It’s not that simple. The use of preventive and interceptive orthodontic appliances is intimately related to a fundamental knowledge of anatomy and physiology. An article in the December 2011 issue, “Space changes after premature loss of deciduous molars among Brazilian children,” aimed to assess dimensional changes in the maxillary and mandibular arches after premature loss of the first and second deciduous molars.

The conclusion suggesting that space maintainers “should only be indicated in cases of premature loss of the second deciduous molars and should be fitted within the first 3 months after the extractions” seems to be questionable, if analyzed separately. We believe that some considerations should have been taken into account during the analysis and discussion of the results.

• 1.

  The observation time (10 months) seems too short to reflect all alterations that might occur during the mixed dentition phase, between 6 and 11 or 12 years of age. Other studies, such as of that of Cuoghi et al, used longer observation times.

• 2.

  In determining the protocol to be followed during space control and maintenance procedures, what determines the type of treatment is the amount of tooth discrepancy (available space minus required space). In patients with positive discrepancies, a little space loss associated with the early loss of deciduous teeth will not have the impact it would have in those with no or negative discrepancies.

• 3.

  The type of malocclusion must be considered. The effect of the premature loss of the maxillary deciduous molars in Class II patients might be much more severe than that in Class I patients.

• 4.

  One should also consider that the premature loss of deciduous molars in the study under analysis was unilateral, affecting the space in only half of the arch. In patients whose premature loss occurs bilaterally, the use of space maintainers could be even more decisive in the maintenance of the arch perimeter, because deleterious effects might be doubled.