Adhesive performance of a caries infiltrant on sound and demineralised enamel

Objective

Resin infiltration is considered as a treatment option for initial caries lesions. As cavitated early lesions might require additional restorative intervention, a caries infiltrant might be also used for enamel conditioning prior to composite insertion. This study aimed to analyse the shear bond strength of a flowable composite to sound and demineralised enamel pretreated with a caries infiltrant, a conventional adhesive or a combination of both.

Methods

Flattened bovine enamel specimens (n = 120) were either demineralised (14 d, acidic buffer, pH 5) or remained untreated. Sound and demineralised specimens (each n = 20) were then treated with: (1) 35% phosphoric acid, conventional adhesive, (2) 15% hydrochloric acid, caries infiltrant or (3) 15% hydrochloric acid, caries infiltrant, conventional adhesive. Shear bond strength of a flowable composite was tested after 24 h water storage (37 °C) and statistically analysed (ANOVA, p ≤ 0.05). The mode of failure was assessed microscopically at 25× magnification.

Results

On demineralised enamel, the combination of caries infiltrant and conventional adhesive showed significantly higher shear bond strength values than the conventional adhesive alone, while both being not significantly different from group 2. No significant differences between the groups could be detected on sound specimens. A higher percentage of cohesive failures could be observed in demineralised samples of group 2 (40%) and 3 (65%), while all other specimens presented almost only adhesive failures.

Conclusion

The use of a caries infiltrant before application of a conventional adhesive did not impair bonding to sound and demineralised enamel and might be beneficial as a pretreatment in demineralised enamel.     

Protection of sound enamel and artificial enamel lesions against demineralisation: Caries infiltrant versus adhesive

Objective

To compare the protective potential of a conventional adhesive, a caries infiltrant and a combination of both against acidic challenge in vitro.

Methods

One-hundred-and-fifty discs from bovine lower central incisors were fabricated. Seventy-five samples remained untreated, whereas the other half was subjected to a demineralisation process (14 days, acidic buffer, and pH 5) to create artificial enamel lesions. Specimens were then radioactively irradiated, and each 15 sound and demineralised specimens were treated with a caries infiltrant (Icon, DMG), an unfilled adhesive (Heliobond, IvoclarVivadent) or a combination of infiltrant and adhesive. Specimens treated with the adhesive followed by a flowable composite (TetricEvoFlow, IvoclarVivadent) served as positive control, while untreated specimens served as negative control. All samples were then subjected to lactic acid for 3 weeks at pH 4. Loss of apatite was determined using the radiochemical method of liquid scintillation. Data were statistically analysed by Kruskal–Wallis-test, one-way ANOVA and Scheffe's post hoc tests (p ≤ .05).

Results

In both sound enamel and artificial caries lesions, untreated specimens showed the highest rate of apatite loss, whereas enamel treated with the adhesive and the flowable composite showed almost complete protection surface against dissolution. The caries infiltrant, the adhesive and the combination of both were able to decrease enamel dissolution, but the adhesive and the combination of adhesive and infiltrant were more effective than the infiltrant alone.

Conclusion

Within the limitations of this in vitro study, the application of an adhesive (alone or in combination with the caries infiltrant) is more effective to protect enamel dissolution than the infiltrant alone.     

Comparison of Knoop and Vickers surface microhardness and transverse microradiography for the study of early caries lesion formation in human and bovine enamel

Objective

The aims of the present laboratory study were twofold: a) to investigate the suitability of Knoop and Vickers surface microhardness (SMH) in comparison to transverse microradiography (TMR) to investigate early enamel caries lesion formation; b) to compare the kinetics of caries lesion initiation and progression between human and bovine enamel.

Design

Specimens (90 × bovine and 90 × human enamel) were divided into six groups (demineralization times of 8/16/24/32/40/48 h) of 15 per enamel type and demineralized using a partially saturated lactic acid solution. SMH was measured before and after demineralization and changes in indentation length (ΔIL) calculated. Lesions were characterized using TMR. Data were analyzed (two-way ANOVA) and Pearson correlation coefficients calculated.

Results

ΔIL increased with increasing demineralization times but plateaued after 40 h, whereas lesion depth (L) and integrated mineral loss (ΔZ) increased almost linearly throughout. No differences between Knoop and Vickers SMH in their ability to measure enamel demineralization were observed as both correlated strongly. Overall, ΔIL correlated strongly with ΔZ and L but only moderately with the degree of surface zone mineralization, whereas ΔZ and L correlated strongly. Bovine demineralized faster than human enamel (all techniques).

Conclusions

Lesions in bovine formed faster than in human enamel, although the resulting lesions were almost indistinguishable in their mineral distribution characteristics. Early caries lesion demineralization can be sufficiently studied by SMH, but its limitations on the assessment of the mineral status of more demineralized lesions must be considered. Ideally, complementary techniques to assess changes in both physical and chemical lesion characteristics would be employed.     

Degree of mineral loss in softened human enamel after acid erosion measured by chemical analysis

Objectives

Erosive attack on enamel leads to a bulk material loss and a partial demineralisation at the lesion body. This zone of softened enamel has a reduced physical stability and large interprismatic porosities. The aim of the current study was to measure the degree of demineralisation with respect to the content of calcium and inorganic phosphorus in softened enamel using ultrasonication and chemical analysis. The erosive demineralisation was to be compared with demineralisation in caries.

Methods

Erosion of 10 polished human enamel samples was performed in 0.3% citric acid adjusted to pH 3.2 at 35 °C in a slowly stirred solution, each in a volume of 15 ml. After erosion the softened enamel was removed by ultrasonication in 2 ml of deionised water and enamel crystals were dissolved by adding 220 μl of 1 M HCl. Substance loss was measured profilometricaly after erosion and after ultrasonication. Surface size of eroded enamel was measured thus volume loss could be calculated. Calcium and phosphate ion concentration in the solutions were measured after ultrasonication.

Results

Citric acid erosion caused a mean substance loss of 16.0 μm (SD 2.5 μm) and further enamel softening of 2.4 μm (SD 1.5 μm). The degree of demineralisation of softened enamel, in comparison the original mineral content, was 62% for calcium and 64% for inorganic phosphorus was calculated.

Conclusion

The high degree of demineralisation shown in the current study explains the instability of softened enamel even against mild physical impact.     

Cariogenic potential of commercial sweeteners in an experimental biofilm caries model on enamel

Objective

Scarce evidence is available on the cariogenic potential of the widely used commercial sweeteners. The aim of this study was to evaluate the effect of several sweeteners on enamel demineralisation and on the cariogenic properties of Streptococcus mutans biofilms in an artificial caries model.

Methods

S. mutans-UA159 biofilms were cultured on bovine enamel slabs and exposed to one of the following commercial sweeteners in tablet or powder form: stevia, sucralose, saccharin, aspartame or fructose. Ten percent sucrose and 0.9% NaCl were used as caries-positive and caries-negative controls, respectively. Slabs/biofilms were exposed to the sweeteners three times per day for 5 min each time. After 5 days, biofilms were recovered to determine: biomass, bacterial counts and intra- and extracellular polysaccharides. Surface microhardness was measured before and after the experiment to assess enamel demineralisation, expressed as percentage of surface hardness loss (%SHL). Data were analysed using analysis of variance (ANOVA) and Bonferroni (p < 0.05).

Results

All tested commercial sweeteners, except fructose, showed less enamel demineralisation than sucrose (p < 0.05). Only saccharine showed less biomass and intracellular polysaccharides than the rest of the groups (p < 0.05). Stevia, sucralose and saccharine reduced the number of viable cells when compared with sucrose (p < 0.05). All sugar alternatives reduced extracellular polysaccharide formation when compared with sucrose (p < 0.05).

Conclusions

Most commercial sweeteners appear to be less cariogenic than sucrose, but still retaining some enamel demineralisation potential. Products containing stevia, sucralose and saccharine showed antibacterial properties and seem to interfere with bacterial metabolism. Further studies are necessary to deepen these findings.     

Wear and morphology of infiltrated white spot lesions

Objectives

To evaluate the toothbrush wear resistance of infiltrated artificial white spot lesions following two infiltration strategies, and to assess their ultramorphology.

Methods

Flat enamel surfaces from freshly extracted bovine teeth were polished and immersed in a Buskes demineralising solution for 30 days to create incipient caries-like lesions (white spots). Two experimental regions on the surface of each tooth were infiltrated with an infiltrant and a commercial etch-and-rinse adhesive. Toothbrush abrasion was applied for 20,000 cycles. Vertical wear loss of the infiltrated areas was measured after 10,000 and 20,000 cycles against unabraded and abraded enamel using confocal laser scanning microscopy (CLSM; multiple t-tests, α = 0.05). Each lesion's surface and cross-section were evaluated under CLSM and scanning electron microscopy after etching and infiltration to assess ultramorphology.

Results

After 20,000 abrasion cycles, a statistically non-significant difference in vertical wear loss was measured for the infiltrant versus the adhesive compared with the original enamel (42.6 ± 20.7 μm vs. 40.4 ± 18.5 μm, p > 0.05). Irregular surface profiles were common for the adhesive-infiltrated group as a result of peeling and blistering of the resin-covering layer. Ultramorphology of the infiltrated lesions revealed different patterns of penetration regarding density and depth.

Conclusions

Although both infiltration strategies had equivalent wear resistance to toothbrush abrasion, surface and morphological aspects pointed to improved surface stability and infiltration quality for the infiltrant material.     

Influence of application time on penetration of an infiltrant into natural enamel caries

Objective

Caries infiltration is an innovative approach to treat medium stages of caries that bridges the gap between preventive and invasive measures, whereby hard tissues are preserved. Special low viscosity resins (infiltrants) showed almost complete penetration into natural lesions when applied for 5 min. Since shorter application times seem to be clinically more feasible, the aim of this in vitro study was to compare the penetration of an infiltrant (Icon pre-product; DMG, Hamburg, Germany) into natural caries lesions after various application times.

Methods

Extracted permanent human posterior teeth showing non-cavitated proximal caries lesions were infiltrated for either 0.5, 1, 3, or 5 min (n = 20) and light-cured. Specimens were prepared and lesion (LD) as well as penetration depths (PD) were analysed using dual fluorescence confocal microscopy.

Results

PD [median (Q25;Q75)] at maximum LD after 0.5 min [159 (27;340) μm] and 1 min [152 (69;375) μm] were significantly lower compared to those after 3 min [414 (338, 518) μm] and 5 min [407 (332;616) μm] (p < 0.05). Deep lesion parts (PD > 500 μm) could be penetrated almost completely after 3 min [98 (88;100)%] and 5 min [100 (81;100)%] application.

Conclusions

Thus, 3 min application of an infiltrant seems to be sufficient to achieve an almost complete penetration of enamel caries.     

Enamel white spot lesions can remineralise using bio-active glass and polyacrylic acid-modified bio-active glass powders

Objective

To evaluate the potential of bio-active glass (BAG) powder and BAG containing polyacrylic acid (PAA-BAG) to remineralise enamel white spot lesions (WSL).

Methods

32 human enamel samples with artificial WSLs were assigned to 4 experimental groups (n = 8); (a) BAG slurry, (b) PAA-BAG slurry, (c) “standardised” remineralisation solution (positive control) and (d) de-ionised water (negative control). Mechanical properties of enamel were assessed using surface and cross-section Knoop microhardness. Micro-Raman spectroscopy in StreamLine™ scan mode was used to scan lesion cross-sections. The intensity of the Raman phosphate peak at 959 cm⁻¹ was fitted and measured producing depth profiles analysed using a double-step fitting function. A further 20 samples (n = 5) were used to obtain 3D images of surfaces using non-contact white light profilometry permitting measurement of lesion step height in relation to the sound enamel reference level, and to scan the lesion surface using scanning electron microscopy (SEM). Data were analysed statistically using one-way ANOVA with Tukey's HSD post-hoc tests.

Results

BAG, PAA-BAG and the remineralisation solution exhibited statistically significantly higher surface and cross-section Knoop microhardness compared to the negative control. Micro-Raman spectroscopy detected significantly higher phosphate content within the treated groups compared to the negative control group. Lesions’ depth was not significantly reduced. SEM images revealed mineral depositions, with different sizes and shapes, within BAG, PAA-BAG and the positive control groups.

Conclusion

BAG and PAA-BAG surface treatments enhance enamel WSL remineralisation, assessed by the resultant improved mechanical properties, higher phosphate content and morphological changes within the artificial lesions.     

In vitro assessment of artificial saliva formulations on initial enamel erosion remineralization

Objectives

Various formulations of artificial saliva are present in the literature and little guidance is available on the standardization of type of saliva for use in in vitro protocols for erosive studies. The aim of this study was to evaluate the remineralizing capacity of different formulations of artificial saliva on initial enamel erosive lesion.

Methods

Bovine enamel blocks were subjected to short-term acidic exposure by immersion in citric acid 0.05 M (pH 2.5) for 15 s, resulting in surface softening without tissue loss. Then 90 selected eroded enamel blocks were randomly and equally divided into 6 groups according to saliva formulation (n = 15): Saliva 1 (contain mucin); Saliva 2 (Saliva 1 without mucin); Saliva 3; Saliva 4; Saliva 5 (contain sodium carboxymethyl cellulose) and control (C) (deionized water). After demineralization enamel blocks were subjected to remineralization by immersion in the saliva's formulations for 2 h. Enamel remineralization was measured by superficial hardness test (% superficial hardness change). The data were tested using ANOVA and Tukey's test (p < 0.05).

Results

All the tested formulations of artificial saliva resulted in significantly higher enamel remineralization compared to control (p < 0.001). Saliva 3 showed higher percentage of enamel remineralization than Saliva 5 (p < 0.05).

Conclusions

Besides the variety of artificial saliva for erosion in vitro protocols, all the formulations tested were able to partially remineralize initial erosive lesions.     

Modification of surface pre-treatment for resin infiltration to mask natural white spot lesions

Objectives

The aims of this study were to investigate an alternative pre-treatment method for resin infiltration using 37% H₃PO₄ with a brush applicator and to evaluate the penetration effect of the infiltrant for masking the natural white spot lesions (WSLs) in human teeth.

Methods

Seventy extracted human molars and pre-molars with non-cavitated WSLs were collected. Thirty teeth met criteria of ICDAS code 2, and were sectioned, providing a total of sixty paired halves. For the control group, 15% HCl gel was applied for 120 s, and 37% H₃PO₄, gel was gently rubbed with a brush applicator for 30 s to the experimental group. Also, to evaluate the penetration effect of the infiltrant by pre-treatment, the specimens were treated with the infiltrant (Icon^®). Thicknesses of the removed surfaces and percentages of the infiltrated areas (IA%) were evaluated by CLSM, and micro-morphological changes were observed by SEM.

Results

The mean thicknesses of removed surface layers were significantly different between the control group (36 ± 7.62 μm) and the experimental group (13 ± 2.76 μm) (p < 0.001). But, the means of IA% were similar in both groups (p > 0.05). In the SEM images, the prism cores were preferentially dissolved in the control group, while the prism peripheries were preferentially dissolved in the experimental group.

Conclusions

Applying 37% H₃PO₄ gel with an applicator brush for 30 s could increase the permeability and minimize removal of the surface layer of natural WSLs. Moreover, the effect of resin infiltration was similar to the control group which was pretreated 15% HCl gel for 120 s in vitro study.

Clinical significance

For resin infiltration, applying 37% H₃PO₄ gel with a brush applicator can preserve the protective surface layers of the WSLs with reduced application time.     

Comparison of sealant and infiltrant penetration into pit and fissure caries lesions in vitro

Objectives

The aim of this in vitro study was to evaluate the penetration of an infiltrant and a sealant, when applied as recommended, into fissure caries lesions.

Methods

The fissure systems of extracted human teeth were classified according to the international caries detection and assessment system (ICDAS, codes: 0, 1, 2). Within each ICDAS-code ten teeth were either etched with 37% H₃PO₄-gel for 60 s and subsequently sealed (‘Fissure Sealing’; Helioseal; Ivoclar Vivadent) or etched with 15% HCl-gel for 120 s and subsequently infiltrated (‘Resin Infiltration’; Icon; DMG). Additionally, ten teeth with ICDAS-code 2 were etched with 37% H₃PO₄-gel for 120 s and infiltrated (‘Soft-Etch-Infiltration’). Specimens were cut perpendicular to their surfaces, polished, and confocal microscopic images were obtained. Lesion depths (LD_max) and penetration depths (PD_max) were measured and percentage penetration was calculated as PP_max = PD_max/LD_max × 100.

Results

Baseline LD_max [median (interquartile range)] for ICDAS-code 2 lesions was 1192 (805–1512) μm. In ICDAS-code 2 lesions PP_max was significantly higher for specimens treated with ‘Resin Infiltration’ [41 (30–78)%] compared to ‘Soft-Etch-Infiltration’ [11 (0–21)%] or ‘Fissure Sealing’ [5 (0–9)%] (p < 0.05; Mann–Whitney test). PP_max did not differ significantly between groups in ICDAS-code 0 and 1 lesions (p > 0.05).

Conclusion

The fissure sealant when applied after etching with H₃PO₄-gel only penetrates superficially into non-cavitated fissure caries lesions. Penetration of an infiltrant is superior in particular after etching with HCl-gel.

Clinical significance

Compared with sealing, infiltration of fissure caries lesions leads to more deeply infiltrated lesions, which might in turn result in superior abilities to hamper caries progression.     

Preventive effect of an iron varnish on bovine enamel erosion in vitro

Objective

The aim of this study was to evaluate, in vitro, the effect of an experimental varnish containing iron on the dissolution of bovine enamel by carbonated beverage.

Methods

Eighty specimens were randomly allocated to four groups (n = 20 per group), according to the following treatments: Fe varnish (FeV, 10 mmol/L Fe), F varnish (FV, 2.71% F), placebo varnish (PV) and control (not treated, NT). The varnishes were applied in a thin layer and removed after 6 h. Then, the samples were submitted to six cycles, alternating re- and demineralisation (only 1 day). Demineralisation was performed with the beverage Coca-Cola^® (10 min, 30 mL/block) and remineralisation with artificial saliva for 1 h. In order to determine the amount of enamel dissolved, the wear was analysed by profilometry. Data were analysed by ANOVA and Tukey's test (p < 0.05).

Results

The mean wear (±S.E.) was significantly lesser for the FeV (0.451 ± 0.018 μm) when compared to the other treatments. The FV caused significantly less wear (0.554 ± 0.022 μm) when compared to PV (0.991 ± 0.039 μm) and NT (1.014 ± 0.033), which did not significantly differ from each other.

Conclusions

The results suggest that the iron varnish can interfere with the dissolution of dental enamel in the presence of acidic beverages.     

Inhibitory effect of silver diamine fluoride on dentine demineralisation and collagen degradation

Objective

To investigate the inhibitory effects of 38% silver diamine fluoride (SDF) on demineralised dentine.

Methods

Human dentine blocks were demineralised and allocated to four groups: SF, F, S and W. The blocks in group SF received a topical application of 38% SDF solution (253,900 ppm Ag, 44,800 ppm F), group F received a 10% sodium fluoride solution (44,800 ppm F), group S received a 42% silver nitrate solution (253,900 ppm Ag) and group W received deionised water (control). They were subjected to pH cycling using demineralisation solution (pH 5) and remineralisation solution (pH 7) for 8 days. The surface morphology, crystal characteristics, lesion depth and collagen matrix degradation of the specimens were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-CT testing and spectrophotometry with a hydroxyproline assay.

Results

The surface morphology under SEM showed evident demineralisation with exposed collagen in groups S and W, but not in group SF. Clusters of granular spherical grains were observed in the cross-sections of specimens in groups SF and F. XRD revealed precipitates of silver chloride in groups SF and S. The mean lesion depths (±SD) of groups SF, F, S and W were 182 ± 32 μm, 204 ± 26 μm, 259 ± 42 μm and 265 ± 40 μm, respectively (SDF, F < S, W; p < 0.01). Groups SF and S had significantly less hydroxyproline liberated from the dentine matrix than groups F and W (p < 0.01).

Conclusion

The use of 38% SDF inhibited demineralisation and preserved collagen from degradation in demineralised dentine.

Clinical significance

SDF application positively influences dentine remineralization.     

Marginal integrity and secondary caries of selectively excavated teeth in vitro

Objectives

Selective caries removal involves sealing of carious dentine beneath restorations, which might decrease their marginal integrity and increase the susceptibility for secondary caries and microleakage. The present study compared these marginal characteristics of restorations in selectively and completely excavated teeth.

Methods

In 32 premolars, shallow and deep artificial lesions were created on pulpo-axial walls of mesial-distal-occlusal cavities, with mesial and distal margins located in enamel and dentine, respectively. Demineralised dentine was either removed or left before adhesively restoring the teeth (n = 8), which were then submitted to thermo-mechanical cycling. The integrity of gingivo-cervical margins was assessed using scanning electron microscopy. In half of each margin, caries was induced adjacent to restorations using a continuous-culture biofilm model, and resulting lesions were evaluated using transversal microradiography. The other half of each margin was used to assess microleakage.

Results

Integrity or microleakage of margins located in enamel did not differ significantly between groups, and bacterial biofilms did not induce distinct caries lesions in enamel. Dentinal margins in teeth with deep compared with shallow lesions showed a significantly higher proportion of marginal imperfections, gaps and microleakage (p ≤ 0.05, Mann–Whitney/χ²-test). In contrast, neither marginal integrity nor microleakage differed significantly between completely and selectively excavated teeth (p > 0.05). Dentinal mineral loss adjacent to restorations did not differ significantly between groups (p > 0.80).

Conclusions

The marginal characteristics of restorations were affected by the depth of sealed or excavated lesions, but not by the performed caries excavation. This study did not find selective excavation detrimental for restoration integrity in vitro.

Clinical significance

Selective excavation of deep lesions was shown to reduce pulpal risks, whilst leaving caries beneath restorations is feared to compromise the marginal characteristics of the subsequently placed restoration. Based on the present in vitro study, such assumptions cannot be supported.     

Comparing two quantitative methods for studying remineralization of artificial caries

Objectives

To compare the detection of changes before and after remineralization of artificial enamel and dentin caries by microCT scanning, polarized light microscopy (PLM) and transverse microradiography (TMR).

Methods

Fourteen extracted premolars were cut into tooth blocks and painted with an acid-resistant varnish leaving one enamel and one dentin surface exposed. The tooth blocks were immersed into demineralizing solution for 4 days to produce artificial caries-like lesions and scanned by microCT. Then the 14 tooth blocks were randomly allocated into two groups. Seven tooth blocks in Group I were cut longitudinally through the exposed surface into 100–150 μm thick sections and microradiographs were taken. The other seven tooth blocks in Group II were left intact. All the tooth blocks and sections were then immersed into remineralizing solution for 5 days. PLM and TMR of the tooth sections in Group I were taken again. Depth of the lesion on the TMR was measured. Tooth blocks in Group II were scanned by microCT.

Results

Mean lesion depth in Group I reduced by 13.0% and 8.2% after remineralization for enamel and dentin, respectively (paired t-test, P < 0.001). In Group II, linear attenuation coefficient (LAC) of the region of interest (ROI) increased by 11.1% and 23.8% after remineralization for enamel and dentin lesions, respectively (paired t-test, P < 0.001).

Conclusion

Both microCT and microradiography are able to detect a change of similar magnitude in the artificial caries lesions after remineralization. MicroCT may be used to substitute TMR and PLM in in vitro studies about caries.     

Saliva substitute in combination with high-concentrated fluoride toothpaste: Effects on demineralised dentin in vitro

Objectives

The aim of this in vitro study was to assess the effects of saliva substitutes (modified with respect to calcium, phosphates, and fluorides) in combination with a high-concentrated fluoride toothpaste on demineralised dentin.

Methods

Before and after demineralisation of bovine dentin specimens (subsurface lesions; 37 °C, pH 5.0, 5 d), one-quarter of each specimen's surface was covered with nail varnish (control of sound/demineralised tissue). Subsequently, specimens were exposed to original Saliva natura (saturation with respect to octacalciumphosphate [S_OCP]: 0.03; SN 0), or to three lab-produced Saliva natura modifications (S_OCP: 1, 2, and 3; SN 1–3) for 2 and 5 weeks (37 °C). An aqueous solution (S_OCP: 2.5) served as positive control (PC). Two times daily (2 min each), Duraphat toothpaste (5000 ppm F⁻; Colgate)/saliva substitute slurry (ratio 1:3) was applied gently. Differences in mineral losses (ΔΔZ) and lesion depths (ΔLD) between values before and after exposure were microradiographically evaluated.

Results

After both treatment periods specimens immersed in SN 0 revealed significantly higher mineral losses (lower ΔΔZ values) and lesion depths (lower ΔLD) compared to PC (p < 0.05; ANOVA). After 5 weeks, specimens stored in SN 1 and 2 showed significantly higher mineral losses compared to PC (p < 0.05), while those stored in SN 3 showed similar results (p > 0.05). No differences in mineral loss could be observed between SN 2 and 3 (p > 0.05).

Conclusions

Under the conditions of this limited protocol, the combination of Saliva natura solutions slightly saturated with respect to OCP in combination with a high-concentrated fluoride toothpaste enabled remineralisation of dentin in vitro.     

Surface conditioning of natural enamel caries lesions in deciduous teeth in preparation for resin infiltration

Objectives

As a conditioning step for resin infiltration into caries lesions, the relatively impermeable surface layer should be removed using hydrochloric acid gel (15%) to achieve improved infiltration, as it could be shown for permanent teeth. It is unclear whether this etching regimen can be transferred to the deciduous dentition, where differences in surface structure have been reported. Thus, the aim of the present study was to evaluate the effect of phosphoric and hydrochloric acid gels on the surface layer reduction of natural lesions of primary teeth.

Methods

Thirty-two extracted or exfoliated primary molars with lesions confined to enamel were selected. Paired lesion halves were partially etched with either 37% phosphoric (H₃PO₄) or 15% hydrochloric acid gel (HCl) for 30 s, 60 s, 90 s, or 120 s, respectively.

Results

Etching with H₃PO₄ resulted in incomplete reduction of the surface layers in all groups [highest percentage reduction (SD) at 120 s: 54 (28)%] as observed with confocal microscopy. In contrast, surface layers could be eroded almost completely [99 (3)%] by etching with HCl for 120 s.

Conclusion

An effective erosion of the surface layer of natural enamel caries in deciduous teeth can be achieved by etching with 15% hydrochloric acid gel for 90–120 s.     

Combined effects of nano-hydroxyapatite and Galla chinensis on remineralisation of initial enamel lesion in vitro

Objectives

The aim of the present study was to investigate the combined effects of nano-hydroxyapatite and Galla chinensis on remineralisation of initial enamel lesion.

Methods

Bovine enamel blocks with in vitro produced initial lesion were used. The lesions were subjected to a pH-cycling regime for 12 days. Each daily cycle includes 4 × 3 min application with one of five treatments: NaF (positive control), deionised water (negative control), crude aqueous extract of G. chinensis (GCE), nano-hydroxyapatite (nano-HA) and GCE with nano-HA. The samples were subsequently evaluated using a microhardness tester, polarised light microscopy (PLM), X-ray diffraction (XRD) and scanning electron microscopy (SEM).

Results

Surface hardness measurements and integrated mineral recovery value obtained from cross-sectional microhardness test (CSMH) revealed that all the treatment groups had significantly greater effect on enhancing remineralisation than that of the negative control group. Detailed investigation of both CSMH and PLM indicated that nano-HA would only help mineral deposition predominate in the outer layer of lesion and had limited capacity to reduce the lesion depth significantly. In GCE–nano-HA combined treatment group, more mineral deposition occurred in the lesion body and lesion depth was reduced significantly. Meanwhile, significantly greater mineral deposition in the outer portion of the lesion was also observed in comparison with GCE group. The results of XRD and SEM also showed that GCE could influence the deposition and adsorption of nano-HA.

Conclusion

There was a significant synergistic effect of combined GCE and nano-HA treatment on promoting the remineralisation of initial enamel lesion.     

Resin composites: Modulus of elasticity and marginal quality

Objective

To investigate how the modulus of elasticity of resin composites influences marginal quality in restorations submitted to thermocyclic and mechanical loading.

Methods

Charisma, Filtek Supreme XTE and Grandio were selected as they were found to possess different moduli of elasticity but quite similar polymerization contraction. MOD cavities (n = 30) were prepared in extracted premolars, restored and then subjected to thermocyclic and mechanical loading. Marginal quality of the restorations before and after loading was analyzed on epoxy replicas under a scanning electron microscope. The percentage of gap-free margins and occurrence of paramarginal fractures were registered. Modulus of elasticity and polymerization contraction were analyzed with parametric and margins with nonparametric ANOVA and post hoc Tukey HSD or Wilcoxon rank-sum tests, respectively. The number of paramarginal fractures was analyzed with exact Fisher tests (α = 0.05).

Results

Grandio demonstrated significantly more gap-free enamel margins than Charisma and Filtek Supreme XTE, before and after loading (p < 0.01), whereas there was no difference between Charisma and Filtek Supreme XTE (p > 0.05). No significant effect of resin composite (p = 0.81) on the quality of dentine margins was observed, before or after loading. Deterioration of all margins was evident after loading (p < 0.0001). More paramarginal enamel fractures were observed after loading in teeth restored with Grandio when compared to Charisma (p = 0.008).

Conclusions

The resin composite with the highest modulus of elasticity resulted in the highest number of gap-free enamel margins but with an increased incidence of paramarginal enamel fractures.

Clinical significance

The results from this study suggest that the marginal quality of restorations can be improved by the selection of a resin composite with modulus of elasticity close to that of dentine, although an increase in paramarginal enamel fractures can result as a consequence.     

The preventive effect of grape seed extract on artificial enamel caries progression in a microbial biofilm-induced caries model

Objectives

The aim of this study was to evaluate the effect of grape seed extract (GSE) on enamel caries lesion formation in an in vitro Streptococcus mutans biofilm model.

Methods

Enamel fragments were prepared from bovine incisors and divided into six treatment groups (n = 12): inoculated Brain Heart Infusion with 1% sucrose (BHIS), 1 mg/mL GSE, 2 mg/mL GSE, 3 mg/mL GSE, 10 ppm fluoride as NaF, and uninoculated BHIS. For biofilm formation, tooth fragments were incubated anaerobically in polystyrene 6-well tissue culture plates containing BHIS, the respective agents, and S. mutans (1 × 10⁵ CFU/mL) for 24 h at 37 °C. Culture medium was replaced with fresh BHIS and respective agents daily over a 7-day period. Following caries lesion formation, lesion depth (LD) and relative optical density (ROD) were determined by polarized light microscopy (PLM) and confocal laser scanning microscopy (CLSM), respectively, to evaluate lesion progression.

Results

LDs of the 2 mg/mL GSE group (122.86 ± 13.41 μm) and the 3 mg/mL GSE group (111.92 ± 11.39 μm) were significantly smaller than those of the 1 mg/mL GSE (198.33 ± 17.70 μm) and control groups (210.86 ± 15.50 μm) (p < 0.05). Compared with the 2 mg/mL and 3 mg/mL groups, the control and 1 mg/mL GSE groups showed significantly lower ROD values when depth was less than 200 μm, indicating greater mineral loss.

Conclusions

Dose-dependent GSE inhibits in vitro enamel caries formation due to its ability to suppress growth of S. mutans and the formation of bio?lm.

Clinical signi?cance

Grape seed extract may be a novel virulence-targeted natural antimicrobial agent for caries prevention.