Effect of supplementary zinc on orthodontic tooth movement in a rat model

ABSTRACT Introduction: Osteoclasts and osteoblasts are responsible for regulating bone homeostasis during which the trace element zinc has been shown to exert a cumulative effect on bone mass by stimulating osteoblastic bone formation and inhibiting osteoclastic bone resorption. Objective: The aim of the present study was to investigate the effects of zinc (Zn) on orthodontic tooth movement (OTM) in a rat model. Material and Methods: A total of 44 male Wistar rats were divided into four groups of 11 animals each and received 0, 1.5, 20 and 50 ppm Zn in distilled water for 60 days. In the last 21 days of the study, nickel-titanium closed coil springs were ligated between maxillary right incisors and first molars of all rats, and tooth movement was measured at the end of this period. Histological analysis of hematoxylin/eosin slides was performed to assess root resorption lacunae, osteoclast number and periodontal ligament (PDL) width. Results: Mean OTM was calculated as 51.8, 49.1, 35.5 and 45 µm in the 0, 1.5, 20 and 50 ppm zinc-receiving groups, respectively. There were no significant differences in neither OTM nor histological parameters among the study groups (p > 0.05). Conclusion: According to the results obtained in the current investigation, increase in supplementary zinc up to 50 ppm does not affect the rate of OTM neither bone and root resorption in rats.

RESUMO Introdução: os osteoclastos e os osteoblastos são responsáveis por regular a homeostase óssea, processo no qual o oligoelemento zinco tem demonstrado exercer um efeito cumulativo sobre a massa óssea, estimulando a formação óssea osteoblástica e inibindo a reabsorção óssea osteoclástica. Objetivo: o objetivo do presente estudo foi investigar os efeitos do zinco (Zn) sobre a movimentação dentária ortodôntica (MDO) em ratos. Métodos: um total de 44 ratos Wistar machos foi dividido em quatro grupos de 11 animais cada, os quais receberam 0; 1,5; 20 e 50ppm de zinco diluído em água destilada, durante 60 dias. Nos últimos 21 dias do estudo, molas helicoidais fechadas de níquel-titânio foram instaladas entre os incisivos direitos e os primeiros molares superiores de todos os ratos, e a movimentação dentária foi medida ao final desse período. Foi realizada análise histológica de cortes corados por hematoxilina-eosina, para avaliar as lacunas de reabsorção radicular, o número de osteoclastos e a espessura do ligamento periodontal. Resultados: as médias da MDO foram estimadas em 51,8; 49,1; 35,5 e 45µm no grupos que receberam, respectivamente, 0; 1,5; 20 e 50ppm de zinco. Não houve diferença significativa entre os grupos experimentais, nem quanto à MDO, nem quanto aos parâmetros histológicos (p > 0,05). Conclusão: segundo os resultados obtidos na presente investigação, verificou-se que um aumento na dose de suplementação com zinco para 50ppm não afeta nem o índice de MDO, nem a reabsorção óssea ou radicular em ratos.

Laser-aided ceramic bracket debonding: a comprehensive review

Different techniques have been introduced for the removal of ceramic brackets. Since the early 1990s, lasers have been used experimentally for debonding ceramic brackets. The goal of this study is to give a comprehensive literature review on laser-aided ceramic bracket debonding. PubMed and Google Scholar databases were used to identify dental articles with the following combination of key words: Ceramic brackets, Debonding, and Laser. Sixteen English articles from 2004 to 2015 were selected. The selected studies were categorized according to the variables investigated including the intrapulpal temperature, shear bond strength, debonding time, enamel damage and bracket failure. Most articles reported decreased shear bond strength and debonding time following laser irradiation without any critical and irritating increase in pulpal temperature. There were no reports of bracket failure or enamel damage. Laser irradiation is an efficient way to reduce shear bond strength of ceramic bracket and debonding time. This technique is a safe way for removing ceramic bracket with minimal impact on intrapulpal temperature and enamel surface and it reduces ceramic bracket failure