Mesial Regions Research Articles

Digital Evaluation of the Depth and Width of Upper and Lower Molar Cavity Preparations of Dental Students

Objective: The aim of this study was to evaluate the mesial and distal seat widths and the buccal, lingual, and axial wall height values of cavity preparations by measuring them with the help of a digital scanner.
 Methods: In this study, 70 randomly selected students of 140 tooth preparations (mandibular molar and a maxillary molar cavities) of phantom jaw models were evaluated. The prepared teeth were scanned with an intraoral scanner. The parameters used in the analysis were the depth values of the buccal and lingual (or palatal) wall depth, the mesial and distal axial wall height, and the mesial and distal seat width values. For main effects and interactions, two-way analysis of variance was used, and for multiple comparisons, Tukey’s test was used (p < .05).
 Results: No significant difference was found in the teeth according to cavity depth. However, a significant difference was found in the cavity regions’ depths or widths. There was no difference between the total buccal (1.93 ± 0.01 mm) and lingual (1.91 ± 0.32 mm) depth values. There was no difference between the total mesial (1.51 ± 0.27 mm) and distal (1.41 ± 0.26 mm) seat width values. There was no difference between the total mesial (1.11 ± 0.35 mm) and distal (1.21 ± 0.27 mm) axial wall height values. 
 Conclusion: It was observed that the students had more difficulty in the distal region of the tooth than in the mesial region. Digital methods in preclinical education can provide objective results in the evaluation of cavity preparations.

Analysis of Alveolar Crest Reduction Post Extraction with the Use of Platelet Rich Fibrin (PRF)

One of the treatments that can be done to treat dental and oral diseases is tooth extraction. However, this procedure can cause significant changes in the dimensions of the alveolar ridge that are unfavorable in subsequent oral rehabilitation. One of the most important things is the preservation of the remaining alveolar ridge after the tooth extraction procedure. The use of Platelet Rich Fibrin (PRF) for the regeneration of soft and hard tissue in wound healing, in the form of immune concentrate and platelets obtained from a single fibrin membrane which contains all the blood constituents useful for healing and immunity. This research is an unblinded, randomized clinical trial with a sample size of 36 patients undergoing tooth extraction. To see the effect of ridge resorption analysis, namely the reduction of the alveolar crest with PRF application. Each research sample is analyzed at each evaluation time. There was a significant difference in alveolar crest reduction in the treatment and control groups which was found in the mesial region (post-extraction days 60 and 90) and distal region (post-extraction days 30, 60 and 90) with a significance value p<0.05. There was a significant difference in the periapical x-ray image in the reduction of the post-extraction alveolar crest in the PRF application group, with better results compared to the group without PRF.

Accuracy of computer-assisted dynamic navigation when performing coronectomy of the mandibular third molar: A pilot study

ObjectivesThe study represents a preliminary evaluation of the accuracy of the dynamic navigation system (DNS) in coronectomy of the mandibular third molar (M3M). MethodsThe study included participants with an impacted M3M near the inferior alveolar canal. The coronectomy planes were designed before the surgery using cone-beam computed tomography (CBCT) imaging data and then loaded into the DNS program. Intraoperatively, the navigation system was used to guide the complete removal of the target crown. Postoperative CBCT imaging was used to assess any three-dimensional deviations of the actual postoperative from the planned preoperative section planes for each patient. ResultsA total of 12 patients (13 teeth) were included. The root mean square (RMS) deviation of the preoperatively designed plane from the actual postoperative surface was 0.69 ± 0.21 mm, with a maximum of 1.45 ± 0.83/-1.87 ± 0.63 mm deviation. The areas with distance deviations < 1 mm, 1–2 mm, and 2–3 mm were 71.97 ± 5.72 %, 22.96 ± 6.57 %, and 4.52 ± 2.28 %, respectively. Most patients showed extremely high convexity of the surface area located in the mesial region adjacent to the base of the extraction socket. There was no observable evidence of scratching of the buccolingual bone plate at the base of the extraction socket by the handpiece drill. ConclusionsThese results provide preliminary support for the use of DNS-based techniques when extracting M3M using a buccal approach. This would improve the accuracy of coronectomy and reduce the potiential damage to the surrounding tissue. Clinical significanceDNS is effective for guiding coronectomy.

Large scale analysis of osteocyte lacunae in klotho hypomorphic mice using high-resolution micro-computed tomography

BackgroundOsteocytes are the most abundant cell type in adult bone, and the morphological characteristics of osteocytes and their lacunae appear to influence bone mass and fragility. Although conventional computed tomography (CT) has contributed greatly to advances in bone morphometry, capturing details of the entire hierarchical assembly, e.g., osteocyte lacuna parameters, has been limited by the analytical performance of CT (> 1 µm resolution). MethodsWe used high-resolution (700 nm) micro-CT to evaluate and compare the osteocyte lacuna parameters over a large scale, i.e., in a maximum of about 45,700 lacunae (average), in tibial metaphyseal cortical bones of wild-type (WT) and αKlotho-hypomorphic (kl/kl) mice, the latter a model that exhibits osteopenia and aberrant osteocytes. ResultsOf osteocyte lacuna parameters, lacunar surface per lacunar volume were significantly lower and lacuna diameter were significantly larger in kl/kl mice compared to WT mice. By analysis of individual osteocyte lacunae, we found that lacunar sphericity in kl/kl mice was higher than that in WT mice, and the diameters in the major and the minor axes were respectively lower and higher in kl/kl mice, especially at the proximal site of the region of interest. ConclusionWe successfully assessed osteocyte lacuna parameters on the largest scale in mice reported to date and found that the shape of osteocyte lacunae of kl/kl mice are significantly different from those of WT mice. Although the mechanisms underlying the lacunar shape differences observed are not yet clear, changes in lacunar geometry are known to affect the transitions of strains to the osteocyte microenvironment and likely local osteocyte response(s). Thus, the fact that the differences are limited to the mesial region near the primary spongiosa suggests the likelihood of site-specific anomalies in mechanosensitive effects in kl/kl osteocytes with consequent site-specific effects bone metabolism and function.

Structure-function coupling increases during interictal spikes in temporal lobe epilepsy: A graph signal processing study

ObjectiveStructure-function coupling remains largely unknown in brain disorders. We studied this coupling during interictal epileptic discharges (IEDs), using graph signal processing in temporal lobe epilepsy (TLE). MethodsWe decomposed IEDs of 17 patients on spatial maps, i.e. network harmonics, extracted from a structural connectome. Harmonics were split in smooth maps (long-range interactions reflecting integration) and coarse maps (short-range interactions reflecting segregation) and were used to reconstruct the part of the signal coupled (Xc) and decoupled (Xd) from the structure, respectively. We analysed how Xc and Xd embed the IED energy over time, at global and regional level. ResultsFor Xc, the energy was smaller than for Xd before the IED onset (p < .001), but became larger around the first IED peak (p < .05, cluster 2, C2). Locally, the ipsilateral mesial regions were significantly coupled to the structure over the whole epoch. The ipsilateral hippocampus increased its coupling during C2 (p < .01). ConclusionsAt whole-brain level, segregation gives way to integrative processes during the IED. Locally, brain regions commonly involved in the TLE epileptogenic network increase their reliance on long-range couplings during IED (C2). SignificanceIn TLE, integration mechanisms prevail during the IED and are localized in the ipsilateral mesial temporal regions.

Use of scanning electron microscope to evaluate the marginal fit of protocol bars obtained through benchtop or intraoral digital scanners

Aim: To evaluate the marginal fit of protocol bars milled from digital models obtained by conventional molding followed by bench scanning or digital molding with an intraoral scanner. Methods: Four morse-cone implants and the mini-pillars were installed in a 3D printed mandible model (master model). Digital models of the master model were obtained by (n=10): (Group A - Conventional) conventional (analog) molding of the master model followed by bench scanning or (Group B - Digital) molding of the master model with an intraoral scanner. All-on-four protocol bars were designed and milled from the digital models for both groups and screwed into the master model. Scanning electron microscopy (SEM) images from the distal, central, and mesial regions of each implant were obtained and the implant-protocol bar marginal fit was measured in an image software (Image J). The mean misfit of each region was analyzed by two-factor ANOVA, Tukey test, and Student’s t-test (0,05 = 0.05). Results: The digital approach (B) showed higher misadaptation than the conventional approach (A, p &lt; 0.05), regardless of the region evaluated. In group A, the central region showed higher maladjustment than the mesial region (p&lt;0.05), however, there were no differences among regions of group B (p&gt;0.05). Conclusion: The conventional method of acquiring digital models using the bench scanner produced bars for the All-On-Four protocol with better marginal fit than the digital models obtained with an intraoral scanner.

Expression Profile of miRs in Mesial Temporal Lobe Epilepsy: Systematic Review.

Temporal lobe epilepsy (TLE) is one of the most common forms of focal epilepsy in children and adults. TLE is characterized by variable onset and seizures. Moreover, this form of epilepsy is often resistant to pharmacotherapy. The search for new mechanisms for the development of TLE may provide us with a key to the development of new diagnostic methods and a personalized approach to the treatment. In recent years, the role of non-coding ribonucleic acids (RNA) has been actively studied, among which microRNA (miR) is of the greatest interest. (1) Background: The purpose of the systematic review is to analyze the studies carried out on the role of miRs in the development of mesial TLE (mTLE) and update the existing knowledge about the biomarkers of this disease. (2) Methods: The search for publications was carried out in the databases PubMed, Springer, Web of Science, Clinicalkeys, Scopus, OxfordPress, Cochrane. The search was carried out using keywords and combinations. We analyzed publications for 2016–2021, including original studies in an animal model of TLE and with the participation of patients with TLE, thematic and systemic reviews, and Cochrane reviews. (3) Results: this thematic review showed that miR‒155, miR‒153, miR‒361‒5p, miR‒4668‒5p, miR‒8071, miR‒197‒5p, miR‒145, miR‒181, miR‒199a, miR‒1183, miR‒129‒2‒3p, miR‒143‒3p (upregulation), miR–134, miR‒0067835, and miR‒153 (downregulation) can be considered as biomarkers of mTLE. However, the roles of miR‒146a, miR‒142, miR‒106b, and miR‒223 are questionable and need further study. (4) Conclusion: In the future, it will be possible to consider previously studied miRs, which have high specificity and sensitivity in mTLE, as prognostic biomarkers (predictors) of the risk of developing this disease in patients with potentially epileptogenic structural damage to the mesial regions of the temporal lobe of the brain (congenital disorders of the neuronal migration and neurogenesis, brain injury, neuro-inflammation, tumor, impaired blood supply, neurodegeneration, etc.).

Correlation between cortical bone thickness at mini-implant insertion sites and age of patient.

ABSTRACTIntroduction: Orthodontic mini-implants (MI) are a reliable alternative to provide temporary orthodontic anchorage. Prior to miniscrew insertion, the best approach would be to evaluate each possible insertion site and measure the cortical bone thickness, and verify whether it would provide adequate primary stability. Objective: This study aimed to evaluate the difference in cortical bone thickness in areas of mini-implants insertion in patients of different ages, by means of cone beam computed tomography (CBCT). Methods: The sample of this retrospective study was composed of 123 CBCT scans, which were used to measure cortical bone thickness in the buccal and palatal inter-radicular space in the mesial region of the first permanent molars. These measures were compared by using the Student’s t-test, ANOVA/Tukey tests, and Linear regression between male and female subjects, from 12 to 30 years old. Results: No significant difference was found in cortical bone thickness between sex, race and sagittal facial patterns. Significantly higher measurement values were observed in patients older than 12 years of age at all sites evaluated. The coefficient β at the adjusted linear regression analysis showed that at each increment in age, mean cortical thickness values increased by 0.06mm in the mandible, 0.03mm in the buccal region and 0.02mm in the palatal region of the maxilla. Conclusions: The increase in cortical bone thickness was positively associated with age; that is, the more advanced the patient’s age was, the less chance there was of failure due to primary stability.

Mapping connectivity fingerprints for presurgical evaluation of temporal lobe epilepsy

BackgroundSurgery may render temporal lobe epilepsy (TLE) patients seizure-free. However, TLE is a heterogenous entity and surgical prognosis varies between patients. Network-based biomarkers have been shown to be altered in TLE patients and hold promise for classifying TLE subtypes and improving pre-surgical prognosis. The aim of the present study is to investigate a network-based biomarker, the weighted degree of connectivity (wDC), on an individual level, and its relation to TLE subtypes and surgical prognosis.MethodsThirty unilateral TLE patients undergoing the same surgical procedure (anterior temporal resection) and 18 healthy controls were included. All patients were followed-up in the same center for a mean time of 6.85 years and classified as seizure-free (SF) and non seizure-free (non-SF). Using pre-surgical resting state functional MRI, whole brain wDC values for patients and controls were calculated. Then, we divided both temporal lobes in three Regions-of-interest (ROIs) -mesial, pole and lateral- as these areas are known to behave differently in seizure onset and propagation, delimiting different TLE profiles. The wDC values for the defined ROIs of each individual patient were compared with the healthy group.ResultsAfter surgery, 14 TLE patients remained SF. As a group, patients had higher wDC than controls in both the temporal pole (p < 0.05) as well as in the mesial regions (p < 0.002) of the to-be-resected temporal lobe. When comparing between SF and non-SF patients, a step-wise binary logistic regression model including all the ROIs, showed that having an increased wDC of the temporal pole (p < 0.05) and the mesial area (p < 0.05) of the to-be-resected temporal lobe was associated with seizure freedom long-term after surgery.ConclusionsThis study provides a network-based presurgical biomarker that could pave the way towards personalized prediction. In patients with TLE undergoing anterior temporal resections, having an increased wDC at rest could be a signature of the epileptogenic area, and could help identifying those patients who would benefit most from surgery.

DNA methylation screening suggests brain origin of cell-free DNA in epilepsy

Cell-free DNA (cfDNA) are small circulating DNA fragments generally defined as cellular death debris. The profiling of the cfDNA methylome has been successfully used to track the origin of these circulating nucleic acids, which greatly upgraded the clinical applicability of liquid biopsies. The prediction of tissue specific cell death may represent a valuable tool in early disease diagnose and identification of undetermined pathology. The main histopathological feature of Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis (MTLE-HS) is severe neuronal death in the mesial regions. Increased cfDNA total levels have been previously reported in MTLE-HS, although the potentially cerebral origin is still undisclosed.

The spatial distribution of focal stacks within the inner enamel layer of mandibular mouse incisors.

Focal stacks are an alternative spatial arrangement of enamel rods within the inner enamel of mandibular mouse incisors where short rows comprised of 2–45 enamel rods are nestled at the side of much longer rows, both sharing the same rod tilt directed mesially or laterally. The significance of focal stacks to enamel function is unknown, but their high frequency in transverse sections (30% of all rows) suggests that they serve some purpose beyond representing an oddity of enamel development. In this study, we characterized the spatial distribution of focal stacks in random transverse sections relative to different regions of the inner enamel and to different locations across enamel thickness. The curving dentinoenamel junction (DEJ) in transverse sections complicated spatial distribution analyses, and a technique was developed to “unbend” the curving DEJ allowing for more linear quantitative analyses to be carried out. The data indicated that on average there were 36 ± 7 focal stacks located variably within the inner enamel in any given transverse section. Consistent with area distributions, focal stacks were four times more frequent in the lateral region (53%) and twice as frequent in the mesial region (33%) compared to the central region (14%). Focal stacks were equally split by tilt (52% mesial vs. 48% lateral, not significant), but those having a mesial tilt were more frequently encountered in the lateral and central regions (2:1) and those having a lateral tilt were more numerous in the mesial region (1:3). Focal stacks having a mesial tilt were longer on average compared to those having a lateral tilt (7.5 ± 5.6 vs. 5.9 ± 4.0 rods per row, p < 0.01). There was no relationship between the length of a focal stack and its location within the inner enamel. All results were consistent with the notion that focal stacks travel from the DEJ to the outer enamel the same as the longer and decussating companion rows to which they are paired. The spatial distribution of focal stacks within the inner enamel was not spatially random but best fit a null model based on a heterogenous Poisson point process dependent on regional location within the transverse plane of the enamel layer.

Sex-, growth pattern-, and growth status-related variability in maxillary and mandibular buccal cortical thickness and density.

ObjectiveThe primary objective of this study was to quantitatively analyze the bone parameters (thickness and density) at four different interdental areas from the distal region of the canine to the mesial region of the second molar in the maxilla and the mandible. The secondary aim was to compare and contrast the bone parameters at these specific locations in terms of sex, growth status, and facial type.MethodsThis retrospective cone-beam computed tomography (CBCT) study reviewed 290 CBCT images of patients seeking orthodontic treatment. Cortical bone thickness in millimeters (mm) and density in pixel intensity value were measured for the regions (1) between the canine and first premolar, (2) between the first and second premolars, (3) between the second premolar and first molar, and (4) between the first and second molars. At each location, the bone thickness and density were measured at distances of 2, 6, and 10 mm from the alveolar crest.ResultsThe sex comparison (male vs. female) in cortical bone thickness showed no significant difference (p > 0.001). The bone density in growing subjects was significantly (p < 0.001) lower than that in non-growing subjects for most locations. There was no significant difference (p > 0.001) in bone parameters in relation to facial pattern in the maxilla and mandible for most sites.ConclusionsThere was no significant sex-related difference in cortical bone thickness. The buccal cortical bone density was higher in females than in males. Bone parameters were similar for subjects with hyperdivergent, hypodivergent, and normodivergent facial patterns.

Characteristics of the transverse 2D uniserial arrangement of rows of decussating enamel rods in the inner enamel layer of mouse mandibular incisors.

The 2D arrangement of rows of enamel rods with alternating (decussating) tilt angles across the thickness of the inner layer in rat and mouse incisor enamel is well known and assumed to occur in a uniform and repetitive pattern. Some irregularities in the arrangement of rows have been reported, but no detailed investigation of row structure across the entire inner enamel layer currently exists. This investigation was undertaken to determine if the global row pattern in mouse mandibular incisor enamel is predominately regular in nature with only occasional anomalies or if rows of enamel rods have more spatial complexity than previously suspected. The data from this investigation indicate that rows of enamel rods are highly variable in length and have complex transverse arrangements across the width and thickness of the inner enamel layer. The majority of rows are short or medium in length, with 87% having < 100 rods per row. The remaining 13% are long rows (with 100–233 rods per row) that contain 46% of all enamel rods seen in transverse sections. Variable numbers of rows were associated with the lateral, central and mesial regions of the enamel layer. Each region contained different ratios of short, medium and long rows. A variety of relationships was found along the transverse length of rows in each region, including uniform associations of alternating rod tilts between neighboring rows, and instances where two rows having the same rod tilt were paired for variable distances then moved apart to accommodate rows of opposite tilt. Sometimes a row appeared to branch into two rows with the same tilt, or conversely where two rows merged into one row depending upon the mesial‐to‐lateral direction in which the row was viewed. Some rows showed both pairing and branching/merging along their length. These tended to be among the longest rows identified, and they often crossed the central region with extensions into the lateral and mesial regions. The most frequent row arrangement was a row of petite length nestled at the side of another row having the same rod tilt (30% of all rows). These were termed ‘focal stacks’ and may relate to the evolution of uniserial rat and mouse incisor enamel from a multilayered ancestor. The mesial and lateral endpoints of rows also showed complex arrangements with the dentinoenamel junction (DEJ), the inner enamel layer itself, and the boundary area to the outer enamel layer. It was concluded that the diversity in row lengths and various spatial arrangements both within and between rows across the transverse plane provides a method to interlock the enamel layer across each region and keep the enamel layer compact relative to the curving DEJ surface. The uniserial pattern for rows in mouse mandibular incisors is not uniform, but diverse and very complex.

Anatomical danger zone reconsidered: a micro-CT study on dentine thickness in mandibular molars.

To investigate the smallest dentine thickness in mesial canals of mandibular molars along the cervical and middle thirds of the root by means of a micro-computed tomographic (micro-CT) technology and digital image analysis. Fifty mesial roots of mandibular molars having two independent canals (mesiobuccal and mesiolingual), in the coronal and middle levels, were selected and scanned in a micro-CT device. After reconstruction procedures, approximately 468 slices per root covering the 7mm below the furcation area of the mesial root were analysed to measure the smallest dentine thickness (danger zone [DZ]) in each slice from both distal and mesial regions of the mesial canals by an automatic segmentation process. The DZ values in the mesiobuccal canals varied from 0.67 to 1.93mm, with an average of 1.13±0.21mm. For the mesiolingual canals, the DZ varied from 0.77 to 1.89mm with an average of 1.10±0.21mm. There was no correspondence in the DZ between the mesiobuccal and mesiolingual canals at the same cross-sectional level in 71% of the specimens. Moreover, the smallest dentine thickness was towards the mesial region of the roots in 22% and 18% of the mesiolingual and mesiobuccal canals, respectively. (Figs 1 and 2 CONCLUSIONS: The smallest dentine thickness was on the mesial plane of the roots in about 40% of the canals. The vertical location of the DZ in relation to the furcation area was in the middle third of the root.

Evaluation of New Bone Formation in Sinus Floor Augmentation With Injectable Platelet-Rich Fibrin-Soaked Collagen Plug: A Pilot Study.

The objective of this study is to evaluate the new bone formation after sinus floor augmentation with collagen plugs used as carriers for injectable platelet-rich fibrin (i-PRF). Postoperative immediate and postoperative 6th month panoramic radiographies of patients treated between January 1, 2015, and February 1, 2018, with sinus floor augmentation using i-PRF-soaked collagen plugs were retrieved from the archives, and subantral bone heights of distal and mesial regions of simultaneously inserted implants were measured with a software program. Statistical analysis was performed to understand whether there is a significant change in new bone formation at 6th month follow-up control. A total of 18 implants were inserted in 12 patients. There was significant new bone formation at 6th month follow-up radiography at mesial and distal regions of inserted implants (P < 0.05). New bone was regenerated with i-PRF carried by collagen plugs in sinus floor augmentation.

An innovative approach to salvage a fractured endodontically treated tooth – A case report of resection, regeneration and restoration

Introduction: The progressing inflammatory periodontal disease, if untreated, results in attachment loss. This can affect the furcation region of multirooted teeth. Hemisection is the splitting of two rooted tooth into two separate portions accompanying crown portion of two-rooted teeth most likely mandibular molars. In the healing phase after hemisection, alveolar bone undergoes additional atrophy as a result of the natural remodelling process. Post-extraction Alveolar Ridge resorption may have an impact on dental implant placement, since sufficient vertical and horizontal volume of alveolar bone should ideally be present at the site of insertion. Alveolar ridge preservation (ARP) procedures have been introduced for aesthetic concern, as well as to prevent alveolar ridge atrophy and maintain adequate dimensions of bone in order to facilitate implant placement in prosthetically driven positions. Case Description: A 51 years old systemically healthy male patient came with a chief complaint of pain and swelling in his lower left back tooth region. On clinical examination, Endodontically treated mandibular first molar manifested bucco-lingual fracture, grade 2 mobility of mesial component, 10 mm probing depth in mesial region and grade 3 furcation involvement. The treatment of the tooth included proposed hemisection of the mesial component followed by socket augumentation and delayed implant placement. After phase 1 therapy, hemisection was performed and mesial root socket was augumented with zenograft and PRF membrane. After 8 months, Osteotomy site was prepared with flapless procedure then narrow, two piece implant of size 3.3 × 11.5 mm was placed in hemisected region of mandibular molar which was followed by provisional restoration at 3 weeks. Conclusion: An innovative approach for a periodontally compromised fractured endodontically treated tooth which was undertaken with a definitive treatment. Keywords: Early loading, Furcation, Hemisection, Mandibular fir

Mesial hyperdontia in Sigmodontinae (Rodentia: Cricetidae), with comments on the evolution of the anteroconid in Myomorpha

Abstract Supernumerary teeth are common dental anomalies reported in rodents, mainly occurring distally to molars. We report the first case of mesial hyperdontia in wild-caught sigmodontine: a simplified tooth anterior to the right first lower molar in Neacomys amoenus. It affected the first molar morphology, which exhibits an underdeveloped mesial region with a reduced anterior conulid, a similar pattern observed in early known myomorph fossils, including lineages that still possess the last premolar. However, only lineages without premolar display an elongated first lower molar with a large anteroconid, as observed in extant Myomorpha. During the odontogenesis in myomorphs, the posteriormost vestigial diastemal tooth bud, located at the same locus of the last lower premolar, has its development arrested and merges with the cap of the first molar. This process might have contributed to the development of an increased anteroconid in this lineage. The abnormal Neacomys’ atavistic phenotype corroborates the hypothesis that the absorption of the primordium of the last lower premolar had played an important role in the development of first molar’s mesial region. Additionally, it also might have promoted the evolutionary transition from a reduced conulid into an enlarged anteroconid, as deduced from the fossil record and developmental evidence

Quantitative analysis of the core 2D arrangement and distribution of enamel rods in cross-sections of mandibular mouse incisors.

Considerable descriptive information about the overall organization of mouse mandibular incisor enamel is available but almost nothing is known about the quantitative characteristics of enamel rod arrangement and distribution in these teeth. This has important implications concerning cell movement during the secretory stage because each ameloblast makes one enamel rod. Knowing how many enamel rods are cut open in a cross‐section of the enamel layer could provide insights into understanding the dynamics of how groups of ameloblasts form the enamel layer. In this study, cross‐sections of fully mineralized enamel were cut on 24 mandibular mouse incisors, polished and etched, and imaged by scanning electron microscopy in backscatter mode. Montaged maps of the entire enamel layer were made at high magnification and the enamel rod profiles in each map were color‐coded based upon rod category. Quantitative analyses of each color layer in the maps were then performed using standard routines available in imagej. The data indicated that that there were on average 7233 ± 575 enamel rod profiles per cross‐section in mandibular incisors of 7‐week‐old mice, with 70% located in the inner enamel layer, 27% located in the outer enamel layer, and 3% positioned near the mesial and lateral cementoenamel junctions. All enamel rod profiles showed progressive increases in tilt angles, some very large in magnitude, from the lateral to mesial sides of the enamel layer, whereas only minor variations in tilt angle were found relative to enamel thickness at given locations across the enamel layer. The decussation angle between alternating rows of rod profiles within the inner enamel layer was fairly constant from the lateral to central labial sides of the enamel layer, but it increased dramatically in the mesial region of the enamel layer. The packing density of all rod profiles decreased from lateral to central labial regions of the enamel layer and then in progressing mesially, decreased slightly (inner enamel, mesial tilt), increased slightly (outer enamel layer) or almost doubled in magnitude (inner enamel, lateral tilt). It was concluded that these variations in rod tilt angle and packing densities are adaptations that allow the tooth to maintain a sharp incisal edge and shovel‐shape as renewing segments formed by around 7200 ameloblasts are brought onto the occluding surface of the tooth by continuous renewal.

Anatomo-radiologic Correlation of the Mesial Aspect of the Temporal Lobe and its Application to Epilepsy Surgery

The study of the mesial aspect has gained importance due to its anatomic complexity and its relationship to the surgical treatment of epilepsy. The aim of this paper is to do an anatomo-radiologic correlation of the morphology and topography of the mesial aspect of the temporal lobe, with its neurosurgical application in the treatment of diseases in the region. Eight (8) adult formalin fixed hemispheres with no pathologic signs were studied. On 4 of them sections within the 3 planes were performed (sagittal, coronal and axial), for radiologic correlation. On the remaining 4, dissection of the mesial region was done, in order to correlate the structures found during surgical approach to the region. Both in the cadaveric hemispheres and in the radiologic images, structures from the mesial region were identified, this included: collateral sulcus, rinal sulcus, parahippocampal gyrus, temporal uncus, hippocampal sulcus, hippocampus with its 3 sectors (head, body and tail), the inferior choroidal point and the collicular point that divides the hippocampus intro 3 sectors (anterior, medium and posterior). With the results obtained, the principal anamoto- radiologic aspects of the approach to the mesial aspect of the temporal lobe were analyzed, comparing them with results of previous reports. The proper knowledge of both morphologic and topographic anatomy of the mesial aspect of the temporal lobe is crucial for both interpreting radiologic studies and a correct surgical approach for surgical treatment of epilepsy.

F123. Ultra-high-density scalp EEG outperforms localized invasive ECoG grids in inferring depth of seizure foci

Introduction During pre-surgical evaluation for medically intractable epilepsy, intracranial electrocorticography (ECoG) is often used to locate seizure foci. However, ECoG grids usually have small spatial coverage because large coverage requires large craniotomies. This may pose difficulties in inferring the depth of the focus, which is important because foci can lie deep inside the brain, e.g. in insular, mesial or basal regions, or within a sulcus. Our team recently demonstrated theoretically [Grover & Venkatesh, Proc. IEEE, ‘17] and experimentally[Robinson et al., Scientific Reports ‘17] that ultra-high-density (UHD) scalp EEG (with sub-centimeter electrode spacing) can recover high spatial resolution information of brain activity. Here, we ask whether UHD-EEG with full scalp coverage can outperform spatially localized ECoG grids in inferring the depth of seizure foci. Methods In our simulation study, ECoG and UHD-EEG electrodes were placed on a template-head MRI. Brainstorm and OpenMEEG were used to generate EEG and ECoG forward models using the Boundary Element Method for the ICBM-152 Brain template with 15,765 dipoles. For 20-electrode ECoG simulations, 8 different locations were considered (over frontal, fronto-parietal, posterior-temporal and occipital regions on left and right hemispheres), with sources at different locations in each case. For 40-electrode ECoG simulations, two adjacent 20-electrode ECoG grids were considered, again for varying source locations. A single radially oriented dipole was manually activated at different depths from each of the 8 locations on the cortex, beneath the 20-electrode ECoG grid. For EEG, 128, 256 and 1378 electrodes (the last being a theoretical UHD EEG system) with whole scalp coverage were considered. Noiseless ECoG and EEG recordings were simulated, and source localization was performed to estimate the source location using the L2-regularized MNE algorithm. Results of source localization were then compared using two standard metrics: the distance of the center of the reconstruction from the true source (bias) and the diffusive extent of the reconstruction (width of Point Spread Function, PSF). Results The reconstruction-bias using UHD-EEG is consistently about 2 cm less than any ECoG reconstruction. PSF widths of deeper sources are observed to be slightly larger for ultra-high-density EEG than other modalities. Nevertheless, visual inference of depth is more accurate using reconstructions of ultra-high-density EEG. Conclusion UHD-EEG can complement other modalities used during pre-surgical evaluation for epilepsy, before and after intracranial electrode implantation, particularly for inferring the presence of a deep seizure focus. ECoG recordings strongly bias reconstructions towards the cortical surface. Future work will similarly compare stereo-EEG and UHD-EEG, for inferring depth of seizure foci, and evaluate how UHD-EEG can inform stereo-EEG electrode placement.