FT-IR photoacoustic depth profiling spectroscopy of enamel

Photoacoustic FTIR spectroscopic study of undisturbed human cortical bone

Chemical pretreatment has been the prevailing sample preparation procedure for infrared (IR) spectroscopic studies on bone. However, experiments have indicated that chemical pretreatment can potentially affect the interactions between the components. Typically the IR techniques have involved transmission experiments. Here we report experimental studies using photoacoustic Fourier transform infrared spectroscopy (PA-FTIR). As a nondestructive technique, PA-FTIR can detect absorbance spectrum from a sample at controllable sampling depth and with little or no sample preparation. Additionally, the coupling inert gas, helium, which is utilized in the PA-FTIR system, can inhibit bacteria growth of bone by displacing oxygen. Therefore, we used this technique to study the undisturbed human cortical bone. It is found that photoacoustic mode (linear-scan, LS-PA-FTIR) can obtain basically similar spectra of bone as compared to the traditional transmission mode, but it seems more sensitive to amide III and ν(2) carbonate bands. The ν(3) phosphate band is indicative of detailed mineral structure and symmetry of native bone. The PA-FTIR depth profiling experiments on human cortical bone also indicate the influence of water on OH band and the cutting effects on amide I and mineral bands. Our results indicate that phosphate ion geometry appears less symmetric in its undisturbed state as detected by the PA-FTIR as compared to higher symmetry observed using transmission techniques on disturbed samples. Moreover, the PA-FTIR spectra indicate a band at 1747 cm(-1) possibly resulting from CO stretching of lipids, cholesterol esters, and triglycerides from the arteries. Comparison of the spectra in transverse and longitudinal cross-sections demonstrates that, the surface area of the longitudinal section bone appears to have more organic matrix exposed and with higher mineral stoichiometry.

Fourier transform infrared photoacoustic spectroscopy study of physicochemical interaction between human dentin and etch-&-rinse adhesives in a simulated moist bond technique

The purpose of this study was to provide the physicochemical interactions at the interfaces between two commercial etch-&-rinse adhesives and human dentin in a simulated moist bond technique. Six dentin specimens were divided into two groups (n=3) according to the use of two different adhesive systems: (a) 2-hydroxyethylmethacrylate (HEMA) and 4-methacryloxyethyl trimellitate anhydrate (4-META), and (b) HEMA. The Fourier transform infrared photoacoustic spectroscopy was performed before and after dentin treatment with 37% phosphoric acid, with adhesive systems and also for the adhesive systems alone. Acid-conditioning resulted in a decalcification pattern. Adhesive treated spectra subtraction suggested the occurrence of chemical bonding to dentin expressed through modifications of the OH stretching peak (3340 cm(-1)) and symmetric CH stretching (2900 cm(-1)) for both adhesives spectra; a decrease of orthophosphate absorption band (1040 to 970 cm(-1)) for adhesive A and a better resolved complex band formation (1270 to 970 cm(-1)) for adhesive B were observed. These results suggested the occurrence of chemical bonding between sound human dentin and etch-&-rinse adhesives through a clinical typical condition.

Application of vibrational spectroscopy to the study of mineralized tissues (review)

The infrared and Raman spectroscopy of bone and teeth tissues are reviewed. Characteristic spectra are obtained for both the mineral and protein components of these tissues. Vibrational spectroscopy is used to study the mineralization process, to define the chemical structure changes accompanying bone diseases, and to characterize interactions between prosthetic implants and tissues. Microspectroscopy allows acquisition of spatially resolved spectra, with micron scale resolution. Recently developed imaging modalities allow tissue imaging with chemical composition contrast.

Infrared spectroscopy: a new frontier in medicine

As we enter the second half of the nineties, one of the major challenges for biological infrared spectroscopists is to transfer the knowledge we have gained from studies on isolated molecules to the complex world of medicine. That it is possible to meet this challenge is suggested by comparison with the development of other biophysical techniques, such as magnetic resonance spectroscopy and imaging, which have already found their place in medical research and practice. The Spectroscopy Group in Winnipeg is developing and evaluating a variety of new IR techniques for the analysis of body fluids and tissues, both in vitro and in vivo. Herein, we review these methodologies, which comprise both instrumental (imaging and spatially localized IR spectroscopy) and interpretational procedures aimed at optimizing the measurements and their conversion to biodiagnostic information.

Adaptive crystal formation in normal and pathological calcifications in synthetic calcium phosphate and related biomaterials

Mineralization and crystal deposition are natural phenomena widely distributed in biological systems from protozoa to mammals. In mammals, normal and pathological calcifications are observed in bones, teeth, and soft tissues or cartilage. We review studies on the adaptive apatite crystal formation in enamel compared with those in other calcified tissues (e.g., dentin, bone, and fish enameloids) and in pathological calcifications, demonstrating the adaptation of these crystals (in terms of crystallinity and orientation) to specific tissues that vary in functions or vary in normal or diseased conditions. The roles of minor elements, such as carbonate, magnesium, fluoride, hydrogen phosphate, pyrophosphate, and strontium ions, on the formation and transformation of biologically relevant calcium phosphates are summarized. Another adaptative process of crystals in biology concerns the recent development of calcium phosphate ceramics and other related biomaterials for bone graft. Bone graft materials are available as alternatives to autogeneous bone for repair, substitution, or augmentation. This paper discusses the adaptive crystal formation in mineralized tissues induced by calcium phosphate and related bone graft biomaterials during bone repair.

Raman spectra of human dentin mineral

Human dentin mineral has been investigated by using micro-Raman spectroscopy. Fluorescence and thermal problems were largely avoided by preparing dentin samples by grinding and ultrasonic agitation in acetone. The Raman spectral features were consistent with those of impure hydroxyapatite containing CO3 and HPO4. While spectral differences between enamel and dentin were clearly observable as changes in the bandwidth of the PO4(3-)V1 band and the intensities of the OH-, CO3(2-) and HPO4(2-) bands, the technique could not detect spectral differences between coronal and root dentin. NaOCl, NaF and APF-gel treatments caused measurable changes in intensities of the bands due to CO3(2-) and HPO4(2-); the results were found to be useful for band assignments. After NaOCl treatment, the Raman bands, presumably due to amide and HPO4(2-), were lost, but the band intensity of the CO3(2-)V1 bands increased by 35-60%. This increase coincided with the appearance of a new broad band (250-300 cm-1). The same treatment on enamel caused no increase in the CO3(2-)V1 band intensity. This NaOCl-induced carbonate could be removed within 20 h in a 1000 ppm NaF solution. These findings indicate that the carbonate ions induced by the NaOCl treatment are presumably in or on the mineral surface. After 3 min of APF-gel treatment on NaOCl-pretreated dentin, the intensities of the hydroxyapatite phosphate bands dropped by approximately 20%, and newly formed CaF2 and HPO4 bands became observable.