The Importance of Flap Design in Third Molar Surgery: A systematic Review

The third molar extraction is a common practice in oral surgery [1,2]. They are present in 90% of the population and around 33% of patients have at least an impacted third molar, whose cause is associated to genetic and environmental factors [3]. The possible complications related to the presence of impacted or retained inferior third molars (infectious, inflammatory, tumors, or neurological complications) forces the surgical extraction in many occasions, either for therapeutic or prophylactic reasons. The surgical exodontia of the inferior third molar implies several postsurgical complications, such as damage into the structures adjacent to the third molar (nerves, bone and soft tissues), and the tissues near the surgical area (tongue and lips among others). In the postsurgical period, pain, inflammation, trismus, early or late infection, or paresthesia have been described. Therefore, designing and implementing an optimum flap would facilitate a better technique, better visibility for the surgeon and minimize complications [4]. There are different types of flaps to perform third molar surgery. The most commonly used are:


Introduction
The third molar extraction is a common practice in oral surgery [1,2]. They are present in 90% of the population and around 33% of patients have at least an impacted third molar, whose cause is associated to genetic and environmental factors [3]. The possible complications related to the presence of impacted or retained inferior third molars (infectious, inflammatory, tumors, or neurological complications) forces the surgical extraction in many occasions, either for therapeutic or prophylactic reasons. The surgical exodontia of the inferior third molar implies several postsurgical complications, such as damage into the structures adjacent to the third molar (nerves, bone and soft tissues), and the tissues near the surgical area (tongue and lips among others). In the postsurgical period, pain, inflammation, trismus, early or late infection, or paresthesia have been described. Therefore, designing and implementing an optimum flap would facilitate a better technique, better visibility for the surgeon and minimize complications [4].
There are different types of flaps to perform third molar surgery. Since there is no agreement on the type of flap which is most advisable, in this review we will try to analyze the advantages and disadvantages of the three most used flaps. or Spanish and clinical trials with a minimum level of incidence 1b, 2b were included [5]. Jadad criteria were applied to the clinical trials [6].

Results
The initial search revealed 134 articles. After reading the abstracts, or the full text if necessary, and exclusion of those which did not fulfill inclusion criteria, 14 articles were selected ( Figure 1).
Out of these resulting studies, 1 was evidence level 1b and level A of recommendation [7] and the remaining 13 were evidence level 2b and level B of recommendation (Table 1). From the analyzed articles, 2 studies had a Jadad index 3, 3 had 2, 6 had 1 and 3 had an index of 0 (Table 1). All were prospective randomized clinical trials except 3 that were not referred to as randomized [4,8,9] and only 1 study was a double blind one [7]. The reviewed clinical acts represent a total of 705 flaps, 298 are envelope flaps, 231 Newmann partial flaps and 176 Newmann partial modified flaps (Table 1). In most of the clinical trials except in the study by Monaco et al. [8] the majority of patients were females [10][11][12] and 3 studies did not specify the male/female ratio. The age range was between 15 to 60 years old (Table 1). While reading the analyzed articles we found two systematic reviews that analyzed 58 and 33 [3,13] studies respectively.

The Importance of Flap Design in Third Molar
Surgery: A Systematic Review

Discussion
On analyzing the data obtained we observed that the different clinical trials do not usually compare the same flaps and that they have a different sample size and level of evidence (Table 1). We

Envelope Flap (Szmyd Flap)
Authors like Baqain et al. [1] observed that the envelope flap ( Figure 2) produces statistically significant less inflammation and trismus compared to the triangular on the second and the seventh day after surgery, and on the 7 th or 14 th days respectively. But, the inflammation stops being significant on the 14 th day. Erdogan et al. [13] who also compared the envelope flap to the partial Newmann flap, referred that the envelope flap results in less inflammation after surgery and better results in pain control, the difference being statistically significant on day 3 and 7 after surgery. Borgonovo et al. [14] concluded that the envelope flap is the simplest to make and the easiest to suture. In agreement with these authors, Sandhu et al. [7] described an increase in dehiscence on the distal surface of the second molar, and the first added that there is more post-op pain than with the bayonet flap. According to Rahpeyma et al. [10] there is also more dehiscence in the envelope flap with respect to the triangular, but it wasn´t statistically significant. Koyuncu et al. [15] reported a significantly greater inflammation on day 2 and 7 after surgery with respect to the modified partial Newmann flap.
Monaco et al. [8] found a greater probing depth on the seventh day of the postoperative period than in the case of the triangular flap.
However, this value is insignificant at the 3 months mark. Finally, Borgonovo et al. [14] pointed out that it is more difficult to carry out ostectomy in this type of flap, compared to the other two.

Modified Partial Newmann Flap
Modified triangular, bayonet or modified Szmyd or L-Shaped incision ( Figure 4). Kirtiloglu et al. [9] reported a better primary healing than the triangular flap and Koyuncu et al. [15] demonstrated significantly less postoperative pain during the first 4 days after surgery with regards to the envelope flap. Silva et al. [4] stated that this flap allowed for a less traumatic surgery than the partial Newmann flap. This aspect could lead to a better healing of Koyuncu et al. [15] in their studies found a greater incidence of alveolar osteitis than in the envelope flap but it wasn't statistically significant. The first one claimed a longer surgical time, even though it was statistically insignificant. Kirk et al. [17] emphasizes more on the increased inflammation that occurs on the second day after surgery. As mentioned previously, Borgonovo et al. [14] talked about greater bone reabsorption than in the envelope flap.

Common Aspects
Different authors have derived conclusions that the flap election is not important. They considered other factors more important, or they did not find significant results to choose one type or other. In this way, Dolanmaz et al. [2] inferred that the degree of impaction, nicotine consumption and the duration of the surgery (this last factor shared by Sandhu et al. [7] have clearly more influence on the primary healing of the wound than the flap design. In the study by Sandhu et al.7 they found that there is no difference in the degree of inflammation between the different flaps mentioned above. These authors, along with Kirk et al. [17] did not find any type of relation between the type of flap and postoperative pain and they did not refer any difference in the presence of dehiscence. Both Koyuncu et al. [15], did not show differences in the maximum incisal opening. Regarding the presence of alveolar osteitis, it was insignificant for Sandhu et al. [7]. In the study by Koyuncu et al. [15] they described that there were no demographic differences. Even for Monaco et al. For both of them Erdogan et al. [13], the level of periodontal healing did not have any importance in the flap selection. When they compared the triangular flap and the bayonet flap, Kirtiloglu et al. [9] found that there weren't significant differences in the plaque index, gingival index and probing depth , (this last one was also not important for Arta et al. [12], when compared to the free gingival margin, the clinical level of insertion and the bone level (these two last factors for Rosa et al. [18] didn't influence the flap design).
Desai et al. [11] did not find any significant differences between the envelope and the triangular flap regarding visibility, accessibility, bleeding and sensibility of the adjacent teeth. In the study by Baqain et al. [1] work, they concluded that the flap to be used in young patients should be in accordance with surgeon's preferences, taking the patient's needs and his oral hygiene into account. Karaca et al. [3] argued that if there is a problem related to the soft tissues around the mandibular second molars, it is not a result of surgery or technique, but of some other process and that more comparatives studies are needed to determine the best technique to be used.

Final Considerations
Therefore, it can be inferred that even though there are a variety  -Easy to perform ostectomy and to circle structures -More inflammation, trismus and facial pain.
-More complicated to make and to suture -More bone reabsorption -Less inflammation.
-Better for ostectomy and circle structures -More complicated to perform and to suture.
-Less number of alveolar osteitis and more surgical time

Conclusion
Modified partial Newmann flap seems to be the most appropriate flap for the exodontia of the third molars considering that its benefits outweigh the risks. However we have a great diversity of flaps and we must personalize each case depending on the characteristics of each patient and on the skill and preference of the surgeon. More detailed studies are needed with bigger and well-designed samples.