الفهرس 
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Abstract
Dental implant therapy is a well documented method for replacing missing teeth. Occlusal overloading above the physiologic bone limit induces microfractures in the bone, stimulating osteoclastic activity that leads to peri-implant crestal bone loss.
The C/I ratio is the relationship between the length of the restoration and the length of the implant embedded in bone.
The relationship between crestal bone loss and non-axial loading has been observed in theoretical mathematical models. An unfavorable C/I ratio has been considered a form of non-axial loading.
It is reasonable to assume that an implant restoration with a long crown and a short fixture creates an unfavorable C/I ratio, while an implant with a short crown and a long fixture creates a favorable ratio. The higher the crown, the longer the lever arm, and consequently the greater the stress at the bone crest.
Some investigators reported a positive correlation between an increased C/I ratio and a higher risk for peri-implant crestal bone loss, while others failed to show such a correlation and even observed an inverse relationship between the C/I ratio and crestal bone loss.
Therefore, this study was conducted to compare the effect of different crown-implant ratios on peri-implant crestal bone levels.
The study was conducted on ten patients in the same age range and medically free. Mandibular posterior areas were selected as they play an important role in the patient’s comfort.
Each patient received two implants of the same width and same design, they differed only in the length of the implant. Each implant supported a single fixed restoration.
The following clinical parameters : gingival index score, plaque index score, bleeding index score and probing depth were conducted at 1, 3, 6 months after prosthetic loading.
Clinical results showed no statistically significant (p-value ≥ 0.05) change in median gingival index scores, plaque index score, bleeding index score and probing depths measurements between short and long implants.
The method we used to measure the marginal bone changes in this study was the Cone Beam Computed Tomography (CBCT) after 6 months of prosthetic loading.
Analysis of marginal bone changes between both implants showed that there was no statistical significant difference between short and long implants (p-value = 0.397).