Orthodontic tooth movement involves applying mechanical forces that induce bone remodeling and bone resorption at the pressure sites and bone formation at the tension sites.1 A cascade of chemical mediators might lead to a signal transmission from the extracellular matrix up to gene modulation, regulating the gene activation or suppression, changing the cytoskeletal structure, and altering the nuclear protein matrix.2,3

Several factors are involved in the bone remodeling process, including receptor activator of nuclear factor kappa B (RANK)-related ligand (RANKL), tumor necrosis factor (TNF), and osteoprotegerin (OPG),4 whose ligand (OPG-L) was identified as a membrane-bound molecule.4,5 Both RANKL and OPG-L can bind to the RANK, which is located on osteoclasts.4,5 Osteoclasts secrete OPG, whose main function is blocking the activity of the osteoclast cells, and consequently the bone resorption.4,5 TNF, interleukin-1 (IL-1), growth factors (transforming growth factor-beta [TGF-β], bone morphogenetic protein [BMP]), and prostaglandin E (PGE) are cytokines that might regulate the OPG/OPG-L ratio, affecting the osteoclast lifecycle, promoting both their differentiation and apoptosis.5 When the balance favors the OPG, the number of active osteoclasts is reduced, whereas when the balance favors OPG-L, the number of active osteoclasts increases.6 Among the mediators of the inflammatory process, interleukin-6 (IL-6), interleukin-1 (IL-1b), epidermal growth factor, TNF-α, and β2 microglobulin were shown to increase during orthodontic treatment.7 The soluble RANKL/OPG ratio could also affect the external apical root resorption (EARR).8 In fact, an increased OPG/RANKL ratio can inhibit cementum resorption and remodeling in cementocytes.9

Furthermore, it has been shown that the vitamin D receptor (VDR)-binding sites in the DNA may stimulate the physiological regulation of different genes at the level of transcription, including RANKL, OPG, cyclooxygenase-2 (COX-2) and IL-6, thus conditioning skeletal growth, muscle and bone homeostasis.10-13

In this context, vitamin D3 was shown to decrease the RANKL/OPG ratio, reducing the osteoclastic bone resorption via VDR in mature osteoblasts. On the other hand, increased levels of vitamin D were shown to increase the RANKL/OPG ratio, inducing osteoclastic bone resorption via VDR in less-mature osteoblasts.14

In 2021, Küchler et al.10 showed that different physiological concentrations of vitamin D and single nucleotide polymorphisms in the VDR gene might regulate the gene expression of the periodontal ligament fibroblasts after simulation of an orthodontic compressive strain. They showed that RANKL was overexpressed, leading to an increased RANKL/OPG ratio during the pressure. This finding confirms that vitamin D might have an impact on the balance between bone formation and resorption, which is considered crucial for the orthodontic tooth movement.10

The scientific interest in vitamin D has been increasing in the last decade. In dentistry, vitamin D supplementation has been proposed to promote oral health.15,16

The scientific literature has been focused on accelerating the rate of tooth movement and on inducing bone turnover in combination with mechanical forces.17,18 The demand for reducing the orthodontic treatment duration has been increased to avoid potential complications, including EARR. Moreover, the potential relationship between calcitriol and orthodontic tooth movement has been recently investigated, although the role of vitamin D on bone remodeling remains a subject of debate and its influence on molecular processes remains widely unknown.19

Therefore, this systematic review aimed to evaluate the current evidence on the role of vitamin D on orthodontic tooth movement, EARR, bone biomarkers expression, and bone remodeling.

Search strategy and selection criteria

On March 14, 2023, 2 authors systematically and independently searched the PubMed, Scopus, and Web of Science databases. The search strategy is reported in Table 1.

Table 1 . Search strategy.

PubMed: ((“vitamin d”[MeSH Terms] OR “vitamin d”[All Fields] OR “cholecalciferol”[MeSH Terms] OR “cholecalciferol”[All Fields] OR “ergocalciferols”[MeSH Terms] OR “ergocalciferols”[All Fields] OR “calcifediol”[MeSH Terms] OR “calcifediol”[All Fields] OR “25 oh d3”[All Fields])) AND (“Orthodontics”[Mesh Terms] OR “Orthodontics”[All Fields]) OR ((“tooth”[MeSH Terms] AND “movement”[MeSH Terms]) OR (“tooth”[All Fields] AND “movement”[All Fields])) OR (“malocclusion”[MeSH Terms] OR “malocclusion"”[All Fields]) OR (“dental occlusion”[MeSH Terms] OR (“dental”[All Fields] AND “occlusion”[All Fields]) OR “dental occlusion”[All Fields]) OR (“oral health”[MeSH Terms] OR “oral health”[All Fields]) OR (“oral status” [All Fields]))

Scopus: TITLE-ABS-KEY (((vitamin d) OR (cholecalciferol) OR (25 oh d3)) AND ((Orthodontics) OR (tooth movement) OR (malocclusion)))

Web of Science: ALL = ((“vitamin d” OR “cholecalciferol” OR “25 oh d3”) AND (“Orthodontics” OR “tooth movement” OR “malocclusion”))

After the duplication removal, the 2 reviewers independently screened all the records for title and abstract, then for full-text. A third reviewer was asked to solve any disagreement between the 2 reviewers through collegial discussion.

The relevant studies were selected based on the following PICO model:

(P) Participants: subjects undergone orthodontic treatment;

(I) Interventions: no restrictions for therapeutic intervention;

(C) Comparators: no restriction for comparators;

(O) Outcome measures: the correlation between orthodontic tooth movement and vitamin D was the primary outcome. Data on vitamin D serum levels, bone biomarker expression, genotype and frequency of VDR polymorphisms, and EARR were investigated as secondary outcomes.

We excluded case reports, case series, abstracts, studies not written in English, and studies including participants with pathological disorders affecting calcium homeostasis.

This systematic review followed the statement of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)20 and was registered on PROSPERO (CRD42022332980).

Data extraction and synthesis

All data were extracted and synthesized into tables, providing a qualitative synthesis of the study characteristics and main findings. The data synthesis was performed by two authors independently based on full-text documents.

The relevant data extracted were: I) title, authors, and publication year; II) nationality; III) sample characteristics; IV) interventions’ characteristics; V) comparator characteristics; VI) outcomes; VII) study results.

Quality assessment

Two independent reviewers assessed the quality of the studies included according to the Joanna Briggs Institute Critical Appraisal Checklist.21 Any disagreement was resolved by a third reviewer.

Through the literature search, 519 studies were recognized. After removing the duplicates, 446 records were considered suitable for title and abstract screening. Out of these, 43 articles were assessed, and 24 were excluded for the following reasons: full-text unavailability (n = 4), no orthodontics disorders (n = 13), no vitamin D outcomes (n = 3), study protocol (n = 2), and language other than English (n = 2).

Consequently, we included 19 studies22-40 as reported by the 2020 PRISMA flow diagram (Figure 1).

Figure 1. PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) 2020 flow diagram.

Out of the 19 included studies, 9 (47.4%) were conducted on animal models,24,25,27-30,32,38,40 and 10 (52.6%) on humans (2 [10.5%] retrospective studies,37,39 5 [26.3%] prospective studies,22,23,26,31,33 1 [5.3%] cross-sectional study,34 and 2 [10.5%] randomized controlled trials35,36).

Eleven studies (57.9%) were performed in Asia22,25,28-30,32,34-37,40: 2 from Iraq,22,36 2 from Saudi Arabia,29,30 3 from Iran,34,37,40 2 from Japan,28,32 1 from China,25 and 1 from India.35 Four studies (21.1%) were performed in the Americas: 2 from the USA,23,33 1 from Canada,38 and 1 from Brazil.26 Four studies (21.1%) were performed in Europe23,27,31,39: 1 from France,23 1 from Germany,39 1 from Turkey,27 and 1 from Poland.31

In the animal studies, 244 subjects (5 cats, 170 Wistar rats, and 69 Dawley rats) were analyzed; the study cohorts ranged from 524 to 6032 subjects, with an overall age ranging from 6 weeks27 to 28 weeks old.32

In the studies involving human, there were 890 participants; the study cohorts ranged from 14.9 years old26 to 36.5 years old.31 Regarding the follow-up evaluations, the longest study follow-up was 6 months.26

Table 2 details all the main characteristics and findings of the papers included in the systematic review.

Table 2 . Main characteristics of the studies included in the present systematic review.

Authors	Journal	Design	Natio-nality	Population	Age (yr)	Intervention	Comparator	Outcome	Time points	Main findings
Al-Attar and Abid (2022)36	International Journal of Dentistry	Randomized controlled trial	Iraq	Total: n = 33; M/F = N/A. Group 1: n = 17; M/F = N/A. Group 2: n = 16; M/F = N/A.	Total: 20.13 ± 1.81; (18–30). Group 1: 20.5 ± 1.61. Group 2: 19.70 ± 1.95.	Group 1: vitamin D3 level was measured before orthodontic intervention; if the level was below the normal value (30 ng/mL), then the participants were referred to an endocrine specialist to optimize the level of vitamin D3 to normal before bonding the appliance. Patients were treated with a fixed orthodontic appliance.	Group 2: orthodontic treatment was performed without measuring the level of vitamin D3 until completion of the alignment phase.. Patients were treated with fixed orthodontic appliance..	- Vitamin D3 level. - Mandibular incisor crowding. - EARR. - Pain perception.	T0 (baseline), T1 (4 wk), T2 (8 wk), T3 (12 wk), T4 (16 wk), and T5 (20 wk)	The results showed that there were statistically significant improvements in time elapsed for the complete alignment of the mandibular incisor crowding (P ≤ 0.001), which was 1 mo shorter in normal vitamin D3 group (23.53% faster), and the improvement percentage was significantly higher in all periods when compared to the CG (P ≤ 0.001). The amount of EARR was not significantly different between groups; however, pain during the first three days of alignment was significantly less in normal vitamin D3 group (P < 0.05).
Al-Hasani et al. (2011)22	International Journal of Pharmacy and Pharmaceutical Sciences	Prospective study	Iraq	Total: n = 15; M/F = N/A	Total: range, 17–28	Group 1: injection of 0.2 mL of calcitriol in DMSO containing 15 pg/mL of calcitriol into the periodontal ligament of the left canines (distal side). The injections were repeated 3 times for every subject (T0, T1, T2). The distalizing orthodontic forces were about 150 g.. Group 2: injection of 0.2 mL of calcitriol in DMSO containing 25 pg/mL of calcitriol into the periodontal ligament of the left canines.. Group 3: injection of 0.2 mL of calcitriol in DMSO containing 40 pg/mL of calcitriol into the periodontal ligament of the left canines..	Right canine: injection of 0.2 mL of DMSO.	Tooth movement	T0 (baseline), T1 (7 days), T2 (14 days), T3 (21 days), T4 (28 days)	The results showed no statistically significant differences in OTM between control and experimental sides, and among the 3 groups. From a clinical point of view, the dose of 25 pg of calcitriol produced about 51% faster rate of experimental canine movement compared to control, whereas 15 pg and 40 pg doses resulted in about 10% accelerated OTM.
Azizi et al. (2022)37	International Journal of Dentistry	Retrospective cohort study	Iran	Total: n = 80; M/F = N/A	Total: range, 12–30	Fixed orthodontic treatment		- Serum level of vitamin D. - EARR. - Root length.	T0 (baseline)	A reduction in root length was noted in all patients, which was significant (P < 0.0001); 75% of patients showed EARR in at least one maxillary incisor. The EARR had no significant correlation with the serum level of vitamin D (P = 0.423).
Iosub Ciur et al. (2016)23	Revista medico-chirurgicala˘˘ a Societa˘˘ţii de Medici şi Naturalişti din Iaşi	Prospective study	France	Total: n = 6; M/F = 3/3	Total: 18	Injection of 0.2 mL of vitamin D3 in DMSO containing 42 pg/mL of vitamin D3 into the periodontal ligament of the experimental canine was administered, once a week, for 3 wk. Canine distalization was achieved using a closed Niti spring of 12 mm which generated a force of 150 g.	The control canine received only conventional orthodontic treatment.	Tooth movement	T0 (baseline), T1 (1 mo)	Results showed an average of 70% more tooth movement for the experimental teeth compared to control ones. The differences between the control and the experimental sides were statistically significant (P = 0.0313).
Collins and Sinclair (1988)24	American Journal of Orthodontics and Dentofacial Orthopedics	Animal study	USA	Young adult cats. Total: n = 5; M/F = N/A.	Total: N/A	Injection of 0.1 mL of 1.25 D in DMSO containing 50 pg/mL of 1.25(OH)2D3 into the periodontal ligament of the left canines. The orthodontic forces were delivered using a light-wire retraction spring.	The right canines received an injection of 0.1 mL of DMSO only. The orthodontic forces were delivered using a light-wire retraction spring.	Cumulative amounts of tooth movement, weekly increments of tooth movement, numbers of mononuclear osteoclasts	T0 (baseline), and T1 (21 days)	After 21 days of canine retraction with a light-wire retraction spring, the teeth that had received weekly intraligamentous injections of 1.25 D had moved 60% further than matched control teeth (P < 0.05). At the histologic level, increased numbers of mononuclear osteoclasts were recruited and activated, resulting in greater amounts of alveolar bone resorption on the pressure side of the periodontal ligament.
Cui et al. (2016)25	Journal of Molecular Histology	Animal study	China	Wistar rats. Total: n = 30; M/F = 30/0. Group 1: n = 12; M/F = 12/0. Group 2: n = 12; M/F = 12/0. Group 3: n = 6; M/F = 6/0.	7-week-old	Group 1: experimental group to examine the effect of 1α,25(OH)2D3 (n = 6) and normal saline (n = 6) on HMGB1 at day 7.. Group 2: experimental group to examine the effect of 1α,25(OH)2D3 (n = 6) and normal saline (n = 6) on HMGB1 at day 28.. The orthodontic forces were delivered using a nickel-titanium coil spring with (force level of 0.5 N) for 5 days.. Vitamin D administration: (100 ng/kg body weight) by gavage once every other day.. Saline: identical volume and frequency..	Group 3: control group to determine basal HMGB1 protein expression	TNF-α, IL-6, and HMGB1	T0 (after 5 days of application of mechanical loading to the tooth), T1 (after 7 days), and T2 (after 28 days)	Expression of IL-6 and TNF-α were time-dependently reduced in the 1α,25(OH)2 vitamin D group compared with the control group at each time point (P < 0.01). Similarly, expression of HMGB1 was decreased over time in both the 1α,25(OH)2 vitamin D and normal saline groups, and 1α,25(OH)2 vitamin D administration enhanced this decline (P < 0.01).
Fontana et al. (2012)26	American Journal of Orthodontics and Dentofacial Orthopedics	Prospective study	Brazil	Total: n = 377; M/F = 169/208. Group 1: n = 160; M/F = 74/86. Group 2: n = 179; M/F = 80/99. Group 3: n = 38; M/F = 15/23.	Total: 14.9; range, 8–21. Group 1: 14.50 ± 3.01 (8–21). Group 2: 15.33 ± 2.64 (9.9–20). Group 3: 16.46 ± 1.93 (11–19).	Group 1: patients treated with edgewise or straight-wire techniques, with EARR ≤ 1.43 mm.. Group 2: patients treated with edgewise or straight-wire techniques, with EARR > 1.43 mm.. EARR of the maxillary incisors was evaluated on periapical radiographs..	Group 3: untreated subjects	EARR, genotype and allele distribution of the VDR TaqI polymorphism, protective effect of allele C	T0 (baseline), and T1 (6 mo)	Differences were observed in VDR Taq1 polymorphism genotype frequency (P = 0.051) between groups. It was observed a weak protective effect of allele C against EARR (CC + CT × TT [OR, 0.29; 95% CI, 0.07–1.23; P = 0.091]) in treated patients compared with control group.
Gratton et al. (2022)38	American Journal of Orthodontics and Dentofacial Orthopedics	Animal study	Canada	Sprague Dawley rats. Total: n = 32; M/F = 32/0. Group 1: n = 8; M/F = 8/0. Group 2: n = 8; M/F = 8/0. Group 3: n = 8; M/F = 8/0. Group 4: n = 8; M/F = 8/0.	N/A	Group 1: experimental gavage - daily solution of vitamin D (50 ng/mL) by gavage.. Group 2: experimental injection-submucosal injection of solution of vitamin D solution, every 2 days in the anterior and palatal region of the maxillary right first molar (volume of 20 mL, vitamin D 1 × 10-10 M, injected at each dose).. A closed nickel-titanium coil of 50 cN force was bonded between the maxillary right first molar and the incisors of each rat at T1, for 7 days..	Group 3: control gavage - daily solution of PBS solution (0.1 M, pH 7.2) by gavage. Group 4: control injection - submucosal injection of solution of PBS solution, every 2 days in the anterior and palatal region of the maxillary right first molar (volume of 20 mL injectedat each dose).. A closed nickel-titanium coil of 50 cN force was bonded between the maxillary right first molar and the incisors of each rat at T1, for 7 days..	- Tooth movement. - Bone morphometry.	T0 (baseline), T1 (10 days), T2 (17 days), T3 (24 days), T4 (47 days)	The systemic vitamin D group showed a lower OTM rate and a lower relapse than the control (P < 0.05).. It also demonstrated increased bone mineral density, bone volume/total volume, and a decrease in total porosity (P < 0.05). The bone structure appeared more fragmented and presented a lower connectivity density than the control (P < 0.05). No statistical difference was found between vitamin D local administration and the other groups for the rate and stability of OTM or bone morphometry..
Kale et al. (2004)27	American Journal of Orthodontics and Dentofacial Orthopedics	Animal study	Turkey	Sprague Dawley rats. Total: n = 37; M/F = 37/0. Group 1: n = 8; M/F = 8/0. Group 2: n = 8; M/F = 8/0. Group 3: n = 8; M/F = 8/0. Group 4: n=8; M/F= 8/0. Group 5: n = 5; M/F = 5/0.	6-week-old	Group 1: appliance control group; orthodontic appliances alone. Group 2: DMSO group; 20 µL injection of DMSO on days 0, 3, and 6.. Group 3: 1.25-dihydroxy-cholecalciferol (1.25-DHCC) group; orthodontic appliances + single injection of 20 µL of 10–10 mol/L, given on days 0, 3, and 6.. Group 4: PGE2 group; orthodontic appliances + a single injection of 0.1 mL of 0.1 µg PGE2 on the day of appliance placement.. Injections were administered with a microsyringe to the gingiva distal to the maxillary incisors..	Group 5: no treatment	Tooth movement, numbers of Howship’s lacunae and capillaries, number of osteoblasts	T0 (baseline), and T1 (9 days)	There was no significant difference in tooth movement between the PGE2 and the 1.25-DHCC groups (P > 0.05). Both PGE2 and 1.25-DHCC enhanced the amount of tooth movement significantly when compared with the control group (P < 0.001). The numbers of Howship’s lacunae and capillaries on the pressure side were significantly greater in the PGE2 group than in the 1.25-DHCC group (Howship’s lacunae: P < 0.001; capillaries: P < 0.005). Compared to the DMSO group and Control, the number of capillaries in the pressure side in the 1.25-DHCC group remains significantly higher (P < 0.001). On the other hand, the number of osteoblasts on the external surface of the alveolar bone on the pressure side was significantly greater in the 1.25-DHCC group than in the PGE2 group (P < 0.001).
Kawakami and Takano-Yama-moto (2004)28	Journal of Bone and Mineral Metabolism	Animal study	Japan	Wistar rats. Total: n = 16; M/F = 16/0. Group 1: n = 8; M/F = 8/0. Group 2: n = 8; M/F = 8/0.	7-week-old	Group 1: a piece of orthodontic elastic band (0.5-mm thickness) was inserted bilaterally between the first and second maxillary molars.. Twenty microliters of 10-10 M. 1.25(OH)2D3 was injected locally in the submucosal palatal area of the root furcation of the right molar, using a 30-gauge needle, once every 3 days (tooth movement [TM] 1.25(OH)2D3). The left side was injected with vehicle (TM phosphate-buffered saline-PBS)..	Group 2: rats without the insertion of elastic bands were injected with the same dose of 1.25(OH)2D3 on the right side (non-TM 1.25(OH)2D3) and with vehicle on the left side (non-TM PBS).	Histomor-phometric indices on the distal and mesial sides of the inter radicular septum of the maxillary first molar	T0 (baseline), T1 (7 days), and T2 (14 days)	Histomorphometric analysis revealed that tooth movement without application of 1.25(OH)2 vitamin D decreased the mineral appositional rate (MAR) on the compression area at 7 days (P < 0.05). Repeated injections of 1.25(OH)2 vitamin D in the orthodontically treated animals distinctly stimulated alveolar bone formation on the mesial side at 14 days. There was a significant increase in MAR associated with elevated osteoblast surface value on the tension surface (P < 0.05).
Khalaf and Almudhi (2022)29	Saudi Dental Journal	Animal study	Saudi Arabia	Wistar rats. Total: n = 16; M/F = 16/0. Group 1: n = 8; M/F = 8/0. Group 2: n = 8; M/F = 8/0.	8–9-week-old	Group 1: rats with induced vitamin D deficiency.. This condition was achieved using an injection of 0.1 mL of Saline and paricalcitol injected 3 times per week for 2 wk for each rat.. An additional week of inactivity was observed, totaling the time to three weeks before commencement of the OTM procedures.. Orthodontic appliances were fixed to initiate tooth movement..	Group 2: rats with average vitamin D serum level. Orthodontic appliances were fixed to initiate tooth movement at T0.	Tooth movement	T0 (baseline, for Group 1 after 3 wk from first injection), T1 (7 days), T2 (14 days), and T3 (21 days)	The overall OTM was compared between groups and showed no statistically significant differences at 0–7 days (P = 0.709), 0–14 days (P = 0.313), or 0–21 days (P = 0.359). The OTM over time was compared separately, and for both groups significant changes were observed over time. In group 1 the pairwise comparisons found significant differences between 0–7 days and 0–14 days (P = 0.013), 0–7 days, and 0–21 days (P < 0.001). Similar results were found in the 2 groups, with significant differences between 0–7 days and 0–14 days (P = 0.014), 0–7 days, and 0–21 days (P = 0.001). The repeated measures ANOVA found the differences to be significant when considered for time (F = 29.9, P < 0.001). There was a significant drop in the OTM over time in both groups. Results showed that vitamin D deficiency did not affect rate of OTM.
Khalaf and Almudhi (2022)30	Journal of Oral Biology and Craniofacial Research	Animal study	Saudi Arabia	Wistar rats. Total: n = 16; M/F = 16/0. Group 1: n = 8; M/F = 8/0. Group 2: n = 8; M/F = 8/0.	Total: N/A	Group 1: rats with induced vitamin D deficiency.. This condition was achieved using injection of 0.1 mL of Saline and paricalcitol injected 3 times per week for 2 wk.. An additional week of inactivity was observed, totaling the time to three weeks before commencement of the OTM procedures.. Orthodontic appliances were fixed to initiate tooth movement..	Group 2: normal rats. Orthodontic appliances were fixed to initiate tooth movement at T0.	Vitamin D, serum level of RANKL concen-tration, OPG concen-tration, and RANKL/OPG ratio	T0 (baseline, for Group 1 after 3 weeks from first injection), and T1 (21 days)	A statistically significant decrease in serum RANKL concentration (P < 0.001) and RANKL/OPG ratio (P < 0.001) on day 21 were seen in the experimental group compared to the control group.
Lesz-czyszyn et al. (2021)31	Nutrients	Prospective study	Poland	Total: n = 114; M/F = 61/53. Group 1: n = 86; M/F = 57/29. Group 2: n = 28; M/F = 4/24.	Total: 36.5 ± 11.8 (18–50)	Group 1: vitamin D deficiency	Group 2: no vitamin D deficiency	25(OH) vitamin D serum levels, malocclusion development ratio	T0 (baseline)	In about 42.1% of patients, the presence of a skeletal defect was found, and in 46.5% of patients, dentoalveolar malocclusion. The most common defect was transverse constriction of the maxilla with a narrow upper arch (30.7%). The concentration of vitamin 25(OH) D in the study group was on average 23.6 ± 10.5 (ng/mL). Vitamin D deficiency was found in 86 subjects (75.4%). Our research showed that vitamin D deficiency could be one of the important factors influencing maxillary development. Patients had a greater risk of a narrowed upper arch (OR = 4.94), crowding (OR = 4.94), and crossbite (OR = 6.16).
Marañón-Vásquez et al. (2023)39	European Journal of Oral Sciences	Retrospective study	Ger-many	Total: n = 143; M/F = 71/72	Total: 13.5 ± 4.5	Orthodontic treatment. A sample of cheek cells (buccal cells) was collected for DNA analysis.		- Vitamin-D-related genes (VDR, GC, CYP27B1, and CYP24A1). - EARR. - Root length.	T1 (initial treatment. radiograph), and T2 (final treatment adiograph).	Individuals carrying the AA genotype in VDR rs2228570 had a 21% higher EARRmol than those having AG and GG genotypes (95% CI: 1.03,1.40).. EARRmol in heterozygous rs2228570, was 12% lower than for homozygotes (95% CI: 0.78–0.99). Participants with the CCG haplotype (rs1544410-rs7975232-rs731236) in VDR had an EARRmol 16% lower than those who did not carry this haplotype.. Regarding CYP27B1 rs4646536, EARRinc in participants who had at least one G allele was 42% lower than for homozygotes AA (95% CI: 0.37–0.93)..
Mora-dinejad et al. (2022)40	American Journal of Orthodontics and Dentofacial Orthopedics	Animal study	Iran	Wistar rats. Total: n = 32; M/F = 32/0. Group 1: n = 8; M/F = 8/0. Group 2: n = 8; M/F = 8/0. Group 3: n = 8; M/F = 8/0. Group 4: n = 8; M/F = 8/0.	N/A	Group 1: vitamin D3 intraperitoneal injection, once every 2 wk for 3 times (2 times [21 days and 7 days] before the appliance placement and 1 time [7 days] after it), each dose of 0.6 mg/kg body weight equivalent to 24,000 IU/kg.. Group 2: alendronate solution, once a week and for a total of 5 times (21, 14, and 7 days before the appliance placement, the day of placement, and 7 days after placement) at a dosage of 7 mg/kg of body weight per week by gavage.. Group 3: alendronate + vitamin D (same doses) Orthodontic appliances: the incisors were distalized at 30 g of force for 2 weeks..	Group 4: only orthodontic appliances	- Tooth movement. - Capillaries, lacunae, osteoclasts, and osteoblasts.	T0 (21 days before the appliance placement). T1 (14 days before the appliance placement). T2 (7 days before the appliance placement). T3 (the day of placement). T4 (7 days after placement).	The OTMs in the groups vitamin D3, ALN+D3, ALN, and control were 1.900 ± 0.237, 1.629 ± 0.219, 0.975 ± 0.145, and 1.565 ± 0.324 mm (P < 0.001), respectively.. The OTM in the ALN group was smaller than all other groups (P < 0.001). The OTM in the D3 group was greater than in the control group (P = 0.054). The ALN+D3 group had greater OTM than the ALN group (P < 0.001) but was not significantly different from the D3 (P = 0.153) or control (P = 0.951) groups. All histologic variables were significantly different across groups (P < 0.001). All the markers in the D3 group were more frequent than those of the other groups (P < 0.001). There were fewer markers in the ALN group than in the control group (P ≤ 0.001). The ALN + D3 group had more markers than the ALN group in terms of capillaries, osteoclasts, and osteoblasts (P ≤ 0.007). The ALN + D3 group was similar to the control group regarding capillaries, osteoclasts, and osteoblasts (P ≥ 0.382)..
Takano-Yama-moto et al. (1992)32	Journal of Dental Research	Animal study	Japan	Wistar rats. Total: n = 60; M/F = 60/0. Group 1: n = 30; M/F = 30/0. Group 2: n = 30; M/F = 30/0.	Group 1: 7-week-old. Group 2: 28-week-old.	The right maxillary first molar was moved buccally with a fixed appliance. The appliances delivered forces ranging from 5 to 20 g.. Twenty gL of 1.25(OH)2D3 (10-10 and 10-8 mol/L) was injected locally into the submucosal palatal area of the root bifurcation of the right first molar..	The left side was injected with PBS.	Tooth movement, calcium, phosphate, and alkaline phosphatase activity	T0 (baseline), and T1 (21 days)	In young rats receiving 10-10 mol/L 1.25(OH)2D3 every three days, tooth movement significantly increased to 126% of that in PBS-injected control rats on day 20. In 1.25(OH)2D3-injected mature rats, tooth movement was stimulated markedly and increased by 245% after 10-10 mol/L of 1.25(OH)2D3, while a dose of 10-8 mol/L of 1.25(OH)2D3 increased of 154% tooth movements compared to PBS-injected controls.. PBS-injected rats had a plateau stage where tooth movement did not occur at all, while there was no such lag-time in the 1.25(OH)2D3-injected group which showed continuous tooth movement. The local injection of 1.25(OH)2D3 did not change serum calcium, phosphate, and alkaline phosphatase activity, and there were no apparent clinical or microscopic side effects..
Tashkandi et al. (2021)33	BMC Oral Health	Prospective study	USA	Total: n = 73; M/F = 30/43. Group 1: n = 18; M/F = 9/9. Group 2: n = 37; M/F = 15/22. Group 3: n = 18; M/F = 6/12.	Total: 21.5 ± 11.1 (8–63). Group 1: 22.78 ± 7.89. Group 2: 20.05 ± 11.74. Group 3: 23.72 ± 12.39.	Group 1: low VitDBP	Group 2: normal VitDBP. Group 3: high VitDBP.	VitDBP, ALP	T0 (baseline), and T1 (6 mo)	VitDBP is a biological marker for bone apposition and clinical tooth movement. Both low (< 2.75 ng/mL) and high (> 6.48 ng/mL) VitDBP levels were associated with reduced tooth movement. Significant (P < 0.05) seasonal changes in VitDBP using a 2-season year model was found with lower levels observed in the summer (Apr–Sep) than in the winter (Oct–Mar).
Tehranchi et al. (2017)34	Dental Research Journal	Cross-sectional study	Iran	Total: n = 34; M/F = 8/26	Total: 16.63 ± 2.84 (12–23)	Group 1: mild vitamin D deficiencies (25-OHD 20–30 ng/mL). Patients were treated with fixed orthodontic treatment..	Group 2: moderate vitamin D deficiencies (25-OHD 10–20 ng/mL). Group 3: severe vitamin D deficiencies (25-OHD < 10 ng/mL).	Vitamin D status, EARR	T0 (baseline), and T1 (end of orthodontic treatment)	The Pearson coefficient between vitamin D status and observed EARR was determined about 0.15 (P = 0.38). Regression analysis revealed that vitamin D status of the patients demonstrated no significant statistical correlation with EARR, after adjustment of confounding variables using linear regression model (P > 0.05).
Varughese et al. (2019)35	The Journal of Contemporary Dental Practice	Randomized controlled trial	India	Total: n = 15; M/F = N/A	Total: 22.5; range, 15–30	Injection of 0.2 mL of 1.25 vitamin D in DMSO containing 50 pg/mL of 1.25 D into the periodontal ligament of the experimental canine was administered at monthly intervals for duration of three months. Canine distalization was achieved using a closed Niti spring, which generated a force of 150 g.	Injection of 0.2 mL placebo gel into the periodontal ligament of the control canine.	Tooth movement and anchorage loss	T0 (baseline), T1 (4 wk), and T2 (8 wk), T3 (12 wk)	About total amount of canine distalization the results showed statistically significant difference (P = 0.000) between experimental and control sides over a period of 3 mo.. About the amount of anchorage loss, no statistically significant results were shown..

Values are presented as mean ± standard deviation and maximum-minimum (range)..

M, male; F, female; N/A, not applicable; DMSO, dimethylsulfoxide; OTM, orthodontic tooth movement is correct; HMGB1, high mobility group box 1; EARR, external apical root resorption; VDR, vitamin D receptor; PBS, phosphate-buffered saline; PGE2, prostaglandin E2; RANKL, receptor activator of nuclear factor-kappa B ligand; OPG, osteoprotegerin; OR, odds ratio; EARRmol, external apical root resorption of lower first molars; EARRinc, external apical root resorption of upper central incisors; CI, confidence interval; ALN, alendronate; VitDBP, vitamin D binding protein; ALP, alkaline phosphatase..

Animal models

Collins and Sinclair24 evaluated the effects of dimethylsulfoxide (DMSO) injections containing 50 pg/mL of 1.25(OH)2D3 into the periodontal ligament of the left canines and 0.1 mL of DMSO alone in the right canines in cat model. After 21 days of canine retraction, they found a significant improvement of 60% (P < 0.05) in the teeth movement in the study group (receiving weekly intraligamentous injections of vitamin D) compared to the control group.

Cui et al.25 investigated the effect of 1.25(OH)2D3 on the expression of high mobility group box 1 (HMGB1) in periodontal ligament cells of rats during orthodontic tooth movement (nickel-titanium coil spring delivering a force level of 0.5 N). The 1.25(OH)2D3 was administered via gavage every other day (100 ng/kg body weight). The expression of HMGB1 was evaluated at 7 and 28 days and compared to the basal expression of HMGB1 protein in a control group. The authors reported a significant reduction in IL-6 and TNF-α expression in the vitamin D group (P < 0.01), suggesting that administration of vitamin D3 might provide a down-regulating expression of HMGB1.

Kale et al.27 compared the effects of injecting PGE2 and 1.25(OH)2D3 into the gingiva distal to the maxillary incisors of rats. PGE2 and 1.25(OH)2D3 significantly (P < 0.001) increased the rate of tooth movement in comparison with the control group.

Kawakami and Takano-Yamamoto28 showed that tooth movement in rats without injection of 1.25(OH)2D3 in the submucosal palatal area decreased the mineral appositional rate on the compression area at 7 days (P < 0.05), whereas repeated injections of 1.25(OH)2D3 in the orthodontically treated animals stimulated alveolar bone formation at 14 days with a significant increase in mineral appositional rate on the tension site (P < 0.05).

In 2022, Gratton et al.38 evaluated the rate of tooth movement in rats after 1.25(OH)2D3 supplementation as an oral solution (50 ng/mL) or submucosal injection of 1.25(OH)2D3 solution, and compared the results to a control group (receiving phosphate-buffered saline solution systemically or focally administered). The authors reported a lower tooth movement rate and relapse in animals receiving systemic vitamin D supplementation compared to the control (P < 0.05).

In the same year, Moradinejad et al.40 assessed the effects of orthodontic appliances combined with vitamin D3 intraperitoneal injection, alendronate solution administration, or vitamin D3 intraperitoneal injection combined with alendronate solution administration. The authors reported significant differences in orthodontic tooth movement between groups, with significant advantages for groups treated with vitamin D3 administration (P < 0.001). In contrast, tooth movement was smaller in rats treated with alendronate alone (P < 0.001).

However, Khalaf and Almudhi29 showed that hypovitaminosis D did not affect the rate of orthodontic tooth movement in rats after orthodontic therapy with fixed appliances at 7, 14, and 21 days. On the other hand, the same authors30 analyzed the effects of vitamin D deficiency on the serum blood levels of RANKL/OPG in rats and showed significantly lower levels of serum RANKL and RANKL/OPG ratio (P < 0.001).

Furthermore, Takano-Yamamoto et al.32 showed that the rate of tooth movement was significantly increased (about 245%) after 10^–10 mol/L injections of 1.25(OH)2D3 into the submucosal palatal area of the right first molar simultaneous with the application of mechanical force (delivered forces ranging from 5 to 20 g).

Human models

In studies involving human, Al-hasani et al.22 treated 15 patients with pre-adjusted fixed appliances and performed maxillary canine retraction with a distalizing force of 150 g. They administered an injection of 0.2 mL of DMSO containing vitamin D3 (calcitriol) into the periodontal ligament of the left canines (distal side). The patients were randomly treated with 15 pg, 25 pg, or 40 pg/0.2 mL vitamin D, and no statistical differences among the 3 groups regarding the rate of orthodontic tooth movement.

Iosub Ciur et al.23 treated 6 patients with fixed appliances and performed maxillary canine retraction (distalizing force: 150 g). They administered an injection of 0.2 mL DMSO containing 42 pg/mL of vitamin D3 into the periodontal ligament of the experimental canine, and was administered weekly for 3 weeks. A significant difference was reported regarding tooth movement between the experimental and control canines (P = 0.0313).

Fontana et al.26 investigated the association between VDR TaqI gene polymorphism and EARR during orthodontic treatment in 377 participants. They evaluated the amount of EARR on periapical radiographs taken before and after 6 months of orthodontic fixed treatment. They concluded that the polymorphism was associated with higher EARR.

In 2021, Leszczyszyn et al.31 evaluated the relationship between vitamin D deficiency and skeletal malocclusion in 114 participants. They found that hypovitaminosis D might increase the risk of crossbite (odds ratio [OR] = 6.16), crowding (OR = 4.94), and narrowed upper arch (OR = 4.94).

In the same year, Tashkandi et al.33 demonstrated that low (< 2.75 ng/mL) and high (> 6.48 ng/mL) levels of vitamin D binding protein were associated with a reduction of tooth movement in 73 orthodontic patients. The study confirmed that optimal vitamin D binding protein saliva levels could only be associated with an adequate rate of orthodontic tooth movement.

In 2023, Marañón-Vásquez et al.39 explored the association between single-nucleotide polymorphisms in vitamin-D-related genes (i.e., VDR, GC, CYP27B1, and CYP24A1) and the amount of EARR subsequent orthodontic treatment in 143 individuals. They reported that the AA genotype in VDR rs2228570 was associated with 21% higher EAAR than those with AG and GG genotypes. As a result, they concluded that vitamin-D-related genes might be significantly associated with orthodontic treatment effects.

On the other hand, Tehranchi et al.34 analyzed 34 patients with mild, moderate, and severe vitamin D deficiency treated with fixed orthodontic appliance. They found no significant differences between groups regarding EARR (P > 0.05). Similarly, in 2022, Azizi et al.37 reported no significant correlation (P = 0.423) between EARR and vitamin D serum levels in 50 patients treated with the same fixed orthodontic appliance.

Al-Attar and Abid36 assessed the effect of vitamin D3 levels on the alignment of mandibular anterior teeth in 33 patients. They found statistically significant advantages in patients with normal vitamin D3 levels regarding the resolution time of mandibular incisors crowding (P ≤ 0.001). In contrast, there was no significant between-group difference regarding the amount of EARR. However, the pain reported by patients during the first 3 days of treatment was significantly lower in the normal vitamin D3 levels group (P < 0.05).

Varughese et al.35 evaluated the total amount of canine distalization using a closed Niti spring (distalizing force: 150 g) in 15 patients. An injection of 0.2 mL of 1.25(OH)2 vitamin D in DMSO, containing 50 pg/mL of vitamin D3, was administered into the periodontal ligament of the experimental canine once a month for 3 months. In contrast, a 0.2 mL placebo gel was injected into the periodontal ligament of the control canine. Statistically significant differences (P = 0.000) were observed between the experimental and control groups over a period of 3 months.

Quality assessment

Fifteen studies (78.95%)22-30,32,33,35,36,38,40 did not present serious risks of bias, whereas 4 studies (21.05%)31,34,37,39 reported at least 1 serious risk of bias, in accordance with the Joanna Briggs Institute Critical Appraisal.41 The main issues regarding study quality included the lack of a control group34,37,39 and multiple measurements of the outcome both pre and post-intervention/exposure.31,37 Tables 3 and 4 describes a detailed quality assessment according to the Joanna Briggs Institute Critical Appraisal.41

Table 3 . Joanna Briggs Institute Critical Appraisal for quasi-experimental studies.

Authors	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8	Q9	Total score
Al-Hasani et al. (2011)22	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Azizi et al. (2022)37	Y	Y	Y	N	N	Y	Y	Y	Y	7
Iosub Ciur et al. (2016)23	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Collins and Sinclair (1988)24	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Cui et al. (2016)25	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Fontana et al. (2012)26	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Gratton et al. (2022)38	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Kale et al. (2004)27	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Kawakami and Takano-Yamamoto (2004)28	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Khalaf and Almudhi (2022)29	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Khalaf and Almudhi (2022)30	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Leszczyszyn et al. (2021)31	Y	Y	Y	Y	N	Y	Y	Y	Y	8
Marañón-Vásquez et al. (2023)39	Y	Y	Y	N	Y	Y	Y	Y	Y	8
Moradinejad et al. (2022)40	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Takano-Yamamoto et al. (1992)32	Y	Y	Y	Y	Y	Y	Y	Y	Y	8
Tashkandi et al. (2021)33	Y	Y	Y	Y	Y	Y	Y	Y	Y	9
Tehranchi et al. (2017)34	Y	Y	Y	N	Y	Y	Y	Y	Y	8

Q1 = Is it clear in the study what is the ‘cause’ and what is the ‘effect’ (i.e. there is no confusion about which variable comes first)?; Q2 = Were the participants included in any comparisons similar?; Q3 = Were the participants included in any comparisons receiving similar treatment/care, other than the exposure or intervention of interest?; Q4 = Was there a control group?; Q5 = Were there multiple measurements of the outcome both pre and post the intervention/exposure?; Q6 = Was follow up complete and if not, were differences between groups in terms of their follow up adequately described and analyzed?; Q7 = Were the outcomes of participants included in any comparisons measured in the same way?; Q8 = Were outcomes measured in a reliable way?; Q9 = Was appropriate statistical analysis used?.

N, no; Y, yes..

Table 4 . Joanna Briggs Institute Critical Appraisal Checklist for randomized controlled trials.

Authors	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8	Q9	Q10	Q11	Q12	Q13	Total score
Al-Attar and Abid (2022)36	Y	Y	Y	Y	Y	Y	Y	Y	Y	Y	Y	Y	Y	13
Varughese et al. (2019)35	Y	Y	Y	Y	Y	Y	Y	Y	Y	Y	Y	Y	Y	13

Q1 = Was true randomization used for assignment of participants to treatment groups?; Q2 = Was allocation to treatment groups concealed?; Q3 = Were treatment groups similar at the baseline?; Q4 = Were participants blind to treatment assignment?; Q5 = Were those delivering treatment blind to treatment assignment?; Q6 = Were outcomes assessors blind to treatment assignment?; Q7 = Were treatment groups treated identically other than the intervention of interest?; Q8 = Was follow up complete and if not, were differences between groups in terms of their follow up adequately described and analyzed?; Q9 = Were participants analyzed in the groups to which they were randomized?; Q10 = Were outcomes measured in the same way for treatment groups?; Q11 = Were outcomes measured in a reliable way?; Q12 = Was appropriate statistical analysis used?; Q13 = Was the trial design appropriate, and any deviations from the standard randomized controlled trial design (individual randomization, parallel groups) accounted for in the conduct and analysis of the trial?.

Y, yes..

This systematic review aimed to evaluate the correlation between vitamin D levels and the rate of tooth movement, EARR, bone biomarker expression, and bone remodeling. Ten studies22-24,27,28,30,35,36,38,40 investigated the effect of local (injections were administered in periodontal ligament or submucosal area) and systemic administration (oral supplementation) of vitamin D3 on the rate of tooth movement. The remaining 9 studies25,26,29,31-34,37,39 investigated the relationship among EARR, bone turnover, bone remodeling markers, and vitamin D.

Vitamin D3 and orthodontic tooth movement

Among the animal studies, 524,27,28,30,38 evaluated the effects of injections of 1.25(OH)2D3 into the periodontal ligament24 or the submucosal area of rat teeth.27,28,30,38 Four studies reported a significant improvement in the rate of orthodontic tooth movement,24,27,28,30 which was increased from 60% to 245%. Only 1 study38 did not report a significant increase in orthodontic tooth movement compared to the controls.

Among the human studies, 322,23,35 evaluated the effects of injection of 0.2 mL of DMSO containing vitamin D3 into the periodontal ligament, on tooth movement. Two studies23,35 reported a significant difference regarding tooth movement between the experimental and control teeth, and the amount of administered vitamin D3 ranged from 42 pg/mL23 to 50 pg/mL.35 Only 1 study22 compared different concentrations of injected vitamin D3 (15 pg, 25 pg, and 40 pg), and found no statistical differences among the 3 groups regarding tooth movement; however, the authors did not compare the amount of tooth movement to a control group. The only randomized controlled trial (RCT)35 performed on humans showed a significant increase in canine distalization with a local administration of vitamin D3, suggesting the potential role of vitamin D as an innovative approach to accelerate tooth movement in orthodontic patients.

Most of the included studies supported the idea that local injection of vitamin D3 during an orthodontic treatment might increase the rate of tooth movement and might potentially reduce the time required to achieve treatment results. However, the non-uniform study designs might have negatively influenced the results in both animal and human studies. Although the results show that vitamin D3 accelerates orthodontic tooth movement, the protocol and outcome methods revealed substantial differences, making it difficult to draw reliable conclusions.

A recent systematic review by Arqub et al.18 investigated the impact of biological agents on orthodontic tooth movement. The study confirmed that vitamin D showed variable effects on bone turnover, possibly related to the different stages of osteoblast maturation. The authors reported that vitamin D might decrease the RANKL/OPG ratio in mature osteoblasts, but increase the RANKL/OPG ratio in less-mature osteoblasts, thus stimulating osteoclastic bone resorption.

In this scenario, genetic polymorphisms in RANK, RANKL, OPG, COX-2 and IL-6 could be involved in the individual rate of orthodontic tooth movement and also with the expression of RANKL, OPG, COX-2 and IL-6 by the human periodontal ligament.42

On the other hand, a recent meta-analysis on the impact of calcitriol on orthodontic tooth movement reported a substantial discrepancy in the level of evidence, highlighting inadequate sample size in the study.19

Only 2 studies evaluated the effects of systemic supplementation of vitamin D3 on tooth movement.38,40 Gratton et al.38 evaluated the effects of oral supplementation and reported a lower tooth movement rate and relapse in animals receiving systemic vitamin D supplementation compared to control. In contrast, Moradinejad et al.40 showed significant differences in orthodontic tooth movement between groups, with significant advantages for groups treated with intraperitoneal administration of vitamin D3. Thus, a lack of consensus has been reported regarding the effects of systemic vitamin D supplementation on tooth movement.

Vitamin D receptor polymorphism, vitamin D serum levels, and external apical root resorption

Four human studies evaluated the correlation between VDR polymorphism, vitamin D serum levels, and EARR.26,34,36,39 Marañón-Vásquez et al.39 suggested a potential association between AA genotype in VDR polymorphism (rs2228570) and EARR. Similarly, Fontana et al.26 evaluated the frequency of the VDR TaqI polymorphism genotype in patients treated with fixed orthodontic appliances to determine its correlation with EARR. The findings showed no significant protective effect of allele C against EARR. Furthermore, the authors concluded that VDR TaqI polymorphism (rs731236), initial root length, and age might be correlated to the EARR.

On the other hand, results from the present systematic review may not support a relationship between serum levels of vitamin D and EARR after orthodontic treatment. Tehranchi et al.34 divided the subjects in the study into three groups according to the grade of hypovitaminosis D and evaluated the EARR of maxillary incisors on periapical radiographs. The results showed that the prevalence of hypovitaminosis D did not change in patients with higher EARR. Al-Attar and Abid36 divided patients into a normal vitamin D3 level group and a control group (unknown vitamin D levels). The authors found a significant reduction in root length after treatment compared to baseline for both groups and no significant difference between the groups.

Recent investigations have explored the main causes of EARR, suggesting its association with age, dentition, and skeletal maturity during orthodontic treatment.43-47 However, the etiopathology of EARR remains unclear.48,49 Booij-Vrieling et al.50 analyzed the expression of muscle segment homeobox 2 (MSX2), RANKL, and VDR in teeth, assessing the serum levels of vitamin-D metabolites in cats with and without tooth resorption. The authors reported that the vitamin D levels in animals did not differ between groups, whereas the amount of expression of VDR protein differed between groups. Results showed that the VDR was expressed in resorptive lesions of permanent teeth of cats, suggesting that 1.25(OH)2 vitamin D might play a role in feline tooth resorption. Moreover, the results suggested that the expression of the VDR by fibroblasts could indicate that vitamin D has an indirect role in the differentiation of odontoclasts, possibly by stimulating RANKL and MSX2 production.

Vitamin D serum levels and RANK, RANKL, and RANKL/OPG ratio

Among the animal studies, Cui et al.25 showed that vitamin D3 administered via gavage could down-regulate the expression of HMGB1, which may influence macrophages to secrete RANKL, contributing indirectly to the formation of osteoclasts.

Among human studies, Khalaf and Almudhi30 correlated the hypovitaminosis D to the serum levels of RANKL/OPG ratio and showed a statistically significant decrease in the concentration of RANKL and RANKL/OPG ratio in patients with hypovitaminosis D compared to the control group.

Vitamin D was reported to affect the RANK/OPG axis, particularly by reducing inflammatory cytokines and modifying the expression of COX-2, OPG, RANKL, and IL-6 genes during orthodontic tooth movement.13 In this context, Yang et al.51 showed that RANKL could be produced by periodontal ligament cells in response to orthodontic tooth movement.

The present systematic review also showed the positive role of vitamin D in reducing pro-inflammatory cytokines (e.g., IL-6, TNF-α, and HMGB1), which are synthesized and secreted by the periodontal ligament cells.25

These results align with Nebel et al.52 which demonstrated the role of 1α,25(OH)2D3 in promoting the expression of cytokines in the periodontal ligament cells. In this scenario, HMGB1 was reported to indirectly affect the proliferation and the differentiation of osteoclasts and the release of proinflammatory cytokine in the early phase of tissue remodeling.25,52 Furthermore, HMGB1 appears to lead the macrophages to produce RANKL and pro-inflammatory cytokines (i.e., IL- 6, IL-8, and TNF-α).53 Moreover, it has been shown that the IL-6 could be overexpressed during the orthodontic tooth movement and involved in bone resorption.54-56

Even though studies have shown the biological effect of vitamin D on bone metabolism, there are insufficient clinical studies and a lack of substantial evidence regarding its influence on orthodontic tooth movement in humans. Well-powered RCT with sufficient sample sizes and extended follow-up periods are needed to evaluate the clinical effects.

Study limitations

Despite the interesting findings, this systematic review has several limitations. Firstly, the effects of vitamin D administration were analyzed in both animal and human, making it difficult to draw clear clinical conclusions. Moreover, there are no standardized protocols and outcome methods for vitamin D supplementation or the assessment of vitamin D serum levels. Lastly, a meta-analysis could not be performed due to the high heterogeneity of conditions, interventions, and outcomes.

The present systematic review evaluated the correlation between vitamin D levels and the rate of tooth movement, EARR, bone biomarker expression, and bone remodeling.

The findings of the included studies supported that vitamin D3 local injections might increase the rate of tooth movement and expedite orthodontic treatment outcomes. However, the non-uniform study designs and different protocols and outcome methods make it challenging to draw reliable conclusions.

Moreover, the results of this systematic review did not support a relationship between VDR polymorphisms, vitamin D serum levels, and EARR. Thus, further investigations are necessary to enhance our understanding on the etiopathology of EARR.

Lastly, it should be taken into consideration that vitamin D might affect the RANK/OPG axis by reducing inflammatory cytokines and modifying the expression of HMGB1, COX-2, OPG, RANKL, and IL-6 genes during orthodontic tooth movement.

In conclusion, due to the low number of high-quality studies involving human, there is a critical need for physicians and scientists to improve the clinical research on the role of vitamin D on orthodontic tooth movement and bone remodeling.

Conceptualization: MF, AS. Data curation: MF, DC, AS. Formal analysis: MF, DC, LL. Investigation: MF, DC, LL. Methodology: AS. Supervision: AS. Validation: MF, DC, LL. Visualization: FA, MM. Writing–original draft: MF, DC, LL. Writing–review & editing: MI, AG, AS. All authors have read and agreed to the published version of the manuscript.

No potential conflicts of interest relevant to this article were reported.

None to declare.