Rat molar eruption and occlusion data were compiled from several studies but several inconsistencies were found, rendering the planning of eruptional studies difficult and imprecise. Our aim was to measure eruption and occlusion days, as well as eruption velocity, in the upper and lower three molars from infancy to end of adolescence in the rat. A total of 19 male and female Wistar rats were scanned daily by micro-computed tomography (CT) from day 15 to 70. We measured the eruption of all maxillary and mandibular molars with reference points at the hard palate and mandibular canal at three stages: pre-emergent, pre-occlusal, and functional. Statistical analysis was performed with a mixed-model analysis of variance (ANOVA) and a Sidak post hoc test. The first molar erupts on average on day 17, the second molar on day 20, and the third molar on day 33. The eruption velocity of the first molar was the highest at 90.9 microns/day (standard error (se) = 12.80), followed by the second molar at 65.9 microns/day (se = 5.80), and the lowest was the third at 47.0 microns/day (se = 3.28), ( p < 0.001). On average, the pre-occlusal phase had the highest velocity at 97.2 microns/day (se = 1.72), the pre-emergent was lower at 84.9 (se = 2.29), and the functional was the lowest at 21.7 (se = 0.45), ( p < 0.001). The eruption rate decreased from the first to third molar and was also different between phases: the pre-occlusal phase had the highest rate, closely followed by the pre-emergent phase while the functional eruption rate was significantly lower than the other phases.
Different demands on the muscles of mastication may influence their functional profile (size and distribution of muscle fibre types), which may change during growth and maturation, potentially influencing craniofacial growth. The aim of this study was to evaluate mRNA expression and cross-sectional area of masticatory muscle fibres compared with limb muscles in young and adult rats. Twenty-four rats were sacrificed at two different ages, namely 12 at 4 weeks (young) and 12 at 26 weeks (adult). The masseter, digastric, gastrocnemius and soleus muscles were dissected. Gene expression of myosin heavy-chain isoforms Myh7 (MyHC-I), Myh2 (MyHC-IIa), Myh4 (MyHC-IIb) and Myh1 (MyHC-IIx) in the muscles was measured using qRT-PCR RNA analysis, and immunofluorescence staining was performed to measure the cross-sectional area of different muscle fibre types. Different muscle types and ages were compared. Significant differences were found in the functional profile between masticatory and limb muscles. For the masticatory muscles, there was an increase in Myh4 expression with age, and this change was more intense for the masseter muscles, which also presented an increase in Myh1 expression, similarly to limb muscles. The fibre cross-sectional area of the masticatory muscles was generally smaller in young rats; however, this difference was less pronounced than in limb muscles.
Objective: Certain malocclusions or unilateral tooth loss can lead to asymmetric functional load of the two mandibular sides during mastication and induce skeletal asymmetries to the condylar process of growing individuals. However, in adults, asymmetric function may have a different impact. The aim of the present study was to investigate three-dimensionally the effects of unilateral masticatory function on the condylar process morphology in growing and adult rats and the adaptive processes to differential condylar loading. Materials and Methods:Fifty-six growing and adult Wistar rats aged 4 and 26 weeks respectively were obtained. The maxillary right molars of the experimental animals were extracted and all animals were followed for 12 weeks. Three-dimensional images were obtained by an in-vivo microcomputed tomography (micro-CT) examination. The following measurements were studied: condylar process height, condylar base width, and condylar cross-sectional surface.Results: While no differences were found with regards to condylar process height and base width, the cross-section of the condyle on the extraction side did not increase during growth in the young rats. No such differences were found in adults. Young rats had statistically significantly shorter condylar height, base width and cross-sectional surface than the adult rats and showed significant growth of these structures during the experimental period. Conclusion:Condylar height and base width growth are not hindered by reduced occlusal function, contrary to the average cross-sectional surface, which implies that the condyle form of growing individuals becomes thinner while maintaining its length, in the absence of occlusal stimuli. The condyle of adult rats with extractions is less affected by occlusion changes.
Οι μεταβολές που επέφερε η ανάπτυξη και η εξέλιξη των Τεχνολογιών της Πληροφορίας και των Επικοινωνιών (ΤΠΕ), σε κοινωνικοοικονομικό, επιστημονικό και τεχνολογικό επίπεδο, σε συνδυασμό με την ταχύτατη παλαίωση της γνώσης, επιδρούν καθοριστικά στην επιστημολογική οπτική για την ουσία της γνώσης και οδήγησαν στην ανάγκη ουσιαστικής ενσωμάτωσης των ΤΠΕ στα εκπαιδευτικά συστήματα και ειδικότερα στο Δημοτικό Σχολείο. Η έρευνα αυτή αποσκοπεί στην εμπειρική διερεύνηση των διαδικασιών ενσωμάτωσης των ΤΠΕ στο Δημοτικό Σχολείο στη χώρα μας και ειδικότερα στην κατασκευή ενός ολιστικού μοντέλου των παραγόντων που επιδρούν στη διαδικασία της ενσωμάτωσης των ΤΠΕ, εντός του κοινωνικού πλαισίου του Δημοτικού Σχολείου. Από την άποψη του θεωρητικού υπόβαθρου και των αντίστοιχων μεθοδολογικών επιλογών υιοθετείται μια ολιστική-πολυπαραγοντική προσέγγιση στην κατεύθυνση της σχολικής βελτίωσης (school improvement). Κατασκευάστηκε ένα θεωρητικό εννοιολογικό πλαίσιο των παραγόντων που εμπλέκονται στην ενσωμάτωση των ΤΠΕ στο Δημοτικό Σχολείο, με βάση τη σχετική βιβλιογραφία, συνεκτιμώντας τα ιδιαίτερα χαρακτηριστικά του Δημοτικού Σχολείου στη χώρα μας. Αυτό το θεωρητικό πλαίσιο ελέγχθηκε ερευνητικά, μέσω ποσοτικής έρευνας, με τη χρήση ενός κατάλληλου ερευνητικού εργαλείου (ερωτηματολόγιο), το οποίο κατασκευάστηκε από την ερευνήτρια. Η ανάλυση των ερευνητικών δεδομένων βασίστηκε στη στατιστική τεχνική της παραγοντικής ανάλυσης (Factor Analysis), ώστε να διερευνηθεί ο βαθμός προσαρμογής των ερευνητικών δεδομένων σε κάθε παράγοντα του θεωρητικού πλαισίου, προκειμένου να προκύψει ένα στατιστικά επικυρωμένο ολιστικό μοντέλο των παραγόντων, οι οποίοι επηρεάζουν άμεσα ή έμμεσα τη διαδικασία ενσωμάτωσης των ΤΠΕ στο Δημοτικό Σχολείο στη χώρα μας. Από τη διαδικασία αυτή κατασκευάστηκαν, επίσης, και οι αντίστοιχες κλίμακες μέτρησης για καθέναν από τους παράγοντες του ολιστικού μοντέλου. Τα αποτελέσματα της έρευνας επιβεβαιώνουν την ισχύ του θεωρητικού-υποθετικού πλαισίου. Ωστόσο, όπως προκύπτει από τα ευρήματα της έρευνας οι παράγοντες που σχετίζονται με τα ατομικά χαρακτηριστικά των δασκάλων και ιδιαίτερα η επιμόρφωση σε θέματα παιδαγωγικής αξιοποίησης των ΤΠΕ, αναδεικνύεται ως ο σημαντικότερος παράγοντας του εμπειρικού μοντέλου. Η έννοια της ετοιμότητας του Δημοτικού Σχολείου για ενσωμάτωση των ΤΠΕ σχεδόν ταυτίζεται με τη χρήση των ΤΠΕ από τους δασκάλους, ενώ καταγράφεται η ανάγκη για βελτίωση των όρων και των προϋποθέσεων που σχετίζονται με τη σχολική βελτίωση και την εκπαιδευτική αλλαγή.
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