Dentin Layer Research Articles

Absence of melatonin during development impairs craniofacial and dental onset in rats.

Herein, we evaluated pinealectomy-induced melatonin absence to determine its effects on craniofacial and dental development in the offspring. Female Wistar rats in three groups, i.e., intact pregnant rats, pinealectomized pregnant rats (PINX), and pinealectomized pregnant rats subjected to oral melatonin replacement therapy, were crossed 30days after surgery. The heads of 7-day-old pups were harvested for cephalometric and histological analyses, and maxillae and incisors were collected for mRNA expression analysis. The PINX pups exhibited a reduction in neurocranial and facial parameters such as a decrease in alveolar bone area, incisor size and proliferation, and an increase in odontoblasts and the dentin layer. Based on incisor mRNA expression analysis, we found that Dmp1 expression was upregulated, whereas Col1a1 expression was downregulated. Maxillary mRNA expression revealed that Rankl expression was upregulated, whereas that of Opn and Osx was downregulated. Our results demonstrated that the absence of maternal melatonin during early life could affect dental and maxillary development in offspring, as well as delay odontogenesis and osteogenesis in maxillary tissues. Our findings suggest that disruptions or a lack of melatonin during pregnancy may cause changes in craniofacial and dental development, at least in animal experiments; however, in humans, these feedings are still poorly understood, and thus careful evaluations of melatonin levels in humans need to be investigated in craniofacial alterations.

Effect of superspeed sintering on translucency, opalescence, microstructure, and phase fraction of multilayered 4 mol% yttria-stabilized tetragonal zirconia polycrystal and 6 mol% yttria-stabilized partially stabilized zirconia ceramics

Statement of problemThe optical properties of recently developed multilayer zirconia have mainly been studied for the effects of conventional sintering and speed sintering but not as much for the effect of superspeed sintering. As superspeed sintering protocols typically require a higher sintering temperature and higher heating and cooling rates than speed- and conventional sintering protocols, the optical properties of superspeed sintered zirconia may be affected differently. PurposeThe purpose of this in vitro study was to investigate the effect of superspeed sintering on the optical properties, microstructure, and phase fraction of multilayered 4 mol% yttria-stabilized (4Y-) and 6 mol% yttria-stabilized (6Y-) zirconia. Material and methodsMultilayered 4Y- and 6Y-zirconia were sectioned. After conventional and superspeed sintering, the translucency parameter (TP), and opalescence parameter (OP) were measured with a spectrophotometer (n=10). To obtain the grain sizes from the field emission scanning electron microscopy (FE-SEM) images for each layer (n=2), more than 500 (6Y-zirconia) and 800 grains (4Y-zirconia) were measured by linear intercept methods. The phase fractions were obtained through X-ray diffraction (XRD) analysis by using the Rietveld method (n=1). The results were analyzed by 3-way ANOVA and post hoc Tukey honest significant difference tests (TP and OP) and by 3-way ANOVA and post hoc Scheffé tests (grain size) (α=.05). ResultsNo layers exhibited a significant difference in TP after superspeed sintering, except the dentin layer (DL) and transition layer 2 (T2) of 4Y- and 6Y-zirconia, respectively. The TP increased (P<.05) in DL for superspeed sintered 4Y-zirconia and decreased (P<.05) in T2 for the superspeed sintered 6Y-zirconia. However, the difference in TP by superspeed sintering was lower than the perceptibility thresholds of 50:50%. The OP decreased (P<.05) in the DL and T2 of 4Y-zirconia after superspeed sintering. For 6Y-zirconia, the OP decreased (P<.05) in all layers except for the transition layer 1 (T1) after superspeed sintering. However, the difference in OP values was minimal, with only a 1.1 difference observed for Zolid Gen-X (4Y) and a range of 1.22 to 1.62 for Katana UTML (6Y) when using superspeed sintering. No significant change was found in the grain size after superspeed sintering of either zirconia. Regardless of the sintering speed, the average grain size of the 6Y-zirconia (conventional: 2.09 to 2.21 μm; superspeed: 2.11 to 2.20 μm) was larger than that of the 4Y-zirconia (conventional: 0.50 to 0.52 μm; superspeed: 0.52 to 0.54 μm). Owing to superspeed sintering, the metastable tetragonal (T′) phase content increased while the tetragonal (T) phase decreased in 4Y-zirconia; in 6Y-zirconia, the cubic (C) phase content increased, while the T′-phase content decreased. ConclusionsSuperspeed sintering did not result in any clinically significant changes in the translucency and opalescence of 4Y- or 6Y-zirconia.

Microstructural features, physicο-mechanical properties, and wear behavior of dental translucent polychromic multilayer zirconia of hybrid composition prepared by milling technology.

The present study determined the mechanical properties and the wear behavior, as results of the micro(nano)structure, of the enamel, transition, and dentine layers, which comprise the polychromic multilayer zirconia materials of hybrid composition fabricated by milling technology. Prismatic blocks were fabricated from two commercial pre-sintered dental polychromic multilayer zirconia materials of hybrid composition, IPS e.max ZirCAD Prime (medium and high translucency, from the dentine to the incisal layer) and 3D Pro ML (translucency gradient, from the dentine to the incisal layer) by milling technique, and then, cut into 3 distinct parts to separate the enamel, transition, and dentine layers. The samples were sintered, thermally treated (similarly to the glazing procedure), and polished for characterization. Their microstructure, mechanical properties (determined by nanoindentation and microhardness), and wear behavior (evaluated by scratch test), were examined. The produced materials had a homogeneous and dense nanostructure, where the grain size decreased from the enamel to dentine layer. The mechanical properties decreased from the dentine to enamel layer. However, the three layers manifested similar dynamic friction coefficient. The differences in the above properties in the three layers negligibly influenced the wear behavior of the entire multilayer zirconia material. The properties of dental restorations produced from polychromic multilayer zirconia of hybrid composition by milling technology (i.e., strong, non-fragile, and esthetic materials), anticipate good performance in oral cavity.

Dentin defects caused by a Dspp−1 frameshift mutation are associated with the activation of autophagy

Dentin sialophosphoprotein (DSPP) is primarily expressed by differentiated odontoblasts (dentin-forming cells), and transiently expressed by presecretory ameloblasts (enamel-forming cells). Disease-causing DSPP mutations predominantly fall into two categories: 5’ mutations affecting targeting and trafficking, and 3’ − 1 frameshift mutations converting the repetitive, hydrophilic, acidic C-terminal domain into a hydrophobic one. We characterized the dental phenotypes and investigated the pathological mechanisms of DsppP19L and Dspp−1fs mice that replicate the two categories of human DSPP mutations. In DsppP19L mice, dentin is less mineralized but contains dentinal tubules. Enamel mineral density is reduced. Intracellular accumulation and ER retention of DSPP is observed in odontoblasts and ameloblasts. In Dspp−1fs mice, a thin layer of reparative dentin lacking dentinal tubules is deposited. Odontoblasts show severe pathosis, including intracellular accumulation and ER retention of DSPP, strong ubiquitin and autophagy activity, ER-phagy, and sporadic apoptosis. Ultrastructurally, odontoblasts show extensive autophagic vacuoles, some of which contain fragmented ER. Enamel formation is comparable to wild type. These findings distinguish molecular mechanisms underlying the dental phenotypes of DsppP19L and Dspp−1fs mice and support the recently revised Shields classification of dentinogenesis imperfecta caused by DSPP mutations in humans. The Dspp−1fs mice may be valuable for the study of autophagy and ER-phagy.

Multi-material polyjet printing for more lifelike endodontic practice teeth.

Root canal therapy is a highly technical procedure that has several unique challenges. Extracted human teeth have traditionally been used to train dental students which have come under increased scrutiny in recent years.1 Multiple published studies have demonstrated the value of three-dimensional (3D) printed teeth for dental education.2-5 A limitation common to these publications has been the inability to 3D print using multiple materials simultaneously.3 One strategy for creating a multi-material tooth was to create a tooth with a hollow pulp chamber and cavity preparation that was later filled with impression material and resin composite, respectively.2 Polyjet printing that allows for the use of six materials with different colors and physical properties was used to create endodontic practice teeth that had a white enamel layer, an A2 shaded dentin and root structure as well as a hollow, red pulp chamber full of a water-soluble, gelatinous support material (J5 Dentajet; Stratasys). A cone beam computed tomography (CBCT) radiograph of an extracted maxillary first premolar was made (75 μm, 90 kV, and 10.0 mA). The pulp chamber and canals were segmented from the reconstruction and Standard Tesselation Language files of the pulp chamber and tooth were exported. A 3D modeling program (Meshmixer, Autodesk) was used to further segment the file into an enamel layer, a dentin and root layer, and a hollow pulp chamber (Figure 1). These three files were brought into the printing software (GrabCAD; Stratasys) as an assembly which allows for the selection of different materials to be printed simultaneously in a single object. The enamel layer was printed using a white resin, DEN847 VeroDent PureWhite, an A2 shade resin for the root layer, MED620 VeroGlaze, the hollow pulp layer was printed using a red resin, RGD 852 VeroMagenta-V, and the hollow cavity of the pulp layer was printed with SUP711. Figure 2 shows the three layers assembled into a single item as well as disassembled into its three constituent parts. PolyJet printing was capable of fabricating endodontic practice teeth with multiple textures throughout the printed item. Figure 3 shows the printed teeth in cross-section and whole demonstrating the three solid materials and the gelatinous material filling the pulp chamber and canals. The canals can be filed with endodontic files and the gelatinous support material removed in a similar fashion to the pulp tissue. The initial expense of 3D printing technology can be high as identified by several authors.3 The use of the described technology in this article was able to produce 100 of the practice teeth in an overnight printing cycle for a per-tooth cost of less than half of one US dollar. With the ease of producing segmented files from a CBCT image of a tooth and the low cost of printing, students can be given greater access to standardized practice teeth for endodontic education. This same process has been applied by the author to design and create practice teeth with soft, excavatable carious lesions for a similarly low cost per tooth.

Polychromatic Composite and Resin Infiltration Restorations in the Esthetic Zone: A Five-year Clinical Report.

This case report describes the use of a combination of a polychromatic resin composite restoration and resin infiltration to achieve a satisfactory esthetic outcome that has lasted over five years. The patient's primary complaint was a desire to replace an existing stained resin composite on the facial and mesial surfaces of the maxillary left central incisor, and a white spot on the facial surface of the maxillary right central incisor. After clinical evaluation, the patient was offered either replacement of the restoration with a polychromatic restoration simulating a white spot, or a combined treatment with polychromatic composite and resin infiltration restorations, which was recommended. The patient selected the latter treatment. A putty matrix was fabricated, and a quick mock-up was done using various enamel and dentin shades of resin composite to determine proper material selection. The previous resin composite restoration was removed, and layers of new dentin, body, and enamel composite were placed. An interproximal matrix was used in order to provide ideal contour and contact. Finishing and polishing procedures were performed. The maxillary right central incisor was treated with resin infiltration in order to subdue the white spot on the facial surface. Polychromatic resin composite and resin infiltration restorations to replace a stained restoration and mask a white spot can achieve desired results in the esthetic zone and maintain them for five years.

Deciduous tooth biomarkers reveal atypical fetal inflammatory regulation in autism spectrum disorder

Atypical regulation of inflammation has been proposed in the etiology of autism spectrum disorder (ASD); however, measuring the temporal profile of fetal inflammation associated with future ASD diagnosis has not been possible. Here, we present a method to generate approximately daily profiles of prenatal and early childhood inflammation as measured by developmentally archived C-reactive protein (CRP) in incremental layers of deciduous tooth dentin. In our discovery population, a group of Swedish twins, we found heightened inflammation in the third trimester in children with future ASD diagnosis relative to controls (n= 66; 14 ASD cases; critical window: -90 to -50days before birth). In our replication study, in the US, we observed a similar increase in CRP in ASD cases during the third trimester (n= 47; 23 ASD cases; -128 to -21days before birth). Our results indicate that the third trimester is a critical period of atypical fetal inflammatory regulation in ASD.

ВЛИЯНИЕ ЭКОТОКСИКАНТОВ НА ЗАЧАТКИ ЗУБОВ ЛАБОРАТОРНЫХ ЖИВОТНЫХ

More than 75% of waste is toxic to the environment and humans. The aim of the study was to invistigate the toxic effect of ecotoxicants on the rudiments of the teeth of laboratory animals. The experiment was carried out on 30 white outbred rats weighing 180–250. All animals were divided into 2 groups: control (Group 1) and experimental (Group 2). During the experiment, all animals of the experimental groups were subjected to inhalation exposure to gasoline and formaldehyde vapors. Animals of the control group were supplied with normal air around the clock. The jaws of rats were decalcified for 30 days in a 10% formic acid solution in a 10% buffered formalin solution. After dehydration of the material in a battery of alcohols of increasing concentration (ethanol - concentration from 70% to 100% absolute) was poured into paraffin according to the generally accepted method. Using a rotary microtome brand LEICA RM 2145 (LEICA, Germany), histological sections 5–8 µm thick were made. The sections were stained with hematoxylin and eosin and picrofuchsin according to the Van Gieson method. Stained sections were examined and photographed using an AXIO IMAGER-Z1 light microscope (CARL ZEISS, Germany). In the control group of rats, a morphological picture of normal tooth histogenesis was observed at a late stage of development. In the structure of the tooth germs of rat pups of the 2nd group, a violation of the processes of histogenesis of most tooth germs and a change in the structure of the periodontal tissues were found. In the epithelium of the gingival mucosa, signs of dystrophic changes were determined, up to cell destruction; in the connective tissue plate of the gingival mucosa, in the periodontium and in the zone of formation of the alveolar bone, signs of inflammatory phenomena were determined in the form of cell infiltrations and circulatory disorders in the form of expansion of the lumens and blood filling of the vessels. In the area of the tooth germs, destructive changes in odontoblasts and enameloblasts were manifested, which was probably one of the reasons for the disruption of the processes of dentinogenesis and enamel formation, expressed in the heterogeneity of the formation of dentin and enamel layers. This confirms the toxic effect of ecotoxicants on the rudiments of the teeth of laboratory animals.

The Capability of Cocoa Pulp Juice (Theobroma cacao L.) on Crown Dentin Smear Layer Removal

Introduction: smear layer is a thin layer formed from tooth structure instrumentation which can prevent the restoration material bonds the tooth structure. Partial smear layer should be removed using dentin conditioner. One of dentin conditioners that is often used is 10% polyacrylic acid. The natural ingredient that is thought to be an alternative to dentin conditioner is cocoa pulp juice because it contains many acidic compounds. Methods: This research is a laboratory experimental study to determine the ability of 100% cocoa pulp juice (Theobroma cacao L.) to remove the crown dentin smear layer and compare it to 10% polyacrylic acid. Eight dental elements were prepared for class I cavities on the middle 1/3 of buccal surface to reach 3 mm in diameter and 2 mm in depth, enamel was prepared until 1 mm in depth of cavity left. The samples were irrigated with sterile aquades and dried. Furthermore, 4 samples were applied 10% polyacrylic acid and 4 samples used cocoa pulp juice, left for 20 seconds, irrigated, dried, and put in the oven for 2x24 hours. The samples were examined for their cavity cleanliness score using Scanning Electron Microscope (SEM) photo with 2000x of magnification. Result: both groups have the same score and statistical test shows that there is no significant difference between them. Conclusion: the 100% cocoa pulp juice was able to clean the smear layer of crown dentin and its ability equal to 10% polyacrylic acid.

Dentinal growth layer counts of captive, known-age, mother and daughter belugas (Delphinapterus leucas): confirming two growth layer groups (GLG/2) per year; consequences for recovery and management

Captive mother and daughter belugas (Delphinapterus leucas) of Hudson Bay origin died at the Vancouver Aquarium, in November 2016, aged29.25 and 21.25 years. Aurora, captured at age three and captive since 1990, gave birth to Qila in 1995. Age and histories being known, the focusof this study was on total number of tooth growth layer groups (GLGs) present; one (GLG/1) or two (GLG/2) per year. Teeth from Aurora indicatedtwo growth layers per year (GLG/2) during pre-capture and captivity. Qila deposited GLG/2 throughout her captive life. Clearly an assumption ofGLG/1 over GLG/2 doubles the duration of all life stages, including lifespan and age at attainment of sexual maturity. Arguments for GLG/1 havebeen based on inferences (e.g. from fallout of bomb radio carbon) from adults of unknown age and history, while those for GLG/2 are based on theprojection of direct observations from newborn, known-age young to 21 and 29 year-old adults from captivity. Use of radiocarbon is ingenious butsuch analyses have not been rigorously tested on marine mammals and the sensitivity to necessary correction factors not addressed. The newinformation from this study contradicts the GLG/1 hypothesis in that such an assumption would place Aurora’s birth at the 1958 peak fallout ofbomb radiocarbon (14C) yet she was born 29 years later in 1987, while the birth of her daughter Qila would pre-date the birth of her mother by 13years. This paper re-assesses three studies that assigned GLG/1 based ages to older adults using GLG/2 and concludes that their supposed birthswould also pre-date the realistic births of their own mothers plus as many as two previous generations. Proponents of GLG/1 have overestimatedthe ages of previous calves-at-capture by 200–800%. Given the growth pattern in teeth of these 21 year and 29 year old female belugas, withincreasingly finer dentine GLGs deposited as the pulp tissue diminishes, it is difficult to envisage the GLG/1 tooth structures of those assumed tobe 60–80 years; none are as yet available. An holistic analysis using direct observations and cross-referenced parameters does not substantiateGLG/1which implies a 40% reduction of the intrinsic rate of natural increase; as a consequence, overestimating historical population size as wellas recovery target population and the predicted date of recovery in Cumberland Sound.

Potentialities of photoactivated disinfection in dentistry

Infection control is an essential part of dental practice. Oral antiseptics should be highly effective against the most common oral pathogens without causing microbial resistance, biocompatible with the human tissues with no interaction with fillings materials. Photoactivated disinfection (PAD) is based on activation of photosensitizers - specific substances releasing active oxygen forms after absorption of the light. The active oxygen forms destroy bacterial cell structures without affecting human cells. The overwhelming majority of Russian and international researchers have reported high effectiveness of PAD in periodontics, implantology and endodontics, whereas the use of PAD in caries treatment and prevention is not so fully understood yet. Earlier studies have demonstrated high sensitivity of cariogenic bacteria to PAD, suggesting it as an additional minimally invasive caries therapy improving treatment effectiveness. PAD spares dental tissues without reduction in the effectiveness of disinfection. It is particularly important in treatment of deep carious lesions and disinfection of thin dentine layer near the pulp. Effectiveness of PAD in caries treatment has been demonstrated for both permanent and deciduous dentition. PAD doesn't affect bond strength to fillings, improves plasticity of dental pulp and dental hard tissues mineralization in children. Effective control of a wide range of bacteria without causing resistance makes PAD a prospective method of treatment and prevention of caries.

The Effect of Varying Dentin Chroma and Enamel Thickness on the Color of A2 Double-layered Resin Composite.

To evaluate chroma (C*) and overall color of double-layered (DL) resin composite (RC) restorations with various dentin shades and enamel thicknesses. Enamel specimens were fabricated using custom-made molds to replicate VITA shade tabs with variant enamel thicknesses (0.5, 0.7, and 1.0 mm) (n=7) from two RC: Clearfil-Majesty (CM) shade (A2), and Vit-l-escence (VL), shade (pearl-neutral). Dentin specimens (shades A1, A2, and A3) were fabricated using custom molds corresponding to the enamel molds. Each enamel specimen was paired with three different dentin specimens. L*a*b* parameters were measured with VITA Easyshade-V. Color difference between DL specimens and the A2 VITA shade tab were calculated with the CIEDE2000 formula. Relationships among enamel thickness, ΔE00, C* of dentin layer, C* of DL, and change in chroma were assessed by Spearman rank correlations. ΔE00 was compared among groups using one-way analysis of variance with Tukey post-hoc adjustment for all possible pairwise group comparisons (experiment-wise α=0.05). There was no statistical difference among C* of DL specimens (p=0.65, 0.53) for CM and VL, respectively. Combinations of enamel thickness/ dentin shade had a significant difference in ΔE00 (p>0.05). No significant correlation was observed among enamel thickness and C* of dentin, and C* of the DL (p>0.05). Significant correlations were observed between ΔE00 of the VL DL and C* DL (r=-0.8, p<0.001); and ΔE00 of CM DL and enamel thickness (r=0.5, p<0.001). Enamel thickness did not affect C* of the dentin layer. Unlike VL RC, variations in dentin shades with CM produced a closer match to the A2 shade tab. Enamel is recommended to be 0.7 mm or less.

The Efficacy and Durability of Three Desensitising Agents for Management of Hypersensitive Teeth: An In Vitro Study

Introduction: Dentine hypersensitivity (DH) is a brief and acute pain produced when dentine is subjected to various stimuli. The treatment for DH has been classified by mode of delivery as at- home and in-office therapy. It was proven that desensitising agents have the capacity for occluding dentinal tubules. The purpose of this study was to evaluate the efficacy and durability of desensitising agents for management of DH. Methods: Twelve non-carious extracted human permanent premolars were sectioned into dentine layer. The dentine disc specimens were divided into four groups. Each group were applied with 8% arginine-calcium toothpaste, 0.24% sodium fluoride toothpaste, 5% potassium nitrate toothpaste and distilled water respectively. Scanning Electron Microscope (SEM) is used to evaluate the magnitude changes of dentinal tubules post treatment with the desensitising toothpastes in terms of the efficacy and durability at day one, week one and week three after application. The data will be analyzed by analysis of variance (ANOVA) using the Statistical Package for the Social Sciences (SPSS) software (version 19.0). Results: All toothpastes demonstrated significant dentinal tubule occlusions. However, 8% arginine-calcium toothpaste showed the greatest percentage of occlusion at day one followed by potassium nitrate toothpaste and sodium fluoride toothpaste. After three weeks, 8% arginine-calcium toothpaste remained the greatest percentage of dentinal tubules occlusion Conclusion: The result revealed that 8% arginine-calcium toothpaste is the most efficient and has longer durability among the other toothpaste. Therefore, with this finding it could help the patient for selection of desensitising toothpaste in managing the DH.

Microtensile bond strength of resin composite to dentin using different adhesive systems and directions of electric current

Thisstudy aimed to evaluate the effect of the electric current direction application on the resin composite-dentin bond strength using three adhesive systems. Human molar teeth were distributed according to the adhesive system (two-step self-etch - Clearfil SE Bond, Kuraray [CSE]; one-step self-etch - Single Bond Universal, 3M ESPE [SBU]; and two-step etch-and-rinse - Adper Single Bond 2, 3M ESPE [SB2]), electric current direction (without electric current - control, direct and reverse electric currents - 35µA), and storage time (24h - immediate and 6 months). Resin composite blocks (Filtek Z350XT, 3M ESPE) were bonded to dentin. The teeth/resin composites specimens were stored in distilled water at 37ºC for 24 hours and 6 months for the microtensile bond strength (µTBS) test (n = 10; ~12 sticks for each tooth). Failure patterns were analyzed on a stereomicroscope and classified as cohesive-dentin, cohesive-resin, adhesive or mixed. Adhesive penetration into dentin and hybrid layer formation were evaluated in a scanning electron microscope (n = 6). Data were submitted to a three-way ANOVA followed by Tukey's post hoc test (α = 0.05). There are no differences in µTBS when the adhesive systems were applied under direct and reverse electric currents, but both electric currents increased the µTBS for all adhesive systems. SBU showed the lowest µTBS values for control groups in both storage times and direct electric current in 6 months of storage. The adhesive failure pattern was more frequently observed in all groups. The electric current formed long resin tags for all adhesive systems. Storage for 6 months did not significantly decrease µTBS values. Both directions of electric current (positive and negative charges) at 35µA can increase the µTBS of the adhesive systems tested to dentin.

Effect of dentin pretreatment with dialdehyde carboxymethyl cellulose on dentin properties and long-term adhesion

ObjectivesThe aim of this in vitro study was to evaluate the effect of pretreatment of dentin with different concentrations (0, 1%, 2.5% or 5%) of dialdehyde carboxymethyl cellulose (DCMC) on the biodegradation rates, mechanical properties of the dentin and long-term dentin bonding (μTBS and nanoleakage). MethodsIn all tests, specimens were designated to 4 groups: Control (without DCMC), DCMC1%, DCMC2.5% and DCMC5%. For the biodegradation evaluation, dentin beams (n = 5) were prepared (2x2x6mm), dehydrated, and demineralized. After, the beams were immersed in test solutions for 24h. After, the biodegradation rate was quantified by hydroxyproline assay. The nano-indentation technique was used to measure nanohardness and elastic modulus. 2 mm thick dentin slices (n = 5) were prepared. After dentin etching, the pretreatment solution (according to groups) was applied for 1 min, followed by drying with absorbent paper. After bonding procedure and restoration, the specimens were polished and the nanohardness and modulus of elasticity were evaluated. For μTBS, the dentin of forty-eight teeth (n = 6) was etched and pretreated for 1 min according to groups, the adhesive system was applied, and resin composite buildups were constructed incrementally. Beams (1 mm2) were obtained and μTBS was evaluated after 24h and 1 year of water storage. 2 beams of each tooth were separated for nanoleakage tests (after 24h and 1 year of water storage). ResultsControl and DCMC1% presented higher biodegradation rates when compared to DCMC2.5% and DCMC5%. The nanohardness of dentin and hybrid layer was higher for DCMC1%, DCMC2.5% and DCMC5% when compared to Control. DCMC2.5 and DCMC5% increased the modulus of elasticity of hybrid layer, when compared to Control and DCMC1%. DCMC1%, DCMC2.5% and DCMC5% showed lower immediate μTBS than Control, but they showed no decrease in μTBS and nanoleakage after 1 year of storage. Control showed significant decrease of μTBS and significant increase of nanoleakage after aging. ConclusionsThe use of DCMC as a dentin pretreatment decreased the biodegradation rate, improved the mechanical properties of dentin, and preserved the long-term bond strength.

INVESTIGATION OF FRACTURE-RESISTANCE OF HUMAN TEETH AT THE DENTIN–ENAMEL JUNCTION USING THE J-INTEGRAL CALCULATION OF FINITE ELEMENT ANALYSIS

Most human teeth have an exposed surface layer of calcified enamel, which is harder than the inner layer of dentin. The interface between the enamel and dentin is called the dentin–enamel junction (DEJ), which ensures that teeth do not collapse and fall off. The purpose of this study was to use finite element analysis software through the [Formula: see text]-integral method and the extended finite element method (XFEM) to simulate three models of DEJ structures: (i) wavy DEJ with no thickness, (ii) rectangle DEJ with a thickness of 0.3[Formula: see text]mm, and (iii) wavy DEJ with a thickness of 0.3[Formula: see text]mm. This paper demonstrates that the layered structure of human teeth plays a positive role in enhancing the fracture strength and preventing the crack from spreading to the depths of teeth. At the same time, we also justify of the scalloped structure and concave orientation of the DEJ interface. The residual stresses in DEJ and its adjacent dentin region are also an important factor of tooth resistance to crack propagation. In addition, the configuration of the DEJ interface and residual stresses in DEJ and dentin areas are further justified by means of XFEM method. The findings in this study provide potential inspiration for the biomimetic design toward strengthening the dentin and dentin-like materials.

The Equine Dental Pulp: Histomorphometric Analysis of the Equine Dental Pulp in Incisors and Cheek Teeth

To maintain a healthy and functional status, equine hypsodont teeth have to produce lifelong large amounts of subocclusal dentin to prevent occlusal pulp exposure, which is caused by occlusal wear. To examine the cyto- and histological components that guarantee the lifelong high productivity of equine pulp, a limited number of ten incisors and ten cheek teeth from seven adult horses (aged 5 to 24 years) and five foals were sampled for preliminary histomorphometric and histomorphological evaluations. Independently of age, the equine dental pulp featured constant layers of predentin and odontoblastic cells, as well as soft connective tissue, composed of a cellular fibrous matrix, in which blood vessels and nerve fibers were embedded. As a result of the progressive deposition of newly formed dentin, the layer of dentin became thicker with age, and the size of the pulp chamber decreased. In contrast to the brachydont teeth, the morphological characteristics of the odontoblastic layer and the width of the predentin layer did not change with age. Therefore, it is assumed that the equine pulp tissue retained their juvenile status, which explains its unchanged ability to produce high amounts of subocclusal dentin. These preliminary, but clinically significant, findings are worthy of further investigation in order to identify strategies for equine-specific endodontic therapies.

Comparison of the Effects of TheraCal LC and Mineral Trioxide Aggregate on Direct Pulp Capping (DPC) Based on Histological Findings.

Background: Direct pulp capping can conserve its vitality by placing materials that promote dentin bridge (DB) formation at the exposure site. This study aimed to determine whether TheraCal LC could produce a layer of reparative dentin. It also compared the histological differences between treatment with mineral trioxide aggregate (MTA) and TheraCal LC.Material and methods: A sample of 20 maxillary and mandibular premolars, which had previously been indicated for extraction in orthodontic therapy, was taken from 10 patients and randomly divided into two halves, a TheraCal LC, and an MTA group. Pulpal exposure was achieved by similar class I preparations, which were restored with a resin-modified glass-ionomer and extracted after ten weeks, noting that these interventions have been performed on live teeth in the oral cavities. The newly formed dentin bridge thickness, the inflammation degree within the pulp tissue, and odontoblast function were thoroughly examined histologically and compared between the two groups using the Mann-Whitney test and an analysis software SPSS (statistical package for the social sciences, v.26, IBM, New York, N, USA), at a significance level of a=0.05.Results: Dentin bridge composition in the TheraCal group had 80% effective tubules and 20% defective tubules, while in the MTA group, the proportions were 90% and 10%, respectively. Dentin bridge thickness in the TheraCal group was greater than 0.25 mm in 60%, and 0.1-0.25 mm in 40% of the sample compared to the MTA group, which had 70% greater than 0.25 mm, and 30% between 0.1 and 0.25 mm in dentin bridge thickness. Statistically, there was no significant difference between both groups (P=0.739).Conclusion: Statistically insignificant differences in dentin bridge composition and thickness produced by both TheraCal and MTA materials render them similar in their effectiveness in treating pulp exposures through pulp capping.

Stability of Cantilever Fixed Dental Prostheses on Zirconia Implants.

Background: The objective was to determine the optimal connector size and position within zirconia disks for implant-supported cantilever fixed dental prostheses (ICFDP). Methods: Two-unit ICFDPs (n = 60) were designed for the premolar region with connector sizes of either 9 or 12 mm2 and positioned in the enamel or dentin layer of two different types of zirconia disks. The restorations were milled and cemented onto zirconia implants. After simulated chewing for 1.2 Mio cycles, the fracture load was measured and fractures were analyzed. Results: No fractures of ICFDPs or along the implants were detected after simulated aging. The mean fracture load values were significantly higher for a connector size of 9 mm2 (951 N) compared with 12 mm2 (638 N). For the zirconia material with a higher biaxial flexural strength, the fracture load values were increased from 751 to 838 N, but more implant fractures occurred. The position within the zirconia disk did not influence the fracture load. Conclusions: A connector size of 9 mm2 and a zirconia material with a lower strength should be considered when designing ICFDPS on zirconia implants to reduce the risk of fractures along the intraosseous implant portion.

A digital workflow for layering composite resin restorations by using 3-dimensionally printed templates to replicate the contralateral tooth accurately and rapidly

This article described a digital workflow for layering composite resin restorations by using a digital software program and 3-dimensionally printed templates. To mimic the appearance of the natural tooth, the computer-aided design was used to copy the shape of the contralateral tooth. Three-dimensionally printed templates to replicate the contralateral tooth accurately and rapidly can help dentists build different layers of dentin and enamel composite resin, achieving layered esthetic outcomes. This workflow provides an efficient and accurate procedure, reduces chairside time, and simplifies the application of the technically sensitive composite resin layering technique.