|Year : 2021 | Volume
| Issue : 2 | Page : 133-138
The war between amalgam and composite: A critical review
Bhumika Kapoor1, Lateef Ahmed2
1 Private Practitioner, Alwar, Rajasthan (B.D.S,M.D.S Conservative Dentistry and Endodontics), Alwar, Rajasthan, India
2 Medical Officer (Dental), CHC Ramgarh, Alwar, Rajasthan, India
|Date of Submission||11-Jul-2020|
|Date of Decision||10-Feb-2021|
|Date of Acceptance||20-Mar-2021|
|Date of Web Publication||22-Jun-2021|
M. S. 13, A.D.A Colony Phase 1, Ramghat Road, Aligarh - 202 001, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Amalgam and composite are the two most famous dental restorative materials till date and the choice between them is still debatable. Amalgam restorations have served the profession well and will continue to do so in the years to come. In terms of longevity, amalgam is superior to composite resins, especially when used for large restorations. In case of small restorations, composite is the restoration of choice as minimum removal of the sound structure is required. Where esthetics is a major concern, composite has a way far than amalgam. Amalgam has served as a better core material and has superior mechanical properties than composite. Composite has an advantage of adhesion over amalgam. This review article compares amalgam and composite as a restorative material.
Keywords: Amalgam, composite, esthetics, longevity, strength
|How to cite this article:|
Kapoor B, Ahmed L. The war between amalgam and composite: A critical review. J Oral Res Rev 2021;13:133-8
| Introduction|| |
Restorations can be broadly classified as direct or indirect. Indirect restorations which are fabricated outside the patient's mouth have better long-term survival rate than direct restorations. The direct restorations have some advantages such as they are less time-consuming, require a single appointment, require less removal of sound tooth structure, and lower cost. These advantages outweigh the clinician as well and patient's preference over indirect restorations. Many materials have been proposed as direct filling material, but amalgam and composites have been most successful.
Amalgam offers certain advantages of low cost, high survival rate, high compressive strength, better tolerance to masticatory forces, excellent wear resistance, less sensitive to moisture contamination, and less technique sensitive. However, its limitations include poor esthetics, lack of adhesion to dental tissues, and complex tooth preparations as compared to composites.
The advantages of composites include esthetics, minimal tooth preparation, ability to bond to tooth structure, and less complex tooth preparations. The disadvantages include polymerization shrinkage which leads to gap formation, sensitive to moisture contamination, technique sensitive, higher cost than amalgam, greater occlusal wear in areas of high stress, marginal percolation with time if inadequate bonding occurs.
| Distribution of Amalgam and Composite Restorations Based on Different Variables|| |
A population-based study was conducted in which posterior restorations of 720 persons were evaluated. Tooth-related variables that were noted were as follows: restorative material, whether amalgam or composite; type of tooth; cavity size; and estimated time in the mouth. Patient variables that were included were the socioeconomic status of the patient, demographics, and oral hygiene. Out of 720 persons that were included, 503 (69.9%) had at least one posterior restoration. A total of 2135 restorations were considered, in which with 943 (43.9%) were composite and 1207 (56.1%) were amalgam restorations. It was seen that men had more amalgam restorations as compared to females. Also, it was found that black- or brown-skinned individuals had more amalgam restorations. Amalgam was less found as the number of involved surfaces increased. Amalgam was used more in molars than in premolars. Also, amalgam restorations declined considerably in relation to composites from older to newer restorations. It was also seen that amalgam was common in persons who had a higher dental caries index.
In 2019, a survey was conducted to evaluate knowledge and awareness among patients about the use of amalgam and composites as restorative materials for posterior teeth. A descriptive study was conducted in a sample of 100 patients, using a self-administered questionnaire where 68% preferred tooth-colored restorations. A detailed audiovisual appraisal about composites and amalgam to analyze their attitude and perception was done. About 30% chose composite, 22% amalgam, and 48% chose to leave the decision with the dentist.
| Comparison of Survival Rate of Amalgam and Composite|| |
Manhart et al. in 2004 showed in a prospective study that annual failure rates of both materials are comparable. However, according to Van Nieuwenhuysen et al. (2003); Bernardo et al. (2007); and Soncini et al., amalgam restorations had better longevity than composite restorations. Opdam et al. in 2007 analyzed in a retrospective study that survival rates of both posterior composite and amalgam were comparable, but chances of secondary caries were more in composite restorations while more fracture failures were related to amalgam restorations. Some studies have shown that the caries risk of the patient plays a significant role in restoration longevity,, and in some studies, more secondary caries has been found next to composite restorations compared with amalgam restorations.,,
The posterior composite restoration was initially indicated in case of small carious lesion. However, the clinicians now use composite to restore large carious lesions too. It was found that more extensive restorations showed reduced longevity., This may be associated with large restorations being more prone to fracture. A retrospective study compared the longevity of three and four /five surface amalgam and composite restorations relative to patients' caries risk. 1949 large class II restorations (1202 amalgam/747 composite) were analyzed. The following parameters were considered: Dates of placement, replacement, and failure were recorded, and caries risk of patients was assessed. Survival was calculated from Kaplan–Meier statistics. After 12 years, 293 amalgam and 114 composite restorations had failed. Large composite restorations showed a higher survival in the combined population and in the low risk group. For three surface restorations in high risk patients, amalgam showed better survival. A study was conducted which concluded that annual failure rates in posterior stress-bearing restorations were: 0%–7% for amalgam restorations, 0%–9% for direct composites.
A long-term, randomized clinical trial was done to compare the longevity of amalgam and composite. A total of 1748 restorations at baseline, were followed for up to 7 years. Overall, 10.1% of the baseline restorations failed. The survival rate of the amalgam restorations was 94.4%; that of composite restorations was 85.5%. Annual failure rates ranged from 0.16% to 2.83% for amalgam restorations and from 0.94% to 9.43% for composite restorations. Secondary caries was the main reason for failure in both materials. It was also concluded that the risk of secondary caries was 3.5 times greater in the composite group.
Thus, it may be concluded that the survival rate of both of these materials is multifactorial and it is depended on various variables. However, in patients with high caries, amalgam has shown excellent performance.
| Microleakage in Amalgam and Composite|| |
Microleakage is defined as the clinically undetectable passage of bacteria, fluids, molecules, or ions between a cavity wall and the restorative material applied to it. It is major factor that influences the survival of a dental restoration. It can cause staining of the tooth structure and marginal breakdown, recurrent caries, pulp involvement, and dentin hypersensitivity. The initial marginal seal of amalgam is less, but eventually, there is less microleakage. This may be attributed because of its corrosion products. Microleakage can be caused due to several factors such as polymerization shrinkage, thermal contraction, absorption of water, and changes in tooth dimension. Polymerization shrinkage of a composite resin can create contraction forces that may disrupt the bond to the cavity walls, leading to marginal failure and subsequent microleakage. The volumetric contraction for most of the modern day composites ranges between 2.6% and 4.8%. Modern dentine bonding agents show bond strengths to dentine higher than 20 MPa, which is beyond the contraction stress generated by polymerization stress (13–17 MPa), the total contraction forces may be higher than the adhesive strength, leading to open margins. One of the major drawbacks of the composite is that there is microleakage at the gingival seat of the class II composite. This may be due to a lack of enamel at the gingival margins leading to less stable cementum dentin substrate for bonding. Cagidiaco et al. demonstrated the presence of an outer layer formed partially by cementum located below the cementoenamel junction that does not allow micromechanical retention by adhesive materials. Microleakage in resin-based restorations placed in deep interproximal boxes can be affected by the orientation of dentinal tubules. The coefficient of thermal expansion of composite resin (25–60 ppm°C-1) is several times larger than that of enamel (11,4 ppm°C-1) and dentin (8 ppm°C-1) 28. This physical property is also responsible for microleakage in resin-based restorations. Microleakage can also result due to mismatched modulus of elasticity leading to loss of mechanical bond.
A study was conducted to compare marginal seal at tooth-material and material-material interfaces in the proximal box in combined amalgam/composite resin restorations in MOD cavities. Marginal adaptation was evaluated at the interface of amalgam-tooth amalgam-composite resin and composite resin tooth. Microleakage was evaluated by means of methylene blue infiltration after 7-day water storage and thermocycling regimen (1500 cycles). It was concluded that despite the fact that amalgam and composite are two entirely different materials their interface revealed the lowest microleakage values.
| Strength of Amalgam and Composite|| |
High-copper amalgams have compressive strengths that range from 380 to 550 MPa. This is very close to enamel and dentin. Therefore, the manufacturers do not pay much emphasis on increasing compressive strength. Composites have compressive strength in the range of 236–256 Mpa. In larger lesions, amalgam is preferred. On the other hand, in smaller carious lesions, composite is preferred to conserve tooth structure as amalgam requires more tooth cutting for proper retention and resistance form. The tensile strength of amalgam is low. During mastication when forces are applied in such a way that tensile stresses are generated and flexion is produced, the amalgam has a tendency to fracture. Sufficient bulk is required to prevent fracture of amalgam restoration since it does have an ability to withstand plastic deformation during high masticatory forces. In case of composite, retention is not obtained from cavity depth rather from micromechanical bonding.
Wear resistance of composites has been considered extensively in longitudinal clinical studies. Large posterior composites that have full occlusal coverage are more prone to fracture because of occlusal contact area and functional contact area wear. Results have demonstrated that microfill composites are the most wear-resistant formulations. However, novel composites display extremely low in vitro and in vivo wear rates. The wear resistance of composites is due to filler particles and not due to the mechanical strength of the composite. Filler particles are harder than polymer and if these filler particles are closely placed then the intervening matrix is protected.
Recent advances in dental composites such as fiber-reinforced composites and nanocomposites have much higher strength and durability. Fiber reinforcement of polymer resins with silane-treated glass fibers acts to strengthen and toughen composites for single and multiple unit restorations. They possess higher flexure strength, excellent in compression, increased hardness, increased resistance to crack propagation, and have very low thermal expansion (structural stability). Composite restorative materials characterized by filler-particle sizes of ≤100 nm are referred as “nanocomposite.” The lower size of the particles leads to less curing shrinkage, negligible marginal leakage, color changes, superior flexural strength, modulus of elasticity, and translucency. Extremely small filler particles have dimensions that are below the wavelength of visible light (0.4–0.8 μm), unable to scatter or absorb visible light. This results in improvement of the mechanical properties, especially wear resistance, improvement of biocompatibility by reducing the elution of components, superior polish, and gloss comparable to microfill composites.
| Esthetics|| |
Amalgam is a usually done in posterior teeth and in class V cavities which are not esthetically critical because of its unesthetic appearance. It is contraindicated in anterior teeth. The composite is a restoration of choice in esthetic areas. Both the composite restoration and tooth structure change in color with age. The analysis of color should be made after hydrating the tooth as drying the tooth structure makes it appear lighter and whiter in color. Moreover, with time, chemical changes in the matrix polymer may cause the composite to appear more yellow. This process is accelerated by exposure to ultraviolet (UV) light, oxidation, and moisture. Self cure composites with high matrix content show more yellowish discoloration. Visible light cured systems that, contain higher filler contents, are modified with UV absorbers and antioxidants are more resistant to color change. Even if a composite is relatively color stable, the tooth undergoes a change in its appearance over time because of dentin darkening from aging. Aged tooth structure appears more opaque and darker yellow. It is a challenge for the clinician to match the rate and type of color change of the composite restoration with the tooth structure.
| Amalgam and Composite as a Core Material|| |
The advantage of using composite as a core material is that it has the ability to bond to the tooth structure as well as post, it is opaque and translucent, has rapid setting. It has shown to protect strength all-ceramic crowns like amalgam core. Loss of marginal integrity at the crown margin can result in leakage and invasion of oral fluids. Hence, 2 mm of sound tooth structure should remain at the margin for optimal composite resin core function. Composite core materials can be used in association with metallic, fiber, or zirconia posts. Loosening of the post, core, and crown with the composite core can occur, but composite cores have been shown to fail more favorably than amalgam. Dental amalgam is a traditional core buildup material with a long history of clinical success. Amalgam can be used with or without a post. With the amalcore technique, amalgam is compacted into the pulp chamber and 2–3 mm coronally of each canal. The remaining pulp chamber should be of sufficient width and depth to provide adequate bulk and retention of the amalgam restoration, and an adequate dentin thickness around the pulp chamber is required for adequate rigidity and strength. The fracture resistance of the amalgam coronal-radicular restoration was adequate with four or more millimeters of the chamber wall, although the extension into the root canal space had little influence. When more retention is required, amalgam can be used with a metallic post and more force is required to dislodge the restoration. However, certain disadvantages like discoloration through cervical gingiva, corrosion and inability to bond to tooth or post are seen in cases where amalgam is used as core material.
| Mercury Toxicity|| |
The issue of mercury toxicity due to dental amalgam has always been a topic of controversy. Mercury is found in the earth's crust and is found in water, food, etc., hence a small amount of mercury can be found in blood and urine, however dental amalgam restoration can only raise the levels of mercury in the body. Mercury is released only during trituration, placement, and removal of amalgam restoration. Once amalgam is set and the reaction is complete there is negligible release of mercury.
Mercury toxicity may occur from organic, inorganic, and elemental forms of mercury. The organic form (methyl and ethyl mercury) is the most toxic form. The main route of entry of mercury into the human body is through the alveoli in the lungs. Metallic mercury can be absorbed through vapors at 80% efficiency. However, mercury gets excreted from the body and does not permanently collect. The average half-life of mercury is 55 days for transport through the body to the point of excretion.
A study conducted by measuring the intraoral vapor levels over a 24-h period in patients with at least nine amalgam restorations showed that the average daily dose of inhaled mercury vapor was 1.7 μg (range from 0.4 to 4.4 μg), which is approximately 1% of the threshold limit value of 300–500 μg/day established by the WHO, based on a maximum allowable environmental level of 50 μg/day in the workplace. In 1993, Berglund determined the daily release of mercury vapor from amalgam restorations made of alloys of the same types and batches as those used in the in vitro part of the study. He carried out a series of measurements on each of eight subjects before and after amalgam therapy and found that none of the subjects were occupationally exposed to mercury. The amalgam therapy, that is, from 3 to 6 occlusal amalgam surfaces and from 3 to 10 surfaces in total had very little influence on the intraoral release of mercury vapor, regardless of amalgam type used, effects were not found on mercury levels in urine and saliva. Berdouses et al. stated that mercury exposure from amalgam can be greatly increased by personal habits such as chewing and brushing. The internal exposure to amalgam-related mercury and estimated the amalgam-related absorbed dose of mercury was evaluated by Halbach et al. Mercury absorbed from amalgam restorations was estimated at up to 3 μg/day for an average number of restorations and 7.4 μg/day for a high amalgam load. These estimates were below the tolerable dose of 30 μg/day as established by the WHO.
Mercury, however, can pose a delayed type IV hypersensitivity reaction as a skin rash in rare situations.
However, it is recommended that if mercury hygiene procedures are followed, the risks of adverse health effects in the dental office could be minimized.
Other drawbacks of amalgam include amalgam blues which is bluish black discoloration of the tooth in which amalgam is used for a long period of time. Amalgam tattoo is a gray, blue, or black area of discoloration on the mucous membranes of the mouth due to entry of dental amalgam into the soft tissues. It is a painless and benign condition. Galvanic corrosion is a type of electrochemical corrosion which occurs when two or more dissimilar metals are in direct physical contact with each other. Here, saliva acts as electrolyte, e.g., two restorations made up of different alloys like amalgam and gold. Crevice corrosion (concentration cell) occurs in space between alloy and tooth due to microleakage of electrolytes. The pulp needs to be protected from amalgam due to its chemical, thermal, electrical, and physical nature. There should be an optimum barrier of ≥2 mm between pulp and amalgam.
| Advances in Dental Amalgam|| |
- Bonding in amalgam is based on a dentinal bonding system developed by Nakabayashi. A mean bond strength of 27 MPa was achieved using a spherical amalgam in one study of bonded amalgam. Bond strength achieved with admixed alloys was slightly lower than those with spherical alloys
- Consolidated silver alloy system was developed, in this spherical form of the alloy was used with fluoroboric acid solution to keep the surface of the silver alloy particles clean. This alloy is compacted into prepared cavity like gold
- Fluoride has been incorporated in dental amalgam for anticariogenic effect. Fluoride amalgam serves as a “slow release device” which deposits fluoride in hard tissues around restorations. The release of fluoride from dental amalgam is considerable during 1st week.
| Conclusion|| |
Both the restorative materials have some advantages and disadvantages. The clinician should make a proper assessment of the case like location of the tooth, remaining tooth structure, extent of caries/tooth damage, occlusal stresses, esthetic considerations, caries index, patient's preference, armamentarium, and cost before deciding the type of restoration material to be used. Amalgam has served as an excellent and versatile restorative material for many years, despite an era of controversy. Amalgam should remain the material of choice for the economic direct restoration of posterior teeth. When esthetic concerns are paramount, tooth-colored materials like composite placed meticulously can provide an acceptable alternative.
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Conflicts of interest
There are no conflicts of interest.
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