Second molar eruption disturbances in borderline extraction orthodontic patients

Nonextraction treatment is associated with a greater prevalence of third molar impactions, whereas data on second molars are lacking. This study investigated whether there is a difference in the prevalence of second molar eruption disturbances when crowding is treated with or without extractions.

Patients were grouped by maxillary and mandibular crowding, including mild crowding (<5 mm) without extractions, borderline crowding (5-9 mm) without extractions, and borderline crowding with extractions. The 535 evaluated arches were from 346 patients aged 10-15 years with unerupted second molars at treatment start. The frequency and severity of second molar eruption disturbances were scored in final records using a severity classification based on a modified Archer system, a hybrid Archer Pell-Gregory system, and a partial impaction scale. Pretreatment panoramic radiographs were scored for impaction-risk indicators. Fisher exact test was used.

In the maxilla, 20.0% of nonextraction patients with borderline crowding had second molar eruption disturbances compared to 5.2% of extraction patients with borderline crowding (P = 0.010). In the mandible, 27.6% of nonextraction borderline crowding patients had second molar eruption disturbances compared to 7.1% of extraction patients with borderline crowding (P = 0.006). There was no difference in the frequency of eruption disturbances between mild crowding without extractions and borderline crowding without extractions. The prevalence of impactions was higher in the maxilla when molars were apically positioned and in the mandible when molars were mesially angulated or had insufficient space pretreatment.

In patients with borderline crowding, extraction treatment reduces the risk of second molar eruption disturbances; however, nonextraction treatment does not increase the risk when compared with patients with mild crowding. When considering extractions for crowding, providers should evaluate second molar impaction-risk indicators on pretreatment radiographs.