited text no. 8
Noar JH, Evans RD. Rare earth magnets in orthodontics: An overview. Br J Orthod 1999;26:29-37.  Back to cited text no. 9
Tümer N, Gültan AS. Comparison of the effects of monoblock and twin-block appliances on the skeletal and dentoalveolar structures. Am J Orthod Dentofacial Orthop 1999;116:460-8.  Back to cited text no. 10
Chintakanon K, Sampson W, Wilkinson T, Townsend G. A prospective study of Twin-block appliance therapy assessed by magnetic resonance imaging. Am J Orthod Dentofacial Orthop 2000;118:494-504.  Back to cited text no. 11
Chavan SJ, Bhad WA, Doshi UH. Comparison of temporomandibular joint changes in Twin Block and Bionator appliance therapy: A magnetic resonance imaging study. Prog Orthod 2014;15:57.  Back to cited text no. 12


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]

  [Table 1]


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