INTRODUCTION

There are various types of skeletal Class III malocclusions, and the selected treatment plan should directly reflect not only the type of Class III malocclusion but also the timing of the treatment. The chin cap can be used to treat excessive mandibular growth by redirecting mandibular growth1 and maxillary protraction can be used in treating retruded maxillae by accelerating maxillary growth2–5 in growing patients. When treating adult patients, orthodontic camouflage treatment can resolve the skeletal discrepancy in moderate cases, and orthognathic surgery should be considered in case of severe skeletal discrepancy.

The prevalence of Class III malocclusion in Koreans occupies approximately 16.7% of the population,6 whereas the percentage of the Class III malocclusion in patients who visited the department of orthodontics was 47.49%.7 Of patients exhibiting Class III malocclusions, maxillary retrognathism was prevalent in 42.5% according to Sanborn8 and 30–40% according to Bell et al.9 Jacobson et al10 reported that the one-quarter of Class III malocclusions demonstrated retruded maxilla in the study of 149 subjects.

In 1944, Oppenheim2 reported that it is impossible to move the mandible backward, but that it is possible to bring the maxilla forward to compensate for mandibular overgrowth when treating Class III malocclusions. In 1971, Delaire3 tried to protract the maxilla using an orthopedic mask. Dellinger4 reported that the maxilla separated from the pterygoid and repositioned anteriorly with orthopedic forces in Macaca monkeys. Nanda5 has shown that the forward movement and the anterior displacement of the maxilla are because of the remodeling of the circummaxillary sutures, in particular the zygomaticomaxillary, zygomaticotemporal, and transverse palatine sutures, and reported that the type of displacement was related to the direction of force. Björk11 reported that appositional growth in the maxillary tuberosity area related to the pyramidal process of the palate and the pterygoid process of the sphenoid is important in growth of the maxilla. McNamara and Brudon12 reported that the treatment effects of the maxillary protraction included an inferioanterior movement of the maxilla and maxillary dentition, clockwise rotation of the mandible, retroclination of the mandibular incisor, and increase of the lower facial height.

Palatal expansion produces a forward and downward movement of the maxilla by affecting the intermaxillary and circummaxillary sutures, and the disruption of these sutures may allow for a more positive reaction to the protraction forces.13 Kambara14 suggested that reactions in the suture when protraction force are applied to the maxilla might occur as a result of an opening of the suture, stretching of sutural connective tissue fibers, new bone deposition, and homeostasis, which had maintained the sutural width.

One of the most important factors in considering facial mask treatment is the optimization of treatment timing. Irie and Nakamura15 suggested that the period of Hellman's dental age IIC and IIIA is the optimal time. Cozzani16 reported that when the patient is treated at age four years, the direction of the growth of the maxilla coincides with the direction of protraction, which results in increased stability. Kambara14 and Jackson et al17 reported that maxillary protraction should be carried out during the growing stage.

Because time, duration, and intensity of maxillofacial growth differ among individuals, the physiologic age has considerable influences on diagnosis, treatment planning, and ultimately the outcome of the treatment. The various assessment methods of growth and development are as follows: evaluation of increments in height, scoring of dental age using calcification and eruption stage of the developing dentition, the secondary sexual characteristics using the menarche and the pubertal voice, and evaluation of skeletal age by maturation of the hand-wrists or vertebrae.

Among various physiologic ages, bone age is indicative of trends in pubertal growth and the assessment of a hand-wrist radiograph has proven to be the most satisfactory method of determining skeletal age. Todd was one of the first investigators to evaluate skeletal maturation, in 1937.18 Greulich and Pyle19 have created a radiographic atlas of the skeletal development of the hand and wrist. Tanner et al2021 reported about the TW1 and TW2 methods of scoring bone maturity by biologic weighted system.

In 1982, Fishman22 proposed the System of Skeletal Maturation Assessment (SMA) that identifies 11 main skeletal maturity indicators (SMIs) that are related to the adolescent period of development. These SMIs are located in six anatomic areas of the first, third, and fifth finger, and radius, and the SMI can be arbitrarily divided into periods of accelerating velocity (SMI 1–3), high velocity (SMI 4–7), and decelerating velocity (SMI 8–11).

Rune et al23 reported that facial changes were not related to skeletal pattern, chronological age, growth peak, and treatment duration. Therefore, a prognosis of the effects was not possible. Sarnäs24 also reported that the effects of maxillary protraction have no relation to the skeletal type, growth peak, or treatment period. Kapust et al25 divided the patients into three chronological groups: 4–7, 7–10, and 10–14 years, and showed minimal statistical differences between the three age groups when comparing angular and linear measurements. Baik26 and Takada27 also divided patients into three groups and showed no statistical differences among the results in those three groups. Hwang et al28 classified subjects into four groups: 5.8–8, 8–10, 10–12, and 12–14 years, but found no relation between maxillary protraction effect and treatment timing. Because the sample sizes in the above studies were too small and were based on chronological age rather than skeletal age, treatment timing relative to physiologic characteristics was not evaluated.

Clinically, a majority of patients exhibiting skeletal Class III malocclusion with maxillary retrognathism visit clinics after their pubertal growth spurt, and inevitably the rapid maxillary expansion (RME) and facial mask would be selected as nonsurgical treatment methods. In this study, we tried to define the correlation between the effects of maxillary protraction and the skeletal age level based on Fishman's System of SMA.

MATERIALS AND METHODS

Subjects

Eighty-five subjects (26 males and 59 females) from the Dankook University Dental Hospital were diagnosed as skeletal Class III malocclusions with maxillary retrognathism, and treated using RME and facial mask.

Using hand-wrist radiographs, all subjects were divided into three developmental groups according to Fishman's System of SMA. Group 1, which represented the accelerating growth velocity subgroup (SMI 1–3), consisted of 34 subjects. The mean chronological age was 9.82 ± 1.50 years, and the mean treatment period was 1.16 ± 0.42 years. Group 2, which represented the high growth velocity subgroup (SMI 4–7), consisted of 32 subjects. The mean chronological age was 11.31 ± 1.16 years, and the mean treatment duration was 1.07 ± 0.33 years. Group 3, which represented the decelerating velocity subgroup (SMI 8–11), consisted of 19 subjects. The mean chronological age was 13.07 ± 1.43 years, and the mean treatment duration was 1.06 ± 0.38 years (Table 1).

TABLE 1.  Chronological Age and Treatment Period of Each Group

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Cephalometric analysis

Cephalometric radiographs were taken before treatment (Pre-Tx) and just after correction of the anterior crossbite (Post-Tx), and traced by one author to avoid interoperate errors. The reference points are shown in Figure 1, and reference lines in Figure 2. The angular, linear, and rotational measurements are shown in Figures 3 through 5.

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Reference points

(1) Sella (S), (2) nasion (N), (3) point A, (4) point B, (5) pogonion (Pg), (6) Condylion (Cd), (7) orbitale (Or), (8) anterior nasal spine (ANS), (9) posterior nasal spine (PNS), (10) menton (Me), (11) gonion (Go), (12) Gnathion (Gn), (13) articulare (Ar), (14) Xi, (15) pterygomaxillary fissure (PT), (16) protuberance menti (PM), (17) CC, (18) sphenoethmoidal point (SE), (19) incision inferius (Mn 1), (20) incision superius (Mx 1), (21) molar inferius (Mn 6), (22) molar superius (Mx 6) (Figure 1).

Reference lines

(1) Horizontal reference line (X): 6° downward from sella-nasion (SN) line at sella. (2) Vertical reference line (Y): perpendicular to the horizontal reference line at sella (Figure 2).

Angular measurements

(1) SNA, (2) SNB, (3) ANB, (4) facial convexity, (5) FMA, (6) FH/Pal Pl, (7) U1/FH, (8) Facial axis, (9) Facial angle, (10) LFH (11) PMV/Oc. Pl, (12) PMV/Ra Pl. (Figure 3).

Linear measurements

(1) ACBL, (2) Mn. Body Length, (3) Effective Mx Length, (4) Effective Mn Length, (5) Overbite, (6) Overjet, (7) U6-Pal Pl, (8) Y-A, (9) Y-Mx 1, (10) Y-Mn 1, (11) Y-Mx 6, (12) Y-Mn 6, (13) Y-B, (14) Y-Pg, (15) X-ANS, (16) X-PNS, (17) X-Mn 1, (18) X-Mx 6, (19) X-Pg (Figures 4 and 5).

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RESULTS

Pretreatment cephalometric values

The mean and standard deviation of initial cephalometric values were calculated (Tables 2 and 3). The mean values for angular measurements for 85 subjects were SNA 79.00°, SNB 80.78°, and facial convexity −2.49°. The maxillary and mandibular length was 81.54 and 117.14 mm, showing skeletal Class III malocclusion with mandibular prognathism and maxillary retrognathism.

TABLE 2.  Pre-Tx. Cephalometric Values; Angular Measurements

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TABLE 3.  Pre-Tx. Cephalometric values; Linear Measurements

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Effects of protraction in groups 1, 2 and 3

The changes in group 1 were statistically significant except PMV/OcPl, overbite, and Y-Mn6 (P < .05) and the changes in group 2 were statistically significant except PMV/OcPl, overbite, and Y-Mn6 (Tables 4 and 5). The changes in group 3 were statistically significant except F. angle, PMV/OcPl, PMV/RaPl, overbite, and Y-Mn6 (P < .05) and had decreased significance in Y-B and Y-Pg.

TABLE 4.  Changes Between Pre-Tx and Post-Tx and Comparison of the Treatment Effect Between Three Groups; Angular Measurements^a

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TABLE 5.  Changes Between Pre-Tx and Post-Tx and Comparison of the Treatment Effect Between Three Groups; Linear Measurements^a

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Correlation between the change of overjet and other changes

The change of overjet correlated with changes of SNA, FMA, LFH, Y-A, Y-Mx.1, X-Mn.1, and X-Pg in groups 1 and 2, with that of U1/FH, Y-Mn1 in group 3, and with that of SNB, Facial axis, Y-Pg, Y-B, and U6-PaPl in all groups (Table 6).

TABLE 6.  Correlation of the Overjet Change and Other Treatment Changes^a

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Skeletal and dentoalveolar changes contributing to overjet and molar relation correction

The correction of overjet was because of 80.1% skeletal and 19.9% dentoalveolar effect in group 1, 84.0% skeletal and 16.0% dentoalveolar effect in group 2, and 63.6% skeletal and 36.4% dentoalveolar effect in group 3 (Figures 6 through 8). The correction of molar relation was because of 112.5% skeletal and −12.5% dentoalveolar effect in group 1, 86.5% skeletal and 13.5% dentoalveolar effect in group 2, and 60.0% skeletal and 40.0% dentoalveolar effect in group 3.

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DISCUSSION

Before 1970, skeletal Class III malocclusion was believed to result from a prognathic mandible. Consequently skeletal Class III malocclusions were treated with a chin cap to inhibit mandibular growth, or by orthognathic surgery after completion of growth. In recent years, however, face mask therapy has become a common technique used to correct the developing Class III malocclusion because of the increasing acceptance of a significant influence of maxillary deficiency in Class III structural etiology. In addition, numerous clinical reports suggest this approach is more successful than other techniques such as chin cap, functional appliance, or camouflage therapy.

Kambara's animal study14 with Macaca irus showed that forward movement and anterior displacement of the maxilla by extra oral forward force are because of the remodeling of the circummaxillary suture and the maxillary tuberosity. The extra oral forward forces are most effective when used as early as possible because of the high degree of cellular activity in the suture area during this time. In her description of the development of sutures involved in the area of the maxilla, the palatine bone, and the sphenoid bones, Melsen29 reported that with increasing age and the developing complexity of the sutural system, attempted disarticulation during the late juvenile and early adolescent periods was always accompanied by fracture of the heavily interdigitated osseous surface.

Hass13 reported that palatal expansion by RME produced a forward and downward movement of maxilla by affecting the intermaxillary and circummaxillary sutures and the disruption of these sutures may help initiate cellular response in the sutures, allowing for a more positive reaction to protraction force. Because the anterior portion of maxilla can be constricted with maxillary protraction3031 and maxillary retrognathic patients also have posterior crossbites because of the transverse maxillary deficiency, the RME is useful in these patients.

One of the most important factors to consider about treatment of skeletal discrepancies is the optimal treatment timing and prognosis of growth by the evaluation of skeletal maturity. Although growth is a sequential phenomenon common to everyone, the onset, intensity, and duration of adolescent growth varies greatly between individuals. Individual growth and development should be evaluated by physiologic age and not by chronological age. Skeletal age can assess the skeletal maturity by the developmental status of individual bones. Radiographs of the hand and wrist are very useful in assessing skeletal maturity because of successive changes from the birth to the completion of growth, in addition to the convenience in taking such radiographs when compared with other regions. Intramembranous ossification is observed around the circummaxillary sutures, and these sutures have an adaptability in the growing facial skeleton.32 Suda et al33 have reported that although the hand-wrist film is based on the endochondral ossification of RUS bones, the skeletal age of facial mask patients was closely correlated with the forward movement of maxilla and increase in palatal length, and consequently, with remodeling of circummaxillary sutures.

CONCLUSION

This cephalometric study evaluated skeletal and dentoalveolar changes induced by RME and facial mask in three groups of 85 subjects exhibiting Class III malocclusion with retruded maxilla.

The major findings were as follows.

1. There was no difference in the effects of maxillary advancement after maxillary protraction between the prepubertal growth peak and the pubertal growth peak group, but there was a decrease in the postpubertal growth peak group.

2. In the postpubertal growth peak group, there was a decrease in maxillary skeletal advancement, although the dentoalveolar effect increased.

3. The posteroinferior rotation of mandible, the increase of lower facial height, and the eruption of maxillary molars showed no correlation with skeletal age.

The results of our study emphasize the importance of performing a biologic evaluation of skeletal maturity and pubertal growth peak in individual patients in the diagnosis and treatment planning of Class III malocclusions.