Early-stage periodontal ligament compression predicts orthodontically induced root resorption in rats

OBJECTIVES

To determine the effect of orthodontic pressure on periodontal ligament (PDL) compression in rats and assess correlation between PDL compression and orthodontically induced root resorption (OIRR).

MATERIALS AND METHODS

Eight female Wistar rats aged 10 weeks underwent surgery to place 2 mini-screws at the center of the palatal plate. 25 cN coil springs connecting the maxillary first molars and mini-screws were applied bilaterally to generate mesial force. Maxillary first molars were assigned to undergo either bodily or tipping movements. Micro-computed tomography (μCT) scans were taken on days 0, 3, 7, and 14, and histological sections were taken on day 14. OIRR was measured from histological sections, and the corresponding PDL compression ratio was quantified using μCT images.

RESULTS

The PDL was compressed by approximately 76% in tipping movement and 55% in bodily movement after 3 days, and by approximately 47% in bodily and tipping movements after 7 days of orthodontic force application. The extent of OIRR in tipping movement was significantly greater than that in bodily movement. A strong positive correlation between OIRR and PDL compression ratio was observed on day 3; however, no correlation was observed on day 7.

CONCLUSIONS

A strong correlation between PDL compression ratio and OIRR was observed at an early stage after the application of orthodontic force regardless of the tooth movement type (bodily or tipping), implying the importance of early stage PDL compression in the induction of OIRR.

Serotonin and orthodontic tooth movement

Peripheral serotonin continuously reveals its unexpected involvements in many organ functions. In bone tissue, there is an increasing evidence for a local serotonergic system affecting the cellular and molecular actors involved in bone turnover. During orthodontic treatment, tooth movement relies on bone remodeling, itself a result of the inflammatory process triggered by application of orthodontic forces to the teeth. Nowadays, many adults proceed to an orthodontic treatment, it therefore seems important to consider physiological growth-related factors and external factors as medications that may influence adverse effects and efficacy of orthodontic treatment techniques. In this review, we focus on peripheral serotonin mechanism of regulation of bone remodeling during orthodontic movement. We discuss the differential effect of serotonin on alveolar bone inflammation that may open new strategies in orthodontics.