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Effect of edgewise treatment and retention on mandibular incisors
E$ect of edgewise treatment and retention on mandibular incisors Miaden
M. Kuftinec,
Richmond,
D.Stom.,
D.M.D.,
Sc.D.*
Vu.
P
roper postitioning of the mandibular incisors is considered to be more critical tha.n any other objective for good results of orthodontic treatment2* (i, g, lo Consequently, many orthodontists in everyday practice carefully evaluate the position of the mandibular incisors before, during, and after treatment in an attempt to achieve stable results and good facial esthetics. Contrary to the principles that prevail in other orthodontic techniques (for instance, removable appliances or the Begg method), in the edgewise technique the mandibular incisors cannot tip freely and therefore should he in a stable position unless intentionally moved into some new, desired 1)osition.l” 1n addition to these teeth being prevented from excessive tipping by tongue musculature on the lingual aspect and the orbicularis oris muscle on the labial aspect,‘, ’ the design of edgewise appliances limits the movement of the mandibular incisors. It is worth noting that proponents of the edgewise philo,sophp have adopted several modifications from light-wire techniques4 in their efforts to obtain desirable tooth movement with maximal efficiency and minimal tissue damage. This study was conducted with two main objectives--( 1) to observe what kind of change, if any, takes place in the position of the mandibular incisors during orthodontic treatment for similar types of malocclusion and during retention and (2) to investigate whether any predictable relationships or dependencies exist among any such changes. As in a previous studg,4 treated subjects were not comparrtl with untrcatctl controls. Instead, cases that required extraction of permanent teeth were compared with those that did not require SLW~ extractions. In addition, Peck ant1 Peck’s7 concept was tested; that is, the mesiodistal to faciolingual index for the mandibular incisors is an important factor in the stability of correction and in predicting the probability of relapse of anterior crowcling and rotations. *Associate Professor, Orthodontic Medical College of Virginia, Fkhool
316
Department, of Dentistry.
Virginia
Commonwealth
University,
Effect of edgewise trentment
Volume Nunabel
68 3
Table
I. Sample
Nonextmction
group
Extraction
Materials
and
140 + 6” 22 5 7* 6 f 3”
months
group
N = 30 16 females 14 males Average age at start of treatment Average time in active treatment Average time in retention standard
317
description
N = 20 10 females 10 males Average age at start of treatment Average time in active treatment Average time in retention
*One
a-Ed retention
148 ?r 8* 26 + 5” 5 2 5*
deviation.
methods
Fifty cases with varying degrees of bimaxillary protrusion, treated at the Medical College of Virginia Orthodontic Clinic with edgewise appliances for correction of Class I malocclusion, were analyzed. Thirty of these cases required extraction of all four first premolars. While all fifty cases had at least 2 mm. of anterior mandibular crowding, the severity of the crowding was the primary factor in deciding whether or not extractions were needed. It appeared, although not specifically indicated in the records, that in all cases with an estimated 5 mm. or more of crowding extraction had been prescribed. The sample included twenty-six females and twenty-four males, and in both nonextraction and extraction groups both sexes were about equally represented (Table I). All fifty cases were judged to have been satisfactorily completed by both functional and esthetic criteria. The records used in this study included standardized orthodontic casts, obtained from alginate impressions poured in white stone, and standardized cephalometric radiograms in norma lateralis. Records were obtained before active treatment, after the fixed appliances were removed, and not less than 4 months out of retention, Extractions were not performed prior to the first set of records. Active treatment was accomplished with edgewise appliances and lasted an average of 22 and 26 months. The retention period lasted an average of 6 or 5 months for the nonextraction and extraction groups, respectively (Table I). An attempt was made to match the two groups with respect to age, race, and ethnic origin; therefore, all differences observed between the two groups are attributed to the two treatment approaches, that is nonextraction versus extraction. The dental casts were used for assessment of anterior mandibular crowding. This was done by visual inspection and estimated in millimeters. The mesiodistal and faciolingual diameters of all four mandibular incisors were determined according to the method of Peck and Peck,7 except that the measurements were taken from the dental casts rather than from the patient’s mouth, since no significant differences could be discerned between oral and cast measurements.3 In order to assess whether crowded incisors were corrected in their position
318
Kuffhec
Table
II. Anterior
Am. J. Orthod. St-ptenzbsr 197:;
mandibular
crowding
Pretreatment Nonextraction group 3.2 + 1.1’
Posttreatment (N
=
Postretention
-
80)
0
2.5 + 2.8”
(76?&%) Extra&ion
group (N = 30) 6.3 + 3.0*
1.6 2 2.1” (25vw
0 (-0.4t)
*One standard deviation. tin eight out of thirty there was spacing in the arch. $Per cent return toward original (relapse).
Table
III.
Mean
M-D
and
F-L widths
Nonextradion Tooth Central incisors Lateral incisors
for
mandibular
groptp
incisors
(N = 80)
Extraction
group
(N = SO)
Y-D
F-L
M-D
F-L
5.44 2 0.32 5.85 + 0.30
5.92 t 0.29 6.06 t 0.35
5.52 t 0.47 5.98 t 0.44
5.93 2 0.38 6.18 + 0.42
via canine expansion, the intercanine distance was measured. This measurement and the previous measurements (mesiodistal and faciolingual diameters) were accomplished by using a modified, calibrated sliding rule, divided in tenths of millimeters. Cephalometric measurements obtained in this study included the mandibular incisor to mandibular plane angle (the IMPAla) and the interincisal angle.g Both angles were measured twice to the nearest half degree. The error of measurement was determined as the standard deviation of differences (8 differences 2)1/2 x Other statistical procedures included routine 2N >’ data reduction (mean, standard deviation, ranges), a. test for significance of differences (Student’s t test), and calculating correlation coefficients.8 * error =
Findings
The error of measurements was found to be consistently smaller than the limit of detection for the linear and angular measurements. Error of estimation for the anterior mandibular crowding relapse was not calculated, since the nature of change in this parameter made this evaluation somewhat difficult. The average anterior crowding before treatment was 3.2 mm. for the nonextraction group and 6.3 mm. for the extraction group. This crowding was corrected in all cases. In fact, in eight out of thirty extraction cases there was 2 mm. of anterior mandibular spacing after completion of active treatment (Table II). The mean values of the mesiodistal and faciolingual diameters, with their respective standard deviations, are presented in Table III. These values are not
Volume Nwnber
68 3
Table
IV.
EfSect of edgewise treatment M-D/F-L
indices for mandibular Nonextradon
Tooth
Extract&m
group
Mean +
S.D.
Range
91.1 96.5
6.8’ 8.8
82 to 107 81 to 124
93.1 96.5
8.6 7.5
75 to 121 82 to 117
distance
Nonextraction group (N = SO) 26.6 ? 2.1 Extraction group (N = JO) 23.9 i: 1.7 VI.
group
Range
Pretreatment
Table
incisors (per cent)
S.D.
Intercanine
V.
319
Mean 2
Central incisor Lateral incisor Table
and retention
IMPA and interincisal Pretreatment
Nonextraction group (N = 50) IMPA 89.0 t 3.2 l/l 128 t 11.5 Extraction group (N = 30) IMPA 93.5 + 6.7 l/l 116 ? 12.0
changes Poettreatnzent
Postretention
26.7 +_ 3.0
26.3 + 2.4
26.4 2 2.8
25.8 t 1.8
angle (l/l)
changes ‘Posttreatment
Postretentbn
90.5 2 4.0 130 + 15.2
90.0 f 2.6 129.5 + 14.0
89.5 f 4.5 140 + 18.6
89.0 + 4.2 137.3 + 14.6
different from those reported by Peck and Peck.’ The mandibular incisors are somewhat (not significantly at the 5 per cent level) larger in the extraction group than in the nonextraction group. When the common indices are calculated for all four incisors (Table IV), it is evident that the ranges encountered allow for some cases to have unfavorable indices.’ The changes in intercanine distance are tabulated in Table V. Both groups showed an insignificant increase during treatment. The only moderately high correlation between any two parameters was observed between the amount of anterior crowding correction and relapse of the intercanine distance expansion (r = 0.68). The measurements obtained from the cephalometric radiograms are compiled in Table VI. The IMPA and the interincisal angle did not follow the same pattern of changes, although these two angles have one common variable-the long axis of the mandibular incisor. Discussion
Perhaps the most interesting observation in this study was that the parameters investigated behaved rather similarly in both groups. It appears that the magnitude of change brought about by treatment, that is, the correction of bimaxillary protrusion along with anterior mandibular crowding, was larger in the extraction group. It was also apparent that, prior to any t.reatment, the
320
Kuffinec
severity of protrusion and the estimaicd amount of anterior crowcling were larger in the extraction cases. Significant differences between the two groups (p 5 0.05) were observed in some parameters. The anterior crowding relapsed more in the nonext,raction group (Table II). The changes in the IMPA and thr interincisal angle were significantly larger in the extraction group (Table VI). Correction of the anterior mandibular crowding revealed several interesting points. The extraction cases were found to have larger mandibular incisors t.han the nonextraction cases, which also correlated with more severe anterior mandibular crowding in the former. These larger, more crowded incisors were corrected into more stable position, supporting the extraction treatment approach. On the other hand, the cases were sometimes overtreated to the point of anterior spacing. This may be the result of more than adequate space in the arch after extractions were performed and of somewhat excessive canine retraction. This spacing, as well as the correction of crowding, relapsecl to an unpredictable degree after retention in the majority of the cases. These findings pose an interesting question as to the validity of attempting to treat cases in which there was slight mandibular anterior crowding. Intercanine distance changed in both groups in spite of precautions against its expansion. In the extraction group this was probably due to distal movement of the canines into wider segments of the arch. In the nonextraction group, canines were expanded buccally, as was the rest of the dental arch. The slight increase in the IMPA supports such an explanation. Examining individual cases in this study, the conclusion was drawn that the more the canines were expanded, the more they relapsed toward their original position. It was postulated by Peck and Peck’ that the mesiodistal to faciolingual ratio or index could be a useful diagnostic and predictive tool for the stability of the mandibular incisors. While this sample as a whole showed favorable ratios, there were cases in which the index was rather unfavorable. Analysis of those cases disclosed that anterior crowding relapsed more than the average amount, thus supporting Peck and Peck’s theory. While cases in the nonextraction group exhibited smaller mesiodistal to faciolingual indices than those in the extraction group, they relapsed more readily. This indicates that factors other than the above-mentioned indices can influence the stability of mandibular incisors, for example, the amount of crowding at the beginning of treatment, the Bolton’s anterior tooth correlation index, the interincisal relationship, etc. Thus, it is not recommended that one start reapproximating incisors in the cases of relatively large indices, as is advocated to be the procedure of choice by Peck and Peck.7 It is suggested, however, that the mesiodistal to faciolingual indices be calculated in addition to the other diagnostic criteria, as they seem to contribute to one’s ability to predict the relapse tendency.” In spite of the fact that all cases showed a bimaxillary protrusion t,endency, from both clinical examination and profile analysis, t,hc IMPA in the nonextraction group averaged 89 degrees. Also, the extraction group’s average IMPA was not overly large. This angle did not change, indicating perhaps careful monitor-
Efect
of edgethe
treaimed
and retention
321
ing and concern about flaring of these teeth. The interincisal angle changed in both groups in the same direction, as would be expected in the cases characterized by protrusion. As noted in Table VI, the angle increased significantly in the extraction group, undoubtedly a result of the availability of more apace in the arches of these cases, thus requiring more anterior retraction to close the extraction sites. From the interpretation of the changes in the two angles combined (Table VI), it appeared that more retraction was accomplished in the maxillary than in the mandibular arch. Such interpretation could be substantiated upon clinical examination of the majority of the cases. Summary
and
conclusions
This study consisted of analyzing clinical records of fifty cases treated for correction of Class I malocclusion with varying degrees of bimaxillary protrusion and anterior mandibular crowding. Thirty of these cases required extraction of all four first premolars. Parameters characterizing changes in position of mandibular incisors during treatment with edgewise appliances and during retention and shortly afterward were studied. All the parameters indicated rather similar changes for the nonextraction and the extraction groups. The relapse of anterior mandibular crowding was significantly larger (p < 0.05) in the nonextraction group. The IMPA and interincisal angle changed significantly more in the extraction group. Upon testing for validity of the mesiodistal to faciolingual indices, it was determined that they predicted stability of the achieved alignment of mandibular incisors. There were, however, individual cases in both groups which did not follow the central tendency. It was observed that the mesiodistal diameters of mandibular incisors were somewhat larger in the extraction cases. There was only one pair of parameters that showed a moderately high intercorrelation (r = 0.68) ; that was between correction of the anterior crowding and relapse of the intercanine expansion. It was observed that the more correction took place, the more readily expanded canines would relapse. An over-all impression is that the mandibular incisors change little in their position to each other and relative to the other structures of the mouth. The question remains: Is this due to our ability to control them well, or due to an inability to move and maintain them in their new position?
REFERENCES
1. Frankel, R.: The treatment of Class II, Division 1 malocclusions with functional correctors, AM. J. ORTHOD. 55: 265-275, 1969. 2. Iyer, V. S.: Utility of the maxillofacial triangle in orthodontic diagnosis, Dent. Record 73: 316-325, 1953. 3. Kaner, P. C.: Validity of M-D/F-L ratio in treatment planning, thesis, Medical College of Virginia, 1974. 4. Kuftinec, M. M., and Glass, R. L. : Stability of the IMPA with reference to the Begg method, Angle Orthod. 41: 264-270, 1971.
322
Kuftinec
5. Kuftinec, M. M.: Behavior of mandibular teeth during orthodontic treatment and retew t,ion, I.A.D.R. Abstr. Ko. 3, 1975. 6. Lindquist, J. T.: The lower incisor-Tts influence on treatment and rsthctics: Asr, J. ORTHOD. 44: 112-140, 1958. 7. Peck, S., and Peck, H.: An index for assessing tooth shape deviations as applied to the mandibular incisors, AM. J. ORTHOD. 61: 384-401, 1972. 8. Snedecor, G. IV., and Cochran, TV. G.: Statistical methods, low Cit,p, 1967, lowa State University Press. 9. Steiner, C. C. : Cephalometrics in clinical practice, Angle Orthod. 29: 8-29, 1959. 10. Tweed, C. H.: Clinical orthodontics, St. Louis, 1966, The C. V. Mosby Company.
Notwithstanding the many technical improvements adopted in the treatment of dentofacial deformities during the last twenty-five years, orthodontists continue to meet with cases that baffle their skill. The frequent, incessant offering of novel methods of treatment certainly warrants the opinion that many preceding modes have failed to accomplish their intended purpose. Reluctantly perhaps, though none the less frankly, we must admit that our immoderate devotion to technic has not attained the satisfaction we anticipated, that many problems remain to vex and irritate us, and that the high hopes of our youth (encouraged by the pretensions of sectarian schools] have not been realized. (B. E. Lischer: On New Methods of Diagnosing Dentofacial Deformities, Int. J. Orthod. Oral Surg. Radiogr. 10: 521-541, 1924.)
M. Kuftinec,
Richmond,
D.Stom.,
D.M.D.,
Sc.D.*
Vu.
P
roper postitioning of the mandibular incisors is considered to be more critical tha.n any other objective for good results of orthodontic treatment2* (i, g, lo Consequently, many orthodontists in everyday practice carefully evaluate the position of the mandibular incisors before, during, and after treatment in an attempt to achieve stable results and good facial esthetics. Contrary to the principles that prevail in other orthodontic techniques (for instance, removable appliances or the Begg method), in the edgewise technique the mandibular incisors cannot tip freely and therefore should he in a stable position unless intentionally moved into some new, desired 1)osition.l” 1n addition to these teeth being prevented from excessive tipping by tongue musculature on the lingual aspect and the orbicularis oris muscle on the labial aspect,‘, ’ the design of edgewise appliances limits the movement of the mandibular incisors. It is worth noting that proponents of the edgewise philo,sophp have adopted several modifications from light-wire techniques4 in their efforts to obtain desirable tooth movement with maximal efficiency and minimal tissue damage. This study was conducted with two main objectives--( 1) to observe what kind of change, if any, takes place in the position of the mandibular incisors during orthodontic treatment for similar types of malocclusion and during retention and (2) to investigate whether any predictable relationships or dependencies exist among any such changes. As in a previous studg,4 treated subjects were not comparrtl with untrcatctl controls. Instead, cases that required extraction of permanent teeth were compared with those that did not require SLW~ extractions. In addition, Peck ant1 Peck’s7 concept was tested; that is, the mesiodistal to faciolingual index for the mandibular incisors is an important factor in the stability of correction and in predicting the probability of relapse of anterior crowcling and rotations. *Associate Professor, Orthodontic Medical College of Virginia, Fkhool
316
Department, of Dentistry.
Virginia
Commonwealth
University,
Effect of edgewise trentment
Volume Nunabel
68 3
Table
I. Sample
Nonextmction
group
Extraction
Materials
and
140 + 6” 22 5 7* 6 f 3”
months
group
N = 30 16 females 14 males Average age at start of treatment Average time in active treatment Average time in retention standard
317
description
N = 20 10 females 10 males Average age at start of treatment Average time in active treatment Average time in retention
*One
a-Ed retention
148 ?r 8* 26 + 5” 5 2 5*
deviation.
methods
Fifty cases with varying degrees of bimaxillary protrusion, treated at the Medical College of Virginia Orthodontic Clinic with edgewise appliances for correction of Class I malocclusion, were analyzed. Thirty of these cases required extraction of all four first premolars. While all fifty cases had at least 2 mm. of anterior mandibular crowding, the severity of the crowding was the primary factor in deciding whether or not extractions were needed. It appeared, although not specifically indicated in the records, that in all cases with an estimated 5 mm. or more of crowding extraction had been prescribed. The sample included twenty-six females and twenty-four males, and in both nonextraction and extraction groups both sexes were about equally represented (Table I). All fifty cases were judged to have been satisfactorily completed by both functional and esthetic criteria. The records used in this study included standardized orthodontic casts, obtained from alginate impressions poured in white stone, and standardized cephalometric radiograms in norma lateralis. Records were obtained before active treatment, after the fixed appliances were removed, and not less than 4 months out of retention, Extractions were not performed prior to the first set of records. Active treatment was accomplished with edgewise appliances and lasted an average of 22 and 26 months. The retention period lasted an average of 6 or 5 months for the nonextraction and extraction groups, respectively (Table I). An attempt was made to match the two groups with respect to age, race, and ethnic origin; therefore, all differences observed between the two groups are attributed to the two treatment approaches, that is nonextraction versus extraction. The dental casts were used for assessment of anterior mandibular crowding. This was done by visual inspection and estimated in millimeters. The mesiodistal and faciolingual diameters of all four mandibular incisors were determined according to the method of Peck and Peck,7 except that the measurements were taken from the dental casts rather than from the patient’s mouth, since no significant differences could be discerned between oral and cast measurements.3 In order to assess whether crowded incisors were corrected in their position
318
Kuffhec
Table
II. Anterior
Am. J. Orthod. St-ptenzbsr 197:;
mandibular
crowding
Pretreatment Nonextraction group 3.2 + 1.1’
Posttreatment (N
=
Postretention
-
80)
0
2.5 + 2.8”
(76?&%) Extra&ion
group (N = 30) 6.3 + 3.0*
1.6 2 2.1” (25vw
0 (-0.4t)
*One standard deviation. tin eight out of thirty there was spacing in the arch. $Per cent return toward original (relapse).
Table
III.
Mean
M-D
and
F-L widths
Nonextradion Tooth Central incisors Lateral incisors
for
mandibular
groptp
incisors
(N = 80)
Extraction
group
(N = SO)
Y-D
F-L
M-D
F-L
5.44 2 0.32 5.85 + 0.30
5.92 t 0.29 6.06 t 0.35
5.52 t 0.47 5.98 t 0.44
5.93 2 0.38 6.18 + 0.42
via canine expansion, the intercanine distance was measured. This measurement and the previous measurements (mesiodistal and faciolingual diameters) were accomplished by using a modified, calibrated sliding rule, divided in tenths of millimeters. Cephalometric measurements obtained in this study included the mandibular incisor to mandibular plane angle (the IMPAla) and the interincisal angle.g Both angles were measured twice to the nearest half degree. The error of measurement was determined as the standard deviation of differences (8 differences 2)1/2 x Other statistical procedures included routine 2N >’ data reduction (mean, standard deviation, ranges), a. test for significance of differences (Student’s t test), and calculating correlation coefficients.8 * error =
Findings
The error of measurements was found to be consistently smaller than the limit of detection for the linear and angular measurements. Error of estimation for the anterior mandibular crowding relapse was not calculated, since the nature of change in this parameter made this evaluation somewhat difficult. The average anterior crowding before treatment was 3.2 mm. for the nonextraction group and 6.3 mm. for the extraction group. This crowding was corrected in all cases. In fact, in eight out of thirty extraction cases there was 2 mm. of anterior mandibular spacing after completion of active treatment (Table II). The mean values of the mesiodistal and faciolingual diameters, with their respective standard deviations, are presented in Table III. These values are not
Volume Nwnber
68 3
Table
IV.
EfSect of edgewise treatment M-D/F-L
indices for mandibular Nonextradon
Tooth
Extract&m
group
Mean +
S.D.
Range
91.1 96.5
6.8’ 8.8
82 to 107 81 to 124
93.1 96.5
8.6 7.5
75 to 121 82 to 117
distance
Nonextraction group (N = SO) 26.6 ? 2.1 Extraction group (N = JO) 23.9 i: 1.7 VI.
group
Range
Pretreatment
Table
incisors (per cent)
S.D.
Intercanine
V.
319
Mean 2
Central incisor Lateral incisor Table
and retention
IMPA and interincisal Pretreatment
Nonextraction group (N = 50) IMPA 89.0 t 3.2 l/l 128 t 11.5 Extraction group (N = 30) IMPA 93.5 + 6.7 l/l 116 ? 12.0
changes Poettreatnzent
Postretention
26.7 +_ 3.0
26.3 + 2.4
26.4 2 2.8
25.8 t 1.8
angle (l/l)
changes ‘Posttreatment
Postretentbn
90.5 2 4.0 130 + 15.2
90.0 f 2.6 129.5 + 14.0
89.5 f 4.5 140 + 18.6
89.0 + 4.2 137.3 + 14.6
different from those reported by Peck and Peck.’ The mandibular incisors are somewhat (not significantly at the 5 per cent level) larger in the extraction group than in the nonextraction group. When the common indices are calculated for all four incisors (Table IV), it is evident that the ranges encountered allow for some cases to have unfavorable indices.’ The changes in intercanine distance are tabulated in Table V. Both groups showed an insignificant increase during treatment. The only moderately high correlation between any two parameters was observed between the amount of anterior crowding correction and relapse of the intercanine distance expansion (r = 0.68). The measurements obtained from the cephalometric radiograms are compiled in Table VI. The IMPA and the interincisal angle did not follow the same pattern of changes, although these two angles have one common variable-the long axis of the mandibular incisor. Discussion
Perhaps the most interesting observation in this study was that the parameters investigated behaved rather similarly in both groups. It appears that the magnitude of change brought about by treatment, that is, the correction of bimaxillary protrusion along with anterior mandibular crowding, was larger in the extraction group. It was also apparent that, prior to any t.reatment, the
320
Kuffinec
severity of protrusion and the estimaicd amount of anterior crowcling were larger in the extraction cases. Significant differences between the two groups (p 5 0.05) were observed in some parameters. The anterior crowding relapsed more in the nonext,raction group (Table II). The changes in the IMPA and thr interincisal angle were significantly larger in the extraction group (Table VI). Correction of the anterior mandibular crowding revealed several interesting points. The extraction cases were found to have larger mandibular incisors t.han the nonextraction cases, which also correlated with more severe anterior mandibular crowding in the former. These larger, more crowded incisors were corrected into more stable position, supporting the extraction treatment approach. On the other hand, the cases were sometimes overtreated to the point of anterior spacing. This may be the result of more than adequate space in the arch after extractions were performed and of somewhat excessive canine retraction. This spacing, as well as the correction of crowding, relapsecl to an unpredictable degree after retention in the majority of the cases. These findings pose an interesting question as to the validity of attempting to treat cases in which there was slight mandibular anterior crowding. Intercanine distance changed in both groups in spite of precautions against its expansion. In the extraction group this was probably due to distal movement of the canines into wider segments of the arch. In the nonextraction group, canines were expanded buccally, as was the rest of the dental arch. The slight increase in the IMPA supports such an explanation. Examining individual cases in this study, the conclusion was drawn that the more the canines were expanded, the more they relapsed toward their original position. It was postulated by Peck and Peck’ that the mesiodistal to faciolingual ratio or index could be a useful diagnostic and predictive tool for the stability of the mandibular incisors. While this sample as a whole showed favorable ratios, there were cases in which the index was rather unfavorable. Analysis of those cases disclosed that anterior crowding relapsed more than the average amount, thus supporting Peck and Peck’s theory. While cases in the nonextraction group exhibited smaller mesiodistal to faciolingual indices than those in the extraction group, they relapsed more readily. This indicates that factors other than the above-mentioned indices can influence the stability of mandibular incisors, for example, the amount of crowding at the beginning of treatment, the Bolton’s anterior tooth correlation index, the interincisal relationship, etc. Thus, it is not recommended that one start reapproximating incisors in the cases of relatively large indices, as is advocated to be the procedure of choice by Peck and Peck.7 It is suggested, however, that the mesiodistal to faciolingual indices be calculated in addition to the other diagnostic criteria, as they seem to contribute to one’s ability to predict the relapse tendency.” In spite of the fact that all cases showed a bimaxillary protrusion t,endency, from both clinical examination and profile analysis, t,hc IMPA in the nonextraction group averaged 89 degrees. Also, the extraction group’s average IMPA was not overly large. This angle did not change, indicating perhaps careful monitor-
Efect
of edgethe
treaimed
and retention
321
ing and concern about flaring of these teeth. The interincisal angle changed in both groups in the same direction, as would be expected in the cases characterized by protrusion. As noted in Table VI, the angle increased significantly in the extraction group, undoubtedly a result of the availability of more apace in the arches of these cases, thus requiring more anterior retraction to close the extraction sites. From the interpretation of the changes in the two angles combined (Table VI), it appeared that more retraction was accomplished in the maxillary than in the mandibular arch. Such interpretation could be substantiated upon clinical examination of the majority of the cases. Summary
and
conclusions
This study consisted of analyzing clinical records of fifty cases treated for correction of Class I malocclusion with varying degrees of bimaxillary protrusion and anterior mandibular crowding. Thirty of these cases required extraction of all four first premolars. Parameters characterizing changes in position of mandibular incisors during treatment with edgewise appliances and during retention and shortly afterward were studied. All the parameters indicated rather similar changes for the nonextraction and the extraction groups. The relapse of anterior mandibular crowding was significantly larger (p < 0.05) in the nonextraction group. The IMPA and interincisal angle changed significantly more in the extraction group. Upon testing for validity of the mesiodistal to faciolingual indices, it was determined that they predicted stability of the achieved alignment of mandibular incisors. There were, however, individual cases in both groups which did not follow the central tendency. It was observed that the mesiodistal diameters of mandibular incisors were somewhat larger in the extraction cases. There was only one pair of parameters that showed a moderately high intercorrelation (r = 0.68) ; that was between correction of the anterior crowding and relapse of the intercanine expansion. It was observed that the more correction took place, the more readily expanded canines would relapse. An over-all impression is that the mandibular incisors change little in their position to each other and relative to the other structures of the mouth. The question remains: Is this due to our ability to control them well, or due to an inability to move and maintain them in their new position?
REFERENCES
1. Frankel, R.: The treatment of Class II, Division 1 malocclusions with functional correctors, AM. J. ORTHOD. 55: 265-275, 1969. 2. Iyer, V. S.: Utility of the maxillofacial triangle in orthodontic diagnosis, Dent. Record 73: 316-325, 1953. 3. Kaner, P. C.: Validity of M-D/F-L ratio in treatment planning, thesis, Medical College of Virginia, 1974. 4. Kuftinec, M. M., and Glass, R. L. : Stability of the IMPA with reference to the Begg method, Angle Orthod. 41: 264-270, 1971.
322
Kuftinec
5. Kuftinec, M. M.: Behavior of mandibular teeth during orthodontic treatment and retew t,ion, I.A.D.R. Abstr. Ko. 3, 1975. 6. Lindquist, J. T.: The lower incisor-Tts influence on treatment and rsthctics: Asr, J. ORTHOD. 44: 112-140, 1958. 7. Peck, S., and Peck, H.: An index for assessing tooth shape deviations as applied to the mandibular incisors, AM. J. ORTHOD. 61: 384-401, 1972. 8. Snedecor, G. IV., and Cochran, TV. G.: Statistical methods, low Cit,p, 1967, lowa State University Press. 9. Steiner, C. C. : Cephalometrics in clinical practice, Angle Orthod. 29: 8-29, 1959. 10. Tweed, C. H.: Clinical orthodontics, St. Louis, 1966, The C. V. Mosby Company.
Notwithstanding the many technical improvements adopted in the treatment of dentofacial deformities during the last twenty-five years, orthodontists continue to meet with cases that baffle their skill. The frequent, incessant offering of novel methods of treatment certainly warrants the opinion that many preceding modes have failed to accomplish their intended purpose. Reluctantly perhaps, though none the less frankly, we must admit that our immoderate devotion to technic has not attained the satisfaction we anticipated, that many problems remain to vex and irritate us, and that the high hopes of our youth (encouraged by the pretensions of sectarian schools] have not been realized. (B. E. Lischer: On New Methods of Diagnosing Dentofacial Deformities, Int. J. Orthod. Oral Surg. Radiogr. 10: 521-541, 1924.)