Growth of the maxillary sinus in children and adolescents: A longitudinal study

Maxillary sinus volumetric and surface area data and growth models from longitudinal samples of children and adolescents are presented. Cone-beam radiographic CT scans from two small retrospective longitudinal samples, one from the Baylor College of Dentistry, Dallas, TX (N=17, 12 females, 5 males, 10.9-17.4 years) and one from a group private orthodontic practice in Nevada (N=15, 9 females, 6 males, 6.4-13.4 years) were used to collect maxillary sinus volumes and surface areas from each individual imaged at two times separated by variable intervals. Volume and surface area values were collected in Analyze^® (Mayo Clinic) and growth models were produced in MLwiN^®, a multi-level modeling program. There is a large degree of inter-individual variation. Surface area and surface-area-to-volume ratio (SA:V) changes are particularly variable. Growth models suggest linear growth in both volume and surface area, without growth spurts.

Secular change in height, sitting height and leg length in rural Oaxaca, southern Mexico: 1968–2000

OBJECTIVE

To evaluate secular changes in height, sitting height and estimated leg length between 1968 and 2000 in residents in a rural Zapotec-speaking community in Oaxaca, southern Mexico.

MATERIALS AND METHODS

Height and sitting height were measured in school children 6-13 years (1968; 1978, 2000), in adolescents 13-17 years (1978, 2002) and adults 19-29 years (1978, 2000). Leg length was estimated as height minus sitting height. The sitting height/ height ratio was calculated. Subjects were grouped by sex into four age categories: 6-9, 10-13, 13-17 and 19-29 years for analysis. The Preece-Baines Model I growth curve was fitted to cross-sectional means for 1978 and 2000.

RESULTS

There were no differences between children 6-9 and 10-13 years in 1968 and 1978 with the exception of the sitting height ratio in girls 6-9 years. Children of both sexes 6-13 years and adolescent boys 13-17 years were significantly larger in the three dimensions in 2000 compared to 1978; adolescent girls differed only in height and sitting height. Adult males in 2000 were significantly taller with longer legs than those in 1978, but the samples did not differ in sitting height and the ratio. Adult females in 1978 and 2000 did not differ significantly in the three dimensions. Rates of secular change in height and sitting height between 1978 and 2000 were reasonably similar in the three age groups of male children and adolescents, but the rate for estimated leg length was highest in 10-13-year-old boys. Secular gains were smaller in adult males, but were proportionally greater in estimated leg length. Girls 6-9 and 10-13 years experienced greater secular gains in height, sitting height and estimated leg length than adolescent and young adult females, while secular gains and rates decreased from adolescent girls to young adult women. Ages of peak velocity for height, sitting height and estimated leg length declined in boys, while only ages of peak velocity for height and estimated leg length declined in girls.

CONCLUSIONS

There are major secular increases in height, sitting height and estimated leg length of children and adolescents of both sexes since 1978. Secular gains in height are of similar magnitude in boys and girls 6-13 years, but are greater in adolescent and young adult males than females. The secular increase in height of young adults of both sexes is smaller than that among adolescents. Estimated leg length accounts for about 60% of the secular increase in height in children of both sexes. Estimated leg length and sitting height contribute equally to the secular increase in height in adolescent boys, whereas estimated leg length accounts for about 70% of the secular increase in height in young adult males. Sitting height contributes about two-thirds of the secular increase in height in adolescent and young adult females.

Reducing within-subject variation in chewing cycle kinematics—a statistical approach

OBJECTIVES

High levels of within-subject variability have limited the use of chewing cycle kinematics in the experimental and clinical context. The purpose of this study was to validate a new strategy for reducing within-subject variability in chewing cycle kinematics, based on the 10 most representative cycles from a chewing sequence.

METHODS

This prospective study included 25 young subjects, with normal class I occlusions. An optoelectronic recording system was used to track chin movements of subjects chewing gum (2.5 g). Computer programs provided estimates for duration and movement as well as the 3D coordinates of the chin point. The total output files were further processed for selection of 10 representative cycles based on standard scores for total duration, excursive ranges in the lateral, vertical and antero-posterior directions. Multilevel modelling procedures were used to test for significant differences.

RESULTS

There were no significant differences in cycle duration or excursions between the estimates for all cycles versus the 10 most representative cycles. Cycle shapes were very similar. There were no statistically significant differences in between-subject variances. All within-subject variances were smaller when using data from the 10 most representative cycles. The reduction of variance was approximately 33% for total duration and 75% for total 3D excursion.

CONCLUSIONS

The results validate the pre-processing strategy that selects the 10 most representative cycles from a sequence without altering cycle duration, excursions or shape or affecting between-subject variation but reducing within-subject variation substantially.

The efficacy of pain control following nonsurgical root canal treatment using ibuprofen or a combination of ibuprofen and acetaminophen in a randomized, double-blind, placebo-controlled study

AIM

To compare ibuprofen, to an ibuprofen/acetaminophen combination in managing postoperative pain following root canal treatment. It is hypothesized that the drug combination will provide more postoperative pain relief than the placebo or ibuprofen alone.

METHODOLOGY

Patients presenting at the Texas A&M Baylor College of Dentistry's graduate endodontic clinic, experiencing moderate to severe pain, were considered potential candidates. Fifty-seven patients were included based on established criteria. Following administration of local anaesthesia, a pulpectomy was performed. The patients were administered a single dose of either: (i) placebo; (ii) 600 mg ibuprofen; or (iii) 600 mg ibuprofen and 1000 mg of acetaminophen. Patients recorded pain intensity following treatment on a visual analogue scale and a baseline four-point category pain scale as well as pain relief every hour for the first 4 h then every 2 h thereafter for a total of 8 h. A general linear model (GLM) analysis was used to analyse the outcome.

RESULTS

Based upon the GLM analysis, there was a significant difference between the ibuprofen and the combination drug group, and between placebo and combination drug groups. There was no significant difference between the placebo and the ibuprofen.

CONCLUSION

The results demonstrate that the combination of ibuprofen with acetaminophen may be more effective than ibuprofen alone for the management of postoperative endodontic pain.

Bolus size and unilateral chewing cycle kinematics

The purpose of this study was to determine how bolus size alters the human chewing cycle. This prospective within-subject design evaluated chewing cycles of 38 young adults between 20 and 38 years of age (21 males and 17 females). An optoelectric jaw tracking system was used to record movements of the chin during unilateral (right sided) chewing of four randomly ordered bolus sizes (1, 2, 4 and 8 g) of gum. Using each subject's 10 most representative cycles, multilevel statistical procedures were used to evaluate jaw kinematics. The results showed that bolus size has no consistent effect on opening, closing or total cycle duration. Cycle excursions increased significantly with increasing bolus size. With increasing bolus sizes, chewing cycle excursions along the three axes increased 52-115%. The greatest differences between bolus sizes occurred when the jaw was changing direction (i.e. passing from opening to closing and from working to balancing sides). However, the increases were proportionate and the shape of the chewing cycle was maintained. In order to maintain cycle duration while increasing excursive ranges, jaw velocities increased significantly, with the greatest differences occurring at approximately 70% of opening and 30% of closing. We conclude that humans adapt to larger bolus sizes by increasing chewing cycle perimeter and by increasing cycle speed, while maintaining cycle shape and duration.

Masticatory performance: a protocol for standardized production of an artificial test food

A protocol for standardizing the production of an artificial test food was established and its reliability was determined. An artificial test food was selected based on its superior properties compared with natural foods. The primary emphasis during production was the incorporation of all 3 cm of paste-hardener and thoroughly kneading the material for 30 s. The curing process was studied to determine overall setting time. After at least 30 min, the physical properties of the test food were ready to be measured. The overall mean hardness of the test food was 489 +/- 60 load grams. Random error between operators was +/-16 load grams while batches differed by +/-13 load grams and individual tablets differed by +/-15 load grams. This protocol provides a reliable standardized method for future masticatory performance studies.

Anthropometric asymmetry in chronically undernourished children from Southern Mexico

In previous studies, environmental stress has been associated with increased structural asymmetry, indicating differential rates of development on either side of the median plane. To analyse the effect of environmental stress upon anthropometric asymmetry, six bilateral measurements and one derived measurement were compared between chronically mild-to-moderately undernourished school children (7-13 years of age) and a well-nourished control sample (5-35 years of age). The undernourished sample was from a subsistence agricultural community in Southern Mexico. The well-nourished comparison (control) sample was middle class, White children and young adults in Texas. Anthropometric asymmetry of the skeleton was not consistently increased in the undernourished school children compared to the well-nourished controls. Arm and estimated mid-arm muscle circumferences had significantly increased asymmetry, but these differences are likely due more to laterality in function or physical work than to undernutrition. Genetic influences are hypothesized to underlie skeletal asymmetry (i.e. differences in development on either side of the median plane).

The effects of bolus hardness on masticatory kinematics

This study investigated how jaw kinematics, including cycle duration, three-dimensional (3-D) excursive ranges and velocities, and cycle shape, changed with increasing hardness of chewing gum. Twenty-six subjects (13 males and 13 females; mean age 23.6 +/- 2.5 years) with Class I normal occlusion were asked to chew two brands of gum with differing hardness. Jaw motion during chewing was tracked with an Optotrak camera at 100 Hz, and all movements were recorded as pure 3-D mandibular movements relative to Frankfort horizontal. Cycle duration did not change significantly with harder gum, but 3-D excursive ranges and velocities increased, except during the occlusal phases of the chewing. Cycle shape was similar for hard and soft gum, but the overall size of the cycle was larger with hard gum. These results suggest that greater muscular effort when chewing harder gum produces a greater acceleration of the mandible in all phases except when the harder gum slows the mandible during the occlusal phases.

Does malocclusion affect masticatory performance?

This purpose of this study was to evaluate the largely untested assumption that malocclusion negatively affects masticatory performance. A sample of 185 untreated subjects (48% male and 52% female) from 7 to 37 years of age, representing subjects with normal occlusion (n = 38), Class I (n = 56), Class II (n = 45), and Class III (n = 46) malocclusion, were evaluated. Masticatory performance was evaluated objectively using artificial (CutterSil, median particle size and broadness of the distribution) and real foods (number of chews for jerky and almonds), and subjectively using a visual analog scale. The results showed no significant differences in age or the body mass index (Wt/Ht2) between the occlusion groups. Subjects with normal occlusion had significantly smaller particle sizes (P = .001) and broader particle distributions (P < .001) than subjects with malocclusion. Compared with the normal occlusion group, the median particle sizes for the Class I, II, and III malocclusion groups were approximately 9%, 15%, and 34% larger, respectively. There were also significant group differences in their subjective ability to chew fresh carrots or celery (P = .019) and firm meat (P = .003). Class III subjects reported the greatest difficulty, followed by Class II subjects, Class I subjects, and subjects with normal occlusion, respectively. We conclude that malocclusion negatively affects subjects' ability to process and break down foods.

An evaluation of growth and stability in untreated and treated subjects

This retrospective longitudinal study compared skeletal and dental changes in orthodontically treated patients with changes in a comparable untreated group to evaluate the relationship between skeletal changes and mandibular incisor crowding. Cephalograms and models of 44 untreated subjects from the Broadbent-Bolton Growth Study and 43 treated patients were evaluated at "posttreatment" (14.3 +/- 1.5 and 15.2 +/- 1.1 years, respectively) and at "postretention" (23.2 +/- 3.4 and 28.9 +/- 3.6 years, respectively). Cranial base and mandibular superimpositions were used to measure cephalometric changes. Tooth-size-arch-length discrepancy, contact irregularity, and space irregularity were measured. In both groups, growth in the vertical dimension was twice that in the horizontal dimension. The untreated subjects, who were younger, exhibited greater yearly vertical growth increments than did the treated subjects. The treated subjects exhibited greater overjet and overbite increases than did the untreated subjects. Yearly changes in tooth-size-arch-length discrepancy were greater in the untreated than in the treated subjects, but there were no differences in the changes in irregularity between the 2 groups. A multivariate regression model, relating posterior facial height (Ar-Go) increase and lower incisor eruption to change in space irregularity, explained 42% of the variation in the untreated group (r = 0.64; P <.001). A weaker relationship was found in the treated group. Overjet change was negatively correlated with tooth-size-arch-length discrepancy. Changes in lower incisor crowding were related to growth in the vertical dimension and lower incisor eruption in both untreated (r = 0.64) and treated (r = 0.51) subjects.

Mandibular rest position: a reliable position influenced by head support and body posture

This prospective study was designed to establish how the positions of the molars and the condyles are related to incisor position in the mandibular rest position and how their positions are altered by changing head posture. Measurements of the mandibular rest position were taken on 24 men (age range, 23 to 35) with normal Class I occlusion, skeletal patterns, and temporomandibular joint function. The movements of 5 landmarks (lower incisor, and condyles and molars bilaterally) were tracked from maximum intercuspation into 4 independent rest positions (upright supported, upright unsupported, supine supported, and supine unsupported) using an optoelectric (Optotrak; Northern Digital, Waterloo, Ontario, Canada) computer system. The positions were based on minimal electromyographic and verbal instructions to swallow, lick the lips, and say "Mississippi." The results showed significant (P <.01) movements of the incisors, the molars, and the condyles into each of the 4 rest positions. Movements of the molars and the condyles into the supported upright posture and the unsupported upright posture differed slightly but significantly because of greater movement into the supported posture. Patterns of mandibular movement were entirely different between the upright and the supine rest positions; the mandible rotated anteriorly in the supine position and posteriorly in the upright position. We concluded that movement into the mandibular rest position from the intercuspal position is not a simple opening rotation of the mandible, and that the pattern of movement is influenced by head support and body postures.

Morphological and positional asymmetries of young children with functional unilateral posterior crossbite

This prospective clinical study evaluated the morphological and positional mandibular asymmetry of young patients with functional unilateral posterior crossbite. The sample included 9 girls and 6 boys (8.8 +/- 1.0 years of age), evaluated at the initiation of treatment and approximately 6 months after the retention phase (1.1 +/- 0.2 years after initiation of treatment). Each patient had a complete unilateral posterior crossbite involving 3 or more posterior teeth, a functional shift from centric relation-intercuspal position, and no signs or symptoms of temporomandibular disorder. A bonded palatal expansion appliance was used to rapidly expand the maxilla (1 month) and retain the treatment changes (6 months). Zonograms were used to assess articular joint spaces, and submental vertex radiographs were used to assess morphological and positional asymmetry. The results showed that the mandible was significantly longer on the noncrossbite side than it was on the crossbite side. The asymmetry was most evident for the ramus and involved both the condylar and the coronoid processes. The posterior and superior joint spaces were larger on the noncrossbite side than they were on the crossbite side. After treatment and retention, the mandible showed no significant morphological asymmetries. Mandibular growth was greater on the crossbite side than it was on the noncrossbite side, and the mandible had been repositioned; the crossbite side had rotated forward and medially toward the noncrossbite side. We concluded that unilateral posterior crossbites produce morphological and positional asymmetries of the mandible in young children, and that these asymmetries can be largely eliminated with early expansion therapy.

Midsagittal facial tissue thicknesses of children and adolescents from the Montreal growth study

Knowledge of changes in soft tissue depths during growth and development is important in applied contexts of forensics and dentistry as well as in growth research. In forensics, applications include facial reproductions, video superimpositions, and child aging/progressions. Garlie and Saunders (1) recently published radiographic data from the Burlington Canadian growth study; here, we present data from a mixed longitudinal sample of French-Canadian children and adolescents. Females (N = 159) range in age from 6 to 18 years: males (N = 129), from 6 to 19 years. Cephalometric measurements include nine soft tissue thicknesses, two hard tissue distances (sella-nasion and nasion-menton), and three measures of nasal projection. Several tissue thicknesses are moderately correlated with one another. The majority of thicknesses show significant sex differences by the time of adolescence; nasion and upper labial thicknesses are significantly different by sex at all ages from 6 to 18 years, as are the two hard tissue distances. However, thickness at nasion, as well as at glabella, changes little over time. Thickness at pogonion is variable and differs most between males and females at age 16; the length of the anterior inferior portion of the nose is significantly different between the ages of 6 and 12. Measurements display small and slow changes during development. The greatest average change per year (c. 2 mm/yr) is for a hard tissue measure, nasion-menton. The nasal and mid-philtrum regions have greater age changes than do other soft tissue variables. Much of the variation remains unexplained by changes with age or differences between sexes.

A new method of evaluating posterior occlusion and its relation to posttreatment occlusal changes

The purpose of this study was to assess the relationship between posterior occlusion and posttreatment changes in other occlusal variables. Pretreatment (T1), posttreatment (T2), and postretention (T3) records were obtained for 49 Class I (n = 23) and Class II (n = 26) extraction cases. Overbite, overjet, mandibular incisor irregularity, right and left molar deviations, midline deviation, and mandibular arch length were measured, and occlusal registrations were made of each set of dental casts. The proximity of posterior occlusal surfaces was measured as the contact or near-contact areas at or below 300 microm thickness, based on the optical densities of scanned images of the posterior occlusal registrations. The treatment changes for overbite, overjet, right and left molar deviation, and arch length were significantly greater in the Class II group, and the reductions in incisor irregularity were greater in the Class I group. No other class differences were found. Overbite, overjet, and incisor irregularity increased after treatment, and arch length continued to decrease, with no significant class differences. Contact and near-contact areas at or below 300 microm constituted 7% of the functional occlusal table for both classes at the end of treatment, having decreased significantly in both groups (21% in Class I and 29% in Class II) during treatment. Because contact and near-contact areas increased in some patients and decreased in others, there were no significant posttreatment changes. Negative correlations were found between contact and near-contact areas at T2 and changes in overjet from T2 to T3, and between contact and near-contact areas at T3 and changes in overbite from T2 to T3. No relationships were found between posterior contact and near-contact area and incisor irregularity. We concluded that (1) the area of actual and near contacts at or below 300 microm decreased significantly with treatment, indicating that, despite excellent treatment results by conventional standards, the proximity of posterior occlusal surfaces lessened; (2) the proximity of the posterior occlusal surfaces should not be expected to increase posttreatment; (3) posttreatment contact and near-contact areas may be factors in overbite and overjet stability; and (4) posttreatment contact and near-contact areas are not related to incisor irregularity.

Changes in the masticatory cycle following treatment of posterior unilateral crossbite in children

In a previous study, we established that young children with unilateral posterior crossbite have a longer mandibular ramus and more superiorly and posteriorly positioned condyles on the crossbite side. In this study, we evaluated chewing cycle shape and duration in 14 of the patients before treatment, and we looked for changes in cycle shape and duration 6 months after treatment with rapid palatal expansion. Mandibular kinematics was recorded while chewing gum using an optoelectric recording system at 100 Hz. Subjects were asked to chew normally for 20 cycles, chew on the crossbite side only for 20 cycles, and chew on the noncrossbite side only for 20 cycles. A special computer program selected the 10 most representative cycles from each series and computed an average duration and an average maximum excursion along 3 orthogonal axes. Multilevel linear models were used to generate an 8th-order polynomial describing average cycle shape and to test for statistically significant differences in shape between the patients and the controls and between the patients before and after treatment. Before treatment, the patients chewed more slowly than did the controls. Treatment shortened their cycle duration to equal control values. Before treatment, the patients also had larger maximum excursions than did the controls and exhibited a reverse-sequence cycle shape when chewing on the crossbite side. Treatment did not alter the patients' abnormal cycle shape. These results suggest that some features of the masticatory kinematics respond to orthodontic treatment alone, but others do not.

The effects of isometric exercise on maximum voluntary bite forces and jaw muscle strength and endurance

The effects of training and exercise on the strength and endurance of limb muscles has been investigated extensively, but the response of the jaw muscles to exercise remains poorly known. The purpose of this study was to determine whether short-term isometric training increases strength and endurance of the superficial masseter and anterior temporalis muscles. Maximum and submaximum voluntary bite forces and corresponding electromyographic (EMG) activity were measured in 28 young adults, randomly divided into exercise and non-exercise (control) groups. Subjects in the exercise group performed isometric clenches against a soft maxillary splint for five 1-min sessions per day over a 6-week period. After exercise, subjects increased their maximum bite forces by 37%, but control subjects' bite forces also increased by 25%. After exercise, EMG levels per unit of bite force generally decreased, but similar decreases were also seen in the non-exercised controls. Masseter muscle activity levels during standardized 10-kg bites decreased after 6 weeks of exercise. Fatigue resistance increased significantly with exercise but did not differ significantly from control values after 6 weeks of exercise. The results of this study indicate that increases in maximum bite force can be easily produced with training, but that actual strengthening of the jaw muscles is more difficult to achieve.

Sex differences in mandibular movements during opening and closing

This study evaluated the sex differences in maximum 3-dimensional opening and closing movements. The sample included 29 men (ages, 23-39 years) and 27 women (ages, 23-35 years), who were selected for normal Class I occlusion, temporomandibular function, and skeletal patterns. Condylar (hinge axis) translation and mandibular incisor movements, were recorded with an optoelectric jaw-tracking system; each participant performed 4 maximum opening/closing cycles. The results showed significant (P <.05) sex differences for incisor opening and closing movements, with most of the differences in the vertical component. Male incisor straight-line distances and curvilinear pathways averaged 52.1 mm and 54.8 mm, respectively. Female straight-line distances and curvilinear pathways averaged 46.0 mm and 48.1 mm, respectively. There were significant (P <.05) sex differences for condylar translation, with most of the differences in the anteroposterior component. Male condyles translated 15.4 to 17.6 mm (straight-line distances) and 20.5 to 20.7 mm (curvilinear pathways); female condyles translated 12.4 to 12.7 mm (straight-line distances) and 16.2 to 17.9 mm (curvilinear pathways). Mandibular length accounted for some of the sex difference in interincisal opening and for most of the sex differences in condylar translation. Closing movements showed the same pattern of sex differences as opening movements. Mandibular opening rotation was approximately 4 degrees larger in men than in women. The shapes of the condylar opening and closing pathways also differed significantly between men and women. For both sexes, condylar translation did not correlate with incisor opening or closing movements. It was concluded that (1) significant sex differences exist in incisor opening movements that are independent of mandibular size, (2) sex differences in condylar translation are dependent on mandibular size, (3) incisor opening movements should not be used as an indicator of condylar translation, and (4) sex differences in the shapes of the condylar pathways indicate sex differences in articular eminence morphologic features.

Predicting upper lip response to 4-piece maxillary LeFort I osteotomy

The purpose of this retrospective study was to understand and predict the multidimensional changes in upper lip morphologic features after segmental (4-piece) maxillary Le Fort I advancement/impaction with VY closure and alar base cinch sutures. The study evaluated longitudinal lateral cephalograms of 57 patients (42 women, 15 men) 27.5 +/- 11.2 years of age before surgery. Lateral cephalograms with teeth in occlusion and lips in repose were taken 2 weeks before surgery and at least 6 months after the operation. Mean postsurgical duration was 15.5 months. The upper lip predictably moved anteriorly in a graduated fashion, from 50% (subnasale) to 90% (labrale superius) the amount of the underlying osseous anterior movement, and showed a slight lengthening (0.73 +/- 1.9 mm) from subnasale to upper lip stomion. The upper lip surface contour was also straightened as a result of the surgical movement. Multiple regression models showed that the anterior changes in the landmarks prosthion and facial surface of the upper incisor were the most important variables in predicting upper lip response. The prediction equations for horizontal movements explained 86% to 94% of the variation, with errors of the estimates that range between 1.27 mm and 1.65 mm. The models, when applied to an independent validation sample of 14 subjects, explained between 86% and 94% of the total variation. The conclusion is that upper lip response after 4-piece Le Fort I advancement/impaction (VY closure and alar base cinch suture) can be accurately predicted.

Positional changes and stability of bone segments during simultaneous bilateral mandibular lengthening and widening by distraction

The purpose of this study was to analyse the skeletal changes and stability of the distracted segments during and after simultaneous widening and bilateral lengthening of the mandible in baboons with a miniaturized intraoral bone-borne osteodistractor. Distraction appliances were activated 5 days after vertical posterior body and midsymphyseal osteotomies at a rate of 0.9 mm/day for 10 days. The appliances were then stabilized for a period of 8 weeks, after which the animals were killed. The distraction gaps and gingival tissues were studied clinically and on standardized radiographs. The proportional movement of the distracted segments that we found supports the clinical use of the miniaturized intraoral bone-borne distraction appliance to widen and lengthen the mandible selectively. It also supports the concept of positioning the mandibular osteodistractors parallel to the common vector of distraction, which should parallel the corrected maxillary occlusal plane.

Postsurgical growth changes in the mandible of adolescents with vertical maxillary excess growth pattern

This case-control study investigates the effects of superior maxillary repositioning by LeFort I osteotomy on adolescent mandibular growth. A total of 15 growing patients (average age, 12.8 years) with vertical maxillary excess who had undergone maxillary surgery were compared with matched untreated control subjects. Lateral cephalograms were evaluated and superimposed to describe the presurgical (1.6 years), surgical, and postsurgical (4.0 years) changes. During the presurgical period, comparisons of traditional measures and mandibular modeling changes showed no significant differences between the 2 groups. During surgery, the maxilla was impacted approximately 3 mm anteriorly and 1 mm posteriorly, which caused a 3.2 degrees autorotation of the mandible. During the postsurgical period, there was no change in the vertical growth pattern of the surgical patients, with the vertical facial heights increasing the same as the control subjects and the mandible rotating backwards. Although there was no inhibition of mandibular growth in the patients postsurgically, there was a decrease in horizontal maxillary growth compared with control subjects. There were clear postsurgical changes in the mandibular modeling and condylar growth, which were indicative of adaptive compensations for surgical mandibular repositioning and autorotation. It is concluded that early maxillary impaction does not normalize or inhibit the vertical maxillary excess growth pattern; mandibular modeling and condylar growth undergo adaptive changes in response to repositioning.

Incisor and mandibular condylar movements of young adult females during maximum protrusion and lateratrusion of the jaw

This study evaluated the correlations between condylar translation and incisor movements during maximum protrusion and lateratrusion. The sample was 27 adult females (23--35 years old), selected for normal temporomandibular function, occlusion, and skeletal patterns. Condylar and mandibular central incisor movements [linear distances (LD) and curvilinear pathways (CP)] were recorded in three dimensions for 20 s with an optoelectric (Optotrak) jaw-tracking system while each participant performed multiple maximum protrusive and lateratrusive cycles. Masticatory analysis and multilevel statistical programs computed the three-dimensional movements of the incisors and condylar hinge axis during protrusion and lateratrusion. CP of the incisor point averaged 12.0 mm (9.3 mm LD) during protrusion, 13.0 mm (11.5 mm LD) during right excursion and 12.3 mm (11.0 mm LD) during left excursion. CP of the condyles averaged 11.9--12.9 (9.2--9.5 LD) mm during protrusion. During lateratrusion the contralateral condyles moved anteroinferiorly 11.6--14.1 mm (9.5--10.2 mm LD); the ipsilateral condyles moved posterolaterally 5.8-6.8 mm (2.3--2.5 mm LD). The left condyles demonstrated more movement than the right condyles during protrusion and than the contralateral condyles during laterotrusion. Relative variation, as measured by the coefficient of variation, was greater for the movements of the ipsilateral than contralateral condyles. Incisor movements were only moderately related to condylar movements between individuals and between replicates; LDs showed stronger correlations than CPs; and correlations were stronger for lateratrusion than protrusion. While incisor and condylar movements were not affected by repeated protrusion, incisor CP (approx. 0.2 mm/cycle) and LD (approx. 0.1 mm/cycle) increased significantly with repeated excursive movements to the left and right. It was concluded that (1) incisor protrusion and lateratrusion provide moderately reliable measures of condylar translation; (2) the linear distances that the incisors move during lateratrusion provide the best measure of contralateral condylar translation; and (3) condylar movements are not affected by repeated protrusion or lateratrusion.

Long-term skeletal and dental effects of mandibular symphyseal distraction osteogenesis

The purpose of this study was to evaluate the effects of mandibular symphyseal distraction osteogenesis using a tooth-borne expansion device. The sample included 20 Hispanic nonsyndromic patients (11 males and 9 females) between 13.5 years and 37.3 years of age. Predistraction (1.5 months before surgery), postdistraction (1 month after surgery), and long-term follow-up (1.3 year after surgery) records included posteroanterior, lateral, and panoramic radiographs and models. Postdistraction radiographic evaluation showed that symphyseal distraction osteogenesis produced insignificant increases in the bicondylar, bigonion, and biantegonion widths; intermolar and, especially, intercanine widths increased significantly and a distraction gap was observed in the symphyseal region. Follow-up model analysis showed the largest width increases between the first molars and second premolars and the smallest width increases between canines and first premolars. The difference between the postdistraction and long-term follow-up width changes was explained by the postdistraction orthodontic effect, which modified the shape of the dental arch. A disproportionate pattern of distraction, characterized by significantly greater dental than skeletal widening, was observed in the second molar and antegonion region. Distraction osteogenesis without presurgical orthodontic treatment produced significant proclination of the mandibular incisors; no proclination was observed in cases with predistraction orthodontic treatment. Dental crowding was resolved by the movement of teeth into the distraction regenerate and concomitant orthodontic treatment. Follow-up radiographs showed transverse skeletal stability of the distraction procedure. We conclude that mandibular symphyseal distraction osteogenesis increased mandibular arch width and partially corrected dental crowding, with a potential for disproportionate distraction patterns and proclination of the mandibular incisors.

Early treatment of vertical skeletal dysplasia: the hyperdivergent phenotype

This cephalometric study evaluated an early nonextraction treatment approach for patients with severe vertical skeletal dysplasia and maxillary transverse constriction. Thirty-eight patients, 8.2 years (+/- 1.2 years) of age, were treated for 1.3 years (+/- 0.3 years) with lip seal exercises, a bonded palatal expander appliance, and a banded lower Crozat/lip bumper. The bonded palatal expander functioned as a posterior bite-block and was fixed in place throughout treatment. Patients with poor masticatory muscle force (79%) wore a high-pull chincup 12 to 14 hours per day. A control group was matched for age, sex, and mandibular plane angle. Treatment changes for chincup and other patients were not significantly different. Overall, treatment significantly enhanced condylar growth, altered it to a more anterosuperior direction, and produced "true" forward mandibular rotation 2.7 times greater than control values. Posterior facial height increased significantly more in patients than in controls, and the maxillary molars showed relative intrusion. In treated patients, articular angle increased, gonial angle decreased, and the chin moved anteriorly twice as much as in controls. Treatment also led to increased overbite and decreased overjet. Maxillary and mandibular expansion did not cause the mandibular plane angle to increase. The 16 patients with openbite malocclusions exhibited a 2.7 mm increase in overbite and inhibition of growth in anterior lower facial height. The aggregate of individual changes demonstrates a net improvement, indicating this treatment approach may be suited for hyperdivergent patients with skeletal discrepancies in all 3 planes of space.

Quantification of human chewing-cycle kinematics

This study introduces new methods of quantifying and evaluating the human chewing cycle. These methods were validated on a sample of 26 young adults (11 women and 15 men) between 20-35 years of age. Movements of the mandibular central incisors were recorded (100 Hz) using an optoelectric computer system while the participants chewed gum. A subsample of 10 cycles was automatically selected, based on multiple objective criteria to ensure representative cycles for each individual. Once representative cycles had been identified, multilevel statistical models were used to evaluate and describe the sample's kinematic patterns. The multilevel procedures allow for missing observations, they do not assume equal intervals, and variation can be partitioned hierarchically. Two-level models showed significantly shorter cycle duration for males (835 msec) than females (973 msec). Inferior-superior (IS) cycle range was 2.6 mm larger and maximum IS velocity was 19.6 mm/sec faster in males than females. There were no significant differences in medial-lateral (ML) and anteroposterior (AP) excursive ranges or velocities. With the exception of cycle duration and ML ranges of motion, random variation was three to five times larger between individuals than between cycles. The three-level models showed that eighth-order polynomials were necessary to describe IS, AP, and ML chewing movements of the entire cycle. The models identified highly significant sex differences in cycle kinematics (excursions, velocities, accelerations, etc.) for each aspect of movement (AP, IS, and ML). It is concluded that this approach provides several important advantages over existing methods, including (a) its objectivity, (b) a more complete description of kinematic patterns, (c) a hierarchical description of variation, and (d) its ability to test hypotheses statistically.

Morphologic and biomechanical correlates with maximum bite forces in orthognathic surgery patients

PURPOSE

The purpose of this study was to determine which factors of craniofacial morphology best predict maximum bite forces and jaw muscle strength (based on [electromyogram] EMG/force slopes) in patients selected for various orthognathic surgical procedures. These factors were then compared for their ability to separate orthognathic surgery patients by their clinical diagnosis.

PATIENTS AND METHODS

Standard lateral cephalograms were taken of 121 orthognathic surgery patients (before treatment) and 80 control subjects to establish multivariate sagittal and biomechanical factors of craniofacial form. Maximum and submaximal bite forces were recorded at 8 tooth positions for each subject. EMG activity was recorded for 3 pairs of muscles (anterior temporalis, posterior temporalis, and superficial masseter) during the isometric bites. The EMG and bite force measurements were used to calculate EMG/force slopes as a measure of jaw muscle strength. The study looked for significant correlations between the morphologic factors and maximum bite force or jaw muscle strength.

RESULTS

Factor analysis determined 12 sagittal and 6 biomechanical factors. However, only 3 of the sagittal and 4 of the biomechanical factors were significantly correlated with maximum bite force or jaw muscle strength. Factors reflecting jaw size were correlated with maximum bite forces and jaw muscle strength but generally did not separate patient groups. The factor most strongly correlated with maximum bite forces separated patients by their relative difference between anterior and posterior facial height. The factor for anteroposterior maxillomandibular discrepancies was not correlated with maximum bite force or jaw muscle strength.

CONCLUSIONS

Many cephalometric measurements used to diagnose craniofacial deformities and to assign patients to particular orthognathic surgical procedures are not correlated with maximum bite forces or jaw muscle strength. Only measurements reflecting relative differences between anterior and posterior facial height are both strongly correlated with maximum bite force and reflect assignment of surgical procedures.

Vertical components of overbite change: a mathematical model

The purpose of this study was to better understand the multidimensional nature of overbite changes that occur during adolescence. The study used longitudinal cephalograms of 181 untreated children (102 males, 79 females) taken at ages 10 and 15. Four major components that directly affect overbite were measured: (1) maxillary vertical displacement, (2) mandibular vertical displacement, (3) upper incisor vertical change within the bone, (4) lower incisor vertical change within the bone. Cranial base, maxillary, and mandibular superimpositions were performed for each subject to assess the vertical changes that occurred in these 4 components and to assess overbite. A multiple regression analysis was used to develop a mathematical model describing the relationships of these components to changes in overbite. The model was validated with an independent subsample and a comparison of subjects whose overbites decreased and those whose overbites increased. The results showed that overbite changed minimally (0.2 mm) over the 5-year period; variation ranged from a 2.4 mm decrease to a 5.6 mm increase. The regression model indicated that the mandibular skeletal changes were twice as important as the mandibular dental changes and about 2.5 times as important as the maxillary changes in effecting overbite change. Within the mandibular skeletal component, vertical growth was more important than mandibular rotation in determining overbite change. The model demonstrated that a multivariate approach is necessary to understand overbite changes. More effective orthodontic treatment might be achieved by focusing on the primary components effecting overbite change, especially those with the greatest potential for therapeutic modification.

Associations between incisor and mandibular condylar movements during maximum mouth opening in humans

This study evaluated the common clinical assumption that condylar translation and mouth opening at the incisor are closely related. The sample studied comprised 27 adult females (23-35 years), selected for normal temporomandibular function, occlusion, and skeletal patterns. Condylar and mandibular central incisor movements (straight-line distances and curvilinear pathways) were recorded in three dimensions (3D) for 20 s with an optoelectric (Optotrak(R)) jaw-tracking system while each participant performed multiple maximum opening cycles. Masticatory analysis and multilevel statistical programs computed the 3D movements of the incisors and condylar hinge axis during opening and closing. The incisor point moved an average straight-line distance of 46.6 mm during opening and 45.9 mm during closing; the lengths of the opening and closing curvilinear pathways were 48.6 and 47.7 mm, respectively. The condyles moved average straight-line distances of 11.9 and 12.2 mm during opening and closing, respectively. The condyles' curvilinear pathways during opening and closing were 14 and 14.6 mm, respectively. Ranges of condylar movement varied widely between individuals. The straight-line distances and curvilinear pathways were highly correlated for the incisors (R=0.98) and the condyles (R=0.98). Neither the straight-line distances nor curvilinear pathways of the incisors were correlated with those of the condyles. Incisor straight-line distances and curvilinear pathways were moderately correlated with mandibular rotation (R(between subjects)=0.82 and R(between repeats)=0.88). During repeated openings, both condylar and incisor excursions increased, but during repeated closings only incisor excursions increased. It is concluded that (1) maximum incisor opening does not provide reliable information about condylar translation and its use as a diagnostic indicator of condylar movement should be limited, (2) healthy individuals may perform normal opening with highly variable amounts of condylar translation, (3) the straight-line distances of the incisor and condyles provide adequate information about the length of the curvilinear pathway, and (4) variation in maximum incisor opening is largely explained by variation in the amount of mandibular rotation.

The demographic outlook for orthodontists in Texas at the start of the next millennium

Like all health care professionals, orthodontists are concerned about the need and demand for their services. Orthodontists should experience an increase in demand for their services as a result of an increasing population and an aging orthodontist population. How many additional orthodontic graduates do we need per year in Texas? Based on many factors, Texas dental schools could graduate additional students per year to be consistent with those factors. In conclusion, it appears that Texas can easily support three graduate orthodontic residency programs. As we enter the next millennium, the future of orthodontics has never looked better.

Interarch tooth size relationships of 3 populations: "does Bolton's analysis apply?"

This study evaluates whether Bolton's interarch ratios extend across populations and genders. The data were derived from systematically collected preorthodontic casts of 180 patients, including 30 males and 30 females from each of 3 populations (black, Hispanic, and white). Forty-eight mesiodistal contact points were digitized on each model, and the lengths of the anterior, posterior, and overall arch segments were calculated. The results showed significant (P <.05) ethnic group differences in all 6 arch segment lengths and in all 3 interarch ratios. Whites displayed the lowest overall ratio (92.3%), followed by Hispanics (93.1%), and blacks (93.4%). The group differences were due primarily to the relationships between the posterior segments. The arch segments of males were significantly larger than females; the overall and posterior ratios were also significantly larger in males than in females. Multiple regression analyses showed that individual differences in the overall ratio were most closely associated with the size of the lower second premolar, followed by the upper lateral incisors, upper second premolars, and the lower central incisors. In combination, these 4 teeth explained approximately 50% of the variation in the overall ratio between subjects. We conclude that interarch tooth size relationships are population and gender specific. Bolton ratios apply to white females only; the ratios should not be indiscriminately applied to white males, blacks, or Hispanics.

Maxillary and mandibular width changes studied using metallic implants

The purpose of this implant study was to evaluate the transverse stability of the basal maxillary and mandibular structures. The sample included 25 subjects between 12 and 18 years of age who were followed for approximately 2.6 years. Metallic implants were placed bilaterally into the maxillary and mandibular corpora before treatment. Once implant stability had been confirmed, treatment (4 first premolar extractions followed by fixed appliance therapy) was initiated. Changes in the transverse maxillary and mandibular implants were evaluated cephalometrically and two groups (GROW+ and GROW++; selection based on growth changes in facial height and mandibular length) were compared. The GROW++ group showed significant width increases of the posterior maxillary implants (P <.001) and the mandibular implants (P =.009); there was no significant change for the anterior maxillary implants. The GROW+ group showed no significant width changes between the maxillary and mandibular implants. We conclude that (1) there are significant width increases during late adolescence of the basal mandibular and maxillary skeletal structures and (2) the width changes are related with growth potential.

A cephalometric and tomographic evaluation of Herbst treatment in the mixed dentition

This study describes combined treatment and posttreatment effects for patients treated with the Herbst appliance in the mixed dentition followed by retention with a prefabricated positioner. The sample included 24 female and 16 male patients with Class II malocclusions. Posttreatment lateral cephalograms were taken an average of 17 months after Herbst removal, when the patients presented for phase II comprehensive orthodontics. The cumulative treatment and retention effects were compared with a sample of untreated Class II controls matched for age, sex, and mandibular plane angle. The overjet and molar relationship were corrected by 3. 4 and 3.3 mm, respectively. A headgear effect of Herbst therapy was observed, as anterior maxillary displacement was reduced by 1.2 mm. Condylar growth was redirected to produce 2.0 mm greater posterior growth in the treatment group. These effects produced significantly greater decreases in SNA (0.8 degrees ) and ANB (1.4 degrees ), and a tendency toward an increase in SNB (0.5 degrees ) Mandibular orthopedic effects resulted in an increase in anterior facial height (1.6 mm) and inferior displacement of the chin. Minimal changes in the displacement of condylion in relation to stable cranial base structures suggest that glenoid fossa displacement does not contribute in a clinically significant way to Class II correction. Pretreatment, immediate posttreatment, and postretention corrected temporomandibular joint tomograms demonstrated a tendency for the condyle to be slightly forward (0.2 mm) at the end of treatment and then to fall back after treatment. Statistically significant joint space changes were limited to the posttreatment period. We conclude that Herbst treatment in the mixed dentition, in combination with retention, produces significant long-term improvements in dental and skeletal relationships as a result of dentoalveolar changes and orthopedic effects in both jaws.

Morphologic and biomechanical determinants in the selection of orthognathic surgery procedures

PURPOSE

This study examined which features of craniofacial morphology are most important in the selection of an orthognathic surgery procedure by 1) producing a small number of composite variables representing multiple measures of craniofacial morphology and craniofacial biomechanics, and 2) looking for correlations between these composite variables and selected orthognathic surgery procedures.

PATIENTS AND METHODS

Lateral cephalograms of 201 adult subjects (71 men and 130 women) were used to generate 47 standard cephalometric measures and 30 biomechanical measures. Of the 201 subjects, 121 were scheduled for orthognathic surgery to treat a variety of dentofacial deformities. Factor analysis reduced the number of variables by identifying underlying latent composite variables, thereby strengthening correlations among the reduced number. Weightings for each factor were than compared among the orthognathic surgery procedures, indicating which factors may have influenced the selection of that procedure.

RESULTS

Factor analysis determined 12 factors (explaining 93% of the variance) for the morphologic measurements and 6 factors (explaining 90% of the variance) for the biomechanical measurements. However, only 6 of the morphology factors (accounting for 53% of the morphologic variance) and 5 of the biomechanics factors (accounting for 69% of the biomechanics variance) significantly separated any of the 10 treatment groups. The separating morphology factors were generally related to relative maxillary and mandibular position or dental relationships. Of these, relative maxilla/mandible anteroposterior position was most important for defining the surgery groups. The biomechanics of the lateral pterygoid muscles did not contribute to separation of the groups.

CONCLUSIONS

Only a subset of available morphologic information was used to select surgical treatment. The most important factors in treatment selection were difference in maxillary and mandibular lengths and differences in anterior and posterior facial height. Standard morphology factors accounting for 40% of the total morphologic variance apparently played no role in selection of treatment. Several biomechanical factors differentiated treatment groups as well as or better than some standard morphology factors.

Masticatory muscle function in patients with spinal muscular atrophy

The purpose of this study was to determine whether spinal muscular atrophy affects masticatory muscle strength and mandibular range of motion. A sample of 15 subjects with spinal muscular atrophy was compared to a sample of age-matched and sex-matched controls. Maximum bite force, masticatory muscle electromyography activity, mandibular ranges of motion and masticatory muscle endurance were evaluated. Results showed that maximum bite forces were one-half as great for the sample with spinal muscular atrophy than for the controls, even though their EMG activity was not significantly different. Slopes of the relationship between electromyography activity and bite force were two to four times steeper for patients with spinal muscular atrophy than controls. Maximum opening and protrusion were reduced to approximately one-half control values. Fatigue times of patients with spinal muscular atrophy were reduced by 30% (17.9 seconds versus 11.1 seconds). We conclude that the masticatory muscles of patients with spinal muscular atrophy are weakened, that their muscles are less efficient, and that they fatigue more quickly than controls. In addition, mandibular movements of these patients take place over a more limited range than unaffected controls.

Incremental growth charts for condylar growth between 6 and 16 years of age

This study provides sex specific reference data for the incremental growth of the mandibular condyle. The results pertain to a mixed-longitudinal sample of 113 males and 108 females followed annually between 6 and 16 years of age (total of 1647 observations). Growth of condylion was evaluated using naturally stable mandibular reference structures. The mean growth curves were estimated by multilevel models using iterative least squares procedures; between subject variation was estimated based on the sample's percentile distributions. Mean yearly velocities of condylar growth for males ranged between 2.1 and 3.1 mm/year. Growth rates decreased during childhood, increased during adolescence, and attained a maximum of 3.1 mm/year at approximately 14.3 years of age. Females showed a more constant rate of condylar growth during childhood (2.0-2.7 mm/year), a smaller adolescent peak (2.3 mm/year) at approximately 12.2 years and rapid deceleration after the peak. These reference data offer orthodontists an objective means of evaluating growth potential and treatment outcome in individual patients. Charts are provided for evaluating condylar growth of individual patients.

Maxillary protraction: treatment and posttreatment effects

This study evaluated the treatment response and posttreatment follow-up of children with Class III malocclusions treated with palatal expansion and reverse-pull face mask to the maxilla. The sample included 22 white children, 9 boys and 13 girls. Treatment began at a mean age of 9.8 years (range 5.6 to 13.3 years) and lasted 0.7 years (range 0.3 to 1.3 years). With a protraction force of 600 to 800 gm, the patients were treated until a 2 mm positive overjet had been attained. Radiographs were taken before treatment (T1), immediately after face mask treatment (T2), and 1.4 years after treatment (T3). An age and sex matched sample of untreated white schoolchildren served as normal controls. The results showed that the anterior maxilla was protracted forward 1.6 mm per year more than normal. The posterior maxilla dropped inferiorly more than the anterior maxilla. The mandible was rotated downward and backward, while the lower incisors were uprighted. The effects on the mandible were attributed to a significant chincup effect exerted by the face mask. After treatment, the maxilla relapsed relatively backward in the anterior and upward in the posterior, negating some of the treatment results. The mandible resumed a normal growth direction, and the lower incisors flared more than normal.

Childhood and adolescent changes of skeletal relationships

This paper describes the development of anteroposterior (AP) and vertical (VER) skeletal relationships. A mixed-longitudinal sample of 49 females and 50 males was followed during childhood and adolescence. Childhood growth changes were assessed from 6 to 10 years for females and 8 to 12 years for males. Adolescent changes were evaluated from 9 to 13 years for females and 11 to 15 years for males. Anteroposterior relationships were described by the horizontal distance between ANS and Pg. Vertical relationships were described by the vertical distance between Pg and Go. Subsamples were defined based on overall changes (AP and VER) that were either greater than or less than average. The results showed that AP and VER relationships were not stable during growth. AP relationships changed over time due to differential growth movements of the mandible (as opposed to the maxilla). There was greater potential for horizontal discrepancies to decrease during childhood than during adolescence. The potential for AP discrepancies to increase was greater during adolescence. The VER relationships increased in the majority of subjects. The subsample whose vertical discrepancies increased most showed less inferior movement of gonion and more inferior movement of pogonion. Inferior movements of Pg and Go were greater during adolescence than childhood.

Condylar growth and glenoid fossa displacement during childhood and adolescence

This study evaluated age and gender differences in the growth of the mandibular condyle and displacement of the glenoid fossa. The results pertain to longitudinal samples of untreated French Canadians, including 118 children and 155 adolescents. Childhood and adolescent growth were described for girls aged between 6 and 10 years and 9 and 13 years, respectively, and for boys aged between 8 and 12 years and 11 and 15 years, respectively. Four-year growth changes of the cephalometric landmarks condylion and articulare were evaluated. Mandibular and cranial/cranial base structural superimpositions were used to assess condylar growth and fossa displacement, respectively. The results showed that the condyle grew between 0.8 and 1.3 mm posteriorly and between 9.0 and 10.7 mm superiorly over the 4-year periods; the articulare landmark showed significantly more posterior and less superior growth than the condylion landmark. Relative to the cranial base reference structures, the fossa was displaced between 1.8 and 2.1 mm posteriorly and between 1.0 and 1.8 mm inferiorly. The articulare showed significantly more inferior movement than the condylion. Boys showed significantly greater superior condylar growth during adolescence than during childhood. The glenoid fossa demonstrated greater posterior and inferior displacement during adolescence than during childhood.

Enamel thickness of the posterior dentition: its implications for nonextraction treatment

This study describes mesial and distal enamel thickness of the permanent posterior mandibular dentition. The sample comprised 98 Caucasian adults (59 males, 39 females) 20 to 35 years old. Bitewing radiographs of the right permanent mandibular premolars and first and second molars were illuminated and transferred to a computer at a fixed magnification via a video camera. Enamel and dentin thicknesses were identified and digitized on the plane representing the maximum mesiodistal diameter of each tooth. The results showed that there were no significant sex differences in either mesial or distal enamel thickness. Enamel on the second molars was significantly thicker (0.3 to 0.4 mm) than enamel on the premolars. Distal enamel was significantly thicker than mesial enamel. There was approximately 10 mm of total enamel on the four teeth combined. Assuming 50% enamel reduction, the premolars and molars should provide 9.8 mm of additional space for realignment of mandibular teeth.

Normal masticatory function of girls and young women: mandibular masticatory movements

Mandibular masticatory movements were evaluated in 10 young adult women and 12 young girls. All subjects had normal occlusion with minimal overjet. Masticatory movements of the incisors were recorded in three dimensions with an Optotrak® camera system while subjects chewed gum in a habitual manner for 20 seconds. A masticatory analysis program divided each masticatory cycle into four phases and averaged the duration, excursions, and velocities of all cycles for each subject. Duration of the total cycle was longer in women because they had longer slow opening and slow closing phases than girls. Women had a significantly larger vertical component of opening during slow opening and the power stroke than girls. Women also had a significantly larger posterior component of opening during slow opening and the power stroke than did girls. At maximum opening, women also tended to have the incisors in a more posterior position. There were no differences between the groups for the amount of maximum lateral excursion during chewing. Vertical velocity during fast opening and fast closing was slower for women, but there were no age-related differences during the slow open and slow close phases. Am. J. Human Biol. 10:53-62, 1998. © 1998 Wiley-Liss, Inc.

The effects of bolus size and chewing rate on masticatory performance with artificial test foods

To better understand 'within subject' variability in masticatory performance of artificial food, this study evaluates the effects of bolus size and chewing rate. Twenty young adult male subjects each participated in two experiments evaluating their ability to process an artificial food (CutterSil). Based on the frequency distributions for the weights of the chewed particles, median particle size and broadness of the particle distribution were estimated. Controlling for the number of chews, the effect of (1) bolus size was evaluated by having each subject chew one whole tablet, four quarters, three quarters or two quarters; (2). chewing rate was evaluated by having the subjects chew first habitually, then at slow (40 cycles/min) and fast (100 cycles/min) rates. The results showed that median particle sizes decreased and the distribution of particles widened with decreasing bolus size. The slow chewing rate produced the smallest particles with the widest distributions, followed by the habitual and fast rates, respectively. The study has shown that bolus size and chewing rate are important source of variation which must be considered in studies of masticatory performance.

Differential growth and maturation in idiopathic growth-hormone-deficient children

This study describes and compares the growth and maturation of idiopathic growth hormone deficiency (IGHD) and evaluates the potential effects of growth hormone therapy. The sample includes 40 idiopathic growth-hormone-deficient children grouped according to duration of growth hormone replacement therapy. Somatic and craniofacial development, skeletal maturation and dental maturation were evaluated and compared. The results showed consistent delays in the maturity indices for IGHD children. Height age displayed the greatest delay (3 years) followed by skeletal age (2.2 years) and dental age (0.8 years). Overall craniofacial growth deficiencies were also demonstrated. Anterior cranial base and mandibular length were most affected; posterior cranial base length and facial heights were least affected. Analysis of covariance, controlling for the starting age of therapy, showed significant differences between children grouped according to duration of growth hormone therapy. Catch-up growth with hormonal therapy was established for height, facial height, skeletal age and posterior cranial base length. It was concluded that the various craniofacial skeletal components have different potentials for growth retardation with IGHD; catch-up growth following growth hormone replacement therapy was greatest for the components with the greatest initial (or baseline) growth potential.

Orthognathic surgery effects on maxillary growth in patients with vertical maxillary excess

This study assesses the effects of superior repositioning of the maxilla by LeFort I osteotomy on adolescent maxillary growth. A total of 48 patients, 23 who were stabilized with rigid fixation (RF) and 25 stabilized with wire fixation (WF), were compared with closely matched unoperated controls. Comparisons were made for the presurgical intervals (2.3 years for RF and 1.3 years for WF groups) and postsurgical intervals (1.9 years for RF and 2.3 years for the WF groups). Lateral cephalograms were evaluated to describe the presurgical and postsurgical spatial changes of the maxilla. During the presurgical interval, there were no significant differences in vertical or horizontal maxillary growth between the WF group and their controls. Although vertical growth changes were similar, the RF group showed slightly more than expected posterior movement of the upper incisor during the presurgical interval. During surgery, the maxilla was advanced approximately 2 mm and impacted approximately 2 mm. After surgery, there were no statistically significant differences in vertical maxillary growth between the two surgical and control groups. Horizontally, the RF group showed maxillary stability, whereas the WF groups showed posterior movement. It is concluded that multiple piece LeFort I osteotomy has little or no effect on vertical maxillary growth; rigid fixation provides superior long-term anteroposterior stability compared with wire fixation.

Improvement of maximum occlusal forces after orthognathic surgery

PURPOSE

A number of studies have reported that maximum voluntary bite forces increase after orthognathic surgery. This study determined rates of long-term improvement in bite forces and looked for both sex-related differences in improvement and for any differences among surgical procedures.

PATIENTS AND METHODS

The study tested 117 patients before surgery and between 6 months and 3 years after surgery. At each trial, unilateral maximum voluntary bite force was measured at four different tooth positions using a standard transducer. Forty-three control subjects were similarly tested. The rate of increase in maximum bite force was calculated separately for male and female patients in various groups of patients and the controls.

RESULTS

The patients had significantly lower maximum bite forces than the controls before surgery and for as long as 2 years after surgery. Within 6 months after surgery, patients' bite forces were already greater than their pre-surgical forces. Patients generally showed steady improvement in bite force thereafter, with male patients improving more quickly than female patients. There were no clear differences among surgical procedures.

CONCLUSIONS

Any temporary reduction in maximum voluntary bite force disappears less than 6 months after orthognathic surgery. Orthognathic surgery improves patients' bite forces, but this improvement may be gradual, requiring many months.