Morphological Changes of Rat Periodontium in Supraocclusal Relations of Individual Teeth in the Age Aspect

Although the issue of the occlusal load influence on the occurrence of pathological phenomena in the body has been discussed for decades, it is still a subject of debate. Pathogenic occlusion is defined as excessive occlusal forces (premature contacts and interference) that can cause injuries to the dentition, including teeth and periodontal tissues. Changes in occlusal dimensions, if not properly performed or treated, can lead to dysfunctions of the dentition, such as joint clicking, difficulty in chewing, occlusal discomfort, muscle fatigue, and pain. Aim: to determine the morphological changes of periodontium in rats of different age groups in the supraocclusal relationship of individual teeth in the age aspect. Materials and methods of the study. The study was conducted on 60 white laboratory rats aged 4 to 22 months and weighing 90 to 330 g. The rats were divided into control (30 animals) and experimental (30 animals) groups. Each group was divided into 3 subgroups (10 animals each) depending on the age of the rats: young, mature and senile. Young animals included rats aged 3 4 months with a weight of 90 100 g; mature animals aged 6-8 months with a weight of 150 170 g; senile rats 20 22 months and weighing 200 220 g. In the experimental group, the state of supraocclusion was modeled by increasing the height of the lower right second molars by placing 1 mm high filling. For the placement of the filling, 37% orthophosphorus etching gel for enamel and dentin (Latus, Ukraine), microapplicators (Latus, Ukraine), the fifth generation Prime&Bond NT adhesive system (Dentsply Sirona, Germany), the universal microhybrid light-curing composite material Latelux (Latus, Ukraine) and the photopolymerizer LED.D (WOODPECKER, China) were used according to the manufacturer's instructions. The experimental animals were withdrawn from the experiment on the 15th day by decapitation under general anesthesia with sodium thiopental. The lower jaws were skeletonized, and dental blocks were cut out in the area of the molars. For histological examination, the dental blocks were fixed in a 10% solution of neutral formalin for two days, dehydrated in alcohols of increasing concentration and embedded in paraffin. Then, sections were made from the obtained preparations on a Shandon Finesse 325 rotary microtome with a section thickness of 4-6 μm. The histological sections were fixed on degreased slides and dried. Van Gieson staining was performed. The width of the periodontal gap was determined using the ZEISS ZEN 3.7 program by Carl Zeiss Microscopy. Results of the study. Histometric analysis has showed significant morphological changes in the experimental group of all age categories. In young rats, the fibrinoid edema phenomena of the periodontal ligament collagen fibers were observed. In mature rats, there was a picture of mucoid edema of collagen fibers of the periodontal ligament. In senile rats, fibrinoid necrosis of collagen fibers of the periodontal ligament were discovered, an inflammatory infiltrate, macrophages and neutrophils, with a predominance of neutrophilic inflammatory microenvironment, and initial hyaline tissue changes were found. In all age groups, there was cement resorption on the lateral surfaces of the tooth root, lacunar resorption of alveolar bone tissue and the presence of a large number of osteoclasts. In senile rats, hypercementosis was determined in the apical part of the root. In the control group of all age categories, neither resorption nor disorganization of connective tissue, nor hypercementosis was detected. Conclusions. The study shows that traumatic occlusion leads to resorption of root and alveolar cementum in all age groups. In young rats, traumatic occlusion causes fibrinoid edema of collagen fibers of the periodontal ligament. In mature rats, traumatic occlusion causes mucoid edema of collagen fibers of the periodontal ligament. In senile rats, traumatic occlusion causes fibrinoid necrosis of collagen fibers of the periodontal ligament, initial hyaline tissue changes and hypercementosis.