Mandibular forces during simulated tooth clenching

Differential, functional loading of the mandibular condyles has been suggested by several human morphologic studies and by animal strain experiments. To describe articular loading and the simultaneous forces on the dental arch, static bites on a three-dimensional finite element model of the human mandible were simulated. Five clenching tasks were modeled: in the intercuspal position; during left lateral group effort; during left lateral group effort with balancing contact; during incisal clenching; and during right molar clenching. The model's predictions confirmed that the human mandibular condyles are load-bearing, with greater force magnitudes being transmitted bilaterally during intercuspal and incisal clenching, as well as through the balancing-side articulation during unilateral biting. Differential condylar loading depended on the clenching task. Whereas higher forces were found on the lateral and lateroposterior regions of the condyles during intercuspal clenching, the model predicted higher loads on the medial condylar regions during incisal clenching. The inclusion of a balancing-side occlusal contact seemed to decrease the forces on the balancing-side condyle. Whereas the predicted occlusal reaction forces confirmed the lever action of the mandible, the simulated force gradients along the tooth row suggest a complex bending behavior of the jaw.     

Effect of jaw opening on the direction and magnitude of human incisal bite forces

The maximum bite force (MBF) appears to be different when measured at different jaw openings (e.g., Manns et al., 1979; Mackenna and Turker, 1983; Lindauer et al., 1993). However, the change could be related to a change in the bite direction. We have measured the MBF on incisors and its direction in three dimensions for different jaw openings in ten subjects. Surface electromyography (EMG) of anterior temporalis and masseter muscles on both sides was recorded simultaneously. The results showed that: (1) the average %MBF increased as the jaw was opened, reached a plateau between 14 and 28 mm of incisal separation, and then decreased at wider jaw openings; (2) the initial forward bite direction with respect to the mandibular occlusal plane shifted backwards during jaw opening; and (3) the activity of the masseter muscles declined and that of the temporalis muscles was largely unchanged, resulting in an increase of the ratio between the activity in temporalis and masseter muscles (T/M). There was a significant correlation between bite direction and jaw opening (r = 0.51, p < 0.001) and between T/M ratio and jaw opening (r = 0.56, p < 0.001). Based on comparative data, we have calculated sarcomere lengths while the jaw is opened and hypothesize that the average %MBF reaches its maximum when the sarcomeres in the masseter muscle achieve their optimum length. A plateau continues during further jaw opening, until those of temporalis reach their optimum length while those of masseter lengthen beyond their optimum length. The change in bite direction was attributed to either a change in the relation between upper and lower bite points as the jaw was opened or the gradual decline of masseter activity at larger openings.     

P2u purinoceptor modulation of intracellular Ca2+ in a human lung adenocarcinoma cell line: down-regulation of Ca2+ influx by protein kinase C

The aim of the present investigation was to study the functional alterations in the stomatognathic system following orthodontic-surgical management of skeletal vertical excess problems. The sample comprised 43 patients who received combined orthodontic-surgical treatment including bilateral vertical ramus osteotomy for posterior repositioning and counterclockwise rotation of the mandible (n = 26) or Le Fort I osteotomy for maxillary impaction (n = 17). All subjects were examined within 1 week before operation and 6 months postsurgery. Methods of examination included: (a) evaluation of dysfunction by means of a clinical index, (b) measurement of mandibular range of motion, (c) assessment of the number and intensity of occlusal contacts, and (d) tomographic evaluation of condyle-fossa relationships. The results of the study indicated that postoperatively (a) there was an increase of patients with dysfunction in the mandibular osteotomy group and a decrease of patients with dysfunction in the maxillary osteotomy group; (b) the maximum interincisal opening decreased significantly in the mandibular osteotomy group; (c) there was a significant increase in the number and intensity of occlusal contacts in both groups; and (d) the shortest posterior and anterior interarticular distances increased significantly in the mandibular osteotomy group.     

Occlusal stability in Class II, Division 1, deep bite cases followed up for many years after orthodontic treatment

This case report analyzes long-term occlusal stability that can be achieved in Class II, Division 1, deep bite cases with active treatment finished during the period of maxillomandibular growth. The analysis was designed to identify occlusal features common to two cases at the end of active treatment and to study how the occlusion changed with growth and jaw movement to achieve stability. The following occlusal features were shared by the two cases at the end of active treatment: (1) AB plane and axes of the maxillary and mandibular posterior teeth were perpendicular to functional occlusal plane; (2) the axis of the lower incisor was almost perpendicular to DC-L1i line; (3) the anterior occlusion was overcorrected to or near an edge-to-edge relationship. Items 1 and 2 remained unchanged throughout the follow-up periods, regardless of growth status, and the overjet and overbite increased during maxillomandibular growth after treatment. During the period of mandibular growth alone, after the end of retention, the axes of maxillary incisors tipped labially; as a result, F line became parallel to CDM line by the end of growth. The labial tipping of maxillary incisors brought the lower incisal edge into contact with or extremely near the inflection point (Bp).1 By the end of growth, the tangent of Bp became parallel to or coincident with DC-L1i line and perpendicular to the axis of the lower incisor, and the DC-L1i lines at various times posttreatment were almost parallel to each other in the two cases. Overjet increased as the maxillary incisors tipped labially, providing proper protrusive and retrusive paths for mandibular guidance. The angle between the functional occlusal plane and CDM line stayed almost the same as at the end of active treatment in the two cases, suggesting a possible change in the angle of eminence in harmony with the functional occlusal plane. These factors apparently contributed to the long-term occlusal stability in the two cases.     

The effect of post milking teat dip and suckling on teat skin condition, bacterial colonisation, and udder health

The aim of this study was to investigate whether in the maxilla and in the mandible the structure of the anterior medial sagittal alveolar and basal bone is related to the overbite. A total of 460 untreated adult subjects were divided into four groups with either deep bite, normal overbite, end-to-end bite, or open bite and were compared. The overbite, lower face height, and anterior alveolar and basal midsagittal cross-sectional areas from the maxilla and the mandible were assessed on lateral cephalometric radiographs. An index was calculated, dividing the sagittal by the vertical dimension of the midsagittal cross-sectional area. A deeper bite coincided with smaller lower face height, larger alveolar and basal areas, and a more widened shape of the symphysis. If the lower face height was introduced as a covariable, the open bite group showed significantly smaller maxillary and mandibular alveolar and basal cross-sectional areas compared with the end-to-end group, the normal overbite group, or the deep bite group. Vertical variation of the overbite probably coincides with a relative hyperdevelopment or hypodevelopment of the symphysis.     

Treatment response to maxillary expansion and protraction

A prospective clinical trial was conducted to determine the skeletal and dental contributions to the correction of overjet and overbite in Class III patients. Thirty patients (12 males and 18 females with a mean age of 8.4 +/- 1.7 years) were treated consecutively with protraction headgear and fixed maxillary expansion appliances. For each patient, a lateral cephalogram was taken 6 months before treatment (T0); immediately before treatment (T1); and 6 months after treatment (T2). The time period (T1-T0) represented changes due to 6 months of growth without treatment; (T2-T1) represented 6 months of growth and treatment. Each patient served as his/her own control. Cephalometric analysis described by Bj?rk (1947) and Pancherz (1982a,b) was used. Sagittal and vertical measurements were made along the occlusal plane (OLs) and the occlusal plane perpendicular (OLp), and superimposed on the mid-sagittal cranial structure. The results revealed the following: with 6 months of treatment, all subjects were treated to Class I or overcorrected to Class I or Class II dental arch relationships. Overjet and sagittal molar relationships improved by an average of 6.2 and 4.5 mm, respectively. This was a result of 1.8 mm of forward maxillary growth, a 2.5-mm of backward movement of the mandible, a 1.7-mm of labial movement of maxillary incisors, a 0.2-mm of lingual movement of mandibular incisors, and a 0.2-mm of greater mesial movement of maxillary than mandibular molars. The mean overbite reduction was 2.6 mm. Maxillary and mandibular molars were erupted occlusally by 0.9 and 1.4 mm, respectively. The mandibular plane angle was increased by 1.5 degrees and the lower facial height by 2.9 mm. Individual variations in response to maxillary protraction was large for most of the parameters tested. Significant differences in treatment changes between male and female subjects were found only in the vertical eruption of mandibular incisors and maxillary and mandibular molars. These results demonstrate that significant overjet and overbite corrections can be obtained with 6 months of maxillary protraction in combination with a fixed expansion appliance.     

Use of activator appliances in pediatric patients treated with costochondral grafts for temporomandibular joint ankylosis: analysis of 13 cases

PURPOSE: The long-term outcomes and clinical results of costochondral transplants used for the treatment of condylar ankylosis of the mandible in children with and without application of postoperative activator appliances are evaluated and compared. MATERIALS AND METHODS: A nonrandomized, retrospective clinical study of 13 cases of condylar ankylosis (16 joints) of the mandible surgically treated during a 9-year period from 1988 to 1997 was performed. All 13 patients were treated by condylectomy and immediate costochondral rib grafts. Nine of these patients underwent long-term postoperative therapy using removable activator appliances. Four patients did not undergo activator therapy postoperatively. Casts, radiographs, photographs, computed tomography (CT) scans, magnetic resonance imaging (MRI) and 99Tc bone scans were used postsurgically to evaluate graft take, condylar growth and function, occlusion, and facial and condylar symmetry. RESULTS:The postoperative and long-term clinical results in both groups showed costochondral growth center transplants to be effective in restoring mandibular growth of the affected side. However, symmetry, arch coordination, correction of occlusal canting, mandibular deviation, facial growth, and prevention of reankylosis were obtained and better controlled only in those cases that underwent long-term orthodontic activator therapy postoperatively and were followed closely. CONCLUSIONS: Children with long-standing condylar ankylosis of the mandible and its resultant facial asymmetry and occlusal canting (secondary to a nonfunctional joint and maxillary compensation) treated with condylectomy and immediate costochondral rib graft reconstruction of the affected joint were treated more favorably when activators were used postsurgically. The patients that failed to comply with or continue activator therapy postsurgically developed complications relating to mandibular deviation, occlusal dysharmony, asymmetry and, in one case, reankylosis of the temporomandibular joint (TMJ).     

Computerized cephalometric evaluation of orthognathic surgical precision and stability in relation to maxillary superior repositioning combined with mandibular advancement or setback

PURPOSE: A computerized, cephalometric, orthognathic surgical program (TIOPS) was applied in orthognathic surgical simulation, treatment planning, and postoperatively to assess precision and stability of bimaxillary orthognathic surgery. PATIENTS AND METHODS: Forty consecutive patients with dentofacial deformities requiring bimaxillary orthognathic surgery with maxillary superior repositioning combined with mandibular advancement or setback were included. All patients were managed with rigid internal fixation (RIF) of the maxilla and mandible and without maxillomandibular fixation (MMF). Preoperative cephalograms were analyzed and treatment plans produced by computerized surgical simulation. Planned, 5-week postoperative and 1-year postoperative maxillary and mandibular cephalometric-positions were compared. RESULTS: In the mandibular advancement group, the anterior maxilla was placed too far superiorly, with an inaccuracy of 0.4 mm. The posterior maxilla and the anterior mandible were placed in the planned positions. The lower posterior part of the mandibular ramus was placed too far anteriorly, with an inaccuracy of 2.0 mm. However, the mandibular condyles were accurately placed. In the setback group, the anterior maxilla was placed too far superiorly and posteriorly, with a vertical and sagittal inaccuracy of 1.0 mm and 0.7 mm, respectively. The posterior part of the maxilla was placed in a posterior position with an inaccuracy of 1.9 mm. The anterior mandible was placed too far anteriorly with an inaccuracy of 0.9 mm. The lower posterior part of the mandibular ramus was placed in a posterior position with an inaccuracy of 0.9 mm. However, the mandibular condyles were accurately placed. The statistical analysis of the 1-year stability data showed that the maxilla had moved 0.3 mm posteriorly in the advancement group and the lower incisors had moved 0.8 mm superiorly. No other significant positional maxillary or mandibular changes were found. In the setback group, the maxilla had moved 0.5 mm posteriorly, the anterior mandible 0.5 mm anteriorly, and the lower incisors 0.7 mm superiorly. No significant positional changes were seen in the mandibular ramus. CONCLUSION: The TIOPS computerized, cephalometric, orthognathic program is useful in orthognathic surgical simulation, planning, and prediction, and in postoperative evaluation of surgical precision and stability. The simulated treatment plan can be transferred to model surgery and finally to the orthognathic surgical procedures. The results show that this technique yields acceptable postoperative precision and stability.     

Reflex jaw motions and jaw stiffness pertaining to whiplash injury of the neck

Because a so-called mandibular whiplash injury requires the absence of short-latency jaw-closing reflexes in order to explain the postulated mechanism of injury (excessive jaw opening); the authors studied the presence and absence and more importantly, the kinematics (duration, displacement, velocity, acceleration) of monosynaptic and possibly, polysynaptic myotatic (stretch) reflexes in the jaw elevator muscles. In six healthy adults jaw jerk maneuvers were elicited through a brisk tap on the chin, and surface electromyography identified elevator reflexes while translational electrognathography identified the kinematics of the reflexes. The maneuvers were done while maintaining the rest position (3% MVC) and moderate clenching of the teeth (30% MVC). Electromyography was also used to identify phasic elevator excitations during a passive brisk neck extension maneuver. A sudden and unexpected elongation of the jaw elevators released autogenic reflex responses that, in conjunction with augmented tissue elasticity (stiffness), elevated the mandible into centric occlusion within approximately 150 milliseconds. In 86% of trials, the responses occurred regardless of the prevailing resting and clenching contractile activities. There was no evidence of a depressor force that consistently would and could anchor the mandible in a position of extreme or moderate depression, the theoretical linchpin of the mandibular whiplash injury. It was concluded that the mandibular locomotor system is very efficient in maintaining the rest and intercuspal positions of the mandible. This study found no evidence corroborating the mechanism claimed to release a so-called mandibular whiplash injury.     

British and West African facial form in ideal occlusion

True lateral cephalometric radiographs of 20 adult male British subjects and 20 Nigerian adult males were collected. All subjects showed an ideal occlusion of the teeth. These radiographs were analysed using a facial polygon joining the points Nasion, Sella, Articulare, Gonion and Menton. Additionally, measurements were made of the axial inclination of the incisor teeth and the distances from the incisal edges and apices of the teeth to the facial plane. Statistical examination of the results using "t" tests revealed that the average British mandible had a longer ramus but shorter body joined at a wider angle than the Negro, that the nasal part of the face was longer on average in the British group and that the incisor teeth, on average, projected further and were inclined further forward in the Nigerian group. A linear discriminant function in only three variables predicted with 100 per cent accuracy membership of the two groups. The three variables were the mandibular body length, the height of the nasal part of the face, and the amount by which the incisal edges of the lower incisor teeth projected beyond the facial plane.     

Effects of primary bone grafting on facial development in patients with unilateral complete cleft lip and palate

The study is based on an anthropometric assessment of X-ray films obtained in 22 adult males with complete unilateral cleft lip and palate treated during childhood with primary bone grafts and in 32 males with the same type of cleft without bone grafting. In the series with bone grafts was recorded a more marked reduction of maxillary depth associated with a larger retrusion than in the series without bone grafts. This deviation was therapeutically compensated by a larger displacement of the mandible backwards which contributes to the increase of mandibular posterior rotation. This provided the possibility to attain an edge to edge bite. Our results confirmed the unfavourable effects of primary bone grafting on maxillary growth and development.     

A study of anterior guidance

PURPOSE: This study focuses on the curvature and inclination of the lingual surfaces of the maxillary anterior teeth from the transition point on the cingulum to the incisal edge. MATERIALS AND METHODS: On 32 sets of mounted casts, 768 measurements were made of the curvature of the lingual surfaces utilizing radius gauges. The inclination of the lingual surface relative to the occlusal plane was recorded. The relationship of the incisal edge of the mandibular teeth to the transition point on the cingulum of the maxillary teeth was determined. Centric occlusion contact was noted on each tooth. RESULTS: Significant differences were found between the measured areas of any one tooth and between the types of teeth. The average radius ranged from 20.5 mm on the mesial ridge of the canine to 5.3 mm in the fossa of the central. The average inclination of the lingual surfaces was 46 degrees. In centric occlusion, 97% of the canines and 59% of the centrals and laterals were in contact with the opposing teeth. These contacts occurred 2.8 mm incisal to the transition point. The centrals contracted two opposing teeth (45%), and canines contacted one opposing tooth (53%). CONCLUSIONS: The function and curvature of the incisor teeth vary considerably from those of the canines. Overcontouring the lingual surfaces of the maxillary incisors to gain contact is not normal and may be detrimental.     

Stability of the mandibular position in occlusion of mandibulectomy patients with lateral discontinuity defect

In mandibulectomy patients with lateral discontinuity defect, the mandible is severely deviated and the occlusion is considered to be unstable. A thorough understanding of the mandibular occlusal position of these patients is important to achieve desirable results in their occlusal rehabilitation. This study compared the stability of the mandibular positions in occlusion, when the opening distance or the biting force was changed during mandibular movements, by simultaneously measuring four points on the mandible three-dimensionally. This study indicated that the mandibular positions in occlusion of these patients were extremely unstable as compared with those of the normal subjects and were considerably different from each other when the opening distance or the biting force was changed during mandibular movements.     

Hemispheric control of motor function: a whole brain echo planar fMRI study

A sample of 130 patients with vertical maxillary hyperplasia; mandibular hypoplasia with a high mandibular plane angle; narrow, tapered maxillary dental arch form; and anterior vertical open bite were collected from three different institutions to evaluate the stability of transverse maxillary arch dimensions after correction of the open bite. Surgical treatment consisted of Le Fort I or bimaxillary osteotomies. Intermolar, interpremolar, and anterior arch widths were measured three-dimensionally on dental casts using a Reflex microscope, and transverse stability after orthodontic or surgical maxillary expansion was analyzed. Orthodontic expansion followed by a one-piece Le Fort I intrusion osteotomy was performed in 77 patients, and surgical maxillary expansion by a multisegment Le Fort I intrusion osteotomy was performed in 53 patients. The increase of transverse arch width and the relapse after orthodontic or surgical expansion were not significantly different. The transverse arch width in these two groups did not relapse in 20% of the patients after a mean follow-up of 69 months. An additional bilateral sagittal split osteotomy had no detectable effect on stability. Patients who underwent a multisegment Le Fort I osteotomy stabilized with rigid internal fixation showed better transverse stability than those with intraosseous wire fixation and maxillomandibular fixation. Maxillary intermolar and interpremolar arch width relapses were not correlated with tongue interposition or loss of interdigitation. The relapse of these arch widths showed significant correlations with clockwise rotation of the mandible but not with changes of overbite or overjet.     

Functional and morphologic changes after combined maxillary intrusion and mandibular advancement surgery

PURPOSE: The purposes of this investigation were 1) to compare the morphology and function of patients with combined vertical maxillary excess (VME) and mandibular retrognathia with that of controls, and 2) to examine how these parameters change after combined maxillary intrusion and mandibular advancement surgery. PATIENTS AND METHODS: Fifteen female VME/retrognathic patients were compared with 26 female controls before and for up to 3 years after orthognathic surgery. Facial skeletal morphology, mandibular range of motion, maximum isometric bite force, and levels of electromyographic activity (EMG) in selected muscles of mastication were measured on all subjects. Where appropriate, one-way analysis of variance (ANOVA) or t-tests were used to compare the patients with controls. Univariate repeated-measures ANOVA was used to study longitudinal changes. RESULTS: Preoperatively, patients' morphologic measurements were characteristic of VME compounded by mandibular retrognathia. At surgery, the maxilla was elevated an average of 2.8 mm, and the mandible was lengthened by an average of 7.1 mm. All of the postoperative morphologic measurements were closer to normal values. The patients' masseter mechanical advantage was significantly lower than that of controls both before and after surgery. Surgically induced changes in mechanical advantage were very small. The patients' maximum range of motion and excursion during mastication were all lower than those of controls before surgery. All measurements of mobility decreased immediately after surgery, with a gradual return to preoperative values. However, even 3 years after surgery, all of the motion measurements remained smaller than those of the controls. Before surgery, the patients had maximum isometric bite forces significantly lower than those of controls. Bite forces increased significantly after surgery, approaching normal values within 2 years. The activity levels in the muscles of mastication during isometric bites were not significantly altered by surgery. CONCLUSIONS: This study confirms that VME/retrognathia patients suffer from substantial deficiencies in their oromotor function. Surgical correction of this particular type of dentofacial deformity improves both the morphologic and functional deficits. Although some changes were not statistically significant, all were toward normalization of the presurgical values.     

Modified condylotomy for chronic nonreducing disk dislocations

OBJECTIVES: To retrospectively evaluate the modified condylotomy procedure for patients with chronic nonreducing disk dislocations of the temporomandibular joint. STUDY DESIGNS: Sixty-three patients underwent 78 modified condylotomies on temporomandibular joints that had chronic nonreducing disk dislocations and that were previously treated unsuccessfully with nonsurgical modalities. Patients were asked to evaluate their pain, headaches, bite, and success rate postoperatively. Comparisons of patients' preoperative and postoperative maximum incisal opening were also made. Transpharyngeal and transcranial radiographs were compared to determine condylar changes. RESULTS: Ninety-four percent felt that their pain was better, one patient (2%) said that his pain was the same, and two patients (4%) felt that their pain was worse. Eighty percent considered their headaches were better, and one patient (2%) considered them worse. Seventy-eight percent said that their bite was the same or better, and 22% said it was worse. Three patients underwent a second surgery. Progressive condylar remodeling occurred in 81%, and regressive condylar remodeling occurred in 6%. The maximum incisal opening change was overall a positive change; 35% had a significant positive change, and 10% had a significant negative change. CONCLUSION: This retrospective study shows that the modified condylotomy should be considered as a surgical alternative in treating patients with chronic nonreducing disk dislocations that have been unsuccessfully treated nonsurgically.     

Juvenile chronic arthritis: a cephalometric analysis of the facial skeleton

A retrospective cross-sectional cephalometric investigation was undertaken to examine the facial form of a group of Finnish children with juvenile chronic arthritis (JCA). Following digitization, the radiographs were divided into three age groups, and according to whether or not 'bird-face' deformity was present. From a total of 67 cases (39 females and 28 males) 19 per cent were judged to be 'affected'. Analyses were carried out and the groups compared using t-tests. The mandible was found to be smaller both in ramal height and body length in the affected sample, with reduction in posterior face height being only partly compensated by increase in bony apposition at the angle producing antegonial notching. There was posterior rotation of the mandible with a reduction in angles S-N-B and S-N-Pog, and an increase in the gonial angle, the angle between the mandibular plane and S-N, maxillary, and occlusal planes. The changes in the maxilla were less marked. Although S-N-A was reduced in all three age groups, it was not significantly so. Maxillary length (ANS-PNS) was significantly smaller in the two younger age groups. In the vertical plane maxillary dimensions were reduced in the two younger age groups. A highly significant increase in the occlusal to maxillary planes angle was observed in all groups. There was, however, no difference in S-N to maxillary planes angle, indicating a more steeply inclined occlusal plane due to subnormally erupted maxillary molars. Although the inter-incisal angle was reduced there was no significant difference in the incisor inclinations in relation to the jaws and despite the posterior rotation of the mandible there was no significant increase in size of overjet or in the frequency of anterior open bite.     

Skeletal stability after mandibular advancement: a comparison of two rigid internal fixation techniques

OBJECTIVE: To compare two different methods of rigid fixation for any difference in postoperative stability after mandibular advancement. MATERIAL AND METHODS: Thirty-eight patients with Class II malocclusion treated by bilateral sagittal split osteotomy (BSSO) and mandibular advancement were selected for this retrospective study. Group A (n = 16) had noncompressive bicortical screws inserted in the gonial area through a transcutaneous approach and Group B (n = 22) had the bone segments fixed with unicortical screws and miniplates on the lateral surface of the mandibular body. Cephalograms were taken preoperatively, 2 days postoperatively, and 6 months after the operation, and a computer program was used to superimpose the three cephalograms and register the advancement and postoperative instability. RESULTS: There was a minimal difference in advancement of the mandible in the two groups. Statistical analysis showed no significant difference in postsurgical stability. However, positive correlation between the amount of advancement and the amount of postsurgical instability was demonstrated using a linear multiple regression test (P = .0002). CONCLUSION: This study indicates that the two different methods of internal rigid fixation of the segments after surgical advancement of the mandible give equal stability postoperatively and their use is a matter of surgical choice.     

A method of studying adaptive changes of the oropharynx to variation in mandibular position in patients with obstructive sleep apnoea

The aim of this study was to develop a method of studying the effects of mandibular advancement on oropharyngeal airway dimensions in the sagittal plane in conscious, supine patients. Six white, dentate, male patients with proven obstructive sleep apnoea had sagittal fluoroscopic recordings taken in the resting supine position. Images were recorded at four frames per second as the mandible was advanced with the teeth in contact to maximum protrusion and then opened. Software in the fluoroscopic imaging system permitted measurement of the change in mandibular position together with oropharyngeal airway dimensions expressed as the narrowest dimension observable in the post-palatal and post-lingual sites. Plotting of airway dimensions during mandibular advancement enabled estimation of the degree of protrusion associated with maximal airway benefits. Progressive mandibular advancement produced variable adaptive changes in the post-palatal and post-lingual regions of the oropharynx. The amount of airway opening appeared to be related to the horizontal and vertical relationships of the face and to the dimensions of the soft palate. The changes in post-palatal and post-lingual airway dimensions were not always identical, despite the observation that both tongue and soft palate were seen to move in unison, with close contact being maintained between the two structures. Jaw opening resulted in synchronous posterior movement of both tongue and soft palate, with consequent narrowing of oropharyngeal airspace. Fluoroscopy is a simple method of assessing upper airway changes with mandibular advancement in the conscious patient. The technique should facilitate the selection of subjects for whom mandibular advancement would seem advantageous. The nature of the adaptive response is dependent on individual structural variation. It is suggested that, where artificial mandibular advancement with dental devices is considered beneficial, jaw opening should be kept to a minimum.     

Control of the vertical dimension in Class II correction using a cervical headgear and lower utility arch in growing patients. Part I

A retrospective cephalometric study was performed comparing three groups of 30 growing patients with Class II, Division 1 malocclusions. Group 1 was treated with a cervical headgear/lower utility arch combination (CHG/LUA), group 2 was treated with a cervical headgear alone (CHG), and the third group was untreated. The average treatment time was 1 year, 6 months. No other appliances were used during this period. Maxillary and mandibular dental and skeletal treatment responses were compared with an analysis of variance (ANOVA) and a Scheffe's test. In addition, a multiple stepwise regression was performed to determine whether pretreatment measures of facial pattern were accurate predictors of mandibular rotational response. Both treatment groups demonstrated significant reduction in maxillary protrusion. The CHG-only group showed significantly greater anterior descent of the palatal plane as compared with the untreated group. The maxillary molars showed significant distal movement in both treatment groups without any extrusion beyond that seen with normal growth. The maxillary incisor demonstrated significant retroclination in the CHG-only group. There was no statistical difference among the groups for variables commonly used for measuring mandibular rotation or protrusion. The change in vertical position of the lower molar was not significantly different among the groups. A CHG as used in this study produced maxillary orthopedic and orthodontic changes without upper molar extrusion beyond that seen with normal eruption and in the absence of an opening rotation of the mandible, even in subjects with dolicocephalic facial patterns. The LUA did not appear to influence lower molar eruption or mandibular rotational response. None of the commonly used predictors of facial pattern, such as the Y-axis, XY-axis, or MP angle, accurately predicted mandibular rotational response. Further study would be necessary to ascertain whether this was a result of their invalidation as predictors, or a result of the treatment strategy employed.