Mercury, silver and selenium in serum before and after removal of amalgam restorations: results from a prospective cohort study in Norway

Figures & data

Table 1. Demographic characteristics and GHC index at baseline, first follow-up (Q2) and change score for participants in the three cohorts with available serum samples at both baseline and follow-up.

	Cohort
	Amalgam (n = 30)	MUPS (n = 25)	Healthy (n = 11)
Female gender, n (%)	18 (60)	21 (84)	8 (72)
Age (years); mean (SD)	52.5 (7.4)	50.3 (10.8)	51.3 (11.2)
Smoking habits, n (%)
No, never ever	11 (36.7)	13 (52.0)	5 (45.5)
No, stopped less than one year ago	1 (3.3)	1 (4.0)	0 (0)
No, stopped more than one year ago	14 (46.7)	6 (24.0)	3 (27.3)
Yes, but not daily	0 (0)	2 (8.0)	2 (18.2)
Yes, daily	4 (13.3)	2 (8.0)	1 (9.1)
Missing data	0 (0)	1 (4.0)	0 (0)
Time between Q1 and Q2 in years; mean (SD)	2.06 (0.50)	2.25 (0.35)	2.14 (0.50)
GHC index, mean (SD)
…. At baseline (Q1)	43.6 (18.0)	37.5 (14.5)	9.2 (16.8)
…. At first follow-up (Q2)	30.1 (14.7)	36.4 (19.8)	5.8 (6.1)
…. change score (Q1-Q2)	13.5 (15.9)^a	1.1 (12.7)^b	3.4 (12.1)^c

(a) p < .001, (b) p = .655, (c) p = .373 for H₀: Change score = 0.

Table 2. Dental treatment sessions with amalgam removal in the amalgam cohort.

	Dentist documentation		Patient documentation
	Number of sessions (n)	Percent	Number of sessions (n)	Percent
Treatment sessions with amalgam removal	179	100	178	100
Rubber dam used	134^a	74.9	137	77.0
…used all the time	117	65.4	106	59.6
…used in part	16	8.9	17	9.6
…missing data regarding part of time	1	0.6	14	7.9
Water-cooling and high-volume evacuation used	169^b	94.4	164	92.1
Additional extraoral dental suction or external air delivered to the patient via nasal mask	26^c	14.5	26^d	14.6
Dietary supplements (vitamins and minerals) used	43	24.0	101^e	56.7
Other preparations (e.g. alcohol, charcoal) used	25	14.0	34^f	19.1

^aAccording to the documentation by the dentist, no rubber dam was used in 45 sessions (involving 16 patients). Of these 16 patients, 11 were treated using rubber dam in some sessions and 5 were treated without using rubber dam in any session.

^bIn 10 sessions (involving 6 patients), use of water-cooling and high-volume evacuation was not documented in the questionnaire.

^cInvolving 7 patients.

^dInvolving 6 patients.

^eInvolving 21 patients.

^fInvolving 10 patients.

Figure 1. Concentration of inorganic Hg in serum (µg Hg/L) in the Amalgam cohort (n = 30), MUPS cohort (n = 25) and in the Healthy cohort (n = 11) at baseline and first follow up. In the box plots upper and lower quartiles and median value are indicated. The highest and lowest values are indicated by the whiskers, while outliers are marked with a circle or an asterisk.

Table 3. Concentration of inorganic Hg (I-Hg), MeHg, Ag and Se in serum (µg/L) at baseline and follow-up.

Mean (SD)
	I-Hg		MeHg		Ag		Se
Cohort	Baseline	Follow-up	Baseline	Follow-up	Baseline	Follow-up	Baseline	Follow-up
Amalgam cohort (n = 30)	0.23 (0.21)	0.01 (0.03)^a	0.43 (0.30)	0.47 (0.36)	0.20 (0.23)	0.20^a (0.80)	78.2 (24.7)	71.5 (13.8)
MUPS cohort (n = 25)	0.17 (0.19)	0.27 (0.51)	0.43 (0.55)	0.45 (0.59)	0.14 (0.13)	0.17 (0.18)	69.0 (15.8)	71.3 (17.6)
Healthy cohort (n = 11)	0.31 (0.45)	0.17 (0.20)	0.47 (0.33)	0.35 (0.23)	0.26 (0.30)	0.16 (0.13)	78.2 (22.8)	72.9 (9.8)
Median (lower and upper quartile)
	I-Hg		MeHg		Ag		Se
Cohort	Baseline	Follow-up	Baseline	Follow-up	Baseline	Follow-up	Baseline	Follow-up
Amalgam cohort (n = 30)	0.24	0.00^a	0.39	0.39	0.12	0.03^a	72.3	67.5
	(0.00, 0.34)	(0.00, 0.00)	(0.20, 0.58)	(0.27, 0.58)	(0.08, 0.22)	(0.03, 0.06)	(62.0, 87.8)	(63.7, 77.1)
MUPS cohort (n = 25)	0.12	0.11	0.29	0.25	0.10	0.12	63.4	68.7
	(0.00, 0.30)	(0.00, 0.28)	(0.07, 0.56)	(0.11, 0.51)	(0.03, 0.17)	(0.03, 0.23)	(59.1, 81.8)	(59.0, 77.7)
Healthy cohort (n = 11)	0.00	0.00	0.58	0.29	0.16	0.21	72.5	74.2
	(0.00, 0.50)	(0.00, 0.36)	(0.13, 0.61)	(0.15, 0.56)	(0.07, 0.39)	(0.03, 0.25)	(64.5, 86.3)	(68.6, 81.2)

^aSignificantly different from baseline value (p < .001; Wilcoxon Signed Rank Test – Exact 2-tailed test).

Mean (and SD; upper part of the table) and median values (and lower and upper quartile; lower part of the table) are given for the three cohorts.

Figure 2. Concentration of MeHg in serum (µg Hg/L) in the Amalgam cohort (n = 30), MUPS cohort (n = 25) and in the Healthy cohort (n = 11) at baseline and first follow up. For explanation of the box plots, see legend to Figure 1.

Figure 3. Concentration of Ag in serum (µg Ag/L) in the Amalgam cohort (n = 30), MUPS-cohort (n = 25) and in the Healthy cohort (n = 11) at baseline and first follow-up. For explanation of the box plots, see legend to Figure 1.

Figure 4. Concentration of Se in serum (µg Se/L) in the Amalgam cohort (n = 30), MUPS-cohort (n = 25) and in the Healthy cohort (n = 11) at baseline and follow-up. For explanation of the box plots, see legend to Figure 1.

Figure 5. Concentration of I-Hg in serum (µg Hg/L) at baseline related to number of tooth surfaces filled with amalgam in the Amalgam cohort (n = 32).

Figure 6. Concentration of Ag in serum (µg Ag/L) at baseline related to number of tooth surfaces filled with amalgam in the Amalgam cohort (n = 32).

Table 4. Correlations between concentration of trace elements in serum (µg/L) at baseline and first follow-up for the Amalgam cohort (n = 30; upper part of table) and for the MUPS and Healthy cohorts (n = 36; lower part of the table).

	I-Hg	MeHg	Ag	Se	I-Hg	MeHg	Ag	Se
	(Baseline)	(Baseline)	(Baseline)	(Baseline)	(Follow-up)	(Follow-up)	(Follow-up)	(Follow-up)
Filled surfaces – amalgam	0.285*	0.185	0.388**	−0.107	0.051	0.046	−0.274	0.032
p-value	0.032	0.153	0.003	0.411	0.739	0.721	0.060	0.803
I-Hg (Baseline)		0.002	0.343**	−0.069	−0.020	−0.007	−0.036	−0.064
p-value		0.986	0.009	0.601	0.900	0.957	0.806	0.626
MeHg (Baseline)	0.302*		0.106	0.301*	0.248	0.439**	−0.157	0.315*
p-value	0.016		0.412	0.019	0.105	0.001	0.279	0.015
Ag (Baseline)	0.489**	0.197		0.042	−0.032	<0.001	0.119	0.097
p-value	<0.001	0.101		0.748	0.835	1.000	0.413	0.453
Se (Baseline)	0.283*	0.475**	.238*		0.235	0.237	0.048	0.517**
p-value	0.024	<0.001	0.047		0.124	0.066	0.740	<0.001
I-Hg (Follow up)	0.562**	0.207	0.290*	0.195		0.222	−0.159	0.273
p-value	<0.001	0.099	0.024	0.118		0.146	0.356	0.074
MeHg (Follow up)	0.443**	0.557**	0.295*	0.461**	0.134		0.054	0.416**
p-value	<0.001	<0.001	0.014	<0.001	0.286		0.707	0.001
Ag (Follow up)	0.403**	0.107	0.599**	0.165	0.344**	.257*		0.080
p-value	0.002	0.376	<0.001	0.171	0.008	0.033		0.580
Se (Follow up)	0.298*	0.319**	0.073	0.449**	0.318*	0.401**	0.150
p-value	0.017	0.006	0.544	<0.001	0.011	0.001	0.213

*p < 0.05 level (2-tailed).

**p < 0.01 level (2-tailed).

Correlation coefficients (Kendall’s tau b) and two tailed p-values (italics) are given.

Figure 7. Mean GHC index (and standard error) at baseline (Q1), and at first (Q2) and second follow-up (Q3). Mean index score at the second follow-up was estimated by use of linear mixed models.

Table 5. Dental treatment procedures related to mean GHC change scores in the Amalgam cohort.

	n	Mean change score (SD)	p-value	Effect size (95%CI)
Rubber dam, water-cooling and high-volume evacuation all the time
Yes	15	17.0 (19.2)
No	17	9.0 (11.5)	.172	0.515 (–0.195 to 1.218)
Additional extraoral dental suction or external air delivered to the patient via nasal mask
Yes	6	16.7 (21.8)
No	26	11.9 (15.0)	.509	0.303 (–0.591 to 1.191)
Dietary supplements (vitamins and minerals) used
Yes	21	15.5 (16.6)
No	11	7.5 (13.6)	.179	0.512 (–0.223 to 1.249)
Other preparations (e.g. alcohol, charcoal) used
Yes	10	17.1 (19.6)
No	22	10.8 (14.0)	.306	0.398 (–0.360 to 1.148)