## 4 Discussion  
This long-term retrospective study confirms the results of previous ones that one-stage surgery may yield similar results as those achieved by two-stage surgery [9; 17; 18; 19; 20; 21; 22] regardless implant brand or type used. In 1996, [PERSON] et al. [9] used a split-mouth design to compare one- vs. two-stage surgery in patients with partial edentulism. [PERSON] et al. [11] later conducted a similar comparison of implant-supported overdentures, and [PERSON] et al. [12] compared the two techniques after insertion of implants in the posterior regions of the jaws. The same conclusions were also reached by [PERSON] et al. [13] [PERSON] et al. [14] went one step further and compared the two methods following immediate implantation, and their findings showed similar successful outcome for both methods.  
Crestal bone loss in association with one- vs. two-stage surgery was tested in several studies and the results showed no significant differences between the two methods [11; 12; 14]. Those findings are compatible with the results of the current study. There were statistically significant differences in choosing the surgical approach between the mandible and the maxilla. A possible explanation for the increased choice of one stage approach in the mandible, as compared to the maxilla, is the ability to achieve greater initial stability with the insertion of a wider implant into the lower jaw which has a higher density of bone than the upper jaw. It can be speculated that the increased number of implants tipped the decision in the direction of a two-stage in order to reduce risk of failure. When more than three implants are needed, the edentulous area usually requires temporary replacement by a removable appliance. This kind of prosthesis exerts early forces on the underlying implant thus risking their success. Therefore the surgeon preferred covering the implants, and uncover then in a second stage surgery.  
It is highly desirable to shorten restorative treatment time, and one-stage surgery fulfills this goal without compromising the long-term clinical results in terms of implant survival and health of the tissue surrounding the implant. One- vs. two-stage implant placement has been a subject of debate. The decision-making process must take into account many factors before a treatment plan can be developed. The data of the present study demonstrated a change of paradigm from two-stage towards one-stage surgery. In 1992-1997, there had been insufficient evidence to support one-stage surgery. The continuous emergence of positive clinical outcome data of one-stage surgery from 1998 up to 2009 and the patients' demand for shortened treatment and fewer surgical procedures may have led to a gradual increase in the prevalence of one-stage surgery from 25% in 2000 up to 53% in 2010 [10; 11; 12; 14].  
Soft tissue parameters need to be considered. The initial incision is less important in two stage surgery. Even if not placed in such a way that allows 2 mm of keratinized gingiva on either side of the implant, keratinized tissue width can be adjusted at second stage surgery. Whenever one-stage surgery is planned, the initial incision should always be performed being attentive to end the operation with >2 mm keratinized soft tissue on buccal and lingual/palatal side of the implant.  
One should also consider study limitations as minimizing cofounders by inclusion criteria and similar distribution between groups, the retrospective nature of the study, implant development/changes over the year, and surgeon's preference/bias all of which can influence the results and could not be considered in the present evaluation.