We appreciate Dr Thakkar’s interest and questions about our article, “Distalization of the maxillary and mandibular dentitions with miniscrew anchorage in a patient with moderate Class I bimaxillary dentoalveolar protrusion” (Chen G, Teng F, Xu TM. Am J Orthod Dentofacial Orthop 2016;149:401-10).
The first questions are how the maxillary and mandibular dentitions were retracted and the amount of the retraction. It is really the point we are also eager to know. However, unlike a rigid tooth, a dentition bonded with fixed appliance is flexible, and the width and length could be changed during retraction; this means that every tooth in the dentition could move in a different way with a different amount. The flexibility and deformability of the dentition is mainly due to the archwire we used and the clearance between the archwire and the bracket slots. The archwire was 0.019 × 0.025-in stainless steel, which is suitable for space closure by sliding mechanics but does not have enough stiffness to control the dentition in 3 dimensions, especially in the transverse dimension. When distalizing the dentition, clearance of about 10° of the incisors mainly exists in the third order, whereas clearance of about 2.5° of the molars exists mainly in the second order. As a result, the tip of the central incisors moved farther than the tip of the second molars. The displacement of the apex of the roots is around 1 mm in both the middle incisors and the second molars. Thus, we believe that the incisors and molars were distally tipped in this case. However, it is still a problem to depict the movement of the whole dentition.
The second question is about the interradicular space. According to our clinical experience, the molar will tip distally, and the space needed for movement of the apex of the root is small when we retract the dentition in this way. The interradicular space is determined by several factors, including the mesiodistal width of the clinical crowns, the mesiodistal width of the roots, the shape and angulation of the neighboring teeth, and the height measured from the root apex. In this moderate Class I bimaxillary dentoalveolar protrusion case, the mesiodistal width of the roots (second premolar and first molar) and the angulation of the neighboring teeth (second premolar and first molar) were favorable. We didn’t quantify the interradicular space because the space was big enough. We usually quantify the space when all the space needs to be fully used. We agree that the dimensions of the miniscrews would decrease the amount of interradicular space available for distal movement, so we emphasized the accurate implantation of the miniscrews.
The third question is that the increase in SNA of 0.8° at posttreatment goes against the claim of distalization of the entire arch. The small increase of SNA doesn’t necessarily mean that A-point moved forward; it may have been caused by downward movement of A-point or just be due to the error of headfilm measurements.