Effect of age on alveolar bone turnover adjacent to maxillary molar roots in male rats: A histomorphometric study

A persistent mineralization process in alveolar bone throughout the postnatal growth stage in rats

OBJECTIVE

Alveolar bone quality is essential for the maxillofacial integrity and function, and depends on alveolar bone mineralization. This study aims to investigate the in vivo changes in alveolar bone mineralization, from the perspective of mineral deposition and crystal transition in postnatal rats.

DESIGN

Nine postnatal time points of Wistar rats, ranging from day 1 to 56, were set to obtain the maxillary alveolar bone samples. Each time point consisted of ninety rats, with 45 females and 45 males. Macromorphology of alveolar bone was reconducted by Micro-Computed Tomography and the mineral content was quantified via Thermogravimetric analysis, Scanning Electron Microscope, High-Resolution Transmission Electron Microscopy and vibrational spectroscopy. Furthermore, the crystallinity and composition were characterized by vibrational spectroscopy, X-ray Diffraction, X-ray Photoelectron Spectroscopy and Selected Area Electron Diffraction.

RESULTS

The progressive increase of mineral deposition was accompanied by substantial growth in alveolar bone mass and volume in postnatal rats. Whereas the mineral percentage initially decreased and then increased, reaching a nadir on postnatal day 14 (P14) when tooth eruption was first observed. Besides, localized mineralization was initiated by the formation of amorphous precursors and then converted into mineral crystals, while there was no statistically significant change in the average crystallinity of the bone during growth.

CONCLUSION

Mineralization of alveolar bone is ongoing throughout the early growth in postnatal rats. Mineral deposition increases with age, whereas the crystallinity remains stable within a certain range. Besides, the mineral percentage reaches its lowest point on P14, which may be attributed to tooth eruption.

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.

Three-dimensional imaging and molecular analysis of the effects of photobiomodulation and mechanical vibration on orthodontic retention treatment in rats : Effects of photobiomodulation and mechanical vibration on orthodontic retention treatment

PURPOSE

We aimed to evaluate and compare effects of photobiomodulation (PBM) and low-magnitude high-frequency mechanical vibration (HFMV) on orthodontic retention.

METHODS

Sixty-four female Wistar albino rats were divided into 9 groups (2 negative and positive controls each, 3 PBM and 2 HFMV groups) and studied for 25 days. In the experimental groups, closed nickel-titanium closed coil springs with a 50 cN force were placed for 10 days between the maxillary incisor and molar. PBM and HFMV were applied daily over long- (15 days) and short-term (7 days) retention periods. The PBM groups received PBM with a single wavelength (650 nm) or higher wavelengths (532, 650, 940 nm) for 9 min per day. HFMV groups received HFMV of 10, 20, and 30 Hz for 10 min per day. Right and left maxilla were assessed using micro-computed tomography imaging and real-time polymerase chain reaction. The amount of tooth movement during the retention period, expression levels of cyclooxygenase‑2 (COX-2), osteoprotegerin (OPG), and receptor activator of nuclear factor-kappa B ligand (RANKL) mRNA gene expression levels, OPG/RANKL ratios, alveolar bone trabecular thickness (Tb.Th), trabecular number (Tb.N), and structure model index were analyzed. Kruskal-Wallis and Mann-Whitney U tests were used for multiple comparisons of the nonparametric distributed data and binary comparisons, respectively.

RESULTS

When using the long-term retention protocol, PBM and HFMV treatment increased Tb.N (p < 0.05) and decreased COX‑2 mRNA gene expression levels (p < 0.05) and Tb.Th (p < 0.05) compared to controls. For short-term retention, PBM and HFMV decreased the amount of relapse tooth movement compared to controls. In addition, Tb.Th (p < 0.05) and the mRNA gene expression levels of COX‑2 and RANKL (p < 0.05) were decreased.

CONCLUSION

PBM and HFMV might be able to support retention after orthodontic tooth movement by reducing bone resorption and increasing bone quality.

Periodontally accelerated osteogenic orthodontics with platelet-rich fibrin in an adult patient with periodontal disease: A case report and review of literature

BACKGROUND

In the clinical scenario, adult patients with periodontal diseases and dental malformation, characterized by dental crowding in lower anterior teeth with the thin biotype, often require orthodontic treatment. This case report aimed to evaluate the clinical and radiographic outcomes of periodontally accelerated osteogenic orthodontics (PAOO) combined with autologous platelet-rich fibrin (PRF) in an adult patient with class I malocclusion along with dental crowding, a thin periodontal biotype, and buccal plate deficiency.

CASE SUMMARY

A 32-year-old female complaining of dental crowding and gingival bleeding was referred to the orthodontic clinic. The patient underwent periodontal risk assessment prior to orthodontic treatment. She was diagnosed with a high risk of gingival recession due to dental crowding, root prominence, loss of buccal plates, and a thin gingival tissue biotype. The treatment regimen included PAOO combined with autologous PRF for alveolar augmentation and interproximal enamel reduction for moderate dental crowding. Clinically, PAOO-assisted orthodontic tooth movement in this case showed enhanced periodontium remodeling. Radiographic outcomes also showed statistically significant improvements (P < 0.01) in the mandibular buccal alveolar bone.

CONCLUSION

This case report suggests the combination of autologous PRF with PAOO to enhance bone augmentation and long-term tissue support in adult orthodontic patients with periodontal disease.

Inhibitory Effects of 4-Hexylresorcinol on Root Resorption Induced by Orthodontic Tooth Movement

Root resorption during orthodontic tooth movement (OTM) is caused by an imbalance between the bone turnover rate and applied mechanical stress. The administration of 4-hexylresorcinol (4HR) increases the bone turnover rate and factors associated with bone formation. Thus, 4HR may show protective activity against root resorption during orthodontic tooth movement (OTM). A total of 40 rats (male: 20; female: 20) were included in this study, and the mandibular first molar was subjected to excessive orthodontic force. The experimental group (n = 20) received 12.8 mg/kg of 4HR every 2 weeks. The controls (n = 20) received a solvent without 4HR. Both groups had the same sex distribution. On Day 28 after the initiation of OTM, all the animals were sacrificed for micro-computed tomography analysis, Western blot analysis, and immunohistochemistry. The ratios of the root length and root volume to the total volume were significantly higher in the experimental group compared to those in the control group (p < 0.05). The expression levels of OPG, RANKL, alkaline phosphatase, and Runx2 in the experimental group according to Western blotting were significantly higher in the experimental group compared to those in the control group (p < 0.05). Their expression was mainly found in the periodontal ligament area. In conclusion, the administration of 4HR decreased the root resorption caused by OTM and increased the expression levels of OPG, RANKL, alkaline phosphatase, and Runx2.

Could medications and biologic factors affect post-orthodontic tooth movement changes? A systematic review of animal studies

Immediately after the removal of orthodontic appliances, the teeth might start to drift away from their corrected position in an attempt to reach a new equilibrium. Medications and biologic factors could potentially modulate these processes. The objective of the present systematic review is to systematically investigate and appraise the quality of the evidence regarding the effect of various medications and biologic factors on the rate of relapse following active tooth movement. Search without restrictions in eight databases and hand searching until April 2020 were conducted. Studies performed on animal models investigating the effects of medication and biologic factors on the rate of relapse following orthodontic tooth movement were considered. Following study retrieval and selection, relevant data were extracted and the risk of bias was assessed. Seventeen studies were finally identified, mostly at either high or unclear risk of bias. Ketorolac did not show any significant effects on relapse, while the administration of tetracycline, atorvastatin, psoralen and raloxifene decreased it. Overall, the same result was observed with bisphosphonates with the exception of low dosage of risedronate, which did not have an effect. Osteoprotegerin and strontium resulted in reduced relapse, but not in the immediate post-administration period. Inconsistent or conflicting effects were noted after the use of simvastatin and relaxin. The quality of the available evidence was considered at best as low. It can be concluded that specific medications and biologic factors may have an effect on the rate of relapse following tooth movement. The orthodontist should be knowledgeable about the substances potentially affecting retention.

Predicting dissolution and transformation of inhaled nanoparticles in the lung using abiotic flow cells: The case of barium sulfate

Barium sulfate (BaSO₄) was considered to be poorly-soluble and of low toxicity, but BaSO₄ NM-220 showed a surprisingly short retention after intratracheal instillation in rat lungs, and incorporation of Ba within the bones. Here we show that static abiotic dissolution cannot rationalize this result, whereas two dynamic abiotic dissolution systems (one flow-through and one flow-by) indicated 50% dissolution after 5 to 6 days at non-saturating conditions regardless of flow orientation, which is close to the in vivo half-time of 9.6 days. Non-equilibrium conditions were thus essential to simulate in vivo biodissolution. Instead of shrinking from 32 nm to 23 nm (to match the mass loss to ions), TEM scans of particles retrieved from flow-cells showed an increase to 40 nm. Such transformation suggested either material transport through interfacial contact or Ostwald ripening at super-saturating conditions and was also observed in vivo inside macrophages by high-resolution TEM following 12 months inhalation exposure. The abiotic flow cells thus adequately predicted the overall pulmonary biopersistence of the particles that was mediated by non-equilibrium dissolution and recrystallization. The present methodology for dissolution and transformation fills a high priority gap in nanomaterial hazard assessment and is proposed for the implementation of grouping and read-across by dissolution rates.

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.

Isoquercitrin, a flavonoid glucoside, exerts a positive effect on osteogenesis in vitro and in vivo

Isoquercitrin (quercetin-3-O-β-d-glucopyranoside) possess various pharmacological effect as a biologically active compound. The aim of the present study was to investigate its potential effects on the proliferation and osteoblastic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) in vitro and bone formation in the mid-palatal suture during rapid maxillary expansion (RME) in vivo. Cell proliferation of rat BMSCs was detected by cell-counting kit- 8 (CCK-8) assay. Alkaline phosphatase (ALP) activity assay and alizarin red staining were used to evaluate osteogenic differentiation of BMSCs. Furthermore, the expression levels of osteogenesis-related genes including runt-related transcription factor 2 (Runx2), bone sialoprotein (BSP) and activating transcription factor 6 (ATF6) were measured by real-time RT-PCR. In vivo, thirty-six male 6-week-old Wistar rats with or without suture expansion receive systemic administration of isoquercitrin or saline solution. Micro-CT, HE and Masson staining were used to compare the morphological changes between the groups. Bone morphogenetic protein 2 (BMP2) expression in the suture was detected using immunohistochemical staining. Our results showed that isoquercitrin significantly promoted cell proliferation, ALP activity and mineral deposition in the range from 0.01 to 1 μM. Moreover, the expression levels of Runx2, BSP and ATF6 were also upregulated. The measurement of micro-CT imaging and histological examinations demonstrated that daily oral administration of isoquercitrin (10 mg/kg) increased bone formation compared to the other groups. Furthermore, the expression level of BMP2 was also augmented in the presence of isoquercitrin. Consequently, those findings showed that isoquercitrin exerts stimulatory effects on osteogenesis in vitro and in vivo, suggesting that isoquercitrin could be a potential candidate for preventing relapse following RME within palatal sutures.

Hyperglycemia induced the Alzheimer's proteins and promoted loss of synaptic proteins in advanced-age female Goto-Kakizaki (GK) rats

Although both type 2 diabetes mellitus (T2DM) and aging are related with Alzheimer's disease (AD), the effects of aging on the Alzheimer's proteins and the synaptic markers in T2DM have not been investigated. This study, we hypothesized that T2DM rats with advanced-age, aggravates the reduction of synaptic proteins and an increase in the Alzheimer's protein markers. Goto-Kakizaki rats (GK) were used as a T2DM group and wild-type rats (WT) were used as a control group. Rats in each group were categorized by age into young-adult (7 months) and advanced-age rats (12.5 months). Blood was collected in all rats to determine plasma glucose and insulin levels. The brains were used for determining the level of Alzheimer's and synaptic proteins. Our data demonstrated that GK rats had a decreased body weight and increased blood glucose levels, compared to their age-matched WT. p-Tau was increased in both advanced-age WT and GK, compared to their young-adult rats. Moreover, amyloid-beta (Aβ) level was higher in advanced-age GK than their age-matched WT. The synaptic proteins were decreased in advanced-age GK, compared to young-adult GK rats. However, no difference in the level of Alzheimer's proteins and synaptic proteins in the brains of young-adult GK compared to age-matched WT was found. Our data suggested that aging contributes to the pathogenesis of AD and the reduction of synaptic proteins to greater extent in a diabetic than in a healthy condition.

Long term bone alterations in aged rats suffering type 1 diabetes

Increasing duration of type 1 diabetes mellitus alters bone metabolism. Clinical studies and experimental studies in long bones of rats with experimentally induced diabetes have reported a decrease in bone density. Few studies have explored this diabetes related alteration in the maxillae. Given that this finding could indicate the possible development of osteopenia in the maxilla in the long term, the present study sought to analyze alterations in alveolar bone in aged rats, 12, 18, and 24weeks after inducing diabetes, and compare alveolar bone response to that of tibial subchondral bone at the same experimental times. Thirty-six male Wistar rats, 130g body weight, were divided into 2 groups: an experimental group (E) receiving a single i.p. 60mg/kg dose of streptozotocin, and a control group (C). Both the control and experimental groups were divided into 3 sub-sets, according to the time of euthanasia: 12, 18 and 24weeks. The alveolar bone and tibiae were examined histologically and histomorphometrically. The results were analyzed using Student's t-test; a value of p<0.05 was considered statistically significant.

RESULTS

Subchondral bone volume and bone activity/remodeling, mainly bone rest, were significantly lower in diabetic animals compared to controls, at both 12 and 18weeks. No differences in alveolar bone parameters were observed between diabetic and control animals at either of the experimental times. Animals surviving at 24weeks showed few trabeculae at rest and severe destruction of dental and periodontal tissues. The results of the present study show that diabetic osteopenia is evident in the tibia at 12 and at 18weeks, whereas its effects on the maxilla can be seen at 24weeks, with substantial destruction of alveolar bone and of the remaining periodontal and dental tissues. All the above observations highlight the need for preventive oral care in diabetic patients, before irreversible damage to dental and periodontal tissues occurs.

Effect of hyaluronic acid on bone formation in the expanded interpremaxillary suture in rats

OBJECTIVE

To evaluate the histomorphometric effects of different molecular weight hyaluronic acid on bone formation in rats after expansion of the interpremaxillary suture.

MATERIAL AND METHODS

Twenty-four male Sprague Dawley rats were divided into three groups. Each group was subjected to expansion for 5 days and retention for 10 days. Group 1 received 50 μl of high molecular weight hyaluronic acid (HMWHA), group 2 received 50 μl of low molecular weight hyaluronic acid (LMWHA), and the control group received same amount of saline solution to the interpremaxillary suture. Ten days after injection, the rats were killed and their maxillas dissected. For the histomorphometric evaluation, blocks were serially sectioned at 10-μm intervals. Sections were stained with hematoxylin-eosin (HE) and evaluated with image analysis software. Bone area (μm²) (BA), bone perimeter of suture borders (μm) (BP), and ratio of osteoblast cells and capillary cells to BA and BP parameters were evaluated.

RESULTS

HMWHA showed a statistically higher ratio of osteoblast and capillary cell scores compared with the LMWHA and control groups (p < 0.05). There were no statistically significant differences in between LMWHA and control groups (p > 0.05).

CONCLUSIONS

Local injection of HMWHA in the interpremaxillary suture after rapid maxillary expansion stimulated new bone formation, which may shorten the retention period and may reduce the risk of relapse. LMWHA has no effect on bone formation in interpremaxillary suture.

Effects of Salvia miltiorrhiza ethanolic extract on lipopolysaccharide-induced dental alveolar bone resorption in rats

Background/purpose

Salvia miltiorrhiza (SM) Bunge (Labiatae/Lamiaceae; common name danshen) is a Chinese medicine that improves blood circulation and inhibits inflammatory response. Thus, it is used for the treatment of cardiac diseases and inflammation. In this study, we aimed to evaluate the effect of an ethanolic extract of SM (SME) on the dental alveolar bone resorption induced by bacterial lipopolysaccharide (LPS) in rats.

Materials and methods

An ethanolic extract was prepared from roots of SM. The major constituents of this extract were determined by high-performance liquid chromatography. The activity of the extract was evaluated in a rat model in which the dental alveolar bone resorption was induced by injection of bacterial LPS into the palatal gingiva around the maxillary molar teeth. The effect of SME on the bone resorption was studied by histologic and histomorphometric analysis.

Results

The number of osteoclasts and the percentage of osteoclasts covering the alveolar bone surfaces were significantly increased in the LPS group compared with those in the phosphate-buffered saline (PBS) group. The number and percentage of the osteoclasts on the bony surfaces were significantly reduced in the SME group in comparison with the LPS group, although it was still higher than the numbers observed in the PBS group.

Conclusion

Because SME reduced bone resorption caused by the injections of bacterial LPS in rats, we suggest that SME might have a protective effect on dental alveolar bone resorption in periodontitis.

Effects of hydrogen-rich water on aging periodontal tissues in rats

Oxidative damage is involved in age-related inflammatory reactions. The anti-oxidative effects of hydrogen-rich water suppress oxidative damage, which may aid in inhibiting age-related inflammatory reactions. We investigated the effects of drinking hydrogen-rich water on aging periodontal tissues in healthy rats. Four-month-old male Fischer 344 rats (n = 12) were divided into two groups: the experimental group (hydrogen-rich water treatment) and the control group (distilled water treatment). The rats consumed hydrogen-rich water or distilled water until 16 months of age. The experimental group exhibited lower periodontal oxidative damage at 16 months of age than the control group. Although protein expression of interleukin-1β did not differ, gene expression of Nod-like receptor protein 3 inflammasomes was activated in periodontal tissues from the experimental group as compared with the control group. Drinking hydrogen-rich water is proposed to have anti-aging effects on periodontal oxidative damage, but not on inflammatory reactions in healthy rats.

Effects of long-term occlusal hypofunction and its recovery on the morphogenesis of molar roots and the periodontium in rats

Objectives:

To investigate the effects of long-term, artificially created, hypofunctional occlusion and its recovery on the morphology of rat molar roots.

Material and Methods:

Eighteen 5-week-old Wistar-strain male rats were randomly divided according to their periodontal conditions into normal, hypofunctional, and recovery groups (n  =  6 in each). In the experimental hypofunctional and recovery groups, a bite-raising appliance was set to produce hypofunction at the molar region. All groups were analyzed at 16 weeks of age using three-dimensional micro-computed tomography. Root length, width, and area as well as the thickness and the area of the periodontal ligament (PDL) space of the maxillary first molar were calculated.

Results:

Roots were longer and narrower in the hypofunctional group than in the control group. The mesial root in particular showed a dramatic change. Root area also decreased significantly in the hypofunctional group compared to the other groups. Moreover, the PDL thickness and area decreased significantly in the hypofunctional group compared to the control group, but increased in the recovery group compared to the hypofunctional group.

Conclusions:

These findings suggest that root size and PDL structure may be reduced due to disuse atrophy resulting from a defect in occlusal function, but may be recovered following a gain of occlusal stimuli.

Local delivery of recombinant osteoprotegerin enhances postorthodontic tooth stability

Relapse after orthodontic tooth movement is a significant problem in orthodontics. The purpose of this study was to examine the efficacy of the osteoclast inhibitor osteoprotegerin-Fc (OPG-Fc) for inhibiting postorthodontic relapse. Rat maxillary molars were moved mesially and allowed to relapse for 24 days. Low-dose (1 mg/kg) or high-dose (5 mg/kg) OPG-Fc or saline was injected adjacent to the molars during relapse. Tooth movement, micro-CT, histologic bone quality, and serum OPG and TRAP-5b were measured. OPG-Fc injections significantly diminished postorthodontic relapse from 63% (0.78/1.20 mm) of total movement in vehicle control rats to 31% (0.31/1.00 mm) in low-dose and 24% (0.28/1.16 mm) in high-dose OPG-Fc groups 24 days after appliance removal. Normalization of bone and periodontal tissues occurred as early as 8 and 16 days in the high- and low-dose OPG-Fc-treated groups, respectively, while the vehicle-treated group showed only partial tissue recovery 24 days following tooth movement. After 24 days of relapse, there was complete recovery to pre-tooth-movement values for bone volume fraction (BVF) and tissue mineral density (TMD) in both the low- and high-dose OPG-Fc groups, while BVF recovered only partially and TMD did not recover in the vehicle control group. Greatly elevated serum OPG levels and reduced serum TRAP-5b levels in OPG-Fc-treated animals indicated systemic exposure to locally injected drug. The profound decrease in postorthodontic relapse by local OPG-Fc administration indicates that osteoclasts are critical to bone maturation following tooth movement and points to the potential pharmacologic use of OPG-Fc or other RANKL inhibitors for orthodontic retention.

Epidemiological aspects of rheumatoid arthritis patients affected by oral bisphosphonate-related osteonecrosis of the jaws

This literature review aims to evaluate the epidemiologic profile of patients with rheumatoid arthritis (RA) that developed a bisphosphonate-related osteonecrosis that affect the jaws (BRONJ), including demographic aspects, as well as clinical and therapeutic issues. A search of PUBMED/MEDLINE, Scopus, and Cochrane databases from January 2003 to September 2011 was conducted with the objective of identifying publications that contained case reports regarding oral BRONJ in RA patients. Patients with RA who develop oral BRONJ are usually women above 60 years taking steroids and long-term alendronate. Most of them have osteoporosis, and lesions, triggered by dental procedures, are usually detected at stage II in the mandible. Although there is no accepted treatment protocol, these patients seem to have better outcomes with conservative approaches that include antibiotic therapy, chlorhexidine, and drug discontinuation.

Histomorphometric study on the effects of age on orthodontic tooth movement and alveolar bone turnover in rats

The aim of this study was to investigate, in a rat model, the effects of age on the amount of tooth movement and concomitant changes in alveolar bone turnover activity adjacent to orthodontically treated tooth roots. Rats (n = 48) of four different age groups (10, 30, 50, and 80 wk of age) were used in the experiment. Maxillary first molars were tipped mesially with a nickel titanium alloy coil-spring for 2 wk by a continuous force of 10 cN. Forty-eight age-matched untreated rats were used as controls. The changes in alveolar bone turnover were assessed histomorphometrically. Two weeks after the start of tooth movement, the amount of tooth movement was found to decrease with age and was significantly different among the four age groups. The histomorphometric study demonstrated that, in all experimental groups, turnover of alveolar bone increased significantly compared with that of each age-matched untreated group. However, the rate of increase decreased in an age-related manner. These results suggest that the age-dependent decrease in alveolar bone turnover activity, in response to mechanical forces, may negatively affect the amount of tooth movement.