Orthodontic relapse in subjects with varying degrees of anteroposterior and vertical dysplasia

Orthodontic relapse in subjects with, . varying degrees qf’anteroposterioy and vertical dysplasia Nagwa Helmy El-Mangoury, B.D.S., MS.* Cuiro,

Egypt

M

ost malocclusions have a vertical and an anteroposterior dysplasia. Only when associated with a quality of stability can orthodontic correction of malocclusions be considered successful. Some of the most glaring types of relapse are the tendency for the overbite, overjet, and/or molar relationship to deteriorate in some seemingly well-treated cases. Orthodontic relapse should be viewed not as an abnormal phenomenon but as an undesirable normal phenomenon which can be minimized by careful diagnosis and treatment planning. The purpose of the present research study was to investigate the orthodontic relapse in subjects with varying degrees of anteroposterior and/or vertical dysplasia by selecting the factors which add most to the relapse problem; studying the equality of the mean vectors of the postretention status (stable or relapse); and testing the interactions of the postretention status versus Angle classification, sex of the patient, and method of treatment (extraction or nonextraction). Materials and methods Sumpl~. The sample consisted of fifty seemingly well-treated orthodontic cases selected from the clinical files of private practices. Criteria for selection of cases were as follows: 1. No labial or palatal clefts. 2. No serious diseases which could affect growth. 3. No skull fractures. 4. No facial operations. 5. Caucasian ethnic origin. 6. Treatment with the edgewise technique. 7. Pretreatment dental casts showing anteroposterior and/or vertical dysplasia (overbite of 4 mm. or more and/or overjet of 4 mm. or more). 8. Posttreatment dental casts revealing successful orthodontic results concerning correction of overbite (overbite = 0 to 3 mm.), correction of overjet (overjet = 0 to 2 mm.), and correction of canine and molar relationships (Class I canine and Angle Class I molar). This article is taken, in part, from a thesis submitted in partial fulfillment of the requirements degree of Master of Science, Department of Orthodontics. Marquette University. Milwaukee. *Fellow of the American Association of University Women.

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1979The

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Table I. Qualitative descriptionof the stablegroup, relapsegroup, and total sample Group torul Quulitutive ~w%thles 1. Sex

2. Class I extraction 3. Class II extraction 4. Class II nonextraction

M&S

Females

Stable

Relupse

25 6

25 6

50 12

12 3

12 1

24 4

13 3

13 5

26 8

5

13

18

2

Y

II

3

4

7

I4

6

20

7

2

7

4

Total

Stable

Relupse

Total

Y

Stable

Relapse

Totul

II

Table II. Quantitativedescriptionof the stablegroup, relapsegroup, and total sample Postretention

Posttreutment

Pretreatment Quuntitutive vuriuhles

Stable

Relupse

Total

Stable

Relapse

Total

Stable

Relapse

Overbite (mm.) Overjet

4.54 5.90

5.48 5.30

5.01 5.60

2.04 0.97

2.60 1.28

2.32 1.12

2.54 1.31

4.34 2.21

Totul

3.44 1.75

9. Postretention dental casts taken a minimum of 2 years out of retention. 10. Clear pretreatment, posttreatment, and postretention lateral cephalograms, taken with the teeth in centric occlusion, corresponding to the dates of the three sets of dental casts. 11. Other usual orthodontic records, including intraoral radiographs (or Panorex), detailed history, and treatment plans. Materials used for tracings and measurements. A mechanical pencil with 0.5 mm. lead (Pentel P 223, an endodontic millimeter ruler (Excecutive No. 45 F), and a precise transparent protractor were used for tracings. Division of the sample. The sample was divided into two groups by comparing the posttreatment dental casts with those taken a minimum of 2 years postretention. If the anterior overjet had not increased, the anterior overbite had not materially deepened, and the canine and molar relationships had been maintained, the case was judged nonrelapse and was placed in the stable group. If all or any of these relationships had deteriorated, as revealed by the postretention casts, the case was considered to have relapsed and was placed in the relapse group. Twenty-five cases were judged nonrelapse and were placed in the stable group. Twenty-five cases were considered to have relapsed and were placed in the relapse group. Table I describes the sample qualitatively, and Table II describes it quantitatively. Records obtained from dental casts. Pretreatment, posttreatment, and postretention dental casts, trimmed in centric occlusion, were used to record overbite, overjet, maxillary and mandibular intercanine widths, maxillary and mandibular intermolar widths, and Angle classification. OVERBITE. With the casts in centric occlusion, the amount of greatest vertical overlap of the maxillary central incisor was marked on the corresponding mandibular central incisor with a soft-lead pencil paralleling the occlusal plane. Then the casts were disen-

Fig. 1. Cephalometric

landmarks.

gaged. Between the mark and the incisal edge of the mandibular central incisor, the measurement was made to the nearest 0.25 mm. OVERJET. The greatest amount of horizontal overlap was recorded from the labial surface of the mandibular central incisor to the lingual surface of the maxillary central incisor by the following method. The casts were occluded and inverted so that the base of the maxillary cast rested on a flat surface. Paralleling the occlusal plane, the long axis of the millimeter ruler was placed against the labial surface of the mandibular central incisor. The measurement was made to the lingual surface of the corresponding maxillary central incisor and recorded to the nearest 0.25 mm. ~NTERCANINE WIDTH. Both maxillary and mandibular intercanine widths were recorded from crown tip to crown tip. In two cases, in which the maxillary canines were unerupted, the center of the alveolar crest was used for measuring. INTERMOLAR WIDTH. Both maxillary and mandibular inter-molar widths were recorded from the center of the occlusal surface of the permanent first molar of one side of the dental arch to that of the other side. ANGLE CLASSIFICATION.' Each case was classified according to the Angle classification. Cephalometric tracings and measurements. During tracings and measurements of the cephalograms, the investigator was unaware of the postretention status (whether stable or relapse). In this manner, cephalometric tracings and measurements were made by a double blind design. CEPHALOMETRIC MEASUREMENTS. A precise transparent protractor was used to make

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Fig. 2. Cephalometric

551

planes.

angular measurements to the nearest 0.25 degree. With the “Excecutive” endodontic ruler, linear measurements were made to the nearest 0.25 mm. Each measurement was repeated twice. The following points were used (Fig. 1): nasion (N); anterior nasal spine (ANS); subspinale or point A (A); supramentale or point B (B); Pogonion (Pg); gnathion (Gn); menton (Me); point D37 (D)-the center of the mass of the cross section of the body of the mandibular symphysis; articulare (Ar); porion (Pr); Y point (Y)-the point on the SN plane established from a perpendicular erected from gonion to the SN plane; sella (S); point X ‘, 28(X)-the point on the SN plane established from a perpendicular erected from point A to the SN plane; orbitale (Or); posterior nasal spine (PNS); upper incisor (U,)the outline of the most labial maxillary permanent central incisor; lower incisor (LJsimilar to Ur; upper molar (U,)-the outline of the permanent maxillary left first molar; lower molar (L,)-similar to Ua. The following reference planes were constructed on each tracing (Fig. 2): Sella nasion plane (SN); Frankfort horizontal plane (FH); palatal plane (PP)-the plane connecting PNS to ANS; functional occlusal plane (OP)-the plane drawn through the region of maximum cuspal interdigitation by connecting the mesiobuccal cusp of U6 to the midinterocclusal point between the maxillary and mandibular left first premolars*; goniongnathion plane (GoGn); mandibular plane (MP)-the plane connecting menton to the most posteroinferior border of the mandibular body; and the Z line“j-the line perpendicular to the SN plane at nasion. The following angular measurements were constructed and *In cases in which the maxillary and/or the mandibular first premolars were absent. the maxillary and/or the mandibular second premolars were used.

** = P ,: 0.01. * = P ,< 0.05.

Table IV. PP-GoGn angle Stuhleg’oup(n = 25)

Relupsr group (n = 25)

PP-GoGn ungla

MUUI

S.D.

Medn

S.D.

Pretreatment Posttreatment Postretention

24.41 24.51 23.46

4.76 4.80 5.80

23.60 21.56 21.26

6.50 6.61 6.64

Table V.

Mandibular

intercanine

width

Mundihular inrercuninr width

Mean

S.D.

Meun

S.D.

Pretreatment Posttreatment Postretention

26.56 27.30 26.88

2.31 1.72 1.83

25.96 21.52 26.52

2.35 1.66 I .74

Stuhle pmlp

(n = 25)

Relqwr

group (n = 251

measured: SNA31; SNB3’; SND37-to represent the relative anteroposterior position of the body of the mandibular symphysis to the cranial plane SN; ANB3’; AXBS, “; AXD; NAPg; Y axis’; gonial angle-the anterosuperior angle formed by the intersection of the mandibular plane with a tangent erected from articulare to the posterior surface of the mandibular ramus; AB-MP? FH-PP16; ODI’“--the algebraic addition of AB-MP and FH-PP angles; NS-PP; NS-OP; NS-GoGn; PP-OP; PP-GoGn; OP-GoGn; U,-L,-interincisal angle; U1-SN; L,-GoGn; and L,-OP. The following linear measurements were constructed and measured: Wits’4-The horizontal difference between two perpendiculars erected from points A and B onto the occlusal plane. When point A is positioned anterior to point B, the measurement is positive, and vice versa. It is to represent the anteroposterior position of the maxillary and the mandibular apical bases relative to the occlusal plane. UAFHz6--The linear distance along the Z line from nasion to ANS. It is to represent the upper anterior facial height. LAFH*“-The linear distance along the Z line from ANS to menton. It is to represent the lower anterior facial height. TAFH”‘-The linear distance along the Z line from nasion to menton. It is to represent the total anterior facial height.

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Table VI. Top predictors selected by the stepwise discriminant analyses Pretreatment minus posttreatment

Posttreatment minus postretention

U,-SN

PP-GoGn*

U&l

L,-APg

TAFH /PFH Gonial angle

L,-APg L,-GoGn

L,-GoGn AXB

Mandibular intercanine width Lower molar height OP-GoGn

Mandibular intercanine* width UAFH/LAFH

L,-APg

AXD

AXD

UAFH/LAFH

Posttreatment

Postretention

FH-PP

U,-SN

U,-SN

Pretreatment Predictors

Gonial angle Mandibular intermolar width Lower incisor height

Note: Under each stage, the predictors are arranged in a descending order; that is, the predictor at the top is more

important than the predictor at the bottom. Predictors which are not marked with an asterisk, by themselves, were not significant. * = P < 0.05 as obtained by the one-way multivariate analysis of variance.

Table VII. Summary of results obtained by the 2

x

2 factorial multivariate

analyses of variance Postretention

status

Stable or relapse Stable or relapse Stable or relapse

Qualitative

variuhles

Angle Class I or II Sex (females or males) Method (extraction or nonextraction)

Over-ail

tests

qf interactions

NS NS NS

PFH-The linear distance between point Y and gonion. It is to represent the posterior facial height. TAFHILAFH-The ratio between the upper and lower anterior facial heights. TAFHIPFH-The ratio between the total anterior facial height and the posterior facial height. Upper incisor height (ZJIH)-The linear distance along the Z line from ANS to the centroid (geometric center of the root as defined by Burstone4) of Ui. Upper molar height (UMH)--Similar to UIH. Lower incisor height (LIH)--The perpendicular distance from the centroid of Li to the GoGn plane. Lower molar heighf (LMH)--Similar to LIH. U,-APg’-The linear distance from the incisal edge of U1 to a line connecting point A and pogonion. If the incisal edge is anterior to the line APg, the measurement is positive, and vice versa. L,-APg3”-The linear distance from the incisal edge of L, to a line connecting point A and pogonion. If the incisal edge is anterior to the line APg, the measurement is positive, and vice versa. Other records. Using the patient’s history and treatment plan, the following variables were recorded: sex (females or males), method (extraction or nonextraction), and age. Statistical methods. The raw data were entered on the “Silent 700” electronic data

554

El-Mungour\

-2 It 1 -- ~- i-STABLE

----__

PDSTR~TENTION STATUS I RELAF'SE

Fig. 3. Changing the PP-GoGn angle. Use of pretreatment base line data resulted in a significant difference between the means of the posttreatment PP-GoGn of the stable and relapse groups at a probability of less than 0.05.

terminal. The statistical analyses were computed at the Marquette University Computer Center. The “Xerox Sigma 9” computer was used. The statistical analyses were computed in the following five stages: (1) pretreatment stage, (2) posttreatment stage, (3) postretention stage, (4) pretreatment minus posttreatment stage, and (5) posttreatment minus postretention stage. For each of these five stages, three stepwise discriminant analyses were done in the following three ways: (1) by using all the quantitative and qualitative variables, (2) by using the quantitative variables alone, and (3) by using the quantitative variables after excluding the overbites and overjets. From among the top predictors in each stage, five variables were selected. Following the discriminant analyses, two types of multivariate analysis of variance were computed: (1) the one-way multivariate analysis of variance and (2) the two by two factorial multivariate analysis of variance. Results The summary of the results is presented in Tables III through VII and in Figs. 3 and 4.

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-0341

POSTRETENTION STATUS -.-. L_ RELAPSE

Fig. 4. Changing the mandibular intercanine width. Use of posttreatment base line data resulted in a significant difference between the means of the postretention mandibular intercanine width of the stable and relapse groups at a probability of less than 0.05.

Discussion A careful review of the literature reveals disagreements as to the factors responsible for anteroposterior and/or vertical orthodontic relapse. This study was designed for the purpose of gaining additional insight into the problem. Fifty seemingly well-treated orthodontic cases were studied by means of pretreatment, posttreatment, and postretention dental casts, lateral cephalograms, and other usual orthodontic records. Literally, relapse is defined as a “slip or fall back into a former worse state.““” Therefore, for a study of anteroposterior and/or vertical orthodontic relapse, the pretreatment dental casts should reveal anteroposterior and/or vertical dysplasia. In the present study, all pretreatment dental casts revealed this dysplasia. In order to avoid studying relapse due to incomplete treatment, only cases in which posttreatment dental casts revealed successful orthodontic results were used. To give the relapse a chance to occur, all postretention dental casts were taken at least 2 years out of retention. To avoid guesswork, clear cephalograms were obtained in all cases. The sample was divided into two groups by comparing posttreatment dental casts with those taken at least 2 years postretention. Twenty-five cases were placed in the stable group, and twenty-five were placed in the relapse group. To avoid false significant results, a double-blind design was performed. Forty-six quantitative and qualitative variables were determined for each stage of treatment. The nature and the quantity of the data required the statistical use of the

multivariate analysis of variance. This analysis is “conct”rncd w~tli ilat~r collt~.~tccl on several dimensions of the same individual.““’ It is to be mcntioncd that this analysis is the most powerful statistical test that can be applied to this sample. For selection of the variables which add most to the predictive power of the function, the stepwise discrimnant analyses were run. The one-way multivariate analyses of v.ariance were done to test the equality of the mean vectors of the stable and the relapse groups. In order to test the interactions between the postretention status (stable or relapse groups) and Angle classification, sex, and treatment method. the two by two factorial multivariate analysts of variance were computed. On the basis of the results obtained from this study. the following observations can be made. When using pretreatment variables alone. posttreatment variables alone. and postretention variables alone. there was no significant difference between the mean vectors of the stable and relapse groups (Table III). In other words, with a sample consisting of seemingly well-treated orthodontic cases, relapse or stability cannot be predicted or judged from one set of records alone. However, when pretreatment base line data were used, there was a statistically significant difference between the mean vectors of the posttreatment stable and relapse groups at a probability of less than 0.01. Also. when posttreatment base line data were used, there was a significant difference between the mean vectors of the postretention stable and relapse groups at a probability of less than 0.05. Thus, the use of base line data improved the analysis. Relapse or stability of an orthodontic case can be predicted by comparing the posttreatment variables to the pretreatment variables. Relapse or stability of an orthodontic case can be judged by comparing the postretention variables to the posttreatment variables. With the pretreatment base line data. there was a statistically significant difference between the means of the posttreatment PP-GoGn of the stable and relapse groups. By looking at Fig. 3 and Table IV. we see that the mean change of the PP-GoGn from pretreatment to posttreatment was 0.16 degree for the stable group and - 2.04 degrees for the relapse group. In other words. by treatment or growth, the PP-GoGn increased very slightly (only 0.16 degree) for the stable group but decreased 2.04 degrees for the relapse group. Thus, decreasing the PP-GoGn was associated with relapse. It is speculated that a decrease in the PP-GoGn could be prevented if one avoided tipping the palatal plane downward anteriorly and avoided intrusion of posterior teeth. In the present study. thirty-five angular and linear cephalometric measurements were recorded on each tracing. This study indicates that, from all these measurements, the PP-GoGn angle is the most important cephalometric measurement associated with relapse. In 1975 Nahoum” emphasized that the angle formed between the palatal and the mandibular planes was the most common skeletal deformity in open-bite subjects. McCauley,‘2 Strang,“‘, :N Hixon,‘:’ Riedel,:r’ Steadman,“” Walter,” Lewis.” Bishara and associates,’and Gardner and Chaconas”’ discussed the importance of maintaining the mandibular intercanine width. In the present study, when posttreatment base line data were used, there was a significant difference between the means of the postretention mandibular intercanine width in the stable and relapse groups. By looking at Fig. 4 and Table V, we see that the mean change in the mandibular intercanine width from posttreatment to postretention was 0.42 mm. for the stable group and 1.00 mm. for the relapse group. This means that the mandibular intercanine width decreased 0.42 mm. in the stable group after retention was discontinued. In the relapse group, the mandibular

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intercanine width decreased 1.OOmm. after the discontinuation of retention. Thus, after retention was discontinued, a decrease in the mandibular intercanine width occurred in both groups but was associated more with the relapse group. Also, the mandibular intercanine width tended to relapse toward its original pretreatment value. Therefore, at the end of active treatment, the mandibular intercanine width should be maintained as originally presented. This study disagrees with Hernandez, i2 who concluded that there does not appear to be a very strong relationship between the intercanine width and the deepening of the overbite. It is to be noted that all his cases were out of retention a minimum of 6 months. In the present study, all cases had been out of retention a minimum of 2 years. Also, in the present study, a double-blind design was performed. It is to be very strongly emphasized that the PP-GoGn and the mandibular intercanine width are not the only two important variables in which changes may lead to relapse. The primary aim of the experimental design and the extremely complicated statistical analyses used is to select the variables which add most to the relapse problem. The present study indicates that the PP-GoGn angle and the mandibular intercanine width are the two most important variables related to orthodontic relapse in seemingly well-treated orthodontic cases. Table VI shows important variables which may lead to relapse. These variables were selected by fifteen stepwise discriminant analyses. Each of these analyses looks, at each step, for the variable which adds most to the predictive power of the function. However, this does not imply that the selected variable, by itself, is significant. In 1974 Kirn”j invented the overbite depth indicator (ODI). In 1975 Nahoum2” questioned the validity of the ODI. In the present study, the ODI did not appear to be of any predictive value. However, FH-PP was at the top of the pretreatment predictors. Thus, it is speculated that the algebraic addition of AB-MP to FH-PP resulted in a decrease in the predictive power. In the present study, Ui-SN, U1-Li, Li-APg, and Li-GoGn were the top posttreatment predictors. It is to be noted that none of these variables, by itself, was significant. However, all of them combined were adding to the relapse problem. Thus, at the end of active treatment, an interincisal angle which is more obtuse than normal accompanied by an upright incisor might be a factor in overbite relapse. This conclusion agrees with the beliefs of Tweed,“’ Corlett,6 Strang,“O Riede1,32Ludwig,” and Schudy.34 In 1950 Freeman9 and Rasmussor? constructed the AXB angle, which varies with the anteroposterior positioning of the maxillary and the mandibular apical bases without taking into account the anteroposterior position of nasion. In 1959 SteineP7 developed point D. According to Steiner, point D is surrounded by sturdy bone and is isolated from the areas where tooth movements and normal growth changes occur. In the present study, the posttreatment AXD and the postretention AXB and AXD might be other factors in relapse since they were selected by the discriminant analyses. The ANB angle did not appear to be of any predictive value. Schudy3”reported that the ANB angle showed little relevance to the depth of the overbite. Porte?’ pointed out that the stability of the overbite was questionable with elongation of posterior teeth. On the other hand, Nemeth and Isaacsonz6concluded that elongated posterior teeth did not contribute to anterior deep overbite relapse. Cole,” Litowitz,” and Schudy3” reported that extrusion of depressed lower incisors contributed to overbite relapse. In the present study, extrusion and intrusion of the teeth were evaluated by using the

centroid of the root. The incisal and occlusal surfaces were not LIW~ for- rtli, ~~al~ratwr~ because they are easily affected by tipping movements.’ When pretreatment base lint data were used, the lower molar height was among the top posttrcatmcnt predictors. When posttreatment base line data were used, the lower incisor height \has among the top postretention predictors. The intrusion and/or extrusion of maxillary teeth were not factors leading to relapse. Thus, it is speculated that. to avoid relapse, the anterior deep overbite might be best treated by intruding the maxillary anterior teeth and/or extruding the maxillary posterior teeth. Further studies are suggested. Schudy”” emphasized the correlation between the overbite and the occlusomandibular plane angle. In the present study, when pretreatment base lint data were used. the OP-GoGn angle was among the posttreatment predictors. At the end of active treatment, the OP-GoGn angle increased in both groups but had increased very little in the stable group (only 0.33 degree). Thus. at the end of active treatment. it is undesirable to increase the angulation of OP-GoGn. Some treatment techniques (Class III and then II elastics, as an example) attempt to tip the occlusal plane upward anteriorly and downward posteriorly. Then they attempt to tip the occlusal plane downward anteriorly and upward posteriorly. At the end of treatment (active and retention). the OP-GoGn angle might rebound to more normal relationships, resulting in relapse. In the present study, when pretreatment base line data were used, the UAFHiLAFH ratio was among the posttreatment predictors. Also, when posttreatment base line data were used, the same ratio was among the postretention predictors. Nahoum”’ suggested that the UFHiLFH should be used to indicate the severity of the vertical dysplasia and to serve as a guide in predicting the treatment results. In the present study, when posttreatment base line data were used, the genial angle was among the postretention predictors. Jensen and Palling’” emphasized the correlation between the overbite and the degree of the gonial angle. Creekmore; re-emphasized this correlation. Richardsons” correlated the longer face with the Ar-Go-Me angle on what was considered purely geometric grounds. McCauleyZ2 and Riedel:j2 suggested that the mandibular intermolar width should be maintained as originally presented. In the present study, when posttreatment base line data were used, the mandibular intermolar width was among the postretention predictors. The maxillary intercanine and intermolar widths did not appear to be of any predictive value. Thus, it can be inferred that the maxillary intercanine and intermolar widths are more stable than the mandibular intercanine and intermolar widths. This conclusion is in agreement with the findings of Bishara and colleagues.” As indicated by Table VII, the over-all tests of interaction of the mean vectors of the postretention status and Angle Classes I and II were not significant. This indicates that there is no significant interaction between orthodontic relapse (or stability) and Angle Class I and II cases. This result is in disagreement with the findings of Bresonis and Grewe” but in agreement with those of Magill.2’ The over-all tests of interaction of the mean vectors of the postretention status and sex were not significant. This implies that there is no significant interaction between orthodontic relapse (or stability) of an orthodontic case and the sex of the patient. Table VII indicates that the over-all tests of interaction of the mean vectors of the postretention status and method (extraction or nonextraction) were not significant. This means that there is no significant interaction between orthodontic relapse (or stability) and

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whether or not extraction was included as a part of the treatment procedures. Thus, pretreatment deep overbite is not necessarily a contraindication to extraction. This result disagrees with the findings of Heid” and Hernandez.” However, it agrees with those of Magill, ” Ludwig,ls and Simons and Joondeph.x It is evident that if adequate mechanotherapy is performed, extraction treatment should not cause overbite relapse. It should be remembered that orthodontic relapse existed before the introduction of extraction treatment. For improving future studies of this type, a larger sample should be used. Summary and conclusions Fifty seemingly well-treated orthodontic cases were studied by means of pretreatment, posttreatment, and postretention dental casts, lateral cephalograms, and other orthodontic records. The sample was restricted to cases exhibiting anteroposterior and/or vertical dysplasia as revealed by pretreatment dental casts. The sample was divided into a stable group and a relapse group. Each group contained twenty-five cases. A double-blind design was used. The raw data were analyzed by the stepwise discriminant analysis and by the multivariate analysis of variance. On the basis of the results obtained from this study, the following conclusions can be drawn: 1. In seemingly well-treated orthodontic cases, relapse or stability can neither be predicted nor judged from one set of records alone. 2. Relapse or stability of an orthodontic case can be predicted by comparing the posttreatment variables with the pretreatment variables. 3. Relapse or stability of an orthodontic case can be judged by comparing the postretention variables to the posttreatment variables. 4. The PP-GoGn angle and the mandibular intercanine width are the two most important variables associated with orthodontic relapse. 5. Changing the PP-GoGn angle, either by treatment or by growth, was associated with relapse. In other words, changes in the PP-GoGn angle tended to be unstable. This suggests that decreasing the PP-GoGn angle should be avoided. 6. In both the stable and the relapse groups, the mandibular intercanine width decreased postretention. This decreasewas associatedmore with the relapse group than with the stable group. 7. The mandibular intercanine width tended to relapse toward its original pretreatment value. This suggeststhat, at the end of active treatment, the mandibular intercanine width should be maintained as originally presented. 8. There was no significant interaction between orthodontic relapse (or stability) and Angle Class I and II cases. 9. There was no significant interaction between relapse (or stability), of an orthodontic case, and the sex of the patient. 10. There was no significant interaction between orthodontic relapse (or stability) and whether or not extraction was included as a part of the mechanotherapy. Thus, the pretreatment deep overbite is not necessarily a contraindication to extraction. The authorexpressesher sincereappreciationto Drs. Robert V. W inders. RusselT. Kittleson, RobertB. Gordon, RobertSchlamer,YehyaA. Mostafa.and. aboveall. to the memoryof Professor Mohammed-HelmyEl-Mangoury.

REFERENCES I. Angle. L. H.: Claasihcation ot maloccIus~~~n. Dent (‘o\m<>s 41: 14~. iX+j 2. Bishara. S. E., Chadha. J. M.. and Potter. R. H.. Stability ot interc:mtnc wtdth. ovcrhtt
method of analysis of the relation of the structures of the lower face to each

other and to the occlusal plane of the teeth. Master’s thesis. Northwestern University, IYSO. Gardner, S. D., and Chaconas, S. J.: Posttreatment and postretention changes following orthodontic therapy, Angle Orthod. 46: I5 I. 1976. Heide, M.: Class II, Division 2. a challenge. Angle Orthod. 27: 159. 1957. HernandeL, J. L.: Mandibular bicanine width relativ>c to overbite. AM. J. ORTHOD. 56:455. lY6Y. Hixon. E. H.: The norm concept ofcephalometrtcs. AM. J. ORTHOD. 42: X9X. 19%. Jacobson, A.: The “Wits” appraisal of jaw disharmony, AM. J. ()RTHOD. 67: 125, 1975.

15. Jensen, E.. and Palling, M.: The gonial angle-A survey, AM. J. ORIHOD. 40: 120. 1954. 16. Kim, Y. H.: Overbite depth indicator with particular reference to anterior open-bite, Acl. J. ORIHOD. 65: 586. 1974. 17. Lewis, P. D.: Arch width, canine position. and mandibular retention, AM. J. ORTHOD. 63: 4x1. 1973. 18. Litowitz, R.: A study of the movements of certain teeth during and following orthodontic treatment, Angle Orthod. 18: 113, 1948. 19. Ludwig, M.: An analysis of anterior overbite relationship changes during and following orthodontic treatment, Angle Orthod. 36: 204, 1966. 20. Ludwig, M. K.: A cephalometric analysis of the relationship between facial pattern. interinctsal angulation, and anterior overbite changes, Angle Orthod. 37: 194, 1967. 21. Magill, J. M.: Changes in the anterior overbite relationship following orthodontic treatment in extraction cases, AM. J. ORTHOD. 46: 755, 1960. 22. McCauley. D. R.: The cuspid and its function in retention, AM, J. ORTIIOD. ORAL SURG. 30: 196, 1944. 23. Morrisson. D. F.: Multivariate statistical methods, New York. 1967, McGraw-Hill Book Company. Inc. 24. Nahoum, H. 1.: Anterior open-bite: A cephalometric analysis and suggested treatment procedures. AM. J. ORTHOD. 67: 513, lY75. 25. Nahoum, H. I.: Vertical proportions: A guide for prognosis and treatment in anterior open-btte. AM. J. ORTHOD. 72: 128, 1977. 26. Nemeth. R. B., and Isaacson, R. J.: Verticle anterior relapse. ARZ. J. ORrtton. 65: 565, 1974. 27. Porter, L. J.: Conservatism in orthodontic procedures and appliances. Ahi. J. ORTHOD. ORAI. SURG. 33: 109, 1947. 28. Rasmussen, D. F.: A radtographic method of analysts of the relation of the structures of the lovver face to the maxillary plane, Master’s thesis, Northwestern University. 1950. 29. Richardson. A.: Skeletal factors in anterior open-bite and deep overbite. Au. J. ORTHOD. 56: 111. 1969. 30. Ricketts, R. M.: Cephalometric synthesis. AM. J. ORTHOD. 46: 647. 1970. 31. Riedel, R. A.: The relation of maxillary structures to cranium in malocclusion and in normal occlusion, Angle Orthod. 22: 142, 1952. 32. Riedel, R. A.: A review of the retention problem, Angle Orthod. 30: 17Y. 1960. 33. Schudy, F. F.: Cant of the occlusal plane and axial inclinations of teeth. Angle Orthod. 33: 69, 1963. 34. Schudy. F. F.: The control of vertical overbite in clinical orthodontics. Angle Orthod. 38: 19. 1968. 35. Simons, M. E., and Joondeph. D. R.: Change in overbite: A ten-year postretention study, Arvr. J. ORTHOD. 64: 349. 1973.

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36. Steadman, S. R.: Changes of intermolar and intercuspid distances following orthodontic treatment, Angle Orthod. 31: 207, 1961. 37. Steiner, C. C.: Cephalometrics in clinical practice, Angle Orthod. 29: 8, 1959. 38. Strang, R. H. W.: Factors of influence in producing a stable result in the treatment of malocclusion, AM. J. ORTHOD. ORAL SURF. 32313,

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39. Strang, R. H. W.: The fallacy of denture expansion as a treatment procedure, Angle Orthod. 19: 12, 1949. 40. Strang, R. H. W.: Axial inclination of teeth in extraction cases, Angle Orthod. 27: 11, 1957. 41. Tweed, C. H.: Indications for the extraction of teeth in orthodontic procedure, AM. J. ORTHOD. ORAL SURG. 30: 405, 1944, 42. Walter. D. C.: Comparative changes in mandibular canine and first molar widths, Angle Orthod. 32: 232, 1962. 43. Woolf, H. B. (editor): Webster’s new collegiate dictionary, ed. 9. Springfield, Mass., 1975, G. & C. Merriam Company. 44 Tulant Hub

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