Reader's Forum

Q1. In the lingual system, the force to the center of resistance of a tooth is different from that in the labial system. In the present case, the upper incisors tipped lingually after intrusion, as shown in the cepha­ lometric superimpositions. I think that the intrusive force against the upper posterior teeth was applied lingually to the center of resistance, and, therefore, the upper posterior teeth tended to tip lingually as they were intruded. An excessive lingual tipping of the posterior teeth would enlarge the buccal corridor and, therefore, impair the smile esthetics. In addition, it would also impair the occlusal contacts on the lin­ gual side. Moreover, an excessive lingual tipping of these teeth would result in the fenestration of alve­ olar bone on the buccal side due to excessive buc­ cal tipping of roots. Did the authors consider these undesirable conditions during intrusion? More­ over, what measures did they adopt to prevent such excessive lingual tipping of the upper posterior teeth? Q2. Intrusive tooth movement has a high risk of root resorption. It is encouraging that there was no marked root resorption in the present case after intrusion. Nevertheless, the results need to be interpreted with caution. Root resorption is a three­dimensional phenomenon, while panoramic radiographs are two­dimensional images and, hence, underestimate root resorption. Compared with pa­ noramic radiography, cone­beam computed tomo­ graphy (CBCT) could more precisely help to monitor patients at risk of developing severe root resorption during orthodontic intrusion.