الفهرس 
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Abstract
Aim: The aim of this study was to investigate the osteogenic potentiality of human dental pulp stem
cells’ (hDPSCs’) secretome implanted in rabbit critical-sized tibial bone defects through dynamic
parameter (primary outcome); which is mineral apposition rate (MAR) as well as static parameters
(secondary outcomes) represented in histomorphometric analysis of the newly formed bone area
percentage and gene expression detection for osteocalcin using quantitative real time polymerase chain
reaction (qRT-PCR).
Methodology: 51 male rabbits weighing 2.5 to 3.5 kilograms received two critical-sized tibial defects
(one defect for each tibia) and were randomly assigned into three equal groups: 1- group I (spontaneously
healing group): the tibial defects were left to heal spontaneously. 2- group II (collagen scaffold group):
the defects received collagen scaffold as a positive control group. 3- group III (hDPSCs’ secretome
group): the defects received collagen scaffold loaded with hDPSCs’ secretome. For measuring the
primary outcome, nine rabbits received subcutaneous injections of oxytetracycline and calcein green at
14 and 28 days postoperatively and they were euthanized after six weeks. The obtained bone specimens
were examined by fluorescent microscope to calculate MAR. While the remaining animals were used for
measuring the secondary outcomes in which; half of the animals were euthanized after three weeks and
the other half after six weeks. At each time interval, half of the bone specimens were examined
histologically by light microscope followed by histomorphometrical analysis to measure bone area
percentage while the other half was used to obtain gene expression analysis for osteocalcin using qRTPCR.
Results: hDPSCs’ group showed superior results and significant improvement of bone healing as
compared to the other two groups throughout the experiment. MAR was greater in hDPSCs’ group
compared to the other two groups (P < 0.05). Histomorphometric analysis revealed significant increase
in bone area percentage in group 3 compared to the other two groups (P < 0.05) in both durations.
Moreover, qRT-PCR results supported our abovementioned results as they revealed higher than normal
levels of osteocalcin in hDPSCs’ group at three weeks and six weeks in comparison to the other two
groups that showed lower levels of expression at both time intervals. (P <0.05)
Conclusion: Collagen scaffold alone showed better healing effect compared to negative control group.
Yet, its regenerative effect was not significant and should be combined with other substances capable of
regenerating bone efficiently. The present study concluded that critical-sized tibial bone defects could be treated with hDPSCs’ secretome loaded on collagen scaffold.
KEY WORDS : Cell free therapy, secretome, dental pulp stem cells, critical-sized bone defect