Posttreatment tooth movement is inevitable, but its degree depends on a variety of factors that are both iatrogenic and innate to each patient. Although various retention techniques have been developed to minimize posttreatment movement, it is unrealistic to believe that the entire dentition can be retained in all dimensions. Relapse is usually considered an adverse phenomenon, but some dimensions of posttreatment tooth movement might actually enhance occlusal function and esthetics. Favorable movement is often considered as “settling” if that aspect of the occlusion is improved over time.

In 1998, the American Board of Orthodontics (ABO) published an objective method of evaluating posttreatment results by using 7 cast measurements and 1 radiographic measurement. Formerly called the Objective Grading System, the ABO now refers to this as the Cast Radiograph Evaluation (C-R Eval). This evaluation technique is used to score final casts and the panoramic radiograph produced within 12 months of debanding. The 8 scoring parameters are alignment/rotations, marginal ridges, buccolingual inclination, overjet, occlusal contacts, occlusal relationships, interproximal contacts, and root angulation. The C-R Eval was developed to increase objectivity in evaluation of treatment results; it uses a point system with precise criteria for cast and radiographic grading to score the case result in terms of finishing and detailing. Each case is scored after individual and group calibration of examiners in an effort to secure equity in grading among all examiners. Hence, 8 aspects of the finished result can be quantified at the time of final records production.

Currently, all 8 parameters of the C-R Eval are weighted equally with 1 point for each deficiency. The deficiencies are clearly defined to the accuracy of 0.5 mm. It became apparent that possibly the parameters that show improvement after treatment should be scored less heavily than those that tend to deteriorate after treatment. In other words, treatment deficiencies that will tend to relapse unfavorably should be scored more heavily than parameters that improve after debanding. The difference in scoring between improving and deteriorating parameters will be herein referred to as weighting. This information can also be helpful to the orthodontic practitioner to prognosticate which aspects of the final treatment result might settle toward the ideal and which will deteriorate over time.

The purpose of this article was to determine posttreatment tooth position changes in orthodontic cases with the intent to predict favorable vs unfavorable movement. This information is to be used to weight certain parameters of the finished result as scored by the C-R Eval. A secondary purpose of this investigation was to compare tooth movement between 2 forms of retention.

Our 2 null hypotheses were that all 7 (cast assessment) parameters of the C-R Eval have equal magnitudes of posttreatment changes, and that fixed and removable retention methods show equal amounts of posttreatment movement.

It is well established that posttreatment changes occur in orthodontic patients, but prediction of favorable vs unfavorable movement is difficult. Little et al demonstrated that more deterioration of alignment occurs between 10 and 20 years after treatment than from debanding to 10 years posttreatment. Only 10% of their 100-patient sample had acceptable alignment after 10 years. Fidler et al noted that posttreatment Class II Division 1 patients relapsed as much as 3.5 mm at first molar and canine relationships, 3 mm in overjet, and 4.5 mm in overbite after treatment. On a more positive note, Razdolsky et al assessed 40 patients at up to 21 months posttreatment and found continuous increases in interarch tooth contacts by 3 months, but buccolingual relationships showed minimal changes. Nett and Huang used the ABO’s cast radiographic evaluation (called the OGS in that article). They assessed 100 random subjects at least 10 years postretention and found that although adverse alignment changes occurred after debanding, significant improvement in marginal ridges, buccolingual relationships, occlusal contacts, and overjet occurred. Occlusal relationships improved insignificantly. None of these studies proposed a weighting factor for the C-R Eval scoring instrument.

Tooth movement during fixed and removable retention is also recognized. Although few studies compared fixed vs removable retention methods with regard to amount of relapse or settling, 1 such study was conducted by Atack et al, whose 58-patient sample demonstrated no difference in mandibular incisor irregularity between bonded canine-to-canine retainers and removable (spring aligner) appliances. They found that movement occurred with either retainer design. They speculated that the movement in the fixed retention group could be related to activity in the bonded wire or wire deformation while the retainer was in place. In a study conducted by Sari et al, 50 orthodontic patients were evaluated by assessment of interocclusal records produced by an impression material technique to record changes in occlusal contacts over time. Twenty-five subjects received maxillary and mandibular Hawley retainers, and 25 used maxillary and mandibular bonded anterior retainers. They also evaluated a control group of 20 subjects. The retained patients were assessed between 14 and 15 months posttreatment, and the control group was assessed at 12 months. These authors concluded that although there were insignificant changes in the control sample, both retention groups had greater numbers of occlusal contacts. More occlusal contacts were noted in the fixed retainer group than in the removable retainer group.