Abstract
In mandibular deficient patients, mandibular growth is not expected after the adolescent growth spurt, so mandibular advancement surgery is often carried out at 13 years. To test if the long-term stability for younger patients is similar to that for adult patients, the authors compared cephalometric changes from 1-year postsurgery (when changes due to the surgery should be completed) to 5-year follow up. 32 patients who had early mandibular advancement with or without simultaneous maxillary surgery (aged up to 16 for girls and 18 for boys), and 52 patients with similar surgery at older ages were studied. Beyond 1-year postsurgery, the younger patients showed significantly greater change in the horizontal and vertical position of points B and pogonion, the horizontal (but not vertical) position of gonion, and mandibular plane angle. 50% of younger patients had 2–4 mm backward movement of Pg and another 25% had >4 mm. 15% of older patients had 2–4 mm change and none had >4 mm. Long-term changes in younger patients who had two-jaw surgery were greater than for mandibular advancement only. Changes in younger groups were greater than for adult groups. Satisfaction with treatment and perception of problems were similar for both groups.
The timing of surgical treatment for younger patients with mandibular deficiency is guided by two considerations. The first is that studies of patients who had mandibular advancement prior to the adolescent growth spurt show little or no forward growth of the mandible after surgery, although vertical growth of the mandible does occur so that downward-backward rotation of the mandible is avoided . The second is that late forward mandibular growth almost never occurs in mandibular deficient patients, as often is the case in patients with mandibular prognathism . Based on this, it seems logical to wait to advance the mandible surgically until after the adolescent growth spurt, except in exceptional situations (for example, severe deficiency leading to sleep apnea or extreme social problems) and in patients who want treatment as soon as possible when the growth spurt is completed or nearly completed . No comparison of long-term changes in patients selected in this way for early surgery with those in older patients has been reported. The objective of this study was to compare long-term changes (from 1 year to 5 years or more postsurgery) in patients with mandibular advancement as soon as growth had apparently stopped with those who had surgical advancement as adults.
Methods
As of March 2009, the data base of the Dentofacial Program at the authors’ institution contained complete records, including 5-year or longer recall, for 32 patients who had mandibular advancement with or without simultaneous maxillary surgery at the age of 16 years or younger for girls and 18 years or younger for boys. Cephalometric changes and psychosocial data for these younger patients were compared with data from 52 older patients who had mandibular advancement at 17 years of age or older for girls and 19 years or more for boys. All these patients had rigid internal fixation. Demographic and pre-treatment characteristics of the sample are shown in Table 1 . The percentage of patients with two-jaw surgery was higher in the younger group and the severity of the skeletal discrepancy was greater in both the two-jaw and mandible only younger patients. Since early surgery is primarily carried out for patients with strong social concerns who want surgery as soon as possible, this difference reflects a degree of selection for severe problems in the younger group.
| Younger, n = 32 | Older, n = 52 | |
|---|---|---|
| Gender | ||
| Male | 11 (34%) | 12 (23%) |
| Female | 21 (66%) | 40 (77%) |
| Pre-treatment | ||
| ANB (°) | 6.7 ± 2.4 | 5.9 ± 2.2 |
| Co-Pg (mm) | 113.3 ± 8.3 | 115.0 ± 7.4 |
| GoGn-SN (°) | 37.9 ± 10.5 | 32.6 ± 8.2 |
| N-Me (mm) | 126.1 ± 9.7 | 121.7 ± 8.9 |
| Surgery type | ||
| Mn advance only | 16 (50%) | 44 (85%) |
| Mn adv + Mx up | 16 (50%) | 8 (15%) |
| Age at surgery (years) | 15.9 ± 1.7 | 34.9 ± 9.6 |
| Male (range) | 16–19 | 20–46 |
| Female (range) | 13–17 | 19–54 |
| Surgery changes | ||
| Genioplasty also | 16 (50.0%) | 8 (15.4%) |
| Co-Pg (mm) | 7.1 ± 3.4 | 5.7 ± 2.8 |
| Change in Pg position | ||
| Horizontal (mm) | 8.2 ± 5.8 | 4.8 ± 4.1 |
| Vertical (mm) | 1.0 ± 5.9 | 3.8 ± 2.8 |
| GoGn-SN change (°) | −3.1 ± 5.5 | 0.5 ± 3.5 |
| Follow up (years) | 6.8 ± 2.6 | 6.9 ± 3.0 |
| Range | 4.5–14.9 | 4.8–20.2 |
The lateral cephalometric radiographs were digitized using the UNC 130-point model . Changes in landmark position and dimensions from 1 to 5 years postsurgery were calculated. For cephalometric changes, the data were evaluated from two perspectives: the mean changes and the percentage of patients with significant clinical change. Analysis of covariance with alpha set at 0.01 was used to compare the change between the two groups from 1 to 5 years, controlling for the 1-year postsurgery values.
A subset of patients in both groups also completed treatment satisfaction (SAT) and long-term condition-specific quality of life questionnaires: problems with occlusion and function (PSPOF), problem perceptions (PSP), and problems with facial sensation (PFS). The questionnaires were developed, refined and the subscale structure identified by factor analysis as part of the preliminary aspects of NIH grant DE10028, Psychosocial vs Clinical Outcomes of Orthognathic Surgery. The questionnaires have been used in multiple projects and the directionality of response over time and between treatment groups has been consistent with the theoretical framework . Each of the questionnaires has subscales related to specific aspects of the index. With alpha set at 0.01, unpaired t -tests were used to compare the average value rating for each subscale of the two groups.
Results
Mean and standard deviations for changes in landmark positions and dimensions from 1-year postsurgery to 5 years or longer in the two groups are shown in Table 2 , and the percentage of patients with changes is illustrated in Figs 1–3 .
| Younger, n = 32 | Older, n = 52 | P -value | |||
|---|---|---|---|---|---|
| Mean | SD | Mean | SD | ||
| Horizontal | |||||
| Point A (mm) | −0.7 | 1.5 | −0.2 | 1.1 | 0.04 |
| Point B (mm) | −2.5 | 1.8 | −0.2 | 1.5 | <0.0001 |
| Gonion (mm) | −1.5 | 2.3 | 0.3 | 2.1 | 0.0015 |
| Pogonion (mm) | −3.0 | 2.3 | -0.3 | 1.5 | <0.0001 |
| Condylion (mm) | −0.4 | 2.0 | 0.1 | 2.4 | 0.39 |
| Mand molar (mm) | −1.3 | 2.4 | −0.1 | 3.1 | 0.06 |
| Vertical | |||||
| Point A (mm) | 0.2 | 2.0 | −0.1 | 1.4 | 0.28 |
| Point B (mm) | 1.1 | 2.3 | −0.2 | 1.8 | 0.005 |
| Gonion (mm) | −0.4 | 3.0 | −0.1 | 3.2 | 0.69 |
| Pogonion (mm) | 1.5 | 2.4 | −0.1 | 1.9 | 0.0004 |
| Condylion (mm) | −0.8 | 1.4 | −0.6 | 2.0 | 0.65 |
| Max Molar (mm) | 0.6 | 1.5 | −0.4 | 1.5 | 0.01 |
| Dimensions | |||||
| Overjet (mm) | 1.0 | 1.1 | 1.2 | 1.2 | 0.61 |
| Overbite (mm) | 0.0 | 1.4 | 1.2 | 1.4 | 0.002 |
| Co-Pg (mm) | 0.2 | 2.1 | 0.0 | 2.7 | 0.91 |
| Co-Gn (mm) | 0.3 | 1.8 | 0.1 | 2.8 | 0.87 |
| Mand plane (°) | 0.5 | 2.0 | −1.3 | 2.2 | 0.001 |
| Pal plane (°) | 0.3 | 2.0 | −0.2 | 1.2 | 0.26 |
Between 1 and >5 years postsurgery, the long-term posterior movement of points B, pogonion (Pg) and gonion (Gn) was significantly greater in the younger patients than in the older ones, with the greatest difference at pogonion (mean change −3 mm for the younger patients, −0.3 mm for the older ones, P < 0.0001) ( Table 2 ). In both groups, only small horizontal changes at condylion (Co) were noted and this difference was not significant.
Slightly more than half of the younger group had 2–4 mm backward movement of pogonion from 1 to >5 years postsurgery, and another 25% had >4 mm backward movement, as opposed to 15% with 2–4 mm and none with >4 mm in the older patients ( Fig. 1 ). The percentage of patients with horizontal changes at gonion was smaller in both groups but the relative difference in percentages for the two groups was similar. Changes at condylion occurred in a minority of the patients in both groups, with an almost identical pattern of change.
Statistically significant differences in vertical landmark positions were noted only for points B and pogonion ( Table 2 ). In the younger group, if the vertical position of pogonion changed, it was much more likely to move up and 15% had a >4 mm upward movement ( Fig. 2 ). In the older group upward and downward changes were equally likely, and only 4% had a >4 mm upward movement. In both groups, changes at gonion occurred in over half the patients, with downward movement predominating, and the pattern was almost identical. At condylion, older patients who had a 2 mm or more change were as likely to have upward as downward movement. In the younger group, none had 2–4 mm upward change while 25% had >4 mm downward movement.
The only statistically significant difference in dimensional changes between the two groups was for the mandibular plane angle ( Table 2 ). Most of those in the older group who had a change showed a decrease in this angle, while in the younger group most of those with change had an increase ( Fig. 3 ). Overjet increased 2–4 mm in about 20% of both groups. Mandibular length (Co-Pg) changed in nearly twice as many older as younger patients, but in both groups the chance of an increase was about equal to the chance of a decrease. A higher percentage of older patients also had a change in ramus height (Co-Gn).
Scores on the psychosocial indices, including the subscales for each index, are shown in Table 3 . For SAT, a higher score indicates greater satisfaction (and therefore is good); for the other indices a higher score indicates more problems (and therefore is bad).
