La force légère et le déplacement orthodontique : revue critique

Mechanical stress alters protein O-GlcNAc in human periodontal ligament cells

Protein O-linked N-acetylglucosamine (O-GlcNAc) is a post-translational modification of intracellular proteins that regulates several physiological and pathophysiological process, including response to various stressors. However, O-GlcNAc's response to mechanical stress has not been investigated yet. As human periodontal ligament (PDL) cells are stimulated by compression force during orthodontic tooth movement that results in structural remodelling, in this study we investigated whether mechanical stress induces any alteration in protein O-GlcNAc in PDL cells. In this study, PDL cells isolated from premolars extracted for orthodontic indications were exposed to 0, 1.5, 3, 7 and 14 g/cm² compression forces for 12 hours. Cell viability was measured by flow cytometry, and protein O-GlcNAc was analysed by Western blot. Cellular structure and intracellular distribution of O-GlcNAc was studied by immunofluorescence microscopy. We found that between 1.5 and 3 g/cm² mechanical compression, O-GlcNAc significantly elevated; however, at higher forces O-GlcNAc level was not increased. We also found that intracellular localization of O-GlcNAc proteins became more centralized under 2 g/cm² compression force. Our results suggest that structural changes stimulated by compression forces have a significant effect on the regulation of O-GlcNAc; thus, it might play a role in the mechanical stress adaptation of PDL cells.

Association of orthodontic force system and root resorption: A systematic review

INTRODUCTION

In this systematic review, we assessed the literature to determine which evidence level supports the association of orthodontic force system and root resorption.

METHODS

PubMed, Cochrane, and Embase databases were searched with no restrictions on year, publication status, or language. Selection criteria included human studies conducted with fixed orthodontic appliances or aligners, with at least 10 patients and the force system well described.

RESULTS

A total of 259 articles were retrieved in the initial search. After the review process, 21 full-text articles met the inclusion criteria. Sample sizes ranged from 10 to 73 patients. Most articles were classified as having high evidence levels and low risks of bias.

CONCLUSIONS

Although a meta-analysis was not performed, from the available literature, it seems that positive correlations exist between increased force levels and increased root resorption, as well as between increased treatment time and increased root resorption. Moreover, a pause in tooth movement seems to be beneficial in reducing root resorption because it allows the resorbed cementum to heal. The absence of a control group, selection criteria of patients, and adequate examinations before and after treatment are the most common methodology flaws.

A systematic review of force decay in orthodontic elastomeric power chains

INTRODUCTION

Elastomeric chains are one of several devices used to provide force for orthodontic tooth movement, but the force they exert diminishes over time and can thus be difficult to control. The objective of this investigation was to provide a systematic review of publications pertinent to force decay in orthodontic elastomeric chains.

MATERIALS AND METHODS

A systematic review was performed via electronic querying of multiple databases for the period 1970-2011. Queries were limited to a set of specific keywords in two languages (English and French). Five main reviews were consulted manually to identify relevant publications. Two investigators sorted out those studies that complied with selection criteria.

RESULTS AND DISCUSSION

A total of 53 studies were found to be relevant to force decay in elastomeric chains, including 22 on force decay over time, seven on the force consequences of pre-stretching, 12 on the impact of the environment on the force delivered, and 11 on clinical efficacy.

CONCLUSION

The force delivered by elastomeric chains decays rapidly over time, affecting their mechanical properties and clinical efficacy when studied in either human saliva or laboratory test media.