Regular nicotine intake increased tooth movement velocity, osteoclastogenesis and orthodontically induced dental root resorptions in a rat model

Abstract

Orthodontic forces have been reported to significantly increase nicotine-induced periodontal bone loss. At present, however, it is unknown, which further (side) effects can be expected during orthodontic treatment at a nicotine exposure corresponding to that of an average European smoker. 63 male Fischer344 rats were randomized in three consecutive experiments of 21 animals each (A/B/C) to 3 experimental groups (7 rats, 1/2/3): (A) cone-beam-computed tomography (CBCT); (B) histology/serology; (C) reverse-transcription quantitative real-time polymerase chain reaction (RT-qPCR)/cotinine serology-(1) control; (2) orthodontic tooth movement (OTM) of the first and second upper left molar (NiTi closed coil spring, 0.25 N); (3) OTM with 1.89 mg·kg^-1 per day s.c. of L(-)-nicotine. After 14 days of OTM, serum cotinine and IL-6 concentration as well as orthodontically induced inflammatory root resorption (OIIRR), osteoclast activity (histology), orthodontic tooth movement velocity (CBCT, within 14 and 28 days of OTM) and relative gene expression of known inflammatory and osteoclast markers were quantified in the dental-periodontal tissue (RT-qPCR). Animals exposed to nicotine showed significantly heightened serum cotinine and IL-6 levels corresponding to those of regular European smokers. Both the extent of root resorption, osteoclast activity, orthodontic tooth movement and gene expression of inflammatory and osteoclast markers were significantly increased compared to controls with and without OTM under the influence of nicotine. We conclude that apart from increased periodontal bone loss, a progression of dental root resorption and accelerated orthodontic tooth movement are to be anticipated during orthodontic therapy, if nicotine consumption is present. Thus patients should be informed about these risks and the necessity of nicotine abstinence during treatment.

Figure 1

Adult orthodontic patient with a long-term consumption of more than 10 cigarettes per day, requiring an orthodontic correction of the dental deep bite and misaligned first upper incisor. (a) Intraoral view; (b) panoramic radiograph of the dentition and alveolar jaw bone. The gingival tissue shows signs of inflammation and a general horizontal periodontal bone loss due to a chronic nicotine-induced periodontitis is evident.

Figure 2

Subcutaneous administration of L(−)-nicotine at a dosage of 1.89 mg per kg gross body weight per day (a) and experimental orthodontic tooth movement (b). To allow a secure injection without potential harm to the animal by inadvertent movements or an otherwise required sedation, a custom-made acrylic box for short-time immobilization (20 s) was used. By means of a NiTi closed coil spring the upper left first and second rat molars (M1/M2) were moved in anterior direction. The contralateral jaw side (wire ligature) served as non-force control (split-mouth design).

Figure 3

CBCT. Tooth movement was quantified within a defined two-dimensional plane of the rat skull in relation to a skull reference plane (SRP) and bias-corrected via the contralateral jaw side: (a) mesial angular tipping of first upper molar (M1), (b, c) mesial movement of second (b) and third (c) upper molars (M2/M3). inc., incisors. CBCT, cone-beam-computed tomography.

Figure 4

Histological sagittal-oblique sections of the distobuccal root of the upper left second rat molar (M2) after 14 days of tooth movement (TRAP-staining, × 40, scale bars: 200 μm). ImageJ-traced TRAP+ area (red-violet) is shown in black. 1, Pulpa dentis (dental pulp); 2, Dentinum (dentine); 3, Substantia ossea dentis (Cementum, cement); 4, Desmodontium (periodontal ligament); 5, Os alveolare (alveolar bone); * former location of wire traction ligature; blue arrows=dentine root resorption areas; CEJ, cemento-enamel junction; FP, furcation point; PBS, phosphate-buffered saline; TRAP, tartrate-resistant acid phosphatase. n=7 (number of samples per experimental group).