In 1907, Edward H. Angle (Fig 2-1) became the father of modern orthodontics. His philosophy of treatment was totally nonextraction,² despite Calvin Case’s challenge³ and advocation of selective extractions in 1905 (Fig 2-2). For the first half of the 20th century, Angle’s philosophy dominated. In 1944, Charles H. Tweed (Fig 2-3) became the most prominent proponent of extractions.⁴ While I was in graduate school during the mid 1960s, Drs Westfall and Gaylord had a large influence on bridging the transients from Tweed to contemporary orthodontics. During the 1970s, the pendulum began to swing again, led by Rolf Frankel in 1971.^5,6 His Functional Regulator 2 screened dental arches from the musculature. This created tension in the alveolar bone, resulting in wider arches for nonextraction treatment.

Fig 2-1 Edward H. Angle.

Fig 2-2 Calvin Case.

Fig 2-3 Charles H. Tweed.

1. Abnormal muscular habits that cannot be controlled by orthodontic treatment. When the oral musculature is out of balance with its environment (Fig 2-4), keeping the teeth in stable positions is virtually impossible. Thumb or finger sucking must be eliminated before orthodontic treatment can be successfully completed. Several techniques can be used to achieve this result. The method of choice is for the orthodontist to take the time to reason with the patient about why this habit must be stopped. Although this technique is time-consuming for the clinician, it is over 90% effective. Other techniques using fixed appliances, such as a tongue rake, can be used if the other approach fails. Mouth breathing negatively affects stability by causing muscular imbalance. Blockage in the airways must be addressed early in treatment. In certain cases, adenoid or tonsil removal may be recommended.
2. Poor growth patterns that do not respond to orthodontic treatment. Excessive vertical growth (vertical maxillary excess) (Fig 2-5) causes abnormally long lower anterior face height, which prevents the patient from being able to keep the lips closed in a relaxed position, thus causing muscular imbalance and potential relapse. Excessive mandibular growth can occur after treatment has been completed, which will cause orthodontic relapse.
3. Poor diagnosis, poor treatment, or poor patient cooperation. These may be the greatest causes of relapse. Diagnosis and treatment are the factors most under the control of the orthodontist.

Certain criteria must be followed and particular goals achieved to maximize the likelihood that a patient will exhibit satisfactory stability over a period of years. In addition to the active therapy, proper retention procedures must be followed.

So where is the state-of-the-art position in diagnosis and treatment planning currently? Treatment choices for gaining space include (1) extraction and (2) nonextraction: interproximal enamel reduction, expansion of arch width, increasing arch length, and flaring of the anterior dentition.

In other words, either increase the space available for teeth or decrease tooth mass. Yet how should this decision be made? Does it really make a difference? Is long-term stability affected?

Fig 2-4 Anterior view of open bite. Open bite causes mouth breathing, which leads to muscular imbalance and thereby threatens stability.

Fig 2-5 (a) Pretreatment cephalometric tracing and radiograph of a patient with vertical maxillary excess. Note that the lips are open while the patient’s muscles are relaxed. (b) Posttreatment cephalometric tracing and radiograph of the same patient. Note that the lips are now closed.

Fig 2-6 Mandibular incisor position and plane angle.

The mandibular incisor position (Fig 2-6) is observed and a decision made as to where the final position should be. Where is the most stable position of the mandibular incisors? Tweed stated that “the lower incisors should be upright on the basal bone.”⁴ It has been my observation that “stable” is the position in which the patient presents. A stable range for mandibular incisors can be from 70 degrees to 110 degrees depending on the skeletal pattern of the patient.

Fig 2-7 Driftodontics. (a) Mandibular arch directly after the extraction of four first premolars. Treatment is initiated on the maxillary arch only. (b) Mandibular arch after driftodontics have occurred, reducing the space between the canines and the second premolars.

Fig 2-8 Nevant’s drawing of the mandibular incisor’s tipping labially 1.42 mm.

The mandibular incisors can be uprighted a great amount and remain stable. Papandreas studied the amount of drift that takes place when four first premolars are extracted in Class I malocclusions and treatment is initiated only on the maxillary arch.¹⁸ This “driftodontics” of the mandibular teeth (Fig 2-7) demonstrated some interesting results. Papandreas found that on an annual basis, (1) the mandibular anterior teeth uprighted an average of 8 degrees; (2) the canines drifted distally and expanded 1.7 mm; and (3) the molars drifted forward only 1.2 mm.

Clinically, this study shows that the mandibular anterior teeth move distally more than the molars move anteriorly. And although the mandibular intercanine width expands, other long-term studies show that this expansion is not stable.

Why would this be true? In my extraction protocol, the maxillary canines are retracted to a wider part of the arch early in treatment. Does it not make sense that these maxillary canines protect the mandibular canines from the perioral musculature during this time period (about 6 months)? However, after all spaces are closed and centric relation and final arch form are obtained, the mandibular canines should show little, if any, intercanine expansion.

Nevant showed some interesting results regarding the advancement of mandibular incisors.¹⁹ In his study of 40 patients (20 each from two practices), the mandibular incisors tipped labially 1.4 mm, 3 degrees in each case (Fig 2-8). Does this indicate that an anterior limit exists as to how far the incisors can be advanced and still be in stable positions? This study, with others, helped us develop the 3-degree rule in advancing mandibular incisors.

In addition to torque control of the mandibular incisors, the maxillary incisors and their relationship with the mandibular incisors must be addressed. To maintain the corrected overbite, good maxillary torque and interincisal angle must be established during treatment (see chapter 4).

In their discussion of the Alexander Discipline, Bernstein et al highlight its effectiveness in leveling the curve of Spee in Class II, Division 1 deep bite cases using nonextraction.²¹ This is accomplished by combining premolar extrusion with minor incisor intrusion (Fig 2-9). Mandibular incisor position is therefore controlled during the leveling process, and excessive flaring is avoided. In addition, although there is a 30% loss after treatment, the–6-degree angulation in the molar band prevents the mandibular molar from tipping back during treatment. In addition, Bernstein et al note that the Alexander Discipline does not cause excessive opening of the vertical dimension during treatment.²¹ The angulation of the functional occlusal plane is altered, and it appears to remain stable over time, making the results of this treatment stable in the long term.

Fig 2-9 (a) Treatment effects of reverse curve of Spee in archwires as demonstrated in the studies of Bernstein et al²¹ and Carcara.²² (b) At an average posttreatment period of 11 years 5 months, the results show no relapse in the premolar area, and thus the leveled arch is maintained.

Fig 2-10 Mandibular incisor angulation.

Fig 2-11 Bracket angulations (in degrees) of the mandibular incisors and canines.

Williams observed that the mandibular lateral incisors should be positioned with more angulation to improve stability ²³ (Fig 2-10). My clinical observation of posttreatment patients over the years has led me to agree that one of the causes of relapse in the mandibular anterior arch is poor artistic positioning of the mandibular lateral incisors. If the incisal edges of the mandibular anterior teeth are aligned evenly, the lateral incisors will be too upright. However, when the roots of the lateral incisors are aligned more parallel to the roots of the canines, relapse seems less severe and may not occur at all (Fig 2-11).

Fig 2-12 Increased interbracket distance. Almost 50% more interbracket distance is obtained with single (left) versus twin (right) brackets.

Fig 2-13 (a) Uprighting molar. (b) Incisor torque control.

Bracket design, bracket placement, and selected individualized forces will allow the teeth to be positioned properly during treatment. These steps are specifically addressed in chapters 6 and 7 of volume 1 of this series.

Finishing procedures,²⁶ band removal, and retainer placement must be properly orchestrated. A regimented retention sequence is then followed that will help enhance long-term stability for the patient.

These clinical observations are the results of more than 40 years of orthodontic practice in which I have treated more than 15,000 patients with fixed edgewise appliances. In addition to clinical observation, research findings by the Baylor Orthodontic Department graduate students^27–30 as well as studies from other programs and individuals show that orthodontic treatment can be stable long after the appliances are removed.