Retrospective study of changes in the sensitivity of the oral mucosa: sagittal split ramus osteotomy (SSRO) versus intraoral vertical ramus osteotomy (IVRO)

Abstract

We investigated changes in the sensitivity of cutaneous points and the oral mucosa after sagittal split ramus osteotomy (SSRO) and assessed the differences between SSRO and intraoral vertical ramus osteotomy (IVRO). The subjects included in this study were 46 patients with mandibular prognathism who underwent IVRO (88 rami) and 30 patients who underwent SSRO (59 rami). An objective evaluation of the neurosensory status of each patient was completed preoperatively and at 1, 4, 8, 12, and 24 weeks postoperatively. Other variables studied for each patient included sex, age, magnitude of mandibular setback, and amount of blood loss during surgery. We found that a neurosensory recovery occurred earlier in the oral mucosa than at cutaneous points. The number of oral mucosa points showing reduced neurosensory function and neurosensory disturbance after SSRO was significantly higher than after IVRO at 1, 4, and 8 weeks ( P < 0.05). The nerve recovery observed after SSRO was delayed for a longer period than that noted in our previous study of IVRO. In conclusion, we found changes in sensitivity at cutaneous points and the oral mucosa after SSRO and assessed the differences between SSRO and IVRO.

Sagittal split ramus osteotomy (SSRO) and intraoral vertical ramus osteotomy (IVRO) are the most commonly used osteotomy procedures to correct mandibular deformities. An altered function of the inferior alveolar nerve (IAN) can complicate mandibular osteotomy and is indicated by sensory changes. The incidence of sensory changes after SSRO has been estimated using various subjective and objective measurements, which vary considerably in their ability to detect and quantify deficits. The incidence of such changes after SSRO ranges between 9% and 85%, while that observed after IVRO ranges from 0% to 36%. The higher incidence after SSRO can be explained by the greater degree of technical difficulty and closer proximity to the nerve during the procedure than for IVRO. Many investigators have reported the incidence of neurosensory disturbances after orthognathic surgery; however, only cutaneous points have been studied, and few authors have examined changes in the tactile sensation of the oral mucosa after Le Fort I osteotomy. In a recent study, we investigated changes in the sensitivity of cutaneous points and the oral mucosa after IVRO. The results showed that neurosensory recovery after IVRO occurs earlier in the oral mucosa than at cutaneous points.

In the present study, we investigated changes in the sensitivity of cutaneous points and the oral mucosa after SSRO and assessed the differences between SSRO and IVRO. Additionally, postoperative changes in sensitivity and the relationships between neurosensory disturbances and the factors associated with SSRO were evaluated.

Patients and methods

Subjects

This was a non-randomized, retrospective (historic) cohort study of patients. Thus, this study was granted an exemption by the institutional review board of our institution. The subjects included 46 patients (20 men and 26 women) with mandibular prognathism who underwent IVRO (88 rami) and 30 patients (eight men and 22 women) who underwent SSRO (59 rami) at our institution between March 2002 and March 2013. Five unilateral cases were included in this study. The patients ranged in age from 16 to 54 years and the mean age was 26.6 years. Each patient was diagnosed with skeletal class III malocclusion with mandibular prognathism after a clinical examination and complete review of the patient’s orthodontic records. Patients with evidence of a syndromic condition, congenital anomaly, or traumatic injury to the jaw or face were excluded.

The IVRO surgical technique used in this study was performed as described by Terry and White. The SSRO surgical technique used was performed as described by Dal Pont. Four surgeons were involved in this study. All surgeons on the surgical team had more than 5 years of experience.

Each patient was administered 100 mg hydrocortisone postoperatively (day 0) and on day 1 after the operation. Two types of osteosynthesis plates were used in the SSRO patients, titanium (23 patients) and absorbable (seven patients). In IVRO cases, the patients underwent intermaxillary fixation (IMF) with stainless steel wires (0.3 mm) and had brackets placed in the maxillary and mandibular arches for 14 days, as per the clinical protocol. In SSRO cases, the patients underwent IMF for 7 days. We instructed all patients to wear elastic bands for 21 days in order to retain the bone fragments during their hospital stay. Functional treatment comprised the use of guiding elastics and a regimen of active mobilization. The active movements with elastic guidance were continued for up to 3 months. The guiding elastics were initially used full time, and the patient was slowly weaned off them. All elastics were removed when the patients were eating.

Methods

An objective evaluation of the neurosensory status of each patient was completed preoperatively and at 1, 4, 8, 12, and 24 weeks postoperatively.

Changes in the sensitivity of various cutaneous points were examined using a Semmes–Weinstein pressure aesthesiometer (Research Designs, Inc., Houston, TX, USA). The monofilaments of the Semmes–Weinstein pressure aesthesiometer were labelled with filament marking values (Fmg) ranging from 1.65 to 6.65. Touch stimulation was performed according to the method described by Bell. Stimulation was initiated with a force of 1.65 Fmg, with the force being increased until the patient became aware of the sensation. The method has been reported previously. Measurements were obtained at three points based on the running courses of the labial inferior ramification, oral angular ramification, and mental ramification: cutaneous point 1 (C1) was located on the vermilion border at one-third of the distance between the oral angles, cutaneous point 2 (C2) was located 5 mm below the oral angle, and cutaneous point 3 (C3) was located at the midpoint of the perpendicular line from cutaneous point 1 to the lower margin of the mentum. Points at which 1.65 Fmg of force was not required prior to surgery were excluded. A point at which 2.36–2.83 Fmg of force was required postoperatively was classified as showing reduced neurosensory function (NSF). Additionally, a point at which more than 3.22 Fmg of force was required postoperatively was classified as showing a neurosensory disturbance (NSD).

Changes in the sensitivity of the oral mucosa were examined using needle puncture. Sensitivity was evaluated on a three-point scale, where ‘3’ indicated fully normal sensitivity, ‘2’ indicated reduced sensitivity, and ‘1’ indicated total numbness. Measurements were obtained in two regions: gingival point 1 (G1; 4 mm under the marginal gingiva of the molar region), gingival point 2 (G2; 4 mm under the marginal gingiva of the incisal region (lateral incisor tooth)), buccal point 1 (B1; on the buccal mucosa 10 mm up from the oral vestibulum of the molar region), and buccal point 2 (B2; on the labial mucosa 10 mm up from the oral vestibulum of the incisal region (lateral incisor tooth)). Sensitivity measurements of 1 and 2 were classified as showing a reduced NSF. The changes in sensitivity after IVRO and SSRO were analysed and compared.

Other variables studied for each patient included sex, age, magnitude of mandibular setback (in millimetres), and amount of blood loss during surgery. The patients were classified into two age groups: those aged ≤25 years and those aged ≥26 years. The magnitude of mandibular movement was classified into two groups: mandibular segments with movement ≤7 mm and mandibular segments with movement >7 mm. The amount of blood loss during surgery was also classified into two groups: blood loss ≤500 ml and blood loss >500 ml.

The relationships between the factors and changes in sensitivity after SSRO were analysed using the method reported in our previous study.

Statistical analysis

StatView J-4.5 software (HULINKS Inc., Tokyo, Japan) was used for the statistical analysis. Data for each group were compared by Mann–Whitney U -test or one-way analysis of variance (ANOVA) and Fisher’s protected least significant difference (PLSD) method. Data are presented as the mean ± standard deviation (SD). A P -value of <0.05 was considered statistically significant.

Methods

An objective evaluation of the neurosensory status of each patient was completed preoperatively and at 1, 4, 8, 12, and 24 weeks postoperatively.

Changes in the sensitivity of various cutaneous points were examined using a Semmes–Weinstein pressure aesthesiometer (Research Designs, Inc., Houston, TX, USA). The monofilaments of the Semmes–Weinstein pressure aesthesiometer were labelled with filament marking values (Fmg) ranging from 1.65 to 6.65. Touch stimulation was performed according to the method described by Bell. Stimulation was initiated with a force of 1.65 Fmg, with the force being increased until the patient became aware of the sensation. The method has been reported previously. Measurements were obtained at three points based on the running courses of the labial inferior ramification, oral angular ramification, and mental ramification: cutaneous point 1 (C1) was located on the vermilion border at one-third of the distance between the oral angles, cutaneous point 2 (C2) was located 5 mm below the oral angle, and cutaneous point 3 (C3) was located at the midpoint of the perpendicular line from cutaneous point 1 to the lower margin of the mentum. Points at which 1.65 Fmg of force was not required prior to surgery were excluded. A point at which 2.36–2.83 Fmg of force was required postoperatively was classified as showing reduced neurosensory function (NSF). Additionally, a point at which more than 3.22 Fmg of force was required postoperatively was classified as showing a neurosensory disturbance (NSD).

Changes in the sensitivity of the oral mucosa were examined using needle puncture. Sensitivity was evaluated on a three-point scale, where ‘3’ indicated fully normal sensitivity, ‘2’ indicated reduced sensitivity, and ‘1’ indicated total numbness. Measurements were obtained in two regions: gingival point 1 (G1; 4 mm under the marginal gingiva of the molar region), gingival point 2 (G2; 4 mm under the marginal gingiva of the incisal region (lateral incisor tooth)), buccal point 1 (B1; on the buccal mucosa 10 mm up from the oral vestibulum of the molar region), and buccal point 2 (B2; on the labial mucosa 10 mm up from the oral vestibulum of the incisal region (lateral incisor tooth)). Sensitivity measurements of 1 and 2 were classified as showing a reduced NSF. The changes in sensitivity after IVRO and SSRO were analysed and compared.

Other variables studied for each patient included sex, age, magnitude of mandibular setback (in millimetres), and amount of blood loss during surgery. The patients were classified into two age groups: those aged ≤25 years and those aged ≥26 years. The magnitude of mandibular movement was classified into two groups: mandibular segments with movement ≤7 mm and mandibular segments with movement >7 mm. The amount of blood loss during surgery was also classified into two groups: blood loss ≤500 ml and blood loss >500 ml.

The relationships between the factors and changes in sensitivity after SSRO were analysed using the method reported in our previous study.

Statistical analysis

StatView J-4.5 software (HULINKS Inc., Tokyo, Japan) was used for the statistical analysis. Data for each group were compared by Mann–Whitney U -test or one-way analysis of variance (ANOVA) and Fisher’s protected least significant difference (PLSD) method. Data are presented as the mean ± standard deviation (SD). A P -value of <0.05 was considered statistically significant.

Results

Prior to surgery, stimulation with the thinnest filament and 1.65 Fmg of force was recognized at 176 of 177 (C1, C2, C3) cutaneous points (99.4%); 2.36 Fmg of force was recognized at one point (0.6%).

Of the 176 points at which 1.65 Fmg of force was recognized prior to surgery, those requiring 2.36–2.83 Fmg of force (reduced NSF) after surgery were as follows: 34 (19.3%) at 1 week after surgery, 26 (14.8%) at 4 weeks after surgery, 29 (16.5%) at 8 weeks after surgery, 26 (14.8%) at 12 weeks after surgery, and 21 (11.9%) at 24 weeks after surgery. Those requiring more than 3.22 Fmg of force (NSD) after surgery were as follows: 61 (34.7%) at 1 week after surgery, 40 (22.7%) at 4 weeks after surgery, 33 (18.8%) at 8 weeks after surgery, 14 (8.0%) at 12 weeks after surgery, and five (2.8%) at 24 weeks after surgery. The number of points showing reduced NSF and NSD at 4, 8, 12, and 24 weeks after surgery was significantly lower than at 1 week after surgery ( P < 0.05). There were no significant differences in the numbers of points showing reduced NSF or NSD at C1, C2, or C3.

The number of points showing reduced NSF or NSD after SSRO was significantly higher than after IVRO at 1, 4, 8, 12, and 24 weeks ( P < 0.05) ( Fig. 1 ).

Jan 17, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Retrospective study of changes in the sensitivity of the oral mucosa: sagittal split ramus osteotomy (SSRO) versus intraoral vertical ramus osteotomy (IVRO)
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