Introduction: Although tooth-colored restorations have found a special place in dentistry today, amalgam is still a loyal material for dentists. It seems that each of these two materials are very good and appropriate if they are used in their own place. As much as the comparison of physical and mechanical properties of amalgam and composite is significant; In the same way, comparing these two materials in terms of the superiority of one over the other lacks value and credibility; In many cases where proper isolation is not possible, the use of composite resin is equivalent to the failure of the treatment, and conversely, the use of amalgam restoration in exposed areas is not justified at all. Based on this, the correct use of each of these two is very important in its place. In this way, the use of amalgam band has a significant effect in improving the clinical behavior of amalgam, which will be briefly explained.
Advantages of amalgam band: Bonding new amalgam to old amalgam or amalgam band to dental tissue has always been discussed. These systems are provided for filling the tooth structure and amalgam band with enamel and dentin or the new amalgam band to the old amalgam. The main advantage of this system in many clinical cases is filling the dentin and improving the resistant shape, but the grip created by it is not noticeable with the macromechanical grip resulting from the cavity gripper.
The primary prescription for amalgam banding is when the remaining dental tissue is weakened and it may be possible to restore the overall resistant shape of the restored tooth by bonding the amalgam. Of course, Amalgam Band can be used routinely under all amalgam restorations, thus saving time by eliminating the need for a base.
During amalgam packing, the new layer creates a strong and reliable bond due to chemical reactions to the previous mass. However, if more than 5 minutes have passed since the time of mixing the amalgam, the new amalgam does not have a chemical bond with the previous amalgam, and other measures such as macromechanical, micromechanical (such as sandblasting) or chemical bonding combined with micromechanical bonding with the help of amalgam bond should be used. .
The use of amalgam band has the following advantages:
- Reduction of marginal leakage and microleakage: Several studies have shown that the use of amalgam band reduces microleakage significantly. Regardless of the type of amalgam used, amalgam bond significantly reduces microleakage compared to varnish or cases where no liner is used.
۲- Strengthening the remaining dental structure and increasing resistance to fracture: In a study conducted at the University of Manitoba, 40 premolars and molars whose buccal or lingual cusp had failed were repaired with amalgam and with the help of amalgam band; After one year, no failure was observed.
In another study, bonding amalgam was shown to increase the buccal cusp strength of a MOD restoration spanning one-third of the buccolingual width by 39 to 61%. On the other hand, it has been shown that restoration of pulpotomy milk teeth with amalgam along with amalgam band increases their strength by 26%.
۳- Resistance to future acid attacks and subsequent reduction of secondary decay
۴– Increase flood and decrease sensitivity after treatment: sensitivity after treatment in amalgam restorations is one of the problems that cause pain to patients after tooth restoration with amalgam. This problem is more observed in spherical amalgams that cause less flooding.
The presence of 2 mm of dentin on the pulp or equivalent material covering the pulp is one of the methods that can reduce the sensitivity after work. Using materials such as zinc phosphate, polycarboxylate, glass ionomer and zinc oxide as a base for amalgam restorations is a traditional method to protect the pulp against thermal, electrical and mechanical stimulation. The new method is to use amalgam band instead of base and liner. In this method, by flooding the dentine tubules and preventing the movement of liquid inside the dentine tubules, no pain or sensitivity is caused. It is worth mentioning ; The use of desensitizing dentin systems, which have the same role as varnish, is effective in reducing post-treatment sensitivities, but it does not replace amalgam bonding and does not include the benefits of amalgam bonding.
Even the use of amalgam band has been very effective in reducing the sensitivities of dental collars. In a study, it was shown that the use of amalgam band with bis4-META has a great effect in reducing sensitivity after treatment at the end of a 6-month period; So that 91% of the treated teeth did not show any sensitivity within 6 months.
۵- Conservative and low cutting and keeping more fabric
۶- Reducing the need for a PIN Slot ، Dovetail ، Hole and other mechanical measures that cause additional tooth grinding and increase the possibility of pulp exposure.
The only problem that may be caused by the use of amalgam band is that due to the penetration of resin into the amalgam, the mechanical properties of the amalgam may be affected, which is not important from a clinical point of view.
The reaction mechanism of amalgam bond systems:
The adhesion created by the amalgam bond is based on the micro-mechanical grip; In this way, the amalgam is packed inside the resin that is not fully cured or is being cured. Based on this, amalgam band can be self-curing or dual-curing. Of course, light cure bondings that are very thick are also known as amalgam bonding, an example of which is PQ Amalgam. In these systems, due to exposure to oxygen, the surface layer is not completely polymerized and its surface layer remains uncured, and thus the amalgam inside is packed and a micromechanical seal is created. Studies have shown that the use of light-cured or dual-cured bandages is more effective than self-curing bandages.
In the dual cure system, the amalgam is packed inside the self-cure component and creates a micromechanical grip. For this purpose, it is necessary to lay the bonding in thicker layers (10 to 50 microns) and condense the amalgam on the resin. Thicker layers of bonding agents can be obtained by adding thickening materials or by applying multiple layers (5 to 8 layers).
Bondings with a high amount of filler also create more adhesion than bondings with less filler. In some amalgam bond systems, such as Amalgam bond plus, a powder called HPA has been added, which increases the thickness of the bonding and thereby increases its adhesion. It seems that this material is a type of resin (methyl methacrylate) that can increase its strength in addition to increasing the thickness of bonding.
The important point in all cases is that the amalgam should be triturated at the same time as light cure or dual cure bondings and packed immediately to achieve maximum adhesion.
Chemical bond resulting from the application of amalgam bond:
In addition to micromechanical locking, in some systems, a chemical bond is created in the interface region. In these systems, there are monomers that are able to create chemical bonds with metal oxides, such as 4-META and MDP.
These monomers have two hydrophilic and hydrophobic ends, to bond with both tooth components (hydrophilic) and amalgam (hydrophobic). The most important monomer in this field is 4-META. Other monomers such as MDP can also create an acceptable bond. This monomer can have a significant effect in creating a chemical bond in addition to creating a micromechanical jam.
In a study, it was shown that the use of amalgam band in Class II composite restorations has a significant effect in reducing post-treatment sensitivities. It seems that the main factor of this decrease in sensitivity is 4-META monomer.
Since these bondings can create a chemical bond with the metal matrix tape, to prevent further problems during removal of the metal tape, such as breaking the marginal ridge, it is necessary to treat the surface of the metal tape with inlay wax or a lubricant such as Vaseline before working. be smeared
Adhesion to teeth and amalgam:
The adhesion mechanism in the amalgam bond system is investigated from two areas: 1- Band with teeth 2- Band with amalgam
- Bonding with teeth: since all bonding steps are similar to the usual method; A suitable hybrid layer is created that creates a flood and reduces sensitivity after treatment.
- Resin bond with amalgam: On the other hand, the amalgam enters the uncured resin and creates a micromechanical grip. The strength of adhesive systems for connecting amalgam to dentin is relatively low and has a bond strength of about 10 to 14 MPa. Although a good bond is established with the tooth, there is a weak micromechanical connection between bonding and amalgam, and most failures occur between amalgam and bonding.
Application of amalgam bond as self-etch and total etch:
Today, there are systems that can be used as self-etch and total etch. In both of these systems, an Activator is provided separately. In the self-etch method, after applying the primer, adhesive with Activator It is mixed and applied to the entire cavity at the same time; However, in the total etch method, after the application of etch acid, the adhesive is first applied alone and cured as in the usual method, and then the adhesive is applied again with Activator It is mixed and applied to the entire cavity at the same time. The reason is that in the Total H method, collagens are exposed, and it is necessary for the adhesive resin to completely penetrate them. Thus, if like the self-etch method, after etching; Adhesive and Activator mixed together, the polymerization reaction of the resin has started and due to the high viscosity of the adhesive resin, it is not possible to penetrate the entire length of the collagen fibers, which will subsequently lead to sensitivity and microleakage. In the self-etch method, due to the non-exposure of collagen fibers, there is no need to use a separate adhesive.
In the self-etch method, the sensitivity after treatment was less; While in the Total H system, due to the greater thickness, the bond strength is greater.
The effect of bonding thickness on amalgam bond strength:
By increasing the thickness of the amalgam bond, the adhesion strength also increases. For this purpose, the use of several bonding layers increases the strength of the shear bond. Some systems, such as Amalgam bond plus, have increased the thickness by adding methyl methacrylate powder; They also increase the strength of the bond mass.
In a study where amalgam band was used on bovine teeth; It was shown that the use of one layer of amalgam bond gives a bond equal to 1 MPa and two layers gives a bond of about 14-15 MPa. Of course, it should be noted that the high thickness of the amalgam band should not prevent its accumulation in the margins.
The effect of amalgam type on adhesion strength:
Based on the studies, it seems that spherical amalgams have more bond strength when used with amalgam bond on dentin or composite. On the other hand, as the amount of spherical particles increases, the strength of the bond also increases.
The effect of Amalgam Bond in creating the adhesion of new Amalgam to Old Amalgam or Composite:
In a study, it was shown that bonding amalgam increases the bond strength of new amalgam to composite or old amalgam. In this study, the surface of composite or old amalgam was sandblasted to increase the micromechanical grip.
The effect of sandblasting enamel and dentin before applying amalgam band:
The study of Nikaido and her colleagues showed that sandblasting the surface of the dentin before applying the amalgam bond does not have a significant effect on the bond strength, but sandblasting the enamel significantly reduces the strength of the amalgam bond.
Glass ionomer as amalgam bond:
Self-curing and light-curing glass ionomer can be considered as amalgam bonds. This means that the amalgam is packed inside the glass ionomer and is mechanically stuck inside. There is also a self-curing component in Glass Ionomer Light Cure, which amalgam must be condensed inside before it hardens completely. In self-curing glass ionomers, it should be ensured that the cement is hardened to 90% so that the integrity of the cement is not lost. On the other hand, if the cement reaches the edges of the cavity, it may be washed away or it may stick to the opposite teeth.
It has been shown in a study that if amalgam bond is used on glass ionomer modified with resin (optical glass ionomer), the bonding strength of amalgam with optical glass ionomer increases. However, by using amalgam bond, there is no need to use glass ionomer.
Use of hypoallergenic resin systems:
If only cavity flooding is considered, cavity fillers can be used. Since these materials are used to cover the exposed surfaces of the root to limit the flow of liquid inside the tubules and reduce the sensitivity of the dentin, they are also called Dentin desensitizer. An expensive list of these products may be labeled as dentin desensitizers, but they are not routinely used for dentin flooding under amalgam.
Prototypes like Gluma 2 were actually the primer of the bonding system. Other materials were also presented, which were actually initiator monomers or polymers dissolved in the solvent, which penetrated the carved surface and dried inside it, or turned into a thin layer of polymer upon hardening.
The performance of the thin desensitizing layer of ivory is similar to varnish, but their moisturizing properties are higher and they create a uniform layer (without pores). This layer actually moisturizes the enamel as well as the dentin, but it is still known as a dentin sealant.
Bonding agents, which are used under insulation restorations such as composite, replace conventional flooring and liners; unless we are very close to the pulp (less than 0.5 mm); In this case, a layer of calcium hydroxide should be placed as a liner.
Introducing some commercial samples of amalgam band:
۱- DenTASTIC Amalgam bonding kit(Pulp dent) : Pulp dent band amalgam system is designed based on amalgam penetration in self-curing resin cement. The method of its application is that first the surface of the tooth is etched and after removing the excess moisture; Its bond, which contains two bottles of adhesive primer A and B, is mixed together to form a dual cure. Due to its low thickness, bonding should be done in 3 layers. There should be no air gap between the layers, and only after the last layer is applied, a light gap is applied to remove the solvent. Since its bandage is dual-cured, its curing is selective; This means that the band can be cured or not cured.
Then the cement, which is called Resilute and consists of two pastes, is mixed in equal amounts and placed on the bonded surface in a thin layer. At the same time, the amalgam must be mixed so that it condenses immediately inside the cavity (delay in condensing the amalgam reduces the effect of the amalgam bond). In this way, the amalgam inside the resin cement becomes micromechanical and increases the shape and resistance of the cavity.
۲- Optibond solo plus(kerr) :
This system includes a fifth generation band with an Activator. Due to the high thickness of this system, it is sufficient to use its bandage as a dual cure. Based on this, first the tooth is etched and after removing excess moisture, its bonding is mixed with Activator to make it a dual cure. At the same time, the amalgam must be triturated in the amalgamator to condense immediately in the cavity. In cases where metal matrix tape is used; Before using the amalgam band, the metal band must be greased with Vaseline or any other lubricant. Otherwise, during the removal of the matrix tape, a fracture may occur in the marginal ridge due to the bond created.
Optibond solo plus also has a self-etch system. In this method, instead of etching the cavity, from the bottle containing acid and primer, which is called under the general name Primer; is used and other steps are the same as before. After placing the Primer in the cavity, its bonding is mixed with the Activator and applied to the entire cavity.
۳- Tg amalgam bond(Tg co):
This amalgam bond can also be used in two ways: self-etch and total etch. The method of working with it is exactly like Optibond solo plus; with the difference that its thickness is low and it should be applied in 2-3 layers; While the thickness of Optibond solo plus is high and one layer of it is enough.
۴- Panavia F2 (Kurrary) :
Panavia is a dual-cure adhesive resin that, in addition to creating a micromechanical bond, can also create a chemical bond due to the presence of a monomer such as MDP. According to the manufacturer’s instructions, the resin surface does not need to be cured and the amalgam can be packed directly on it.
۵–Amalgam bond plus(parkell): In this system, in addition to the micromechanical bond, the chemical bond resulting from 4-META is also significant. Its chemical composition is:
۱۰% citric acid ، ۲% ferric chloride > HEMA، ۴-META in MMA and TBB activator و PMMA “high-performance additive”
۶- Scotch bond multi purpose plus(3M) :
It is a fourth generation band that has a separate catalyst. In the last step (after etching and priming), the adhesive is mixed with the catalyst and a dual cure bond is obtained. In this way, the amalgam is bonded by penetrating the self-cure component and some amounts of the light-cure component.
۷– Nano bond (Pentron) :
This bonding is designed in such a way that it can be used as self-etch or total etch. In this system, an activator has been supplied separately. In the self-etch method, after applying the primer, the adhesive is mixed with the activator and applied to all the holes at the same time. In the total etch method, after applying the etch acid, the adhesive is mixed with the activator and applied to the entire cavity at the same time.
۸- All bond 2-Amalgambond plus(Bisco) :
This system can provide good and acceptable flooding due to having monomers for chemical bonding. In a study, it was shown that the use of amalgam bond or All bond 2 is effective for bonding amalgam or composite to enamel and dentin and there is no significant difference.
In another study, it was shown that neither amalgam bond nor All bond 2 had any change in bond strength over time.
Clinical application method:
In some cases due to economic reasons, lack of time, the possibility of weakening the remaining tissue and to prevent possible damage to the dental pulp; Instead of replacing the entire amalgam mass, it is decided to cover it with composite to create a suitable aesthetic for the patient.
In these cases, it is very important to create a macromechanical lock in the first degree and a micromechanical lock in the second degree. Therefore, with the help of a fine process bur, holes with a depth of more than 0.5 mm are created inside the amalgam. Then its surface is roughened with the help of a burr. In the next step, the surrounding enamel is polished and etched. Then bonding is mixed with activator and applied to the entire surface of enamel and amalgam at the same time. Then the amalgam surface is covered with opaquer or opaque tint and finally it is repaired with composite.
It should be noted that most of the time there is no ready and commercial amalgam bonding, but it is necessary to prepare a separate activator along with the bonding so that it can be mixed together and applied to the entire surface of the tooth at the same time.
Dr. Kasri Tabari – restorative and cosmetic specialist
Dr. Neda Khoi – Dentist