## 1 Introduction  
The connections between success of dental implantation and various systemic conditions have been started to be investigated and published during the past decade [1; 2; 3]. It is well known that any conditions that interfere with normal homeostasis of bone might have detrimental effects on the survival of dental implants [4]. Understanding the medically-compromised conditions that might affect dental implants, for example diabetes mellitus or osteoporosis, helps reduce failures and complications following the treatment [3]. Diabetes mellitus impairs bone healing, therefore, this systemic condition has to be taken into the consideration for dental implant treatment. Four hundred and twenty-two million people worldwide were diagnosed with diabetes mellitus (DM) in 2014 and the number of affected people is estimated to be on the rise [5]. The increasing number of DM cases is due to increasing prevalence of obesity, since these two disorders are metabolically associated [6]. Increasing sugar intake, physical inactivity and sedentary life are the key factors for developing these two disorders, commonly found among people in developed countries [7; 8]. The most common forms of DM are type 1 and type 2. Type 1 (T1 DM), or insulin-dependent diabetes mellitus is the result of failure of the pancreas to produce insulin. Type 2 (T2 DM),or non-insulin-dependent diabetes, results from deficiency in insulin production, or its mechanism of action, or both. Unlike T1 DM, T2 DM is linked to obesity, which is the predominant form in the adult population, contributing about 90% to 95% of diabetes cases [9]. This form of diabetes is characterized by insulin resistance, hyperglycemia and dysfunction of the pancreas to produce sufficient insulin. All of these disorders can be seen in the late stage of T2 DM [10]. In addition, obesity and T2 DM contribute to metabolic syndrome, which is associated with abdominal obesity, blood lipid disorders, inflammation, insulin resistance or full-blown diabetes, and increased risk of developing cardiovascular disease [11]. T2 DM is associated with various systemic complications, including microvascular and macrovascular complications, such as retinopathy, nephropathy, neuropathy, cerebrovascular disease and cardiovascular disease [12]. Furthermore, DM has been found to be associated with increased prevalence of periodontitis and tooth loss [13], impaired wound healing, and increased susceptibility to infection [14]. Glycemic control is important for long term maintenance of DM to prevent associated major complications, such as cardiovascular diseases [15]. Glycoslated hemoglobin percentage (HbA1c) is considered a more reliable indicator for glycemic level in the previous six to eight weeks than fasting plasma glucose (FPG) [16]. The quality of glycemic control was found, in some studies [17; 18; 19; 20], to affect the survival of dental implants and the healing of their supporting bone whereas, in others studies no differences were found [21; 22; 23]. \"Well-controlled: \"better-controlled,\" \"moderately-controlled,\" and \"poorly-controlled\" DM are among the common terms to describe the quality of diabetic condition by different researchers in their respective studies. To determine the cut-off point for HbA1c to differentiate between well- and poorly-controlled DM is unclear, although many authors consider HbA1c of more than 8% as poorly-controlled [24]. This is possibly the reason why the results of bone healing around dental implants in T2 DM were inconsistent due to different methods to define the glycemic status of the patients. The long-term clinical performance of dental implants in diabetic patients is less than in healthy individuals [25; 26; 27]. Moreover, many clinical studies have investigated the effect of T2 DM on soft and hard tissue healing following dental implant treatment [18; 19; 20; 28].