Table 2.

Characteristics of the in vitro studies and their results.

Author, Year [Reference]	Main Objective	Intervention, Dose, and Frequency	Results
Rekha et al, 2014 [7]	Evaluation of the in vitro efficacy of Vit. D on osteoblastic activity in both fetal and adult osteoblasts	1. Collection of samples: – fetal osteoblasts—calvariae and long bones from the fetuses of two pregnant rabbits – adult osteoblasts—radii from two adult white rabbits 2. Isolation, culture, extension, and characterization 3. Placement of viable cells in the osteogenic environment with or without 1.25-dihydroxyvitamin D3	Fetal osteoblasts compared to adult osteoblasts have shown a significant increase in mineralization upon the addition of Vit. D. This reflects a high therapeutic potential of fetal osteoblasts along with Vit. D3 in bone regeneration.
Kim et al, 2018 [8]	Evaluation of the effects of 1.3-dihydroxyvitamin D3 on the proliferation, differentiation, and mineralization of the matrix of osteoblast-like MC3T3-E1 cells in vitro	MC3T3-E1 osteoblastic cells and 1.25-dihydroxyvitamin D3 were prepared	The authors suggest that 1.25-dihydroxyvitamin D3 positively affects cell differentiation and matrix mineralization. Therefore, it can function as a stimulating factor in the formation of osteoblastic bone and can be used as an additive in the treatment of bone regeneration.
Nah et al, 2019 [9]	Synthesis of conjugated GNPs (gold nanoparticles) with VGNPs (vitamin D-conjugated GNPs) to allow improved osteogenesis	Synthesizing GNPs conjugated with VGNPs	VGNPs can be applied as potent carriers that enhance osteogenic differentiation. The results of this study could help design a nanoparticle system for the treatment of osteoporosis in the field of bone tissue engineering.
Chen et al, 2020 [10]	Construction of a biofunctional multilayer structure containing Vit. D and calcitonin (CT) on a titanium alloy implant (Ti6Al7Nb)	1. Molecules of β-cyclodextrin (β-CD) molecular reservoirs grafted on chitosan molecules and loaded with calcitriol (Vit. D) 2. Molecular complex co-assembled with calcitonin (CT) 3. Ti6Al7Nb substrate	In vitro results show that the released Vit. D and CT individually regulated the expression of the calcium-binding protein (including calbindin-D9k and calbindin-D28k) and BMP2 in osteoblasts in peri-implant regions to stimulate their deposition and differentiation from Ca. Micro-CT results and in vivo histological analyses also demonstrate that a coloaded Vit. D/CT implant can dramatically improve bone remodelling under osteoporosis.
Mahdavi et al, 2020 [11]	The aim of the study was to obtain new scaffolds with drug release capability usable in bone tissue engineering	Manufacturing of graphene (GO) oxide scaffolds loaded with gelatin (G)–hydroxyapatite (HA)–Vit. D with different concentrations using the solvent casting method	The results demonstrated the potential of these scaffolds to induce bone regeneration.
Petrescu et al, 2020 [12]	To establish a new differentiation protocol using cannabidiol (CBD) and Vit. D for better and faster osteogenic differentiation of mesenchymal stem cells (MSCs) derived from dental tissue	1. MSC harvesting, isolation, and characterization 2. Evaluation of the effects of CBD and Vit. D in terms of osteogenic differentiation of stem cells	This study provides evidence for a better understanding of the effects of CBD and Vit. D on MSC populations of dental origin, supporting the development of tissue engineering in the field of dentistry.
Abdelgawad et al, 2020 [13]	Evaluation of the effects of photobiomodulation and Vit. D (as an anabolic factor) on HPDLSCs (human periodontal ligament stem cells) for bone regeneration	1. Collection, isolation, and characterization of periodontal ligament stem cells 2. Their division into six groups: groups I and II, control and (10−7 Mol) vitamin D, respectively; group III, irradiation at 1 J/cm2; group IV, irradiation at 1 J/cm2 and culture with Vit. D; group V, irradiation at 2 J/cm2; group VI, irradiation at 2 J/cm2 and culture with Vit. D	Laser irradiation at 2 J/cm2 combined with Vit. D improved osteoblast differentiation and proliferation of the cultured HPDLSCs.