Molecular mechanisms underlying the effect of tooth shortening on memory dysfunction in Wistar male rat

OBJECTIVE

We investigated the effects of molar tooth shortening on the mRNA expression of the AβPP/BACE1, BDNF/TrkB, and Bax/Bcl-2 signaling pathways in the Wistar male rat hippocampal regions.

DESIGN

Four groups (n = 5 per group) of male Wistar rats (control, SRM (shortened right molar), SLM (shortened left molar), and SBM (shortened bilateral molar)) were used. RNA was isolated from the hippocampus and transformed into cDNA. Real-time quantitative PCR was used to evaluate the mRNA expression levels of AβPP, BACE1, Bax, Bcl-2, BDNF, and TrkB.

RESULTS

Differential mRNA expression was observed in rat groups. SBM significantly upregulated the AβPP, BACE1, and Bax mRNA expressions, whereas the expression levels of Bcl-2, BDNF, and TrkB were decreased. SRM and SLM approximately had the same effect on the expression enhancement of AβPP, BACE1, and Bax; however, SRM was more effective than SLM in increasing the expression of these genes.

CONCLUSIONS

Symmetrical molar teeth shortening affected the mRNA expression of AβPP and BACE1, which is related to learning and memory dysfunction.

Tooth agenesis patterns and variants in PAX9: A systematic review

Mutations in PAX9 are the most common genetic cause of tooth agenesis (TA). The aim of this study was to systematically review the profiles of the TA and PAX9 variants and establish their genotype-phenotype correlation. Forty articles were eligible for 178 patients and 61 mutations (26 in frame and 32 null mutations). PAX9 mutations predominantly affected molars, mostly the second molar, and the mandibular first premolar was the least affected. More missing teeth were found in the maxilla than the mandible, and with null mutations than in-frame mutations. The number of missing teeth was correlated with the locations of the in-frame mutations with the C-terminus mutations demonstrating the fewest missing teeth. The null mutation location did not influence the number of missing teeth. Null mutations in all locations predominantly affected molars. For the in-frame mutations, a missing second molar was commonly associated with mutations in the highly conserved paired DNA-binding domain, particularly the linking peptide (100% prevalence). In contrast, C-terminus mutations were rarely associated with missing second molars and anterior teeth, but were commonly related to an absent second premolar. These finding indicate that the mutation type and position contribute to different degrees of loss of PAX9 function that further differentially influences the manifestations of TA. This study provides novel information on the correlation of the PAX9 genotype-phenotype, aiding in the genetic counseling for TA.

On edge chipping in molar teeth from blunt occlusal contact

Edge chipping is a leading failure mode in dental teeth. Virtually all chipping studies are limited to Vickers indentation on polished cusps of molar teeth. Such works are here extended to spherical contact. Occlusal loads are applied on the tooth's central fossa or a polished cusp using ball radii ranging from 0.4 to 5.16 mm. The chip dimensions are characterized by h/Dm and D/Dm, where h, D and Dm denote indent distance, chip size and tooth crown diameter. For the fossa loading, h/Dm, D/Dm and the least chipping force Pch are virtually independent of ball radius r for r < ≈ 4 mm. In this range, h/Dm and D/Dm lie between ≈0.30 to 0.36 and 0.51 to 0.69, respectively, while Pch equals ≈1330 N. For r > ≈ 4 mm, the failure occurs by debonding of enamel sectors from the dentin core. In the case of cusp loading, h/Dm < ≈ 0.3 while D/Dm and Pch vary with r. For relatively small h or large r, the failure occurs as soon as radial cracks initiate under the loading point. For a load applied near a cusp tip, the failure occurs by enamel debonding. Finally, the present work is easily extendable to fossil teeth of hominins and apes as well as prosthetic teeth. The morphological features obtained in such studies should provide quantitative means to assess the relationships between chip dimensions, chipping force and diet characteristics.

Morphological and radiological mapping of dental cusps in relation to spatial constraints on tooth shape of one humped camel (Camelus dromedarius)

A significant extent of researches in veterinary study have been focused on dental structure; however, there are scanty ones on the orientation and identification of their cusps. Therefore, the present article aimed to spot a light on arrangement pattern of dental cusps in the camel as a folivorous and graminivorous animal. This study was conducted on eight heads of adult, healthy camel of both sexes, collected from slaughter houses. To perform exact orientation of cusps of molar teeth, additional radiological and CT scans were performed on the mandible as a landmark that should facilitate the reading of cusps map. It was evident that, the cusps are arranged in crescentic appearance, seledontal form, with two cusps on each side, paracone and hypocone on the lingual surface and protocone and metacone on the vestibular aspect. Thus, camels cannot wear bite like equines, which would interfere with their constant chewing method. The camels' dental cusps provide some of the finest examples of convergent evolution, which offer insights both into correlates between form and function, and into how the ability of euthomorphic cusps in intrapability and stabilization of food items and its comminution between formidable cusps and occlusal spillway in between. Further studies should be done on the brachydontteeth and tropospheric cusps to fill the functional anatomy gap of teeth, in addition to diversity of cusps form. This study is considered a basic comparative anatomical study for normal healthy dentition and forensic practice, in addition to its importance in detection of local aspects of dental problems in camels.

On the evolution of the morphology and resilience of molar cusps in fossil hominid teeth

Teeth play an important role in evolutionary studies due to their good preservation and direct link to diet. The present work makes use of a previously generated database on molar teeth of fossil hominids which consists of cuspal enamel thickness d_c, dentin horn angle φ and section width D, all measured on a given histological tooth section. These data are here interpreted with the aid of "fracture stress" Q_F = P_F/D² and geological age t, where P_F is the occlusal force needed to cause cusp failure as determined from d_c and φ. Q_F is virtually a constant in non-hominins ("apes") while monotonically increasing toward present time in hominins. These two trends intersect at t = t_s = 4.5 (0.11) mya, a value similar to other divergence estimates. Q_F was fitted with a function f(t) which is proportional to (d_c/D)². The monotonic variation of Q_F and in turn d_c/D with t contrasts the more complex behavior generally characterizing other physical entities of fossil hominids. The increase in d_c/D in hominins promotes tooth resilience and in turn life span. Finally, it is suggested that P_F provides an upper bound to the maximum bite force produced by the jaw structure.

Cheek tooth erosion in male babirusa (genus Babyrousa)

The wear on the occlusal surfaces of male babirusa cheek teeth was evaluated in 53 skulls of Babyrousa babyrussa from Buru and the Sula Islands and 87 skulls of B. celebensis from Sulawesi, Indonesia. Based on the comparative lengths of their continually growing maxillary canine teeth, the skulls were divided into five 'age categories' (A-E). Numerical and symbolic codes representing tooth wear were applied to each pillar (cusp region) of the mandibular and maxillary permanent third and fourth premolar teeth, and the first, second and third permanent molar teeth. There was no significant difference between the tooth wear patters of skulls in groups A and B, or in groups C and D, and so these were amalgamated. There was close correspondence in wear patterns between each side of the mouth in both species and in each age group. The wear patterns of the mandibular and maxillary teeth, although not identical, were very similar, as were the wear patterns of both species. In group A+B for both species tooth wear was relatively slight, with the M1 teeth experiencing most relative wear. There was almost no wear of the M3 teeth. In group C+D substantial wear of upper and lower M1 was evident. In group E more widespread wear of the cheek teeth was seen, with increased severity of M1 tooth wear, yet there was comparatively much less M2 and M3 tooth wear. The pattern of cheek tooth wear of the Babyrousa spp. was different from that shown by Susscrofa. Differences in diet selection and processing were highlighted as potential contributing factors. The pattern of cheek tooth wear in male babirusa was not adequate for use to monitor their age.

The Effect of Photobiomodulation on the Depth of Anesthesia During Endodontic Treatment of Teeth With Symptomatic Irreversible Pulpitis (Double Blind Randomized Clinical Trial)

Introduction: Achieving appropriate anesthesia in patients with symptomatic irreversible pulpitis in mandibular molars during endodontic treatment is always one of the most challenging aspects. Photobiomodulation (PBM) has been used in dentistry due to its anti-inflammatory properties and regenerative effects. This study evaluates the effects of PBM in the depth of anesthesia in inferior alveolar nerve block. Methods: In this randomized clinical trial, 44 patients requiring endodontic treatment in lower molar, left or right were selected, half of them were randomly treated with PBM therapy. Laser irradiation by 980 nm diode laser with a single dose (15 J/cm2, for 20 seconds) before anesthesia was performed at the buccal aspect. Inferior alveolar nerve block was performed once. Success was defined as no or mild pain (no need for any supplemental injection), based on the visual analogue scale during access cavity preparation. Results were evaluated using SPSS software.

RESULTS

The results of this study showed that the necessity for supplemental injection was lower in the group receiving laser than in the group without laser (P = 0.033). The mean pain intensity during dentin cutting was lower in the group receiving laser than in the group without laser (P = 0.031). Also, the mean pain intensity during pulp dropping was lower in the group receiving laser, than the group without laser (P = 0.021). Conclusion: Based on the results of this study, it seems that the application of PBM before anesthesia is effective on increasing depth of anesthesia.

The Adjunctive Use of the Erbium, Chromium: Yttrium Scandium Gallium Garnet Laser in Closed Flap Periodontal Therapy. A Retrospective Cohort Study

Objectives:

The current periodontal literature has been inconsistent in finding an added advantage to using lasers in periodontal therapy. The aim of this study was to compare treatment outcomes following root surface instrumentation alone (NL group), or with adjunctive use of Erbium, Chromium: Yttrium Scandium Gallium Garnet (Er,Cr:YSGG) laser (L group).

Material and Methods:

Patients diagnosed with generalized chronic periodontitis, having a minimum of 1 year follow up were selected by a blinded party for inclusion in a retrospective analysis from patients treated prior to and after integration of laser in a single clinic setting. Probing depths (PD) of all sites ≥5 mm and full mouth bleeding scores were analyzed. Further analysis was carried out on the treatment outcomes of only the molar teeth and of pockets >6mm.

Results:

53 patients were included (25 NL,28 L). There was no significant difference between baseline PDs (NL=6.19mm, L=6.27mm, range 5-11mm). The mean PD after one year was 2.83mm (NL) 2.45mm (L), with the mean PD reductions being 3.35mm (NL) and 3.82mm (L) (p<0.002). The mean PD reduction for the molars were 3.32mm (NL) and 3.86mm (L) (p< 0.007), and for ≥7mm group were 4.75mm (NL) compared to 5.14mm (L) (p< 0.009). There was significantly less bleeding on probing in the laser group after one year (p<0.001)

Conclusion:

Both treatment modalities were effective in treating chronic periodontitis, but the added use of laser may have advantages, particularly in molar tooth sites and deeper pockets. Further research with RCTs is needed to test this hypothesis further.

On crack growth in molar teeth from contact on the inclined occlusal surface

Extracted human molar teeth are indented by hard balls laid at the central fossa, sectioned, and their interior examined for damage. Contact on the fissured enamel coat generally occurs on three distinct spots. The main forms of damage are radial cracks growing from the DEJ to the occlusal surface and median radial and cylindrical cracks growing from a contact spot to the DEJ. For large balls failure by edge chipping near a cusp apex may occur. The median cracks tend to run unstably to the DEJ upon reaching the middle part of the enamel coat. The corresponding load, PFM, and the load needed to initiate radial cracks at the DEJ, PFR, are taken to signal crown failure. The mean values of PFM and PFR are on the order of 1000N. A conical bilayer model defined by thickness d, inclination angle θ, failure stress σF and toughness KC of the enamel coat is developed to assess crown failure. The analytical predictions for PFR and PFM agree well with the tests. The results indicate that enamel thickness is so designed as to ensure that PFR and PFM just exceed the maximum bite force under normal conditions while the choice of θ seems to reflect a compromise between needs to resist crown failure and break hard food particles. Both PFR and PFM are greatly reduced with reducing d, which points to the danger posed by tooth wear. The analytical expressions for PFR and PFM may also apply to other multi-cusp mammalian or prosthetic molar crowns. Cone cracking, suppressed in the anisotropic tooth enamel, may be an important failure mode in prosthetic crowns.

Role of multiple cusps in tooth fracture

The role of multiple cusps in the biomechanics of human molar tooth fracture is analysed. A model with four cusps at the bite surface replaces the single dome structure used in previous simulations. Extended finite element modelling, with provision to embed longitudinal cracks into the enamel walls, enables full analysis of crack propagation from initial extension to final failure. The cracks propagate longitudinally around the enamel side walls from starter cracks placed either at the top surface (radial cracks) or from the tooth base (margin cracks). A feature of the crack evolution is its stability, meaning that extension occurs steadily with increasing applied force. Predictions from the model are validated by comparison with experimental data from earlier publications, in which crack development was followed in situ during occlusal loading of extracted human molars. The results show substantial increase in critical forces to produce longitudinal fractures with number of cuspal contacts, indicating a capacity for an individual tooth to spread the load during mastication. It is argued that explicit critical force equations derived in previous studies remain valid, at the least as a means for comparing the capacity for teeth of different dimensions to sustain high bite forces.