###### Abstract  
The aim of this study is to investigate the effects of serum vitamin D levels on the healing of different bone graft materials. Thirty-six male rats were divided into three groups and fed special feeds containing different amounts of vitamin D for 6 weeks before the surgical phase: the high serum vitamin D level group (group H) 10,000 iu/kg vitamin D3; the standard serum vitamin D level group (group C) 1000 iu/kg D3; and the low-level vitamin D group (group L) 100 iu/kg vitamin D3. Under general anesthesia, four defects with a diameter of 5 mm were created in the calvaria of the rats. The defects were augmented with autogenous grafts, allografts, xenografts, or left empty. The serum vitamin D level was measured before the surgery and before sacrifice. At the end of the 6 th week, the subjects were sacrificed, and histological and histomorphometric analyses were performed. Study results show that in all graft types, as vitamin D levels increase, the number of new bone formations increases. There was no significant difference between the graft materials in terms of new bone formation criteria in group L. In group H and group C, the highest new bone formation was seen in the allograft group (1.48 \(\pm\) 0.07, 0.66 \(\pm\) 0.19, respectively). Prospective randomized clinical studies are required to evaluate the effect of vitamin D dose on the success of augmentation procedures in the clinic.  
vitamin D; bone grafts; bone defect; new bone formation; rat calvaria; animal model +
Footnote †: journal: Medical  
(1.25[OH]\({}_{2}\)D), in the kidneys. The 1.25[OH]\({}_{2}\)D ligand binds to vitamin D receptors (VDRs) with high affinity and later increases the intestinal absorption of both calcium and phosphor. Also, vitamin D actively participates in bone formation, resorption and mineralization, and protection of neuromuscular function. \"25-hydroxy vitamin D (25[OH]D)\", the form of vitamin D found in serum, is used to measure vitamin D levels. The values of serum vitamin D (25 OHD) between 0 and 30 ng/mL, between 40 and 80 ng/mL, and >150 ng/mL are, respectively, regarded as insufficient, sufficient, and toxic [2,3].  
In clinical practice, vitamin D deficiency is usually treated with pre-vitamin D2 and pre-vitamin D3 supplements in order to increase the serum 25(OH)D level, but due to their longer half-life, pre-vitamin D3 supplements are preferred in the treatment of vitamin D deficiency [4].  
Vitamin D is known to have an effect on the health of many tissues and systems such as the veins, the brain, the skeletal system, the cardiovascular system, the immune system, the endocrine system, and the neuromuscular system [5].  
There are recent studies on the effects of serum vitamin D levels on bone healing. In clinical studies, vitamin D deficiency was found to be associated with delayed union [6].  
Experimental studies found that vitamin D supplements accelerated the process of callus formation and the healing of fractures. Many scientific studies have reported that vitamin D is effective in osseointegration and bone metabolism in dentistry [7]. But, there are not sufficient studies on the effect of vitamin D levels on augmentation procedures [8]. This study was conducted with the aim of determining the effects of low, normal, and high levels of serum vitamin D on the bone formation capacity of different graft materials used in the augmentation of intraosseous defects.