- Email: [email protected]
Orthodontic relapse, apical root resorption, and crestal alveolar bone levels
P
TICLE
orztic r+elapse, apical Too ~e~o~~~io~~ Eveolar bone levels endy Sharpe, D.D.S., Brian Reed, D.D.S., MS., .I. ADan Poison, D.D.S., MS. Rochester,
N. Y.
This investigation examined the relationship of postorthodontic treatment relapse to crestal alveoIar bone support and root resorption. Thirty-six persons having completed the retention phase of orthodontics at least IO years earlier were divided into two groups based on the amount of relapse crowding of the mandibular anterior teeth. Eighteen subjects (relapse group) exhibited 2 mm or more of mandibular anterior relapse crowding and 18 subjects (nonrelapse group) exhibited no mandibular anterior relapse crowding. At time of recall, full-mouth series of periapical and bitewing r~di~~ra~hs were obtained as well as lateral cephalometric films to ailow comparison with similar iateral cephalometric films obtained at pretreatment and retention time points. The radiographs were examined to assess three parameters: root resorption, crestal alveolar bone levels, and changes in the position and angulation of the maxillary incisors. The subjects in the relapse group had ~~derg~n~ longer periods of treatment and exhibited a greater prevalence of root resorption; they also ~~s~~~y~d significantly greater crestal alveolar bone level distances, indicating greater loss of bone support than that observed in the nonrelapse group. The distances that teeth were translated seemed to affect the extent of root resorption and crestal bone loss with smaller amounts of tooth translation seemingly more prone to demonstrate tissue loss, The findings of lhis investigation suggest may be a relationship between orthodontic relapse and the parameters of increased rout re and decreased crestal alveolar bone levels. (AM J ORTHOD DENTOFAC ORTHOP 1987; ey words: Orthodontic
treatment, postretention, relapse, root resorption, alveolar crest loss
osttreatment relapse of corrected tooth positions is a major conce’m in orthodontic treatment.lm3 A periodontium incorporating adequate root length and bone support has been stated to be an important factor in the maintenance of posttreatment stability. ‘.’ Reduction of crestal alveolar bone support and reduction of root length by root resorption, however, have both been reported as sequelae of orthodontic treatment.4-7 Consequently, it was the purpose of this investigation to examine the relationship between posttreatment relapse and the parameters of crestal alveolar bone support and root resorption. ~AT~~iA~S AND METHODS The subjects in the study sample consisted of 36 persons who had completed the retention phase of orthodontic treatment at least 10 years earlier. Subjects were selected on the basis of the availability of complete records and the absence of root resorption prior to treatment. Plaster casts were used to divide these persons This study was supported in part by National Institute for Dental Research Grant DE82413 and is partial fulfiibnent for a certificate of proficiency. Ohiodontic Department, Eastman Dental Center, Rochester, N.Y., 1984.
into study and control groups on the basis of the amount of relapse crowding of the mandibular anterior teeth8 The study group (relapse group) consisted of I8 persons with 2 mm or more of mandibular anterior relapse crowding. The control group (nonrelapse group) comprised 18 persons with no mandibular anterior relapse crowding. Because of the limited number of subjects satisfying these criteria, it was not possible to match subjects for other factors. The resulting sex distribution and pretreatment malocclusion djs~~b~tio~ for the study and control groups are shown in Table I. In the study group, the mean age at treatment initiation was 11.3 years, the mean duration of treatment was 43.3 months, and the mean age at recall was 29.0 years. The respective figures for the control group were 12.7 years, 3 1.5 months, and 28.7 years. Trcatrn~~~ in the study group included extraction for IQ persons; in the control group, I1 persons were treated by extraction. The medical history was noncontributory for all subjects. At the time of recall (at least 10 years postretention), a full-mouth series of periapical and bitewing radiographs was obtained for each subject. radiographs were completed by means of the long-cone Fara~~e~ingtechnique.’ Exposure and processing of the films were per-
Speciai at-tick
formed undes standardized conditions. In addition, lateral cephalometric films were obtained at recall to allow comparison with similar lateral cephalometric films obtained at pretreatment and retention time points. The radiographs were examined to assess three parameters: root resorption, crestal alveolar bone levels, and changes in position and angulation of the maxillary incisors. %reeorpt~o~ Periapicai radiographs for each individual were scored by one examiner on an illuminated x-ray viewer using direct vision. The roots of the maxillary and mandibular central incisors, canines and first molars were scored according to the following criteria: 0 = No aFica1root resorption i = Slight blunting of the root apex ?. = Moderate blunting of the root apex up to one fourth of the root length 3 = Excessive blunting of the root apex beyond one fourth of the root length A total of 323 roots were assessed in the study group and 324 in the control group. The resuiting data were examined to determine: I. The number of subjects in each group with at least one tooth exhibiting apical root resorption 2. The prevalence of apical root resorption relative to six tooth types: maxillary central incisors, maxillary canines, maxillary first molars, mandibular central incisors, mandibular canines, and mandibular first molars 3. The severity of root resorption relative to group and tootb type A resorption score was determined for each subject by adding the resorption scores for all of the teeth examined. A mean group resorption score was then calculated using the sum of the scores for the 18 subjects within each of the groups. In addition, the mean resorption scores were calculated for each tooth type using the sum of resorption scores for the particular tooth type and the number of teeth of that type examined. This was done separately for the study and control groups. Student’s t test was performed to determine whether a statistically significant difference existed between the means at the P < 0.05 level of significance. Inter- and intragroup differences were examined.
Crestai alveolar bone levels were determined by a single examiner by measuring the distance between the cementoenamel junction (CEJ) of the tooth and the crest of the alveolar bone”.‘0-12with a plastic millimeter ruler. Bitewing radiographs were used to assess the inter-
Table I. Distribution of sample 1 Study (N = 18)
j Cnmroi
(N = 181
sex Male Female Angle classzjkation Class I 1 Class II, Division Class II, Division 2 Class III
12 6
5 13
II
s 7 2 1
5 I I
proximal tooth surfaces from the distal of the canine to the distal of the first molar. Periapical radiographs were used to assessthe mesial surface of the central incisors. Each radiograph was projected with a magnification factor of x 9.1 onto a white surface to facilitate measuring. The measured values were then reduced by the 9.1 magnification factor to give true vaiues for the cementoenamel junction to alveolar crest distances. The mean CEJ-alveofar crest distance was determined for each tooth surface examined (mesial of central incisors, distal of canines, mesial and distal of premolars, mesial and distal of first molars) in both the study and control groups. Student’s t test was performed to determine whether there were statistically significant differences between the groups. Intra- and intergrotip differences were examined. Changes in position and angulation maxillary incisors
of t
The same examiner compared tracings of the lateral cephalometric films for two time intervals-namely, pretreatment to retention and retention to recaii. Tracacings were superimposed along the palatal plane, registering at the anterior nasal spine. Changes in the position and anguiation of the upper incisor to the point A pogonion plane were determined in millimeters and degrees. This was done to investigate the correlation between direction and degree of incisal movement with apical root resorption and changes in crestal alveolar bone levels. RESULTS Root resorption As previously mentioned, the extent of root resorption was determined by measurements attained from radiographic films. The errors in the radiographic parameters were assessed by replicate measurements using previously described techniques”,” and were found to be within the 5% to 9% range. The number of subjects displaying root resorption on at least one tooth was high for both the study (16 of 18 subjects) and the
MUXillU Central incisors Canines Mesiobuccal root-first molars Bistobuccal root-first molars Palatal root-first molars Mandible Central incisors Canines Mesial root-first molars Distal root-first molars Total Maxillary Mandibular COMBINED MAXILLARY
AND MANDIBULAR
19136 3136 7136 9136 0136
52.7 8.3 19.4 25.0 0
1 i/36 2/36 i/36 2136 0136
30.4 5.6 2.8 5.6 0
16135 5136 0136 6136
45.7 13.9 0 16.7
17136 3136 1136 6136
47.2 8.3 8.3 16.7
381180 271143 651323
21.1 18.9 20.1
161180 271144 431324
8.9 18.8 13.3
Table
Table 111.Severity of root resorption at recall
IV. Patients’ resorption scores
Total Mean Range Maxilla Central incisors Canines Max. 6 Mesiobuccal root Distobuccal root Palatal root Mandible Central incisors Canines Mand. 6 Mesial root Distal root
0.94 0.83
0.18 0.05
0.50 0.11
0.15” 0.07
0.44 0.51 0.00
0.16 0.12 0.00
0.03 0.19 0.00
0.03* 0.14* 0.00
0.60 0.36
0.12 0.18
0.56 0.08
0.11 0.05*
0.00 0.25
0.00 0.10
0.06 0.38
0.05 0.15
-
*T test P < 0.05.
control (15 of 18) groups. The presence of root resorption was greater in the study group because of a greater prevalence of root resorption in the maxillary arch of the study group (Table II). The prevalence of root resorption in the mandibular arch was similar in both groups. Data for the specific tooth types showed that the highest prevalence of root resorption occurred for the maxillary and mandibular central incisors (Table II). In addition, the maxillary central incisors showed the greatest intergroup difference. The first molars in both arches for both groups showed the next greatest prevalence of resorption, followed by the canines. The distal
112 6.22 o-22
64 3.55 o-12
buccal root of the maxillary molars and the distal root of the mandibular molars displayed more resorption than their corresponding mesial roots. This trend was most marked in the mandibular molars. Root resorption was not observed on the palatal roots of the maxillary molars in either group. For all other roots in the maxillary arch, the study group always showed a greater prevalence of root resorption. This was statistically significant for the central incisors and buccal roots of the first molars. On the other hand, in the mandibular arch only the canines demonstrated more prevalent root resorption in the study group; this difference was not statistically significant. Table III gives findings for the severity of root resorption. The severity of root resorption was significantly greater in the study group for the maxillary central incisors, buccal roots of the maxillary molars, and mandibular canines. The mandibular central incisors also showed a greater numerical severity of root resorption in the study group, but the difference was not significant. None of the tooth types showed significantly greater resorption severity witllin the control group. The mean resorption score per subject (6.22) was almost twice as high in the study group compared with the control group (3 55) (Table IV).
wume
91
Special articie
Number 3
le V. Crestal alveolar bone levels-data
derived from bitewing radiographs
Maxilla First molars Premolars Canines iMandible First molars Premolars Canines *Significant
at the P < 0.05 level.
Table VI. Crestal alveolar bone levels-Data derived from periapical radiographs
Maxilla Central
incisors
Table VII. Severity of root resorption (maxillary central incisors) in extraction and nonextraction cases
1.51
0.09”
1.25
0.09
1.50
0.08*
1.27
0.08
Study Control
0.950 0.795
0.937 0.566
Mandible Central *Significantly
incisors greater,
P < 0.05.
responding control group values. This was statistically significant at the 0.05 level.
Alveolar crest levels
Changes in position and angulatio maxillary incisors
Table V shows findings for crestal alveolar bone levels for both groups obtained from bitewing radiographs. Several trends were evident. For the study group, CEJ-alveolar crest distances were larger (meaning the crestal alveolar bone was further removed from the cementoenamel junction) than values obtained from corresponding control group locations. Distal surface measurements were always larger than mesial surface measurements with the exception of the maxillary first molar in the control group. Measurements were always higher in the maxilla than in the mandible. The CEJalveolar crest dimensions were significantly greater in the study group for the distal aspects of the maxillary first molars, the maxillary premolars, and the mandibular first molars, and the mesial aspect of the mandibular premolar-s. Table VI shows the crestal alveolar bone level measurements obtained from the periapical films of the maxillary and mandibular central incisors. As with the other tooth types, the study group values showed greater crestal alveolar bone level measurements than the cor-
The study group had a greater prevalence of root resorption and displayed significantly greater crestal alveolar bone level distances, indicating greater loss of bone support. These differences were quite small on the average, but nevertheless in certain areas they were statistically significant. An attempt was made to determine whether a relationship existed between changes in the position and angulation of teeth incident to tooth movement and the exhibited tissue loss. Superimposition of the lateral cephalometric tracings failed to show any pattern to changes in axial inclination of the central incisors that was specific to either the study or control. group. Subjects in both groups demonstrated an almost equal distribution of root movements to the Iabial or lingual aspect. This was consistent for both time periods examined (pretreatment through retention and retention through recall). Data for the subjects within each group who had been treated by premolar extraction showed a trend. The severity of root resorption in the maxillary incisor area was higher in those study and control group sub-
Sharp
et al.
Ie WI. Mean positional changes of the maxiliary incisor to point A-pogonion plane Mean
Initial Study
Retention
Control
scores for
to retention
Control
Study
resorption
2.68 3.25
5.27 8.80
1.50 1.55
1.86 4.55
to recall
jects who had undergone extractions as part of orthodontic therapy (Table VII). The translation movement (as measured in millimeters and’ degrees) during the retraction of the maxillary incisors to close spaces was greater in the nonrelapse group. This was true for the treatment period and for the retention to recall period, although it was pronounced in the latter (Table VIII). The mean dimensional changes were less for the maxillary incisors of the relapse subjects when compared with the control or nonrelapse subjects.
The occurrence of root resorption in persons treated orthodontically has been widely reported.4.7.‘“-‘y In this investigation both the study (relapse) and control (nonrelapse) groups had undergone orthodontic treatment, and both groups had experienced root resorption within the range of previous findings.7.‘3.‘7,1*.20The current study was designed (1) to determine whether there were any significant differences in the prevalence, distribution, or severity of root resorption between the relapse and nonrelapse groups, and (2) if differences did exist, to determine whether they bore a relationship to orthodontic relapse. The same answers were sought with respect to the loss of crestal alveolar bone support. Findings showed definite trends for greater reduced root length and alveolar bone support in the relapse group. Many of these trends were statistically significant. The most consistently affected tooth type was the maxillary central incisor, which demonstrated more revalent root resorption, more severe root resorption, and greater reduction of crestal alveolar bone levels in the relapse group. These differences were all statistically significant. In the mandibular anterior region, marked by at least 2 mm of crowding, the central incisors showed significantly less crestal alveolar bone height and the canines showed significantly more severe root resorption in the relapse group. In contrast, prev-
alence of root resorption, severity of root. resorption, and reduction in crestal alveolar bone height were never significantly greater in the nonr~lapse,gro~~, regardless of tooth type. Consequently, findings of the present investigation suggest a possible relationship between reduced periodontal support and orthodontic relapse. In considering such a relationship, the parameters of root length and crestal alveolar bone height were examined because both influence the total area of subcrestal periodontal support available for a tooth. The subcrestal periodontium is considered that part of the periodontium apical to the crest of alveolar bone. It is that portion of the periodontium that would provide stability for the tooth in opposition to the forces responsible for orthodontic relapse-that is, supracrestal fiber retractiorP6 and muscular activity of the tongue and facial musculatures. Therefore, any reduction in subcrestal periodontal support by root resorption, loss of crestal alveolar bone height, or both would presumably enhance the tendency for relapse. The alternative explanation for a rela~ionsbi~ between orthodontic relapse and the parameters of root resorption and crestal alveolar bone loss is that the process of relapse actually produces these two effects. In the case of root resorption, investigators have suggested that resorption stops when active orthodontic treatment is complete. “.‘6-‘E IIowever, studies have not compared precisely the extent of root resorption immediately posttreatment with exte~ided ~osttreatment (recall) time points. Nor have studies examined groups comprised specifically of relapse cases. F~~bermore, continued root resorption following active o~hodo~tic treatment has been reported. “Jo With regard to crestal alveolar bone levels, studies have shown no significant difference when comparing o~bodontically treated and nontreated persons at long-term ~osto~bodontic time points. 6.7,28This suggests that any reduction in crestal alveolar bone levels occurring after o~bodo~tic treatment is not related to the original orthodontic treatment. Once again, however, no evaluation bas been made of persons specifically characterized by o~hodo~tic relapse. The nature of relapse means that the occurrence of tooth movement and the biologic mechanism of tooth movement are the same, regardless of the force (orthodontic or muscular). Therefore, if root reso~t~on and loss of crestal alveolar bone are sequelae of tooth movement under orthodontic forces, it is probably they also occur during the tooth movement of relapse. It may be only that the extent of resorption and cresta! bone loss is modified by the magnitude, directions and duration of relapse forces so that it is not clinically obvious. It is also likely that there has never been a precise comparison of immediate posttreatment levels of root re-
Speciai article tion and crestal alveolar bone with postrelapse levels in a study group comprising marked relapse cases. The findings of this investigation suggest there is a relationship between orthodontic relapse and the parameters of increased root resorption and decreased crestal alveolar bone levels. Such a relationship could be explained by two factors. First, teeth having experienced reduced subcrestal periodontal support through root resorption and/or crestal alveolar bone loss during orthodontic treatment may have a greater disposition toward relapse due to decreased resistance against relapse forces. Second, teeth that relapse may undergo additional root resorption and/or crestal alveolar bone loss during the tooth movement of relapse. It is possible that both of these phenomena contributed in varying degrees to the increased tendency for greater root resorption and greater reduction in crestal alveolar bone found in the relapse group. The distances that teeth were translated were noted to affect the extent of root resorption and crestal bone loss with smaller amounts of tooth translation seemingly more prone to demonstrate tissue loss. This was also observed in the molar region. It was noted that a larger number of subjects exhibiting relapse wore headgear during treatment than was recorded for the nonrelapse group. The effect of the cervical headgear, as used at that time, was primarily to move maxillary molars distally, frequently extruding the distal aspect of the tooth; in other less frequent instances, the molars were tipped distally. In this study there was significantly greater alveolar crest bone loss on the distal aspect of the maxillary molars in the relapse group. One might hypothesize that this may be due to the extrusive effect of the headgear during treatment on the distal aspect of the molar or to pressure in the distally located alveolar crest incident to distal tipping of the upper molar. In the former case, extrusion of the distal root of the upper molar could account for the larger CEJ-alveolar crest distances in that area. In the latter case, distal tipping against the second molar may have caused some distal alveolar crest resorption accounting for greater CEJ-alveolar crest distances on tbe distal aspect of the upper molar. In either instance, the indications are that care must be taken in distal molar movement under headgear therapy. The retrospective nature of this investigation imposed limitations that must be emphasized in the interpretation of results. Sample selection was dictated by the availability of complete records and the absence of root resorption prior to treatment. This resulted in some differences between the study and control groups. For example, the mean age of the control group was
1.4 years older than that of the study group at tine initiation of treatment; the mean duration of ~eatrn~nt was 11.8 months less for the control group. The age difference may be significant because a link has been suggested between resorption and age of treatment anset.18*27At the same time, longer treatment may be associated with more root resorption. Another consideration is that longer treatment time may reflect more severe malocclusion and/or different treatment mechanics. In turn, relapse may be related to the extent and/or mechanics of tooth movement required to correct more severe malocclusions. A further limitation exists in the absence of data at the completion of active treatment. Thus, it is not clear what portion of the root length and crestal alveolar bone changes took place during active treatment and what portion occurred during the posttreatment relapse period. Despite certain limitations within a retrospective study design, the current investigation suggests that, among many other factors, relapse tendencies might be correlated with tissue loss. As a group, patients exhibiting relapse were found to have more extensive alveolar crest loss, which would reduce periodontal support because numbers of fibers predominate in the crestal region. Furthermore, they were found to exhibit more extensive apical root resorption; this too would reduce periodontal fiber support although probably not in the greater numbers to be found in the crestal region. Surprisingly, these were correlated with the less extensive tooth movement. It goes without saying that crestal bone loss and apical root resorption should be avoided as much as possible because of their effects on loss af periodontal support. This may be helpful in reducing the expression of relapse following o~hod~~tic correction. REFERENCES 1. Riedel R. A review of the retention problem. AM J ORTWD 1960;30:179-99. 2. Thurow RC. Edgewise orthodontics. 2nd ed. St. Louis: The C. V Mosby Company, 1966:2X&74. 3. Carriere .I. Retention: Concepts and clinical implications. In: Cook J, ed. Transactions of the third international orthodontic congress. St. Louis: The C. V. Mosby Company, 1975:524-7. 4. Ketcham AH. 1. A preliminary report of an investigation of apical root resorption of permanent teeth. Int J Ortho Oral Surg Radiog 1927;13:97-127. 5. Sjolien T, Zachrisson B. Periodontal bone support and tooth length in orthodontically treated and untreated persons. Ard J ORTHOD 1973;64:28-37. 6. Zachrisson BU, Alnaes L. Periodontal condition in orthodontically treated and untreated individuals. II. Alveolar bone loss: Radiographic findings. Angle Orthod 1974;44:48-55. 7. Hollender L, Ronnerman A, Thilander B. Root resorption, marginal bone support and clinical crown length in orthodontically treated patients. Eur J Orthod 1980;2: 197-205.
Sharge et al.
8. Little R. The irregularity index: A quantitative score of mandibular anterior alignment. AM .I ORTHOD 1975;68:554-63. 9. Rinn Corporation. Utilization of the extension cone paralleling, bisecting angle and interproximal techniques with Rinn instruments. Elgin, Illinois: Rinn Carp, 1975:10-33. 10. Baxter DH. The effect of orthodontic treatment on alveolar bone adjacent to the cemento-enamel junction. Angle Orthod 1967; 373541. 11. Reed BE, Polson AM. Relationships between bitewing and periapical radiographs in assessing crestal alveolar bone levels. J Periodontol 1984;55:22-7. 12. Polson AM, Reed BE. Long-term effect of orthodontic treatment on crestal alveolar bone levels. J Periodontol 1984;55:28-34. 13. DeShields R. A study of root resorption in treated Class II, Division I malocclusions. Angle Orthod 1969;39:23 I-45. 14. VonderAhe G. Post-retention status of maxillary incisors with root end resorption. Angle Orthod 1973;43:247-55. 15. Newman W. Possible etiologic factor in external root resorption. AM J ORTHOD
1975;67:522-39.
16. Rygh P. Orthodontic root resorption studies by electron microscopy. Angle Orthod 1977;47:1-16. i7. Ronnerman A, Larsson E. Overjet, overbite, intercanine distance and root resorption in orthodontically treated patients. Swed Dent J 1981;5:21-7. 18. Linge B, Linge L. Apical root resorption in upper anterior teeth. Eur J Orthod 1983;5:173-83. 19. Mattison G. Orthodontic external root resorption-endodontic considerations. J Endod 1983;9:253-6. 20. Phillips J. Apical root resorption under orthodontic therapy. Angle O\Thod 1955;25:1-22.
21. Reitan K. Clinical and histologic observations ment during and after orthodontic treatment.
on tooth moveAiw J ORTHQD
1967;53:721-45.
22.
Edwards J. A study of the periodontium during orthodontic rotation of teeth. AM J ORTHOD 1968;54:441-61. 23. Reitan K. Biomechanical principles and reactions. In: Graber TM, ed. Current orthodontic concepts and techniques. Philadelphia: WB Saunders Co, 1969:chap 2. 24. Edwards J. A surgical procedure to eliminate rotational relapse. Ah! J ORTHOD 1970;57:35-46. 25. Strahan J, Mills J. A preliminary report on the severing of gingival fibres following rotation of teeth. Dent Pratt 1970;21: 101-2. 26. Boese L. Fiberotomy and reproximation without lower retention 9 years in retrospect. Part II. Angle C&hod 1980;50: 169-78. 27. Goldson L, Hendrikson C. Root resorption during Begg treatment: A longitudinal roentgeno:ogic study. AM J ORTHOD 1975;68:55-66.
28.
Hamp S, Lundstrom F, Nyman S. Periodontal conditions in adolescents subjected to multiband orthodontic treatment with controlled oral hygiene. Eur J Orthod 1982;4:77-86.
Reprint requests to: Dr. J. Daniel Subtelny Eastman Dental Center 625 Elmwood Ave. Rochester, NY 14620
TICLE
orztic r+elapse, apical Too ~e~o~~~io~~ Eveolar bone levels endy Sharpe, D.D.S., Brian Reed, D.D.S., MS., .I. ADan Poison, D.D.S., MS. Rochester,
N. Y.
This investigation examined the relationship of postorthodontic treatment relapse to crestal alveoIar bone support and root resorption. Thirty-six persons having completed the retention phase of orthodontics at least IO years earlier were divided into two groups based on the amount of relapse crowding of the mandibular anterior teeth. Eighteen subjects (relapse group) exhibited 2 mm or more of mandibular anterior relapse crowding and 18 subjects (nonrelapse group) exhibited no mandibular anterior relapse crowding. At time of recall, full-mouth series of periapical and bitewing r~di~~ra~hs were obtained as well as lateral cephalometric films to ailow comparison with similar iateral cephalometric films obtained at pretreatment and retention time points. The radiographs were examined to assess three parameters: root resorption, crestal alveolar bone levels, and changes in the position and angulation of the maxillary incisors. The subjects in the relapse group had ~~derg~n~ longer periods of treatment and exhibited a greater prevalence of root resorption; they also ~~s~~~y~d significantly greater crestal alveolar bone level distances, indicating greater loss of bone support than that observed in the nonrelapse group. The distances that teeth were translated seemed to affect the extent of root resorption and crestal bone loss with smaller amounts of tooth translation seemingly more prone to demonstrate tissue loss, The findings of lhis investigation suggest may be a relationship between orthodontic relapse and the parameters of increased rout re and decreased crestal alveolar bone levels. (AM J ORTHOD DENTOFAC ORTHOP 1987; ey words: Orthodontic
treatment, postretention, relapse, root resorption, alveolar crest loss
osttreatment relapse of corrected tooth positions is a major conce’m in orthodontic treatment.lm3 A periodontium incorporating adequate root length and bone support has been stated to be an important factor in the maintenance of posttreatment stability. ‘.’ Reduction of crestal alveolar bone support and reduction of root length by root resorption, however, have both been reported as sequelae of orthodontic treatment.4-7 Consequently, it was the purpose of this investigation to examine the relationship between posttreatment relapse and the parameters of crestal alveolar bone support and root resorption. ~AT~~iA~S AND METHODS The subjects in the study sample consisted of 36 persons who had completed the retention phase of orthodontic treatment at least 10 years earlier. Subjects were selected on the basis of the availability of complete records and the absence of root resorption prior to treatment. Plaster casts were used to divide these persons This study was supported in part by National Institute for Dental Research Grant DE82413 and is partial fulfiibnent for a certificate of proficiency. Ohiodontic Department, Eastman Dental Center, Rochester, N.Y., 1984.
into study and control groups on the basis of the amount of relapse crowding of the mandibular anterior teeth8 The study group (relapse group) consisted of I8 persons with 2 mm or more of mandibular anterior relapse crowding. The control group (nonrelapse group) comprised 18 persons with no mandibular anterior relapse crowding. Because of the limited number of subjects satisfying these criteria, it was not possible to match subjects for other factors. The resulting sex distribution and pretreatment malocclusion djs~~b~tio~ for the study and control groups are shown in Table I. In the study group, the mean age at treatment initiation was 11.3 years, the mean duration of treatment was 43.3 months, and the mean age at recall was 29.0 years. The respective figures for the control group were 12.7 years, 3 1.5 months, and 28.7 years. Trcatrn~~~ in the study group included extraction for IQ persons; in the control group, I1 persons were treated by extraction. The medical history was noncontributory for all subjects. At the time of recall (at least 10 years postretention), a full-mouth series of periapical and bitewing radiographs was obtained for each subject. radiographs were completed by means of the long-cone Fara~~e~ingtechnique.’ Exposure and processing of the films were per-
Speciai at-tick
formed undes standardized conditions. In addition, lateral cephalometric films were obtained at recall to allow comparison with similar lateral cephalometric films obtained at pretreatment and retention time points. The radiographs were examined to assess three parameters: root resorption, crestal alveolar bone levels, and changes in position and angulation of the maxillary incisors. %reeorpt~o~ Periapicai radiographs for each individual were scored by one examiner on an illuminated x-ray viewer using direct vision. The roots of the maxillary and mandibular central incisors, canines and first molars were scored according to the following criteria: 0 = No aFica1root resorption i = Slight blunting of the root apex ?. = Moderate blunting of the root apex up to one fourth of the root length 3 = Excessive blunting of the root apex beyond one fourth of the root length A total of 323 roots were assessed in the study group and 324 in the control group. The resuiting data were examined to determine: I. The number of subjects in each group with at least one tooth exhibiting apical root resorption 2. The prevalence of apical root resorption relative to six tooth types: maxillary central incisors, maxillary canines, maxillary first molars, mandibular central incisors, mandibular canines, and mandibular first molars 3. The severity of root resorption relative to group and tootb type A resorption score was determined for each subject by adding the resorption scores for all of the teeth examined. A mean group resorption score was then calculated using the sum of the scores for the 18 subjects within each of the groups. In addition, the mean resorption scores were calculated for each tooth type using the sum of resorption scores for the particular tooth type and the number of teeth of that type examined. This was done separately for the study and control groups. Student’s t test was performed to determine whether a statistically significant difference existed between the means at the P < 0.05 level of significance. Inter- and intragroup differences were examined.
Crestai alveolar bone levels were determined by a single examiner by measuring the distance between the cementoenamel junction (CEJ) of the tooth and the crest of the alveolar bone”.‘0-12with a plastic millimeter ruler. Bitewing radiographs were used to assess the inter-
Table I. Distribution of sample 1 Study (N = 18)
j Cnmroi
(N = 181
sex Male Female Angle classzjkation Class I 1 Class II, Division Class II, Division 2 Class III
12 6
5 13
II
s 7 2 1
5 I I
proximal tooth surfaces from the distal of the canine to the distal of the first molar. Periapical radiographs were used to assessthe mesial surface of the central incisors. Each radiograph was projected with a magnification factor of x 9.1 onto a white surface to facilitate measuring. The measured values were then reduced by the 9.1 magnification factor to give true vaiues for the cementoenamel junction to alveolar crest distances. The mean CEJ-alveofar crest distance was determined for each tooth surface examined (mesial of central incisors, distal of canines, mesial and distal of premolars, mesial and distal of first molars) in both the study and control groups. Student’s t test was performed to determine whether there were statistically significant differences between the groups. Intra- and intergrotip differences were examined. Changes in position and angulation maxillary incisors
of t
The same examiner compared tracings of the lateral cephalometric films for two time intervals-namely, pretreatment to retention and retention to recaii. Tracacings were superimposed along the palatal plane, registering at the anterior nasal spine. Changes in the position and anguiation of the upper incisor to the point A pogonion plane were determined in millimeters and degrees. This was done to investigate the correlation between direction and degree of incisal movement with apical root resorption and changes in crestal alveolar bone levels. RESULTS Root resorption As previously mentioned, the extent of root resorption was determined by measurements attained from radiographic films. The errors in the radiographic parameters were assessed by replicate measurements using previously described techniques”,” and were found to be within the 5% to 9% range. The number of subjects displaying root resorption on at least one tooth was high for both the study (16 of 18 subjects) and the
MUXillU Central incisors Canines Mesiobuccal root-first molars Bistobuccal root-first molars Palatal root-first molars Mandible Central incisors Canines Mesial root-first molars Distal root-first molars Total Maxillary Mandibular COMBINED MAXILLARY
AND MANDIBULAR
19136 3136 7136 9136 0136
52.7 8.3 19.4 25.0 0
1 i/36 2/36 i/36 2136 0136
30.4 5.6 2.8 5.6 0
16135 5136 0136 6136
45.7 13.9 0 16.7
17136 3136 1136 6136
47.2 8.3 8.3 16.7
381180 271143 651323
21.1 18.9 20.1
161180 271144 431324
8.9 18.8 13.3
Table
Table 111.Severity of root resorption at recall
IV. Patients’ resorption scores
Total Mean Range Maxilla Central incisors Canines Max. 6 Mesiobuccal root Distobuccal root Palatal root Mandible Central incisors Canines Mand. 6 Mesial root Distal root
0.94 0.83
0.18 0.05
0.50 0.11
0.15” 0.07
0.44 0.51 0.00
0.16 0.12 0.00
0.03 0.19 0.00
0.03* 0.14* 0.00
0.60 0.36
0.12 0.18
0.56 0.08
0.11 0.05*
0.00 0.25
0.00 0.10
0.06 0.38
0.05 0.15
-
*T test P < 0.05.
control (15 of 18) groups. The presence of root resorption was greater in the study group because of a greater prevalence of root resorption in the maxillary arch of the study group (Table II). The prevalence of root resorption in the mandibular arch was similar in both groups. Data for the specific tooth types showed that the highest prevalence of root resorption occurred for the maxillary and mandibular central incisors (Table II). In addition, the maxillary central incisors showed the greatest intergroup difference. The first molars in both arches for both groups showed the next greatest prevalence of resorption, followed by the canines. The distal
112 6.22 o-22
64 3.55 o-12
buccal root of the maxillary molars and the distal root of the mandibular molars displayed more resorption than their corresponding mesial roots. This trend was most marked in the mandibular molars. Root resorption was not observed on the palatal roots of the maxillary molars in either group. For all other roots in the maxillary arch, the study group always showed a greater prevalence of root resorption. This was statistically significant for the central incisors and buccal roots of the first molars. On the other hand, in the mandibular arch only the canines demonstrated more prevalent root resorption in the study group; this difference was not statistically significant. Table III gives findings for the severity of root resorption. The severity of root resorption was significantly greater in the study group for the maxillary central incisors, buccal roots of the maxillary molars, and mandibular canines. The mandibular central incisors also showed a greater numerical severity of root resorption in the study group, but the difference was not significant. None of the tooth types showed significantly greater resorption severity witllin the control group. The mean resorption score per subject (6.22) was almost twice as high in the study group compared with the control group (3 55) (Table IV).
wume
91
Special articie
Number 3
le V. Crestal alveolar bone levels-data
derived from bitewing radiographs
Maxilla First molars Premolars Canines iMandible First molars Premolars Canines *Significant
at the P < 0.05 level.
Table VI. Crestal alveolar bone levels-Data derived from periapical radiographs
Maxilla Central
incisors
Table VII. Severity of root resorption (maxillary central incisors) in extraction and nonextraction cases
1.51
0.09”
1.25
0.09
1.50
0.08*
1.27
0.08
Study Control
0.950 0.795
0.937 0.566
Mandible Central *Significantly
incisors greater,
P < 0.05.
responding control group values. This was statistically significant at the 0.05 level.
Alveolar crest levels
Changes in position and angulatio maxillary incisors
Table V shows findings for crestal alveolar bone levels for both groups obtained from bitewing radiographs. Several trends were evident. For the study group, CEJ-alveolar crest distances were larger (meaning the crestal alveolar bone was further removed from the cementoenamel junction) than values obtained from corresponding control group locations. Distal surface measurements were always larger than mesial surface measurements with the exception of the maxillary first molar in the control group. Measurements were always higher in the maxilla than in the mandible. The CEJalveolar crest dimensions were significantly greater in the study group for the distal aspects of the maxillary first molars, the maxillary premolars, and the mandibular first molars, and the mesial aspect of the mandibular premolar-s. Table VI shows the crestal alveolar bone level measurements obtained from the periapical films of the maxillary and mandibular central incisors. As with the other tooth types, the study group values showed greater crestal alveolar bone level measurements than the cor-
The study group had a greater prevalence of root resorption and displayed significantly greater crestal alveolar bone level distances, indicating greater loss of bone support. These differences were quite small on the average, but nevertheless in certain areas they were statistically significant. An attempt was made to determine whether a relationship existed between changes in the position and angulation of teeth incident to tooth movement and the exhibited tissue loss. Superimposition of the lateral cephalometric tracings failed to show any pattern to changes in axial inclination of the central incisors that was specific to either the study or control. group. Subjects in both groups demonstrated an almost equal distribution of root movements to the Iabial or lingual aspect. This was consistent for both time periods examined (pretreatment through retention and retention through recall). Data for the subjects within each group who had been treated by premolar extraction showed a trend. The severity of root resorption in the maxillary incisor area was higher in those study and control group sub-
Sharp
et al.
Ie WI. Mean positional changes of the maxiliary incisor to point A-pogonion plane Mean
Initial Study
Retention
Control
scores for
to retention
Control
Study
resorption
2.68 3.25
5.27 8.80
1.50 1.55
1.86 4.55
to recall
jects who had undergone extractions as part of orthodontic therapy (Table VII). The translation movement (as measured in millimeters and’ degrees) during the retraction of the maxillary incisors to close spaces was greater in the nonrelapse group. This was true for the treatment period and for the retention to recall period, although it was pronounced in the latter (Table VIII). The mean dimensional changes were less for the maxillary incisors of the relapse subjects when compared with the control or nonrelapse subjects.
The occurrence of root resorption in persons treated orthodontically has been widely reported.4.7.‘“-‘y In this investigation both the study (relapse) and control (nonrelapse) groups had undergone orthodontic treatment, and both groups had experienced root resorption within the range of previous findings.7.‘3.‘7,1*.20The current study was designed (1) to determine whether there were any significant differences in the prevalence, distribution, or severity of root resorption between the relapse and nonrelapse groups, and (2) if differences did exist, to determine whether they bore a relationship to orthodontic relapse. The same answers were sought with respect to the loss of crestal alveolar bone support. Findings showed definite trends for greater reduced root length and alveolar bone support in the relapse group. Many of these trends were statistically significant. The most consistently affected tooth type was the maxillary central incisor, which demonstrated more revalent root resorption, more severe root resorption, and greater reduction of crestal alveolar bone levels in the relapse group. These differences were all statistically significant. In the mandibular anterior region, marked by at least 2 mm of crowding, the central incisors showed significantly less crestal alveolar bone height and the canines showed significantly more severe root resorption in the relapse group. In contrast, prev-
alence of root resorption, severity of root. resorption, and reduction in crestal alveolar bone height were never significantly greater in the nonr~lapse,gro~~, regardless of tooth type. Consequently, findings of the present investigation suggest a possible relationship between reduced periodontal support and orthodontic relapse. In considering such a relationship, the parameters of root length and crestal alveolar bone height were examined because both influence the total area of subcrestal periodontal support available for a tooth. The subcrestal periodontium is considered that part of the periodontium apical to the crest of alveolar bone. It is that portion of the periodontium that would provide stability for the tooth in opposition to the forces responsible for orthodontic relapse-that is, supracrestal fiber retractiorP6 and muscular activity of the tongue and facial musculatures. Therefore, any reduction in subcrestal periodontal support by root resorption, loss of crestal alveolar bone height, or both would presumably enhance the tendency for relapse. The alternative explanation for a rela~ionsbi~ between orthodontic relapse and the parameters of root resorption and crestal alveolar bone loss is that the process of relapse actually produces these two effects. In the case of root resorption, investigators have suggested that resorption stops when active orthodontic treatment is complete. “.‘6-‘E IIowever, studies have not compared precisely the extent of root resorption immediately posttreatment with exte~ided ~osttreatment (recall) time points. Nor have studies examined groups comprised specifically of relapse cases. F~~bermore, continued root resorption following active o~hodo~tic treatment has been reported. “Jo With regard to crestal alveolar bone levels, studies have shown no significant difference when comparing o~bodontically treated and nontreated persons at long-term ~osto~bodontic time points. 6.7,28This suggests that any reduction in crestal alveolar bone levels occurring after o~bodo~tic treatment is not related to the original orthodontic treatment. Once again, however, no evaluation bas been made of persons specifically characterized by o~hodo~tic relapse. The nature of relapse means that the occurrence of tooth movement and the biologic mechanism of tooth movement are the same, regardless of the force (orthodontic or muscular). Therefore, if root reso~t~on and loss of crestal alveolar bone are sequelae of tooth movement under orthodontic forces, it is probably they also occur during the tooth movement of relapse. It may be only that the extent of resorption and cresta! bone loss is modified by the magnitude, directions and duration of relapse forces so that it is not clinically obvious. It is also likely that there has never been a precise comparison of immediate posttreatment levels of root re-
Speciai article tion and crestal alveolar bone with postrelapse levels in a study group comprising marked relapse cases. The findings of this investigation suggest there is a relationship between orthodontic relapse and the parameters of increased root resorption and decreased crestal alveolar bone levels. Such a relationship could be explained by two factors. First, teeth having experienced reduced subcrestal periodontal support through root resorption and/or crestal alveolar bone loss during orthodontic treatment may have a greater disposition toward relapse due to decreased resistance against relapse forces. Second, teeth that relapse may undergo additional root resorption and/or crestal alveolar bone loss during the tooth movement of relapse. It is possible that both of these phenomena contributed in varying degrees to the increased tendency for greater root resorption and greater reduction in crestal alveolar bone found in the relapse group. The distances that teeth were translated were noted to affect the extent of root resorption and crestal bone loss with smaller amounts of tooth translation seemingly more prone to demonstrate tissue loss. This was also observed in the molar region. It was noted that a larger number of subjects exhibiting relapse wore headgear during treatment than was recorded for the nonrelapse group. The effect of the cervical headgear, as used at that time, was primarily to move maxillary molars distally, frequently extruding the distal aspect of the tooth; in other less frequent instances, the molars were tipped distally. In this study there was significantly greater alveolar crest bone loss on the distal aspect of the maxillary molars in the relapse group. One might hypothesize that this may be due to the extrusive effect of the headgear during treatment on the distal aspect of the molar or to pressure in the distally located alveolar crest incident to distal tipping of the upper molar. In the former case, extrusion of the distal root of the upper molar could account for the larger CEJ-alveolar crest distances in that area. In the latter case, distal tipping against the second molar may have caused some distal alveolar crest resorption accounting for greater CEJ-alveolar crest distances on tbe distal aspect of the upper molar. In either instance, the indications are that care must be taken in distal molar movement under headgear therapy. The retrospective nature of this investigation imposed limitations that must be emphasized in the interpretation of results. Sample selection was dictated by the availability of complete records and the absence of root resorption prior to treatment. This resulted in some differences between the study and control groups. For example, the mean age of the control group was
1.4 years older than that of the study group at tine initiation of treatment; the mean duration of ~eatrn~nt was 11.8 months less for the control group. The age difference may be significant because a link has been suggested between resorption and age of treatment anset.18*27At the same time, longer treatment may be associated with more root resorption. Another consideration is that longer treatment time may reflect more severe malocclusion and/or different treatment mechanics. In turn, relapse may be related to the extent and/or mechanics of tooth movement required to correct more severe malocclusions. A further limitation exists in the absence of data at the completion of active treatment. Thus, it is not clear what portion of the root length and crestal alveolar bone changes took place during active treatment and what portion occurred during the posttreatment relapse period. Despite certain limitations within a retrospective study design, the current investigation suggests that, among many other factors, relapse tendencies might be correlated with tissue loss. As a group, patients exhibiting relapse were found to have more extensive alveolar crest loss, which would reduce periodontal support because numbers of fibers predominate in the crestal region. Furthermore, they were found to exhibit more extensive apical root resorption; this too would reduce periodontal fiber support although probably not in the greater numbers to be found in the crestal region. Surprisingly, these were correlated with the less extensive tooth movement. It goes without saying that crestal bone loss and apical root resorption should be avoided as much as possible because of their effects on loss af periodontal support. This may be helpful in reducing the expression of relapse following o~hod~~tic correction. REFERENCES 1. Riedel R. A review of the retention problem. AM J ORTWD 1960;30:179-99. 2. Thurow RC. Edgewise orthodontics. 2nd ed. St. Louis: The C. V Mosby Company, 1966:2X&74. 3. Carriere .I. Retention: Concepts and clinical implications. In: Cook J, ed. Transactions of the third international orthodontic congress. St. Louis: The C. V. Mosby Company, 1975:524-7. 4. Ketcham AH. 1. A preliminary report of an investigation of apical root resorption of permanent teeth. Int J Ortho Oral Surg Radiog 1927;13:97-127. 5. Sjolien T, Zachrisson B. Periodontal bone support and tooth length in orthodontically treated and untreated persons. Ard J ORTHOD 1973;64:28-37. 6. Zachrisson BU, Alnaes L. Periodontal condition in orthodontically treated and untreated individuals. II. Alveolar bone loss: Radiographic findings. Angle Orthod 1974;44:48-55. 7. Hollender L, Ronnerman A, Thilander B. Root resorption, marginal bone support and clinical crown length in orthodontically treated patients. Eur J Orthod 1980;2: 197-205.
Sharge et al.
8. Little R. The irregularity index: A quantitative score of mandibular anterior alignment. AM .I ORTHOD 1975;68:554-63. 9. Rinn Corporation. Utilization of the extension cone paralleling, bisecting angle and interproximal techniques with Rinn instruments. Elgin, Illinois: Rinn Carp, 1975:10-33. 10. Baxter DH. The effect of orthodontic treatment on alveolar bone adjacent to the cemento-enamel junction. Angle Orthod 1967; 373541. 11. Reed BE, Polson AM. Relationships between bitewing and periapical radiographs in assessing crestal alveolar bone levels. J Periodontol 1984;55:22-7. 12. Polson AM, Reed BE. Long-term effect of orthodontic treatment on crestal alveolar bone levels. J Periodontol 1984;55:28-34. 13. DeShields R. A study of root resorption in treated Class II, Division I malocclusions. Angle Orthod 1969;39:23 I-45. 14. VonderAhe G. Post-retention status of maxillary incisors with root end resorption. Angle Orthod 1973;43:247-55. 15. Newman W. Possible etiologic factor in external root resorption. AM J ORTHOD
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16. Rygh P. Orthodontic root resorption studies by electron microscopy. Angle Orthod 1977;47:1-16. i7. Ronnerman A, Larsson E. Overjet, overbite, intercanine distance and root resorption in orthodontically treated patients. Swed Dent J 1981;5:21-7. 18. Linge B, Linge L. Apical root resorption in upper anterior teeth. Eur J Orthod 1983;5:173-83. 19. Mattison G. Orthodontic external root resorption-endodontic considerations. J Endod 1983;9:253-6. 20. Phillips J. Apical root resorption under orthodontic therapy. Angle O\Thod 1955;25:1-22.
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Edwards J. A study of the periodontium during orthodontic rotation of teeth. AM J ORTHOD 1968;54:441-61. 23. Reitan K. Biomechanical principles and reactions. In: Graber TM, ed. Current orthodontic concepts and techniques. Philadelphia: WB Saunders Co, 1969:chap 2. 24. Edwards J. A surgical procedure to eliminate rotational relapse. Ah! J ORTHOD 1970;57:35-46. 25. Strahan J, Mills J. A preliminary report on the severing of gingival fibres following rotation of teeth. Dent Pratt 1970;21: 101-2. 26. Boese L. Fiberotomy and reproximation without lower retention 9 years in retrospect. Part II. Angle C&hod 1980;50: 169-78. 27. Goldson L, Hendrikson C. Root resorption during Begg treatment: A longitudinal roentgeno:ogic study. AM J ORTHOD 1975;68:55-66.
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