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Apical root resorption of upper incisors caused by intrusive tooth movement: A radiographic study
Apical root resorption of upper incisors caused by intrusive tooth movement: A radiographic study L. Ft. Dermaut* and A. De Munck** Ghent, Belgium The purpose of the study was to investigate whether root resorption of the upper incisors occurs during intrusion of maxillary incisors. It examines the possibility of a relationship between the amount of root shortening and duration of the intrusive force. The ratio of root length before and after intrusion was compared in 20 patients. In 66 incisors with an intrusion period of 29 weeks, an intrusion of 3.6 mm was performed. The control group consisted of 15 patients who underwent no orthodontic treatment. Consequently, 56 incisors had no intrusion. The follow-up time between 2 measurements was r26 weeks. The findings clearly showed root shortening after intrusion. A mean resorption of 16% of the original root length was found. In comparison, none of the control patients showed root shortening. No correlation has been found between the amount of resorption and the amount and duration of intrusion. In combination with the apical deflection of the root, the nasal floor was occasionally a limiting factor for intrusion and this may have caused root resorption. (AM J ORTHOD DENTOFAC ORTHOP 90: 321-326, 1966.)
Key words: Apical resorption, upper incisors, intrusion, radiographs, tooth movement
A
s early as 1914, Ottolengui’ reported on apical root resorption caused by orthodontic treatment. Since then many studies on resorption after orthodontic treatment have been published.2-24 The resorption usually occurs in the upper incisors.3~6~7~‘o~‘p~20-22 Oppenheim’ suggested that the morphology of the roots of the incisors was a catalyst in root resorption. Different kinds of movement possibly related to root resorption have been radiographically examined during the past several decades. De Shields,12 Linge and Linge,23 and Ronnerman and Larssonz5 have studied root resorption with radiography of the anterior maxillary teeth after orthodontic movement. Comparison of radiographic studies is difficult because of the large differences in methods and techniques. However, it is generally accepted that extensive tooth displacements, torque movements, and jiggling forces” are responsible for root resorption, The only radiographic study on root resorption mentioning intrusion as a causative factor is the one by De Shields. I2 However, he did not examine root resorption in cases limited to intrusive mechanics only. Furthermore, De Shields found no correlation between vertical orthodontic movements and root resorption. Radiographic studies on root resorption deal only From the University of Ghent. *Chairman, Department of Orthodontics. **Assistant Professor, Department of Orthodontics.
with apical resorption; buccal and lingual resorption are less perceptible on intraoral radiographs. According to the histologic study of Henry and Weinmann (1951),’ the most frequent idiopathic root resorptions occur in the apical area, “Resorption occurs more readily upon surfaces facing toward the direction of physiologic movement.” In several histologic studies in humans and animals (Reitan,14 Stenvik and Mj6r,15 Bunch,28 and Dellingeti9), resorption after intrusion was observed. Regarding measurement of the amount of resorption on radiographs, most radiographic studies refer to an arbitrary score that represents a specific amount of resorption. Linge and Linge23v24are exceptions; an approximation is replaced by precise measurement of root resorption. This was the only study with clear, standardized radiographs. Ten Hoeve and Mulie state that the classical Begg treatment is also responsible for root resorption through tipping movements in the upper anterior teeth followed by torque movement in the third stage. This is in agreement with the findings of Goldson and Henrikson.” These authors induce open bite by means of intrusion of the upper anterior teeth in an attempt to place teeth in as broad a bony area as possible between the palatal and the buccal cortices. Ten Hoeve2’ hypothesizes that this method may help to avoid root resorption. The purpose of our radiographic study was to search for a relation between isolated intrusion and root re321
322 Dermaut and De Munck
Fig. 1. Intrusion arch wire with coil and second-order (arrow) to avoid interference with canine bracket.
Am. J. Orthod.
Dmfac. Orthop. October 1986
bend
sorption in the upper anterior teeth. The potential relationship between the amount of root resorption and the amount and duration of the intrusion will be examined further. MATERIALS AND METHODS Subjects Experimental group. Intrusive force was placed on the upper maxillary central and lateral incisors in 20 patients-ten girls and ten boys. Resorption in these 20 patients was examined on 66 anterior teeth-35 central incisors and 31 lateral incisors. Foggy or questionable radiographs were eliminated from the study. When intrusion occurred, the ages of the experimental group ranged from 11 to 37 years, but only three patients were over 20 years of age. The average age of the group was 15 years. The mean intrusion period was 29 weeks with a range of 8 to 64 weeks. Control group. The control group consisted of 15 persons, mostly dental students. These seven female and eight male subjects had undergone no previous orthodontic treatment. Root shortening was measured in 58 anterior teeth-29 central and 29 lateral incisors. With an age range between 16 and 25 years, the average age in the control group was 22 years. The incisors were examined for root resorption with an average interval of 28 weeks (from 24 to 32 weeks). Method Intrusion technique. After a short period of light wire alignment of the upper arch with Begg brackets (with the exception of 1 patient with edgewise brackets) and before the reduction of overjet, intrusive forces were exerted to obtain anterior bite opening. Teeth in which torque or uprighting had been performed were excluded from the study to avoid additional causes for root resorption.
Fig. 2. Determination of the amount of intrusion according to Liu and Herschleb.” 7, Intrusive component (used in this study). 2, Retrusive component.
A slightly modified Burstone technique was used.30 An attempt was made to transmit all forces to the upper anterior teeth. Anchorage of the molars was maintained using high-pull headgear and a palatal bar. The intrusion arch consisted of a coil 3 mm in diameter and 2.5 windings. This created a constant force. Interference of premolars and canines was avoided by means of second-order bends that bypassed these teeth (Fig. 1). An 0.018 inch round Australian arch wire was used for that purpose. In all but four patients, the intrusion arch was not inserted directly in the upper anterior brackets. Rather, it was ligated to a sectional ribbon arch consolidating the four upper anterior teeth (Fig. 1). In this way the intruding force was passed through the center of resistance in an attempt to avoid “flaring out” of the upper incisors. Intrusion of the four upper anterior teeth was performed with a practically constant force of 100 g. Through the continuing action of the intrusion arch, the necessity of activation was reduced to a minimum (Burstonem) . Measuring the amount of intrusion. With the above intrusion technique, intrusion and some i-etrusion were obtained simultaneously. The net amount of intrusion was measured for each patient on the lateral cephalogram. Because the short period of preintrusion alignment was not expected to affect root length, the first lateral cephalogram was taken just before starting the intrusion, The second lateral cephalogram was taken immediately after intrusion of the four anterior teeth. With both cephalograms, the palate and the most protruded incisor were traced. For the purposes of this study, it has been arbitrarily accepted that the amount of intrusion, as measured for one incisor, was comparable to that for the other three incisors in the same
Volume 90 Number 4
Apical root resorption of upper incisors caused by intrusion 323
Flg. 3. Radiographs before and after intrusion. Rx and Rx’, Distance from cementoenamel junction to incisal edge before (Rx) and after (Rx’) intrusion. Ry and Ry’, Root length before (Ry) and after (Ry’) intrusion. -
patient. On the same cephalogram, it was not possible to distinguish the complete outlines of each of the four incisors. Compared to the palatal construction line (PNSANS), intrusion was measured as follows: on the lateral cephalogram the center of resistance (CR,) is defined at two thirds of the distance from the incisal edge; CR, is marked on the palatal plane and registered on the anterior nasal spine. The vertical displacement of the upper incisor is the measure of the amount of actual intrusion (Fig. 2). Intraoral radiographic technique. To measure the amount of resorption, a precise, long-cone radiographic technique was used (Van De P0e1~~).There was neither distortion nor enlargement when the film was parallel to the tooth and the rays perpendicular to the film (Van Aken33). Adapting the film on the palate is generally not simple. Barr and Gr@n34recommended placing the film at a 15” angle to the teeth, extending the periapical zone to approximately 3 mm above the apex. With a very high palate and short teeth, this adaptation is supefiuous. The predetermined angle between the film and tooth gives a uniform enlargement of the image. Two radiographs were taken, one before the intrusion (but after alignment) and one after the intrusion. Thus, the observed resorption was limited to the resorption occurring during the active intrusion period. The central and lateral incisors of the same quadrant
were registered on a single intraoral radiographic film to limit the patient’s exposure to radiation. Calculation of the resorption. The radiographs have been enlarged x 3 and were printed on photographic paper. After enlargement, landmark identification was no less accurate and measurement accuracy was improved. Each tooth has been delineated on these photographs. The longitudinal axis was constructed through the center of the incisal edge in the direction of the pulp canal. The construction of the longitudinal axis of the tooth on the first and second photographs was identical (Fig. 3). Whenever the cementoenamel junctions at the mesial or distal aspects of the tooth were visible in both photographs, they were marked and projected perpendicularly on the tooth axis (Linge and Linge23*U). In a few patients the definition of the cementoenamel junction was insufficient. In these cases other distinguishable reference structures on the tooth crown were used. Because it was believed that the precise distance between the incisal margin (and tooth apex) and the constructed cementoenamel junction could not be measured with sufficient accuracy, accurate measurement of absolute amounts of root resorption was not deemed possible. Hence, the relation between the rooth length before ;;).g&) after (y’) intrusion was calculated as follows 1.
.
Am. .I. Orthod.
324 Dermaut and De Munck n ExP
Dentofac. Orthop. October 1986
each of the control teeth with the procedure mentioned above. The mean was 0.99 (SD = 0.08). The t test showed no significant difference.
25 I
Results
1
a6
0.1
a8
as
1
1.1
1.2
,y
v
Flg. 4. Bar graph illustrating the distribution of root length ratios in the experimental and control groups. y/y’, Ratio between root length before and after intrusion.
In the experimental group, the mean intrusion of the incisors was 3.6 mm (SD = 1.6 mm). Contrary to the control group, in the experimental group the y’Iy relations were smaller than 1 (x = 0.82, SD = 0.10). A statistically significant difference was found between the mean root lengths of the experimental and the control teeth. The distribution of root length ratio in both groups is illustrated in Fig. 4. No difference could be found between the central (n = 35) and the lateral (n = 31) incisors (difference of proportions of 0.04 was insignificant). There was little correlation between the amount of resorption and the amount of intrusion (for the lateral incisors, r = 0.26; for the central incisors, r = 0.18; for both, r = 0.03). These low correlations of coefficients indicate that there was only a slight relation, if any, between the amounts of intrusion and resorption. There was no relation between the duration of intrusion and the amount of resorption (r = -0.02). DISCUSSION
3Rx -=3RY
x
3Rx’ -=3 Ry’
x’
y’ Y b.Y x, = Rx’ * Y’ x=Ry Y’ Rx and Rx’: Distance from cementoenamel junction to incisal edge on x-ray films before (Rx) intrusion and after (Rx’) intrusion Ry and Ry’: Root length on x-ray films before (Ry) and after (Ry’) intrusion x and xl: distancefrom cementocnameljunction to incisal edge before (x) and after (xl) intrusion Since x = x’, Rx*y -=RY
Rx * Ry’ -=Ry*x’
Rx-y’ RY’
y’ y
Reliability of the method. The reliability of the intraoral, radiographic measuring method was tested in the control group. Assuming no measurable root resorption occurred (no therapy and a short investigation period), no change should be observed and measurements should be the same. Nevertheless, the relation y’/y was calculated for
During orthodontic intrusion, resorption of the upper incisors was obvious. No difference in resorption could be found between the central and lateral incisors. However, there were marked differences among the incisors in the same patient. It has been explained why the absolute amount of resorption was not calculated; however, the relation between root lengths before and after treatment indicates a mean root resorption of 18%. Starting from an average root length of 13 mm (according to Wheele?), a mean resorption of 2.5 mm was found in this study. In 552 patients 11 years or older, Linge and Linge” found less than 1 mm of resorption of the upper incisors after orthodontic therapy. There was less resorption in younger children. They concluded that the chances of resorption increase when orthodontic movements take place after the root is completed. Comparing the study by Linge and Linge with this study, intrusion seemed to cause more resorption than overall orthodontic treatment (torque, Class II elastics, rectangular wire). An apical deflection was found in 13 incisors. These teeth were not more responsive to resorption than the others. The position of the roots in relation to the buccal and palatal cortices was also examined. This infor-
Volunle 90 Number 4
Apical root resorption
mation is not always clear on the lateral cephalogram and must be carefully interpreted. In the study’s sample, the position of the root was more favorable after intrusion to both cortical plates. Intrusion of incisors at the beginning of treatment has been suggested by Ten Hoevez6 in an attempt to prevent resorption. It should be emphasized that Ten Hoeve was referring to palatal and/or buccal resorption. In the present study only apical resorption was measured. We could not establish any relation between the amount of apical resorption and the position of the apex in relation to the nasal floor. Apical resorption was found in these cases only in combination with apical deflection. Because the occurrence was limited to only six teeth, this conclusion must be interpreted cautiously. As mentioned previously, theFe was no significant correlation between the amount of root resorption and achievable intrusion (r = 0.03 for both incisors together). This is partially in agreement with Phillips,” who could not find any relation between the amount of sagittal tooth displacement and resorption. No relation could be found between the amount of resorption and the duration of the intrusion mechanics (r = - 0.02). Several authors334, “f ‘u* *‘z23indicated that they could prove a relation existed between the amount of resorption and the duration of the orthodontic movement. However, a comparison of the results of the current study with studies previously cited is not really a valid one. The treatment period was shorter. The experimental time was limited to the period of intrusion. At the start of treatment, in some patients distal molar tipping occurred more frequently than intrusion because of poor handling of the reaction forces. In several of the cases in the experimental group, the treatment time was relatively long because of poor patient cooperation (wearing headgear). These cases might have influenced the average treatment time since only moderate intrusion was noticed. The authors want to thank Dr. SC. W. De Coster, head of the Center of Image Analysis and Quality Control, for his help in the processing of the data. They are grateful also to Mr. G. Dermout for the pictures, to Mr. Vanderdonck for helping in translation, and to Mrs. B. Jouret for typing the manuscript. REFERENCES 1. Ottolengui R: The physiological and pathological resorption of tooth roots. Items of Interest 36: 332-362, 1914. 2. Ketcham A: A progress report of an investigation of apical root resorption of permanent teeth. Int J Orthodontia, Oral Surg, Radiogr 15: 310, 1929.
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325
3. Rudolph CE: A comparative studyin root resorptionin permanent teeth. J Am Dent Assoc 23: 822, 1936. 4. Rudolph, CE: An evaluation of root resorption occurring during orthodontic treatment. J Dent Res 19: 295, 1940. Becks H: Orthodontic prognosis. AM J OR~OD 25: 610-624, 1939. Hernley S: The incidence of root resorption of vital permanent teeth. J Dent Res 20: 133-141, 1941. Oppenheim A: Human tissue response to orthodontic intervention of short and long duration. Ahl J ORTHODORAL SURG28: 263, 1942. 8. Hemy JL, Weinmann JP: The pattern of resorption and repair of human cementum. J Am Dent Assoc 42: 270-290, 195 1. 9. Jacobson 0: Clinical significance of root resorption. AM J ORTHOD38: 687-696, 1952. 10. Massler M, Malone AJ: Root resorption in human permanent teeth. AM J ~RTHOD40: 619-633, 1954. 11. Phillips JR: Apical root resorption under orthodontic therapy. Angle Orthod 25: 1, 1955. 12. De Shields RW: A study of root resorption in treated Class II, Division 1 malocclusions. Angle Orthod 39: 231-245, 1969. 13. Rosenberg HN’: An evaluation of the incidence and amount of apical root resorption and dilaceration occurring in orthodontitally treated teeth having incompletely formed roots at the beginning of Begg treatment (Abst.) AM J QRTHOD61: 524-525, 1972. 14. Reitan K: Initial tissue behavior during apical root resorption. Angle Orthod 44: 68-82, 1974. 15. Stenvik A, Mjiir IA: pulp and dentine reactions to experimental tooth intrusion. A histologic study of the initial changes. AM J ORTHOD57: 370-385, 1970. 16. Stenvik A, MjGr IA: The effect of experimental tooth intrusion on pulp and dentine. Oral Surg Oral Med Oral Path01 32: 639648, 1971. 17. Stenvik A: The effect of extrusive orthodontic forces on human pulp and dentin. Stand J Dent Res 79: 430-435, 1971. 18. Morse PH: Resorption of upper incisors following orthodontic treatment. Dent Pratt 22: 21-35, 1971. 19. Sjolien T, Zachrisson BU: Periodontal bone support and tooth length in orthodontically treated and untreated persons. AM J ORTHOD64: 28-37, 1973. 20. Newman WG: Possible etiologic factors in external root resorption. AM J ORTHOD67: 522-539, 1975. 21. Goldson L, Hemikson CD: Root resorption during Begg treatmenf: A longitudinal roentgenologic study. AM J ORTHOD68: 55, 1975. 22. Hollender L, Ronnermsn A, Thilander B: Root resorption, marginal bone support and clinical crown length in orthodontically treated patients. Eur J Ortbod 2: 197-205, 1980. 23. Linge BO, Linge L: Apikale Wurzelresoxptionen der oberen Fro&tine. Eine longitudinale rijntgenologische Untersuchung in einer kieferorthopiidische praxis. Forts&r Kieferorthop 41: 276-288, 1980. 24. Linge BO, Linge L: Apical root resorption ip upper anterior teeth. Eur J Ortbod 5: 173-183, 1983. 25. Rijnnerman A, Larsson E: Overjet, overbite, intercanine distance and root resorption in ortbodontically treated patients. Swed Dent J 5: 21-27, 1981. 26. Ten Hoeve A, Mulie MR: The effect of anteropostero inciser repositioning on the palatal cortex as studied with laminagraphy. J Clin Orthod 10: 804-822, 1976. 27. Ten Hoeve A: Personal communication, 1981.
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and De Munck
28. Bunch WB: Tissue changes occurring in dogs incident to depressing movements. Angle Grthod 12: 177-183, 1942. 29. Dellinger EL: A histologic and cephalometric investigation of premolar intrusion in the Macaca speciosa monkey. AM J ORTHOD 53: 325-355,1967. 30. Burstone CR: Deep overbite correction by intrusion. AM J ORTHOD 72: l-22,
1977.
31. Liu SY, Herschleb CW: Controlled movement of maxillary incisors in the Begg technique. AM J ORTHOD 80: 300-3 15, 1981. 32. Van de Poe1 ACM, Duinkerke .:SH: Waarom long-cone techniek? Ned Tijdschr Tandheelk:. tlL: 188-194, 1975. 33. Van Aken J: Optimum conditio:’ 5 for intraoral roentgenograms. Oral Surg Oral Med Oral Path01 27: 475-491, 1969.
I
34. Barr JH, Gr@n P: Palate contour as a limiting factor in intraoral X-ray technique. Gral Surg Oral Med Oral Path01 12: 459-472, 1959. 35. Wheeler RC: Dental anatomy, physiology and occlusion. Philadelphia, 1974, W.B. Saunders Co.
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to:
Dr. L. Dcrmaut Department of orthodontics State University of Gent De Pintelaan 135 B-9000 Gent, Belgium
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I
Key words: Apical resorption, upper incisors, intrusion, radiographs, tooth movement
A
s early as 1914, Ottolengui’ reported on apical root resorption caused by orthodontic treatment. Since then many studies on resorption after orthodontic treatment have been published.2-24 The resorption usually occurs in the upper incisors.3~6~7~‘o~‘p~20-22 Oppenheim’ suggested that the morphology of the roots of the incisors was a catalyst in root resorption. Different kinds of movement possibly related to root resorption have been radiographically examined during the past several decades. De Shields,12 Linge and Linge,23 and Ronnerman and Larssonz5 have studied root resorption with radiography of the anterior maxillary teeth after orthodontic movement. Comparison of radiographic studies is difficult because of the large differences in methods and techniques. However, it is generally accepted that extensive tooth displacements, torque movements, and jiggling forces” are responsible for root resorption, The only radiographic study on root resorption mentioning intrusion as a causative factor is the one by De Shields. I2 However, he did not examine root resorption in cases limited to intrusive mechanics only. Furthermore, De Shields found no correlation between vertical orthodontic movements and root resorption. Radiographic studies on root resorption deal only From the University of Ghent. *Chairman, Department of Orthodontics. **Assistant Professor, Department of Orthodontics.
with apical resorption; buccal and lingual resorption are less perceptible on intraoral radiographs. According to the histologic study of Henry and Weinmann (1951),’ the most frequent idiopathic root resorptions occur in the apical area, “Resorption occurs more readily upon surfaces facing toward the direction of physiologic movement.” In several histologic studies in humans and animals (Reitan,14 Stenvik and Mj6r,15 Bunch,28 and Dellingeti9), resorption after intrusion was observed. Regarding measurement of the amount of resorption on radiographs, most radiographic studies refer to an arbitrary score that represents a specific amount of resorption. Linge and Linge23v24are exceptions; an approximation is replaced by precise measurement of root resorption. This was the only study with clear, standardized radiographs. Ten Hoeve and Mulie state that the classical Begg treatment is also responsible for root resorption through tipping movements in the upper anterior teeth followed by torque movement in the third stage. This is in agreement with the findings of Goldson and Henrikson.” These authors induce open bite by means of intrusion of the upper anterior teeth in an attempt to place teeth in as broad a bony area as possible between the palatal and the buccal cortices. Ten Hoeve2’ hypothesizes that this method may help to avoid root resorption. The purpose of our radiographic study was to search for a relation between isolated intrusion and root re321
322 Dermaut and De Munck
Fig. 1. Intrusion arch wire with coil and second-order (arrow) to avoid interference with canine bracket.
Am. J. Orthod.
Dmfac. Orthop. October 1986
bend
sorption in the upper anterior teeth. The potential relationship between the amount of root resorption and the amount and duration of the intrusion will be examined further. MATERIALS AND METHODS Subjects Experimental group. Intrusive force was placed on the upper maxillary central and lateral incisors in 20 patients-ten girls and ten boys. Resorption in these 20 patients was examined on 66 anterior teeth-35 central incisors and 31 lateral incisors. Foggy or questionable radiographs were eliminated from the study. When intrusion occurred, the ages of the experimental group ranged from 11 to 37 years, but only three patients were over 20 years of age. The average age of the group was 15 years. The mean intrusion period was 29 weeks with a range of 8 to 64 weeks. Control group. The control group consisted of 15 persons, mostly dental students. These seven female and eight male subjects had undergone no previous orthodontic treatment. Root shortening was measured in 58 anterior teeth-29 central and 29 lateral incisors. With an age range between 16 and 25 years, the average age in the control group was 22 years. The incisors were examined for root resorption with an average interval of 28 weeks (from 24 to 32 weeks). Method Intrusion technique. After a short period of light wire alignment of the upper arch with Begg brackets (with the exception of 1 patient with edgewise brackets) and before the reduction of overjet, intrusive forces were exerted to obtain anterior bite opening. Teeth in which torque or uprighting had been performed were excluded from the study to avoid additional causes for root resorption.
Fig. 2. Determination of the amount of intrusion according to Liu and Herschleb.” 7, Intrusive component (used in this study). 2, Retrusive component.
A slightly modified Burstone technique was used.30 An attempt was made to transmit all forces to the upper anterior teeth. Anchorage of the molars was maintained using high-pull headgear and a palatal bar. The intrusion arch consisted of a coil 3 mm in diameter and 2.5 windings. This created a constant force. Interference of premolars and canines was avoided by means of second-order bends that bypassed these teeth (Fig. 1). An 0.018 inch round Australian arch wire was used for that purpose. In all but four patients, the intrusion arch was not inserted directly in the upper anterior brackets. Rather, it was ligated to a sectional ribbon arch consolidating the four upper anterior teeth (Fig. 1). In this way the intruding force was passed through the center of resistance in an attempt to avoid “flaring out” of the upper incisors. Intrusion of the four upper anterior teeth was performed with a practically constant force of 100 g. Through the continuing action of the intrusion arch, the necessity of activation was reduced to a minimum (Burstonem) . Measuring the amount of intrusion. With the above intrusion technique, intrusion and some i-etrusion were obtained simultaneously. The net amount of intrusion was measured for each patient on the lateral cephalogram. Because the short period of preintrusion alignment was not expected to affect root length, the first lateral cephalogram was taken just before starting the intrusion, The second lateral cephalogram was taken immediately after intrusion of the four anterior teeth. With both cephalograms, the palate and the most protruded incisor were traced. For the purposes of this study, it has been arbitrarily accepted that the amount of intrusion, as measured for one incisor, was comparable to that for the other three incisors in the same
Volume 90 Number 4
Apical root resorption of upper incisors caused by intrusion 323
Flg. 3. Radiographs before and after intrusion. Rx and Rx’, Distance from cementoenamel junction to incisal edge before (Rx) and after (Rx’) intrusion. Ry and Ry’, Root length before (Ry) and after (Ry’) intrusion. -
patient. On the same cephalogram, it was not possible to distinguish the complete outlines of each of the four incisors. Compared to the palatal construction line (PNSANS), intrusion was measured as follows: on the lateral cephalogram the center of resistance (CR,) is defined at two thirds of the distance from the incisal edge; CR, is marked on the palatal plane and registered on the anterior nasal spine. The vertical displacement of the upper incisor is the measure of the amount of actual intrusion (Fig. 2). Intraoral radiographic technique. To measure the amount of resorption, a precise, long-cone radiographic technique was used (Van De P0e1~~).There was neither distortion nor enlargement when the film was parallel to the tooth and the rays perpendicular to the film (Van Aken33). Adapting the film on the palate is generally not simple. Barr and Gr@n34recommended placing the film at a 15” angle to the teeth, extending the periapical zone to approximately 3 mm above the apex. With a very high palate and short teeth, this adaptation is supefiuous. The predetermined angle between the film and tooth gives a uniform enlargement of the image. Two radiographs were taken, one before the intrusion (but after alignment) and one after the intrusion. Thus, the observed resorption was limited to the resorption occurring during the active intrusion period. The central and lateral incisors of the same quadrant
were registered on a single intraoral radiographic film to limit the patient’s exposure to radiation. Calculation of the resorption. The radiographs have been enlarged x 3 and were printed on photographic paper. After enlargement, landmark identification was no less accurate and measurement accuracy was improved. Each tooth has been delineated on these photographs. The longitudinal axis was constructed through the center of the incisal edge in the direction of the pulp canal. The construction of the longitudinal axis of the tooth on the first and second photographs was identical (Fig. 3). Whenever the cementoenamel junctions at the mesial or distal aspects of the tooth were visible in both photographs, they were marked and projected perpendicularly on the tooth axis (Linge and Linge23*U). In a few patients the definition of the cementoenamel junction was insufficient. In these cases other distinguishable reference structures on the tooth crown were used. Because it was believed that the precise distance between the incisal margin (and tooth apex) and the constructed cementoenamel junction could not be measured with sufficient accuracy, accurate measurement of absolute amounts of root resorption was not deemed possible. Hence, the relation between the rooth length before ;;).g&) after (y’) intrusion was calculated as follows 1.
.
Am. .I. Orthod.
324 Dermaut and De Munck n ExP
Dentofac. Orthop. October 1986
each of the control teeth with the procedure mentioned above. The mean was 0.99 (SD = 0.08). The t test showed no significant difference.
25 I
Results
1
a6
0.1
a8
as
1
1.1
1.2
,y
v
Flg. 4. Bar graph illustrating the distribution of root length ratios in the experimental and control groups. y/y’, Ratio between root length before and after intrusion.
In the experimental group, the mean intrusion of the incisors was 3.6 mm (SD = 1.6 mm). Contrary to the control group, in the experimental group the y’Iy relations were smaller than 1 (x = 0.82, SD = 0.10). A statistically significant difference was found between the mean root lengths of the experimental and the control teeth. The distribution of root length ratio in both groups is illustrated in Fig. 4. No difference could be found between the central (n = 35) and the lateral (n = 31) incisors (difference of proportions of 0.04 was insignificant). There was little correlation between the amount of resorption and the amount of intrusion (for the lateral incisors, r = 0.26; for the central incisors, r = 0.18; for both, r = 0.03). These low correlations of coefficients indicate that there was only a slight relation, if any, between the amounts of intrusion and resorption. There was no relation between the duration of intrusion and the amount of resorption (r = -0.02). DISCUSSION
3Rx -=3RY
x
3Rx’ -=3 Ry’
x’
y’ Y b.Y x, = Rx’ * Y’ x=Ry Y’ Rx and Rx’: Distance from cementoenamel junction to incisal edge on x-ray films before (Rx) intrusion and after (Rx’) intrusion Ry and Ry’: Root length on x-ray films before (Ry) and after (Ry’) intrusion x and xl: distancefrom cementocnameljunction to incisal edge before (x) and after (xl) intrusion Since x = x’, Rx*y -=RY
Rx * Ry’ -=Ry*x’
Rx-y’ RY’
y’ y
Reliability of the method. The reliability of the intraoral, radiographic measuring method was tested in the control group. Assuming no measurable root resorption occurred (no therapy and a short investigation period), no change should be observed and measurements should be the same. Nevertheless, the relation y’/y was calculated for
During orthodontic intrusion, resorption of the upper incisors was obvious. No difference in resorption could be found between the central and lateral incisors. However, there were marked differences among the incisors in the same patient. It has been explained why the absolute amount of resorption was not calculated; however, the relation between root lengths before and after treatment indicates a mean root resorption of 18%. Starting from an average root length of 13 mm (according to Wheele?), a mean resorption of 2.5 mm was found in this study. In 552 patients 11 years or older, Linge and Linge” found less than 1 mm of resorption of the upper incisors after orthodontic therapy. There was less resorption in younger children. They concluded that the chances of resorption increase when orthodontic movements take place after the root is completed. Comparing the study by Linge and Linge with this study, intrusion seemed to cause more resorption than overall orthodontic treatment (torque, Class II elastics, rectangular wire). An apical deflection was found in 13 incisors. These teeth were not more responsive to resorption than the others. The position of the roots in relation to the buccal and palatal cortices was also examined. This infor-
Volunle 90 Number 4
Apical root resorption
mation is not always clear on the lateral cephalogram and must be carefully interpreted. In the study’s sample, the position of the root was more favorable after intrusion to both cortical plates. Intrusion of incisors at the beginning of treatment has been suggested by Ten Hoevez6 in an attempt to prevent resorption. It should be emphasized that Ten Hoeve was referring to palatal and/or buccal resorption. In the present study only apical resorption was measured. We could not establish any relation between the amount of apical resorption and the position of the apex in relation to the nasal floor. Apical resorption was found in these cases only in combination with apical deflection. Because the occurrence was limited to only six teeth, this conclusion must be interpreted cautiously. As mentioned previously, theFe was no significant correlation between the amount of root resorption and achievable intrusion (r = 0.03 for both incisors together). This is partially in agreement with Phillips,” who could not find any relation between the amount of sagittal tooth displacement and resorption. No relation could be found between the amount of resorption and the duration of the intrusion mechanics (r = - 0.02). Several authors334, “f ‘u* *‘z23indicated that they could prove a relation existed between the amount of resorption and the duration of the orthodontic movement. However, a comparison of the results of the current study with studies previously cited is not really a valid one. The treatment period was shorter. The experimental time was limited to the period of intrusion. At the start of treatment, in some patients distal molar tipping occurred more frequently than intrusion because of poor handling of the reaction forces. In several of the cases in the experimental group, the treatment time was relatively long because of poor patient cooperation (wearing headgear). These cases might have influenced the average treatment time since only moderate intrusion was noticed. The authors want to thank Dr. SC. W. De Coster, head of the Center of Image Analysis and Quality Control, for his help in the processing of the data. They are grateful also to Mr. G. Dermout for the pictures, to Mr. Vanderdonck for helping in translation, and to Mrs. B. Jouret for typing the manuscript. REFERENCES 1. Ottolengui R: The physiological and pathological resorption of tooth roots. Items of Interest 36: 332-362, 1914. 2. Ketcham A: A progress report of an investigation of apical root resorption of permanent teeth. Int J Orthodontia, Oral Surg, Radiogr 15: 310, 1929.
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3. Rudolph CE: A comparative studyin root resorptionin permanent teeth. J Am Dent Assoc 23: 822, 1936. 4. Rudolph, CE: An evaluation of root resorption occurring during orthodontic treatment. J Dent Res 19: 295, 1940. Becks H: Orthodontic prognosis. AM J OR~OD 25: 610-624, 1939. Hernley S: The incidence of root resorption of vital permanent teeth. J Dent Res 20: 133-141, 1941. Oppenheim A: Human tissue response to orthodontic intervention of short and long duration. Ahl J ORTHODORAL SURG28: 263, 1942. 8. Hemy JL, Weinmann JP: The pattern of resorption and repair of human cementum. J Am Dent Assoc 42: 270-290, 195 1. 9. Jacobson 0: Clinical significance of root resorption. AM J ORTHOD38: 687-696, 1952. 10. Massler M, Malone AJ: Root resorption in human permanent teeth. AM J ~RTHOD40: 619-633, 1954. 11. Phillips JR: Apical root resorption under orthodontic therapy. Angle Orthod 25: 1, 1955. 12. De Shields RW: A study of root resorption in treated Class II, Division 1 malocclusions. Angle Orthod 39: 231-245, 1969. 13. Rosenberg HN’: An evaluation of the incidence and amount of apical root resorption and dilaceration occurring in orthodontitally treated teeth having incompletely formed roots at the beginning of Begg treatment (Abst.) AM J QRTHOD61: 524-525, 1972. 14. Reitan K: Initial tissue behavior during apical root resorption. Angle Orthod 44: 68-82, 1974. 15. Stenvik A, Mjiir IA: pulp and dentine reactions to experimental tooth intrusion. A histologic study of the initial changes. AM J ORTHOD57: 370-385, 1970. 16. Stenvik A, MjGr IA: The effect of experimental tooth intrusion on pulp and dentine. Oral Surg Oral Med Oral Path01 32: 639648, 1971. 17. Stenvik A: The effect of extrusive orthodontic forces on human pulp and dentin. Stand J Dent Res 79: 430-435, 1971. 18. Morse PH: Resorption of upper incisors following orthodontic treatment. Dent Pratt 22: 21-35, 1971. 19. Sjolien T, Zachrisson BU: Periodontal bone support and tooth length in orthodontically treated and untreated persons. AM J ORTHOD64: 28-37, 1973. 20. Newman WG: Possible etiologic factors in external root resorption. AM J ORTHOD67: 522-539, 1975. 21. Goldson L, Hemikson CD: Root resorption during Begg treatmenf: A longitudinal roentgenologic study. AM J ORTHOD68: 55, 1975. 22. Hollender L, Ronnermsn A, Thilander B: Root resorption, marginal bone support and clinical crown length in orthodontically treated patients. Eur J Ortbod 2: 197-205, 1980. 23. Linge BO, Linge L: Apikale Wurzelresoxptionen der oberen Fro&tine. Eine longitudinale rijntgenologische Untersuchung in einer kieferorthopiidische praxis. Forts&r Kieferorthop 41: 276-288, 1980. 24. Linge BO, Linge L: Apical root resorption ip upper anterior teeth. Eur J Ortbod 5: 173-183, 1983. 25. Rijnnerman A, Larsson E: Overjet, overbite, intercanine distance and root resorption in ortbodontically treated patients. Swed Dent J 5: 21-27, 1981. 26. Ten Hoeve A, Mulie MR: The effect of anteropostero inciser repositioning on the palatal cortex as studied with laminagraphy. J Clin Orthod 10: 804-822, 1976. 27. Ten Hoeve A: Personal communication, 1981.
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and De Munck
28. Bunch WB: Tissue changes occurring in dogs incident to depressing movements. Angle Grthod 12: 177-183, 1942. 29. Dellinger EL: A histologic and cephalometric investigation of premolar intrusion in the Macaca speciosa monkey. AM J ORTHOD 53: 325-355,1967. 30. Burstone CR: Deep overbite correction by intrusion. AM J ORTHOD 72: l-22,
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31. Liu SY, Herschleb CW: Controlled movement of maxillary incisors in the Begg technique. AM J ORTHOD 80: 300-3 15, 1981. 32. Van de Poe1 ACM, Duinkerke .:SH: Waarom long-cone techniek? Ned Tijdschr Tandheelk:. tlL: 188-194, 1975. 33. Van Aken J: Optimum conditio:’ 5 for intraoral roentgenograms. Oral Surg Oral Med Oral Path01 27: 475-491, 1969.
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34. Barr JH, Gr@n P: Palate contour as a limiting factor in intraoral X-ray technique. Gral Surg Oral Med Oral Path01 12: 459-472, 1959. 35. Wheeler RC: Dental anatomy, physiology and occlusion. Philadelphia, 1974, W.B. Saunders Co.
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Dr. L. Dcrmaut Department of orthodontics State University of Gent De Pintelaan 135 B-9000 Gent, Belgium
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