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Vertical changes following first premolar extractions
Vertical changes following first premolar extractions Julie Ann Staggers, DDS, MS" Winchester, Va.
Orthodontic treatment involving the extraction of first premolars has been implicated in the dental literature as an etiologic factor in the development of temporomandibular joint (TMJ) disorders. Authors have proposed that the extraction of first premolars causes a decrease in the vertical dimension of occlusion. The purpose of this study was to investigate the validity of this claim. Records of 45 Class I, nonextraction cases and 38 Class I, first premolar extraction cases were obtained. The pretreatment and posttreatment cephalographs were digitized, and several cephalometric variables were examined to evaluate the vertical changes occurring as a result of orthodontic treatment. Statistical analysis of the data revealed no significant differences between the vertical changes occurring in the extraction and nonextraction groups. On average, orthodontic treatment in both groups produced an increase in the cephalometric vertical dimensions that were examined. (AMJ ORTHOD DENTOFACORTHOP 1994;105:19-24.)
O r t h o d o n t i c extractions continue to be a controversial issue in dentistry today. What role extractions play in the cause or cure of temporomandibular joint (TMJ) disorders has been extensively debated in tile dental literature. Yet most of what has been published has been personal opinions and case reports, not scientific studies, t-6 First premolar extractions are considered by many to be an etiologic factor in TMJ disorders. 24-6s These persons believe that extraction of premolars permits the posterior teeth to move forward resulting in a decrease in the vertical dimension of occlusion. The mandible is then allowed to overclose, and the muscles of mastication become foreshortened. As a result, TMJ problems are likely to occur. Although this theory is popular, particularly among general practitioners, no controlled study has published results supporting this hypothesis. Another theory that has been proposed is that first premolar extractions lead to overretraction of the anterior teeth, particularly the maxillary anteriors. 2"4"9This 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. An examination of the TMJ literature reveals a wide range of opinions as to the origin and treatment of temporomandibular disorders, but little scientific data have been presented to back up these opinions. Reynders I published a review of 91 TMJ articles ap-
=Assistant Professor, Department of Onhodonlics, Medical College of Georgia School of Dentistry. Copyright 9 1994 by the American Association of Orthodontists. 0889-5406/94/$I.00 + 0.10 811138239
pearing in the literature from 1966 to 1988. Fifty-five of these publications were author viewpoint articles, 30 were case reports, and only 6 articles were reports of sample studies. Of the 55 author viewpoint articles, I0 publications reported that orthodontic treatment improved TMJ disorders, and 8 articles reported that orthodontic treatment caused TMJ disorders. Four other publications indicated no relationship between TMJ disorders and orthodontic treatment. The bulk of the remaining 55 author viewpoint articles suggested that orthodontic treatment may or may not cause TMJ disorders. Reynders' review of the published case reports also demonstrated varying opinions on how orthodontic treatment affects temporomandibular disorders. Of the 30 published case reports 23 indicated that orthodontic treatment cured TMJ disorders, but this may not be representative of the true relationship since 15 of these case reports were published by the same author. The remaining seven case reports implied that treatment can cause or cure TMJ disorders. Four of the six sample studies reviewed by Reynders showed that orthodontic treatment had no influence on temporomandibular disorders. The other two studies indicated that orthodontic treatment may cure TMJ problems. Since 1988 more sample studies have been published. Four studies addressed the influence of orthodontic treatment on condylar position, 1~ and another study investigated the incidence of joint sounds in orthodontic patients. '4 Still, current literature reflects some uncertainty as to whether orthodontic treatment is an etiologic factor in temporomandibular disorders. Many factors are involved, yet changing the vertical dimension with the extraction of first premolars is very 19
;tO Staggers
American Journal of Orthodontics and Dentofacial Orthopedics January 1994
MP~
Fig. 1. Cephalometric variables evaluating vertical dimensions. Fig. 2. Cephalometric variables evaluating vertical dimensions. often considered to be a primary etiologic factor in TMJ problems, despite the lack o f scientific documentation. With this in mind, the purpose of this study was to evaluate the vertical changes occurring in patients treated orthodontically with first premolar extractions and compare these changes with those occurring in patients treated orthodontically without extractions.
MATERIALS AND METHODS Records of 45 nonextraction patients and 38 maxillary and mandibular first premolar extraction patients were obtained from the orthodontics clinic at West Virginia University School of Dentistry. 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, ANB angle, A and B points to nasal vertical, and A and B points to the occlusal plane measurement. ~, The pretreatment ages of the extraction patients ranged from 9 years, 10 months to 28 years, 4 months with the mean age of 14 years, 5 months. The pretreatment ages of the nonextraction group ranged from 9 years, 5 months to 16 years, i i months with the mean age of 12 years, 10 months. Each patient had maxillary and mandibular straight wire appliances as part of their orthodontic treatment. The pretreatment and posttreatment lateral cephalographs were traced and digitized by one operator. All the cephalographs were taken on the same radiographic unit.
For both the extraction and the nonextraction groups, pretreatment and posttreatment cephalometric values were calculated by Dentofacial Planner version 5.3 (Dentofacial Softwear Inc., Toronto, Canada). Eight cephalometric measurements were selected to evaluate vertical changes. The cephalometric values examined were mandibular plane to horizontal plane (MP to HP), facial height (N-Me), facial height ratio (N-ANS/ANS-Me), soft tissue facial height (G-Me'), soft tissue facial height ratio (G-Sn/Sn-Me'), maxillary first molar to the palatal plane (6 to PP) and mandibular first molar to the mandibular plane (6 to MP) as described by Burstone" and Legan. ~ In addition, the ratio of the anterior face height to the posterior face height was examined. The eephalometric measurements surveyed are summarized in Figs. 1 and 2. Pretreatment yalues were subtracted from posttreatment values to obtain the changes produced by orthodontic treatment. The changes in these cephalometric variables resulting from orthodontic treatment were compared for statistical differences using t tests with a Bonferroni correction.
RESULTS Statistical analysis o f the cephalometric data revealed no significant differerlces between the extraction
Staggers 91
American Journal of Orthodontics and Dentofaclal Orthopedics Volume 105, No. I
Table I. Means, standard deviations, and p values for the cephalometric parameters in the extraction and nonextraction groups Extraction Variable
N-Me (mm) N-ANS/ANS-Me G-Me' (mm) G-Sn/Sn-Me' MP-HP (~ to PP (mm) 6 to MP (mm) PFH : AFH
Mean
5.38 - 1.38 4.20 -3.30 0. l I 1.96 2.72 0.65
Nonextraction SD
4.74 3.78 5.66 8.04 2.53 2.00 1.98 2.25
and the nonextraction groups. The means and standard deviations for the cephalometric parameters for the extraction and nonextraction groups are given in Table I. . The results did not support the hypothesis that extractions in conjunction with orthodontic treatment result in a loss of vertical dimension. On average, the change in all cephalometric measurements from before treatment to after treatment reflected an increase in the vertical dimension. The average posttreatment values for the facial height ratio (N-ANS/ANS-Me) and the soft tissue facial height ratio (G-Sn/Sn-Me') were less than the average pretreatment values, but this was to be expected. In these ratios, as the lower face height increases, the ratio denominators (ANS-Me and SnMe') get larger, and as a result the overall ratios decrease. The mean changes resulting from treatment, either extraction or nonextraction, reflected a slight increase in mandibular plane angle, extrusion of the maxillary and mandibular first molars and an increase in anterior face height. Only 7 of the 83 patients (three in the extraction group and four in the nonextraction group) in the study had a decrese in their anterior facial height (N-Me). This decrease ranged from 0.5 to 1.8 mm.
DISCUSSION 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. 2,3,~.6.8 On the contrary, orthodontic treatment resulted in an increase in all the cephalometric parameters examined, and the increases in the extraction group were no different than in the nonextraction group. This is an expected conclusion when the indications for extractions and extraction mechanics are clearly understood. In Class I malocclusions, premolars are ex-
Mean 5.08 -2.68 4.94 -2.42 0.14 1.39 2.25 0.68
SD 3.57 3.16 4.62 5.71 1.97 1.67 1.87 1.97
t value 0.33 1.71 - 0.66 -0.58 - 0.06 1.40 I. 12 - 0.06
p vahte 0.74 0.09 0.5 I 0.56 0.95 0.16 0.26 0.95
tracted primarily to relieve tooth/arch length discrepancies and to reduce the procumbancy of the anterior teeth. Frequently, much of the extraction space is consumed by relieving 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 the posterior teeth. If anchorage is maintained, then very little protraction of the posterior teeth occurs, and the supposed loss of vertical dimension cannot happen. However, in a patient with a Class II or III malocclusion when a portion of the extraction spaces is used to correct the molar relationship, the molars are protracted. Yet this protraction does not necessarily produce a loss of vertical dimension. Most of orthodontic mechanics are extrusive in nature, and this extrusion appears to maintain or even increase the vertical dimension. This orthodontic extrusion was demonstrated in this study by the mean increase in the upper 6 to palatal plane and the lower 6 to mandibular measurements. If one is to accept the theory that posterior protraction reduces the vertical dimension, one must assume that the temporomandibular joints function as simple hinges, yet they do not. tlowever, supposing for a moment that this is true, consider Fig. 3. If CR is the center of rotation for the condyle, one can construct an imaginary right triangle with the molar occlusion representing one side of the triangle (v). Mathematically v can be determined with the following formula: v Sin0 = T solving forv, v = l(sin0) Now suppose that the molars are protracted forward 3.5 mm, which is half of a premolar extraction site and is approximately the amount needed to correct an end-toend Class II molar relationship. The i,,ertical position of the molars (v) remains unchanged, but the 0 is re-
22 Staggers
American Journal of Orthodontics and Dentofacial Orthopedics January 1994
Fig. 3. Hypothetical triangle with molar occlusion, v, as one side.
duced to ~b. The new angle ~b can be determined as described below. sin + =
V
1 +3.5
from above, v = 1 (sin 0) sin + =
1 (sin 0) 1+3.5
If the original angle 0 is 25 ~ and l is 75 mm, then the angle resulting from the simulated protraction, ~b, would be 23.8 ~ One could question whether a reduction in the original angle of 1.2 ~ truly represents a loss of vertical dimension. Even if the original angle, 0, were 40 ~ the resulting angle after simulated protraction, ~b, would be 37.8 ~ only a reduction of 2.2 ~ The patients in this study were all dentally and skeletally Class I, and consequently, there was no need for posterior protraction. If this study had involved patients with Class II malocclusions, some protraction of the mandibular molars would have bc~n expected, but how the vertical dimension of occlusion would have been affected can not be determined from the results of the present study. Changes in the vertical dimension in patients with Class II malocclusions after premolar extractions, and thus mandibular molar protraction, certainly warrant investigation since this protraction is the reason some authors condemn premolar extractions in 'patients with Class I1 malocclusionsY .5-6.s However, one must not ignore the fact that Class II mechanics such as Class II elastics, Tweed anchorage preparation, and cervical headgear are all extrusive in nature, and one might expect that the vertical dimension would be increased as a result of extractions and Class II mechanics. The effect of growth on the vertical dimension of
the face cannot be ignored in this study. As the mandible develops, it is displaced downward and forward because of primary and secondary displacement.17 Facial height increases as a result of facial growth. Most of the patients included in this study had growth potential, and thus part of the mean increase in the vertical measurements may be contributed to growth. It has been well documented that orthodontics in conjunction with orthopedic appliances or orthopedic forces can alter the facial growth pattern. Yet, alteration of growth with extractions has not been documented. If the vertical dimension of occlusion is a critical etiologic factor in TMJ disorders, a high incidence of TMJ problems among totally edentulous persons would be expected, yet this is not reported in the literature. This raises many questions such as do the alveolar processes accommodate or do denture teeth compensate for errors in the vertical dimension of occlusion of dentures? Why are edentulous persons who do not have dentures not having more TMJ problems? Do the temporomandibular joints and the length of the muscles of mastication accommodate after the loss of the entire dentition. One would expect the loss of the entire dentition to have a more profound effect on the TMJ than the loss of four premolars. The lack of a high incidence of TMJ disorders among edentulous persons suggests that the vertical dimension of occlusion may not be as major of an etiologic factor as some believe. In addition to decreased vertical dimension, posterior displacement of the condyles has long been associated with TMJ disorders, z.4-9.18 However, it is difficult to assess the actual position of the condyle in the fossa. Condylar position as determined from a corrected transcranial radiograph is 'more reliable than from a noncorrected transcranial, but both techniques can produce variable results. J9.2oEven tomograms may produce
Staggers 23
American Journal of Orthodontics and Dentofacial Orthopedics Volume 105, No. 1
varying condylar positions on the same patients, depending on the technique used. '~ The variability in the radiographic position of die condyle may lead to a misdiagnosis of posterior positioning of the condyle and may mislead dentists into concluding that posterior condylar positioning is an etiologic factor. Even with proper radiographic techniques, a posteriorly positioned condyle may not be a sign of disease. A study by Blaschke and Blaschke 2"-revealed that condylar position was variable among symptom-free patients. Weinberg 18 reported that 36% of the symptomfree patients that he evaluated with tomography had posteriorly displaced condyles. Pandis 2~conveyed that condylar shape may influence the apparent position of the condyle in the fossa on a tomogram. These authors concur that posterior positioning of the condyles may be a variant of normality. Despite the results of Pandis, Weinberg and the Blaschkes, many authors 2"4"9continue to propose that orthodontic treatment causes posterior positioning of the condyles. However, Gianelly '~ investigated condylar position in orthodontic patients treated with the extraction of maxillary and mandibular first premolars and compared them with nonorthodontically treated controls. He found no differences in condylar position between the extraction and the nonorthodontically treated groups. In addition, he found no relationship between deep overbite and condylar position. In a follow-up study, Gianelly" compared the condylar positions of persons orthodontically treated with the extraction of maxillary first premolars only and compared them with nontreated persons. Once again he found no difference in the condylar positions of the two groups. A study by Kundinger ~2 further supported the conclusions of Gianelly. Another study done by Luecke ~3 showed an actual net forward displacement of the mandible and the condylar basal bone in 70% of maxillary first premolar extraction cases examined. In addition, he found that condylar position was not correlated with the amount of incisor retraction. The results of the studies of Gianelly, Kundinger and Luecke and those of the Blaschkes do not support the theory that extractions cause posterior displacement of the condyle. Even if the results of these studies are not considered, it is hard to rationalize the beliefs of the "functional orthodontists" who promote the posteriorly displaced condyle theory along with the loss of vertical dimension theory. According to the first theory, the incisors are overretracted, thus forcing the mandible distally. However, for the overretraction to occur, anchorage must maintain the position of the molars. Yet, if the molar positions are maintained, how then can the
molars also move anteriorly and cause th e "loss of vertical dimension." The two theories contradict each other as to what really happens to posterior teeth, and the "functional orthodontists" make no attempt to explain this paradox. Therefore, one can conclude at least one of the theories must be incorrect, and the lack of scientific evidence sheds doubt on the other. Dentists providing TMJ treatment have speculated that there is a high incidence of TMJ disorders among orthodontically treated persons in an attempt to imply causation. However, results of a study by Sadowsky 23 stated that the incidence of temporomandibular symptoms among orthodontically treated persons was no different from untreated persons. Even though many TMJ patients have previously undergone orthodontic treatment, this could be an economic factor, not an etiologic factor. Patients who can afford to have orthodontic treatment, usually can also afford to have TMJ therapy, which is frequently expensive. Patients who cannot afford orthodontic treatment may also not be able to afford TMJ treatment. As a result, there may be an extensive population of nonorthodontic patients who have TMJ disorders, but do not seek treatment for economic reasons. Therefore merely evaluating t h e percentage of previously orthodontically treated patients presenting for TMJ therapy may not reveal the tree underlying percentage that exists in the overall population. In fact, Egermark-ErikssonZ" ! reported that the incidence of TMJ symptoms was age related, and symptoms increase from 30% to 60% between the ages 7 to 15 years. He thought it was merely coincidental that these are the common ages that persons undergo orthodontic treatment. A review of epidemiologic investigations by Tallents 25 indicated that there is a high incidence of subjective and objective TMJ symptoms not only in those receiving orthodontic treatment, but also in the overall pediatric population. Williamson 26 reported that 35% of the patients (ages 6 to i6 years) presenting for orthodontic treatment demonstrated TMJ pain, TMJ clicking, or both, as well as pain, in the muscles of mastication before initiating any orthodontic treatment. SUMMARY
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. This study does not Support the theory that first premolar extractions reduce the vertical dimension of occlusion, and thus predispose extraction patients to TMJ disorders. On the contrary, orthodontic treatment, both extraction and nonextraction, resulted
24
Staggers
in an mean increase in the cephalometric parameters that were examined. How premolar extractions influence condylar position and whether other aspects of orthodontic treatment predispose patients to TMJ disorders cannot be determined from this present study; further research is indicated. Controlled studies investigating each of these areas continue to be the most desirable method of detemfining the role of orthodontic treatment in temporomandibular disorders. 1 express my appreciation to the residents, staff, and particularly Cathy Myers of West Virginia University Department of Orthodontics for their assistance with the records used in this project.
REFERENCES 9 I. Reynders RM. Orthodontics and temporomandibular disorders: a review of the literature. AM J ORTIIOD DF.N'rOFACORTIIOP 1990;97:463 -7 I. 2. Witzig JW, Spahl TJ. The clinical management of basic raaxillofacial orthopedic appliances. Littleton, Massachusetts: PSG Publishing, 1987:161-216. 3. Bowbecr GR. The sixth key to facial beauty and TMJ health. Funct Orthod 1987;4:4-22. 4. Levy PH. Clinical implications of mandibular repositioning and the concept of alterable centric relation. Int J Orthod 1979;17:625. 5. Perry HT. Adolescent temporomandibular dysfunction. AM J Oamoo 1973;63:5:517-25. 6. Tulley WJ. The role of extractions in orthodontic treatment. Br Dent J 1959;107:199-205. 7. Wilson tiE. Extraction of second permanent molars in orthodontic treatment. Orthodontist 1971;3:i8-24. 8. Wyatt NE. Preventing adverse effects on the temporomandibular joint through orthodontic treatment. AM J ORTIIOD DENTOFAC Oa'ntOV 1987;91:493-9. 9. Farrar WB, McCarty WL. A clinical outline of temporomandibular joint diagnosis and treatment. Montgomery, Alabama: Walker, 1983:84-5. I0. Gianelly AA, Hughes HM, Wohlgemuth P, Gildea G. Condylar position and extraction treatment. AM J ORTItOD DENTOFACOR"ntOP 1988;93:201-5. I 1. Gianelly AA, Cozzani M, Boffa J. Condylar position and maxillary first premolar extraction. AM J ORmOD DEmOFACORTHOP 1991 ;99:473-6.
American Journal of Orthodontics and Dentofacial Orthopedics January 1994
12. Kundinger KK, Austin BP, Christensen LV, Donegan SJ, Ferguson DJ. An evaluation of temporomandibular joints and jaw muscles after orthodontic treatment involving premolar extractions. AM J OR'mOO DENTOFACOamoP 1991;100:110-5. 13. Lueeke PE, Johnson LE. The effect of maxillary first premolar extraction and incisor retraction on mandibular position: testing the central dogma of "functional orthodontics". AM J ORTHOD DEN'rOFACORTrIOP 1992;101:4-12. 14. Sadowsky C, Theisen TA, Sakols El. Orthodontic treatment and temporomandibular sounds--a longitudinal study. A.'a J ORTHOD DEN'rOFAe OR'mOP 1991 ;99:44 I-7. 15. Burstone CJ, James RB, Legan HL, Murphy GA, Norton LA. Cephalometrics for orthognathic surgery. J Oral Surg 1978; 36:269-77. 16. Legan IlL, Burstone CJ. Soft tissue cephalometrics for orthognathic surgery. J Oral Surg 1980;38:744-51. 17. Enlow DH. Handbook of facial growth. Philadelphia: WB Saunders, 1990:58-148. 18. Weinberg LA. Role of condylar position in TMJ dysfunctionpain syndrome. J Prosthet Dent 1979;41:636-43. 19. Delbalso AM. Maxillofacial imaging. Philadelphia: WB Saunders, 1990:609-1 I. 20. Pandis N, Karpac J, Trevino R, William B. A radi~raphic study of condylar position at v aridus depths of cut in dry skulls with axially corrected lateral tomograms. AM J ORTllOD DENTOFAC OR'nlOP 1991;100:116-22. 21. Goaz PW, White SC. Oral radiology principles and interpreiations. St. Louis: CV Mosby, 1982:588. 22. Blaschke DD, Blaschke TJ. Normal TMJ bony relationships in centric occlusion. J Dent Res 1981;60:98-104. 23. Sadowsky C, Polson AM. Temporomandibular disorders and functional occlusion after orthodontic treatment: results of two long-term studies. AM J OaTHOD 1984;86:386-90. 24. Egermark-Eriksson I, Carlsson GE, lngervall B. Prevalence of mandibular dysfunction and orofaeial parafunction in 7-, 11-, and 15-year-old Swedish children. Eur J Orthod 198 I;3:!63-72. 25. Tallents RH, Catania J, Sommers E. Temporomandibular joint findings in pediatric population and young adult: a critical review. Angle Orthod 1991;61:7-16. 26. Williamson EH. Temporomandibular dysfunction in pretreatment adolescent patients. AM J OR'n~OD 1977;72:429-33.
Reprint requests to: Dr. Julie A. Staggers 154 Creekside Ln. Winchester, VA 22602
Orthodontic treatment involving the extraction of first premolars has been implicated in the dental literature as an etiologic factor in the development of temporomandibular joint (TMJ) disorders. Authors have proposed that the extraction of first premolars causes a decrease in the vertical dimension of occlusion. The purpose of this study was to investigate the validity of this claim. Records of 45 Class I, nonextraction cases and 38 Class I, first premolar extraction cases were obtained. The pretreatment and posttreatment cephalographs were digitized, and several cephalometric variables were examined to evaluate the vertical changes occurring as a result of orthodontic treatment. Statistical analysis of the data revealed no significant differences between the vertical changes occurring in the extraction and nonextraction groups. On average, orthodontic treatment in both groups produced an increase in the cephalometric vertical dimensions that were examined. (AMJ ORTHOD DENTOFACORTHOP 1994;105:19-24.)
O r t h o d o n t i c extractions continue to be a controversial issue in dentistry today. What role extractions play in the cause or cure of temporomandibular joint (TMJ) disorders has been extensively debated in tile dental literature. Yet most of what has been published has been personal opinions and case reports, not scientific studies, t-6 First premolar extractions are considered by many to be an etiologic factor in TMJ disorders. 24-6s These persons believe that extraction of premolars permits the posterior teeth to move forward resulting in a decrease in the vertical dimension of occlusion. The mandible is then allowed to overclose, and the muscles of mastication become foreshortened. As a result, TMJ problems are likely to occur. Although this theory is popular, particularly among general practitioners, no controlled study has published results supporting this hypothesis. Another theory that has been proposed is that first premolar extractions lead to overretraction of the anterior teeth, particularly the maxillary anteriors. 2"4"9This 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. An examination of the TMJ literature reveals a wide range of opinions as to the origin and treatment of temporomandibular disorders, but little scientific data have been presented to back up these opinions. Reynders I published a review of 91 TMJ articles ap-
=Assistant Professor, Department of Onhodonlics, Medical College of Georgia School of Dentistry. Copyright 9 1994 by the American Association of Orthodontists. 0889-5406/94/$I.00 + 0.10 811138239
pearing in the literature from 1966 to 1988. Fifty-five of these publications were author viewpoint articles, 30 were case reports, and only 6 articles were reports of sample studies. Of the 55 author viewpoint articles, I0 publications reported that orthodontic treatment improved TMJ disorders, and 8 articles reported that orthodontic treatment caused TMJ disorders. Four other publications indicated no relationship between TMJ disorders and orthodontic treatment. The bulk of the remaining 55 author viewpoint articles suggested that orthodontic treatment may or may not cause TMJ disorders. Reynders' review of the published case reports also demonstrated varying opinions on how orthodontic treatment affects temporomandibular disorders. Of the 30 published case reports 23 indicated that orthodontic treatment cured TMJ disorders, but this may not be representative of the true relationship since 15 of these case reports were published by the same author. The remaining seven case reports implied that treatment can cause or cure TMJ disorders. Four of the six sample studies reviewed by Reynders showed that orthodontic treatment had no influence on temporomandibular disorders. The other two studies indicated that orthodontic treatment may cure TMJ problems. Since 1988 more sample studies have been published. Four studies addressed the influence of orthodontic treatment on condylar position, 1~ and another study investigated the incidence of joint sounds in orthodontic patients. '4 Still, current literature reflects some uncertainty as to whether orthodontic treatment is an etiologic factor in temporomandibular disorders. Many factors are involved, yet changing the vertical dimension with the extraction of first premolars is very 19
;tO Staggers
American Journal of Orthodontics and Dentofacial Orthopedics January 1994
MP~
Fig. 1. Cephalometric variables evaluating vertical dimensions. Fig. 2. Cephalometric variables evaluating vertical dimensions. often considered to be a primary etiologic factor in TMJ problems, despite the lack o f scientific documentation. With this in mind, the purpose of this study was to evaluate the vertical changes occurring in patients treated orthodontically with first premolar extractions and compare these changes with those occurring in patients treated orthodontically without extractions.
MATERIALS AND METHODS Records of 45 nonextraction patients and 38 maxillary and mandibular first premolar extraction patients were obtained from the orthodontics clinic at West Virginia University School of Dentistry. 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, ANB angle, A and B points to nasal vertical, and A and B points to the occlusal plane measurement. ~, The pretreatment ages of the extraction patients ranged from 9 years, 10 months to 28 years, 4 months with the mean age of 14 years, 5 months. The pretreatment ages of the nonextraction group ranged from 9 years, 5 months to 16 years, i i months with the mean age of 12 years, 10 months. Each patient had maxillary and mandibular straight wire appliances as part of their orthodontic treatment. The pretreatment and posttreatment lateral cephalographs were traced and digitized by one operator. All the cephalographs were taken on the same radiographic unit.
For both the extraction and the nonextraction groups, pretreatment and posttreatment cephalometric values were calculated by Dentofacial Planner version 5.3 (Dentofacial Softwear Inc., Toronto, Canada). Eight cephalometric measurements were selected to evaluate vertical changes. The cephalometric values examined were mandibular plane to horizontal plane (MP to HP), facial height (N-Me), facial height ratio (N-ANS/ANS-Me), soft tissue facial height (G-Me'), soft tissue facial height ratio (G-Sn/Sn-Me'), maxillary first molar to the palatal plane (6 to PP) and mandibular first molar to the mandibular plane (6 to MP) as described by Burstone" and Legan. ~ In addition, the ratio of the anterior face height to the posterior face height was examined. The eephalometric measurements surveyed are summarized in Figs. 1 and 2. Pretreatment yalues were subtracted from posttreatment values to obtain the changes produced by orthodontic treatment. The changes in these cephalometric variables resulting from orthodontic treatment were compared for statistical differences using t tests with a Bonferroni correction.
RESULTS Statistical analysis o f the cephalometric data revealed no significant differerlces between the extraction
Staggers 91
American Journal of Orthodontics and Dentofaclal Orthopedics Volume 105, No. I
Table I. Means, standard deviations, and p values for the cephalometric parameters in the extraction and nonextraction groups Extraction Variable
N-Me (mm) N-ANS/ANS-Me G-Me' (mm) G-Sn/Sn-Me' MP-HP (~ to PP (mm) 6 to MP (mm) PFH : AFH
Mean
5.38 - 1.38 4.20 -3.30 0. l I 1.96 2.72 0.65
Nonextraction SD
4.74 3.78 5.66 8.04 2.53 2.00 1.98 2.25
and the nonextraction groups. The means and standard deviations for the cephalometric parameters for the extraction and nonextraction groups are given in Table I. . The results did not support the hypothesis that extractions in conjunction with orthodontic treatment result in a loss of vertical dimension. On average, the change in all cephalometric measurements from before treatment to after treatment reflected an increase in the vertical dimension. The average posttreatment values for the facial height ratio (N-ANS/ANS-Me) and the soft tissue facial height ratio (G-Sn/Sn-Me') were less than the average pretreatment values, but this was to be expected. In these ratios, as the lower face height increases, the ratio denominators (ANS-Me and SnMe') get larger, and as a result the overall ratios decrease. The mean changes resulting from treatment, either extraction or nonextraction, reflected a slight increase in mandibular plane angle, extrusion of the maxillary and mandibular first molars and an increase in anterior face height. Only 7 of the 83 patients (three in the extraction group and four in the nonextraction group) in the study had a decrese in their anterior facial height (N-Me). This decrease ranged from 0.5 to 1.8 mm.
DISCUSSION 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. 2,3,~.6.8 On the contrary, orthodontic treatment resulted in an increase in all the cephalometric parameters examined, and the increases in the extraction group were no different than in the nonextraction group. This is an expected conclusion when the indications for extractions and extraction mechanics are clearly understood. In Class I malocclusions, premolars are ex-
Mean 5.08 -2.68 4.94 -2.42 0.14 1.39 2.25 0.68
SD 3.57 3.16 4.62 5.71 1.97 1.67 1.87 1.97
t value 0.33 1.71 - 0.66 -0.58 - 0.06 1.40 I. 12 - 0.06
p vahte 0.74 0.09 0.5 I 0.56 0.95 0.16 0.26 0.95
tracted primarily to relieve tooth/arch length discrepancies and to reduce the procumbancy of the anterior teeth. Frequently, much of the extraction space is consumed by relieving 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 the posterior teeth. If anchorage is maintained, then very little protraction of the posterior teeth occurs, and the supposed loss of vertical dimension cannot happen. However, in a patient with a Class II or III malocclusion when a portion of the extraction spaces is used to correct the molar relationship, the molars are protracted. Yet this protraction does not necessarily produce a loss of vertical dimension. Most of orthodontic mechanics are extrusive in nature, and this extrusion appears to maintain or even increase the vertical dimension. This orthodontic extrusion was demonstrated in this study by the mean increase in the upper 6 to palatal plane and the lower 6 to mandibular measurements. If one is to accept the theory that posterior protraction reduces the vertical dimension, one must assume that the temporomandibular joints function as simple hinges, yet they do not. tlowever, supposing for a moment that this is true, consider Fig. 3. If CR is the center of rotation for the condyle, one can construct an imaginary right triangle with the molar occlusion representing one side of the triangle (v). Mathematically v can be determined with the following formula: v Sin0 = T solving forv, v = l(sin0) Now suppose that the molars are protracted forward 3.5 mm, which is half of a premolar extraction site and is approximately the amount needed to correct an end-toend Class II molar relationship. The i,,ertical position of the molars (v) remains unchanged, but the 0 is re-
22 Staggers
American Journal of Orthodontics and Dentofacial Orthopedics January 1994
Fig. 3. Hypothetical triangle with molar occlusion, v, as one side.
duced to ~b. The new angle ~b can be determined as described below. sin + =
V
1 +3.5
from above, v = 1 (sin 0) sin + =
1 (sin 0) 1+3.5
If the original angle 0 is 25 ~ and l is 75 mm, then the angle resulting from the simulated protraction, ~b, would be 23.8 ~ One could question whether a reduction in the original angle of 1.2 ~ truly represents a loss of vertical dimension. Even if the original angle, 0, were 40 ~ the resulting angle after simulated protraction, ~b, would be 37.8 ~ only a reduction of 2.2 ~ The patients in this study were all dentally and skeletally Class I, and consequently, there was no need for posterior protraction. If this study had involved patients with Class II malocclusions, some protraction of the mandibular molars would have bc~n expected, but how the vertical dimension of occlusion would have been affected can not be determined from the results of the present study. Changes in the vertical dimension in patients with Class II malocclusions after premolar extractions, and thus mandibular molar protraction, certainly warrant investigation since this protraction is the reason some authors condemn premolar extractions in 'patients with Class I1 malocclusionsY .5-6.s However, one must not ignore the fact that Class II mechanics such as Class II elastics, Tweed anchorage preparation, and cervical headgear are all extrusive in nature, and one might expect that the vertical dimension would be increased as a result of extractions and Class II mechanics. The effect of growth on the vertical dimension of
the face cannot be ignored in this study. As the mandible develops, it is displaced downward and forward because of primary and secondary displacement.17 Facial height increases as a result of facial growth. Most of the patients included in this study had growth potential, and thus part of the mean increase in the vertical measurements may be contributed to growth. It has been well documented that orthodontics in conjunction with orthopedic appliances or orthopedic forces can alter the facial growth pattern. Yet, alteration of growth with extractions has not been documented. If the vertical dimension of occlusion is a critical etiologic factor in TMJ disorders, a high incidence of TMJ problems among totally edentulous persons would be expected, yet this is not reported in the literature. This raises many questions such as do the alveolar processes accommodate or do denture teeth compensate for errors in the vertical dimension of occlusion of dentures? Why are edentulous persons who do not have dentures not having more TMJ problems? Do the temporomandibular joints and the length of the muscles of mastication accommodate after the loss of the entire dentition. One would expect the loss of the entire dentition to have a more profound effect on the TMJ than the loss of four premolars. The lack of a high incidence of TMJ disorders among edentulous persons suggests that the vertical dimension of occlusion may not be as major of an etiologic factor as some believe. In addition to decreased vertical dimension, posterior displacement of the condyles has long been associated with TMJ disorders, z.4-9.18 However, it is difficult to assess the actual position of the condyle in the fossa. Condylar position as determined from a corrected transcranial radiograph is 'more reliable than from a noncorrected transcranial, but both techniques can produce variable results. J9.2oEven tomograms may produce
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American Journal of Orthodontics and Dentofacial Orthopedics Volume 105, No. 1
varying condylar positions on the same patients, depending on the technique used. '~ The variability in the radiographic position of die condyle may lead to a misdiagnosis of posterior positioning of the condyle and may mislead dentists into concluding that posterior condylar positioning is an etiologic factor. Even with proper radiographic techniques, a posteriorly positioned condyle may not be a sign of disease. A study by Blaschke and Blaschke 2"-revealed that condylar position was variable among symptom-free patients. Weinberg 18 reported that 36% of the symptomfree patients that he evaluated with tomography had posteriorly displaced condyles. Pandis 2~conveyed that condylar shape may influence the apparent position of the condyle in the fossa on a tomogram. These authors concur that posterior positioning of the condyles may be a variant of normality. Despite the results of Pandis, Weinberg and the Blaschkes, many authors 2"4"9continue to propose that orthodontic treatment causes posterior positioning of the condyles. However, Gianelly '~ investigated condylar position in orthodontic patients treated with the extraction of maxillary and mandibular first premolars and compared them with nonorthodontically treated controls. He found no differences in condylar position between the extraction and the nonorthodontically treated groups. In addition, he found no relationship between deep overbite and condylar position. In a follow-up study, Gianelly" compared the condylar positions of persons orthodontically treated with the extraction of maxillary first premolars only and compared them with nontreated persons. Once again he found no difference in the condylar positions of the two groups. A study by Kundinger ~2 further supported the conclusions of Gianelly. Another study done by Luecke ~3 showed an actual net forward displacement of the mandible and the condylar basal bone in 70% of maxillary first premolar extraction cases examined. In addition, he found that condylar position was not correlated with the amount of incisor retraction. The results of the studies of Gianelly, Kundinger and Luecke and those of the Blaschkes do not support the theory that extractions cause posterior displacement of the condyle. Even if the results of these studies are not considered, it is hard to rationalize the beliefs of the "functional orthodontists" who promote the posteriorly displaced condyle theory along with the loss of vertical dimension theory. According to the first theory, the incisors are overretracted, thus forcing the mandible distally. However, for the overretraction to occur, anchorage must maintain the position of the molars. Yet, if the molar positions are maintained, how then can the
molars also move anteriorly and cause th e "loss of vertical dimension." The two theories contradict each other as to what really happens to posterior teeth, and the "functional orthodontists" make no attempt to explain this paradox. Therefore, one can conclude at least one of the theories must be incorrect, and the lack of scientific evidence sheds doubt on the other. Dentists providing TMJ treatment have speculated that there is a high incidence of TMJ disorders among orthodontically treated persons in an attempt to imply causation. However, results of a study by Sadowsky 23 stated that the incidence of temporomandibular symptoms among orthodontically treated persons was no different from untreated persons. Even though many TMJ patients have previously undergone orthodontic treatment, this could be an economic factor, not an etiologic factor. Patients who can afford to have orthodontic treatment, usually can also afford to have TMJ therapy, which is frequently expensive. Patients who cannot afford orthodontic treatment may also not be able to afford TMJ treatment. As a result, there may be an extensive population of nonorthodontic patients who have TMJ disorders, but do not seek treatment for economic reasons. Therefore merely evaluating t h e percentage of previously orthodontically treated patients presenting for TMJ therapy may not reveal the tree underlying percentage that exists in the overall population. In fact, Egermark-ErikssonZ" ! reported that the incidence of TMJ symptoms was age related, and symptoms increase from 30% to 60% between the ages 7 to 15 years. He thought it was merely coincidental that these are the common ages that persons undergo orthodontic treatment. A review of epidemiologic investigations by Tallents 25 indicated that there is a high incidence of subjective and objective TMJ symptoms not only in those receiving orthodontic treatment, but also in the overall pediatric population. Williamson 26 reported that 35% of the patients (ages 6 to i6 years) presenting for orthodontic treatment demonstrated TMJ pain, TMJ clicking, or both, as well as pain, in the muscles of mastication before initiating any orthodontic treatment. SUMMARY
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. This study does not Support the theory that first premolar extractions reduce the vertical dimension of occlusion, and thus predispose extraction patients to TMJ disorders. On the contrary, orthodontic treatment, both extraction and nonextraction, resulted
24
Staggers
in an mean increase in the cephalometric parameters that were examined. How premolar extractions influence condylar position and whether other aspects of orthodontic treatment predispose patients to TMJ disorders cannot be determined from this present study; further research is indicated. Controlled studies investigating each of these areas continue to be the most desirable method of detemfining the role of orthodontic treatment in temporomandibular disorders. 1 express my appreciation to the residents, staff, and particularly Cathy Myers of West Virginia University Department of Orthodontics for their assistance with the records used in this project.
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American Journal of Orthodontics and Dentofacial Orthopedics January 1994
12. Kundinger KK, Austin BP, Christensen LV, Donegan SJ, Ferguson DJ. An evaluation of temporomandibular joints and jaw muscles after orthodontic treatment involving premolar extractions. AM J OR'mOO DENTOFACOamoP 1991;100:110-5. 13. Lueeke PE, Johnson LE. The effect of maxillary first premolar extraction and incisor retraction on mandibular position: testing the central dogma of "functional orthodontics". AM J ORTHOD DEN'rOFACORTrIOP 1992;101:4-12. 14. Sadowsky C, Theisen TA, Sakols El. Orthodontic treatment and temporomandibular sounds--a longitudinal study. A.'a J ORTHOD DEN'rOFAe OR'mOP 1991 ;99:44 I-7. 15. Burstone CJ, James RB, Legan HL, Murphy GA, Norton LA. Cephalometrics for orthognathic surgery. J Oral Surg 1978; 36:269-77. 16. Legan IlL, Burstone CJ. Soft tissue cephalometrics for orthognathic surgery. J Oral Surg 1980;38:744-51. 17. Enlow DH. Handbook of facial growth. Philadelphia: WB Saunders, 1990:58-148. 18. Weinberg LA. Role of condylar position in TMJ dysfunctionpain syndrome. J Prosthet Dent 1979;41:636-43. 19. Delbalso AM. Maxillofacial imaging. Philadelphia: WB Saunders, 1990:609-1 I. 20. Pandis N, Karpac J, Trevino R, William B. A radi~raphic study of condylar position at v aridus depths of cut in dry skulls with axially corrected lateral tomograms. AM J ORTllOD DENTOFAC OR'nlOP 1991;100:116-22. 21. Goaz PW, White SC. Oral radiology principles and interpreiations. St. Louis: CV Mosby, 1982:588. 22. Blaschke DD, Blaschke TJ. Normal TMJ bony relationships in centric occlusion. J Dent Res 1981;60:98-104. 23. Sadowsky C, Polson AM. Temporomandibular disorders and functional occlusion after orthodontic treatment: results of two long-term studies. AM J OaTHOD 1984;86:386-90. 24. Egermark-Eriksson I, Carlsson GE, lngervall B. Prevalence of mandibular dysfunction and orofaeial parafunction in 7-, 11-, and 15-year-old Swedish children. Eur J Orthod 198 I;3:!63-72. 25. Tallents RH, Catania J, Sommers E. Temporomandibular joint findings in pediatric population and young adult: a critical review. Angle Orthod 1991;61:7-16. 26. Williamson EH. Temporomandibular dysfunction in pretreatment adolescent patients. AM J OR'n~OD 1977;72:429-33.
Reprint requests to: Dr. Julie A. Staggers 154 Creekside Ln. Winchester, VA 22602