Deformation/recovery cycle of the periodontal ligament in human teeth with single or dual contact points

The recovery of the human periodontal ligament after transitory tooth deflection is largely obscured. The objective here was to determine the periodontal deformation/recovery cycle of a tooth with a single or dual contact point. ‘Single contact point’, refers to a tooth with a contact point on one side but not on the other; ‘dual contact point’ refers to a tooth with two contact points. The hypothesis that a single contact point will recover more slowly due to periodontal changes, as reported in hypofunctional conditions, was tested. The tightness of the contact point between contiguous mandibular premolars (P1–P2) during a deformation/recovery cycle was measured in three groups: group 1, single contact point of P2 (14 individuals with a missing mandibular first molar); group 2, dual contact point of the contralateral P2 (same 14 individuals with no missing mandibular first molar); group 3, dual contact point of both P2 (32 individuals with no missing mandibular first molars). The deformation/recovery cycle was initiated by placing a spacer for 1 min between P1 and P2. The recovery of the contact point P1–P2 to the initial tightness was recorded in five consecutive measurements: four of these were taken at 1-min intervals and an additional measurement was made 30 min later. The contact-point tightnesses of group 1 were significantly (P<0.001) lower (∼50%) than those of the control groups (groups 2 and 3). All groups showed a similar viscoelastic recovery pattern consisting of a short-term elastic response (after 1 min, 82% of the pre-deformation level was regained) and a long-term viscous response (after 30 min, an additional 6% was regained). Thus, contact-point tightness adjacent to an extraction site is strongly affected by the absence of the tooth and presumably due to reorganisation of the transseptal fibres, but this has no effect on the periodontal ligament deformation/recovery cycle, which showed a uniform viscoelastic response independent of contact-point tightness (rejecting the null hypothesis).