Important Aspects of Long-Term Stability

Journal of Clinical Orthodontics
Bjorn U. Zachrisson, DDS, MSD, PHD

Rotational Relapse

  • Broken Contact Points and Under-correction of Rotations
    • Common mistake is under-correction of rotations (9/10ths orthodontics)
    • Studies have shown that untreated normal occlusion in children can develop noticeable crowding in the mandibular incisors and that it is most commonly associated with broken contact points
    • Small contact points are not great, some advocate reshaping for larger contacts
  • Placing 2-2 Outside 3-3
    • Mandibular anterior is most common region for post-treatment relapse and crowding
    • Moderate crowding can be masked by placing the four incisors as a block outside the mesial contacts of the lower cuspids with the distal contact of the lateral slightly labial to the mesial of the cuspid
  • Early Correction of Rotations
    • Some claim the key to incisor stability is early treatment – possibly related to the stage of the transeptal fibers
    • Transeptal fibers do not develop until the CEJ of erupting teeth pass the bony border of the alveolus, therefore early correction implies that the correction occurred before the fiber arrangement is established
    • Many other factors also contribute – transosseous fibers, initial degree of rotation, effectiveness of fibrotomy procedure, retention appliance, length of retention
    • Fibrotomies appear more successful for maxillary anteriors than mandibulars – thought that lowers respond to tissue pressure more and rotate to the path of least resistance
    • SEM and TEM studies have shown that relapse is more associated with the elastic properties of the whole compressed gingival tissue than the stretched collagen fibers

Transverse Relapse

  • Mandibular Intercuspid Width
    • Do not increase cases with “normal” intercuspid width (24-26mm)
    • There is a decrease from post-treatment to post-retention in most cases
    • The decrease is greater for cases where the Intercuspid distance was increased
  • Mandibular Archform
    • Pretreatment archform should also not be altered and should be as close as possible to the pretreatment archform
  • Maxillary Archform
    • Maxillary archform should be altered in some cases – i.e. Class 2 Div. 1 patients where it is necessary to alter to archform to coordinate it with the lower
    • The greater the treatment change the greater the tendency for post-retention change
  • Rapid Maxillary Expansion
    • There are not many studies and there is no evidence to support that a stable enlargement of the maxillary basal bone that exceeds normal growth can occur
  • Clinical Implications
    • Best guidelines to future dental and archform stability may be the patient’s pretreatment mandibular Intercuspid width and mandibular archform
    • The maxillary archform should be respected but may need to be altered to coordinate with the mandibular arch
    • Fullness of smile should not be sought through lateral expansion and tipping of the maxillary teeth but rather through adjustment of the crown torque of the maxillary cuspids and bicuspids

Vertical Relapse

  • Deep Overbite
    • Deep overbites are caused by over-eruption of maxillary incisors, mandibular incisors or a combination of both
    • To achieve ideal function and esthetics it is important to determine which teeth are over-erupted, to analyze the lower lip-maxillary incisor relationship and to establish an optimal interincisal angle
  • Relationship Between Vertical Relapse and Mandibular Anterior Crowding
    • Many authors attribute overbite maintenance to the torque and axial inclination of the incisors – too upright in relation to each other will lead to a tendency to over-erupt following appliance removal
    • Another important factor is that the available space for the mandibular anterior teeth decreases as overbite increases
    • As the deep bite returns in a treated case the incisal edges of the mandibular incisors will occlude against the labiolingually thicker portion of the maxillary teeth which in turn restricts their space and produces lower incisor crowding or more rarely maxillary spacing
  • Mandibular First Bicuspid Extractions, Vertical Relapse, and Anterior Crowding
    • Excessive retraction of lower cuspids starts a vicious cycle – since the maxillary cuspids must occlude properly they end up over retracted and this leads to upper and lower incisors being too retracted which increased the need for anterior crown and root torque which can take a long time and is hard to achieve. 
    • Because of this mandibular first bicuspid extraction cases can end of with too large of an interincisal angle which in turn increases the possibility of vertical relapse and mandibular incisor crowding
    • U.S. Orthodontist seem to extract lower first bicuspids over seconds
    • Maxillary and mandibular second bicuspids were removed in only 7% of U.S. orthodontic extraction cases and maxillary first and mandibular seconds in only 8%.
    • Poor morphology is one reason for extracting lower 4s
    • One way to get around the problem of extracting lower 4s is to use an OCS between the 6 and 5 and then treat the like a lower 5 extraction case once the 5 contacts the 3
  • Clinical Implications
    • To correct in excessive overbite, we should intrude the offending teeth and an establish an ideal lower lip-to-maxillary incisor relationship and interincisal angle
    • When mandibular bicuspid extraction is necessary it is beneficial to consider extracting the 5s over the 4s if possible

Third Molars

  • Three-Dimensional Effects on Erupting Teeth
    • Post-pubertal mandibular crowding in both treated and untreated subjects appears multi-factorial
    • Mesially directed force is the most important cause of later mandibular crowding in the early teen years but direct cause and effect has been difficult to establish
    • Main reason thought for erupting thirds and late crowding to be controversial is the difficulty to perform a well isolated study
    • Normal eruption patterns are an upward and mesial direction – so one could see how eruption of thirds could cause crowding
  • Clinical Implications
    • Early extraction of mandibular third (or second) molars may make the first molars erupt in a less mesial direction
    • Mandibular third molar germs occupy space. If they are extracted, this space can probably be used for distal uprighting of the mandibular second molars in non-extraction therapy
    • Present studies of third molars are not optimally designed to establish any direct relationship between mandibular third molar eruption and increased mandibular crowding

Prolonged Retention

  • Retention Period
    • The retention period for both adolescent and adult patients should be indefinite – but this is considered impractical – so it is suggested that for males it be into their mid 20s and early 20s for females
    • The above also implies that the third molar situation has resolved it self
  • Fixed Retainers
    • When prolonged retention is given it is important that it be simple, safe, and hygienic
    • The authors preferred method is a solid mandibular 3-3 bar bonded only to the cuspids combined with a removable maxillary hawley
    • The patient needs to know to contact someone if the retainer ever breaks
  • Clinical Implications
    • Prolonged retention is recommended in adolescents to help withstand the effects of the post-pubertal growth period, at least until the third-molar situation has been resolved

Conclusion

  • The high prevalence of residual malocclusion after orthodontic therapy may be due to the following:
    • Incomplete correction of some details
    • Relapse due to unintended or deliberate lateral or frontal expansion, return of habits, inadequate retention, unfavorable growth pattern, tongue or orofacial muscle activity, or imbalances between mandibular posture and occlusal or eruptive forces, among other causes
    • Normal post-pubertal growth activity and maxillomandibular adjustments after the retention period
  • Cases treated to excellent results apparently have better long-term stability than those with 9/10ths orthodontics. Keys to improve long term stability include:
    • Full correction of rotations
    • Avoid altering lower Intercuspid distances
    • Ensure a small interincisal angle by monitoring torque
    • Use prolonged retention

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