Enamel Dentin Research Articles

Hardness and indentation modulus of human enamel and dentin

Information on mechanical properties of human enamel and dentin and effect of load on their deformation and damage tolerance is very important in the development of successful dental materials. In this study, the hardness, indentation modulus and deformation characteristics of tooth have been investigated across the lingual–buccal enamel and dentin cross‐section by instrumented indentation up to 1500‐nm indentation depth. We realized and examined the distribution of hardness and modulus at different areas of enamel and dentin with the aim to understand deformation behaviour at these different locations. Scanning electron microscopy was used for the microstructure characterization of the enamel and dentin and their deformation behaviour. Raman spectroscopy analyses were carried out for determination of the enamel and dentin composition as well. The average values of hardness and modulus for enamel in the occlusal area are 5.35 ± 0.19 and 98.1 ± 1.5 GPa, in the inner area 3.68 ± 0.5 and 81.8 ± 5 GPa and in the area close to the dentin–enamel junction 2.83 ± 0.27 and 71.4 ± 4.1 GPa, respectively. The average values of hardness and modulus of dentin in the area close to the dentin–enamel junction are 0.71 ± 0.05 and 21.27 ± 0.76 GPa and in the inner area 0.65 ± 0.06 and 19.79 ± 0.93 GPa, respectively. The effect of the indentation location on deformation and mechanical properties was clarified.

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.

A human lower third molar from the Acheulean site of Cueva del Ángel (Lucena, Córdoba, Spain)

AbstractObjectivesTo present a new dental specimen that will provide additional evidence for a better understanding of early European Upper Pleistocene hominin morphological variability.Materials and MethodsWe described the morphology of this human right lower third molar at both the outer enamel surface and the enamel–dentine junction by means of micro‐computed tomography. In order to better understand hominin diversity, our morphological and metrical results were compared with those of other hominins obtained from published research. We provide a direct aspartic acid racemization dating of the molar.ResultsThe direct dating (104.3 ka) situates the molar within the Marine isotopic stage 5d. The crown dimensions are comparable to those of the Sima de los Huesos sample and modern humans. The combination of a continuous middle trigonid crest and a well‐developed anterior fovea lies within the range of morphological variation reported for Neanderthal lower molars. The distal portion of the molar has a prominent protostylid.DiscussionCrown and root morphology of this molar fits within the Neanderthal morphological pattern. However, both its dimensions and the absence of a hypoconulid tend to position this specimen away from contemporaneous Neanderthals and rather relate it more closely to some Middle Pleistocene populations.ConclusionsA new dental specimen is added to the Iberian Peninsula fossil record from the Marine isotopic stage 5, attesting to some degree of dental variability in the early Upper Pleistocene.

Crystallographic and Physicochemical Analysis of Bovine and Human Teeth Using X-ray Diffraction and Solid-State Nuclear Magnetic Resonance.

Dental research often uses bovine teeth as a substitute for human teeth. The aim of this study was to evaluate differences in the crystalline nanostructures of enamel and dentin between bovine and human teeth, using X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (NMR). The crystallite size (crystallinity) and microstrains were analyzed using XRD with the Rietveld refinement technique and the Halder-Wagner method. The 31P and 1H NMR chemical environments were analyzed by two-dimensional (2D) 1H-31P heteronuclear-correlation (HETCOR) magic-angle spinning (MAS) NMR spectroscopy. Enamel had a greater crystallite size and fewer microstrains than dentin for both bovine and human teeth. When compared between the species, the bovine apatite had a smaller crystallite size with more microstrains than the human apatite for both dentin and enamel. The 2D HETCOR spectra demonstrated that a water-rich layer and inorganic HPO4- ions were abundant in dentin; meanwhile, the hydroxyl group in the lattice site was more dominant in enamel. A greater intensity of the hydroxyl group was detected in human than in bovine for both dentin and enamel. For 31P projections, bovine dentin and bovine enamel have wider linewidths than human dentin and human enamel, respectively. There are differences in the crystallite profile between human and bovine. The results of dental research should be interpreted with caution when bovine teeth are substituted for human teeth.

Nanoindentation and Atomic Force Microscopy Derived Mechanical and Microgeometrical Properties of Tooth Root Cementum

In the present research, nanoindentation, atomic-force microscopy and optical microscopy were used to study the mechanical and microgeometrical parameters of tooth tissues. A nanoindentation test unit equipped with Berkovich indenter was used to determine the values of the reduced Young’s modulus and indentation hardness and both nanoindentation and atomic force microscopy using a diamond probe on a silicon cantilever were used to study microgeometrical parameters of human tooth root cementum. Three areas of cementum were studied: the cervical region near the dentine–enamel junction, the second third of the tooth root, and the apex of the tooth root. The interpretation of the results was carried out using the Oliver–Pharr method. It was established, that the mechanical properties of cementum increase from the cervical region to the central part of the root, then decrease again towards the apex of the tooth root. On the contrary, the microgeometrical characteristics of cementum practically do not demonstrate any change in the same direction. A decrease in the roughness parameters in the direction from cellular cementum to dentine was observed. Additionally, a decrease in the reduced Young’s modulus and indentation hardness of dentine in the cervical area compared to dentine in the crown part of the tooth was found using nanoindentation. The investigation of the dentine–cementum junction with high resolution revealed the interspaced collagen fiber bridges and epithelial rests of Malassez, whose sizes were studied. The parameters of the topographic features of the cementum in the vicinity of the lacunae of cementocytes were also established.

Multidisciplinary management of an enamel–dentine crown fracture with insufficient inter-occlusal restorative space: A case report

Dental trauma occurs commonly in young patients, can be complex to treat and can have negative psychological and social impacts on patients' lives. This case report outlines a multidisciplinary team approach to restoration of a traumatized anterior tooth with delayed presentation, insufficient inter-occlusal space for restoration and history of multiple failed restorations. This case report demonstrates orthodontic and restorative techniques for the management of insufficient inter-occlusal space and the indirect restoration of a traumatized anterior tooth. CPD/Clinical Relevance: A multidisciplinary team approach can be used to reorganize a patients' occlusion to provide the inter-occlusal space required to provide restorations.

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.

Enamel and dentin in Enamel renal syndrome: A confocal Raman microscopy view.

Enamel Renal Syndrome (ERS) is a rare genetic disorder caused by biallelic mutations in Family with sequence similarity 20A (FAM20A) gene encoding the secretory pathway pseudokinase FAM20A. ERS is characterized by hypoplastic amelogenesis imperfecta (AI), impaired tooth eruption, intra-pulpal calcifications, gingival fibromatosis and nephrocalcinosis of various severity. Previous studies showed that the hypoplastic enamel was also hypomineralized but its chemical composition has not been extensively studied. Furthermore it is currently unclear whether dentinal defects are associated with AI in ERS patients. The objective of the study was to provide a structural and chemical analysis of enamel, dentin and dentin enamel junction (DEJ) in ERS patients carrying four, previously reported, distinct mutations in FAM20A. Chemical cartography obtained with Raman microscopy showed that compared to control samples, ERS enamel composition was severely altered and a cementum-like structure was observed in some cases. Chemical composition of peripulpal dentin was also affected and usual gradient of phosphate intensity, shown in DEJ profile, was absent in ERS samples. DEJ and dentinal anomalies were further confirmed by scanning electron microscopy analysis. In conclusion, our study shows that enamel formation is severely compromised in ERS patients and provides evidence that dentinal defects are an additional feature of the ERS dental phenotype.

CALCIFYING ODONTOGENIC CYST ASSOCIATED WITH COMPLEX ODONTOMA: A CASE REPORT

A 29-year-old man presented an asymptomatic growth in the anterior maxilla, causing a normochromic, hard swelling in the left upper alveolar mucosa, measuring 20 × 20 mm, for an unknown period. Cone beam computed tomography revealed a well-circumscribed unilocular mixed lesion, with a large central hyperintense component, causing disruption of the vestibular bone cortex. An incisional biopsy was performed, and the histopathologic diagnosis was a calcifying odontogenic cyst. Surgical excision was conducted. Gross examination showed a brown-colored fibrous and hard fragment measuring about 27 × 19 × 18 mm. On microscopic evaluation, a cystic capsule lined by nonkeratinized epithelium with polyhedral cells, basal layer cells with hyperchromatic and polarized nuclei, and numerous ghost cells were observed associated with multiple irregular deposits of dentin and inorganic enamel. The final diagnosis was calcifying odontogenic cyst associated with complex odontoma. The patient was under clinical follow-up for 2 years and no recurrence was observed.

Morphological Study of Dental Structure in Dentinogenesis Imperfecta Type I with Scanning Electron Microscopy

Background: Dentinogenesis imperfecta type I (DGI-I) is a hereditary alteration of dentin associated with osteogenesis imperfecta (OI). Aim: To describe and study the morphological characteristics of DGI-I with scanning electron microscopy (SEM). Material and methods: Twenty-five teeth from 17 individuals diagnosed with OI and 30 control samples were studied with SEM at the level of the enamel, dentin–enamel junction (DEJ) and four levels of the dentin, studying its relationship with clinical–radiographic alterations. The variables were analysed using Fisher’s exact test, with a confidence level of 95% and asymptotic significance. Results: OI teeth showed alterations in the prismatic structure in 56%, interruption of the union in the enamel and dentin in 64% and alterations in the tubular structure in all of the cases. There is a relationship between the severity of OI and the morphological alteration of the dentin in the superficial (p = 0.019) and pulpar dentin (p 0.004) regions. Conclusions: Morphological alterations of the tooth structure are found in OI samples in the enamel, DEJ and dentin in all teeth regardless of the presence of clinical–radiographic alterations. Dentin structural anomalies and clinical dental alterations were observed more frequently in samples from subjects with a more severe phenotype of OI.

Detection limit of electron spin resonance for Japanese deciduous tooth enamel and density separation method for enamel-dentine separation.

Electron spin resonance (ESR) dosimetry is one of the most powerful tools for radiation dose reconstruction. The detection limit of this technique using human teeth is reported to be 56 mGy or 67 mGy; however, the absorbed dose of Fukushima residents after the Fukushima Daiichi Nuclear Power Plant (FNPP) accident was estimated to be lower than this detection limit. Our aim is to assess the absorbed radiation dose of children in Fukushima Prefecture after the accident; therefore, it is important to estimate the detection limit for their teeth. The detection limit for enamel of deciduous teeth of Japanese children separated by the mechanical method is estimated to be 115.0 mGy. The density separation method can effectively separate enamel from third molars of Japanese people. As we have collected thousands of teeth from children in Fukushima, the present technique may be useful to examine their external absorbed dose after the FNPP accident.

Modifications of the Dental Hard Tissues in the Cervical Area of Occlusally Overloaded Teeth Identified Using Optical Coherence Tomography.

Background and objectives: Occlusal overloads produce a series of manifestations in teeth, especially attrition and non-carious cervical lesions (NCCL). Optical Coherence Tomography (OCT) can highlight and evaluate tooth lesions. The aim of this study was to examine the changes of dental hard tissues in the cervical area because of occlusal overload by macroscopic examination and using in vitro Swept Source OCT examination. Materials and Methods: The study was performed on 21 extracted teeth with occlusal trauma. After macroscopic and OCT examination, the 2D OCT images were transformed into 3D images using ImageJ software. Statistical analysis of macroscopic and OCT images was performed with Statistical Package for Social Sciences. Results: On 21 teeth, 88 cervical lesions (cracks) were identified. Upper premolars with an occlusal Smith and Knight tooth wear score of 2 had the most NCCL. Statistical analysis revealed significant differences in the median widths of cervical lesions between teeth with score 1 and score 3. Additionally, we obtained statistically significant differences in median widths between the buccal and oral surfaces. Conclusions: These cracks can be considered precursors of NCCL. NCCL can be located on dental surfaces in the cervical area other than the buccal one. A 3D reconstruction of OCT images emphasized that cracks are located especially at enamel level, evolving towards the enamel–dentin junction, with multiple ramifications.

Evaluation of the Effect of Anti-COVID-19 Mouthwashes on Shear Bond Strength of Composite Resin Restorations to Dentin and Enamel: An “In Vitro Study”

Objectives Given the high prevalence of the coronavirus and the high risk of virus transfer to dentists, the use of mouthwashes, which can potentially eliminate this virus, is suggested before dental procedures. Since these mouthwashes may affect the bond strength of composite resin restorations to teeth, this study was conducted to investigate the effect of recommended mouthwashes on the shear bond strength of composite resin restorations to dentin and enamel in selective etch and rinse and two-step self-etch bonding systems. Methods Five groups of posterior teeth (n = 15) were selected for five groups of cetylpyridinium chloride 0.07%, povidone-iodine 1%, hydrogen peroxide 1%, and chlorhexidine 0.2% as mouthwash and distilled water as the control group. The buccal enamel and lingual dentin of each tooth were rinsed after immersion in a mouthwash. After 20 seconds of enamel acid-etching and 15 seconds of dentin priming, they were impregnated with an adhesive, and composite cylinders were placed on the dentin and enamel surfaces of the tooth. The shear bond strength test was performed after 24 hours, and results were analyzed by ANOVA and paired t-test (α = 0.05). Results The mean shear bond strength of enamel to composite was significantly (p < 0.05) higher than that of dentin to composite in each study group, but no significant difference was found between the mean shear bond strength of composite to enamel (p = 0.199) and to dentin (p = 0.335) after the use of mouthwashes and that of the control group. Conclusion The use of mouthwashes used in this study did not have negative effects on the shear bond strength of composite to enamel and dentin.

The Critical Role of MMP13 in Regulating Tooth Development and Reactionary Dentinogenesis Repair Through the Wnt Signaling Pathway.

Matrix-metalloproteinase-13 (MMP13) is important for bone formation and remodeling; however, its role in tooth development remains unknown. To investigate this, MMP13-knockout (Mmp13 −/− ) mice were used to analyze phenotypic changes in the dentin–pulp complex, mineralization-associated marker-expression, and mechanistic interactions. Immunohistochemistry demonstrated high MMP13-expression in pulp-tissue, ameloblasts, odontoblasts, and dentin in developing WT-molars, which reduced in adults, with human-DPC cultures demonstrating a >2000-fold increase in Mmp13-expression during mineralization. Morphologically, Mmp13 −/− molars displayed critical alterations in the dentin-phenotype, affecting dentin-tubule regularity, the odontoblast-palisade and predentin-definition with significantly reduced dentin volume (∼30% incisor; 13% molar), and enamel and dentin mineral-density. Reactionary-tertiary-dentin in response to injury was reduced at Mmp13 −/− molar cusp-tips but with significantly more dystrophic pulpal mineralization in MMP13-null samples. Odontoblast differentiation-markers, nestin and DSP, reduced in expression after MMP13-loss in vivo, with reduced calcium deposition in MMP13-null DPC cultures. RNA-sequencing analysis of WT and Mmp13 −/− pulp highlighted 5,020 transcripts to have significantly >2.0-fold change, with pathway-analysis indicating downregulation of the Wnt-signaling pathway, supported by reduced in vivo expression of the Wnt-responsive gene Axin2. Mmp13 interaction with Axin2 could be partly responsible for the loss of odontoblastic activity and alteration to the tooth phenotype and volume which is evident in this study. Overall, our novel findings indicate MMP13 as critical for tooth development and mineralization processes, highlighting mechanistic interaction with the Wnt-signaling pathway.

Early Neanderthals in contact: The Chibanian (Middle Pleistocene) hominin dentition from Velika Balanica Cave, Southern Serbia

Neanderthals are Eurasian fossil hominins whose distinctive morphology developed in the southwestern corner of Europe and later spread throughout the continent, reaching Southwest Asia before the Late Pleistocene and spreading into Central Asia by 59–49 ka. The timing, tempo, and route of the Neanderthal movements eastward are poorly documented. The earliest probable evidence of Neanderthals in Asia comes from Karain E Cave (Anatolia, Turkey), dated to 250–200 ka. We present four Chibanian (Middle Pleistocene) hominin specimens, representing at least two individuals, from Velika Balanica Cave (Serbia): a permanent upper third molar (BH-2), a deciduous upper fourth premolar (BH-3) refitted to a poorly preserved maxillary fragment with the permanent first molar in the alveolus (BH-4), and a permanent upper central incisor (BH-5). We provide descriptions of the teeth, as well as a comparative analysis of the well-preserved M1 (BH-4), including assessments of cusp angles, relative occlusal polygon area, relative cusp base areas, two- and three-dimensional enamel thickness, and taurodontism. Morphology of both the occlusal surface and the enamel dentine junction of the M1 indicates that the maxillary fragment and associated dP4 belonged to an early Neanderthal child. The heavily worn I1 and M3 are consistent with the Neanderthal morphology, although they are less distinct taxonomically. These Chibanian remains with provenance from layer 3a are constrained by two thermoluminescence dates: 285 ± 34 ka and 295 ± 74 ka. They represent the earliest current evidence of Neanderthal spread into the Eastern Mediterranean Area. We discuss these findings in light of recent direct evidence for cultural connections between Southwestern Asia and Southeast Europe in the Chibanian.

Traumatic dental injuries and their sequelae in visually impaired adolescents.

Traumatic dental injuries are a public health problem. Visual impairment can be considered a risk factor for traumatic dental injury given the difficulties imposed upon visually impaired patients by limited physical perception. The aim of this study was to evaluate the frequency of traumatic dental injuries and their sequelae in adolescents with visual impairment. Adolescents (12-18years) with visual impairment (blind or low vision) and no other special needs were included in the study. Data were collected after a clinical and radiographic examination. Data regarding gender, age, type of visual impairment, site of traumatic dental injury, tooth type, and affected tissues, care, and sequelae were obtained. The data were analyzed descriptively and with the chi-square test (p<.05). Among 96 adolescents (65% blind; 55% female), 20.8% (n=20) reported they had previously experienced a traumatic dental injury of 33 teeth (78.8% maxillary central incisors). Combined injuries (30.3%; n=10) were the most common traumatic dental injuries, followed by concussion (27.3%, n=9) and enamel-dentine fractures (21.2%, n=7). Sequelae were observed in 27.3% (n=9) of the teeth affected by a traumatic dental injury, and apical periodontitis (77.8%, n=7) was the most common. The frequency of traumatic dental injuries among visually impaired adolescents can be considered high, and the observed sequelae could have been minimized if adequate clinical and radiographic follow up had been carried out. These results suggest the importance of enhanced educational efforts to reduce traumatic dental injuries.

Automatic exposure compensation in intraoral digital radiography: effect on the gray values of dental tissues

BackgroundThis study aimed to investigate the effect of automatic exposure compensation (AEC) of intraoral radiographic systems on the gray values of dental tissues in images acquired with or without high-density material in the exposed region using different exposure times and kilovoltages. The influence of the distance of the high-density material was also investigated.MethodsRadiographs from the molar region of two mandibles were obtained using the RVG 6100 and the Express systems, operating at 60 and 70 kV and 0.06, 0.10, and 0.16 s. Subsequently, a titanium implant was inserted in the premolar’s socket and other images were acquired. Using the ImageJ software, two regions of interest were determined on the enamel, coronary dentine, root dentine, and pulp of the first and second molars to obtain their gray values.ResultsIn the RVG 6100, the implant did not affect the gray values (p > 0.05); the increase in kV decreased it in all tissues (p < 0.05), and the exposure time affected only the root dentine and pulp. In the Express, only enamel and coronary dentine values changed (p < 0.05), decreasing with the implant presence and/or with the increase in exposure factors. The distance of the implant did not affect the results (p > 0.05).ConclusionsAEC’s performance varies between the radiographic systems. Its effect on the gray values depends not only on the presence or absence of high-density material but also on the kV and exposure time used.

Caries progression and need for reintervention on occlusal ICDAS 4 lesions after different treatments: a retrospective university-based study

Objective: To assess the caries progression and the need for reintervention on occlusal ICDAS 4 lesions afterdifferent treatments. Material and Methods: The sample consisted of records of children treated in a public settingwho had at least an occlusal ICDAS 4 lesion in primary and/or permanent molars. The radiographic images ofICDAS 4 lesions at the first and last appointments were classified as absence of radiolucency, radiolucent imageat the enamel–dentin junction, at the outer half or inner of the dentin. The need for retreatment after differenttreatments (non-invasive - topical fluoride applications, oral hygiene instructions and dietary guidance, microinvasive- resin-based sealant, or invasive - restoration) was assessed by reviewing clinical and radiographicrecords. The need for retreatment was defined as any complication requiring mending (e.g., caries progression,total loss of sealant, or restoration failure). The Poisson regression model was used to investigate the associationbetween individual and tooth-related variables and the outcome. Results: Among the 111 lesions in 81 patients,most (73.0%) lesions were in primary molars. Most lesions (52.3%) did not exhibit radiolucency, whereas 29.7%had radiolucency at the outer half of the dentin. The mean follow-up was 18.8 ± 6.5 months. After follow-up,82.9% of the lesions did not require retreatment. The prevalence of ICDAS 4 lesions that did not need retreatmentwas higher among lesions with radiolucency at dentin (p=0.01). Conclusion: Most occlusal ICDAS 4 lesions didnot require reintervention, especially those exhibiting radiolucency in the outer half of the dentin.KEYWORDSDental caries; Clinical decision-making; Dental radiography.

A software approach for identifying the effect of dental caries on dentin-enamel junction.

Dental decay is the most prevalent oral disease worldwide since more than 2.4 billion people suffer from caries of permanent teeth. Therefore, any details about its progression into the hard-dental tissues could contribute to unravelling the mechanisms underlying this process. We have analyzed dental tissue sections with and without caries in order to detect structure differences corelating them with clinical aspects observable from the tooth surface. Our working hypothesis was based on finding a link between the process of tertiary dentin laying (as a response to coronal caries) and the subsequent obliteration of dentin tubules. We have selected N=10 extracted teeth with/without coronal caries, resin-embedded and sectioned them. A specific software was used to digitally quantify the density of unobliterated dentin tubules reaching the dentin–enamel junction (DEJ), considering as positive threshold criteria the presence of the odontoblast process inside the analyzed tubule. This study showed the differences between the healthy and carious-affected hard-dental coronal tissues. More odontoblast processes reached the DEJ in unaffected teeth. Using specific software, we have quantified their density decrease near a lesion. We have studied the dynamics of the carious study and measured the consequent structural modifications of the dentin. In conclusion, there is a significant difference between the number of dentin tubules containing odontoblast processes that reach the DEJ in healthy/altered tissues. The tooth reacts not only by production of tertiary dentin to protect the pulp chamber, but also by obliteration of dentin tubules, thus reducing the number of odontoblast processes reaching the DEJ. This pilot study could serve as the starting point in developing a dedicated software that could deliver a personalized pattern for decay progression by analyzing one single tooth and extrapolate the result to all the patient’s remaining ones.

A machine learning approach to investigate the materials science of enamel aging

Understanding aging of tooth tissues is critical to the development of patient-centric oral healthcare. Yet, the traditional methods for analyzing the composition–structure–property relationships of hard tissues have limitations when considering aging and other factors. ObjectiveTo apply unsupervised machine learning tools to pursue an understanding of relationships between the composition and mechanical behavior of aging enamel. MethodsMolar teeth were collected from primary (age ≤ 8), young adult (24 ≤ age ≤ 46) and old adult (55 ≤ age) donors. The hardness and elastic modulus were quantified using nanoindentation as a function of distance from the Dentin Enamel Junction (DEJ) within the cervical, cuspal and inter-cuspal regions of the enamel crown. Similarly, a co-located analysis of the chemical composition and structure was performed using Raman spectroscopy. A Self-Organizing Maps (SOMs) algorithm was implemented to identify multi-dimensional composition–property relationships. ResultsThe hardness and elastic modulus are positively correlated to crystallinity and negatively correlated with carbonate substitution. Furthermore, the effects from fluoridation on the age-dependent properties of enamel is non-linear and depends on its location. The contributions of fluoridation to the enamel properties are different in the cervical and non-cervical regions and appear to be unique within primary and senior adult teeth. SignificanceBased on the findings, unsupervised learning methods can reveal complicated non-linear structure–property relationships in tooth tissues and help to understand the materials science of aging and its consequences.