- Email: [email protected]
Expansion of the lower arch concurrent with rapid maxillary expansion
Expansion of the lower arch concurrent maxillary expansion
with rapid
Robin A. Sandstrom, DDS, MS,* Lewis Klapper, DDS, MSc, DSc,** and Stavros Papaconstantinou, LDS, MS, Dr. Dent.* Athens, Greece, and Chicago, 111.
The effect of rapid maxillary expansion on the mandibular intercanine and intermolar widths during treatment and its stability after retention was studied. In addition, the relationships between the interarch change and the facial types and ages of the subjects of the sample were evaluated. The sample consisted of 17 cases for the study of intercanine width, and 22 nonextraction cases for the study of the intermolar width. Initial, final, at least 2-years postretention models, and initial lateral cephalograms were analyzed. Treatment and postretention changes for the intercanine width and the mesial and distal intermolar widths were calculated and tested for significance. Mean expansions of the intercanine width of 1 .l mm and of the intermolar width of 2.8 mm postretention were found to be statistically significant. There were no correlations found between the amount of increase in arch width and the facial types and ages of the subjects. (AM J ORTHOD DENTOFAC ORTHOP 1988;94:296-302.)
T
he recent literature’.2,4.7.8.‘9.24on the stability of the lower arch after orthodontic treatment shows a tendency for the intercanine width to lose the expansion gained during treatment, with the teeth moving toward their initial positions. The intermolar width indicates a similar pattern, with a smaller tendency toward relapse. In contrast, Walte?3 concluded that mandibular arch width could be expanded permanently. The findings on the amount of interarch change display variation. This n?ay possibly be attributed to the differing posttreatment time, sample distribution as to facial and malocclusion types, and sample size of the different studies. Although the literature has provided little guidance for predicting which cases tolerate greater expansion, there appears to be a tendency for the Class II, Division 2 cases to show a greater potential for retaining some increase in arch width.” In addition, Schulhof and associates2oderived a formula indicating that a patient with a brachyfacial pattern will have a wider arch than the dolichofacial type. Some clinicians’6,‘7 have concluded that intercanine expansion is more stable after extractions. However, this has been contradicted2~4~8.‘9~2’~24 by others who have demonstrated no significant difference between extraction and nonextraction groups. Clinical observation has given some indication9~10~12~25 of the possibility of achieving a stable ex-
pansion of the lower arch subsequent to expansion of the midpalatal suture. Haas,9.‘0 using a midpalatal suture-opening appliance without any treatment in the lower arch, observed that the mandibular arch tended to follow the maxillary teeth by tipping laterally. In a later study,‘* he reported on the long-term posttreatment evaluation of rapid palatal expansion. Some cases achieved and maintained an expansion of 3 to 4 mm in the lower intercanine width, and up to 6 mm in the intermolar width. He claimed that mandibular intercanine width can be increased in the nongrower if the apical base of the maxillary complex is permanently widened. Wertzz5 reported on cases that underwent palatal expansion. At the completion of suture opening, he observed that there had been an average mandibular intermolar increase of 5 mm. When the palatal-splitting appliance was removed, the younger patients showed a negligible change, but there was an average increase of almost 1 mm in those patients more than 18 years of age. The purpose of this study was to evaluate the effect of rapid maxillary expansion on the mandibular intercanine and intermolar widths during treatment and its stability after retention. The relationships between the interarch change and facial types and ages of the subjects of the sample were also studied. MATERIALS AND METHOD
This article is based on a thesis submitted in partial fulfillment of science degree, Loyola University *In private practice, Athens.
**Chairman, 296
Orthodontic
Department,
School of Dentistry.
Loyola University.
for the master
The material used for this study included the records of 28 cases from the private practice of Andrew Haas, of Cuyahoga Falls, Ohio. All patients had undergone
Volume 94 Number
Lower arch expansion concurrent
4
rapid maxillary expansion with a tissue-borne appliance according to Dr. Haas’ published technique’-” and subsequent orthodontic treatment. The records consisted of the initial, posttreatment, and postretention study models, and the initial lateral cephalogram of each patient. The man’dibular canine and molar arch widths were analyzed separately. Cases meeting the necessary requirements were included in both groups.
with RME
297
+4j QUADRANT
QUADRANT
Ii
Treatment-Decrease
I
Treatment-Increase
Canines
This group comprised 17 cases-8 male and 9 female patients. The mean age at initiation of treatment was 14 years, with a range of 9.6 to 19.6 years. After treatment, a fixed lingual retainer was placed for an average of 5.6 years, with a range of 2 to 8 years. The postretention models were required at least 2 years after the removal of tihe lingual retainer. It was also required that these cases possess the permanent mandibular canines in the initial models.
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Measurements
Measurements were taken between the cusp tips of permanent canines and between the summits of the mesiolingual and distolingual cusps of the permanent first molars. When the teeth displayed extensive abrasion or restorations, other landmarks such as the labial and lingual central ridges of the canines and the grooves and fissures in the first molars were used to select the most reproducible points. Each cast was then placed on the base of a :surveyor. The dots were recorded with a two-dimensional digitizer connected to a 360 IBM computer. Measurements were recorded to the nearest 0.01 mm. Error of the method
To verify the accuracy of the method, all dimensions were measured independently by two observers. A twosample t test was performed between the changes in intercanine and intermolar widths as measured by one observer against the same changes as measured by the second observer. The results indicated there was no significant difference between the two observers’ measurements of thelse changes at p -=L0.01.
Post-treatment-Decrease
IV
Treatment-Increase
~
Post-treatment-Decrease
, /
7-4
-3
-2 Treatment
Fig.
Molars
This group consisted of 22 cases- 11 male and 11 female patients. The mean age at initiation of treatment was 12.6 years, with a range of 6.4 to 21.9 years. The postretention models were taken an average of 8.8 years after the end of treatment, with a minimum of 2 years required. Cases with extractions of permanent teeth of the lower arch !excluding third molars) were not included in this group.
QUADRANT I I
Treatment-Decrease
7
z0
Ill
1. ExplanaZon
-1 Change
Y
Cl
t2
in Dimension
of the four-quadrant
+3
t4
I” mm.
graph.
Analysis
Three changes in arch width were studied: 1. Treatment change: Difference between initial and posttreatment measurements 2. Postretention change: Difference between the posttreatment and postretention measurements 3. Net change: Difference between initial and postretention measurements Student’s t test was performed to determine whether these changes in arch widths were significantly different from zero. To determine whether the mesial points of the molars were significantly more expanded than the distal points, a two-sample t test was performed between the net change of the mesial intermolar width against the net change of the distal intermolar width. The data were plotted in the four-quadrant graph as described by Arnold.’ The X or horizontal axis is the treatment axis. The Y or vertical axis is the posttreatment axis. Any change during treatment or posttreatment may be quantitatively shown along the X axis and Y axis, respectively (Fig. 1). The initial lateral cephalograms of the entire sample were classified into facial types. The facial type index was calculated with the five measurements used by Ricketts” to describe facial types and the formula described by Christie.6 For each measurement the amount of clinical deviation from the norm according to sex and age was determined as follows: Clinical
deviation
from norm =
Measured value - Norm Clinical deviation
298
Sandstrom,
Klapper,
and
Am. J. Orthod.
Papaconstantinou
Dentofac. Orthop. October 1988
Table I. Changes in width (mm) Treatment Width
Mean
Intercanine Intermolar mesial Intermolar distal
2.2 3.3 2.9
Postretention
change
SD
Range
1.3 2.0 2.0
-0.1 to 4.4 -0.6 to 6.7 -0.9 to 7.4
change
Mean
SD
Range
-1.0 -0.5 -0.3
0.9 1.7 2.0
-3.5 to -0.1 -3.5 to 3.9 -4.3 to 4.9
Net change Mean
1.1 2.8 2.5
SD
Range
1.5 2.2 2.5
-0.3 to 3.8 - 1.3 to 8.5 - 1.5 to 8.6
Positive = increase; negative = decrease.
Table II. Statistical significance of width changes Dimension Pretreatment
Observer vs. posttreatment
= Treatment
Intercanine width
Intermolar (distal) Posttreatment
vs. postretention
= Posttreatment
Intercanine width Intermolar (mesial) Intermolar (distal) Pretreatment
vs. postretention
Intercanine width Intermolar (mesial) Intermolar (distal)
P
change
A B A B A B
Intermolar (mesial)
t
6.74 6.52 7.45 7.76 6.05 6.90
p p p p p p
< < < < L <
o.ooo5 o.ooo5 o.ooo5 o.ooo5 0.0005 o.ooo5
A B A B A B
-5.02 - 3.46 - 1.01 -1.85 -0.42 -0.99
p p p p p p
< < > > > >
0.005 0.005 0.05* 0.05* 0.05* 0.05*
A B A B A B
3.01 2.94 5.90 5.61 4.73 4.64
p p p p p p
< < < c < <
0.005 0.005 0.0005 o.ooo5 0.0005 o.ooo5
change
= Net change
*Values not statistically significant.
The clinical deviations from the norm for each of the five measurements were then averaged to calculate the facial type index. Then, each patient’s facial type index was correlated against its corresponding intercanine and intermolar net changes in width, and a t test was run to confirm whether there was a significant relationship between these two factors. The age of each member of the sample at initiation of treatment was correlated against the respective intercanine and intermolar net changes in width. A t test was run between these two factors. FINDINGS
Table I shows the means, standard deviations, and ranges of the treatment, posttreatment, and net changes for the intercanine width and the mesial and distal intermolar widths. These values are the average between observers A and B. Fig. 2 graphically displays the
average increase in width during treatment and the subsequent postretention decrease for the three dimensions studied. It is readily apparent that the canines display a greater posttreatment decrease in width than the molars. Table II shows the significance of the treatment, posttreatment, and net changes for the intercanine width and the mesial and distal intermolar widths. The t values and their levels of significance are displayed separately for each observer in this table. The increase during treatment was significant for each of the three dimensions studied at p = 0.0005. In the posttreatment interval, there was a significant decrease in intercanine width at p = 0.05, while the decrease observed for the intermolar width was not found to be statistically significant at p = 0.05. The net change was significant for the canines and for the molars at p = 0.0005. The results of the paired t tests were consistent for both
Volume 94 Number
Lower arch expansion concurrent
4
with RME
299
1 +4 Mesial .+3
QUADRANT
II
QUADRANT
E $+2
I
I
I! z +1 .c
Width
I ,
H ,” x 0 E m-1 E 2 F
j
l .., l
QUADRANT
III
‘*
. .
QUADRANT
: a-3 Treatment Change
.
.
r-2 lnltial
l l
IV
.
Net Change -4
Fig. 2. Change during treatment and postretention of the canine and intermolar widths.
/
-4
observers in all cases, indicating that the results obtained were independent of the observer. Intercanine width
The mean net change in intercanine arch width was 1.1 mm, SD 1.5 mm. The data of the changes in width during treatment and posttreatment are plotted in Fig. 3. Sixteen of 17 cases show a treatment increase and a posttreatment decrease. lntermolar widths
The mean expansion retained was 2.8 mm, SD 2.2 mm, for the mesial arch width; and 2.5 mm, SD 2.5 mm, for the distal arch width. The results of the two-sample t test, which was performed between the mean net change displayed by the mesial points as compared with the (distal point on the molars, show there was no significant difference (p = 0.1). This demonstrates that the molars had been evenly expanded rather than rotated. The data of the treatment and posttreatment changes are shown in Figs. 4 and 5 for the mesial and distal intermolar widths, respectively. These graphs are similar to those shown in Fig. 3 except for the addition of a Z axis. Any (case above the Z axis indicates a net gain in width; any case below the Z axis indicates a net loss in width. The observations on the frequency of the net mesial and distal intenmolar widths may be summarized as follows: 1. Sixty-eight percent of the mesial and 55% of the distal measurements exhibited a pattern of treatment increase with posttreatment decrease. 2. Twenty-three percent of the mesial and 32% of the distal measurements exhibited a pattern of
I
-3
I
-2
I
-1
Treatment
/
Y
1
+1
/
+2
I
+3
I
+4
Change in Width in mm.
Fig. 3. Treatment change and posttreatment change in intercanine width of 17 cases.
increase during treatment with a further posttreatment increase. Fig. 6 is a histogram representing the frequency of the facial-type distribution of the entire sample. A minus sign ( - ) indicates a dolichofacial tendency. A plus sign ( + ) indicates a brachyfacial tendency. It is obvious from the graph that this sample displays a marked tendency toward the dolichofacial type. Table III shows the correlations and t tests between (1) the net changes of the canine arch widths and the mesial and distal molar arch widths, and (2) the respective facial-type indices of the sample. It shows there is no correlation. Table IV displays the correlations and t tests between (1) the net changes of the intercanine widths and the mesial and distal intermolar widths, and (2) the corresponding age of the sample at initiation of treatment. It shows there is no significant relationship. DISCUSSION
The results of this study indicate that a statistically significant increase of the mandibular intercanine and intermolar widths may be achieved when orthodontic treatment is combined with rapid maxillary orthopedic expansion. An important aspect of this study is that the entire sample was treated by one clinician, Dr. Haas, whose particular techniqueg.“.12 is relevant to the results of this study.
300
Sandstrom, Klapper,
Am. .I. Orthod.
and Papaconstantinou
+7
13
+6
12
:+5 E +4
11
5+3 s .E +2
9
Dentofac. Orthop. October 1988
10
8
g+1 2 x
7
O-1 r;
6
E -2
5
2 -3
4
+ -4
3
5 -5 a
-6
-2 -7-6-S-4-3-2-1
Y+1+2+3+4+5+6+7
Treatment
Change
-1
Standard
0
+1
+2
Deviations
in Width in mm.
Fig. 6. Facial type index. On 2 axis-original
and Post-retention mesial intermolar widths remain the same.
Below Z axis - Effective
decrease
in width.
Above Z axis - Effective
increase
in width.
Fig. 4. Treatment change and posttreatment change in mesial intermolar width of 22 cases.
Table III. T tests and correlations between the net change in intercanine width, mesial and distal intermolar widths and facial types of the sample Dimension
Canine Mesial molar Distal molar *Values
.E al !i 6 5 E 2 7L
not statistically
Correlation
t
0.28 -0.05 -0.05
1.16 0.25 0.25
P
p > 0.10* p > 0.10* p > 0.10*
significant.
+2
Table IV. T tests and correlations between the net change in intercanine width, mesial and distal intermolar widths and the age of the sample
+1 x -1 -2 -3
T
-4 -5
:
-6
Dimension
Canine Mesial molar Distal molar -7-6-6-4-3-2-l
0.30 -0.13 -0.05
ItI
p
1.16 0.38 0.25
p > 0.10* p > 0.10* p > 0.10*
Yt1+2+3+4+5+6+7
*Values Treatment
Correlation
not statistically
significant.
Change in Width in mm
On Z axis - Original and Post-retention widths the same.
distal intermolar
Below Z axis - Effective
decrease
in wtdth.
Above Z axis -Effective
increase
in width
Fig. 5. Treatment change and posttreatment change in distal intermolar width of 22 cases.
lntercanlne width The pattern of treatment increase and posttreatment decrease observed in this study is in accordance with other investigations’~2,7,‘g,24of the changes of intercanine
width after conventional orthodontic treatment. However, in this sample only 48% of the expansion gained during treatment was lost postretention as compared with a loss of 77% observed by Welch,24 76.3% observed by Amott,’ 71.4% observed by Bishara, Chadha, and Potter,4 and 58% observed by Gardner and Chaconas .’ The mean net increase in intercanine width of 1.1 mm found in this study is greater than the net increase found in other orthodontic studies, such as 0.22 mm shown by Bishara and associates,4 0.52 mm shown by Welch,24 -0.17 mm shown by Dona,’ 0.51 mm in extraction and 0.58 mm in nonextraction cases shown
Volume 94 Number 4
Lower arch expansion concurrent
by Gardner and Chaconas,’ and -0.4 shown by Shapiro.” The net increases found in the previously cited studies were not statistically significant. Only when the samples in two of the studies, by Amott’ and Shapiro,” were divided according to malocclusions could a significant increas,e in Class II, Division 2 cases be found. In the present study, there were no cases of Class II, Division 2 malocclusion. The increase in intercanine width of 1.1 mm found in this study is clearly the result of treatment and not growth since the presence of the permanent canines in the initial models was required. It has been shown that no further increase in the intercanine width is to be expected after the eruption of the permanent canines, but a decrease is possible, ranging from 0.5 to 1.5 mm1.3.5’13.14 22 Intermolar
widlths
To compare the results of the present study to other investigations, the mesial intermolar net expansion was evaluated because it is the point that other have selected for their measurements. studies 1~2~7~8~‘9~2‘1 The findings show that the net mesial intermolar expansion achieved and retained in this study was 2.8 mm, I~I2.2 mm SD. This is greater than 1.2 mm, 11.5 mm SD, found by Dona, and 0.9 mm, 4 1.3 mm SD, found by Arnold,* in their nonextraction samples. It is alsa’ greater than 2 mm, ? 1.8 SD, found by Gardner and! Chaconas,8 and 1 mm, rt 1.9 SD, found in Shapiro’s sample. I9 In Class II, Division 2 cases, Shapiro found a net expansion of 1.5 mm, which is less than that found in this study. As noted previously, the present sample did not include Class II, Division 2 cases. The sample used for the study of intermolar widths had a mean age at initiation of treatment of 12.6 years, with half the group younger than this age. Although this sample is 1:oo small to divide and analyze statistically according to age, it is of interest to note that the mean expansion for the cases under 12 years of age was 3.5 mm, which is greater than the 2.8 mm found in the entire sample. Furthermore, of the eight cases that displayed a pattern of treatment increase with a further posttreatment increase, six were under 12 years of age. It may be inferred that any increase in width occurring before the age of 12 that may have occurred as a result of growth does not preclude additional expansion obtained as a result of treatment. In the present study, there was no relationship found between the amount of interarch expansion achieved and retained, and the facial typing of the sample. There is no support to the widespread notion that brachyfacial types can sustain more expansion than other facial types. Schulholf and associateszOdescribed a formula
with RME
301
that establishes an individualized norm for intercanine width, indicating that even though brachyfacial types do have wider arches, they do not tolerate more expansion beyond their norm than other facial types. Class II, Division 2 cases, which usually indicate brachyfacial type, have been proved to retain a greater orthodontic expansion.” However, this is probably because the lower teeth in these cases are usually enclosed in the upper dentition and lingually positioned due to the excessive overbite. The stability of the expanded mandibular arch width may be the result of an altered muscular balance exerted on the dentition by the buccinator muscles, which have been carried laterally by the maxillary expansion. It may also be attributed to the altered forces of occlusion. Factors that may contribute to the variation of the amount of expansion retained may be the amount of initial incisor crowding, the initial lingual inclination of the mandibular buccal segments, the changes in skeletal pattern in the facial lateral cephalogram, or the initial arch width. Another important factor may be the difference between the initial arch width of each individual and the ideal arch width, according to Schulhof ‘s individualized norms ,‘Ocorrelated to the amount of expansion retained. CONCLUSION
1. The mean increase of the intercanine width, retained after at least a 2-year postretention period, was 1.1 mm. This gain is small but statistically significant as compared with its initial width; it is higher than the expansion found to occur with conventional orthodontic treatment. 2. The mean expansion of the intermolar width, retained after at least a 2-year postretention period, was 2.8 mm. This is statistically significant as compared with its initial width; it is higher than the expansion found with conventional orthodontic treatment. 3. There were no correlations found between the net expansion of the intercanine and intermolar widths and the facial types and ages of the subjects. We would like to express our gratitude to Dr. Andrew Haasfor making this study possibleby offering the invaluable material from his private practice. REFERENCES 1. Amott RD. A serial study of dental arch measurements on orthodontic subjects [Master’s thesis]. Evanston, Illinois: Northwestem University, 1962. 2. Arnold ML. A study of the changes of the mandibular intercanine and intermolar widths during orthodontic treatment and following post-retention period of five or more years [Master’s thesis]. Seattle: University of Washington, 1963. 3. Barrow GV, White R Jr. Developmental change8 of the maxillary and mandibular dental arches. Angle Orthod 1952;22:41-6.
302 Sandstrom, Klapper,
Am. J. Orthod.
and Papaconstantinou
4. Bishara SE, Chadha JM, Potter RB. Stability of the intercanine width, overbite, and overjet correction. AM .I ORTHOD 1973; 63588-95. 5. Brown VP, Jensen D. Changes in the dentition from the early teens to the early twenties. Acta Odontol Stand 1951;9: 177-92. 6. Christie T. Cephalometric patterns of adults with normal occlusions. Angle Orthod 1977;47:128-35. 7. Dona A. An analysis of dental casts of patients made before and after orthodontic treatment [Master’s thesis]. Seattle: University of Washington, 1952. 8. Gardner DS, Chaconas SJ. Post-treatment and post-retention changes following orthodontic therapy. Angle Orthod 1977;46: 186-92. 9. Haas A. Rapid expansion of the maxillary dental arch and nasal cavity by opening the mid-palatal suture. Angle Orthod 1961;31:73-90. 10. Haas A. The treatment of maxillary deficiency by opening the mid-palatal suture. Angle Orthod 1965;65:200-17. 11. Haas A. Expansion, just the beginning of dentofacial orthopedics. Alvl J ORTHOD 1970;57:219-54. 12. Haas A. Long term post-treatment evaluation of rapid palatal expansion. Angle Orthod 1980;50:189-217. 13. Knott V. Longitudinal study of dental arch widths at four stages of dentition. Angle Orthod 1972;42:200-13. 14. Moorrees CFA, Chadha MJ. Available space to the incisors during dental development. A growing study based on physiologic age. Angle Orthod 1965;35: 12-22. 15. Moorrees CFA. The dentition of the growing child. Cambridge: Harvard University Press, 1959:99-100. 16. Moyers RE, Van Der Linden FPG, Riolo ML, McNamara JA.
Dentofac. Orthop. October 1988
Standards of human occlusal development. Monograph 5, Craniofacial Growth Series. Ann Arbor: 1976. Center for Human Growth and Development, University of Michigan. 17. Nance HN. The limitations of orthodontic treatment. AM J ORTHOD ORAL SURG 1947;33:253-301.
Ricketts RM, Bench RW, Guguino CF, Hilgers JJ, Schulhof RJ. Bioprogressive therapy. Denver: Rocky Moutain Orthodontics, 1971. 19. Shapiro PA. Mandibular arch form and dimension. AM J ORTHOD 18.
1974;66:58-70.
20. Schulhof RJ. The mandibular dental arch. Part III. Buccal expansion. Angle Orthod 1978;48:303-10. 21. Sondi A. Dimensional changes in the dental arches of orthodontically treated cases. AM J ORTHOD 1980;77: 1-12. 22. Speck NT. A longitudinal study of the developmental changes in human lower dental arches. Angle Orthod 1950;20:215-28. 23. Walter DC. Comparative changes in mandibular canine and first molar widths. Angle Orthod 1962;32:232-40. 24. Welch KN. A study of treatment and post-retention dimensional changes in mandibular dental arches [Master’s thesis]. Seattle: University of Washington, 1965. 25. Wertz R. Mid-palatal suture opening: a normative study. AM J ORTHOD 1977;71:367-81. Reprint
requests
to:
Dr. Robin Sandstrom Papathanasiou St. Peania, Attica Greece
with rapid
Robin A. Sandstrom, DDS, MS,* Lewis Klapper, DDS, MSc, DSc,** and Stavros Papaconstantinou, LDS, MS, Dr. Dent.* Athens, Greece, and Chicago, 111.
The effect of rapid maxillary expansion on the mandibular intercanine and intermolar widths during treatment and its stability after retention was studied. In addition, the relationships between the interarch change and the facial types and ages of the subjects of the sample were evaluated. The sample consisted of 17 cases for the study of intercanine width, and 22 nonextraction cases for the study of the intermolar width. Initial, final, at least 2-years postretention models, and initial lateral cephalograms were analyzed. Treatment and postretention changes for the intercanine width and the mesial and distal intermolar widths were calculated and tested for significance. Mean expansions of the intercanine width of 1 .l mm and of the intermolar width of 2.8 mm postretention were found to be statistically significant. There were no correlations found between the amount of increase in arch width and the facial types and ages of the subjects. (AM J ORTHOD DENTOFAC ORTHOP 1988;94:296-302.)
T
he recent literature’.2,4.7.8.‘9.24on the stability of the lower arch after orthodontic treatment shows a tendency for the intercanine width to lose the expansion gained during treatment, with the teeth moving toward their initial positions. The intermolar width indicates a similar pattern, with a smaller tendency toward relapse. In contrast, Walte?3 concluded that mandibular arch width could be expanded permanently. The findings on the amount of interarch change display variation. This n?ay possibly be attributed to the differing posttreatment time, sample distribution as to facial and malocclusion types, and sample size of the different studies. Although the literature has provided little guidance for predicting which cases tolerate greater expansion, there appears to be a tendency for the Class II, Division 2 cases to show a greater potential for retaining some increase in arch width.” In addition, Schulhof and associates2oderived a formula indicating that a patient with a brachyfacial pattern will have a wider arch than the dolichofacial type. Some clinicians’6,‘7 have concluded that intercanine expansion is more stable after extractions. However, this has been contradicted2~4~8.‘9~2’~24 by others who have demonstrated no significant difference between extraction and nonextraction groups. Clinical observation has given some indication9~10~12~25 of the possibility of achieving a stable ex-
pansion of the lower arch subsequent to expansion of the midpalatal suture. Haas,9.‘0 using a midpalatal suture-opening appliance without any treatment in the lower arch, observed that the mandibular arch tended to follow the maxillary teeth by tipping laterally. In a later study,‘* he reported on the long-term posttreatment evaluation of rapid palatal expansion. Some cases achieved and maintained an expansion of 3 to 4 mm in the lower intercanine width, and up to 6 mm in the intermolar width. He claimed that mandibular intercanine width can be increased in the nongrower if the apical base of the maxillary complex is permanently widened. Wertzz5 reported on cases that underwent palatal expansion. At the completion of suture opening, he observed that there had been an average mandibular intermolar increase of 5 mm. When the palatal-splitting appliance was removed, the younger patients showed a negligible change, but there was an average increase of almost 1 mm in those patients more than 18 years of age. The purpose of this study was to evaluate the effect of rapid maxillary expansion on the mandibular intercanine and intermolar widths during treatment and its stability after retention. The relationships between the interarch change and facial types and ages of the subjects of the sample were also studied. MATERIALS AND METHOD
This article is based on a thesis submitted in partial fulfillment of science degree, Loyola University *In private practice, Athens.
**Chairman, 296
Orthodontic
Department,
School of Dentistry.
Loyola University.
for the master
The material used for this study included the records of 28 cases from the private practice of Andrew Haas, of Cuyahoga Falls, Ohio. All patients had undergone
Volume 94 Number
Lower arch expansion concurrent
4
rapid maxillary expansion with a tissue-borne appliance according to Dr. Haas’ published technique’-” and subsequent orthodontic treatment. The records consisted of the initial, posttreatment, and postretention study models, and the initial lateral cephalogram of each patient. The man’dibular canine and molar arch widths were analyzed separately. Cases meeting the necessary requirements were included in both groups.
with RME
297
+4j QUADRANT
QUADRANT
Ii
Treatment-Decrease
I
Treatment-Increase
Canines
This group comprised 17 cases-8 male and 9 female patients. The mean age at initiation of treatment was 14 years, with a range of 9.6 to 19.6 years. After treatment, a fixed lingual retainer was placed for an average of 5.6 years, with a range of 2 to 8 years. The postretention models were required at least 2 years after the removal of tihe lingual retainer. It was also required that these cases possess the permanent mandibular canines in the initial models.
QUADRANT
a
-3
Measurements
Measurements were taken between the cusp tips of permanent canines and between the summits of the mesiolingual and distolingual cusps of the permanent first molars. When the teeth displayed extensive abrasion or restorations, other landmarks such as the labial and lingual central ridges of the canines and the grooves and fissures in the first molars were used to select the most reproducible points. Each cast was then placed on the base of a :surveyor. The dots were recorded with a two-dimensional digitizer connected to a 360 IBM computer. Measurements were recorded to the nearest 0.01 mm. Error of the method
To verify the accuracy of the method, all dimensions were measured independently by two observers. A twosample t test was performed between the changes in intercanine and intermolar widths as measured by one observer against the same changes as measured by the second observer. The results indicated there was no significant difference between the two observers’ measurements of thelse changes at p -=L0.01.
Post-treatment-Decrease
IV
Treatment-Increase
~
Post-treatment-Decrease
, /
7-4
-3
-2 Treatment
Fig.
Molars
This group consisted of 22 cases- 11 male and 11 female patients. The mean age at initiation of treatment was 12.6 years, with a range of 6.4 to 21.9 years. The postretention models were taken an average of 8.8 years after the end of treatment, with a minimum of 2 years required. Cases with extractions of permanent teeth of the lower arch !excluding third molars) were not included in this group.
QUADRANT I I
Treatment-Decrease
7
z0
Ill
1. ExplanaZon
-1 Change
Y
Cl
t2
in Dimension
of the four-quadrant
+3
t4
I” mm.
graph.
Analysis
Three changes in arch width were studied: 1. Treatment change: Difference between initial and posttreatment measurements 2. Postretention change: Difference between the posttreatment and postretention measurements 3. Net change: Difference between initial and postretention measurements Student’s t test was performed to determine whether these changes in arch widths were significantly different from zero. To determine whether the mesial points of the molars were significantly more expanded than the distal points, a two-sample t test was performed between the net change of the mesial intermolar width against the net change of the distal intermolar width. The data were plotted in the four-quadrant graph as described by Arnold.’ The X or horizontal axis is the treatment axis. The Y or vertical axis is the posttreatment axis. Any change during treatment or posttreatment may be quantitatively shown along the X axis and Y axis, respectively (Fig. 1). The initial lateral cephalograms of the entire sample were classified into facial types. The facial type index was calculated with the five measurements used by Ricketts” to describe facial types and the formula described by Christie.6 For each measurement the amount of clinical deviation from the norm according to sex and age was determined as follows: Clinical
deviation
from norm =
Measured value - Norm Clinical deviation
298
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Klapper,
and
Am. J. Orthod.
Papaconstantinou
Dentofac. Orthop. October 1988
Table I. Changes in width (mm) Treatment Width
Mean
Intercanine Intermolar mesial Intermolar distal
2.2 3.3 2.9
Postretention
change
SD
Range
1.3 2.0 2.0
-0.1 to 4.4 -0.6 to 6.7 -0.9 to 7.4
change
Mean
SD
Range
-1.0 -0.5 -0.3
0.9 1.7 2.0
-3.5 to -0.1 -3.5 to 3.9 -4.3 to 4.9
Net change Mean
1.1 2.8 2.5
SD
Range
1.5 2.2 2.5
-0.3 to 3.8 - 1.3 to 8.5 - 1.5 to 8.6
Positive = increase; negative = decrease.
Table II. Statistical significance of width changes Dimension Pretreatment
Observer vs. posttreatment
= Treatment
Intercanine width
Intermolar (distal) Posttreatment
vs. postretention
= Posttreatment
Intercanine width Intermolar (mesial) Intermolar (distal) Pretreatment
vs. postretention
Intercanine width Intermolar (mesial) Intermolar (distal)
P
change
A B A B A B
Intermolar (mesial)
t
6.74 6.52 7.45 7.76 6.05 6.90
p p p p p p
< < < < L <
o.ooo5 o.ooo5 o.ooo5 o.ooo5 0.0005 o.ooo5
A B A B A B
-5.02 - 3.46 - 1.01 -1.85 -0.42 -0.99
p p p p p p
< < > > > >
0.005 0.005 0.05* 0.05* 0.05* 0.05*
A B A B A B
3.01 2.94 5.90 5.61 4.73 4.64
p p p p p p
< < < c < <
0.005 0.005 0.0005 o.ooo5 0.0005 o.ooo5
change
= Net change
*Values not statistically significant.
The clinical deviations from the norm for each of the five measurements were then averaged to calculate the facial type index. Then, each patient’s facial type index was correlated against its corresponding intercanine and intermolar net changes in width, and a t test was run to confirm whether there was a significant relationship between these two factors. The age of each member of the sample at initiation of treatment was correlated against the respective intercanine and intermolar net changes in width. A t test was run between these two factors. FINDINGS
Table I shows the means, standard deviations, and ranges of the treatment, posttreatment, and net changes for the intercanine width and the mesial and distal intermolar widths. These values are the average between observers A and B. Fig. 2 graphically displays the
average increase in width during treatment and the subsequent postretention decrease for the three dimensions studied. It is readily apparent that the canines display a greater posttreatment decrease in width than the molars. Table II shows the significance of the treatment, posttreatment, and net changes for the intercanine width and the mesial and distal intermolar widths. The t values and their levels of significance are displayed separately for each observer in this table. The increase during treatment was significant for each of the three dimensions studied at p = 0.0005. In the posttreatment interval, there was a significant decrease in intercanine width at p = 0.05, while the decrease observed for the intermolar width was not found to be statistically significant at p = 0.05. The net change was significant for the canines and for the molars at p = 0.0005. The results of the paired t tests were consistent for both
Volume 94 Number
Lower arch expansion concurrent
4
with RME
299
1 +4 Mesial .+3
QUADRANT
II
QUADRANT
E $+2
I
I
I! z +1 .c
Width
I ,
H ,” x 0 E m-1 E 2 F
j
l .., l
QUADRANT
III
‘*
. .
QUADRANT
: a-3 Treatment Change
.
.
r-2 lnltial
l l
IV
.
Net Change -4
Fig. 2. Change during treatment and postretention of the canine and intermolar widths.
/
-4
observers in all cases, indicating that the results obtained were independent of the observer. Intercanine width
The mean net change in intercanine arch width was 1.1 mm, SD 1.5 mm. The data of the changes in width during treatment and posttreatment are plotted in Fig. 3. Sixteen of 17 cases show a treatment increase and a posttreatment decrease. lntermolar widths
The mean expansion retained was 2.8 mm, SD 2.2 mm, for the mesial arch width; and 2.5 mm, SD 2.5 mm, for the distal arch width. The results of the two-sample t test, which was performed between the mean net change displayed by the mesial points as compared with the (distal point on the molars, show there was no significant difference (p = 0.1). This demonstrates that the molars had been evenly expanded rather than rotated. The data of the treatment and posttreatment changes are shown in Figs. 4 and 5 for the mesial and distal intermolar widths, respectively. These graphs are similar to those shown in Fig. 3 except for the addition of a Z axis. Any (case above the Z axis indicates a net gain in width; any case below the Z axis indicates a net loss in width. The observations on the frequency of the net mesial and distal intenmolar widths may be summarized as follows: 1. Sixty-eight percent of the mesial and 55% of the distal measurements exhibited a pattern of treatment increase with posttreatment decrease. 2. Twenty-three percent of the mesial and 32% of the distal measurements exhibited a pattern of
I
-3
I
-2
I
-1
Treatment
/
Y
1
+1
/
+2
I
+3
I
+4
Change in Width in mm.
Fig. 3. Treatment change and posttreatment change in intercanine width of 17 cases.
increase during treatment with a further posttreatment increase. Fig. 6 is a histogram representing the frequency of the facial-type distribution of the entire sample. A minus sign ( - ) indicates a dolichofacial tendency. A plus sign ( + ) indicates a brachyfacial tendency. It is obvious from the graph that this sample displays a marked tendency toward the dolichofacial type. Table III shows the correlations and t tests between (1) the net changes of the canine arch widths and the mesial and distal molar arch widths, and (2) the respective facial-type indices of the sample. It shows there is no correlation. Table IV displays the correlations and t tests between (1) the net changes of the intercanine widths and the mesial and distal intermolar widths, and (2) the corresponding age of the sample at initiation of treatment. It shows there is no significant relationship. DISCUSSION
The results of this study indicate that a statistically significant increase of the mandibular intercanine and intermolar widths may be achieved when orthodontic treatment is combined with rapid maxillary orthopedic expansion. An important aspect of this study is that the entire sample was treated by one clinician, Dr. Haas, whose particular techniqueg.“.12 is relevant to the results of this study.
300
Sandstrom, Klapper,
Am. .I. Orthod.
and Papaconstantinou
+7
13
+6
12
:+5 E +4
11
5+3 s .E +2
9
Dentofac. Orthop. October 1988
10
8
g+1 2 x
7
O-1 r;
6
E -2
5
2 -3
4
+ -4
3
5 -5 a
-6
-2 -7-6-S-4-3-2-1
Y+1+2+3+4+5+6+7
Treatment
Change
-1
Standard
0
+1
+2
Deviations
in Width in mm.
Fig. 6. Facial type index. On 2 axis-original
and Post-retention mesial intermolar widths remain the same.
Below Z axis - Effective
decrease
in width.
Above Z axis - Effective
increase
in width.
Fig. 4. Treatment change and posttreatment change in mesial intermolar width of 22 cases.
Table III. T tests and correlations between the net change in intercanine width, mesial and distal intermolar widths and facial types of the sample Dimension
Canine Mesial molar Distal molar *Values
.E al !i 6 5 E 2 7L
not statistically
Correlation
t
0.28 -0.05 -0.05
1.16 0.25 0.25
P
p > 0.10* p > 0.10* p > 0.10*
significant.
+2
Table IV. T tests and correlations between the net change in intercanine width, mesial and distal intermolar widths and the age of the sample
+1 x -1 -2 -3
T
-4 -5
:
-6
Dimension
Canine Mesial molar Distal molar -7-6-6-4-3-2-l
0.30 -0.13 -0.05
ItI
p
1.16 0.38 0.25
p > 0.10* p > 0.10* p > 0.10*
Yt1+2+3+4+5+6+7
*Values Treatment
Correlation
not statistically
significant.
Change in Width in mm
On Z axis - Original and Post-retention widths the same.
distal intermolar
Below Z axis - Effective
decrease
in wtdth.
Above Z axis -Effective
increase
in width
Fig. 5. Treatment change and posttreatment change in distal intermolar width of 22 cases.
lntercanlne width The pattern of treatment increase and posttreatment decrease observed in this study is in accordance with other investigations’~2,7,‘g,24of the changes of intercanine
width after conventional orthodontic treatment. However, in this sample only 48% of the expansion gained during treatment was lost postretention as compared with a loss of 77% observed by Welch,24 76.3% observed by Amott,’ 71.4% observed by Bishara, Chadha, and Potter,4 and 58% observed by Gardner and Chaconas .’ The mean net increase in intercanine width of 1.1 mm found in this study is greater than the net increase found in other orthodontic studies, such as 0.22 mm shown by Bishara and associates,4 0.52 mm shown by Welch,24 -0.17 mm shown by Dona,’ 0.51 mm in extraction and 0.58 mm in nonextraction cases shown
Volume 94 Number 4
Lower arch expansion concurrent
by Gardner and Chaconas,’ and -0.4 shown by Shapiro.” The net increases found in the previously cited studies were not statistically significant. Only when the samples in two of the studies, by Amott’ and Shapiro,” were divided according to malocclusions could a significant increas,e in Class II, Division 2 cases be found. In the present study, there were no cases of Class II, Division 2 malocclusion. The increase in intercanine width of 1.1 mm found in this study is clearly the result of treatment and not growth since the presence of the permanent canines in the initial models was required. It has been shown that no further increase in the intercanine width is to be expected after the eruption of the permanent canines, but a decrease is possible, ranging from 0.5 to 1.5 mm1.3.5’13.14 22 Intermolar
widlths
To compare the results of the present study to other investigations, the mesial intermolar net expansion was evaluated because it is the point that other have selected for their measurements. studies 1~2~7~8~‘9~2‘1 The findings show that the net mesial intermolar expansion achieved and retained in this study was 2.8 mm, I~I2.2 mm SD. This is greater than 1.2 mm, 11.5 mm SD, found by Dona, and 0.9 mm, 4 1.3 mm SD, found by Arnold,* in their nonextraction samples. It is alsa’ greater than 2 mm, ? 1.8 SD, found by Gardner and! Chaconas,8 and 1 mm, rt 1.9 SD, found in Shapiro’s sample. I9 In Class II, Division 2 cases, Shapiro found a net expansion of 1.5 mm, which is less than that found in this study. As noted previously, the present sample did not include Class II, Division 2 cases. The sample used for the study of intermolar widths had a mean age at initiation of treatment of 12.6 years, with half the group younger than this age. Although this sample is 1:oo small to divide and analyze statistically according to age, it is of interest to note that the mean expansion for the cases under 12 years of age was 3.5 mm, which is greater than the 2.8 mm found in the entire sample. Furthermore, of the eight cases that displayed a pattern of treatment increase with a further posttreatment increase, six were under 12 years of age. It may be inferred that any increase in width occurring before the age of 12 that may have occurred as a result of growth does not preclude additional expansion obtained as a result of treatment. In the present study, there was no relationship found between the amount of interarch expansion achieved and retained, and the facial typing of the sample. There is no support to the widespread notion that brachyfacial types can sustain more expansion than other facial types. Schulholf and associateszOdescribed a formula
with RME
301
that establishes an individualized norm for intercanine width, indicating that even though brachyfacial types do have wider arches, they do not tolerate more expansion beyond their norm than other facial types. Class II, Division 2 cases, which usually indicate brachyfacial type, have been proved to retain a greater orthodontic expansion.” However, this is probably because the lower teeth in these cases are usually enclosed in the upper dentition and lingually positioned due to the excessive overbite. The stability of the expanded mandibular arch width may be the result of an altered muscular balance exerted on the dentition by the buccinator muscles, which have been carried laterally by the maxillary expansion. It may also be attributed to the altered forces of occlusion. Factors that may contribute to the variation of the amount of expansion retained may be the amount of initial incisor crowding, the initial lingual inclination of the mandibular buccal segments, the changes in skeletal pattern in the facial lateral cephalogram, or the initial arch width. Another important factor may be the difference between the initial arch width of each individual and the ideal arch width, according to Schulhof ‘s individualized norms ,‘Ocorrelated to the amount of expansion retained. CONCLUSION
1. The mean increase of the intercanine width, retained after at least a 2-year postretention period, was 1.1 mm. This gain is small but statistically significant as compared with its initial width; it is higher than the expansion found to occur with conventional orthodontic treatment. 2. The mean expansion of the intermolar width, retained after at least a 2-year postretention period, was 2.8 mm. This is statistically significant as compared with its initial width; it is higher than the expansion found with conventional orthodontic treatment. 3. There were no correlations found between the net expansion of the intercanine and intermolar widths and the facial types and ages of the subjects. We would like to express our gratitude to Dr. Andrew Haasfor making this study possibleby offering the invaluable material from his private practice. REFERENCES 1. Amott RD. A serial study of dental arch measurements on orthodontic subjects [Master’s thesis]. Evanston, Illinois: Northwestem University, 1962. 2. Arnold ML. A study of the changes of the mandibular intercanine and intermolar widths during orthodontic treatment and following post-retention period of five or more years [Master’s thesis]. Seattle: University of Washington, 1963. 3. Barrow GV, White R Jr. Developmental change8 of the maxillary and mandibular dental arches. Angle Orthod 1952;22:41-6.
302 Sandstrom, Klapper,
Am. J. Orthod.
and Papaconstantinou
4. Bishara SE, Chadha JM, Potter RB. Stability of the intercanine width, overbite, and overjet correction. AM .I ORTHOD 1973; 63588-95. 5. Brown VP, Jensen D. Changes in the dentition from the early teens to the early twenties. Acta Odontol Stand 1951;9: 177-92. 6. Christie T. Cephalometric patterns of adults with normal occlusions. Angle Orthod 1977;47:128-35. 7. Dona A. An analysis of dental casts of patients made before and after orthodontic treatment [Master’s thesis]. Seattle: University of Washington, 1952. 8. Gardner DS, Chaconas SJ. Post-treatment and post-retention changes following orthodontic therapy. Angle Orthod 1977;46: 186-92. 9. Haas A. Rapid expansion of the maxillary dental arch and nasal cavity by opening the mid-palatal suture. Angle Orthod 1961;31:73-90. 10. Haas A. The treatment of maxillary deficiency by opening the mid-palatal suture. Angle Orthod 1965;65:200-17. 11. Haas A. Expansion, just the beginning of dentofacial orthopedics. Alvl J ORTHOD 1970;57:219-54. 12. Haas A. Long term post-treatment evaluation of rapid palatal expansion. Angle Orthod 1980;50:189-217. 13. Knott V. Longitudinal study of dental arch widths at four stages of dentition. Angle Orthod 1972;42:200-13. 14. Moorrees CFA, Chadha MJ. Available space to the incisors during dental development. A growing study based on physiologic age. Angle Orthod 1965;35: 12-22. 15. Moorrees CFA. The dentition of the growing child. Cambridge: Harvard University Press, 1959:99-100. 16. Moyers RE, Van Der Linden FPG, Riolo ML, McNamara JA.
Dentofac. Orthop. October 1988
Standards of human occlusal development. Monograph 5, Craniofacial Growth Series. Ann Arbor: 1976. Center for Human Growth and Development, University of Michigan. 17. Nance HN. The limitations of orthodontic treatment. AM J ORTHOD ORAL SURG 1947;33:253-301.
Ricketts RM, Bench RW, Guguino CF, Hilgers JJ, Schulhof RJ. Bioprogressive therapy. Denver: Rocky Moutain Orthodontics, 1971. 19. Shapiro PA. Mandibular arch form and dimension. AM J ORTHOD 18.
1974;66:58-70.
20. Schulhof RJ. The mandibular dental arch. Part III. Buccal expansion. Angle Orthod 1978;48:303-10. 21. Sondi A. Dimensional changes in the dental arches of orthodontically treated cases. AM J ORTHOD 1980;77: 1-12. 22. Speck NT. A longitudinal study of the developmental changes in human lower dental arches. Angle Orthod 1950;20:215-28. 23. Walter DC. Comparative changes in mandibular canine and first molar widths. Angle Orthod 1962;32:232-40. 24. Welch KN. A study of treatment and post-retention dimensional changes in mandibular dental arches [Master’s thesis]. Seattle: University of Washington, 1965. 25. Wertz R. Mid-palatal suture opening: a normative study. AM J ORTHOD 1977;71:367-81. Reprint
requests
to:
Dr. Robin Sandstrom Papathanasiou St. Peania, Attica Greece