Title Extraction of Mandibular Third Molars Does Not Minimize Lower Arch Crowding
Clinical Question In a healthy adult patient, does extraction of mandibular third molars reduce the chance of late lower arch crowding when compared to no treatment?
Clinical Bottom Line The association of impacted, absent or erupted mandibular third molars and late lower arch anterior crowding is not strong enough to justify prophylactic removal or to predict the patient group at risk.
Best Evidence  
PubMed ID Author / Year Patient Group Study type
(level of evidence)
23385508Karasawa/2013300 Brazilian adolescent and adult volunteers with impacted, erupted, extracted or congenitally absent third molars.Cross-Sectional Study
Key resultsThe odds ratio of having lower third molars absent or present was 0.737, which fell into the 95 percent confidence interval. The odds ratio for having both upper and lower premolars absent or present was 1.221, which also fell into the 95 percent confidence interval. The presence or absence of mandibular and/or maxillary third molars, as well as the presence or absence of maxillary and mandibular premolars was found to have no influence on mandibular incisor crowding.
9668994Harradine/199877 patients with mean age of 20 years old, all of whom had undergone active orthodontic treatment in the upper arch, and only premolar extractions or no treatment in the lower arch . 44 were randomly selected to have third molars removed.Randomized Controlled Trial
Key resultsThe very small differences between first and second digitizations indicated an absence of systematic error and the random error variance was less than 3 percent of the total variance for all variables. The study reported a small but clinically insignificant increase in crowding with impacted third molars. There was an increase in incisor irregularity of 1.1 millimeters when third molars were present, compared to 0.8 millimeters third molars were extracted. There was no clinical or statistically significant differences in the inter-canine width between the groups.
Evidence Search MeSH terms: “molar, third”, “tooth extraction”, “tooth, impacted”, "malocclusion”
Comments on
The Evidence
In the cross-sectional study, 300 volunteers filled out a questionnaire and were given an oral examination to confirm the data. Observations of lower arch crowding and third molar presence were made without consideration for other known etiologic factors. Facial growth patterns, arch form, tooth size, and para-functional habits were among some of the other data not collected in this study. However, the data collected and statistical analyses performed suggested that there is no correlation between the presence of mandibular third molars and lower incisor crowding. In the Randomized Controlled Trial, only 77 of the original 164 patients were evaluated five years after completion of retention. Owing to the high percentage of non-responders, entry and exit casts were digitized and analyzed, and it was determined that there was no statistical difference between patients who entered and completed the trial and those who entered it and did not complete the 5-year review. The high drop-out rate, however, is a cause for concern. The study would also have allowed for better interpretation if the length of follow-up was 10 to 15 years. Some patients in the study had mandibular premolar extractions; however, the study doesn't compare the results between premolar extraction and non-extraction groups.
Applicability Although there is suggestion of the value of prophylactic removal of third molars to reduce the chance of late lower arch anterior crowding, the evidence does not support this. Impacted third molars are just one of the factors that cause late lower arch anterior crowding, in addition to differential mandibular growth, physiologic mesial drift, occlusion that applies anteriorly-directed forces on mesially-tipped teeth, and post-orthodontic relapse.
Specialty (General Dentistry) (Oral Surgery) (Orthodontics)
Keywords Third molars, crowding, extraction
ID# 2652
Date of submission 03/28/2014
E-mail reyesca@livemail.uthscsa.edu
Author Charles A. Reyes
Co-author(s) e-mail
Faculty mentor Peter T. Gakunga, BDS, MS, PhD
Faculty mentor e-mail gakunga@uthscsa.edu
Basic Science Rationale
(Mechanisms that may account for and/or explain the clinical question, i.e. is the answer to the clinical question consistent with basic biological, physical and/or behavioral science principles, laws and research?)
None available
Comments and Evidence-Based Updates on the CAT
None available