The nature, significance, parameters, influencing factors and testing of implant primary stability were studied by a literature review. Primary stability is a kind of anchorage force at the interface between the implant and bone, and it is merely mechanical. The significance of primary stability is to keep the implant unmovable so that the new bone can grow undisturbed on the surface of the implant without interference from fibrous tissue. The implant is finally bound to the bone by osseointegration. The most common assessments of primary stability are insertion torque (IT), the implant stability quotient (ISQ) of the resonance frequency analysis (RFA) and Periotest. IT is more commonly used to directly imply initial stability. At present, no consensus has been reached regarding the concrete parameters of primary stability to predict osseointegration. Implant osseointegration could be developed through all phases of primary stability. However, the excessive primary stability would cause mini-bone fractures, followed by bone necrosis at the interface and the final failure of implantation. Primary stability is influenced by three factors: implant design, bone condition of alveolar bone, and surgical technique. Under the condition of a lack of primary stability and immediate implantation, there may be the possibility of successful osseointegration. Therefore, it is necessary to re-examine the accuracy of the current elaboration on the primary stability. It is related directly to whether the clinic can choose the appropriate implant treatment path.

The periodontal bone defect might be formed on the distal surface of the second molar root followed the extraction of the mandibular third molar. The occurrence and prognosis of the complication would be influenced by the age of extraction, the impaction level of the third molar, local inflammation, health state of adjacent tooth, etc. The periodontal bone defect of the second molar would be severer and had poorer prognosis in the case of extraction for the older patients, deeper impaction of the third molar, local inflammation, food impaction, adjacent tooth caries. From the prophylactics, it was beneficial for the prevention of the complication or reducing severity of the complication when the extraction of lower third molar was performed before the age of 25 years old. The periodontal bone defect could be effectively repaired by transplanting bone graft.