Microscopic and histochemical study of odontoclasts in physiologic resorption of teeth of the polyphyodont lizard, Liolaemus gravenhorsti

A conserved tooth resorption mechanism in modern and fossil snakes

Whether snakes evolved their elongated, limbless bodies or their specialized skulls and teeth first is a central question in squamate evolution. Identifying features shared between extant and fossil snakes is therefore key to unraveling the early evolution of this iconic reptile group. One promising candidate is their unusual mode of tooth replacement, whereby teeth are replaced without signs of external tooth resorption. We reveal through histological analysis that the lack of resorption pits in snakes is due to the unusual action of odontoclasts, which resorb dentine from within the pulp of the tooth. Internal tooth resorption is widespread in extant snakes, differs from replacement in other reptiles, and is even detectable via non-destructive μCT scanning, providing a method for identifying fossil snakes. We then detected internal tooth resorption in the fossil snake Yurlunggur, and one of the oldest snake fossils, Portugalophis, suggesting that it is one of the earliest innovations in Pan-Serpentes, likely preceding limb loss.

Histology of human teeth: Standard and specific staining methods revisited

OBJECTIVE

Histological techniques have long been an integral part of dental research. Especially the processing of complex tissues poses specific challenges, however, literature offers only few technical references. Objectives of this study were therefore to optimize histological staining methods and compile detailed protocols for preparation and staining of dental tissues.

METHODS

Human teeth were collected and fixed with 4 % formaldehyde solution after extraction. Subsequently, teeth were decalcified in 17 % EDTA or Morse's solution over a period of 28 days. The extent of decalcification was determined by weight loss and radiography. After sectioning, histological staining methods were optimized for their use on teeth. These included hematoxylin-eosin, Masson trichrome, Masson-Goldner trichrome and May-Gruenwald-Giemsa staining. Nerve fibres were visualized by luxol fast blue staining and Bodian silver staining. In addition, specific methods like TRAP, modified Brown and Brenn as well as picrosirius red staining with light polarization or fluorescence were applied and optimized.

RESULTS

Preparation of an artificial access to the pulp chamber was essential to ensure prompt penetration of the chemicals. Decalcification with Morse's solution took at least two weeks but was more efficient than 17 % ETDA, where thorough demineralization was achieved only after three weeks. The staining methods exhibited differences not only regarding their ability to display specific structures of interest, but also in terms of reproducibility.

CONCLUSION

High-quality histology of teeth can only be achieved after optimal tissue preparation and accurate staining. A complementary use of staining techniques is necessary to answer specific research questions.

Tooth attachment and pleurodont implantation in lizards: Histology, development, and evolution

Squamates present a unique challenge to the homology and evolution of tooth attachment tissues. Their stereotypically pleurodont teeth are fused in place by a single "bone of attachment", with seemingly dubious homology to the three-part tooth attachment system of mammals and crocodilians. Despite extensive debate over the interpretations of squamate pleurodonty, its phylogenetic significance, and the growing evidence from fossil amniotes for the homology of tooth attachment tissues, few studies have defined pleurodonty on histological grounds. Using a sample of extant squamate teeth that we organize into three broad categories of implantation, we investigate the histological and developmental properties of their dental tissues in multiple planes of section. We use these data to demonstrate the specific soft- and hard-tissue features of squamate teeth that produce their disparate tooth implantation modes. In addition, we describe cementum, periodontal ligaments, and alveolar bone in pleurodont squamates, dental tissues that were historically thought to be restricted to extant mammals and crocodilians. Moreover, we show how the differences between pleurodonty and thecodonty do not relate to the identity of the tooth attachment tissues, but rather the arrangements of homologous tissues around the teeth.

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

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.

Fate of Worn-Out Functional Teeth in the Upper Jaw Dentition of Sicyopterus japonicus (Gobioidei: Sicydiinae) During Tooth Replacement

Mochizuki and Fukui (Jpn J Ichthyol 30 () 27-36) studied the development and replacement of the upper jaw teeth in a Japanese fish species, Sicyopterus japonicus (Gobioidei: Sicydiinae), and they reported that worn-out functional teeth in the upper jaw were not shed outside the skin but were taken into the soft tissue of the upper jaw and completely resorbed there. To date, however, this phenomenon appears poorly documented. Furthermore, the mechanism for the resorption of these teeth remains to be determined. In this study, we examined this phenomenon by using 3D microcomputed tomography (m-CT), scanning electron microscopy (SEM), and various techniques of light (LM) and electron (EM) microcopy. This study demonstrated that the upper jaw dentition of this fish was more or less simultaneously replaced with the replacement occurring during short time periods and that the lingual movement of the replacement teeth to the functional tooth position advanced simultaneously in a given row. Furthermore, our study also revealed that many worn-out functional teeth were engulfed by the oral epithelium, invaginated into the lingual shallow ditch of the premaxilla, and were resorbed/degraded completely by numerous foreign body giant cells rather than by odontoclasts during periods of at least three intervals of tooth replacement. The complete resorption/degradation of worn-out functional teeth in the soft tissue of the upper jaw suggests the possibility of the reuse of their components (minerals such as Ca and P, including Fe) for rapid and successional production of new replacement teeth in the upper jaw of adult S. japonicus. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 301:111-124, 2018. © 2017 Wiley Periodicals, Inc.

Meloxicam medication reduces orthodontically induced dental root resorption and tooth movement velocity: a combined in vivo and in vitro study of dental-periodontal cells and tissue

Non-steroidal anti-inflammatory drugs (NSAID) are used to alleviate pain sensations during orthodontic therapy but are also assumed to interfere with associated pseudo-inflammatory reactions. In particular, the effects of partially selective COX-2 inhibition over the constitutively expressed COX-1 (11:1) on periodontal cells and tissue, as induced by the NSAID meloxicam, remain unclear. We investigate possible adverse side-effects and potentially useful beneficial effects during orthodontic therapy and examine underlying cellular and tissue reactions. We randomly assigned 63 male Fischer344 rats to three consecutive experiments of 21 animals each (cone-beam computed tomography; histology/serology; reverse-transcription quantitative real-time polymerase chain reaction) in three experimental groups (n = 7; control; orthodontic tooth movement [OTM] of the first/second upper left molars [NiTi coil spring, 0.25 N]; OTM with a daily oral meloxicam dose of 3 mg/kg). In vitro, we stimulated human periodontal ligament fibroblasts (hPDL) with orthodontic pressure (2 g/cm²) with/without meloxicam (10 μM). In vivo, meloxicam significantly reduced serum C-reactive protein concentration, tooth movement velocity, orthodontically induced dentine root resorption (OIRR), osteoclast activity and the relative expression of inflammatory/osteoclast marker genes within the dental-periodontal tissue, while presenting good gastric tolerance. In vitro, we observed a corresponding significant decrease of prostaglandin E₂/interleukin-6/RANKL(-OPG) expression and of hPDL-mediated osteoclastogenesis. By inhibiting prostaglandin synthesis, meloxicam seems to downregulate hPDL-mediated inflammation, RANKL-induced osteoclastogenesis and, consequently, tooth movement velocity by about 50%, thus limiting its suitability for analgesia during orthodontic therapy. However, its protective effects regarding OIRR and good tolerance profile suggest future prophylactic application, which merits its further investigation.

Interactive effects of periodontitis and orthodontic tooth movement on dental root resorption, tooth movement velocity and alveolar bone loss in a rat model

BACKGROUND

Many adult orthodontic patients suffer from chronic periodontitis with recurrent episodes of active periodontal inflammation. As their number is steadily increasing, orthodontists are more and more frequently challenged by respective treatment considerations. However, little is currently known regarding interactive effects on undesired dental root resorption (DRR), tooth movement velocity, periodontal bone loss and the underlying cellular and tissue reactions.

MATERIAL AND METHODS

A total of 63 male Fischer344 rats were used in three consecutive experiments employing 21 animals each (A/B/C), randomly assigned to 3 experimental groups (n=7, 1/2/3), respectively: (A) CBCT; (B) histology/serology; (C) RT-qPCR-(1) control; (2) orthodontic tooth movement (OTM) of the first/second upper left molars (NiTi coil spring, 0.25N); (3) OTM with experimentally induced periodontitis (cervical silk ligature). After 14days of OTM, we quantified blood leukocyte level, DRR, osteoclast activity and relative gene expression of inflammatory and osteoclast marker genes within the dental-periodontal tissue as well as tooth movement velocity and periodontal bone loss after 14 and 28 days.

RESULTS

The experimentally induced periodontal bone loss was significantly increased by concurrent orthodontic force application. Periodontal inflammation during OTM on the other hand significantly augmented the extent of DRR, relative expression of inflammatory/osteoclast marker genes, blood leukocyte level and periodontal osteoclast activity. In addition, contrary to previous studies, we observed a significant increase in tooth movement velocity.

CONCLUSIONS

Although accelerated tooth movement would be favourable for orthodontic treatment, our results suggest that orthodontic interventions should only be performed after successful systematic periodontal therapy and paused in case of recurrent active inflammation.