An interesting article titled “Association between the presence of a partially erupted mandibular third molar and the existence of caries in the distal of the second molars,” appears in the International Journal of Oral and Maxilofacial Surgery by S. G. M. Falci and et. al. (October 2012, pp. 1270-1274). The article mentions how previous studies have shown that caries on the mandibular second molar due to the presence of partially erupted third molars has varied between 7% and 32%. The article criticizes prior work where studies based their prevalence data on panoramic radiographs which is not as good as periapical radiographs when diagnosing caries. The authors state
“The lack of sample characterization, the absence of sample calculation, the deficient or inadequate statistical analysis and the absence of a description of the eligibility criteria, discredits the scientific evidence of these previous studies.”
The authors performed an aprior sample size calculation and determined they needed 246 radiographs for adequate statistical type I and type II errors I presume. Some key findings are found in the results section of the paper.
The authors state
“The univariate logistical regression analysis showed that male patients, and patients aged 23–57 years, are the most likely to be affected by distal caries on the second molar. With respect to radiographic characteristics, mandibular third molars with an angulation between 31 and 108 degrees, a distance of 3–10 mm to the second molar and those classified as horizontal or mesioangular, were most likely to be linked to distal caries on the second molar.“
The authors also state
“The multivariate logistical regression analysis showed that only an angulation greater than 31 degrees (OR = 8.5 IC95%: 1.7–43.8) and the patient’s gender [being male] (OR = 3.3; IC95%: 1.4–7.7), had a statistically significant link to distal caries on the second molar, after adjusting for the age variable.”
Another interesting observation from this study as noted in the discussion is
“The percentage of patients in this study aged 23–57 years who showed signs of caries (19.3%), was higher than in those 16–22 years (8.8%). This finding is statistically significant. This result mirrors those of other studies”
One should also note that 177 female patients were included in the study with 17 of them (19.6%) showing signs of distal caries on the mandibular second molar and that 69 male patients were included in the study with 16 of them (23.2%) showing signs of distal caries on the mandibular second molar.