Long-term protective effect of surface sealants against erosive wear by intrinsic and extrinsic acids

Effects of in vitro erosion on surface texture, microhardness, and color stability of resin composite with S-PRG fillers

OBJECTIVES

To evaluate the effect of acid erosion on different physical properties of resin composite with S-PRG (surface pre-reacted glass) fillers, by conducting simulations of intrinsic and extrinsic sources.

MATERIALS AND METHODS

Cylindrical samples (Ø6 vs. 2 mm) of a conventional nanohybrid resin composite (Forma, Ultradent) and of a nanohybrid resin composite with S-PRG filler (Beautifil II, Shofu) were exposed to erosive cycling (5 days), based on (n=12) remineralizing solution (control); 0.3% citric acid (pH=2.6); or 0.01 M hydrochloric acid (pH=2). Roughness (Ra), microhardness (KHN), and color (CIEL*a*b*, CIEDE2000, and Vita scale (SGU)) factors were analyzed at the initial and final time points, and the general color changes (ΔE_ab, ΔE₀₀, ΔSGU) were calculated. Final images were obtained using scanning electron microscopy (SEM). The data were evaluated by generalized models, Mann-Whitney, Wilcoxon, Kruskal-Wallis, and Dunn tests (α=0.05).

RESULTS

Regarding KHN, there was no difference between the groups or the time periods (p = 0.74). As for Ra, there was a significant increase in the Ra of both composites after cycling with hydrochloric acid, but only the resin composite with S-PRG filler showed a change in Ra after cycling with citric acid (p = 0.003). After cycling with citric and hydrochloric acid, the highest Ra values were found for the resin composite with S-PRG filler (p < 0.0001), corroborating the result of images (SEM) indicating loss of filler and porosities in this material. The resin composite with S-PRG filler showed higher ΔE_ab and ΔE₀₀, in addition to more negative ΔSGU values and lower L* values after exposure to both acids, compared to the control (p < 0.05).

CONCLUSION

The acidic conditions altered the roughness and color stability of the materials tested, pointing out that the resin composite containing S-PRG filler showed greater degradation of its physical properties than the conventional resin composite.

CLINICAL RELEVANCE

Bioactive materials are relevant, considering that their properties interact with dental hard tissues; however, the S-PRG-based resin composite showed greater degradation under acidic conditions than the conventional resin composite.

Resin infiltrant protects deproteinized dentin against erosive and abrasive wear

Objectives

This study aimed to investigate the anti-erosive/abrasive effect of resin infiltration of previous deproteinized dentin.

Materials and Methods

Dentin slabs were randomly assigned to 3 groups (n = 15): Control (no deproteinization; no resin infiltrant applied), RI (no deproteinization; resin infiltrant applied), and DRI (deproteinization; resin infiltrant applied). After undergoing the assigned treatment, all slabs were subjected to an in vitro cycling model for 5 days. The specimens were immersed in citric acid (0.05 M, pH = 3.75; 60 seconds; 3 times/day) and brushed (150 strokes). Between the challenges, the specimens were exposed to a remineralizing solution (60 minutes). The morphological alterations were analyzed by mechanical profilometry (µm) and scanning electron microscopy (SEM). Data were submitted to one-way analysis of variance (ANOVA) and Tukey tests (p < 0.05).

Results

Control and RI groups presented mineral wear and did not significantly differ from each other (p = 0.063). DRI maintained a protective layer preserving the dentin (p < 0.001). After erosive/abrasive cycles, it was observed that in group RI, only 25% of the slabs partially evidenced the presence of the infiltrating, while, in the DRI group, 80% of the slabs presented the treated surface entirely covered by a resin-component layer protecting the dentin surface as observed in SEM images.

Conclusions

The removal of the organic content allows the resin infiltrant to efficiently protect the dentin surface against erosive/abrasive lesions.

Effect of Cold Atmospheric Pressure Plasma Coupled with Resin-Containing and Xylitol-Containing Fluoride Varnishes on Enamel Erosion

Purpose

Considering the suggested advantages of cold atmospheric plasma (CAP) in increasing the fluoride uptake by the enamel, this study aimed to assess enamel erosion following the application of helium CAP and two types of fluoride varnishes.

Methods

The microhardness of 70 bovine enamel specimens was measured using a Vickers hardness tester. The specimens were randomly divided into 7 groups (n = 10): control, CAP (P), resin-containing fluoride varnish (RF), CAP + resin-containing fluoride varnish (PRF), fluoride varnish (F), CAP + fluoride varnish (PF), and erosion (E). The specimens in the control and erosion groups did not receive CAP or fluoride varnish. All specimens underwent erosive challenge 4 times/day using hydrochloric acid and artificial saliva except for the control specimens that remained in distilled water during the course of the study. After 5 days of erosive challenge, microhardness was measured again, and the percentage of microhardness change was calculated. Surface roughness of two specimens in each group was assessed by atomic force microscopy (AFM). Data were analyzed using one-way ANOVA followed by Tamhane's post-hoc test.

Results

The percentage of microhardness change in all groups was significantly higher than that of the control group. All groups showed significantly lower percentage of microhardness change compared with the E group except for the P group; no significant difference was noted in microhardness change of P and E groups. Other experimental groups had no significant difference with each other. Surface roughness was the highest in PRF and the lowest in the F group.

Conclusion

CAP application had no significant effect on increasing the enamel resistance to erosion. However, enamel resistance to erosion increased significantly after fluoride varnish application alone or fluoride varnish application combined with CAP. No significant difference was noted between the two types of varnishes in this regard. CAP increased the surface roughness while fluoride varnish application alone decreased the roughness.

Dentin tubule obturation of a bioglass-based dentin desensitizer under repeated exposure to lactid acid and brushing

Background

Dentin hypersensitivity is a frequent finding especially in periodontitis patients. Conventional treatment aims for obstruction of dentin tubules by disabling liquid and osmotic fluctuation to and from the pulpal chamber. A novel bioglass-based desensitizer was shown to obstruct tubules and to resist periodic exposure to lactic acid. Whether this obstruction is resistant to brushing had not been tested so far. Accordingly, the present study aimed to assess dentin tubule obstruction after repeated acid exposure and brushing.

Methods

Sixty dentin discs were cleaned with 17% EDTA, mounted into a pulp fluid simulator and randomly divided into 3 groups: No surface treatment in Group A, Seal&Protect® in group B and DentinoCer in group C. Discs were exposed to 0.1 M non-saturated lactic acid thrice and standardized brushing twice a day for 12 days. At baseline and after 2, 4 and 12 d samples were removed from the setting and prepared for top-view SEM analysis to assess tubule obstruction using the Olley score. Discs were then vertically cut and the section surface morphologically assessed using backscatter imaging. For both vertical and sectional surfaces EDX analysis was used to characterize the surface composition in the tubular and inter-tubular area.

Results

Group A showed clean tubular lumina at all time points. From day 2 onwards dentin showed exposed collagen fibers. Group 2 initially showed a complete surface coverage that flattened out during treatment without ever exposing tubules. At baseline, samples of Group C displayed a complete homogeneous coverage. From day 2 on tubules entrances with obstructed lumen became visible. While on day 4 and 12 the dentin surface exposed collagen fibers the lumina remained closed. EDX analysis of the vertical and horizontal views showed that P and Ca were predominant elements in both the inter- and tubular dentin while Si peaks were found in the tubule plugs.

Conclusion

While group B displayed a packed layer on the surface during the whole investigation time group C samples lost their superficial layer within 48 h. Tubule plugs containing considerable Si proportions indicated previous presence of DentinoCer, while high Ca and P proportions suggest obturation by dentin-like material.

The effects of intrinsic and extrinsic acids on nanofilled and bulk fill resin composites: Roughness, surface hardness, and scanning electron microscopy analysis

The objective of this study was to examine the effects of extrinsic or intrinsic acids on nanofilled and bulk fill resin materials in vitro. A total of 90 disks were prepared using dental restorative material (Filtek Z350XT, GrandioSO, Filtek Bulk Fill, X-tra fil). Thirty disks of each material were sub-divided into three groups (n = 10) that were immersed for 7 days in deionized water (DW), 5% citric acid (CA-pH 2.1), or 0.1% hydrochloric acid (HCl-pH = 1.2). Surface hardness and roughness (stylus profilometer by R_a parameter) analysis were performed before and after immersion. Morphological changes were evaluated by scanning electron microscopy. The data were analyzed by two-way ANOVA and Tukey's test (α = 0.05). All tested materials did not show significant differences in the effects of the DW, CA, or HCl solutions on surface roughness (p = .368). Likewise, the hardness loss was not affected by the solutions tested (p = .646), but there was a difference in the resin type (p = .002). Filtek Bulk Fill resin hardness was less affected, while Filtek Z350XT and GrandioSO presented the most hardness loss after 7 days of solution immersion. In terms of this experimental study, the results demonstrate the effectiveness of the mechanical properties (roughness and hardness surface) of nanofilled and bulk fill resin materials to resist erosion from extrinsic and intrinsic acids, therefore being potential candidates for dental applications.

Resin-Based Materials Protect Against Erosion/Abrasion-a Prolonged In Situ Study

While patient compliance is key to preventive measures related to dental erosion, the application of resin-based materials could serve as an additional treatment to inhibit erosion progression. This in situ study evaluated the effect of applying resin-based materials, including resin infiltrant, on previously eroded enamel subjected to prolonged erosive and abrasive challenges. The factors under study were types of treatment (infiltrant [Icon], sealant [Helioseal Clear], adhesive [Adper Scotchbond Multi-Purpose Plus], and control [no treatment]); wear conditions (erosion [ERO] and erosion + abrasion [ERO + ABR]) and challenge time (5 and 20 days) in a single-phase study. The blocks were prepared from bovine enamel, eroded (0.01 M HCl, pH 2.3 for 30 seconds) and randomized among treatments, wear conditions, and volunteers. The application of resin-based materials followed the manufacturers' recommendations. Twenty-one volunteers wore the palatal intraoral device, in which one row corresponded to ERO and the other to ERO + ABR. In each row, all treatments were represented (2 blocks per treatment). For 20 days, the erosive challenge was performed 4 times/day (immersion in 0.01 M HCl, pH 2.3, for 2 minutes) for the ERO condition. For the ERO + ABR condition, two of the erosive challenges were followed by abrasion for 15 seconds with fluoride dentifrice slurry. Enamel and/or material loss was measured using profilometry (initial, after treatment, and after the end of the fifth and 20th days of in situ erosive challenge) and analyzed by ANOVA models and Tukey's test (α=0.05). The results showed that the application of resin-based materials did not cause superficial enamel loss. The infiltrant group showed a thicker layer of material above the enamel compared with the other materials (p=0.001). After the erosive challenge, there was no difference between the conditions ERO and ERO + ABR (p=0.869). All materials protected the enamel against erosion progression compared with the control group (p=0.001). Based on these results, we conclude that the application of resin-based materials results in protection of previously eroded enamel subjected to in situ erosive and abrasive challenge for 20 days.

[Tooth Erosions Associated with Gastroesophageal Reflux: Cause, Prevention and Restorative Therapy]

Tooth Erosions Associated with Gastroesophageal Reflux: Cause, Prevention and Restorative Therapy Abstract. Dental erosions are caused by the recurring contact of solutions which are unsaturated in tooth minerals,ith hard tooth substances. This initially leads to softening and later to an irreversible loss of hard tooth substance. Erosion is observed particularly with excessive consumption of acidic foods (e.g. soft drinks or citrus fruits) but also in connection with gastrointestinal (gastroesophageal reflux disease) or psychosomatic diseases (anorexia nervosa or bulimia nervosa). The aim of this article is to define dental erosions, their causes, prevalence and consequences as well as possible preventive measures. Based on a clinical example of a patient with reflux-related erosions, a therapy option with direct composite tooth build-up is presented.

Performance of a bioglass-based dentine desensitizer under lactid acid exposition: an in-vitro study

Background

Dentine hypersensitivity is especially frequent in patients with pronounced periodontal attachment loss. Aim of the treatment is an obstruction of the dentine tubules in order to inhibit liquid or osmotic motion, which is considered as trigger for pain sensations. Novel approaches aim for obstruction by calcium phosphate compounds in order to rely on biocompatible compounds. It was the aim of the study to optically investigate the morphology and to assess the fluid permeability of treated dentine surfaces.

Methods

Dentine discs were pretreated in an ultrasonic bath with 17% EDTA to clean the lumina of the dentine tubules. Samples of group A remained untreated while Seal&Protect® as a conventional desensitizer was applied for group B and DentinoCer in group C. Discs were mounted into a pulp fluid simulator (PFS) with a methylene blue solution in order to create a flow pressure of 0.5 bar. Over 12 d, discs were exposed three times per day to 0.1 M nonsaturated lactic acid. At baseline and after 2, 8 and 12 d samples were removed from PFS and prepared for SEM analysis. Tubule obstruction was assessed quantitatively using Olley scores and by qualitative description of the surface. Absorption spectrometry was used to assess the concentration of leaked methylene blue outside the samples in order to estimate dentine permeability.

Results

Untreated discs showed clean lumina of all tubules at all time points and magnifications. From day 2 onwards dentine showed exposed collagene fibers due to acid exposition. Seal&Protect® initially showed homogenous dentine surface coverage that got a more granulomatous aspect in the course of treatment time. Few samples showed sporadic tubules with open lumen at day 8 and 12. Group C showed samples with a homogeneous, even surface. Narrow slits in the superficial layer are visible from day 4 on, but the dentine surface remained invisible and dentine tubules were closed till the end of the investigation period.

Conclusion

Over 12 d of lactid acid exposure, samples showed complete coverage of the dentine tubules in the chosen in-vitro-model when treated with Seal&Protect® or DentinoCer.

Effects of staining and polishing on different types of enamel surface sealants

OBJECTIVE

To assess surface discoloration of four enamel sealants based on different chemical compositions after exposure to artificial aging and staining solutions. Furthermore, their cleanability after polishing will be evaluated.

MATERIALS AND METHODS

Selected sealants were a composite resin-based sealant with fillers (Pro Seal), a composite resin-based sealant without fillers (Light BondSealant), a resin-modified glass ionomer-based sealant (ClinproXT Varnish) and a silicon-based sealant (Protecto). Natural teeth served as medium. Immersion solutions were water, juice, tea, and turmeric. In a standardized setting, all samples were measured seven times with a spectroradiometer (Photoresearch PR670) at baseline, after thermocycling; 7 days; 2 and 4 weeks of immersion; and after finally polishing.

RESULTS

Thermocycling had no significant effect on color stability. After exposure to staining solutions, all sealed surfaces showed significant color changes. Color change predominately occurred for all sealants in the first week of staining (P ≤ .01). Best resistance to staining decreased as follows: Protecto > Light Bond Sealant > ProSeal > Clinpro XT Varnish. Surface cleaning by polishing significantly reduced the color change.

CONCLUSION

Sealed enamel surfaces are prone to discoloration, which is most prominent in filled composite and glass-ionomer-based sealants. Staining can be reduced by polishing; however, in this in vitro setting the original color could not be restored.

CLINICAL SIGNIFICANCE

Enamel sealants might exert adverse effects in terms of discoloration. This should be taken into consideration by clinicians and patients, particularly when sealants are applied in esthetically critical areas.

Calcium Charge and Release of Conventional Glass-Ionomer Cement Containing Nanoporous Silica

The aim of this study was to evaluate calcium charge and release of conventional glass-ionomer cement (GIC) containing nanoporous silica (NPS). Experimental specimens were divided into two groups: the control (GIC containing no NPS) and GIC-NPS (GIC containing 10 wt % NPS). The specimens were immersed in calcium chloride solutions of 5 wt % calcium concentration for 24 h at 37 °C, whereupon the calcium ion release of the specimens was measured. The calcium ion release behavior of GIC-NPS after immersion in the calcium solution was significantly greater than that of the control. Scanning electron microscopy and electron-dispersive X-ray spectroscopy results indicated that calcium penetrated inside the GIC-NPS specimen, while the calcium was primarily localized on the surface of the control specimen. It was demonstrated that NPS markedly improved the calcium charge and release property of GIC.

Protective Effect of Adhesive Systems associated with Neodymium-doped Yttrium Aluminum Garnet Laser on Enamel Erosive/Abrasive Wear

AIM

This study evaluated the efficacy of self-etching adhesive systems associated or not associated with the neodymium-doped yttrium aluminum garnet (Nd:YAG) laser on the protection against enamel erosive/abrasive wear.

MATERIALS AND METHODS

Bovine enamel specimens were demineralized with 0.3% citric acid (5 minutes). The samples were randomly assigned to eight groups (n = 20): SB - Single Bond Universal (3M/ESPE); SB+L - Single Bond Universal + laser (80 mJ/10 Hz); FB - Futurabond U (Voco); FB+L -Futurabond U + laser; GEN - G-aenial bond (GC); GEN+L -G-aenial bond + laser; L - laser irradiation; and C - no treatment. The laser was applied before light curing. The samples were subjected to erosive/abrasive challenges (0.3% citric acid - 2 minutes and tooth brushing four times daily for 5 days). Enamel surface loss was recovered profilometrically by comparison of baseline and final profiles. The adhesive layer thickness, retention percentage of the protective layer, and microhardness of cured adhesive were measured. Data were analyzed using one-way analysis of variance and Tukey's test (5%).

RESULTS

There were significant differences for all parameters (p = 0.0001). Mean values ± SD and results of the Tukey's test were: Surface wear: GEN - 4.88 (±1.09)a, L - 5.04 ± 0.99)a, FB - 5.32 (±0.93)ab, GEN + L - 5.46 (±1.27)abc, SB + L - 5.78 (±1.12)abc, FB + L - 6.23 (±1.25)bc, SB - 6.35 (±1.11)c, and C - 6.46 (±0.61)c; layer thickness: GEN - 15.2 (±8.63)c, FB - 5.06 (±1.96)a, GEN + L - 13.96 (±7.07)bc, SB + L - 4.24 (±2.68)a, FB + L - 9.03 (±13.02)abc, and SB - 7.49 (±2.80)ab; retention: GEN - 68.89 (±20.62)c, FB - 54.53 (±24.80)abc, GEN + L - 59.90 (±19.79)abc, SB + L - 63.37 (±19.30)bc, FB + L - 42.23 (±17.68) a, and SB - 47.78 (±18.29)ab; microhardness: GEN - 9.27 (±1.75)c; FB - 6.99 (±0.89)b; GEN + L - 6.22 (±0.87)ab; SB + L - 15.48 (±2.51)d; FB + L - 10.67 (±1.58)c; SB - 5.00 (±1.60)a.

CONCLUSION

The application of Futurabond U and G-aenial bond on enamel surface, as well as the Nd:YAG laser irradiation alone, was able to reduce the enamel wear. The use of laser after the adhesive systems did not improve their efficacy.

CLINICAL SIGNIFICANCE

Erosive/abrasive wear is a prevalent condition in clinical practice affecting many patients. The association of adhesive systems and Nd:YAG laser is of considerable clinical interest because it assesses new treatments to reduce the erosive/abrasive wear that would help dentists in clinical treatment decisions to reduce enamel wear and achieve a successful treatment.

Microleakage and Shear Bond Strength of Composite Restorations Under Cycling Conditions

OBJECTIVES

The aim of this study was to evaluate microleakage and shear bond strength of composite restorations under different cycling conditions.

METHODS AND MATERIALS

Class V cavities were prepared in the buccal and lingual surfaces of 30 human molars (n=60). A further 60 molars were used to prepare flat enamel and dentin specimens (n=60 each). Cavities and specimens were divided into six groups and pretreated with an adhesive (self-etch/Clearfil SE Bond or etch-and-rinse/Optibond FL). Composite was inserted in the cavities or adhered to the specimens' surfaces, respectively, and submitted to cycling (control: no cycling; thermal cycling: 10,000 cycles, 5°C to 55°C; thermal/erosive cycling: thermal cycling plus storage in hydrochloric acid pH 2.1, 5 minutes, 6×/day, 8 days). Microleakage was quantified by stereomicroscopy in enamel and dentin margins after immersion in silver nitrate. Specimens were submitted to shear bond strength testing. Statistical analysis was done by two-way analysis of variance and Kruskal-Wallis tests (p<0.05).

RESULTS

Microleakage in enamel margins was significantly lower in the control group compared with thermal cycling or thermal/erosive cycling. Erosive conditions increased microleakage compared with thermal cycling (significant only for Clearfil SE Bond). No significant differences were observed in dentin margins. Bond strength of enamel specimens was reduced by thermal cycling and thermal/erosive cycling when Clearfil SE Bond was used and only by thermal/erosive cycling when Optibond FL was used. No differences were observed among dentin specimens.

CONCLUSIONS

Thermal/erosive cycling can adversely affect microleakage and shear bond strength of composite resin bonded to enamel.

Dentin Protection of Different Desensitizing Varnishes During Stress Simulation: An In Vitro Study

OBJECTIVE

The aim of this study was to investigate dentin protection of different desensitizing varnishes (light- and self-curing) during acid action/abrasion stress and thermocyclic loading in vitro.

METHODS

Dentin discs of 2 mm thickness were cut from 120 human molars, embedded, and polished. Specimens were randomized into five groups (n=24): A, negative control; B, Gluma Desensitizer; C, Cervitec plus (self-curing); D, Seal&Protect; and E, Admira Protect (light-curing). In groups B-E, varnish was applied on two-thirds of the dentin surface, and one-third acted as internal control. Stress cycle (2 cycles/day) for specimens were as follows: 1, acid action (pH: 2.9: five minutes); 2, remineralization (synthetic saliva: 60 minutes); 3, brushing (100 strokes); 4, thermocycling (five cycles); and 5, remineralization (synthetic saliva: six hours) for each group (n=12) for 30 (15 days) or 60 times (30 days). Specimens were analyzed using an incident light microscope. Substance loss was measured in micrometers. Statistical analysis was performed with the multiple contrast test (p<0.05).

RESULTS

Groups B and C had a significantly lower dentin loss than A (p<0.01). After 30 days, group A showed the highest dentin loss (p<0.01), whereas the other groups lacked a significant difference regarding their substance loss (dentin and/or varnish; p>0.05). Varnish layer loss was shown for groups D and E with a remaining protective layer; groups A-C showed dentin removal.

CONCLUSION

All four varnishes are protective compared with an untreated control. Light-curing varnishes might provide higher dentin protection than self-curing materials.

Effectiveness of resin-based materials against erosive and abrasive enamel wear

OBJECTIVE

The objective of this study was to test the effectiveness of resin-based materials against erosive enamel wear under erosive and abrasive challenges by orange juice and tooth brushing.

METHODS

Fifty enamel specimens from third molars were assigned to five groups: ICON resin infiltration with no etching (ICON-NE), ICON resin infiltration with 15 % HCl etching (ICON-AE), Seal & Protect sealant (S&P), Tetric EvoFlow (TEF), and control. Erosive lesions were first created on enamel, then treated with resin-based materials. Erosive and abrasive challenges by orange juice and tooth brushing were repeated after treatments. Erosive wear of the treated areas was measured with 3D scanning microscopy, and data were analyzed using ANOVA and paired t tests.

RESULTS

Treatments with ICON, S&P, and TEF created a protective material coating of 4.5 ± 1.9 μm, 44.3 ± 8.1 μm, and 84.6 ± 15.7 μm in thickness on the lesion surfaces, respectively. After 15 cycles of erosive and abrasive challenges, enamel or material losses were 21.9 ± 2.3 μm for control, 24.5 ± 4.0 μm for ICON-NE, 24.6 ± 7.4 μm for ICON-AE, 11.2 ± 4.1 μm for S&P, and 3.9 ± 1.9 μm for TEF, respectively. The protective coatings were completely lost in the ICON infiltration groups but remained intact in both the S&P and TEF groups after erosive and abrasive challenges.

CONCLUSION

In contrast to a resin sealant and a flowable composite, ICON infiltration resin was not effective in protecting enamel surfaces from erosive and abrasive wear.

CLINICAL RELEVANCE

Sealant and flowable composite resin may create protective coatings on eroded enamel surfaces and prevent further tissue loss.

Influence of removing excess of resin-based materials applied to eroded enamel on the resistance to erosive challenge

OBJECTIVES

The aim of this study was to evaluate the effect of removing excess of resin-based materials applied to eroded enamel, subjected to erosive challenge.

METHODS

Bovine enamel blocks were immersed in HCl 0.01M, pH 2.3, for 30s under agitation at 50 rpm in room temperature, in order to form a softened erosion lesion. The blocks were then randomly divided into eight groups (n=12) and treated as follows: Cn- and Ce-control without treatment, Hn- and He-fissure resin sealant (Helioseal Clear(®)), An- and Ae-self-etch adhesive (Adhese(®)), In- and Ie-infiltrant (Icon(®)); being n-with excess removal and e-without excess removal of the material. After application of the materials, the blocks were immersed in HCl for 2 min, followed by immersion in artificial saliva for 120 min. This cycle was repeated four times a day for five days. Material thickness and enamel wear were assessed using profilometry. Data were analyzed by two-way ANOVA and Tukey's test (P<0.05).

RESULTS

Groups He, Ae, and Ie resulted in the formation of a layer of material over enamel, being similar effective in inhibiting erosion progression (P>0.05). Groups Hn, An, and In (with excess removal) were similar to controls (Cn, Ce) and resulted in near enamel loss after application and after erosive challenge (P>0.05).

CONCLUSIONS

Resin-based materials are able to protect enamel against erosion only when they are present over enamel, as a physical barrier.

CLINICAL SIGNIFICANCE

The resin-based materials demonstrated potential to prevent the progression of erosion lesions when the material remains on the dental surface.

Protective effects of resin sealant and flowable composite coatings against erosive and abrasive wear of dental hard tissues

OBJECTIVES

To test the effectiveness of sealant and flowable composite coating on eroded enamel, dentin and cementum under erosive/abrasive challenges in vitro.

METHODS

A total of 108 tissue sections (36 each for enamel, dentin and cementum) from third molars were assigned to three groups: Seal & Protect sealant (S&P), Tetric EvoFlow composite (TEF) and control. Erosive/abrasive lesions were created on each specimen by citric acid and brushing with toothpaste. S&P and TEF were applied to the lesions and subjected to erosive/abrasive cycling included 24 cycles of immersion in citric acid (pH 3.6) for 60min, followed by remineralization for 120min and brushing with toothpastes for 600 strokes at 150g. Erosive wear of materials or dental tissues were measured with 3D scanning microscopy and data were analyzed using ANOVA.

RESULTS

Treatments with S&P and TEF created a protective material coating of 42.7±17.8μm and 150.8±9.9μm in thickness, respectively. After 24 cycles of erosive/abrasive challenges, tissue losses were -346.9±37.3μm for enamel, -166.5±26.3μm for dentin and -164.7±18.2μm for cementum in untreated controls, as compared to material losses of -24.4±3.3μm for S&P, and -10.8±4.4μm for TEF, respectively. Both S&P and TEF were effective in protecting enamel, dentin and cementum against erosive tooth wear (p<0.01). S&P exhibited faster wear than TEF (p<0.01) and showed spotted peeling in a third of the specimens. TEF remained intact on all three types of dental tissues at the end of the 24 cycles of erosive/abrasive challenges.

CONCLUSIONS

A thin coating of flowable composite resin 150μm in thickness may provide long-term protection against erosive/abrasive tooth wear. Resin sealant may provide adequate protection for dental hard tissues in short-term and may require repeated applications if long-term protection is desired.

In Vitro Effects of Resin Infiltration on Enamel Erosion Inhibition

Resin-based materials that show promising effects for preventing the progression of erosion have been studied. This in vitro study evaluated the effects of applying resin-based materials, including resin infiltration, on previously eroded enamel subjected to erosive challenges. The influence of enamel surface etching prior to application of the material was also studied. Bovine enamel blocks were immersed in hydrochloric acid (HCl), 0.01 M (pH 2.3), for 30 seconds in order to form a softened erosion lesion. The blocks were then randomly divided into nine groups (n=12) and treated as follows: C = control without treatment; Hel = pit & fissure resin sealant (Helioseal Clear); Adh = two-step self-etching adhesive system (AdheSe); Tet = two-step conventional adhesive system (Tetric N-bond); and Inf = infiltrant (Icon). The Helno, Adhno, Tetno, and Infno groups received the same materials without (or with no) surface conditioning. The depth of the material's penetration into softened erosion lesions was qualitatively analyzed using reflection and fluorescence confocal microscopy. After application of the materials, the blocks were immersed in HCl for two minutes; this step was followed by immersion in artificial saliva for 120 minutes four times a day for five days (erosive cycling). Both the enamel alteration and material thickness were analyzed using profilometry, and the results were submitted to Kruskal-Wallis and Dunn tests (p>0.05). Images from the confocal microscopy showed minimal penetration of Adh/Adhno and deep penetration of Inf/Infno into the erosive lesions. The groups Hel, Adh, Inf, Tetno, and Infno resulted in the formation of a layer of material over the enamel, which was effective in inhibiting the progression of erosion. In conclusion, the infiltrant, with or without etching, was able to penetrate and protect the enamel against dental erosion. The other resin-based materials, except for the two-step conventional adhesive, were able to penetrate and inhibit the progression of erosive lesions only when they were applied after enamel etching.

In vitro studies on the cytotoxic potential of surface sealants

OBJECTIVE

The objective of this in vitro study was an initial screening of the cytotoxic potential of widely used smooth enamel surface sealants.

MATERIALS AND METHODS

A total of 20 products were allocated to four groups based on their chemical composition: (1) filled resin-based sealants, (2) unfilled resin-based sealants, (3) a resin-modified, glass ionomer-based sealant, and (4) silicone-based sealants. All materials were applied to human enamel slices both in accordance with manufacturers' instructions and in additional experiments applying 50% undercuring and 50% overcuring. An agar overlay assay was then used to test the specimens following ISO 10933. The cytotoxic potential of each material was interpreted based on a reaction index that summarized the decolorization and lysis scores obtained.

RESULTS

The cytotoxic potential decreased as follows: unfilled resin-based sealants > filled resin-based sealants > resin-modified, glass ionomer-based sealant > silicone-based sealants. In 75% of the resin-based products, deliberate undercuring was associated with more extensive decolorization zones, leading to higher rates of cytotoxic potential in two of those products. Overcuring, by contrast, was associated with a tendency for smaller decolorization zones in 50% of the resin-based products.

CONCLUSION

Surface sealants derived from resin monomers exhibited cytotoxic potential in the agar overlay assay. There is also evidence of a possible association with curing, as undercuring can increase the cytotoxic potential, whereas normal curing (as per manufacturers' instructions) or overcuring may help minimize such effects. More research into the biological implications of these materials is needed, especially with regard to their potential impact on the adjacent gingiva.

Three-dimensional profilometric assessment of early enamel erosion simulating gastric regurgitation

OBJECTIVES

A priority research area in minimal intervention dentistry is the characterization of the early stages of dental erosion. The aim of this in vitro study was to assess the effect of short, repetitive erosive challenges to human enamel over 2 min at pH 1.5 and 3.0 under conditions simulating gastric regurgitation.

METHODS

Enamel surfaces were subjected to erosive challenges at pH 1.5 (Group 1, n=10) and pH 3.0 (Group 2, n=9) for periods of 30s (stage 1), 60s (stage 2) and 120 s (stage 3). Quantitative changes were assessed longitudinally by measuring the 3D average surface roughness (Sa) values using 3D confocal microscopy. Qualitative micrographic assessment of surface changes was also conducted by using environmental scanning electron microscopy.

RESULTS

Linear mixed model analysis showed significant effects of the pH values (p<0.001) and the stages (p<0.001) on the observed Sa values. Post hoc tests showed significant increases in the Sa values between baseline and other stages in both groups (p<0.01). The mean Sa values also increased significantly from stage 1 to stage 2 in Group 1 (p<0.05). Micrographic analysis displayed severely etched enamel rods in Group 1, but only subtle changes in Group 2.

CONCLUSIONS

The complexity of the enamel surface is influenced by both acid concentration (pH value) and duration of acid exposure during early stages of erosion. Erosion occurring under conditions simulating GORD can be detected in its initial stages, opening up the possibilities of early diagnosis and management of this condition.

CLINICAL SIGNIFICANCE

Erosive tooth wear occurs progressively and insidiously, often creating complex treatment challenges. This emphasizes the need for early diagnosis and management in accordance with minimal intervention philosophy. Our findings provide a foundation for further research that could lead to the development of highly-sensitive clinical diagnostic tools and preventive strategies.

Biological evaluation of enamel sealants in an organotypic model of the human gingiva

OBJECTIVES

Various sealant materials have been suggested to decrease decalcification during orthodontic treatment. However, only a few in vitro studies on the cytotoxicity of resinous pit and fissure sealants have been published, and to the best of our knowledge no similar studies are available for the enamel sealants used in orthodontics. Therefore, we aimed to characterize the possible adverse effects of enamel sealants, especially on the gingival epithelium.

METHODS

Organotypic cultures of the human gingival mucosa were used to assess the possible impact of six enamel sealants. Differentiation and apoptosis were determined by immunofluorescent staining. The pro-inflammatory cytokines IL-1β and IL-6 were quantified by ELISA. Cytotoxicity was measured using MTS assays in monolayer cultures of human gingival fibroblasts. Leaching of monomers from enamel sealants was quantified using HPLC.

RESULTS

The differentiation of the organotypic gingival mucosa remained unaffected. All under-cured and several standard-cured sealants (Light Bond™ Sealant, Light Bond™ Filled Sealant, and L.E.D. Pro Seal®) significantly induced apoptosis in the organotypic model. Light Bond™ Sealant, Light Bond™ Filled Sealant, and L.E.D. Pro Seal® caused a significant induction of pro-inflammatory cytokines. Reducing curing time had an influence on cytotoxicity in monolayer cultures of primary human oral cells. All resin-based sealants leached monomers.

SIGNIFICANCE

Enamel sealants might exert adverse effects on the gingival epithelium. Due to the vicinity of the enamel sealant to the gingival epithelium, and the large surface area of applied sealants, these materials should be carefully applied and sufficiently cured.

Influence of light-curing mode on the cytotoxicity of resin-based surface sealants

Background

Surface sealants have been successfully used in the prevention of erosive tooth wear. However, when multiple tooth surfaces should be sealed, the light-curing procedure is very time-consuming. Therefore, the aim of this study was to investigate whether reduced light-curing time (while maintaining similar energy density) has an influence on resin-based surface sealant cytotoxicity.

Methods

Bovine dentine discs were treated as follows: group 1: untreated, groups 2–5: Seal&Protect and groups 6–9: experimental sealer. Groups 2 and 6 were light-cured (VALO LED light-curing device) for 40 s (1000 mW/cm²), groups 3 and 7 for 10 s (1000 mW/cm²), groups 4 and 8 for 7 s (1400 mW/cm²) and groups 5 and 9 for 3 s (3200 mW/cm²). Later, materials were extracted in culture medium for 24 h, and released lactate dehydrogenase (LDH) activity as a measure of cytotoxicity was determined photometrically after cells (dental pulp cells and gingival fibroblasts) were exposed to the extracts for 24 h. Three independent experiments, for both sample preparation and cytotoxicity testing, were performed.

Results

Overall, lowest cytotoxicity was observed for the unsealed control group. No significant influence of light-curing settings on the cytotoxicity was observed (p = 0.537 and 0.838 for pulp cells and gingival fibroblasts, respectively). No significant difference in the cytotoxicity of the two sealants was observed after light-curing with same light-curing settings (group 2 vs. 6, 3 vs. 7, 4 vs. 8 and 5 vs. 9: p > 0.05, respectively).

Conclusions

Shortening the light-curing time, while maintaining constant energy density, resulted in no higher cytotoxicity of the investigated sealants.

Durability of the anti-erosive effect of surfaces sealants under erosive abrasive conditions

OBJECTIVE

To test the durability of sealants applied for prevention of erosive dentine mineral loss under erosive/abrasive conditions.

METHODS

Forty-eight bovine dentine samples doped with (32)P were randomly allocated to four groups (1-4). All samples performed a de- and remineralizations pre-cycling (6 × 1 min erosion in HCl: pH 3.0, mean time and overnight immersion in artificial saliva) for 1 day. Sealing was done as follows; (1) unsealed, (2) Seal & Protect, (3) K-0184 (experimental sealer) and (4) OptiBond FL. After sealing, samples were immersed in HCl for 3 h (baseline measurement). Then, the following erosive/abrasive and remineralisations cycling was performed for 8 days: 3 h/day erosion with HCl, 600 brushing strokes/day and storage in artificial saliva for the rest of the day. Sealer permeability was evaluated by assignation of (32)P in the acid used for the erosive attacks.

RESULTS

At baseline, the significantly highest dentine loss was observed for the unsealed control group, while the mineral loss was not statistically significantly different between the sealed groups 2 and 3. At all days of the erosive/abrasive and remineralizations cycling and cumulatively the significantly highest mineral loss was observed for group 1, while the significantly lowest mineral loss was observed for the samples sealed with Seal & Protect (group 2) and K-0184 (group 3). In all groups, no significant increase in the (32)P release was observed.

CONCLUSION

Surface sealants are able to reduce the erosive dentine mineral loss and maintain this erosion-preventing efficacy over the whole duration (simulating 8 month in-vivo) of the erosive/abrasive cycling.

Impact of erosive conditions on tooth-colored restorative materials

OBJECTIVES

To give an overview of the impact of erosive conditions on the behavior of tooth-colored restoratives and performance of dental adhesives.

METHODS

Acid-induced erosive lesions of enamel and dentin often need restorative procedures for rehabilitation. Nowadays, mostly tooth-colored restoratives (ceramics or resin composites), which are adhesively fixed to the dental substrate are used for this purpose. In some cases it might be necessary to seal the exposed dentin before achieving this goal in order to combat hypersensitivities and to protect those teeth from further erosive and abrasive loss. Moreover, it is conceivable that patients will fall back into their old "erosive behavior" after the application of restoratives. The following overview describes in how far intra-oral erosive conditions might affect the integrity of restorative materials, such as composite resins and ceramics, or of dentin sealants. Additionally, the use of erosively altered enamel and dentin as substrate for adhesive technologies is elucidated.

RESULTS

In the literature, information of the behavior of tooth-colored restoratives under still persisting erosive conditions are limited and mostly based on in vitro-studies. There is information that the adhesion of dental adhesives to eroded dentin is compromised as compared to regular dentin. The impact of erosive conditions relevant for the oral cavity on ceramics and resin composites seems to be rather low, although only few clinical studies are available.

SIGNIFICANCE

The review showed that erosive conditions might have only little impact on behavior of tooth-colored restorative materials, such as composites and ceramics. Dentin sealants also seem to be rather resistant against erosive conditions and might therefore serve as an intermediary treatment option for exposed dentin surfaces. The adhesion of dentin adhesives to eroded dentin might be increased by mechanical pre-treatment of the substrate, but needs further investigation.

Influence of light-curing mode on the erosion preventive effect of three different resin-based surface sealants

Objectives. To investigate if reducing the light-curing time (while maintaining similar energy density) of resin-based surface sealants influences their erosion-preventive potential and mechanical stability after thermomechanical loading. Methods. Dentine samples were treated as follows: group 1—untreated, groups 2–4—Seal&Protect, groups 5–7—experimental sealer, and groups 8–10—Syntac Classic system. Groups 2, 5 and 8 were light-cured for 10 s (1000 mW/cm²), groups 3, 6 and 9 for 7 s (1400 mW/cm²), and groups 4, 7, and 10 for 3 s (3200 mW/cm²). After water storage (7 d), first measurement was performed to evaluate baseline permeability of the sealants. After a thermomechanical loading (5000 cycles, 50/5°C, 12000 brushing strokes) a second evaluation of permeability was conducted (measurement 2). Permeability was tested by storing the samples in HCl (pH 2.3; 24 h) and measuring the dentine calcium release by atomic absorption spectroscopy. Results. For the first and second measurements, no influence of light-exposure time on permeability was observed (ANOVA: P > 0.05). No significant difference in the stability of the respective sealants was observed when light-cured for different durations. Conclusion. Shortening the light-curing time, while maintaining energy density constant, has no influence on permeability and stability of the investigated sealants.