Introduction
The aims of this study were to report contemporary orthodontic extraction frequencies at a university center and to investigate what patient-related factors might influence the likelihood of extraction.
Methods
The records of 2184 consecutive patients treated at the University of North Carolina from 2000 to 2011 were analyzed. Year-by-year rates for overall orthodontic extractions and for extraction of 4 first premolars were calculated. Logistic regression, adjusting for all recorded patient risk factors for extraction, was used to examine both the changes in extraction frequencies over time and the influence of individual patient factors on the odds of extraction.
Results
Small linear decreases in orthodontic extraction frequency overall (OR, 0.91; 95% CI, 0.88-0.95) and in extraction of 4 first premolars (OR, 0.95; 95% CI, 0.90-0.99) were seen. The overall extraction rate was 37.4% in 2000, and it fell just below 25% from 2006 onward. Four first premolar extraction rates ranged from 8.9% to 16.5%. Extractions were significantly more likely as crowding and overjet increased (OR, 1.2; 95% CI, 1.14-1.25; OR, 1.1; 95% CI. 1.07-1.19), as overbite decreased (OR, 0.8; 95% CI, 0.77-0.89), with Class II dental or skeletal relationships (OR, 1.5; 95% CI, 1.12- 2.05; OR, 1.4; 95% CI, 1.04-1.85), and for nonwhite patients (OR, 3.0; 95% CI, 2.2-4.06 for other races; OR, 4.1; 95% CI, 3.03-5.66 for African Americans).
Conclusions
Extractions were just as likely to be associated with Class II dental and skeletal problems and with open-bite problems as with crowding alone.
Highlights
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Overall orthodontic extraction rates showed a mild decreasing trend from 2000 to 2006.
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Overall extraction rates remained near 25% after 2006.
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Extraction of 4 first premolars decreased slightly but remained just above 10%.
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Extraction odds increased with increasing crowding or overjet.
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Extraction odds increased with decreasing overbite or Class II malocclusion.
The extraction of permanent teeth for orthodontic reasons has been a topic hotly debated in the past and continues to be of interest in the specialty of orthodontics. For the clinician, it is important, regardless of practice philosophy, to have an understanding of contemporary rates of extraction as an adjunct to comprehensive orthodontic treatment.
Historically, reported extraction rates have varied widely from less than 25% of patients to more than 80%. Data derived from surveys of practicing orthodontists have been shown to have significant inaccuracies. For this reason, data generated from institutions where many patients are treated using a variety of treatment philosophies are preferred because they can provide more meaningful epidemiologic information.
In the early 1990s, Proffit summarized extraction rates over a 40-year period at the University of North Carolina. He found that the rate of extraction increased from 30% in 1953 to a peak of 76% in 1968 before falling to nearly 28% again in 1993. Importantly, most of the fluctuation in these rates was apparently driven by a change in the frequency of extraction of all 4 first premolars, with other extraction patterns showing less change. The changes in 4 first premolar extractions were attributed to an evolving orthodontic philosophy regarding the stability of alignment after arch expansion, to advances in bonded rather than banded orthodontic appliances, and to the esthetic impact of incisor position on the soft tissues of the face.
More recently, Janson et al reported the experience of a Brazilian university with changes in extraction rates over time. They found that over a 35-year period, the extraction rate fell from nearly 86% of all patients in 1973 to 46% in 2007, with a concurrent downward trend in the rate of 4 first premolar extractions over the same time period as well. The authors theorized that the decrease in extraction rate was due to variables similar to those discussed by Proffit, as well as a fear of a connection between tooth extraction and temporomandibular joint dysfunction, and also changes in the use of growth modification, interproximal reduction, and maxillary expansion.
Both of these institution-based studies used a model by which the outcome (extraction) was the focus of the investigation. In this way, extraction patterns were used to generate insight as to trends in treatment styles: eg, the extraction of 2 premolars in an arch to camouflage an anteroposterior issue vs the extraction of 4 premolars for crowding or protrusion. Treatment strategy, including the extraction pattern and appliances or methods used, is an important component in understanding the current use of tooth extraction in orthodontics. In this study, however, we focused not on appliances or techniques as an explanation for extraction frequency but, instead, on patient-related factors alone.
Given the breadth of individual orthodontic practice styles today, it is important to understand extraction frequencies as a function of patient demographic and diagnostic parameters that might influence the decision to extract (eg, age, race, crowding, overjet, overbite). Up to this point, no institution-derived data to this effect have been widely published.
An understanding of what patient-related variables might be most closely associated with an increased odds of orthodontic extraction might aid the modern clinician in understanding his or her use of diagnostic information to make individual treatment decisions. This type of information might be of particular use in orthodontic training programs to aid future generations of orthodontists in gaining a better perspective of the need for orthodontic extractions, as well the need for the skills to manage extraction patients. Additionally, this information might improve patient communication because often patients would like a better understanding of how the treatment recommended for them compares with treatments frequently recommended for other patients.
The aims of this investigation were to report extraction frequencies at a university center at the beginning of the 21st century and to use an epidemiologic model to investigate what patient demographic or diagnostic factors might influence the likelihood of extraction in the contemporary practice of orthodontics.
To address these aims, the records of 2184 patients treated in the Department of Orthodontics at the University of North Carolina from 2000 to 2011 were analyzed.
Material and methods
The Graduate Clinic in the Department of Orthodontics at the University of North Carolina provides orthodontic and dentofacial orthopedic care using a resident-attending model. For each patient treated, pretreatment patient-related variables are recorded using a standardized format and stored in a centralized digital database. Among the demographic and diagnostic variables recorded for each patient are a number of potential factors that might influence the likelihood of orthodontic tooth extractions.
All characteristics meaningfully recorded for each patient that could be a risk factor for orthodontic extraction are reported in Table I . Consecutive patients were selected as participants in this study if their comprehensive orthodontic treatment began no earlier than January 1, 2000, and ended by December 31, 2011 (2011 was the final year for which data were available). Inclusion criteria were complete pretreatment and posttreatment data in the digital database for each participant. The outcome measured was extraction of teeth for orthodontic purposes, other than third molars. Extractions of deciduous teeth were not included. Since the study was designed to investigate patient-related factors (rather than treatment-related factors) using an epidemiologic approach, all extractions of permanent teeth for orthodontic purposes, including those performed during a first phase of early treatment or in conjunction with growth modification or orthognathic surgery were included. Approval for this study was given by the Institutional Review Board before data were gathered (number 132184).
| Characteristic | Overall median (IQR) or % n = 2184 | Year 2000 median (IQR) or % n = 115 | Year 2005 median (IQR) or % n = 102 | Year 2010 median (IQR) or % n = 326 | P value ∗ |
|---|---|---|---|---|---|
| Sex (%) | |||||
| Female | 58.0 | 56.0 | 52.9 | 58.3 | 0.624 |
| Male | 42.0 | 44.0 | 47.1 | 41.7 | |
| Race (%) | |||||
| White | 68.6 | 82.3 | 68.6 | 63.5 | <0.001 |
| African American | 16.4 | 11.5 | 17.6 | 15.0 | |
| Other | 15.0 | 6.2 | 13.7 | 21.5 | |
| Age at start of treatment (y) | 14.1 (12.7 -16.8) | 13.4 (12.2-15.5) | 14.1 (12.4-16.2) | 14.5 (13.0-19.2) | <0.001 |
| Reduced gingival attachment (%) | 34.4 | 38.3 | 50.0 | 20.0 | <0.001 |
| Initial overjet (mm) | 4.0 (2.0-5.0) | 4.0 (3.0-6.0) | 3.0 (3.0-5.0) | 4.0 (2.0-5.0) | 0.264 |
| Initial maxillary crowding (mm) | 2.0 (0.0 -4.0) | 2.0 (0.0-5.0) | 2.0 (0.0-5.0) | 2.0 (0.0-5.0) | 0.823 |
| Initial mandibular crowding (mm) | 3.0 (0.0-5.0) | 2.0 (0.0-5.0) | 2.0 (0.0-4.3) | 3.0 (1.0-5.0) | 0.214 |
| Initial curve of Spee (mm) | 2.0 (1.0-3.0) | 2.0 (2.0-3.0) | 2.0 (2.0-3.0) | 2.0 (1.0-3.0) | 0.001 |
| Initial overbite | 3.0 (2.0-5.0) | 4.0 (2.0-5.0) | 3.0 (2.0-5.0) | 3.0 (2.0-5.0) | 0.186 |
| Skeletal anteroposterior relationship (%) | |||||
| Class I | 47.0 | 44.7 | 47.1 | 50.9 | 0.792 |
| Class II | 38.9 | 36.8 | 37.3 | 34.0 | |
| Class III | 14.1 | 18.4 | 15.7 | 15.0 | |
| Angle classification (%) | |||||
| Class I | 47.1 | 49.1 | 54.9 | 42.3 | 0.162 |
| Class II | 43.4 | 42.0 | 33.3 | 46.3 | |
| Class III | 9.5 | 8.9 | 11.8 | 11.6 | |
∗ Level of statistical significance set to P = 0.05; chi-square or Kruskal-Wallis test to compare years 2000, 2005, and 2010.
Statistical analysis
In addition to descriptive statistics for the participant characteristics that might have an impact on risks for extraction, year-by-year extraction rates overall and for 4 first premolars in combination were calculated. Third molar extractions were not included in any data or analyses. Logistic regression was used to analyze the trend in extraction rate over time. Multivariate analyses were used to compare participant characteristics at 5-year intervals. Across the entire sample, logistic regression, adjusting for all possible risk factors for extraction in Table I , was used to examine the influence of individual characteristics on the odds for extraction of teeth for orthodontic purposes. Results are reported as odds ratios (OR) with 95% confidence intervals (95% CI) as measures of variance. Odds ratios report associations in terms of the odds that a certain outcome (eg, tooth extraction) will occur with a certain exposure (eg, a Class II dental relationship). All analyses were 2-sided and conducted using software (version 9.2; SAS, Cary, NC), with the level of statistical significance set at P = 0.05.
Results
Characteristics of the 2184 participants included in the study are reported in Table I . Since these variables were not normally distributed, as determined by Kolmogorov-Smirnov tests, medians and interquartile ranges are reported.
Participant characteristics that might influence extraction frequency were compared at 5-year intervals (2000, 2005, and 2010) in Table I . There was a statistically significant difference in racial composition of participants across these time points ( P <0.001), with a consistently decreasing proportion of white participants; there were more African American participants in 2005 but more other patients in 2010 (other includes Asian, Hispanic, and Native American). Participant age showed significant differences across the years examined ( P <0.001), with a small rise from 2000 to 2010. Similarly, the proportion of participants who had at least 1 tooth with clinically apparent reduced attached gingiva (less than 1 mm present) varied across these years ( P <0.001). Initial curve of Spee also showed a statistically significant (but not clinically significant) difference across these years ( P = 0.001). These results confirm that participant characteristics that might influence extraction frequency did, in fact, vary over time.
Extraction rates by year are given in the Figure . Overall extraction frequency was at its highest in 2000 at 37.4%, dropped to a low of 17.6% in 2005, and remained consistently just below 25% from 2006 through 2011. The frequency of 4 first premolar extractions (included here for comparison with other reports rather than for detailed analysis) similarly reached a high in 2000 at 16.5% but then remained relatively consistent just above 10%, ranging as low as 8.9% in 2006 and 2010 and as high as 13.4% in 2008.
To account for fluctuation in participant characteristics from year to year, a logistic regression model, adjusted for all the characteristics in Table I , showed that the odds of extraction chronologically by year were 0.91 overall and 0.95 for 4 first premolars ( Table II ). In other words, when controlling for all factors in Table I that might vary from year to year, there was a linear downward trend in the odds of extraction from 2000 to 2011. When the quadratic term was applied to the overall rate, there was no significant change in odds of extraction by year ( Table II ). The quadratic term was tested since there was an apparent frequency drop at 2005 and then a subsequent increase. The nonsignificant result confirmed that the downward trend in extractions over time followed a linear path from 2000 to 2011, rather than a parabolic path as might be suggested by visual inspection of the data in the Figure .
