Harmful health effects of dental composite resins. A systematic review
This systematic review summarised research on the health effects of dental composite materials and amalgam on patients and care providers.
We identified few direct health-related effects of different dental materials.
There were somewhat higher mercury levels in urine in the amalgam group, both after five years and seven years.
Little or no differences between the groups were reported for kidney function, neurological function, neuropsychological function, psychosocial function or physical development.
Dental caries, or tooth decay is a dental disease that causes cavities in the teeth. The enamel breaks down first and then the dentin if the process not is interrupted by proper treatment. Dental caries is a chronic disease that in most people is evolving slowly, but it can be prevented. When the tooth structure is damaged, the repair and later maintenance is required. Dental caries is one of the most commonly occurring disease conditions in the world, both among children and adults. Of the five-year-olds that were investigated in Norway in 2012, almost 19 percent needed dental treatment. The corresponding numbers for twelve-and 18-years-old were respectively 44.5 percent and 82 percent. Over the last 25 years there has been a steady decline in the prevalence of dental caries among Norwegian children and adults.
For over 150 years amalgam has been used as dental tooth filling material to repair teeth that are attacked by caries. Amalgam was prohibited for use as a dental filling material in Norway from 2008 due to the risks of mercury on the environment. Tooth-coloured plastic materials (composite materials) are now the first choice as filling material for Norwegian dentists. The composite material is made up of two components A composite filling consists of an organic polymermatrice (plastic) and a filler that mainly consist of inorganic compounds. There are different types of composite materials. These can be grouped according to the polymer array's composition, type chemical binding, consistency or flow properties.
Composite fillings are used in individuals of all age groups and are thus important seen from a public health perspective. In children and adolescents the exposure time in the mouth is long and it is therefore essential to use safe and durable materials. Children can be exposed in two dental sets, where the treatment of milk teeth is of short-term character, but the fillings are more pulp-near and it is more difficult to ensure good curing of the material. Children’s bodies are smaller and more vulnerable to exposure of toxic and endocrine disruptive substances. One can therefore expect greater health effects if children get fillings earlier, and especially if they get new fillings in permanent teeth (double exposure). This differs from the situation in adults who often replace amalgam with composite fillings.
The objective of this systematic review is to summarize research on the health effects of different types of dental composite materials on patients and care providers, and to compare the effect of these with other types of filling materials.
We searched systematically for literature in the following databases: AMED (Ovid), CINAHL (EBSCO), Cochrane Central Register of Controlled Trials, Embase (Ovid), MEDLINE (Ovid), Science Direct, SveMed + and TOXLINE (National Library of Medicine). The search was carried out in June 2014, and updated in April 2016.
Our inclusion criteria were:
Population: Patients who have received dental fillings
Intervention: Tooth filling with dental composite materials
Comparison: Other composites or tooth filling material
Outcomes: Health damaging outcomes
Study design: Randomised controlled trials (RCT), quasi-randomised trials, prospective cohorts and case-control studies.
We made the selection of studies in several phases; firstly, on the basis of the title and summary in the references that were identified in our searches, and secondly, after review of the full text articles. Three researchers have reviewed the results from the searches independently of each other. In cases of doubt or disagreement we sought consensus by discussion or by consulting a third person. After the inclusion, two of the researchers assessed, independently of each other, the primary studies by using the methodological quality of a checklist, "risk of bias".
We summarised the results for each of the relevant outcome objectives for the individual measures and the assessment for each outcome across of the included studies. To assess the quality of the documentation, and the confidence we assign to the summarized results, we used "Grading of Recommendations Assessment, Development and Evaluation" (GRADE).
We found 3404 references in the systematic search for individual studies. We obtained the full text version of 595 references. Thirty-nine of these articles met the inclusion criteria for health effect, of which 30 articles dealt with sensitivity by use of composite materials. One of these studies had a follow up of 17 years. These studies were controlled observational studies and have a median follow-up time of three years. They did not report health effects other than sensitivity and they are listed in the appendix and have not been summarised. Finally, we included two studies, with approximately 1000 children from the United States and Portugal, with results from nine publications. We found no studies that have measured the health effects on adult patients or health care professionals who work with composite materials.
We identified no direct health-related effects of different dental materials versus amalgam. The included studies measured kidney function, neurological function, neuropsychological function, psychosocial function or physical development, as indicators for health effects (surrogate effects). In the American study the level of mercury in urine after five years was 0.6 μ g/g (IQR 0.5-0.9 μ g/g) corrected for creatinine in the composite group and 0.9 μ g/g (IQR 0.5-1.3 μ g/g) in the amalgam group. In the Portuguese study the values were 1.3 μ g/g in the composite group and 2.8 μ g/g in the amalgam group. We also have results from seven years of follow up in Portugal; at seven years the mercury values in urine were 1.6 μ g/g in the composite group and 2.4 μ g/g in amalgam group (p<0,01). In the urine, there were higher mercury levels in the amalgam than in the composite group on all measurements throughout the study, with the exception of baseline level. There were no differences between the groups on renal markers (such as albumin) (p < 0.3).
The results from the studies indicate small or no differences between the groups when it comes to neurological function. The average nerve cord speed in the tibialis nerve was 50.8 (SD 5.1) m/s in the composite group and 50.2 (SD 5.1) m/s in the amalgam group after seven years. There were no clear differences in Neurological Severity Score, with a score of 0.6 (SD 0.9) in the composite group and 0.5 (SD 0.8) in the amalgam group.
In the Comprehensive Test of Non-verbal Intelligence (CTONI), a kind of IQ test, the composite group and the amalgam group had a score of 81 (SD 12), after seven years. There was little or no difference between the groups on psychosocial function. The Child Behaviour Checklist (CBCL) measured 45.0 (SD 11.0) in the composite group and, in comparison, 44.7 (SD 10.7) in the amalgam group after five years. Body Fat (BF) measured 24.3 (SD 1,1) in the composite group and 24,4 (SD 1,1) in the amalgam group.
We judged the documentation to be of moderate to low quality. This means that we have limited confidence in the effect estimates. The individual studies had low risk of bias. However, most outcomes were only reported on one study.
The two identified studies included more than 1000 children and had a follow-up time of five and seven years. The studies showed no difference in health outcomes between children who got composite fillings and amalgam fillings. A significant proportion of children randomly assigned to amalgam fillings also got composite fillings in their front teeth. We consider that the validity of the result to Norwegian conditions is somewhat limited because the children had significantly more fillings than what is common among Norwegian children in the same age group.
It does not seem to matter if children get amalgam or composite fillings, regarding the dental filling material’s influence on most surrogate end-points related to health. We lack trials that compare different composite dental fillings and report other health outcomes than sensitivity in the teeth with long-term follow up.