A comparative study of temporomandibular symptoms following mandibular advancement by bilateral sagittal split osteotomies: rigid versus nonrigid fixation

Rigid fixation to attach proximal and distal segments during bony healing of osteotomy sites has become increasingly popular. The effects of rigid fixation on the temporomandibular joints have been questioned. The purpose of this study was to evaluate the effects of rigid fixation after bilateral sagittal split osteotomies on temporomandibular dysfunction symptoms. Forty patients who had mandibular advancement surgery were evaluated for temporomandibular joint dysfunction. Twenty had received rigid fixation, and twenty had received nonrigid fixation. It was determined that there was no statistically significant difference in temporomandibular signs or symptoms between patients who were treated with rigid internal fixation for bilateral sagittal split osteotomies for mandibular advancement and those patients who were treated with nonrigid wire fixation.     

Psychological function in orthognathic surgical patients before and after bilateral sagittal split osteotomy with rigid and wire fixation.

A multisite randomized controlled trial was conducted to compare the psychological function of patients who undergo surgical correction of a Class II malrelation with bilateral sagittal split osteotomy with either wire or rigid fixation. Subjects were 31 male and 86 female patients referred by orthodontists. Psychopathological symptoms and psychological distress were measured with the Symptom Checklist-90 Revised at the following times: before placement of orthodontic appliances, 1 to 2 weeks presurgery, and 1 week, 8 weeks, 6 months, and 2 years postsurgery. Patients' satisfaction with their surgical outcome was measured with a 3-item questionnaire. Results showed no statistically significant differences in psychological function or satisfaction between patients treated with wire or rigid fixation. Psychological function was within normal limits immediately before surgery. Psychological parameters did not determine patient satisfaction, even among patients who met an operational definition of "psychopathological caseness." Psychological symptoms and general distress increased modestly immediately after surgery for both groups and then progressively declined over the succeeding 2 years, eventually reaching levels that were significantly lower than presurgical levels. It was concluded that (1) rigid and wire fixation do not differ in their effects on psychological function and satisfaction; (2) patients who seek orthognathic surgery for a Class II malocclusion are psychologically healthy, ie, comparable to normal populations, immediately before surgery; (3) presurgical psychological function does not determine satisfaction with surgical outcome; and (4) psychological function tends to improve during the 2 years after surgery.     

Long-term evaluations of temporomandibular disorders in patients undergoing orthognathic surgery compared with a control group

OBJECTIVE: The purpose of this study was to investigate alterations in signs and symptoms of temporomandibular disorders (TMDs) in patients undergoing orthognathic surgery compared with a healthy group. STUDY DESIGN: Signs and symptoms of TMD in orthognathic surgery patients were evaluated before surgery, 1 week after removal of intermaxillary fixation, and 1 and 2 years after surgery by means of Helkimo's Anamnestic and Dysfunction Indexes. At initial and final examinations, signs and symptoms of TMD of orthognathic surgery patients were compared also with those of healthy patients. The lengths of condylar pathways during opening, medial, and protrusive movements in orthognathic surgery patients were evaluated with axiography. RESULTS: A statistically significant reduction was noted for the TMD symptoms and signs 2 years after surgery compared with before surgery. At initial examination, orthognathic surgery patients did not report TMD signs and symptoms significantly more often than healthy subjects. At final examination, improvements in TMD symptoms of orthognathic surgery patients were found when compared with healthy subjects. CONCLUSION: The results of this study suggested that functional status of temporomandibular joint can be improved with orthognathic surgery, but no association could be clearly shown between TMD symptoms and the type of dentofacial deformity.     

The effect of physiotherapy on post-temporomandibular joint surgery patients

The purpose of this study was to investigate the effect of physiotherapy on rehabilitation of patients who had temporomandibular joint (TMJ) surgery. The treatment group consisted of 22 post-surgical patients who were treated with physiotherapy, and the non-treatment group consisted of 22 post-surgical patients who received no physiotherapy. The assessment tools were made using visual analogue scale (VAS) and craniomandibular index (CMI) which consisted of dysfunction index (DI) and palpation index (PI). All patients received follow-up for 7 months. The subjects were measured three times; before surgery, 6 weeks after surgery and 7 months after surgery. On the 6 week post-surgery assessment, DI and total CMI scores of the treatment group were significantly lower (P < 0.05) than those of the non-treatment group. On the assessment performed 7 months after surgery, all variables were significantly lower (P < 0.05) for the treatment group compared with those of the non-treatment group. The findings of the study indicate that physiotherapy has a positive effect in relieving pain and restoring TMJ function after surgery.     

Complications of orthognathic surgery: a comparison between wire fixation and rigid internal fixation

This retrospective review compares the results of using rigid internal fixation (RIF) and wire fixation for orthognathic surgery patients. The records of two groups of demographically similar patients who underwent comparable surgery, performed by the same four attending surgeons at the same institutions during the same time period (1983 to 1986), were evaluated for complications and unanticipated treatment results. The most striking finding of this study is the general similarity between the two groups. However, differences in frequency of excessive weight loss and persistent restriction of mandibular opening suggest a benefit from early mobility of the mandible that comes with RIF. Because there was no concomitant increase in complications or unexpected results of treatment, the introduction of RIF for orthognathic surgery may offer patients some potential advantages.     

Temporomandibular dysfunction in 1,516 patients before and after orthognathic surgery

Functional disturbances, together with esthetic considerations, are important reasons for patients to seek orthognathic surgical treatment. Functional disorders may include signs and symptoms of temporomandibular disorders (TMD), such as joint pain, chewing problems, joint noises, headaches, etc. This paper reports on TMD before and after orthognathic surgery in 1,516 patients. It is based upon the patients' own evaluations as recorded 2 years after surgery. Preoperatively 43% and postoperatively 28% of the patients reported subjective symptoms of TMD. This difference indicates an overall beneficial effect of orthognathic surgery on TMD signs and symptoms. Patients with mandibular retrognathia did not improve as much as patients with mandibular prognathia. Sagittal ramus osteotomy was less effective than vertical ramus osteotomy in relieving TMD symptoms when performed on similar diagnoses.     

A comparative study of skeletal and dental stability between rigid and wire fixation for mandibular advancement

This study examined the skeletal and dental stability after mandibular advancement surgery with rigid or wire fixation for up to 2 years after the surgery. Subjects for this multisite, prospective, randomized, clinical trial were assigned to receive rigid (n = 64) or wire (n = 63) fixation. The rigid cases received three 2-mm bicortical position screws bilaterally and elastics; the wire fixation subjects received inferior border wires and 6 weeks of skeletal maxillomandibular fixation with 24-gauge wires. Cephalometric films were obtained before surgery, and at 1 week, 8 weeks, 6 months, 1 year, and 2 years after surgery. Skeletal and dental changes were analyzed using the Johnston's analysis. Before surgery both groups were balanced with respect to linear and angular measurements of craniofacial morphology. Mean anterior advancement of the mandibular symphasis was 5.5 mm (SD, 3.2) in the rigid group and 5.6 mm (SD, 3.0) in the wire group. Two years after surgery, mandibular symphasis was unchanged in the rigid group, whereas the wire group had 26% of sagittal relapse. Dental compensation occurred to maintain the corrected occlusion, with the mandibular incisor moving forward in the wire group and posteriorly in the rigid group. However, at 2 years after surgery, when most subjects were without braces, the overjet and molar discrepancy had relapsed similarly in both groups.     

Skeletal stability after mandibular advancement with rigid versus wire fixation.

PURPOSE: This study examined the stability of skeletal changes after mandibular advancement surgery with rigid or wire fixation up to 2 years postoperatively. PATIENTS AND METHODS: Subjects for this multisite, prospective, clinical trial received rigid (n = 78) or wire (n = 49) fixation. The rigid cases were fixed with three 2-mm bicortical position screws and 1 to 2 weeks of skeletal maxillomandibular fixation with elastics, and the wire fixation subjects were fixed with inferior border wires and had 6 weeks of skeletal maxillomandibular fixation with 24-gauge wires. Cephalometric radiographs were obtained before orthodontics, immediately before surgery, and at 1 week, 8 weeks, 6 months, 1 year, and 2 years after surgery. Linear cephalometric changes were referenced to a cranial base coordinate system. RESULTS: Before surgery, both groups were balanced with respect to linear and angular measurements of craniofacial morphology. Mean anterior sagittal advancement of the mandibular symphysis was 4.92 +/3.01 mm in the rigid group and 5.11 +/- 3.09 mm in the wire group, and the inferior vertical displacement was 3.37 +/- 2.44 in the rigid group and 2.85 +/- 1.78 in the wire group. The vertical changes were similar in both groups. Two years postsurgery, the wire group had 30% sagittal relapse of the mandibular symphysis, whereas there was no change in the rigid group (P < .001). Both groups experienced changes in the orientation and configuration of the mandible. CONCLUSIONS: Rigid fixation is a more stable method than wire fixation for maintaining mandibular advancement after sagittal split ramus osteotomy.     

Rigid internal fixation and the effects on the temporomandibular joint and masticatory system: A prospective study

A prospective study of 22 patients who underwent a bilateral sagittal osteotomy to advance the mandible and subsequent rigid internal fixation, were examined for signs and symptoms of temporomandibular joint (TMJ) pain and masticatory dysfunction. A modified Helkimo index was used to analyze the anamnestic, clinical, and occlusal data. In addition, 12 of the cases chosen at random were mounted on a semiadjustable (SAM2) articulator and analyzed with the mandibular position indicator (MPI) to determine the amount and the direction of condylar displacement postoperatively. Anamnestic dysfunction decreased because of a reported decrease in muscular pain, joint noise, headache frequency, and parafunctional habits postoperatively. Clinical dysfunction remained unchanged, with a decrease in muscular soreness but with an increased incidence of joint clicking of 7%. The increased incidence of temporomandibular joint pain postoperatively was 4%. Increase in clinical dysfunction was most often seen in women and older patients. Occlusal dysfunction decreased, with the majority of interferences remaining after surgery as a result of insufficient lingual crown torque of the maxillary buccal segments. Occlusion is thought to have played only a minor role in temporomandibular joint and masticatory dysfunction. Reduction in range of motion was 10%, indicating the added benefit of early mobilization with rigid internal fixation procedures. The MPI study found the condyles inferiorly or inferoposteriorly displaced less than 1 mm from their preoperative position. These findings suggest that rigid internal fixation had no adverse effects on the temporomandibular and masticatory system. The variable responses and results can be attributed, at least in part, to the heterogenous population of patients studied and the variations in surgical techniques employed.     

Mandibular range of motion with rigid/nonrigid fixation

Decreased mandibular range of motion that followed orthognathic surgery and that was treated by wire osteosynthesis and 6 weeks of maxillomandibular fixation (MMF) has been previously documented. The present study evaluated maximum interincisal opening (MIO) in 49 subjects undergoing a bilateral sagittal ramus osteotomy (BSRO) with advancement or a BSRO with advancement and a concomitant LeFort I maxillary osteotomy with the patients having either rigid or nonrigid fixation. The group with rigid fixation had early function and mild physiotherapy. The nonrigid group had wire osteosynthesis, MMF that was maintained for 6 weeks, and no postoperative physiotherapy. Patients who underwent a BSRO with rigid fixation experienced a 3.5 mm decrease in MIO (6.9%). Those who had a BSRO and a LeFort I osteotomy with rigid fixation had a 3.3 mm decrease in MIO (6.6%). In contrast, nonrigidly fixed BSRO subjects had a 16.8 mm decrease (29.6%), while those who underwent a combined BSRO and LeFort I osteotomy had a 13.9 mm decrease (26.1%). This study showed that rigid fixation combined with early function and mild physiotherapy resulted in improved MIO postoperatively, as compared to the MIO in a group in which these treatments were not used.     

骨性Ⅱ类错伴颞下颌关节紊乱矫正后的长期稳定性

目的:研究骨性Ⅱ类错伴颞下颌关节紊乱患者在正颌-正畸联合治疗后面型和咬合的长期稳定性。方法:选择10例在本院正颌-正畸中心治疗结束3年以上、资料齐全的骨性Ⅱ类错患者,男2例,女8例,平均年龄(22.3±2.9)岁,治疗结束平均随访期(2.63±1.36)a。治疗方案为术前正畸、正颌手术、术后正畸,手术根据面型测量数据采用双颌手术或上颌手术+颏成形,术中采用坚强内固定。比较治疗前(T0)、治疗结束(T1)和随访结束(T2)的X线头影测量数据,评价颞下颌关节(TMJ)症状量表和MRI的变化。采用SPSS16.0软件包分别对治疗前、随访结束与治疗结束的测量数据进行配对t检验。结果:覆盖平均增加0.62mm,有显著性差异,其余骨性、牙性复发和软组织改建无统计学意义;随访结束UI-NA距离、覆盖和覆变化>2mm占10%,Go-Co长度变化>2mm占20%,软组织颏前点的变化量>2mm占40%,LI-NB距离和颏唇沟的深度变化均小于2mm;所有患者关节症状无加重,MRI未见髁突吸收加重,盘髁关系未见明显改变。结论:骨性Ⅱ类错伴TMD患者通过正颌-正畸联合治疗,能获得面型美观和正常的咬合关系,远期面型结构及咬合关系未见明显复发趋势,未发现TMJ症状加重趋势。     

Effect of orthognathic surgery on the temporomandibular joint in patients with anterior open bite

This study examined the prevalence of temporomandibular joint (TMJ) signs and symptoms in patients with anterior open bite. The influence of orthognathic surgery on the TMJ in these patients and the interaction of occlusal and psychologic variables on the presence and/or persistence of pain was studied. A retrospective survey of 83 patients with an anterior open bite who underwent orthognathic surgery was carried out. Records were examined for the prevalence of abnormal TMJ signs and symptoms, including pain. A survey was mailed to these patients that consisted of: (1) the TMJ Scale, (2) the Symptom Checklist 90 (SCL90), (3) the Spielberger State-Trait Anxiety Inventory (STAI), and (4) a visual analog scale on which patients indicated their degree of satisfaction with the procedure. Thirty-seven (42%) patients responded to the survey, and 13 (15%) also attended a clinical and radiographic examination. Multiple regression analysis was used for statistical analysis of the factors contributing to the presence and/or persistence of pain. In the preoperative group, the prevalence of pain was 32%, dysfunction 40%, and limitation of opening 7%. Age and gender were significantly associated with the presence of pain. The overall prevalence of abnormal TMJ signs and symptoms was not significantly different after orthognathic surgery. An abnormal psychologic profile was the most significant factor associated with the presence and/or persistence of pain. It is concluded that that the prevalence of temporomandibular disorders in anterior open bite patients increases with age, is significantly higher in females, and is not influenced by other occlusal variables. Furthermore, orthognathic surgery does not significantly influence temporomandibular disorders in patients with anterior open bite. Female patients, particularly those with an abnormal psychologic profile, are at a higher risk of persistent postoperative TMJ pain.     

髁突矢状骨折手术中关节盘复位的应用

目的 探讨髁突囊内骨折开放手术中关节盘复位及固定方法的选择及疗效评判。方法 选择因髁突骨折接受手术治疗,且随访期超过6个月的36例患者为研究对象,骨折类型以髁突矢状骨折为主;术中采用长螺钉内固定,依据关节盘移位及损伤程度分别对关节盘采用缝合法（22侧）及锚固法（14侧）进行复位。术后1、3、6个月及1年进行随访,选择手术前及手术后6个月为时间点详细记录Fricton颞下颌关节紊乱指数（CMI）相关的各项指标,从临床和颞下颌关节（TMJ）功能两方面评估术后恢复情况。结果 两组患者术后TMJ功能改善,CMI分别从治疗前的0.213±0.162和0.273±0.154下降到0.059±0.072和0.064±0.068（P<0.05）。两组不同关节盘复位及固定方法之间比较,CMI、肌肉压痛指数和TMJ功能障碍指数差异无统计学意义（P>0.05）。结论 2种方法处理关节盘均可以有效地改善创伤导致的TMJ功能障碍,关节盘复位及固定方法的选择以关节盘移位及损伤程度作为参考。     

Effects of wire and miniplate fixation on mandibular stability and TMJ symptoms following orthognathic surgery

The effects of wire and miniplate fixations on mandibular stability and temporomandibular joint (TMJ) symptoms were analyzed in 145 patients in whom mandibular prognathism had been corrected by the bilateral sagittal split osteotomy (BSSO). The subjects were divided into two groups based on the method of fixation. Group I consisted of 105 patients treated with intraosseous wiring and group II consisted of 40 patients treated with titanium miniplates. The mean maxillomandibular fixation periods for groups I and II were 48 days and 23 days, respectively. Lateral cephalograms were taken immediately before surgery, within a week after surgery, and at least a year after surgery. Changes in the positions of the incisal edge of the lower central incisors, point B, pogonion, and menton were examined. TMJs were examined clinically for pain, sounds, movements, and limitations before treatment and at least a year after surgery. In both groups, the mean of the horizontal relapses was correlated to the magnitude of their surgical movements. In group II, the mean horizontal relapse was smaller, but not significantly more than that of group I. There was no statistical difference in the pre‐ and postoperative incidence of TMJ signs and symptoms between the two groups. It can be concluded that miniplate fixation for the BSSO procedure has the advantages of shortening the maxillomandibular fixation period and maintaining the postoperative stability of the mandible without causing adverse effects on the TMJ.     

Mandibular range of motion after bilateral sagittal split ramus osteotomy with wire osteosynthesis or rigid fixation

OBJECTIVES: An analysis was conducted to compare mandibular range of motion among Class II patients treated with wire osteosynthesis or rigid internal fixation after surgical mandibular advancement.Study Design: Patients randomly received wire osteosynthesis and 8 weeks of maxillomandibular fixation (n = 49) or rigid internal fixation (n = 78). Mandibular range of motion was measured 2 weeks before surgery and 8 weeks, 6 months, and 1, 2, and 5 years after surgery. RESULTS: Both groups showed decreased mobility in all movement dimensions that progressively recovered to near presurgical levels over the 5-year follow-up period. The difference in range of motion between treatment groups was not statistically significant. Changes in proximal and distal segment position could not explain decreased mobility. CONCLUSIONS: Similar decreases in mandibular mobility occurred with wire and rigid fixation of a bilateral sagittal split ramus osteotomy after surgery. Long-term changes were statistically, but not clinically, significant.     

Patient perceptions of pain, paresthesia, and swelling after orthognathic surgery.

The aims of this study were to determine patients' perceptions of pain, paresthesia, and swelling after orthognathic surgery and to analyze the association between these perceptions and neuroticism, temporomandibular joint dysfunction, and mood states among the patients. Levels of pain, paresthesia, and swelling were measured by two self-appraisals that were developed for this research. Perceptions of facial discomfort decreased with time and varied according to the surgical procedure. Patients who scored high on neuroticism tests reported greater levels of temporomandibular joint symptoms before surgery and greater experiences of pain 2 years after surgery. Perceived pain appeared to exert a negative influence on mood states up to 2 years following surgery. These results reveal the importance of continued psychological support for orthognathic surgery patients throughout their course of treatment.     

A comparison of skeletal and dental changesbetween rigid and wire fixation for bilateral sagittal split osteotomy

For two years, this multisite prospective clinical trial examined longitudinalskeletal and dental changes after bilateral sagittal split osteotomy for mandibular advancement in which either rigid or wire fixation was used. Subjects in the rigid fixation group (n = 78) received 2-mm bicortical position screws, while the subjects in the wire fixation group (n = 49) received inferior border wires. Skeletal and dental changes were measured from cephalometric films taken immediately before surgery, one week after surgery, and at eight weeks, six months, one year, and two years after surgery. In both groups, the overbite and overjet increase with time, but were not different from each other. The B-point in the wire group progressively moved posteriorly, and at two years, it had relapsed 28%. In the rigid fixation group, there was a transient anterior movement of the B-point during the first six months and by two years after surgery, the B-point was unchanged from immediate post surgery. Dental changes occurred in both groups. These changes, however, were not able to accommodate the skeletal changes, resulting in similar increases in both overbite and overjet in both groups of patients. These results have implications for the orthodontists in management of the postmandibular advancement occlusion.     

Long-term study of temporomandibular joint surgery with alloplastic implants compared with nonimplant surgery and nonsurgical rehabilitation for painful temporomandibular joint disc displacement

PURPOSE: The purpose of this study was to determine the long-term objective and subjective outcomes of temporomandibular joint (TMJ) implant surgery for the treatment of painful TMJ disc displacement using temporary Silastic (Dow Corning Corporation, Midland, MI), permanent Silastic, or Proplast (Vitek, Houston, TX) implants to replace the disc. These cases were compared with other cases of the same diagnosis treated with either nonsurgical rehabilitation or nonimplant surgery involving discectomy or disc repair procedures. MATERIALS AND METHODS: A cross-sectional study was conducted among 466 patients who received treatment for unilateral or bilateral TMJ disc displacement before January 1, 1990. The 5 treatment groups noted above were compared for long-term outcomes. Objective outcome measurements for jaw function were performed using a calibrated examiner and the Craniomandibular Index (CMI). Subjective (self-reported) outcomes were obtained relative to jaw function (Mandibular Function Impairment Questionnaire [MFIQ]), symptom severity (Symptom Severity Index [SSI]), and the impact of pain (Global Pain Impact [GPI] scale). RESULTS: The results, adjusted for gender, baseline tomogram score, and baseline symptom scores, showed that the nonsurgical rehabilitation group (n = 159) and the group having TMJ surgery without implants (n = 149) had statistically better results than the group who underwent surgery with a Proplast implant (n = 94). These between-group differences included both objective signs (CMI), and subjective reports of jaw function (MFIQ), symptom severity (SSI), and global pain impact (GPI). The MFIQ score associated with the nonsurgical rehabilitation group was also statistically better than for the Silastic implant groups, including both the temporary (n = 31) and permanent (n = 33) implants. Clinical differences between groups were slight. CONCLUSION: This study suggests that the use of interpositional disc implants in TMJ surgery is not associated with improved outcomes when compared with nonimplant surgery or nonsurgical rehabilitation.     

Cost comparison of genioplasty: when indicated,wire osteosynthesis is more cost effective than plate and screw fixation

Purpose

This retrospective study was conducted to determine the difference in the cost of genioplasty according to the osseous fixation technique used.

Patients and methods

A retrospective study among orthognathic surgery patients treated over a 54-month period ending in June 30, 2011 was conducted. Immediately post surgery, panoramic and cephalometric radiographs of these patients were assessed to determine the presence of genioplasty procedure and the type of fixation used. The cost of the actual fixation used by the surgeons was compared with that which the cost would have been had the surgeons used the criteria described in the hypotheses, for plate and screws fixation when genioplasty is performed.

Results

A review of 1,498 orthognathic surgery patients revealed that 473 of these patients underwent genioplasty. Out of 473 patients, 425 had genioplasty to either advance and-or superiorly reposition the chin. Of these, 230 had wire osteosynthesis and 243 had some form of rigid fixation. The unit cost of fixation for genioplasty when wire osteosynthesis is used is less than C$5.00. The mean unit cost estimate in our patient group when pre-bent plates are used was C$542.00. All 230 patients in whom wire osteosynthesis was used demonstrated stable fixation of the bony parts and no immediate postsurgical adjustment was required in any patient.

Conclusions

For patients requiring genioplasty to advance and-or superiorly reposition the chin, it is possible to use wire osteosynthesis to achieve accurate and stable fixation while reducing the fixation cost by more than C$500.00 per case. The surgeon should include cost considerations in the selection of treatment methods.     

Rigid versus wire fixation for mandibular advancement: Skeletal and dental changes after 5 years

The bilateral sagittal split osteotomy (BSSO) is the most common surgical procedure for the correction of mandibular retrognathism. Commonly, the proximal and distal segments are fixated together with either wire or rigid screws or plates. The purpose of this study was to compare long-term (5 years) skeletal and dental changes between wire and rigid fixation after BSSO. In this multisite, prospective, randomized clinical trial, the rigid fixation group received three 2-mm bicortical position screws, and the wire fixation group received inferior border wires and 6 weeks of skeletal maxillomandibular fixation with 24-gauge wires. Cephalometric films were obtained 2 weeks before surgery and at 1 week, 8 weeks, 6 months, 1 year, 2 years, and 5 years after surgery. Linear cephalometric changes were referenced to a cranial base coordinate system. Before surgery, both groups were comparable with respect to linear and angular measurements of craniofacial morphology. Both groups underwent similar surgical changes. Skeletal and dental movements occurred in both groups throughout the study period. Five years after surgery, the wire group had 2.2 mm (42%) of sagittal skeletal relapse, while the rigid group remained unchanged from immediately postsurgery. Surprisingly, at 5 years, both groups had similar changes in overbite and overjet. This was attributed to dental changes in the maxillary and mandibular incisors. Although rigid fixation is more stable than wire fixation for maintaining the skeletal advancement after a BSSO, the incisor changes made the resultant occlusions of the 2 groups indistinguishable.