Laboratory evaluation of toothbrush/toothpaste abrasion resistance after smooth enamel surface sealing

Nanotechnology for Dentistry: Prospects and Applications

In the XXI century, application of nanostructures in oral medicine has become common. In oral medicine, using nanostructures for the treatment of dental caries constitutes a great challenge. There are extensive studies on the implementation of nanomaterials to dental composites in order to improve their properties, e.g., their adhesive strength. Moreover, nanostructures are helpful in dental implant applications as well as in maxillofacial surgery for accelerated healing, promoting osseointegration, and others. Dental personal care products are an important part of oral medicine where nanomaterials are increasingly used, e.g., toothpaste for hypersensitivity. Nowadays, nanoparticles such as macrocycles are used in different formulations for early cancer diagnosis in the oral area. Cancer of the oral cavity-human squamous carcinoma-is the sixth leading cause of death. Detection in the early stage offers the best chance at total cure. Along with diagnosis, macrocycles are used for photodynamic mechanism-based treatments, which possess many advantages, such as protecting healthy tissues and producing good cosmetic results. Application of nanostructures in medicine carries potential risks, like long-term influence of toxicity on body, which need to be studied further. The introduction and development of nanotechnologies and nanomaterials are no longer part of a hypothetical future, but an increasingly important element of today's medicine.

In vitro surface analysis of the brushing resistance of orthodontic sealants using two different profilometric evaluation methods

The enamel can be protected by applying orthodontic sealants at the bracket base to avoid the development of white spot lesions caused by inadequate oral hygiene. The aim of this study was to investigate the mechanical resistance of five commonly used orthodontic sealants against brushing in comparison to a positive group. Hydroxyapatite discs were bonded with a metal bracket and a piece of arch-wire was ligated in order to simulate a daily clinical situation (n = 48). Samples were divided into 6 groups of respectively 8 specimens. Sealants were applied around the bracket base according to manufacturer's instructions. Following sealants were used: Group 1: Pro Seal (Reliance Orthodontic Products, Itasca, Illinois, USA); 2: Light Bond (Reliance Orthodontic Products, Itasca, Illinois, USA); 3: ClinproXT Varnish (3M ESPE, Seefeld, Germany); 4: ProtectoCaF2 Nano (BonaDent GmbH, Frankfurt am Main, Germany); 5: Fluor Protector and 6: Tetric EvoFlow (both Ivoclar Vivadent AG, Schaan Liechtenstein). Tooth brushing were simulated for 6 weeks and 6 months with an electric toothbrush. The sealant thickness was measured by mechanical (MP) and optical profilometry (OP) at baseline, after 6 weeks and after 6 months of brushing. Statistical analysis was performed according to two mixed linear models and post hoc Tukey-Kramer comparisons. The significance level was set at 5% (α ≤ 0.05). Pro Seal (MP: 9%; OP: 22%) and Light Bond (MP: 19%; OP: 16%) showed the lowest changes in sealant thickness after 6 months of simulated brushing. ClinproXT Varnish and Tetric EvoFlow recorded no statistically significant results (p > 0.05). The fluoride varnishes ProtectoCaF2 Nano and Fluor Protector could not be conclusively evaluated since the thickness of the sealants could not be determined at baseline. The results of both evaluation methods MP and OP are in good agreement. Pro Seal and Light Bond were resistant against tooth brushing and were able to adequately keep the bracket environment sealed even after 6 months. The two different measuring methods, MP and OP, provide a precise impression of the changes in the surface.

OCT evaluation of orthodontic surface sealants: a 12-month follow-up randomized clinical trial

OBJECTIVES

The aim of this single-center randomized controlled trial (NCT03753256) was to assess orthodontic surface sealant layer thickness and integrity in vivo during a 12-month follow-up by optical coherence tomography (OCT).

MATERIALS AND METHODS

Using a split-mouth design, quadrants of 20 patients treated with fixed orthodontic appliances were included. Quadrants were randomly assigned to the sealants Pro Seal® (PS) or Opal® Seal™ (OS). OCT scans were performed immediately after the application of the sealants and after 3, 6, 9, and 12 months. Sealant layer thicknesses and their integrity were determined at 5 regions of interest (ROIs) known for high risks of demineralization. Sealant integrity loss was determined using a self-developed scale.

RESULTS

A total of 16 patients successfully completed the study. The studied sealants showed significant differences in initial layer thickness. Mean layer thickness was significantly lower for PS (67.8 μm, (95% CI, 56.1-79.5)) than for OS (110.7 μm, (95% CI, 97.3-124.1)). Layer thickness loss was significant after 3 months for PS and after 6 months for OS. Sealant integrity was compromised in more than 50% of the ROIs already after 3 months for both sealants.

CONCLUSIONS

Patients treated with fixed orthodontic surface sealants lost the integrity of the protective layer in more than 50% of cases after 3 months, and the layer thickness of the sealants was significantly reduced after 3-6 months.

CLINICAL RELEVANCE

The protective effect against demineralization lesions of orthodontic sealants in patients treated with fixed appliances appears to be limited in time. Further preventive measures should be investigated.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT03753256).

Abrasion of Pro Seal® and Opal® Seal™ by professional tooth cleaning protocols: results from an in vitro study and a randomized controlled trial

BACKGROUND

The integrity of orthodontic surface sealants after professional tooth cleaning (PTC) has previously only been evaluated in vitro. Recently, we have shown that optical coherence tomography (OCT) can successfully be used for the longitudinal assessments of sealant thickness in vitro and in vivo.

OBJECTIVES

Thus, the aim of the present study was to assess the sealant thickness after PTC in vitro and in vivo by OCT.

TRIAL DESIGN

Single-centre four-arm parallel-group randomized controlled trial.

METHODS

Ninety-six extracted human teeth were randomly assigned to the surface sealants Pro Seal® (PS) and Opal® Seal™ (OS) and to PTC protocols: (1) polishing with brush and prophy paste (Cleanic®) or (2) erythritol air-polishing. Sealant thickness was assessed by OCT immediately after application (baseline), after thermocycling and after polishing for totals of 5, 10, 15, 30, 60, 90, and 120 seconds. Additionally, a clinical trial was conducted. Therefore, using a split-mouth design, quadrants of 20 patients and PTC protocols were randomized by an external randomization centre using computer generated tables to assign the surface sealants and PTC protocols. Sealant thicknesses were analysed at baseline, before and after PTC. Due to the optical properties of sealants, a complete blinding was not feasible.

RESULTS

In vitro both sealants revealed significant layer thickness losses after both PTC protocols. PS lost 0.77 µm/s [95% CI (confidence interval): 0.67, 0.87] from air-polishing and 0.43 µm/s (95% CI: 0.37, 0.49) from polishing with brush while OS lost 0.44 µm/s (95% CI: 0.32, 0.55) from air-polishing and 0.79 µm/s (95% CI: 0.68, 0.89) from polishing with brush of layer thickness. Sealant thickness loss of was significantly higher after erythritol air-polishing for PS and after polishing with brush for OS. The results of a concurrent randomized controlled trial (RCT) were comparable to those achieved in the in vitro part of this study.

LIMITATIONS

Long-term surface sealant abrasion should be validated by additional RCTs.

CONCLUSIONS

For PTC on surface sealant treated teeth, low abrasive protocols should be used. Air-polishing should be avoided on PS protected teeth and polishing with brush on OS treated teeth.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03753256.

Influence of enamel sealing with a light-cured filled sealant before bracket bonding on the bond failure rate during fixed orthodontic therapy

PURPOSE

Fluoride-containing adhesives for enamel sealing are commonly used for the prevention of white spot lesions during fixed orthodontic treatment. Thus, we examined whether enamel sealing with L.E.D. ProSeal® (Reliance Orthodontic Products Inc., Itasca, IL, USA) before bracket bonding increases the rate of bond failure during orthodontic treatment.

METHODS

In 20 adolescents (11-16 years, 10 male/10 female) at the start of fixed therapy, self-ligating SmartClip™SL3 metal brackets (3M Unitek, Monovia, CA, USA) were bonded to cleaned and conditioned (40% H₃PO₄, 30 s) buccal enamel surfaces of all permanent teeth except molars using Transbond™ XT (3M Unitek). In a split-mouth design, either L.E.D. ProSeal® (1st/3rd quadrant) or Clinpro™ XT Varnish (2nd/4th quadrant; 3M Unitek) was applied to enamel surfaces before (ProSeal®) or after (Clinpro™ XT Varnish) bracket bonding (200 teeth each; light curing: 20 s, Ortholux™ Luminous, 3M Unitek). Cumulative bond failure as total number of teeth with bracket detachment since start of therapy was documented every 3 months for a total of 12 months.

RESULTS

Cumulative bond failure was higher for enamel sealing before bonding from 6 months onward reaching significance at 12 months (34/200) compared to sealing after bonding (24/200): p = 0.038; Cramér's V = 0.488; odds ratio (OR) = 1.5; relative risk (RR) = 1.4. The higher loss rate was limited to the lower arch, but evident within 3 months reaching significance at 9 and 12 months (p = 0.019/0.011, V = 0.636/0.630; OR = 1.7/1.75, RR = 1.5/1.6). In general, cumulative bond failure at 12 months was higher in the lower arch, but this was only significant for teeth sealed before bonding (p = 0.001, V = 0.303, OR = 3.4, RR = 2.8).

CONCLUSIONS

Enamel sealing with L.E.D. ProSeal® should be performed after bracket bonding to prevent increased bond failure and bracket loss in the lower dental arch.

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.

Integrity testing of a smooth surface resin sealant around orthodontic brackets using a new Fluorescence-aided Identification Technique (FIT)

OBJECTIVE:

To investigate the integrity of a fluorescing resin-based sealant placed around orthodontic brackets using the Fluorescence-aided Identification Technique (FIT).

MATERIALS AND METHODS:

Standard brackets were bonded to the buccal surfaces of 17 extracted sound permanent premolar crowns sealed with ProSeal^®. Specimens were thermocycled (20,000 cycles, 5-55°C), and toothbrushing was simulated using an electric toothbrush and artificial aqueous toothpaste slurry. Changes in the sealed area were measured after one, two, three, and four alternating thermocycling-brushing cycles simulating 2 years of wear. Digital images were captured applying FIT (405 nm) using a digital camera-equipped stereomicroscope. ImageJ was used to measure sealant integrity and loss.

RESULTS:

There was a time-dependent decrease in sealed areas by between 21% and 100% (mean 54%). The sealant lost its integrity immediately after the first cycle, and unfilled areas were observed in all samples.

CONCLUSIONS:

The analyzed sealant lost its integrity over time. Using the proposed FIT, sealed surfaces were easily verified and quantified.

Assessing abrasion of orthodontic surface sealants using a modified ophthalmic optical coherence tomography device

OBJECTIVE

Optical coherence tomography (OCT) is a clinical standard in ophthalmology. Currently, its application in dentistry is gaining increasing interest. In this study, we tested the possibility to use a modified commercially available spectral domain OCT (SD-OCT) to assess the layer thickness of orthodontic surface sealants.

MATERIALS AND METHODS

Reference samples of surface sealants for calibration and repeatability testing were measured using a micrometer screw. SD-OCT measurements were compared with micro-CT and light microscopic analyses. After validating the calibration of the SD-OCT, surface sealant layer thickness after aging (thermo cycling) and simulation of professional tooth cleaning (PTC) was assessed using the SD-OCT on 45 extracted teeth assigned to three test groups (n = 15 each): Light Bond™ Sealant, Pro Seal®, and Opal® Seal.

RESULTS

SD-OCT showed excellent repeatability and accuracy for measurements of surface sealant layer thickness. Compared with micro-CT, SD-OCT showed better accordance with the reference measurements. The analysis of surface sealants after thermo cycling and PTC revealed poor resistance of Light Bond after only aging and demonstrated substantial wear of all sealants after aging and PTC.

CONCLUSION

Imaging using commercially available ophthalmic SD-OCT might represent a suitable non-invasive methodology for longitudinal assessments of surface sealant layer thickness in vitro and in vivo.

CLINICAL RELEVANCE

SD-OCT might be a suitable non-invasive method for longitudinal assessments of surface sealant durability in clinical trials.

Microhardness and Roughness of Infiltrated White Spot Lesions Submitted to Different Challenges

A white spot lesion is the first clinical sign of a caries lesion and represents mineral loss from the enamel subsurface. The purpose of this study was to evaluate the microhardness and surface roughness of white spot lesions after application of a resin infiltrant and subjection to different challenges. Caries-like lesions were induced in bovine enamel discs (n=50), and the specimens were randomly divided into five study groups (n=10): demineralized enamel (negative control, G1), infiltrated enamel (G2), infiltrated enamel submitted to brushing (G3), infiltrated enamel submitted to pH cycling (G4), and infiltrated enamel submitted to artificial aging (G5). Half of each enamel surface was used as its own positive control. Roughness data were analyzed using the Kruskal-Wallis test followed by the Dunn test. Results from microhardness were analyzed by two-way analysis of variance, followed by the Tukey test for multiple comparisons. The level of significance was set at 5%. Microhardness and roughness values obtained from the test side of the specimens were significantly lower compared with the sound enamel for all groups. Microhardness values obtained for G2, G3, and G5 were not significantly different. Values found for G1 were significantly lower compared with those for G2, G3, and G5. The lowest microhardness values were observed for G4, which was significantly different from the other groups. Surface roughness was not significantly different between G2 and G3. The resin infiltrant presented superiority over the unprotected white spot lesions, as they were more resistant to mechanical and aging challenges. However, resin infiltration was not able to reestablish the properties of sound enamel and was not resistant to a new cariogenic challenge.

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.

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.