Class I malocclusion:
Angle Class I malocclusion is characterized by normal anteroposterior molar relationship, which may or may not be accompanied by skeletal changes—in the vertical or transverse planes or dental changes. Bimaxillary dental protrusion, characterized by pronounced
labial inclination of maxillary and mandibular incisors combined with excessive overjet, expose patients to dental trauma and compromise aesthetics. In deciding which teeth to extract for Class I correction the first or second premolars are usually selected due to their location in the dental arch. However, the extraction of a first permanent molar compro- mised by caries or extensive restoration may be an alternative that ensures the preservation of a healthy tooth instead of one that has already been manipulated.
treating a Class I malocclusion by means of comprehensive orthodontics, there are two main therapeutic approaches: extraction and non-extraction. Extractions are routinely used to address dental crowding and reduce protrusion of the teeth and the overlying soft tissue. The alternative treatment is expansion of the arches. The extraction rate in orthodontics shows strong variations depending on the decade and socioeconomic factors. In the 1950s, 10% of the cases were treated with extractions whereas in the following decade, the percentage climbed up to 50% until the 1980s when it dropped to the contemporary number of 30% .
In diagnosing and treatment planning a case, the orthodontist examines a series of variables that lead him to his final decision. These variables are the measurements of the cephalometric analysis and the models along with the age and sex of the patient. Other factors like periodontal condition, restorations, and congenitally missing or extracted teeth also have an impact on the decision In. After taking all of the above factors into consideration, the treatment plan is established and the need for or not for extractions is justified .
The knowledge of the variables which account for favoring one therapeutic approach over the other will help expedite the decision making and will serve to establish treatment predictors. The numerical value of these variables will also be a valuable tool when diagnosing a Class I case. In order to identify which variables have an impact on the orthodontist’s decision whether to extract or not, it is necessary to know in which characteristics patients treated in one way tend to differ from those treated in another way. The characteristics of the patient that lead a clinician to a given treatment decision are known as confounding variables. Discriminant analysis is the ideal statistical multivariate technique that deals simultaneously with large numbers of confounding variables . Discriminant analysis has been proven to mimic effectively the decision process of experienced orthodontists . The main reason that this analysis is employed in current orthodontic retrospective surveys is its ability to predict group membership, to identify patients who could belong to either group (borderline), and to establish treatment predictors