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To systematically review the effects of functional appliances (FA) using incremental vs maximal mandibular advancement regarding cephalometric measurements in class II malocclusion individuals and to assess patient-centred-outcomes. Six electronic databases were searched without restrictions up to April 2020. We included randomized and non-randomized controlled trials using identical FA. Trials involving participants who used adjunct appliances, inter-maxillary elastics, who received surgical treatment or that recruited individuals with cleft lip/palate or craniofacial deformity/syndrome were excluded. Risks of bias assessments were performed using the Cochrane risk of bias tool-2 and ROBINS-I tools. Mean differences (MD) with their 95% confidence intervals were calculated from random-effects meta-analyses. The GRADE tool was used to assess the certainty of the evidence. Six studies were included. Low to very low certainty of evidence indicated that incremental mandibular advancement resulted in greater gains in mandibular length (MD = 0.89 [0.38, 1.34], P = .0005), anterior mandibular displacement (MD = 0.73 [0.40, 1.06], P .0001) and SNB angle (MD = 0.44 [0.02, 0.85], P = .04). No significant differences were found for maxillary, dento-alveolar and upper airway outcomes between construction bite protocols (P .05). Study design and appliance-related factors influenced the results of the subgroup analyses. Existing evidence is inadequate to assess patient-related response and long-term outcome could not be assessed. Currently, there are a heterogeneous number of studies with low quality and methodological issues can lead to biases that strongly limit an evidence-based conclusion. Weak evidence suggests gains in mandibular skeletal parameters in the short term using FA with incremental mandibular advancement. Randomized trials evaluating key topics such as patient-centred outcomes need to be conducted to guide clinical management. PROSPERO (CRD42019147436).

Simple Summary Extreme growth of the lower jaw is an essential determinant of facial appearance and treatment is challenging. The mandibular joint is important for mandibular growth and backward traction may be applied to address its protrusion. Nevertheless, the conclusions following animal experiments have been contradictory; additionally, joint disorders could arise because of abnormal, traumatic pressure. Our aim was to review the impact on the condyle and the jaw of their distal displacement as found in published research involving rats and rabbits, up to October 2020. In those animals, the mandibular/condylar retraction led to occlusal improvement, but some relapse might be anticipated. The mandibular condyle remained more posteriorly, restriction of further growth was observed, the posterior surface became more flattened, but it became thicker in its neck. The dimensional alterations persisted for the entire period of study and the mandible resumed its inherited growth pattern after the discontinuation of the orthopedic force. Posterior mandibular displacement may be anticipated to produce clinically significant restriction in condylar growth, mainly attributed to remodeling. The properties of the applied force may affect the timing of mandibular formation or just prove traumatic. Outcome stability is a matter of concern and more studies are required to resolve the issue. Abstract Treating extreme mandibular growth is challenging. The mandible is pushed backwards to address itsprotrusion. Nevertheless, conclusions after such displacement in animals have been contradictory. The aim of the present review is to present measurable alterations of the mandible and the condyle following retractionin healthy rats or rabbits. PubMed, Scopus and Web of Science were accessed for relevant studies up to October 2020. Eligibility was determined by the PICOS process, while the risk of bias was estimated with SYRCLE’s risk of bias tool. Retraction resulted in a more distal molar occlusion and the condyle rested more posteriorly. Mandibular anteroposterior bilateral growth restriction was achieved, the condylar process measured smaller and its angulation increased. The condylar neck thickened, its posterior surface flattened, the coronoid process was measured longer, and enlarged retromolar density was registered. Differences in the ramus height and the intercondylar distance were insignificant. Changes persisted for the period of study and subsequently the mandible resumed its inherited growth pattern. The timing of mandibular shaping and TMJ outcomes might depend on the properties of the applied force. Stability is of concern and well-structured, long-term studies are expected to resolve the issue and further clarify the results of posterior mandibular displacement.

Current scientific evidence on how orthognathic surgery affects the airways morphology remains contradictory. The aim of this study is to investigate the existence and extension of a neutral-impact interval of bony segments displacement on the upper airways morphology. Its upper boundary would behave as a skeletal displacement threshold differentiating minor and major jaw repositioning, with impact on the planning of the individual case. Pre- and post-operative cone beam computed tomographies (CBCTs) of 45 patients who underwent maxillo-mandibular advancement or maxillary advancement/mandibular setback were analysed by means of a semi-automated three-dimensional (3D) method, 3D models of skull and airways were produced, the latter divided into the three pharyngeal subregions. The correlation between skeletal displacement, stacked surface area and volume was investigated. The displacement threshold was identified by setting three ∆Area percentage variations. No significant difference in area and volume emerged from the comparison of the two surgical procedures with bone repositioning below the threshold (approximated to +5 mm). A threshold ranging from +4.8 to +7 mm was identified, varying in relation to the three ∆Area percentages considered. The ∆Area increased linearly above the threshold, while showing no consistency in the interval ranging from −5 mm to +5 mm.

La pérdida prematura de molares primarios predispone a maloclusiones incluyendo apiñamiento, impactación de dientes permanentes y alteración de la relación molar y canina. El objetivo del presente estudio es determinar el efecto de las pérdidas prematuras de molares primarios sobre la relación incisiva horizontal. El estudio es documental, retrospectivo y observacional. Se evaluaron los registros ortodóncicos (historias clínicas, fotografías y radiografías) de 209 pacientes con edades entre 4 a 15 años. La relación incisiva horizontal se consideró normal (grupo 1) cuando hubo contacto entre en borde incisal del incisivo inferior con la cara palatina del superior, aumentada (grupo 2) cuando había distancia positiva entre ellos y negativa (grupo 3) cuando los bordes incisales se encontraban a tope o en mordida cruzada. Los datos se analizaron utilizando coeficiente Pearson (p?0,001). El 22% (45 pacientes) presentó pérdidas prematuras. La prevalencia de pérdidas prematuras no tuvo diferencia significativa entre géneros y fue mayor en el grupo de 7 a 9 años. De los pacientes con pérdidas prematuras, 6 (13,3%) se clasificó en el grupo 1; 12 (26,7%) en el grupo 2 y 27 (60%) en el grupo 3. Hubo asociación positiva entre el número de molares perdidos y la presencia de mordida cruzada anterior, siendo la media de molares perdidos mayor (4, 7) en el grupo 3. Se demostró que las pérdidas prematuras de molares primarios tienen una relación estadísticamente significativa con la mordida cruzada anterior, siendo posible que la falta de soporte oclusal posterior favorezca el desplazamiento protrusivo de la mandíbula.

espanolLa extraccion del tercer molar es un procedimiento comun en cirugia oral. Una de las complicaciones es la fractura mandibular. Con una incidencia postoperatoria menor a un 0.005%. Los factores que contribuyen al riesgo de fractura del angulo mandibular despues de una extraccion del tercer molar incluyen el nivel de impactacion, la anatomia del diente, infecciones locales previas, edad, sexo, presencia de formaciones quisticas y bruxismo entre otras. Presentamos un caso clinico de fractura mandibular postoperatoria a las cinco semanas tras la exodoncia del 47 y 48 incluidos en posicion horizontal. El objetivo final del tratamiento de una fractura mandibular es la consolidacion osea manteniendo la oclusion dental. En nuestro caso, al no tratarse de una fractura que sobrepasaba las corticales y sin desplazamiento mandibular, no fue subsidiaria de un tratamiento quirurgico y se resolvio con reposo funcional. EnglishThe lower third molar extraction is a common procedure in oral surgery. One of its complications, although uncommon, is the mandibular fracture. Postoperatively, it has an incidence lower than 0.005%. The factors that may contribute to the risk of the mandibular angle fracture after an extraction of the third molar include the leve! of impaction are the anatomy of the tooth, previous local infections, age, sex, cysts and bruxism among others. We present a clinical case of postoperative mandibular fracture at five weeks after the extraction of 47 and 48 included in horizontal position. The ultimate treatment goal of a mandibular fracture is to reach a bone consolidation with the premorbid dental occlusion. In our case, as it was not a fracture that surpassed the cortical and there was not a mandibular displacement, it was not need a surgical treatment so it was resolved with functional rest.

Objectives Three-dimensional evaluation of skeletal mandibular changes following Herbst appliance treatment. Setting and Sample Population Retrospective case–control study, based on a sample size calculation. Twenty-five pubertal patients treated with Herbst appliance (HAG), and 25 matched Class II patients who received other non-orthopaedic dental treatments (CG). Material and Methods Three-dimensional models were generated from pre-treatment (T0) and post-treatment (T1) cone beam computed tomograms. Volumetric registration on the cranial base was used to assess mandibular displacement; volumetric regional registration was performed to evaluate mandibular growth. Quantitative measurements of X, Y, Z and 3D Euclidian changes, and also qualitative visualization by colour-mapping and semi-transparent overlays were obtained. Results Downward displacement of the mandible was observed in both HAG and CG (2.4 mm and 1.5 mm, respectively). Significant forward displacement of the mandible was observed in the HAG (1.7 mm). HAG showed greater 3D superior and posterior condylar growth than the CG (3.5 mm and 2.0 mm, respectively). Greater posterior growth of the ramus was noted in the HAG than in CG. Conclusions Immediately after Herbst therapy, a significant mandibular forward displacement was achieved, due to increased bone remodelling of the condyles and rami compared to a comparison group. Three-dimensional changes in the direction and magnitude of condylar growth were observed in Herbst patients.

Introduction Recent studies have shown some contradictory results when evaluating the consequences of orthodontic-surgical treatments on the pharyngeal airway. Therefore, the purpose of this study was to correlate the amount of jaw displacement with the volume variation and the minimal cross-sectional area of the pharyngeal airway. A comparison was made between the correlations with the percentage and the absolute values of the measurement variations. Methods Forty-two patients were divided into 2 groups according to the kind of orthognathic surgery that they had undergone. Group 1 had 22 subjects who had undergone maxillary advancement associated with mandibular setback, and group 2 had 20 patients who had undergone maxillomandibular advancement. The pharyngeal airway was divided into the upper segment and the lower segment, and the sum of these volumetric measures resulted in the total volume. The maxillary and mandibular displacements were assessed using closest point iteration after a voxel-wise cone-beam computed tomography superimposition. Hence, jaw displacements were correlated, using Pearson's correlation and linear regression analysis, to the volume variations of the pharyngeal airway (first time separately and then both groups together) and to the minimal cross-sectional area variation. Results The strongest correlation found was between maxillary displacement and the upper segment in group 2 (r = 0.898, R2 = 0.888; P ≤0.001). With the groups' data combined, the variables mandibular displacement and the lower segment showed a linear correlation (r = 0.921, R2 = 0.914; P ≤0.001). Maxillary displacement showed a strong positive correlation with the minimal cross-sectional area variation in group 2 (r = 0.710, R2 = 0.604; P ≤0.01). Conclusions Correlations with the percentage values were substantially stronger than the correlations with the absolute values. Stronger positive correlations were found between the jaw's displacement and the volume variation of the volume segment that was closer to it in both kinds of surgeries. Only the maxillary displacement is a reliable predictor of the minimal cross-sectional area variation after maxillomandibular advancement.

AIM: To conduct an epidemiological study and find the prevalence of some transverse anomalies of occlusion in children aged 7-17 years from the region of Plovdiv; to determine the most appropriate time for early orthodontic treatment based on the results of the study. MATERIAL AND METHODS: The study included 883 children from Plovdiv (7-17 years old). The children were studied by means of extraoral examination, a clinical examination of dental arches and occlusion and by doing a clinical test to assess mandibular displacement. RESULTS: The prevalences of mandibular deviation, laterognathia and posterior crossbite (unilateral or bilateral of single teeth or a group of teeth) were 30.4%, 1.02%, 10.53%, respectively. CONCLUSION: Our results are consistent with the results reported by other authors which indicate that these malocclusions cannot self-regulate and for this reason they should be subject to strict prevention and early treatment.

Traditionally, superimposition of lateral cephalograms has been performed using the cranial base as a reference. However, the direction of mandibular displacement observed by using this technique often conflicts with the observations made by clinicians. This occurs because superimposition using the cranial base does not take into account changes in the maxilla resulting from growth and/or treatment that may affect the mandible. A technique of superimposing the maxilla and mandible together as a unit using the maxillary base as reference has been proposed. (The term maxillary base will be used throughout this article to mean the maxilla and mandible observed together as one unit.) It attempts to define true mandibular displacement as a result of orthodontic treatment mechanics and growth. Significant difference in mandibular displacements between the two superimposition methods have been reported on treated Class II samples. No reports have been made on treated and control Class III samples. The objective of this study was to compare the direction of mandibular displacements using the two methods of superimposition (cranial base versus maxillary base) in a control and treated sample of Class III subjects. The control sample received no treatment and the treated sample underwent orthopedic treatment with protraction headgear. Mandibular displacements were measured by plotting three mandibular landmarks pogonion (Pog), gnathion (Gn), and menton (Me). Superimpositions were made on the pretreatment (T1) and posttreatment (T2) films to determine the differences in vector angles, thus quantifying the direction of mandibular displacement. The results showed significant difference in mandibular displacements (alpha vector angles of Pog, Gn, and Me) in both the treatment group and the control group when comparing the cranial base and maxillary base superimposition methods ( P P

Orthodontic tooth movement is dependent upon the remodeling of the periodontal ligament and alveolar bone by mechanical means. Facial sutures are also fibrous articulations, and by remodeling these joints, one can alter the positional relationships of the bones of the facial skeleton. As might be expected from the structure and mobility of the temporomandibular joint (TMJ), this articulation is more resistant to mechanical deformation, and whether functional mandibular displacement can alter the growth of the condyle remains controversial. Clinical investigations of the effects of the Andresen activator and its variants on dentofacial growth suggest that the changes are essentially dento-alveolar. However, with the popularity of active functional appliances, such as the Herbst and twin-block based on ’jumping the bite’, attention has focused on how they achieve dentofacial change. Animal experimentation enables informed decisions to be made regarding the effects of orthodontic treatment on the facial skeleton at the tissue, cellular, and molecular levels. Both rat and monkey models have been widely used, and the following conclusions can be drawn from such experimentation: (1) Facial sutures readily respond to changes in their mechanical environment; (2) anterior mandibular displacement in rat models does not increase the mitotic activity of cells within the condyle to be of clinical significance, and (3) mandibular displacement in non-human primates initiates remodeling activity within the TMJ and can alter condylar growth direction. This last conclusion may have clinical utility, particularly in an actively growing child.

This paper describes the orthodontic treatment of two cases presented by the winner of the William Houston gold medal at the Membership in Orthodontics examination at the Royal College of Surgeons of Edinburgh and which also won the British Orthodontic Society (BOS) cases prize in 2013. The first case describes the management of a 20-year-old female patient with a Class II division 2 malocclusion complicated by moderate upper and severe lower arch crowding, increased overjet and overbite, a crossbite and centreline discrepancies. Treatment involved a combination of a transpalatal arch, temporary anchorage devices and fixed appliances. The second case describes the management of a 15-year-old male patient with a Class I malocclusion complicated by crossbites affecting the right buccal segment and UR2, an associated mandibular displacement forward and to the right, mild upper arch crowding and a centreline discrepancy. Treatment involved a combination of a quad-helix, headgear and fixed appliances.

目的: 本研究の目的は, 健常者および顎機能障害者の習慣性咬合位から咬頭嵌合位への下顎変位を三次元的に解析し, その変位量および変位方向の違いを明らかにすることである.方法: 被検者として, 健常有歯顎者6名と顎関節部の雑音を有する顎機能障害者6名を選択した. Light clenchingと30% MVC (Maximum voluntary clenching) の咬合力を発揮させて採得した, 2種類のシリコーンバイトを試料として, 非接触形状計測を行った. 頭部X線CTから, 頭蓋顔面骨の三次元構築データを抽出し, その解剖学的標点から, 基準座標を設定した. テフロン球をマーカーとして三次元構築データの位置合わせを行った後に, 上下顎歯列咬合面の位置合わせにより, 習慣性咬合位から咬頭嵌合位への下顎変位を算出した. 下顎変位を表現するパラメータとして, 下顎咬合平面を決定する三角形の重心の変位量および変位方向をMOD (Movement of dentition), 左右側下顎頭最上点の変位量および変位方向をMOC (Movement of condyle) とした.結果: 健常者に比べて顎機能障害者では, MOD, MOCともに下顎変位量が有意に大きかった. また変位方向については, すべての顎機能障害者において, 下顎歯列部では上方に, 下顎頭部では後方に変位する傾向が認められた.結論: 習慣性咬合位から咬頭嵌合位への下顎変位が, 顎関節雑音の発症に関連している可能性が示された.

SUMMARY This study investigated mandibular displacement and masticatory muscle activity during clenching in lateral occlusal position in relation to the lateral occlusal pattern. Twenty healthy human subjects (mean = 26·5 years) volunteered for this study. Metallic occlusal overlays were fabricated for the lower working side canine to second molar and non-working side second molar in order to simulate a canine protected occlusion, group function occlusion and bilateral balanced occlusion (balancing contact). Three-dimensional displacements of the bilateral condyle and electromyography (EMG) activities in the bilateral masseter, anterior and posterior temporalis were recorded during maximal clenching. The experimental occlusal pattern was revealed to have statistically significant effects on both condylar displacement and EMG activity (P

Introduction Anterior cross bite is a common malocclusion and early treatment is indicated. Determining its prevalence is important to plan orthodontic services. Objective To assess the prevalence and associated features of anterior cross bite in pre-adolescent patients attending an orthodontic clinic. Methods A hospital based cross sectional study was conducted in patients attending the Division of Orthodontics, University Dental Hospital, Peradeniya. Seven hundred and twenty one consecutive patients were examined for anterior cross bite. All patients who consented were examined and anterior cross bite were recorded when maxillary incisor/s occluded lingually to mandibular incisor/s in centric occlusion. Mandibular displacement, gingival recession, tooth mobility, presence of posterior cross bite and skeletal pattern were also assessed. Results Sample consisted of 721 patients, of whom 193 (26.7%) had anterior cross bite. Twenty two (11.4%) had both anterior and posterior cross bite. Among patients with anterior cross bite 62% had unilateral involvement and 38% had bilateral involvement. One hundred (51.8%) had involvement of only one incisor while 64 (33.2%) had involvement of two incisors. Class 1 skeletal pattern was found in 103 (53.37%) patients with anterior cross bite, Class 2 skeletal pattern in 33 (17.1%) and Class 3 skeletal pattern in 57 (29.53%). Mandibular displacement was present in 93 (48.19%) patients and 5 (2.5%) showed tooth wear in anterior cross bite. Gingival recession was seen in 43 (22.3%) and tooth mobility of involved lower incisors in 12 (6.2%). Conclusion The prevalence of anterior cross bite is high in pre-adolescent patients attending an orthodontic clinic.

BACKGROUND: In some individuals with obstructive sleep apnea (OSA), oronasal continuous positive airway pressure (CPAP) leads to poorer OSA correction than nasal CPAP. The authors hypothesized that this results from posterior mandibular displacement caused by the oronasal mask.OBJECTIVE: To test this hypothesis using a mandibular advancement device (MAD) for mandibular stabilization.METHODS: Subjects whose OSA was not adequately corrected by oronasal CPAP at pressures for which nasal CPAP was effective were identified. These subjects underwent polysomnography (PSG) CPAP titration with each nasal and oronasal mask consecutively, with esophageal pressure and leak monitoring, to obtain the effective pressure (Peff) of CPAP for correcting obstructive events with each mask (maximum 20 cmH2O). PSG titration was repeated using a MAD in the neutral position. Cephalometry was performed.RESULTS: Six subjects with mean (± SD) nasal Peff 10.4±3.0 cmH2O were studied. Oronasal Peff was greater than nasal Peff in all subjects, with obstructive events persisting at 20 cmH2O by oronasal mask in four cases. This was not due to excessive leak. With the MAD, oronasal Peff was reduced in three subjects, and Peff 2O could be obtained in two of the four subjects with Peff >20 cmH2O by oronasal mask alone. Subjects’ cephalometric variables were similar to published norms.CONCLUSION: In subjects with OSA with higher oronasal than nasal Peff, this is partially explained by posterior mandibular displacement caused by the oronasal mask. Combination treatment with oronasal mask and MAD may be useful in some individuals if a nasal mask is not tolerated.

This study investigated mandibular displacements during clenching in the lateral mandibular position in relation to lateral occlusal relationships. Twelve healthy human subjects (mean=26.7 years) volunteered for this study. Acrylic occlusal devices were fabricated for the lower working-side canine, working-side second molar and balancing-side second molar in order to simulate a dominant canine guidance, working-side interference (WI), balancing-side interference (BI) and bilateral balanced occlusion (BO). Vertical displacements of the mandible were recorded by linear variable differential transformers during submaximal clenching in the right lateral position. The four experimental occlusal conditions were revealed to have a significant effect on mandibular displacement patterns (ANOVA, P < 0.001). A dominant canine raiser caused a mandibular elevation with the smallest displacement at the working-side premolar and the largest displacement at the balancing-side second molar. Clenching on a WI or BI caused a mandibular elevation with the smallest displacement at the working- or balancing-side second molar, respectively. A BO resulted in the smallest upward displacement among the four experimental conditions. These results suggest that the nature of reaction forces at the temporomandibular (TM) joints caused by the elevation of the mandible varies in a predictable manner depending upon lateral occlusal relationships.

To study the role of periodontal mechanoreceptors in the modulation of the human jaw-jerk reflex, 60 reflexes were elicited in each of six healthy individuals under three different conditions: (a) with unilateral tooth support on the ipsilateral side; (b) with support on the contralateral side; and (c) with support and local anesthesia of the periodontal tissues on the ipsilateral side. During all conditions, background muscle activity and mandibular displacement were kept as constant as possible. Using on-surface EMG and the amplitude of the first peak of the biphasic jaw-jerk potential as the outcome variable, a condition-dependent reflex amplitude was found for the visually controlled right anterior temporalis muscle. Specifically, the ‘ipsilateral support plus anesthesia’ condition yielded higher amplitudes than the ‘ipsilateral support’ condition. Highest amplitudes were found for the ‘contralateral support’ condition. It was concluded that periodontal mechanoreceptors on the ipsilateral side have an inhibitory effect on the jaw-jerk reflex amplitude in the anterior temporalis muscle.

To investigate the relationship between occlusal scheme and joint loading, mandibular displacement was measured during lateral clenching under experimentally altered occlusal conditions. Acrylic occlusal devices were fabricated for the lower working-side canine, working-side second molar, and balancingside second molar. With the aid of these devices, various occlusal states were simulated. Eight healthy subjects volunteered for this study and performed clenching tasks. Vertical displacements of the mandible were recorded by linear variable differential transformers, and the results were as follows:1. Clenching efforts in the lateral mandibular position caused elevation of the mandible.2. When a single occlusal device was placed unilaterally, the amount of the upward displacement near the supporting tooth tended to be smallest.3. Insertion of three occlusaldevices (bilateral tooth contacts) reduced the amplitude of mandibular displacement.These results suggested that the nature of reaction forces at the temporomandibular joints caused by the elevation of the mandible would be influenced by the occlusal status.

African American orthodontic patients often present with morphologic characteristics that prompt the extraction of premolars. Referring dentists, however, commonly see extraction as a cause of "dished in" profiles, collapsed arches, and temporomandibular dysfunction. If true, these claims imply that African American patients are disproportionately at risk of clinical misadventure. Unfortunately, a meaningful long-term comparison of alternative treatments--be it retrospective or prospective--requires samples of patients who were equally susceptible to the two alternatives. Thus, if a retrospective study is to be free of susceptibility bias, the samples must be matched with respect to the anatomic differences that prompted the clinicians' choice of treatments. The goals of this investigation, therefore, were the following: to gather a large sample of African American expatients and to identify by means of discriminant analysis the characteristics that seem to have been important to the extraction decision, to use this knowledge to assemble subsamples of extraction and nonextraction expatients (both Class I and II) who were similar before treatment, and, finally, to recall them so that the long-term impact of the two strategies could be compared. In the end, 60 expatients--30 extraction and 30 nonextraction--were recalled, on average, nearly 8 years after the completion of treatment. In general, both treatments reduced irregularity and neither seemed to produce posterior mandibular displacement. Premolar extraction led to a modest reduction in dental and soft tissue protrusion (half the incisor retraction minus one); nonextraction, by way of contrast, produced an increase. Long term, the difference between the two treatments was about 2 mm at the upper lip and 4 mm at the lower. Excessive profile flattening was not a common finding. Our findings thus imply that the various "functional orthodontic" arguments against premolar extraction do not apply to African Americans any more than they do to whites.

Statement of problem. Though computer-based systems for recording three-dimensional jaw motion and muscle activity during mastication are common, few computer programs are available to analyze the resultant data. Few studies have discussed the variability over time of the many parameters of the masticatory cycle now measurable by computer systems. Purpose. The purposes of this study were to (1) use a custom computer program, (MAS), for analysis of long-term repeated measurements of mandibular motion and muscle activity; (2) determine sex differences for mandibular movements and activity of the muscles involved during mastication; and (3) determine the variability over time and the statistical power of these methods. Materials and methods. Masticatory cycles of 20 normal men and 17 normal women were examined during mastication of a constant bolus at a sampling rate of 500 fps. Measurements included duration of chewing cycle and its component phases, mandibular displacement in three dimensions, and electromyographic activity in the temporalis and masseter muscles. The MAS custom computer program was used for analysis. Two-way repeated measures analysis of variance was used to compare the men with the women over three trials at 0, 6, and 12 months. The variability over time associated with each measurement was also estimated. Results. Timing of the phases of the chewing cycle were most repeatable between trials, whereas lateral excursions and muscle force magnitudes were the least repeatable measures. Durations of total cycle, its slow-open and fast-close phases, were significantly longer for the female group, and their bursts of muscle activity tended to be longer. The amount of vertical mandibular excursion tended to be greater for men. There were no gender-related differences in the amplitude of muscle activity. Conclusions. This study demonstrated that men have significantly shorter chewing cycles with faster velocities than women. Men used significantly greater chewing force than women, although their electromyographic activity levels were equivalent. The masticatory measurements made by the MAS program had differing amounts of variation over time. Total duration of the chewing cycle and amount of opening varied the least, whereas amount of lateral excursion and jaw muscle electromyographic magnitudes exhibited the greatest variation. (J Prosthet Dent 1997;78:179-86.)

The purpose of this study was to investigate the postsurgical stability of the mandible in Japanese skeletal Class II patients who underwent sagittal split ramus osteotomy (SSRO). Twelve female patients who underwent surgical mandibular advancement with rigid osseous fixation using titanium miniplates were selected for this study. Seven patients underwent mandibular advancement only, and 5 patients underwent mandibular advancement in conjunction with genioplasty. The postsurgical stability of the mandible was evaluated by cephalometric analysis. As the result, the average mandibular position was stable after SSRO. No relationship was observed between the amount of mandibular displacement following surgery and that during postsurgical treatment, as well as between the amount of mandibular displacement and the mandibular plane angle immediately before surgery.

The methods of creating inferior traction on a unilateral condyle using bilateral and unilateral bite plates on the molars and unilateral pivot were examined. Different patterns of mandibular displacement were also examined, i. e., voluntary clenching, manual unilateral elevation of the mandible, and unilateral and bilateral myo-monitor pulse stimulation (myo-pulsing). Displacement of the condyle was measured with a computerized axiograph.Inferior traction on a condyle did not arise during voluntary clenching with the pivot or either of the bite plates. Voluntary clenching apparently caused the condyle to be pressed anterosuperiorly against the glenoid fossa. Manual unilateral elevation with the pivot created inferior traction of the condyle (1.3-1.4mm) on the pivot side but superior movement (0.9-1.0mm) also caused the condyle to be pressed against the glenoid fossa on the contralateral side. Plate side pulsing created inferior traction on the contralateral condyle without creating pressure on the pulsing side both with and without bite plates. Then non-plate side pulsing created inferior traction on the contralateral condyle without creating pressure on the pulsing side.In conclusion, unilateral myo-pulsing with the pivot or the unilateral bite plate was the most effective for creating the inferior traction effect on the contralateral condyle, while voluntary clenching was ineffective.

Intercuspal position (ICP) is the most important position in all functional mandibular positions for the stomatognathic system. While the clenching level was gradually increased, dynamic stability of the ICP in 10normal subjects and 10patients with temporomandibular disorders (TMD) was evaluated from occlusal contacts, deviation of the incisal point of the mandible and bilateral anterior temporalis and masseter muscle activity.The obtained results were as follows:1. Increases in the clenching level produced changes in the location of occlusal contacts of ICP in TMD patients.2. During clenching of ICP, displacement of the mandible in TMD patients was greater than in normal subjects.3. During clenching of ICP, activity of the masseter muscle had a greater effect on the occlusal contact stability than the anterior temporalis muscle.

In order to investigate the characteristics and reproducibility of the mandibular position during phonation of a Japanese syllabary single sound, intra- and inter-individual variations of the mandibular position were analyzed in 10 normal subjects using the Sirognathograph Analyzing System.Results were summerized as follows:1. With regard to the characteristics of the mandibular position during phonation of each vowel pronunciation, the order of the amount of the mandibular displacement in the vertical and anterior-posterior directions from maximum to minimum was IA/, /E/, /O/, /I/, and /U/ vowel pronunciation.2. With regard to the characteristics of the mandibular position during phonation of each consonant pronunciation, IS/ consonant pronunciation showed the smallest mandibular displacement in the vertical and anterior-posterior directions of all the consonant pronunciation.3. Phonation of each distinct single sound was performed at each characteristic mandibular position. However, high degree of reproducibility of the mandibular position during phonation was demonstrated in every subjects.4. The mandibular position during phonation of a Japanese syllabary has a little inter-individual variations in both antero-posterior and lateral direction. However, they showed a large inter -individual variation in superio-inferior direction.

Studies of the development of mastication in the normal growing individual have received little attention in the literature. The aim of this study was to determine whether changes in oral motor function occurred during growth. Ninety healthy individuals with normal occlusion were divided into six groups of males and females, 9-10, 13-15, and 20-22 years of age. Oral motor function, with respect to mandibular displacement and velocity, was monitored with an opto-electronic method. The results revealed that the total duration of the masticatory cycle was not influenced by age or gender. However, the time distribution between the different phases was found to be influenced by the age factor, causing a longer opening time and a shorter closing time in the adults. In mastication, both mandibular displacement and the mandibular velocity in closing were less in females. A reduction of the masticatory opening velocity and an increase in closing velocity were observed with increasing age. Physiological maturation of the masticatory system due to central and peripheral changes and functional adjustments due to changes in dentition and skeletal growth may be the underlying reasons for our findings.

The purpose of this study was to investigate the long-term changes in the skeletal Class III profile subsequent to chincap therapy. The sample consisted of 63 Japanese girls who had skeletal Class III malocclusions before treatment. All underwent chincap therapy from the beginning of treatment. The duration of chincap therapy varied but averaged 4½ years. The samples were divided into the following three groups according to their ages when chincap therapy was started: A group that started at 7 years of age ( n = 23), a group that started at 9 years of age ( n = 20), and one that started at 11 years of age ( n = 20). The data were derived from lateral cephalometric head films, taken serially at the ages of 7, 9, 11, 14, and 17 years. Skeletal facial diagrams were constructed by X-Y coordinates of representative cephalometric landmarks. The data were analyzed statistically. The results of the present study were as follows: (1) The mandible showed no forward growth during the initial stages of chincap treatment in all three groups. (2) Patients who had entered treatment at 7 and 9 years of age appeared to show a catch-up manner of mandibular displacement in a forward and downward direction before growth was completed. (3) There was no statistical difference in the final skeletal profile between the group that had entered treatment at age 7 and the one that had entered at age 11. In conclusion, the skeletal profile was greatly improved during the initial stages of chincap therapy, but such changes were often not maintained thereafter. This finding indicated that chincap therapy did not necessarily guarantee positive correction of skeletal profile after complete growth.

Objective To record maxillary and mandibular displacement with articular growth and in response to bimaxillary surgical repositioning in patients with hemifacial microsomia (HFM) and to observe ipsilateral corpus/ramus growth in severely affected children. Design Prospective roentgen stereometric analysis (mean age 7 years 10 months to 18 years 0 months) and retrospective profile and panoramic roentgenograms. Mean total observation period was 9 years 1 month. Setting Department of Plastic and Reconstructive Surgery, Malmö University Hospital (Malmö, Sweden). Patients Twenty-one patients consecutively diagnosed from 1976 through 1988 with HMF, five of whom had bimaxillary surgery. Interventions Surgery was performed at the Department of Plastic and Reconstructive Surgery. Implants were inserted at the initial reconstructive surgical procedure under general anesthesia. Roentgen examinations were performed in connection with continued clinical evaluations and treatment. Main Outcome Measures Stereo roentgenograms were digitized at the Department of Orthopedic Surgery, Malmö University Hospital (Malmö, Sweden). Results Displacement of the jaws with articular growth and in response to bimaxillary surgical repositioning varied interindividually with no apparent common pattern. Relapse displacement occurred several years after bimaxillary surgery. Mandibular growth changes were found in the corpus/ramus area and alveolar process on the affected side. Conclusions A marked interindividual variability of maxillary and mandibular displacement indicates that the relevance of statistical analysis of HFM growth data may be questioned. We would suggest that precise and accurate longitudinal recordings of growth and response to surgery in individual HFM patients be more appropriate.

The aims of this study were (1) to evaluate cephalometric changes in subjects with Class II Division 1 malocclusion who were treated with headgear (HG) or Fränkel function regulator (FR) and (2) to compare findings from regional superpositions of cephalometric structures with those from conventional cephalometric measurements.Cephalographs were taken at baseline, after 1 year, and after 2 years of 65 children enrolled in a prospective randomized clinical trial. The spatial location of the landmarks derived from regional superpositions was evaluated in a coordinate system oriented on natural head position. The superpositions included the best anatomic fit of the anterior cranial base, maxillary base, and mandibular structures.Both the HG and the FR were effective in correcting the distoclusion, and they generated enhanced differential growth between the jaws. Differences between cranial and maxillary superpositions regarding mandibular displacement (Point B, pogonion, gnathion, menton) were noted: the HG had a more horizontal vector on maxillary superposition that was also greater (.0001P.05) than the horizontal displacement observed with the FR. This discrepancy appeared to be related to (1) the clockwise (backward) rotation of the palatal and mandibular planes observed with the HG; the palatal plane's rotation, which was transferred through the occlusion to the mandibular plane, was factored out on maxillary superposition; and (2) the interaction between the inclination of the maxillary incisors and the forward movement of the mandible during growth.Findings from superpositions agreed with conventional angular and linear measurements regarding the basic conclusions for the primary effects of HG and FR. However, the results suggest that inferences of mandibular displacement are more reliable from maxillary than cranial superposition when evaluating occlusal changes during treatment.

Forward mandibular displacement in animal models is associated with faster and/or redirected condylar growth. Here the effect of forward displacement induced with an intraoral appliance on modelling/remodelling of the mandibular condyle was investigated in eight, 4-month-old, castrated male Merino sheep, randomly allocated to experimental and control groups (n=4 in each group). The study period was 15 weeks, during that time, (1). calcein, (2). tetracycline, and (3). alizarin red S fluorochromes were given to all animals from day 1. Midsagittal sections of the temporomandibular joints were selected for analysis. Dynamic variables of bone formation, static indices of bone-forming and -resorbing activity, and structural indices of trabecular bone were estimated histomorphometrically. The sampling site was divided into two regions for analysis: (a). a 'subchondral region' (2 and 3 labels only), believed to be the bone newly formed during the experimental period; (b). a 'central region' (labelled by all three fluorochromes), believed to be the bone that existed before the experiment. Regional differences in adaptive response were found. In the experimental group, the bone-volume fraction (BV/TV) of the subchondral regions had decreased, although the specific bone-surface and bone-formation rates had increased. This low BV/TV was associated with decreased trabecular thickness and increased trabecular separation. In the central condylar region of the experimental group, BV/TV was unchanged, but an increased osteoid surface was apparent when the eroded surface was taken into consideration. These adaptive condylar responses to forward mandibular displacement appeared to be the result of increased osteoblastic activity. Further studies are recommended to examine why the subchondral and central regions responded differently.

The pattern of mandibular movement during chewing is influenced by several central and peripheral factors. The aim of the present study was to determine whether changes in masticatory function, characterized by mandibular velocity and displacement, occurred during individuals' normal growth. Forty-seven children, 9-15 years of age, were followed over a 6-year period. All had an Angle Class I occlusion with no obvious orthodontic problems. Oral motor function with respect to mandibular displacement, duration, and velocity was monitored 3-dimensionally with an opto-electronic method. The chewing cycle was divided into an opening, closing, and occlusal phase. Total body height was measured. During the follow-up period, all masticatory variables except the 3-dimensional opening distance showed significant changes. The total chewing cycle duration, the opening and occlusal time of the chewing cycle, and the 3-dimensional closing distance increased during the growth period, while the closing time of the chewing cycle, the 2-dimensional lateral and vertical distances and both the opening and closing velocity decreased. The children who grew proportionally most in height during the 6-year period, i.e. the youngest children in the group studied, showed a significantly larger decrease in the opening velocity. From this study it becomes evident that the variables of the chewing cycle undergo a continuous process of change during growth. This is possibly a reflection of anatomical changes, maturation of the central nervous system, and altered functional demands.

This paper describes the treatment of a malocclusion involving a unilateral crossbite where there was no mandibular deviation into maximum intercuspation. Treatment involved the use of a modified quad helix which was active mainly on the affected side. This modification allowed arch expansion in the area where it was required.

Aim To illustrate a simple effective method for early treatment of pseudo Class III in the mixed dentition and to highlight the advantages of early treatment by showing a 4-year follow-up of the treatment effects. Subjects Twenty-one consecutive southern Chinese patients with a mean age of 9.6 years were included in the early treated group with pseudo Class III malocclusion. Methods Lateral cephalometric films taken at the beginning and at the end of treatment were analysed. The arithmetic mean and standard deviation (SD) were calculated for each cephalometric variable and paired t-tests were performed to assess the statistical significance of the treatment effects. Results Anterior crossbites and mandibular displacements were eliminated after the treatment. The angulation of the upper incisors to the maxillary plane showed an increase by a mean of 9.5° (P < 0.001), while the angulation of the lower incisors to the mandibular plane showed a decrease by a mean of 4.9° (P < 0.001). Conclusion In pseudo Class III malocclusion, proclination of upper incisors and/or retroclination of lower incisors with simple fixed appliances contribute to the correction of anterior crossbite and the elimination of mandibular displacement. Proclination of upper incisors, use of Leeway space and arch width increase provide space required for the eruption of the premolars and canines.

Food texture is known to influence several mastication parameters such as forces, muscular activities or mandibular displacement. This preliminary study was conducted to examine whether jaw movement recordings could be a reliable method to investigate food texture properties. Masticatory movements were recorded with an electromagnetic system. The subjects sat with their head in a magnetic field. Two coils were attached on the central upper and lower incisors. These receiver coils recorded a current when in the magnetic field. Five foods were chosen to display various rheological behaviours (meat, coconut, 2 cheeses and chocolate). All samples were prepared in standardised dominoe shape. Six replicates of each food were randomly presented and 8 subjects, free of any dental pathology, were asked to perform free style mastication. Durations, amplitudes and velocities of opening and closing phases of the masticatory cycles were measured. These movement parameters allowed discrimination between the foods. For all parameters there was significant variation between subjects. The main finding was the demonstration that mastication differed with the type of food chewed and thus this method of recording mandibular movements during mastication could be of a great interest for objective studies of food texture and to determine the basis of food texture perception.

The position of the condyle within the glenoid fossa was investigated in 21 adult patients with untreated skeletal Class III relationships and 18 adult patients with normal occlusions as controls. Axial computerized tomography (CT) was used for precise measurements of the bony structures of the temporamandibular joints. In horizontal sections, the mediolateral dimensions of the condyles of the patient group were found to be statistically higher in the fossa. The anteroposterior glenoid fossa dimensions were found to be smaller in Class III malocclusions. The smaller anterior joint space dimensions in the Class III relationships were also found to be statistically significant. The analysis of the measurements suggests that relative condylar protrusion with a relative mediolateral elongation of the condyle within a relatively smaller glenoid fossa are correlated with the anterior mandibular displacement in skeletal Class III malocclusions.

In order to investigate whether there are bilateral differences in the sensitivity of the mandibular stretch (jaw-jerk) reflex between patients with a myogenous craniomandibular dysfunction (CMD) and healthy controls free from signs and symptoms of CMD, jaw-jerk reflexes were elicited under standardized conditions in two groups of 10 gender- and age-matched subjects. The reflexes were recorded bilaterally from the masseter and the anterior temporal muscles by means of bipolar surface electromyogram (EMG). Reflex amplitudes at a mandibular displacement of exactly 80 μm and at a background muscle activity of exactly 12% maximum voluntary contraction were determined from relations between reflex amplitude and jaw displacement. These were obtained at a visually controlled, constant clenching level. For both groups, comparisons were made between reflex amplitudes from the right- and the left-hand side. In CMD patients with predominantly unilateral jaw muscle pain, comparisons were also made between the pain and non-pain sides. Although significant side asymmetries were found in many individuals, no significant differences were found among bilateral asymmetries in reflex sensitivity between patients and controls. No influence of pain side on the asymmetries was found. It was concluded that neuromuscular factors do not cause significant bilateral differences in the sensitivity of the jaw-jerk reflex between patients with myogenous CMD and controls. In a control experiment, in which eight healthy control subjects participated, the influence of a possible asymmetry in jaw displacement on the reflex sensitivity was evaluated. To achieve this, reflexes were elicited not only by means of a bilaterally imposed mandibular load, but also by means of loading via a unilateral bite-fork, so that an equal, constant jaw displacement could be imposed successively on both sides of the mandible. As no significant differences were found in bilateral asymmetries in reflex sensitivity between unilateral and bilateral mandibular loading, the influence of a possible asymmetrical jaw displacement on side asymmetries in the jaw-jerk reflex sensitivity is negligible in our experimental model.

The effect of the treatment of Angle Class II, Division 2 malocclusion was studied in 22 children by x-ray cephalometry and by recording the relation between the retruded and the intercuspal mandibular positions. The treatment was performed in three phases. In the first phase the upper incisors were proclined, and the deep bite was corrected with an upper removable plate. In the second phase the distal occlusion was corrected with an activator. The result was retained in the third phase with a second activator designed for retention. The relation between the retruded (RCP) and the intercuspal (ICP) mandibular positions was recorded with wax bites and dental casts mounted in a modified gnathothesiometer. The anteroposterior distance between RCP and ICP was large before the start of the treatment. The distance was unchanged after proclination of the upper incisors and correction of the deep bite but decreased after correction of the distal occlusion and increased again somewhat during the retention phase. The proclination of the upper incisors and the correction of the deep bite (phase one of the treatment) did not result in mandibular anterior positioning. This fact and the results of the recordings of the relation between RCP and ICP were interpreted as evidence that the mandible is not posteriorly displaced in Class II, Division 2 malocclusion.

Summary Experiments were carried out to study changes in masticatory movements in the chewing sequence of young dentate persons and complete denture wearers rehabilitated with bridges on osseo-integrated implants (OIB) in the lower jaw. Two test foods were used in the dentate group (apple, bread) and bread in the OIB group. A computer-based opto-electronic system (Selspot) was employed to record and analyse all single chewing cycles, regarding parameters reflecting, chewing rhythm, mandibular velocity and displacement. The different parameters were tested both intra- and inter-individually versus the series of the single and overall chewing cycles in the masticatory sequences respectively. The results indicated that different subjects performed different patterns of mastication within the chewing period when chewing the same type of food. Different test foods (texture, size) also seemed to affect the chewing pattern in a different way, e.g. mandibular displacement showed an obvious reduction when chewing apple, probably due to the bigger size of the bolus. The inter- and intra-individual analysis showed in some parameters discrepancies implying problems in analysing the chewing pattern within the chewing sequence without using both methods.