Duration of effectiveness of Botulinum toxin type A in excessive gingival display: a systematic review and meta-analysis

Abstract Botulinum toxin type A is effective in reducing excessive gingival display caused by hyperfunctional upper lip elevator muscles; however, this effect is transient. This study aimed to determine the duration of the effectiveness of botulinum toxin type A on a gummy smile. A systematic search was conducted using Medline (PubMed), Scopus, and Web of Science electronic databases, from 1970 to March 2017 with no language restriction; the search included studies evaluating adult patients with excessive gingival display who were treated with botulinum toxin and were followed-up for at least 3 months. OpenGrey and Clinical Trial Registry were also consulted. Quality assessment was applied to determine the level of evidence and bias, and a meta-analysis was performed. Of 2181 full texts, 71 were obtained, with 3 prospective studies meeting the selection criteria. The gingival display was significantly reduced to baseline with 2, 4, and 8 weeks of treatment. The gingival display considerably reduced at the baseline-2-week comparison (–4.44 mm using raw data and–4.05 mm using the standard difference) and increased throughout the weeks of follow-up. There is scant evidence to determine the duration of the effectiveness of toxin type A on a gummy smile. The effect tends to be stable until at least 8 weeks of follow-up, and the gingival exposure may not return to baseline within 12 weeks of follow-up. Well-designed randomized clinical trials with a minimum of 6 months of follow-up are necessary to strengthen the evidence.

摘要：A型肉毒毒素（Botulinum Toxin Type A）可有效改善由上唇提肌功能亢进引发的牙龈过度暴露，但该疗效具有一过性。本研究旨在明确A型肉毒毒素改善露龈微笑（gummy smile）的疗效持续时间。本研究系统检索了1970年至2017年3月期间Medline（PubMed）、Scopus及Web of Science电子数据库，未设置语言限制；纳入评估接受肉毒毒素治疗且至少随访3个月的牙龈过度暴露成年患者的相关研究，同时检索了OpenGrey及临床试验注册库。研究开展质量评估以明确证据等级与偏倚情况，并进行了荟萃分析。在2181篇全文文献中，最终纳入71篇，其中3项前瞻性研究符合纳入标准。治疗后2、4及8周时，牙龈暴露量均较基线显著降低。基线至2周时牙龈暴露量显著减少（原始数据为–4.44 mm，标准化均数差为–4.05 mm），且在后续随访周期中呈逐步升高趋势。目前关于A型肉毒毒素改善露龈微笑的疗效持续时间的证据仍较为有限。其疗效至少可稳定至随访8周，且在随访12周内牙龈暴露量可能未恢复至基线水平。未来需开展设计严谨的随机临床试验，且至少随访6个月，以进一步强化相关证据等级。