Concepts of Retention


Concepts of Retention

A basic distinction is made between retention of limited duration and long-term retention. The definitions relate to the duration of the retention, rather than to the mode of the retention (such as removable or fixed).

Retention Protocol

A general rule of thumb suggests that the duration of retention should be equal to or longer than the duration of active treatment. However, most contemporary orthodontists recommend that for shorter treatment durations in particular, long-term retention is advisable. Long-term retention with removable appliances can be difficult to achieve, however, as it relies heavily on patient compliance. Aids for monitoring the patient’s retainer wear have long been sought, and many attempts have been made to enhance or monitor patient compliance. A modern, cost effective option is available in the form of a microchip that is polymerized into the retainer acrylic (TheraMon, Fig. 9.3 ). TheraMon is an abbreviation of “therapeutic monitoring.” A thermosensitive microchip records the amount of time spent in the oral cavity. The information can then be read wirelessly and downloaded to a computer.

Relapse Prevention Based on the Original Malocclusion

Although there are no scientific data on the potential for relapse to the original malocclusion, it appears empirically sound to incorporate the pretreatment situation into the design of the retention protocol.

Standard Retainers

Following correction of dental alveolar discrepancies, retention with standard removable appliances, such as a Schwartz plate or Hawley or Van der Linden retainers, is generally sufficient. These retainers allow good settling of the occlusion, as they involve only little interocclusal interference, if any. Settling can be satisfactorily achieved with these appliances while at the same time maintaining the alignment of the labial segments ( Figs. 9.4 and 9.5 ).

Case Study 9.1 (Fig. 9.4)

Patient: G.B., female, age 14.

Diagnostic records: models, panoramic radiograph, lateral cephalometric radiograph, intraoral/extraoral photographs.

Main findings: buccally positioned tooth 13 and right-sided unilateral open bite.

Treatment aims: alignment of tooth 13 and establishment of solid occlusion.

Appliances: Self-ligating brackets.

Archwire sequence: 0.012 SE, 0.016 SE, 0.016 × 0.022 SE, 0.018 × 0.025 SE, 0.019 × 0.025 SS.

Alternative treatment strategy: n/a.

Active treatment time: 11 months.

Retention: three-dimensional retention, allowing settling.

Fig. 9.4 1–24 1–5 The pretreatment situation, with tooth 13 positioned buccally and a right-sided open bite. 6–10 Self-ligating brackets with full initial 0.012 SE archwire, immediately fully engaged in all brackets. 11–19 Treatment progress with alignment of tooth 13 (top), subsequent settling of the occlusion (center), and the final result (bottom). 20–24 Retention was achieved with a Van der Linden retainer in the maxilla and a modified Hawley retainer in the mandible. The Van der Linden retainer makes it possible to correct the position of the canine during retention if necessary. The residual space in the area of 22 can be closed by activating the labial bow. The appliance is retained by two c-clasps at the first molars. This design allows vertical settling of the occlusion. 19–23 The result after 1 year of retention.

The modified Hawley retainer has two Adams clasps on first molars to which the labial bow is soldered. This design shortens the labial bow and makes it more resistant to deformation in comparison to a Begg retainer but yet allowing settling of the posterior occlusion.

Case Study 9.2 (Fig. 9.5)

Patient: J.H., female, age 13.

Diagnostic records: models, panoramic radiograph, lateral cephalometric radiograph, intraoral/extraoral photographs.

Main findings: deep bite and class II tendency with maxillary and mandibular anterior crowding.

Treatment aims: bite opening and alignment.

Appliances: Self-ligating brackets, anterior bite elevators.

Archwire sequence: 0.012 SE, 0.016 SE, 0.016 × 0.022 SE, 0.018 × 0.025 SE, 0.019 × 0.025 SS.

Alternative treatment strategy: n/a.

Active treatment time: 10 months.

Retention: three-dimensional retention with Hawley retainers.

Fig. 9.5 1–23 1–5 The pretreatment situation shows a deep bite with an accentuated curve of Spee. The diagnostic work-up revealed a dentoalveolar cause, with adequate skeletal bases. 6–10 Self-ligating brackets with a ligated 0.012 SE archwire. The fixed-appliance therapy was supported by anterior bite planes, which allowed for extrusion of buccal segments, and intrusion of incisors. Anteroposterior correction with elastics. The treatment aims were achieved in 10 months. 11–13 An inadequately settled posterior occlusion became apparent after debonding. 14–18 Maxillary and mandibular Hawley retainers were used for retention and to allow settling of the posterior occlusion.

Retention of Transverse Corrections

After transverse corrections (particularly expansion of the upper jaw), a Hawley retainer or Schwartz plate is customarily used for retention. These can be fitted with a partially preexpanded midline screw. If the appliance is not worn for some time, the screw can be contracted, and the plate can be inserted again and then reexpanded to its original size.

Retention of Class II Cases

Orthodontically corrected skeletal discrepancies of the class II type often benefit from long-term retention of the sagittal correction. The present authors prefer to use vacuum-formed retainers fitted with the advancement components of Kinzinger’s Functional Mandibular Advancer (FMA) ( Fig. 9.6 ).7 , 8 The vacuum-formed retainers provide good retention of the alignment of the labial segments while at the same time being rigid and retentive enough to allow forward positioning of the lower jaw. If required, minor tooth movement is possible with these retainers by means of an individual set-up ( Fig. 9.7 ).

Retention in Class III Cases

Further developments in patients with a previously corrected class III malocclusion are difficult to anticipate, as the residual growth potential remains unknown. It therefore seems all the more important to achieve a final result with good cusp embrasure and anterior coupling, as a tight occlusal relationship is considered to be the best form of retention for class III patients. Tissue or tooth borne functional appliances (such as Fränkel III, ‘Reverse Twin Block’ and ‘Reverse Double Plate’ respectively) should also be considered for retention of treated class III malocclusions.

Fig. 9.6a, b Components of Kinzinger’s Functional Mandibular Advancer (FMA). The guiding rods can be attached to the support bar with an Allen screw in three different positions. The appliance is fabricated to a protrusive wax bite with the guiding rods in the most distal position, allowing later activation by moving them mesially.
Fig. 9.7a–d Functional Mandibular Advancer splints in an overcorrected position. The working models shows the guiding mechanism of the appliance and an integrated set-up for the mandibular incisors. Simple removal of the guiding rods by unscrewing the fixtures allows for follow-up of the stability of the class II correction.
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Jul 7, 2020 | Posted by in Orthodontics | Comments Off on Concepts of Retention
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