SIMS of biomineralized tissues: present trends and potentials.

The technique of dynamic secondary ion mass spectrometry (SIMS) has, during the 1980s, become a firmly established tool in the microanalytical and microstructural characterization of dental hard tissues. SIMS has proved to be outstandingly suited for charting the distributions of most elements, even at extremely low concentrations, in tooth and bone materials. In-depth concentration profiles as well as surface distribution maps of elements have been recorded with excellent (sub-micron) morphologic resolution. In spite of documented success, only relatively few teams, in a handful of countries, are presently engaged, to any significant extent, in conducting tooth or bone research by the application of SIMS. For dental-medical-surgical laboratories, a partial reason for non-communication is a lack of information about SIMS and its particular assets. Another reason may be connected with an essentially groundless reputation, among non-specialists, of SIMS being an exclusive and expensive technique. Among SIMS laboratories, on the other hand, the inertia in tackling biomineralization is partly due to some particular artifacts of analysis, hitherto not generally known and controlled. The present paper briefly sketches the chief principles of modern SIMS, emphasizing factors of special relevance in the characterization of biomineralized tissues. Examples of recent applications are provided. Present procedures and their limitations are discussed, especially with regard to elemental quantification and imaging. Suggestions for relatively simple modifications to existing routines are offered with the aim of enhancing the ease and availability of SIMS in odontological and surgical research.

The effect of a low fluoride containing toothpaste on the development of dental caries and microbial composition using a caries generating model device in vivo.

The purpose of the study was to evaluate the effect of daily use of a low fluoride containing toothpaste (250 ppm F) on the uptake of fluoride and development of enamel lesions as well as the prevalence of lactobacilli and mutans streptococci in dental plaque compared to the use of placebo toothpaste. 16 children were selected with homologous premolar teeth. The teeth were cemented with orthodontic bands ad modum Ogaard for plaque accumulation and enamel lesion development. The plaque accumulated during 4 weeks was collected and analysed for lactobacilli and mutans streptococci. The teeth were further analysed by secondary ion mass spectrometry (SIMS), determining the concentration profiles of fluoride and other elements in the outermost enamel and in the lesion. The results show that although significant amounts of fluoride were taken up in the surface enamel from the fluoride toothpaste, the extent of the lesions was not influenced compared to teeth brushed with a non F-toothpaste. Neither were microbiological differences in the dental plaque found between the groups. An interesting observation was that early demineralization of enamel took place without detectable levels of mutans streptococci in the overlaying dental plaque. The conclusion is that fluoride taken up in enamel from F-toothpaste has no significant influence on enamel lesion development if a cariogenic dental plaque with high levels of acid producing microorganisms is continuously attached to the enamel surface.

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.

Fluorine profiles in human enamel after in vitro treatment with dentifrices of different compositions and acidities.

Fluorine uptake has been measured in human enamel after in vitro treatment with slurries of dentifrices of different compositions and acidities. Secondary ion mass spectrometry (SIMS) was used to determine the quantitative in-depth distribution profiles of fluorine. Five dentifrices were examined: ACTA (pH 5.5) with 250, 1000 and 1500 ppm F as NaF; Colgate (pH 7) with 1000 ppm F as MFP and 400 ppm F as NaF; and Pepsodent (pH 7) with 1000 ppm F as MFP. The results establish that acidulated dentifrice with low F concentration gives about the same fluorine uptake in near-surface enamel as do pH 7 dentifrices with higher F contents. In addition, at depths greater than ca 3 microns, the low F acid dentifrice in fact introduces considerably higher levels of fluorine, and yields at least three times deeper penetration, than do the non-acidulated toothpastes. The study illustrates the advantages of enhanced fluorine uptake, and thereby improved cariostatic effect, by using acidulated dentifrices even at relatively low fluoride concentration.

Effect of topical F- solutions on caries-like lesions in root surfaces.

Topical F- solutions, NaF, SnF2, TiF4, or Fe-Al-NaF, were applied to root surfaces to examine the effect on caries-like lesions produced in vitro. Extracted premolars were treated with a solution for 10 min prior to a 20-day period in acid gel. The lesions were studied by microradiography and light microscopy, and concentration profiles of 12 elements were determined by secondary ion mass spectrometry. The results indicated that the solutions retarded the development of lesions. The greatest effect was obtained with TiF4 and SnF2 solutions. Element analyses revealed that high concentrations of F (up to 3.5%) accumulated in the outer third of the lesion and that SnF2 and TiF4 formed depots in the cementum, although both Sn and Ti also penetrated the lesion. NaF had a weaker effect on lesion formation, but induced a high F concentration in the demineralized zones. The Fe-Al-F solution affected the lesion only marginally and deposited a relatively low F concentration in the lesion, although Fe and Al penetration and depot formation were noted.

Elemental imaging of dental hard tissues by secondary ion mass spectrometry.

High resolution imaging by secondary ion mass spectrometry (SIMS) has been employed in a chemical-microstructural pilot study of different classes of hard tissues from human and rat. The special scanning ion microprobe instrumentation permitted the recording of element-resolved images with a lateral resolution of about 50 nm. Sharp distribution micrographs were obtained for Ca+, F- and CN-, and in selected specimens for Na+, K+, Mg+, O-, Cl-, C- and PO-. Several trends in the elemental kinetics of mineralization were comprehensively illustrated and new aspects were indicated. The paper points out the broad scope of interest, and the potentialities of unique applications, in SIMS imaging of biomineralized tissues, the conditions for efficient employment of the recently developed technique are briefly discussed and demonstrated.

Fluorine levels in in vitro remineralized enamel after treatment with 1000 ppm F as NaF, MFP or mixed solutions.

By means of secondary ion mass spectrometry (SIMS) an investigation has been made of the F uptake and the transport of fluorine-carrying ions in artificially carious human enamel after in vitro remineralization. The fluoridation was effected from solutions of pure Na2FPO3 (MFP), pure NaF, or mixtures of MFP and NaF, always with a total F content of 1000 atom-ppm. The recorded in depth profiles of F concentration show that, after 14 days of remineralization, 1) neither the acquired F levels nor the F distributions are greatly dependent on whether fluoridation is from NaF, MFP or mixtures, 2) the F distribution shape is not strongly influenced by a 3-month storage followed by remineralization, 3) the penetration of F beyond the lesion is generally deeper from NaF than from MFP, and 4) the effect of long storage on penetration depth is mainly noticeable for MFP-treated specimens.

Quantitative ion probe microanalysis of biological mineralized tissues.

The technique of secondary ion mass spectrometry (SIMS) combines outstanding sensitivity of element detection with excellent morphological resolution. During the last decade this has been exploited in numerous studies of biomineralizations. The range of microanalytical applications of SIMS in this field has expanded considerably in connection with the recent development of second-generation instrumentation, offering superior ion optics, improved control of intrinsic mass spectra, and suppression of the artifacts of surface charge-up. Factors affecting the detection limits, quantification and spatial resolution have been delineated particularly with regard to in-depth profiling and point analysis. Examples of odontological applications, ranging from element mapping to quantitative diffusion studies, have served to illustrate the potentialities as well as the intricacies of the SIMS technique.

Oxidation of noble metal alloys for porcelain veneer crowns.

It has been found that oxide-forming elements in the alloy are important for the blood strength between the metal and the procelain. The purpose of the present investigation was to study the formation of oxides during pretreatment and firing of porcelain. Four commerically available Ceramo-Metal alloys were studied. The specimens were heated at 980 degrees C for five hours in air, and the weight was continuously recorded. In addition porcelain was fired on to the alloys. Metallographic examinations were conducted on both oxidized and fired speciments. The weight gain data also indicated an increased oxygen uptake with a larger amount of oxidizable elements in the alloy. Most of the oxygen gain and time indicated that the oxygen uptake was diffusion controlled. The weight gain data also indicated an increased oxygen uptake with larger amount of oxidizable elements in the alloy. Most of the oxygen in the oxidize alloys was located as oxide along grain boundaries in the metal.

Indepth distributions of elements in teeth, determined by ion probe analysis.

The technique of secondary ion mass spectrometry has been applied to dental hard tissue. The method offers high sensitivity (ppb-ppm) to most elements, a topographic surface resolution of about 1 micron, and a practical depth resolution in the 10 nm range. Quantitative analysis has entailed the use of external standards or the adaptation of a thermodynamic model of the secondary ionization mechanism. The intrinsic mass spectra of secondary ions from apatite material have been studied to assess the practical detection limits for most elements of the periodic table. Fluorine studies have been performed on enamel subjected to different prophylactic treatments. The atomic mechanism of fluorine mobility in teeth have been studied in diffusion anneals. The distributions of different elements (F, Cl, P, Li, Na, K, Rb, Mg, Sr, Ba, Al, C, Pb) have been investigated in dependence of depth in the enamel and dentin from different environments.

SIMS study of element concentration profiles in enamel and dentin.

The ion probe technique has been employed for the determination of the concentrations of P, F, Cl, C, Na, K, Mg, Sr, Al, and Si at different depths in human tooth. The applicability of the method depends selectively on the element's position in the periodic table, but may be regarded as good for a wide range of microelements of dental interest.

Ion probe study of fluorine gradients in outermost layers of human enamel.

F concentrations in the outermost layers of human tooth enamel were studied with the aid of a secondary ion microanalyzer. Concentration profiles were recorded in continuous sputtering analysis from the surface down to a depth of about 0.3 micrometer. Samples previously subjected to topical fluoride treatment were compared with reference specimens. In some samples, the results were compared with those obtained at greater depths by macroscopic etching analysis.