OBJECTIVE: To assess the success rate of spontaneous space closure after extraction of the first permanent molar (FPM) in the maxilla and the mandible, and to identify the factors that make spontaneous space closure most favorable in each.
METHODS: A retrospective records-based cohort study was conducted through a search of the database of the Public Dental Service, Stockholm County Council, Stockholm, for young adults born between 2000 and 2001, who underwent extraction of one or more FPM between 2006 and 2016. A total of 995 extracted teeth were identified, of which 203 teeth in 155 patients met the inclusion criteria.
RESULTS: Of the 203 extracted teeth, 166 (81.8%) did not receive any orthodontic treatment. The success rate for space closure in orthodontically treated patients was 91.9%. The success rate for spontaneous space closure was 84.3%. All unsuccessful spontaneous space closure in the maxilla occurred in patients older than 12 years. The dental developmental stage of the second permanent molar (SPM) had a statistically significant association with spontaneous space closure in the mandible (P < .001).
CONCLUSIONS: The success rate of spontaneous space closure was high (84.3%) and was higher in the maxilla (94.1%) than the mandible (74.1%). Age at time of extraction and dental developmental stage of the SPM were significant factors for successful spontaneous space closure in the maxilla and mandible, respectively.

OBJECTIVE: The aim of this study was to determine the prognostic factors, such as the developmental stage of second permanent molar (SPM), the angulation of SPM, and presence/absence of the third molar associated with the spontaneous space closure after the mandibular first permanent molars (FPM) extraction.
METHODS: A total of 177 mandibular SPMs were evaluated in this cross-sectional study. The prognostic factors determining successful space closure such as SPM developmental stage, SPM angulation, and presence/absence of the third molar were evaluated.
RESULTS: The mean age of the patients at the time of extraction of SPM was 9.4 years and post-extraction assessment at the time of the study was 12.7 years. Of the total 177 mandibular SPMs, 36 SPMs (20.3%) were at Demirjian stage D, 63 (35.6%) at stage E, 60 (34%) at stage F, 18 (10.1%) at stage G. 18 SPMs (10.1%) had distal angulation, 23 SPMs (13.0%) had mesial angulation and 136 SPMs (76.9%) had upright angulation. At the time of radiographic assessment, 79.1% of the mandibular quadrants showed evidence of third molar formation. Of the 177 mandibular SPMs, 93 (52.5%) exhibited successful space closure in the mandibular arch.
CONCLUSIONS: There is no statistical significance between the chronological age and the developmental stage of the mandibular SPM with regard to the successful spontaneous space closure at the time of the dental extraction of FPMs. The presence of the mandibular third molar may be a consideration for spontaneous space closure in the mandibular arch.