Three-dimensional study of human dental fissure enamel by synchrotron X-ray microtomography.

The three-dimensional morphology of human tooth fissures and the quantification of mineral distribution in fissure enamel are pertinent to the development and diagnosis of caries. Synchrotron X-ray microtomography was used to measure linear attenuation coefficients (at 25 keV) at high spatial resolution with a volume-imaging element (cubic voxel) of 4.9x4.9x4.9 microm3 in a block from a human premolar that included part of a stained fissure. From the linear attenuation coefficient, the mineral concentration, expressed as gHAp cm-3 (where HAp is stoichiometric hydroxyapatite), was calculated. The mean mineral concentration in bulk enamel was 2.84 gHAp cm-3. Well-defined regions (1.5-2.6 gHAp cm-3), extending up to approximately 130 microm from the base of some narrower lengths of the fissure and up to approximately 50 microm deep from the fissure surface, were attributed to hypomineralization. Other regions of low mineral concentration, some (1.4-2.3 gHAp cm-3) lying within the expected course of the fissure base and some (2.2-2.7 gHAp cm-3) deep to the pit, were also considered to be of developmental origin. However, a diffuse distribution of low mineral concentrations (2.2-2.7 gHAp cm-3) in the pit walls was attributed primarily to demineralization from caries. The fissure contained heterogeneous material (

[The penetration of various adhesives into early enamel lesions in vitro]. / Penetration verschiedener Adhäsive in initiale Schmelzläsionen in vitro.

The aim of the present study was to evaluate the penetration depth (PD) and the thickness of the oxygen inhibition layer (OIL) of a fissure sealant (Helioseal, Vivadent) and various adhesives (Heliobond, Excite, Vivadent; Resulcin, Merz; Solobond M, Voco; Prompt L-Pop, 3M-Espe) applied to enamel lesions in vitro. From 27 bovine teeth 54 enamel specimens were prepared and covered with nail varnish (control) thus obtaining three windows for treatment. After demineralisation (pH 5.0, 14 d) two of the windows were etched with phosphoric acid (20%, 5 s), whereas the third area served as control. The specimens were divided randomly into six groups (n = 9) and the respective adhesive was applied (90 s), either once or twice. Light-curing followed each application. Enamel slabs (perpendicular to the surface) were cut and studied after infiltration with a fluorescent low-viscous resin using confocal microscopy (CLSM). The image of the lesion was divided into two areas with different grey values. Lesion depths were calculated (ImageJ) from the surface to that point in the lesion where the grey value clearly changed to a darker grey value. The zone with the darker grey values marked the front of demineralisation. Mean lesion depths (+/- SD) after demineralisation were measured at 105 (+/- 21) microm. After single application, Resulcin [89 (+/- 22)%] and Helioseal [98 (+/- 6)%] had almost completely penetrated the lesion. Heliobond [126 (+/- 33)%] and Excite [184 (+/- 40)%] penetrated even deeper than the defined lesion. For Excite double application decreased the OIL significantly (p = 0.03; adjusted paired t-test). Adhesives are capable to penetrate artificial initial enamel lesions completely. Follow-up studies are needed to confirm this effect for natural lesions.

Mineralization of human premolar occlusal fissures. A quantitative histochemical microanalysis.

The mechanisms of cariogenesis in occlusal fissures remain elusive because of limited information about fissure structure and wall mineralization. The purpose of the present study was to determine the correlation between morphological patterns in occlusal fissures in human premolars and quantitative histochemical patterns of mineralization in the walls of these formations. We used scanning electron microscopy and quantitative X-ray microanalysis with the peak-to-local background ratio method and microcrystalline calcium salts as standards. We distinguished three morphological patterns of fissures in scanning electron microscopic images. The wall of the fissures was less mineralized than the control enamel in all three types of fissures. Because the fissure walls are hypomineralized, we suggest that practicing dentists should take into account the degree of mineralization when they are preparing the fissures for the application of sealant.

Fluoride in enamel lining pits and fissures of the occlusal groove-fossa system in human molar teeth.

The fluoride (F) distribution in enamel lining the occlusal fissures of human molars and premolars is difficult to investigate by normal microsampling techniques, yet this information is of importance as fissures are particularly susceptible to caries. We have used the proton probe to map the distribution of F and Ca in sections of 17 molar teeth collected from Danish and New Zealand populations. The caries status of the sectioned fissure was determined by microradiography or visually after drying. The probe scans were graphed as density images, surface plots and topographical plots. Sound enamel bordering grooves and fissures showed a high-F surface layer, in 1 sample approximately 60 microm wide near the fissure bottom but gradually widening to double this width near the fissure opening, and up to 200 microm wide in grooves, while underlying enamel had a low and almost constant F level. In this respect fissure and groove enamel resembled smooth surface enamel. The F concentration fluctuated along the surface layer, reaching maximum values ranging from 1,800 to 4,200 ppm in 5 non-carious fissures. Incipient caries in fissure enamel usually but not always resulted in an increase in F in the outer layer, the F maximum values in 5 such samples ranging from 1,900 to 7,200 ppm. F maximum values in outer enamel were higher in 7 samples showing advanced caries, 2, 700-10,000 ppm. The lesion subsurface body usually showed normal F values, as did carious dentine in the advanced lesions. The variable characteristics of the outer layer in sound fissure enamel are likely to be the result of a developmental process rather than environmental influences. The fact that we normally failed to find increased F concentrations in subsurface carious fissure enamel or in underlying carious dentine suggests that F does not diffuse into the deep part of fissure lesions, and probably has minimal effect on slowing the progress of such lesions, a suggestion in accord with clinical findings on the F effect on fissure caries.

Identification of human serum albumin in human caries lesions of enamel: the role of putative inhibitors of remineralisation.

Carious attack on enamel is not a unidirectional process but involves both demineralisation and remineralisation. The chemistry of carious attack on enamel has, to a large extent, now been clarified as far as mineral components are concerned but little attention, however, has been paid to the identity of organic material in carious lesions and its possible role in the caries process. The only clear information available is that organic material accumulates with time within enamel lesions. The present study was aimed at identifying a specific protein component known to bind to hydroxyapatite (albumin) in carious lesions with a view to investigating its role in the disease process. The distribution of albumin within both white spot and fissure lesions and adjacent sound enamel of extracted human teeth was investigated using SEM immunohistochemistry on undermineralised sections of human enamel and employing a polyclonal antibody to human serum albumin. The nature of the protein, i.e. whether it was in the form of intact molecules or degraded fragments, was investigated by Western blotting, employing the same antibody. The immunohistochemistry revealed the presence of albumin within both interproximal white spot and fissure lesions with little if any present in sound enamel. The Western blotting indicated that the albumin was in the intact form with no evidence of degradation products. The ability of albumin to bind and to inhibit growth of calcium phosphate crystals raises the question as to the possible role of such a molecule in the development of carious lesions.

The effect of normal pulsed Nd-YAG laser irradiation on pits and fissures in human teeth.

The effects of normal pulsed Nd-YAG laser irradiation on the acid resistance of human dental enamel of pits and fissures, the cleaning of the pit and fissure contents and fluoride uptake into deep pits and fissures were examined. The acid resistance of the pit and fissure enamel was evaluated by the amount of dissolved calcium per square millimeter of the surface area. The pit and fissure enamel treated with laser irradiation obtained an acid resistance 30% higher than that of the unlased controls. The cleaning effect of laser irradiation on the pit and fissure contents was compared with chemicomechanical and mechanical methods. The laser irradiation was found to clean the pits and fissures to a greater depth without alterating the shape of pits and fissures, compared with the other two methods. The distribution of calcium, phosphorus and fluoride in the enamel of the pits and fissures was then measured by electron probe microanalyzer. At the entrance and in the deep part of the pits and fissures, the fluoride content of the enamel treated with acidulated phosphate fluoride after laser irradiation was higher than that of the enamel treated with acidulated phosphate fluoride alone. These results thus suggest that Nd-YAG laser irradiation might be effective in increasing the acid resistance of the pit and fissure enamel, while removing the pit and fissure debris contents and increasing the fluoride uptake into the pit and fissure enamel.

Effect of dental plaque age and bacterial composition on the pH of artificial fissures in human volunteers.

Changes in sucrose-induced plaque pH profiles and the microbial composition of occlusal tooth surface fissures were analyzed using wire telemetry and bacterial culturing techniques. Four human volunteers wore appliances containing artificial fissures constructed with ion-sensitive field-effect transistor (ISFET) electrodes for 1, 2 and 4 days; 1 subject kept the electrode for 3 weeks. After monitoring the plaque pH response at the base of the fissure to a 10% (w/v) sucrose rinse the plaque was removed and analyzed for total viable bacteria, total and specific streptococci, lactobacilli and Actinomyces spp. One-day-old plaque showed a rapid drop in plaque pH to a minimum of 4.8 +/- 0.2, with 2-day-old plaque showing the most acidogenic pH profile (minimum pH 4.6 +/- 0.2). The 4-day-old plaque response was less acidogenic (minimum pH 5.0 +/- 0.3) than the results from days 1 and 2. Responses from 13- and 21-day-old fissure plaques showed greatly decreased acidogenic responses (day 21 minimum pH 5.7). Viable bacteria recovered from the fissure increased from approximately 4 x 10(6) colony-forming units on day 1 to 1.2 x 10(7) on days 2 and 4 and 1.7 x 10(7) on day 21. Streptococci (greater than 50%) and Actinomyces (greater than 10%) dominated in the fissure plaques and their levels were related to minimum pH. Since fissure plaque of all ages tested contained high concentrations of acidogenic bacteria, the decreased acidogenic response at the base of fissures with increasing plaque age suggests that maturing fissure plaques provide an increasingly greater diffusion barrier to fermentable carbohydrates.