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Relapse following maxillary expansion
Relapse following
maxillary
expansion Dr. Mevv
A study of twenty-five
consecutive
cases
John Mew Tunbridge
Wells, England
Twenty-five patients consecutively treated with maxillary expansion were studied. Both successful slnd unsuccessful cases were included, but five were excluded for other reasons. The expansion was measured 2 or 3 months out of retention to allow the overexpansion to settle. Measurements were made again 2X years out of retention. The net expansion had been 3.5 mm., and this had subsequently not relapsed. Possible easons for this are discussed. The associated improvement in dental alignment was measured by an index which is also discussed.
Key words: Semi-rapid maxillary expansion, consecutive cases, overexpansion, relapse, Little’:; index
A
lthough expansion of the maxilla
is one of
the oldest forms of orthodontic treatment, its use has consistently evoked professional controversy. Timms’ describes well the conflicting views of those who have recommended slow expansion, rapid expansion, or no expansion at all. The debate seems to have been all the, more heated because little scientific evidence existed to support any of these views. Opinions were nevertheless so firmly stated that one could be forgiven for wondering if it was, indeed,
the same human animal
that was be-
ing treated in each instance. While individual cases abound, there appear to have been few studies conducted on consecutive cases. A most scientific study was carried out by Skieller,2 who inserted metal implants into thirteen girls and seven boys, using an expansion appliance very similar to the Stage 1 bioblock used in this series.3 This was opened at the rate of 0.5 mm. per week for 7 months and then maintained for 12 months. The cases were not consecutive, and many had cross-bites. Skieller found that both the teeth and the vault widened and that the vault continued to widen both during retention and thereafter. The teeth, however, commenced to relapse at the end of the expansion and continued to do so out of retention, with the relapse amounting on average to about 25 percent of the total opening. Although he does not mention it, Skieller’s figures show that the dental relapse was less for the patients under 9 years old and noticeably higher for those over 12 years of age. He estimates that, at a rate of opening of 0.5 mm. per week, the widening is one-fifth the result of growth at the palatal suture and four-fifths of tooth movement. More recently Storey,4 working on rabbits, sug56
gested that the ideal rate of opening would be about 1 mm. per week, and this has been recommended clinically by several operators. 5-7 Another change in recent years has been the introduction of overexpansion. Haas* has probably been the forerunner in this field, as his publications show. Harold Chapman9 believed that expansion should be used only for cross-bites and certain Class II cases prior to intermaxiliary traction. Attitudes in the United Kingdom were also influenced by Townend’s” rather subjective paper entitled “The Comedy of Expansion and the Tragedy of Relapse. ” It seems possible that the recent introduction of “semirapid” or “slow” expansion at 1 mm. per week, coupled with the use of overexpansion, may justify a reassessment of these views. The present study was undertaken to explore this possibility. THE STUDY Material
It is not easy to collect random cases for a study of this nature. Clinicians will inevitably wish to prove themselves and, even if the cases ware “average” initially, they are unlikely to remain so during treatment. It was thought that these cases should already have received the initial expansion on the chosen day to avoid the possibility of previous case selection or any special attention influencing the results. Also, case selection would need to be made by a third party and should be based on strict parameters. It was decided to exclude only (I ) children younger than 8 or older than 16 years, (2) children unable to attend regularly (that is, those at boarding school), and (3) transfer cases. Other than these, the first twenty-five cases that ooO2-9416/83/010056+06$00.60/0
0
1983 The C. V. Mosby Co.
Volume 83 Number 1
Relapse following
maxillary
expansion
57
Fig. 1. The two versions of the expansion appliance used in this series, the choice depending on the mandibular plane angle.
Table I ---
I
I
I
Intermolar widths (mm.)
YearslMonths Out of retention
Patient
Class
Before
After
A B C D E F G H I J K L M N* 0 P* Q R S T U v* W X Y Average
II/2 II/ 1 II/ 1 II/2 II/l III 1 I II/2 III? III 1 II/ 1 I II/ 1 III 1 II12 I II/ 1 I I III 1 III 1 1 III 1 III 1 I
1314 1210 1112 9110 1019 1116 1218 1114 1.511 812 1317
18/O 315 32.0 1714 211 33.2 1614 317 33.3 1418 l/11 31.1 l5/10 119 28.2 1II4 116 28.0 1713 213 33.4 16/l l/11 27.6 20/8 314 36.4 1218 117 30.3 1815 2110 34.0 Less than 1 year out of retention 1810 216 28.0 1317 314 31.3 1712 1/O 31.3 16/O 3/o 33.7 18/l 311 30.7 In retention Less than 1 year out of retention 1612 II8 30.6 1518 313 26.6 1645 2/11 32.7 Upper first premolars missing 1411 l/4 28.7 Further treatment for ectopic eruption 1614 214 31.10
1316 912 12110 1115 1312
1211 1017 ll/lO 915 1 l/8
Before
Slipped contacts (mm.)
After
Our of retention
Before
34.8 37.5 37.5 34.5 31.8 35.6 37.4 33.5 38.7 31.9 37.1
34.8$ 36.5 37.9 33.7 32.9 34.9 37.0 32.7 38.7 31.3 37.5
IS’/, 18 6 17 4 17 1 1‘I2 7’1, 6 8 2’1,
10 5 4 5 5’12 2’1, 8 2’1, 2 6
32.7t 34.1 35.5 36.2 35.3t
31.8 34.4$ 35.3 35.8 33.7$
7’12 6 9 9 8
2 IV2 2 ‘I2 4 2’1,
35.2 29.9 35.6t
35.1 28.4 34.2
6 I’ll 5’1,
1 2’1, 2’1,
36.lt
32.9
2’1,
1
34.54
34.47
8.69
Out of retention
3.56
*Only expansion appliances used. tRelapse measured from overexpanded position *Less than 15 months’ retention.
underwent expansion after April 27, 1975, were selected. The cases were nearly a year into treatment at the time of selection, and no elimination was permitted on the grounds of poor results or poor cooperation, although these and other problems were noted. All the patients appeared to be Anglo-Saxon with the exception of Patients W and X, two sisters of Per-
sian origin. Of the twenty-five patients, ten were boys and fifteen were girls. These were grouped together. Fifteen patients had Class II, Division 1 malocclusions, and three had Class II, Division 2 malocclusions. While there were no frank Class III cases, four of the Class I cases had one or more incisors in cross-bite at the commencement of treatment. Of seven Class I
58
Mew
Am. J. Orthod. January 1983
Fig. 2. Occlusal views of the maxillary arch beforehand of retention. (See Table I for details.)
cases, Patients L and R had bilateral cross-bites, Patients S and Y had unilateral cross-bites, and Patient V had incisor spacing. Technique
All cases were treated with bioblock Stage 1 appliances (Fig. l),y and a semirapid rate of expansion equivalent to 1 mm. per week was used.8 The actual amount of expansion obviously varied from case to case and was greater for older patients and for those with poor posture, in whom experience has shown that relapse is likely to be greater. Several patients required more than one expansion appliance, either because of breakage or because the single expansion screw could not provide enough widening.
and afterward. Most cases are some years out
In addition to the expansion provided by the widening of the screw, the paired catenary wires behind the upper incisors were adjusted forward 1 mm. at each visit to ensure the correct arch width/arch length relationship (Fig. 1). This provided additional space, and the action of the labial and palatal wires in unison assisted with the alignment and rotation of the incisors. The stated objective of this stage of treatment is to obtain an ideal catenary curve of the maxillary arch with a space of 2.5 mm. between the upper canines and first premolars to accommodate subsequent relapse. The cases were overexpanded 2 to 4 mm. because this is part of the philosophy of bioblock and other forms of treatment.4 Retention was continued for as
Relapse following maxillary expansion
Volume 83 Number 1
59
Fig. 2 (Cont’d).
long as the clinical situation indicated, usually between 1% and 4 years, depending upon the patient’s age and/or any improvement in posture. Inevitably some of the patients did not complete the recommended retention period; these are marked $ in Table I. The maxillary expansion was often accompanied by mandibular correction with other bioblock appliances. This might be expected to assist in supporting the expanded maxilla. Cases not provided with other types of appliance are marked with an asterisk. Fixed appliances were used only in Patients R, S, W, and Y who, by coincidence, have been excluded for other reasons (see below). At the time of this writing, Patients L, R, and S are less than 1 year out of retention, and Patient Y is receiving further treatment for ectopic eruption. These have been excluded from the table, together with one girl (Patient W) whose second premolars were missing. However, all twenty-five cases are illustrated for comparison of these results with the others (Fig. 2).
Extractions In only two of the included cases were any maxillary teeth extracted. In Patients B and P upper second molars were extracted to reduce the chance of the third molars being impacted. Extractions of upper second molars were also recommended for Patients D and G but were declined. Mandibular extractions were also recommended in some cases. Measurements Relapse of overexpansion presents special difficulties. When should the expansion be measured in order to establish the amount of relapse? It would be of little value to measure relapse of the overexpansion, but how can this be distinguished from any undesirable relapse of the remaining expansion that may occur later? It was decided that measurement should be postponed between 2 and 4 months after retention had stopped so that the overexpansion could undergo its initial relapse and that this figure should be compared with the pretreatment and postretention measurements. For four
60
Am. J. Orthod. Janunq~ 1983
Mew
Fig. 3. Patient U with 7.5 mm. of slipped contacts before treatment.
Fig. 4. Patient G with 8 mm. of slipped contacts after treatment, illustrating how the wider arch looks more attractive than Patient U despite greater irregularity.
cases marked * in Table I, this rather precise point was missed and the overexpanded measurement was used instead. These four, therefore, indicate more relapse than was actually the case. The expansion was measured to 0.1 mm. with vernier calipers as the minimum distance at gingival level between the upper first molars. If research is to have a practical value, it must have clinical relevance. Expansion is carried out primarily to eliminate cross-bite, reduce dental crowding, and enable rotations and alignment of the teeth to take place. Success is perhaps best judged on this basis rather than in millimeters of intermolar or intercanine width. For this purpose an index was used, based on the work of Little,” who recorded the crowding of lower incisors by measuring the distance between the slipped contacts. Although not intended for the upper arch, it adapted well. It proved repeatable (see below) and gave an adequate guide of both crowding and rotations, failing only when adjacent teeth were rotated in opposite directions (not a common occurrence). Some estimation had to be made when permanent teeth had not erupted.
RESULTS (TABLE
REPEATABILITY
OF THE MEASUREMENTS
In ten cases (five in the permanent dentition and five in the mixed dentition) measurements of the slipped contacts were repeated after an interval of 1 week. The standard deviation between the first two sets was 0.8 mm., which is not significant, although it was slightly higher (1.48 mm.) for the five mixed-dentition cases which required some estimation. The standard deviation for the ten intermolar widths was 0.03 mm.-a small deviation for a biologic measurement. The reason for this is probably that the minimal unit of measurement (0.1 mm.) was sufficiently large for several cases to achieve identical figures on remeasurement.
I)
The principal point of interest is that the net intermolar increase of 3.5 mm. did not relapse. The slipped contacts improved, on average, more from 8.5 mm. to less than 3.5 mm. DISCUSSION
The lack of relapse requires explanation because it is not in agreement with previous findings.2, ‘* The proponents of this treatment philosophy would claim that it was due to the rate of opening (1 mm. per week), combined with the overexpansion and long retention. However, there are other factors that should be considered. Previous studies have been based on the maximum expansion, and the truth is that these results are not comparable. Obviously, most of the relapse takes place initially and measurements taken 2 to 4 months later are likely to appear more stable. On the other hand, the relapse is to some extent irrelevant, as the object is expansion, and in all cases the “out-of-retention” widening of the upper arch was sufficient to accommodate the lower arch (Fig. 2) without cross-bite. Most clinicians would welcome the means to achieve a permanent expansion of 3.5 mm. when that is required Natural growth must account for some of the widening that has taken place during the 2% years since the retention was stopped. Not much intermolar growth would be expected in this period, however, especially as the children already averaged 14 years of age at the end of retention. Moorrees13 suggested a growth of 1 mm. per year for boys and a reduction of 1 mm. per year for girls. Several authors,14 however, have drawn attention to the irregularity of growth, and it seems that, while the normal maxillae may grow at this rate, narrow maxillae often do not grow at all. In view of the
Relapsefollowing maxillary expansion 61
Volume 83 Number 1
treatment provided, these maxillae presumably fell into this category. During the initial expansion, the teeth tilt to some extent but tend to upright spontaneously during the long period of retention. This means that the widening at the end of retention is less than that gained initially and considerably less than the actual opening of the screw. Expansion alone will usually distort the arch form, which is why the bioblock technique combines the expansion with proclination produced by the catenary wires. It could be argued justifiably that the expansion might have been less stable without the lengthening which allowed the mandible to be brought forward with the activator, an obvious requirement for the Class II cases. Only three cases were treated by expansion alone. Unfortunately, one of these, Case V, was measured from the overexpanded position, giving an artificially high reading. However, the others (N and P) gave readings similar to the rest of the study. It could also be argued that the space gained for alignment of the incisors was as much due to the action of the catenary wires as the expansion but, as both are necessary to create the correct catenary arch curve, there seems to be little reason to disassociate them. The use of slipped contact points as an index of lower incisor crowding was suggested by Little.” No norms exist for upper incisors but 3 mm. seems excellent with less than 5 mm. acceptable, whereas over 10 mm. begins to look rather crowded. This index, however, does not indicate the advantage of the flatter incisal curve. For instance, Patient U had 7.5 mm. of slipped contacts before treatment (Fig. 3) but looks less appealing than Patient G, whose slipped contacts were 8 mm. after treatment (Fig. 4). Only one case approached the unacceptable (Patient A with 10 mm. of slipped contacts), and examination of the case records shows that appliance wear was intermittent from the sixth month onward and ceased 15 months after commencement when a dog destroyed the appliance. The only other high figure,was in Patient G, just discussed (Fig. 4), for whom the initial expansion was not sufficient to create the 2.5 mm. space which is recommended behind each upper canine for the duration of retention. My opinion is that recurrent crowding is always likely if this precaution is ignored, especially as the boy in question did not accept the recommended extraction of second molars at this stage. Patients A, N, and Q did not complete the retention period; Q was also measured from the overexpanded position. However, Patients A and N hardly relapsed at
all and, although Q relapsed 1.6 mm., the net expansion was still 4.6 mm. Overexpansion has introduced a new factor to research in this field which makes it impossible to compare these findings with previous work. However, it is to be hoped that these results can be repeated by others and that clinicians will be encouraged to use maxillary expansion more frequently. It may be of interest for readers to know that, as a result of this study, I now overexpand to a greater extent than beforehand. CONCLUSION
It seems that, under certain conditions, maxillary expansion can provide a useful increase in arch size. In this series, where overexpansion was combined with proclination and the subsequent wearing of an activator, incisor alignment was achieved without extractions in all but two of the twenty included cases. A permanent expansion of 3.5 mm. was obtained with little tendency to relapse. To misquote Townend’O “ . . . Expansion may be comic but extraction can be tragic. ’’ REFERENCES 1. Timms, D.: Rapid maxillary expansion Chicago, 1981, Quintessence Publishing Company. 2. Skieller, V.: Expansion of the midpalatal suture by removable plates analysed by the implant method, Trans. Eur. Qrthod. Sot. pp. 143-158, 1964. 3. Mew, J. R. C.: Bio-block therapy AM. J. ORTHOD. 76: 29-50, 1979. 4. Storey, E.: Tissue response to the movement of bones, AM. J. ORTHOD. 64: 229-241, 1973. 5. Mew, J. R. C.: Semi-rapid maxillary expansion, Br. Dent. J. 143: 301-306, 1977. 6. Hicks, E. P.: Slow maxillary expansion, AM. J. ORTHOD. 73: 121-141, 1978. I. Cotton, L. A.: Slow maxillary expansion, AM. J. ORTHOD. 73: l-24, 1978. 8. Haas, A. J.: Long-term posttreatment evaluation of rapid palatal expansion, Angle Orthod. 50: 189-217, 1980. 9. Chapman, H.: Tooth extraction as an orthodontic measure, Int. Dent. J. 1: 101-130, 1950. 10. Townend, B. R.: The comedy of expansion and the tragedy of relapse, Dent. Mag. Oral Top. 72: 153-166, 1955. 11. Little, R. M.: The irregularity index-A quantitative score of mandibular anterior alignment, AM. J. ORTHOD. 68: 554-563, 1975.
12. Labret, L. M. L.: Expansion with labiolingual and removable appliances, AM. J. ORTHOD. SO: 786-787, 1964. 13. Moorrees, C. F. A.: The dentition of the growing child, Cambridge, 1959, Harvard University Press. 14. Foster, T. D., Grundy, M. C., and Lavelle, C. L. B.: A longitudinal study of dental arch growth, AM. J. ORTHOD. 72: 309-313,
1977.
maxillary
expansion Dr. Mevv
A study of twenty-five
consecutive
cases
John Mew Tunbridge
Wells, England
Twenty-five patients consecutively treated with maxillary expansion were studied. Both successful slnd unsuccessful cases were included, but five were excluded for other reasons. The expansion was measured 2 or 3 months out of retention to allow the overexpansion to settle. Measurements were made again 2X years out of retention. The net expansion had been 3.5 mm., and this had subsequently not relapsed. Possible easons for this are discussed. The associated improvement in dental alignment was measured by an index which is also discussed.
Key words: Semi-rapid maxillary expansion, consecutive cases, overexpansion, relapse, Little’:; index
A
lthough expansion of the maxilla
is one of
the oldest forms of orthodontic treatment, its use has consistently evoked professional controversy. Timms’ describes well the conflicting views of those who have recommended slow expansion, rapid expansion, or no expansion at all. The debate seems to have been all the, more heated because little scientific evidence existed to support any of these views. Opinions were nevertheless so firmly stated that one could be forgiven for wondering if it was, indeed,
the same human animal
that was be-
ing treated in each instance. While individual cases abound, there appear to have been few studies conducted on consecutive cases. A most scientific study was carried out by Skieller,2 who inserted metal implants into thirteen girls and seven boys, using an expansion appliance very similar to the Stage 1 bioblock used in this series.3 This was opened at the rate of 0.5 mm. per week for 7 months and then maintained for 12 months. The cases were not consecutive, and many had cross-bites. Skieller found that both the teeth and the vault widened and that the vault continued to widen both during retention and thereafter. The teeth, however, commenced to relapse at the end of the expansion and continued to do so out of retention, with the relapse amounting on average to about 25 percent of the total opening. Although he does not mention it, Skieller’s figures show that the dental relapse was less for the patients under 9 years old and noticeably higher for those over 12 years of age. He estimates that, at a rate of opening of 0.5 mm. per week, the widening is one-fifth the result of growth at the palatal suture and four-fifths of tooth movement. More recently Storey,4 working on rabbits, sug56
gested that the ideal rate of opening would be about 1 mm. per week, and this has been recommended clinically by several operators. 5-7 Another change in recent years has been the introduction of overexpansion. Haas* has probably been the forerunner in this field, as his publications show. Harold Chapman9 believed that expansion should be used only for cross-bites and certain Class II cases prior to intermaxiliary traction. Attitudes in the United Kingdom were also influenced by Townend’s” rather subjective paper entitled “The Comedy of Expansion and the Tragedy of Relapse. ” It seems possible that the recent introduction of “semirapid” or “slow” expansion at 1 mm. per week, coupled with the use of overexpansion, may justify a reassessment of these views. The present study was undertaken to explore this possibility. THE STUDY Material
It is not easy to collect random cases for a study of this nature. Clinicians will inevitably wish to prove themselves and, even if the cases ware “average” initially, they are unlikely to remain so during treatment. It was thought that these cases should already have received the initial expansion on the chosen day to avoid the possibility of previous case selection or any special attention influencing the results. Also, case selection would need to be made by a third party and should be based on strict parameters. It was decided to exclude only (I ) children younger than 8 or older than 16 years, (2) children unable to attend regularly (that is, those at boarding school), and (3) transfer cases. Other than these, the first twenty-five cases that ooO2-9416/83/010056+06$00.60/0
0
1983 The C. V. Mosby Co.
Volume 83 Number 1
Relapse following
maxillary
expansion
57
Fig. 1. The two versions of the expansion appliance used in this series, the choice depending on the mandibular plane angle.
Table I ---
I
I
I
Intermolar widths (mm.)
YearslMonths Out of retention
Patient
Class
Before
After
A B C D E F G H I J K L M N* 0 P* Q R S T U v* W X Y Average
II/2 II/ 1 II/ 1 II/2 II/l III 1 I II/2 III? III 1 II/ 1 I II/ 1 III 1 II12 I II/ 1 I I III 1 III 1 1 III 1 III 1 I
1314 1210 1112 9110 1019 1116 1218 1114 1.511 812 1317
18/O 315 32.0 1714 211 33.2 1614 317 33.3 1418 l/11 31.1 l5/10 119 28.2 1II4 116 28.0 1713 213 33.4 16/l l/11 27.6 20/8 314 36.4 1218 117 30.3 1815 2110 34.0 Less than 1 year out of retention 1810 216 28.0 1317 314 31.3 1712 1/O 31.3 16/O 3/o 33.7 18/l 311 30.7 In retention Less than 1 year out of retention 1612 II8 30.6 1518 313 26.6 1645 2/11 32.7 Upper first premolars missing 1411 l/4 28.7 Further treatment for ectopic eruption 1614 214 31.10
1316 912 12110 1115 1312
1211 1017 ll/lO 915 1 l/8
Before
Slipped contacts (mm.)
After
Our of retention
Before
34.8 37.5 37.5 34.5 31.8 35.6 37.4 33.5 38.7 31.9 37.1
34.8$ 36.5 37.9 33.7 32.9 34.9 37.0 32.7 38.7 31.3 37.5
IS’/, 18 6 17 4 17 1 1‘I2 7’1, 6 8 2’1,
10 5 4 5 5’12 2’1, 8 2’1, 2 6
32.7t 34.1 35.5 36.2 35.3t
31.8 34.4$ 35.3 35.8 33.7$
7’12 6 9 9 8
2 IV2 2 ‘I2 4 2’1,
35.2 29.9 35.6t
35.1 28.4 34.2
6 I’ll 5’1,
1 2’1, 2’1,
36.lt
32.9
2’1,
1
34.54
34.47
8.69
Out of retention
3.56
*Only expansion appliances used. tRelapse measured from overexpanded position *Less than 15 months’ retention.
underwent expansion after April 27, 1975, were selected. The cases were nearly a year into treatment at the time of selection, and no elimination was permitted on the grounds of poor results or poor cooperation, although these and other problems were noted. All the patients appeared to be Anglo-Saxon with the exception of Patients W and X, two sisters of Per-
sian origin. Of the twenty-five patients, ten were boys and fifteen were girls. These were grouped together. Fifteen patients had Class II, Division 1 malocclusions, and three had Class II, Division 2 malocclusions. While there were no frank Class III cases, four of the Class I cases had one or more incisors in cross-bite at the commencement of treatment. Of seven Class I
58
Mew
Am. J. Orthod. January 1983
Fig. 2. Occlusal views of the maxillary arch beforehand of retention. (See Table I for details.)
cases, Patients L and R had bilateral cross-bites, Patients S and Y had unilateral cross-bites, and Patient V had incisor spacing. Technique
All cases were treated with bioblock Stage 1 appliances (Fig. l),y and a semirapid rate of expansion equivalent to 1 mm. per week was used.8 The actual amount of expansion obviously varied from case to case and was greater for older patients and for those with poor posture, in whom experience has shown that relapse is likely to be greater. Several patients required more than one expansion appliance, either because of breakage or because the single expansion screw could not provide enough widening.
and afterward. Most cases are some years out
In addition to the expansion provided by the widening of the screw, the paired catenary wires behind the upper incisors were adjusted forward 1 mm. at each visit to ensure the correct arch width/arch length relationship (Fig. 1). This provided additional space, and the action of the labial and palatal wires in unison assisted with the alignment and rotation of the incisors. The stated objective of this stage of treatment is to obtain an ideal catenary curve of the maxillary arch with a space of 2.5 mm. between the upper canines and first premolars to accommodate subsequent relapse. The cases were overexpanded 2 to 4 mm. because this is part of the philosophy of bioblock and other forms of treatment.4 Retention was continued for as
Relapse following maxillary expansion
Volume 83 Number 1
59
Fig. 2 (Cont’d).
long as the clinical situation indicated, usually between 1% and 4 years, depending upon the patient’s age and/or any improvement in posture. Inevitably some of the patients did not complete the recommended retention period; these are marked $ in Table I. The maxillary expansion was often accompanied by mandibular correction with other bioblock appliances. This might be expected to assist in supporting the expanded maxilla. Cases not provided with other types of appliance are marked with an asterisk. Fixed appliances were used only in Patients R, S, W, and Y who, by coincidence, have been excluded for other reasons (see below). At the time of this writing, Patients L, R, and S are less than 1 year out of retention, and Patient Y is receiving further treatment for ectopic eruption. These have been excluded from the table, together with one girl (Patient W) whose second premolars were missing. However, all twenty-five cases are illustrated for comparison of these results with the others (Fig. 2).
Extractions In only two of the included cases were any maxillary teeth extracted. In Patients B and P upper second molars were extracted to reduce the chance of the third molars being impacted. Extractions of upper second molars were also recommended for Patients D and G but were declined. Mandibular extractions were also recommended in some cases. Measurements Relapse of overexpansion presents special difficulties. When should the expansion be measured in order to establish the amount of relapse? It would be of little value to measure relapse of the overexpansion, but how can this be distinguished from any undesirable relapse of the remaining expansion that may occur later? It was decided that measurement should be postponed between 2 and 4 months after retention had stopped so that the overexpansion could undergo its initial relapse and that this figure should be compared with the pretreatment and postretention measurements. For four
60
Am. J. Orthod. Janunq~ 1983
Mew
Fig. 3. Patient U with 7.5 mm. of slipped contacts before treatment.
Fig. 4. Patient G with 8 mm. of slipped contacts after treatment, illustrating how the wider arch looks more attractive than Patient U despite greater irregularity.
cases marked * in Table I, this rather precise point was missed and the overexpanded measurement was used instead. These four, therefore, indicate more relapse than was actually the case. The expansion was measured to 0.1 mm. with vernier calipers as the minimum distance at gingival level between the upper first molars. If research is to have a practical value, it must have clinical relevance. Expansion is carried out primarily to eliminate cross-bite, reduce dental crowding, and enable rotations and alignment of the teeth to take place. Success is perhaps best judged on this basis rather than in millimeters of intermolar or intercanine width. For this purpose an index was used, based on the work of Little,” who recorded the crowding of lower incisors by measuring the distance between the slipped contacts. Although not intended for the upper arch, it adapted well. It proved repeatable (see below) and gave an adequate guide of both crowding and rotations, failing only when adjacent teeth were rotated in opposite directions (not a common occurrence). Some estimation had to be made when permanent teeth had not erupted.
RESULTS (TABLE
REPEATABILITY
OF THE MEASUREMENTS
In ten cases (five in the permanent dentition and five in the mixed dentition) measurements of the slipped contacts were repeated after an interval of 1 week. The standard deviation between the first two sets was 0.8 mm., which is not significant, although it was slightly higher (1.48 mm.) for the five mixed-dentition cases which required some estimation. The standard deviation for the ten intermolar widths was 0.03 mm.-a small deviation for a biologic measurement. The reason for this is probably that the minimal unit of measurement (0.1 mm.) was sufficiently large for several cases to achieve identical figures on remeasurement.
I)
The principal point of interest is that the net intermolar increase of 3.5 mm. did not relapse. The slipped contacts improved, on average, more from 8.5 mm. to less than 3.5 mm. DISCUSSION
The lack of relapse requires explanation because it is not in agreement with previous findings.2, ‘* The proponents of this treatment philosophy would claim that it was due to the rate of opening (1 mm. per week), combined with the overexpansion and long retention. However, there are other factors that should be considered. Previous studies have been based on the maximum expansion, and the truth is that these results are not comparable. Obviously, most of the relapse takes place initially and measurements taken 2 to 4 months later are likely to appear more stable. On the other hand, the relapse is to some extent irrelevant, as the object is expansion, and in all cases the “out-of-retention” widening of the upper arch was sufficient to accommodate the lower arch (Fig. 2) without cross-bite. Most clinicians would welcome the means to achieve a permanent expansion of 3.5 mm. when that is required Natural growth must account for some of the widening that has taken place during the 2% years since the retention was stopped. Not much intermolar growth would be expected in this period, however, especially as the children already averaged 14 years of age at the end of retention. Moorrees13 suggested a growth of 1 mm. per year for boys and a reduction of 1 mm. per year for girls. Several authors,14 however, have drawn attention to the irregularity of growth, and it seems that, while the normal maxillae may grow at this rate, narrow maxillae often do not grow at all. In view of the
Relapsefollowing maxillary expansion 61
Volume 83 Number 1
treatment provided, these maxillae presumably fell into this category. During the initial expansion, the teeth tilt to some extent but tend to upright spontaneously during the long period of retention. This means that the widening at the end of retention is less than that gained initially and considerably less than the actual opening of the screw. Expansion alone will usually distort the arch form, which is why the bioblock technique combines the expansion with proclination produced by the catenary wires. It could be argued justifiably that the expansion might have been less stable without the lengthening which allowed the mandible to be brought forward with the activator, an obvious requirement for the Class II cases. Only three cases were treated by expansion alone. Unfortunately, one of these, Case V, was measured from the overexpanded position, giving an artificially high reading. However, the others (N and P) gave readings similar to the rest of the study. It could also be argued that the space gained for alignment of the incisors was as much due to the action of the catenary wires as the expansion but, as both are necessary to create the correct catenary arch curve, there seems to be little reason to disassociate them. The use of slipped contact points as an index of lower incisor crowding was suggested by Little.” No norms exist for upper incisors but 3 mm. seems excellent with less than 5 mm. acceptable, whereas over 10 mm. begins to look rather crowded. This index, however, does not indicate the advantage of the flatter incisal curve. For instance, Patient U had 7.5 mm. of slipped contacts before treatment (Fig. 3) but looks less appealing than Patient G, whose slipped contacts were 8 mm. after treatment (Fig. 4). Only one case approached the unacceptable (Patient A with 10 mm. of slipped contacts), and examination of the case records shows that appliance wear was intermittent from the sixth month onward and ceased 15 months after commencement when a dog destroyed the appliance. The only other high figure,was in Patient G, just discussed (Fig. 4), for whom the initial expansion was not sufficient to create the 2.5 mm. space which is recommended behind each upper canine for the duration of retention. My opinion is that recurrent crowding is always likely if this precaution is ignored, especially as the boy in question did not accept the recommended extraction of second molars at this stage. Patients A, N, and Q did not complete the retention period; Q was also measured from the overexpanded position. However, Patients A and N hardly relapsed at
all and, although Q relapsed 1.6 mm., the net expansion was still 4.6 mm. Overexpansion has introduced a new factor to research in this field which makes it impossible to compare these findings with previous work. However, it is to be hoped that these results can be repeated by others and that clinicians will be encouraged to use maxillary expansion more frequently. It may be of interest for readers to know that, as a result of this study, I now overexpand to a greater extent than beforehand. CONCLUSION
It seems that, under certain conditions, maxillary expansion can provide a useful increase in arch size. In this series, where overexpansion was combined with proclination and the subsequent wearing of an activator, incisor alignment was achieved without extractions in all but two of the twenty included cases. A permanent expansion of 3.5 mm. was obtained with little tendency to relapse. To misquote Townend’O “ . . . Expansion may be comic but extraction can be tragic. ’’ REFERENCES 1. Timms, D.: Rapid maxillary expansion Chicago, 1981, Quintessence Publishing Company. 2. Skieller, V.: Expansion of the midpalatal suture by removable plates analysed by the implant method, Trans. Eur. Qrthod. Sot. pp. 143-158, 1964. 3. Mew, J. R. C.: Bio-block therapy AM. J. ORTHOD. 76: 29-50, 1979. 4. Storey, E.: Tissue response to the movement of bones, AM. J. ORTHOD. 64: 229-241, 1973. 5. Mew, J. R. C.: Semi-rapid maxillary expansion, Br. Dent. J. 143: 301-306, 1977. 6. Hicks, E. P.: Slow maxillary expansion, AM. J. ORTHOD. 73: 121-141, 1978. I. Cotton, L. A.: Slow maxillary expansion, AM. J. ORTHOD. 73: l-24, 1978. 8. Haas, A. J.: Long-term posttreatment evaluation of rapid palatal expansion, Angle Orthod. 50: 189-217, 1980. 9. Chapman, H.: Tooth extraction as an orthodontic measure, Int. Dent. J. 1: 101-130, 1950. 10. Townend, B. R.: The comedy of expansion and the tragedy of relapse, Dent. Mag. Oral Top. 72: 153-166, 1955. 11. Little, R. M.: The irregularity index-A quantitative score of mandibular anterior alignment, AM. J. ORTHOD. 68: 554-563, 1975.
12. Labret, L. M. L.: Expansion with labiolingual and removable appliances, AM. J. ORTHOD. SO: 786-787, 1964. 13. Moorrees, C. F. A.: The dentition of the growing child, Cambridge, 1959, Harvard University Press. 14. Foster, T. D., Grundy, M. C., and Lavelle, C. L. B.: A longitudinal study of dental arch growth, AM. J. ORTHOD. 72: 309-313,
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