In arguing the case of whether amalgam is safe or not, the discussion has often been turned to compare the physical properties of various filling materials. The Dental Association still claim that dental mercury amalgam is a far superior filling material and that composite fillings are not only inferior but that they only last a very short time. The types of scare tactics used by such organizations are intended to distract our attention from the fact that amalgam is in fact the greatest source of mercury to the general population and that the stuff simply is not safe. I do not believe that an argument about physical properties of any material can carry more weight than the responsibility of placing health care as our number one priority. It is like suggesting that because Thalidomide stops morning sickness for some women we should still be using it. Mechanics is not an excuse to disregard systemic effects.

To make matters worse the claim that amalgam is a far superior material to composite as a filling material simply does NOT reflect the scientific research, which is even published in the dental journals. Most of this short paper carries annotated references from some of this literature. As you read them it will become clear to you that in fact it is the composite materials which are superior to dental amalgam as a tooth restorative material from a purely mechanical perspective. They carry the added advantage that they also look like teeth and are generally almost non-toxic. Ironically, this view is also held by Dr Peter Magnus who in 1992 was president of the Australian Dental Association (NSW branch). In an interview on radio 2UE, 16th February 1992, the reporter asked him if he used amalgam in his practice. His response was: "I personally don't"
Reporter: "Why is that?"
Dr Magnus: "Because I believe today we have materials which are probably better and not so environmentally unfriendly."

Others, in official positions, have expressed the view that amalgam is not such a good material. Quintessence International is one of the most respected international dental journals. In 1995 the editor-in-chief of Quintessence (Volume 26, Number 3,1995), Dr Richard Simonsen wrote:

"Amalgam should never be used as a restorative material in paediatric dentistry."
Why? Because better alternatives are available.

"Amalgam should never be used as a first time restorative material."
Why? Because better alternatives are available.

"Move Over Amalgam - At Last"

To add to the inaccuracy of the Australian Dental Association comments are the statements made by Dr. Harold Loe, the Director of the National Institute of Dental Research ( NIDR), who stated in the September, 1993 edition of "Dental Products Report":

"That first filling is a critical step in the life of a tooth. Using amalgam for the first filling requires removing a lot of the tooth substance, not only diseased tooth substance but healthy tooth substance as well. So, in making the undercut you sacrifice a lot, and this results in a weakened tooth. The next thing you know the tooth breaks off, and you need a crown. Then you need to repair the crown...and so it continues to the stage where there is no more to repair and you pull the tooth. With the first filling you should do something that can either restore the tooth or retain more healthy tooth substance. Use new materials-composites or materials you can bond to the surface without undercuts. You can do this with little removal of the tooth substance so that the core of the tooth is still there."

With these statements, made by such respectable authorities, it is amazing that the dental associations continue to spread misinformation.

Comparison of Filling Techniques And Their Consequences

Amalgam fillings do not stick to the tooth. To retain the filling in the tooth, the cavity must be prepared with 'undercuts'. These undercuts not only lock in the amalgam filling but also cut off the nutrient supply to the dentine above the cut. Therefore the tooth structure above and to the side of the filling becomes brittle.

All metals in the mouth will undergo some corrosion. Amalgam also corrodes at a reasonably fast rate. When amalgam corrodes it also expands and it does so in all directions. The force created by this expansion will often create minute fractures in the tooth that is already more brittle due to the shape of the cavity preparation. At this stage the patient returns to the dentist to report that all they were eating was some soft bread and the tooth broke!

To repair such a problem, the dentist will usually drill a small hole into the dentine and insert a self-tapping screw - called a pin. The pin is reinforcement for the amalgam filling which will go back in. Even if this pin is made of titanium it will undergo corrosion when in contact with amalgam. Again the corrosion will cause an enlargement of the pin (sometimes up to five times its diameter) which will then crack the tooth further - but this time lower down the root surface.

This tooth is now a candidate for a crown because the filling, which has to go back into the tooth, is now so large that it cannot sustain the forces of chewing for very long.

Composite fillings do stick to the tooth. They are bonded chemically and mechanically to the tooth. They do not require a cavity, which is undercut and therefore do not require such a large or damaging cavity. In fact a composite filling can be used to rebuild a broken cusp without the use of pins or other mechanical support. I personally have not used a pin for years and have had great success with such restorations.

Studies comparing the fracture resistance of the tooth when filled with amalgam or composite indicate that amalgam will weaken the tooth structure whereas bonded composite fillings will strengthen the tooth. There is absolutely NO reason to continue the use of mercury amalgam!

Secondary Decay Under Fillings

Another bit of misinformation, which is often touted about by the dental associations, is that secondary decay is much greater with composite fillings than amalgam. This is completely false. When amalgam corrodes it not only does so on the chewing or exposed surfaces, but also corrodes on the side, which is in contact with the tooth- the deep part of the cavity. The corrosion products react with the calcium and phosphorous in the tooth, with the formation of hydrochloric acid. This acid then dissolves the tooth structure which is called secondary decay. The newer term for this is Crevice Corrosion. This does not happen with composites.

Toxicity

Mercury is one of the most toxic substances known to man. Amalgam is made of 50% mercury which leaches from the set amalgam all of the time. Recent research is indicating that the breakdown products of composites and glass ionomer cements are between 300 times and 1.6 million times below the Tolerable Daily Intake levels. By comparison the mercury from amalgam is about 4 times greater than the Tolerable Daily Intake levels.

Although different people may show sensitivity to different composites, they are not subjected to the high level of poisoning as with dental mercury amalgam.

As a cautionary note, there has been one study published, which shows that some composites (those based on BIS-GMA) may break down to two materials (Bisphenol-A and Bisphenol-A dimethacrylate) which have been shown to be estrogenic. It is therefore advisable, for patients who have a hormone-related cancer, to avoid such materials if possible. With this warning in mind it is still preferable to replace all amalgam fillings. Mercury from amalgam will reduce the body's level of Selenium. Several studies have shown that cancer rates increase as the body's selenium levels drop.

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Referenced Abstracts - Composites

References which demonstrate the functional ability of plastic composite resin fillings

Replacement of missing cusps: an in vitro study.

LC; Smith-BG

J-Dent. 1994 Apr; 22(2): 118-20

One of the commonest methods of replacing a missing cusp, a pinned amalgam restoration, was compared with three adhesive restorative techniques, two of them with additional pin retention. All the teeth were subjected to occlusal / lateral forces and loaded to fracture in an Instron testing machine. A layered restoration of glass ionomer cement replacing the dentine, and resin composite replacing the enamel, without pins required more force to fracture than any of the other techniques including the pinned amalgam restoration. A composite restoration with dentine bonding agent and additional pin retention was second best and significantly better than the pinned amalgam restoration. A cermet restoration with additional pin retention required slightly less force to fracture than pin-retained amalgam restorations, but not significantly so.

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Clinical evaluation of a highly wear resistant composite.

Dickinson-GL; Gerbo-LR; Leinfelder-KF

Am-J-Dent. 1993 Apr; 6(2): 85-7

The purpose of this clinical study was to determine the long-term potential of a resin composite restorative material.

The colour matching ability of the material never fell below 96%. The percent of restorations exhibiting a surface texture similar to enamel never fell below 90% Alfa. At the end of 3 years, the total average loss of material was only 28 microns. No clinical evidence of bulk fracture was detected .... 79% of the restorations were Class II complex restorations with the replacement of at least one cusp!

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Evaluation of occlusal marginal adaptation of Class II resin-composite restorations

ASDC-J-Dent-Child. Jul-Oct. 1993

describes the results of an evaluation of the occlusal marginal adaptation of Class II restorations in a clinical trial. The margins of 183 resin composite and 61 amalgam restorations, made by three dentists, were assessed. Resin composite restorations showed more 'excellent' margins than amalgam restorations (64.5 percent and 21.3 percent, respectively).

The variable mainly influencing the marginal adaptation of the composite restorations was the dentist.

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Three-year follow-up of five posterior composites: in vivo wear.

Willems-G; Lambrechts-P; Braem-M; Vanherle-G

J-Dent. 1993 Apr; 21(2): 74-8

The wear of five posterior composites was evaluated in Class II cavities over a 3-year period with an accurate 3D-measuring technique. A clinical evaluation was also performed. The ultrafine compact-filled composites (Willems et al., 1992) showed acceptable wear rates ranging from 110 to 149 microns after 3 years. This is very similar to the wear rate of human enamel on molars, which is about 122 microns after 3 years. It can be concluded that the investigated composites can be considered as amalgam alternatives.

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Directed Shrinkage Technique in Class V Composite Restorations: in Vivo Microscopic Evaluation and Clinical Procedure,

Ferrari, M.,

Practical Periodontics and Aesthetic Dentistry, Vol. 5, No. 7, September 1993, pp. 29-36.

The study examined the leakage in vivo of Class V restorations with chemically-cured composite bases. Class V cavities were prepared at the CEJ in six periodontally hopeless teeth in six patients. The cavities were total etched, All-Bond 2 and Bisfil 2B (Bisco) were applied, and Z100 (3M) was used to complete the restorations. After 30 days, the teeth were extracted, dyed, sectioned, and scored for leakage. The results showed no enamel margins leaked, with only one cervical margin showing minimal leakage.

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Longevity of dental restorations in selected patients from different practice environments.

Mahmood-S; Smales-RJ

Aust-Dent-J. 1994 Feb; 39(1): 15-7

The objective of the study was to evaluate the long-term survivals or longevity of dental restorations placed in selected patients from different practice environments in two countries. The case histories of 46 adult patients with 622 restorations placed in three private practices in Pakistan were followed for a minimum of 10 years, and compared with similar assessments of 50 adult patients with 966 restorations placed in a dental hospital in Australia. Amalgam and composite resin restorations showed similar survivals in both countries, but cast gold restorations had much lower survivals in the Pakistan group of patients. In both countries, restoration survivals were significantly better in females, and when patients attended less frequently for treatment. For the Australian group, changes in dental operators also gave significantly better survivals, and there were significant restoration survival differences present between the three practices in Pakistan.

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Evaluation of occlusal marginal adaptation of Class II resin composite inlays.

Kreulen-CM; van-Amerongen-WE; Borgmeijer-PJ; Gruythuysen-RJ

ASDC-J-Dent-Child. 1994 Jan-Feb; 61(1): 29-34

In this paper, the results of a clinical study of the occlusal marginal adaptation of indirect Class II resin composite inlays are presented. The margins of 180 resin composite and 60 amalgam restorations, made by three dentists, were assessed, shortly following their placement. An indirect, photographic method has been applied to assess marginal adaptations. The restorations were classified into excellent and non-excellent marginal adaptation categories and on this basis influencing factors were determined. Resin composite inlays appeared to have a greater percentage of 'excellent' margins than amalgam restorations (46.1 percent and 6.7 percent, respectively). The dentist was the variable that most influenced the marginal adaptation. Variability in the period elapsing between applying the restoration and conducting the assessments is discussed as a factor that may impair a fair comparison with initial results for direct composites.

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Three-year follow-up of five posterior composites: in vivo wear.

Willems-G; Lambrechts-P; Braem-M; Vanherle-G

J-Dent. 1993 Apr; 21(2): 74-8

The wear of five posterior composites at occlusal contact areas (OCA) and contact free occlusal areas (CFOA) was evaluated in Class II cavities over a 3-year period with an accurate 3D-measuring technique. A clinical evaluation was also performed. The ultrafine compact-filled composites (Willems et al., 1992) showed acceptable OCA-wear rates ranging from 110 to 149 microns after 3 years. This is very similar to the OCA-wear rate of human enamel on molars, which is about 122 microns after 3 years. The fine compact-filled composite had an unacceptable OCA-wear value of 242 microns after 3 years. The ultrafine midway-filled composite showed an exceptionally high CFOA-wear value of 151 microns after 3 years, which gave the impression of it being gradually washed out of the cavity. Clinically, 70% of the restorations made with the ultrafine midway-filled composite showed excellent colour match after 3 years. For most of the compact-filled composites slightly opaque fillings were noted and 63% of the restorations made with one of these materials were clearly opaque. It can be concluded that the investigated ultrafine compact-filled composites can be considered as amalgam alternatives as far as their wear resistance is concerned.

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Posterior adhesive composite resin: a historic review.

Fusayama-T

J-Prosthet-Dent. 1990 Nov; 64(5): 534-8

This landmark study by one of our great pioneers, graphs resin vs. amalgam failures and shows resin (Clearfill Posterior - a self-cured resin) far superior in the long term. This study is included in his text book published last year and makes fascinating reading. It is now relatively old, but Fusayama's team are (were - he's retired) world leaders in resin technology although his technique is clinically complex and I don't use it. In Japan this technique is taught at undergraduate level!

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Recovery from Amyotrophic Lateral Sclerosis and from Allergy after Removal of Dental Amalgam Fillings.

Redhe, O; Pleva, J. Int. J. Risk Safety Medicine. (1994): 4, 229-236.

An evaluation of 100 cases of poisoning and immunological effects in dental amalgam patients, documented in clinical practice.

The patient had suffered for a long period from neurological problems. In 1984, following a complete neurologic evaluation, a diagnosis of amyotrophic lateral sclerosis (ALS) was made at the department of neurology of the University Hospital in Umea, Sweden. It is of unknown etiology and considered to be 100% fatal. No further visit to the clinic was proposed, as the disease is pernicious and there is no known therapy for ALS.

A dentist recognised the symptoms as those familiar in the patient group with health problems attributable to dental amalgam fillings. Patient history revealed the onset or exacerbation of neurologic symptoms following placement of amalgam dental fillings. The patient had 34 tooth surfaces filled with amalgam, most of which were shallow and of moderate extent.

With the consent of the patient, all amalgams were removed and replaced with alternative material. Treatment was completed in March 1984. Removal of the amalgam in the first tooth that had originally given post-operative problems resulted in an exacerbation of symptoms, with a continued recurrence of exacerbation following each subsequent replacement.

Following the replacement of the last DA, the patient's entire condition rapidly improved. Six weeks following the final replacement, the patient was able to go up stairs without experiencing back pain. Pains in the mouth also receded and the sore throat, present during the whole history of the disorder, recovered. Five months after completion of the DA removal, the patient returned to the same University Hospital at Umea for a week-long follow-up investigation, after which the following notation was placed in her record: "The neurologic status is completely without comment. Hence, the patient does not show any motor neuron disease of type ALS. She has been informed that she is in neurological respect fully healthy."

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