An article written by Lilian-Harumi Karasawa and 4 others titled ” Cross-sectional study of correlation between mandibular incisor crowding and third molars in young Brazilians,” appears in Med Oral Patol Oral Cir Bucal (currently in press the version I have looked at but was accepted in November 2012). The article sets out to examine the correlation between lower incisor crowding and the mandible third molar (lower wisdom tooth). The ability of a lower wisdom tooth to have lower incisor crowding has been debated and looked at by many researchers over the years. See for example Review of the Wisdom Behind Third Molar Extractions. The possibility that a lower wisdom tooth can cause crowding is often given as a justification for removing a lower wisdom tooth to prevent abnormal orthodontic conditions.
In this study the researchers took 300 healthy Brazilian young adults which include 134 men with mean age 20.4±2.40 years-old and 166 women with mean age 20.5±2.43 years-old. The young adults filled out forms regarding their age, gender, and characteristics of their wisdom teeth such as if they were present or absent. This information was confirmed by oral examination and a recent panoramic radiography. Those in the study wearing prothesisis, had orthodontic appliances, and were missing teeth other than third molars were excluded. The researchers performed multiple logistic regression to analyze the relationship between mandibular incisor crowding and gender, upper and/or lower third-molar and/or premolars presence.
The results of the logistic regression showed that any of the studied factors influenced (p > 0.05) the mandibular incisor crowding. The odds ratio of a lower third molar when predicting manibular incisor crowding was found to be 0.7374 with a 95% confidence interval of (0.32, 1.70). The authors state “the results of the present study did not present correlation between third molars and lower incisor crowding.”
It is important to note that this study used a cross sectional design and not a longitudinal design. The authors state
“Cross-sectional studies like the present study can also be considered a satisfactory evaluation to observe the variables studied because do not present limitations as the longterm studies, can analyze the occurrence of events at the same time and its possible correlations.”
The authors state in the conclusion
“Although many theories have attempted to explain the reasons of the lower incisor crowding, many factors correlated or not among them, can be responsible for that dental condition. The present study does not provide enough clinical evidences about third molars as the etiologic factor in the late lower dental arch crowding”