We appreciate the interest from the readers of the AJO-DO in our article (Fukaya S, Kanzaki H, Miyamoto Y, Yamaguchi Y, Nakamura Y. Possible alternative treatment for mandibular asymmetry by local unilateral IGF-1 injection into the mandibular condylar cavity: Experimental study in mice. Am J Orthod Dentofacial Orthop 2017;152:820-9).
We want to respond to the comments and question.
Thank you for the question about the dosage. We would like to explain the issues from 2 points: the injection volume and the amount of IGF-1 injected into the temporomandibular joint (TMJ) cavity. Regarding the injection volume into the TMJ cavity, we used mice for in-vivo experiments, whereas Suzuki et al used rats. Due to the difference of body sizes between rats and mice, researchers have injected 50 μL in rats, and 10 μL or 20 μL in mice. We first examined the adequate injection volume in mice, and the results of the pilot study showed that 20 μL was the adequate injection volume in mice. Therefore, we decided to inject 20 μL in our experiments.
The TMJ cavity in mice is small compared with that in rats. A high concentration of IGF-1 should be injected. We injected 20 μL of the solution containing 20 μg of IGF-1 into each cavity, which means that 1 mg per milliliter of IGF-1 was used in this study. On the other hand, Suzuki et al injected 20 μL of the solution of 50 μg per milliliter of IGF-1; this means that 1 μg of IGF-1 was injected per site. Compared with the study of Suzuki et al, we injected a 20-fold higher amount of IGF-1 into the TMJ cavity and obtained significant unilateral growth promotion. We had first examined the appropriate amount of IGF-1 for local injection in mice, and the results of our pilot study showed that 20 μg of IGF-1 per site is the appropriate amount, as far as we tested. Therefore, we decided to inject 20 μg of IGF-1 per site in our experiments.
Regarding the number of mice for each experiment, thank you for allowing us to confirm this. We wrote the total number of mice in each group in the Material and methods section (p. 821). In addition, the number of mice used for the bone apposition labeling study was also described on page 822. The detailed numbers of mice used for each experiment, such as histomorphometery, immunohistochemistry, and RT-PCR analysis, were described in the figure legends (Figs 3-7), respectively.
We hope that this additional information is satisfactory to you and the other readers of the AJO-DO.
∗ The viewpoints expressed are solely those of the author(s) and do not reflect those of the editor(s), publisher(s), or Association.