Stability of fixation methods in large mandibular advancements after sagittal split ramus osteotomy: an in vitro biomechanical study

Abstract

Sagittal split ramus osteotomy (SSRO) with large mandibular advancements is a common surgical procedure and could be indicated for patients with sleep apnoea. As a large variety of fixation methods is used for the stabilisation of SSRO, a biomechanical test model was used to analyse which fixation technique was most stable. For this in vitro study, 80 polyurethane hemimandibles with a prefabricated SSRO were used as substrates. Loads in Newtons were recorded at displacements of the mandibular incisive edge at 1 mm, 3 mm and 5 mm. The samples were divided into two groups: mandibular advancements of 10 mm and 15 mm. In both groups, four fixation techniques were used: (A) one four-hole miniplate; (B) two four-hole miniplates; (C) one four-hole miniplate plus one bicortical screw; and (D) three bicortical screws in an inverted-L arrangement. In group 1, three bicortical screws resulted in the best stability, and in group 2, two miniplates resulted in the best stability. The use of two miniplates did not show significant differences between both groups. Other fixation methods showed more stability with 10 mm advancements. This study therefore suggests that in SSRO with advancements exceeding 10 mm, the use of two miniplates is the optimal means of providing rigid fixation.

Biomechanical Evaluation of a New Fixation Method for Stabilization of Sagittal Split Ramus Osteotomy After Mandibular Advancement

“…In the case of similar or larger mandibular advancements, comparable results have been observed in other studies. 13,14,15 According to the results of the present study, it might not be very effective in clinical cases of larger mandibular advancements to add only 1 bicortical screw in the retromolar area next to a 4-hole single miniplate fixation. Instead, the authors suggest adding a second miniplate if more rigidity is required during the immediate postoperative period.…”

“…7 The use of multiple miniplates also adds to stability. 13,15 However, this increases the hardware costs and placement is not always feasible because of the lack of available bone surface. For this reason, the use of an increased number of plates is also associated with an increased risk for plate removal following orthognathic surgery.…”

“…To standardize placement of the fixation materials and the length of mandibular advancement, a drill jig custom-made according to the method of Kuik et al was used. 13 Using the jig for guidance, the hemimandibles were predrilled. All plates and screws were bent and fixated by one investigator (KK).…”

“…[9][10][11][12] Regarding mandibular advancements up to 10 mm, the use of 3 titanium bicortical screws placed in an inverted-L pattern has presented the most stability. 4,13,14 However, in the case of extremely large advancements (i.e. >15 mm), 2 titanium miniplates presented more stability than 3 titanium bicortical screws in an inverted-L pattern.…”

“…>15 mm), 2 titanium miniplates presented more stability than 3 titanium bicortical screws in an inverted-L pattern. 13 Two miniplates can also be connected with each other, which is known as a "gridplate." It is thought that connecting the 2 miniplates could provide additional stability.…”