Nonextrmction orthodontic therapy: Posttreatment dental arnd skeletal stability Gayle Glenn, D.D.S., M.S.D.,* Peter M. Sinclair, D.D.S., M.S.D.,** and Richard G. Alexander, D.D.S., M.S.D.*** Dallas, Texas To assess the long-term stability of nonextraction orthodontic treatment, the dental cast and cephalometric records of 28 cases were evaluated. Thirty cephalometric and seven cast parameters were ex.amined before treatment, posttreatment, and an average of almost 8 years postretention. Results showed overall long-term stability to be relatively good. Relapse patterns seen were similar in nature, but intermediate in extent, between untreated normals and four first premolar extraction cases. !Significant decreases were seen in arch length and intercanine width during the postretention period despite minimal changes during treatment. incisor irregularity increased slightly postretention; intermolar width, overjet, and overbite displayed considerable long-term stability. Mandibular incisor mesiodistal and faciolingual dimensions were not associated with either pretreatment or posttreatment incisor crowding. Class II malocclusions with large ANB values and shorter mandibular lengths showed increased incisor irregularity, shorter arch lengths, and deeper overbites at the postretention stage, suggesting that the amount and direction of facial growth may have been partially responsible for maturational changes seen during the postretention period. (AM J ORTHOD DENTOFAC OHTHOP 1987;92:321-8.) 1 c onsiderable controversy still surrounds the question of whether better long-term results are achieved by extraction or by nonextraction therapy. In the past, in the search for long-term stability, both ex- traction and nonextraction philosophies have held sway. l-3 Many theories have been proposed as to the cause of relapsed and clinicians have suggested guide- lines to enhance stability including placing the teeth upright over basal bone,3,’ overcorrection of the mal- occlusion,6 obtaining proper accusal relationships and function,’ avoiding overexpansion,’ and taking into ac- count muscle balance and harmony.7-9 Numerous stud- ies have been da’ne to assess the amount and type of relapse seen pos’tretention in orthodontically treated cases. ‘“-‘5 In general, these studies have noted a de- crease in arch length and arch width with increases in incisor crowding, overbite, and overjet. Attempts have been made to correlate postretention changes to pretreatment variables, but with little suc- cess.“-” Untreated normal cases have been followed to Based on a thesis by Gayle Glenn submitted to the Department of Orthodontics. Baylor College of Dentistry, Baylor University, in partial fulfillment of the requirements for the degree of master of science in dentistry. This research was supported in part by Baylor College of Dentistry research funds. *Orthodontist in private practice. **Associate Professor, Department of Orthodontics, Baylor College of Den- tistry. ***Clinical Professor. Department of Orthodontics. determine whether their maturational changes are sim- ilar to those seen in treated cases.‘“-” It has been sug- gested that orthodontic therapy may temporarily alter the course of normally occurring physiologic changes; however, following the period of retention, the matu- ration process may resume.” The majority of the long-term studies conducted to date have been on extraction cases and it has been sug- gested that different, and perhaps less severe, changes might be seen in the relapse patterns of nonextraction cases.“.‘3.‘4 The purpose of this study therefore was to quantify the skeletal and dental posttreatment changes seen in a sample of nonextraction orthodontic cases. The intent was also to search for associations of value between cephalometric and dental cast parameters that might act as clinically useful predictors of the post- treatment changes. MATERIALS AND METHODS The subjects of this sample comprised 28 nonex- traction orthodontically treated cases (14 Class I and 14 Class II, Division 1) randomly selected from the files of one of the authors (R.G.A.) on the basis of availability of long-term records. All cases achieved acceptable posttreatment results and had been out of retention for a minimum of 3 years (Table I). All the cases in this sample were treated using an 0.01%inch slot, nontorqued edgewise appliance incor- porating a mixture of twin and single brackets, which 321
Gayle Glenn, D.D.S., M.S.D.,* Peter M. Sinclair, D.D.S., M.S.D.,** and Richard G. Alexander, D.D.S., M.S.D.*** Dallas, Texas
To assess the long-term stability of nonextraction orthodontic treatment, the dental cast and cephalometric records of 28 cases were evaluated. Thirty cephalometric and seven cast parameters were ex.amined before treatment, posttreatment, and an average of almost 8 years postretention. Results showed overall long-term stability to be relatively good. Relapse patterns seen were similar in nature, but intermediate in extent, between untreated normals and four first premolar extraction cases. !Significant decreases were seen in arch length and intercanine width during the postretention period despite minimal changes during treatment. incisor irregularity increased slightly postretention; intermolar width, overjet, and overbite displayed considerable long-term stability. Mandibular incisor mesiodistal and faciolingual dimensions were not associated with either pretreatment or posttreatment incisor crowding. Class II malocclusions with large ANB values and shorter mandibular lengths showed increased incisor irregularity, shorter arch lengths, and deeper overbites at the postretention stage, suggesting that the amount and direction of facial growth may have been partially responsible for maturational changes seen during the postretention period. (AM J ORTHOD DENTOFAC OHTHOP 1987;92:321-8.)
1 c onsiderable controversy still surrounds the question of whether better long-term results are achieved by extraction or by nonextraction therapy. In the past, in the search for long-term stability, both ex- traction and nonextraction philosophies have held sway. l-3 Many theories have been proposed as to the cause of relapsed and clinicians have suggested guide- lines to enhance stability including placing the teeth upright over basal bone,3,’ overcorrection of the mal- occlusion,6 obtaining proper accusal relationships and function,’ avoiding overexpansion,’ and taking into ac- count muscle balance and harmony.7-9 Numerous stud- ies have been da’ne to assess the amount and type of relapse seen pos’tretention in orthodontically treated cases. ‘“-‘5 In general, these studies have noted a de- crease in arch length and arch width with increases in incisor crowding, overbite, and overjet.
Attempts have been made to correlate postretention changes to pretreatment variables, but with little suc- cess. “-” Untreated normal cases have been followed to
Based on a thesis by Gayle Glenn submitted to the Department of Orthodontics. Baylor College of Dentistry, Baylor University, in partial fulfillment of the requirements for the degree of master of science in dentistry. This research was supported in part by Baylor College of Dentistry research funds. *Orthodontist in private practice. **Associate Professor, Department of Orthodontics, Baylor College of Den- tistry. ***Clinical Professor. Department of Orthodontics.
determine whether their maturational changes are sim- ilar to those seen in treated cases.‘“-” It has been sug- gested that orthodontic therapy may temporarily alter the course of normally occurring physiologic changes; however, following the period of retention, the matu- ration process may resume.”
The majority of the long-term studies conducted to date have been on extraction cases and it has been sug- gested that different, and perhaps less severe, changes might be seen in the relapse patterns of nonextraction cases.“.‘3.‘4 The purpose of this study therefore was to quantify the skeletal and dental posttreatment changes seen in a sample of nonextraction orthodontic cases. The intent was also to search for associations of value between cephalometric and dental cast parameters that might act as clinically useful predictors of the post- treatment changes.
MATERIALS AND METHODS
The subjects of this sample comprised 28 nonex- traction orthodontically treated cases (14 Class I and 14 Class II, Division 1) randomly selected from the files of one of the authors (R.G.A.) on the basis of availability of long-term records. All cases achieved acceptable posttreatment results and had been out of retention for a minimum of 3 years (Table I).
All the cases in this sample were treated using an 0.01%inch slot, nontorqued edgewise appliance incor- porating a mixture of twin and single brackets, which
321
322 Glenn, Sinclair, and Alexander Am. J. Orthod. Dentofac. Orthop. October 1987
Fig. 1. Cephalometric points digitized.
evolved into the &i-Simplex Discipline.* The treat- ment technique incorporated some basic Tweed philos- ophy and used cervical headgear in the majority of the cases along with Class II elastics in the finishing stages.
Lateral cephalograms and dental casts were taken pretreatment (Tl), posttreatment (T2), and postreten- tion (T3). Forty-one points were digitized? on each cephalogram (Fig. 1) and a total of 30 cephalometric variables were computed+! comprising 15 angular mea- surements, ten linear measurements, and five facial pro- portions.
The following seven measurements were made on each mandibular dental cast with dial calipers§ accurate to the nearest one tenth of a millimeter: intercanine and intermolar width (Fig. 2, A), arch length as suggested by Nance5 (Fig. 2, B), overbite and overjet, incisor Irregularity Index as suggested by Little23 (Fig. 3), the mesiodistal and faciolingual dimensions of the man- dibular incisors as suggested by Boltonz4 and by Peck and Peck.*’
*Ormco Cap, Glendora, Calif. tHipad digitizer, Houston Instruments, Austin, Texas. SApple II-Plus, Apple Computer, Cupertino, Calif. OHelios dial calipers, Schnieder and Kern, Niederhall, West Germany.
Statistical analysis involved the use of means and standard deviations for all dental and cephalometric pa- rameters, followed by the one-way analysis of variance and Tukey’s test to evaluate changes across time in which a significance level of P < 0.05 was selected. A Pearson product-moment correlation coefficient was used to assess possible associations among variables snd a level of clinical significance was established at r = 0.7. All analyses were conducted separately for the Class 1 and Class II groups and then for the com- bined sample.
RESULTS Dental cast data
1. Arch length. Arch length was increased in 50% of the cases in the sample during treatment; however, only a small, statistically nonsignificant increase was noted (X = +0.2 mm, P = NS) (Table 11). During the postretention period (T2 to T3), arch length de- creased significantly in 96% of the cases (St = -2.4 mm, P < O.OOl), resulting in a mean arch length at T3 that was 2.2 mm less (P < 0.001) than at pretreatment. All cases that showed increased arch length with treat- ment decreased at postretention with the trends being similar for the Class I and Class II groups. A significant correlation was noted between the pretreatment and the postretention arch lengths (r = 0.83, P < 0.001).
2. Intercanine width. Sixty-eight percent of the cases showed increases in intercanine width with treat- ment (Table II); however, the mean increase of 0.6 mm was not statistically significant. At postretention 89% of the cases showed some constriction of their inter- canine widths (X = - 1.0 mm, P < 0.001). Ninety- five percent of the cases whose intercanine widths were increased during treatment showed reductions in the postretention period.
3. Intermolar width. Intermolar width was in- creased in 71% of the cases during treatment (X = -+9 mm, P < 0.05) and decreased in 60% of cases postretention (X = -0.5 mm, P = NS). Of the cases expanded during treatment, 75% showed relapse during the postretention period.
4. Overjet. Both groups showed significant de- creases with treatment (X = -4.1 mm, P < 0.001) with no significant postretention relapse occurring (Table II).
5. Overbite. Overbite was reduced significantly with treatment in both groups (TI = - 1.9 mm, P < 0.001) and showed no significant postretention increase (Table II).
6. Irregularity Index. Pretreatment incisor irregu- larity ranged from 0.9 mm to 5.9 mm with a mean of 2.9 mm. Sixty-four percent of cases had minimal ir-
Volume 92 Number 4
Nonextraction orthodontic therapy 323
A = Intercanine width; B = Intermolar width A + B = Arch Length
A B Fig. 2. A, lntercanine and intermolar widths. 6, Arch length.
regularity before treatment (c3.5 mm) and 36% had moderate inciso.r irregularity (3.5 to 6.5 mm).15 Treat- ment produced a significant decrease in irregularity (X = - 1.9 mm, P < O.OOl), but a 1.2 mm postre- tention increase (P < 0.001) was also noted (Table II). At T3, 86% of cases exhibited minimal incisor irreg- ularity, 12% showed a moderate level of irregularity, and only 1 case (4%) was classified as severe (>6.5 mm). Fifty-five percent of the cases with minimal pre- treatment irregularity showed a net improvement over the three time periods; 80% of the cases with moderate incisor irregularity were better at T3 than at Tl.
7. Mesiodistal and faciolingual tooth dimensions. Twenty-eight percent of the cases in the sample had mesiodistal/faciolingual tooth size ratios outside the ac- cepted range. 2s However, a great deal of variation was noted in both the mesiodistal diameter and MD/FL in- dex measurements, and no relationships could be de- tected to either pretreatment or postretention incisor irregularity.
Cephalometric clata
I. Anteroposterior skeletal relationships (Table III, Nos. 1 through 8). The data showed an inhibition of forward maxillary growth during treatment as evidenced by decreases in SNA (51 = -2.O”, P < 0.001) and no increase in maxillary length as measured from articulare to A point (Table III). The changes seen were significant for both groups, but more so in the Class II sample. From T2 to T3, a 3.4-mm increase in maxillary length was noted (P < 0.001) primarily from changes occur- ring in the Class II group.
Anteroposterior mandibular growth as measured from articulare toI B point continued from Tl through T3 in both groups, although little change was noted in the SNB angle. ,4 decrease of 2” in the ANB angle from Tl to T2 (P < 0.001) was noted with little change occurring postretention (X = -0.2”, P = NS).
Irregularity Index = A + 6 + C + D = E
Fig. 3. Incisor Irregularity Index.
2. Mandibular rotation (Table III, Nos. 9 through 11). The results showed a tendency for the mandible to rotate backward with treatment (Table III), although the changes were very small and only a 1.2” increase in the Y axis was significant (P < 0.01). At postreten- tion the mandible rotated forward with small but sig- nificant changes seen in both the MP-FH (F; = - 1.4”, P < 0.01) and MP-SN (X = - l.l”, P < 0.01) mea- surements (Table III).
3. Facial heights (Table III, Nos. 12 through 18). Linear measurements of posterior facial height (S-Go and Ar-Go) showed significant increases in both sam- ples from both Tl to T2 and T2 to T3. Both hard- and soft-tissue anterior vertical facial proportions showed few changes. A significant increase (P < 0.001) in midfacial height (N-ANS, subnasale to stomion) was
324 Glenn, Sinclair, and Alexander Am. J. Orthod. Dentofac. Onhop. October 1987
Table I. Sample characteristics Mean pretreatment
age (Tl) (yr-mo)
Class I 12-9 Class II 12-5 Combined 12-I
Mean posttreatment age (T2) (yr-mo)
14-10 14-8 14-9
Mean postretention age (T3) (yr-mo)
28-O 25-2 26-l
Mean time postretention W-W
9-l 6-9 7-11
Table II. Dental cast measurements
Pretreatment (Tl) Posttreatment (T2) Postretention (T3) i 5 SD i + SD : ? SD
Arch length (mm) Class I Class II Combined
Intercanine width (mm) Class I Class II Combined
lntermolar width (mm) Class I Class II Combined
Overjet {mm) Class I Class 11 Combined
Overbite (mm) Class I Class II Combined
Irregularity Index Class I Class II Combined
58.5 k 3.0 58.9 + 2.4 56.5 t 2.8* 61.5 -t 3.7 61.5 + 3.1 59.1 ? 3.6* 60.0 ” 3.6 60.2 2 3.0 57.8 f 3.5*
25.1 f 1.4 25.6 -+ 1.1 24.6 + l.l* 25.6 f 1.7 26.4 z 1.4 25.4 + 1.3* 25.4 k 1.6 26.0 ” 1.3 25.0 I!Z 1.2*
43.4 i 1.4 44.2 k 1.9* 43.1 2 1.7* 43.2 f 2.1 44.3 t 1.8 44.3 ” 2.2 43.3 f 1.8 44.2 k 1.9* 43.7 2 2.0
4.8 2 2.2 2.2 2 0.F 2.6 2 0.7 7.5 k 2.4 2.1 t 0.6* 3.2 f 1.8 6.2 f 2.7 2.1 2 0.7* 2.9 f 1.1
4.1 k 1.5 2.4 2 0.6* 2.8 t 0.9 4.5 -c 1.8 3.1 t 0.8* 3.2 k 1.1 4.6 2 1.6 2.7 k 0.8* 3.0 k 1.0
3.3 2 1.2 1.1 ? 0.6* 2.6 2 1.6* 2.4 k 1.4 0.8 ” 0.4* 1.8 k 1.9* 2.9 f 1.4 1.0 2 0.5* 2.2 t 1.7*
*Indicates a statistically significant difference (P < 0.05) from the previous measurement.
noted with treatment resulting in small changes in facial proportions that then remained constant from T2 to T3 (Table III).
4. Incisorpositions (Table III, Nos. 19 through 28). Maxillary incisor position was evaluated with reference to several cephalometric planes (that is, S-N, FH, pal- atal plane, and N-A point). No significant changes were found. The trend was for the maxillary incisors to up- right slightly with treatment and then to procline to a lesser degree from T2 to T3.
Lower incisors were also found to have proclined during treatment; the only statistically significant change was a 1.4 mm forward movement of the lower incisor to the A-PO line (P < 0.001). Mandibular in- cisor positions remained relatively stable from T2 to T3, showing no significant change.
5. Molar positions (Table III, Nos. 29 and 30). Vertical alveolar development was seen to occur to a significant extent during treatment and continued from T2 to T3 (Table III). No differences were noted between Class I and Class II samples.
Interparameter correlations
Few clinically significant correlations (r > 0.7) were found for parameters on the dental casts. Arch length at T3 was found to be strongly correlated to the Tl value (r = 0.83); the postretention intercanine (r = 0.57) and intermolar (r = 0.63) widths showed only weak associations to their pretreatment values. Arch length at T3 was also found to be weakly asso- ciated with the postretention intercanine (r = 0.60) and intermolar (I = 0.56) widths. In the Class II sample
\'olume 92 Number 4
Nonextraction orthodontic therapy 325
Table III. Cephalometric data--Combined sample (X + SD)
--- *Indicates a statistidly significant difference (P < 0.05) from the previous measurement.
only, the amount of postretention overbite was found to be closely correlated to the amount of postretention incisor irregularity (r = 0.76).
When correlating dental cast and cephalometric pa- rameters, it was found that for the Class II sample only the arch length at postretention was correlated to the amount of incisor irregularity (r = - 0.7 1) and to the degree of antemposterior skeletal discrepancy, that is, ANB (r = -0.74). The Class II sample also showed correlations at T3 between incisor irregularity and man- dibular position, that is, ANB angle (r = 0.65) and Ar-B point distance (r = - 0.70). The degree of over- bite in Class Il[ cases at T3 was also found to be associated with the postretention mandibular position, that is, ANB angle (Y = 0.63) and Ar-B point (r = -0.73). No significant correlations were found in either the Class I or combined samples.
DISCUSSION
Overall, the impression gained from the data was of considerable long-term stability for the majority of
the parameters evaluated in this sample of mild to moderate malocclusions treated without extractions (Fig. 4).
One of the most closely evaluated changes was that of arch length. In this study arch length was not in- creased significantly during treatment, but showed sig- nificant reductions postretention. The magnitude of this decrease (- 2.4 mm) was similar in both nature and amount to both untreated normals ( - 2.0 mm) and to extraction cases ( - 2.5 mm) evaluated 10 years out of retention. ‘5,20 This information might be taken to imply that similar maturation processes affecting arch length were at work in all three groups.
Intercanine width and its immutability have long been the subject of heated discussions in the orthodontic literature.’ The present study tends to support the opin- ion that increases in intercanine width are not stable and that long-term changes will usually lead to a re- duction in intercanine width, frequently beyond the original value.4.26 The extent of the postretention changes seen in this group of patients was slightly
326 Glenn, Sinclair, and Alexander Am. J. Orthod. Dentofac. Orthop. October 1987
Fig. 4. A through C, Dental casts of representative nonextraction Class I case at pretreatment (A), posttreatment (B), and postretention (C). D through F, Representative nonextraction Class II case at pretreatment (D), posttreatment (E), and postretention (C).
greater than that seen in untreated normals,20 approxi- mately equal to those seen in other nonextraction stud- ies,” and about half of that seen in some long-term evaluations of extraction cases.15 It is interesting to note that the final mandibular intercanine widths in all three groups were quite similar (24 to 26 mm) and these findings are in agreement with other studies of normal arch width,28.29 suggesting perhaps a biologically opti- mum range for achieving stability.
Previous studies have shown distinct differences be- tween extraction and nonextraction groups regarding the long-term stability or intermolar width.“,‘3,30 In the extraction groups intermolar distance decreased during treatment and continued to decrease postretention; in the nonextraction groups there was a maintenance, and in a few cases some increase, in the intermolar width.
In the present study only very small changes were seen both during and after treatment and they tended to sup- port the concept of the stability of intermolar distance, particularly in Class II cases, which even tended to maintain some small increases in intermolar width through the postretention period.“*‘3
Overjet and overbite remained remarkably stable in this study, unlike previous reports; the slight ten- dency for a postretention increase in overjet seen in the Class II cases was similar to previous reports.‘5~3’
The present study showed a significant (+ 1.2 mm) increase in incisor irregularity during the postretention period. This change was somewhat more noticeable than that seen in untreated normals (+ 0.7 mm) while being less than half that seen in a sample of extraction cases ( + 2.9 mm). “,*O It should be noted, however, that
Nonextraction orthodontic therapy 327
this sample’s initial Irregularity Index of 2.9 mm was similar to that seen in untreated normals (2.2 mm) and differed greatly from the extraction sample’s value of 7.3 mm. It is not surprising therefore that, at the post- retention evaluation, the degree of incisor irregularity in this sample (2.2 mm) should be closer to the un- treated normals (2.7 mm) than to the postretention value of 4.6 mm for the initially more severely crowded ex- traction cases. This study did note a mean net improve- ment in incisor irregularity similar to those reported by Gallerano”’ and Little, Wallen, and Riedel,” but dif- fered from the results of Kaplani who showed his non- extraction group with greater postretention crowding than seen initially. The changes seen in this study also appeared to be less variable and unpredictable than those reported for extraction cases” with the exception of Sandusky’s study”” of Tweed extraction cases, which showed minimal long-term relapse. These findings could be taken as confirmation of the suggestion that, although orthodontic therapy may temporarily alter the course of normally occurring physiologic changes, fol- lowing the retention period maturation processes may resume.” The lseverity of the postretention changes seen, however, s#eemed to bear some relationship to the severity of the initial malocclusion. In other words, although the three groups were moving in a similar direction, they appeared to be on different “tracks” with regard to the exl:ent of the changes being manifested.
This study l%led to find any relationship between incisor mesiodistal and faciolingual tooth dimensions, using the 13olton’” and Peck and PeckZs analyses, and the degree of either pretreatment or postretention incisor irregularity. These findings are in agreement with the majority of studies in this area.“.33-“6 These results should not be taken to mean that incisor crowding could not be associated with significant abnormalities of tooth size (for example, peg lateral incisors) because cases of this type were excluded from the present sample.
Evaluation 01’ the cephalometric parameters showed few changes that might contribute to posttreatment re- lapse. As also noted in both extraction’(’ and untreated normal*’ samples, the mandibular plane angle was found to decrease at postretention; the Class 11 group tended to show some forward rebound of the maxilla following Class II correction by means of headgear. With no significant relapse noted, the present study confirmed previous findings that incisor positions re- main very stable during the postretention period. ‘h.“.‘7.77
One of the objectives of this study was to search for associations of value among parameters that might aid in diagnosis and treatment planning. In contrast to other studies, which were generally unsuccessful, a few interrelationships of potential clinical value were found,
In the Class II sample only, a series of interrela- tionships was noted among the final arch length, over- bite, incisor crowding, mandibular size, and degree of retrognathism, which led to the following scenario. Larger ANB values and shorter mandibular lengths in Class II malocclusions are associated with shorter arch lengths, greater overbite, and increased mandibular in- cisor irregularity at the postretention stage.j8 These find- ings therefore tend to support the suggestion that the amount and direction of facial growth in the postreten- tion period may be at least partially responsible for the maturational changes seen in the dentition.‘7.3”-J’
The exact mechanisms of relapse remain to be dis- covered and some might argue that the changes seen in the present postretention sample were due to the type of mechanotherapy used. The presentation of results from similar long-term studies may help to resolve this debate. If a gradation of responses is truly seen in the severity of relapse ranging from untreated normals to severely crowded extraction cases, then a study of the long-term stability of a sample of moderate to severely crowded cases treated by nonextraction therapy might shed considerable further light upon the matter.
SUMMARY
On the basis of the dental cast and cephalometric records from a sample of 28 cases evaluated long-term following nonextraction therapy, the following conclu- sions were reached:
1. Overall stability was relatively good. The re- lapse patterns seen were similar in nature, but intermediate in extent, between untreated nor- mals and four first premolar extraction cases.
2. Arch length and intercanine width decreased significantly at postretention despite minimal changes in treatment.
3. Overjet, overbite, and intermolar width re- mained relatively stable following treatment.
4. Incisor irregularity increased at postretention, but a long-term net improvement was still evident.
5. The Bolton and Peck and Peck analyses failed to show any association between mesiodistal and faciolingual tooth size and either pretreatment or postretention incisor irregularity.
6. Class 11 malocclusions with large ANB values and short mandibular lengths were associated with increased incisor irregularity, shorter arch lengths, and deeper overbites at the postretention stage.
The authors would like to thank Drs. Moody Alexander, Henri Petit, and Jim Thrash for their assistance with this project. In addition, the authors thank Lee Martin for statis-
320 Glenn, Sinclair, and Alexander
tical assistance and Mrs. Martha Black for typing the manuscript.
REFERENCES 1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
Angle EG. Treatment of malocclusion of the teeth: Angle’s sys- tem. 7th ed. Philadelphia: SS White Dental Manufacturing Co, 1907. Brodie AG. The fourth dimension in orthodontics. Angle Orthod 1954;24:15-30. Tweed CJ. Indications for the extraction of teeth in orthodontic procedures. AM J ORTHOD ORAL SURG 1944;30:405-28. Riedel RA. Retention. In: Graber TM, Swain BF, eds. Current orthodontic concepts and techniques. Philadelphia: WB Saunders Company, 1975. Nance HN. The limitations of orthodontic treatment. Diagnosis and treatment in the permanent dentition. AM J ORTHOD ORAL SURG 1947;33:253-301. Ricketts RM. Bioprogressive therapy as an answer to orthodontic needs. AM J OR~OD 1976;70:241-68. Strang RHW. Factors associated with successful orthodontic treatment. AM J ORTHOD 1952;38:790-800. Rogers AP. Making facial muscles our allies in treatment and retention. Dent Cosmos 1922;64:71 l-30. Proflit WR. The facial musculature in its relation to the dental occlusion. In: Carlson DS, McNamara IA, eds. Muscle adap- tation in the craniofacial region. Ann Arbor: University of Mich- igan, 1978. Gallerano R. Mandibular anterior crowding-A post-retention study. [Masters thesis]. Seattle: University of Washington, School of Dentistry, 1976. Gardner SD, Chaconas SJ. Post-treatment and post-retention changes following orthodontic therapy. Angle Orthoc! 1976;46: 151-61. Kaplan R. Mandibular third molars and post-retention crowding. AM J ORTHOD 1974;66:41 I-30. Shapiro PA. Mandibular dental arch form and dimension. AM J ORTHOD 1974;66:58-70. Schudy GF. Post-treatment craniofacial growth: its implications in orthodontic treatment. AM J ORTHOD !974;65:39-57. Little RM, Wallen TR, Riedel RA. Stability and relapse of man- dibular anterior alignment-First premolar cases treated by tra- ditional edgewise orthodontics. AM J ORTHOD 1981;80:349-64. Shields TM, Little RM, Chapko MK. Stability and relapse of mandibular anterior alignment-A cephalometric appraisal of first premolar extraction cases treated by traditional edgewise orthodontics. AM J ORTHOD 1985;87:27-38. Gilmore CA, Little RM. Mandibular incisor dimensions and crowding. AM J ORTHOD 1984;86:493-502. Barrow GV, White JR. Developmental changes of the maxillary and mandibular dental arches. Angle Orthod 1952;22:41-6. DeKock WH. Dental arch depth and width studies longitudinally 12 years of age to adulthood. AM J ORTHOD 1972;62:56-66. Sinclair PM, Little RM. Maturation of untreated normal occlu- sions. AM J ORTHOD 1983;83:114-23. Sinclair PM, Little RM. Dentofacial maturation of untreated normals. AM J ORTHOD 198.5;88:146-56. Horowitz S, Hixon E. Physiologic recovery following ortho- dontic treatment. AM J ORTHOD 1969;55:1-4.
Am. .I. Orthod. Dentofac. Orthop. October 1987
23. Little RM. The Irregularity Index: a quantitative score of man- dibular anterior alignment. AM J ORTHOD 1975;68:554-63.
24. B&on WA. Disharmony of tooth size and its relation to the analysis and treatment of malocclusion. Angle Orthod 1958; 28: 113-30.
25. Peck S, Peck H. Crown dimensions and mandibular incisor align- ment. Angle Orthod 197?;42:148-53.
26. Strang R. The fallacy of denture expansion as a treatment pro- cedure. Angle Orthod 1949;19:12-22.
27. Lundstrom A. Malocclusions of the teeth regarded as a problem in connection with the apical base. INT J ORTHOD 1925;I 1:591- 602.
28. Staley RN, Stuntz WF$ Peterson LC. A comparison of arch widths in adults with normal occlusion and adults with Class II, Division 1 malocclusion. AM J ORTHOD 198>;88:163-9.
29. Moorrees CFA. The dentition of the growing child. Cambridge: Harvard University Press, 1959.
30. Walter DC. Changes in the form and dimensions of dental arches resulting from orthodontic treatment. Angle Orthod 1953;23: 3-18.
31. Uhde MD, Sadowsky C, Begole EA. Long term stability of dental relationships after orthodontic treatment. Angle Orthod 1983;53:240-52.
32. Sandusky WC. A long-term postretention study of Tweed ex- traction treatment [Master’s thesis]. University of Tennessee, 1983.
33. Lundstrom A. Variations of tooth size in the etiology of mal- occlusion. AM J ORTHOD 1955;41:872-6.
34. Faslicht J. Crowding of mandibular incisors. AM J ORTHOD 1972;61:374-83.
35. Smith RJ, Davidson WM, Gipe GP. Incisqr shape and incisor crowding: a re-evaluation of the Peck and Peck ratio. AM J ORTHOD 1982;82:231-5.
36. Keene A, Engle G. The mandibular dental arch. Part IV. Pre- diction and prevention of lower anterior relapse. Angle Orthod 1979;49:173-80.
37. BjBrk A, Skieller V. Facial development and tooth eruption. An implant study at the age of puberty. AM J ORTHOD 1972;62: 339-83.
38. Raineri WA. Late lower anterior crowding: growth and ortho- dontic treatment. Orthodontic certificate. Rochester, New York: Eastman Dental Center, 1982.
39. Litowitz R. A stqdy of the movement of certain teeth during and following orthodontic treatment. Angle Orthod 1948; 18: 113-31.
40. Huckaba GW. The physiologic basis of relapse. AM J ORTHOD 1952;38:335-50.
41. Lavergne J, Gasson N. The influence of jaw rotation on the morphogenesis of malocclusion. AM J ORTHOD 1978;73:658-66.
42. Issacson R, Zapfel R, Worms F, Erdman A. Effects of rotational jaw growth on the occlusion and profile. AM J ORTHOD 1977;72:276-86.
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