# Impact and Stability of mandibular Setback after Intraoral Vertical Ramus Osteotomy
## 1 Introduction  
Today there are two commonly used techniques to treat mandibular prognathism: Intraoral Vertical Ramus Osteotomy (IVRO) and Sagittal Split Ramus Osteotomy (SSRO) [1]. In 1849, [PERSON] was the first to describe mandibular osteotomy; almost 50 years later, [PERSON] used mandibular body osteotomy for the treatment of mandibular prognathism, which was used until the 1970s of the last century. In 1957, [PERSON] and [PERSON] first reported on SSRO, which has evolved through a number of modifications, including the transition to rigid internal fixation suggested by [PERSON] [2]. The first IVRO was described by [PERSON] in 1968 and refined later on by [PERSON] and [PERSON] in the 1970s [1, 2]. The IVRO osteotomy technique has not changed much in recent years, but different designs for the ramus osteotomy have been developed. These designs refer to the shape of the cut made on the posterior part of the ramus, such as the oblique and vertical osteotomy. Although theoretically there might be differences in the frequencies of postoperative sensory changes according to the osteotomy design, there have been no previous studies to confirm them [2, 3]. Although both techniques (SSRO and IVRO) provide good stability, there is still a disagreement concerning the preferable procedure for the treatment of mandibular prognathism [4, 5, 6]. [PERSON] et al. performed a systematic review and meta-analysis that found that among 678 patients subdivided into two groups (SSRO N-318 and IVRO-341), there was no statistically significant difference regarding horizontal skeletal stability, but the SSRO group had more stability in the vertical dimension (\(p\) = 0.02) [6]. There are several advantages and disadvantages to each surgical technique. The main advantage of the IVRO is the lower prevalence of inferior alveolar nerve (IAN) damage compared to the damage created by the SSRO technique. The prevalence of immediate sensory damage in IVRO is 0-36%, while the prevalence of long-term damage is considered lower at 2.3-14% [7]. The reported risk of a long-term IAN deficit after an SSRO is highly variable and has been reported to be 0% to 75%, with an average of 33% for objective testing [8]. Moreover, in addition to the possible sensory damage to IAN, there are studies that have reported the incidence of lingual nerve (LN) dysfunction using the SSRO technique. [PERSON] et al. reported that 19.4% of 134 patients experienced LN sensory changes, and 69% of them reported sensory changes still present one year after the surgery [2,9]. When genioplasty is performed in addition to IVRO, and even more significantly in addition to SSRO, it increases the prevalence of sensory damage--there are several studies with different protocols that make it difficult to establish a clear connection--but even in patients that underwent only genioplasty, the prevalence for sensory damage can be as high as 20% [10, 11, 12, 13]. Another benefit of IVRO is its ability to improve TMD symptoms due to anterior inferior movement of the condyle that reduces pressures on the articular disc and repositions the condyle in its physiologic equilibrium except for cases of condylar displacement or luxation from the glenoid fossa. On the other hand, the use of SSRO can increase TMD symptoms due to the difficulty in reproducing the proper position of the condyle [14,15]. The main disadvantage of IVRO is the need for prolonged intermaximillary fixation (IMF) that affects the patient's quality of life in the immediate post-surgical period. This includes jaw immobility, a liquid diet that may cause weight loss, the late recovery of normal mouth-opening function, and possible periodontal damage. For those reasons and with the development of the rigid fixation that eliminates the need for IMF, the majority of oral and maxillofacial centers use SSRO as the favorable method, particularly in Europe and North America [1]. In our center, we still often perform IVRO for the treatment of mandibular prognathism.