40
41
Table 2. Demographics regarding variables “AGE”, “DURATION OF TREATMENT” (months), “ANGLE CLASSIFICATION”, “ORTHODONTIC TREATMENT PLAN“, and “MONTHS IN RETENTION”.
Control placebo (N=12)
Control bleaching
(N=12)
Debonded placebo
(N=12)
Debonded bleaching (N=12)
Retention placebo
(N=12)
Retention bleaching (N-12) Age (Mean (SD)) 21.9(0.6) 22 (0.4) 22.3 (3.5) 27.3(13.4) 24.4 (5.9) 19.4 (1.2) Months in
retention (Mean (SD))
32.7 (14.4)
27.2 (15.3) Duration of
treatment(months) (Mean (SD))
24 (5.8) 27.1 (6.8) 30.3 (8.5) 24.8 (5.9)
Orthodontic treatment plan N(%, within column)
Non extraction 7 (58.3%) 10(83.3%) 9 (81.8%)
Extraction 5 (41.7%) 2 (16.7%) 2 (18.2%)
Angle Classification N (%, within column
Class I 7(58.3%) 3 (25%) 1 (9.1%) 6 (46.2%) 8 (34.8%) 9 (36%) Class II Division 1 3 (25%) 2 (16.7%) 2 (18.2%) 4 (30.8%) 5 (21.7%) 6 24%) Class II Division 1
Subdivision Right 1 (8.3%) 1 (8.3%) 3 (27.3%) 4 (17.4%) 1 (4%) Class II Division 1
Subdivision Left 1 (8.3%) 1 (8.3%) 1 (4.3%) 1 (4%)
Class II Division 2 4 33.3%) 1 (9.1%) 1 (7.7%) 1 (4.3%) 5 (20%) Class II Division 2
Subdivision Right 1 (9.1%) 1 (7.7%) 1 (4.3%) 1 (4%)
Class III 1 (8.3%) 3 (27.3%) 1 (7.7%) 3 (13%) 2 (8%)
42 Tooth 13- L* parameter
Sample descriptive statistics of the L* color parameter for Tooth 13 are presented in Tables 3 and Table 4, Appendix I. The analysis of variance model (2×3 Anova) used to study mean L* differences between GROUPS at baseline (1d pre) is given in Table 5. Statistically significant mean differences were observed between the three GROUPS (p=0.005). One linear mixed model was used to study differences between baseline(1d pre) and follow up TIMEPOINTS and a second linear mixed model (Ancova) with the baseline measurement as a covariate was used to study the effects of GROUP, INTERVENTION, TIMEPOINTS and their interactions on color parameter L*.
Table 5. Tests of Between-Subjects Effects for Tooth 13-L* at baseline (1d pre).
Source Type III Sum of Squares df Mean Square F p-value
Corrected Model 53.39 5 10.678 3.172 0.013
Intercept 368494 1 368494 109480.2 <0.001
INTERVENTION 8.842 1 8.842 2.627 0.11
GROUP 38.734 2 19.367 5.754 0.005
INTERVENTION × GROUP 4.868 2 2.434 0.723 0.489
Error 218.78 65 3.366
Total 369954.3 71
Corrected Total 272.17 70
In comparisons between baseline (1d pre) and follow up regarding GROUP and INTERVENTION, for all BLEACHING GROUPS statistically significant differences were found between baseline and all subsequent TIMEPOINTS (p<0.001) (Table 6, Appendix I).
Results of the study of the factors GROUP, INTERVENTION AND TIMEPOINTS are presented in Table 7. The covariate “L* at baseline (1d pre)” had a statistically significant positive correlation with the follow up measurements.
The effects of INTERVENTION, TIMEPOINTS and INTERVENTION × TIMEPOINTS
43
on L* measurements were statistically significant (p<0.001). The effect of the three-way interaction INTERVENTION × GROUP × TIMEPOINTS was statistically significant, p=0.002 and studied in more detail with pair-wise comparisons.
Table 7. Results for Tooth 12-L* parameter from a linear mixed model.
Source Numerator df Denominator df F p-value
Intercept 1 62.054 2.559 0.115
L* at Baseline (1d pre) 1 62.008 1086.019 <0.001
INTERVENTION 1 63.518 134.782 <0.001
Group 2 64.679 1.467 0.238
Timepoints 5 117.725 48.15 <0.001
INTERVENTION × Group 2 62.625 0.115 0.891
INTERVENTION × Timepoints 5 117.725 63.231 <0.001
Group × Timepoints 10 117.487 0.81 0.619
INTERVENTION × Group × Timepoints 10 117.487 3.103 0.002
Estimated mean values and 95%CI for Tooth 13 based on mean (L* at baseline (1d pre) = 72.15 are shown in Figure 5 and Table 8, Appendix I.
Figure 5. Estimated mean values for Tooth 13, based on mean (L* at baseline (1d pre) = 72.15.
44
In comparisons between levels of INTERVENTION for the CONTROL, DEBONDED AND RETENTION GROUPS placebo mean value was significantly less than BLEACHING, at all following TIMEPOINTS (p<0.001) (Table 9, Appendix I). No statistical significant differences were found between levels of GROUP (Table 10, Appendix I).
Comparisons between TIMEPOINTS for PLACEBO-CONTROL, PLACEBO- DEBONDED and PLACEBO-RETENTION GROUP are presented in Table 11 through Table 13, Appendix I. Comparisons between TIMEPOINTS for BLEACHING-CONTROL, BLEACHING-DEBONDED and BLEACHING-RETENTION revealed that the mean of the L* measurements at 20min pre was less than all other TIMEPOINTS (Table 14 through Table 16, Appendix I).
Results for Tooth 13-L* parameter of study of the effect of confounders are given in Table 17 and Table 18.
Table 17. Results for Tooth 13-L* parameter from the linear mixed model of the effect of cofounders when GROUP = DEBONDED.
Source Numerator df Denominator df F Sig.
Intercept 1 17.345 0.914 0.352
DURATION OF TREATMENT (months) 1 17.615 9.267 0.007
ORTHODONTIC TREATMENT PLAN 1 17.373 0.029 0.867
baseline (1d pre) 1 17.311 161.459 <0.001
ANGLE CLASSIFICATION 5 17.398 1.62 0.207
INTERVENTION 1 17.746 27.86 <0.001
Timepoints 5 61.65 23.377 <0.001
INTERVENTION × Timepoints 5 61.65 13.008 <0.001
A statistically significant relation was found between “DURATION OF TREATMENT (months)” and L* (p<0.05) in the DEBONDED GROUP only. The introduction of confounders did not affect the statistically significant
45
interaction between IINTERVENTION and TIMEPOINTS for either GROUP (Table 17 and Table 18).
Table 18. Results for Tooth 13-L* parameter from the linear mixed model of the effect of cofounders when GROUP = RETENTION.
Source Numerator df Denominator df F Sig.
Intercept 1 12.536 2.116 0.17
DURATION OF TREATMENT (months) 1 12.551 2.039 0.178
ORTHODONTIC TREATMENT PLAN 1 12.516 1.026 0.33
Months in retention 1 13.229 0.08 0.782
baseline (1d pre) 1 12.529 104.04 <0.001
ANGLE CLASSIFICATION 5 12.873 1.233 0.349
INTERVENTION 1 12.763 15.755 0.002
Timepoints 5 77.094 35.128 <0.001
INTERVENTION × Timepoints 5 77.094 36.283 <0.001
Tooth 13- a* parameter
Sample descriptive statistics of Tooth 13 for the a* color parameter are presented in Table 19 and Table 20, Appendix I. The analysis of variance model is presented Table 21. Results of the study of the factors GROUP, INTERVENTION and TIMEPOINTS are presented in Table 22.
Table 21. Tests of Between-Subjects Effects for Tooth 13- a* parameter at baseline (1d pre).
Source Type III Sum of Squares df Mean Square F p-value
Corrected Model 5.1 5 1.02 1.226 0.307
Intercept 2226.176 1 2226.176 2674.733 <0.001
INTERVENTION 0.735 1 0.735 0.883 0.351
Group 0.821 2 0.411 0.493 0.613
INTERVENTION × Group 3.706 2 1.853 2.226 0.116
Error 54.099 65 0.832
Total 2290.017 71
Corrected Total 59.199 70
46
Table 22. Results for Tooth 13- a* parameter from a linear mixed model.
Source Numerator df Denominator df F p-value
Intercept 1 65.041 2548.341 <0.001
INTERVENTION 1 65.041 8.637 0.005
Group 2 65.041 0.572 0.567
Timepoints 6 211.516 34.339 <0.001
INTERVENTION × Group 2 65.041 1.667 0.197
INTERVENTION × Timepoints 6 211.516 36.483 <0.001
Group × Timepoints 12 209.253 0.821 0.629
INTERVENTION × Group × Timepoints 12 209.253 1.684 0.072
Estimated mean values and 95%CI’s from the linear mixed model are presented in Figure 6 and in Table23, Appendix I.
Figure 6. Estimated mean values for Tooth 13- a* parameter from the linear mixed model.
Results of comparisons between levels of INTERVENTION are presented in Table 24, Appendix I. Pair wise comparisons between TIMEPOINTS for
47
PLACEBO and BLEACHING level of INTERVENTION are shown in Table 25, Appendix I and Table 26, Appendix I.
Results of the study of the effect of cofounders for Tooth 13- a* parameter are presented in Table 27 and Table 28. A statistically significant relation was found between “DURATION OF TREATMENT (months)” and a* (p=0.001);
“ORTHODONTIC TREATMENT PLAN” and a* (p<0.05); “ANGLE CLASSIFICATION”
and a* (p<0.001) for the DEBONDED GROUP. A statistically significant relation was also found for “MONTHS IN RETENTION” and a* (p<0.05) in the RETENTION GROUP.
Table 27. Results for Tooth 13- a* parameter of the effect of the confounders when GROUP = DEBONDED.
Source Numerator df Denominator df F p-value
Intercept 1 18.416 140.367 <0.001
DURATION OF TREATMENT (months) 1 17.931 16.217 0.001
ORTHODONTIC TREATMENT PLAN 1 17.79 4.716 0.044
ANGLE CLASSIFICATION 5 17.77 10.187 <0.001
INTERVENTION 1 14.118 12.347 0.003
TIMEPOINTS 6 63.104 6.365 <0.001
INTERVENTION × Timepoints 6 63.104 8.987 <0.001
Table 28. Results Tooth 13- a* parameter of the effect of the confounders when GROUP = RETENTION.
Source Numerator df Denominator df F p-value
Intercept 1 14.875 26.431 <0.001
DURATION OF TREATMENT (months) 1 14.857 0.114 0.740
ORTHODONTIC TREATMENT PLAN 1 14.879 0.083 0.778
MONTHS IN RETENTION 1 15.832 4.604 0.048
ANGLE CLASSIFICATION 5 15.117 3.076 0.041
INTERVENTION 1 16.533 0.013 0.91
Timepoints 6 47.841 14.654 <0.001
INTERVENTION × Timepoints 6 47.841 13.165 <0.001
48 Tooth 13- b* parameter
Sample descriptive statistics of Tooth 13 for the b* color parameter are presented in Tables 29 and 30, Appendix I. The analysis of variance model is shown in Table 31. For all GROUPS, when INTERVENTION was PLACEBO, the mean value at baseline (1d pre) was statistically significant greater than the mean value at 20min post only (Table 32, Appendix I). For all GROUPS, when INTERVENTION was BLEACHING the mean value at baseline (1d pre) was statistically significant greater than mean values at all following TIMEPOINTS (p<0.001) (Table 33, Appendix I).
Table 31. Tests of Between-Subjects Effects for Tooth 13- b* at baseline (1d pre).
Source Type III Sum of Squares df Mean Square F p-value
Corrected Model 55.377 5 11.075 1.694 0.149
Intercept 40124.938 1 40124.938 6137.384 <0.001
INTERVENTION 4.175 1 4.175 0.639 0.427
Group 43.803 2 21.901 3.35 0.041
INTERVENTION × GROUP 5.73 2 2.865 0.438 0.647
Error 424.956 65 6.538
Total 40777.581 71
Corrected Total 480.333 70
Results of the study of the factors GROUP, INTERVENTION and TIMEPOINTS are presented in Table 34. The effect of the three-way interaction INTERVENTION × GROUP × TIMEPOINTS on the b* parameter was statistically significant (p=0.009) and studied further in more detail.
49
Table 34. Results for Tooth 13- b* parameter from a linear mixed model.
Source Numerator df Denominator df F p-value
Intercept 1 63.876 0.4 0.529
b* at Baseline (1d pre) 1 63.921 820.348 <0.001
INTERVENTION 1 66.082 153.815 <0.001
GROUP 2 66.021 0.792 0.457
TIMEPOINTS 5 211.163 100.513 <0.001
INTERVENTION × Group 2 66.176 2.122 0.128
INTERVENTION × Timepoints 5 211.163 51.409 <0.001
GROUP × TIMEPOINTS 10 211.584 2.164 0.021
INTERVENTION × GROUP × TIMEPOINTS 10 211.584 2.441 0.009
Estimated mean values and 95%CI’s for Tooth 13, based on mean (b* at baseline (1d pre ) = 23.79 are presented in Figure 7 and in Table 35, Appendix I.
Figure 7. Estimated mean values for Tooth 13, based on mean (b* at baseline (1d pre ) = 23.79
50
In pair wise comparisons between levels of INTERVENTION in all GROUPS it was observed that PLACEBO mean value was greater than BLEACHING at all subsequent TIMEPOINTS (p<0.001) (Table 36, Appendix I).
Comparisons between levels of GROUP showed that CONTROL mean value was less than DEBONDED at PLACEBO-20min post (p<0.001) and greater than RETENTION at BLEACHING-90d post (p=0.012) (Table 37, Appendix I).
Comparisons between TIMEPOINTS for PLACEBO-CONTROL, PLACEBO- DEBONDED and PLACEBO-RETENTION are presented in Tables 38 through Table 40, Appendix. Comparisons between TIMEPOINTS for BLEACHING- CONTROL, BLEACHING-DEBONDED AND BLEACHING-RETENTION revealed that the mean b* measurements at 20min pre were statistically significant greater than the mean at any other TIMEPOINT (p<0.001) (Table 41 through Table 43, Appendix I).
Results for Tooth 13- b* parameter of the study of the effect of confounders are presented in Table 44 and Table 45.
Table 44. Results of the study of the effect of cofounders for Tooth 13-b*
parameter when GROUP = DEBONDED.
Source Numerator df Denominator df F Sig.
Intercept 1 16.864 15.516 0.001
DURATION OF TREATMENT (months) 1 16.167 2.516 0.132
ORTHODONTIC TREATMENT PLAN 1 16.596 7.857 0.012
baseline (1d pre) 1 16.464 186.178 <0.001
ANGLE CLASSIFICATION 5 16.223 3.432 0.026
INTERVENTION 1 16.781 80.537 <0.001
TIMEPOINTS 5 66.274 38.598 <0.001
INTERVENTION × Timepoints 5 66.274 19.367 <0.001
51
A statistically significant relation was found between “ORTHODONTIC TREATMENT PLAN” and b* (p<0.05); “ANGLE CLASSIFICATION” and b* (p<0.05) for the DEBONDED GROUP only (Table 44 and Table 45).
Table 45. Results of the study of the effect of cofounders for Tooth 13-b*
parameter when GROUP = RETENTION.
Source Numerator df Denominator df F Sig.
Intercept 1 12.96 422.392 <0.001
DURATION OF TREATMENT (months) 1 12.978 4.478 0.054
ORTHODONTIC TREATMENT PLAN 1 12.98 0.38 0.548
Months in retention 1 13.09 1.041 0.326
baseline (1d pre) 1 12.959 0.045 0.835
ANGLE CLASSIFICATION 5 13.034 1.893 0.164
INTERVENTION 1 13.004 0.036 0.853
Timepoints 5 76.146 35.36 <0.001
INTERVENTION × Timepoints 5 76.146 36.644 <0.001
Tooth 13-ΔΕ
Sample descriptive statistics for Tooth 13-ΔΕ are presented in Tables 46 and 47, Appendix I. Results from the linear mixed model are presented in Table 48.
Table 48. Results for Tooth 13-ΔΕ (Type III Tests of Fixed Effects) from a linear mixed model with INTERVENTION, GROUP as fixed factors, TIME as a fixed and random factor.
Source Numerator df Denominator df F p-value
Intercept 1 64.85 482.592 <0.001
INTERVENTION 1 64.85 141.731 <0.001
GROUP 2 64.849 0.06 0.942
TIME 5 147.874 51.014 <0.001
INTERVENTION × GROUP 2 64.849 2.06 0.136
INTERVENTION × TIME 5 147.874 70.942 <0.001
GROUP × TIME 10 147.916 1.101 0.365
INTERVENTION × Group × Time 10 147.916 2.093 0.028
52
Estimated mean values and 95%CI’s for Tooth 13-ΔΕ, are presented in Figure 8 and Table 49, Appendix I.
Figure 8. Estimated mean values for Tooth 13-ΔΕ; T2: 20min pre, T3: 20min post, T4: 7d post, T5: 14d post, T6: 21d post and T7: 90d post.
Comparisons between levels of INTERVENTION revealed that for the CONTROL, DEBONDED and RETENTION GROUPS, PLACEBO ΔΕ mean value was statistically significantly lower than BLEACHING, at all subsequent ΔΕ(TIMEPOINT, 1d pre) (Table 50, Appendix I).
In pair wise comparisons between levels of GROUP, it was observed that in the PLACEBO GROUP, CONTROL ΔΕ mean value was greater than both DEBONDED at ΔΕ (20min pre , 1d pre) (p=0.013) and RETENTION at ΔΕ (20min pre , 1d pre) (p=0.006) (Table 51, Appendix I).
Pair wise comparisons between levels of TIMEPOINTS for PLACEBO-CONTROL, PLACEBO-DEBONDED and PLACEBO-RETENTION GROUP are presented in Table
53
52 through Table 54, Appendix I. For the BLEACHING-CONTROL, BLEACHING- DEBONDED and BLEACHING-RETENTION GROUPS the mean ΔΕ(20min pre, 1d pre) was statistically significant lower than the means of all subsequent ΔΕ(TIMEPOINT, 1d pre) (Table 55 Appendix I through Table 57 Appendix I) Results of the study of the effect of cofounders for Tooth 13- ΔΕ are presented in Table 58 and Table 59.
Table 58. Results for Tooth 13-ΔΕ from the linear mixed model of the effect of confounders when GROUP = DEBONDED.
Source Numerator df Denominator df F Sig.
Intercept 1 34.358 32.603 <0.001
DURATION OF TREATMENT (months) 1 18.32 1.048 0.319
ORTHODONTIC TREATMENT PLAN 1 18.343 0.448 0.512
ANGLE CLASSIFICATION 5 18.345 4.223 0.010
INTERVENTION 1 21.373 30.98 <0.001
Time 5 49.55 10.758 <0.001
INTERVENTION × Time 5 49.55 8.688 <0.001
Table 59. Results for Tooth 13-ΔΕ from the linear mixed model of the effect of confounders when GROUP = RETENTION.
Source Numerator df Denominator df F Sig.
Intercept 1 15.263 23.275 <0.001
DURATION OF TREATMENT (months) 1 11.371 6.707 0.025
ORTHODONTIC TREATMENT PLAN 1 11.363 0.09 0.770
MONTHS IN RETENTION 1 10.905 0.61 0.452
ANGLE CLASSIFICATION 5 11.135 1.071 0.426
INTERVENTION 1 20.282 73.783 <0.001
TIME 5 18.957 63.714 <0.001
INTERVENTION × TIME 5 18.957 68.825 <0.001
54
For the DEBONDED GROUP “ANGLE CLASSIFICATION” and for the RETENTION GROUP “DURATION OF TREATMENT (months)” were found to be related to ΔΕ values (p<0.05) (Table 58 and Table 59).
Tooth 12- L* parameter
Sample descriptive statistics of Tooth 12 for the L* color parameter are presented in Tables 60 and 61, Appendix II. The analysis of variance model is shown in Table 62. Statistically significant mean differences were observed between the three GROUPS, F(2, 63)= 6.278, p=0.003.
Table 62. Tests of Between-Subjects Effects for Tooth 12-L* at baseline (1d pre).
Source Type III Sum of Squares df Mean Square F p-value
Corrected Model 68.16 5 13.632 4.263 0.002
Intercept 373427.91 1 373427.9 116778.6 <0.001
INTERVENTION 15.416 1 15.416 4.821 0.032
Group 40.15 2 20.075 6.278 0.003
INTERVENTION × Group 14.022 2 7.011 2.192 0.120
Error 201.458 63 3.198
Total 375782.524 69
Corrected Total 269.618 68
Results of comparisons between baseline(1d pre) and follow up TIMEPOINTS, when INTERVENTION was PLACEBO are presented in Table 63, Appendix II.
When INTERVENTION was BLEACHING the mean value at baseline (1d pre) was statistically significant less than the mean value at 20min post (p<0.001), 7d post (p<0.001), 14d post (p=0.036 and p<0.001) and 21d post (p<0.001) for the CONTROL and RETENTION GROUPS and 20min post (p<0.001), 7d post (p<0.001), 14d post (p<0.001), 21d post (p=0.003) and 90d post (p=0.005) for the DEBONDED GROUP (Table 64, Appendix II).
55
Results of the study of the factors GROUP, INTERVENTION and TIMEPOINTS are presented in Table 65.
Table 65. Results for Tooth 12-L* parameter from a linear mixed model.
Source Numerator df Denominator df F p-value
Intercept 1 89.189 1.159 0.285
L* at Baseline (1d pre) 1 89.17 1117.569 <0.001
INTERVENTION 1 61.115 34.767 <0.001
Group 2 61.545 0.258 0.773
Timepoints 5 111.93 27.223 <0.001
INTERVENTION × Group 2 59.52 0.253 0.777
INTERVENTION × Timepoints 5 111.93 18.123 <0.001
Group × Timepoints 10 113.045 0.835 0.596
INTERVENTION × Group × Timepoints 10 113.045 1.157 0.327
Estimated mean values and 95%CI for Tooth 12-L* parameter are presented in Figure 9 and Table 66, Appendix II.
Figure 9. Estimated mean values for Tooth 12-L* parameter based on mean (L*
at baseline (1d pre ) = 72.15.
56
In comparisons between PLACEBO and BLEACHING for all three GROUPS, statistically significant differences were observed between baseline and mean values at 7d post, 14d post, 21d post and at 90d post (p<0.001) (Table 67, Appendix II).
Comparisons between TIMEPOINTS for PLACEBO are presented in Table 68, Appendix II. In comparisons between TIMEPOINTS for BLEACHING mean value at 20min pre was less than the mean value at 20min post, 7d post, 14d post, 21d post and 90d post (p<0.001). Also, mean value at 7d post was less than the mean value at 90d post (p=0.020) (Table 69, Appendix IΙ).
Results for Tooth 12-L* parameter of the study of the effect of confounders are presented in Table 70 and Table 71.
Table 70. Results of the study of the effect of cofounders for Tooth 12- L*parameter when GROUP = DEBONDED.
Source Numerator df Denominator df F p-value
Intercept 1 15.85 5.174 0.037
DURATION OF TREATMENT (months) 1 15.536 0.337 0.570
ORTHODONTIC TREATMENT PLAN 1 15.203 3.614 0.076
baseline (1d pre) 1 15.701 137.761 <0.001
ANGLE CLASSIFICATION 5 15.326 3.342 0.031
INTERVENTION 1 15.858 12.881 0.002
Timepoints 5 65.111 14.712 <0.001
INTERVENTION × Timepoints 5 65.111 5.077 0.001
A statistically significant relation was found between “ANGLE CLASSIFICATION”
and L* for the DEBONDED GROUP (p<0.05) and “MONTHS IN RETENTION” and L* for the RETENTION GROUP (p<0.05).
57
Table 71. Results of the study of the effect of cofounders for Tooth 12- L*parameter when GROUP = RETENTION.
Source Numerator df Denominator df F p-value
Intercept 1 10.758 1.894 0.197
DURATION OF TREATMENT (months) 1 10.593 0.936 0.355
ORTHODONTIC TREATMENT PLAN 1 10.447 0.353 0.565
MONTHS IN RETENTION 1 11.511 10.424 0.008
baseline (1d pre) 1 10.747 123.64 <0.001
ANGLE CLASSIFICATION 5 10.963 1.701 0.215
INTERVENTION 1 10.954 4.64 0.054
TIMEPOINTS 5 70.711 14.978 <0.001
INTERVENTION × Timepoints 5 70.711 12.138 <0.001
Tooth 12- a* parameter
Sample descriptive statistics of Tooth 12-a* parameter are presented in Tables 72 and 73, Appendix II. The analysis of variance model is shown in Table 74. No statistically significant mean differences were observed between GROUPS, INTERVENTION or their interaction, hence the analysis was implemented using all TIMEPOINTS. Results of the study of factors GROUP, INTERVENTION and TIMEPOINTS are presented in Table 75.
Table 74. Tests of Between-Subjects Effects for Tooth 12-a* at baseline (1d pre).
Source Type III Sum of Squares df Mean Square F p-value
Corrected Model 3.403 5 0.681 0.745 0.593
Intercept 1053.374 1 1053.374 1152.661 <0.001
INTERVENTION 1.251 1 1.251 1.369 0.246
Group 0.911 2 0.455 0.498 0.610
INTERVENTION × GROUP 1.438 2 0.719 0.787 0.460
Error 57.573 63 0.914
Total 1125.22 69
Corrected Total 60.976 68
58
Table 75. Results for Tooth 12-a* parameter from a linear mixed model.
Source Numerator df Denominator df F p-value
Intercept 1 63.17 1406.831 <0.001
INTERVENTION 1 63.17 0.572 0.452
GROUP 2 63.172 0.697 0.502
TIMEPOINTS 6 220.455 13.845 <0.001
INTERVENTION × Group 2 63.172 1.454 0.241
INTERVENTION × Timepoints 6 220.455 14.795 <0.001
Group × Timepoints 12 220.59 1.256 0.247
INTERVENTION × Group × Timepoints 12 220.59 1.1 0.362
Estimated mean values and 95%CI’s from the linear mixed model for Tooth 12- a* parameter are presented in Figure 10 and Table 76, Appendix I.
Figure 10. Estimated mean values for Tooth 12-a* parameter from the linear mixed model.
The conclusion from the pair wise comparisons with the Bonferroni method was the same for the three GROUPS. Concerning comparisons between
59
PLACEBO and BLEACHING, PLACEBO mean value was greater than BLEACHING, at 7d post (p=0.041) and at 14d post (p=0.030) (Table 77, Appendix II).
Comparisons between TIMEPOINTS for PLACEBO level of INTERVENTION are presented in Table 78, Appendix II. In comparisons between TIMEPOINTS for BLEACHING level of INTERVENTION it was observed that 1d pre and 20min pre mean values were greater than mean values at all subsequent TIMEPOINTS;
(p<0.001) (Table 79, Appendix II).
Results from the linear mixed model for Tooth 12-a*parameter of the study of the effect of cofounders are presented in Table 80 and Table 81.
Table 80. Results of the study of the effect of cofounders for Tooth 12-a*
parameter when GROUP = DEBONDED.
Source Numerator df Denominator df F p-value
Intercept 1 23.769 14.826 0.001
DURATION OF TREATMENT (months) 1 23.769 0.006 0.939
ORTHODONTIC TREATMENT PLAN 1 23.759 2.218 0.150
ANGLE CLASSIFICATION 5 23.758 1.355 0.276
INTERVENTION 1 23.719 3.957 0.058
Timepoints 6 104.706 4.744 <0.001
INTERVENTION × Timepoints 6 104.706 5.856 <0.001
Table 81. Results of the study of the effect of cofounders for Tooth 12-a*
parameter when GROUP = RETENTION.
Source Numerator df Denominator df F p-value
Intercept 1 34.655 31.096 <0.001
DURATION OF TREATMENT (months) 1 34.734 9.461 0.004
ORTHODONTIC TREATMENT PLAN 1 34.744 0.312 0.58
MONTHS IN RETENTION 1 35.336 0.051 0.823
ANGLE CLASSIFICATION 5 35.018 9.281 <0.001
INTERVENTION 1 34.873 0.329 0.57
Timepoints 6 27480453.73 12.661 <0.001
INTERVENTION × Timepoints 6 27480453.73 11.694 <0.001
60
A statistically significant relation was found between “DURATION OF TREATMENT (months)” and a* and “ANGLE CLASSIFICATION” and a* for the RETENTION GROUP only (Table 80 and Table 81).
Tooth 12- b* parameter
Sample descriptive statistics for Tooth 12-b* parameter are presented in Tables 82 and 83, Appendix II. The analysis of variance model is given in Table 84.
Table 84. Tests of Between-Subjects Effects for Tooth 12-b* at baseline (1d pre).
Source Type III Sum of Squares df Mean Square F p-value
Corrected Model 57.689 5 11.538 2.02 0.088
Intercept 24165.568 1 24165.57 4230.557 <0.001
INTERVENTION 1.279 1 1.279 0.224 0.638
GROUP 48.914 2 24.457 4.282 0.018
INTERVENTION × GROUP 7.472 2 3.736 0.654 0.523
Error 359.865 63 5.712
Total 24872.829 69
Corrected Total 417.554 68
Results from the linear mixed model regarding GROUP when INTERVENTION was PLACEBO are presented in Table 85, Appendix II. When INTERVENTION was BLEACHING it was observed that the mean value at baseline (1d pre) was statistically significant greater than the mean value at 20min post, 7d post, 14d post, 21d post and 90d post for the CONTROL, DEBONDED AND RETENTION GROUPS (p<0.001) (Table 86, Appendix II).
Results of the study of the factors GROUP, INTERVENTION and TIMEPOINTS are presented in Table 87.
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Table 87. Results for Tooth 12-b* parameter from the linear mixed model.
Source Numerator df Denominator df F
p- value
Intercept 1 88.151 5.074 0.027
b* at Baseline (1d pre) 1 83.152 3490.675 <0.001
INTERVENTION 1 59.088 103.484 <0.001
GROUP 2 60.956 0.316 0.73
TIMEPOINTS 5 74.16 43.081 <0.001
INTERVENTION × GROUP 2 59.328 0.577 0.564
INTERVENTION × TIMEPOINTS 5 74.16 20.91 <0.001
GROUP × TIMEPOINTS 10 74.196 0.896 0.541
INTERVENTION × GROUP ×
TIMEPOINTS 10 74.196 0.67 0.749
Estimated mean values and 95%CI’s for Tooth 12 based on mean (b* at baseline (1d pre) = 18.84 are presented in Figure 11 and Table 88, Appendix II.
Figure 11. Estimated mean values, based on mean (b* at baseline (1d pre )) = 18.84.
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The conclusion from the pair wise comparisons was the same for the three GROUPS. In comparisons between PLACEBO and BLEACHING, PLACEBO mean value was greater than BLEACHING, at 20min post (p=0.010), 7d post, 14d post, 21d post and at 90d post; (p<0.001) (Table 89, Appendix II).
Pair-wise comparisons between TIMEPOINTS for PLACEBO level of INTERVENTION are presented in Table 90, Appendix II. In comparisons between TIMEPOINTS for BLEACHING level of INTERVENTION only 20min pre mean value was greater than the mean value at all following TIMEPOINTS (p<0.001) (Table 91, Appendix II).
Results of the study of the effect of cofounders for Tooth 12-b* parameter are presented in Table 92 and Table 93.
Table 92. Results for Tooth 12-b* parameter from the linear mixed model of the effect of cofounders when GROUP = DEBONDED.
Source Numerator df Denominator df F Sig.
Intercept 1 16.601 1.799 0.198
DURATION OF TREATMENT (months) 1 15.623 0.106 0.749
ORTHODONTIC TREATMENT PLAN 1 15.615 1.371 0.259
baseline (1d pre) 1 15.638 510.086 <0.001
ANGLE CLASSIFICATION 5 15.636 0.726 0.614
INTERVENTION 1 24.3 22.252 <0.001
TIMEPOINTS 5 32.138 9.344 <0.001
INTERVENTION × TIMEPOINTS 5 32.138 5.347 0.001
No significant relation was found between any of the confounders and b* in either group (p>0.05) (Table 92 and Table 93).
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Table 93. Results for Tooth 12-b* parameter from the linear mixed model of the effect of cofounders when GROUP = RETENTION.
Source Numerator df Denominator df F Sig.
Intercept 1 9.989 2.197 0.169
DURATION OF TREATMENT (months) 1 10.009 0.934 0.357
ORTHODONTIC TREATMENT PLAN 1 10.067 1.927 0.195
Months in RETENTION 1 11.388 0.335 0.574
baseline (1d pre) 1 10.315 227.014 <0.001
ANGLE CLASSIFICATION 5 10.496 0.518 0.758
INTERVENTION 1 10.664 9.957 0.009
TIMEPOINTS 5 56.532 24.474 <0.001
INTERVENTION × TIMEPOINTS 5 56.532 6.347 <0.001
Tooth 12- ΔΕ
Sample descriptive statistics for Tooth 12-ΔΕ are presented in Tables 94 and 95, Appendix II. The study of the factors GROUP, INTERVENTION and TIME is shown in Table 96.
Table 96. Results for Tooth 12-ΔΕ from a linear mixed model.
Source Numerator df Denominator df F p-value
Intercept 1 64.689 530.56 <0.001
INTERVENTION 1 64.689 68.893 <0.001
Group 2 64.702 0.115 0.891
Time 5 178.383 68.615 <0.001
INTERVENTION × GROUP 2 64.702 1.499 0.231
INTERVENTION × TIME 5 178.383 17.501 <0.001
GROUP × TIME 10 179.067 0.761 0.666
INTERVENTION × GROUP × TIME 10 179.067 0.488 0.896
The interaction effect of INTERVENTION × TIME on ΔΕ measurements was statistically significant and was further studied with pair wise comparisons.
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Estimated mean values and 95%CI’s for Tooth 12-ΔΕ are shown in Figure 12 and Table 97, Appendix II.
Figure 12. Estimated mean values for Tooth 12-ΔΕ; T2: 20min pre, T3: 20min post, T4: 7d post, T5: 14d post, T6: 21d post and T7: 90d post.
The conclusion from the pair wise comparisons was the same for the three GROUPS. In comparisons between PLACEBO and BLEACHING it was observed that PLACEBO ΔΕ mean value was lower than BLEACHING, at all subsequent ΔΕ(TIMEPOINT, 1d pre) (Table 98, Appendix II).
Pair-wise comparisons between TIMEPOINTS for PLACEBO level of INTERVENTION are presented in Table 99, Appendix II. In comparisons between TIMEPOINTS for BLEACHING level of INTERVENTION the mean ΔΕ(20 min pre, 1d pre) was statistically significant lower than the mean at all following ΔΕ(TIMEPOINT, 1d pre) (p<0.001). Also, the mean ΔΕ(7d post, 1d pre)