Expression of CBFA1 and collagen X in the mandibular condyle under mechanical strain

Abstract

AIM: Core binding factor a1 (Cbfa1) is a crucial transcriptional factor for chondrocyte maturation and osteoblast differentiation in the mandibular condyle during natural growth. Type X collagen marks the onset of endochondral ossification in the condyle. It is important to understand tissue responses to different commonly used treatment modalities. Therefore, their expression in response to single-step and stepwise mandibular advancement could offer an insight into the effect of mechanical strain on condylar tissue. The aim of this study was to quantitatively assess the amount of mRNA expression of Cbfa1 and type X collagen in response to single-step and stepwise mandibular advancement. MATERIALS AND METHOD: Four hundred and twenty 35-day-old female Sprague-Dawley rats were randomly divided into 20 experimental and 10 control groups corresponding to 10 time points. Experimental animals were either fitted with a single-step bite-jumping appliance with 4 mm mandibular advancement or stepwise bite-jumping appliance with 2 mm advancement initially and another 2 mm advancement after 30 days. The rats were sacrificed after 3, 7, 14, 21, 30, 33, 37, 44, 51 and 60 days. Mandibular condylar cartilages were dissected immediately under microscope and total RNA was extracted. Cbfa1 and type X collagen mRNA were quantified with real-time RT-PCR. RESULTS: Quantitative analysis demonstrated that Cbfa1 and collagen X mRNA expression for all three groups reached a peak on experimental day 21. Comparing single-step with stepwise advancement, expression of Cbfa1 and collagen X were consistently higher during the first advancement than the stepwise advancement. In response to the second mandibular advancement, both Cbfa1 and type X collagen levels were significantly higher than levels expressed in the single advancement and untreated controls. CONCLUSION: Mandibular advancement promotes chondrocyte maturation and osteoblast differentiation by upregulating the level of Cbfa1. Stepwise advancement produces a higher level of Cbfa1 and type X collagen expression leading to more cartilage engaging in endochondral ossification.