Impaction risk increases significantly with each year of late third molar development in Western Canadian youths.

Objective: Third molar (M3) impaction affects millions of patients annually worldwide yet its etiology is unclear. Here we study an underexplored risk factor for impaction, later versus earlier M3 development, towards calculating impaction risk as a resource for clinicians.

Design: A total of 324 M3 areas (157 maxillary, 167 mandibular) were studied using retrospective CBCT scans and orthopantomograms of 99 Western Canadians (57 females, 42 males) aged 6-24 years.

Unexpected variation of human molar size patterns.

A tenet of mammalian, including primate dental evolution, is the Inhibitory Cascade Model, where first molar (M1) size predicts in a linear cline the size and onset time of the second (M2) and third (M3) molars: a larger M1 portends a progressively smaller and later-developing M2 and M3. In contemporary modern Homo sapiens, later-developing M3s are less likely to erupt properly. The Inhibitory Cascade Model is also used to predict molar sizes of extinct taxa, including fossil Homo.

Third-molar mineralization as a function of available retromolar space.

Objective: To test in the maxilla and mandible for an association between stage of third-molar (M3) mineralization and space in the jaws for M3 eruption. Mineralization is hypothesized to be delayed not only for impacted M3s but also for M3s with eruption space less than their mesiodistal crown diameter.

Material And Methods: Retrospective cone beam computed tomography (CBCT) scans of 37 females and 32 males aged 17-24 years, for a total sample of 197 upper and lower M3s, were used to assess the status of M3 eruption and measure the M3 crown diameter (CD) relative to the length of the retromolar space (RS).