Catherine Nyssen-Behets

Does orthodontic loading influence bone mineral density around titanium miniplates? An experimental study in dogs

OBJECTIVES To evaluate whether orthodontic loading has an effect on miniplate stability and bone mineral density (BMD) around the screws supporting those miniplates. SETTING AND SAMPLE POPULATION Two miniplates were inserted in each jaw quadrant of 10 dogs. MATERIAL AND METHODS Two weeks later, coil springs were placed between the miniplates of one upper quadrant and between those of the contralateral lower quadrant. The other miniplates remained non-loaded. The dogs were sacrificed 7 or 29 weeks after surgery, and the jaws were scanned with peripheral Quantitative Computed Tomography (pQCT) to assess BMD. RESULTS The success rate was not significantly different for the loaded and the non-loaded miniplates, but was significantly higher for the maxillary compared to the mandibular ones. Mobility, associated with local inflammation, most often occurred during the transition between primary and secondary stability. pQCT showed higher BMD around mandibular vs. maxillary screws, without significant difference between loaded and non-loaded ones. Furthermore, load direction did not lead to any significant difference in BMD. CONCLUSION Miniplate stability and BMD of the adjacent bone did not appear to depend significantly on orthodontic loading, but rather on the receptor site anatomy.

Orthodontic loading of titanium miniplates in dogs: microradiographic and histological evaluation

OBJECTIVES The objectives of this animal study were to evaluate if orthodontic loading has an impact on osseointegration of screws supporting miniplates, and to describe the histological components of the bone-screw interface. MATERIALS AND METHODS Eighty orthodontic miniplates were placed in the jaws of 10 dogs. After 2 weeks, a 125 g force was applied between the miniplates of one upper quadrant of each dog and between those of the controlateral lower quadrant. The others, nonloaded miniplates, were considered as controls. Five dogs were sacrificed 7 weeks after implantation and the remaining five dogs after 29 weeks [Short Term (ST) and Long Term (LT) groups, respectively]. Fluorochromes were injected at implantation and at sacrifice. Jaw quadrants were dissected, embedded, cut into undecalcified transverse sections through the screws and finally submitted to microradiographic analysis to allow assessment of bone-implant contact (BIC) and bone volume/total volume (BV/TV). The sections were observed under UV light and stained in order to examine them under ordinary light. RESULTS Osseointegration occurred around 90/160 screws and consisted mainly in limited repair and remodelling processes of lamellar bone, without inflammation. Wide variations were observed in BIC and BV/TV, but without any significant difference, neither between the loaded and the nonloaded screws, nor according to the direction of load, whereas they were significantly higher in the LT than in the ST group. Nonosseointegrated screws were surrounded by fibrous tissue. Osteoblastic activity, when present in front of these screws, was not sufficient to achieve stability. CONCLUSIONS Osseointegration underlying orthodontic anchorage was not affected by loading. BIC increased with time and varied according to implantation site. Particularly the tight-fitting screw insertion appeared crucial in determining the appropriate bone healing response.

Microradiography and Fluorescence Microscopy of Bone Remodeling on the Basal Crypt of Permanent Mandibular Premolars in Dogs during Eruption

Alveolar bone of erupting teeth was studied in order to define the types of calcified tissues deposited as well as the rate of tooth growth. The third (P3) and fourth (P4) mandibular premolars of 30 dogs aged 12-24 weeks were analyzed by microradiography and microscopy in fluorescent and ordinary light. The bone plate separating P3 and P4 from the mandibular canal presented a complex arrangement of lamellar and woven bone, and even of chondroid tissue. During the pre-eruptive phase, this plate shifted towards the base of the mandible by means of selective resorption and apposition activities. As soon as the furcation was formed, bone apposition appeared on the alveolar side and became the main activity under P3 at the outset of eruption. Under the roots of P4 it occurred 4 weeks later. Dynamic morphometry in fluorescence microscopy showed that eruption progressed faster than the radicular growth. The formation of interradicular bone underwent the same acceleration as the eruption. However, though the tissues were formed at a high rate, it cannot be inferred therefrom that they are responsible for tooth shifting. They might just fill the space left by the erupting tooth.

Molecular Study of a Hoxa2 Gain-of-Function in Chondrogenesis: A Model of Idiopathic Proportionate Short Stature

In a previous study using transgenic mice ectopically expressing Hoxa2 during chondrogenesis, we associated the animal phenotype to human idiopathic proportionate short stature. Our analysis showed that this overall size reduction was correlated with a negative influence of Hoxa2 at the first step of endochondral ossification. However, the molecular pathways leading to such phenotype are still unknown. Using protein immunodetection and histological techniques comparing transgenic mice to controls, we show here that the persistent expression of Hoxa2 in chondrogenic territories provokes a general down-regulation of the main factors controlling the differentiation cascade, such as Bapx1, Bmp7, Bmpr1a, Ihh, Msx1, Pax9, Sox6, Sox9 and Wnt5a. These data confirm the impairment of chondrogenic differentiation by Hoxa2 overexpression. They also show a selective effect of Hoxa2 on endochondral ossification processes since Gdf5 and Gdf10, and Bmp4 or PthrP were up-regulated and unmodified, respectively. Since Hoxa2 deregulation in mice induces a proportionate short stature phenotype mimicking human idiopathic conditions, our results give an insight into understanding proportionate short stature pathogenesis by highlighting molecular factors whose combined deregulation may be involved in such a disease.

Influence of sodium hypochlorite on Er:YAG laser-irradiated dentin and its effect on the quality of adaptation of the composite restoration margins.

OBJECTIVE The aims of this in vitro study were to evaluate: (1) the influence of 5% NaOCl application on Er:YAG-irradiated dentin; and (2) its effect on the quality of adaptation of the composite restoration margins. BACKGROUND DATA Previous research has shown that Er:YAG dentin irradiation produces a thermally affected tissue layer that results in lower bond strength than that of nonirradiated dentin. The removal of this thermally-affected layer may enhance the quality of dentin bonding. MATERIALS AND METHODS Forty-nine caries-free extracted human molars were transversely sectioned in order to totally expose the dentin. Four standardized cavities were created on the dentinal surface of each molar. First, two cavities were irradiated with Er:YAG laser (2.94 nm): 150 mJ, 10 Hz, variable square pulse (VSP) mode (100 μsec), beam diameter=0.9 mm, speed of irradiation=1 mm/sec, 20% air and 20% water. Then, one of irradiated cavities and one of nonirradiated cavities were treated for 30 sec with 5% NaOCl solution. Finally, they went through a standard bonding treatment for composite restoration, etching, bonding, and composite filling. We obtained four groups of cavities: (1) one control group of nonirradiated cavities not pretreated with NaOCl; (2) one group of nonirradiated cavities, pretreated with NaOCl; (3) one group of irradiated cavities, not pretreated with NaOCl; and (4) one group of irradiated cavities, pretreated with NaOCl. All samples were subjected to thermocycling. Every cavity was immersed into a 0.5% solution of methylene blue. The percentage of dye penetration (microleakage) in the composite-dentin interface was evaluated. Six molars were analyzed by scanning electron microscope. RESULTS Dye infiltration depth was significantly reduced in irradiated cavities treated with 5% NaOCl solution. CONCLUSIONS The application of a 5% NaOCl solution on Er:YAG irradiated cavities can significantly improve the marginal quality of composite bonding.

Management of root perforations using MTA with or without er / YAG laser irradiation : an in vitro study

The aim of this in vitro study is to compare the microleakage of a root perforation sealed with MTA (mineral trioxide aggregate) (group M) to that sealed with MTA following Er:YAG laser irradiation (group ML). Forty-two recently extracted human monoroot teeth were used. Two cavities were prepared on each root surface. Randomly, on each root, the exposed dentine of one cavity was irradiated prior to MTA filling using an Er:YAG laser with the following settings: 200 mJ/pulses under an air water spray, 10 Hz, pulse duration of 50 μsec, and 0.7 mm beam diameter. All cavities were then sealed with MTA. submitted to thermocycling and immersed in 2% methylene blue dye solution for 12 h. The penetration of methylene blue in the microleakage of cavity was observed and recorded. The mean value dye penetration in cavities sealed with MTA following Er:YAG laser irradiation (23.91 ± 14.63%) was lower than that of unlased cavities sealed only with MTA (25.17 ± 17.53%). No significant difference was noted. The use of an Er:YAG laser beam for dentinal conditioning prior to MTA filling of perforated roots did not decrease significantly the microleakage of MTA sealing when compared to the conventional use of MTA filling.

Postnatal growth defect in mice upon persistent Hoxa2 expression in the chondrogenic cell lineage

Hoxa2 is a homeotic transcription factor, which is downregulated once chondrogenic differentiation is initiated. We previously generated a transgenic mouse model, which turns Hoxa2 on in cells expressing Collagen II A1, i.e. in cells entering chondrogenesis. As a consequence, mice display a general embryonic delay of ossification and then a postnatal growth defect. Col2a1-Cre mice were crossed with an inducible β-actin driven Hoxa2 transgene. Spines, vertebrae and limbs were measured and skeletal elements were studied by X-ray, microCT, pQCT, TEM, western-blotting, histomorphometry and immunohistochemistry. Mice expressing Hoxa2 in chondrogenic cells feature a proportionate short stature phenotype with a severe lordosis, which appeared significant from postnatal day 4. Analysis of both cartilage and bone development in affected embryos and mice from birth till P35 did not reveal any major defect in histogenesis, except a reduced number of chondrocytes in the vertebral anlage at E13.5. In conclusion, the sustained expression of Hoxa2 in the chondrocyte lineage is characterized by a proportionate short stature resulting from skeletal growth defect. The indepth analysis of cartilage and bone histogenesis points towards an initial deficit in cell mobilization to enter chondrogenesis.

The Fate of the Quiescent Surfaces of Lamellar Bone

Microradiographic and histologic analysis of undemineralized bone was performed in 62 subjects aged 18-97 years. Ten of these samples were also submitted to scanning electron microscopy. Besides the usual lamellar bone remodeling, all types of bone surfaces, namely both haversian and vascular canals and the endosteal and trabecular surfaces, were involved in weathering alterations of the superficial lamellae, resulting in eroded outlines, less deeply notched than the Howship lacunae and devoid of osteoclast. Present as soon as early adult life and randomly distributed, these aspects were recorded in all the bone pieces examined. These observations were consistent with the hypothesis of a particular destructive process in all the quiescent lamellar bone surfaces without osteoclast participation, termed delitescence, which could be partly responsible for age-related bone loss.

Microradiographic and histological evaluation of the bone-screw and bone-plate interface of orthodontic miniplates in patients

OBJECTIVES To describe the tissue reactions at the bone-titanium interface of orthodontic miniplates in humans. MATERIALS AND METHODS Forty-two samples, consisting of tissue fragments attached or not to miniplates or their fixation screws, were collected from 24 orthodontic patients treated with miniplate anchorage, at the time of removal of their miniplates. The samples were embedded in methylmethacrylate and cut into undecalcified sections which were submitted to microradiographic analysis. The sections were also stained and examined under ordinary light. RESULTS Three types of reactions were observed both on the histological sections and on the microradiographs. 1. The majority of the stable miniplates were easy to remove (34/42). The tissue samples collected consisted mainly in mature lamellar bone with some medullary spaces containing blood vessels, 2. two screws were highly osseointegrated and required the surgeon to remove them by trephining (2/42). They were surrounded by bone tissue which extended to the miniplate. The histological features were similar to the previous group, though the bone-screw contact was higher, and 3. in six samples obtained after unstable miniplate removal during the treatment, we observed either some woven bone trabeculae or loose connective tissue, without any histological sign of inflammation. LIMITATIONS AND CONCLUSION For evident ethical reasons, our data were limited by the size of the tissue fragments and the limited number of patients and variety of clinical presentations. The healing reactions consisted mainly in mature lamellar bone tissue sparsely in contact with the screw or the miniplate, with signs of a moderate remodelling activity.

Isolated bilateral transverse agenesis of the distal segments of the lower limbs at the level of the knee joint in a human fetus

Congenital limb anomalies occur in Europe with a prevalence of 3.81/1,000 births and can have a major impact on patients and their families. The present study concerned a female fetus aborted at 23 weeks of gestation because she was affected by non‐syndromic bilateral absence of the zeugopod (leg) and autopod (foot). Autopsy of the aborted fetus, X‐ray imaging, MRI, and histochemical analysis showed that the distal extremity of both femurs was continued by a cartilage‐like mass, without joint cavitation. Karyotype was normal. Moreover, no damaging variant was detected by exome sequencing. The limb characteristics of the fetus, which to our knowledge have not yet been reported in humans, suggest a developmental arrest similar to anomalies described in chicks following surgical experiments on the apical ectodermal ridge of the lower limbs.