Surface topography of enamel and dentine from primary teeth following infrared Nd-YAG laser irradiation: An in vitro study

Data on the effects of laser radiation on primary teeth are scarce. This study investigates the effects of exposing sound enamel, photo-initiated sound enamel, sound dentine and carious dentine of extracted primary teeth to a pulsed neodymium-yttrium aluminium garnet laser (Nd-YAG, wavelength 1.06 μm, pulse length 15μs). Each type of tissue was exposed to three fiuences. Qualitative and quantitative assessments of the irradiated areas revealed that the most marked changes were produced in carious dentine, followed in ranking order by sound dentine, photo-initiated enamel and sound enamel. Evidence of thermal damage to the hard tissues peripheral to the fibre-optic tip, and considerable inter-sample variation were found. The experimental evidence obtained in this in vitro study does not support the clinical use of pulsed laser at 1.06 μm wavelength for cutting primary enamel and dentine.     

Metabolic expression of intrinsic developmental programs for dentine and enamel biomineralization in serumless,chemically-defined,organotypic culture

Summary Biomineralization was investigated using embryonic mouse mandibular first molars (M₁) cultured in the presence or absence of fetal calf serum. Metabolic features including cell division and Ca²⁺ and phosphate incorporation into dentine and enamel extracellular matrices were analyzed. The relative timing and magnitude of DNA synthesis for serumless cultures was comparable toin vivo controls. Isotopic calcium and phosphate incorporation into the mineral phase of dentine and enamel matrices, in the absence of serum, fluctuated during development. Molar tooth morphogenesis, cytodifferentiation, and extracellular matrix formation approximated late crown-stage development in serumless cultures. Von Kossa histochemical staining indicated calcium phosphate salt formation in serumless cultures. Analysis of anhydrous fixation-prepared enamel and dentine representing serumless cultured explants indicated that crystal size and orientation were comparable toin vivo enamel and dentine. In contrast, serum-supplemented cultures showed atypical crystal size and orientation. Calcium/phosphorous (Ca/P) ratio values for serumless cultures after 21 days showed Ca/P enamel values of 2.03 (SD±0.04, p<0.025) and dentine values of 1.89 (SD±0.01, p<0.025). Electron diffraction patterns of enamel and dentine formed in serumless cultures were principally those of highly-ordered crystalline hydroxyapatite. Our results suggest that tissue-specific dentine and enamel biomineralization is regulated by endogenous factors intrinsic to the developmental program of embryonic tooth organs during serumless culture.     

Quantification of dentine shape in anthropoid primates

The external shape and thickness of the enamel component of primate molars have been employed extensively in phylogenetic studies of primate relationships. The dentine component of the molar crown also has been suggested to be indicative of phylogenetic relationships, but few studies have quantified dentine morphology in order to evaluate this possibility. To explore the utility of dentine shape as an indicator of phylogenetic affinity, a two-dimensional geometric morphometric analysis (EDMA-II) was performed using nine homologous land-marks on a sample of sectioned maxillary molars of extant ceboid, cercopithecoid, and hominoid primates. Results indicate that dentine shape (the configuration of the enamel-dentine junction, or EDJ) can distinguish taxa at every taxonomic level examined, including superfamilies, subfamilies, and closely related genera and species. This supports the idea that dentine morphology may be useful for phylogenetic studies. It is further suggested that the morphology of the EDJ may be more conservative than enamel morphology, and perhaps better-suited to phylogenetic studies. Among the samples studied, cercopithecoid primates have a unique dentine shape, and it is suggested that the development of bilophodont molars may be related to the distinctive EDJ configuration in cercopithecoids.     

Altered Phosphorylation of Rat Dentine Phosphoproteins by Fluoride In Vivo

Dentine phosphoproteins have been proposed to have an important role in mineralization. This study focused on the influence of fluoride on the biochemical composition of dentine phosphoproteins and attempts to relate changes to the altered mineralization witnessed during fluorosis. Wistar rats were rendered fluorotic by the administration of 20 ppm sodium fluoride in their drinking water ad libitum, a nonfluorotic group received double-distilled, deionized water only. After 17 weeks, the teeth showed signs of fluorosis. The incisors were removed, split longitudinally, and the pulps were removed. Teeth were powdered and demineralized in 10% EDTA with protease inhibitors, after which the organic matrix was extracted with 4 M guanidinium chloride. Phosphoproteins were selectively precipitated from the soluble extract by the addition of 1.0 M calcium chloride and further purified by anion exchange chromatography. SDS-PAGE revealed two protein bands with molecular weights of 130 kDa and 66 kDa in the nonfluorotic fraction and 116 kDa and 66 kDa in the fluorotic fraction. Western blotting analysis identified the 66 kDa band as α₂-HS glycoprotein which co-precipitated with phosphoproteins. Electroelution of the protein bands was performed with subsequent biochemical analyses. Phosphate content was determined for each protein band and was detectable in the 116 kDa and 130 kDa bands from the fluorotic and nonfluorotic samples, respectively, with a decreased level noted in the 116 kDa band. The presence of phosphate and the amino acid analysis of these bands suggested their identity to be dentine phosphoproteins. No changes in the ratio of amino acids was detected in fluorotic samples. The fluoride-induced alterations to the biochemical structure of dentine phosphoproteins would appear to influence the phosphorylation of these macromolecules only, possibly affecting posttranslational events. Such alterations may play a role in disrupting the patterns of mineralization seen during fluorosis. Received: 14 November 1997 / Accepted: 9 July 1998     

The effect of grinding of human dentine examined by X-ray diffraction, infrared spectroscopy, and electron microscopy

Analysis of human dentine by infrared spectrophotometry suggests that ball-grinding may result in damage of the apatite crystallites. The present study includes further assessments of this effect by X-ray diffraction, infrared spectroscopy, and electron microscopy. Each of three coarse-ground dentine samples (Group I) was divided into three portions of 30 mg. One of these portions was ball-ground for approximately 1 min (Group II), the second portion for 6 min (Group III), and the third portion for 23 min (Group IV). The 002 reflection showed line broadening, most marked from Group II to III. Electron microscopy showed a gradual change in crystallite appearance with increased grinding, most pronounced from Group II to III. These observations indicate that by prolonged grinding a limit is approached where no further changes in the crystallites occur. Electron microscopy also indicated that fracture of the crystallites might have occurred. This was probably accompanied by strains in the lattice. The infrared spectra indicated that no breakdown of the apatite structure had occurred during the entire grinding.     

A modified glass ionomer cement to mediate dentine repair

ObjectivesGlass ionomer cements (GIC) can be used to protect dentine following caries removal. However, GIC have little biological activity on biological repair processes, which means that neo-dentine formation remains reliant on limited endogenous regenerative processes. Wnt/β-catenin signalling is known to play a central role in stimulating tertiary dentine formation following tooth damage and can be stimulated by a range of glycogen synthase kinase (GSK3) antagonists, including lithium ions.MethodsHere, we created lithium-containing bioactive glass (BG) by substituting lithium for sodium ions in 45S5 BG. We then replaced between 10 and 40% of the powder phase of a commercial GIC with the lithium-substituted BG to create a range of formulations of ‘LithGlassGIC’. In vitro physical properties of the resulting glasses were characterised and their ability to stimulate reactionary dentine formation in mouse molars in vivo was tested.ResultsLithium release from LithGlassGIC increased with increasing lithium content in the cement. In common with unmodified commercial GIC, all formations of LithGlassGIC showed in vitro toxicity when measured using an indirect cell culture assay based on ISO10993:5, precluding direct pulp contact. However, in a murine non-exposed pulp model of tooth damage, LithGlassGIC quickly released lithium ions, which could be transiently detected in the saliva and blood. LithGlassGIC also enhanced the formation of tertiary dentine, resulting in a thickening of the dentine at the damage site that restored lost dentine volume. Dentine regeneration was likely mediated by upregulation of Wnt/β-catenin activity, as LithGlassGIC placed in TCF/Lef:H2B-GFP reporter mice showed enhanced GFP activity.SignificanceWe conclude that LithGlassGIC acts as a biological restorative material that promotes tertiary dentine formation and restores tooth structure.     

An in-vitro study investigating the effect of air-abrasion bioactive glasses on dental adhesion,cytotoxicity and odontogenic gene expression

ObjectiveTo assess the microtensile bond strength (MTBS) and interfacial characteristics of universal adhesives applied on dentine air-abraded using different powders. The analysis includes the cytotoxicity of the powders and their effect on odontogenic gene expression.MethodsSound human dentine specimens were air-abraded using bioglass 45S5 (BAG), polycarboxylated zinc-doped bioglass (SEL), alumina (AL) and submitted to SEM analysis. Resin composite was bonded to air-abraded or smear layer-covered dentine (SML) using an experimental (EXP) or a commercial adhesive (ABU) in etch&rinse (ER) or self-etch (SE) modes. Specimens were stored in artificial saliva (AS) and subjected to MTBS testing after 24 h and 10 months. Interfacial nanoleakage assessment was accomplished using confocal microscopy. The cytotoxicity of the powders was assessed, also the total RNA was extracted and the expression of odontogenic genes was evaluated through RT-PCR.ResultsAfter prolonged AS storage, specimens in the control (SML) and AL groups showed a significant drop in MTBS (p > 0.05), with degradation evident within the bonding interface. Specimens in BAG or SEL air-abraded dentine groups showed no significant difference, with resin-dentine interfaces devoid of important degradation. The metabolic activity of pulp stem cells was not affected by the tested powders. SEL and BAG had no effect on the expression of odontoblast differentiation markers. However, AL particles interfered with the expression of the odontogenic markers.SignificanceThe use of bioactive glass air-abrasion may prevent severe degradation at the resin-dentine interface. Unlike alumina, bioactive glasses do not interfere with the normal metabolic activity of pulp stem cells and their differentiation to odontoblasts.     

Observations on fluid flow from exposed dentine in primary teeth: An in vitro study

ObjectiveTo investigate fluid flow through dentine in primary teeth in vitro using the replica technique, and to compare the results with those obtained from permanent dentine.DesignThe experiments were carried out on 22 extracted, mandibular, primary, incisor teeth. The incisal edge was removed to 1 mm below the dentino-enamel junction and half the exposed surface etched with phosphoric acid. The exposed dentine was blotted dry and the pressure in the pulp cavity held at 0, 15, 30 or 45 cm H₂O above atmospheric for 30 s. Fluid that accumulated on the dentine surface was recorded with impression material and a replica made with epoxy resin which was examined in a scanning electron microscope.ResultsStructures resembling fluid droplets were present in the replicas of unetched dentine in all 22 teeth, and at all the pulpal pressures tested. The droplets formed at 45 cm H₂O were significantly larger (median diam., 5.14 mm; interquartile range, 3.26 mm; Friedman repeated measures analysis of variance on ranks (RMAVR) and Tukey test) than those formed at other pressures. There was no evidence of droplets in the replicas of etched dentine with any of the pulpal pressures.ConclusionsThese results demonstrate that fluid will tend to flow from dentine in deciduous teeth when it is exposed. They are similar to those obtained in a previous study in this laboratory on permanent teeth. The fact that fluid droplets were absent from etched dentine suggests that, after being blotted, the etched dentine matrix absorbed fluid that tended to flow out through the dentinal tubules.     

一种新型通用型牙本质粘结剂对牙本质粘结强度的体外评价

目的:评价一种新型通用型牙本质粘结剂(All Bond Universal,ABU)对牙本质的粘结强度,为临床选择合适的粘结剂提供参考依据。方法:选取人体12颗无龋坏磨牙,磨除牙釉质暴露牙本质面,分别用酸蚀-冲洗法和一步自酸蚀法使用All Bond Universal粘结剂,在其上堆砌树脂,并与酸蚀-冲洗粘结剂Prime&Bond NT(PBN)和一步法自酸蚀粘结剂G Bond(GB)进行对照。试样于37℃去离子水储存24 h后,每颗牙齿垂直于粘结面制备出0.81 mm2的树脂/牙本质试件,进行牙本质粘结微拉伸强度(μTBS)测试。结果:通用型牙本质粘结剂All Bond Universal在两种粘结方法下,其粘结力均高于对照组;就All Bond Universal本身而言,酸蚀-冲洗技术可以提高其粘结强度。结论:这种新型牙本质粘结剂具有较高的粘结强度,并且酸蚀-冲洗技术能提高其粘结力。     

Combined effect of smear layer characteristics and hydrostatic pulpal pressure on dentine bond strength of HEMA-free and HEMA-containing adhesives

Objective

This study evaluated the combined effect of smear layer characteristics with hydrostatic pulpal pressure (PP) on bond strength and nanoleakage expression of HEMA-free and -containing self-etch adhesives.

Methods

Flat dentine surfaces were obtained from extracted human molars. Smear layers were created by grinding with #180- or #600-SiC paper. Three HEMA-free adhesives (Xeno V, G Bond Plus, Beautibond Multi) and two HEMA-containing adhesives (Bond Force, Tri-S Bond) were applied to the dentine surfaces under hydrostatic PP or none. Dentine bond strengths were determined using the microtensile bond test (μTBS). Data were statistically analyzed using three- and two-way ANOVA with Tukey post hoc comparison test. Nanoleakage evaluation was carried out under a scanning electron microscope (SEM).

Results

Coarse smear layer preparation and hydrostatic PP negatively affected the μTBS of HEMA-free and -containing adhesives, but there were no significant differences. The combined experimental condition significantly reduced μTBS of the HEMA-free adhesives, while the HEMA-containing adhesives exhibited no significant differences. Two-way ANOVA indicated that for HEMA-free adhesives, there were significant interactions in μTBS between smear layer characteristics and pulpal pressure, while for HEMA-containing adhesives, there were no significant interactions between them. Nanoleakage formation within the adhesive layers of both adhesive systems distinctly increased in the combined experimental group.

Conclusion

The combined effect of coarse smear layer preparation with hydrostatic PP significantly reduced the μTBS of HEMA-free adhesives, while in HEMA-containing adhesives, these effects were not obvious.

Clinical significance

Smear layer characteristics and hydrostatic PP would additively compromise dentine bonding of self-etch adhesives, especially HEMA-free adhesives.