Prosthodontics & Occlusion · patient case question
What best explains the difference between the two sides?
Patient case: Two missing first molars behaving differently
Patient: Male, 40 years old
Chief Complaint: “Food keeps packing on my lower left.”
Background: Both mandibular first molars, #19 and #30, were extracted at some point in the past and were never replaced. No orthodontic history. No parafunction reported.
Findings: On the LEFT, tooth #18 is tipped mesially, the edentulous space is visibly reduced, and contact with #20 is lost. On the RIGHT, tooth #31 stands upright and the space is close to its original mesiodistal width. Bone levels, periodontal condition and occlusal scheme are comparable on the two sides.
Show answer and explanation
Correct answer: A. The two teeth were extracted at different times
- A. CORRECT. Mesial drift and tipping of the tooth distal to an unrestored space is a TIME-DEPENDENT process. The mesial component of occlusal force acts continuously, and once the interproximal contact is lost there is nothing to resist it. Given one patient, comparable bone, comparable periodontal support and the same occlusal scheme on both sides, the only variable that accounts for marked tipping on one side and none on the other is how LONG each space has been open — #19 was lost considerably earlier than #30.
- B. Right and left mandibular bone density in a healthy patient is essentially symmetrical, and drift is driven by occlusal force vectors and lost proximal contact rather than by trabecular density.
- C. A habitual chewing side alters wear facets, calculus distribution and plaque accumulation. It does not selectively produce this degree of mesial tipping on the opposite side, and the stem gives no evidence of it.
- D. Ectopic eruption is a DEVELOPMENTAL event occurring at the time the tooth erupts, long before these extractions. The stem describes a tooth that has tipped INTO an acquired space.
Note: The full sequence after an unreplaced posterior tooth is worth reciting: mesial tipping of the distal tooth, over-eruption of the opposing tooth, drifting and rotation of the adjacent tooth, loss of proximal contact with food impaction, plaque retention and localised periodontal breakdown, and eventually a reduced prosthetic space. Clinically it matters because a tipped #18 usually needs orthodontic UPRIGHTING before it can carry a bridge retainer or receive a well-aligned restoration.
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