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Twin-block Re-activation

Mosman, Sydney, Australia

S. J. Littlewood

Department of Orthodontics, St Luke’s Hospital, Bradford, UK

Address for correspondence: J. A. Brennan, Suite 2, 357 Military Rd, Mosman, Sydney, NSW 2088, Australia. Email: brennanjean{at}hotmail.com

Received 11 June 2005; accepted 12 July 2005

	Abstract

Top Abstract Introduction Methods of re-activation of... A new approach to... Discussion Conclusion References

 
This paper briefly reviews reasons for re-activating Twin-blocks, discussing different approaches and describing a new, simple, cost effective approach, which can be undertaken at the chairside.

Key words: Twin-block, re-activation, functional appliances

	Introduction

Top Abstract Introduction Methods of re-activation of... A new approach to... Discussion Conclusion References

 
Clark¹ introduced the Twin-block (TB) over 20 years ago and it has achieved widespread use, particularly in the UK, where it is the most popular functional appliance used for Class II correction.² One of the many advantages of the TB is the ability to increase the degree of mandibular advancement by adapting the existing appliance. This re-activation has been recommended for a number of reasons.

Patient comfort
Re-activation of the appliance in a sagittal direction is often required during treatment. Patients may not tolerate the required¹ initial mandibular advancement. In cases with larger overjets, sequential additions to the acrylic biteblocks are usually necessary to achieve the recommended edge-to-edge incisor relationship, whilst maintaining patient comfort and compliance.

Reduction of undesirable dento-alveolar forces and maximizing skeletal change
Mills,³ following a review of the literature, concluded that correction of Class II division 1 malocclusions with functional appliances was achieved primarily through tipping of the teeth. Falck and Frankel,⁴ suggested that sequential advancement using a Frankel appliance resulted in less dento-alveolar effects in the correction of Class II malocclusions. In addition, several authors^4–6 suggest that regular, incremental advancement is better tolerated by the patient, as it reduces TMJ symptoms and produces improved sagittal growth of the mandible. However, Banks et al.⁷ conducted a randomized, controlled clinical trial on 200 patients aged between 10 and 14 years, investigating the effectiveness of incremental versus maximum bite advancement during TB therapy. They concluded that incremental advancement produced no advantages over initial maximum protrusion. This failure of sequential movement to confer a positive clinical effect has also been confirmed in patients using modified TB appliances.^8,9

The best quality current evidence would therefore seem to suggest that incremental re-activation of TB appliances does not produce greater skeletal changes. However, the re-activation of TB appliances may be required in those cases where the patient cannot comfortably achieve maximum protrusion immediately. The aim of this paper is to introduce a quick and reliable way to achieve re-activation at the chairside, without the use of the laboratory.

	Methods of re-activation of TBs

Top Abstract Introduction Methods of re-activation of... A new approach to... Discussion Conclusion References

 
Laboratory re-activation
The re-activation of the appliance can be carried out on articulators in the laboratory. Clark¹ recommended laboratory additions of cold-cured acrylic to the mesially-inclined plane of the upper bite blocks. This has the disadvantage of involving 2 clinical appointments for the patient and additional laboratory costs, but with the advantages of a well-trimmed, polished appliance and no residual monomer.

Chairside re-activation
Two methods are currently used.

Cold-cured acrylic. Cold-cured activation involves the mixing of powdered acrylic with liquid monomer to produce an acrylic paste, which can be added to the inclined planes of the TB. This can be messy, time-consuming, requires polishing and has the added complication of leaching residual monomer. Alternatively, preformed acrylic buttons, in varying dimensions, can be fabricated by the technician and added using the cold-cured acrylic (Figure 1).

View larger version (77K): [in this window] [in a new window]   Figure 1 Acrylic reactivation tablet attached to upper twin block

View larger version (58K): [in this window] [in a new window]   Figure 2 Twin Block with advancement screw

	A new approach to re-activation: chairside addition of light-cured acrylic

Top Abstract Introduction Methods of re-activation of... A new approach to... Discussion Conclusion References

 
In this article, we introduce a system of re-activation of the TB appliance, which is quick, reliable, with minimal cost.

Material.
Triad^TM Visible Light Cure Custom Tray Material: this is a pre-mixed sheet containing bis-methacrylate and silicon dioxide.

Thickness.
Two millimeter thick sheets in pink/translucent.

Bonding agents.
VLC bonding agent containing methyl methacrylate.

Cost.
Twenty-four sheets cost 97.50, 15 ml of bonding agent 11.20.

Clinical steps

• Establish how much activation of the appliance is needed and whether this needs to be symmetrical.
  
• Encourage the patient to posture to the desired point with both appliances in situ.
  
• Remove the upper TB from the mouth, dry and roughen the mesially inclined planes with an acrylic bur (Figure 3). Paint a thin layer of bonding agent onto the surface (Figure 4).
  
• Cut an area equivalent to the inclined plane of the TB from the sheet of acrylic (Figure 5). Then, working extra-orally, place on each of the blocks until the required degree of advancement is achieved (Figure 6). An initial set is achieved by shining the curing light for 10 seconds.
  
• Place the upper appliance back into the mouth and ensure the addition fits against the upper teeth. Now encourage the patient gently to posture forward bringing the bite blocks together, ensuring even contact (Figure 7).
  
• Cure the acrylic intra-orally for 40 seconds (Figure 8) Remove the TB from the mouth and cure each addition for a further 2 minutes with the light. Degudent^TM (www.degudent.com) also produce a visible light-curing box (Tungsten halogen light, 275W, 965) in which both sides can be cured simultaneously.
  
• Polish edges with a rubber cup if required.
  

View larger version (107K): [in this window] [in a new window]   Figure 3 Roughening surface of block

View larger version (155K): [in this window] [in a new window]   Figure 4 Applying bond to block

View larger version (81K): [in this window] [in a new window]   Figure 5 Cutting acrylic to size

View larger version (96K): [in this window] [in a new window]   Figure 6 Getting correct fit on block

View larger version (97K): [in this window] [in a new window]   Figure 7 Occlude blocks before fully curing

View larger version (100K): [in this window] [in a new window]   Figure 8 Curing light-cured acrylic

	Discussion

Top Abstract Introduction Methods of re-activation of... A new approach to... Discussion Conclusion References

The Triad visible light cure (VLC) acrylic resin system was introduced by Dentsply De Trey in 1983. This was superseded in the 1990s with a second-generation system ‘Triad 2000’. It has previously been tested as an orthodontic base plate material, but was not found to be sufficiently durable.¹¹ However, as a material for simple re-activation of TBs, the material offers great potential. The new technique described here has some benefits over currently available methods.

The advantages of this approach are:

• quick, easy chairside activation within 5 minutes;
  
• cost-effectiveness;
  
• minimal residual monomer;
  
• minimal occlusal adjustment and polishing required;
  
• asymmetric activation possible;
  
• allows trimming of bite blocks to allow settling in deep bite cases;
  
• good occlusal contact in patients with increased vertical proportions.
  

	Conclusion

Top Abstract Introduction Methods of re-activation of... A new approach to... Discussion Conclusion References

 
The addition of light-cured acrylic provides an easy, and efficient way of re-activating TB appliances at the chairside. It can also be used to modify other removable appliances such as acrylic bite planes.

	Acknowledgments

 
We would like to thank acknowledge the contribution of the following people to the compilation of this article: Colin Melrose, Jonathan Sandler for Figure 1, Ortho-Care (UK) Ltd for kind permission to use Figure 2, and James Winters, Dentsply GB.

	References

Top Abstract Introduction Methods of re-activation of... A new approach to... Discussion Conclusion References

 
1 Clark WJ. The Twin Block technique. A functional orthopedic appliance system. Am J Orthod Dentofacial Orthop 1988; 93(1): 1–18.[CrossRef][Medline]

2 Chadwick SM, Banks P, Wright JL. The use of myofunctional appliances in the UK: a survey of British orthodontists. Dent Update 1998; 25(7): 302–8.[Medline]

3 Mills JR, The effect of functional appliances on the skeletal pattern. Br J Orthod 1991; 18(4): 267–75[Abstract]

4 Falck F, Frankel R. Clinical relevance of step-by-step mandibular advancement in the treatment of mandibular retrusion using the Frankel appliance. Am J Orthod Dentofacial Orthop 1989; 96(4): 333–41.[CrossRef][Medline]

5 Du X, Hagg U, Rabie AB. Effects of headgear Herbst and mandibular step-by-step advancement versus conventional Herbst appliance and maximal jumping of the mandible. Eur J Orthod 2002; 24(2): 167–74.[Abstract/Free Full Text]

6 Malmgren O, Omblus J. Treatment with an orthopaedic appliance system. Eur J Orthod 1985; 7(3): 205–14.[Abstract/Free Full Text]

7 Banks P, Wright J, O’Brien K. Incremental versus maximum bite advancement during twin-block therapy: a randomized controlled clinical trial. Am J Orthod Dentofacial Orthop 2004: 126(5): 583–8.[CrossRef][Medline]

8 Gill DS, Lee RT. Prospective clinical trial comparing the effects of conventional Twin-block and mini-block appliances: Part 1. Hard tissue changes. Am J Orthod Dentofacial Orthop 2005; 127(4):465–72[CrossRef][Medline]

9 DeVincenzo JP, Winn MW. Orthopedic and orthodontic effects resulting from the use of a functional appliance with different amounts of protrusive activation. Am J Orthod Dentofacial Orthop 1989; 96(3):181–90.[CrossRef][Medline]

10 Carmichael GJ, Banks PA, Chadwick SM. A modification to enable controlled progressive advancement of the twin block appliance. Br J Orthod 1999; 26(1): 9–13.[Abstract/Free Full Text]

11 Eden SE, Kerr WJS, Brown J. A clinical trial of light cure acrylic resin for orthodontic use. J Orthod 2002: 29(1): 51–55.[Abstract/Free Full Text]

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