Root resorption following active

in maxillary central incisors orthodontic treatment

Scott Copeland, D.D.S., M.S.,* and Larry J. Green, D.D.S., Ph.D.** Derry, N. H. and Buffalo, N. g.

The purpose of this study was to determine if apical root resorption associated with orthodontic treatment continues after the termination of active treatment (that is, the removal of fixed appliances). A sample of 45 subjects who had experienced root resorption during treatment was selected from the orthodontic clinic at the State University of New York at Buffalo. The length of the maxillary central incisors was measured from lateral cephalometric radiograms taken before treatment, after active treatment, and after retention. From these data, the resorption occurring during and after active treatment was calculated. The mean amount of root resorption during active treatment was 2.93 ram. The mean amount of root resorption during the posttreatment period was 0.1 mm. There was a statistical difference between these two means using the Student's t test at the 0.05 level of significance. The reliability coefficient comparing the first tracings and measurements in the 19 cases that were retraced and remeasured was r = 0.993. The data from this radiographic study support the hypothesis that root resorption associated with orthodontic treatment ceases with the termination of active treatment. There was also evidence to suggest that when posttreatment root resorption does occur, it is not necessarily associated with large amounts of root resorption during the active treatment period. It is more likely associated with other factors, such as traumatic occlusion and active force-delivering retainers. (AM J ORTHOD 89: 51-55, 1986.)

Key words: Root resorption, apical, incisor, cephalometric, orthodontic

A p i c a l root resorption is one of the most common iatrogenic problems associated with orthodon- tic treatment. It is becoming an increasingly more se- rious problem from a medicolegal standpoint. It appears that no practitioner is able to avoid this problem com- pletely. Consequently, a great deal of research has been published on this topic, particularly research undertaken from a clinical point of view. However, much contro- versy exists concerning its cause and predisposing fac- tors. One important question of interest to orthodontists is, once root resorption has begun will it continue after active treatment is terminated? Several clinical studies have been conducted relative to this question. ~.2 These studies used intraoral radiograms or panoramic-type films to determine root resorption and were comparative rather than quantitative in nature. Root resorption has been quantitatively measured by lateral cephalometric radiograms, but not during postretention periods? -6 In

This article is based on a thesis submitted i n partial fulfillment of the require- merits for the degree of Master of Science, Department of Orthodontics, State University of New York at Buffalo. *Present address: 132 E. Broadway, Derry, N. H. In private practice. **Professor, Department of Orthodontics, State University of New York at Buffalo.

this study root length was measured before treatment, at the debanding, and at some point during the retention period (usually 2 years). Quantitative measurements were made from lateral cephalometric radiograms to determine if root resorption continued after active ortho- dontic treatment had been completed. The positive hy- pothesis was that root resorption does not continue once fixed appliances have been removed.

Much controversy exists in the literature as to the exact definition of root resorption. In this study external apical root resorption was defined as any reduction in length of a maxillary central incisor measured from the tip of the incisal edge to the apex of the root. Loss of clinical root length caused by periodontal disease was not considered nor was lateral external root resorption. Only the maxillary central incisors were measured as they are considered by many authors 7-1° to be among the most frequently affected teeth.

METHODS AND MATERIALS

The sample was drawn from the patient files at the State University of New York at Buffalo, Department of Orthodontics. The criteria for case selection were (1) the availability of a pretreatment, posttreatment, and

51

52 Copeland and Green Am. J. Orthod. January 1986

\

\ \\

\ Fig. 1. Root and crown landmarks for incisor tooth length.

postretention lateral cephalometric radiogram for each patient and (2) evidence of apical root resorption on the posttreatment films.

More than 1,000 patient files were screened to iden- tify cases exhibiting root resorption greater than 1 mm during active treatment. The length of the shorter max- illary central incisor on the pretreatment lateral ceph- alometric radiogram was assessed with a divider and compared to the posttreatment length to determine if 1 mm or more of resorption had occurred. If the incisors were crowded in such a way that the central incisor apices could not be differentiated from those of the lateral incisors or canines, the case was not included in the sample. If any film was of such poor quality that a measurement could not be made, such a film was also eliminated. Other reasons for case rejection were (1) obvious root resorption before treatment and (2) im- mature roots before treatment.

Fifty-six cases were found to meet the initial re- quirements, but 11 were eliminated for one or more of the foregoing reasons. A final sample of 45 subjects

was large enough to anNyze statistically and was con- sidered to be a representative sample of all the ortho- dontic patients at the clinic who had experienced apical root resorption. All the patients were treated with edge- wise appliances.

Thirteen of the subjects were male; 32 were female. The range of age at the beginning of treatment was from 10 years 3 months to 23 years 5 months with a mean of 13 years 1 month. The mean duration of active treatment was 2 years 10 months. The range of active treatment time was from ! year 4 months to 4 years 11 months. The mean for the period of time between the termination of active treatment and the final cephalo- metric radiogram was 2 years 4 months with a range from 9 months to 6 years 2 months.

All of the cephalometric radiograms in the present study were taken on the same Broadbent-Bolton* ceph- alometer by the same technician. The central incisors were measured from films taken at three different times (pretreatment, posttreatment, and some point during the retention period--usual ly 2 years after debanding). These measurements were then compared to determine the extent of root resorption occurring during active treatment and during the retention or posttreatment period.

The pretreatment, posttreatment, and final radio- grams were gathered for each patient and identified with a random number. The apex and incisal edge of the shorter of the two maxillary central incisors were marked on acetate paper with a pinprick. The pinpricks were circled in pencil for easier location and the acetate paper was marked with the same number as the ceph- alometric film (Fig. 1). Dental casts were occasionally used to more accurately determine the incisal edge. The three radiograms for each patient were compared during the landmark identification procedure to maintain con- sistency, that is, to establish that the same incisal edge and apex were identified in all three films.

After this landmark identification procedure had been performed on all of the radiograms, the acetate tracings were shuffled. The distance between the two pinpricks was then measured for each tracing by means of Helios dial caliperst calibrated to 1/2o of a millimeter. The acetate tracings were then reshuffled and remea- sured following the same procedure. The two replicated measurements for each tracing were averaged and the mean was used as the length of the tooth for that par- ticular cephalometric film.

The pretreatment, posttreatment, and final means

were recorded for each patient. The amount of apical

*Bolton Fund, Western Reserve University, Cleveland, Ohio. tMager Scientific Inc., Ann Arbor, Mich.

Volume 89 Root resorption in maxillary central incisors 53 Number 1

Table I. Summary of resorption data

Active treatment resorption

(mm)

Posttreatment resorption

(mm)

Range 1.1 to 7.35 - 0 . 4 to +0.95 Mean 2.93 0.1

Variance 2.1 0.09 Standard 1.45 0.3

deviation

root resorption during active treatment was determined for each patient by subtracting the posttreatment length from the pretreatment length. The posttreatment root resorption was similarly calculated by subtracting the final length from the posttreatment length. The mean and standard deviation were calculated for the active treatment resorption and the posttreatment resorption. These statistics were compared using the Student's t test for the difference between two means with a level of significance of 0.05.

Nineteen of the cases were randomly selected and retraced by the same procedure. These tracings were shuffled and measured twice, as before. The mean of the two measurements was calculated and compared to the data from the initial tracings. A reliability coeffi- cient was calculated to determine the reliability of the tracing and measurement procedure as follows:

Pearson r = n~xy - (Nx)(Zy)

~SnZx~- (Zx)~ /nZY 2 - (Ey)~

RESULTS

The resorption data are summarized in Table I and Fig. 2.

The mean amount of apical root resorption during active treatment was 2.93 mm with a range from 1.1 mm to 7.35 mm. The standard deviation was 1.45 mm. The mean amount of root resorption after active treat- ment was 0.1 mm with a range from - 0.4 mm to 0.95 ram. The standard deviation was 0.3 ram.

The null hypothesis stated that there was no differ- ence between the mean root resorption during the active treatment period (from the beginning of treatment to the removal of fixed appliances) and the postactive. treatment period (from the removal of fixed appliances to the final cephalometric radiogram). The level of sig- nificance was set at 0.05; using the Student's t test for the difference between two means where population variances were not equal, the critical value was found to be 1.68. The t-test statistic was calculated to be 12.8. Therefore, the null hypothesis was rejected (P <

3 . 0 ~ - 1 2 -

2.5

E 2.0

0 ,¢,,.

'1.5

O D~ c -

a ~.0

0 . 5

I I Active Orthodontic Post-Active Treatment Period Treatment Period

Fig. 2. Mean root resorption during active orthodontic treatment and postactive treatment periods.

0.005). It was concluded that there is a difference be- tween the average amount of apical root resorption that occurs during the active treatment period and the av- erage amount of resorption that occurs during the post- active treatment per iod-- the former being considerably greater than the latter.

The reliability coefficient obtained from compari- sons of the first and second tracings and measurements of 19 cases was 0.993.

DISCUSSION

Most researchers believe that root resorption does not continue once active orthodontic treatment is ter- minated.~-3'l~'n The findings of this study support pre- vious clinical studies by Vonder Ahe 2 and Ronnerman and Larsson.I Vonder Ahe, in a study of 57 patients from 12 different practices, found that root resorption did not continue after active treatment. The average case was out of retention 6.5 years and some were 17 years posttreatment. Ronnerman and Larsson evaluated root resorption cases at 3 and 10 years postactive treat- ment and found no evidence that root resorption had continued. These studies based their conclusions on comparisons of periapical, occlusal, and panoramic ra-

54 Copeland and Green Am. J. Orthod. January 1986

diograms. The data used in the present study were quan- titative and obtained from linear cephalometric mea- surements of maxillary central incisors. Because these teeth are located near the midsagittal plane, sequential measurements could be more accurately compared since magnification was more consistent and radiographic distortion minimized.

In this study the average amount of posttreatment resorption was only 0.1 mm, an amount that could be accounted for by several different explanations. First, it may be assumed that the resorption process continued for a short period of time after active treatment. Wainwright ~3 described evidence from his study sug- gesting that root resorption induced by orthodontic forces may continue for several days after the forces are removed. After this time repair cementum is de- posited on the affected root surfaces. Reitan ~4,~5 be- lieved resorption could continue for as much as a week after tooth movement was stopped and that cementum repair required 5 to 6 weeks of orthodontic inactivity. This could account for the resorption that occurred dur- ing the posttreatment period. Although the retention period was considered to be one of nonactive treatment in this study, all the patients wore maxillary Hawley retainers and either mandibular Hawley retainers or fixed retainers from canine to canine. Activated retain- ers may also explain some of the posttreatment resorp- tion because an active labial bow could have exerted significant orthodontic forces during the retention pe- riod. Gholston and Mattison ~6 recently reported a single case where resorption continued for 3 years postreten- tion. Such cases are presumably rare and causative fac- tors such as occlusal trauma must be taken into con- sideration.

The range for the posttreatment root resorption was from - 0 . 4 mm to + 0 . 9 5 mm. The most plausible explanation for the negative values was measurement error since the possibility of teeth increasing in length was removed by eliminating from the sample subjects with maxillary incisors with immature roots. Rygh j2 and others H'13,~7-~9 described the process of cementum repair as primarily a repair of small resorption lacunae; thus it is unlikely that there would be a net increase in measureable root length as a result of this process.

It is likely that resorption did not continue in most subjects. This is supported by the fact that the mean posttreatment resorption was nearly zero (0.1 ram). Posttreatment resorption values in 92% of the subjects were between - 0 . 4 mm and + 0.4 mm. Measurement error probably accounted for a major portion of the standard deviation of 0.3 ram.

Only four subjects (8% of the sample) showed post- treatment resorption values greater than 0.4 mm. In

these cases, particularly active retainers may expiain the continuation of the resorption process. Occlusal trauma may also have been a causative factor in post- treatment root resorption. It is interesting to note that these four cases were not always associated with large amounts of resorption observed during the active treat- ment period. The subject showing the greatest amount of posttreatment root resorption (0.95 mm) demon- strated only 2.3 mm of root resorption during the active treatment period, which is less than the mean for that period. Conversely, the subject with the greatest amount of active treatment resorption (7.35 mm) showed - 0.2 mm of oosttreatment resorption. Since 92% of the sample did not show significant amounts of resorption during the posttreatment period and only four cases demonstrated any significant amount of resorption during this period, a coefficient of correlation between resorption during and after active treatment could not be calculated with statistical significance. However, it appears that the amount of active-treatment root re- sorption and posttreatment resorption are not correlated and that other factors such as occlusal trauma and active retainers may be responsible for posttreatment root re- sorption.

The clinical sequelae of root resorption is also a topic of interest. Vonder Abe 2 reported only one case of mobility out of 57 resorption cases. Phillips 2° stated that the degree of root loss in most situations was "clin- ically insignificant" and "not endangering the life or function of the dentition." Others are less optimistic. Oppenheim is believed that shortened roots could never resist the stress of function as well as or as long as unresorbed roots. One study 13 found that resorption of- ten led to mobility and at times exfoliation of the tooth. Root resorption then should be quantified to make more valid judgments on its clinical sequelae.

The technique used in this study to measure root resorption of the maxillary central incisors appeared to be very reliable. This was supported by the fact that the reliability coefficient (r) comparing the 19 cases that were retraced and remeasured to the original trac- ings and measurements was 0.993.

Two subjects in this study had maxillary central incisors that had been treated endodontically before orthodontic treatment. In these subjects it was possible to visualize root resorption relative to their root canal fillings. In the pretreatment radiogram of one subject, the apex and the end of the endodontic filling material were coincidental. In the posttreatment and final radio- grams, the filling material extended beyond the apex for a distance equal to the amount of root resorption. These cases supported the validity of the measurement procedure used in this study.

Volume 89 Root resorpt ion in maxi l lary central incisors 55 Number 1

Wainwright 13 points out that root resorption occur- ring on root surfaces other than the apex is often not seen radiographically. It was noted in this study that apical resorption is easily detected by most radiographic techniques when the root apices are obviously blunted or distorted. However, in many subjects the resorption pattern was so symmetric that it could be overlooked if the roots were not actually measured from radiograms and compared to films taken at an earlier time. Previous studies to determine the incidence of root resorption and its relationship to various treatment procedures have different definitions of root resorption. Many of these studies could be repeated using a quantitative definition of apical root resorption and a measurement procedure similar to the one described in this study.

Many practitioners rely on periapical radiograms of the maxillary anterior teeth to assess root resorption during treatment; others use the panoramic radiograms. But root resorption can be more accurately assessed with less radiation by measuring the length of a central incisor from a progress cephalometric film and com- paring it to the initial film. If there is no apical root resorption seen in the maxillary or mandibular central incisors, then significant apical resorption occurring in other teeth is less likely because the anterior teeth are the most frequently affected. 7-~°

Root resorption is one of the most serious iatrogenic problems associated with orthodontic treatment and its diagnosis can only be made by maintaining adequate records. If resorption is discovered, treatment goals must be reassessed and a decision should be made to terminate treatment or arrive at a treatment compromise and, when necessary, stop applying forces. The results of this study indicate that the termination of active treat- ment will essentially stop further apical root resorption.

REFERENCES 1. Ronnerman A, Larsson E: Overjet, overbite, intercanine distance

and root resorption in orthodontically treated patients. A ten year follow-up study. Swed Dent J 5: 21-27, 198t.

2. Vonder Ahe G: Postretention status of maxillary incisors with root-end resorption. Angle Orthod 43: 247-255, 1973.

3. Hall A: Upper incisor root resorption during stage II of the Begg technique. Br J Orthod 5: 47-50, 1978.

4. Morse P: Resorption of upper incisors following orthodontic treatment. Trans Br Soc'for Study of Orthod, 1970-71, 49-63.

5. Plets J, Isaacson R, Speidel T, Worms F: Maxillary central incisor root length in orthodontically treated and untreated pa- tients. Angle Orthod 44: 43-47, 1974.

6. Wickwire N, McNeil M, Norton L, Dwell R: The effects of tooth movement upon endodontically treated teeth. Angle Orthod 44" 235-242, 1974.

7. DeSheilds R: A study of root resorption in treated Class II, Division 1 malocclusions. Angle Orthod 39: 231-245, 1969.

8. Goldson L, Henrikson C: Root resorption during Begg treatment. A longitudinal roentgenographic study. AM J ORTHOD 68: 55- 66, 1975.

9. Massler A, Malone A: Root resorption in human permanent teeth. AM J ORTHOD 40: 619-631, 1954.

10. Sjolien T, Zachrisson B: Periodontal bone support and tooth length in orthodontically treated and untreated persons. AM J OR~OD 64: 28-37, 1973.

11. Reitan K: Initial tissue behavior during apical root resorption. Angle Orthod 44: 68-82, 1974.

12. Rygh P: Orthodontic root resorption studied by electron mi- croscopy. Angle Orthod 47: 1-16, 1977.

13. Wainwright M: Facial lingual tooth movement. Its influence on the root and cortical plate. AM J ORTHOD 64: 278-302, 1973.

14. Reitan K: Biomechanical principles and reactions. In Graber TM, Swain BF (editors): Current orthodontic concepts and techniques, ed 2. Philadelphia, 1975, W.B. Saunders Company, pp 196- 213.

15. Reitan K: Bone formation and resorption during reversed tooth movement. In Kraus BS, Reidel RA (editors): Vistas in ortho- dontics. Philadelphia, 1962, Lea & Febiger, pp 69-84.

16. Gholston L, Mattison G: An endodontic-orthodontic technique for esthetic stabilization of extremely resorbed teeth. AM J ORTHOD 83: 435-440, 1983.

17. Harry MR, Sims MR: Root resorption in bicuspid intrusion: A scanning electron microscope study. Angle Orthod 52: 235-258, 1982.

18. Oppenheim A: Human tissue response to orthodontic intervention of short and long duration. AM J ORTHOD 28: 263-301, 1942.

19. Stenvik A, Mjor I: Pulp and dentine reactions to experimental tooth intrusion. AM J ORTHOD 57: 370-385, 1970.

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Reprint requests to: Dr. Scott Copeland 132 E. Broadway Derry, NH 03038