Three-dimensional changes of the hyoid bone and airway volumes related to its relationship with horizontal anatomic planes after bimaxillary surgery in skeletal Class III patients

Objective:To evaluate longitudinal changes of the hyoid bone position and pharyngeal airway space after bimaxillary surgery in mandibular prognathism patients.Materials and Methods:Cone-beam computed tomography scans were taken for 25 mandibular prognathism patients before surgery (T0), 2 months after surgery (T1), and 6 months after surgery (T2). The positional displacement of the hyoid bone was assessed using the coordinates at T0, T1, and T2. Additionally, the volume of each subject''s pharyngeal airway was measured.Results:The mean amount of posterior maxilla impaction was 3.76 ± 1.33 mm as the palatal plane rotated 2.04° ± 2.28° in a clockwise direction as a result of bimaxillary surgery. The hyoid bone moved backward (P < .05, P < .001) and downward (P > .05, P < .05) at 2 months and 6 months after surgery, while the total volume of the pharyngeal airway significantly decreased at the same time points (P < .001, P < .001). There was significant relationship between the changes of the hyoid bone position and airway volume at 2 months after surgery (P < .05). The change of the palatal plane angle was positively correlated to the decrease in the total airway volume (P < .001).Conclusions:The null hypothesis was rejected. The hyoid bone moved inferoposteriorly, and the pharyngeal airway volume decreased for up to 6 months after bimaxillary surgery. The decrease in the pharyngeal airway volume was correlated to the changes in the palatal plane inclination and the positional change of the hyoid bone.     

Relapse of skeletal class III with anterior open bite after bimaxillary orthognathic surgery depending on maxillary posterior impaction and mandibular counterclockwise rotation

The goal of this study is to evaluate relapse after orthognathic surgery of skeletal class III with anterior open bite depending on the posterior impaction and mandibular counterclockwise rotation. Patients (n = 29) were divided into two groups according to the change of mandibular occlusal plane angle (MnOP): Group A had a clockwise change of MnOP > 0° (n = 11) and Group B had a counterclockwise change of MnOP < −2° (n = 18). Lateral cephalograms were analyzed preoperatively, and at immediate stage, six weeks, six months, and one year after surgery. One year after surgery, the stability of the maxilla was good in both groups. Upward movement of the mandible was observed six weeks after surgery due to mandibular autorotation. The amount of mean relapse was small, although a significant difference was observed horizontally between groups. Group B demonstrated more forward movement of B point, pogonion, and menton than Group A (p < 0.05). SNB angle increased in both groups (p < 0.05). At one year follow up, good occlusal stability was observed in both groups with positive overbite. Our study suggested that bimaxillary procedures with clockwise and counterclockwise rotation of mandibular occlusal planes for correction of mandibular prognathism with anterior open bite appeared to be relatively stable procedures.     

Influence of unilateral maxillary first molar extraction treatment on second and third molar inclination in Class II subdivision patients

Objective:To assess the maxillary second molar (M2) and third molar (M3) inclination following orthodontic treatment of Class II subdivision malocclusion with unilateral maxillary first molar (M1) extraction.Materials and Methods:Panoramic radiographs of 21 Class II subdivision adolescents (eight boys, 13 girls; mean age, 12.8 years; standard deviation, 1.7 years) before treatment, after treatment with extraction of one maxillary first molar and Begg appliances and after at least 1.8 years in retention were retrospectively collected from a private practice. M2 and M3 inclination angles (M2/ITP, M2/IOP, M3/ITP, M3/IOP), constructed by intertuberosity (ITP) and interorbital planes (IOP), were calculated for the extracted and nonextracted segments. Random effects regression analysis was performed to evaluate the effect on the molar angulation of extraction, time, and gender after adjusting for baseline measurements.Results:Time and extraction status were significant predictors for M2 angulation. M2/ITP and M2/IOP decreased by 4.04 (95% confidence interval [CI]: −6.93, 1.16; P  =  .001) and 3.67 (95% CI: −6.76, −0.58; P  =  .020) in the extraction group compared to the nonextraction group after adjusting for time and gender. The adjusted analysis showed that extraction was the only predictor for M3 angulation that reached statistical significance. M3 mesial inclination increased by 7.38° (95% CI: −11.2, −3.54; P < .001) and 7.33° (95% CI: −11.48, −3.19; P  =  .001).Conclusions:M2 and M3 uprighting significantly improved in the extraction side after orthodontic treatment with unilateral maxillary M1 extraction. There was a significant increase in mesial tipping of maxillary second molar crowns over time.     

Relationship of maxillary molar root angulation and palatal vault height

If the vertical angulation of maxillary molar roots could be reliably predicted, this might affect the choice of roots resection procedures. In an attempt to develop this prediction, angulation of palatal roots was compared to palatal vault height. Human cadaveric maxillae with molars were sectioned faciopalatally through each tooth root to the palatal midline and photographed. Root angles and palatal height were measured on the photographs in relation to a reference line connecting buccal and palatal cementoenamel junctions (CEJ). Palatal vault heights were classified as low, medium, or high according to the perpendicular distance from the midpalatal suture to the reference line. Root angles were subtended by a line following the length of pulp canals and perpendicular to the CEJ reference. Analysis by Spearman's Rank Correlation Coefficient demonstrated a weak nonsignificant relationship between palatal vault height and the angulation of the various maxillary molar roots. Thus, palatal vault height would not be a reliable predictor of root angulation if this were to be used as a basis for root retention.     

Pharyngeal airway space,hyoid bone position and head posture after orthognathic surgery in Class III patients

Objective:To determine the effect of orthognathic surgery on pharyngeal airway in Class III patients and to (1) compare the results of different surgical techniques, (2) determine the change at the position of the hyoid bone, and (3) evaluate the craniocervical posture changes related to pharyngeal airway change.Materials and Methods:Forty-eight Class III adult patients were included in the study to assess airway space after orthognathic surgery. Nine patients were treated with maxillary advancement, seven patients were treated with mandibular set back, and 32 patients were treated with bimaxillary surgery. Cephalometric records were taken before treatment, after surgery, and about 1 year after surgery (at the end of the treatment).Results:No differences were determined at the position of hyoid bone and craniocervical posture. Nasopharyngeal area was significantly increased in all groups (P < .05). Oropharyngeal area and SPSS and IPS parameters were significantly decreased after mandibular set back operation (P < .05). In bimaxillary and maxillary advancement groups, PPS parameter was significantly increased (P < .01), and IPS parameter was significantly decreased (P < .05). No differences were detected at oropharyngeal and hypopharyngeal areas in bimaxillary and maxillary advancement groups.Conclusion:Different surgical procedures have different effects on pharyngeal airway space.     

Cone-beam computed tomography classification of the mandibular second molar root morphology and its relationship to panoramic radiographic appearance

Oral Radiology - This study aimed to clarify the relationship between the panoramic radiographic appearance and the longitudinal cone-beam computed tomography (CBCT) classification of root...     

Soft tissue response after Class III bimaxillary surgery: Impact of surgical change in face height and long-term skeletal relapse

Objective:To analyze the impact of surgical change in anterior face height and skeletal relapse on the long-term soft tissue profile.Materials and Methods:Cephalometric radiographs of 81 patients taken before surgery and at five time points during a 3-year follow-up period were analyzed. All patients had Le Fort I and bilateral sagittal split osteotomies. The patients were divided into three subgroups according to the change in anterior face height during surgery. Calculations of soft to hard tissue ratios were based on the long-term soft tissue response relative to the surgical repositioning.Results:The horizontal surgical repositioning varied considerably, depending on whether anterior face height was increased or decreased. For upper lip prominence, the pattern of long-term change was the same irrespective of change in face height. In all groups, upper lip thickness decreased in both the short term and the long term, particularly in patients with surgical increase in face height. Lower lip thickness increased in the short term but decreased during the follow-up period. There were significant associations between horizontal soft tissue and corresponding hard tissue changes, except for soft tissue A-point and upper lip, when face height was increased. The ratios were higher for mandibular variables than for maxillary variables, particularly for B-point and pogonion when anterior face height had decreased.Conclusion:A change in facial height influences the soft tissue response. The mandibular soft tissues closely follow skeletal relapse beyond 2 months postsurgery. The findings have clinical implications for the relative maxillary and mandibular repositioning when planning surgery.     

Preoperative incisor inclination in patients with Class III dentofacial deformities treated with orthognathic surgery

Our aim was to evaluate cephalometrically the preoperative inclination of the incisors in a group of 50 patients with Class III dentofacial deformities whose immediate preoperative lateral cephalometric radiographs were analysed after they had been treated by maxillary advancement. The radiographs were hand-traced by the same operator who made the cephalometric analysis. Mean values for each measurement were compared with the normal values using Student's t-test (p<0.05). Results showed significantly increased inclination of the upper incisors, with a mean U1-NA angle of 27.58° and a mean U1-PP angle of 116°. The lower incisors were also inclined lingually, with a mean L1-NB angle of 22.53° and a mean IMPA of 83.13°. Thirty-five of the patients had labial inclination of the upper, and 28 lingual inclination of the lower, incisors. Mean inclinations of upper and lower incisors differed from the normal values, and the inclination of the lower incisors was more likely to be decompensated than that of the upper incisors.     

骨性III类错牙合畸形患者正颌手术前后咀嚼肌功能变化的初步研究

目的:应用肌电图仪评价骨性III类错牙合畸形患者正颌手术前后咀嚼肌功能的变化。方法:收集16例骨性III类错牙合畸形需正颌手术病例和20例正常牙合对照组,应用MedelecSynergy肌电图仪分别在静息放松、正中紧咬、前伸、开口、侧方和咀嚼运动时,测定双侧颞肌前束、咬肌和二腹肌前腹的表面募集电位,并计算其肌不对称指数运动。病例组在术后3个月和6个月时重复测定,采用t检验进行统计学分析,并与对照组进行比较。结果:手术前病例组咀嚼肌电位小于对照组,尤以紧咬和咀嚼时差异显著(P<0.05),肌不对称指数与对照组无差异。术后3个月时,部分肌功能恢复,但紧咬和咀嚼时募集电位下降显著(P<0.001),肌不对称指数也增大,提示此时肌功能尚未完全恢复。术后6个月各种功能运动时的募集电位均大于术前水平,肌不对称指数则基本小于术前水平,说明肌功能有所改善。结论:骨性III类错牙合畸形患者手术前咀嚼肌功能弱于对照组,正颌手术矫正了颌骨位置和咬合关系,改善了患者的咀嚼肌功能。     

Bone-anchored maxillary protraction to correct a class III skeletal relationship: A multicenter retrospective analysis of 218 patients

This study evaluated the impact of class III correction by elastic traction on four miniplates and the failure rate of bone-anchored miniplates in nonsyndromic patients. A total of 218 patients (112 males and 106 females; average 11.4 years), treated by 38 orthodontists, received four miniplates (total 872 miniplates) from 2008 to 2016 at three maxillofacial centers in two countries. Factors affecting the success and failure of the miniplates were retrospectively examined and skeletal changes on cephalometric radiographs examined for 52 patients. Elastic traction was performed for 22.9 months, on average. The miniplate survival rate was 93.6%; 25.7% of the patients suffered failure of one of the miniplates. Postoperative antibiotics and placement of the neck of the miniplate in the attached gingiva significantly improved the success rate. Miniplate failure was six times higher in the maxilla and occurred more in younger patients. Self-drilling screws were significantly better than self-tapping screws for fixing the miniplate. Small cephalometric changes were seen: SNA (+1.9°), SNB (+0.4°), ANB (+1.4°), Wits analysis (+1.3 mm). In conclusion, bone-anchored maxillary protraction on four miniplates is an effective method for correcting a class III relationship, but has less skeletal effect than previously reported in the literature.     

Accuracy of patient-specific implants and additive-manufactured surgical splints in orthognathic surgery — A three-dimensional retrospective study

IntroductionBecause of the many limitations of conventional surgery planning for the treatment of orthognathic deformities, as well as advancements in computer-assisted planning, there is an urgent need for technical devices that transfer the surgical plan into the operating theatre. In this regard, additive-manufactured, patient-specific implants (PSI) and additive-manufactured interocclusal splints represent promising approaches. The aim of this retrospective study was to compare the accuracy of these two devices, with regard to preoperative virtual treatment planning for maxillary Le-Fort I advancement surgery using IPS CaseDesigner^®, and based on a new analysis method without the use of landmarks.Materials and methodsA retrospective evaluation of 18 class III patients (n(PSI) = 9; n(splint) = 9), who had undergone virtually planned orthognathic surgery (including maxillary Le Fort I advancement), was performed. The preoperative treatment plan and the postoperative outcome were combined to calculate the translational and rotational discrepancies between the 3D planning and the actual surgical outcome.ResultsFor the PSI and splint groups the accuracy of left/right positioning was 0.51 mm ± 0.48 and 1.11 mm ± 1.32 respectively. The accuracy of anterior/posterior positioning was 0.39 mm ± 0.26 and 1.42 mm ± 0.87, and that of up/down-positioning was 0.44 mm ± 0.31 and 0.62 mm ± 0.47. The rotational discrepancies were less than 2° in both groups. Conclusion: The findings demonstrate that both PSI and splint approaches can accurately transfer the virtual planning into the operating theatre. However, PSIs show an overall higher accuracy, especially for anterior/posterior translational movement (p < 0.002).     

第二磨牙存在状态对远移第一磨牙效果的临床研究

目的分析上颌第二磨牙的不同存在情况对口外弓远移上颌第一磨牙的影响,并评价临床疗效。方法临床选取磨牙Ⅱ类Ⅰ分类关系口外弓远移磨牙病例30例,其中拔除上颌第二磨牙7例,平均年龄18.4岁;上颌第二磨牙未萌13例,平均年龄11.7岁;上颌第二磨牙已萌10例,平均年龄16.9岁。根据治疗前后牙列模型及头颅侧位片,测量分析磨牙远移总量、总时间、下磨牙近移量等指标,评价临床疗效。结果拔除组上颌第一磨牙远移速度最快;拔除组磨牙的远中倾斜显著小于已萌组;3组中上颌第二前磨牙向近中移动、上前牙轴倾度增加不明显,且拔除组小于其他2组。结论在严格把握适应证的前提下,对于某些特定病例,拔除上颌第二磨牙可以有效提高疗效和简化疗程。     

TMD in class III patients referred for orthognathic surgery: Psychological and dentition-related aspects

ObjectiveTo investigate temporomandibular disorders (TMD), psychosocial, and occlusal variables in class III orthognathic surgery patients with respect to the control subjects, and to compare psychosocial and occlusal features in class III patients with different Research Diagnostic Criteria for TMD (RDC/TMD) diagnoses.Materials and methodsThe study enrolled 44 class III patients referred for orthognathic surgery and 44 individuals without a malocclusion. TMD, depression and somatization were assessed by RDC/TMD. Occlusal analysis included Helkimo's Occlusal Index items, overjet and overbite.ResultsIn the controls, patients with class III deformities had higher prevalence of myogenic TMD, increased grade of chronic pain, and more occlusal deviations. Within the study group, TMD patients reported higher depression score (P < 0.01), myofascial pain was related to higher depression and somatization grades (P < 0.01, P < 0.05 respectively), and disc displacement showed relation with RCP-ICP slide interferences (P < 0.05).ConclusionWith respect to subjects without a malocclusion, TMD in class III dentofacial deformities is similar in prevalence, but differs in clinical appearance. Occlusal, but not psychosocial features deviate from those in the controls. While psychosocial variables accompanied TMD and myofascial pain, increased RCP-ICP slide was related to disc displacement in class III patients.     

骨性III类错畸形患者正颌手术前后下颌运动轨迹变化的初步研究

目的:应用下颌运动轨迹仪评价骨性III类错牙合畸形患者正颌手术前后下颌运动的变化。方法:对15例骨性III类错牙合畸形需正颌手术病例和20例正常牙合对照组,采用ARCUSDigma下颌运动轨迹仪测定受试者最大开口运动,前伸及左右侧边缘运动距离,记录由计算机通过切牙运动模拟的双侧髁突的运动轨迹间的最大差数(MRC)。通过自身比较以及与对照组比较,评价患者在术前、术后3个月及6个月时下颌运动的变化以及髁突运动的对称性。采用团体t检验和配对t检验进行统计学处理。结果:术前患者除开口度外,其他运动距离均小于对照组,前伸运动差异显著(P<0.05);开口时MRC值大于对照组(P<0.05)。术后3个月时,开口度及左侧运动距离下降,前伸和右侧运动略有增加;MRC呈上升趋势。术后6个月时,下颌运动距离均有所增加,除开口度外其余均超过术前水平,与对照组无统计学差异;MRC小于术前水平且与对照组差异无显著性。结论:骨性III类错牙合畸形患者下颌运动水平与正常牙合存在差异,髁突运动对称性较差。正颌手术能够有效地改善患者的下颌运动功能。