Position Of Pogonion Research Articles

P-67896721-188 - Is there a correlation of the asymmetry among the three thirds of the face?

Introduction Facial asymmetry (FA) is a well-described condition with a high global incidence that negatively impacts individuals functionally and aesthetically. Besides the higher incidence of FA, there is still a lack of knowledge about the etiology and clinical classification in scientific literature. The current most used classifications are based on 2-D methodology and specific anatomical regions of the mandible, which can lead to planning limitations. Purpose In this study, we propose a 3-D methodology to quantitatively and qualitatively analyze the patient's facial asymmetry and achieve a personalized surgical treatment. Methods Ninety-nine patients were recruited, only 36 patients met the study's inclusion criteria with a clear indication to ortho surgical treatment and for 3-D planning. Through landmarks in the anatomical structures of interest, the measurements related to intramandibular, middle and upper thirds of the face included the difference of right and left sides in the vertical and horizontal direction in relation to predetermined plans. Results The clinical characteristics of the study population are: skeletal Class III (94.4%) and prevalence in the initial diagnosis of hemimandibular elongation (72.4%). Moderate correlation was found between condylar height/dif with pogonion position (p-value=0.500) and maxillary canting with ramus height/diff (p-value=0.514). Conclusion We could not find any relation between the FA pattern and measurements of the three-thirds of the face. Facial asymmetry (FA) is a well-described condition with a high global incidence that negatively impacts individuals functionally and aesthetically. Besides the higher incidence of FA, there is still a lack of knowledge about the etiology and clinical classification in scientific literature. The current most used classifications are based on 2-D methodology and specific anatomical regions of the mandible, which can lead to planning limitations. In this study, we propose a 3-D methodology to quantitatively and qualitatively analyze the patient's facial asymmetry and achieve a personalized surgical treatment. Ninety-nine patients were recruited, only 36 patients met the study's inclusion criteria with a clear indication to ortho surgical treatment and for 3-D planning. Through landmarks in the anatomical structures of interest, the measurements related to intramandibular, middle and upper thirds of the face included the difference of right and left sides in the vertical and horizontal direction in relation to predetermined plans. The clinical characteristics of the study population are: skeletal Class III (94.4%) and prevalence in the initial diagnosis of hemimandibular elongation (72.4%). Moderate correlation was found between condylar height/dif with pogonion position (p-value=0.500) and maxillary canting with ramus height/diff (p-value=0.514). We could not find any relation between the FA pattern and measurements of the three-thirds of the face.

The Effect of Condylar Regeneration After Different Disc Repositioning Surgeries in Adolescents with Skeletal Class II Malocclusion

To evaluate the effect of different temporomandibular joint (TMJ) disc repositioning surgeries for the treatment of anterior disc displacement (ADD) in juvenile patients with skeletal Class II malocclusion. Patients (< 20 years, cervical vertebral maturation stage, IV-V) who had bilateral TMJ ADD with skeletal Class II malocclusion were treated by disc repositioning surgery (mini-screw anchor, [MsA]; or opening suturing, [OSu]). Magnetic resonance imaging (MRI) and lateral cephalometric films before and more than 12 months after surgery were collected from all patients. Changes of SNA, SNB, ANB, incisor overjet, pogonion position (pg'-G'), and condylar height were measured before and after surgery in different disc reposition surgeries and compared by statistical analysis. Eighty-four patients with an average age of 16.44 years and follow-up time of 14.60 months (12 to 33 months) were included in the study. Among them, 16 patients had a mean follow-up of 14.8 months without treatment before disc repositioning. Their condylar height was significantly decreased (P = .004) by MRI measurement. Six patients who had cephalometric films showed significantly decreased SNB (P = .042) and increased overjet (P = .037). After disc repositioning by either OSu (54 cases) or MsA (30 cases), condylar height, SNB were significantly increased and overjet, Pg'-G', ANB were decreased in both groups (P < 0.001). There was more new bone height in OSu than MsA (P = .004), but no significant differences in SNB, ANB, overjet and Pg'-G' between the 2 groups (P > .05). The new bone height was significantly correlated with the surgical method (P = .029), age (P = .015), SNB (P = .008), overjet (P = .048) and pg'-G' (P = .001). Both types of disc repositioning method can effectively promote condylar regeneration and improve skeletal Class II malocclusion in adolescents with ADD. Disc repositioning by OSu obtained more new bone height than MsA.

Mandibular shape prediction using cephalometric analysis: applications in craniofacial analysis, forensic anthropology and archaeological reconstruction

BackgroundThe human mandible is variable in shape, size and position and any deviation from normal can affect the facial appearance and dental occlusion.ObjectivesThe objectives of this study were to determine whether the Sassouni cephalometric analysis could help predict two-dimensional mandibular shape in humans using cephalometric planes and landmarks.Materials and methodsA retrospective computerised analysis of 100 lateral cephalometric radiographs taken at Kingston Hospital Orthodontic Department was carried out.ResultsResults showed that the Euclidean straight-line mean difference between the estimated position of gonion and traced position of gonion was 7.89 mm and the Euclidean straight-line mean difference between the estimated position of pogonion and the traced position of pogonion was 11.15 mm. The length of the anterior cranial base as measured by sella-nasion was positively correlated with the length of the mandibular body gonion-menton, r = 0.381 and regression analysis showed the length of the anterior cranial base sella-nasion could be predictive of the length of the mandibular body gonion-menton by the equation 22.65 + 0.5426x, where x = length of the anterior cranial base (SN). There was a significant association with convex shaped palates and oblique shaped mandibles, p = 0.0004.ConclusionsThe method described in this study can be used to help estimate the position of cephalometric points gonion and pogonion and thereby sagittal mandibular length. This method is more accurate in skeletal class I cases and therefore has potential applications in craniofacial anthropology and the ‘missing mandible’ problem in forensic and archaeological reconstruction.

An analysis for the variability of soft tissue facial profile

The purpose of this study was to investigate whether there is relationships between the skeletal craniofacial structures and the variability of facial profile. The sample consist of 100 cephalometric films [50 males & 50 females for adults (18-25years) having normal dental class I occlusion] collected from POP department, collage of dentistry in Mosul university. The sample classified according to skeletal classification into class I, II, & III also classified according to the profile into:- cisprofile,orthoprofile&transprofiles We measured the length of 3 skeletal bases, in addition to the position of pogonion& the thickness of soft tissue covering the anterior aspect of middle and lower face area. The variables entered spss computer system for analysis, we found that males have more skeletal CII & III than females, but females have more skeletal Cl II. males have larger records for all the variables & the difference is significant

“Spontaneous” correction capacity of skeletal Class II malocclusions in growing patients after upper and lower arch coordination using fixed appliances: A prospective controlled clinical study

ObjectiveTo determine the effect of arch coordination on the dentoskeletal jaw base relationship and the mandibular growth pattern in growing skeletal Class II patients. Materials and MethodsLeveling, aligning, and upper/lower arch coordination were done in 30 Class II/1 growing patients with preadjusted edgewise fixed appliances. After arch coordination was achieved without transverse discrepancy and occlusal interferences, the 6-month experimental passive observation period was started. The records were compared with 30 untreated patients who served as controls. The initial (T0) and post-coordination+observation (T1) cephalograms of two groups were analyzed and compared using standard cephalometric parameters, Pancherz analysis, and cranial base superimposition. ResultsSagittal maxillary growth in the treated group was slightly restricted, in turn resulting in a decrease in profile convexity. Mandibular sagittal growth did not differ between groups, but the mandible rotated posteriorly in the treated and anteriorly in the control group. The upper incisors were retroclined and retruded in the treated group, resulting in overjet reduction. The lower incisors were intruded in the treated group, leading to overbite reduction. The cephalometric superimposition over the stable structures of the anterior cranial base showed higher prevalence for the forward rotation with forward pogonion position and increased vertical dimension in the control group. ConclusionsUpper and lower arch coordination alone does not seem to affect mandibular growth; however, because of a posterior rotation of the mandible, it does affect the direction of mandibular growth in some patients, although not in the desired therapeutic direction. (ClinicalTrials.in.th: TCTR20170706003).

High-efficiency Combination Treatment of Submental Neck Fullness.

Background:Fat accumulation, skin laxity, and muscle contraction cause aging cervical fullness. Combining botulinum toxin to treat muscle contraction, and technique-oriented microfocused ultrasound for skin laxity, can improve cervical fullness without requiring lipolysis. Gel-assisted depth adjustment (GADA) is a depth-targeting, image-guided approach using an appropriate gel volume to precisely heat tissue layers during real-time visualization.Methods:A 41-year-old woman presented with moderate submental neck fullness and saggy cheeks. An appropriate gel volume was applied as determined by the targeted tissue layer’s distance from the skin. The submental and submandibular areas received 112 lines of 0.9 J/cm2 microfocused ultrasound with visualization (MFU-V) from a 4.5-mm transducer and 0.3 J/cm2 from a 3-mm transducer to treat the SMAS and dermosubcutis, respectively. For concomitant jowling, these transducers delivered 111 MFU-V lines to the lower cheek. Six units of incobotulinumtoxinA was injected in 1 point at the mandible to modulate hyperactive mentalis muscles. The platysma received 10U of incobotulinumtoxinA per cheek, whereas downturned mouth corners received 4U of incobotulinumtoxinA.Results:One-month posttreatment, submentum improvements included changes of the vertical pogonion position, more mandible angularity, and a straighter mandibular line. Anterior chin projection was more pronounced and the pogonion had more inferior displacement, creating a younger appearance in the chin-neck complex. Patients followed-up for 3 months also demonstrated these changes.Conclusions:Delivering MFU-V using the GADA technique effectively tightens submental and submandibular soft tissues. When combined with incobotulinumtoxinA, muscles in the chin and perioral area are relaxed. Thus, GADA yields significant clinical improvement and patient satisfaction.

The effect of disc repositioning and post-operative functional splint for the treatment of anterior disc displacement in juvenile patients with Class II malocclusion

PurposeTo evaluate the effect of temporomandibular joint (TMJ) disc repositioning and post-operative functional splint for the treatment of anterior disc displacement (ADD) in juvenile patients with Class II malocclusion. Materials and methodsJuvenile patients (≤20 years) who had bilateral TMJ ADD with and Class II malocclusion treated by disc repositioning and functional splints were included in the study. Magnetic resonance imaging (MRI) and cephalometric radiographs before surgery (T0), immediately after surgery (T1) and more than 3 months after surgery (T3) were obtained in all patients. Cephalometric values including condylar height, overjet, SNA, SNB and pogonion position etc. were measured and compared before and after disc repositioning by statistical analysis. Fourteen patients (13 female, 1 male) were included in this study. Their average age was 16.7 years (range, 12–20 years). ResultsSeven patients with 14 joints had an MRI at least 6 months (6–24 months, mean 14.3) prior to disc repositioning. When compared to the MRI taken just prior to surgery, of those 14 joints, 9 condyles (64.3%) had evidence of bone resorption, 5 condyles (35.7%) had new bone formation mostly at the posterior part of the condyle (21.4%). These MRIs showed the condylar height was reduced 0.81 mm ± 0.61 (P = 0.013). Pre-operative cephalometric radiographs showed increased overjet (P = 0.039). The mean post-operative follow-up was 9.4 months (range, 4–13 months). Postoperative MRI showed the condylar height increased 1.74 ± 0.98 mm after disc repositioning (P < 0.001). Newly generated bone was observed on all condyles. 84.6% of the new bone was formed on the superior and posterior-anterior surfaces. Postoperative cephalometric radiographs showed the SNB angle increased 1.83 ± 1.56°(P < 0.001), pogonion position (pg’-G′) moved anteriorly 2.18 ± 3.13 mm (P = 0.028) and incisor overjet decreased 3.55 ± 1.86 mm (P < 0.001), whereas significant changes were not found in SNA, Sn - G Vert, Y-Axis, U1 SN, IMPA (L1-MP) and U1-L1 (P > 0.05). ConclusionConservative treatment for ADD with Class II malocclusion in juvenile patients may cause condyle resorption and aggravate the dentofacial deformity. Disc repositioning combined with post-operative functional splints can effectively promote condylar growth and help correct the dentofacial deformity.

Treatment effects of mandibular anterior position training versus a fixed Class II corrector in growing patients with skeletal Class II malocclusion

PurposeTo compare treatment effects of Class II elastics and anterior mandibular position training against fixed Class II corrector (PowerScope™) during the correction of skeletal Class II malocclusion with fixed appliance in growing patients. Materials and methodsThirty-six growing patients with skeletal Class II malocclusion with a retruded pogonion position were randomly allocated to the Class II elastics or PowerScope™ groups. Preadjusted edgewise fixed appliances were used in both treatment groups. Skeletal, dental and profile changes were compared using lateral cephalograms taken before (T0), after initial alignment (T1) and after Class I obtained (T2) for 16/18 patients in the Class II elastics group and 15/18 patients in the PowerScope™ group. ResultsThe duration of treatment was significantly longer for the Class II elastics group than PowerScope™ group. In terms of skeletal changes, Class II elastics increased mandibular length, midfacial length and mandibular plane angle significantly more than the PowerScope™. In terms of dental changes, Class II elastics increased dental height significantly more than the PowerScope™. ConclusionsBoth treatment modalities reduced severity of Class II malocclusion and decreased profile convexity. Class II elastics with anterior mandibular position training increased mandibular length more but required longer treatment duration. The PowerScope™ had a greater effect on maxillary dento-alveolar restriction. (ClinicalTrials.in.th: TCTR 20180220003).

Aesthetic outcomes and morphological changes in chin parameters after mandibular distraction and subsequent advancement genioplasty in patients with mandibular micrognathia

Despite the wide uses of mandibular distraction osteogenesis (MDO), no study appears to have evaluated the use of MDO and subsequent advancement genioplasty. This study addressed lower facial third aesthetics in a consecutive series of subjects with micrognathia who underwent MDO and subsequent advancement genioplasty. Standard cephalometric measurements were performed pre-MDO, at the end of consolidation, and at 1 week, 6 months, and 12 months after genioplasty. At the end of follow-up, questionnaires were given to measure patient satisfaction. Forty patients were included, 33 of whom underwent genioplasty. The mean patient age was 22.35±1.12years. Pre-genioplasty cephalometric measurements showed that all patients had a deficient chin position and projection; they were dissatisfied with their facial aesthetics. Post-genioplasty cephalometric measurements showed that the hard and soft tissue pogonion had moved significantly: 8.4±2.3mm and 11.0±2.11mm, respectively. According to the questionnaire, the patients were satisfied with the final results. The MDO reduced the amount of chin advancement and minimized relapses; the soft tissue response of the lower facial third was more sensitive to genioplasty than isolated MDO. MDO and genioplasty lead to a modest horizontal chin movement that achieves the preferred pogonion position and projection.

Sequencing of bimaxillary surgery in the correction of vertical maxillary excess: retrospective study

The aim of this study was to evaluate the precision of bimaxillary surgery performed to correct vertical maxillary excess, when the procedure is sequenced with mandibular surgery first or maxillary surgery first. Thirty-two patients, divided into two groups, were included in this retrospective study. Group 1 comprised patients who received bimaxillary surgery following the classical sequence with repositioning of the maxilla first. Patients in group 2 received bimaxillary surgery, but the mandible was operated on first. The precision of the maxillomandibular repositioning was determined by comparison of the digital prediction and postoperative tracings superimposed on the cranial base. The data were tabulated and analyzed statistically. In this sample, both surgical sequences provided adequate clinical accuracy. The classical sequence, repositioning the maxilla first, resulted in greater accuracy for A-point and the upper incisor edge vertical position. Repositioning the mandible first allowed greater precision in the vertical position of pogonion. In conclusion, although both surgical sequences may be used, repositioning the mandible first will result in greater imprecision in relation to the predictive tracing than repositioning the maxilla first. The classical sequence resulted in greater accuracy in the vertical position of the maxilla, which is key for aesthetics.

The effects of surgically assisted rapid maxillary expansion (SARME) on the dental show and chin projection

ObjectiveTo quantify the postoperative changes of the dental show and chin projection following SARME using 3D CBCT imaging. Material and methods78 patients with transversal maxillary hypoplasia and mandibular hypoplasia who underwent SARME were enrolled into the study. A cone beam computed tomography (CBCT) scan was acquired preoperatively and at least 1 year postoperatively. 3D postoperative changes in the dental show and pogonion position were measured based on soft tissue and hard tissue landmarks. Results68 patients (87%) exhibited a postoperative increase in the dental show. The dental show was increased by a mean of 2.2 ± 2.0 mm (p < 0.01). The mean horizontal and vertical displacement of the chin (pogonion) following SARME was 1.6 ± 2.5 mm posteriorly and 1.6 ± 2.0 mm inferiorly (p < 0.01). An inferior displacement of the maxilla and maxillary tooth as well as a consequent clockwise pitch of the mandible seemed to play a role in inducing these postoperative changes. ConclusionAn increase in dental show and a posterior and inferior displacement of the chin should be considered prior to SARME to prevent undesirable postoperative changes of the facial esthetics.

The stability following advancement genioplasty with biodegradable screw fixation

The purpose of this study was to compare postoperative stability using biodegradable screws with that of metal plates for fixation of advancement genioplasty. We studied patients who had advancement genioplasty alone or at the same time as other orthognathic surgery including mandibular setback. We assessed the lateral cephalographs at different time points (preoperatively, and 7 days, 3 months, 6 months, and 12 months postoperatively). A total of 54 patients were enrolled and 27 patients were assigned to each group. The position of pogonion was stable 12 months postoperatively, and the amount of skeletal advancement was reflected in soft tissue close to 100%. There were no clinical differences between biodegradable screws and conventional metal plates used for fixation. Biodegradable fixation for advancement genioplasty is a good option for patients who would require a second operation for removal of the plates.

Systematic review of the surgery-first approach in orthognathic surgery.

The surgery-first approach in orthognathic surgery has recently created a broader interest in completely eliminating time-consuming preoperative orthodontic treatment. Available evidence on the surgery-first approach should be appraised to support its use in orthognathic surgery. A MEDLINE search using the keywords "surgery first" and "orthognathic surgery" was conducted to select studies using the surgery-first approach. We also manually searched the reference list of the selected keywords to include articles not selected by the MEDLINE search. The search identified 18 articles related to the surgery-first approach. There was no randomized controlled clinical trial. Four papers were excluded as the content was only personal opinion or basic scientific research. Three studies were retrospective cohort studies in nature. The other 11 studies were case reports. For skeletal Class III surgical correction, the final long-term outcomes for maxillofacial and dental relationship were not significantly different between the surgery-first approach and the orthodontics-first approach in transverse (e.g., intercanine or intermolar width) dimension, vertical (e.g., anterior open bite, lower anterior facial height) dimension, and sagittal (e.g., anterior-posterior position of pogonion and lower incisors) dimension. Total treatment duration was substantially shorter in cases of surgery-first approach use. In conclusion, most published studies related to the surgery-first approach were mainly on orthognathic correction of skeletal Class III malocclusion. Both the surgery-first approach and orthodontics-first approach had similar long-term outcomes in dentofacial relationship. However, the surgery-first approach had shorter treatment time.

Evaluation of Upper Airway Dimensional Changes and Hyoid Position Following Mandibular Advancement in Patients With Skeletal Class II Malocclusion

Class II skeletal malocclusion due to mandibular deficiency is considered a risk factor for sleep disorders due to oropharyngeal airway deficiencies. In view of the above, a prospective interventional study was undertaken to evaluate upper airway dimensional changes and position of hyoid bone by comparing pretreatment and posttreatment lateral cephalograms. The objective also included the establishment of the ratio of mandibular advancement to increase in airway dimensions. Pretreatment and posttreatment lateral cephalograms of 20 adults (13 females and 7 males) with skeletal class II malocclusion treated by combined orthodontics and bilateral sagittal split ramus osteotomy was evaluated for changes in posterior airway space (PAS), superior airway space (SAS), minimum airway space (MAS), hyoid bone position (MP-H), effective mandibular length (Co-Gn), mandibular corpus length (Go-Pg), and pogonion position (N perpendicular-Pg). The cephalograms were manually traced by a single operator and the data analyzed using MINITAB 13.2 version software. There was a statistically highly significant (P = 0.0001) increase in PAS, SAS, MP-H, Co-Gn, and Go-Pg. The mean ratio of mandibular advancement to increase PAS, SAS, and MAS was 1:0.35, 1:0.34, and 1:0.24, respectively. Hyoid bone moved superiorly and in an anterior direction by 2.1 ± 2.8 mm and was found to be statistically highly significant (P = 0.0001). The study showed an overall increase in airway dimension and improvement in hyoid position. Thus, the procedure may be considered beneficial in reducing upper airway collapsibility and preventing sleep disorders due to oropharyngeal airway deficiencies in skeletal class II malocclusion.

Long-Term Stability of Surgical Mandibular Setback

To test the relationship between positional changes of the proximal segments during surgery and the positional rebound of the mandible during the postsurgical period of orthodontic treatment. The sample included records for 34 patients who had received sagittal split surgery for the correction of mandibular prognathism. Data were collected from standardized cephalometric radiographs taken immediately prior to surgery (T2), immediately following surgery (T3), and following the completion of orthodontic treatment (T4). Linear and angular changes in the orientation of the posterior border of the ascending ramus between time points T2, T3, and T4 were measured relative to superimposition on the anterior cranial base. In addition, linear changes in the position of pogonion between T3 and T4 were measured. The magnitude of linear displacement of the posterior border of the proximal segment during surgery (T2 to T3) was statistically significantly correlated (r=.61) with the magnitude of linear displacement of pogonion during the postsurgical phase of orthodontic treatment (T3 to T4). There was a strong relationship between the magnitude of angular (r=.67) displacement of the posterior border of the proximal segments during surgery (T2 to T3) and the magnitude of angular rebound of the posterior border of the proximal segments that occurred during the postsurgical phase of orthodontic treatment (T3 to T4). When rigid fixation procedures alter the position of the proximal segments during sagittal split osteotomy of the mandible, the proximal segments tend to go back toward their presurgical positions following surgery.

Cephalometric analysis of the consolidation phase following bilateral pediatric mandibular distraction.

The goal of the consolidation phase of mandible distraction is to maintain the improvement in maxillomandibular form and relationship while the generated tissue ossifies. During this period, external deforming forces can act on the healing generated bone. The purpose of this study was to describe the potential cephalometric changes that occur following pediatric bilateral mandibular distraction using external devices. Retrospective lateral superimposition cephalometric analyses. Thirty-five cases of pediatric mandible distraction were reviewed. Seven of these cases were included in the study after exclusion criteria were applied. These cases represented a group with severe congenital dysmorphology and a mean device activation of 26.5 mm. Changes in pogonion position, symphyseal plane rotation, mandible length, and mandible length relative to maxillary length during the 18 to 36 days of activation, the eight weeks of consolidation, and the 1-year period following removal of the distraction device were measured. All patients demonstrated variable changes in position of the mandible during the consolidation phase. The most common were retrusion of pogonion, a decrease in mandible length, and a clockwise rotation of the symphyseal plane. In some cases the changes that occurred during consolidation were greater than those that occurred on 1-year follow-up. The consolidation phase of distraction osteogenesis is a dynamic phase and should not be assumed to be static. Multicenter use of this cephalometric technique would help to identify potential risk factors associated with postactivation changes.

Cephalometric Analysis of the Consolidation Phase Following Bilateral Pediatric Mandibular Distraction

Abstract Objective: The goal of the consolidation phase of mandible distraction is to maintain the improvement in maxillomandibular form and relationship while the generated tissue ossifies. During this period, external deforming forces can act on the healing generated bone. The purpose of this study was to describe the potential cephalometric changes that occur following pediatric bilateral mandibular distraction using external devices. Design: Retrospective lateral superimposition cephalometric analyses. Participants: Thirty-five cases of pediatric mandible distraction were reviewed. Seven of these cases were included in the study after exclusion criteria were applied. These cases represented a group with severe congenital dysmorphology and a mean device activation of 26.5 mm. Main Outcome Measures: Changes in pogonion position, symphyseal plane rotation, mandible length, and mandible length relative to maxillary length during the 18 to 36 days of activation, the eight weeks of consolidation, and the 1-...

Cephalometric appraisal of posttreatment vertical changes in adult orthodontic patients

The purpose of this study was to evaluate vertical facial changes in adult orthodontic patients and to evaluate the stability of these changes. Thirty-three patients (8 males and 25 females) were examined. The patients had been treated with full fixed edgewise appliance mechanics and exhibited at least 1.0° of clockwise rotation of the mandible during treatment. Mandibular rotation was determined by the angular change in the Y-axis to the Frankfort plane. Twelve angular and 14 linear skeletal and dental measurements and 3 skeletal ratios were derived from pretreatment (T1), posttreatment (T2), and postretention (T3) cephalometric radiographs. Paired t tests were used to compare vertical changes that occurred as a result of orthodontic treatment and their stability or relapse tendency during the retention and postretention periods. Twenty-five percent (P <.001) of the opening rotation of the mandible recovered during the posttreatment period, resulting in a significant overall rotation that was maintained. Both treatment and posttreatment changes in the Y-axis angle showed a high correlation with the horizontal position of pogonion (r = −0.797 and −0.889, respectively). Only overjet showed a low correlation between treatment changes and posttreatment changes in the Y-axis angle. Stepwise regression analysis of pretreatment variables and treatment changes failed to predict the behavior of the Y-axis angle change. (Am J Orthod Dentofacial Orthop 2000;118:378-84)

下顎枝矢状分割法を施行した骨格性下顎前突患者における術後１５年以上にわたる顎態の変化について

The purpose of this study was to clarify the longterm dentofacial changes after sagittal splitting osteotomies in skeletal Class III patients.The lateral cephalograms of 7 females observed for more than fifteen years after surgery were used. The postoperative changes in the position of Pogonion were measured.The results were as follows:1) From five years to fifteen years after surgery, Pogonion moved antero-posteriolly and vertically. However, five patients who had stable occlusion revealed less displacement.2) Pogonion of two patients showing some relapse occlusion-wise moved more backwardly and downwardly from two years postoperatively to more than five years postoperatively. Some continuous positional changes of Pogonion was observed even fifteen years after surgery.The less Pogonion displacement was, the more stable the occlusion was. However, when greater Pogonion displacement is observed, the patient should be given more careful postoperative management.

Mandibular growth estimated by four cephalometric measurements

Mandibular growth was estimated by four cephalometric measurements on three lateral cephalograms of 21 subjects. The estimates made by three standard cephalometric approaches were compared with that made by a "scientific" method. The scientific method was based on the change in position of the cephalometric landmark condylion on cephalograms orientated on two metal implants inserted in the mandible. The other three investigated "standard" cephalometric methods were each based on estimating the difference in length between two cephalometric landmarks: (1) pogonion-condylion, (2) pogonion-articulare, and (3) maximum mandibular length. In general, the individual estimates of the amount of mandibular growth by the scientific method and that estimated by each of the standard cephalometric methods were not proportional. Some factors affected the estimates of mandibular growth. For example, (1) the growth direction of the condyle, (2) the change in position of pogonion on the mandible during the growth, and (3) the apposition of bone on the chin in some cases. The amount of mandibular growth, which is estimated by the standard cephalometric methods, and growth velocity curves, which is based on such estimates, are therefore not valid. Accordingly, conventional cephalometric analyses are not as reliable at traditionally envisaged.