Loss of root length and crestal bone height before and during treatment in adolescent and adult orthodontic patients Edward F. Harris, PhD, and William C. Baker, DDS Memphis, Tenn. It is broadly documented that orthodontic tooth movement enhances the risk of apical root resorption and loss of alveolar crestal bone height, but virtually all studies have focused on the conventional adolescent patient. In this study, samples from adolescent and adult patients were matched for sex, malocclusion, and treatment regimen. In-treatment changes in root length were the same for both groups, whereas loss of crestal bone height was somewhat greater in adults. Major differences, however, were found at the start of treatment: Adults (x = 28 years) had significantly shorter roots and greater alveolar recession than the young teenagers (~ = 12 years). Consequently, treatment per se does not place adults at greater risk; it is the involvement extant at the start of mechanotherapy that merits careful evaluation. (AMJ ORTHOD DENTOFACORTHOP 1990;98:463-9.)

I t has long been observed that the repositioning of teeth by orthodontic treatment can lead to loss of root length and/or decrease in alveolar crestal bone height) "7 To the practitioner's benefit, these changes typically are minor in the majority of patients, and the esthetic and functional benefits of treatment readily outweigh the minor risk of these iatrogenic changes. Moreover, it should not go unrecognized that both of these conditions--root blunting and loss of alveolar crestal height--progress with age if not treated. As outlined by Massler and Perreault, s and more recently by Moyers, 9 root resorption also occurs as a normal function of aging in permanent teeth under perfectly normal conditions. These considerations take on additional relevance when viewed in the context of the changing demographics of the typical orthodontic practice: a greater proportion of adults is now seeking orthodontic treatment)°'" Since it is well established that bone remodeling occurs at a slower pace in adults, largely as a function of reduced osteoblastic activity, ~2 a comparison between the responses to orthodontic treatment of matched sets of adults and adolescents is worthwhile. One possible finding is that the adults (typically younger adults, in their 20s and 30s) have the same changes in alveolar bone and tooth root lengths as do adolescents. Alternatively, and for a variety of reasons, adults may From the Department of Orthodontics, College of Dentistry, The Health Sciences Center, University of Tennessee. 811116430

well constitute a distinct subgroup. The fact that adults are no longer growing may increase the tooth-to-bone changes required to correct malocclusion. '3,t4 It also is known, for example, that initiation of tooth movement is slower in adults but, once started, appears to progress at a fairly rapid rate. ~-t7 On the other hand, Alexander ts has suggested that, because of greater bone density in adults, it can be difficult to achieve the extent of tooth movement often seen in adolescents. The histologic picture also differs. The periodontal tissues in adults are largely quiescent. Alveolar structures are composed of dense lamellated bone, with fewer openings and clefts into the marrow spaces, and the spaces are smaller and less cellular) s't~'t9 Both cell populations and vascularization are reduced in the adult periodontal ligament and alveolar process, and there is a decreased ratio of ground substance to collagen in the PDL as well, with fewer fibroblasts, osteoblasts, and cementoblasts. 2° The increased mineralization of adult bone coincides with a decrease in osteoid tissue. Taken together, these features result in a longer hyalinization phase in adults as well as a longer mobilization phase for actual orthodontic movement.~9"2x A broad spectrum of other changes has been documented for bones outside the craniofacial complex, -'226 but it is not clear how closely changes in alveolar bone parallel these ageprogressive patterns. 27"3°In sum, however, several lines of evidence suggest that adult patients may respond differently to the conventional regimen of full-banded orthodontic treatment than adolescent patients. 463

464

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Harris and Baker

ships by the end of active treatment. All patients were treated by one experienced orthodontist, who used 10-2 directional-force mechanics. 33 All patients in the study also had four premolars extracted to correct their malocclusions. The sample was restricted to female patients, partly to constrain the intersex variability in root dimensions 3~ but, more important, because women are far more likely than men to seek orthodontic treatment. None of these cases had been treated previously.

Measurement techniques

Fig. 1. Schematic drawing of mandibular molar assessment. The measurement of alveolar crestal bone height was taken parallel with the long axis of the tooth from the cemento-enamel junction to Z point."°

We report here on an assessment of changes in adolescent versus adult orthodontic patients, all of whom received the same regimen of mechanotherapy. Changes in the root lengths of selected teeth and of alveolar crestal bone height are compared in the two age groups.

MATERIALS AND METHODS Sample selection A major orthodontic problem in Europe and the Americas is the Class II molar relationship. 3~'32Records of the 59 orthodontic patients (29 adolescents, 30 adults) that we selected for the study met the following six rather stringent criteria for homogeneity: (1) all patients had a Class II sagittal molar relationship of at least a one-half cusp discrepancy bilaterally, as determined from the dental casts; (2) all had a Division I incisor angulation; (3) all were females; (4) standardized pretreatment and posttreatment lateral cephalograms and panoramic radiographs were available for each; (5) each had a full complement of permanent teeth, except for third molars, at the start of treatment; and (6) each had Class I molar and canine relation-

Paired pretreatment and posttreatment measurements were taken of the root lengths of five teeth for each patient: the central incisor, canine, and first molar (longest distal root) in the maxilla and the canine and first molar (distal root) in the mandible. Measurements of the incisor and canines were taken from the standardized lateral cephalogram according to the method of Copeland and Green. 35They were corrected for magnification, which averaged 6%. Molar root lengths were measured from panoramic radiographs according to the method of ~gaard 36 and Reed et al. 37 Selected trials were assessed for enlargement by means of radiopaque millimetric grids (ADA Products Inc., Milwaukee, Wis.) attached to the lingual surfaces of the molars during the exposure, with the magnification factor averaging 1.03. Measurements were made on the radiographs with Max-Cal electronic calipers (Fowler Tools, Boston, Mass.) interfaced to a microcomputer. All radiographs were made on the same cephalometric and panoral machines. Visual assessment of the root morphology was also used to categorize the degree of blunting into one of five ordinal stages, according to the descriptions of Levander and Malmgren: 38 0 - - N o discernible erosion or blunting and complete apexification. 39 1--Irregular root, contour, notably para-apically. 2 - - R o o t blunting with minor resorption. 3 - - S e v e r e root resorption having decreased the length between one fifth and one third of the original length. 4 - - E x t r e m e resorption exceeding one third of the original length. Alveolar crestal bone height was measured at two sites, the facial aspect of the maxillary central incisor and the distal aspect of the lower first molar following the method of Baxter ~° to obtain the distance from the cementoenamel junction (CEJ) to the highest point on the alveolus immediately distal to the tooth (termed the Z point, Fig. 1).

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465

Table I. Means and standard errors, by age grade and tests, for differences in central tendencies among adolescents (n = 29) and adults (n = 30) Adults

Adolescents Variable* Time in treatment Pretreatment status Maxillary Ii root length Maxillary C root length Maxillary MI root length Mandibular C root length Mandibular M I root length MaxiUary I1 facial bone height Maxillary M 1 distal bone height Posttreatment status Maxillary I1 root length Maxillary C root length Maxillary M I root length Mandibular C root length Mandibular MI root length Maxillary I1 facial bone height Maxillary M I distal bone height

SE

7c

SE

Difference of meanst

F ratio

2.5

0.072

2.5

0.062

- 0.08

0.7

27.5 29.8 23.5 26.4 27.2 0.8 0.7

0.358 0.598 0.346 0.534 0.465 0.100 0.097

25.6 29.7 23.2 25.4 26.0 1.2 1. I

0.420 0.506 0.482 0.551 0.368 0.80 0.128

1.95 0.20 0.29 1.02 1.20 -0.43 - 0.42

12.6:[: 0. I 0.2 1.8 4.1 :[: 10.81: 6.9:1:

26.0 28.8 22.4 25.7 26.2 0.8 0.9

0.299 0.505 0.341 0.446 0.443 0.093 0.078

24.2 28.8 22.4 23.9 25.3 1.4 1.7

0.414 0.413 0.476 0.440 0.371 0.150 0.152

1.75 0.08 0.03 1.75 0.93 -0.64 - 0.85

11.9~t 0.0 0.0 7.8:1: 2.5 13.6:[: 25.3:[:

x

Central incisor (II), canine (C), and first molar (M1). tAdolescent-minus-adult means calculated before rounding for tabulation.

,p < 0.05.

Table II. Descriptive statistics of in-treatment changes (mm) and tests for differences between adolescent (n = 29) and adult (n = 30) patients Adolescents Variable Maxillary I1 root length Maxillary C root length Maxillary MI root length Mandibular C root length Mandibular MI root length Maxillary I1 facial bone height Maxillary MI distal bone height

Adults

x

SE

x

SE

Difference of means

F ratio

- 1.6" - 1.0" - 1. I -0.7* - 1.0' 0.0 0.2

0.239 0.284 0.182 0.331 0.169 0.141 0.111

- 1.4" - 0.9* - 0.8* - 1.5* -0.9* 0.2 0.6*

0.173 0.250 0.166 0.325 0.214 0.145 0.105

-0.20 - 0.13 - 0.32 0.83 -0.14 - 0.21 - 0.42

0.4 0. I 1.6 3.2 0.3 1. I 7.3*

*p < 0.05 for the two-tail test Ho:~ = 0.

Patient age Intervals All adolescents in this series were between 10.6 and 14.1 years of age, with a mean of 12.5 +_. 0.80 years, when initial records were taken. Adult patients ranged from 20.0 to 40.0 years, with a mean of 27.9 _ 5.3 years.

as changes during treatment. The univariate repeatedmeasures analysis of variance model (which is deterministically the same as a pairing design t test) was used to assess in-treatment changes in each variable, a4 The ordinal-scale data on root morphology were assessed by means of X2 analysis using StatView 512 + (BrainPower Inc., Calabasas, Calif.).

Statistical analysis All measurements were corrected for radiographic magnification. 4t The conventional one-way completely randomized analysis of variance model az'43 was used to test for differences among the adolescents and adults at the start and again at the end of treatment, as well

RESULTS While it is a common perception that adult patients require longer treatment periods, this was not true for the cases studied here. Both groups had average intreatment times of 2.5 years _ 0.35.

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Harris and Baker

Table III. Counts o f root resorption b y tooth, age, and time of examination* Tooth and age group

Maxillary central incisor Adolescents Adults Maxillary canine Adolescents Adults Maxillary first molar Adolescents Adults Mandibular canine Adolescents Adults Mandibular first molar Adolescents Adults

None

Slight

Minor

Moderate

Examination

(0)

(1)

(2)

(3-4)

Pre-TX Post-TX Pre-TX Post-TX

29 7 22 3

0 15 4 17

0 3 0 6

0 l 0 0

Pre-TX Post-TX Pre-TX Post-TX

29 12 23 12

0 9 l 8

0 4 0 4

0 0 0 0

Pre-TX Post-TX Pre-TX Post-TX

29 13 24 12

0 11 0 8

0 2 0 4

0 0 0 0

Pre-TX Post-TX Pre-TX Post-TX

29 7 20 7

0 11 4 8

0 4 0 7

0 0 0 0

Pre-TX Post-TX Pre-TX Post-TX

29 13 24 13

0 12 0 6

0 1 0 4

0 0 0 1

*The tests for an increase in the prevalence of the detectable level of resorption were significant (p < 0.05) by the Fisher exact test. In contrast, none of the five interage comparisons was significantaccoring to the Kolmogorov-Smimovtwo-sample test..5 Sample sizes varied, since unevenness in radiographic quality precluded making all measurements on all films.

Root resorption The most striking issue, from our perspective, was the number and distribution o f statistically significant differences among adolescents and adults at the s t a r t o f treatment (Table I). In each of the five root-length comparisons, adult patients' teeth had the shorter mean length, and this difference achieved statistical significance for the maxillary central incisor and the mandibular first molar. These same contrasts were evident at the end o f treatment, where again all five means were smaller for the adult patients, with the differences for the same two teeth achieving significance. The differences at the start of treatment contrasted sharply with the absence of any significant differences between adult and adolescent patients' teeth durhTg treatment (Table II). The two groups had very comparable changes, both losing an average o f 1.0 to 1.5 m m o f root length (with the highest rates for the max]llary incisor).

of this component o f the analysis are two-fold: (1) the data are essentially independent o f the confounding influences o f anatomic size, magnification, and angulation (parallax) and (2) initial stages o f erosion do not affect length appreciably, since they are periapical. 4".s'47 Discernible periapical erosion was seen only infrequently before treatment (Table III); when data on all five teeth were pooled, the prevalence o f erosion was zero for the adolescent patients (0/145) and 7% for t h e adult patients (9/122). Positive occurrences increased substantially in both age groups during treatment (Fig. 2), and it is noteworthy that the two series responded very similarly. By the end of treatment, some degree o f erosion was evident in 58% (73/125) o f the adolescent patients and 61% (73/120) o f the adult patients. These two ratios were identical (X2 = 0.2, p = 0.70), indicating that the rate o f apical erosion was statistically identical for the two groups.

Qualitative assessments

Alveolar crestal bone height

The results o f visual assessment for apical erosion and blunting are listed in Table III. The primary merits

Loss o f bony attachment paralleled these differences in root length (Table I). Both at the time o f initial

Volume 98 Number 5

Root resorption in adolescents and adults

467

1.0.

p. '~

0.6.

e0

e-

C 0

0

¢O

o

0.4,

X

o IX

~

0.2,

~ t

TX 1

II1

o

Ii

~

oo,~.=

0.0

,

None

"~r-,~ "~'" Adult "rx ~Ad'~olescent TX . . . . . . . Age of Patient

T Slight Moderate Severe Extreme

)

Degreeof Resorption Fig. 2. Distributions of grades of root resorption at start and termination of orthodontic therapy in adolescent (solid lines) and adult (dashed lines) patients. Individual tooth counts are pooled, since there was no statistically significant difference among them; moreover, the two age groups had other striking similarities and were not significantly different at the start or end treatment.

of

records and at completion of the cases, adult patients had lower average bone heights. Adult patients had 55% greater distances from CEJ to Z point at diagnosis, and this difference increased to about 80% 2.5 years later, at removal of the appliances. This enhanced loss of height during treatment achieves statistical significance for the maxillary molar site (Table IlL DISCUSSION

Positive covariations between orthodontic tooth movement and external root resorption are now broadly documented? '485° Newman 5~ and Goultschin and coworkers 7 list several relevant issues, including hormonal, genetic and nutritional factors, root morphology, nature of the tooth movement, characteristics and degree of the forces applied, and duration of treatment. It has also been suggested that the age of the patient can be a predisposing consideration, 5'46 but it is particularly important in this context to distinguish between age per se and other factors associated with a patient who happens to be an adult: Since both periodontal disease and DMF scores are strongly age-progressive from an epidemiologic perspective, ~-''53 the effects of orthodontic treatment plus age need to be distinguished from those of age plus compromised oral health. Musich ~7has suggested that 60 to 75% of adult patients seeking orthodontic treatment have medicodental problems that are significant considerations in therapy planning, and that adult patients frequently require multipleprovider dental care to resolve their occlusal problems. It seems reasonable to suspect that there may well be

Fig. 3. Schematic depiction of results documented here. While external apical root resorption and loss of alveolar crestal bone height are both age-progressive without orthodontic mechanotherapy, treatment interacts synergistically to increase the rate of transient loss and push the cases to a higher plateau of resorption and bone loss. It is important to note, however, that the degree and rate of in-treatment changes are effectively the same whether treatment is performed during a patient's adolescence or adulthood. These results are also an endorsement of early intervention, since it appears that teeth with incompletely formed roots are at low risk of resorption. ','8

only a superficial covariation between age and increased dental and periodontal problems during treatment (Fig. 3). In the present study, all patients had intact dentitions without prosthetic appliances; their oral health was good at the start of treatment, and it was maintained by patient cooperation and periodic checkups by the general dentist and hygienist. This attention to regular care may well have had an effect on the outcome of our research• Indeed, we had a much larger series of adult patients at our disposal, but most were excluded before analysis because they did have a full complement of teeth and a Class II, Division 1 malocclusion. If completeness of natural dentition had not been a criterion, the adult group might well have shown more loss of root length and bony support both before and during treatment? 4"~ Also, while the present series consists wholly of female patients, studies that have tested for a sex difference have reported ambiguous results (as might be inferred from differences in hormonal balances), s6 Rudolph ~6 reported a significantly higher prevalence of root resorption in female patients, whereas Phillips 4 found no difference.

Rootresorption The prime focus of this work was to ascertain whether adults had greater root resorption during treatment compared to a series of adolescents of the same

Am. J. Orthod. Dentofac. Orthop. November 1990

468 Harris and Baker sex who had received comparable treatment. The conclusion, based on samples of five teeth from throughout the dentition, is that age, per se, is not an important contributory factor in root resorption. Greater age, with concomitant differences in bone density and capacities. for remodeling, ~6'19was not found to have a measurable impact. On the other hand, the adult patients in our study were young, with a mean starting age o f 27.9 years, but the difference between the two groups did correspond to the interval during which the great majority of adults interested in orthodontic therapy seek treatment.

Bony support Previous researchers s?59 have documented greater CEJ-to-crestal bone distances (i.e., less bony support) at the end of orthodontic treatment than in untreated controls, but ridding this begs the question o f whether the differences already existed before mechanotherapy. This question has also been raised by ~Jgaard. a6 When comparisons are made across ages, this difference can be of particular concern. In the present study, the adult patients had substantial differences before treatment and, indeed, the in-treatment changes, while they showed greater loss of bony support in the adults, were modest compared to the preexisting differences recorded in the initial records. The two molar sites measured here were on the distal border; given the distal tipping o f these teeth during anchorage preparation, it is possible that these were pressure-bearing areas and therefore resorptive early in treatment, but would change to tension sites as the posterior teeth were pitted against the anterior teeth for retraction in these four-premolar extraction cases. 33 If crestal bone levels had been measured on the leading (mesial) border or adjacent to extraction sites, the changes would presumably have been larger. 57's9'6°

Age factors It is a common perception that adults may well be at greater risk of root resorption and loss o f alveolar crestal bone height; indeed, among potential patients, those who are adult tend to be scrutinized more for existing problems that could predispose them to loss of dental support. In this study, the adult patients exhibited the same degree of loss durhzg full-banded mechanotherapy. Only the starting conditions differed. It is well documented that induced tooth movement enhances the risk of resorption, but it appears that adult patients simply seek treatment after a more advanced duration o f "idiopathic" lOSS, s'rz the result o f more years since tooth formation (Fig. 3). Typical in-treatment changes become clinically relevant when the patient has already lost so much support that the functional and esthetic

benefits of treatment are not sufficient to justify another millimeter or so of root length and/or another millimeter o f alveolar support, on the average (Table II).

OVERVIEW Two orthodonticaUy treated groups, one consisting of adolescents and the other of adults, were matched for sex, malocclusion, and treatment regimen. Root lengths of selected teeth and alveolar crestal bone heights were measured before and after treatment: 1. Substantial differences were present before treatment: Adult patients had significantly shorter roots and greater alveolar recession than the young teenagers. 2. Adult patients did exhibit somewhat greater crestal bone loss during treatment (approximately 0.6 to 0.8 mm), but the differences between their bone loss and that of teenagers during treatment was less than the differences at the start of treatment. 3. In the absence o f compromising conditions (e.g., high DMF scores, periodontitis) adult patients are not inherently more likely than adolescents to lose dental support during treatment. We acknowledge the considerable efforts of Dr. James L. Vaden in providing the cases used in this study.

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Loss of root length and crestal bone height before and during treatment in adolescent and adult orthodontic patients.

It is broadly documented that orthodontic tooth movement enhances the risk of apical root resorption and loss of alveolar crestal bone height, but vir...
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