ABSTRACT
Objective: The aim of this research project was to determine whether the sizes of the first
molars allow clinicians to achieve the first goal of an ideal clinical outcome. Material and Methods: Seventy-eight sets of dental casts that have been presented to the American Board
of Orthodontics were evaluated. A Boley gauge was used to measure the length from
the mesiobuccal cusp to the distobuccal cusp of the maxillary first molar and the
length from the mesiobuccal groove of the mandibular first molar to the occlusal embrasure
between the mandibular first and second molars. These two measurements were taken
on both sides of each set of dental casts for a total of four measurements per set.
Results: The maxillary measurements ranged from 3.6 to 6.9 mm with an average of 5.2 mm. The
mandibular measurements ranged from 5.0 to 8.0 mm with an average of 6.5 mm. The data
were tested for normality and found to be equally distributed. A t-test revealed significant
differences in tooth sizes between maxillary and mandibular first molars on both sides.
On average, the mesiodistal length measured on maxillary first molars was about 80%
of that of their mandibular counterparts. Only 5 of the 78 sets of dental casts evaluated
had equal maxillary and mandibular measurements on one side (either left or right),
and none of them had equal measurements on both sides. Conclusion: Clinicians have to understand that tooth size discrepancies do exist in patients
and that these discrepancies make the completion of a perfect case challenging.
Key words:
Dental occlusion - mandible - maxilla - molar tooth - permanent dentition
