## 4 Discussion  
Occlusal forces affect the bone surrounding an oral implant. Mechanical stress can have both positive and negative consequences for bone tissue and maintaining the osseointegration of an oral implant [10]. An adequate magnitude of immediate load can promote peri-implant osteogenesis, while excessive load can cause breakdown of peri-implant tissue [13].  
Immediate loading may reduce the treatment duration and prevent the resorption of the bone surrounding extraction sockets; however, a cautious approach should be taken as overloading may lead to failure of the implant with elongated treatment duration and may lead to dystrophy of the surrounding tissues [14].  
The major difference between natural teeth and dental implants is the presence of the periodontal ligament, which effectively distributes the dynamic load in natural teeth.  
Periodontal tissues contain various load-distributing components such as minerals, fibrillar proteins and globular proteins. The fibrillar proteins interact with globular proteins, interstitial fluid and blood [15; 16; 17]. These components with their respective constitutive properties could have different load-bearing responses individually or combined, depending on the rate of loading [18].  
\begin{table}
\begin{tabular}{l c c c} \hline
**Unit** & **Mean Compressive Strength (N)** & **Standard Deviation** & **Mean Sinking (mm)** \\ \hline
1 unit & 1274.9 1  & 83.3 & 0.69 \\
2 unit & 1039.8 1  & 82.3 & 0.60 \\
3 unit & 1587.6 1  & 267.5 & 0.78 \\ \hline \end{tabular}
\end{table}
Table 2: Comprehensive fracture strength of used provisional restorations.  
Figure 4: Load displacement of provisional restorations.  
Thus, the existence of shock absorbing before obtaining firm osseointegration might effectively distribute the loading to the implant and make immediate loading more successful.  
The present study evaluated provisional restoration using a healing cap for load buffering. Since this was an in vitro study, conditions that may cause spontaneous dislodge of provisional restorations, such as water leakage in cement, did not occur. If such displacement occurs in clinic, the dentist may simply check the occlusion and reattach provisional restoration and the implant will be safe. The results revealed that provisional restorations showed sinking tendencies to certain extents until the point of fracture. Considering the range of sinking in a natural tooth is 0.05-0.1 mm under 45 kgf, the present study showed 0.3-0.5 mm sinking under 45 kgf, which exhibits the protection capability of a plastic fabricated cap applied on implants between natural teeth [19].  
The results of the study showed detachment in all temporary restorations fabricated with plastic caps under a force less than 30 N. This force may be considered relatively weak compared to the normal bite force of humans. Although there are differences in the direction of the force, the fall off of the temporary restoration may prevent the adverse external force. Paying careful attention to the occlusal scheme and characteristics of force is especially crucial in the case of screw-retained implants, as force cannot be dispersed or lost through the loosening of healing cap, but rather passing directly down the body of implant. This creates an adverse environment that may eventually cause ossteointegration failure of implant.  
Considering that the maximal bite forces on posterior teeth are 330-800 N, the fracture strength shown in the present study had the capacity to withstand the subject's occlusal forces [20; 21; 22; 23; 24; 25].  
The notably low fracture resistance in two-unit restorations may be explained by our selection of the point part as the point of force loaded rather than directly on the abutment. Also, there might be limitations in this study that prevented perfect simulation of clinical situations. Further studies should include the standardized method of force loading.