A two-year comparative assessment of retention of arch width increases between modified vacuum-formed and Hawley retainers: a multi-center randomized clinical trial

Progress in Orthodontics

Table 3 Mixed ANOVA interaction effect

Variable	Time interval	HR group	95% confidence interval	mVFR group	95% confidence interval	Mixed ANOVA P value (Interaction effect)
Variable	Time interval	Mean ± SD (mm)	95% confidence interval	Mean ± SD (mm)	95% confidence interval	Mixed ANOVA P value (Interaction effect)
ICW						.83
	T0	37.20 ± 2.46	36.09–38.30	38.04 ± 2.00	36.97–39.12
	T1	37.19 ± 2.55	36.05–38.32	37.93 ± 2.02	36.83–39.03
	T2	37.07 ± 2.53	35.96–38.17	37.80 ± 1.92	36.73–38.87
	T3	36.80 ± 2.78	35.61–37.99	37.55 ± 1.99	36.40–38.70
	T4	36.90 ± 2.65	35.76–38.04	37.65 ± 1.93	36.54–38.76
IPMW						.63
	T0	45.39 ± 1.88	44.33–46.45	47.10 ± 1.84	46.04–48.17
	T1	45.37 ± 1.88	44.29–46.46	46.87 ± 1.92	45.79–47.96
	T2	45.26 ± 1.94	44.10–46.41	46.77 ± 2.08	45.62–47.92
	T3	44.80 ± 1.92	43.62–45.97	46.40 ± 2.17	45.22–47.57
	T4	44.61 ± 2.13	43.39–45.82	46.31 ± 2.12	45.09–47.52
IFMW1						.22
	T0	51.16 ± 1.73	50.12–52.21	53.35 ± 2.29	52.37–54.33
	T1	51.31 ± 1.66	50.27–52.36	53.15 ± 2.35	52.17–54.14
	T2	51.16 ± 1.79	50.07–52.26	53.01 ± 2.43	51.97–54.04
	T3	50.88 ± 1.82	49.78–51.98	52.93 ± 2.42	51.89–53.97
	T4	50.74 ± 2.00	49.64–51.85	52.86 ± 2.31	51.82–53.90
IFMW2						.46
	T0	52.34 ± 2.09	51.14–53.54	54.26 ± 2.56	53.13–55.39
	T1	52.50 ± 2.16	51.24–53.75	54.20 ± 2.71	53.02–55.38
	T2	52.27 ± 2.15	51.00–53.54	54.11 ± 2.75	52.91–55.30
	T3	52.09 ± 2.29	50.80–53.39	53.96 ± 2.75	52.73–55.18
	T4	52.04 ± 2.21	50.78–53.31	54.05 ± 2.71	52.86–55.25

HR indicates Hawley retainer; mVFR, modified vacuum-formed retainer; SD, standard deviation; ICW, intercanine width; IPMW, interpremolar width; IFMW1, interfirst molar mesiobuccal cusp width-; IFMW2, interfirst molar distobuccal cusp width; T0, at debond; T1, 3-month retention; T2, 6-month retention; T3, 12-month retention; T4, 24-month retention