Orthodontic records at seventeen

Correct answer: C. Mamelons on the maxillary central incisors

• A. This IS expected. Third molars typically complete root formation between 18 and 25 years, so open apices at 17 are normal — and third molar development is used in forensic age estimation for exactly this reason.
• B. This IS expected. Root formation of the permanent second molars completes at roughly 14 to 16 years, so fully formed roots at 17 are entirely normal.
• C. CORRECT as the exception. MAMELONS are the three rounded tubercles on the incisal edge of a NEWLY ERUPTED permanent incisor, representing the three developmental lobes of the crown. They are worn away by normal incisal function within a few years of eruption — and permanent incisors erupt at 7 to 9 years, so by 17 they should be long gone. Their PERSISTENCE means the incisors are not making functional contact, which points directly to an ANTERIOR OPEN BITE. In this patient the finding is not merely unexpected, it is diagnostic of the problem.
• D. This IS expected. Cementum is deposited THROUGHOUT life, unlike enamel. Continued apical and lateral apposition means it is thicker at 17 than at 8, and thicker still in old age.

Note: The trap is that mamelons feel like a ‘young person’ finding, and 17 feels young. The relevant age is the ERUPTION age of the tooth, not adolescence generally. Retained mamelons in an adult should always prompt a look at the incisal relationship — open bite, an edge-to-edge relationship, or a missing antagonist.

Correct answer: D. Skeletal Class II with an anterior open bite

• A. Skeletal Class III is ANB LESS than 2 degrees, often negative, with a concave profile and a reverse overjet. This patient's SNA exceeds SNB by 6 degrees, which is the opposite relationship.
• B. Skeletal Class I is ANB of roughly 2 to 4 degrees with a straight profile. This patient's ANB is +6. A deep bite is EXCESSIVE vertical overlap of the incisors — the opposite of what is described.
• C. The skeletal classification is right but the vertical description is wrong. There is NO vertical overlap of the incisors, which is an open bite, not a deep bite.
• D. CORRECT. ANB is the angular difference between SNA and SNB and expresses the anteroposterior relationship of maxilla to mandible relative to the cranial base. Normal is roughly 2 to 4 degrees; GREATER than 4 is SKELETAL CLASS II, here from a retrusive mandible (SNB 78) rather than a protrusive maxilla. The absence of vertical incisor overlap in occlusion is an ANTERIOR OPEN BITE, and the combination of Class II with open bite, a high mandibular plane angle, lip incompetence and a tongue thrust is a coherent and common vertical growth pattern.

Note: Keep SKELETAL classification (ANB, from the cephalogram) distinct from ANGLE'S classification (molar relationship, from the teeth). They often agree but need not, because dental compensation can mask a skeletal discrepancy entirely. Other values worth carrying: SNA 82±2°, SNB 80±2°, SN to mandibular plane about 32°, and the Frankfort-mandibular plane angle about 25°.