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The effect of first premolar extraction on vertical dimension
ORIGINAL ARTICLE The effect of first premolar extraction on vertical dimension ˙Ilken Kocadereli DDS, PhD Ankara, Turkey The purpose of this study was to evaluate the vertical changes occurring in Class I patients treated orthodontically with first premolar extraction and to compare these changes with those occurring in Class I patients treated orthodontically without extractions. Records of 40 Class I nonextraction cases (24 girls, 16 boys) and 40 Class I maxillary and mandibular first premolar extraction cases (23 girls, 17 boys) were obtained. The pretreatment and posttreatment cephalograms were digitized, and 6 linear and 8 angular cephalometric measurements were selected to evaluate vertical changes. Evaluation of the treatment results of the extraction and nonextraction cases showed that the vertical changes occurring after the extraction of maxillary and mandibular first premolars were not different than those occurring in the nonextraction cases. (Am J Orthod Dentofacial Orthop 1999;116:41-5)
T
he extraction of premolars as a practical form of orthodontic therapy has been accepted for many years; but there is a controversy concerning the effect of premolar extraction on the vertical dimension. First, premolar extraction is considered by many to be an etiologic factor in temporomandibular joint (TMJ) disorders. It has been suggested that orthodontic forward movement of the posterior teeth after mandibular and maxillary premolar extraction leads to a reduction in vertical dimension.1-3 The mandible is then allowed to overclose; as a result, it was thought that TMJ problems are likely to occur. There are no published results to support this theory. Another theory that has been proposed is that first premolar extractions lead to overretraction of the anterior teeth, particularly the maxillary anteriors.4,5 This overretraction of anterior teeth is thought to displace the mandible and the condyles posteriorly. Posterior condylar displacement has long been associated with TMJ disorders. As with the previous hypothesis, this theory has not been substantiated by research. Garlington6 attempted to reduce the vertical dimension through early removal of the remaining deciduous teeth and enucleation of the second premolars; although there was a statistically significant decrease in lower facial height, the MPA decreased by only 0.8°. Pearson7 showed a mean decrease in MPA of 3.9° after premolar extraction, with vertical chincups used before and during orthodontic therapy. There was, how-
Associate Professor at Department of Orthodontics, Faculty of Dentistry, Hacettepe University, Ankara, Turkey. Reprint requests to: Dr ˙Ilken Kocadereli, Süslü Sokak No: 4/6, Mebusevleri Tandoˇgan 06580, Ankara Turkey. Copyright © 1999 by the American Association of Orthodontists. 0889-5406/99/$8.00 + 0 8/1/94585
ever, no follow-up study to determine whether the mandibular plane angle reopened to its original position after treatment. Cusimano et al8 analyzed the premolar extraction cases and found no over collapse of the vertical dimension; on the contrary, the vertical dimension was either maintained or slightly opened. The purpose of this study was to evaluate the changes in vertical dimension occurring in Class I patients treated orthodontically with first premolar extraction and to compare these changes with those occurring in Class I patients treated orthodontically without extraction. SUBJECTS AND METHOD
Records of 40 nonextraction patients (24 girls, 16 boys) and 40 maxillary and mandibular first premolar extraction patients (23 girls, 17 boys) were obtained.
Fig 1. Linear cephalometric measurements. 41
42 Kocadereli
American Journal of Orthodontics and Dentofacial Orthopedics July 1999
Fig 2. Angular cephalometric measurements.
Table I. Comparison
of the pretreatment ages of extraction and nonextraction groups of male and female patients
Extraction group (yr) Nonextraction group (yr) Mean age (yr) *Extraction
Female patients
Male patients
t Value
P value
12.38 ± 2.62 12.43 ± 2.36 12.82 ± 2.37*
12.38 ± 2.18 12.28 ± 1.88 12.31 ± 2.19†
–1.08 1.68 1.43
.294 .114 .162
group (n = 40). group (n = 40).
†Nonextraction
All patients were dentally and skeletally Class I. The assessment of the skeletal relationship was based on the patient’s pretreatment SNA angle, SNB angle, and ANB angle.9 The pretreatment ages of the extraction patients was 12.82 ± 2.37 years and the pretreatment ages of the nonextraction group was 12.31 ± 2.19 years. In the nonextraction group the mean age of the girls was 12.43 ± 2.36 years; and the mean age of the boys was 12.28 ± 1.88 years. In the extraction group the mean age of the girls was 12.38 ± 2.62 years; and the mean age of the boys was 12.38 ± 2.18 years (Table I). Each patient had maxillary and mandibular edgewise appliances as part of their orthodontic treatment. Extraoral appliances were not used in any of these cases. The pretreatment and posttreatment lateral cephalograms were taken on the same radiographic unit and traced and digitized by 1 operator. For both the extraction and the nonextraction groups, pretreatment and posttreatment cephalometric values were calculated by RMO JOE program (Rocky Mountain Orthodontics, Jiffy Orthodontic Evaluation). Six linear and 8 angular cephalometric measurements were selected to evaluate vertical changes.
Linear measurements (Fig 1) 1. A6 molar position to PTV (millimeters) 2. Posterior face height (millimeters) 3. Anterior face height (millimeters) Posterior face height/anterior face height ratio (%) 4. Menton to ANS (millimeters) 5. SL (millimeters) 6. Ramus height (CF-Go; millimeters) Angular measurements (Fig 2) 1. Lower facial height angle 2. Facial depth angle 3. Facial axis angle 4. Mandibular plane to Frankfurt horizontal plane (angle) 5. Total face height angle 6. Mandibular arc angle 7. SellaNasion to GonionGnathion (angle) 8. Facial taper (conic angle) The cephalometric measurements surveyed are summarized in Figs 1 and 2. The changes in these cephalometric variables resulting from orthodontic treatment were compared for statistical differences with paired samples t test.
Kocadereli 43
American Journal of Orthodontics and Dentofacial Orthopedics Volume 116, Number 1
Table II. Means
and standard deviations and P and t values for the cephalometric parameters in the extraction and nonextraction groups Extraction group (n = 40)
Nonextraction group (n = 40) Final
Difference
t P Value value
13.55 ± 4.16 82.53 ± 7.18
0.37 ± 4.29 4.18 ± 4.11
–2.09 .043† –6.89 .000*
123.0 ± 7.14 127.68 ± 6.74
4.67 ± 5.05 –5.86 .000* 118.15 ± 7.31 123.92 ± 6.88
5.98 ± 5.14
–7.41 .000*
65.67 ± 4.32
66.03 ± 5.34
0.35 ± 2.81 –0.79 .435
70.95 ± 5.55 43.20 ± 7.77 65.10 ± 5.57
Parameter
Initial
Final
A6 to P-T-V (mm) Posterior face height (mm) Anterior face height (mm) Posterior/anterior face height (%) Menton-ANS (mm) SL distance (mm) Ramus height (CF-Go; mm) Lower face height (angle) Facial depth angle Facial axis angle Mandibular plane– Frankfurt horizontal plane angle Total face height angle Mandibular arc angle SellaNasion-GonionGnathion angle Facial taper (conic angle) SNA angle SNB angle ANB angle
11.93 ± 4.77 79.65 ± 8.50
15.68 ± 4.17 83.17 ± 8.83
Difference
t P Value value
3.75 ± 4.63 –5.12 .000* 3.53 ± 4.36 –5.12 .000*
Initial 12.23 ± 4.22 78.15 ± 6.61
66.40 ± 5.14
66.63 ± 5.71
0.05 ± 2.51
–0.57 .569
73.88 ± 6.54 2.93 ± 3.16 –5.86 .000* 43.10 ± 9.32 –0.05 ± 5.28 0.12 .907 68.10 ± 5.23 2.83 ± 3.90 –5.01 .000*
67.30 ± 5.51 43.13 ± 7.79 63.25 ± 6.24
70.74 ± 5.61 43.65 ± 7.39 67.28 ± 5.95
3.78 ± 3.72 0.52 ± 4.26 4.05 ± 3.75
–6.17 .000* –0.78 .440 –6.70 .000*
49.25 ± 4.16
49.55 ± 4.61
0.30 ± 2.56 –0.74 .464
46.87 ± 5.03
47.00 ± 4.78
0.12 ± 3.00
–0.26 .793
83.50 ± 3.80 82.28 ± 3.68 29.65 ± 5.16
83.80 ± 3.74 0.30 ± 2.76 –0.69 .495 81.70 ± 4.42 –0.57 ± 2.66 1.37 .179 29.28 ± 5.83 –0.38 ± 3.17 0.75 .459
84.33 ± 3.91 84.45 ± 3.94 26.30 ± 6.91
84.90 ± 2.99 83.38 ± 3.73 26.40 ± 6.44
0.65 ± 2.40 –0.77 ± 2.42 0.10 ± 2.96
–1.02 .315 2.95 .005‡ –0.21 .832
63.68 ± 4.29
63.53 ± 4.51 –0.10 ± 2.64
0.36 .721
60.90 ± 5.87
60.90 ± 5.88
0.28 ± 2.87
0.00 1.000
30.93 ± 5.86
31.65 ± 5.45
0.73 ± 3.92 –1.17 .249
32.05 ± 6.12
33.92 ± 6.27
1.48 ± 4.45
–2.76 .009†
36.88 ± 5.52
36.98 ± 7.26
0.10 ± 3.54 –0.18 .859
34.75 ± 6.42
35.03 ± 7.01
0.27 ± 2.85
–0.61 .545
66.95 ± 4.28
67.12 ± 4.53
0.25 ± 1.93 –0.58 .568
69.47 ± 5.13
68.90 ± 5.57
–0.57 ± 1.81
2.01 .051
79.43 ± 3.90 75.83 ± 3.62 3.58 ± 2.24
78.55 ± 3.97 –0.87 ± 2.47 75.52 ± 4.12 –0.30 ± 2.31 3.08 ± 1.98 –0.50 ± 1.75
78.10 ± 4.02 75.32 ± 3.65 3.10 ± 2.44
77.48 ± 3.76 75.40 ± 3.37 2.35 ± 2.38
–0.62 ± 2.23 0.08 ± 2.26 –0.70 ± 1.51
1.78 .084 –0.21 .835 3.20 .003‡
2.24 .031† 0.82 .417 1.80 .079
≤ .000. < .05. ‡P ≤ .005.
*P †P
RESULTS
The means and standard deviations, P and t values for the cephalometric parameters for extraction and nonextraction groups are given in Table II. In the extraction group, the changes in A6 molar position to PTV, posterior face height, anterior face height, menton to ANS, and ramus height were statistically significant (P < .05; Table II). In the nonextraction group the changes in A6 molar position to PTV, posterior face height, anterior face height, menton to ANS, ramus height, facial axis angle, and mandibular arc angle were statistically significant (P < .05; Table II). Statistical analysis of the cephalometric data revealed no significant differences between the extraction and nonextraction groups, except A6 molar position to PTV, which showed the mesial molar movement in the extraction group (Table III). Evaluation of the treatment results of
the extraction and nonextraction cases showed that the vertical changes occurring after the extraction of first premolars were not different than those occurring in the nonextraction cases. The results of this study did not support the hypothesis that premolar extraction results in a loss of vertical dimension of occlusion. DISCUSSION
The purpose of this study was to evaluate the changes in vertical dimension occurring in Class I patients treated orthodontically with first premolar extraction and to compare these changes with those occurring in Class I patients treated orthodontically without extraction. The vertical dimension of the occlusion is thought to be a critical etiologic factor in temporomandibular joint disorders. The results of this study showed that the changes in vertical dimension
44 Kocadereli
American Journal of Orthodontics and Dentofacial Orthopedics July 1999
Table III. Comparison
of the differences between the initial-final difference for the extraction and the nonextraction groups Cephalometric variable (n = 40)
t Value
P value
A6 molar position to PTV (mm) Posterior face height (mm) Anterior face height (mm) Posterior/anterior face height ratio (%) Menton to ANS (mm) SL (mm) Ramus height (CF-Go; mm) Lower facial height angle Facial depth angle Facial axis angle Mandibular plane to Frankfurt horizontal plane angle Total face height angle Mandibular arc angle SellaNasion to GonionGnathion angle Facial taper (conic angle) SNA angle SNB angle ANB angle
3.58 –0.81 –1.21 0.54 –1.07 –0.59 –1.53 0.26 –0.61 0.45 –0.83
.001* .422 .234 .596 .292 .558 .133 .793 .546 .658 .412
–0.62 –0.82 –0.27 1.86 –0.45 –0.89 0.62
.538 .419 .790 .070 .659 .381 .541
*P ≤ .001.
both in extraction and in nonextraction groups were similar. On average, most of the changes in linear cephalometric measurements from before treatment to after treatment reflected an increase in the vertical dimension. Thus the results of this study did not support the theory that extraction of first premolars produces a loss in the vertical dimension of occlusion as suggested by several authors.1-3 Retrospective sample studies10-15 and longitudinal sample studies16-18 have consistently failed to demonstrate a causative link between orthodontic treatment (including premolar extraction) and temporomandibular joint disorders. In Angle Class I malocclusions, the extraction of premolars was to relieve tooth-arch length discrepancy. In most cases the extraction space is used to relieve crowding, and the remainder is used to retract the anterior teeth. When the anterior teeth are being retracted, the objective of anchorage is to maintain the position of posterior teeth. If anchorage is maintained, then the supposed loss of vertical dimension cannot happen.19 The patients included in this study were all dentally and skeletally Class I. Most of the extraction space was used to relieve crowding, and there was minimal need for posterior protraction. The vertical position of the posterior teeth was maintained, and loss of vertical dimension did not occur. This was shown by insignificant changes in the angular cephalometric measurements (Table II). The effect of growth on the vertical dimension of
the face is an important factor. As the mandible develops, it is displaced downward and forward because of primary and secondary displacement.20 Facial height increases as a result of facial growth. The patients included in this study (both extraction and nonextraction groups) had growth potential (Table I). Statistically significant increases in the linear cephalometric measurements were attributed to downward and forward displacement of the mandible. Facial growth direction may be altered by the use of orthopedic appliances, but alteration of growth with extraction has not been documented. The results of this study showed that in Angle Class I patients the extraction of maxillary and mandibular first premolars did not cause a loss in vertical dimension and is in accordance with the findings of Staggers.19 CONCLUSION
Evaluation of the treatment results of extraction and nonextraction cases showed that the vertical changes occurring after the extraction of first premolars were not different than those occurring in the nonextraction cases. This study demonstrates that the attempt to help control (close) the vertical dimension with the extraction of first premolars is not possible. It also disproves the hypothesis that the extraction of premolars leads to a loss of vertical dimension, which in turn leads to TMJ disorders. REFERENCES 1. Tulley WJ. The role of extractions in orthodontic treatment. Br Dent J 1959;107:199205. 2. Wyatt NE. Preventing adverse effects on the temporomandibular joint through orthodontic treatment. Am J Orthod 1987;91:493-9. 3. Bowbeer GR. The sixth key to facial beauty and TMJ health. Funct Orthod 1987;4:4-22. 4. Witzig JW, Spahl TJ. The clinical management of basic maxillofacial orthopedic appliances. Littleton (MA): PSG Publishing; 1987. p. 161-216. 5. Farrar WB, Mc Carty WL. A clinical outline of temporomandibular joint diagnosis and treatment. Montgomery (AL): Walker; 1983. p. 84-5. 6. Garlington MA. Changes in mandibular plane angles after second bicuspid enucleation [master’s thesis]. Long Beach: University of Southern California; 1987. 7. Pearson LE. Vertical control through use of mandibular intrusive forces. Angle Orthod 1973;43:194-200. 8. Cusimano C, McLaughlin RP, Zernik JH. Effects of first bicuspid extraction on facial height in high-angle cases. J Clin Orthod 1993;27:594-8. 9. Burstone CJ, James RB, Legan HL, Murphy GA, Norton LA. Cephalometrics for orthognathic surgery. J Oral Surg 1980;38:744-51. 10. Sadowsky C, Bebole EA. Long term status of temporomandibular joint function and functional occlusion after orthodontic treatment. Am J Orthod 1980;78:201-12. 11. Sadowsky C, Polson AM. Temporomandibular joint disorders and long term occlusion after orthodontic treatment: results of two long term studies. Am J Orthod 1980;86: 386-90. 12. Dibbets JMH, van der Weele LT. Orthodontic treatment in relation to symptoms attributed to dysfunction of the temporomandibular joint: a 10 year report of the University of Groningen study. Am J Orthod 1987;91:193-205. 13. Luecke PE, Johnston LE. The effect of maxillary first premolar extraction and incisor retraction on mandibular position: testing the central dogma of “functional orthodontics.” Am J Orthod Dentofac Orthop 1992;101:4-12. 14. Egermark I, Thilander B. Craniomandibular disorders with special reference to orthodontic treatment: an evaluation from childhood to adulthood. Am J Orthod Dentofac Orthop 1992;101:28-34. 15. Rendell JK, Norton LA, Gay T. Orthodontic treatment and temporomandibular joint disorders. Am J Orthod Dentofac Orthop 1992;101:84-7. 16. Krenemak CR, Kinser DD, Harman HA, Menard CC, Jakobbsen JR. Orthodontic risk
American Journal of Orthodontics and Dentofacial Orthopedics Volume 116, Number 1
factors for temporomandibular disorders (TMD): I. Premolar extractions. Am J Orthod Dentofac Orthop 1992; 101:13-20. 17. Hirata RH, Heft MW, Hernandez B, King GL. Longitudinal study of signs of temporomandibular disorders (TMD) in orthodontically treated and non treated groups. Am J Orthod Dentofac Orthop 1992;101:35-40. 18. Årtun J, Hollender LG, Truelove EL. Relationship between orthodontic treatment,
Kocadereli 45
condylar position, and internal derangement of the temporomandibular joint. Am J Orthod Dentofac Orthop 1992;101:48-53. 19. Staggers JA. Vertical control changes following first premolar extractions Am J Orthod Dentofac Orthop 1994;105:19-24. 20. Enlow DH. Handbook of facial growth. Philadelphia: WB Saunders Co; 1990. p. 58-148.
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Zachary Stratton Smith: DOB, 8/16/88 (age 11). Pierced left ear, blond hair, braces on teeth, prescription glasses, hates country music. Zachary is in need of orthodontic attention in order to maintain the quality of his dental work. Chelsea Paige Smith: DOB, 7/14/91 (age 8). Pierced ears, 2 little scars on neck, blond curly hair, loves Barbie dolls, animals, and country music. If anyone should have information about these people, please contact your nearest FBI office. You can find the telephone number on the first page of every phone book.
T
he extraction of premolars as a practical form of orthodontic therapy has been accepted for many years; but there is a controversy concerning the effect of premolar extraction on the vertical dimension. First, premolar extraction is considered by many to be an etiologic factor in temporomandibular joint (TMJ) disorders. It has been suggested that orthodontic forward movement of the posterior teeth after mandibular and maxillary premolar extraction leads to a reduction in vertical dimension.1-3 The mandible is then allowed to overclose; as a result, it was thought that TMJ problems are likely to occur. There are no published results to support this theory. Another theory that has been proposed is that first premolar extractions lead to overretraction of the anterior teeth, particularly the maxillary anteriors.4,5 This overretraction of anterior teeth is thought to displace the mandible and the condyles posteriorly. Posterior condylar displacement has long been associated with TMJ disorders. As with the previous hypothesis, this theory has not been substantiated by research. Garlington6 attempted to reduce the vertical dimension through early removal of the remaining deciduous teeth and enucleation of the second premolars; although there was a statistically significant decrease in lower facial height, the MPA decreased by only 0.8°. Pearson7 showed a mean decrease in MPA of 3.9° after premolar extraction, with vertical chincups used before and during orthodontic therapy. There was, how-
Associate Professor at Department of Orthodontics, Faculty of Dentistry, Hacettepe University, Ankara, Turkey. Reprint requests to: Dr ˙Ilken Kocadereli, Süslü Sokak No: 4/6, Mebusevleri Tandoˇgan 06580, Ankara Turkey. Copyright © 1999 by the American Association of Orthodontists. 0889-5406/99/$8.00 + 0 8/1/94585
ever, no follow-up study to determine whether the mandibular plane angle reopened to its original position after treatment. Cusimano et al8 analyzed the premolar extraction cases and found no over collapse of the vertical dimension; on the contrary, the vertical dimension was either maintained or slightly opened. The purpose of this study was to evaluate the changes in vertical dimension occurring in Class I patients treated orthodontically with first premolar extraction and to compare these changes with those occurring in Class I patients treated orthodontically without extraction. SUBJECTS AND METHOD
Records of 40 nonextraction patients (24 girls, 16 boys) and 40 maxillary and mandibular first premolar extraction patients (23 girls, 17 boys) were obtained.
Fig 1. Linear cephalometric measurements. 41
42 Kocadereli
American Journal of Orthodontics and Dentofacial Orthopedics July 1999
Fig 2. Angular cephalometric measurements.
Table I. Comparison
of the pretreatment ages of extraction and nonextraction groups of male and female patients
Extraction group (yr) Nonextraction group (yr) Mean age (yr) *Extraction
Female patients
Male patients
t Value
P value
12.38 ± 2.62 12.43 ± 2.36 12.82 ± 2.37*
12.38 ± 2.18 12.28 ± 1.88 12.31 ± 2.19†
–1.08 1.68 1.43
.294 .114 .162
group (n = 40). group (n = 40).
†Nonextraction
All patients were dentally and skeletally Class I. The assessment of the skeletal relationship was based on the patient’s pretreatment SNA angle, SNB angle, and ANB angle.9 The pretreatment ages of the extraction patients was 12.82 ± 2.37 years and the pretreatment ages of the nonextraction group was 12.31 ± 2.19 years. In the nonextraction group the mean age of the girls was 12.43 ± 2.36 years; and the mean age of the boys was 12.28 ± 1.88 years. In the extraction group the mean age of the girls was 12.38 ± 2.62 years; and the mean age of the boys was 12.38 ± 2.18 years (Table I). Each patient had maxillary and mandibular edgewise appliances as part of their orthodontic treatment. Extraoral appliances were not used in any of these cases. The pretreatment and posttreatment lateral cephalograms were taken on the same radiographic unit and traced and digitized by 1 operator. For both the extraction and the nonextraction groups, pretreatment and posttreatment cephalometric values were calculated by RMO JOE program (Rocky Mountain Orthodontics, Jiffy Orthodontic Evaluation). Six linear and 8 angular cephalometric measurements were selected to evaluate vertical changes.
Linear measurements (Fig 1) 1. A6 molar position to PTV (millimeters) 2. Posterior face height (millimeters) 3. Anterior face height (millimeters) Posterior face height/anterior face height ratio (%) 4. Menton to ANS (millimeters) 5. SL (millimeters) 6. Ramus height (CF-Go; millimeters) Angular measurements (Fig 2) 1. Lower facial height angle 2. Facial depth angle 3. Facial axis angle 4. Mandibular plane to Frankfurt horizontal plane (angle) 5. Total face height angle 6. Mandibular arc angle 7. SellaNasion to GonionGnathion (angle) 8. Facial taper (conic angle) The cephalometric measurements surveyed are summarized in Figs 1 and 2. The changes in these cephalometric variables resulting from orthodontic treatment were compared for statistical differences with paired samples t test.
Kocadereli 43
American Journal of Orthodontics and Dentofacial Orthopedics Volume 116, Number 1
Table II. Means
and standard deviations and P and t values for the cephalometric parameters in the extraction and nonextraction groups Extraction group (n = 40)
Nonextraction group (n = 40) Final
Difference
t P Value value
13.55 ± 4.16 82.53 ± 7.18
0.37 ± 4.29 4.18 ± 4.11
–2.09 .043† –6.89 .000*
123.0 ± 7.14 127.68 ± 6.74
4.67 ± 5.05 –5.86 .000* 118.15 ± 7.31 123.92 ± 6.88
5.98 ± 5.14
–7.41 .000*
65.67 ± 4.32
66.03 ± 5.34
0.35 ± 2.81 –0.79 .435
70.95 ± 5.55 43.20 ± 7.77 65.10 ± 5.57
Parameter
Initial
Final
A6 to P-T-V (mm) Posterior face height (mm) Anterior face height (mm) Posterior/anterior face height (%) Menton-ANS (mm) SL distance (mm) Ramus height (CF-Go; mm) Lower face height (angle) Facial depth angle Facial axis angle Mandibular plane– Frankfurt horizontal plane angle Total face height angle Mandibular arc angle SellaNasion-GonionGnathion angle Facial taper (conic angle) SNA angle SNB angle ANB angle
11.93 ± 4.77 79.65 ± 8.50
15.68 ± 4.17 83.17 ± 8.83
Difference
t P Value value
3.75 ± 4.63 –5.12 .000* 3.53 ± 4.36 –5.12 .000*
Initial 12.23 ± 4.22 78.15 ± 6.61
66.40 ± 5.14
66.63 ± 5.71
0.05 ± 2.51
–0.57 .569
73.88 ± 6.54 2.93 ± 3.16 –5.86 .000* 43.10 ± 9.32 –0.05 ± 5.28 0.12 .907 68.10 ± 5.23 2.83 ± 3.90 –5.01 .000*
67.30 ± 5.51 43.13 ± 7.79 63.25 ± 6.24
70.74 ± 5.61 43.65 ± 7.39 67.28 ± 5.95
3.78 ± 3.72 0.52 ± 4.26 4.05 ± 3.75
–6.17 .000* –0.78 .440 –6.70 .000*
49.25 ± 4.16
49.55 ± 4.61
0.30 ± 2.56 –0.74 .464
46.87 ± 5.03
47.00 ± 4.78
0.12 ± 3.00
–0.26 .793
83.50 ± 3.80 82.28 ± 3.68 29.65 ± 5.16
83.80 ± 3.74 0.30 ± 2.76 –0.69 .495 81.70 ± 4.42 –0.57 ± 2.66 1.37 .179 29.28 ± 5.83 –0.38 ± 3.17 0.75 .459
84.33 ± 3.91 84.45 ± 3.94 26.30 ± 6.91
84.90 ± 2.99 83.38 ± 3.73 26.40 ± 6.44
0.65 ± 2.40 –0.77 ± 2.42 0.10 ± 2.96
–1.02 .315 2.95 .005‡ –0.21 .832
63.68 ± 4.29
63.53 ± 4.51 –0.10 ± 2.64
0.36 .721
60.90 ± 5.87
60.90 ± 5.88
0.28 ± 2.87
0.00 1.000
30.93 ± 5.86
31.65 ± 5.45
0.73 ± 3.92 –1.17 .249
32.05 ± 6.12
33.92 ± 6.27
1.48 ± 4.45
–2.76 .009†
36.88 ± 5.52
36.98 ± 7.26
0.10 ± 3.54 –0.18 .859
34.75 ± 6.42
35.03 ± 7.01
0.27 ± 2.85
–0.61 .545
66.95 ± 4.28
67.12 ± 4.53
0.25 ± 1.93 –0.58 .568
69.47 ± 5.13
68.90 ± 5.57
–0.57 ± 1.81
2.01 .051
79.43 ± 3.90 75.83 ± 3.62 3.58 ± 2.24
78.55 ± 3.97 –0.87 ± 2.47 75.52 ± 4.12 –0.30 ± 2.31 3.08 ± 1.98 –0.50 ± 1.75
78.10 ± 4.02 75.32 ± 3.65 3.10 ± 2.44
77.48 ± 3.76 75.40 ± 3.37 2.35 ± 2.38
–0.62 ± 2.23 0.08 ± 2.26 –0.70 ± 1.51
1.78 .084 –0.21 .835 3.20 .003‡
2.24 .031† 0.82 .417 1.80 .079
≤ .000. < .05. ‡P ≤ .005.
*P †P
RESULTS
The means and standard deviations, P and t values for the cephalometric parameters for extraction and nonextraction groups are given in Table II. In the extraction group, the changes in A6 molar position to PTV, posterior face height, anterior face height, menton to ANS, and ramus height were statistically significant (P < .05; Table II). In the nonextraction group the changes in A6 molar position to PTV, posterior face height, anterior face height, menton to ANS, ramus height, facial axis angle, and mandibular arc angle were statistically significant (P < .05; Table II). Statistical analysis of the cephalometric data revealed no significant differences between the extraction and nonextraction groups, except A6 molar position to PTV, which showed the mesial molar movement in the extraction group (Table III). Evaluation of the treatment results of
the extraction and nonextraction cases showed that the vertical changes occurring after the extraction of first premolars were not different than those occurring in the nonextraction cases. The results of this study did not support the hypothesis that premolar extraction results in a loss of vertical dimension of occlusion. DISCUSSION
The purpose of this study was to evaluate the changes in vertical dimension occurring in Class I patients treated orthodontically with first premolar extraction and to compare these changes with those occurring in Class I patients treated orthodontically without extraction. The vertical dimension of the occlusion is thought to be a critical etiologic factor in temporomandibular joint disorders. The results of this study showed that the changes in vertical dimension
44 Kocadereli
American Journal of Orthodontics and Dentofacial Orthopedics July 1999
Table III. Comparison
of the differences between the initial-final difference for the extraction and the nonextraction groups Cephalometric variable (n = 40)
t Value
P value
A6 molar position to PTV (mm) Posterior face height (mm) Anterior face height (mm) Posterior/anterior face height ratio (%) Menton to ANS (mm) SL (mm) Ramus height (CF-Go; mm) Lower facial height angle Facial depth angle Facial axis angle Mandibular plane to Frankfurt horizontal plane angle Total face height angle Mandibular arc angle SellaNasion to GonionGnathion angle Facial taper (conic angle) SNA angle SNB angle ANB angle
3.58 –0.81 –1.21 0.54 –1.07 –0.59 –1.53 0.26 –0.61 0.45 –0.83
.001* .422 .234 .596 .292 .558 .133 .793 .546 .658 .412
–0.62 –0.82 –0.27 1.86 –0.45 –0.89 0.62
.538 .419 .790 .070 .659 .381 .541
*P ≤ .001.
both in extraction and in nonextraction groups were similar. On average, most of the changes in linear cephalometric measurements from before treatment to after treatment reflected an increase in the vertical dimension. Thus the results of this study did not support the theory that extraction of first premolars produces a loss in the vertical dimension of occlusion as suggested by several authors.1-3 Retrospective sample studies10-15 and longitudinal sample studies16-18 have consistently failed to demonstrate a causative link between orthodontic treatment (including premolar extraction) and temporomandibular joint disorders. In Angle Class I malocclusions, the extraction of premolars was to relieve tooth-arch length discrepancy. In most cases the extraction space is used to relieve crowding, and the remainder is used to retract the anterior teeth. When the anterior teeth are being retracted, the objective of anchorage is to maintain the position of posterior teeth. If anchorage is maintained, then the supposed loss of vertical dimension cannot happen.19 The patients included in this study were all dentally and skeletally Class I. Most of the extraction space was used to relieve crowding, and there was minimal need for posterior protraction. The vertical position of the posterior teeth was maintained, and loss of vertical dimension did not occur. This was shown by insignificant changes in the angular cephalometric measurements (Table II). The effect of growth on the vertical dimension of
the face is an important factor. As the mandible develops, it is displaced downward and forward because of primary and secondary displacement.20 Facial height increases as a result of facial growth. The patients included in this study (both extraction and nonextraction groups) had growth potential (Table I). Statistically significant increases in the linear cephalometric measurements were attributed to downward and forward displacement of the mandible. Facial growth direction may be altered by the use of orthopedic appliances, but alteration of growth with extraction has not been documented. The results of this study showed that in Angle Class I patients the extraction of maxillary and mandibular first premolars did not cause a loss in vertical dimension and is in accordance with the findings of Staggers.19 CONCLUSION
Evaluation of the treatment results of extraction and nonextraction cases showed that the vertical changes occurring after the extraction of first premolars were not different than those occurring in the nonextraction cases. This study demonstrates that the attempt to help control (close) the vertical dimension with the extraction of first premolars is not possible. It also disproves the hypothesis that the extraction of premolars leads to a loss of vertical dimension, which in turn leads to TMJ disorders. REFERENCES 1. Tulley WJ. The role of extractions in orthodontic treatment. Br Dent J 1959;107:199205. 2. Wyatt NE. Preventing adverse effects on the temporomandibular joint through orthodontic treatment. Am J Orthod 1987;91:493-9. 3. Bowbeer GR. The sixth key to facial beauty and TMJ health. Funct Orthod 1987;4:4-22. 4. Witzig JW, Spahl TJ. The clinical management of basic maxillofacial orthopedic appliances. Littleton (MA): PSG Publishing; 1987. p. 161-216. 5. Farrar WB, Mc Carty WL. A clinical outline of temporomandibular joint diagnosis and treatment. Montgomery (AL): Walker; 1983. p. 84-5. 6. Garlington MA. Changes in mandibular plane angles after second bicuspid enucleation [master’s thesis]. Long Beach: University of Southern California; 1987. 7. Pearson LE. Vertical control through use of mandibular intrusive forces. Angle Orthod 1973;43:194-200. 8. Cusimano C, McLaughlin RP, Zernik JH. Effects of first bicuspid extraction on facial height in high-angle cases. J Clin Orthod 1993;27:594-8. 9. Burstone CJ, James RB, Legan HL, Murphy GA, Norton LA. Cephalometrics for orthognathic surgery. J Oral Surg 1980;38:744-51. 10. Sadowsky C, Bebole EA. Long term status of temporomandibular joint function and functional occlusion after orthodontic treatment. Am J Orthod 1980;78:201-12. 11. Sadowsky C, Polson AM. Temporomandibular joint disorders and long term occlusion after orthodontic treatment: results of two long term studies. Am J Orthod 1980;86: 386-90. 12. Dibbets JMH, van der Weele LT. Orthodontic treatment in relation to symptoms attributed to dysfunction of the temporomandibular joint: a 10 year report of the University of Groningen study. Am J Orthod 1987;91:193-205. 13. Luecke PE, Johnston LE. The effect of maxillary first premolar extraction and incisor retraction on mandibular position: testing the central dogma of “functional orthodontics.” Am J Orthod Dentofac Orthop 1992;101:4-12. 14. Egermark I, Thilander B. Craniomandibular disorders with special reference to orthodontic treatment: an evaluation from childhood to adulthood. Am J Orthod Dentofac Orthop 1992;101:28-34. 15. Rendell JK, Norton LA, Gay T. Orthodontic treatment and temporomandibular joint disorders. Am J Orthod Dentofac Orthop 1992;101:84-7. 16. Krenemak CR, Kinser DD, Harman HA, Menard CC, Jakobbsen JR. Orthodontic risk
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factors for temporomandibular disorders (TMD): I. Premolar extractions. Am J Orthod Dentofac Orthop 1992; 101:13-20. 17. Hirata RH, Heft MW, Hernandez B, King GL. Longitudinal study of signs of temporomandibular disorders (TMD) in orthodontically treated and non treated groups. Am J Orthod Dentofac Orthop 1992;101:35-40. 18. Årtun J, Hollender LG, Truelove EL. Relationship between orthodontic treatment,
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condylar position, and internal derangement of the temporomandibular joint. Am J Orthod Dentofac Orthop 1992;101:48-53. 19. Staggers JA. Vertical control changes following first premolar extractions Am J Orthod Dentofac Orthop 1994;105:19-24. 20. Enlow DH. Handbook of facial growth. Philadelphia: WB Saunders Co; 1990. p. 58-148.
KIDNAPPED Friday, December 19, 1997 Antioch, California
Zachary Stratton Smith and Chelsea Paige Smith: Abducted by Elizabeth Anne Stratton (39), their mother. Mother’s hair may be bleached red or blonde; she is a heavy smoker. They may be using the alias last names of Gould, Pugh, or Twain. Last seen driving a white ‘94 Dodge Shadow, Lic #3NDP620.
Zachary Stratton Smith: DOB, 8/16/88 (age 11). Pierced left ear, blond hair, braces on teeth, prescription glasses, hates country music. Zachary is in need of orthodontic attention in order to maintain the quality of his dental work. Chelsea Paige Smith: DOB, 7/14/91 (age 8). Pierced ears, 2 little scars on neck, blond curly hair, loves Barbie dolls, animals, and country music. If anyone should have information about these people, please contact your nearest FBI office. You can find the telephone number on the first page of every phone book.