## 4 Discussion  
To the best of our knowledge, this is the first study that histologically and histomorphetrically evaluates the effects of the serum vitamin D level on autogenous grafts, allografts, and xenografts used in the treatment of bone defects. The results of this study demonstrate that higher vitamin D levels lead to an increase in the number of new bone formations in all defect types. [PERSON] et al. evaluated the effect of vitamin D on fracture healing in osteopororotic rats. A fracture line was created by osteotomy in the femurs of all rats in the experimental and control groups. The experimental group was administered 1.25(OH)2D3, 0.1 ug/kg/day via oral gavage. All the animals were sacrificed in the sixth and sixteenth weekend, and the fracture lines were examined histomorphometrically. The histomorphometric data obtained 6 weeks after the fracture demonstrated that the 1.25(OH)2D3-administered group had a 23% higher total callus volume compared to the control group. New bone volume and trabecular number displayed the same tendency. No histological differences were observed in the groups in week 16 [10]. This might be due to a period of 4-8 weeks being considered sufficient for long-term bone healing for rat metabolism. For this reason, the period between the surgical operation and the sacrifice was determined to be 6 weeks, which is the period that is usually preferred in experimental studies in the literature. In an in vivo study on rats conducted in 2017 by [PERSON] et al., the experimental animals were separated into three different groups, and feed containing 20,000 iu/kg and 8000 iu/kg vitamin D was used as high vitamin D dosage, while 1000 iu/kg vitamin D containing feed was used in the control group. The tibias of sacrificed animals were dissected following a special 4-week feed. The mechanical endurance and cortical and trabecular morphologies of the bones were examined. The findings demonstrated that the animals in the highest vitamin D group had higher volumes of trabecular and cortical bones and also had higher mechanical endurance and fracture resistance in their tibias, while there was no statistically significant difference regarding the volume and hardness of the bones between the normal vitamin D and low vitamin D groups. The research argued that the results of the study indicated that vitamin D supplements in diet increase bone health in general, and it is helpful to have a higher bone volume to prevent osteoporosis in adulthood [11]. The vitamin D levels were not measured in this study, so it cannot be concluded whether the vitamin D level in the control group was, in fact, insufficient, or if 20,000 iu in the high vitamin D group could, in fact, be considered high enough. Similar to the studies conducted by [PERSON] et al. and [PERSON] et al., our study also measured the highest number of new bone formations and the lowest defect distance in the high vitamin D group in the empty defect group after 6 weeks, and autogenous grafts, xenografts, and allografts were used for the treatment of intraosseous defects in our study. The findings indicated that high vitamin D levels had significantly higher numbers of new bone formations compared to the control and low vitamin D groups. Compared to grafts, the highest number of new bone formations in the high vitamin D and control groups was observed in allograft-applied cases, while in the low vitamin D group, the autogenous graft-applied cases had the highest number. In their in vivo study, [PERSON] et al. evaluated the effect of vitamin D supplements on bone regeneration in alloplastic bone graft-applied defects. The premolars of dogs were extracted and 3 months later, standard defects with a 4 mm diameter and a 6 mm depth were prepared and then applied to alloplastic grafts. The experimental group was orally administered 37.5 iu vitamin D tablets each day for 4 weeks. The control group was fed a standard diet. The pre- and post-implant surgery vitamin D levels in the experimental animals were not measured.