CLINICAL SECTION
Journal of Orthodontics, Vol. 42, 2015, 248– 252
Removable cast chrome cobalt retainers for extended or indefinite period clinical use Simon Ash1, Parmjit Singh2 and Eliakim Mizrahi3 1,2
BPP University, London, UK; 3Private practice, UK
Patients are frequently being asked to wear orthodontic retainers for as long as they want their teeth to remain in the post-treatment position. Fixed retainers, which are placed on the lingual surface of anterior teeth only, have the advantage of minimal compliance issues but are not without their problems related to wire fracture, adhesive failure and potential gingival or periodontal disease. Plastic retainers, although associated with relatively good aesthetics and compliance, have limitations related to their physical and mechanical properties. This paper describes a chrome cobalt metal retainer that could be used as a long-term retainer with few drawbacks. The properties of chrome cobalt are described and the clinical procedure is outlined. Key words: Chrome cobalt, removable retainer, retention Received 5 December 2014; accepted 23 February 2015
Introduction Angle stated in 1907 that ‘the problem involved in retention is so great as to test the utmost skill of the most competent orthodontist, often being greater than the difficulties being encountered in the treatment of the case up to this point’ (Angle, 1907). Currently, even after a century of continually progressive clinical treatment, extensive research and widespread in depth discussion, the regime for orthodontic retention remains a topic of unresolved passionate debate. In recent years, orthodontists have advocated the need for ‘retention for life’ to overcome the challenges associated with retention and relapse (Little et al., 1988; McGuinness, 2008). This philosophy is a consequence of the recognition that teeth will continue to move throughout life. Therefore, to maintain the desired result, there has to be a commitment on the part of the patient to a period of retention, which in many cases, extends for an indefinite period of time. Both the type of retainer and the retention regimen are now being considered just as important as the duration of retention (Lang et al., 2002). The methods for retention are broadly divided into fixed (bonded) and removable retainers. Methods for fixed retainer placement are varied and have been described (Zachrisson, 1977; Lee, 1981) with some clinicians advocating a preference for fixed retention regimes over removable retainers (Cerny et al., 2009). A survey of opinions comparing fixed versus removable retainers revealed that patients also favoured fixed retainers over those that were removable (Cerny et al., 2009).
Fixed retainers generally incorporate the maxillary and or mandibular six anterior teeth only and therefore have little effect in retaining the buccal segments. Consequently, clinicians are often obliged to additionally prescribe removable retainers to include and influence the full dentition. A survey of retention regimes in the United Kingdom found that vacuum formed thermoplastic retainers were more popular in National Health Service practice and hospital environments as well as private practice settings (Singh et al., 2009). Despite these retainers not being intended to be worn for long periods of time, 80% of respondents advocated indefinite retention with vacuum formed thermoplastic retainers and 72% with Hawley retainers. Fixed retainers were found to be more frequently used in private practice than in any of the other clinical settings (Singh et al., 2009). Following the era of vulcanite denture materials (McCabe and Walls, 2008), the introduction of acrylic resin was a major landmark in clinical dentistry and its associated disciplines; acrylic resin has now been in clinical use since 1940. Currently, conventional removable retainers comprise two groups, the acrylic ‘Hawley’ type retainer and the ‘Essix’ thermoformed plastic retainers (Sheridan et al., 1993; Littlewood et al., 2006). In spite of the many improvements in the chemical and physical properties of acrylic resins, ‘Hawley’ type retainers, which are constructed of either cold or heat cured acrylic and usually incorporate stainless steel wire components, have their drawbacks. The physical properties of the main constituent material is still characterised as being comparatively soft, weak and flexible. Typically,
*Address for correspondence: Parmjit Singh. E-mail: [email protected] # 2015 British Orthodontic Society
DOI 10.1179/1465313315Y.0000000006
JO 2015
Clinical Section
acrylic resins have a modulus of elasticity of 2.5 GPa, a tensile strength of 85 MPa and hardness value of 20 Vickers Hardness Numbers (VHN) (McCabe and Walls, 2008). The stainless steel components, while being stronger, more durable and more stable, suffer from work hardening. With constant and/or intermittent use over a period of time, the flexing of stainless steel wires used for cribs, finger springs or labial bows, become work-hardened and liable to fracture. The risk of fracture is further compounded by the physical interfaces between dissimilar materials such as acrylic and stainless steel when exposed to extremes of temperature. The pressure or vacuum formed ‘Essix’ type retainer is made from a thermoformed plastic and while the retainer may provide a satisfactory short-term means of retention, it has a limited life expectancy. Plastics worn in the mouth can deteriorate with time; the material is porous, absorbs water, discolours and is prone to wear (Gardner et al., 2003). These drawbacks alter the mechanical properties of the retainer. Colonisation of these acrylic and plastic materials by bacteria warrant the need for meticulous cleaning (Chang et al., 2014). Discolouration can also occur to varying degrees. Furthermore, high water temperatures often used during the cleaning process will distort the thermoformed plastic retainers and to a lesser extent, acrylic-based retainers. In spite of the aesthetic advantages of these retainers, for many patients, the above drawbacks discourage long term compliance with removable retainer wear. Both vacuumformed thermoplastic and Hawley retainers have been shown to be less than optimal at holding corrections of the maxillary and mandibular labial segments (Rowland et al., 2007) and associated with considerable breakages (Hichens et al., 2007; Sun et al., 2011). In an effort to overcome the inadequacies of the acrylic and thermoformed plastic-based appliances used for patients with snoring and sleep apnoea, Ash and Smith (2004) have previously described a mandibular advancement appliance whose baseplates were constructed of chrome cobalt metal framework carrying acrylic inclined bite blocks similar to that used with a Twin Block functional appliance (Clark, 1982). Adapting the chrome cobalt framework, the authors developed a smaller and less obtrusive removable retainer with minimal coverage to provide long term strength, stability, facilitate the maintenance of good oral hygiene and contribute to long term patient compliance. This retainer has the added advantages of using simple well-established laboratory technology at a reasonably low cost (Ash, 2004).
Chrome cobalt retainer design Chrome cobalt as a base metal is incredibly hard having a modulus of elasticity of 220 GPa, a tensile strength
Removable cast chrome cobalt retainers
249
850 MPa and a VHN of 420 (McCabe and Walls, 2008). The material is able to withstand permanent deformation from the normal forces generated within the oral cavity; it is also both durable and scratch resistant. It has excellent corrosion resistant properties by virtue of the tenacious thin surface layer of chromic oxide (McCabe and Walls, 2008.) The material does not absorb moisture and is not readily colonised by oral bacteria or fungi. It is easily cleaned and appliances made from chrome cobalt can withstand, without fear of distortion, the reasonably high temperatures experienced when placed in boiling water. Chrome cobalt has been used as the material of choice in partial denture construction for many years (McCabe and Walls, 2008). As with any retainer, the appliance should be designed primarily to maintain the teeth in their corrected and aligned positions with particular attention to any tooth movements that are prone to relapse. Consideration needs to be given to balancing the retention capability of the appliance on the dentition while at the same time maximising patient comfort. The mandibular chrome cobalt retainer has a skeleton design (Figure 1). A thin, strong, and comfortable lingual plate covers the full lingual surface of the dentition. Occlusal rests extending from the lingual plate are placed on the buccal teeth to control any changes in the vertical position of these teeth (Figure 2). A close fitting labial bow ensures that, in conjunction with the lingual plate, the lower incisor and canine teeth are optimally retained (Figure 3). As with conventional partial denture construction, the dentition is surveyed on the working model to establish the correct path of insertion, clasps are designed with a dual function; they give retention to the retainer itself as well as provide retention to the teeth that were moved during
Figure 1 The mandibular chrome cobalt retainer with a skeleton design
250
Ash et al.
Clinical Section
JO 2015
incisor and canine teeth (Figure 3). As with the mandibular retainer, occlusal rests and clasps are placed on the buccal teeth. In occlusion, the posterior teeth are discluded by the metal onlays when either one or both of the retainers are worn. Ideally, upper and lower retainers should be worn simultaneously to ensure chrome cobalt to chrome cobalt contact via the metal onlays. This will reduce the risk of any long term chrome cobalt to tooth contact that may result in tooth wear. The extent of occlusal coverage is dependant on the occlusion and is at the discretion of the clinician.
Clinical management Figure 2 Occlusal rests extending from the lingual plate are placed on the buccal teeth to control any changes in the vertical position of these teeth
1. Primary retainers. After placement of fixed retainers in the desired arches, and following removal of active orthodontic appliances, impressions are taken for the construction of either acrylic ‘Hawley’ type retainers or thermoformed plastic ‘Essix’ type retainers. These retainers can be constructed within a short space of time and allow for minor tooth movements and occlusal settling to take place. 2. Final retainers. Once the occlusion has settled to the satisfaction of the clinician, a further set of accurate impressions are taken and should be cast in stone. The models are surveyed, the retainers are designed and the cast chrome cobalt retainers are produced. Laboratories producing cast chrome cobalt appliances require time, in some cases several weeks, during which time the treated dentition must be retained, hence another reason for the need to construct initial rapidly produced removable retainers. 3. Patient selection. Chrome cobalt retainers are associated with additional cost in terms of clinical time, laboratory time and materials, therefore, a judgement
Figure 3 A close fitting labial bow ensures that, in conjunction with the lingual plate, the incisor and canine teeth are optimally retained
orthodontic treatment. The correct path of insertion contributes to retention of the appliance. As the retainer and all its components are constructed from cast chrome cobalt, the appliance has minimal flexibility. To reduce the risk of inadvertent soft tissue injury during retainer insertion or removal, circumferential molar clasps are preferred to the open-ended distal clasps on the terminal molars. For the maxillary retainer, a horseshoe skeleton design with the baseplate covering part of the palate is preferred (Figure 4). Again, a close fitting labial bow retains the
Figure 4 The maxillary chrome cobalt retainer with a horseshoe skeleton
JO 2015
Clinical Section
has to be made with regard to the patient’s age and suitability for the provision of metal retainers in the knowledge that some patients may not wear the retainers or will fail to take adequate care of them. 4. Clinical instructions. Patients are instructed to wear both upper and lower cast metal retainers at night as their principal retainer. The ‘Essix’ or ‘Hawley’ type retainers may be kept and used as back up retainers if the need arises. In the event of a patient requiring restorative dentistry, they are advised to take both the chrome cobalt and ‘Essix/Hawley’ type retainers with them to the dentist to ensure that the restorative work can be accommodated or adapted without disturbing the fit of the retainers.
Associated clinical conditions Tooth clenching, bruxism and tempero-mandibular joint pain dysfunction (TMD) are clinical conditions that may require the use of removable appliances for an extended or indefinite period of time (Al-Ani et al., 2005). These appliances are generally constructed of acrylic or thermoformed plastic materials and again suffer the limitations of these materials as described previously. Patients presenting with periodontally comprised dentitions may in some cases benefit from dental splinting either post-orthodontic treatment or irrespective of orthodontics. While the six anterior teeth may be splinted using a conventional fixed lingual retainer, the posterior teeth would require the long term use of a removable retainer. Once again, for extended clinical use, acrylic or thermoformed plastic materials would suffer from the same drawbacks described above. In cases specifically requiring disocclusion, flat smooth occlusal coverage may be a solution. To splint mobile teeth, labial and/or lingual cast bars may be designed either in the form of a clasp or merely as a passive retainer. Clearly, the design of any retainer or therapeutic removable appliance will be based on the requirements for each individual case. Based on the limitations of the physical properties of plastic materials, it is our recommendation that for clinical conditions that require removable appliances to be worn for extended periods of time, the material of choice should be cast chrome cobalt.
Conclusion There is an increasing importance placed on the need for indefinite retention post-orthodontic treatment. Fixed retainers provide a discrete and low maintenance option for the anterior teeth; however, the remaining dentition
Removable cast chrome cobalt retainers
251
has traditionally required the need for an acrylic or thermoformed plastic retainer. For long term use, these materials have their limitations and cast chrome cobalt metal should be considered as an alternative material. Indefinite period of use of removable appliances for the treatment of para-functional clinical conditions such as clenching and bruxism and periodontal splinting could also be constructed in cast chrome cobalt. The physical characteristics of this material make it ideal for long term intra oral use. As part of an on-going developmental process of this appliance, the next steps should involve proper testing in appropriate clinical trials, looking particularly at patient satisfaction, compliance, cost-effectiveness and long term effects on the occlusion. Disclaimer Statements Contributors All authors contributed equally to the manuscript. Funding None. Conflicts of interest Simon Ash is Managing Director of Somnowell Ltd which is one of a number of companies that make chrome cobalt appliances. Ethics approval None. References Al-Ani Z, Grey RJ, Davies SJ, Sloan P, Glenny AM. Stabalization splint therapy for the treatment of temperomandibular pain: a systematic review. J Dent Educ 2005; 69: 1242 – 1250. Angle EH. Malocclusion of Teeth. 7th edn. Philadelphia: The SS White Dental Manufacturing Company, 1907. Ash SP. Retention. In Mizrahi E (ed.). Orthodontic Pearls. London: Taylor and Francis, 2004. 164 p. Ash SP, Smith AM. Chrome cobalt mandibular advancement appliances for managing snoring and obstructive sleep apnoea. J Orthod 2004; 31: 295–299. Cerny R, Cockrell D, Lloyd D. A survey of patient opinions on fixed vs. removable retainers. J Clin Orthod 2009; 43: 784 – 787. Chang CS, Al-Awadi S, Ready D, Noar J. As assessment of the effectiveness of mechanical and chemical cleaning of essix orthodontic retainer. J Orthod 2014; 41: 110 – 117. Clark WJ. The twin block traction technique. Eur J Orthod 1982; 4: 129 – 138. Gardner GD, Dunn WJ, Taloumis L. Wear comparison of thermoplastic materials used for orthodontics retainers. Am J Orthod Dentofacial Orthop 2003; 124: 294 – 297. Hichens L, Rowland H, Williams A, Hollinghurst S, Ewings P, Clark S, et al. Cost-effectiveness and patient satisfaction: Hawley and vacuum-formed retainers. Eur J Orthod 2007; 29: 372 – 378. Lang G, Alfter G, Go¨z G, Lang GH. Retention and stability - taking various treatment parameters into account. J Orofac Orthop 2002; 63: 26 –41. Lee RT. The lower incisor bonded retainer in clinical practice: a three year study. Br J Orthod 1981; 8, 15 – 8. ˚ rtun J. An evaluation of changes in mandibular anterior Little RM, Riedel RA, A alignment from 10 to 20 years post-retention. Am J Orthod Dentofacial Orthop 1988; 93: 423 – 428. Littlewood SJ, Millett DT, Doubleday B, Bearn DR, Worthington HV. Orthodontic retention: a systematic review. J Orthod 2006; 33: 205 –212.
252
Ash et al.
Clinical Section
McCabe JF, Walls AWG. Applied Dental Materials. 8th edn Oxford: Wiley-Blackwell Publishing, 2008. McGuinness NJ. Orthodontic evolution: an update for the general dental practitioner. Part 2: psychosocial aspects of orthodontic treatment, stability of treatment and the TMJ-orthodontic relationship. J Ir Dent Assoc 2008; 54: 128–131. Rowland H, Hichens L, Williams A, Hills D, Killingback N, Ewings P, et al. The effectiveness of Hawley and vacuum-formed retainers: a single-center randomized controlled trial. Am J Orthod Dentofacial Orthop 2007; 132: 730 – 737.
JO 2015
Sheridan JJ, LeDoux W, McMinn R. Essix retainers: fabrication and supervision for permanent retention. J Clin Orthod 1993; 27: 37 – 45. Singh P, Grammati S, Kirschen R. Orthodontic retention patterns in the United Kingdom. J Orthod 2009; 36: 115 – 121. Sun J, Yu YC, Liu MY, Chen L, Li HW, Zhang L, et al. Survival time comparison between Hawley and clear overlay retainers: a randomized trial. J Dent Res 2011; 90: 1197 – 1201. Zachrisson BU. Clinical experience with direct-bonded orthodontic retainers. Am J Orthod 1977; 71: 440 – 448.
Journal of Orthodontics, Vol. 42, 2015, 248– 252
Removable cast chrome cobalt retainers for extended or indefinite period clinical use Simon Ash1, Parmjit Singh2 and Eliakim Mizrahi3 1,2
BPP University, London, UK; 3Private practice, UK
Patients are frequently being asked to wear orthodontic retainers for as long as they want their teeth to remain in the post-treatment position. Fixed retainers, which are placed on the lingual surface of anterior teeth only, have the advantage of minimal compliance issues but are not without their problems related to wire fracture, adhesive failure and potential gingival or periodontal disease. Plastic retainers, although associated with relatively good aesthetics and compliance, have limitations related to their physical and mechanical properties. This paper describes a chrome cobalt metal retainer that could be used as a long-term retainer with few drawbacks. The properties of chrome cobalt are described and the clinical procedure is outlined. Key words: Chrome cobalt, removable retainer, retention Received 5 December 2014; accepted 23 February 2015
Introduction Angle stated in 1907 that ‘the problem involved in retention is so great as to test the utmost skill of the most competent orthodontist, often being greater than the difficulties being encountered in the treatment of the case up to this point’ (Angle, 1907). Currently, even after a century of continually progressive clinical treatment, extensive research and widespread in depth discussion, the regime for orthodontic retention remains a topic of unresolved passionate debate. In recent years, orthodontists have advocated the need for ‘retention for life’ to overcome the challenges associated with retention and relapse (Little et al., 1988; McGuinness, 2008). This philosophy is a consequence of the recognition that teeth will continue to move throughout life. Therefore, to maintain the desired result, there has to be a commitment on the part of the patient to a period of retention, which in many cases, extends for an indefinite period of time. Both the type of retainer and the retention regimen are now being considered just as important as the duration of retention (Lang et al., 2002). The methods for retention are broadly divided into fixed (bonded) and removable retainers. Methods for fixed retainer placement are varied and have been described (Zachrisson, 1977; Lee, 1981) with some clinicians advocating a preference for fixed retention regimes over removable retainers (Cerny et al., 2009). A survey of opinions comparing fixed versus removable retainers revealed that patients also favoured fixed retainers over those that were removable (Cerny et al., 2009).
Fixed retainers generally incorporate the maxillary and or mandibular six anterior teeth only and therefore have little effect in retaining the buccal segments. Consequently, clinicians are often obliged to additionally prescribe removable retainers to include and influence the full dentition. A survey of retention regimes in the United Kingdom found that vacuum formed thermoplastic retainers were more popular in National Health Service practice and hospital environments as well as private practice settings (Singh et al., 2009). Despite these retainers not being intended to be worn for long periods of time, 80% of respondents advocated indefinite retention with vacuum formed thermoplastic retainers and 72% with Hawley retainers. Fixed retainers were found to be more frequently used in private practice than in any of the other clinical settings (Singh et al., 2009). Following the era of vulcanite denture materials (McCabe and Walls, 2008), the introduction of acrylic resin was a major landmark in clinical dentistry and its associated disciplines; acrylic resin has now been in clinical use since 1940. Currently, conventional removable retainers comprise two groups, the acrylic ‘Hawley’ type retainer and the ‘Essix’ thermoformed plastic retainers (Sheridan et al., 1993; Littlewood et al., 2006). In spite of the many improvements in the chemical and physical properties of acrylic resins, ‘Hawley’ type retainers, which are constructed of either cold or heat cured acrylic and usually incorporate stainless steel wire components, have their drawbacks. The physical properties of the main constituent material is still characterised as being comparatively soft, weak and flexible. Typically,
*Address for correspondence: Parmjit Singh. E-mail: [email protected] # 2015 British Orthodontic Society
DOI 10.1179/1465313315Y.0000000006
JO 2015
Clinical Section
acrylic resins have a modulus of elasticity of 2.5 GPa, a tensile strength of 85 MPa and hardness value of 20 Vickers Hardness Numbers (VHN) (McCabe and Walls, 2008). The stainless steel components, while being stronger, more durable and more stable, suffer from work hardening. With constant and/or intermittent use over a period of time, the flexing of stainless steel wires used for cribs, finger springs or labial bows, become work-hardened and liable to fracture. The risk of fracture is further compounded by the physical interfaces between dissimilar materials such as acrylic and stainless steel when exposed to extremes of temperature. The pressure or vacuum formed ‘Essix’ type retainer is made from a thermoformed plastic and while the retainer may provide a satisfactory short-term means of retention, it has a limited life expectancy. Plastics worn in the mouth can deteriorate with time; the material is porous, absorbs water, discolours and is prone to wear (Gardner et al., 2003). These drawbacks alter the mechanical properties of the retainer. Colonisation of these acrylic and plastic materials by bacteria warrant the need for meticulous cleaning (Chang et al., 2014). Discolouration can also occur to varying degrees. Furthermore, high water temperatures often used during the cleaning process will distort the thermoformed plastic retainers and to a lesser extent, acrylic-based retainers. In spite of the aesthetic advantages of these retainers, for many patients, the above drawbacks discourage long term compliance with removable retainer wear. Both vacuumformed thermoplastic and Hawley retainers have been shown to be less than optimal at holding corrections of the maxillary and mandibular labial segments (Rowland et al., 2007) and associated with considerable breakages (Hichens et al., 2007; Sun et al., 2011). In an effort to overcome the inadequacies of the acrylic and thermoformed plastic-based appliances used for patients with snoring and sleep apnoea, Ash and Smith (2004) have previously described a mandibular advancement appliance whose baseplates were constructed of chrome cobalt metal framework carrying acrylic inclined bite blocks similar to that used with a Twin Block functional appliance (Clark, 1982). Adapting the chrome cobalt framework, the authors developed a smaller and less obtrusive removable retainer with minimal coverage to provide long term strength, stability, facilitate the maintenance of good oral hygiene and contribute to long term patient compliance. This retainer has the added advantages of using simple well-established laboratory technology at a reasonably low cost (Ash, 2004).
Chrome cobalt retainer design Chrome cobalt as a base metal is incredibly hard having a modulus of elasticity of 220 GPa, a tensile strength
Removable cast chrome cobalt retainers
249
850 MPa and a VHN of 420 (McCabe and Walls, 2008). The material is able to withstand permanent deformation from the normal forces generated within the oral cavity; it is also both durable and scratch resistant. It has excellent corrosion resistant properties by virtue of the tenacious thin surface layer of chromic oxide (McCabe and Walls, 2008.) The material does not absorb moisture and is not readily colonised by oral bacteria or fungi. It is easily cleaned and appliances made from chrome cobalt can withstand, without fear of distortion, the reasonably high temperatures experienced when placed in boiling water. Chrome cobalt has been used as the material of choice in partial denture construction for many years (McCabe and Walls, 2008). As with any retainer, the appliance should be designed primarily to maintain the teeth in their corrected and aligned positions with particular attention to any tooth movements that are prone to relapse. Consideration needs to be given to balancing the retention capability of the appliance on the dentition while at the same time maximising patient comfort. The mandibular chrome cobalt retainer has a skeleton design (Figure 1). A thin, strong, and comfortable lingual plate covers the full lingual surface of the dentition. Occlusal rests extending from the lingual plate are placed on the buccal teeth to control any changes in the vertical position of these teeth (Figure 2). A close fitting labial bow ensures that, in conjunction with the lingual plate, the lower incisor and canine teeth are optimally retained (Figure 3). As with conventional partial denture construction, the dentition is surveyed on the working model to establish the correct path of insertion, clasps are designed with a dual function; they give retention to the retainer itself as well as provide retention to the teeth that were moved during
Figure 1 The mandibular chrome cobalt retainer with a skeleton design
250
Ash et al.
Clinical Section
JO 2015
incisor and canine teeth (Figure 3). As with the mandibular retainer, occlusal rests and clasps are placed on the buccal teeth. In occlusion, the posterior teeth are discluded by the metal onlays when either one or both of the retainers are worn. Ideally, upper and lower retainers should be worn simultaneously to ensure chrome cobalt to chrome cobalt contact via the metal onlays. This will reduce the risk of any long term chrome cobalt to tooth contact that may result in tooth wear. The extent of occlusal coverage is dependant on the occlusion and is at the discretion of the clinician.
Clinical management Figure 2 Occlusal rests extending from the lingual plate are placed on the buccal teeth to control any changes in the vertical position of these teeth
1. Primary retainers. After placement of fixed retainers in the desired arches, and following removal of active orthodontic appliances, impressions are taken for the construction of either acrylic ‘Hawley’ type retainers or thermoformed plastic ‘Essix’ type retainers. These retainers can be constructed within a short space of time and allow for minor tooth movements and occlusal settling to take place. 2. Final retainers. Once the occlusion has settled to the satisfaction of the clinician, a further set of accurate impressions are taken and should be cast in stone. The models are surveyed, the retainers are designed and the cast chrome cobalt retainers are produced. Laboratories producing cast chrome cobalt appliances require time, in some cases several weeks, during which time the treated dentition must be retained, hence another reason for the need to construct initial rapidly produced removable retainers. 3. Patient selection. Chrome cobalt retainers are associated with additional cost in terms of clinical time, laboratory time and materials, therefore, a judgement
Figure 3 A close fitting labial bow ensures that, in conjunction with the lingual plate, the incisor and canine teeth are optimally retained
orthodontic treatment. The correct path of insertion contributes to retention of the appliance. As the retainer and all its components are constructed from cast chrome cobalt, the appliance has minimal flexibility. To reduce the risk of inadvertent soft tissue injury during retainer insertion or removal, circumferential molar clasps are preferred to the open-ended distal clasps on the terminal molars. For the maxillary retainer, a horseshoe skeleton design with the baseplate covering part of the palate is preferred (Figure 4). Again, a close fitting labial bow retains the
Figure 4 The maxillary chrome cobalt retainer with a horseshoe skeleton
JO 2015
Clinical Section
has to be made with regard to the patient’s age and suitability for the provision of metal retainers in the knowledge that some patients may not wear the retainers or will fail to take adequate care of them. 4. Clinical instructions. Patients are instructed to wear both upper and lower cast metal retainers at night as their principal retainer. The ‘Essix’ or ‘Hawley’ type retainers may be kept and used as back up retainers if the need arises. In the event of a patient requiring restorative dentistry, they are advised to take both the chrome cobalt and ‘Essix/Hawley’ type retainers with them to the dentist to ensure that the restorative work can be accommodated or adapted without disturbing the fit of the retainers.
Associated clinical conditions Tooth clenching, bruxism and tempero-mandibular joint pain dysfunction (TMD) are clinical conditions that may require the use of removable appliances for an extended or indefinite period of time (Al-Ani et al., 2005). These appliances are generally constructed of acrylic or thermoformed plastic materials and again suffer the limitations of these materials as described previously. Patients presenting with periodontally comprised dentitions may in some cases benefit from dental splinting either post-orthodontic treatment or irrespective of orthodontics. While the six anterior teeth may be splinted using a conventional fixed lingual retainer, the posterior teeth would require the long term use of a removable retainer. Once again, for extended clinical use, acrylic or thermoformed plastic materials would suffer from the same drawbacks described above. In cases specifically requiring disocclusion, flat smooth occlusal coverage may be a solution. To splint mobile teeth, labial and/or lingual cast bars may be designed either in the form of a clasp or merely as a passive retainer. Clearly, the design of any retainer or therapeutic removable appliance will be based on the requirements for each individual case. Based on the limitations of the physical properties of plastic materials, it is our recommendation that for clinical conditions that require removable appliances to be worn for extended periods of time, the material of choice should be cast chrome cobalt.
Conclusion There is an increasing importance placed on the need for indefinite retention post-orthodontic treatment. Fixed retainers provide a discrete and low maintenance option for the anterior teeth; however, the remaining dentition
Removable cast chrome cobalt retainers
251
has traditionally required the need for an acrylic or thermoformed plastic retainer. For long term use, these materials have their limitations and cast chrome cobalt metal should be considered as an alternative material. Indefinite period of use of removable appliances for the treatment of para-functional clinical conditions such as clenching and bruxism and periodontal splinting could also be constructed in cast chrome cobalt. The physical characteristics of this material make it ideal for long term intra oral use. As part of an on-going developmental process of this appliance, the next steps should involve proper testing in appropriate clinical trials, looking particularly at patient satisfaction, compliance, cost-effectiveness and long term effects on the occlusion. Disclaimer Statements Contributors All authors contributed equally to the manuscript. Funding None. Conflicts of interest Simon Ash is Managing Director of Somnowell Ltd which is one of a number of companies that make chrome cobalt appliances. Ethics approval None. References Al-Ani Z, Grey RJ, Davies SJ, Sloan P, Glenny AM. Stabalization splint therapy for the treatment of temperomandibular pain: a systematic review. J Dent Educ 2005; 69: 1242 – 1250. Angle EH. Malocclusion of Teeth. 7th edn. Philadelphia: The SS White Dental Manufacturing Company, 1907. Ash SP. Retention. In Mizrahi E (ed.). Orthodontic Pearls. London: Taylor and Francis, 2004. 164 p. Ash SP, Smith AM. Chrome cobalt mandibular advancement appliances for managing snoring and obstructive sleep apnoea. J Orthod 2004; 31: 295–299. Cerny R, Cockrell D, Lloyd D. A survey of patient opinions on fixed vs. removable retainers. J Clin Orthod 2009; 43: 784 – 787. Chang CS, Al-Awadi S, Ready D, Noar J. As assessment of the effectiveness of mechanical and chemical cleaning of essix orthodontic retainer. J Orthod 2014; 41: 110 – 117. Clark WJ. The twin block traction technique. Eur J Orthod 1982; 4: 129 – 138. Gardner GD, Dunn WJ, Taloumis L. Wear comparison of thermoplastic materials used for orthodontics retainers. Am J Orthod Dentofacial Orthop 2003; 124: 294 – 297. Hichens L, Rowland H, Williams A, Hollinghurst S, Ewings P, Clark S, et al. Cost-effectiveness and patient satisfaction: Hawley and vacuum-formed retainers. Eur J Orthod 2007; 29: 372 – 378. Lang G, Alfter G, Go¨z G, Lang GH. Retention and stability - taking various treatment parameters into account. J Orofac Orthop 2002; 63: 26 –41. Lee RT. The lower incisor bonded retainer in clinical practice: a three year study. Br J Orthod 1981; 8, 15 – 8. ˚ rtun J. An evaluation of changes in mandibular anterior Little RM, Riedel RA, A alignment from 10 to 20 years post-retention. Am J Orthod Dentofacial Orthop 1988; 93: 423 – 428. Littlewood SJ, Millett DT, Doubleday B, Bearn DR, Worthington HV. Orthodontic retention: a systematic review. J Orthod 2006; 33: 205 –212.
252
Ash et al.
Clinical Section
McCabe JF, Walls AWG. Applied Dental Materials. 8th edn Oxford: Wiley-Blackwell Publishing, 2008. McGuinness NJ. Orthodontic evolution: an update for the general dental practitioner. Part 2: psychosocial aspects of orthodontic treatment, stability of treatment and the TMJ-orthodontic relationship. J Ir Dent Assoc 2008; 54: 128–131. Rowland H, Hichens L, Williams A, Hills D, Killingback N, Ewings P, et al. The effectiveness of Hawley and vacuum-formed retainers: a single-center randomized controlled trial. Am J Orthod Dentofacial Orthop 2007; 132: 730 – 737.
JO 2015
Sheridan JJ, LeDoux W, McMinn R. Essix retainers: fabrication and supervision for permanent retention. J Clin Orthod 1993; 27: 37 – 45. Singh P, Grammati S, Kirschen R. Orthodontic retention patterns in the United Kingdom. J Orthod 2009; 36: 115 – 121. Sun J, Yu YC, Liu MY, Chen L, Li HW, Zhang L, et al. Survival time comparison between Hawley and clear overlay retainers: a randomized trial. J Dent Res 2011; 90: 1197 – 1201. Zachrisson BU. Clinical experience with direct-bonded orthodontic retainers. Am J Orthod 1977; 71: 440 – 448.
