Ultrastructure of dentine carious lesions

Investigation of the effect of Tideglusib on the hydroxyapatite formation, crystallinity and elasticity of conditioned resin-dentin interfaces

OBJECTIVES

To investigate the effect of dentin infiltration with polymeric nanoparticles (NPs) doped with tideglusib (TDg) (TDg-NPs) on hydroxyapatite formation, crystallinity and elasticity of conditioned resin-dentin interfaces.

METHODS

Dentin conditioned surfaces were infiltrated with NPs or TDg-NPs. Bonded interfaces were created, stored for 24 h and submitted to mechanical and thermal challenging. Resin-dentin interfaces were evaluated through nanoindentation to determine the modulus of elasticity, X-ray diffraction and transmission electron microscopy through selected area diffraction and bright-filed imaging.

RESULTS

TDg-NPs provoked peaks narrowing after the diffraction-intensity analysis that corresponded with high crystallinity, with an increased modulus of Young after load cycling in comparison with the samples treated with undoped NPs. New minerals, in the group of TDg-NPs, showed the greatest both deviation of line profile from perfect crystal diffraction and dimension of the lattice strain, i.e., crystallite, grain size and microstrain and 002 plane-texture. The new minerals generated after TDg-NPs application and mechanical loading followed a well defined lineation. Undoped NPs mostly produced small hydroxyapatite crystallites, non crystalline or amorphous in nature with poor maturity.

CONCLUSIONS

Tideglusib promoted the precipitation of hydroxyapatite, as a major crystalline phase, at the intrafibrillar compartment of the collagen fibrils, enabling functional mineralization. TDg-NPs facilitated nucleation of crystals randomly oriented, showing less structural variation in angles and distances that improved crystallographic relative order of atoms and maturity. Nanocrystals inducted by TDg-NPs were hexagonal prisms of submicron size. Thermal challenging of dentin treated with TDg-NPs have provoked a decrease of functional mineralization and crystallinity, associated to immature hydroxyapatite.

CLINICAL SIGNIFICANCE

New polycrystalline lattice formation generated after TDg-NPs infiltration may become correlated with high mechanical performance. This association can be inferred from the superior crystallinity that was obtained in presence of tideglusib. Immature crystallites formed in dentin treated with undoped NPs will account for a high remineralizing activity.

Visualization of carious lesions with polarized and depolarized light microscopy

Polarized light microscopy (PLM) is an established method in dental histology for investigating the ultrastructure and carious process of teeth. This study introduces a novel approach for measuring the degree of polarization (DOP) in a modified PLM setup and uses the DOP to assess the changes of the optical properties of enamel and dentin due to caries. The validation is provided by a comparison with complementary imaging methods, i.e. standard PLM and µCT. The results show that demineralization is reliably displayed by the DOP in accordance with the common imaging methods, and that this quantitative analysis of depolarization allows the characterization of the different pathohistological zones of caries.

Synchrotron X-ray Studies of the Structural and Functional Hierarchies in Mineralised Human Dental Enamel: A State-of-the-Art Review

Hard dental tissues possess a complex hierarchical structure that is particularly evident in enamel, the most mineralised substance in the human body. Its complex and interlinked organisation at the Ångstrom (crystal lattice), nano-, micro-, and macro-scales is the result of evolutionary optimisation for mechanical and functional performance: hardness and stiffness, fracture toughness, thermal, and chemical resistance. Understanding the physical-chemical-structural relationships at each scale requires the application of appropriately sensitive and resolving probes. Synchrotron X-ray techniques offer the possibility to progress significantly beyond the capabilities of conventional laboratory instruments, i.e., X-ray diffractometers, and electron and atomic force microscopes. The last few decades have witnessed the accumulation of results obtained from X-ray scattering (diffraction), spectroscopy (including polarisation analysis), and imaging (including ptychography and tomography). The current article presents a multi-disciplinary review of nearly 40 years of discoveries and advancements, primarily pertaining to the study of enamel and its demineralisation (caries), but also linked to the investigations of other mineralised tissues such as dentine, bone, etc. The modelling approaches informed by these observations are also overviewed. The strategic aim of the present review was to identify and evaluate prospective avenues for analysing dental tissues and developing treatments and prophylaxis for improved dental health.

Dexamethasone and zinc loaded polymeric nanoparticles reinforce and remineralize coronal dentin. A morpho-histological and dynamic-biomechanical study

OBJECTIVE

To investigate the effect of novel polymeric nanoparticles (NPs) doped with dexamethasone (Dex) on viscoelasticity, crystallinity and ultra-nanostructure of the formed hydroxyapatite after NPs dentin infiltration.

METHODS

Undoped-NPs, Dex-doped NPs (Dex-NPs) and zinc-doped-Dex-NPs (Zn-Dex-NPs) were tested at dentin, after 24 h and 21 d. A control group without NPs was included. Coronal dentin surfaces were studied by nano-dynamic mechanical analysis measurements, atomic force microscopy, X-ray diffraction and transmission electron microscopy. Mean and standard deviation were analyzed by ANOVA and Student-Newman-Keuls multiple comparisons (p < 0.05).

RESULTS

At 21 d of storage time, both groups doped with Dex exhibited the highest complex, storage and loss moduli among groups. Zn-Dex-NPs and Dex-NPs promoted the highest and lowest tan delta values, respectively. Dex-NPs contributed to increase the fibril diameters of dentin collagen over time. Dentin surfaces treated with Zn-Dex-NPs attained the lowest nano-roughness values, provoked the highest crystallinity, and produced the longest and shortest crystallite and grain size. These new crystals organized with randomly oriented lattices. Dex-NPs induced the highest microstrain. Crystalline and amorphous matter was present in the mineral precipitates of all groups, but Zn and Dex loaded NPs helped to increase crystallinity.

SIGNIFICANCE

Dentin treated with Zn-Dex-NPs improved crystallographic and atomic order, providing structural stability, high mechanical performance and tissue maturation. Amorphous content was also present, so high hydroxyapatite solubility, bioactivity and remineralizing activity due to the high ion-rich environment took place in the infiltrated dentin.

Effect of Method of Removing Caries-Affected Dentin on the Bond Strength of Composite Resin to Root Canal Dentin

The adhesion of composite resin to caries-affected dentin differs from the adhesion of resin to sound dentin. We evaluated the bond strengths of dual-cure resin composites applied to caries-affected root canal dentin under various clinical conditions and using several caries removal indicators. In the dye stain 1 group, caries were removed to a pale pink stain level using a caries detector. In the dye stain 2 group, caries were removed to a stain-free level using a caries detector. In the probing group, caries were removed to the level of hardness based on probing with a sharp explorer. Additionally, a sound dentin group was used as a control. We compared the resin composite microtensile bond strengths and failure mode distribution among the groups. The bond strengths (MPa) of the probing (64.6 ± 11.9) and the sound dentin (68.7 ± 11.1) groups were significantly higher than those of the dye stain 1 (46.9 ± 7.9) and 2 (47.5 ± 8.4) groups (p < 0.05). The removal of caries-affected dentin using a dentin-hardness-based technique showed higher tensile strength than that using a dye stain technique involving removal to any color level. Thus, the caries removal technique used on root canal dentin affects the bond strength of the resin composite.

Assessment of the remineralisation induced by contemporary ion-releasing materials in mineral-depleted dentine

OBJECTIVES

Evaluate the ability of current ion-releasing materials to remineralise bacteria-driven artificial caries lesions.

MATERIALS AND METHODS

Standardised class I cavities were obtained in 60 extracted human molars. Specimens underwent a microbiological cariogenic protocol (28 days) to generate artificial caries lesions and then were randomly divided into four restorative groups: adhesive + composite (negative control); glass ionomer cement (GIC); calcium silicate cement (MTA); and resin-modified calcium silicate cement (RMTA). Microhardness analysis (ΔKHN) was performed on 40 specimens (10/group, t = 30 days, 45 days, 60 days in artificial saliva, AS). Micro-CT scans were acquired (3/group, t = 0 days, 30 days, and 90 days in AS). Confocal microscopy was employed for interfacial ultra-morphology analysis (2/group, t = 0 days and 60 days in AS). Additional specimens were prepared and processed for scanning electron microscopy (SEM) and FTIR (n = 3/group + control) to analyse the ability of the tested materials to induce apatite formation on totally demineralised dentine discs (60 days in AS). Statistical analyses were performed with a significance level of 5%.

RESULTS

Adhesive + composite specimens showed the lowest ΔKHN values and the presence of gaps at the interface when assessed through micro-CT even after storage in AS. Conversely, all the tested ion-releasing materials presented an increase in ΔKHN after storage (p < 0.05), while MTA best reduced the demineralised artificial carious lesions gap at the interface. MTA and RMTA also showed apatite deposition on totally demineralised dentine surfaces (SEM and FTIR).

CONCLUSIONS

All tested ion-releasing materials expressed mineral precipitation in demineralised dentine. Additionally, calcium silicate-based materials induced apatite precipitation and hardness recovery of artificial carious dentine lesions over time.

CLINICAL RELEVANCE

Current ion-releasing materials can induce remineralisation of carious dentine. MTA shows enhanced ability of nucleation/precipitation of hydroxyapatite compared to RMTA and GIC, which may be more appropriate to recover severe mineral-depleted dentine.

Ultrastructural Analysis of Er:YAG Lased Bovine Dentin Contaminated by Cariogenic Bacteria

Objective: The purpose of this study is to investigate the crystal structure of bacteria-contaminated bovine dentin after Er:YAG laser irradiation at various energy densities from macroscale, microscale, and nanoscale. Background: Er:YAG laser can change the morphology and chemical components of dentin. Few preliminary researchers investigate the laser effect on crystal in dentin tissue. Methods: Twenty dentin specimens from bovine incisors were cocultured with S. mutans (UA 159) and divided into four groups with diverse Er:YAG laser irradiation energy (0, 6.37, 12.73, 19.11 J/cm²). The ultrastructure of dentin before and after laser irradiation was investigated with nanoanalytical electron microscopy. X-ray diffraction provided the information of lattice parameters in dentin. The morphology of dentin was observed by scanning electron microscopy. High-resolution transmission electron microscope images and selected-area electron diffraction patterns were obtained for characterizing crystal domain size, structure, and microenvironment of dentin. Results: The combination of these methods disclosed that there exist mineralized, demineralized, and remineralized dentin in the bacteria-invaded dentin and can be feasibly recognized using morphological features. Laser treatments influence hydroxyapatite (HAp) crystals in dentin tissue in different ways: needle HAp in mineralized dentin tissue keeps intact with laser irradiation of no higher than 19.11 J/cm²; laser irradiation improves the crystallinity of lamella HAp by domain growth and rearranges its growth orientations. Conclusions: We report an unprecedented presence of remineralization zone consisting of lamella HAp crystals with distinct high-index planes. These findings have broad implications on the role of laser operation in driving biomineralization and shed new insights into a possible relationship between laser irradiation and remineralization.

Characterization of dynamic process of carious and erosive demineralization - an overview

To review the analytical methods for carious and erosive demineralization an initial search of peer-reviewed scientific literature from the digital library database of PubMed/Medline indexed journals published up to early 2022 was carried out based on keywords relevant to the topic criteria including bibliographic citations from the papers to gather the most updated information. This current review aims to provide an updated overview of the advantages, limitations, and potential applications of direct and indirect research methods available for studying various dynamic stages of carious and erosive demineralization in enamel and dentin. This paper categorizes and describes the most suitable, frequently adopted and widely used quantitative and qualitative techniques in in vitro/in vivo research which are well-established, emerging, or comparatively novel techniques that are being explored for their potential validation.

The effect of surface pre-reacted glass-ionomer filler eluate on dental pulp cells and mineral deposition on dentin: In vitro study

The effects of surface pre-reacted glass-ionomer (S-PRG) filler on pulpal cells and on the composition of dentinal deposits were investigated. Proliferation (CCK-8), cytotoxicity (LDH), and differentiation activity (ALP) tests, along with cell morphology observations, were conducted at 6 and 24 h after treatment of pulpal cells with different S-PRG filler eluate concentrations. Dentinal surfaces were immersed in deionized water or S-PRG filler eluate followed by immersion in deionized water or simulated body fluid and observed under scanning electron microscope and elemental analysis using energy dispersive x-ray spectrometer. At 24 h, there were significant differences in CCK-8 and ALP activity values between the groups in a concentration-dependent manner. LDH test data were not significantly different among the groups. Cell morphology was not altered at either exposure time. However, decreased cellular density was observed with the highest eluate concentration. Crystalline deposits and occluded dentinal tubules were observed in samples immersed in S-PRG filler with a later immersion in simulated body fluid, which also showed higher concentrations of certain ions compared to surfaces that were not initially treated with S-PRG filler. The lowest two eluate concentrations did not show significant toxicity. S-PRG enhanced the effect of simulated body fluid in the formation of mineral deposits.

Clinical efficacy and the antimicrobial potential of silver formulations in arresting dental caries: a systematic review

Background

The use of silver-formulation as microbicide to arrest dentinal caries is gaining popularity. The primary objective of the present appraisal was to systematically review the clinical (in vivo) applications and antimicrobial potential of silver-containing formulations in arresting dentinal caries. Our secondary aim was to sum up the available in vitro applications of silver-containing formulations against cariogenic microbes isolated from dentine lesions.

Methods

Ovid MEDLINE, EBSCO host, Web of Science, and Cochrane Library databases was searched between January 2009–May 2019.

Results

In vivo: We observed conflicting evidence of antimicrobial efficacy of SDF on a diverse array of microbial taxa present in carious dentine of primary and permanent teeth. Moreover, there is insufficient evidence on the application of AgNP-fluoride as an effective microbicidal against cariogens of dentine lesions.

In vitro: We found a good evidence of microbicidal efficacy of silver diamine fluoride (SDF) on selective cariogenic microbes in human dentine model. Additionally, a good evidence was noted of in vitro application of silver nanoparticles (AgNPs) as a useful microbicidal against S. mutans adhesion, growth and subsequent biofilm formation in human dentine models.

Conclusions

Taken together, in vitro evidence indicates the promising antimicrobial potential of silver-based formulations (SDF and nanosilver) against the predominant cariogenic flora, particularly from dentine lesions. Post-treatment clinical data of either the bactericidal and bacteriostatic effects of SDF or nanosilver are sparse. Furthermore, the current understanding of the specific size, concentration, antimicrobial mechanisms, and toxicological aspects of nano-silver compounds is inadequate to draw firm conclusions on their clinical utility.

Three-dimensional observation and analysis of remineralization in dentinal caries lesions

The remineralization mechanism in dental caries lesions is not completely understood. This study reports on ultrastructural and chemical changes observed within arrested caries lesions. Carious human teeth were observed using scanning electron microscopy (SEM) and focused-ion-beam (FIB)-SEM. The crystals detected in the caries lesions were characterized by transmission electron microscopy (TEM), along with chemical element mapping using energy-dispersive spectroscopy (EDS)-STEM. FIB-SEM 3D reconstructions revealed a severely damaged dentin surface abundantly covered by bacteria. Although the dentin tubules were clogged up to a depth of 100 μm, bacterial invasion into dentin tubules was not observed. TEM crystal analysis and EDS-STEM revealed the presence of Ca and P, as well as of Mg within the HAp crystals deposited inside the dentin tubules. It was concluded that extensive remineralization with deposition of Mg-HAp crystals had occurred in dentin tubules of caries-arrested dentin. Understanding the natural remineralization process is thought to be helpful for developing clinical biomimetic remineralization protocols.

Ion-modified nanoparticles induce different apatite formation in cervical dentine

AIM

To investigate if crystallinity and ultrastructure are modified when cervical dentine is treated with four different nanogels-based solutions for remineralizing purposes.

METHODOLOGY

Experimental nanogels based on polymeric nanoparticles (NPs) and zinc, calcium or doxycycline-loaded NPs were applied to citric acid etched dentine to facilitate the occlusion of tubules and the mineralization of the dentine surface. Dentine surfaces were studied by X-ray diffraction and transmission electron microscopy through selected area diffraction and bright-field imaging.

RESULTS

Crystals at the dentine surface were identified as hydroxyapatite with the highest crystallographic maturity and crystallite size in dentine treated with Zn-NPs-based gel. Texture increased in all samples from 24 h to 7 days, except in dentine surfaces treated with Zn-NPs gel. Polyhedral, plate-like and drop-like shaped apatite crystals constituted the bulk of minerals in dentine treated with Zn-NPs gel, after 7 days. Polymorphic, cubic and needle-like shaped crystals distinguished minerals, with more amorphous characteristics in dentine treated with Ca-NPs gel after 7 days than that found when Zn-NPs were applied. Doxycycline-NPs produced the smallest crystallites with poor crystallinity, maturity and chemical stability.

CONCLUSIONS

Crystalline and amorphous phases of newly formed hydroxyapatite were described in both types of dentine treated with Zn-NPs as well as Ca-NPs gels with multiple shapes of crystallites. Crystal shapes ranged from rounded/drop-like or plate-like crystals to needle-like or polyhedral and cubic apatite appearance.

Clinical performance of laminate and non-laminate resin composite restorations: a systematic review

BACKGROUND

A systematic review was undertaken to determine the clinical outcomes of resin modified glass-ionomer cement or glass-ionomer cement-resin composite (RMGIC/GIC-RC) laminate restorations and flowable resin composite (FRC)-lined RC restorations compared to that of non-laminate RC restorations.

METHODS

Electronic databases were searched and filtered for relevant papers by assessing titles, abstracts and full-text articles. Randomized controlled clinical trials (RCTs) were included, comparing the clinical performance of RMGIC/GIC-RC laminate restorations and FRC-lined restorations with RC restorations as the control. The articles were categorized and critically appraised. Raw data were used for a fixed effects meta-analysis.

RESULTS

Thirteen articles were included in the review. Five evaluated FRC-lined restorations, and eight studies evaluated RMGIC/GIC-RC laminate restorations, comparing with non-laminate RC restorations. Three of eight RMGIC/GIC-RC laminate restorations assessed only postoperative sensitivity. A meta-analysis could only be conducted in three studies with the FRC-lined restorations as the intervention. The meta-analysis found no significant difference in clinical failures between FRC-lined RC restorations and RC restorations with no lining (p > 0.05).

CONCLUSIONS

Based on current clinical evidence, a FRC lining is no more advantageous than RC restorations with no FRC lining. More long-term RCTs are required, particularly for evaluating RMGIC/GIC-RC laminate restorations.

Three-Year Effects of Deproteinization on the In Vitro Durability of Resin/Dentin-Eroded Interfaces

Objective:

To evaluate the effect of sodium hypochlorite on the immediate and three-year bonding properties of a resin-eroded dentin interface produced by one of two adhesive strategies.

Methods and Materials:

Forty-eight molars were randomly assigned to six experimental groups, according to the combination of the adhesive strategy (etch-and-rinse and self-etch) and the dentin surface (control groups without erosion, eroded dentin surface [ED], and eroded dentin surface + NaOCl 5.2% [ED + NaOCl]). After completing restoration, specimens were stored in water (37°C) for 24 hours and then sectioned into resin–dentin beams (0.8 mm2) to be tested under tension (0.5 mm/min) immediately thereafter or after three years of water storage. To assess nanoleakage (NL), specimens were immersed in silver nitrate solution and examined by scanning electron microscopy at both time points. The dentin-etching pattern was examined under a scanning electron microscope. Data were subjected to appropriate statistical analysis (α=0.05)

Results:

In both strategies, a more pronounced and significant reduction of the microtensile bond strength (μTBS) values was observed for the ED groups (p=0.0001) after three years. However, in the ED + NaOCl group, μTBS values were maintained after three years of water storage. Furthermore, application of NaOCl to eroded dentin significantly reduced the immediate NL values and also preserved these values after three years of water storage for both adhesive strategies (p&gt;0.05). When considering the ED group, a superficial removal of the smear layer and enlarged lumen tubules in comparison to control were present. However, for ED + NaOCl, there was a total removal of the smear layer and significant numbers of collagen fibrils were exposed.

Conclusion:

The use of NaOCl may maintain the long-term stability of a resin-eroded dentin interface formed by etch-and-rinse and self-etch adhesives.

Morphological evaluation of artificial caries-affected dentin after applying FCP-COMPLEX

FCP-COMPLEX is a newly-developed solution that contains fluoride, calcium, and phosphoric acid. It has the potential to reinforce caries-affected dentin. The purpose of this study was to evaluate the effect of FCP-COMPLEX on the morphology of bovine artificial caries-affected dentin (ACAD). FCP-COMPLEX, 2% sodium fluoride solution, and distilled water were applied to bovine ACAD and the effect on acid-induced damage was observed. Scanning electron microscopy was used to evaluate morphology after acid application. Energy dispersive X-ray spectroscopy was used for mapping and quantitative analyses of the dentin surface, and for line analysis of dentin-adhesive interface. The FCP-COMPLEX precipitated on the dentin surface and fluoride, calcium, and phosphorus were detected at a higher level in the FCP-COMPLEX group. The area of acid damage in caries-affected dentin was reduced by FCP-COMPLEX. In conclusion, FCP-COMPLEX significantly increased the deposition of fluoride onto bovine ACAD and inhibited demineralization.

The Difference of Structural State and Deformation Behavior between Teenage and Mature Human Dentin

Objective. The cause of considerable elasticity and plasticity of human dentin is discussed in the relationship with its microstructure. Methods. Structural state of teenage and mature human dentin is examined by using XRD and TEM techniques, and their deformation behavior under compression is studied as well. Result. XRD study has shown that crystallographic type of calcium hydroxyapatite in human dentin (calcium hydrogen phosphate hydroxide Ca9HPO4(PO4)5OH; Space Group P63/m (176); a = 9,441 A; c = 6,881 A; c/a = 0,729; Crystallite (Scherrer) 200 A) is the same for these age groups. In both cases, dentin matrix is X-ray amorphous. According to TEM examination, there are amorphous and ultrafine grain phases in teenage and mature dentin. Mature dentin is stronger on about 20% than teenage dentin, while teenage dentin is more elastic on about 20% but is less plastic on about 15% than mature dentin. Conclusion. The amorphous phase is dominant in teenage dentin, whereas the ultrafine grain phase becomes dominant in mature dentin. Mechanical properties of human dentin under compression depend on its structural state, too.

Repair of dentin defects from DSPP knockout mice by PILP mineralization

Dentinogenesis imperfecta type II (DGI-II) lacks intrafibrillar mineral with severe compromise of dentin mechanical properties. A Dspp knockout (Dspp-/-) mouse, with a phenotype similar to that of human DGI-II, was used to determine if poly-L-aspartic acid [poly(ASP)] in the "polymer-induced liquid-precursor" (PILP) system can restore its mechanical properties. Dentin from six-week old Dspp-/- and wild-type mice was treated with CaP solution containing poly(ASP) for up to 14 days. Elastic modulus and hardness before and after treatment were correlated with mineralization from Micro x-ray computed tomography (Micro-XCT). Transmission electron microscopy (TEM)/Selected area electron diffraction (SAED) were used to compare matrix mineralization and crystallography. Mechanical properties of the Dspp-/- dentin were significantly less than wild-type dentin and recovered significantly (P < 0.05) after PILP-treatment, reaching values comparable to wild-type dentin. Micro-XCT showed mineral recovery similar to wild-type dentin after PILP-treatment. TEM/SAED showed repair of patchy mineralization and complete mineralization of defective dentin. This approach may lead to new strategies for hard tissue repair.

Submicron-to-nanoscale structure characterization and organization of crystals in dentin bioapatites

The aim of this study was to ascertain the crystal morphology and to assess the ultrastructure and texture changes of sound (SD) and caries-affected dentin (CAD) after being restored with Zn-free and Zn-containing amalgam.

Morphological aspects and physical properties of enamel and dentine of Sus domesticus: A tooth model in laboratory research

This study aims to describe and analyze morphological and physical properties of deciduous teeth of Sus domesticus. Ultrastructural analysis, mineral composition and microhardness of enamel and dentine tissues were performed on 10 skulls of S. domesticus. External anatomic characteristics and the internal anatomy of the teeth were also described. Data regarding microhardness and ultrastructural analysis were subjected to statistical tests. For ultrastructural analysis, we used the analysis of variance (ANOVA) with Tukey's post hoc (p≤0.05) test. In the analysis of microhardness, the difference between the enamel and dentine tissues was analyzed by a Student's t test. Values were expressed as mean with standard error. The results of ultrastructural analysis showed the presence of an enamel prism pattern. A dentinal tubule pattern was also observed, with a larger diameter in the pulp chamber and the cervical third, in comparison to middle and apical thirds. We observed an average microhardness of 259.2kgf/mm(2) for enamel and 55.17kgf/mm(2) for dentine. In porcine enamel and dentine, the chemical elements Ca and P showed the highest concentration. The analysis of internal anatomy revealed the presence of a simple root canal system and the occurrence of main canals in the roots. The observed features are compatible with the functional demand of these animals, following a pattern very similar to that seen in other groups of mammals, which can encourage the development of research using dental elements from the pig as a substitute for human teeth in laboratory research.

Is It Possible to induce Artificial Caries-affected Dentin using the Same Protocol to Primary and Permanent Teeth?

AIM

This in vitro study compared the mineral loss of natural and artificially-created caries-affected dentin in primary and permanent teeth using the same protocol to induce caries lesions.

MATERIALS AND METHODS

Twenty molars presenting natural occlusal dentin caries lesions (10 primary-PriC and 10 perma-nent-PermC; control group), and 20 sound molars (10 primary -PripH and 10 permanent-PermpH; experimental group), were selected. Occlusal cavities were prepared in teeth of the experimental group that were submitted to pH-cycling for 14 days to simulate caries-affected dentin. All specimens were longitudinally sectioned and prepared in order to obtain Knoop micro-hardness values from 15 to 250 urn depth, starting in bottom of center of natural lesions or cavities. The microhardness (KHN) data were submitted to three-way repeated measures analysis of variance (ANOVA) and Tukey's tests (α = 0.05).

RESULTS

Considering all depths, there was no statistically significant differences (p > 0.05) between the mineral loss of the control (PriC = 30.9 ± 6.4 and PermC = 40.8 ± 8.6) and experimental (PripH = 27.3 ± 11.1 and PermpH = 35.5 ± 14.0) groups, neither between primary and permanent teeth.

CONCLUSION

The mineral loss of the artificially-created caries-affected dentin is similar to that from naturally developed dentin caries lesions.

CLINICAL SIGNIFICANCE

The pH-cycling model may be a suitable method to simulate caries-affected dentin in both permanent and primary teeth.

Effect of epigallocatechin-3-gallate application for remaining carious dentin disinfection

CONTEXT

Epigallocatechin-3-gallate (EGCG) is a flavonoid extracted from green tea that demonstrated antimicrobial activity.

AIMS

To evaluate the efficacy of EGCG 0.5%, 1%, and 2% concentrations as an antimicrobial solution in dentin caries-like lesions induced in a bacterial-based in vitro model.

MATERIALS AND METHODS

Twenty-five human dentin specimens were submitted to a microbial-based caries model by immersion in brain heart infusion (BHI) broth inoculated with Streptococcus mutans UA159, for 5 days. After the demineralization period, the specimens were randomly divided into groups: Group I: 0.9% saline solution; Group II: 2% chlorhexidine digluconate; Group III: 0.5% EGCG; Group IV: 1% EGCG; and Group V: 2% EGCG. After the treatments, carious dentin samples were harvested from dentin specimens and analyzed by colony-forming unit (CFU) counts. Data were analyzed by ANOVA and Tukey's test.

RESULTS

Log reduction values (SD, CFU.mg(-1)) for Groups I-V were: 5.02 (0.16), 3.96 (0.43), 4.74 (0.26), 4.89 (0.56), and 4.91 (0.40), respectively. There was no statistical difference between the EGCG concentrations and saline solution (P > 0.05). Furthermore, there was no statistical difference between EGCG concentrations (P > 0.05). However, there was a statistically significant difference between the chlorhexidine digluconate group and the other groups (P < 0.05).

CONCLUSION

EGCG at the studied concentrations were not effective in eliminating S. mutans from dentin caries-like lesions.

Biomimetic remineralization of dentin

OBJECTIVES

Remineralization of demineralized dentin is important for improving dentin bonding stability and controlling primary and secondary caries. Nevertheless, conventional dentin remineralization strategy is not suitable for remineralizing completely demineralized dentin within hybrid layers created by etch-and-rinse and moderately aggressive self-etch adhesive systems, or the superficial part of a caries-affected dentin lesion left behind after minimally invasive caries removal. Biomimetic remineralization represents a different approach to this problem by attempting to backfill the demineralized dentin collagen with liquid-like amorphous calcium phosphate nanoprecursor particles that are stabilized by biomimetic analogs of noncollagenous proteins.

METHODS

This paper reviewed the changing concepts in calcium phosphate mineralization of fibrillar collagen, including the recently discovered, non-classical particle-based crystallization concept, formation of polymer-induced liquid-precursors (PILP), experimental collagen models for mineralization, and the need for using phosphate-containing biomimetic analogs for biomimetic mineralization of collagen. Published work on the remineralization of resin-dentin bonds and artificial caries-like lesions by various research groups was then reviewed. Finally, the problems and progress associated with the translation of a scientifically sound concept into a clinically applicable approach are discussed.

RESULTS AND SIGNIFICANCE

The particle-based biomimetic remineralization strategy based on the PILP process demonstrates great potential in remineralizing faulty hybrid layers or caries-like dentin. Based on this concept, research in the development of more clinically feasible dentin remineralization strategy, such as incorporating poly(anionic) acid-stabilized amorphous calcium phosphate nanoprecursor-containing mesoporous silica nanofillers in dentin adhesives, may provide a promising strategy for increasing of the durability of resin-dentin bonding and remineralizing caries-affected dentin.

A Zn-doped etch-and-rinse adhesive may improve the mechanical properties and the integrity at the bonded-dentin interface

OBJECTIVE

The objective of the study was to determine if zinc-doped etch-and-rinse dentin adhesive may induce therapeutic effects within the resin-dentin interface.

METHODS

Human acid-etched dentin was infiltrated with Adper™ Single Bond Plus (SB, 3M ESPE, St. Paul, MN, USA), SB doped with 10wt.% ZnO nanoparticles (ZnO-SB) or SB doped with 2wt.% ZnCl2 (ZnCl2-SB). AFM/nanoindentation analysis was performed on fully hydrated specimens to evaluate the nanomechanical properties (Hi: hardness; Ei: modulus of elasticity) across the resin-dentin interface after different SBF storage periods (24h, 1m, 3m). Confocal laser microscopy (CLSM) was used to evaluate the ultramorphology and micropermeability at 24h and 3m of SBF storage.

RESULTS

SB control specimens exhibited a decrease in Hi in the hybrid layer (HL) and bottom of the hybrid layer (BHL) and a decrease in Ei in the HL after 3m of SBF storage, indicating that severe degradation occurred in the control interface. ZnO-SB bonded specimens preserved the initial Hi and Ei at the HL and BHL subsequent SBF storage; ZnCl2-SB bonded specimens showed a decrease in Ei, in the HL over time. CLSM analysis confirmed that both Zn-doped adhesives were able to preserve the integrity of the HL.

SIGNIFICANCE

Specific formulation of Zn-doped etch-and-rinse adhesives may offer the possibility to maintain the nano-mechanical properties along the dentin-bonded interface by inhibiting dentin MMPs and by protective mineral crystals formation within the resin-dentin interface. Clinical advantages may be expected by preserving and improving the integrity of the hybrid layer when Zn-doped adhesives are employed.

X-ray microdiffraction, TEM characterization and texture analysis of human dentin and enamel

Human tooth is a complex bioceramic composite, which consists of enamel, dentin and the interface, the dentin-enamel junction (DEJ). The crystal properties and ultrastructure of the inorganic phase through the thickness of healthy human molar teeth were investigated using X-ray microdiffraction (μXRD), electron diffraction and transmission electron microscopy (TEM) techniques. The XRD data were analysed using the Le Bail profile fitting approach. The size and the texture of the crystallites forming enamel and dentin in the crown part of teeth were measured using both techniques and then compared. Results showed that the thickness of dentin crystallites was found to decrease towards the DEJ, whereas the thickness of the enamel crystallites increased from the DEJ towards the outer layers. It was demonstrated that enamel exhibited an increase of texture in 002 lattice planes from the DEJ towards the outer layers. Texture was also detected in 102 lattice planes. The texture effect in 002 planes at the scale of less than 1 μm was also demonstrated in dentin. The variation of lattice parameters as a function of the position within the thickness of dentin and enamel was also observed. The values of the nonuniform microstrain in the dentin and enamel crystallites were from 1.40 × 10(-6) % to 4.44 × 10(-5) %. The good correlation between XRD and TEM indicated that μXRD is a useful technique to study crystallography and microstructure of heterogeneous enamel and dentin. The observed gradient characteristics of texture and crystallite size in enamel and dentin maybe an evolutionary outcome to resist wear and fracture, thereby contributing to the excellent mechanical properties of teeth.

Antimicrobial effect of chlorhexidine digluconate in dentin: In vitro and in situ study

Aim:

The aim of this study was to evaluate a very short-term in vitro and in situ effect of 2% chlorhexidine-digluconate-based (CHX) cavity cleanser on the disinfection of dentin demineralized by cariogenic bacteria.

Materials and Methods:

Human dentin slabs were randomly allocated and used in 2 distinct phases, in vitro and in situ, for obtaining demineralized dentin. In vitro, the slabs (n=15) were immersed for 5 days in BHI broth inoculated with Streptococcus mutans CTT 3440. In situ, a double-blind design was conducted in one phase of 14 days, during which 20 volunteers wore palatal devices containing two human dental dentin slabs. On 5^th day in vitro and 14^th day in situ, the slabs were allocated to the two groups: Control group (5 μl of 0.9% NaCl solution) and CHX group (5 μl of 2% chlorhexidine digluconate solution, Cavity Cleanser™ BISCO, Schaumburg, IL, EUA), for 5 minutes. The microbiological analyses were performed immediately before and after the treatments.

Results:

The log reductions means found for CHX treatment on tested micro organisms were higher when compared to Control group either in vitro or in situ conditions.

Conclusions:

Our results showed that CHX was effective in reducing the cultivable microbiota in contaminated dentin. Furthermore, although the use of chlorhexidine-digluconate-based cavity disinfectant did not completely eliminate the viable microorganisms, it served as a suitable agent to disinfect tooth preparations.

Dentin caries activity in early occlusal lesions selected to receive operative treatment: findings from the Practitioners Engaged in Applied Research and Learning (PEARL) Network

BACKGROUND

Members of the practice-based research network Practitioners Engaged in Applied Research and Learning (PEARL) Network investigated the dentin caries activity in early occlusal lesions and its relationship to patient age, preoperative tooth sensitivity and radiographic appearance, as well as its influence on preparation depth and volume.

METHODS

PEARL Network practitioner-investigators (P-Is) (n = 45), general dentists who were trained but whose methods were not calibrated, conducted a study regarding postoperative hypersensitivity in resin-based composite restorations. The P-Is enrolled as study participants 613 patients with occlusal carious lesions that, in the P-Is' clinical judgment, required restoration. The P-Is used baseline radiographs to assess the depth and extent of the lesions. Data for 671 restorations included baseline sensitivity; ranking of dentin caries activity on the opening of the enamel; radiographic visibility (n = 652); and measurements of preparation depth, width and length.

RESULTS

P-Is found rapidly progressing dentin caries in 38.5 percent (258 of 671) of lesions and slowly progressing (and potentially inactive dentin) caries in the remainder of the lesions. Rapidly progressing caries was not related to the participant's age or participant-reported preoperative hypersensitivity but was related to the lesion depth as seen radiographically (P < .001) and depth (P < .001) and volume (P < .001) of the preparation. Molars had slightly higher but not statistically significant levels of caries activity.

CONCLUSION

Rapidly progressing dentin caries, while present in only 38.5 percent of lesions, was related to the lesion's radiographic appearance but not to the participant's age or the study tooth's pre-operative sensitivity.

CLINICAL IMPLICATIONS

On the basis of the low level of rapidly progressing dentin caries in this study population and the fact that slowly progressing caries can be inactive or remineralizing, the authors advise sealing versus operative treatment of early or shallow occlusal lesions.

Microbiochemical analysis of carious dentine using Raman and fluorescence spectroscopy

The aim of this study was to evaluate and correlate objectively the microspectroscopically derived biochemical components of sound, infected and affected carious dentine with their microhardness and autofluorescence (AF) characteristics. Over 3 million high-resolution Raman spectra from 8 extracted human carious teeth were recorded using Raman spectrometer with parallel spectrum acquisition. Green AF signals across each carious lesion from all samples were acquired with a similar spatial resolution using confocal fluorescence microscopy. The Knoop microhardness (KHN) from a total of 233 co-localized areas was recorded from the same samples and allocated subjectively into the three zones. Cluster analysis of the Raman data, performed using in-house software, produced five independent spectral components representing mineral content, protein content, porphyrin fluorescence (PF), putative infected dentine signal (IDS) and affected dentine signal (ADS). The distributions of the 5 Raman components and the AF signal were matched across all samples and their average values were calculated for each corresponding KHN area. The infected dentine was defined significantly by the KHN, AF and by the relative contribution of the mineral, PF and IDS clusters. Protein cluster was not statistically related to the KHN or AF. A delineation between affected and sound dentine was observed using the KHN, AF, PF and ADS parameters. This study concludes that micro-Raman spectroscopy can provide a non-invasive and objective evaluation of different carious dentine zones. Being able to detect and assess clinically the caries-affected dentine during minimally invasive operative caries management is important to control the risk of unnecessary tissue removal.

Apatite crystal protection against acid-attack beneath resin-dentin interface with four adhesives: TEM and crystallography evidence

OBJECTIVES

Interaction between specific functional groups and apatite crystals may contribute to adhesion. The present study investigated effects of four adhesives with different compositions on protection of crystals beneath the hybrid layer against acid-attack using transmission electron microscopy (TEM) and selected area electron diffraction (SAED).

METHODS

Human dentin was bonded with four adhesives; two with a carboxylic-based functional co-polymer (PAA): three-step etch-and-rinse Scotchbond Multi-Purpose (SMP, 3M ESPE) and one-step self-etch Adper Easy Bond (AEB, 3M ESPE), and two with a phosphate-based functional monomer (MDP): two-step etch-and-rinse Clearfil Photo Bond (CPB, Kuraray Medical) and two-step self-etch Clearfil SE Bond (CSE, Kuraray Medical). The specimens were the either left untreated (control) or subjected to acid-base challenge with demineralizing solution (pH 4.5) and 5% NaClO. All specimens were processed and observed by TEM. SAED was used to identify the presence or absence of apatite crystallites at the base or beneath hybrid layer before and after acid-base challenge.

RESULTS

An apatite-rich zone was observed beneath the partially demineralized hybrid layer of CSE. The zone was thinner in AEB, but a demineralization-susceptible area was found beneath it. The etch-and-rinse adhesives (SMP and CPB) demonstrated completely or predominantly demineralized hybrid layers, which were devoid of the acid-resistant apatite-rich zone.

SIGNIFICANCE

TEM/SAED evidence disclosed that the preserved dentin apatite crystals beneath the thin hybrid layer of the mild self-etch adhesives were protected against acid. Diffusion of reactive components beyond the hybrid layer, and their chemical bonding potential with the remaining crystals created the acid-base resistant zone.

Characterization of an epoxy filler for piezocomposites compatible with microfabrication processes

Miniature ultrasound transducer arrays that can operate at frequencies above 30 MHz are needed for high-resolution medical imaging. One way to achieve this is with a kerfless structure based on 1-3 connectivity piezocomposite with the electrodes defined by photolithography. To achieve this, not only does the composite need planar, parallel, and smooth surfaces, but it must also be made with an epoxy filler compatible with the chemicals, heat, and vacuum required for photolithography. This paper reports full characterization of an epoxy suitable for fine-scale kerfless array fabrication, including photolithographic processing. Material properties have been investigated as a function of cure temperature and for compatibility with solvents. By increasing the cure temperature, the crosslinking between the epoxy and the hardener in- creases, resulting in a higher glass transition temperature. The cured epoxy consequently has better resistance to both heat and solvents. An elevated cure temperature, near 100°C, is required to optimize material properties for photolithography on 1-3 piezocomposites. The acoustic properties of the epoxy have also been studied. These are similar to other epoxies used in piezocomposite fabrication and no significant changes have been observed for the different cure temperatures.

Increased matrix metalloproteinase-2 and bone sialoprotein response to human coronal caries

BACKGROUND

It has been suggested that host matrix metalloproteinase-2 (MMP-2) present in dentin may be involved in caries progression, however, its response to caries is not known. Bone sialoprotein (BSP) has been implicated in dentin mineralization and MMP-2 modulation.

OBJECTIVE

To identify and compare the distribution of MMP-2 and BSP in healthy human coronal dentin and those with early caries.

METHODS

Freshly extracted 3rd molars and premolars with and without early caries were fixed, demineralized and subjected to immunohistochemistry using a monoclonal anti-MMP-2 antibody and monoclonal anti-BSP antibody with an avidin-biotin complex method. Immunoreactivity was visualized with 3,3'-diaminobenzidine substrate and observed under light microscopy.

RESULTS

Immunohistochemical analysis revealed that MMP-2 and BSP are not detected in the tubule lumens of healthy dentin. However, intense immunoreactivity for MMP-2 and BSP was detected in association with the full length of the caries-affected dentinal tubules. The MMP-2 and BSP at the dentino-enamel junction appeared unaltered.

CONCLUSION

The results indicate that MMP-2 and BSP may be actively secreted by odontoblasts in response to carious insult. MMP-2 and BSP accumulation in the caries-affected dentinal tubules may indicate their potential involvement in the host defense mechanism which results in calcification of regions affected by the carious process.

Application of polychromatic µCT for mineral density determination

Accurate assessment of mineral density (MD) provides information critical to the understanding of mineralization processes of calcified tissues, including bones and teeth. High-resolution three-dimensional assessment of the MD of teeth has been demonstrated by relatively inaccessible synchrotron radiation microcomputed tomography (SRµCT). While conventional desktop µCT (CµCT) technology is widely available, polychromatic source and cone-shaped beam geometry confound MD assessment. Recently, considerable attention has been given to optimizing quantitative data from CµCT systems with polychromatic x-ray sources. In this review, we focus on the approaches that minimize inaccuracies arising from beam hardening, in particular, beam filtration during the scan, beam-hardening correction during reconstruction, and mineral density calibration. Filtration along with lowest possible source voltage results in a narrow and near-single-peak spectrum, favoring high contrast and minimal beam-hardening artifacts. More effective beam monochromatization approaches are described. We also examine the significance of beam-hardening correction in determining the accuracy of mineral density estimation. In addition, standards for the calibration of reconstructed grey-scale attenuation values against MD, including K(2)PHO(4) liquid phantom, and polymer-hydroxyapatite (HA) and solid hydroxyapatite (HA) phantoms, are discussed.

Biodegradation of resin-dentin interfaces increases bacterial microleakage

Bis-GMA-containing resin composites and adhesives undergo biodegradation by human-saliva-derived esterases, yielding Bis-hydroxy-propoxy-phenyl-propane (Bis-HPPP). The hypothesis of this study is that the exposure of dental restorations to saliva-like esterase activities accelerates marginal bacterial microleakage. Resin composites (Scotchbond, Z250, 3M) bonded to human dentin were incubated in either buffer or dual-esterase media (pseudocholinesterase/cholesterol-esterase; PCE+CE), with activity levels simulating those of human saliva, for up to 90 days. Incubation solutions were analyzed for Bis-HPPP by high-performance liquid chromatography. Post-incubation, specimens were suspended in a chemostat-based biofilm fermentor cultivating Streptococcus mutans NG8, a primary species associated with dental caries, for 7 days. Bacterial microleakage was assessed by confocal laser scanning microscopy. Bis-HPPP production and depth and spatial volume of bacterial cell penetration within the interface increased with incubation time and were higher for 30- and 90-day PCE+CE vs. buffer-incubated groups, suggesting that biodegradation can contribute to the formation of recurrent decay.

In vitro remineralization of severely compromised bonded dentin

Biomimetic remineralization is potentially useful for the remineralization of incompletely resin-infiltrated collagen matrices created by etch-and-rinse adhesives. In this study, we tested the hypothesis that structurally altered dentin collagen cannot be remineralized to the same hierarchical order and dimension seen in structurally intact dentin collagen. The remineralization medium consisted of a set Portland cement/simulated body fluid system containing polycarboxylic acid and polyvinylphosphonic acid as biomimetic analogs. Remineralization of air-dried, collapsed hybrid layers was apparent after one month, with hybrid layers remineralized to 80-90% of their thickness after 2-4 months. A hypermineralized layer was seen on the hybrid layer surface, and tubular orifices were occluded with apatite deposits that resembled those present in non-carious cervical dentin. Structurally altered collagen is unlikely to be remineralized to the same hierarchical order and dimension as seen in intact dentin. The aggressively air-dried acid-etched dentin remineralization model also sheds light on the mechanism of sclerotic dentin formation.

Failure of a glass ionomer to remineralize apatite-depleted dentin

Remineralization of demineralized dentin lesions adjacent to glass-ionomer cements (GICs) has been reported in the literature. This study tested the hypothesis that a strontium-based GIC can remineralize completely demineralized dentin by nucleation of new apatite crystallites within an apatite-free dentin matrix. Human dentin specimens were acid-etched, bonded with Fuji IX(GP), and immersed in a calcium-and-phosphate-containing 1.5X simulated body fluid (SBF) for 1-4 months. Polyacrylic acid and polyvinylphosphonic acid biomimetic analogs were added to the SBFs to create 2 additional remineralization media. Specimens were processed by transmission electron microscopy (TEM). No apatite deposition could be identified in the completely demineralized dentin in any of the specimens immersed in the 3 remineralization media, despite TEM/EDX evidence of diffusion of ions specific to the strontium-based GIC into the demineralized dentin. The hypothesis was rejected; mineral concentration alone is not a sufficient endpoint for assessing the success of contemporary remineralization strategies.

Evaluation of the antimicrobial effect of photodynamic antimicrobial therapy in an in situ model of dentine caries

Photodynamic antimicrobial therapy (PACT) promotes bacterial death as a result of the photosensitization of microbial components. This study evaluated the effect of PACT on dentine caries produced in situ. Over the course of 14 d, 20 volunteers wore intra-oral devices containing human dentine slabs that were treated 10 times daily with a 40% sucrose solution. Afterwards, the antimicrobial effect of toluidine blue O, associated with 47 or 94 J cm(-2) of a light-emitting diode, was evaluated. Before and after the treatments, dentine samples were analysed with regard to the total number of microorganisms, total streptococci, mutans streptococci, and lactobacilli. Significant reductions in the bacterial count were observed for PACT with both energy densities tested, with the following values observed for 47 and 94 J cm(-2) of irradiation: for total streptococci, 3.45 and 5.18; for mutans streptococci, 3.08 and 4.16; for lactobacilli, 3.24 and 4.66; and for total microorganisms, 4.29 and 5.43, respectively. The control, treated with 94 J cm(-2) of irradiation alone, was also effective against all bacteria. To conclude, PACT was effective in killing oral microorganisms present in dentine caries produced in situ and may be a useful technique for eliminating bacteria from dentine carious lesions before restoration.

Ultrastructural observations and growth of occluding crystals in carious dentine

The aim of the present study was to investigate the ultrastructural mechanisms involved in the formation of caries-induced intratubular dentine. Conventional, high resolution and scanning transmission electron microscopy, electron diffraction and energy-dispersive X-ray spectroscopy techniques were used to study the ultrastructure of the inorganic phase in the transparent zone of carious dentine. The results demonstrated that the bulk of the inorganic phase in caries-induced intratubular dentine had an apatite crystal structure with the presence of additional Mg-substituted beta-TCP (beta-tricalcium phosphate) phase in the carious region. Highly oriented apatite crystallites observed in intratubular dentine demonstrated a regulated biomineralization process during the formation of inorganic phase in this region, whereas Mg beta-TCP crystals were presumably formed purely via "dissolution/precipitation" mechanism. The study demonstrated the importance of "dissolution/precipitation" process and the growth kinetics of Mg-substituted beta-TCP crystals in understanding the process of formation of calcium-phosphate crystallites in carious intratubular dentine.