Introduction
Orthodontic treatment planning requires skill and expertise with considerable practice variations. The aims of this study were to review retrospectively the pretreatment records of patients with Class I malocclusion and to identify variables that could play a role in the treatment decision.
Methods
From the available records of 1500 orthdontic patients, the pretreatment records of 202 patients were selected at random. Inclusion and exclusion criteria were applied, and the surviving records were divided into extraction (n = 92) and nonextraction (n = 92) treatment groups. Skeletal, dental, and soft tissue measurements were obtained from pretreatment lateral cephalograms and dental casts of subjects with bilateral Class I molar relationships. Data were statistically analyzed by binary logistic regression tests.
Results
The results showed that the variables of lower anterior facial height, E-plane to upper lip, and maxillary and mandibular incisor inclinations were significantly increased in the extraction group ( P <0.05), whereas spacing in the mandibular arch and increased overbite were statistically significant in the nonextraction treatment group ( P <0.05). According to the model, the odds of nonextraction treatment are 1.29 and 1.24 times that of extraction treatment for every 1-mm increase in overbite and spacing in the mandibular arch, respectively.
Conclusions
Vertical facial pattern, overbite, mandibular tooth size-arch length discrepancy, lip position, and maxillary and mandibular incisor inclinations are a few of the important variables that should not be overlooked when planning orthodontic treatment. The findings of this study could facilitate the treatment planning process for patients with Class I malocclusion.
Highlights
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Increased overbite suggests nonextraction treatment.
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Proclined maxillary and mandibular incisors, and procumbent upper lips favor extraction treatment.
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Study findings will facilitate treatment planning for Class I malocclusions.
Extractions in orthodontics have always been a controversial issue. This treatment approach contradicts the philosophy of Edward Angle, who believed that arch expansion could provide sufficient space for ideal positioning of the teeth. With the increase in the numbers of patients with relapse treated by the nonextraction approach, orthodontists have considered extractions unavoidable in certain malocclusions to improve the stability and predictability of orthodontic results. Even though extractions were required in many clinical scenarios, the rate of extraction has historically varied; it was 10% in the 1950s, 50% in the next decade, only 30% in the 1980s, and 25% from 2000 to 2006. The trends have mirrored the recent practice of a nonextraction approach due to concerns regarding temporomandbiular joint pain, facial esthetics, and patients’ demands for fuller and more prominent lips for a more youthful appearance. In Class I extraction patients, all first premolars are frequently removed because they occupy an intermediate position in the arch, facilitating the correction of dental protrusion, midline discrepancies, crowding, and lip procumbency, resulting in a pleasing facial profile with less chance of posttreatment relapse.
The choice of the extraction vs nonextraction approach in the current era of orthodontic treatment is yet to be well elucidated. In our study, we aimed to retrospectively review the pretreatment records of patients with Class I malocclusion and to identify the skeletal, dental, and soft tissue variables that could play roles in the decision-making process.
Material and methods
The principal investigator retrospectively selected 202 pretreatment records of patients with Class I malocclusion by a simple random sampling technique from the data of 1500 orthodontic patients at the Section of Dentistry, Department of Surgery, Aga Khan University Hospital, Karachi, Pakistan. from 2006 to 2016. Of these, 92 records each were carefully chosen for the extraction and nonextraction groups that matched our strict inclusion criteria. An exemption was taken from the ethical review committee of our institution before data collection (4078-Sur-ERC-16). The treatment plan for all orthodontic patients visiting our clinics is routinely determined by a team of orthodontists after critically evaluating each patient’s photographs, cephalometric readings, and cast measurements.
For this study, subjects were selected on the basis of following criteria: (1) full set of permanent teeth including the second molars with bilateral Class I molar relationships. (2) complete pretreatment records with good quality standardized lateral cephalograms and dental casts; (3) no significant medical history, and no dental or craniofacial anomalies, syndromes, history of trauma, or previous orthodontic treatment; and (4) no decayed, missing, or periodontally compromised teeth. All patients included in our study were treated by 2 clinicians (A.S., M.F.) using the current treatment philosophy for correcting a Class I malocclusion.
The lateral cephalograms obtained for our study were recorded in natural head position with the same machine with the head parallel to the Frankfort horizontal plane and the teeth in centric occlusion. These radiographs were recorded with rigid head fixation and a 152-cm source to the midsagittal plane distance and a 15-cm film to the midsagittal plane distance using an Orthoralix 9200 device (Gendex–KaVo, Milan, Italy). Cephalometric landmarks were identified according to the classic definitions in the orthodontic literature. From these landmarks, various cephalometric measurements were derived including SNA, SNB, and ANB angles; Nasion perpendicular to point A, Nasion perpendicular to Pog. Wits appraisal, SN-Go.Gn angle, FMA, lower anterior facial height, UI-SN angle, IMPA, nasolabial angle, and relationship of upper and lower lips with respect to the E and S planes. Overjet, overbite, upper and lower dental midlines, and maxillary and mandibular tooth size-arch length discrepancies were measured on dental casts using a digital vernier caliper (0-150 mm ME00183; Dentaurum, Pforzheim, Germany) with accuracy of 0.02 mm and reliability of 0.01 mm as per the manufacturer’s specifications.
We randomly selected 35 lateral cephalograms and 35 dental casts from the total sample; these were reevaluated by the principal investigator (B.A.) after an interval of 3 weeks for intraexaminer reliability. The intraclass correlation coefficient had a value greater than 0.90 for all measured variables. Interexaminer reliability was also evaluated after a few weeks, with a value greater than 0.78 for all measured parameters.
Statistical analysis
We used data analysis and statistical software (version 12.0, Stata; StataCorp, College Station, Tex) to analyze the collected data. Descriptive statistics were calculated for all the quantitative variables. A binary logistic regression model was built to assess the effect of different independent variables on the extraction and nonextraction outcomes. The binary logistic regression technique is most often used to model the relationship between a binary outcome variable and a set of covariates. In the current study the binary outcome variable was the treatment decision—nonextraction or extraction—and a set of independent variables from cephalograms and dental casts was used. Multicollinearity was checked among the independent variables using the Pearson correlation. Multicollinearity is a phenomenon in which if 2 or more independent variables in a multiple or binary regression model are highly correlated, then any 1 variable can be linearly predicted from the others with substantial accuracy. Hence, the variables with a correlation value greater than 0.8 were considered to be highly correlated, and only 1 of those variables was then entered to generate the final model.
Results
A univariate model was generated after applying logistic regression analysis; it showed that ANB angle, vertical facial pattern, maxillary and mandibular incisor inclinations, overbite, upper dental midline discrepancy, mandibular tooth size-arch length discrepancy, and the relationship of the upper and lower lips to the E-plane and S-plane were significantly different between both treatment groups. After we checked the multicollinearity between the independent variables, the final multivariable model in the Table incorporates 1 skeletal variable, 4 dental variables, and 1 soft tissue variable that showed significant differences between the treatment groups. According to the model, the odds of nonextraction treatment were 1.29 times that of extraction treatment for every 1 mm of increase in overbite. This indicates that a patient with an increased overbite would have approximately 1.2 times more chance of being treated with nonextraction mechanics compared with a patient with a reduced overbite. Similarly, the odds of nonextraction treatment were 1.24 times that of extraction treatment for every 1 mm of increase in spacing. Therefore, a Class I patient with spacing in the arches would have a greater probability of being treated with nonextraction mechanics.
| Variable | β coefficient | Odds ratio | P Value | 95% CI |
|---|---|---|---|---|
| Skeletal | ||||
| Lower/total anterior facial height ratio (%) | −0.21 | 0.81 | 0.007 | 0.70-0.94 |
| Dental | ||||
| UI-SN (°) | −0.07 | 0.93 | 0.012 | 0.88-0.98 |
| IMPA (°) | −0.16 | 0.85 | <0.001 | 0.79-0.91 |
| Overbite (mm) | 0.25 | 1.29 | 0.020 | 1.04-1.60 |
| Mandibular tooth size-arch length discrepancy (mm) | 0.21 | 1.24 | <0.001 | 1.13-1.36 |
| Soft tissue | ||||
| E-plane to lower lip (mm) | −0.21 | 0.81 | 0.003 | 0.71-0.93 |
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