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Objective: This study aimed to examine the morphology of maxillary canines (MxCs) by means of micro-computed tomography (micro-CT). Materials and methods: The root canal configurations (RCCs) of 97 maxillary canines of a mixed Swiss-German population were analyzed using micro-CT. After representing the internal morphology by 3-D software imaging, the RCC results were described using a four-digit system code indicating the main root canal from coronal to apical thirds and the main foramina number. Results: The most frequently observed RCCs of the MxC of the Swiss-German population were 1-1-1/1 (77.3%), followed by 1-1-1/2 (14.4%), 1-1-2/2 (4.1%), and finally 1-1-1/3 and 1-2-1/1 with 2.1% each. One physiological foramen was observed in 79.4% of the samples, two in 18.6%, and only 2.1% had three foramina. In 52.6% of the MxC samples, accessory and connecting canals were identified, with the majority located in the apical third of the root. Conclusions: This study contributes detailed information about the RCCs of MxC. The most prevalent RCC is 1-1-1/1, with accessory or connecting canals present in over half of the samples. However, it is noteworthy that in more than one-fifth of the examined samples, a particularly challenging RCC was observed. This should be considered when selecting treatment techniques. Clinical relevance: This study presents the root canal configurations in maxillary canines of a Swiss-German population and emphasizes the importance of influencing endodontic treatment decisions and outcomes.

Deep learning allows automatic segmentation of teeth on cone beam computed tomography (CBCT). However, the segmentation performance of deep learning varies among different training strategies. Our aim was to propose a 3.5D U-Net to improve the performance of the U-Net in segmenting teeth on CBCT. This study retrospectively enrolled 24 patients who received CBCT. Five U-Nets, including 2Da U-Net, 2Dc U-Net, 2Ds U-Net, 2.5Da U-Net, 3D U-Net, were trained to segment the teeth. Four additional U-Nets, including 2.5Dv U-Net, 3.5Dv5 U-Net, 3.5Dv4 U-Net, and 3.5Dv3 U-Net, were obtained using majority voting. Mathematical morphology operations including erosion and dilation (E&D) were applied to remove diminutive noise speckles. Segmentation performance was evaluated by fourfold cross validation using Dice similarity coefficient (DSC), accuracy, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV). Kruskal–Wallis test with post hoc analysis using Bonferroni correction was used for group comparison. P  < 0.05 was considered statistically significant. Performance of U-Nets significantly varies among different training strategies for teeth segmentation on CBCT ( P  < 0.05). The 3.5Dv5 U-Net and 2.5Dv U-Net showed DSC and PPV significantly higher than any of five originally trained U-Nets (all P  < 0.05). E&D significantly improved the DSC, accuracy, specificity, and PPV (all P  < 0.005). The 3.5Dv5 U-Net achieved highest DSC and accuracy among all U-Nets. The segmentation performance of the U-Net can be improved by majority voting and E&D. Overall speaking, the 3.5Dv5 U-Net achieved the best segmentation performance among all U-Nets.

This study aimed to assess the viability of dental cells following time-dependent carbamide peroxide teeth-whitening treatments using an in-vitro dentin perfusion assay model. 30 teeth were exposed to 5% or 16% CP gel (4 h daily) for 2-weeks. The enamel organic content was measured with thermogravimetry. The time-dependent viability of human dental pulp stem cells (HDPSCs) and gingival fibroblast cells (HGFCs) following either indirect exposure to 3 commercially available concentrations of CP gel using an in-vitro dentin perfusion assay or direct exposure to 5% H 2 O 2 were investigated by evaluating change in cell morphology and by hemocytometry. The 5% and 16% CP produced a significantly lower (p < 0.001) enamel protein content (by weight) when compared to the control. The organic content in enamel varied accordingly to the CP treatment: for the 16% and 5% CP treatment groups, a variation of 4.0% and 5.4%, respectively, was observed with no significant difference. The cell viability of HDPSCs decreased exponentially over time for all groups. Within the limitation of this in-vitro study, we conclude that even low concentrations of H 2 O 2 and CP result in a deleterious change in enamel protein content and compromise the viability of HGFCs and HDPSCs. These effects should be observed in-vivo.

We investigated the effect of femtosecond (fs) laser ablation of enamel and dentin for different pulse wavelengths: infrared (1030 nm), green (515 nm), and ultra-violet (343 nm) and for different pulse separations to determine the optimal irradiation conditions for the precise removal of dental hard tissues with the absence of structural and compositional damage. The ablation rates and efficiencies were established for all three laser wavelengths for both enamel and dentin at room temperature without using any irrigation or cooling system, and the surfaces were assessed with optical and scanning electron microscopy, optical profilometry, and Raman spectroscopy. We demonstrated that 515 nm fs irradiation provides the highest rate and efficiency for ablation, followed by infrared. Finally, we explored the temperature variations inside the dental pulp during the laser procedures for all three wavelengths and showed that the maximum increase at the optimum conditions for both infrared and green irradiations was 5.5 °C, within the acceptable limit of temperature increase during conventional dental treatments. Ultra-violet irradiation significantly increased the internal temperature of the teeth, well above the acceptable limit, and caused severe damage to tooth structures. Thus, ultra-violet is not a compatible laser wavelength for femtosecond teeth ablation.

This experimental phantom study investigates current standard of care protocols in cone beam computed tomography (CBCT), energy-integrating-detector (EID) CT, and photon-counting-detector (PCD) CT regarding their potential in delineation of dental root canals. Artificial accessory canals (diameters: 1000, 600, 400, 300 and 200 μm) were drilled into three bovine teeth mounted on a bovine rib as a jaw substitute. The phantom was scanned in two dental CBCTs, two EID-CTs and a PCD-CT using standard clinical protocols. Scans from a micro-CT served as reference standard. Spatial resolution was evaluated via line profiles through the canals, whereby visibility compared to surrounding noise and compared to the ground truth were assessed. PCD-CT was able to delineate all artificial canals down to 200 μm diameter. In CBCT and EID-CT canals could only be reliably detected down to 300 μm. Also, PCD-CT showed a considerably smaller width-divergence from the ground trough with 4.4% at 1000 μm and 35.1% at 300 μm compared to CBCT (13.5 and 72.9%) and EID-CT (10.1 and 115.7%). PCD-CT provided superior resolution, accurate size measurement, and enhanced detection of small dental root canals, thereby offering improvements in diagnostic capabilities compared to CBCT and EID-CT systems.

Enamel is the hardest and most resilient tissue in the human body. Enamel includes morphologically aligned, parallel, ∼50 nm wide, microns-long nanocrystals, bundled either into 5-μm-wide rods or their space-filling interrod. The orientation of enamel crystals, however, is poorly understood. Here we show that the crystalline c -axes are homogenously oriented in interrod crystals across most of the enamel layer thickness. Within each rod crystals are not co-oriented with one another or with the long axis of the rod, as previously assumed: the c -axes of adjacent nanocrystals are most frequently mis-oriented by 1°–30°, and this orientation within each rod gradually changes, with an overall angle spread that is never zero, but varies between 30°–90° within one rod. Molecular dynamics simulations demonstrate that the observed mis-orientations of adjacent crystals induce crack deflection. This toughening mechanism contributes to the unique resilience of enamel, which lasts a lifetime under extreme physical and chemical challenges. Enamel is the hardest tissue in the body and has been widely studied, yet aspects of its structure remain unclear. Here, the authors report on a study of the orientation and alignment of enamel crystals and challenge previous assumptions.

As early as 1955, there were studies on the multiple bellies of the temporalis muscle (TM), which is considered to contain two or three layers. However, some historical literature proposed that the sphenomandibularis (SM), one of the bellies of TM, should be considered a newly discovered independent muscle. Many scholars have extremely inconsistent views on this statement. Here, we conducted an anatomical study to clarify the existence and morphological characteristics of the SM. We dissected 14 formaldehyde-fixed and 6 fresh-frozen human cadaver heads using three approaches, including vascular casting in 10 cases. 15 sets of consecutive P45 sheet‑plastinated sections were analyzed, including 5 coronal, 5 sagittal, and 5 horizontal planes. SM has distinct anatomical features. This strip-like muscle extends from the maxillary surface of the greater wing of the sphenoid bone to the temporal crest behind the retromolar trigone of the mandible. Ours is the first detailed description of SM through combining gross anatomy with the P45 sheet plastination technique. The special anatomical location of this belly may be related to compression of the maxillary nerve, anatomy of the pterygopalatine fossa, identification of the buccal nerve, comprehension of the fascial-tendinous complex, and a deeper understanding of the masticatory system. We recommend the name Sphenomandibularis as a further reference and to distinguish it from TM.

This study aimed to analyze the prevalence of radix molaris in a subpopulation of Brazil’s Northeast region using cone-beam computed tomography (CBCT). A total of 1092 CBCT exams and 3315 teeth (1541 first and 1774 s mandibular molars) were analyzed in axial, coronal, and sagittal planes using the PreXion 3D Viewer software. The teeth morphologies were analyzed and the occurrence of radix molaris , location, tooth, type ( entomolaris and paramolaris ) and patients’ gender were recorded. The data were expressed in the form of absolute and percentage frequencies and statistically analyzed using Pearson’s Chi-square test ( P  < .05). Fifty-nine patients (5.40%) and 71 teeth (2.14%) presented radix molaris , which was most frequently identified in first mandibular molars (2.92%) than in second mandibular molars (1.47%) ( P  < .05). No significant differences in the occurrence of radix molaris considering the gender of patients (36 women [5.22%] and 23 men [5.72%)] were observed ( P  > .05). It was observed that 92.96% of the teeth affected by the anatomical variation studied were classified as radix entomolaris. The bilateral prevalence of radix molaris was approximately 20.34% of the cases involving only first molars ( P  < .05). The occurrence of radix molaris was higher in first mandibular molars, regardless of the gender of patients.

Dentin sialophosprotein (DSPP) is cleaved into the N-terminal dentin sialoprotein (DSP) proteoglycan and the C-terminal dentin phosphoprotein (DPP; the most acidic proteins in humans). To define the functions of DSP and DPP, we generated a Dspp −DPP mouse model using CRISPR/Cas9 technology and compared tooth mineralization in Dspp −DPP and Dspp −/− mice in the C57BL/6 background. In both mice, the initiation of dentin mineralization was associated with matrix vesicles. Odontoblasts appeared normal with odontoblastic processes. In Dspp −/− mice, limited mineralized dentin was observed. In Dspp −DPP/−DPP mice, dentin globules (calcospherites) with varied mineral density and unmineralized interglobular dentin were observed throughout the circumpulpal dentin. The area of predentin was smaller compared to Dspp −/− mice, but larger than wild-type mice. In Dspp −/− and Dspp −DPP/−DPP mice, enamel formation was comparable to wild-type. In both mice, Dmp1 expression in differentiating and differentiated odontoblasts was altered. We propose a model for dentin mineralization in which DSP, enriched in the peritubular dentin, propagates mineralization within the hypomineralized calcospherites in the intertubular dentin while DPP is essential for the maturation of calcospherite mineralization in the circumpulpal dentin. We conclude that DSP and DPP are dispensable for the initiation of dentin and enamel mineralization, but critical for circumpulpal dentin mineralization.

Dental materials are challenged by wear processes in the oral environment and should be evaluated in laboratory tests prior to clinical use. Many laboratory wear-testing devices are high-cost investments and not available for cross-centre comparisons. The ‘Rub&Roll’ wear machine enables controlled application of force, chemical and mechanical loading, but the initial design was not able to test against rigid antagonist materials. The current study aimed to probe the sensitivity of a new ‘Rub&Roll’ set-up by evaluating the effect of force and test solution parameters (deionized water; water + abrasive medium; acid + abrasive medium) on the wear behaviour of direct and indirect dental resin-based composites (RBCs) compared with human molars against 3D-printed rod antagonists. Molars exhibited greater height loss than RBCs in all test groups, with the largest differences recorded with acidic solutions. Direct RBCs showed significantly greater wear than indirect RBCs in the groups containing abrasive media. The acidic + abrasive medium did not result in increased wear of RBC materials. The developed method using the ‘Rub&Roll’ wear machine in the current investigation has provided a sensitive wear test method to allow initial screening of resin-based composite materials compared with extracted human molars under the influence of different mechanical and erosive challenges.