Distal Grooves Research Articles

Root groove depth and inter-orifice canal distance as anatomical predictive factors for danger zone in the mesial root of mandibular first molars.

This study evaluated the danger zone (DZ) in mesial roots of mandibular molars and the correlation between anatomical references of the DZ and some anatomical landmarks including tooth/root length, depth of mesial and distal grooves, and inter-canal orifices distance. Twenty-eight mesial roots of mandibular molars with 2 independent canals were scanned and divided into 2 groups according to root length. The anatomical landmarks were correlated (Pearson or Spearman coefficients) with root level, thickness, and position of the DZ and also compared (independent samples t or Mann-Whitney tests) between the 2 groups at α = 5%. No statistical difference was observed between groups regarding DZ parameters and depth of mesial and distal grooves (P > 0.05). Orifice distance in group 2 (4.49 ± 0.75 mm) was significantly greater than group 1 (3.76 ± 0.89 mm) (P < 0.05). Significant correlations (P < 0.05) were found between (i) DZ level and root/tooth length (r = 0.54 and 0.49, respectively), (ii) DZ thickness and distal groove depth (r = - 0.45), and orifice distance (r = 0.38), and (iii) DZ position and depth of mesial (r = 0.39) and distal (r = 0.40) grooves. Other variables such as root length and distal groove depth (r = 0.28), and orifice distance and mesial groove depth (r = 0.36) were also correlated (P < 0.05). The length of tooth/root, the distance of canal orifices, and the depth of mesial/distal grooves of mesial roots of mandibular molars might be predictive factors for the root level, position, and thickness of the DZ. The length, distance of mesial canal orifices, and the depth of mesial and distal grooves of the mesial roots of mandibular molars might be moderate predictive factors for the root level, position, and thickness of the DZ.

Binding Interface of Gapdh to the Au Rich Elements from TNF-Alpha mRNA Revealed by Hydrogen Deuterium Exchange Coupled with Mass Spectrometry

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a ubiquitous protein primarily known for its glycolytic function. More recent studies have revealed GAPDH as a multifaceted, multifunctional protein involved in various cellular processes including iron homeostasis, heme transport, apoptosis, tumerogenesis, oxidative stress response, chromatin structure among many others. As part of its multifunctional purpose, GAPDH has been shown to bind to various cellular RNAs and has been classified as a non-canonical RNA binding protein. In particular, it has been shown to bind AU-rich element of mRNA transcripts and consequently affecting translation. However, the detailed structural characterization of the RNA bound complex has remained elusive. The RNA binding site remains unknown thereby restricting potential therapeutic strategies. Our previous studies established that GAPDH binds the AU rich element of TNF-α mRNA transcript via a two-step model. In addition, we have shown that a T229K mutant of GAPDH displayed altered RNA and NAD+ binding properties, potentially signaling to a linkage between RNA binding and the cofactor. Hydrogen deuterium exchange coupled with mass spectrometry (HDX-MS) revealed that the T229K mutant induced conformational changes into distal grooves along the P-axis of the tetrameric protein. In this study, we have mapped the binding interfaces of three GAPDH constructs displaying varying NAD+ binding properties with the AU rich element from TNF-α mRNA using HDX-MS. A largely common pattern of localized protection from exchange pointed to the grooves along the P-axis as the RNA binding interfaces, as hypothesized. Additionally, some variations in HDX protection point to potential conformational basis for the linkage with NAD+ binding.

Crown morphology and variation of the lower premolars of Zhoukoudian Homo erectus

Traditional descriptive observation and advanced geometric morphometric are employed to study the morphological characteristics of Zhoukoudian mandibular premolars, and simultaneously with the specimens of Australopithecus, African early Homo, Homo erectus in other areas of Asia except Zhoukoudian, Europe Pleistocene fossil hominins, and recent Chinese (72 P3 and 69 P4 on the whole) being included as comparisons. Results suggest obvious evolutionary changes in the occlusal morphology and crown outline shape of mandibular premolars. Australopithecus P3s are found with extremely asymmetrical crown outlines, prominent mesial and distal vertical grooves on the buccal side, open foveas, and well-developed talonids, and P4s with similarly asymmetrical crown outlines, distinct mesial and distal vertical grooves on the buccal side, and “H” type of grooves combination. These characteristics are also expressed in the later hominin specimens, but with a decreased extent and lower frequency. The P3s of recent Chinese, slightly asymmetrical in the crown lingual contours, and P4s, basically symmetrical in the crown outlines, become faint or disappeared in the mesial or distal vertical buccal grooves, and decreased in the talonid size. It is suggested that Zhoukoudian mandibular premolars preserve some primitive traits of earlier hominins, including asymmetrical crown outlines and prominent mesial and distal vertical grooves of buccal side. Moreover, Zhoukoudian specimens exhibit obvious morphological variation between individuals, expressed mainly by aspects of mesial and distal vertical buccal grooves in various degrees, symmetry or asymmetry extent of crown lingual contour, relative location of polygon to the corresponding surrounding outline, as well as the relative size of talonid. When compared with Homo erectus from the other areas of Asia, Zhoukoudian specimens show their similarity with those of Xichuan and S-1, and at the same time great discrepancy with S-6 in the occlusal morphology and crown outline shape. When it comes to the relationship between specimens of Europe Pleistocene and Zhoukoudian, disparity is expressed in a stronger way than the corresponding similarity.

Impact of Interproximal Groove Placement and Remaining Coronal Tooth Structure on the Fracture Resistance of Endodontically Treated Maxillary Anterior Teeth

This in vitro study investigated the effect of grooves, remaining tooth structure, and their combination on tooth fracture resistance of endodontically treated anterior teeth with cast dowel and cores. Sixty extracted maxillary anterior teeth of similar dimensions were endodontically treated and then randomly divided into three groups of 20 teeth each. The teeth in the first group were cut horizontally at the widest part of their anatomical crowns. Three hundred and sixty degree 1 and 2 mm axial walls for ferrule effect were provided for the teeth in the second and the third groups, respectively. Cast dowel and cores were fabricated for all teeth. Each group was then subdivided in two groups: one with no grooves and another with mesial and distal grooves. Hence, six groups were created as follows: (1) teeth with no remaining coronal tooth structure and no grooves (group A-control); (2) teeth with no remaining coronal tooth structure, with mesial and distal grooves (group B); (3) teeth with 1 mm remaining coronal tooth structure, with no grooves (group C); (4) teeth with 1 mm remaining coronal tooth structure, with mesial and distal grooves (group D); (5) teeth with 2 mm remaining coronal tooth structure and no grooves (group E); and (6) teeth with 2 mm remaining coronal tooth structure, with mesial and distal grooves (group F). Complete cast crowns were then fabricated for all teeth. A universal testing machine applied controlled loads to the teeth at a crosshead speed of 2.54 mm/min at an angle of 130 degrees to the long axes of the teeth until failure occurred. The loads were applied 2 mm lower than the incisal edges of the specimens. Descriptive statistics, one-way ANOVA (alpha= 0.05) and Tukey's honestly significant difference (HSD) tests were used to determine the effect of failure loads among the tested groups (alpha= 0.05). The mean failure loads were (N): group A (control), 151.21 +/- 38.18; group B, 221.53 +/- 107.03; group C, 295.35 +/- 81.92; group D, 270.20 +/- 76.01; group E, 491.70 +/- 180.36; group F, 432.67 +/- 193.83. Group E presented the highest failure load and group A (control) the lowest. The inclusion of interproximal grooves on the cast dowel and cores of endodontically treated anterior teeth with 1-2 mm of remaining coronal tooth structure does not significantly lower the failure threshold.

An in vitro study of dentin exposure during resin-bonded fixed partial denture preparation

Objectives The aim of this in vitro study was to investigate whether dentin is exposed during tooth preparation for resin-bonded fixed partial dentures and, if so, to quantify the amount of dentin exposure. Method and materials Twenty extracted premolars were prepared in the following manner: The palatolingual and proximal axial surfaces were reduced by 0.50 mm. Mesial and distal grooves, 1.00 mm in depth, and mesial and distal occlusal rest seats, measuring 2.00 mm buccolingually × 1.50 mm mesiodistally × 1.00 mm deep, were prepared. The specimens were stained with a modified van Gieson's stain to identify dentin exposure, mounted on a jig to allow standardization, and photographed after 30-degree rotation to create a panoramic image of each tooth. The image was modified and analyzed to measure the percentage of the preparation area that exhibited dentin exposure. Results Dentin exposure was noted in all specimens. The mean area of dentin exposure was 11.06 mm 2 (16.15% of the preparation area). The minimum and maximum areas of dentin exposure were 4.07 mm 2 (7.03%) and 19.73 mm 2 (27.28%), respectively. Conclusion Dentin is exposed during resin-bonded fixed partial denture preparation if current tooth preparation guidelines are followed, despite the commonly made recommendation that the preparation remain within enamel. The region of the grooves consistently exhibited exposed dentin; exposure at the cervical margin was variable. — Reprinted with permission of Quintessence Publishing.

Evaluation of resistance form for prepared teeth

Resistance form of preparations for which castings were made in a large dental laboratory was evaluated. Each preparation was also evaluated for the placement of grooves. Evaluation of resistance form was done by grasping the casting between thumb and index finger and attempting to roll the uncemented casting off the die with finger pressure. Each preparation was tested for resistance form in all directions (buecal, lingual, mesial, and distal), from a fixed, point of rotation. Evaluation was by tooth groups: incisors, canines, premolar, and molars. The preparations were found to have resistance form in 96% of the incisors, 92% of the canines, 81 % of the premolars and only 46% of the molars. Only nine of 294 preparations evaluated had grooves. Mesial or distal grooves provided resistance to buecal and lingual dislodgment, and buccal or lingual grooves provided resistance to mesial and distal dislodgment.