Table 2.

Residual stain scores of the apically facing thread surfaces for the different instruments and the defects for the surgical approach (a) and non-surgical approach (b)

	30°	60°	90°
a) Surgical approach
Gracey curette	1.31 ± 0.42 A	1.41 ± 0.45 A	1.32 ± 0.38 A
	1.00 (0.5)	1.50 (0.5)	1.25 (0.5)
Ultrasound	1.48 ± 0.41 A	1.34 ± 0.36 A	3.09 ± 1.07 B
	1.50 (0.5)	1.50 (0.5)	2.75 (1.5)
Air powder abrasion	1.25 ± 0.39 A	1.34 ± 0.49 A	2.79 ± 1.18 B
	1.00 (0.5)	1.00 (0.5)	2.75 (2.0)
b) Non-surgical approach
Gracey curette	1.38 ± 0.16 A	1.3 ± 0.15 A	1.1 ± 0.15 CE
	1.5 (0.25)	1.25 (0.25)	1.0 (0.25)
Ultrasound	1.4 ± 0.17 A	1.09 ± 0.17 C	1.09 ± 0.12 CE
	1.5 (0.25)	1.0 (0.06)	1.0 (0.25)
Air powder abrasion	2.82 ± 0.47 B	1.96 ± 0.55 D	2.7 ± 0.7 BF
	2.75 (0.656)	1.81 (0.75)	2.5 (0.91)

Means ± standard deviations and medians (interquartile ranges), the latter as second lines in rows

Scores were ranging from one (residual stain >95%) to six (residual stain <5%)

Different capitals indicate groups with statistically significant differences (p < 0.001), as assessed by pairwise Wilcoxon-rank-sum-tests with p-value adjustments for multiple comparisons according to Holm