Which periodontal fibre group primarily resists ROTATIONAL forces on a tooth?

Correct answer: D. Transseptal fibres

• A. Horizontal fibres resist lateral and tipping forces in the mid-root region.
• B. Apical fibres resist vertical intrusive forces and protect the neurovascular bundle entering the apex.
• C. Alveolar crest fibres resist intrusive, extrusive and lateral tipping forces, and maintain the tooth in its socket.
• D. CORRECT per the source key. The transseptal fibres run horizontally from the cementum of one tooth, over the alveolar crest, to the cementum of the adjacent tooth, tying the whole arch together as a continuous unit. Because they connect teeth to one another rather than to bone, they resist rotational and mesiodistal displacement and are a principal reason teeth relapse rotationally after orthodontic treatment.

Note: ⚑ Worth discussing in the group: some texts attribute rotational resistance to the free gingival CIRCULAR fibres, which encircle the tooth within the marginal gingiva. This is exactly why circumferential supracrestal fiberotomy is performed to reduce rotational relapse after orthodontics. Both answers appear in board materials; transseptal is what the source keyed.