Characteristics of the patient, the treatment plan, and the practitioner's office were examined to evaluate causes for variation in the duration of orthodontic treatment. From six offices 118 patients were evaluated. All patients were treated in a single phase with fixed appliances. Appliances were worn for an average of 23.1 months. The mean duration for offices ranged from 19.4 to 27.9 months. Thirty-eight percent of the patients had extractions, and 32% wore headgear. Fifty percent of the variation in treatment duration among patients was explained by a five-step multiple regression equation. The variables entering this equation were (1) number of extracted premolars, (2) number of broken appointments, (3) pretreatment mandibular plane angle, (4) pretreatment ANB angle, and (5) pretreatment Salzmann Index. Observations within each office suggested that the time spent by individual clinicians in detailed finishing, which would not be detected by measures such as the Salzmann Index, was an important source of unexplained variation in treatment duration. (AM J ORTHOO DENTOFACORTHOP 1992;102:45-51.)

Many orthodontic patients are concerned about the length of time that they will be required to wear fixed appliances. Accurate estimates o f treatment duration would also be useful to clinicians for efficient office management. Nevertheless, there have been few studies evaluating the duration o f treatment or the variables that affect it. Estimates o f treatment duration for individual patients are made almost entirely on the basis of subjective clinical experience. In this study, we attempt to identify features of the office, clinician, patient, malocclusion, and treatment plan that affect variation between patients and offices in the duration o f fixed appliance treatment.

MATERIALS AND METHODS Data collection Data were collected from six private offices in the exclusive practice of orthodontics. To reduce the effects of a local standard of care or single educational approach, practitioners were selected from several different ge~raphic regions and gradaute orthodontic programs. Practitioners were selected on the basis of availability of necessary recor.ds and a willingness to participate. No treatment criteria or prescreening of the offices was used to select participants. Case selection within each office was limited to white patients with no orthodontic treatment before placement of full fixed labial appliances, only a single course of fixed treatment, and no impacted teeth other than maxillary canines or third molars. Patients without complete records were not included. Each practice was visited for 1 to 3 full days. In each

From theDepartmentof O~hodontics, WashingtonUniversitySchoolof Dental Medicine. 811133617

practice a list of all debandings for a 1- or 2-year period between 1987 and 1989 was made available. Cases were numbered in chronologic order by debanding date and selected according to a computer-generated list of random numbers. In one practice there were not enough cases that met all criteria, therefore one case was selected from 1986. Data were collected for each patient from pretreatment and posttreatment lateral cephalometric radiographs, dental casts, photographs, and office charts. Pretreatment and posttreatment lateral cephalometric radiographs were traced. Measurements taken on each subject included: 1. ANB: The angle between the A point-nasion line and the nasion-B point line. 2. Mandibular plane angle: The angle between a line formed by menton and constructed gonion and the sella-nasion line. 3. Upper facial height/lower facial height ratio: The nasion-menton line was divided into upper and lower portions by a perpendicular line through the anterior nasal spine. Changes during treatment for these three measurements were determined by subtracting the pretreatment value from the posttreatment vaIue. Pretreatment and posttreatment dental casts (intraoral photographs in one practice) were used to determine the severity of malocclusion as measured by the Salzmann Index, ''~ which takes into account teeth that are missing, crowded, rotated, blocked out, spaced, and the presence of mesioocclusion, disto-occlusion, crossbite, open bite, and excessive overbite or overjet. The posttreatment value of the Salzmann Index was adjusted to allow for planned Class II and Class III results. To avoid negative numbers, the change during treatment was calculated by subtracting the posttrcatment Salzmann Index from the pretrcatment value. Variables collected from the individual patient records included: 45

46 F i n k a n d Smith

Am. J. Orthod. Dentofac. Orthop. July 1992

T a b l e I. D e s c r i p t i v e statistics b y office: c a t e g o r i c a l v a r i a b l e s

Males Females Headgear used Impacted canines' Surgical cases Extractions (all types) Incisor extractions Two premolar extractionsb Four premolar extractions' Active retention Passive retention Office variables Number of chairs Number of chairside assistants Number of debandings per year Practitioner variable Years practicing orthodontics

Office no. 1 n = 19

Office no. 2 n = 20

Office no. 3 n = 20

Office no. 4 n = 20

Office no. 5 n = 20

Office no. 6 n = 19

Total n = 118

No. [ Percent

No. [ Percent

No. [ Percent

No. [ Percent

No. [ Percent

No. [ Percent

No. I Percent

11 5

42 58 26

It 9 3

55 45 15

12 8 4

60 40 20

1 1

5 5

1 I

5 5

0 2

0 10

13

60

6

30

6

0

0

0

0

2

10

5

11

58

4 15

21 79

8

5 15 0 0

25 75 0 0

8 12 14 I

6 13 12

32 68 63

50 68 38

42 58 32

1 l

5 5

4 8

3 7

4

40 60 70 5 10 20

I

5

2

30

8

40

7

37

44

36

0

0

3

15

0

0

0

0

3

3

25

0

0

2

l0

2

10

0

0

11

9

1

5

6

30

3

15

2

l0

7

37

30

25

19 1

95 5

0 20

0 100

0 20

0 100

0 20

0 100

2 17

10 89

25 93

21 79

4 2

19 22

5 5

4 2

10 4

8 5

150

700

300

240

350

180

14

26

15

7

25

24

"In office no. 6, one patient had two impacted canines. bin offices no. 2 and no. 4, one patient had two premolars and one lower incisor extracted. 'In offices no. 1 and no. 4, one patient had three premolar extractions, with the fourth premolar missing.

I. Treatment duration, beginning with the placement of the first arch wire and ending with complete bracket removal, measured in months. 2. Total number of office visits during treatment. Office visits included bonding, banding, appliance adjustments (elastics, wires, ligatures, headgear, emergency appointments), but did not include visits solely for oral hygiene instruction or broken appointments. 3. Total number of broken appointments. 4. Age o f t h e patient at the beginning of treatment measured to the nearest whole month. 5. Sex of the patient. 6. Whether headgear was used (types of headgear or duration of headgear wear were not considered). 7. Number of impacted canines. An impacted canine was defined as the impossibility "for further movement along the axis of the displaced (canine) to take place owing to a physical obstruction such as the incisor root. ''3 8. Whether orthognathic surgery was part of the treatment.

9. Number and type of extracted teeth. 10. Use of active or passive retention, and if applicable, months of active retention. These data were used to calculate several ratio variables: (l)frequeneyofappointments = totalnumberofvisits/treatment duration, (2) frequency of broken appointments = total number of broken appointments/treatment duration, (3) ratio of broken appointments to kept appointments = total number of broken appointments/total number of office visits, and (4) frequency of scheduled appointments = (total number of office visits + total number of broken appointments)/treatment duration. Additional observations recorded for each office included the number of chairs used for orthodontic treatment (not including a records chair) and the number of chairside assistants. Finally, the number of years the practitioner had been in orthodontic practice and the total number of patients debanded in 1988 were recorded.

Data analysis Differences between offices were evaluated by one-way analysis of variance for each measurement. A Tukey-HSD

Volume 102 Number 1

test was used to identify significantly different pairs of means following an overall significant F ratio. Pearson correlation coefficients were calculated between each variable and treatment duration. Multiple regression equations to predict treatment duration were calculated with three separate subsets of independent variables: (l) patient characteristics, (2) treatment characteristics, and (3) office characteristics. The significant independent variables from each of these equations were then used to calculate a single general multiple regression equation to predict treatment duration. The deviation of each patient (the residual) from this overall equation was averaged for all patients in each office to compare treatment duration between offices following removal of the variance explained by the best set of independent variables. RESULTS

Tables 1 and 11 list the descriptive statistics for all variables, separately for each office and for the total sample. Data were collected on 118 patients (50 males and 68 females) ranging in age from 8 years 5 months to 50 years 11 months at the beginning of treatment. Fixed appliances were worn an average of 23.1 months, with a range of from 9 to 44 months. The severity of malocclusion at the beginning of treatment as measured by the Salzmann Index ranged from 3 to 32 points with a mean of 16.7, whereas the mean Salzmann Index at the end of treatment was 1.1. Ninety-eight percent (116 patients) were treated with a pretorqued preangulated appliance. Four offices used an 0.018-inch bracket slot, one office used an 0.022 slot, and one office used a combination of 0.018 inch in the anterior segment and 0.022 inch in the posterior segment. Headgear was used in 38 cases (32%), but frequency of use differed substantially among the offices. There were three cases of one impacted maxillary canine and one case of bilateral impacted maxillary canines. Four offices had one surgery case each and two offices had two surgery cases, for a total of eight surgery cases (6.8%). Forty-four (38%) of the patients had extractions. Twenty-eight patients had four premolars extracted, 11 had two premolars extracted, 2 had three premolars extracted (in both of these cases the fourth premolar was missing), and 3 had one or more lower incisors extracted. One practice used tooth positioners routinely, two offices used active retention in 21% and 10% of their sample, and three offices used only passive retention. Monthly appointment frequency ranged from 0.88 to 1.3, with a mean of 1.14 appointments per month. When converted to days between appointments, the range was 26.4 days to 39.0 days, with an overall mean of 34.2 days. Practice size ranged from 150 to 700 patients debanded in 1988, and from 19 chairs with 22 chairside

Dttralio/I o f Ireatme/zl

47

assistants to 4 chair and two chairside assistants. One of the practices was a partnership; the other five were individual clinicians. The orthodontists had been in exclusive practice for from 7 to 26 years. Four practitioners were Diplomates of the American Board of Orthodontists, and two were preparing for the Phase III examination. The mean duration of treatment within an office varied from a high of 27.85 months in office no. 3 to a low of 19.45 months in office no. 4, for a mean difference of 8.40 months between the two most extreme offices. The differences among offices in treatment duration are statistically significant (F = 4.32, p = 0.001). Office no. 3, with the greatest mean treatment duration, had a lower frequency of appointments than four of the other five offices, and thus did not have a greater than average number of visits per patient. Office no. 1, with the largest number of office visits per patient (29.16), had an average treatment duration only 1.1 months greater than the average for the entire group. Correlation coefficients and linear regressions were calculated between several variables and the duration of treatment. When these statistics are determined for mean values from each office, no statistically significant relationships are observed. This is due to the small sample size (N = 6) and the resulting weak statistical power. When the data are evaluated on the basis of 118 individual observations, several relationships emerge. As might be expected, there is a strong positive relationship between the total number of office visits and the duration of treatment (duration = 5.4 + 0.70 visits; r = 0.69). The number of broken appointments is also positively correlated with treatment duration (r = 0.27). Of the clinical measurements, only the change in the Salzmann Index (r = 0.18) and the pretreatment ANB angle (r = 0.21) are significantly related to treatment duration. Table III shows the results of several stepwise nmltiple regression analyses used to identify the combination of variables that have the greatest effect on the duration of treatment. An analysis with only variables defined as characteristics of the patient identifies the pretreatment ANB angle, the pretreatment mandibular plane angle, and the pretreatment Salzmann Index as significantly related to treatment duration with a multiple correlation of 0.34. The age and sex of the patient and the pretreatment anterior facial height ratio did not add further to prediction. An analysis of treatment characteristics also produced a three-step equation with the number of extracted premolars, the number of broken appointments, and the use of headgear significantly predicting treat-

48

Fink and Smith

Am. d. Orthod. Dentofac. Orthop. July 1992

Table II. Means and standard deviations for variables measured on each patient within offices Office no. I

Office no. 2 v = 20

n = 19

I SD Treatment time (mo.) Total office visits Number of broken appointments Age Pretreatment Salzmann Index A Salzmann Index (pretreatment-posttreatment) Duration of active retention (mo.)

x

I

SD

Office no. 3 n = 20

;

I

24.26 29.16 1.58 16.57 16.37 16.32 1.82

6.61 7.57 !.90 7.78 5.75 5.79 4.03

20.95 25.50 0.60 21.47 18.40 14.95 3.65

6.93 8.15 1.14 i 1.58 6.22 5.61 1.98

27.85 24.15 1.70 17.22 18.25 17.00

4.53 4.28 3.01 9.77 6.22 5.97

4.00 - 1.74 35.34 - 1.34 0.78 0.02

2.86 2.49 8.05 4.56 0.09 0.09

1.85 0.20 32.98 0.43 0.76 0.00

2.54 !.20 4.74 0.82 0.07 0.04

1.45 0.07 33.45 1.08 0.75

2.76 1.42 7.80 2.49 0.06

-0.02

0.03

1.21 0.07 0.06 1.28

0.09 0.11 0.09 0.14

1.24 0.03 0.03 1.27

0.18 0.05 0.05 0.17

0.88 0.06 0.07 0.93

0.15 0.08 0.13 0.13

Cephalometric measurements

ANB (pretreatment) A ANB (posttreatment-preteatment) MP (pretreatment) A MP (posttreatment-pretreatment) UFH/LFH (pretreatment) A UFH/LF}I (posttreatment-pretreatment) Total appointments/treatment duration Broken appointments/treatment duration Broken appointments/total appointments Totalappointments + broken appointments/treatment duration

ment duration. Variables not included in the equation were the presence or absence of incisor extractions and the duration of active retention. The teeth extracted during treatment were classified in several different ways to select the method that resuited in the strongest relationship to treatment duration. Patients were categorized by (I) number of extracted teeth, (2) number of extracted premolars, (3) extraction or nonextraction, (4) premolar extraction versus all others, and (5) two premolar extraction, four premolar extraction, and all others. Of these five methods, the best results (greatest explained variance) were obtained by evaluating the number of extracted premolars. The two equations in Table III with this variable have regression coefficients rounded to 0.9. This indicates that each extracted premolar adds 0.9 months to the duration of treatment, or 1.8 months for a two premolar case and 3.6 months for a case with four premolars extracted. The third set of variables, which included office chhracteristics such as the number of chairs, number of assistants, number of debandings per year, and number of years the practitioner had been practicing orthodontics, showed no statistically significant relationship to treatment duration. The predictive value of the six significant variables from the first two multiple regression equations were evaluated by combining them in a single general equation. A five-step equation that included the number of

premolars extracted, number of broken appointments, pretreatment mandibular plane angle, pretreatment ANB angle, and pretreatment Salzmann Index had a multiple correlation of 0.50 with treatment duration. This equation was used to compute a predicted treatment duration for each patient. The individual deviations from the predicted duration were used to evaluate differences in duration of treatment between patients in each office when these five variables had been taken into account. The mean of the treatment duration residuals differed by up to 7 months (shortest in office no. 4 and longest in office no. 3) after all variation explained by the five variables in the multiple regression equation had been removed. DISCUSSION

There are few studies with which the present results can be compared. As discussed by Vig et al., 4 orthodontic research has traditionally focused on effects of treatment, rather than on epidemiologic questions related to the efficacy of treatment. The average duration of treatment in these 118 cases from six offices was 23.1 months. Cases were selected to include only patients treated in a single phase. This result is similar to Alger's 5 mean treatment duration of 22.0 months for patients selected by similar criteria, but shorter than the mean of 31 months reported by Vig et al., 4 who included patients treated in two and three phases.

~,blume 102 A'umber I

Duration

Office no. 4 n = 20

Office n o . 5 n = 20

of treatment

Total n = 118

Office no. 6 n = 19

SD

]

[

SD

19.45 22.10 1.30 20.19 17.05 14.55

3.52 3.75 2.47 10.66 5.06 4.11

23.45 28.30 1.25 18.03 14.65 13.60

6.37 5.61 1.74 10.76 6.62 6.53

22.79 23.11 0.74 15.39 15.37 15.37 0.13

8.38 6.34 1.45 4.85 5.75 5.75 0.43

23.12 25.37 1.24 18.18 16.70 15.29 0.93

6.67 6.55 2.07 9.58 6.00 5.66 2.26

0.95 0.25 33.48 - 0.13 0.81 0.01

i.63 !.19 4.65 1.65 0.06 0.04

3.20 -0.80 35.80 0.43 0.79 -0.02

1.81 i.67 7.37 1.96 0.08 0.04

2.50 - 1.47 33.95 0.11 0.79 - 0.02

2.60 1.50 6.79 1.45 0.08 0.04

2.31 -0.56 34.16 0.11 0.78 0.00

2.57 1.79 6.63 2.50 0.08 0.05

1.14 0.06 0.05 1.21

O. ! I O. I 1 0.09 0.17

1.30 0.05 0.04 1.35

0.54 0.06 0.06 0.53

1.07 0.03 0.03 1.10

0.28 0.04 0.05 0.27

1.14 0.05 0.05 1.19

0.30 0.08 0.08 0.30

The most important variable measured in this study for explaining differences among patients in the duration of treatment was the extraction of premolars. Nonextraction cases averaged 21.95 months, two premolar cases averaged 25.0 months, and four premolar extraction cases averaged 26.18 months. These results are also similar to those of Alger, s who found extraction cases to average 4.6 months longer than nonextraction cases. The study by Vig et al.,4 which placed particular emphasis on the consequences of extractions on treatment duration, requires careful evaluation. They found an average treatment duration of 31.3 months for nonextraction cases and 31.2 months for extraction cases, with no significant difference. However, in every individual practice, the mean duration for extraction cases was greater than for nonextraction cases. This seemingly paradoxical result was due to a very short mean treatment duration in one office that had a very fiigh percentage of extraction cases. As reported by Brown 6 in the thesis from which these data were derived, when the subgroup of patients treated in one phase were evaluated, extraction cases averaged 2.7 months longer than nonextraction cases. Another important variable affecting the duration of treatment was the number of broken appointments. The correlation coefficient between each patient's treat~ ment duration and the number of broken appointments was 0.27, and broken appointments entered the combined multiple regression equation as the second vari-

49

able after the number of premolars extracted. It is likely that the variable "broken appointments" serves as a measure of overall patient compliance. Patients with broken appointments are more likely to exhibit other forms of noncompliance, such as lack of headgear or rubber band wear, and increased appliance breakage. Orthodontists have long recognized the importance of compliance for efficient treatment, 7 and the effect found here is not unexpected. The remaining variables contributing to the prediction of treatment duration in the combined multiple regression equation reflect the severity of the malocclusion, namely, the ANB angle, Salzmann Index, and mandibular plane angle. With increases in the ANB angle and increases in the Salzmann Index, treatment lengthens as expected. Increases in the mandibular plane angle, however, result in a decrease in the duration of treatment of almost 0.3 months for each degree. This may reflect treatment duration for deep overbite and/or open bite cases rather than a linear trend for mandibular plane angles within one or two standard deviations from the mean. When examined alone with treatment duration, the slope of the regression for mandibular plane angle was also negative ( - 0.14), and the probability was near significance (0.13). We note that although in one office the Salzmann Index was determined from photographs rather than from casts, there were no significant differences between offices in pretreatment Salzmann Index or in the change during treat-

50

Fink and Smith

Am. J. Orthod. Dentofac. Orthop. July 1992

Table III. Stepwise multiple regression analysis Equation I. Patient characteristics

I 1. ANB (pretreatment) 2. Mandibularplane angle (pretreatment) 3. SalzmannIndex (pretreatment)

r

I

0.205 0.272 0.335

I 0.042 0.074 0. i 12

r 0.009 0.017 0.029

Treatment duration = 25.59 + 0.618 (ANB pretreatment) - 0.222 (Mandibularplane angle pretreatment) + 0.221 (Salzmann Index pretreatment). F = 4.80. P = 0.003.

Equation II. Treatment characteristics

I. Premolarextractions 2. Broken appointments 3. Headgear

0.277 0.359 0.404

0.077 0.129 0.163

0.010 0.008 0.033

Treatment duration = 25.57 + 0.883 (Numberof extracted premolars) + 0.762 (Numberof broken appointments) - 2.628 (Headgear). F = 7.40. P =