Pore size measurements and some age-related changes in human alveolar bone and rat femur

Age-related alveolar bone maladaptation in adult orthodontics: finding new ways out

Compared with teenage patients, adult patients generally show a slower rate of tooth movement and more pronounced alveolar bone loss during orthodontic treatment, indicating the maladaptation of alveolar bone homeostasis under orthodontic force. However, this phenomenon is not well-elucidated to date, leading to increased treatment difficulties and unsatisfactory treatment outcomes in adult orthodontics. Aiming to provide a comprehensive knowledge and further inspire insightful understanding towards this issue, this review summarizes the current evidence and underlying mechanisms. The age-related abatements in mechanosensing and mechanotransduction in adult cells and periodontal tissue may contribute to retarded and unbalanced bone metabolism, thus hindering alveolar bone reconstruction during orthodontic treatment. To this end, periodontal surgery, physical and chemical cues are being developed to reactivate or rejuvenate the aging periodontium and restore the dynamic equilibrium of orthodontic-mediated alveolar bone metabolism. We anticipate that this review will present a general overview of the role that aging plays in orthodontic alveolar bone metabolism and shed new light on the prospective ways out of the impasse.

Age-related osteogenesis on lateral force application to rat incisor – Part III: Periodontal and periosteal bone remodeling

Objectives:

This study was aimed to compare the histological pattern of bone modeling on either periodontal or periosteal side induced by lateral orthodontic tooth movement in different age groups.

Material and Methods:

A total of 50 male Sprague-Dawley rats (25 rats in the adult group – 52 weeks and 25 rats in the young group – 10 weeks) were utilized in this study. Each age group was classified into the control, 3 days, 7 days, 14 days, and 21 days groups (five rats in each) by the duration of experimental device application. A double-helical spring was produced using 0.014” stainless steel wire to provide 40 g lateral force to the left and right incisors. Hematoxylin-eosin staining, proliferating cell nuclear antigen (PCNA) immunohistochemical staining, fibroblast growth factor receptor 2 (FGFR2) immunohistochemical staining, and Masson trichrome staining were performed; and the slides were subject to histological examination.

Results:

In 7 days, active bone modeling represented by the scalloped surface was observed on the periosteal side of the crestal and middle alveolus at the pressure side in the young group, while similar changes were observed only on the crestal area in the adult group. In the young group, the number of PCNA-positive cells increased significantly on the crestal area and middle alveolus on the 3, 7, and 14 day groups, with subsequent decrease at 21 days. In the adult group, PCNA-positive cells were localized on the crestal area throughout the period. In the young group, FGFR2-positive cells were observed mainly on the crestal and middle alveolus at 3, 7, and 14 days than the control group. In the adult group, these cells appeared on the crestal and middle alveolus in the 3 days group, but mainly on the crestal area at 14 days. In the young group, FGFR2-positive cells were observed on the crestal and middle alveolus on the 3, 7, and 14 days groups more than on the control group. In the adult group, these cells appeared on the crestal and middle alveolus in the 3 days group, but mainly on the crestal area in the 14 days group. In Masson trichrome stain, an increased number of type I collagen fibers were observed after helical spring activation in both age groups. Large resorption lacunae indicating undermining bone resorption were progressively present in both young and adult groups.

Conclusion:

According to these results, orthodontic tooth movement may stimulate cell proliferation and differentiation primarily on the periosteal side according to progressive undermining bone resorption on the periodontal side. This response may lead to prominent bone modeling during tooth movement in the young group, compared to the relatively delayed response in the adult group.

Age effect on orthodontic tooth movement rate and the composition of gingival crevicular fluid : A literature review

PURPOSE

To evaluate and form a comprehensive understanding of the effect of patient age on bone remodeling and consequently on the rate of orthodontic tooth movement (OTM).

METHODS

A systematic search in PubMed and Embase from 1990 to December 2017 was performed and completed by a hand search. Prospective clinical trials which investigated the rate of OTM and/or studies assessing age-related changes in the composition of gingival crevicular fluid (GCF) in older compared to younger study groups were included. Study selection, data extraction and risk of bias were assessed by two authors.

RESULTS

Eight studies fulfilled the inclusion criteria. Among them, four evaluated the rate of OTM and six investigated mediators in the GCF (prostaglandin E₂, interleukin [IL]-1β, IL‑6, IL‑1 receptor antagonist, receptor activator of nuclear factor kappa‑Β ligand, osteoprotegerin, granulocyte-macrophage colony-stimulating factor, pentraxin 3). Patient age ranged between 16 and 43 years for older and <16 years for younger groups. In most of the studies, the younger patients showed faster OTM in the first phase of treatment and more pronounced cytokine levels. Older patients had a delayed reaction to orthodontic forces.

CONCLUSION

The small number of included studies and large heterogeneity in study design give limited clinical evidence that the older patients are less responsive to orthodontic force in comparison to younger patients. The initial cellular response to orthodontic force is expected to be delayed in older patients. Control intervals during orthodontic treatment should be adjusted to the individual's treatment response.

Age effects on orthodontic treatment: adolescents contrasted with adults

Skeletodental treatment changes in 30 adolescent girls and 26 women who had Class II, Division 1 malocclusions were contrasted cephalometrically, primarily with the McNamara analysis. The data show that adult treatment does not obligate the practitioner to longer treatment. In this study, both age groups were treated in 2.5 years on the average. Apical base corrections were achieved with equal facility in both groups by the posterior remodeling of point A, and this (in conjunction with unrestrained mandibular growth) is the major source of correction in the adolescents. In adults, in whom growth is trivial, an appreciable source of sagittal correction is the steepening of the occlusal plane. Several sequelae of Class II elastic force occurred as by-products of molar correction in the adults: increased mandibular molar eruption, increased maxillary molar intrusion, increased maxillary incisor eruption, increased mandibular incisor intrusion, and steepening of the occlusal plane.

Characteristics of an ovariectomized osteopenic rat model

Although osteoporosis induced by ovariectomy (Ovx) in the rat has been widely used as a model for postmenopausal osteoporosis in humans, the findings of different investigators are not always consistent. This might be mainly due to differences in the age of the animals at Ovx, time after Ovx, and the variables measured. Therefore, in the present study, Ovx was performed at 4, 10, or 52 weeks and bone changes were observed in rats for 6 months. The effects of Ovx on body weight, femoral length, and femoral volume were marked in rats operated on at the age of 4 weeks, slight in rats operated on at the age of 52 weeks, and intermediate in rats operated on at the age of 10 weeks. A reduction in the ratio of cortical thickness to bone width at the midshaft of the femur was observed only in rats ovariectomized at 52 weeks of age. The specific gravity of the femur and the density of the metaphysis of the femur decreased after Ovx in all rats. The ratio of ash weight to dry weight of the femur, a measure of the normal calcification of bone, was unchanged shortly after Ovx but gradually decreased in all rats.

The effect of age on tooth movement and mineral density in the alveolar tissues of the rat

A comparison of tooth movement cycles and changes in alveolar tissue mineral densities was made between young (21 to 28 days old) and adult (90 to 100 days old) rats. An initial 60-g mesial tipping force was applied to the maxillary first molars; tooth movement was estimated by measuring the opening between first and second molars, and tissue mineral density by sample ash weight per cubic centimeter. A characteristic three-part tooth movement cycle was found in both groups of rats. This cycle consists of an early "instantaneous" movement that is a function of the viscoelastic properties of the tissues, a delay period during which little tooth movement occurs due to hyalinization and undermining resorption, and a late period during which bone remodeling and tooth movement occur. Compared with the adult group, the amount of "instantaneous" movement in the young rats was greater (P less than 0.001), the delay period was shorter, and the rate of late tooth movement was faster (P less than 0.001). The young rats had significantly lower (P less than 0.05) mineral densities before orthodontic treatment. Both groups experienced a slight but insignificant increase in density followed by rapid declines to a nadir that was not different between the groups. The young rats reached this point by day 5 and the adults by day 7. The point of lowest mineral density occurred in the treated alveolar tissues toward the end of the delay period for each group and was followed by a return to control values at rates that were not significantly different between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)