ORIGINAL ARTICLE
Relapse of anterior crowding in patients treated with extraction and nonextraction of premolars
Aslıhan Ertan Erdinc,a Ram S. Nanda,b and Erdal Is¸ ıksalc Izmir, Turkey, and Oklahoma City, Okla
Introduction: The purpose of this study was to evaluate long-term stability of incisor crowding in orthodontic patients treated with and without premolar extractions. Methods: Dental casts and cephalometric records of 98 patients were evaluated before treatment (T1), at posttreatment (T2), and at postretention (T3). Half of the patients had been treated with extractions, and half were treated nonextraction. Results: Irregularity, as measured by the irregularity index, decreased 5.51 mm in the extraction group and 2.38 mm in the nonextraction group. Mandibular incisor irregularity increased 0.97 mm in the extraction group and 0.99 mm in the nonextraction group, respectively, in the postretention period. Maxillary incisor irregularity relapse was smaller than mandibular incisor relapse for both groups. Intercanine width expanded during treatment. At T3, mandibular intercanine width decreased in both groups, but the differences were not statistically significant. At T3, intermolar width was stable, arch depth decreased, overbite and overjet slightly increased, SN mandibular plane angle decreased, and incisor positions in both groups tended to return to T1 values. Clinically acceptable stability was obtained. Conclusions: With the exception of the interincisal angle, no statistically significant differences were recorded between the extraction and nonextraction groups from T2 to T3. No statistically significant correlations were found between any variables studied and mandibular incisor irregularity at T1, T2, and T3. (Am J Orthod Dentofacial Orthop 2006;129:775-84)
major goal of orthodontic treatment is to arises as to which treatment procedure is most helpful achieve long-term stability of posttreatment in achieving long-term stability. Aocclusion. Several investigators have evaluated Previous long-term studies on relapse of anterior treatment results and long-term posttreatment stability of crowding have most often evaluated patients treated orthodontically treated malocclusions.1-5 The stability of with extractions.2,3,7-11 Different results might be seen aligned teeth is variable and largely unpredictable. This in the relapse patterns of patients treated without variability might be due to severity and type of malocclu- extractions12-19 or by comparing extraction and nonex- sion, treatment approach, patient cooperation, or growth traction groups.4,20-27 6 and adaptability of the hard and soft tissues. Many theories have been proposed and controver- Premolar extraction to permit alignment of crowded sies exist about the cause of relapse. Protrusion and teeth has been an accepted procedure for decades and final position of the mandibular incisors might influ- continues to be a common treatment modality for ence the stability of orthodontic treatment. The pre- patients with crowded arches. However, mandibular treatment position of the mandibular incisors is the best incisors suffer from relapse and crowding despite their guide for their labiolingual position of stability.7,28 retraction during extraction treatment. Because of Nance29 asserted that flaring the mandibular incisors is changing concepts of facial soft-tissue profile esthetics never a successful treatment technique. Brodie30 stud- and late growth changes, the trend in orthodontics has ied nonextraction orthodontic patients, and Cole31 stud- been toward nonextraction treatment. The question thus ied extraction patients; both concluded that the axial aResearch fellow, Department of Orthodontics, Faculty of Dentistry, University inclination of teeth disturbed by orthodontic treatment of Ege, Izmir, Turkey. tends to return to pretreatment conditions. Weinberg bProfessor and Endowed Chair, Department Orthodontics, University of and Sadowsky16 reported that the protrusion of man- Oklahoma College of Dentistry, Oklahoma City. cProfessor and chairman, Department Orthodontics, Faculty of Dentistry, dibular incisors can predispose them to relapse. On the University of Ege, Izmir, Turkey. other hand, Freitas et al19 reported that final mandibular Reprint requests to: Dr Ram S. Nanda, Department of Orthodontics, University incisor inclination and linear protrusion do not influ- of Oklahoma, College of Dentistry, P.O. Box 26901, 1001 Stanton L. Young 32 Blvd, Oklahoma City, OK 73190; e-mail, [email protected]. ence crowding relapse. Schulaf et al reported that the Submitted, September 2004; revised and accepted, February 2006. mandibular incisor anteroposterior position relative to 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. various cephalometric values had no relationship to doi:10.1016/j.ajodo.2006.02.022 postretention crowding of mandibular incisors. 775 776 Erdinc, Nanda, and Is¸ıksal American Journal of Orthodontics and Dentofacial Orthopedics June 2006
3 time periods: pretreatment (T1), at the end of active treatment (T2), and at postretention (T3). The group was equally divided into nonextraction and extraction groups. The nonextraction group (n ϭ 49) included 19 males and 30 females, mean ages 14 years 1 month at T1, 16 years 3 months at T2, and 20 years 11 months at T3. The mean treatment time was 1 year 9 months, and the mean postretention time was 4 years 8 months. The extraction group (n ϭ 49) also included 19 males and 30 females, with mean ages of 12 years 11 months at T1, 14 years 8 months at T2, and 19 years 7 months at T3. The mean treatment time was 2 years 2 months, and the mean postretention time was 4 years 11 months. In the extraction group, the maxillary and mandib- ular first premolars were extracted. All patients evalu- ated in this study had pretreatment malocclusions of Angle Class I or Class II Division 1. There were 28 Class I and 21 Class II Division 1 patients in each group. All patients were treated with edgewise mechanics and achieved acceptable posttreatment results, both maxillary and mandibular arches were retained with Hawley retain- Fig 1. Cast measurements. ers; the postretention period was at least 2 years. None of the subjects had congenitally missing permanent teeth or was treated with rapid palatal expansion.
Investigators found that the most frequent cause of mandibular incisor instability was expansion of inter- Analysis of dental casts canine width during treatment.18,23,25 It has been re- Dental casts were measured by 1 investigator ported that stable results can be gained only when (A.E.E.) on the mandibular and maxillary dental casts, mandibular intercanine width is maintained.14,25,33 Yet to the nearest 0.01 mm with a digital caliper. The it has also been shown that maintenance of the pretreat- following measurements were obtained for each set of ment intercanine distance during treatment does not casts. All measurements were linear. guarantee stability of the mandibular incisors’ align- ment.19,21 Arch-length decrease in the postretention 1. Incisor irregularity: the sum, in millimeters, of the stage might cause incisor crowding. Kahl-Nieke et al22 5 distances between the anatomic contacts from the and Årtun et al23 reported that arch-length increase is mesial aspect of the left canine through the mesial associated with crowding relapse. aspect of the right canine according to the method Another factor might be that postadolescent growth described by Little.35 of the jaws affects stability and influences orthodontic 2. Canine-canine width: distance between crown tips treatment results over the long term. Sampson34 and of the right and left canines. In some cases, this Vaden et al10 reported that growth rotation is greater in value could not be measured at T1 because the the mandible than in the maxilla, and that might be a permanent canines were not yet erupted (Fig 1, A). factor in the higher incidence of mandibular crowding. In the extraction group, 46 maxillary intercanine Evidence from the literature indicates many vari- widths and 48 mandibular intercanine widths and, ables and conflicting points of view. The intent of this in the nonextraction group, 47 maxillary interca- study was to search for associations between cephalo- nine widths and 49 mandibular intercanine widths metric and dental-cast parameters that might be clini- were measured. In the extraction group, intercanine cally useful predictors of posttreatment alignment of widths of only 4 patients and, in the nonextraction incisors. patients group, intercanine widths of only 2 patients were not measured. MATERIAL AND METHODS 3. First premolar-first premolar width: distance be- The sample consisted of complete records (dental tween the central fossae of the first premolars in casts and cephalometric radiographs) of 98 patients from both jaws (Fig 1, B). American Journal of Orthodontics and Dentofacial Orthopedics Erdinc, Nanda, and Is¸ıksal 777 Volume 129, Number 6
Fig 3. Linear and angular measurements. Fig 2. Cephalometric landmarks.
The cephalometric landmarks were 1, porion; 2, 4. Second premolar-second premolar width: distance sella; 3, nasion; 4, orbitale; 5, A-point; 6, M-point; 7, between the central fossae of the second premolars posterior nasal spine; 8, maxillary incisor apex point; 9, in both jaws (Fig 1, C). maxillary incisor tip point; 10, mandibular incisor tip 5. First molar-first molar width: distance between point; 11, mandibular incisor apex point; 12, B-point; the central fossae of the first molars in both jaws 13, pogonion; 14, menton; 15, gonion; and 16, articu- (Fig 1, D ). lare. 6. Arch depth: perpendicular length from the midpoint Maxillary Point M,36 representing the midpoint of between the maxillary and mandibular central inci- the premaxilla in the midsagittal plane, was located on sors to the line drawn between the mesial anatomic the tracings according to the superior anterior, and the contact points of the first molars (Fig 1, E). palatal outlines of the premaxilla and the midpoint were 7. Overjet: distance parallel to the occlusal plane from identified with concentric circles to find the circle that the incisal edges of the most labial maxillary to the best fit the premaxilla or the outlines of the premaxilla. most labial mandibular central incisor recorded in This point was used in drawing the palatal plane. millimeters. Cephalometric planes were drawn as shown in 8. Overbite: amount of vertical incisal overlap of the Figure 3, and the following measurements were made. maxillary and mandibular central incisors recorded To assess sagittal changes in jaw relationship, measure- in millimeters. ments were made from Points A and B to the vertical Analysis of lateral cephalometric radiographs plane (VP), which was drawn perpendicular to the horizontal plane (7° to sella-nasion line) at sella. To analyze the lateral cephalometric radiographs, the 16 cephalometric landmarks shown in Figure 2 1. VP to A point (mm): line formed perpendicular to were located, and 4 angular and 5 millimetric variables the VP at A-point. were measured (Fig 3). The measurements were made 2. VP to B point (mm): line formed perpendicular to by 1 investigator (A.E.E.). The cephalograms were the VP at B-point. traced and digitized with the Dentofacial Planner digi- 3. Palatal plane to menton (mm): line formed perpen- tizing pad (Dentofacial Software Inc, Toronto, Can- dicular to the palatal plane at menton (lower face ada), and the information was stored and analyzed on a height). computer. 4. Mandibular central incisor to NB (mm). 778 Erdinc, Nanda, and Is¸ıksal American Journal of Orthodontics and Dentofacial Orthopedics June 2006
5. Pogonion to NB (mm). statistically significant difference during the postreten- 6. Maxillary central incisor to SN angle. tion period in both groups. 7. Incisor-mandibular plane angle (IMPA). Pearson correlation coefficients were used to deter- 8. Interincisal angle. mine whether there were simple pairwise correlations 9. SN to mandibular plane angle. between the variables of this study. These estimates were obtained to assess mandibular incisor stability at The posttreatment cephalometric changes were T1, T2, and T3. No significant correlations (r Ͼ0.7) used as predictor variables to test whether growth of were identified that would help predict postretention any of the skeletal units after treatment was signifi- incisor irregularity. cantly associated with dental changes measured from the casts. Dental-cast data Both groups showed statistically significant de- Method error creases in overjet with treatment. No significant pos- Twenty randomly selected orthodontic models were tretention relapse occurred. remeasured 1 month later to estimate the error of Overbite decreased 1.22 mm in the extraction group measurement. The paired t test for differences between and 1.54 mm in the nonextraction group during the the replications showed no statistically significant dif- treatment period. These changes were statistically sig- ferences. These results indicated the reliability of the nificant. However, statistically significant relapse oc- measurements. curred at T3 for both groups. To determine the error of tracing, digitizing, and The extraction patients had higher irregularity in- measuring, 20 cephalograms were randomly selected, dex values than the nonextraction patients at TI. The retraced, and redigitized by the same examiner 1 month irregularity index was 5.57 mm for mandibular teeth after the initial procedure. The paired t test for differ- and 4.40 mm for maxillary teeth in the extraction ences between the replications showed statistically no group; this corresponds to moderate irregularity accord- significant differences and indicated the reliability of ing to Little.35 In the nonextraction group, the irregu- the measurements. larity indexes were 2.38 mm for the mandibular teeth and 1.94 mm for the maxillary teeth; this is minimal Statistical analysis irregularity. Treatment produced a statistically signifi- cant decrease in maxillary and mandibular incisor Means and standard deviations were calculated for irregularity in both groups, and mandibular incisor the T1, T2, and T3 measurements and for the differ- irregularity increased significantly—0.97 and 0.99 mm ences between the T1 and T2 measurements, and the T2 in the extraction and nonextraction groups, respective- and T3 measurements. Analyses of the changes during ly—during the postretention period. Maxillary incisor treatment and postretention were performed separately. irregularity increased less than mandibular incisor ir- In each treatment group (extraction and nonextraction), regularity from T2 to T3, and these changes were not a paired t test was used to determine whether a change statistically significant. was significantly different from 0. Differences between In both groups, mandibular intercanine width in- the treatment groups were tested by using analysis of creased significantly during treatment and decreased variance with treatment and sex as factors. No signifi- significantly at postretention. cant influence by sex was found. The level of signifi- After treatment, in the extraction group, the in- cance was predetermined at the 0.01 level of confi- crease in maxillary intercanine width was not statisti- dence. In addition, Pearson correlation coefficients cally significant, but the increase in the nonextraction were used to evaluate the association between the group was significant. No statistically significant re- cast and cephalometric variables. All analyses were lapse occurred in maxillary intercanine width in either performed with software (version 8.1, SAS Institute, group. Cary, NC). At T2, interpremolar width decreased significantly in the extraction group in both jaws, but, in the RESULTS nonextraction group, maxillary interpremolar width Tables I and II give the average changes from T1 to significantly increased, and mandibular interpremolar T2, and T2 to T3. Table III gives the statistical width showed a slight increase. At T3, the premolar significance of differences between the extraction and width decreased in both groups. nonextraction groups for the changes from T2 to T3. Of Maxillary and mandibular intermolar width de- all the measurements, only interincisal angle showed a creased significantly in the extraction group at T2 and American Journal of Orthodontics and Dentofacial Orthopedics Erdinc, Nanda, and Is¸ıksal 779 Volume 129, Number 6
Table I. Means and standard deviations of cephalometric and dental variables of extraction group (n ϭ 49) at T1, T2, and T3, and differences in measurements from TI to T2 and T2 to T3
T1 T2 T3 T2-T1 T3-T2
Variable ϪX SD ϪX SD ϪX SD ϪD P SD ϪD P SD
Cast analysıs 1. Overjet (mm) 4.01 2.01 1.36 1.10 1.69 1.24 Ϫ2.65 S 2.02 0.34 NS 1.04 2. Overbite (mm) 3.33 1.47 2.10 0.81 2.55 1.07 Ϫ1.22 S 1.61 0.45 S 1.05 3. Mand incisor irregularity 5.57 2.60 0.06 0.22 1.03 1.44 Ϫ5.51 S 2.6 0.97 S 1.4 4. Mand 3-3 width (mm) 26.03 1.98 27.16 1.78 26.36 1.57 1.13 S 2.22 Ϫ0.79 S 0.97 5. Mand 4-4 width (mm) — — — — — — — — — — — — 6. Mand 5-5 width (mm) 32.90 3.19 30.73 2.43 30.52 2.45 Ϫ2.17 S 2.32 Ϫ0.21 NS 1.07 7. Mand 6-6 width (mm) 39.63 2.71 36.98 2.08 37.08 2.09 Ϫ2.65 S 2.09 0.10 NS 1.13 8. Mand arch length (mm) 22.43 1.82 17.62 1.33 16.95 1.29 Ϫ4.81 S 1.49 Ϫ0.67 S 0.6 9. Max incisor irregularity 4.40 3.24 0.00 0.00 0.19 0.48 Ϫ4.4 S 3.24 0.19 NS 0.48 10. Max 3-3 width (mm) 34.24 2.55 35.24 2.18 35.00 1.97 0.92 NS 2.25 Ϫ0.24 NS 0.84 11. Max 4-4 width (mm) — — — — — — — — — — — 12. Max 5-5 width (mm) 38.07 2.78 37.01 2.05 36.80 1.92 Ϫ1.06 S 2.44 Ϫ0.22 NS 1.11 13. Max 6-6 width (mm) 44.71 2.71 42.89 2.28 42.91 2.16 Ϫ1.82 S 2.06 0.01 NS 1.18 14. Max arch length (mm) 27.09 2.64 21.67 1.25 21.18 1.32 Ϫ5.43 S 2.21 Ϫ0.49 S 0.64 Lateral cephalometrıc analysıs 15. VP to A (mm) 72.52 4.97 72.79 4.81 74.08 4.55 0.27 NS 2.16 1.29 S 2.13 16. VP to B (mm) 66.48 6.08 67.12 6.45 69.19 6.15 0.64 NS 3.38 2.07 S 3.42 17. Lower face height (mm) 64.63 4.46 68.08 4.46 69.10 4.97 3.45 S 2.10 1.02 S 2.06 18. SN-MP angle (°) 34.90 4.67 34.64 4.99 33.18 5.27 Ϫ0.26 NS 1.86 Ϫ1.46 S 1.97 19. Max 1/SN angle (°) 104.26 6.02 98.13 6.32 99.49 6.15 Ϫ6.14 S 7.24 1.36 NS 5.07 20. IMPA (°) 95.07 6.20 92.97 8.08 93.23 8.01 Ϫ2.10 NS 6.40 0.26 NS 3.52 21. Interincisal angle (°) 125.75 8.91 134.26 8.93 134.10 8.83 8.50 S 9.77 Ϫ0.16 NS 5.98 22. Mand 1 to NB distance (mm) 5.80 1.83 4.59 1.61 4.70 1.72 Ϫ1.22 S 1.57 0.11 NS 0.70 23. PgNB distance (mm) 0.84 1.73 2.30 2.25 2.89 2.12 1.46 S 1.12 0.58 S 0.70
X, Mean, D, mean of differences; P, significance; S, P value Ͻ.01; NS, nonsignificant. Mand, Mandibular; Max, maxillary; 1, central incisor; 3, canine; 4, first premolar; 5, second premolar; 6, first molar. remained stable at T3. In the nonextraction group, this ment and continued to increase at T2 for both groups. width slightly expanded during treatment; it was not These changes were statistically significant. statistically significant and increased slightly during In both groups, SN/MP angle was stable during postretention period. treatment (T2), but the decrease at T3 was statistically In the extraction group, maxillary and mandibular significant. arch depth decreased during treatment (T2) and contin- The mandibular incisor axial inclination showed dif- ued to decrease at T3. These changes were statistically ferences between the 2 groups at the 3 times. During T2, significant. In the nonextraction group, the increase in a statistically insignificant decrease occurred in IMPA in mandibular arch depth during treatment was not statis- the extraction group. During the same period, this angle tically significant, but, in the maxillary arch, only a increased significantly in the nonextraction group. At T3, small insignificant decrease was recorded. At the post- a small insignificant increase in IMPA in the extraction retention period (T2 to T3), statistically significant group was reported. In the nonextraction group, it de- decreases occurred for the maxillary and mandibular creased, and this reduction was statistically significant. arch depths in both groups. Mandibular central incisor to NB measurements de- creased in accordance with the decrease in IMPA in the Cephalometric data extraction group and increased in accordance with the Anteroposterior mandibular and maxillary growth increase in IMPA in the nonextraction group. The man- measured from vertical plane to Points A and B showed dibular incisors in nonextraction group proclined with that the increases were not statistically significant from treatment (T2) and then retroclined at T3. In the extraction T1 to T2 in both groups. At T3, statistically significant group, the mandibular incisors retroclined with treatment increases occurred for maxillary and mandibular (T2) and then proclined to a lesser degree from T2 to T3. growth in both groups. The changes were statistically significant at T2 but insig- Lower anterior face height increased during treat- nificant at T3 in both groups. 780 Erdinc, Nanda, and Is¸ıksal American Journal of Orthodontics and Dentofacial Orthopedics June 2006
Table II. Means and standard deviations of cephalometric and dental variables of nonextraction group (n ϭ 49) at T1, T2, and T3, differences in measurements from TI to T2 and T2 to T3
T1 T2 T3 T2-T1 T3-T2
Variable ϪX SD ϪX SD ϪX SD ϪD P SD ϪD P SD
Cast analysıs 1. Overjet (mm) 4.05 2.40 1.68 1.22 2.08 1.41 Ϫ2.37 S 2.45 0.4 NS 1.27 2. Overbite (mm) 3.54 1.24 2.00 0.65 2.41 0.81 Ϫ1.54 S 1.36 0.41 S 0.85 3. Mand incisor irregularity 2.38 2.18 0.00 0.00 0.99 1.16 Ϫ2.38 S 2.18 0.99 S 1.16 4. Mand 3-3 width (mm) 25.71 2.08 26.43 1.71 25.95 1.65 0.74 S 1.44 Ϫ0.48 S 0.78 5. Mand 4-4 width (mm) 29.21 2.16 29.94 2.01 29.63 1.95 0.73 S 1.55 Ϫ0.31 NS 1.02 6. Mand 5-5 width (mm) 34.60 2.27 35.09 2.13 34.74 2.19 0.49 NS 1.57 Ϫ0.35 NS 0.97 7. Mand 6-6 width (mm) 40.21 2.80 40.48 2.58 40.61 2.66 0.27 NS 1.63 0.13 NS 0.97 8. Mand arch length (mm) 22.44 1.99 22.89 1.50 21.76 1.54 0.45 NS 1.62 Ϫ1.13 S 0.91 9. Max incisor irregularity 1.94 2.07 0.00 0.00 0.12 0.47 Ϫ1.94 S 2.07 0.12 NS 0.47 10. Max 3-3 width (mm) 33.47 2.91 34.59 2.33 34.50 2.25 1.13 S 1.93 Ϫ0.09 NS 0.84 11. Max 4-4 width (mm) 34.14 2.37 36.16 2.23 35.83 2.14 2.01 S 2.09 Ϫ0.33 NS 0.86 12. Max 5-5 width (mm) 39.53 2.17 41.18 2.43 41.03 2.13 1.56 S 1.84 Ϫ0.15 NS 0.85 13.Max 6-6 width (mm) 45.41 2.74 45.80 2.75 46.17 2.69 0.39 NS 1.94 0.37 NS 0.93 14. Max arch length (mm) 27.04 2.56 27.02 1.72 26.33 1.75 Ϫ0.02 NS 2.15 Ϫ0.69 S 0.76 Lateral cephalometrıc analysıs 15. VP to A (mm) 71.57 4.54 72.28 4.67 73.68 4.82 0.71 NS 2.84 1.40 S 3.02 16. VP to B (mm) 65.92 6.18 67.06 6.77 69.19 6.90 1.14 NS 4.11 2.13 S 4.57 17. Lower face height (mm) 62.64 5.72 66.49 5.67 69.18 6.11 3.85 S 2.53 2.70 S 2.82 18. SN-MP angle (°) 33.16 6.34 33.18 6.61 31.62 7.00 0,02 NS 1.70 Ϫ1.57 S 2.20 19. Max 1/SN angle (°) 104.21 6.70 106.03 5.91 105.71 5.28 1.81 NS 7.94 Ϫ0.32 NS 3.85 20. IMPA (°) 94.92 7.24 100.56 7.73 97.78 7.43 5.63 S 5.46 Ϫ2.78 S 4.47 21. Interincisal angle (°) 127.71 10.76 120.23 7.76 124.90 8.16 Ϫ7.48 S 11.58 4.67 S 6.70 22. Mand 1 to NB distance (mm) 4.81 1.82 5.97 1.64 5.65 2.00 1.16 S 1.19 Ϫ0.32 NS 0.86 23. PgNB distance (mm) 1.96 1.90 2.39 1.96 2.86 2.24 0.43 S 0.77 0.47 S 0.76
X, Mean, D, mean of differences; P, significance; S, P value Ͻ.01; NS, nonsignificant. Mand, Mandibular; Max, maxillary; 1, central incisor; 3, canine; 4, first premolar; 5, second premolar; 6, first molar.
In the extraction group, the maxillary incisors this stability. It is therefore important to investigate retroclined with treatment and then proclined to a lesser long-term changes in the dentitions of patients treated degree from T2 to T3. The changes in the extraction with both treatment regimens. group at T2 were statistically significant, but the There was an age difference of 1 year 2 months at changes at T3 were not significant. In the nonextraction T1 between the extraction and nonextraction groups. group, the maxillary incisors proclined with treatment Based on age at T1, most subjects in the sample were (T2), and a small degree of retroclination occurred at experiencing or were on the verge of the pubertal spurt. T3. These changes were not statistically significant. However, after orthodontic treatment (approximately 2 In the nonextraction group, because of the procli- years), no statistically significant differences attribut- nation of the mandibular and maxillary incisors, the able to skeletal growth changes were recorded. interincisal angle decreased significantly with treat- The average incisor irregularity index was smaller ment, and these proclined teeth uprighted from T2 to in the nonextraction than in the extraction group. Both T3 with significant increases in interincisal angles. In groups showed improvement with treatment. This the extraction group, the interincisal angle significantly should be obvious for extraction and nonextraction increased with treatment and stayed stable from T2 to treatment decisions. Observation at T3 did not relate to T3. This was the only change between the groups that the pretreatment incisor irregularity or crowding of was statistically significant at T3 (Table III). incisors. In agreement with Little et al,12 we found no correlation in the postretention increase in irregularity DISCUSSION with the severity of crowding before treatment. Based on the results of this study, ideal orthodontic At T3, maxillary alignment was stable, but the treatment should achieve long-term stability of incisor mandibular incisors relapsed an average of 1 mm in alignment. Controversy exists as to which treatment both groups. This was considered a minimal relapse by decision—extraction or nonextraction—will lead to Little,35 and it was smaller than the results of other American Journal of Orthodontics and Dentofacial Orthopedics Erdinc, Nanda, and Is¸ıksal 781 Volume 129, Number 6
Table III. Comparison of changes at postretention (T3-T2) between extraction and nonextraction groups
Extraction Nonextraction
Variable ϪD P SD ϪD P SD P
Cast analysıs 1. Overjet (mm) 0.34 NS 1.04 0.4 NS 1.27 NS 2. Overbite (mm) 0.45 S 1.05 0.41 S 0.85 NS 3. Mand incisor irregularity 0.97 S 1.4 0.99 S 1.16 NS 4. Mand 3-3 width (mm) Ϫ0.79 S 0.97 Ϫ0.48 S 0.78 NS 5. Mand 4-4 width (mm) — — — Ϫ0.31 NS 1.02 — 6. Mand 5-5 width (mm) Ϫ0.21 NS 1.07 Ϫ0.35 NS 0.97 NS 7. Mand 6-6 width (mm) 0.10 NS 1.13 0.13 NS 0.97 NS 8 .Mand arch length (mm) Ϫ0.67 S 0.6 Ϫ1.13 S 0.91 NS 9. Max incisor irregularity 0.19 NS 0.48 0.12 NS 0.47 NS 10. Max 3-3 width (mm) Ϫ0.24 NS 0.84 Ϫ0.09 NS 0.84 NS 11. Max 4-4 width (mm) — — — Ϫ0.33 NS 0.86 — 12. Max 5-5 width (mm) Ϫ0.22 NS 1.11 Ϫ0.15 NS 0.85 NS 13. Max 6-6 width (mm) 0.01 NS 1.18 0.37 NS 0.93 NS 14. Max arch length (mm) Ϫ0.49 S 0.64 Ϫ0.69 S 0.76 NS Lateral cephalometrıc analysıs 15. VP to A (mm) 1.29 S 2.13 1.40 S 3.02 NS 16. VP to B (mm) 2.07 S 3.42 2.13 S 4.57 NS 17. Lower face height (mm) 1.02 S 2.06 2.70 S 2.82 NS 18. SN-MP angle (°) Ϫ1.46 S 1.97 Ϫ1.57 S 2.20 NS 19. Max 1/SN angle (°) 1.36 NS 5.07 Ϫ0.32 NS 3.85 NS 20. IMPA (°) 0.26 NS 3.52 Ϫ2.78 S 4.47 NS 21. Interincisal angle (°) Ϫ0.16 NS 5.98 4.67 S 6.70 S 22. Mand 1 to NB distance (mm) 0.11 NS 0.70 Ϫ0.32 NS 0.86 NS 23. PgNB distance (mm) 0.58 S 0.70 0.47 S 0.76 NS
X, Mean, D, mean of differences; P, significance; S, P value Ͻ.01; NS, nonsignificant. Mand, Mandibular; Max, maxillary; 1, central incisor; 3, canine; 4, first premolar; 5, second premolar; 6, first molar. studies.2,23 This was probably because the postretention intergroup differences at T3. Maxillary intercanine observation period was longer in their studies. There is width was more stable than that of the mandible from a tendency for increases in mandibular anterior crowding T2 to T3. Bishara et al42 reported similar results. We with time.37,38 In contrast, Ludwig39 reported that all found no correlation between the increase in incisor incisor relapse occurs within a year or 2 after retention irregularity and the decrease in intercanine width. This ends. Gardner and Chaconas20 noted that 1 year was finding agrees with previous reports.2,3,9,43,44 ample time for any relapse to occur. Rossouw et al25,26 With treatment, intermolar width responded differ- and Årtun et al23 also reported no significant difference ently in the extraction and the nonextraction patients. In between groups. In contrast, Uhde et al27 and Paquette et the nonextraction patients, intermolar width increased al21 stated that nonextraction patients had greater relapses. as a result of treatment, with a slight increase during the Kahl-Nieke et al22 reported that the extraction group had postretention period. In the extraction patients, inter- more relapse than the nonextraction sample. molar width decreased during treatment and slightly Intercanine width expanded with treatment, but, at increased at postretention. At postretention, both T3, mandibular intercanine width relapsed in both groups showed similar changes. The intergroup differ- groups. Mandibular intercanine width increased by ences were not statistically significant. Premolar extrac- averages of 1.13 mm in the extraction sample and 0.74 tions resulted in forward movement of the molars into mm in the nonextraction sample with treatment. Our a narrower part of the alveolar trough; this resulted in results are comparable with those of Paquette et al,21 narrowing of the intermolar width. We saw only small Luppanapornlarp and Johnston,24 Uhde et al,27 and changes at T3; this supported the concept of stability of BeGole et al.40 According to Gianelly,41 this slightly intermolar width.18,20,44,45 larger increase in patients treated with premolar extrac- Second premolar width for the extraction patients tions might reflect lateral movement as the canines are showed a decrease with treatment and an additional moved distally into the premolar sites. Similar to the slight decrease at postretention. In the nonextraction findings of Årtun et al,23 we found no significant group, the small width increase with treatment reversed 782 Erdinc, Nanda, and Is¸ıksal American Journal of Orthodontics and Dentofacial Orthopedics June 2006 slightly at postretention. The average changes between in the measurements through time. This corroborated the 2 groups were not statistically significant; this was the results of Little et al,2 who reported that no similar to the observation of Gardner and Chaconas.20 descriptive characteristics, such as Angle class, length of There was a statistically significant decrease in arch retention, age at start of treatment, or sex, and none of the depth from T2 to T3 in both groups. It had no correlation measured variables, such as initial or end of active to the uprighting of the incisors and incisor irregularity. treatment alignment, overbite, overjet, arch width, or arch The increase in overbite was statistically significant length, were of value in predicting the long-term result. from T2 to T3. This finding agrees with previous The success of orthodontic treatment is judged by studies.2,10,46 Overbite increase at postretention is re- the long-term stability of the results. In this study, both ported to be related to the amount reduced during extraction and nonextraction treatments showed excep- treatment, with only 30% to 50% of the correction is tionally good stability. However, the nonextraction retained.2,7,27 It was about 27% in our sample. patients started with minimal anterior irregularity, There was no change in SN/MP from T1 to T2 in whereas the extraction patients had moderate crowding. the nonextraction group and only a small decrease in Our results should not be interpreted as endorsing the extraction group. The latter might be due to extrac- nonextraction treatment for patients with moderate to tion of premolars, mesialization of premolars, and severe crowding. The decision for nonextraction or mandibular rotation. However, there were significant extraction depends on the clinician’s diagnosis and the decreases in both groups. These decreases might be treatment plan. From these results, all that we can say due to growth changes as reported by Nanda.47 Nanda is that the outcome of treatment and the postretention and Nanda48 also stated that any posttreatment skeletal stability were similar in both groups. We referred to the changes can attenuate, exaggerate, or maintain the mean data, and individual patients might behave differ- dentoskeletal relationship. ently. The parameters observed at T2 and T3 remained Sakuda et al49 and Freitas et al19 reported that the within clinically acceptable stable limits. The minimal degree of relapse in crowding was related to facial changes noticed in incisor alignment could be ascribed to patterns. Our sample was mostly average based on the natural changes.25,54 It is assumed that, if the teeth are, mandibular plane and lower anterior face height. We irrespective of the type of treatment, correctly placed, the found no correlation between growth pattern and finished dentition will be reasonably stable. But human crowding of relapse. dentition is in a dynamic state, continually changing The mandibular incisor axial inclination showed throughout life. The degree of relapse is confounded by differences between the 2 groups. At the end of active the normal events of growth and aging that invariably treatment, the mandibular incisors were more upright in follow treatment. Considerable craniofacial alterations the extraction group and more proclined in the nonex- occur beyond 17 years of age and are accompanied by traction group. During postretention, in the extraction compensatory changes in the dentition. Orthodontists group, the uprighted teeth showed a slight proclination, have little control over these biologic processes. Patients and, in the nonextraction group, the incisors were and their parents must be informed, at the start of retroclined. There was a tendency for the mandibular treatment, of the expected long-term changes in tooth incisors to rebound, especially in patients with in- positions. If orthodontists and their patients desire stable creased axial inclinations. These findings could be treatment outcomes, retention should be a lifelong process interpreted to support the contention of Blake and for which the patient assumes responsibility. Biby50 that the initial position of the mandibular inci- sors is the best guide for their stable labiolingual CONCLUSIONS position. Several investigators noted a rebound effect for displaced incisors.18,51-53 In the nonextraction 1. In this study, stability was exceptionally good. group, the interincisal angle significantly decreased 2. Only the interincisal angle showed a significant with treatment, and, because of the rebound of the difference between the extraction and nonextrac- incisors’ position, this angle significantly increased at T3 tion groups at T3. In the extraction group, the maxillary and mandibular 3. There were no statistically significant correlations teeth were uprighted during treatment, and the interincisal between any variables studied and mandibular angle was more stable in the extraction group at T3. The incisor irregularity at T1, T2, or T3. No predictor results showed no positive correlation with final mandib- of clinical value was found. ular incisor inclination and crowding relapse. 4. Minimal incisor crowding occurred at T3. The The postretention irregularity index was not signif- relapse patterns were similar for the extraction and icantly correlated to any measured variables or changes nonextraction treatment modalities. American Journal of Orthodontics and Dentofacial Orthopedics Erdinc, Nanda, and Is¸ıksal 783 Volume 129, Number 6
5. Intercanine width increased with treatment and 15. Sadowsky C, Schneider BJ, BeGole EA, Tahir E. A long-term relapsed during T3 in both groups. stability after orthodontic treatment: nonextraction with pro- 6. Intermolar width was stable during T3 in the longed retention. Am J Orthod Dentofacial Orthop 1994;106: 243-9. extraction and nonextraction patients. 16. Weinberg M, Sadowsky C. Resolution of mandibular arch crowd- 7. In both groups, arch depth decreased at T3. ing in growing patients with Class I malocclusions treated nonex- 8. Overjet and overbite decreased with treatment, and traction. Am J Orthod Dentofacial Orthop 1996;110:359-64. a small relapse was seen in both groups. 17. Azizi M, Shrout MK, Haas AJ, Russell CM, Hamilton EH Jr. A 9. SN/MP angle decreased from T2 to T3 in both retrospective study of Angle Class I malocclusions treated orthodontically without extractions using two palatal expansion groups. methods. Am J Orthod Dentofacial Orthop 1999;116:101-7. 10. Lower anterior face height increased during treat- 18. Yavari J, Shrout MK, Russell CM, Haas AJ, Hamilton EH. ment in both groups and continued to increase in Relapse in Angle Class II Division 1 malocclusion treated by T3, as part of the normal growth process. tandem mechanics without extraction of permanent teeth: a retrospective analysis. Am J Orthod Dentofacial Orthop 2000; We thank Dr T. Dandajena for assistance in pro- 118:34-42. gramming the Dentofacial Planner for the cephalomet- 19. Freitas KMS, Freitas MR, Henriques JFC, Pinzan A, Janson G. ric measurements. Postretention relapse of mandibular anterior crowding in patients treated without mandibular premolar extraction. Am J Orthod Dentofacial Orthop 2004:125:480-7. REFERENCES 20. Gardner SD, Chaconas SJ. Posttreatment and postretention 1. King EW. Relapse of orthodontic treatment. Angle Orthod changes following orthodontic therapy. Angle Orthod 1976;46: 1974;44:300-15. 151-61. 2. Little RM, Wallen TR, Riedel RA. 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