Bovine Enamel Surfaces Research Articles

Electron-microscopic demonstration of proline-rich proteins, statherin, and histatins in acquired enamel pellicles in vitro.

Proline-rich proteins (PRPs), histatins, and statherin are salivary proteins that exhibit high affinities for hydroxyapatite surfaces. In vitro experiments with parotid submandibular/sublingual or whole saliva have shown these proteins to adsorb selectively to tooth surfaces. This investigation focuses on the histo-morphological identification of PRPs, histatins, and statherin in acquired enamel pellicles. Synthetic hydroxyapatite or bovine enamel were exposed to glandular secretions, and whole saliva and pellicle precursor proteins were identified immunohistologically by electron microscopy. Results obtained by back-scattered scanning electron microscopy showed these proteins to be present in pellicles. Pellicles displayed a distinct structure consisting of a sponge-like meshwork of microglobules. Interconnections between structural elements were identified in submandibular/sublingual and whole saliva pellicles only. Transmission electron microscopy of pellicles formed on bovine enamel surfaces revealed a tendency for preferential localization of precursor proteins within the protein film. Since the data showed the presence of pellicle precursors in pellicles derived both from glandular secretions and from whole saliva, it is likely that PRPs, histatins, and statherin are integral components of acquired enamel pellicles in vivo.

Photomechanical drug delivery into bacterial biofilms.

To investigate whether photomechanical waves generated by lasers can increase the permeability of a biofilm of the oral pathogen Actinomyces viscosus. Biofilms of Actinomyces viscosus were formed on bovine enamel surfaces. The photomechanical wave was generated by ablation of a target with a Q-switched ruby laser and launched into the biofilm in the presence of 50 microg/ml methylene blue. The penetration depth of methylene blue was measured by confocal scanning laser microscopy. Also, the exposed biofilms were irradiated with light at 666 nm. After illumination, adherent bacteria were scraped and spread over the surfaces of blood agar plates. Survival fractions were calculated by counting bacterial colonies. Confocal scanning laser microscopy revealed that a single photomechanical wave was sufficient to induce a 75% increase in the penetration depth of methylene blue into the biofilm. This significantly increased the concentration of methylene blue in the biofilm enabling its photodestruction. Photomechanical waves provide a potentially powerful tool for drug delivery that might be utilized for treatment of microbial infections.

Scanning microradiographic studies of rates of in vitro demineralization in human and bovine dental enamel

The aim was to measure frequently and with precision the local integrated mineral loss through small areas of the natural surface of human and bovine enamel during in vitro demineralization using an X-ray photon-counting system (scanning microradiography). The method used was an adaptation of photographic longitudinal microradiography in which the attenuation of X-rays through the enamel is measured in the direction of acid attack, i.e., normal to the enamel surface. The mass of mineral (assumed to be hydroxyapatite) per unit exposed area was measured over 15 μm dia. circles at a series of positions as a function of time in blocks of human and bovine enamel immersed in 0.1 mol/l acetic acid buffered to pH 4.0 with NaOH. There was an initial period (approx. 45 h for human, approx. 75 h for bovine enamel) during which the mineral loss with time was sigmoidal, followed by a nearly linear loss for the remainder of the experiment, in some cases up to 500 h. The initial sigmoidal period may be due to properties of surface enamel or be associated with the development of a surface layer overlying subsurface demineralization. The essentially constant rate of mineral loss after the surface layer has formed confirms earlier observations and is consistent with a rate-limiting process occurring at the dissolving enamel surfaces of the advancing front, and not by transport of ions within the lesion. Small perturbations from a linear loss were seen, which were approximately periodic for human enamel. The slope of the linear period was rather constant within one human or bovine block, but variable between blocks without a clear distinction between human and bovine enamel.

Effect of air-powder polishing on adhesion of bonding systems to tooth substrates

Objectives. The air-powder polisher was introduced to provide a method to quickly remove stains and plaque. The purpose of this study was to evaluate what effect preparing teeth with an air-powder polisher (Air-flow 2, Shofu) has on bonding to enamel and dentin substrates. Methods. The bonding systems used in this study were one-step etching/priming systems (KBT-5, Kanebo; and Clearfil Liner Bond II, Kuraray) and a two-step etching/priming system (Superbond D-Liner Plus, Sun Medical). Bovine enamel and dentin surfaces were prepared and finished with 600-grit silicon carbide paper. Then the surfaces were either not treated (control) or air-powder polished for 15 s. A 4-mm bonding area was demarcated, and the tooth substrates were bonded with the three bonding systems according to the manufacturers' instructions. Tensile bond strengths were measured 24 h after storage in water at 37°C. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses were performed on air-powder polished specimens to determine changes in the surface morphology and detect residual material from the air-powder polisher. SEM and transmission electron microscopic (TEM) observations of the interface between the bonding resins and dentin were performed to detect variations in the hybrid layers of the control and treated specimens. Results. The results indicated that air-powder polishing did not influence the tensile bond strength to enamel, but adversely affected the tensile bond strength to dentin for the one-step systems, but not for the two-step system. Changes to the enamel surface after air-powder polishing were minimal, but an increase in surface roughness and complete removal of the smear layer were observed on dentin. SEM and TEM observations of the resin/dentin interface suggested that the air-powder polisher might cause superficial maceration of the collagen fibers on the dentin surface. This change may have decreased the ability of the etching/priming agents and bonding resin to penetrate into the dentin, which would have resulted in a poor quality hybrid layer. Significance. For those systems that contain only an acidic primer for dentin conditioning, the use of air-powder polishing for surface preparation prior to restoration of dentin margin cavities is contraindicated because of the loss of reliable bonding.

The Topographic Changes of Nd: YAG Laser on Different Black Mediators Coated Bovine Enamel Surfaces

The Topographic Changes of Nd: YAG Laser on Different Black Mediators Coated Bovine Enamel Surfaces

Progression and Surface Ultrastructure of in vitro Caused Erosive Lesions in Human and Bovine Enamel

Surface prismatic and aprismatic human enamel and unpolished or diamond-polished specimens of bovine enamel, with test and control surfaces on each studied block, were immersed in phosphoric acid containing cola beverage (pH 2.6) and citric or malic acid containing sports drinks (pH 2.8 and 3.4, respectively) for 15-180 min. The specimens were then prepared and studied in a JEOL 35C scanning electron microscope. In human aprismatic surface enamel an irregular type of dissolution was observed, with severely affected areas adjacent to less affected ones. Prismatic human and bovine specimens showed a characteristic dissolution where initial erosion after 15 min immersion was seen to affect specifically the prism sheath areas. Longer immersion caused dissolution of enamel prism cores followed by interprismatic areas. In bovine enamel malic acid affected least the surface ultrastructure when compared with citric and phosphoric acids after 15-30 min of immersion, but thereafter no difference was observed between the acids in causing erosion. Diamond-polished enamel was found more liable to erosion than non-polished enamel. Thus, the structure of enamel greatly modified the progression of in vitro caused erosion, in particular in human tooth specimens.

The Formation and Remineralization of Artificial White Spot Lesions: A Constant Composition Approach

Artificial white spot lesions have been prepared on bovine enamel surfaces by the controlled addition of lactate buffer containing methylhydroxydiphosphonate ions. The rates of remineralization have been measured using a constant composition method in solutions of calcium phosphate of low supersaturation. Deposition of new hydroxyapatite solid phase takes place exclusively within the white spot lesion at a rate appreciably slower than that of an acid-etched enamel surface, probably due to the presence of methylhydroxydiphosphonate located within the intact surface region of the lesion.

Exchange of fluoride between bovine enamel and the surface-related cells of the oral bacterium Streptococcus mutans

Standard areas of intact bovine enamel surface were fluoridated with dental F-varnish for 24 h and then cleaned from varnish residues and thoroughly rinsed with distilled water. Sucrose fermentation by a plaque-like layer of Streptococcus mutans cells covering such an enamel surface was accompanied by a rapid but transient accumulation of F of enamel origin by the Strep. mutans cells and by a pH drop in the plaque to pH 4.0. The uptake of F from the surface by the control cells, utilizing their carbohydrate stores and causing a smaller pH-drop, was slow but no release of F back to the cell exterior took place within 18 h. In a second experiment, F-varnished and placebo-varnished bovine enamel granules were used as above, but they were not thoroughly washed after being varnish-treated and cleaned. Both the sucrose-fermenting and the control layer of Strep. mutans rapidly released appreciable but equal amounts of fluoride from the F-treated enamel. The accumulation of F of enamel origin by the Strep. mutans cells with or without sucrose was rapid and of almost the same magnitude. In the model with the sucrose-utilizing Strep. mutans and the F-treated enamel granules, the plaque pH-drop was less and the dissolution of the enamel Ca and P completely prevented compared to the respective changes in the sucrose-utilizing model with placebo-treated enamel granules.

Bovine enamel hardness and its Ca-, P-, Mg- and F-contents modified by the bacterium Streptococcus mutans, artificial dental plaque and fluoride

A layer of cells from buffered Strep. mutans suspension (pH 5.8), with or without sucrose, was centrifuged on bovine enamel surfaces. Fluoride was added to a part of the samples (final F 25 parts 10 6 ). Control and test samples were incubated at 37°C for 18 h. The pH of the fermenting plaque dropped to 4.15. When F was present, the final pH was 4.45. Microhardness of the enamel surface was reduced by the presence of sucrose but less in the presence of F. Enamel Ca was liberated during fermentation, but only into the fluid and less in the presence of F. The weight ratio of Ca and P released by sugar fermentation was 3.14 and 1.91 when F was present. The F content of enamel surface was only slightly increased ( 130 parts 10 6 ) by the F in distilled water alone. Subsurface enamel gained more F ( 280 parts 10 6 ). When artificial plaque was present, addition of F increased the F content of enamel surface by 450 parts 10 6 and F of subsurface by 210 parts 10 6 . The addition of F increased the enamel F content to the greatest extent under the fermenting plaque, 680 parts 10 6 in surface and 400 parts 10 6 in subsurface enamel, compared to the values of the enamel under non-fermenting plaque.

The remineralization of fluoride-treated bovine enamel surfaces.

Various etching methods are examined with respect to their ability to induce the surface nucleation and growth of fluorapatite from solutions of low, sustained supersaturation with respect to hydroxyapatite and fluorapatite. The constant composition kinetics method enables the rates of remineralization to be precisely determined, and the possibility of the direct growth of fluorapatite on calcium fluoride crystals in calcium phosphate solutions of low supersaturation has also been examined.

A rotating disc study of enamel dissolution in HEDP solution under simulated white spot conditions.

A rotating disc method has been used to study simulated white spot formation at a bovine enamel surface in the presence of 1-hydroxy-1-ethane-1, 1-diphosphonic acid (HEDP) at PH = 5.0. The reaction appears to be accompanied by the slow precipitation of a CaHEDP phase within the pores of the "intact" layer.

A kinetic and morphological study of mineralization of bovine tooth enamel surfaces

A new constant composition method was used to study the kinetics of remineralization of enamel surfaces. The labial enamel surfaces were treated with 20 per cent phosphoric acid, 0.05 M HCl, EDTA (2 per cent, pH 4.0) yielding Type I etched surface and with EDTA (1–2 per cent, pH 7.0) to give a Type II etched surface. Remineralization experiments were made in stable supersaturated calcium phosphate solutions undersaturated with respect to dicalcium phosphate dihydrate and octacalcium phosphate phases, at pH 7.40 and 37 °C. Type I-etched surfaces yielded similar remineralization rates, but these were greater than those for Type II surfaces. Confirmation of hydroxyapatite as the exclusive remineralizing phase was made by various physico-chemical methods. Scanning electron microscopy of the remineralized phase, suggested various sites for remineralization.

Enamel microhardness and fluoride uptake underneath fermenting and non-fermenting artificial plaque.

Washed cells of Streptococcus sanguis were used to form artificial plaque on the surface of bovine enamel and incubated underneath buffer solutions, initial pH 6, for 36 h at 37 degrees C. The decrease in the microhardness of the enamel surface under fermenting "plaque" could be prevented with fluoride. Enamel under a fermenting "plaque" took up significantly more (P less than 0.0u) fluoride than enamel under a non-fermenting "plaque" (initial F- in buffer: 10 parts/10(6)). The artificial plaque did not accumulate fluoride. Within fermenting "plaques/, the pH decreased significantly more without flouride (P less than 0.01) than with fluoride. Fluoride combined with sucrose more than negated the softening of the enamel caused by sucrose fermentation, i.e. it increased the hardness above the original values. The diffusion of fluoride through the fermenting artificial plaque was more rapid than through a non-fermenting plaque. These findings suggest that caries-conducive circumstances may promote fluoride uptake by enamel compared with non-caries-conducive circumstances.

Cariogenicity of nine sugars tested with an intraoral device in man.

Nine sugars and sugar alcohols were assessed for their effect on experimental caries with an Intraoral Cariogenicity Test (ICT). Sample bovine enamel surfaces were submitted to simulated cariogenic co

An intraoral model used for studies of fluoride incorporation in enamel

Abstract. The effect of fluoride on experimental cariogenicity in man was investigated by using bovine enamel surfaces mounted in oral prosthetic appliances. Samples of sound and presoftened enamel were exposed to simulated cariogenic or noncariogenic conditions for 1 week. The samples were periodically immersed in vitro in solutions containing 1 ppm fluoride. For the cariogenic condition, the immersion solution was 3% sucrose, for the noncariogenic condition, water. After the experimental period, the sample enamel was assessed for hardness change and fluoride incorporation. Under the non‐cariogenic condition, partial remineralization and high fluoride incorporation were found in the presoftened enamel; both hardness change and fluoride incorporation in sound enamel were minor. The cariogenic condition contributed to higher enamel softening and higher fluoride uptake by both types of samples. The findings suggest a mechanism through which intermittent cariogenesis and remineralization in the presence of fluoride may contribute to increased tooth resistance to caries.

Ultrasonic measurement of dental enamel demineralization

The DONAR (digital ultrasonic system) has been used to continuously measure the displacement, due to etching by hydrochloric acid, of the surface of bovine enamel and to monitor the development of a demineralized layer. Conventional pulse echoes are used to measure displacements of the order of micrometres with an uncertainty no greater than 0.1 μm. The demineralized zone in one instance attained a maximum thickness of 5 μm and was much less in other experiments.

Effect of fluoride on etched human and bovine tooth enamel surfaces as demonstrated by scanning electron microscopy

An experimental area of labial enamel of both human and bovine incisor teeth was treated for 1 min with a solution containing 50 per cent phosphoric acid and 7 per cent (by weight) of dissolved zinc oxide. Several fluoride salts were applied topically for 5 min to the treated area. These included 1 per cent titanium tetrafluoride, 2 per cent zirconium tetrafluoride, 2 per cent sodium fluoride, 2 per cent phosphorulated sodium fluoride and 8 per cent stannous fluoride. The treated surfaces were then coated with gold/palladium and examined in a scanning electron microscope. With the exception of stannous fluoride, a reaction product was demonstrated on the enamel surfaces. Since fluoride salts are known to reduce resin bond strength, it was concluded that the physical presence of a reaction product is a very likely contributing factor.

The Influence of Phosphoric Acid Etching on Retention of Acrylic Resin to Bovine Enamel

A study was made to determine whether bonding of a direct filling resin to bovine enamel surfaces was increased by pretreating the surfaces with a 50% phosphoric acid solution for 60 seconds. Tensile strength tests were used to measure the bond strength of the resin to the enamel surface. Results indicated that the pretreatment with the 50% phosphoric acid significantly increased the bonding of the direct filling resin, and the use of a cavity sealer in conjunction with the acid etching enhanced the retention of the resin to the enamel surface. Further laboratory tests in which stress is applied to restorations, and a well-controlled clinical evaluation are needed to substantiate the findings in this study.

Study of the effect of calcium, phosphate, fluoride and hydrogen ion concentrations on the remineralization of partially demineralized human and bovine enamel surfaces

Increases of calcium, phosphate and hydroxyl ion concentrations, and addition of 1 ppm fluoride to remineralizing solutions increased the rate of enamel remineralization. Fluoride ions lowered the solution concentrations of calcium, phosphate and hydroxyl ions required for demineralization-remineralization equilibrium. The ionic strength of the remineralizing solutions (0.075 to 0.225 M NaCl) was without effect on enamel remineralization, but prevented spontaneous precipitation of the mineralizing solutions. Remineralized enamel was as resistant to dissolution by weak acids as natural mineralized enamel, and enamel remineralized in solutions containing 1 ppm fluoride was more resistant than naturally mineralized enamel.