EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...

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12 10 Incisor Irregularity (mm) 8 6 4 2 0 Fixed Retention Remove Figure 4-17. Box plot of Incisor Irregularity at the recall examination, by kind of retention. In the fixed group, 25% of the cases (17/69) exceed the clinically-acceptable limit of 3.5 mm suggested by Little. This contrasts with 29% in the removable group (28/97). This difference is not large, but it is suggestive that the interval of fixed retention has a long-term benefit in at least some patients. 99
only sample changed significantly more ( x = 0.3 mm)—though the change probably is of no clinical consequence. Multivariate Analysis The prior results, looking at the variables one by one, do not suggest which variables are the most influential. In this section, stepwise discriminant functions analysis (e.g., Cooley and Lohnes 1971) was used to identify which of our set of cast and cephalometric variables evaluated at the end of treatment were most influential in distinguishing between those cases who received a fixed retainer compared to those who were given Hawley retainers alone. In other words, which variables observed by the orthodontist at the end of the active phase of treatment might have influenced the choice of whether to place a fixed retainer? Discrimination functions analysis was used to select just the subset of variables that maximally discriminate between the two kinds of retention. As an initial screening, all posttreatment variables (k = 32) were input and evaluated in a stepwise fashion, and four of these were entered with P values less than the conventional alpha level of 0.05. These are, in order of entry, (1) Incisor Depth, (2) Overbite, (3) Total Chin, and (4) Incisor Irregularity. (As an aside, prior probabilities were assumed to be equal, the variables were treated as linear rather than quadratic, and a common covariance matrix was assumed.) Figure 4-18 is a plot of the means of the four variables that maximally distinguish between the two sorts of retention. It happens that each of these variables has a larger average value in the sample treated with a fixed retainer. This is not anticipated, but it does make interpretation simple. Evaluated at the end of treatment, the most-distinguishing variables are: (1) greater incisor depth, (2) greater overbite, (3) greater total chin dimension, and (4) greater Incisor Irregularity. This is the statistical result, but it is suggestive that the orthodontist was attuned to at least most of these differences. Just these four variables then were input into a second analysis. Using all four variables, the discriminant functions correctly classified 72% of the cases as to the type of retention (105/166). The canonical plot (Figure 4-19) shows that there is considerable scatter among cases, but that Incisor Depth and Overbite are the important discriminators along the first canonical axis. Cases with greater Incisor Depths and deeper Overbites were much more likely to receive a fixed retainer. The other two variables, Total Chin and Incisor Irregularity, contribute statistically (but less) to the discrimination between groups. It is of note that Incisor Depth—a variable undocumented in most studies—is shown to be the single most discriminatory variable. Clinically, Incisor Depth (Figure 3-5) is 100
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EFFICACY OF TEMPORARY FIXED RETENTI
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DEDICATION This thesis is dedicated
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ABSTRACT Instability of the occlusi
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CHAPTER 5. DISCUSSION .............
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LIST OF FIGURES Figure 3-1. All cas
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Figure 4-14. Box plot of the distri
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Joondeph and Riedel (1994, p 908) d
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Strang (1952, p 794) claimed that
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malocclusion must be maintained if
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e aimed at maintaining, in most ins
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three time intervals: during treatm
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mechanical treatment does not neces
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elation, the masticatory system wil
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exerted on the denture from the buc
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In summary, the variance in tongue
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Sinclair and Little (1983, p 114) a
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Study and 43 orthodontically treate
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and Sakols 1982; Vaden et al. 1997;
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years postretention. Årtun et al.
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adjustment, if necessary. This abil
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Duration of Retention The premise i
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The reduction in tooth structure of
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4. The most stable position of the
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CHAPTER 3. MATERIALS AND METHODS Sa
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The present sample consisted of the
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Figure 3-2. Illustration of how mol
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Figure 3-3. Illustration showing di
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Figure 3-5. Illustration showing mi
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Figure 3-6. Illustration showing an
Page 59 and 60: Figure 3-8. Illustration showing in
Page 61 and 62: 34. LR3 cusp tip point. 35. Right d
Page 63 and 64: Figure 3-10. Illustration showing o
Page 65 and 66: Figure 3-11. Illustration of Inciso
Page 67 and 68: 3. Go, Gonion (anatomic): The most
Page 69 and 70: Figure 3-13. Depiction of the angle
Page 71 and 72: Figure 3-15. Illustration of the me
Page 73 and 74: Figure 3-17. Illustration of the me
Page 75 and 76: Figure 3-19. Illustration of the an
Page 77 and 78: Figure 3-21. Illustration of the up
Page 79 and 80: Figure 3-22. Illustration of the to
Page 81 and 82: Figure 3-24. Illustration of the po
Page 83 and 84: the “older” Tweed force system,
Page 85 and 86: The null hypothesis is: There was n
Page 87 and 88: Figure 4-1. Distribution of the 166
Page 89 and 90: occlusal issues are tolerated by bo
Page 91 and 92: 40 35 30 FMA (degrees) 25 20 15 10
Page 93 and 94: Figure 4-4. Plot of the average val
Page 95 and 96: larger ANB at the recall examinatio
Page 97 and 98: 21 19 Total Chin (mm) 17 15 13 11 9
Page 99 and 100: Figure 4-8. Box plot of the distrib
Page 101 and 102: which a Class I relationship was no
Page 103 and 104: Figure 4-11. Plot of mean Curve of
Page 105 and 106: Figure 4-13. Box plot of the distri
Page 107 and 108: Table A-4 addresses the question of
Page 109: Figure 4-16. Bar chart of the avera
Page 113 and 114: 3 2 1 0 Canonical Variate 2 -1 -2 R
Page 115 and 116: 8 Anterior Discrepancy (ADisc) 6 4
Page 117 and 118: 40 Incisor Aspect Ratio (IAR) 30 20
Page 119 and 120: 1.5 Incisor Segment Depth (ISD) 1 0
Page 121 and 122: more stable (i.e., the mean change
Page 123 and 124: Molar Correction (MC) 10 8 6 4 2 0
Page 125 and 126: Anterior Segment Width (ASW) 1 0 -1
Page 127 and 128: final vertical positions. This phas
Page 129 and 130: decreased in both arches during the
Page 131 and 132: Figure 5-1. Plot of average Incisor
Page 133 and 134: Based on the present results, the u
Page 135 and 136: these variables indicate more anter
Page 137 and 138: and the hassle associated with plac
Page 139 and 140: Figure 5-2. Scatter-plot graph refl
Page 141 and 142: stability?” and “for how long?
Page 143 and 144: About two-thirds (64%) of the corre
Page 145 and 146: Baume LJ, Horowitz HS, Summers CJ,
Page 147 and 148: Case CS. Techniques and principles
Page 149 and 150: Glenn G, Sinclair PM, Alexander RG.
Page 151 and 152: Joondeph DR. Retention and relapse.
Page 153 and 154: Littlewood SJ, Millett DT, Doubleda
Page 155 and 156: Ormiston JP, Huang GJ, Little RM, D
Page 157 and 158: Rosenstein SW, Jacobson BN. Retenti
Page 159 and 160: Steadman SR. A philosophy and pract
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Zachrisson BU, Büyükyilmaz T. Bon
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Table A-1. Descriptive statistics a
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Table A-2. Descriptive statistics a
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Table A-3. Descriptive statistics f
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APPENDIX B. ANCOVA TESTS OF THE COM
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Table B-1. Continued. Sex Retention
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Table C-1. Results of ANCOVA tests
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Table D-1. Descriptive statistics,
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Table E-1. Two-way ANOVA tests eval
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VITA Mark Owens was born on January
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EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...

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