angle classification today, and post-treatment stability.
is considered the father of modern orthodontics. he classified malocclusions by the relationship of the mesio-buccal cusp of the upper first molar and the mesio-buccal groove of the lower first molar.
- class i: when the mesio-buccal cusp of the upper molar sits in the mesio-buccal groove of the lower first molar.
- class ii: when the upper molar cusp is placed anteriorly and there is an overjet (div1) or there is a compensatory retroclination of the upper incisors (div 2)
- class iii when the lower molar is anteriorly displaced, with or without a negative overjet (mandibular prognathy or maxillary retrognathism)
this classification has been the trademark of orthodontic treatment planing, since 1900 and it can be applied the same way on the upper and lower canine and premolars.
but have we gone any forward from what angle was teaching at the start of the 20th century, and how valuable is this classification today, what is the impact and is there a necessity to finish all our cases on a class i molar reletionship?
a revised classification was introduced from birte melsen and d.liu with a paper published in 2001 at the orthodontics and craniofacial research (reappraisal of class ii molar relationships, diagnosed from the lingual)
according to this key article on 459 clinically diagnosed class ii cases, found 85% of those cases been with upper molars rotated mesial, giving a more severe class ii from the buccal than the relationship was actually, once those molars were derotated. 55% of those cases were actually class i when classified from the lingual.
the angle classification, is the heritage of the orthodontic field, and also the way for orthodontists around the world to communicate with each-other when discussing a certain case or an article. for that it is valuable, but it does not affect solely the treatment option that will be chosen, or the success of the finished treatment or the big question of post-treatment stability.
there is a large number of factors mentioned through out the literature concerning stability post treatment. factors such as arch length, mandibular canine width, initial malocclusion and severity, extractions or non-extractions treatment, class i finishing and more. although some of those factors might seem logical to relate with the stability that is not the case especially in the long run, such as 10-20 years post treatment.
studies of little such as the one published in 1990 at the british journal, stability and relapse of dental alignment
shows (study of 600 cases with 10 years plus post treatment records, par index):
- arch length of treated cases reduces in retention, but so does in untreated cases
- mandibular canine width reduces in the long run, but it does wether if there was expansion during treatment or not.
- mandibular anterior crowding is a continuing phenomenon during the 20-40years range and maybe beyond.
- third molar absence, impaction or eruption seems to have a non significant impact in the anterior lower crowding.
- degree of post retention anterior crowding, can not be predicted individually with the up to date registrations and pre-treatment data collected.
another study from kuijpers jagtman, long term stability of orthodontic treatment in 2000
, (1016 patients sample with up to 10 years in retention) shows:
- 50% of the relapse, took place in the first 2 years in retention.
- largest relapse tendency was found on the lower anterior crowding, that after 10 years in retention, it was increased even more than the pre-treatment crowding of those patients.
with results like those, perhaps the straggle from us orthodontists of finishing a case correcting a 1mm midline discrepancy of the lower, or spending 2 months with artistic bends on the lower front to achieve a correction of 1mm contact point discrepancy, are only of "academic" value, and the minute that the plier debonds the bracket from the lower central, the correction we were straggling for 2 months is lost.
perhaps orthodontists should focus more on the aesthetics, from the patient's prospective. the chief complain of our patients, what brought them on our clinic doorstep. informing our patients of the certainty of the relapse after their orthodontic correction of their smile, and the need from their side to follow the retention protocol given, for life, if they want to sustain the result of their treatment.