The effects of space closure of the mandibular first molar area in adults.pdf

American Journal of ORTHODONTICS

Founded in 1915 Volume 85 Number 6 June, 1994

Copyright 0 1984 by The C. V. Mosby Company

ORIGINAL ARTICLES

The effects of space closure of the mandibular Jirst molar area in adults

Barney M. Horn, D.D.S.,* and Patrick K. Turley, D.D.S., M.S.D., M.Ed.** Los Angeles, Calif. Dr. Horn

There is little information regarding the orthodontic closure of remodeled, edentulous spaces in the posterior area of the mandible. The present study was undertaken to determine the dental and periodontal changes that occur when mandibular first molar areas are closed in adults. Fourteen adult patients were selected from private orthodontic practices. Pre- and posttreatment study models were used to measure the mesiodistal length of the edentulous space and the buccolingual width of the alveolar ridge. The amount of crown and root movement of the second molar and premolar was measured from lateral cephalometric radiographs. From pre- and posttreatment panoramic or periapical radiographs, the anatomic changes of the second molar and adjacent periodontium were also measured. Every case showed significant space closure (x = 6.2 mm) ranging from 2.7 to 11.5 mm. There was crestal bone loss (x = 1.3 mm) mesial to the second molar in all but five cases. These latter cases showed bone addition. As the molar moved mesially, the alveoiar ridge increased in width an average of 1.2 mm. The adult patient who showed the greatest amount of space closure and the least amount of molar bone loss had (1) mesiodistal space of 6.0 mm, (2) buccolingual ridge width of 7.0 mm, and (3) mesial molar bone level 1 .O mm apical to the cementoenamel junction. The results of this study indicate that space closure is not only possible but may aid the treatment of certain cases. Space closure should be considered as a potential solution to the absence of mandibular first permanent molars.

Key words: First molar area, mandible, remodeled, space closure, bone loss

A common clinical finding in the adult orthodontic patient is the absence of the mandibular first molar. When the first molar is lost, the second molar usually tips mesially , the second premolar drifts distally, and the alveolar ridge becomes narrower. The second molar is particularly susceptible to abnormal stresses and bony breakdown, and pocket formation may occur mesial to the inclined molar.

Many orthodontists assume that if the buccolingual

From the Section of Orthodontics, School of Dentistry, University of Califor- nia Los Angeles. Based on a thesis submitted by the senior author in partial fulfillment of the requirements for a certificate in orthodontics, University of California Los Angeles. The research was pa&ally funded by the Foundation for Orthodontic Research. *Practicing orthodontist in Manhattan Beach, Calif. **Associate Professor and Acting Chairman, Section of Orthodontics.

width of the alveolar ridge is constricted, the second molar should not be moved mesially since this will result in a loss of bone support.* Moreover, there are problems of gingival dehiscence, root parallelism, and incomplete space closure. It has been shown, however, that spaces of 10 mm or more can be closed in the posterior region of the mandible.3

There is little information regarding the closure of remodeled edentulous spaces in the posterior area of the mandible. The purpose of this research is to examine the dental and periodontal changes that occur when mandibular first molar areas are closed orthodontically in adults and to compare the findings with those of a previous study .3

REVIEW OF THE LITERATURE

Edward H. Angle4 called the first molar the key to occlusion. Certainly, this tooth is very important in

457

458 Horn and Turley Am. J. Orthod. June 1984

maintaining the stability of the dentition, as can be seen by the complications that result when it is prematurely lost. Vanarsdall and Swartz5 described the common sequelae to the missing mandibular first molar as (1) mesially inclined second and/or third molars, (2) distal drifting of the premolar-s, (3) extrusion of the maxillary molars, (4) altered gingival form with constriction of the edentulous ridge, (5) infrabony defect mesial to the inclined molar, (6) stepped marginal ridges, (7) food impaction, and (8) posterior bite collapse. The conse- quences in the maxillary arch are usually not as severe as those in the mandibular arch. The maxillary second molar may come forward in a relatively untipped manner with the long axis converging apically . The premolar may or may not drift distally.

There are several alternatives in treating the missing mandibular first molar. Graber states that space closure of the molar area is seldom possible or desirable with limited orthodontic therapy. Movement of posterior teeth is often difficult because of the greater root surface area, the increased tissue resistance, and the anchorage needs involved. Since there is a consequence of umwanted tooth movement elsewhere when posterior teeth are moved, partial correction may be the optimal result obtainable. He advocates uprighting the second molar to its normal position and stabilizing it with a fixed or removable prosthesis.

Kessle? suggested that if the buccolingual width of the second molar alveolus is wider than the adjacent edentulous ridge, the tooth should not be moved mesially since this will result in a loss of bone support. Moreover, if there is a definite periodontal osseous defect on the mesial aspect of the inclined molar, uprighting the tooth and tipping it distally may widen the de- feet , necessitating an autogenous hip marrow graft. The uprighting of mesially inclined molars is not a panacea. The possibility exists that uprighting some teeth may cause bone loss and furcation involvement.

In contrast, Brown6 showed that uprighting of molars produced significant reduction in the depth of exist- ing periodontal defects and highly desirable changes in the gingival architecture. The gingival margin moved from a coronal position approaching the marginal ridge to a more inferior location adjacent to the cementum of the anatomic root. This increased the length of the clinical crown with a concurrent decrease in the depth of the periodontal pocket. However, he also found that the alveolar bone level decreased between 0.5 and 1 .O mm, along with the reduction of total pocket depth. He considered this amount to be therapeutically insignificant.

Ingber showed that forced eruption can correct isolated one- or two-wall infrabony osseous defects. Ex- trusion of a tooth from its alveolus causes a stretching

of the gingival and periodontal ligament fibers. This results in a coronal shift of the bone at the base of the defect as the tooth moves occlusally . These vertical osseous defects frequently occur along with an inclined alveolar crest on the mesial side of the second molar.

Roberts and associate9 noted that if the relationship between the alveolar crest and the cementoenamel junction is constant during molar uprighting, the angu- lar osseous crest mesial to the tipped molar is not only eliminated but also somewhat reversed in inclination, corresponding to the amount of extrusion which occurs. Moreover, if extrusive forces are used to correct vertical osseous defects, they should follow the correction of molar inclination in order to have better control of the rapid molar extrusion and the periodontal inflammation.

Although most clinicians caution against closing edentulous first molar spaces, this procedure has been attempted in certain situations. Stepovich3 studied the changes in the edentulous ridge and adjacent teeth before and after closure of first molar spaces in the mandible. The first molar areas had no evidence of the residual socket. The sample consisted of eight teen- agers and eight adults who had completed orthodontic treatment. He found that the buccolingual width of the alveolar ridge can be changed by orthodontic treatment. In teen-agers the alveolar bone readily followed the tooth as it was moved into an edentulous space that was narrower than the tooth. In contrast, half of the adult patients resisted the formation of any new bone during space closure; the other half developed only minimal amounts of new bone. Crestal bone loss mesial to the second molar was evident in both groups, but the adult group showed twice as much loss. Root resorption was not seen in the teen-age group; in the adult group, resorption occurred in only two of eight patients. Stepovich concluded that spaces of 10 mm or more can be closed without tipping in both the teen-age and the adult patient. However, closed spaces were difficult to maintain in the adult patient.

MATERIALS AND METHODS

Fourteen adult patients ranging in age from 20 to 39 years were selected from private orthodontic practices. From these patients nineteen quadrants with edentulous mandibular first molar spaces were used in the study. (five patients had bilateral absence of first molars.) All patients had been fully treated with edgewise orthodontic appliances. The first molar areas lacked radiographic evidence of a residual socket. The patients had complete pre- and posttreatment records that included plaster casts, lateral cephalometric radiographs, and panoramic or periapical radiographs.

Volume 85 Number 6

Effects of space closure of mandibular first molar area 459

From the pre- and posttreatment study models, the mesiodistal length of the edentulous space and the buccolingual width of the alveolar ridge were measured with dial calipers. The mesiodistal length was measured from contact point to contact point of the teeth adjacent to the edentulous space. The buccolingual width of the alveolar ridge before treatment was measured in a manner described by Stepovich .3 A point was located at the middle of the ridge mesiodistally. The calipers were placed 4 mm apical to this point on the buccal and lingual aspects, and the width of the ridge was recorded. The posttreatment width of the ridge was measured similarly if there was incomplete space closure. If there was complete space closure, a point on the ridge beneath the contact point of the second premolar and the second molar crown was used. Again the calipers were placed 4 mm apical to this point to measure the width.

The amount of crown and root movement of the second molar and second premolar was measured from the pre- and posttreatment lateral cephalometric tracings. First, a Ricketts eleven-factor summary analysis was performed. I7 The corpus axes of the two tracings were then superimposed at PM point (protruberance menti). The occlusal plane of the pretreatment tracing was traced onto the posttreatment cephalometric tracing. Perpendicular lines to the occlusal plane were drawn from the following points (Fig. 1, A): (A) the most mesial point of the second molar crown, (B) the most inferior point on the mesial root of the second molar, (D) the most distal point of the second premolar crown, and(E) the most inferior point on the root of the second premolar.

By measuring the change in these points from T, to T,, the following information was obtained:

A-The distance that the second molar crown moved mesiodistally (M-D).

B-The distance that the second molar root moved M-D.

C-The distance that the second molar crown moved vertically.

D-The distance that the second premolar crown moved M-D.

E-The distance that the second premolar root moved M-D.

The anatomic changes in the second molar and adjacent periodontium were measured from the pre- and posttreatment panoramic or periapical tracings (Fig. 1, B). First, the second molar, second premolar, and the interproximal alveolar bone were traced. An occlusal plane of the second molar was then drawn; this plane was determined from the best fit of the pre- and posttreatment molar. Lines parallel to the molar

Fig. 1. A, The pre and posttreatment tracings were superimposed along the corpus axis at PM to determine the amount of crown and root movement of the second molar and

premolar. A, Second molar crown movement M-D; 8, second molar root movement M-D; C, second molar crown movement vertically: D, second premolar crown movement M-D; E, second premolar root movement M-D. B, The anatomic changes of the second molar and adjacent periodontium were measured from the pre- and posttreatment panoramic or periapical tracings. f, Crestal bone change; G, molar root resorption; /-/, vertical alveolar ridge change; I, cementoenamel junction change (indicating x-ray distortion).

occlusal plane were drawn from the following points: (1) crestal bone mesial to the molar, (2) cementoenamel junction (CEJ) mesial to the molar, (3) the most inferior point on the mesial root of the molar, and (4) the interproximal bone halfway between the molar and the premolar.

By measuring the change in these lines from T, to TZ the following information was obtained:

F-Amount of crestal bone change. G-Amount of molar root resorption. H-Amount of vertical alveolar ridge change. I-Change in cementoenamel junction position. Of the nineteen edentulous spaces studied, periapi-

cal radiographs were taken of eleven and panoramic radiographs were taken of eight. To minimize mea- surement errors, the elongation or foreshortening factor in the radiographs was calculated by measuring the change in the position of the cementoenamel junction


Table IA. Dental changes with space closure (mm)

Space closure Mesiodistal tooth movement

Mesiodistal space Net Crown movement Root movement space

Tl T2 closure Molar Premolar Molar Premolar

Range 3.5 0.0 2.7 -1.1 -0.4 I.0 -3.1 to to to to to to to

12.6 1.1 11.5 8.9 5.9 15.7 5.3 Mean 6.9 0.7 6.2 4.1 2.0 1.1 2.0 T test significance NA NA 0.01 0.01 0.01 0.01 0.01 Standard deviation 2.3 0.6 2.5 2.6 1.9 3.6 2.0

Positive values indicate mesial movement of molars and distal movement of premolars. NA = Test for statistical significance not applicable.

Table 18. Periodontal changes with space closure (mm)

Vertical bone change

Bone height Net

T, 7-2 change Buccolingaal alveolar change

Range 5.5 6.5 -4.2 to to to - 1.6 to 4.8

10.6 14.4 1.8 Mean 8.0 9.3 -1.3 +1.2 T test significance NA NA 0.01 0.01 Standard deviation 2.8 3.0 1.7 1.1

Positive values indicate mesial movement of molars and distal movement of premolars. NA-Test for statistical significance not applicable

Root resorption

-3.3 to 1.3

-1.3 0.01 1.2

(I in Fig. l), which should change much like the other anatomic landmarks.

The facial pattern of the patient was determined from the measurements of five cephalometric angles: facial axis, mandibular arc, mandibular plane, facial plane, and lower face height. A composite number was derived by determining the clinical deviations from the norm of these angles. A positive number indicated a more brachyfacial pattern, while a negative value indicated a doliocofacial pattern.

A computerized statistical analysis was performed on the collected data: (1) the range, mean, and standard deviation of all variables, (2) t tests for significant changes from pretreatment to posttreatment, (3) correlation coefficients of all variables matched against each other, and (4) multiple regression analysis for prediction of space closure and molar bone loss.

RESULTS

Space closure was accomplished in all patients with closing loops on rectangular wires. The treatment time ranged from 23 months to 52 months.

Space closure

The size of the edentulous space prior to treatment ranged from 3.5 mm to 12.6 mm, with a mean of 6.9 mm (Table I). Thirteen quadrants had openings of 6 mm or more (Table II). In every case there was significant space closure with a mean of 6.2 mm. How- ever, in only 5 of 19 quadrants were spaces completely closed on the posttreatment models. Twelve cases showed mesiodistal openings of less than 1 mm after treatment, with an average opening of 0.7 mm (Figs. 2, D, 9, 10). In one case that started with 12.6 mm of space, only 1.1 mm of space remained after treatment.

Mesiodistal tooth movement

The amount of mesiodistal movement of both the crown and root of the second molar and premolar was determined by measuring the changes in these landmarks from the T1 and T2 cephalometric tracings. The molar crown moved mesially an average of 4.1 mm, with the greatest movement being 8.9 mm (Table I). On the average the molar moved mesially twice as much as the premolar moved distally-4.1 mm versus

Effects of space closure of mandibularjrst molar area 461 Volume 85 Number 6

Table II. Space closure and tooth movement (mm)

Space closure Mesiodistal tooth movement*

Mesiodistal space Crown movement Root movement Net

space Molar Premolar Molar Premolar Patient Side Tl 7-2 closure crown movement root movement

J. D. L 6.2 1.2 5.0 4.4 1.5 2.6 1.8 M. R. R 7.3 0 7.3 -1.1 5.8 1.0 1.5 D. K. L 6.5 1.7 4.8 3.2 1.1 5.0 1.1 G. H. R 5.1 0 5.1 0.5 3.5 7.5 2.6 L. B. L 7.7 0.6 7.1 7.5 -0.4 8.7 0 J. T. L 8.3 1.6 6.1 5.9 0.3 5.8 5.3 L. s. R 9.8 1.5 8.3 1.5 0.4 12.2 1.8 c. L. L 3.1 0.6 3.1 1.4 2.1 5.8 1.9 D. S. L 8.1 0.6 1.5 4.1 2.8 10.3 1.9

R 3.5 0.8 2.1 1.7 1.6 5.5 -3.1 E. H. L 5.0 0.8 4.2 4.5 0.7 3.6 1.0

R 9.2 0 9.2 3.9 4.1 1.4 2.1 A. D. R. L 1.1 1.4 6.3 4.6 1.7 5.5 -0.6

R 12.6 1.1 11.5 8.9 3.4 15.7 4.5 E. D. L 6.9 0.8 6.1 5.7 1.3 10.1 3.4

R 5.6 0 5.6 4.9 1.0 9.5 3.0 M. H. L 6.4 0 6.4 6.3 0 9.5 2.8

R 1.5 1.0 6.5 0.1 5.9 3.0 5.3 S. D. L 3.5 0.6 2.9 2.8 1.5 5.7 0.2

*Positive values indicate mesial movement of molars and distal movement of premolars.

2.0 mm (Fig. 2, B). Five quadrants showed more distal movement of the premolar than mesial movement of the molar (Table II). Only one case showed distal movement of the second molar.

The roots of the second molar moved mesially almost twice as much as the crown (7.1 mm versus 4.1 mm), indicating significant uprighting. Only three cases showed more crown movement than root movement (that is, tipping). Six cases had molar root movement of 9.5 mm or more, with the greatest amount being 15.7 mm. Figs. 8, 9, and 10 illustrate a case in which the roots moved mesially 12.2 mm. Prior to treatment all second molars were tipped mesially. As the molars were uprighted and moved mesially during treatment, they erupted an average of 1.5 mm.


Examination of vertical bone changes with treatment revealed crestal bone loss mesial to the second molar in all but five cases (Table III). In those latter cases there appeared to be an increase in bone as the molar moved mesially (Figs. 3 to 7). On the average, however, there was - 1.3 mm of vertical bone loss, with a range of 1.8 mm (bone addition) to -4.2 mm (bone loss) (Table I). Fig. 8 illustrates a case with - 2.5 mm of vertical bone loss.

Buccolingual alveolar width change

Examination of the change in buccolingual width of the alveolar ridge revealed that the ridge increased in width an average of 1.2 mm as the molar moved mesially (Table I, Figs. 4 and 6). The values ranged from - 1.6 mm (decrease) to 4.8 mm (increase). Seven cases had a narrower ridge (j7 = 0.8 mm) in the posttreatment models, indicating slight bone loss with treatment (Fig. 9). There was no correlation between ridge width and change in vertical bone height.

Root resorption

Root resorption of the second molar was minimal. There was an average of only 1.3 mm of resorption, with the greatest resorption being 3.3 mm (Table I, Figs. 3,5, and 8). Only four cases had more than 2 mm of resorption. Four cases showed a root-length increase of up to 1.3 mm (Table III). This apparent root lengthening was due to elongation in the radiographs, a problem that will be discussed later.

Correlation coefficients

Correlation coefficients between forty-one variables were used to test for significant linear relationships. There were several notable findings:

1. The higher the bone level on the mesial aspect of


Fig. 2. A, Pre- and posttreatment cephalometric tracings of Patient A.D.R. showing distal premolar movement greater than mesial molar movement (4.7 mm distal versus 3.9 mm mesial), right side. B, Mesial molar movement greater than twice the distal premolar movement (4.6 mm mesial versus 1.7 mm distal), left side

the second molar at Tr, the greater the amount of bone loss at T2 (r = 0.546).

2. The older the patient, the greater the amount of molar eruption (r = 0.7 16).

3. The higher the molar bone level at Ti, the greater the amount of mesiodistal space at T2 (r = 0.492).

4. The wider the alveolar ridge at T1 , the greater the amount of mesiodistal space at T, (r = 0.478).

5. The facial pattern of the patient did not correlate significantly with any of the other variables in the study.

Fig. 2 (Contd). C, Pretreatment study casts. D, Posttreatment study casts showing 1.4 mm space opening on left side.

Prediction of space closure

In order to predict the amount of mesiodistal space after treatment, a multiple regression analysis was performed. Nine variables were analyzed as potential predictors. It was found that three of the variables (mesiodistal space, width of alveolar ridge, and mesial molar bone height, all at T,) were significantly (P < 0.01) related to the amount of mesiodistal space at TZ. An equation was derived to predict the amount of mesiodistal space after treatment:

M-D space at T2 = 1.15 mm + 0.07 mm (M-D space at Tl + 0.18 mm) width of ridge at

T, _ 1.95 mm (bone height on mesial side of molar at T1)* (CEJ height on mesial side of molar at Tl)

The multiple correlation coefficient is 0.73, and the standard error of a predicted value is 0.43 mm.

*The bone and CEJ height of the molar were measured from the molar occlusal table.

Volume 85 Number 6

Effects of space closure of mandibular jirst molar area 463

Table III. Alveolar bone changes and root resorption (mm)


Vertical bone height Net

vertical Patient Side T, T* bone change

J. D. L 8.0 11.6 -3.6 M. R. R 9.5 9.1 -0.2 D. K. L 10.2 14.4 -4.2 G. H. R 1.3 8.5 -1.2 L. B. L 7.1 7.6 -0.5 J. T. L 7.6 11.6 -4.0 L. s. R 5.5 8.0 -2.5 c. L. L 8.4 8.0 0.4 D. S. L 7.1 10.4 -2.1

R 5.8 7.9 -2.1 E. H. L 8.1 7.5 0.6

R 8.0 7.5 0.5 A. D. R. L 6.6 8.4 - 1.8

R 1.9 9.5 - 1.6 E. D. L 8.0 8.9 -0.9

R 9.3 7.5 1.8 M. H. L 7.1 6.5 1.2

R 10.6 11.8 -1.2 S. D. L 10.1 11.5 - 1.4

Net

Buccolingwl alveolar Root

width change resorption

0.5 1.3 4.8 -1.6

-0.2 0.5 0.8 -0.4 1.5 -1.5

-1.6 -0.4 -1.0 -1.7

1.2 -1.5 3.5 0.7

-0.4 -2.2 1.5 -2.1 2.8 -1.3

-0.9 - 1.4 2.4 -1.6 3.1 1.3 3.2 -2.8 2.2 -3.3

-0.6 -1.9 -1.2 -1.6

Prediction of vertical bone change

A multiple regression analysis was also performed, with the same nine variables as predictors of molar bone loss. It was found that only the bone height on the mesial aspect of the molar at T1 was significantly (p < 0 .Ol) related to the amount of molar bone loss. An equation was derived to predict the amount of molar bone loss on the mesial part of the tooth after space closure: Molar bone loss = 1.48 mm (CEJ height on mesial aspect of molar at T,) - 1.17 mm (bone height on mesial aspect of molar at Tz).* The multiple correlation coefficient is 0.55, and the standard error of a predicted value is 1.5 mm.

DISCUSSION

The findings in the study indicate that orthodontic space closure can be achieved with edentulous, remodeled mandibular first molar spaces. All nineteen quadrants showed significant space closure, with a mean of 6.2 mm (Table I). In sixteen quadrants there was bodily movement of second molars, with the roots coming forward almost twice as much as the crowns (7.1 mm versus 4.1 mm, Table I). Six cases showed molar root movement of 9.5 mm or more, with the

*Assume no radiographic magnification at TZ.

greatest amount being 15.7 mm (Table II). Similarly, Stepovich3 also showed that second molars can be moved forward through edentulous areas without tipping. This is in contrast with the viewpoint of Graber, who states that space closure of the mandibular first molar area is seldom possible because of the greater molar root surface area and increased tissue resistance. The results of the study indicate that space closure not only is possible but also may aid in the treatment of certain cases, such as those with anterior crowding. Cases that might normally require extraction of premolars to alleviate crowding were treated without ex- tractions by using the space provided by the missing first permanent molars. In these cases space closure occurred reciprocally with mesial molar movement and distal premolar movement (Figs. 2, C, D, and 10, A and B) .

In fourteen out of nineteen quadrants, some space existed between the second molar and the second premolar on the posttreatment models. In most cases it was not known whether the space had opened after treatment or whether the space was never entirely closed. In attempting to maintain space closure, Hatasakag observed that the best postretention results were in cases in which roots and crowns were positioned in normal, upright parallel positions. EdwardslO suggested that ex-

464 Horn and Tut&y Am. J. Orthod. June 1984

Fig. 3. Periapical radiograph of right first permanent molar area of Patient M.H., showing bone level prior to space closure. 8, Radiograph showing 1.8 mm vertical bone addition after space closure. 2.8 mm of root resorption occurred on the second molar.

cess gingival tissue could be a factor associated with residual spaces and advocated the surgical removal of any tissue that accumulates interproximally during treatment. In this study the mesiodistal space and the buccolingual width of the alveolar ridge prior to treatment were significantly (P < 0.01) related to the amount of space left after treatment. Those quadrants with less than 1 mm of residual space started with edentulous spaces that averaged 6.0 mm and a ridge width of 6.8 mm. Cases that began with a wider ridge actually showed more space after treatment. Although the dis- tribution pattern showed some individual variation, an adult patient with an edentulous space of this approxi- mate size would have a favorable probability of maintaining good space closure after treatment.

KesslerZ suggested that moving a molar into a remodeled, constricted mandibular ridge could result in loss of periodontal support. In studying recent first premolar extraction sites that were closed orthodontically, Baxter observed that the mesial aspect of the mandibular second premolars had 0.10 mm of bone

Fig. 3 (Contd). C and D, Tracings of right first permanent molar shown in A and B, before and after space closure.

loss after treatment. With a similar extraction se- quence, Zachrisson and Alnaes12 found that the second premolars had 0.22 mm of bone loss when compared to homologous, untreated teeth. Although the figures from these studies may be statistically significant, the clinical significance of these values may be minimal. In examining remodeled extraction sites of the mandibular first molar area, Stepovich3 found that the mesial aspect of the second molar lost 2.0 mm of bone as it was uprighted and moved forward. The results in this study were similar to those of Stepovich in that there was a tendency for the mesial bone height to decrease with treatment. The nineteen quadrants averaged 1.3 mm of crestal bone loss mesial to the second molar with treatment. The range varied from + 1.8 mm (bone addition) to -4.2 mm (bone loss). Although bone loss is to be avoided if at all possible, the consequence of moderate molar bone loss is not necessarily a contraindication to closure of the edentulous space. If hygiene can be maintained by the patient or the dentist, space closure may be a reasonable alternative to a fixed prosthesis. Fixed prostheses are often considered the best solution for replacement of missing teeth. However, they also

Volume 85 Number 6


Fig. 4. Pre- and posttreatment study casts showing 3.2 mm increase in buccolingual alveolar ridge width after space closure (right side, Patient M.H.).

have their shortcomings: (1) initial expense, (2) replacement due to caries, (3) reduction of two teeth in crown preparation for abutments, and (4) limited orthodontics may still be needed to upright the tipped second molar. Hence, both space closure and a fixed prosthesis should be considered as potential solutions to missing teeth.

In examining etiologic factors associated with periodontal bone loss, Skillen13 and Stuteville* showed that the presence of gingival inflammation during orthodontic tooth movement may augment alveolar crest resorption. Similarly, Suomi and associates15 observed that the maintenance of optimal oral hygiene in adults retards the rate of alveolar bone loss. In this study the nature of the patients oral hygiene and the presence or absence of gingival inflammation during orthodontic therapy could not be determined. Only radiographs and plaster casts were available for study. In attempting to identify factors which might be related to bone loss with treatment, the mesial bone height of the molar prior to treatment was the only statistically significant (P < 0.01) variable. Cases with a higher mesial bone level at the start of treatment actually showed the

Fig. 5. A, Periapical radiograph of left first permanent molar area of Patient M.H., showing bone level prior to space closure. B, Radiograph showing 1.2 mm vertical bone addition after space closure; 3.3 mm of root resorption occurred on the second molar.

greatest amount of bone loss with treatment. This finding is difficult to explain since cases with prior periodontal bone loss might be more prone to bone loss with treatment. In contrast, however, a tooth being moved through a lesser volume of bone support might move more easily, thus resulting in less overall bone loss. With regard to our findings, however, even though cases with higher pretreatment bone levels ex- perienced the most bone loss, the changes did not compromise the periodontal support of these teeth and hence a successful result with space closure was achieved. However, other factors appear to be relevant when the characteristics of those that showed less than 1 mm of bone loss (Group 1) are compared to those that showed more than 2 mm of bone loss (Group 2). In comparison, Group 1 had (1) a shorter mesiodistal space prior to treatment (6.5 mm versus 7.1 mm), (2) a narrower alveolar ridge width (6.7 mm versus 7.7 mm), and (3) a molar bone level that was more apical to the cementoenamel junction (1.2 mm versus 0.3 mm). There was considerable individual variation in both


Fig. 5 (Contd). C and D, Tracings of left first permanent molar shown in A and 9, before and after space closure.

groups. It is noteworthy that the figures for mesiodistal space and width of ridge in Group 1 are very similar to those in the group with less than 1 mm of residual space. Therefore, the adult patient who showed the least amount of molar bone loss and the greatest amount of space closure met the following criteria: (1) mesiodistal space of approximately 6 mm or less, (2) buccolingual ridge width of approximately 7 mm, and (3) mesial molar bone level of approximately 1 mm apical to the cementoenamel junction.

As space closure occurs, there is not only vertical bone change mesial to the second molar but also buccolingual change to the alveolar ridge. Examination of the change in the width of the alveolar ridge shows that the width increased an average of 1.1 mm after treatment. The values ranged from - 1.6 mm (width decrease) to 4.8 mm (width increase). Stepovich3 found that four out of eight adult patients resisted formation of any new bone. The other half developed only a small amount of new bone. In this study seven quadrants had

Fig. 6. Pre- and posttreatment study casts showing 2.2 mm increase in buccolingual alveolar ridge width after space closure (left side, Patient M.H.).

a narrower ridge after treatment, with a mean decrease of 0.8 mm. However, these cases prior to treatment had a much wider ridge than the average (8.6 mm versus 7.2 mm) and, even after treatment, there appeared to be a sufficient amount of bone interproximally (7.8 mm).

Root resorption is always a major concern in tooth movement. In this study root resorption of the second molar was minimal. There was an average of 1.3 mm of resorption, with the greatest amount being 3 $3 mm. Only four cases had more than 2 mm of root resorption. In those six cases in which the roots traveled 9.5 mm or more, only 1.7 mm of root length was lost. Similarly, Stepovich3 found minimal change in root length in six out of eight patients, with the average amount of resorption being 0.4 mm. Phillips16 observed, in his study of apical root resorption under orthodontic therapy, that 96% of mandibular second molars showed no resorption at all. The remaining 4% exhibited minimal blunting of the root apices. Moreover, there was no correlation between the amount of apical root loss and the amount of tooth movement through bone.

In this study three cases showed a root length in-

Volume 85 Number 6


Fig. 7. Pre- and posttreatment study casts of mandibular arch in Patient M.H.

crease as great as 1.3 mm, which is attributed to radiographic distortion. Despite making corrections for magnification, there are still slight errors in the radiographic values. Periapical radiographs were available in eleven cases and panoramic radiographs were available in eight. Ideally, it would have been better to use only one type of radiograph, but this was not possible.

The overall periodontal health of the mandibular second molar after space closume is certainly pertinent to the success of the case. An examination of the patients before and after treatment to determine pocket depths, amount of attached gingiva, tooth mobility, and gingival recession would provide valuable information to the clinician. However, this step was beyond the scope of this project. A future study should include monitoring the patients gingival health along with using a standardized, reproducible radiographic tech- nique to document the periodontal changes accompany- ing space closure.

CONCLUSIONS

1. Mandibular second molars can be moved forward through remodeled, edentulous first molar areas

Fig. 8. A, Periapical radiograph of first permanent molar area of Patient L.S., showing bone level prior to space closure. 8, Ra- diograph showing 2.5 mm of bone loss after space closure; 1.7 mm of root resorption was measured on the first permanent molar.

in adults. Although every case showed significant space closure, only five cases had complete space closure.

2. In the majority of cases space closure occurred by bodily movement of the molars, with the roots moving mesially almost twice as much as the crowns.

3. On the average, the width of the alveolar ridge increased buccolingually 1.1 mm as the second molar moved forward. However, seven cases had narrower alveolar ridges after treatment.

4. With treatment there was crestal bone loss mesial to the second molars in all but five cases.

5. Root resorption of the molars was minimal. 6. The adult patient who showed the greatest

amount of space closure and the least amount of molar bone loss met the following criteria: (1) mesiodistal space of approximately 6 mm or less, (2) buccolingual width of the ridge of approximately 7 mm, and (3) mesial molar bone level of approximately 1 mm apical to the cementoenamel junction.

7. Space closure is not only possible but may aid


Fig. 8 (Contd). C and D, Tracings of first molar area shown in A and 6, before and after space closure.

Fig. 10. Pre- and posttreatment study casts of mandibular arch in Patient L.S.

Fig. 9. Pre- and posttreatment study casts showing 1.0 mm decrease in buccolingual alveolar ridge width after space closure (Patient L.S.).

the treatment of certain cases. Space closure should be considered a potential solution to the absence of mandibular first permanent molars.

The formulas and recommendations for space closure and molar bone loss are only guidelines to help the clinician decide if space closure of this type is feasible. The equations were derived from a select group of nineteen quadrants, and there remains some error in the size of a predicted value. Therefore, the clinician must still exercise sound clinical judgment before initiating orthodontic therapy,

The authors would like to acknowledge the special assis- tance of Dr. Kunihiko Miyashita of Tokyo, Japan, Mr. Gary Engel of The Foundation for Orthodontic Research in the collection of the data and preparation of the manuscript, and the Word Processing Center of the UCLA School of Dentistry for the typing of the manuscript.

REFERENCES 1. Graber TM: Orthodontics: principles and practice, ed. 3,

Philadelphia, 1972, W.B. Saunders Company. 2. Kessler M: Interrelationships between orthodontics and peri-

odontics. AM J ORTHOD 70: 154-172, 1976. 3. Stepovich ML: A clinical study on closing edentulous spaces in

the mandible. Angle Orthod 49: 227-233, 1979.

Volume 85 Number 6

Effects of space closure of mandibular first molar area 469

8.

9.

10.

11.

12.

Angle EH: New system of regulation and retention. Dent Regis- ter 41: 497-603, 1887. Vanarsdall RL, Swartz ML: Molar uprighting, Ormco catalog No. 740-0014, Glendora, Calif., 1980, Ormo Corporation. Brown IS: The effect of orthodontic therapy on certain types of periodontal defects. .I Periodontol44: 742-756, 1973. Ingber JS: Forced eruption. Part 1. A method of treating isolated one and two wall infrabony osseous defects-rationale and case report. J Periodontol45: 199-206, 1974. Roberts W, Chacker F, Burstone C: A segmental approach to mandibular molar uprighting. AM J 0~~~0~81: 177-184, 1982. Hatasaka HH: A radiographic study of roots in extraction sites. Angle Orthod 46: 64-68, 1976. Edwards JG: The prevention of relapse in extraction cases. AM J ORTHOD 60: 128-141, 1971. Baxter DH: The effect of orthodontic treatment on alveolar bone adjacent to the cementoenamel junction. Angle Orthod 37: 34-49, 1967. Zachrisson BU, Alnaes L: Periodontal condition in orthodon-

13.

14.

15.

16.

tically treated and untreated individuals. II. Alveolar bone loss: radiographic findings. Angle Orthod 44: 48-55, 1974. Skillen WG: Tissue changes the result of artificial stimuli and injury. J Am Dent Assoc 27: 1554-1563, 1940. Stuteville OH: Injuries to the teeth and supporting structures caused by various orthodontic appliances, and methods of pre- venting these injuries. J Am Dent Assoc 24: 1494-1507, 1937. Suomi JD, West TD, Chang JJ, McClendon BJ: The effect of controlled oral hygiene procedures on the progression of periodontal disease in adults: radiographic findings. J Periodontol 42: 562-564, 1971. Phillips JR: Apical root resorption under orthodontic therapy. Angle Orthod 25: 1-21, 1955

Reprint requests to: Dr. Patrick Turley Center for Health Sciences University of California School of Dentistry 10833 Le Conte Los Angeles, CA 90024

The effects of space closure of the mandibular first molar area in adults.pdf

Documents