Inclusion of Second Molars and Outcomes of Orthodontic Treatment

Objectives: This retrospective study evaluated orthodontic cases and attempted to determine whether a significant correlation exists between the case outcome measured using the Cast-Radiographic Examination (CRE) and the initial eruption status of the second molars, as well as the inclusion and/or timing of banding or bonding (b/b) of the second molars. 

Methods: This study reviewed an initial sample of 569 consecutively completed cases from a graduate orthodontic clinic.  Inclusion criteria for the study included: 1) Cases completed between July 2006 and 2008, 2) Non-surgical cases, 3) Cases with complete pre-treatment/post-treatment records and 4) Cases with a minimum Discrepancy Index (DI) of 10.  For cases meeting the specified criteria (n=209) the DI and CRE scores, as well as, information regarding the (b/b) of second molars were recorded in a randomized de-identified Excel spreadsheet.  DI and CRE measurement reliability was assessed using interclass correlation coefficients (ICC).  Descriptive statistics and multiple regression analysis were completed.  Significance was established at 0.05. 

Results:  Excellent reliability was observed for both DI and CRE measurements (ICC>0.90).  The average overall CRE score was 27.7 and the average second molar CRE scores was 10.2, 36.8% of the total CRE.  No significant correlations were observed between overall CRE score and the (b/b) time of second molars, as well as the eruption status or inclusion of the second molars.  Treatment time was significantly impacted by both the bonding time (P=0.0012) and DI (p=0.0016).

Conclusions: Though the initial eruption status and the (b/b) timing of the second molars do not appear to affect overall CRE scores, clinicians should not treat second molars indiscriminately.  Our results support previous studies that illustrate second molars account for approximately one-third of the overall CRE score.  Therefore, an improvement in second molar CRE score would correspond to an improved total CRE score and improved orthodontic outcome.