Patterns of change in mandibular and facial shape associated with the use of forces to retract the maxilla

[Validity of randomized clinical trials in evaluating the outcome of Class II treatments]

Despite on-going debates about their efficacy, functional appliances are still widely accepted and used by clinicians. According to the RCTs and their interpretations, the end result would be the same and you will not have more than 2 mm of difference between different treatment modalities; however it has been repeatedly proven that there are significant variations between individuals in relation to their dental and skeletal changes and that is the most important common finding of all the studies in this field. This aspect of individual variation to treatment has to be considered and discussed in detail with patients and parents. We should not forget that the patient has 25% chance of obtaining a very good skeletal result and 25% chance of a very poor result or in between in 50% of the cases, instead of basing our treatment decision on the averages. Despite extensive research including the RCTs in the area of Class II correction using different treatment modalities many questions remain unanswered. Future research in growth and genetics has the potential to clarify important points in patient selection and treatment outcome.

Cervical Headgear Effects on the Morphology of the Cervical Vertebrae and Cervical Posture

OBJECTIVE

To test the hypothesis that use of cervical headgear has an important effect on the morphology of the cervical vertebrae and cervical posture.

MATERIALS AND METHODS

The material consisted of pretreatment and posttreatment lateral cephalograms and initial hand-wrist films of 30 subjects who were receiving cervical headgear therapy. Preobservation and postobservation control cephalograms and preobservation hand-wrist films of 15 untreated subjects served as controls. The average treatment time for the treatment group was 9.06 +/- 1.02 months, and the average observation period for the control group was 10.0 +/- 1.1 months. A paired t-test was applied to compare the changes occurring during the examination and observation periods in both groups. In addition, Student's t-test was performed to assess the differences between the groups.

RESULTS

The results of the paired t-test showed that within each group there were statistically significant differences in the majority of measurements concerning the morphology of the cervical vertebrae, whereas the measurements concerning cervical posture showed no significant changes in either group. According to the results of the Student's t-test, however, no statistically significant changes between the treatment and control group were present except with regard to two measurements.

CONCLUSIONS

Changes in the cervicovertebral morphology in the treatment group were achieved more by growth than by cervical headgear treatment. Although high individual variations were found in postural variables, cervical posture did not change over a period of 9 months either in the treatment group or in the control group.

The role of cervical headgear and lower utility arch in the control of the vertical dimension

INTRODUCTION

This study was carried out to evaluate the treatment changes in skeletal and dental parameters in growing patients.

METHODS

The sample consisted of 24 subjects with Class II Division 1 malocclusion. Half of the patients were treated with cervical headgear alone (group C, n = 12), and the other half received a combination of cervical headgear and lower utility arch (group CU, n = 12). The treatment groups were compared with a matched untreated control group (n = 12). The mean ages of the subjects at the beginning of the study were 8.85 +/- 1.19 years in group C, 9.23 +/- 0.76 years in group CU, and 8.62 +/- 0.78 years in the control group. The cervical headgear was used with an expanded inner bow and a 15 degrees to 20 degrees upward bend of the longer outer bow, worn 12 to 14 hours a day, with a force of 450 to 500 g per side. The lower utility arch was designed as described in the bioprogressive technique. Treatment changes were assessed on lateral cephalometric radiographs.

RESULTS

The cervical headgear produced Class II correction through maxillary orthopedic and orthodontic changes. Anterior face height increased more in the treatment groups than in the control group. The treatment groups also displayed statistically significant increases in ramus height. Due to these effects, mandibular plane orientation stayed relatively unchanged. There was no opening rotation of the mandible in the treatment groups. The lower utility arch produced intrusion and lingual tipping of the mandibular incisors and distal tipping without extrusion of the mandibular molars. The treatment groups showed significant anterior descents of the palatal plane. Maxillary molar total extrusion produced by cervical headgear treatment was an average of no more than 1 mm as compared with the control group. The utility arch did not appear to influence mandibular rotational response.

Effect of cervical headgear wear on dynamic measurement of head position

The aim of this study was to identify the effect of cervical headgear (CHG) wear on dynamic measurement of head posture during walking. Six male and 10 female patients (mean age, 11.9 +/- 1.9 years) who were receiving CHG therapy for correction of a Class II molar relationship as part of their orthodontic treatment were included in this study. Dynamic head posture measurements were recorded using an inclinometer and data logger apparatus during a walking session of 5 minutes. This procedure was repeated before (T1) and after (T2) insertion of CHG. The T1 and T2 measurements were repeated twice at 30-minute intervals. The mean dynamic head posture was calculated for each subject using the collected data. The means of these measurements were statistically compared using a paired t-test. Of the 16 subjects, 14 showed a cranial flexion with CHG wear in relation to T1 (1.4 to 8.9 degrees). The other two subjects showed a cranial extension of -1.6 and -3.8 degrees. The mean values at T1, T2 and T1-T2 were 1.4, -1.8, and 3.1 degrees, respectively, which indicated a mean cranial flexion at T2 in relation to T1. According to the paired sample t-test, there were statistically significant differences between the two measurements of dynamic head posture recorded before and after CHG insertion (P < 0.001). CHG wear causes a significant cranial flexion which may be responsible for its effects on the mandible.

Activator versus cervical headgear: superimpositional cephalometric comparison

Clinical trials comparing activator and headgear treatment have shown comparable effectiveness in the total result achieved, but the mechanism of correction is still uncertain. Most studies have used conventional cephalometric methods to evaluate treatment effects, and this might be a factor for the inconclusive results. The aim of this retrospective investigation was to compare the effects of activator and cervical headgear treatment with a superimpositional cephalometric method that could discern between vertical and horizontal effects as well as skeletal, dental, and rotational treatment results. The sample consisted of 2 groups of Class II Division 1 patients, treated without extraction by the same clinician (22 patients were treated with a modified activator-type functional appliance, and 30 patients were treated with a combination of cervical headgear and fixed edgewise appliances). Lateral cephalometric radiographs taken at the beginning of treatment and after Class II molar correction were evaluated conventionally and with a superimpositional method. Regarding the conventional cephalometric measurements, the only difference in the anteroposterior dimension between the 2 treatment modalities was the significantly reduced SNA angle in the headgear group. Both appliances appeared to produce minimal changes in FMA and GoGn-SN angles, and there were no statistically significant differences between the treatment groups. Regional superimpositions showed differences in the movement of molars: the maxillary molar was found to move more posteriorly and inferiorly in the headgear group. Conversely, the mandibular molar was found to move toward the occlusal plane more in the activator group. Assessment of mandibular skeletal changes showed that the mandible moved anteriorly by approximately 1 mm more in the activator than in the headgear group. The overall effect of the 2 appliances was found to be clinically comparable. However, the individual components of change showed differences characteristic of each appliance.

Changes in mandibular position and upper airway dimension by wearing cervical headgear during sleep

We previously reported that the wearing of cervical headgear induced forward displacement of the mandible in awake subjects. However, it was unclear whether such mandibular displacement also occurred during sleep. The purpose of this study was to examine changes in mandibular position and oropharyngeal structures that were induced by the wearing of cervical headgear during sleep. Ten healthy adults (7 male and 3 female) who gave their informed consent were included in this study. A pair of lateral cephalograms was taken with the patient in the supine position with and without cervical headgear at end-expiration during stage 1 to 2 non-rapid-eye-movement sleep. The Wilcoxon signed-rank test was used for a statistical analysis. The amount of jaw opening was significantly decreased by the wearing of the cervical headgear (P <.05), although no significant anteroposterior mandibular displacement was induced. The sagittal dimension of the upper airway was significantly reduced (P <.05); however, no significant changes were observed in the vertical length of the upper airway. Although the hyoid bone and the third cervical vertebra moved significantly forward by the wearing of the cervical headgear (P <.05), the relationship among the mandibular symphysis, the hyoid bone, and the third cervical vertebra did not change. These results suggest that cervical headgear significantly reduced the sagittal dimension of the upper airway during sleep, although there was no significant anteroposterior displacement of the mandible.

Changes in mandibular growth direction during and after cervical headgear treatment

Cervical headgear is widely used to modify sagittal growth in growing patients. However, cervical headgear can affect vertical growth as well. The purpose of this retrospective cephalometric study was to examine mandibular growth changes in 30 growing Class II patients treated with cervical headgear and full edgewise appliances and to compare those changes with the changes occurring in 26 untreated controls. Cephalometric data were obtained from lateral cephalometric radiographs representing pretreatment, posttreatment, and postretention for each patient and from chronologically comparable radiographs for the control subjects. During the 4-year treatment or observation period, the mean mandibular rotation was 0.25 degrees in the treatment group and -1.7 degrees in the control group. After an average posttreatment period of 6 years 5 months, the mandible had rotated -1.5 degrees in the treatment group and -0.7 degrees in the control group. Mean changes in the y-axis angle and the mandibular plane angle during retention were not different between the 2 groups. Mandibular rotation during retention did not show any significant inverse correlation with mandibular rotation during treatment. These findings suggest that mandibular rotation during retention reflects the inherent growth pattern of an individual that is reasserted after treatment, rather than rebound. There were no significant differences in the size of the mandible between the 2 groups during the study period. None of the variables reflecting pretreatment morphology of the face had a clinically significant bearing on mandibular rotation. Vertical changes in the maxillary and mandibular molars showed no significant correlation with mandibular rotation, which suggests that the changes in vertical dimension of the dentition are not a major determinant of the rotational change of the mandible.

Effects of different vectors of forces applied by combined headgear

The effects of various directed forces applied by combined headgear were evaluated in this study. The study material consisted of 30 patients with Class II dental relationships and steep mandibular plane angles. Three groups of 10 patients each were formed. In the first treatment group, forces of 150 gm per side were used for the high-pull component and the cervical component. In the second treatment group, forces of 200 gm per side for the high-pull component and 100 gm per side for the cervical component were applied. In the third treatment group, forces of 100 gm per side were applied for the high-pull component and 200 gm per side for the cervical component. Distal tipping of upper molar was greatest in the third treatment group. Intrusion of the upper molar in the second treatment group and extrusion of the upper molar in the third treatment group were statistically significant. Changes in occlusal and mandibular plane angles showed significant differences between the groups.

An evaluation of two-phase treatment with the Herbst appliance and preadjusted edgewise therapy

The purpose of this study was to evaluate the skeletal and dentoalveolar changes occurring during two-phase orthodontic treatment. A cephalometric study of Class II correction was carried out in 40 subjects (20 females, 20 males) who had been treated with the acrylic-splint Herbst appliance immediately followed by a second phase of preadjusted edgewise therapy. The average age at the start of Herbst therapy was 12.5 +/- 0.8 years for females and 13.6 +/- 1.2 years for males. Descriptive cephalometric data were compared with the normative values derived from the University of Michigan Elementary and Secondary School Growth Study. Control values were generated for each of the 40 Herbst patients based on gender, initial age, and duration of treatment. The results of this study indicate that the Class II correction achieved during Phase I treatment with Herbst appliance was due mainly to an increase in mandibular length, as well as distal movement of the maxillary molars and mesial movement of the mandibular molars and incisors. The accelerated mandibular growth rate observed during Herbst therapy was followed by a diminished growth rate during the edgewise phase that was less than control values. The overall increase in mandibular length was slight (approximately 1 mm), but significantly greater than control data for the whole group and the male subgroup; however, it was not significantly different between the treatment group and control data in the female subgroup. There were no significant treatment effects on lower anterior facial height and the mandibular plane angle at the end of either phase of treatment. The skeletal changes contributed to 55% of the molar correction during the Herbst therapy, whereas at the end of the second phase of treatment, skeletal change accounted for 80%. Significant anteroposterior dentoalveolar rebound was seen during the edgewise phase.

The effects of Twin Blocks: a prospective controlled study

This prospective controlled study investigated the net effects of the Twin Block functional appliance taking into account the effects of normal growth in an untreated control group. The treatment group consisted of 36 subjects, mean age of 12.4 years, consecutively treated with Twin Block appliances for an average period of 0.9 years. Each subject had immediate pre- and posttreatment lateral cephalograms. The control group consisted of 27 subjects with a mean age of 12.1 years. These patients were observed for a mean time of 1.2 years and had radiographic investigation at the initial consultation and immediately before the start of Twin Block therapy. The data were then annualized and subjected to multiple regression analysis. In the treatment group, a reduction in ANB of 2.0 degrees (p < 0.001) was observed largely because of an increase in SNB of 1.9 degrees (p < 0.001). No statistically significant restraint in the maxillary growth was observed. Treatment resulted in an increase in Ar-Pog of 5.1 mm (p < 0.001) compared with the control group increase in Ar-Pog of 2.7 mm, resulting in a net gain of 2.4 mm. The overjet was reduced by combination of a net maxillary incisor retroclination of 10.8 degrees (p < 0.001), net mandibular incisor proclination of 7.9 degrees (p < 0.001) and forward movement of the mandible. Buccal segment relationships were corrected by means of lower molar eruption, restraint in the eruption of the upper molars and forward growth or repositioning of the mandible. Any possible fossa adaption was not assessed.

Cervical neckgear--villain or savior?

An understanding of growth and development and the effect our appliances have on a person's growth and development is necessary in the selection of the therapeutic appliances we choose to use, out of the multitude available. Timing of treatment is also important in effecting positive changes in skeletal and dental relationships. Early treatment to correct skeletal discrepancies and gain arch length can allow for an increase in nonextraction therapy. Cervical extraoral appliances, maxillary fixed expansion appliances, and mandibular labial "E" arches can be used early to effectively reduce of skeletal discrepancies and to gain arch length without the fear of rotating the mandible down and back, permanently increasing the mandibular plane angle. Case reports are presented to illustrate the beneficial changes that can occur with early treatment with these appliances.

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.

Facial growth of males and females compared by tensor analysis

This study compares and contrasts the longitudinal differences in facial development between 18 male and 22 female subjects, employing the technique of tensor analysis. Children were examined in two age ranges: prepubertal (aged 7-10 years) and post-pubertal (15-20 years of age). Both the changes over time and the differences in amount and direction of growth between the sexes were subjected to statistical analysis. A tensor analysis permits the computation of differences in form (that is in size and shape) without specifically measuring either. Mean values for 21 hard and soft tissue landmarks were determined for both males and females at each age. Customized computer software allowed examination of the growth changes between 32 selected groups of points. Results indicated that the tensor analysis reinforced and supplemented the more conventional descriptions of facial growth. Females grew a smaller amount over the period examined than their male peers and development was in a relatively more vertical direction. These differences in growth between the sexes were highly statistically significant.

Vertical changes in high-angle Class II, division 1 patients treated with cervical or occipital pull headgear

Before, after, and 2 years after treatment serial radiographs of two samples of patients with high mandibular plane angle Class II, Division 1 nonextraction who were treated were evaluated retrospectively. One sample comprised patients treated with cervical headgear (CHG), and the other was treated with occipital headgear (OPHG). No significant differences were found when mandibular plane angle or facial height changes, anterior or posterior, were compared. Regarding vertical changes, only maxillary molar height, relative to both sella-nasion and palatal plane, and occlusal plane angle changes were significantly different when cervical and occipital-pull headgear were compared. In both groups of patients, responses to treatment were highly variable and only subtle vertical differences were apparent between mean changes in the cervical and occipital-pull samples.

Dental and skeletal contributions to occlusal correction in patients treated with the high-pull headgear-activator combination

The purpose of this study was to examine dental and skeletal changes in patients treated with the high-pull headgear-activator combination. A group of 40 consecutively treated subjects with a Class II molar relationship and a minimum of 5 mm overjet was used for this study. The results showed that Class II correction often was achieved by distal repositioning of the maxillary teeth (mean, 0.07 mm) and mesial repositioning of the mandibular teeth (mean, 3.3 mm) with a wide range of variation. Correlation of maxillary molar repositioning with total interarch occlusal change showed a positive relationship; however, a weak correlation suggested that other variables were contributing factors, in addition to distal upper molar positioning. The change in mandibular molar position compared with the movement of pogonion strongly suggests that forward growth of the mandible is important to the correction of the Class II malocclusion. When total molar repositioning in the upper jaw was correlated with total molar repositioning in the lower jaw, a strong inverse correlation was found, indicating that upper molar movement parallels lower molar movement.

Mandibular molar displacement secondary to the use of forces to retract the maxilla

Using previously described computer-aided techniques, we have been able to characterize quantitatively the displacements of the lower first molar associated with the use of several different therapeutic modalities that are conventionally employed to retract the maxilla in the treatment of Class II malocclusion. The total displacement of the molar has been partitioned into two components associated respectively with displacement of the entire mandible and with local interosseous migration (dental compensation) of the molar within the mandible. A further attempt has been made to partition treatment-associated effects from nontreatment-associated effects. While considerable variability in effect was observed within each sample on a case-by-case basis, some important normative trends did emerge. Contrary to our expectations, it was found that in each of the treatment groups, the mean local intraosseous rotational effect (Table IIB.2) was of greater magnitude than the mean effect of mandibular rotation (Table IIB.1). The character of the intraosseous rotation differed significantly (P less than 0.05) between the control group and each of the treatment groups. In the control group, a mean mesial crown tipping (that is, "proclination") was noted. In each of the treatment groups, a mean distal crown tipping ("uprighting") was noted. In both the cervical and intraoral groups, the lower molar tended to displace mesially more than in the control or high-pull groups. This mesial displacement derived from the mesial displacement of the mandible (Table IIC.3), rather than from displacement of the tooth within the bone (Table IIC.4). In both the high-pull and the intraoral groups, the lower molar erupted within the mandible significantly more than in the control and cervical groups (Table IIC.6). The statistically significant supereruption/extrusion of the upper molar in the cervical group (Table IIC.2) was not accompanied by an associated inhibition of the eruption of the lower first molar (Table IIC.6). In general, it seems reasonable to infer that the growth-related displacement of the mandible influenced the final position of the lower first molar more profoundly than did the treatment-associated displacement of the upper molar.

Cephalometric changes associated with treatment using the activator, the Fränkel appliance, and the fixed appliance

Treatment with the activator, the Fränkel appliance, and the edgewise appliance was compared in three separate groups; each group consisted of twenty-five nonextraction cases of Class II, Division 1 malocclusion. Hard- and soft-tissue profile changes caused by growth and treatment were assessed by means of pretreatment and posttreatment lateral cephalograms. Anterior movement of A point was 1.6 mm more in the activator group than in the fixed-appliance group. The most anterior point on the maxillary incisor moved 1.5 mm more distally in the fixed-appliance sample than in the functional groups. Among the three groups, the activator sample showed the most anterior movement of the mandible (2.3 mm); the fixed group showed the least (0.6 mm). The fixed-appliance group showed more posterior rotation of the mandible than the activator group. However, relative to cranial base, the movement of the mandibular symphysis was not statistically different in the three groups. There were little differences among the treatment groups with regard to changes in the soft-tissue profile. In clinical terms, there was a remarkable similarity in the changes that occurred in the three treatment groups.

Holographic and cephalometric study of the relationship between craniofacial morphology and the initial reactions to high-pull headgear traction

Eight macerated human child skulls with a dental age of approximately 9.5 years (mixed dentition) were consecutively subjected to an experimental standardized high-pull headgear traction system attached to the maxilla at the first permanent molar area via an immovable acrylic resin splint covering all teeth. This system produced tensile forces from 0.5 to 3.5 N (1 N = 0.10 kg) per side. Laser holography was used to measure displacements in a three-dimensional coordinate system. Displacements varied in direction. In addition, conventional cephalometric analysis of standardized lateral roentgen cephalograms was performed. Displacements and cephalometric data were then compared. Results indicate that the direction of initial displacements of bones of the facial skeleton bears a definite relationship to the morphology of the individual skull. In skulls with high divergency values (large angles, sella-nasion-occlusal plane, sella-nasion-mandibular plane), displacements are in a backward and posterior downward direction; in skulls with a small sella-nasion-occlusal plane angle, backward displacements occur in a direction almost parallel to the occlusal plane.

Prediction of mandibular rotation: an empirical test of clinician performance

An experiment was conducted in an attempt to determine empirically how effective a number of expert clinicians were at differentiating "backward rotators" from "forward rotators" on the basis of head-film information which might reasonably have been available to them prior to instituting treatment for the correction of Class II malocclusion. As a result of a previously reported ongoing study, pre- and posttreatment head films were available for 188 patients treated in the mixed dentition for the correction of Class II malocclusion and for 50 untreated Class II subjects. These subjects were divided into 14 groups (average size of group, 17; range, 6 to 23) solely on the basis of type of treatment and the clinician from whose clinic the records had originated. From within each group, we selected the two or three subjects who had exhibited the most extreme backward rotation and the two or three subjects who had exhibited the most extreme forward rotation of the mandible during the interval between films. The sole criterion for classification was magnitude of change in the mandibular plane angle of Downs between the pre- and posttreatment films of each patient. The resulting sample contained 32 backward-rotator subjects and 32 forward-rotator subjects. Five expert judges (mean clinical experience, 28 years) were asked to identify the backward-rotator subjects by examination of the pretreatment films. The findings may be summarized as follows: (1) No judge performed significantly better than chance. (2) There was strong evidence that the judges used a shared, though relatively ineffective, set of rules in making their discriminations between forward and backward rotators. (3) Statistical analysis of the predictive power of a set of standard cephalometric measurements which had previously been made for this set of subjects indicated that the numerical data also failed to identify potential backward rotators at a rate significantly better than chance. We infer from these findings that the ability of clinicians to identify backward rotators on the basis of information available at the outset of treatment is poor. Hence, we believe that it is unlikely that such predictions play any consequential operational role in the planning of successful orthodontic therapy at the present state of the art.

A study of mandibular shape

The technique of medial axis transformation of the outline form was used for the specific analysis of mandibular shape. When used to compare mandibular shape derived from lateral cephalographs between three equal samples of 30 female patients aged 12-15 years, marked overall similarity was noted between patients with Classes I, II and III occlusions. There were however subtle contrasts including the degree of coronoid and condylar separation and orientation of the ramus relative to the corpus. Such constancy of mandibular form derived from this technique of investigation was marked contrast to the data of traditional cephalometric studies which combine both size and shape parameters together. This study therefore demonstrated that shape appears less variable than size.

Superimpositional assessment of treatment-associated changes in the temporomandibular joint and the mandibular symphysis

This article analyzes differences in the measured displacement of the condyle and of progonion when different vectors of force are delivered to the maxilla in the course of non-full-banded, Phase 1, mixed-dentition treatment for the correction of Class II malocclusion. The 238-case sample is identical to that for which changes in other parameters of facial form have been reported previously. Relative to superimposition on anterior cranial base and measured in a Frankfort-plane-determined coordinate system, we have attempted to identify and quantitate (1) the displacement of each structure which results from local remodeling and (2) the displacement of each structure which occurs as a secondary consequence of changes in other regions of the skull. We have also attempted to isolate treatment effects from those attributable to spontaneous growth and development. At the condyle, we note that in all three treatment groups and in the control group there is a small but real downward and backward displacement of the glenoid fossa. This change is not treatment induced but, rather, is associated with spontaneous growth and development. (See Fig. 5.) Some interesting differences in pattern of "growth at the condyle" were noted between samples. In the intraoral (modified activator) sample, there were small but statistically significant increases in growth rate as compared to the untreated group of Class II controls. To our surprise, similar statistically significant increases over the growth rate of the control group were noted in the cervical sample. (See Table III, variables 17 and 18.) Small but statistically significant differences between treatments were also noted in the patterns of change at pogonion. As compared to the untreated control group, the rate of total displacement in the modified activator group was significantly greater in the forward direction, while the rate of total displacement in the cervical group was significantly greater in the downward direction. There were no statistically significant differences in the rate of total displacement of pogonion between the high-pull sample and the control sample. (See Table IV, variables 21 and 22.

Quantitative analysis of the orthodontic and orthopedic effects of maxillary traction

This article analyzes differences in displacement of ANS and of the upper first molar when different vectors of force are delivered to the maxilla in non-full-banded Phase I mixed-dentition treatment of Class II malocclusion. The sample is identical to that for which we have previously reported differences in change in several key measures of mandibular and facial shape. It includes a cervical-traction group, a high-pull-to-upper-molar group, a modified-activator group, and an untreated Class II control group. Using newly developed computer-conducted procedures, which are described, we have been able to partition the orthodontic and orthopedic components of upper molar displacement and also to isolate treatment effects from those attributable to spontaneous growth and development. In the region of ANS, small but statistically significant and clinically meaningful differences were noted between treatments. When the intercurrent effects of growth and development had been factored out (Table III), orthopedic distal displacement of ANS was significantly greater in the high-pull and cervical groups than in the activator group. Orthopedic downward displacement of ANS was seen to be significantly greater in the cervical group than in the high-pull and activator groups. In the region of the first molar cusp, mean distal displacement of the tooth as an orthopedic effect was found to be almost identical in the cervical and high-pull groups (although variability was greater in the cervical group), but the mean orthodontic effect was significantly greater in the high-pull group than in the cervical group. In the cervical group, where relatively light forces were used for relatively long treatment periods on average, more of the total distal displacement of the upper molar was of an orthopedic character than of an orthodontic character. Conversely, in the high-pull group, in which relatively heavier forces tended to be used for briefer treatment periods, most of the distal displacement at the upper molar was of an orthodontic character. These observations are contrary to expectations from conventional orthodontic theory. In the activator-treated group, roughly equal components of the treatment-associated distal displacement of the upper molar were of the orthodontic and orthopedic types. As concerns changes in the vertical direction in the region of the molar cusp, significant intrusion of both the orthopedic and orthodontic types was seen in the high-pull sample as compared to each of the other groups examined.(ABSTRACT TRUNCATED AT 400 WORDS)