Prediction of mandibular growth rotation

A review of anterior open bite

Anterior open bite malocclusion is reviewed under the headings of aetiology, morphology and treatment. The aetiology is discussed within the classification originally described by Dockrell in 1952. The morphological differences between skeletal and dental open bite together with the extra oral, intra oral, and cephalometric characteristics are described. Recognition is given to the recent developments in maxillo facial surgery and the importance of a combined surgical and orthodontic approach to the treatment of skeletal open bite. The merits of the palatal crib either on a fixed or removable appliance to break a thumb sucking habit are discussed in relation to the dental open bite. The relationship of post treatment stability to the adequate removal or modification of the aetiological factor is stressed.

Rocker jaws

Most adult Polynesian mandibles are of the rocker form. Polynesian crania possess a very open cranial base angle and a large upper facial height. The mandibular growth rotations necessary to maintain occlusion in the presence of this cranial morphology lead to development of an exceptionally closed ramus-body angle, with consequent loss of the antegonial notch and appearance of the rocker form.

A longitudinal study of dental arch growth

Changes in dental arch size and form were assessed by means of univariate and multivariate analysis in a longitudinal study of children between 2 and 10 years of age. The multivariate analysis served to assess the arches as a biologic whole rather than as a series of independent dimensions. Dental arches do not seem to undergo a steady rate of change up to the age of 10 years. In the arches anterior to the first permanent molars, peaks of growth occur between 2 and 3 years and 7 and 8 years in the maxilla, and between 2 and 3 years and 5 and 6 years in the mandible. In the arches, including the first permanent molars, peaks of growth occur between 6 and 8 years in the maxilla and between 9 and 10 years in the mandible.

The effects of Begg treatment on the lower labial segment in Class II cases

A report is presented on eleven Class II cases which had been treated by the Begg technique. The cases were analysed from 1 to 3·5 years following retention, with particular emphasis being placed on changes to the lower labial segment. Where relevant, comparisons are made with growth study standards. The use of the lower incisor—Mandibular planes angle (IMPA) is described and criticized and an alternative linear measurement is used to describe changes in the sagittal position of the lower incisors. The results indicate that despite widely held views, it is possible to obtain stable results, following radical alteration to the lower incisor position. There was a trend towards an overall lingual movement of lower incisor apices.

Growth of the maxilla in three dimensions as revealed radiographically by the implant method

By use of the implant method the growth of the maxilla was analysed from profile and frontal (postero-anterior) cephalometric radiographs in nine boys with normal primary occlusion who were followed annually up to adult age without receiving any orthodontic treatment.

The proportion of sutural and appositional growth in height was determined from profile radiographs with reference to implants in the infrazygomatic crest. The sutural lowering of the maxillary corpus was, on average, about twice as big as the apposition at the floor of the orbits. The resorptive lowering of the nasal floor amounted to about one-third of the appositional growth in height of the alveolar process.

Our study suggests that the contour of the anterior surface of the zygomatic process could be used as a reference structure in growth analysis as this contour kept a constant relation to implants in the infrazygomatic crest and closely followed the natural growth rotation of the maxilla.

In relation to the implants, the dentition as a whole drifted forward on the maxillary corpus, simultaneously with a smaller decrease in arch length which was partly related to a differentiated development in width of the maxilla.

Measurements between bilateral implants on frontal radiographs proved that the growth in the median suture was greater posteriorly than anteriorly, whereby the two halves of the maxilla rotate in relation to each other in the transverse plane. This was reflected in the development of the dental arch as the increase in the bi-molar width showed a high correlation with the sutural growth posteriorly in the medium suture, while the increase in the bi-canine width was lesser. The forward drift of the dental arch led to a reduction in incisor spacing, which may give rise to an incisal secondary crowding.

Direction and intensity of mandibular rotation in the sagittal adjustment during growth of the jaws

A material of 22 patients with metallic implants in both jaws has been used to study, longitudinally on lateral headplates, the relationship between the degree of mandibular rotation, the difference in amount of growth of both jaws, represented by the value (E), and the sagittal intermaxillary relationship (G). It has been established that the variation of sagittal intermaxillary relationship and the variation of the degree of mandibular rotation are two phenomena presenting a "balance mechanism" when related to the value (E). The different combinations of these three variables during mandibular growth are proposed, represented in diagrams. This study reveals that several possible mandibular responses correspond to a single given initial condition.

Operational definitions of mandibular morphogenetic and positional rotations

A material of 30 patients with metallic implants was used in a longitudinal study, based on lateral headplates, of the mandibular rotational pattern. The complexity of the rotational phenomenon in the mandibular rotation has necessitated the proposal of some operational definitions: morphogenetic and positional rotations of the mandible. A relationship has been established between the variation of the gonial angle and the variation of both morphogenetic and positional rotations of the mandible. A relationship has been established between the variation of the condylar growth direction and the variation of both morphogenetc and positional rotations of the mandible: this relationship is the strongest when the morphogenetic rotation of the corpus is considered.

Facial growth: before, during, and following orthodontic treatment

A longitudinal growth study was done on nineteen persons, involving three types of malocclusion and several types of treatment. Facial growth direction of the middle and lower face was compared during pretreatment, treatment, and posttreatment phases of the individuals. The individuals in the sample varied in direction of facial growth, Some individuals had an almost horizontal growth direction, and others had a vertical growth direction. The individuals in the sample varied in their degree of response to orthodontic treatment. Several had no change from their normal growth direction. Several had a deviation in direction associated with orthodontic treatment. The deviation was clockwise in nature and the direction changed from horizontal to vertical or from vertical to slightly backward of vertical. Middle and lower face tended to move in conjunction during all phases. If ANS moved in a horizontal direction, pogonion tended to move in a horizontal direction. If ANS moved in a vertical direction, pogonion tended to move in a vertical direction. If ANS stopped moving forward, pogonion stopped moving forward.

The long face syndrome: vertical maxillary excess

There is a clinically recognizable facial morphology, the long face syndrome, which has been incompletely described in the literature. On the basis of the clinical summary in thirty-one adults with this syndrome, an analysis of esthetics, skeletal morphology, and occlusion was undertaken. Herein we report on these findings, which confirm that this basic dentofacial deformity is associated with excessive vertical growth of the maxilla. Dental open and closed bite are two variants of the syndrome. An increased mandibular ramus height is associated with the closed-bite group.

Measurement of tooth movement

1. Tooth movement relative to the alveolar bone can be precisely described only by superimposing on fixed points in the bone. Implants are the best known way today. Over short-term studies laminagraphy and the use of bony trabeculations are also useful. Remodeling occurs extensively on bony surfaces, making them too labile for use as stable landmarks. To project small amounts of tooth movement based on the use of such methods is so questionable as to represent little better than a guess or a clinical impression. 2. Growth can be separated into vertical and anteroposterior vectors with respect to the dentition. Since the occlusion is the concern, orientation of vertical and anteroposterior vectors to the occlusal plane is a reasonable baseline. The vertical and anteroposterior dental changes may not show a linear relationship in the anterior and posterior parts of the mouth when jaw rotations are occurring. 3. Growth can be disproportionate in either the vertical and/or the anteroposteroir plane of space. If the vertical increments of the anterior face differ from the vertical increments at the posterior face, mandibular rotations occur. This growth is accompanied by dental compensations that tend to mask the rotation. Therefore, open bite and deep bite are frequently skeletal growth problems. 4. Disproportional forward growth of the maxilla or mandible in an anteroposterior direction can lead to Class II or III relations. The growth that leads to Class II or Class III is accompanied by dental migrations that tend to mask this disproportionate growth. Orthodontic treatment of growth disproportionalities usually represents attempts to make the teeth further compensate. If surgical options are elected, the dental compensations should be removed prior to surgery in order to achieve a full surgical correction. 5. The teeth tend to move and grow in the opposite direction of the growth disproportionality. The teeth tend to mask the disproportionality. Thus, in an open bite, the incisors tend to move vertically further than in deep bites. Vertical imbalances may be more difficult to mask. Backward rotation of the mandible requires more vertical movement at the incisor than at the molar just to maintain vertical incisor relationships.

Vertical control: a multifactorial problem and its clinical implications

In this article we have tried to analyze the importance of vertical control in orthodontic cases, as well as the factors affecting it. From the cases presented, it can be assumed that: 1. In vertically growing or nongrowing persons (high-angle cases), the application of proper directional forces becomes extremely critical because a clockwise rotation of the mandible can occur very promptly and is very undesirable. 2. In cases with favorable growth potential, the results may be acceptable, even if the forces applied during treatment are not absolutely controlled; in other words, Mother Nature may often compensate for inappropriate or miscalculated treatment procedures.

Late results of activator-treatment: a cephalometric study

The purpose of this study was to analyse cephalometrically the long-term effect of Activator treatment on the dentofacial skeleton in 50 consecutively treated cases of postnormal and prenormal occlusion. Comparisons of dentofacial form between successful and unsuccessful cases were performed. The results of the study showed that the sagittal relationship between the jaws became normal in postnormal and prenormal cases during Activator treatment. The effect was achieved mainly by reciprocal dentoalveolar changes of the maxilla and mandible supported by a retardation of the forward growth of the maxilla in Class II cases and a stimulation of the forward growth of the maxilla in Class III cases. The normal downward-forward growth of the mandible appeared unaffected. The effect of Activator treatment on the vertical growth of the jaws was a significant increase in lower face height (bite-raising). No tendency to induce a harmful posterior growth rotation of the mandible was noted. Before treatment there was no highly significant difference in the morphology of the dentofacial skeleton between successfully and unsuccessfully treated Activator cases, except for the basal relationship between the jaws (ss-n-sm) which was larger in the successful cases. It would rather appear that good cooperation, high growth intensity and a favourable growth pattern of the patient together with a well constructed appliance is of decisive importance for a successful result of treatment.

The effect of different extraction sites upon incisor retraction

1. From this study, it was found that in cases treated by the Begg technique one can anticipate greater retraction of the anterior dental units in nonextraction (see article) cases, in both types of premolar extraction cases, and in cases, involving extraction of first molars plus first premolars than would be expected on the basis of root surface area resistance values. 2. There is a likely explanation for this. Molars were maintained upright and allowed to move bodily only while incisors were not only moved bodily but often partially tipped as well. 3. The actual mean anterior retraction in first molar extraction cases exhibited a close approximation to the expected mean anterior retraction values in relation to root surface resistance values. 4. Second premolar extraction is one answer to overretraction and has the added edge of creating even less incisor retraction than second premolar extraction. 5. It was also found that the extraction of premolars alone did not result (see article) in a significant change in the increased eruption of the third molars into functional occlusion. A very significant improvement in the rate of sucessful third molar eruption was found in first molar extraction cases and in cases involving extraction of first molars plus first premolars. 6. The mean ages of the patients in the various treatment categories at the start of treatment were similar enough to each other to suggest that age at the start of treatment had no bearing on the success rate of third molar erup tion. Extraction-site selection seemed to be the dominating factor in successful third molar eruption. 7. It was found that the group of cases that exhibited the least amount of anterior retraction also inhibited the least amount of anterior relapse and, conversely, the group of cases exhibiting the greatest amount of anterior retraction also exhibited the greatest amount of anterior relapse. (see article) 8. The nonextraction cases, with no extraction space to close, were treated in the shortest mean time, while the eight-tooth (first molar plus first premolar) extraction cases having the greatest amount of extraction space required the greatest amount of mean treatment time.9. In conclusion, it can be said that changing the location of the extraction site resulted in a change in relative root surface areas of the opposing anchor units in the anterior and posterior segments. There was a definite and predictable change in the amount of anterior retraction achieved by varying the location of the extraction site. This should be considered in the diagnosis, so that a desired treatment goal for the final position of the incisors within the facial profile can be achieved.

Growth of the vomero-premaxillary suture in children with bilateral cleft lip and palate. A histological and roentgencephalometric study

The significance of the vomero-premaxillary suture (VPS) in mid-facial development in patients with complete bilateral cleft lip and palate (C-BCLP) was evaluated. Histological analysis of the VPS in eight specimens, ranging in age from full term to 22 months, revealed evidence of growth at both sutural borders. Various theories to explain the consistent presence of secondary cartilage, localized mainly to the posterior end of the suture, were assessed. It was considered most likely that the formation of cartilage was promoted by mechanical stresses, set up during a period of rapid growth. Roentgencephalometric data from seven C-BCLP patients (age range: 2-7 months) demonstrated the existence of a true, rather than a relative, premaxillary protrusion. Five patients had metallic implants inserted on either side of the VPS at the time of initial surgery and were followed up roentgencephalometrically to ages ranging from 5 to 36 months. Although continuous growth was recorded in the VPS, there was a post-surgical decrease in the premaxillary protrusion. On the basis of both the histology and roentgencephalometry it was concluded that traumatic surgery involving the VPS would be likely to contribute to the impaired mid-facial growth sometimes seen in operated C-BCLP patients.

Arcial growth with metallic implants in mandibular growth prediction

The present investigation was undertaken to determine whether the Ricketts theory of arcial growth of the mandible can be put to practical use by the clinician to predict mandibular morphology. Eight subjects (six girls and two boys) were selected from the earliest implant samples at the Orthodontic Department of Emory University School of Dentistry. The initial cephalograms were coded and sent to Ricketts, and a 6-year manual growth forecast using the arcial method was requested. The final cephalograms were traced and compared. The three tracings (initial, prediction, and final) were superimposed over the metallic implants and presented on a case-by-case basis. The forecasts, in form, were clinically acceptable in five of the eight cases. In two of the cases (girls) (Cases 2 and 4) a hand-wrist radiograph to determine skeletal age would have improved their accuracy. The forecast in Case 2 was not acceptable. In view of our results in this small sample, the arcial method appears valid for prediction of amndibular growth; however, hand-wrist radiographs will improve the accuracy of short-range predictions of the amount of growth expected. For this reason, the orthodontist should constantly monitor his patients, watching for each individual to assert himself.

Adaptation of the mandible in children with adenoids

In a sample of lateral x-ray cephalograms of children with obstructing adenoids, a dorsal rotation of the mandibular ramus was found to characterize the facial skeleton. The mandibular body and the condylar process were not correspondingly rotated. The findings suggest that dorsal rotation of the mandible occurring in association with various pathologic processes could always be primarily a response to an encroachment of the pharyngeal space. A possible involvement of the clivus region, to a minor degree, was also indicated. The need for "tailormade" cephalometric methods in studies of specific problems is stressed.

The retroclined upper incisor

In the interest of further clarification of the interaction of the multiple causative factors of upper incisor retroclination, the development of Class II Division 2 occlusion is contrasted to that of Class I. The patients whose records were used had not received orthodontic treatment.

It was found that upper incisor retroclination in Class II Division 2 occurred after their emergence into the oral cavity. The effect is attributed to the upper incisors being able to erupt well within the cover of the lower lip through a combination of circumstances related to the proportional balance of the patient's facial structures in the vertical dimension.

The lower lip would guide the upper incisors into retroclined positions, only if the latter were unobstructed by digit, tongue or other teeth of either arch.

This implied not only a critical balance in size and relationship of the facial structures in the vertical dimension but also equally critical balances in the antero-posterior and lateral dimensions, without which the lower lip factor alone would be ineffective.

Mandibular anterior crowding in relation to tooth size and craniofacial morphology

In the present study the problem of mandibular anterior crowding was investigated by comparing a group of adults having approximately ideal occlusion (n = 27) with a group with corresponding occlusion except for a slight crowding in the mandibular anterior segment (n = 39). Both sexes were represented. A statistical evaluation revealed that in the latter group the mesiodistal diameter of the four mandibular incisor teeth was significantly greater, whereas the intercanine width and the frequency of third molars were the same in both groups. A comparison of the craniofacial morphology of the two groups displayed limited differences, and only the basal sagittal jaw relationship and the mandibular inclination differed significantly. No significant correlations were observed between the space conditions and any of the variables studied.

The problem of overbite in Class II, division 2 malocclusion

The paper studies 60 Class II, Division 2 malocclusions, from lateral skull radiographs taken before treatment and at least 1 year after the end of retention. In the first part of the paper the nature of the malocclusion is analysed. It usually exhibits a Class II skeletal pattern, and while this is on average milder than for Class II, Division I, there is a marked variation between individuals. Other factors are a high inter-incisal angle, a high lip-line, and in some cases a small lower facial height. The upper and lower facial heights, on the other hand, are not appreciably greater than normal.

The results of treatment are then analysed. Successful overbite reduction would seem to be associated with a reduction in inter-incisal angle and a relative lowering of the lower lip-line. Growth appears to be important in achieving overbite reduction. It is suggested that favourable rotation of the mandible may be a factor in overbite reduction in some cases, and this would repay further study.

Finally attention is turned to the effect of incisor proclination. This was usually more successful in the lower jaw, but again there was wide individual variation.