Microradiographic study on the effects of salivary proteins on in vitro demineralization of bovine enamel

Beyond dissolution: Xerostomia rinses affect composition and structure of biomimetic dental mineral in vitro

Xerostomia, known as dry mouth, is caused by decreased salivary flow. Treatment with lubricating oral rinses provides temporary relief of dry mouth discomfort; however, it remains unclear how their composition affects mineralized dental tissues. Therefore, the objective of this study was to analyze the effects of common components in xerostomia oral rinses on biomimetic apatite with varying carbonate contents. Carbonated apatite was synthesized and exposed to one of the following solutions for 72 hours at varying pHs: water-based, phosphorus-containing (PBS), mucin-like containing (MLC), or fluoride-containing (FC) solutions. Post-exposure results indicated that apatite mass decreased irrespective of pH and solution composition, while solution buffering was pH dependent. Raman and X-ray diffraction analysis showed that the addition of phosphorus, mucin-like molecules, and fluoride in solution decreases mineral carbonate levels and changed the lattice spacing and crystallinity of bioapatite, indicative of dissolution/recrystallization processes. The mineral recrystallized into a less-carbonated apatite in the PBS and MLC solutions, and into fluorapatite in FC. Tap water did not affect the apatite lattice structure suggesting formation of a labile carbonate surface layer on apatite. These results reveal that solution composition can have varied and complex effects on dental mineral beyond dissolution, which can have long term consequences on mineral solubility and mechanics. Therefore, clinicians should consider these factors when advising treatments for xerostomia patients.

In vitro remineralization of enamel with a solution containing casein and fluoride

The aim of the present study was to investigate the effects of casein in a remineralization solution on enamel remineralization. Bovine blocks were demineralized for 21 days, then, allocated into four groups. The specimens were remineralized for 21 days in the following artificial saliva solutions: 1) 0 µg/mL casein, 0 ppm fluoride (F) (C0-F0); 2) 0 µg/mL casein, 1 ppm F (C0-F1); 3) 10 µg/mL casein, 0 ppm F (C10-F0); and 4) 10 µg/mL casein, 1 ppm F (C10-F1). Micro-CT analyses were performed once a week. Specimens were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The present results suggest that casein by itself inhibits remineralization, whereas the coexistence of casein and F promotes the remineralization of caries bodies by interrupting mineral deposition on the enamel surface.

In vitro Candida albicans biofilm formation on different titanium surface topographies

Objectives

To investigate if differences in titanium implant surface topography influence Candida albicans biofilm formation.

Materials and Methods

Titanium discs were prepared and characterized using a profilometer: Group A (R_a 0.15 µm, smooth), Group B (R_a 0.64 µm, minimally rough) and Group C (R_a 1.3 µm, moderately rough). Contact angle and surface free energy (SFE) were determined for each group. Non-preconditioned titanium discs were incubated with C. albicans for 24 h. In additional experiments, the titanium discs were initially coated with human saliva, bovine serum albumin or phosphate-buffered saline for 2 h before incubation with C. albicans for 24 h. The amount of fungal biofilm formation was quantified using a colorimetric assay.

Results

C. albicans biofilm formation was significantly lower (p < 0.05) on the minimally rough titanium surface compared to smooth and moderately rough surfaces. The titanium surface displaying the lowest SFE (Group B) was associated with significantly lower (p < 0.05) C. albicans biofilm formation than the other two groups. Salivary coating resulted in greater adherence of C. albicans with increased surface roughness.

Conclusions

The minimally rough titanium discs displayed lowest SFE compared to smooth and moderately rough surfaces and showed the least C. albicans biofilm formation. This study demonstrated that C. albicans biofilm formation increased in a SFE-dependent manner. These findings suggest that SFE might be a more explanatory factor for C. albicans biofilm formation on titanium surfaces than roughness. The presence of a pellicle coating may negate the impact of SFE on C. albicans biofilm formation on titanium surfaces.

The combined approach to evaluation of mechanical behavior of tooth enamel in artificially induced caries lesions

Improved knowledge of caries initiation and progression on the base of modern mechanobiology could facilitate effective preventing and therapeutic strategies. Not all of previously developed experimental models of artificial caries comply with required standards. The aim of the study was to investigate microstructural and mechanical properties of 12 artificial caries lesions, induced on human intact premolars according to original protocol. The tooth specimens were subjected to imaging by X-ray CT system Nikon Metrology XT H 225, with further morphometric analysis of lesion geometry, depth, surface layer thickness and mineral density in the areas of interest. Mechanical characteristics (penetration depth, microhardness, elastic modulus) in enamel lesion, perifocal intact enamel and remote zones were obtained using Micro CombiTester system. Clinically all lesions fully corresponded to ICDAS – 2 code. According to µCT data, LDµCT of the lesions ranged from 346.4 to 531 µm, mineral density range from 2.03±0.15 g/cm3 in transparent zone to 1.05±0.08 g/cm3 in the surface zone of the lesion. Microhardness of demineralized enamel lesion more than 5 times reduced in comparison with perifocal and remote intact enamel. Nanoindentation and µCT data are corresponds to those presenting on the base of other classical protocols of artificial caries formation and close to the typical mechanical characteristics of enamel caries in vivo.

Effects of soy and bovine milk beverages on enamel mineral content in a randomized, double-blind in situ clinical study

Soy beverages are promoted as healthy alternatives to bovine milk even though they can contain added sugar.

OBJECTIVES

To compare enamel mineral content after consumption of bovine milk or a soy beverage in a double-blind, randomized, cross-over in situ clinical study.

MATERIALS AND METHODS

Human enamel slabs with subsurface lesions were prepared and inserted into intra-oral appliances worn by volunteers who consumed 200 ml of either bovine milk or a soy beverage over a 60 s period once a day for 15 days. Enamel lesion depth and mineral content were measured using transverse microradiography. Saliva samples were collected immediately after consuming the beverages and calcium, inorganic phosphate and fluoride levels analysed. Data were statistically analysed using a linear mixed model.

RESULTS

Depth of the enamel subsurface lesions increased by 7.1 ± 2.0 μm and mineral content decreased by 47 ± 22 vol% min.μm after consumption of the soy beverage indicating demineralization. However, after consumption of bovine milk the depth of the lesions decreased by 7.6 ± 3.5 μm and mineral content increased by 202 ± 43 vol% min.μm indicating remineralization. The changes were significantly different (p < 0.001) between the two beverages. Fluoride levels were similar in the saliva samples for both beverages, however the calcium and inorganic phosphate levels for the bovine milk group were significantly higher (p < 0.02) than those for the soy beverage group.

CONCLUSIONS

In this randomized, double-blind in situ clinical trial consumption of a soy beverage demineralized enamel whereas bovine milk produced remineralization.

CLINICAL SIGNIFICANCE

Although soy beverages are promoted as healthy alternatives to bovine milk the added sugar and low calcium bioavailability of the soy drink makes frequent consumption a caries risk. (Trial registration no. ISRCTN19137849).

The presence of acquired enamel pellicle changes acid-induced erosion from dissolution to a softening process

Erosive wear undermines the structural properties of enamel resulting in irreversible enamel loss. A thin protein layer formed from natural saliva on tooth surfaces, acquired enamel pellicle (AEP), protects against erosive wear. The exact components in saliva responsible for such protection are not yet known. We prepared three solutions containing different components: proteins and ions [natural saliva (NS)], minerals with no proteins [artificial saliva (AS)] and neither proteins nor ions [deionised water (DW)]. To assess the protection of the three solutions against citric acid enamel erosion, enamel specimens were immersed in the corresponding solution for 24 h. All specimens were then exposed to five erosion cycles, each consisted of a further 30 min immersion in the same solution followed by 10-min erosion. Mean step height using a non-contacting profilometer, mean surface microhardness (SMH) using Knoop microhardness tester (final SMH), and roughness and 2D profiles using atomic force microscopy were measured after five cycles. The final SMH values were compared to the starting values (after 24 hr). NS group had significantly less tissue loss but greater SMH change (P < 0.0001) than AS and DW groups. Specimens in NS were softer and rougher (P < 0.001) but less eroded than specimens in AS and DW.

The Effect of Mucin in Artificial Saliva on Erosive Rehardening and Demineralization

The effect of mucin in artificial saliva on rehardening (RE-experiment) and inhibition (DE-experiment) of erosion was evaluated. The treatment groups were: artificial saliva with mucin, artificial saliva without mucin, human saliva, and water. For the RE-experiment, after immersion of enamel blocks in citric acid (4 min), hardness was measured and blocks were subjected to treatment for 2 h. For the DE-experiment, sound blocks were subjected to treatment for 2 h and immersed in citric acid (4 min). Percentages of hardness recovery (RE) and loss (DE) were analyzed (ANOVA/Tukey's test). The salivas promoted similar rehardening, but only the saliva with mucin was similar to human saliva with regard to enamel protection against erosion.

Salivary Proteins-A Barrier on Enamel Demineralization: An in vitro Study

AIM

The aim of this study is to evaluate the protective effect of the salivary proteins on the demineralization of enamel.

MATERIALS AND METHODS

Twenty freshly extracted human molar teeth were used in this study. Enamel samples (2 mm thickness) were prepared from the buccal and lingual surfaces of the teeth selected. An acid-resistant nail varnish was used to cover every aspect of the sample, except an area of 5 * 5 mm limited by an adhesive tape. After drying, the adhesive tape was removed, exhibiting a rectangular area on the enamel surface. Samples were divided into two groups: Group I (10 samples): Each sample was coated by 100 μg of albumin for 2 hours at 37°C. Group II (10samples): Each sample was exposed to 100 μL of deionized water.Samples were washed by dipping once in deionized water. They were then disposed into individual tubes containing demineralization solution for 1, 2, 3, and 4 minutes at 37°C with gentle agitation. The demineralization solution was utilized to determine the calcium loss from specimens at 1, 2, 3, 4 minutes using an ultraviolet-visible spectrophotometer.

RESULTS

Calcium loss was less from the albumin-coated samples than control group at all times and was statistically significant (p < 0.05). Also, calcium loss was maximum at the end of 1 minute, and it decreased as time interval increased and was statistically significant (p < 0.001).

CONCLUSION

Albumin has provided a strong protection against enamel demineralization at all times compared to the one without it.

HOW TO CITE THIS ARTICLE

Hegde MN, Sajnani AR. Salivary Proteins-A Barrier on Enamel Demineralization: An in vitro Study. Int J Clin Pediatr Dent 2017;10(1):10-13.

Inhibition of hydroxyapatite growth by casein, a potential salivary phosphoprotein homologue

Salivary phosphoproteins are essential in tooth mineral regulation but are often overlooked in vitro. This study aimed to evaluate the effect of casein, as a salivary phosphoprotein homologue, on the deposition and growth of hydroxyapatite (HA) on tooth surfaces. Hydroxyapatite growth was quantified using seeded crystal systems. Artificial saliva (AS) containing HA powder and 0, 10, 20, 50, or 100 μg ml(-1) of casein, or 100 μg ml(-1) of dephosphorylated casein (Dcasein), was incubated for 0-8 h at 37°C, pH 7.2. Calcium concentrations were measured using atomic absorption spectroscopy (AAS). Surface precipitation of HA on bovine enamel and dentine blocks, incubated in similar conditions for 7 d, was examined using field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) with selected area electron diffraction (SAED). Casein adsorption was assessed using modified Lowry assays and zeta-potential measurements. The AAS results revealed a concentration-dependent inhibition of calcium consumption. Hydroxyapatite precipitation occurred when no casein was present, whereas precipitation of HA was apparently completely inhibited in casein-containing groups. Adsorption data demonstrated increasingly negative zeta-potential with increased casein concentration and an affinity constant similar to proline-rich proteins with Langmuir modelling. Casein inhibited the deposition and growth of HA primarily through the binding of esterized phosphate to HA active sites, indicating its potential as a mineral-regulating salivary phosphoprotein homologue in vitro.

The impact of stannous, fluoride ions and its combination on enamel pellicle proteome and dental erosion prevention

Objectives

To compare the effects of stannous (Sn) and fluoride (F) ions and their combination on acquired enamel pellicle (AEP) protein composition (proteome experiment), and protection against dental erosion (functional experiment).

Methods

In the proteome experiment, bovine enamel specimens were incubated in whole saliva supernatant for 24h for AEP formation. They were randomly assigned to 4 groups (n=10), according to the rinse treatment: Sn (800ppm/6.7mM, SnCl₂), F (225ppm/13mM, NaF), Sn and F combination (Sn+F) and deionized water (DIW, negative control). The specimens were immersed 3× in the test rinses for 2min, 2h apart. Pellicles were collected, digested, and analyzed for protein content using liquid chromatography electrospray ionization tandem mass spectrometry. In the functional experiment, bovine enamel specimens (n=10) were similarly treated for pellicle formation. Then, they were subjected to a five-day erosion cycling model, consisting of 5min erosive challenges (15.6 mM citric acid, pH 2.6, 6×/d) and 2min treatment with the rinses containing Sn, F or Sn+F (3×/d). Between the treatments, all specimens were incubated in whole saliva supernatant. Surface loss was determined by profilometry.

Results

Our proteome approach on bovine enamel identified 72 proteins that were common to all groups. AEP of enamel treated with Sn+F demonstrated higher abundance for most of the identified proteins than the other groups. The functional experiment showed reduction of enamel surface loss for Sn+F (89%), Sn (67%) and F (42%) compared to DIW (all significantly different, p<0.05).

Conclusion

This study highlighted that anti-erosion rinses (e.g. Sn+F) can modify quantitatively and qualitatively the AEP formed on bovine enamel. Moreover, our study demonstrated a combinatory effect that amplified the anti-erosive protection on tooth surface.

Impact of acquired enamel pellicle modification on initial dental erosion

The acquired enamel pellicle that forms on the tooth surface serves as a natural protective barrier against dental erosion. Numerous proteins composing the pellicle serve different functions within this thin layer. Our study examined the effect of incorporated mucin and casein on the erosion-inhibiting potential of the acquired enamel pellicle. Cyclic acidic conditions were applied to mimic the erosive environment present at the human enamel interface during the consumption of soft drinks. One hundred enamel specimens were prepared for microhardness tests and distributed randomly into 5 groups (n = 20) that received the following treatment: deionized water, humidity chamber, mucin, casein, or a combination of mucin and casein. Each group was exposed to 3 cycles of a 2-hour incubation in human saliva, followed by a 2-hour treatment in the testing solution and a 1-min exposure to citric acid. The microhardness analysis demonstrated that the mixture of casein and mucin significantly improved the erosion-inhibiting properties of the human pellicle layer. The addition of individual proteins did not statistically impact the function of the pellicle. These data suggest that protein-protein interactions may play an important role in the effectiveness of the pellicle to prevent erosion.

Adhesion of Candida albicans to various dental implant surfaces and the influence of salivary pellicle proteins

Dental implants may be considered a potential reservoir for (re)infection with oral Candida albicans. Our aim was to evaluate initial fungal adhesion to three differentially textured titanium and one zirconia implant surface, and to correlate these findings to differences in specific surface characteristics (surface roughness (R(a)) and surface free energy (SFE)). Additionally, we investigated the influence of salivary protein films and two pellicle proteins (mucin and albumin). Implant surfaces were characterized by perthometer (R(a)) and goniometer (SFE) measurements. Implant specimens were rinsed with human whole saliva, mucin, albumin, or phosphate buffered saline and incubated in C. albicans suspension for 2.5h. Adherent fungi were quantified by means of a bioluminometric assay. The lowest amount of fungal cells was found on sand-blasted titanium, whereas zirconia implants did not show any reduced potential to adhere C. albicans. The influence of the implant SFE on fungal biofilm formation appears to be more important than the influence of R(a). The protein mucin enhanced C. albicans accumulation. In contrast, albumin is unlikely to be involved in the adhesion process of C. albicans.

Sugar alcohols, caries incidence, and remineralization of caries lesions: a literature review

Remineralization of minor enamel defects is a normal physiological process that is well known to clinicians and researchers in dentistry and oral biology. This process can be facilitated by various dietary and oral hygiene procedures and may also concern dentin caries lesions. Dental caries is reversible if detected and treated sufficiently early. Habitual use of xylitol, a sugar alcohol of the pentitol type, can be associated with significant reduction in caries incidence and with tooth remineralization. Other dietary polyols that can remarkably lower the incidence of caries include erythritol which is a tetritol-type alditol. Based on known molecular parameters of simple dietary alditols, it is conceivable to predict that their efficacy in caries prevention will follow the homologous series, that is, that the number of OH-groups present in the alditol molecule will determine the efficacy as follows: erythritol >/= xylitol > sorbitol. The possible difference between erythritol and xylitol must be confirmed in future clinical trials.

Radiation-related damage to dentition

Because of typical tissue reactions to ionising radiation, radiotherapy in the head and neck region usually results in complex oral complications affecting the salivary glands, oral mucosa, bone, masticatory musculature, and dentition. When the oral cavity and salivary glands are exposed to high doses of radiation, clinical consequences including hyposalivation, mucositis, taste loss, trismus, and osteoradionecrosis should be regarded as the most common side-effects. Mucositis and taste loss are reversible consequences, usually subsiding early post-irradiation, whereas hyposalivation is commonly irreversible. Additionally, the risk of rampant tooth decay with its sudden onset and osteonecrosis is a lifelong threat. Thus, early, active participation of the dental profession in the development of preventive and therapeutic strategies, and in the education and rehabilitation of patients is paramount in consideration of quality-of-life issues during and after radiotherapy. This Review focuses on the multifactorial causes of so-called radiation caries and presents possible treatment strategies to avoid loss of dentition.

Microradiographic study on the effects of mucin-based solutions used as saliva substitutes on demineralised bovine enamel in vitro

Sialic acids and proteins bound to mucins are known to form complexes with calcium, and this mechanism may hamper the remineralization of calcium-containing mucin-based saliva substitutes. Thus, the aim of this investigation was to evaluate the effects of adding various concentrations of calcium phosphate to self-made mucin-containing solutions on demineralised bovine enamel in vitro. Bovine specimens were prepared, embedded in epoxy resin, and polished to 4000 grit. Subsequently, the surfaces of the specimens were partially covered with nail varnish, thus serving as a control of sound enamel, and demineralised (37 degrees C; pH 5.0) for 14 (19 groups; n=10) or 28 days (three groups; n=9). After demineralization, the specimens were exposed to mucin-based solutions (30 g/l) with various saturations with respect to apatites containing 0.1 mM NaF, CaCl(2) (0-20 mM) and KH(2)PO(4) (0-52 mM) at two different pH values (5.5 or 6.5). A fluoride-free solution and the commercially available saliva substitute Saliva Orthana (Orthana, Kastrup, Copenhagen Denmark) served as controls. The differences in mineral loss (DeltaDeltaZ) between the values prior to (DeltaZ(Demin)) and after storage (DeltaZ(Effect)) in the various solutions were evaluated from microradiographs of thin sections (100 microm). The general linear model revealed a significant dependency of DeltaDeltaZ for calcium (P=0.006), but not for phosphate (P=0.081) or pH (P=0.114). DeltaZ(Effect) was only significantly reduced compared with DeltaZ(Demin) in the group with the highest saturation with respect to hydroxyapatite (P<0.05; t-test). In conclusion, mucin-based saliva substitutes with an adequate composition are able to remineralize bovine enamel in vitro.