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CASE REPORT
Year : 2019  |  Volume : 22  |  Issue : 3  |  Page : 432-438

Mini-implant-supported twin-block appliance: An innovative modification


Department of Orthodontics and Dentofacial Orthopedics, Maulana Azad Institute of Dental Sciences, New Delhi, India

Date of Acceptance08-Oct-2018
Date of Web Publication6-Mar-2019

Correspondence Address:
Dr. T Tripathi
Senior Professor and Head, Department of Orthodontics and Dentofacial Orthopedics, Maulana Azad Institute of Dental Sciences, New Delhi - 110 002
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_342_18

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   Abstract 


Twin block is a commonly used appliance for correction of retrognathic mandible in growing patients. However, it has a drawback of causing lower incisor proclination, which reduces its potential of achieving maximum skeletal effects. Thus, we introduced a novel modification in the present design to facilitate greater anteroposterior effects in skeletal dimension. The aim of the present case reports is to evaluate the efficacy of this modified twin block. Here we present two cases treated with mini-implant-supported twin-block appliance, which successfully controlled the lower incisor position, thereby increasing the envelope for orthopedic correction in class II myofunctional therapy. This modification is useful in growing patients with retruded mandible to achieve maximum skeletal effects.

Keywords: Anchorage, class II, functional appliance, mini-implant, twin block


How to cite this article:
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

How to cite this URL:
Tripathi T, Singh N, Rai P, Gupta P. Mini-implant-supported twin-block appliance: An innovative modification. Niger J Clin Pract [serial online] 2019 [cited 2019 Mar 22];22:432-8. Available from: http://www.njcponline.com/text.asp?2019/22/3/432/253450




   Background Top


The challenge in the management of skeletal class II malocclusion in growing patients is to achieve maximum skeletal correction with minimal dental changes. Twin block is one of the most commonly used appliance to achieve functional correction of skeletal class II malocclusion.[1] One of the major drawbacks of twin-block appliance is overjet correction mainly by dentoalveolar changes (60%), which includes the proclination of lower incisors.[2] Various authors have proposed modifications in twin-block appliance to circumvent this undesirable effect of lower incisor proclination.[3],[4],[5] However, all these methods have only partial control over the lower incisor position. Hence, we devised a novel modification in the contemporary design, which provided absolute control over the position of mandibular incisors.


   Appliance Design Top


The present modification of the standard twin block comprises maxillary and mandibular components. Maxillary components consist of delta clasps and labial bow, whereas mandibular components include delta and ball end clasps similar to standard twin block. The following modifications were incorporated in the mandibular appliance:

  1. Wire hooks: Wire hook element was incorporated in the region of incisal capping with free end projecting distal to canine on both the sides [Figure 1]a.
  2. Mini-implants: Two orthodontic mini-implants (1.5 × 9 mm × 9 mm, Infinitas, DB Orthodontics, CA, USA) were inserted bilaterally on lower arch between the mandibular second premolar and first molar under aseptic conditions after the administration of local anesthesia [Figure 1]b. Radiovisiograph (RVG) was taken to verify the intended position and stability of mini-implants.
  3. Intraoral elastics: Elastics of dimension 3/8” (4 oz, 150 g of force, TP Orthodontics, Indiana, USA) were attached to the wire hooks to exert class I distalizing force taking anchorage from mini-implants [Figure 1]c.
Figure 1: Modified twin-block appliance showing components (denoted by arrow). (a) Wire hook; (b) mini-implants; (c) restraining elastic

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   Case 1 Top


A 13-year-old male patient reported to the Department of Orthodontics and Dentofacial Orthopedics with a chief complaint of forwardly placed upper front teeth. On extraoral examination, the patient had a convex profile, incompetent lips, retrognathic chin, and deep mentolabial sulcus. Intraoral examination revealed Angle's class II division 1 malocclusion with an overjet of 14 mm and spacing in the upper arch [Figure 2]. The cephalometric analysis [Table 1] revealed a skeletal Class II pattern (ANB = 6°) with retrognathic mandible (SNB = 76°), reduced mandibular length (Co-Gn = 101 mm), proclined maxillary anteriors (Upper 1 to NA = 42°), and incisor mandibular plane angle (IMPA) of 94°. The patient had an average growth pattern (SN-GoGn = 32°) and was in cervical vertebral maturation index (CVMI) transition stage. Clinically, the patient showed positive visual treatment objective (VTO) [Figure 3].
Figure 2: Pretreatment photographs and lateral cephalogram of Case 2

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Table 1: Pre- and posttreatment cephalometric measurements of Case 1

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Figure 3: Pretreatment profile and VTO photographs of Case 1

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Treatment objectives:

  1. To correct skeletal class II discrepancy
  2. To achieve class I molar and canine relation
  3. Consolidation of spaces in upper arch
  4. To prevent flaring of lower incisors
  5. Improvement of patient's soft tissue profile.


Treatment plan and progress

The pretreatment overjet was 14 mm, which entailed a stepwise advancement with an initial bite registration taken at 6 mm sagittal advancement and 4 mm vertical opening. The modified twin block was fabricated and inserted with relevant instructions for appliance wear. The patient was recalled after 3 days and no discomfort was reported with the appliance. At this stage, mini-implants were inserted to anchor the restraining elastics. A RVG [Figure 4] was taken to verify the position of the mini-implants and elastics were attached bilaterally from mini-implants to the hooks. The patient was advised to wear the appliance for 24 h along with elastics which were replaced daily. The upper arch expansion was done by activating the screw one turn per week to achieve coordination of the upper and lower arches. The pterygoid response was achieved in 6 weeks. Further sagittal advancement of 2 mm was carried out by addition of acrylic in the inclined planes of upper block after 2 months of achievement of pterygoid response.
Figure 4: RVG of Case 1 showing mini-implant placed between mandibular second premolar and first molar

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Treatment results

The class I molar and canine relationship was achieved successfully in 10 months with improvement in the profile of the patient [Figure 5]. Post myofunctional records [Table 1] revealed a decrease in the ANB angle by 4° with an increase in mandibular length by 4.5 mm (Co-Gn = 105.5 mm). The Pitchfork analysis [6] revealed an overall overjet reduction of 7.5 mm with 66.6% skeletal change and 33.3% dental changes [Figure 6]. The dental effects seen were due to tipping of proclined upper incisors, which was desirable. However, there was almost no change in the position of lower incisors (IMPA = 94°) [Table 1]. The final occlusion was unsettled which requires fixed orthodontic therapy.
Figure 5: Postfunctional photographs and lateral cephalogram of Case 2

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Figure 6: (a) Superimposition is performed on the nasal line, palatal curvature, and anterior contour of the keyridge. All measurements are done parallel to MFOP. Maxillary change is measured at the SE points, ABCH at the D points, upper molar change at the mesial contact points, and incisor change at the incisal edges. (b) The superimposition is done on D points lying on a common perpendicular line to MFOP by displacing tracings along the MFOP. Again, all measurements are performed parallel to MFOP. Lower molar change is measured at the mesial contact points and incisor change at the incisal edges. (c) The tracings are displaced again until the mesial contact points of the upper molars are lying on a common perpendicular line to MFOP. The molar intercuspation change is measured at the mesial contact points of the lower molars. This measurement can be compared with the calculated intercuspation change. The difference should not exceed 0.2 mm. (d) The tracings are displaced again until the incisal edges of the upper incisors are lying on a common perpendicular line to MFOP. The overjet change is measured at the incisal edges of the lower incisors. This measurement can also be compared with the calculated overjet change. The difference should not exceed 0.2 mm. (e) Pitchfork analysis of Case 1. MFOP=Mean functional occlusal plane; SE point=Intersection of greater wing of sphenoid and cribriform plate of ethmoid; ABCH=Apical base change; D point=Geometric center of symphysis

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   Case 2 Top


A 12-year-old female presented with a convex profile, incompetent lips, deep mentolabial sulcus and Angle's class II division 1 malocclusion with an overjet of 11 mm [Figure 7]. She had a skeletal Class II pattern (ANB = 5°) with a retrognathic mandible (SNB = 75°), reduced mandibular length (Co-Gn = 95 mm), proclined maxillary anteriors (Upper 1 to NA = 38°), and IMPA of 99°. The patient had an average growth pattern (SN-GoGn = 27°), was in CVMI transition stage, and showed positive VTO [Figure 8].
Figure 7: Pretreatment photographs and lateral cephalogram of Case 1

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Figure 8: Pretreatment profile and VTO photographs of Case 2

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Treatment objectives:

  1. To correct skeletal class II discrepancy
  2. To achieve class I molar and canine relation
  3. To prevent flaring of lower incisors
  4. Improve soft tissue profile of the patient.


Treatment plan and progress

The twin-block appliance was fabricated and inserted following bite registration initially at 5 mm sagittal advancement and 5 mm vertical opening. Further 1 mm advancement was carried out after achieving pterygoid response.

Treatment protocol and results

The treatment objectives were achieved in 9 months with improvement in the patient's profile [Figure 9]. The pitchfork analysis revealed overjet correction by 8.5 mm with 65% skeletal change and 35% dental effects [Figure 10]. The dental changes were primarily due to tipping of the proclined maxillary anteriors with absolute control over lower incisors position [Table 2].
Figure 9: Postfunctional photographs and lateral cephalogram of Case 1

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Figure 10: (a-d) Superimposition same as in Figure 6. (e) Pitchfork analysis of Case 2

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Table 2: Pre and posttreatment cephalometric measurements of Case 2

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   Discussion Top


Myofunctional appliance therapy is the treatment of choice in growing class II patients.[7] Among all myofunctional appliances, twin block is most commonly used, owing to its greater acceptability by the patient along with good results.[8] Twin-block appliance brings about mandibular advancement and maxillary retrusion, thereby improving sagittal skeletal jaw relationship. Besides skeletal base changes, influence on overjet, palatal tipping of maxillary, and labial tipping of mandibular incisors are also observed. The proclination of lower incisor limits the forward displacement of mandible, thereby reducing the scope of desired skeletal correction.[9]

Various modifications have been proposed to prevent the lower incisor proclination, for example, southend clasp,[3] acrylic labial bow,[4] ball clasps,[10] and acrylic capping.[5] Lower incisors proclination was reported by Trenouth and Desmond [3] (1.4°), Lund and Sandler [10] (7.9°), Mills and McCulloch [4] (5.2°), Toth and McNamara [11] (2.8°), Sidlauskas [12] (3.2°), and van der Plas et al.[13] (2.8°), even after using the above-mentioned modifications to prevent incisor flaring. Thus, there was a need for a method to control the position of lower incisors in order to maximize the scope of orthopedic correction in twin-block therapy.

Mini-implants have long been used for providing a means of eliminating dentoalveolar side effects by providing absolute anchorage from bone. Although mini-implant is a popular method of anchorage control in orthodontics, their use in combination with the twin-block appliance has not yet been reported. This preliminary case report describes how a combination of mini-implant and twin block can control the proclination of the lower incisors during treatment. We devised a method to control lower incisor position by attaching elastics from mini-implants to hooks incorporated in mandibular component of twin block. The restraining elastics take anchorage from mini-implants placed between mandibular second premolar and first molar to exert a class I distalizing force, which negate the forward thrust of the twin-block appliance on lower incisors, hence, eliminating the lower incisor flaring and maximizing the skeletal effects in overjet reduction. In the present cases, we achieved class I canine and molar relationships at the end of treatment. However, this should be followed by fixed orthodontic mechanotherapy to achieve final settling of the occlusion. The results give credence to the present modification of twin block in skeletal correction of class II malocclusion. Similar results were observed with combination of fixed functional appliances and mini-implants, wherein lower incisors proclination was controlled as suggested by Aslan et al.[14] and Elkordy et al.[15]

We found that this modification is novel and first of its kind, which claims no change in position of lower incisors after twin-block appliance therapy. Such an appliance is highly beneficial and indicated in cases with severely proclined lower incisors where maximum orthopedic correction is desired.


   Future Scope Top


The present modification of the most popular myofunctional appliance has been used successfully in two patients. The results of the present cases can be validated by use of this appliance in a larger sample.


   Conclusion Top


The use of mini-implant anchorage with twin-block therapy can provide absolute control over the position of lower incisors, thereby increasing the envelope for orthopedic correction in class II myofunctional therapy. This should be followed by fixed orthodontic treatment for proper settling of occlusion.


   Clinical Significance Top


Mini-implant-supported twin block is beneficial in tapping full potential of achieving skeletal effects by absolute control over lower incisors. Thus, this modification pre-empts the loss of precious growing years and imparts greater stability of the orthopedic treatment results.

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

Nil

Conflict of interest

There are no conflicts of interest.



 
   References Top

1.
Clark WJ. The twin block traction technique. Eur J Orthod 1982;4:129-38.  Back to cited text no. 1
    
2.
Sidlauskas A. The effects of the twin-block appliance treatment on the skeletal and dentoalveolar changes in Class II Division 1 malocclusion. Medicina (Kaunas) 2005;41:392-400.  Back to cited text no. 2
    
3.
Trenouth MJ, Desmond S. A randomized clinical trial of two alternatives designs of twin-block appliance. J Orthod 2012;39:17-24.  Back to cited text no. 3
    
4.
Mills C, McCulloch K. Treatment effects of the twin block appliance: A cephalometric study. Am J Orthod 1998;114:15-24.  Back to cited text no. 4
    
5.
Morndal O. The effect on the incisor teeth of activator treatment: A follow-up study. Br J Orthod 1984;11:214-20.  Back to cited text no. 5
    
6.
Johnston LE Jr. Balancing the books on orthodontic treatment: An integrated analysis of change. Br J Orthod 1996;23:93-102.  Back to cited text no. 6
    
7.
McNamara JA. Components of Class II malocclusion in children 8-10 years of age. Angle Orthod 1981;51:177-202.  Back to cited text no. 7
    
8.
Chadwick SM, banks P, Wright JL. The use of myofunctional appliances in the UK: A survey of British orthodontists. Dent Update 1998;25:302-8.  Back to cited text no. 8
    
9.
Antonarakis GS, Kiliaridis S. Short-term anteroposterior treatment effects of functional appliances and extraoral traction on class II malocclusion. A meta-analysis. Angle Orthod 2007;77:907-14.  Back to cited text no. 9
    
10.
Lund DL, 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. 10
    
11.
Toth LR, McNamara JA Jr. Skeletal and dentoalveolar adaptations produced by twin-block appliance treatment. Am J Orthod Dentofacial Orthop 1999;116:597-609.  Back to cited text no. 11
    
12.
Sidlauskas A. The effects of the twin-block appliance treatment on the skeletal and dentoalveolar changes in Class II Division 1 malocclusion. Medicina (Kaunas). 2005;41:392-400.  Back to cited text no. 12
    
13.
van der Plas MC, Janssen KI, Pandis N, Livas C. Twin block appliance with acrylic capping does not have a significant inhibitory effect on lower incisor proclination. Angle Orthod 2017;87:513-8.  Back to cited text no. 13
    
14.
Aslan B, Kucukkaraca E, Turkoz C, Dincer M. Treatment effects of the Forsus Fatigue Resistant Device used with miniscrew anchorage. Angle Orthod 2014;84:76-87.  Back to cited text no. 14
    
15.
Elkordy SA, Abouelezz AM, Fayed MM, Attia KH, Ishaq RA, Mostafa YA. Three-dimensional effects of the mini-implant-anchored Forsus Fatigue Resistant Device: A randomized controlled trial. Angle Orthod 2016;86:292-305.  Back to cited text no. 15
    


    Figures

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

  [Table 1], [Table 2]



 

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