Both PMMA (polymethylmetacrylate) microspheres (PM) and stabilized hyaluronic acid (HA) are recently used for facial augmentation. The aim of this study was to test functional effect, durability, and safety of the injection of these two materials into true vocal folds, and test their availability as injection laryngoplasty materials in vivo canine model. The study was carried out with 16 beagle dogs (8 males and 8 females, average weight of 12.4 kg). No biological difference was detected between two groups; PM (Artecoll) injection and HA (Restylane) injection group. After inducing complete unilateral paralysis of the recurrent laryngeal nerve of the dogs, either PM or HA was injected into the paralyzed vocal fold. One, 3, 6, and 9 months after the injection, clinical outcomes and videostroboscopic findings were evaluated by investigators who were blind to the injection materials. Histological study and microscopic computerized augmentation dimension analysis were also performed. In HA injection group, up to 30% the HA was gradually resorbed over time. However, in PM group, the dimension of the augmented region after 9 months was similar to that after 1 month. In both groups, the mucosal waves of the vocal folds decreased in amplitude and periodicity, but they were still well detected during the follow-up periods. Acute immune reaction to HA was not detected, but some degree of foreign body reaction occurred in PM injection group. Both PM and HA are safe and relatively durable in vocal folds and they are considered as useful candidates for injection laryngoplasty.
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