Incidence and severity of root resorption in orthodontically moved premolars in dogs.

OBJECTIVES: To study treatment-related factors for external root resorption during orthodontic tooth movement. DESIGN: An experimental animal study. SETTING AND SAMPLE POPULATION: Department of Orthodontics and Oral Biology, University Medical Centre Nijmegen, The Netherlands. Twenty-four young adult beagle dogs. EXPERIMENTAL VARIABLE: Mandibular premolars were bodily moved with continuous or intermittent controlled orthodontic forces of 10, 25, 50, 100, or 200 cN according to standardized protocols. At different points in time histomorphometry was performed to determine the severity of root resorption. OUTCOME MEASURE: Prevalence of root resorptions, defined as microscopically visible resorption lacunae in the dentin. Severity of resorption was defined by the length, relative length, depth, and surface area of each resorption area. RESULTS: The incidence of root resorption increased with the duration of force application. After 14-17 weeks of force application root resorption was found at 94% of the root surfaces at pressure sides. The effect of force magnitude on the severity of root resorption was not statistically significant. The severity of root resorption was highly related to the force regimen. Continuous forces caused significantly more severe root resorption than intermittent forces. A strong correlation (0.60 < r < 0.68) was found between the amount of tooth movement and the severity of root resorption. CONCLUSIONS: Root resorption increases with the duration of force application. The more teeth are displaced, the more root resorption will occur. Intermittent forces cause less severe root resorption than continuous forces, and force magnitude is probably not decisive for root resorption.

The postnatal development of the temporal part of the human temporomandibular joint. A quantitative study on skulls.

The morphology of the temporal part of the human temporomandibular joint (TMJ) changes drastically during postnatal development. The glenoid fossa will acquire its characteristic S shape and a tubercle will develop. The combined results of the literature and of this study allow a reconstruction of the actual growth processes. The roof of the glenoid fossa appears to enlarge forward by remodeling while sagittal and vertical growth is mainly achieved by deposition at the top of the tubercle. These latter changes result in a steeper slope of the eminence and take place in 3 phases, parallelling the eruption of the first incisors, the permanent first molars and the permanent second molars. While the zygomatic arch thickens by deposition at all surfaces, it also remodels downward relative to the external meatus. As a result, the neonate anulus occupies a lower position relative to this arch than does the adult meatus.

[Orthodontic treatment and root resorption]. / Orthodontische behandeling en wortelresorptie.

Root resorption after orthodontic treatment occurs frequently. The biologic process of tooth movement and root resorption is described. Furthermore, attention is given to the frequency and severity of root resorption, diagnostics and aspects of the orthodontic treatment which aggravate root resorption. Displacement of teeth with resorptions that already exist or with deviating rootforms is riskfull.

Closing of dentinal tubules by glutardialdehyde treatment, a scanning electron microscopy study.

The properties of dentin are strongly influenced by the so-called smear layer. This layer is always present on the dentin surface after cutting, drilling, sawing, etc. The smear layer can be removed by various chemical treatments, such as those of acid etching or ethylenediaminetetraacetic acid (EDTA). These treatments remove the smear layer and open the tubules. In this paper, the effect on the smear layer of human dentin of treatment with a 2% glutardialdehyde (GDA) solution at pH 3.5 for 2 min and a 0.5-M EDTA solution at pH 7.4 for 4 min was investigated by scanning electron microscope (SEM). The dentin samples were dried by air or critical-point drying before SEM photography was employed. The number of open dentin tubules was quantified on micrographs of EDTA- and GDA+EDTA-treated dentin. The results show that the GDA treatment fixed part of the smear layer and the superficial dentin surface in such a way that at least 50% of the tubules remained closed after EDTA treatment. By closing the dentinal tubules, the GDA-fixed layer might have a positive effect on dentin hypersensitivity, root caries, and bonding of composite to dentin.

Secondary caries in dentine around composites: a wavelength-independent microradiographical study.

Composite restorations are prone to develop secondary caries if a gap exists between tissue and restoration. The aim of this article was to quantify the effects of a fluoridating and non-F composite on secondary dentine caries in vitro as a function of time. The mineral loss in dentine was assessed in an artificial gap of 200 microns width at the composite/dentine interface; the samples were demineralised in a carboxymethylcellulose gel (pH = 5, 37 degrees C) for 8 weeks. Once a week the mineral content of the samples was determined using non-destructive wavelength-independent microradiography (WIM). After 8 weeks transversal microradiography (TMR) was done on the samples to investigate the mineral distribution of the dentine lesions. The WIM results show that the fluoride-releasing composite decreased the dentine demineralisation statistically significantly with respect of the non-F control by approximately 45%. The mineral loss values are found to be strictly proportional to time; the demineralisation reduction is expected to continue over extended periods of clinical relevance. The TMR results show that the fluoridating composite reduced the mineral loss values significantly with respect to the non-F control by approximately 55%, but had a negligible effect on the lesion depth values. This study indicates that WIM is an accurate and reliable technique to measure in vitro secondary dentine caries next to a composite restoration as a function of time.

Long-term fluoride release of visible light-activated composites in vitro: a correlation with in situ demineralisation data.

Fluoridated composites are able to reduce or inhibit secondary caries around fillings. The aims of this study were firstly to investigate the amount of F released in vitro from composites with a F content between 0 and 26 vol% as a function of time over a 1-year period. A second aim was to correlate the in vitro data on F release with enamel demineralisation data in situ after a 1-month period. The results show that all fluoridated composites release sizable amounts of F in solution, the total amounts of F released from three composites were proportional to log t over at least 1 year. In one case proportionality of the total amount of F released with t was observed. Possible mechanisms of F release are considered. The results presented also show a linear relation between the log of in vitro F release data and the effects on enamel demineralisation in situ next to the composite. Extrapolation of the data reveals that a F release of about 200-300 micrograms/cm2 over a 1-month period from a fluoridated composite would completely inhibit secondary caries under plaque conditions.

Secondary caries in situ around fluoride-releasing light-curing composites: a quantitative model investigation on four materials with a fluoride content between 0 and 26 vol%.

In the literature, secondary caries around composite restorations is reported often. Fluoridated composites are therefore interesting materials because they might reduce or inhibit secondary caries. In this article an in situ model investigation is presented in which the effect of F-releasing composites on enamel demineralisation around an artificial gap of 200 microns width was quantified after 1 month. The fluoride content of the composites varied between 0 and 26 vol%. The beneficial effect of the fluoride released was larger in the gap than at the outer enamel surface. In the gap, all fluoridated composites reduced the enamel demineralisation statistically significantly with respect to the non-fluoridated control. Microradiography showed a reduction of lesion depth values of 27-45%, and a reduction of mineral loss values of 25-56%. At the outer enamel surface next to the artificial gap, a beneficial fluoridation effect was measurable only near the most fluoridated composite. The results indicate that fluoridated composites may play a role in the future prevention of secondary caries.

Effect of glutardialdehyde on secondary caries in situ.

In this paper the results are presented on the effect glutardialdehyde (GDA) on the in situ demineralization of human enamel and dentine around an artificial gap of 200 microns width. In this model secondary enamel and dentine caries is simulated in situ; the mineral loss was quantified. The results show that a 2-min application of a 2% acidic GDA solution reduces dentine demineralization substantially, but does not influence enamel demineralization. Microradiography showed a reduction of mineral loss values around the gap in dentine by about 30%. The beneficial effect of GDA on dentine is presumably a combined result of collagen fixation, the reduced diffusion of calcium and phosphate ions out of the dentine lesion, and antibacterial action. The results indicate that GDA might play a role in the future reduction or prevention of secondary dentine caries.