The early removal of first permanent molars has several possible effects to the occlusion. This blog reviews some of the key aspects of first molar extractions of children, the ideal timing of their removal, as well as the role of balancing and compensatory extractions in light of the recent update to the first molar extraction guidelines by the Royal College of Surgeons of England. The topic of first molar extractions is debated, partly because the theory underpinning the ideal timing of extractions, balancing and compensatory extractions is very much plausible, however clinical observations and published research paints a less clear picture of what occurs, and indeed the value in elective extractions.
The removal of 1st molars are frequent, although rarely an orthodontists first choice, the experience of caries and molar-incisor hyper-mineralization, result in 12% of orthodontic clinic patients having loss of one or more of their first permanent molars Bradbury 1985. The prospect of reducing the need to orthodontically close the first molar space of 10.5 mm and preventing occlusal interference through over-eruption and tipping has resulted in interest in finding the ideal time for extraction. The established theory also considers elective removal of other first molars to reduce the space through spontaneous second molar mesial movement, as well as preventing occlusal interferences through over-eruption, as well as asymmetric changes. The terms compensating and balancing describe this process:
This blog will address both the timing of first molar extraction for spontaneous space closure, and the second half will assess the elective removal of other first molars for compensation and balancing.
Although this seems to be the most obvious topic to determine the success of spontaneous space closure in children, the large range of ages within the literature reduce the usability of the research. A systematic review concluded spontaneous space closure following maxillary first permanent molars occurred in 72% (CI 95% 63-82) of cases, with the highest chance in the 8.5-10 year old group. However, in the mandible the overall chance of spontaneous space closure was much lower at 48% (CI 95% 0.39; 0.58), with the highest chance of closure in the 10.5-11.5 year old age group Eichenberger 2015.
At this stage it is worth addressing why there is a difference in the probability of spontaneous space closure between the maxillary and mandibular second molars, there have been two reasons proposed; 1/ bony density is greater in the mandible, increasing the resistance to tooth movement, 2/ eruption paths differ. The maxillary second molar erupts distally, with a relatively mesial position of the apex. and during space closure the crown tips mesially as it uprights Crabb 1971. To contrast this the mandibular second molar erupts mesially with the apex positioned relatively distal to the first molar. As a consequence the second molar apex has a greater distance to move during space closure Crabb 1971.
Angulation of the second molar, presence of the third molar and the root development of the second molar, are the three variables considered when evaluating the patient’s likelihood of spontaneous space closure. The maxillary arch has a higher success rate of spontaneous space closure than the mandible, and interestingly none of the three variables seem to effect space closure in the maxilla. However the variables do effect the less willing mandibular space closure:
Mesial angulation second molar shows a greater likelihood of space closure 64-89%, when compared to upright or disto-angular second molars Patel 2017. The presence of third permanent molars has a consistent correlation between the presence of the mandibular developing third molars and spontaneous space closure of the mandibular first molar p=0002 Patel 2017. Root development of second molar through the timing of the calcification of the bifurcation has been proposed to increase the likelihood of spontaneous space closure. Research exploring second molar root development has found little relationship with mandibular second molar root development Teo 2015 Patel 2017.
Too early. Prior to the age of 8 the removal of the 1st molar can result in distal drifting of the 2nd premolar or bicuspid. The reason distal drifting occurs at this stage is due to the available space distal the 2nd premolar, and absence of the first molar to prevent distal drift Gill 2001. A solution of removal of the 2nd primary molar at the time of 1st molar removal has been proposed Gill 2001.
Too late. Once the 2nd molar has fully erupted, the probability of space closure occurring reduces, as well as other negative movement such as mesial tipping and rolling of the second molar and a scissor bite Gill 2001.
If the maxillary 1st molar is removed, the mandibular 1st molar is unlikely to over-erupt, however if the mandibular molar is removed there is a risk of the maxillary molar over-erupting. The consequences of the over-eruption of the maxillary first molar are two: first the over-eruption prevents spontaneous space closure by preventing mesial movement of the mandibular second molar, second there is reduced occlusal space in the mandibular arch for a prosthetic replacement of the first permanent molar. Another options instead of compensating to prevent over-eruption, the simple use of a retainer or a removable appliance will prevent over-eruption [Williams and Gowans, 2003].
A unilateral extraction of a first molar can result in both a dental and skeletal asymmetry. A study of an untreated sample with unilateral extractions of either maxillary or mandibular first molar found a small difference in the centrelines of 0.6 mm and 1.1 mm, but what was interesting was a mandibular asymmetry was found in both groups, a unilateral maxillary extraction on average resulted in a 1.32 mm mandibular asymmetry, and a mandibular unilateral extraction resulted in a 1.2 mm mandibular asymmetry. The reason for the skeletal asymmetry has been hypothesised as: 1/ asymmetry in muscular structure caused by unilateral chewing might cause asymmetry in skeletal structures, 2/ dental malocclusion caused by early loss of a first molar might be a factor for the development of such asymmetries.
The recently updated guidelines by the Royal College of Surgeons of England have changed their position on compensation need following mandibular first molar removal. The recommendations are: ” compensating … upper FPM (maxillary first molar) should not be routinely carried out unless there is a clear occlusal requirement or likelihood of the upper FPM (mandibular first molar) being unopposed for a significant period of time”. The current guidelines oppose the theory of compensation, and should only be implemented if there is an extended period of time the tooth is unopposed Noah 2023.
The current guidelines state “Routine balancing extraction of a sound FPM to preserve a dental centreline is not recommended unless part of a comprehensive orthodontic treatment plan.” Again the guidelines have seemingly contradicted the principle of balancing, however the research found a very small clinical difference, which are unlikely to be of significance to the management of routine patients.
The timing of first molar extractions vary depending on the arch in question. The maxillary arch is forgiving, with a broad range of interceptive timings and little influence of dental development, In the maxillary arch it is possible to achieve spontaneous space closure in the majority of cases. The mandible however is the less amenable jaw, with mesial angulation of the second molar and presence of the 3rd molar predictive factors for spontaneous space closure.
From the current guidelines the principles of compensation and balancing have been formally contested, and the elective removal of first molars now considered the reserve for the exception, rather than the previously considered rule.
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