EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...

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Sexual Dimorphism The patient’s sex is included in the statistical analyses because this aspect of the sample can have confounding effects on the interpretations if not controlled. Males are characteristically larger than females as a statistical average, males grow more during adolescence and for a longer time following adolescence than girls (e.g., Tanner et al. 1962; van der Linden 1986; Ursi et al. 1993), and so sexual dimorphism can influence the results if left uncontrolled. For several of the variables, such as dental arch dimensions, patient’s sex is largely a nuisance variable, where its interpretation has no important clinical consequence. For other variables, such as whether one sex is more prone to relapse, knowledge of the patient’s sex can provide clinical insights. For each of the three examination periods, a two-way factorial analysis of variance was used as a screening device for each of the 32 variables to assess whether the type of retention (fixed versus removable) affects the results while controlling for patient’s sex. The same was done for the in-treatment changes and the posttreatment changes. All of these results are listed in Appendix B. Again, “sex” was included to control for this known source of variation, and for completeness, we summarize the differences in sexual dimorphism in this section. Appendix C lists the results of testing whether the amount of change depends on the type of retention, with patient’s sex and time-out-of-treatment as covariates. We list descriptive statistics for these variables in Appendix D. Prior literature (e.g., Moorrees 1959; Knott 1961; 1972; De Koch 1972; Bishara et al. 1989) led us to expect that some dental arch dimensions would be statistically larger in boys at the start of treatment (Table D-1), but results show that most of the significant variables actually reflect the worse malocclusions in boys. Of the 17 significant variables, only maxillary intermolar width, mandibular intermolar width, and anterior segment perimeter are due to boys being larger than girls; the 14 other variables reflect access-to-treatment differences, where boys seeking orthodontic treatment have a more severe malocclusion than girls (Blair and Harris 2008; Glassell and Harris 2008). That is, epidemiologically, there are very few sex differences between boys and girls in the frequency or severity of malocclusion (e.g., Kelly and Harvey 1977). In contrast, most orthodontic practices are composed of a majority of girls (often with a sex ratio of 2-to-1) because girls (and their parents) are more aware of and more concerned with minor occlusal issues (Anderson 2010). The severity of the malocclusion has to be somewhat greater for boys to seek treatment. This pattern is evident in these results (Table D-1), where, as examples, the mean status of overbite, overjet, ANB, AOBO, and the Curve of Spee are all larger (clinically more severe) in boys than girls. This suggests to us that minor 77
occlusal issues are tolerated by boys (and their parents), whereas the “bar is lower” for girls, who are more apt to seek treatment for lesser malocclusions (e.g., Shaw 1981, 1991). By the end of the active phase of treatment (Table D-2), most of the esthetic sex differences have been resolved. In concert, these adolescents now are older and have experienced the majority of their adolescent growth. At the end of treatment, the suite of significant male-female differences now is composed primarily of arch size variables, such as sex differences in arch lengths and widths. Because most of the posttreatment sex differences are due to sexual dimorphism (boys larger than girls), it appears that both sexes were treated orthodontically to similar posttreatment results. Also, it is not evident from these statistics that any of these cases was not treated to a clinically-acceptable outcome. Table D-3 lists the 16 variables with significant sex differences at the longterm recall examination. Some of these (inter-canine widths, inter-molar widths) are due to the full-elaboration of sexual dimorphism towards the end of early adulthood ( x = 32.9 years of age at T3), but others are due to sex differences in the nature of the posttreatment changes. These latter changes probably are some complex consequence of patients’ failures to wear retainers in combination with sex differences in skeletal growth following treatment (Little et al. 1988). While there was no significant difference in mean mandibular inter-canine widths or FMIA between the sexes at the end of treatment, significant differences do appear at the recall examination. Maxillary inter-canine widths, inter-molar widths, and anterior and posterior face heights remained significantly larger in males at the recall examination. Downs’ occlusal plane remained steeper in females at the recall examination, but ANB and FMA became significantly larger in females as compared to the males. Two graphs are provided here to make this point. Figure 4-2 shows that FMIA is, on average, a significantly smaller angle in women than in men (P = 0.0011). Figure 4-3 shows that the average FMA is significantly lower in men than in women (P = 0.0200) at the recall examination. Ignoring these sex differences—even though they are no clinical consequence— can confound (distort) the statistical findings. Review of Table D-3 shows that several of the occlusal measures (e.g., anterior and midarch discrepancies, and Incisor Irregularity) are not listed as being statistically significant. It is speculated that, by achieving similar posttreatment results, males and females can expect to see few significant occlusal differences between them, with the only differences being those attributed to size differences between the sexes. 78
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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;
Page 37 and 38: years postretention. Årtun et al.
Page 39 and 40: adjustment, if necessary. This abil
Page 41 and 42: Duration of Retention The premise i
Page 43 and 44: The reduction in tooth structure of
Page 45 and 46: 4. The most stable position of the
Page 47 and 48: CHAPTER 3. MATERIALS AND METHODS Sa
Page 49 and 50: The present sample consisted of the
Page 51 and 52: Figure 3-2. Illustration of how mol
Page 53 and 54: Figure 3-3. Illustration showing di
Page 55 and 56: Figure 3-5. Illustration showing mi
Page 57 and 58: 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: Figure 4-1. Distribution of the 166
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 and 110: Figure 4-16. Bar chart of the avera
Page 111 and 112: only sample changed significantly m
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
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Figure 5-2. Scatter-plot graph refl
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stability?” and “for how long?
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About two-thirds (64%) of the corre
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Baume LJ, Horowitz HS, Summers CJ,
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Case CS. Techniques and principles
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Glenn G, Sinclair PM, Alexander RG.
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Joondeph DR. Retention and relapse.
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Littlewood SJ, Millett DT, Doubleda
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Ormiston JP, Huang GJ, Little RM, D
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Rosenstein SW, Jacobson BN. Retenti
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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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