Comparison of the number and diameter of dentinal tubules in human and bovine dentine by scanning electron microscopic investigation

Spectrophotometric insights: calcium hydroxide influences tooth discolorations induced by short-term application of antibiotic/corticosteroid pastes

OBJECTIVES

This in vitro study aimed to assess the influence of a calcium hydroxide dressing regarding the relative color change (ΔE) of enamel-dentin specimens previously exposed to antibiotic/corticosteroid pastes.

MATERIALS AND METHODS

Eighty bovine enamel-dentin specimens with a cylindrical central cavity were randomly allocated to four groups: NEG (empty), POS (blood), LED (Ledermix), and ODO (Odontopaste) (n = 20 each). The materials were applied and sealed with self-adhesive resin luting material. After 3 weeks, the materials were removed and a calcium hydroxide (Ca(OH)₂) dressing was placed in all cavities. After a further 3-week storage period, the cavities were restored with resin-based composite. Spectrophotometric color measurements were taken over 6 months, and ΔE values were calculated. A Tukey's multiple comparison test was performed to assess significant differences within the treatment groups (p < 0.05).

RESULTS

Tooth discolorations were present after 3 weeks in LED (ΔE 29.14 ± 6.55) and POS (ΔE 18.05 ± 7.03); NEG and ODO remained color stable (ΔE 3.2 ± 1.36 and ΔE 2.3 ± 1.16). The 3-week Ca(OH)₂ dressing decreased discolorations of POS (ΔE 15.93 ± 6.63; p = 0.37), whereas LED showed a further significant increase (ΔE 39.55; p < 0.0001). Between the end of the Ca(OH)₂ dressing and the final restoration no significant color changes were observed in any group (p > 0.9).

CONCLUSIONS

Discolorations induced by LED progressed during the Ca(OH)₂ dressing despite careful removal of all residues.

CLINICAL RELEVANCE

Calcium hydroxide might negatively affect the discoloring potential of Ledermix. This highlights the need for direct intracanal application methods of Ledermix ensuring a material-free access cavity or alternative antibiotic/corticosteroid pastes such as Odontopaste should be used.

Evaluation of bond strength of resin cement to Er:YAG laser-etched enamel and dentin after cementation of ceramic discs

The purpose of this study was to investigate the shear bond strength (SBS) of ceramic discs luted to differently etched enamel and dentin surfaces. Occlusal surfaces of 64 carious-free human molars and vestibule surfaces of 64 first maxillary incisors were ground to get flat superficial dentin and flattened enamel respectively. After generating 4 groups according to the surface etching method (37% orthophosphoric acid, Er:YAG laser-contact handpiece/scanning handpiece (1 or 2 times of scanning)), ceramic discs were luted to the surfaces with adhesive resin cement (Variolink N, Vivadent Ets., Schaan/Liechtenstein). After etching and cementation, thermocycling of 5000 cycles (Sd Mechatronık Gmbh, Feldkirchen-Westerham, Germany) and SBS test (Servopulser EHFFD1; Shimadzu, Kyoto, Japan) were performed respectively. The surface morphologies of 2 specimens, etched enamel and dentin, prepared for each group were examined with SEM analysis. Failure modes were determined under a USB digital microscope. Data were analyzed with one-way analysis of variance (ANOVA) and Tukey HSD test (α = 0.05). SBS values in dentin surfaces showed statistically significant differences (p < 0.05) among tested groups. The highest SBS among dentin groups was determined in the group which had 2 times etching by Er:YAG laser (11.42 MPa) by a scanning handpiece. No statistical differences were observed in the other dentin or enamel groups. Laser etching seems to be a viable alternative to acid etching on both enamel and dentin surfaces while double etching of dentin with a scanning handpiece can improve the adhesion.

Interfacial Fracture Toughness Comparison of Three Indirect Resin Composites to Dentin and Polyether Ether Ketone Polymer

OBJECTIVES

 Advances in laboratory composites and their high wear resistance and fracture toughness have resulted in their growing popularity and increasing use for dental restorations. This study sought to assess the fracture toughness of three indirect composites bonded to dental substrate and polyether ether ketone (PEEK) polymer.

MATERIALS AND METHODS

 This in vitro study was conducted on two groups of dental and polymer substrates. Each substrate was bonded to three indirect composite resins. Sixty blocks (3 × 3 × 12 mm) were made of sound bovine anterior teeth and PEEK polymer. Sixty blocks (3 × 3 × 12 mm) were fabricated of CRIOS (Coltene, Germany), high impact polymer composite (HIPC; Bredent, Germany), and GRADIA (Indirect; GC, Japan) composite resins. Composites were bonded to dentin using Panavia F 2.0 (Kuraray, Japan). For bonding to PEEK, Combo.lign (Bredent) and Visio.Link (Bredent) luting cements were used. In all samples, a single-edge notch was created by a no. 11 surgical blade at the interface. The samples were subjected to 3,500 thermal cycles, and their fracture toughness was measured in a universal testing machine (Zwick/Roell, Germany) by application of four-point flexural load.

STATISTICAL ANALYSIS

 Data were analyzed using one-way analysis of variance, Kruskal-Wallis.

RESULTS

 The fracture toughness of CRIOS-PEEK interface was significantly higher than HIPC-PEEK. The fracture toughness of GRADIA-PEEK was not significantly different from that of HIPC and CRIOS. The fracture toughness of GRADIA-dentin was significantly higher than HIPC-dentin.

CONCLUSION

 Considering the limitations of this study, GRADIA has the highest bond strength to dentin, while CRIOS shows the highest bond strength to PEEK.

Influence of Tooth Pigmentation on H2O2 Diffusion and Its Cytotoxicity After In-office Tooth Bleaching

Clinical Relevance

Pigments in tooth structures affect the diffusion of H2O2 through enamel and dentin. The bleaching methodology can be impacted.

SUMMARY

Objective: The aim of this study was to evaluate the influence of the presence of pigments in tooth structures on the trans-enamel and trans-dentin diffusion of hydrogen peroxide (H2O2) and its cytotoxicity after carrying out an in-office bleaching therapy.

Methods and Materials: A bleaching gel with 35% H2O2 was applied for 45 minutes (three times for 15 minutes) on enamel and dentin discs (n=6), either previously submitted to the intrinsic pigmentation protocol with a concentrated solution of black tea, or not, defining the following groups: G1, unbleached untreated discs (control 1); G2, unbleached pigmented discs (control 2); G3, bleached untreated discs; G4, bleached pigmented discs. The discs were adapted to artificial pulp chambers, which were placed in wells of 24-well plates containing 1 mL culture medium (Dulbecco’s modified Eagle’s medium [DMEM]). After applying the bleaching gel on enamel, the extracts (DMEM + components of bleaching gel that diffused through the discs) were collected and then applied on the cultured MDPC-23 odontoblast-like cells. Cell viability (methyl tetrazolium assay and Live & Dead, Calcein AM, and ethidium homodimer-1 [EthD-1] probes), the amount of H2O2 that diffused through enamel and dentin (leuco-crystal violet product), and the H2O2-mediated oxidative cell stress (SOx) and components of degradation were assessed (analysis of variance/Tukey; α=0.05).

Results: There was no significant difference between the groups G1 and G2 for all the parameters tested (p&gt;0.05). Reduction in the trans-enamel and trans-dentin diffusion of H2O2 occurred for G4 in comparison with G3. Significantly lower cell viability associated with greater oxidative stress was observed for G3 (p&lt;0.05). Therefore, in-office tooth bleaching therapy performed in pigmented samples caused lower cytotoxic effects compared with untreated samples submitted to the same esthetic procedure (p&lt;0.05).

Conclusion: According to the methodology used in this investigation, the authors concluded that the presence of pigments in hard tooth structures decreases the trans-enamel and trans-dentin diffusion of H2O2 and the toxicity to pulp cells of an in-office bleaching gel with 35% H2O2.

The influence of centrifugation and inoculation time on the number, distribution, and viability of intratubular bacteria and surface biofilm in deciduous and permanent bovine dentin

The present study aimed to assess the influence of centrifugation and inoculation time on the number, distribution, and viability of intratubular bacteria and surface monospecies E. faecalis biofilm.

MATERIALS AND METHODS

Forty-four semicylindrical specimens cut from primary (n = 22) and permanent (n = 22) bovine teeth were randomly assigned to the experimental groups. Teeth of each type were inoculated with E. faecalis with and without centrifugation for 1 and 14 days. The number, localization, viability of bacteria and depth of their penetration were assessed with bacterial culturing of dentin shavings, scanning electron microscopy (SEM) and confocal laser electron microscopy (CLSM). Three-way ANOVA with post-hoc Tukey test were used to assess the influence of different experimental setups on dentin infection.

RESULTS

Severe dentin infection was observed in permanent and deciduous teeth after centrifugation and 1-day incubation: bacteria reached the full length of dentinal tubules and colony-forming units were too numerous to count. The volume of green fluorescence didn't differ significantly in permanent teeth compared with deciduous (p = 1.0). After 1-day stationary inoculation, small number of cultivable bacteria and few viable bacteria in dentinal tubules were found in both groups. After 14-day stationary inoculation, the dentin infection according to CLSM was deeper in deciduous teeth compared with permanent (p = 0.006 and p = 0.019 for centrifugation and stationary inoculation, respectively).

CONCLUSION

The most even and dense dentin infection was observed in primary and permanent bovine teeth after centrifugation and 1-day inoculation, and in deciduous teeth after 14-day stationary inoculation.

Influence of de-remineralization process on chemical, microstructural, and mechanical properties of human and bovine dentin

OBJECTIVES

This study compared the chemical composition, microstructural, and mechanical properties of human and bovine dentin subjected to a demineralization/remineralization process.

MATERIALS AND METHODS

Human and bovine incisors were sectioned to obtain 120 coronal dentin beams (6 × 1 × 1 mm³) that were randomly allocated into 4 subgroups (n = 15) according to the time of treatment (sound, pH-cycling for 3, 7, and 14 days). Three-point bending mechanical test, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), thermogravimetric (TG), and X-ray diffraction (XRD) techniques were employed to characterize the dentin samples.

RESULTS

Regarding chemical composition at the molecular level, bovine sound dentin showed significantly lower values in organic and inorganic content (collagen cross-linking, CO₃/amide I, and CO₃/PO₄; p = 0.002, p = 0.026, and p = 0.002, respectively) compared to humans. Employing XRD analyses, a higher mineral crystallinity in human dentin than in bovines at 7 and 14 days (p = 0.003 and p = 0.009, respectively) was observed. At the end of the pH-cycling, CI (ATR-FTIR) and CO₃/PO₄ ratios (ATR-FTIR) increased, while CO₃/amide I (ATR-FTIR), PO₄/amide I (ATR-FTIR), and %mineral (TG) ratios decreased. The extension by compression values increased over exposure time with significant differences between dentin types (p < 0.001, in all cases), reaching higher values in bovine dentin. However, flexural strength (MPa) did not show differences between groups. We also observed the correlation between compositional variables (i.e., PO₄/amide I, CI, and %mineral) and the extension by compression.

CONCLUSIONS

Human and bovine dentin are different in terms of microstructure, chemical composition, mechanical strength, and in their response to the demineralization/remineralization process by pH-cycling.

CLINICAL RELEVANCE

These dissimilarities may constitute a potential limitation when replacing human teeth with bovines in in vitro studies.

AN ALTERNATIVE TO PERIODIC HOMOGENIZATION FOR DENTIN ELASTIC STIFFNESS

Dentin, the main tissue of the tooth, is made of tubules surrounded by peri-tubular dentin (PTD), embedded in a matrix of inter-tubular dentin (ITD). The PTD and the ITD have different relative fractions of collagen and hydroxyapatite crystals. The ITD is typically less rigid than the PTD, which can be seen as a set of parallel hollow cylindrical reinforcements in the ITD matrix. In this paper, we extend Hashin and Rozen’s homogenization scheme to a nonuniform distribution of hollow PTD cylinders, determined from image analysis. We relate the transverse isotropic elastic coefficients of a Representative Elementary Volume (REV) of dentin to the elastic and topological properties of PTD and ITD. The model is calibrated against experimental data. Each sample tested is consistently characterized by Environmental Scanning Electron Microscopy (ESEM), nanoindentation and Resonant Ultrasound Spectroscopy (RUS), which ensures that macroscopic mechanical properties measured are correlated with microstructure observations. Despite the high variability of microstructure descriptors and mechanical properties, statistical analyses show that Hashin’s bounds converge and that the proposed model can be used for back-calculating the microscopic Poisson’s ratios of dentin constituents. Three-point bending tests conducted in the laboratory were simulated with the Finite Element Method (FEM). Elements were assigned transverse isotropic elastic parameters calculated by homogenization. The tubule orientation and the pdf of the ratio inner/outer tubule radius were determined in several zones of the beams before testing. The remainder of the micro-mechanical parameters were taken equal to those calibrated by RUS. The horizontal strains found experimentally by Digital Image Correlation (DIC) were compared to those found by FEM. The DIC and FEM horizontal strain fields showed a very good agreement in trend and order of magnitude, which verifies the calibration of the homogenization model. By contrast with previous studies of dentin, we fully calibrated a closed form mechanical model against experimental data and we explained the testing procedures. In elastic conditions, the proposed homogenization scheme gives a better account of microstructure variability than micro–macro dentin models with periodic microstructure.

Regional contribution of proteoglycans to the fracture toughness of the dentin extracellular matrix

This study investigated the contribution of small leucine rich proteoglycans (SLRPs) to the fracture toughness of the dentin extracellular matrix (ECM) by enzymatically-assisted selective removal of glycosaminoglycan chains (GAGs) and proteoglycans (PGs) core protein. We adapted the Mode III trouser tear test to evaluate the energy required to tear the dentin ECM. Trouser-shaped dentin specimens from crown and root were demineralized. Depletion of GAGs and PGs followed enzymatic digestion using chondroitinase ABC (c-ABC) and matrix metalloproteinase 3 (MMP-3), respectively. The legs from specimen were stretched under tensile force and the load at tear propagation was determined to calculate the tear energy (T, kJ/m²). SLRPs decorin and biglycan were visualized by immunohistochemistry and ECM tear pattern was analyzed in SEM. Results showed T of crown ECM was not affected by PGs/GAGs depletion (p = 0.799), whereas the removal of PGs significantly reduced T in root dentin ECM (p = 0.001). Root dentin ECM exhibited higher T than crown (p < 0.03), however no regional difference are present after PG depletion (p = 0.480). Immunohistochemistry confirmed removal of GAGs and PGs. SEM images showed structural modifications after PGs/GAGs removal such as enlargement of dentinal tubules, increased interfibrillar spaces and presence of untwisted fibrils with increased diameter. Findings indicate that the capacity of the PGs to unfold and untwist contribute to the dentin ECM resistance to tear, possibly influencing crack growth propagation. The regional differences are likely an evolutionary design to increase tooth survival, that undergoes repetitive mechanical loading and load stress dissipation over a lifetime of an individual.

Insights into the reinforcement role of peritubular dentine subjected to acid dissolution

Human dentine is a mineralised dental tissue that consists of dentinal tubules surrounded by two distinct dentinal phases: peritubular dentine (PTD) and intertubular dentine (ITD). Dental caries, which manifests itself as a consequence of demineralisation, is one of the most common chronic diseases that affect the function of human teeth. Due to the difference in the packing density of crystallites, PTD and ITD exhibit different reaction rates to acid dissolution. The present study evaluates how the effective Young's modulus degrades and how the effective stress redistributes in demineralised human dentine as a result of incremental acid dissolution process. An analytical two-layer composite model is proposed and used for the effective Young's modulus calculation. 3D numerical representative volume elements (RVEs) with different variations in PTD fraction and dentinal tubule density are established to evaluate effective stress redistribution and examine the critical factors that can affect the mechanical performance. The models are then applied on an actual dentine bulk sample. The results reveal how PTD serves as a protection to ITD thus highlight the important role that PTD plays for the structural integrity of dentine. The obtained insights are crucial for advancing the understanding of a variety of natural and therapeutic effects from the mechanical perspective, e.g. the mechanical performance assessment of human dentine subject to complex dynamic processes of de- and re-mineralisation that can occur in human dental caries and dental treatments. It will ultimately inspire the biomimetic design towards strengthening the dentine and dentine-like materials.

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

Background

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

Methods

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

Results

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

Conclusion

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

Pulp Aspects of Traumatic Dental Injuries in Primary Incisors: Dark Coronal Discoloration

Dark coronal discoloration is a common outcome of traumatic dental injuries in primary incisors. However, there are only a few research studies on the mechanism that causes dark discoloration, the condition of the pulp, and the preferred treatment of such teeth. This article is a summary of the author's research studies and personal experience regarding dark coronal discoloration of traumatized primary incisors.

Ultrastructural and Chemical Composition of Dentin and Enamel in Lab Animals

Statement of the Problem:

Human tooth is clinically the most appropriate material that can be used for in-vitro dental research. However, there are limitations and drawbacks for using human teeth. Therefore, alternatives to samples of human teeth for dental studies are necessary.

Purpose:

This study purposed to evaluate and compare the microstructure and chemical composition of enamel and dentin of teeth in some lab animals.

Materials and Method:

In this experimental study, teeth of mouse, rabbit, guinea pig, dog, cat, and sheep were used. Scanning electron microscope observations and X-ray diffraction analysis were performed on samples.

Results:

This study revealed resemblance in general structure of dentin and enamel between mentioned animals and human. The minimum mean of dentinal tubules diameter is found in guinea pig (0.5µ), while the highest is in cat (1.5µ). Also the lowest and the highest mean intertubular distance was measured respectively in guinea pig (3µ) and sheep (4.8µ) and the maximum and minimum mean diameter of rods was measured in rabbit (6.6µ) and guinea pig (1.5µ), respectively.

Conclusion:

The recorded details and the measured values indicate great resemblance between dog and human dentin and enamel. Cat is in the second place for dentinal studies; sheep and guinea pig have the least resemblance to human within the scope of the reviewed criteria.

Fracture Resistance of Immature Incisors Following Root Filling with Various Bioactive Endodontic Cements Using an Experimental Bovine Tooth Model

Objective The aim of this study was to compare the fracture resistance of immature bovine roots when using ProRoot MTA, CEM Cement, and Biodentine as root filling materials.

Materials and Methods An immature bovine tooth model was developed by removing the coronal and apical portions of 70 bovine incisors 8 mm above and 12 mm below the cementoenamel junction (CEJ). The specimens were then divided into five groups: ProRoot MTA, CEM Cement, Biodentine, gutta-percha/AH26 sealer, and control. All groups received a 5-mm apical plug with a temporary restorative material. Then, the remaining root canal space was filled with one of the afore-mentioned materials. After setting, the specimens were mounted in acrylic resin. Then, 3 mm coronal to the CEJ from the buccal side of the teeth and at a 135°angle to the long axis, the specimens were loaded until fracture.

Results The specimens in the Biodentine (2196 N) and ProRoot MTA (2103 N) groups had significantly greater fracture resistance in comparison to the control group ( p = 0.01). No significant difference was found between CEM Cement, gutta-percha and sealer AH26, and control groups. No significant differences occurred between the four experimental groups ( p = 0.45).

Conclusion Filling the root canal space with ProRoot MTA and Biodentine contributed to higher fracture resistance values.

Coronal tooth discoloration induced by regenerative endodontic treatment using different scaffolds and intracanal coronal barriers: a 6-month ex vivo study

Objective

The aim of this study was to evaluate discoloration of teeth undergoing regenerative endodontic procedures (REPs) using blood clot or platelet-rich fibrin (PRF) as the scaffolds and different calcium silicate-based materials as the intracanal coronal barriers in an ex vivo model.

Materials and Methods

Forty-eight bovine incisors were prepared and disinfected using 1 mg/mL double antibiotic paste (DAP). The specimens were then randomly divided into 2 groups (n = 24) according to the scaffolds (blood or PRF). After placement of scaffolds each group was divided into 2 subgroups (n = 12) according to the intracanal coronal barriers (ProRoot MTA or Biodentine). The pulp chamber walls were sealed with dentin bonding agent before placement of DAP and before placement of scaffolds. The color changes (∆E) were measured at different steps. The data were analyzed using 2-way analysis of variance.

Results

Coronal discoloration induced by DAP was not clinically perceptible (ΔE ≤ 3.3). Regarding the type of the scaffold, coronal discoloration was significantly higher in blood groups compared with PRF groups at the end of REP and after 1 month (p < 0.05). However, no significant difference was found between PRF and blood clot after 6 months (p > 0.05). Considering the type of intracanal coronal barrier, no significant difference existed between ProRoot MTA and Biodentine (p > 0.05).

Conclusions

With sealing the dentinal tubules of pulp chamber with a dentin bonding agent and application of DAP as an intracanal medicament, coronal color change of the teeth following the use of PRF and blood sealed with either ProRoot MTA or Biodentine was not different at 6-month follow-up.

Postulated release profile of recombinant human bone morphogenetic protein-2 (rhBMP-2) from demineralized dentin matrix

Demineralized dentin matrix (DDM) has been used as a recombinant human bone morphogenetic protein-2 (rhBMP-2) carrier in many clinical trials. To optimize the clinical safety and efficacy of rhBMP-2 with DDM, efforts have been made to improve the delivery of rhBMP-2 by 1) lowering the administered dose, 2) localizing the protein, and 3) prolonging its retention time at the action site as well as the bone forming capacity of the carrier itself. The release profile of rhBMP-2 that is associated with endogenous BMP in dentin has been postulated according to the type of incorporation, which is attributed to the loosened interfibrillar space and nanoporous dentinal tubule pores. Physically adsorbed and modified, physically entrapped rhBMP-2 is sequentially released from the DDM surface during the early stage of implantation. As DDM degradation progresses, the loosened interfibrillar space and enlarged dentinal tubules release the entrapped rhBMP-2. Finally, the endogenous BMP in dentin is released with osteoclastic dentin resorption. According to the postulated release profile, DDM can therefore be used in a controlled manner as a sequential delivery scaffold for rhBMP-2, thus sustaining the rhBMP-2 concentration for a prolonged period due to localization. In addition, we attempted to determine how to lower the rhBMP-2 concentration to 0.2 mg/mL, which is lower than the approved 1.5 mg/mL.

Pulp aspects of traumatic dental injuries in primary incisors: Dark coronal discoloration

Dark coronal discoloration is a common outcome of traumatic dental injuries in primary incisors. However, there are only a few research studies on the mechanism that causes dark discoloration, the condition of the pulp, and the preferred treatment of such teeth. This article is a summary of the author's research studies and personal experience regarding dark coronal discoloration of traumatized primary incisors.

Comparative evaluation of fracture resistance using two rehydration protocols for fragment reattachment in uncomplicated crown fractures

BACKGROUND/AIMS

Uncomplicated crown fracture is the most common traumatic dental injury. The International Association of Dental Traumatology has recommended fragment reattachment as the best method for restoring uncomplicated crown fractures of permanent teeth. Dehydration can affect fracture resistance after reattachment. However, a standard protocol for rehydration is still lacking. Hence, the aim of this study was to design a humidification chamber and assess its efficacy for improving the rehydration of tooth fragments and increasing fracture resistance after reattachment.

MATERIALS AND METHODS

Sixty mandibular bovine incisors with similar dimensions and free of any structural deformities were fractured and randomized into five groups: Group I, Control Group (sound teeth); Group II (dehydrated for 24 hours); Group III (rehydrated in distilled water for 15 minutes); Group IV (rehydrated in a humidification chamber for 15 minutes); and Group V (restored with composite). A humidification chamber was designed and used for rehydration for 15 minutes in Group IV. Fragments in Group III were immersed in distilled water for 15 minutes. Reattachment procedures and materials remained the same in all groups. Fracture resistance was tested in a universal testing machine, and statistical analysis was done by Stata-14.

RESULTS

The Control Group with sound teeth (Group I) exhibited a maximum value of 282 ± 10.32 N, while Group II (fragment reattached without rehydration) had the least fracture resistance, 49.75 ± 5.2 N. Rehydration by means of the humidification chamber protocol (Group IV) resulted in significantly higher fracture resistance (150.54 ± 6.49 N) than in Group III (rehydration by means of immersion).

CONCLUSIONS

Fracture resistance after fragment reattachment was significantly affected by the rehydration of fragments for 15 minutes in the humidification chamber. Fragment reattachment after rehydration showed better fracture resistance than the composite restorations.

Antimicrobial action of photodynamic therapy in root canals using LED curing light, curcumin and carbopol gel

AIM

To evaluate the capacity of carbopol gel to maintain the intensity of a LED curing light (blueLED) along the length of prepared root canals in bovine teeth, and to assess the antimicrobial capacity of curcumin photoactivated by a LED curing light in the presence of carbopol gel.

METHODOLOGY

Experiment 1: Eight straight roots of bovine incisors were standardized to a length of 15 mm, and the root canals instrumented up to a size 120 K-file. The LED curing light was irradiated inside the root canals using an aluminium collimator (1.5 mm in diameter) placed at the orifice (n = 8). Initially, the irradiation was performed in empty root canals and then repeated with the root canals filled with carbopol gel. Simple standardized photographs of the roots were taken with a digital camera in the mesial perspective during the irradiation procedure and the images analysed in OriginLab software to verify the light intensity along the length of the root. Experiment 2: Twenty dentine blocks were obtained from the cervical third of bovine incisors using a trephine bur. Biofilms were induced for 21 days on the blocks using Enterococcus faecalis (ATCC 4083) at 10⁹ cells mL^-1 . The blocks were treated according to the groups (n = 5): positive control; standard PDT (methylene blue + diode Laser); curcumin; LED curing light; and curcumin + LED curing light. After the treatment, the samples were dyed with Live/Dead BacLight Bacterial Viability solution and fluorescence images were obtained by Confocal Scanning Laser Microscopy (CSLM). Experiment 3: Thirty-two roots of bovine incisors were prepared as described in experiment 1. Their dentinal tubules were contaminated and the root canals treated according to the groups (n = 8): positive control; standard PDT; curcumin + LED curing light; curcumin + carbopol gel + LED curing light. The specimens were sectioned longitudinally and the split roots were treated with the Live/Dead dye to obtain fluorescence images by CSLM. All images were processed using BioImageL software to measure the percentage of viable bacteria and the data analysed statistically using the nonparametric Kruskal-Wallis test (α < 0.05).

RESULTS

In Experiment 1, carbopol gel did not improve the intensity of LED light transmission along the root canal. In Experiment 2, a significant decrease (P < 0.05) in bacterial viability occurred in the following order: positive control < only LED curing light < only curcumin < curcumin + LED curing light = standard PDT; and in Experiment 3 positive control = curcumin + LED curing light ≤ curcumin + gel + LED curing light ≤ standard PDT.

CONCLUSION

Similar disinfection effectiveness was obtained using curcumin + LED curing light and methylene blue + 660 nm LASER (standard PDT). The use of carbopol gel did not favour a greater transmission of LED light along the root canal and also resulted in less bacterial killing when used in endodontic PDT.

Biomimetic transformation of polyphosphate microparticles during restoration of damaged teeth

OBJECTIVE

In the present study, we investigated the fusion process between amorphous microparticles of the calcium salt of the physiological polymer comprising orthophosphate units, of inorganic polyphosphate (polyP), and enamel.

METHODS

This polymer was incorporated as an ingredient into toothpaste and the fusion process was studied by electron microscopy and by synchrotron-based X-ray tomography microscopy (SRXTM) techniques.

RESULTS

The data showed that toothpaste, supplemented with the amorphous Ca-polyP microparticles (aCa-polyP-MP), not only reseals tooth defects on enamel, like carious lesions, and dentin, including exposed dentinal tubules, but also has the potential to induce re-mineralization in the enamel and dentin regions. The formation of a regeneration mineralic zone on the tooth surface induced by aCa-polyP-MP was enhanced upon exposure to artificial saliva, as demonstrated by SRXTM. Energy dispersive X-ray analysis revealed an increase in the calcium/phosphorus atomic ratio of the enamel deposits to values characteristic for the particles during the treatment with polyP applied in the toothpaste, indicating a fusion of the particles with the tooth mineral.

SIGNIFICANCE

Our results suggest that toothpaste enriched with aCa-polyP-MP is a promising biomimetic material for accelerating enamel and dentin restoration.

Volume and/or Time of NaOCl Influences the Fracture Strength of Endodontically Treated Bovine Teeth

Abstract The aim of this study was to evaluate whether amplifying the volume and/or time of contact of NaOCl affects the fracture strength of endodontically treated bovine teeth. Four bovine incisors from 10 animals were allocated into 4 groups using a split-mouth design. Root canals were instrumented using a sequence of 4 manual stainless steel files and irrigated with a 5.25% alkalized NaOCl solution. The total volume and time of irrigation, per sample, varied among the groups as following: standard volume and time of contact - 15 mL/11.5 min; volume raise - 30 mL/11.5 min; time of contact raise - 15 mL/19 min; and volume and time of contact raise - 30 mL/19 min. Samples were subjected to a fracture resistance assay. At p=0.05, two-way ANOVA statistically scrutinized the results. Effect size of NaOCl time of contact and volume were also calculated (η2). The variation in time (p=0.000), volume of irrigation (p=0.000) and the combination of both (p=0.038) negatively influenced the fracture resistance. Standard volume and time of irrigation showed the highest fracture strength while isolated increase in volume or time reduced in 25% and 37%, respectively, the fracture resistance; the simultaneous increase in volume and time of irrigation promoted a reduction of 47%. Effect size of NaOCl time of contact was superior (0.746) than the volume (0.564). Raising the volume and/or time of a 5.25% alkalized NaOCl solution reduces the fracture resistance of endodontically treated bovine teeth.

Mechanical properties, microstructure and morphological properties of badger teeth

The structure, composition and mechanical properties of badger teeth were characterized. At the same time, the difference between badger teeth and human teeth were analyzed. The micrographs of samples showed that badger teeth contained two layers – that is, enamel and dentin. In contrast to hardness, it indicated that the enamel has a higher hardness than dentin, and both are higher than those of humans. Meanwhile, badger teeth have an obvious hardness difference in enamel and dentin. And the badger enamel has a significant anisotropy, the hardness and the elasticity modulus in the cross-section were higher than those in the axial section. Fourier-transform infrared spectroscopy tests show that both the enamel and dentin consisted of carbonate–hydroxylapatite and hydroxyapatite crystals. And X-ray powder diffraction tests show that both the crystal amounts and size of enamel tended to be higher than those of dentin. The water, organic matrix and biomineral of each species were determined by thermogravimetry. Dentin had higher contents of water, organic matrix and carbonate (CO3) than enamel. In the natural world, the mechanical properties of badger teeth are related to their microstructures and compositions, which potentially provide an inspiration for machinery and bionic designs.

The Tooth: Its Structure and Properties

This article provides a brief review of recent investigations concerning the structure and properties of the tooth. The last decade has brought a greater emphasis on the durability of the tooth, an improved understanding of the fatigue and fracture behavior of the principal tissues, and their importance to tooth failures. The primary contributions to tooth durability are discussed, including the process of placing a restoration, the impact of aging, and challenges posed by the oral environment. The significance of these findings to the dental community and their importance to the pursuit of lifelong oral health are highlighted.

Changes in deciduous and permanent dentinal tubules diameter after several conditioning protocols: In vitro study

Innovators conditioning protocols are emerged in permanent dentin, however for deciduous dentin the information is limited; the aim of this study was to evaluate in vitro diameter of deciduous and permanent dentinal tubules after several conditioning protocols. Eighty dentin samples were distributed in sixteen groups (n = 5 p/g) and dentin surface was conditioned as follow: G1D/G1P acid etching; G2D/G2P, self-etch adhesive; G3D/G3P, G4D/G4P, Er: YAG laser irradiation at 200 mJ-25.5 J/cm² and 300 mJ-38.2 J/cm² , at 10 Hz under water spray respectively; G5D/G5P, G6D/G6P, G7D/G7P, and G8D/G8P were irradiated under the same energy densities followed phosphoric acid or self-etch adhesive conditioning. The sample dentin of deciduous and permanent teeth was analyzed with scanning electron microscopy and tubule diameter was evaluated by Image Tools Scandium program. Data were subjected to one-way analysis ANOVA to compare among groups with a level of significance at p ≤ .05. For deciduous dentin, diameters were from 1.52 ± 0.32 µm in G3D to 3.88 ± 0.37 µm in G1D; narrowest and widest diameter, respectively (p < .000). While permanent dentin tubules exhibited diameters from 1.16 ± 0.16/1.19 ± 0.12 µm in G7P/G8P to 2.76 ± 0.28 µm in G6P; narrowest and widest diameter, respectively (p < .000). All dentin conditioning protocols produced more open dentin tubules (diameter size) in deciduous dentin than permanent, specific conditioning protocols are required for each tissue (deciduous or permanent dentin), since same protocol produced stronger effects on primary dentin, which is important for dental clinical success in children and adolescents.

Intradentinal antimicrobial action and filling quality promoted by ultrasonic agitation of epoxy resin-based sealer in endodontic obturation

The aim of this study was evaluate the influence of ultrasonic activation (UA) of AH Plus to improve canal and isthmus filing, and analyse the antimicrobial effect against Enterococcus faecalis within dentinal tubules.

Mineral trioxide aggregate enriched with iron disulfide nanostructures: an evaluation of their physical and biological properties

The purpose of this study was to characterize mineral trioxide aggregates (MTA) enriched with iron disulfide (FeS₂ ) nanostructures at different concentrations, and to investigate their storage modulus, radiopacity, setting time, pH, cytotoxicity, and antimicrobial activity. Iron disulfide nanostructures [with particle size of 0.357 ± 0.156 μm (mean ± SD)] at weight ratios of 0.2, 0.4, 0.6, 0.8, and 1.0 wt% were added to white MTA (wMTA). The radiopacity, rheological properties, setting time, and pH, as well as the cytotoxicity (assessed using the MTT assay) and antibacterial activity (assessed using the broth microdilution test) were determined for MTA/FeS₂ nanostructures. The nanostructures did not modify the radiopacity values of wMTA (~6 mm of aluminium); however, they reduced the setting time from 18.2 ± 3.20 min to 13.7 ± 1.8 min, and the storage modulus was indicative of a good stiffness. Whereas the wMTA/FeS₂ nanostructures did not induce cytotoxicity when in contact with human pulp cells (HPCs) and human gingival fibroblasts (HGFs), they showed bacteriostatic activity against Staphylococcus aureus, Escherichia coli, and Enterococcus faecalis. Adding FeS₂ nanostructures to MTA might be an option for improving the root canal sealing and antibacterial effects of wMTA in endodontic treatments.

Three-dimensional ultrastructural analysis of the interface between an implanted demineralised dentin matrix and the surrounding newly formed bone

Previous investigators have reported that transplanted demineralised dentin matrix (DDM) influences bone formation in vivo. However, the specific mechanism of how dentinal tubules contribute to bone formation has not been determined with regard to DDM transplantation therapy. In this study, we ultrastructurally investigated how DDM contacted the surrounding newly formed bone using a scanning electron microscopy (SEM) three-dimensional reconstruction method that is based on focused ion beam slicing and SEM (FIB/SEM). A pulverised and processed DDM derived from human teeth was implanted into rat calvarial bone defects, and a series of X-ray computed tomographic images were obtained over 12 weeks. Implants with surrounding new bone were removed and histologically examined using FIB/SEM. After obtaining objective block-face images, the target boundary face was reconstructed three-dimensionally. The osteocytes of the new bone tissue surrounding the DDM formed a network connected by their cellular processes and formed bone tissue. It is also interesting that the cellular processes of the osteocytes extended into the dentinal tubules, and that bone tissue with canaliculi had formed and filled the DDM surface.

Demineralized Dentin Matrix (DDM) As a Carrier for Recombinant Human Bone Morphogenetic Proteins (rhBMP-2)

A bone graft and bone graft substitute should have at least one of the following properties: it should be (1) osteogenic, (2) osteoinductive and/or (3) osteoconductive. In addition, bone graft substitutes should be biocompatible and bioresorbable as well as easy to use and cost effective. Autologous cancellous bone is the clinical gold standard in bone grafting procedures1, 4 and it has osteogenic, osteoinductive, and osteoconductive properties. Because of disadvantages associated with harvesting autologous bone graft material, such as requiring an additional operation and possible donor site morbidity, there is a need for an alternative in terms of enhancing the bone healing for the treatment of large bony defects. One possible option is a newly developed biomaterial, the demineralized dentin matrix (DDM). It is based on autogenous tooth dentin and is produced through demineralization. It is osteoconductive and osteoinductive due to the fact that dentin contains extracellular Type I collagen and various growth factors. Based on the demineralization process the factors stay available to the host environment. In 1965, Urist already showed the formation of ectopic bone after implanting DDM into muscle pouches in rodents. DDM is used for example in dental surgery in the treatment of extraction socket preservation and guided bone regenerations. It functions as a scaffold to support bone regeneration, but can also be used as a carrier for rhBMP-2. When DDM serves as a carrier, it combines the properties of the grafting material with those of the delivered substances. This chapter will present the experimental and clinical studies of DDM for rhBMP-2 carrier as well as alternatives of bone graft substitute.

Prevention of coronal discoloration induced by regenerative endodontic treatment in an ex vivo model

OBJECTIVES

The aim of this study was to assess the effect of sealing the pulp chamber walls with a dentin-bonding agent (DBA) on prevention of discoloration induced by regenerative endodontic procedures (REPs) in an ex vivo model.

MATERIALS AND METHODS

Ninety-six bovine incisors were prepared and randomly divided into two groups. In one group, the pulp chamber walls were sealed with DBA before placement of triple antibiotic paste (TAP) containing minocycline inside the root canals, but in the other group, DBA was not applied. After 4 weeks, the root canals were filled with human blood and each group was then randomly divided into four subgroups (n = 12) according to the endodontic cements placed over the blood clot (ProRoot MTA, OrthoMTA, RetroMTA, or Biodentine). The color changes (∆E) were measured at different steps. The data were analyzed using t test and two-way ANOVA.

RESULTS

The specimens in which dentinal walls of pulp chamber were sealed with DBA showed significantly less coronal discoloration at each step of regenerative treatment (p < 0.001). However, application of DBA did not completely prevent the clinically perceptible coronal color change. Sealing the blood clot with different endodontic cements did not result in significant difference in coronal discoloration (p > 0.05).

CONCLUSIONS

Sealing the pulp chamber walls before insertion of TAP decreased coronal discoloration following REP using different endodontic cements but did not prevent it.

CLINICAL RELEVANCE

Discoloration of teeth undergoing REPs is an unfavorable outcome. Considering the significant contribution of TAP containing minocycline to the coronal tooth discoloration even after sealing the pulp chamber walls, the revision of current guidelines in relation to the use of TAP with minocycline might need to be revised.

Evidence for programmed odontoblast process retraction after dentine exposure in the rat incisor

OBJECTIVE

To re-examine the morphology and potential functions of odontoblasts in intact rat incisors and after cavity preparation into dentine.

DESIGN

Intact incisors were fixed, decalcified, snap frozen and sectioned (10μm), before staining with rhodamine phalloidin or antibodies for cyto-skeletal proteins: vimentin and actin, ion transporter: NaK-ATPase, and dendritic cell marker: OX6. Samples with cavity were processed similarly and stained for actin and vimentin before comparing the lengths of odontoblast processes (OP) at baseline, 3h and 24h (n=5 for each group).

RESULTS

Actin was expressed through the full length of OP, while vimentin immunoreactivity was not uniform, with 4 distinct regions. OP showed morphological complexity with fine branches emanating within different regions of dentine. Novel actin-positive tree-like OP were identified within predentine which reduced in intensity and length toward the incisal portion of the tooth. Specimens with cavities showed time-dependant pulpal retraction of OP.

CONCLUSIONS

Differences in structural antibody expression suggest functional variations in OP within different regions of dentine. The role of actin positive OP in predentine is not known, but could be related to dentine deposition, cellular stability or sensing mechanisms. Cavity preparation into dentine was followed by programmed retraction of OP which could be controlled either mechanically by the spatial limitation of the OP within dentinal tubules or structurally by the presence of vimentin, in addition to actin, in the mid-dentine.

Poly(N-isopropylacrylamide)-hydroxyapatite nanocomposites as thermoresponsive filling materials on dentinal surface and tubules

HYPOTHESIS

Dental decay, asa consequence of exposure to acidic foods and drinks, represents one of the most important tooth pathologies. Recently, enamel and dentinal surface remineralization using hydroxyapatite nano- and microparticles has been proposed; however, commercial remineralizing toothpastes are quite expensive, mostly due to the high costs of hydroxyapatite. Hence, we propose a thermoresponsive hybrid nanocomposite material as filler for tooth defects. The use of thermoresponsive composite particles aims at filling exposed dentinal tubules in response to a change of temperature in the oral cavity. In addition, the presence of the organic matrix contributes to the occlusion of the dentinal tubules, therefore reducing the needed amount of hydroxyapatite.

EXPERIMENTS

Poly-N-isopropylacrylamide microgels containing different amounts of hydroxyapatite nanoparticles were prepared via radical polymerization in the presence of N-N'-methylenebisacrylamide as cross-linker followed by mechanical grinding. The nano- and microstructure of the hydrogels and their thermal behavior were studied via small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Defected teeth were treated with a dispersion of nanocomposite microparticles to simulate toothpaste action.

FINDINGS

The hydrogels maintain their structure and thermal responsiveness when loaded with an amount of hydroxyapatite nanoparticles up to 2.3%w/w. In addition, the lower critical solution temperature is not affected by the presence of the mineral particles. Exposed dentinal tubules on the surface of test tooth samples were successfully occluded after 15 cycles of treatment with a dispersion of nanocomposite microparticles alternated with washing steps.

Bond Capability of Universal Adhesive Systems to Dentin in Self-etch Mode after Short-term Storage and Cyclic Loading

Objective:

The aim was to evaluate, in vitro, the tensile bond strength to dentin of Scotchbond Universal (SU), All-Bond Universal (AU) and One Coat 7 Universal (OC7) adhesives applied in self-etch mode, after 24 h of storage and after 500,000 loading cycles, using Clearfil SE Bond (SE) as a control.

Materials and Methods:

The adhesives were applied on the dentin of bovine teeth, followed by the application of a composite resin. Thirty specimens were obtained for each adhesive. Half of the specimens were submitted to cyclic loading for 500,000 cycles. All specimens were submitted to a tensile bond strength test in a universal testing machine at a crosshead speed of 0.5 mm/minute.

Results:

According to two-way ANOVA and Tukey’s test (α=5%), the interaction between the adhesive and cyclic loading factors was significant (p=0.001). The means followed by the same letter represent no significant difference in the bond strength (MPa) after 24 h: OC7=7.86^A (±2.90), SU=6.78^AB (±2.03), AU=5.61^BC (±2.32), and SE=3.53^C (±1.89). After cyclic loading, SE, SU and AU maintained bond strength comparable to 24 h period. There was a significant decrease only for OC7.

Conclusion:

SU, AU and OC7 had bond strength to dentin comparable to that of SE. Only OC7 had decreased bond strength to dentin after cyclic loading.

Bovine Tooth Discoloration Induced by Endodontic Filling Materials for Primary Teeth

Objective. This study evaluated the discoloration potential of endodontic materials used in primary teeth. Material and Methods. Dentine-enamel blocks were prepared from 75 bovine teeth, assorted in five experimental groups (n = 15). The tested materials included an MTA-based material; zinc oxide and eugenol cement (ZOE); Vitapex; and calcium hydroxide thickened with zinc oxide (Calen + ZO). The color measurements were performed using a spectrophotometer at the following intervals: prior to (T0) and after placement of the filling (T1) and after 1 week (T2), 1 month (T3), 3 months (T4), 6 months (T5), and 9 months (T6). Data were submitted to ANOVA with repeated measures and Tukey's test. Results. The time had a significant effect on the color variation (ΔE₀₀^⁎) (p < 0.0001). The effect of the materials on the color variation (ΔE₀₀^⁎) was statistically significant (p = 0.004). Interactions between time and materials demonstrated a significant effect on the values (ΔE₀₀^⁎) (p < 0.0001). The ZOE cement showed the highest darkening effect (p = 0.018). Conclusion. The MTA-based material showed the smallest discoloration during the experimental time; however, it was similar to the other materials and to the control group. Zinc oxide and eugenol showed higher discoloration.

From molecules to macrostructures: recent development of bioinspired hard tissue repair

This review summarizes the bioinspired strategies for hard tissue repair, ranging from molecule-induced mineralization, to microscale assembly to macroscaffold fabrication.

Tissue dissolution and modifications in dentin composition by different sodium hypochlorite concentrations

OBJECTIVES

To determine the organic matter dissolution and changes in dentin chemical composition promoted by different concentrations of NaOCl over time.

MATERIAL AND METHODS

Fragments of bovine muscle tissue were weighed before and after 5, 10, and 15 min of immersion in the groups (n=10): G1- 0.9% saline solution; G2- 1% NaOCl; G3- 2.5% NaOCl; and G4- 5% NaOCl. Bovine dentin fragments were subjected to the same irrigants and absorption spectra were collected by Attenuated Total Reflectance of Fourier Transform Infrared Spectroscopy (ATR-FTIR) before and after 0,5, 1, 2, 3, 5, 8, and 10 min of immersion in the solutions. The ratios of the amide III/phosphate and carbonate/phosphate absorption bands were determined. The tissue dissolution and carbonate/phosphate ratios were submitted to the two-way analysis of variance (ANOVA) with Tukey's multiple-comparison test (α<0.05) and to the one-way analysis of variance with Tukey's (α<0.05). The amide III/phosphate ratio was analyzed by Friedman test (α<0.05) and the Kruskal-Wallis test with Dunn's post-hoc (α<0.05).

RESULTS

The increase in NaOCl concentration and contact time intensified the dissolution of organic matter and dentin collagen with reduction in the amide III/phosphate ratio. Significant differences between all groups (p<0.05) were observed in the dissolution of organic matter at 10 min and in the amide III/phosphate ratio between the saline solution and 5% NaOCl at 5 min. The carbonate/phosphate ratio decreased significantly in G2, G3, and G4 after 0,5 min of immersion (p<0.05), but more alterations did not occur in the subsequent periods (p>0.05). Intergroup differences were not observed in this ratio (p>0.05).

CONCLUSIONS

The increase in the exposure time and in the concentration of NaOCl solution lead to an increase in the tissue dissolution and dentin collagen deproteination. Furthermore, some carbonate ions are removed from the dentin inorganic phase by the NaOCl.

Effect of Gamma Radiation and Endodontic Treatment on Mechanical Properties of Human and Bovine Root Dentin

Abstract This study evaluated the effect of gamma radiation and endodontic treatment on the microhardness and flexural strength of human and bovine root dentin. Forty single-rooted human teeth and forty bovine incisor teeth were collected, cleaned and stored in distilled water at 4 °C. The human and bovine teeth were divided into 4 groups (n=10) resulting from the combination of two study factors: first, regarding the endodontic treatment in 2 levels: with or without endodontic treatment; and second, radiotherapy in two levels: with or without radiotherapy by 60 Gy of Co-60 gamma radiation fractioned into 2 Gy daily doses five days per week. Each tooth was longitudinally sectioned in two parts; one-half was used for the three-point bending test and the other for the Knoop hardness test (KHN). Data were analyzed by 3-way ANOVA and Tukey HSD test (α=0.05). No significant difference was found for flexural strength values. The human dentin had significantly higher KHN than the bovine. The endodontic treatment and radiotherapy resulted in significantly lower KHN irrespective of tooth origin. The results indicated that the radiotherapy had deleterious effects on the microhardness of human and bovine dentin and this effect is increased by the interaction with endodontic therapy. The endodontic treatment adds additional negative effect on the mechanical properties of radiated tooth dentin; the restorative protocols should be designed taking into account this effect.

Relined Fiberglass Post: Effect of Luting Length, Resin Cement, and Cyclic Loading on the Bond to Weakened Root Dentin

This study evaluated the effects of luting length of the post, the resin cement, and cyclic loading on pull-out bond strength of fiberglass posts relined with composite resin in weakened roots. The canals of 80 bovine incisors were endodontically treated and weakened with diamond burs. The teeth were randomly divided into eight groups (n=10) according to the luting procedures of the relined fiberglass post (RFP): In groups 1, 2, 3, and 4, the RFPs were luted with RelyX ARC, and in groups 5, 6, 7, and 8 they were luted with RelyX U200. In groups 1, 3, 5, and 7, the RFPs were luted at a length of 5 mm, and in groups 2, 4, 6, and 8 they were luted at a length of 10 mm. Specimens from groups 3, 4, 7, and 8 were submitted to cyclic loading. Specimens were subjected to a pull-out bond strength test in a universal testing machine. The results (MPa) were analyzed by three-way analysis of variance and the Tukey post hoc test (α=0.05). Six human upper anterior teeth were used to analyze the bond interface by confocal laser scanning microscopy (CLSM). The pull-out bond strength of RFPs luted with RelyX U200 was statistically higher than that of RelyX ARC. Cyclic loading influenced the bond strength only for the luting length of 5 mm. CLSM analysis revealed the formation of resin cement tags for both materials. Luting length is an important factor in retaining RFPs in weakened roots when they are subjected to cyclic loading, and RelyX U200 resulted in greater bond strengths to the root canal in comparison with RelyX ARC.

Influence of Different Etching Modes on Bond Strength to Enamel using Universal Adhesive Systems

INTRODUCTION

The adhesive systems and the techniques currently used are designed to provide a more effective adhesion with reduction of the protocol application. The objective of this study was to evaluate the bond strength of universal adhesive systems on enamel in different etching modes (self-etch and total etch).

MATERIALS AND METHODS

The mesial and distal halves of 52 bovine incisors, healthy, freshly extracted, were used and divided into seven experimental groups (n = 13). The enamel was treated in accordance with the following experimental conditions: FUE-Universal System - Futurabond U (VOCO) with etching; FUWE - Futurabond U (VOCO) without etching; SB-Total Etch System - Single Bond 2 (3M); SBUE-Universal System - Single Bond Universal (3M ESPE) with etching; SBUWE - Single Bond Universal (3M ESPE) without etching; CLE-Self-etch System - Clearfil SE Bond (Kuraray) was applied with etching; CLWE - Clearfil SE Bond (Kuraray) without etching. The specimens were made using the composite spectrum TPH (Dentsply) and stored in distilled water (37 ± 1°C) for 1 month. The microshear test was performed using the universal testing machine EMIC DL 2000 with the crosshead speed of 0.5 mm/minute. The bond strength values were analyzed using statistical tests (Kruskal-Wallis test and Mann-Whitney test) with Bonferroni correction.

RESULTS

There was no statistically significant difference between groups (p < 0.05), where FUE (36.83 ± 4.9 MPa) showed the highest bond strength values and SBUWE (18.40 ± 2.2 MPa) showed the lowest bond strength values. The analysis of adhesive interface revealed that most failures occurred between the interface composite resin and adhesive.

CONCLUSION

The universal adhesive system used in dental enamel varies according to the trademark, and the previous enamel etching for universal systems and the self-etch both induced greater bond strength values.

CLINICAL SIGNIFICANCE

Selective enamel etching prior to the application of a universal adhesive system is a relevant strategy for better performance bonding.

Study of invasion and colonization of E. faecalis in microtubes by a novel device

Enterococcus faecalis (E. faecalis) is a species that has frequently been isolated from root canal of patients suffering from persistent periodontitis. To a great degree, the resistance of E. faecalis to irrigating solutions and intracanal medicaments is due to its invasion into the dentinal tubules. In this study, we developed a device to observe the dynamic process of the bacterial invasion into microtubes. According to the diameter of the dentinal tubules and other microstructures in the root canals, we designed four different size microtubes with different lengths in this device. As expected, E. faecalis is able to steadily grow in this device and penetrate into the microtubes, and a continuous observation is achieved. We found that the depth and speed of bacterial penetration, the extent of colonization and the arrangement of the bacteria in the microtubes are strongly influenced by the size of the microtube. The length of the microtube also influences the speed and depth of the bacterial invasion. Bacteria in microtubes with a similar diameter to the real dentinal tubules showed a discontinuous distribution, which is consistent with the final bacterial distribution in the native dentinal tubules. Considering the device's advantages such as its ability to provide real-time observations, its ability to be modified as necessary, and its standardized operation, it has great potential to be widely used as a platform for the observation of the interaction of different bacteria during an invasion course and to test the efficacy of new antibacterial agents in dentistry.

Evaluation of the Diode laser (810nm,980nm) on dentin tubule diameter following internal bleaching

BACKGROUND

The aim of this study was to evaluate the effect of diode laser irradiation and bleaching materials on the dentinal tubule diameter after laser bleaching.

MATERIAL AND METHODS

The dentin discs of 40 extracted third molar were used in this experiment. Each disc surface was divided into two halves by grooving. Half of samples were laser bleached at different wavelengths with two different concentrations of hydrogen peroxide. Other half of each disc with no laser bleaching remained as a negative control. Dentin discs were assigned randomly into four groups (n=10) with following hydrogen peroxide and diode laser wavelength specifications; Group 1 (30% - 810 nm), group 2 (30% - 980 nm), group 3 (46% - 810 nm) and group 4 (46% - 980 nm). All specimens were sent for scanning electron microscopic (SEM) analysis in order to measure tubular diameter in laser treated and control halves. Data were analyzed by ANOVA and Tukey test (p<0.05).

RESULTS

A significant reduction in dentin tubule diameter was observed in groups 1, 2 and 4. There was no significant difference between groups 1 and 2 and between groups 3 and 4 after bleaching.

CONCLUSIONS

The SEM results showed that diode laser was able to reduce dentin tubule diameter and its effect on dentin was dependent on chemical action of bleaching material.

KEY WORDS

Laser, diode, dentin, tubule, diameter.

Tooth discoloration induced by a novel mineral trioxide aggregate-based root canal sealer

Objectives:

The aim of this study was to evaluate tooth discoloration caused by contact with a novel injectable mineral trioxide aggregate (MTA)-based root canal sealer (Endoseal; Maruchi, Wonju, Korea) compared with a widely used resin-based root canal sealer (AHplus; Dentsply De Trey, Konstanz, Germany) and conventional MTA (ProRoot; Dentsply, Tulsa, OK, USA).

Materials and Methods:

Forty standardized bovine tooth samples were instrumented and divided into three experimental groups and one control group (n = 10/group). Each material was inserted into the cavity, and all specimens were sealed with a self-adhesive resin. Based on CIE Lab system, brightness change (ΔL) and total color change (ΔE) of each specimen between baseline and 1, 2, 4, and 8 weeks were obtained.

Results:

At all time points, Endoseal showed no significant difference in ΔL and ΔE compared to AHplus and control group (P > 0.05), whereas the ProRoot group showed significantly higher ΔL and ΔE values than the Endoseal group at 2, 4, and 8 weeks (P < 0.05). Therefore, Endoseal showed less discoloration than conventional MTA and a similar color change to AHplus.

Conclusions:

Within the limitations of this study, our data indicate that the MTA-based sealer produces a similar amount of tooth discoloration as AHplus which is considered to be acceptable.