Quantification of free water in human dental enamel

Erosion behaviour of human, bovine and equine dental hard tissues

Dental hard tissues from different species are used in dental research, but little is known about their comparability. The aim of this study was to compare the erosive behaviour of dental hard tissues (enamel, dentin) obtained from human, bovine and equine teeth. In addition, the protective effect of the pellicle on each hard tissue under erosive conditions was determined. In situ pellicle formation was performed for 30 min on enamel and dentin samples from all species in four subjects. Calcium and phosphate release was assessed during 120 s of HCl incubation on both native and pellicle-covered enamel and dentin samples. SEM and TEM were used to examine surface changes in native enamel and dentin samples after acid incubation and the ultrastructure of the pellicle before and after erosive exposure. In general, bovine enamel and dentin showed the highest degree of erosion after acid exposure compared to human and equine samples. Erosion of human primary enamel tended to be higher than that of permanent teeth, whereas dentin showed the opposite behaviour. SEM showed that eroded equine dentin appeared more irregular than human or bovine dentin. TEM studies showed that primary enamel appeared to be most susceptible to erosion.

Time-Lapse In Situ 3D Imaging Analysis of Human Enamel Demineralisation Using X-ray Synchrotron Tomography

Caries is a chronic disease that causes the alteration of the structure of dental tissues by acid dissolution (in enamel, dentine and cementum) and proteolytic degradation (dentine and cementum) and generates an important cost of care. There is a need to visualise and characterise the acid dissolution process on enamel due to its hierarchical structure leading to complex structural modifications. The process starts at the enamel surface and progresses into depth, which necessitates the study of the internal enamel structure. Artificial demineralisation is usually employed to simulate the process experimentally. In the present study, the demineralisation of human enamel was studied using surface analysis carried out with atomic force microscopy as well as 3D internal analysis using synchrotron X-ray tomography during acid exposure with repeated scans to generate a time-lapse visualisation sequence. Two-dimensional analysis from projections and virtual slices and 3D analysis of the enamel mass provided details of tissue changes at the level of the rods and inter-rod substance. In addition to the visualisation of structural modifications, the rate of dissolution was determined, which demonstrated the feasibility and usefulness of these techniques. The temporal analysis of enamel demineralisation is not limited to dissolution and can be applied to other experimental conditions for the analysis of treated enamel or remineralisation.

A Pilot Study on High Wavenumber Raman Analysis of Human Dental Tissues

Water plays a critical role in dental tissues including enamel and dentin. The characterization of water structure analysis was primarily conducted by nuclear magnetic resonance. Raman spectroscopy is a powerful analytic technology with capability for structure analysis in materials. However, acquiring high wavenumber Raman signals from dental tissues was challenging due to either the fluorescence interference under laser illumination or reduced sensitivity of CCD detectors. In this study, we demonstrate a pilot research on high wavenumber Raman analysis in dental tissues using a customized Raman spectrometer based on an InGaAs detector. A signal located at 3570 cm^-1 is found dominating the O-H region Raman spectra of enamel but is barely detectable from dentin. The profiles of the high wavenumber region Raman spectra changes with the locations in enamel, as well as the polarization of the excitation laser beam. The results suggest that the size or crystallinity differences of hydroxyapatite crystals are the main cause of the spectral variation from dentin to enamel, and could be partially responsible for the variation among different locations in enamel.

A literature review of dental erosion in children

Dental erosion is increasingly recognized as a common condition in paediatric dentistry with complications of tooth sensitivity, altered aesthetics and loss of occlusal vertical dimension. The prevalence of erosion in children has been reported to range from 10% to over 80%. The primary dentition is thought to be more susceptible to erosion compared to the permanent dentition due to the thinner and less mineralized enamel. The aim of this paper was to critically review dental erosion in children with regards to its prevalence, aetiology, diagnosis and prevention. The associations between erosion and other common conditions in children such as caries and enamel hypoplasia are also discussed.

Effect of applying a sustained force during bonding orthodontic brackets on the adhesive layer and on shear bond strength

The objective of this research was to investigate the effect of applying a sustained seating force during bonding on the adhesive layer and on shear bond strength (SBS) of orthodontic brackets. Forty human premolars divided into two groups were included in the study. Stainless steel brackets were bonded to the premolars with Transbond XT light cure adhesive and Transbond Plus Self Etch Primer (SEP). The brackets in both groups were subjected to an initial seating force of 300 g for 3 seconds, sufficient to position the bracket. The seating force was maintained throughout the 40 seconds of light curing in group 2. SBS was tested 24 hours after bracket bonding with a shear blade using an Instron testing unit at a crosshead speed of 2 mm/minute. A Student's t-test was used to compare the bond strength of the two groups and a chi-square test to compare the frequencies of the adhesive remnant index (ARI) scores. The mean SBS was significantly different between the two groups (P=0.025). The bond strength was higher (mean 8.15±0.89 MPa) in group 2 compared with group 1 (mean 7.39±1.14 MPa). There was no significant difference (P=0.440) in the ARI scores between the two groups. Applying a sustained seating force during orthodontic bracket bonding improves bond strength but does not change the distribution of the ARI scores.

Changes in dimensions and weight of human dentine after different drying procedures and during subsequent rehydration

Shrinkage of dentine and the decrease in its weight after drying were measured. Three drying procedures were used, freeze-drying and drying in nitrogen at 60 and 100 degrees C. The dentine was subsequently rehydrated while measuring its dimensions. Rehydrated dentine was weighed. Dentine weight decreased by 10.2, 9.0 and 10.5% with the three different drying procedures. Shrinkage was about equal with all three methods. Linear dimensional changes were 1.7-2.0% in the plane perpendicular to the tubules and 1.4-1.7% in the direction of the tubules. During rehydration, freeze-dried dentine and dentine dried at 60 degrees C regained its original wet dimensions and weight. Dentine dried at 100 degrees C showed some permanent shrinkage and weight loss.