# The Influence of Loading Program on the Stimulated Callus Mineralization
## 5 Discussion  
In our study the computational callus remodeling model is used to estimate how the loading program effects the callus density distribution during the stimulated healing process. Also, an attempt to establish the optimal loading program was made, leading to the most homogeneous distribution of material properties with nominal values kept on a desired level. Two sub-optimal approaches are studied in order to get closer to possible clinical treatment. Based on the numerical results, the callus remodeling response can be evaluated. The results of this study suggest a significant difference in the callus maximal density value between all three analyzed loading programs performed in the same time interval. The highest values of the density is obtained using the optimally-controlled model. All three programs provide satisfactory density distribution, although the intermittent programs require more time to achieve the designated 200 MPa Young's modulus value. There are three assumptions that have to be considered as limitations to accurately predict the outcomes of the callus distribution. First, the callus remodeling algorithm used in this work does not include the individual differences of the tissue density due to sex, age, diseases, osteoporosis, pharmacology treatment, and other patient-specific factors. Therefore, the influence of these factors on the callus remodeling process should be considered in the future study. That could mainly be achieved by variation of the model constant parameters. Due to that fact, the results presented and discussed here must be taken qualitatively and quantitative data will be different for each particular patient case. Second, the starting point of the iterative analysis is a homogeneous distribution of tissue density with [PERSON]'s modulus equal to 2 MPa. In fact, the callus density in the first day of the healing process was not fully investigated or thoroughly described [23; 42; 43; 44]. Third, isotropic material properties were considered instead of anisotropic, which are closer to the true material. However, as mentioned before, in the process of mineralization, the callus tissue acquires the features of a cortical bone, which in the literature is mainly modeled as an isotropic material. Moreover, the very small thickness of the callus layer justifies this simplification. One may observe from the above results that the proposed loading programs have a big influence on the bone density distribution. The predicted outcomes are not far different to those experienced in reality. It is known that too big a load can cause substantial damage or irreversible fracture in the tissues which are not strong enough [45; 46]. Therefore, to strengthen the callus tissue after trauma, the load must be applied at an adequate rate and of an adequate value dictated by the bone density at the particular point of healing time. Qualitative and quantitative comparison between results shows a sufficient degree of resemblance between the computational results and the clinical CT data. Also, numerical studies prove that efficient healing of the tissue may be obtained in the realistic load-controlled treatment (intermittent program). Simulations of callus remodeling, validated and compared with clinical data, are proven as a helpful way to elucidate the mechanisms behind bone healing. The effect of callus remodeling and the influence of the loading program on the healing process are critical for the development of planning the rehabilitation process. It is expected that this analyses of callus remodeling can contribute to the development of new loading programs used during patient rehabilitation. In the future, a detailed 3D analysis will be performed so that more a complex model of the callus and the mandible can be considered and more thorough solutions can be reached. The outcome of this research demonstrates the importance of the computational biomechanics due to the limitations in obtaining clinical data and experimental results.