Advances in Dental Materials

The use of materials to rehabilitate tooth structures is constantly changing. Over the past decade, newer material processing techniques and technologies have significantly improved the dependability and predictability of dental material for clinicians. The greatest obstacle, however, is in choosing the right combination for continued success. Finding predictable approaches for successful restorative procedures has been the goal of clinical and material scientists. This article provides a broad perspective on the advances made in various classes of dental restorative materials in terms of their functionality with respect to pit and fissure sealants, glass ionomers, and dental composites.

The use of materials to rehabilitate tooth structures is constantly changing to the benefit of the patient and clinician. Over the past decade, newer material processing techniques and technologies have significantly improved the dependability and predictability of dental material for clinicians. The greatest obstacle, however, is in choosing the right combination for continued success. Finding predictable approaches for successful restorative procedures has been the goal of clinical and material scientists. Any dental material used in the oral cavity must satisfy some basic perquisites: they must be similar to tooth structures in their physical and mechanical properties, resist masticatory forces, and possess an appearance similar to natural dentin and enamel. Restorative materials used in the oral environment must fulfill form, function, esthetics, and biocompatibility. The ideal material, however, does not exist because many do not fulfill all prerequisites. Fortunately, recent advances in material science, which are described in this article, have closed the gap significantly. This article provides a broad perspective on the advances in functionality of various classes of dental restorative materials, namely pit and fissure sealants, glass ionomers, and dental composites.

Pit and fissure sealants

Several improvements have been made in the materials that are used as sealants. Fluoride-containing sealants were introduced to dentistry with an expected benefit from their anticariogenic properties. This sealant consists of dimethacrylate monomers with sodium fluoride and poly (methyl methacrylate-co-methacryloyl) fluoride. However, compared with the glass ionomers, these resin sealants have less total availability and release of fluoride to induce anticariogenic effects. The addition of fluoride did not alter the retention properties of the sealants, causing manufacturers to develop techniques of incorporating fluoride ions onto the resin chemistry. Clinical data proving the anticaries advantage of these fluoride-containing sealants are still lacking.

In effort to improve the longevity of these sealants, researchers and clinicians suggest incorporating a bonding agent layer between the sealants and the saliva-contaminated enamel. This technique shows promise, with better retention of these sealants and reduced microleakage in both in vitro and in vivo studies. The addition of a bonding agent decreases the risk for failure by 47% for occlusal sealants and 65% for buccal/lingual sealants. One potential explanation could be attributed to the flexibility features offered by the newer generations of bonding agents, especially when they were analyzed in class v restorations. The combined primer, adhesive, and resin complex layer resulted in a stronger long-term bond.

Subsequently, with the development of the self-etching adhesive resin, clinicians began to evaluate the efficacy of using a self-etching adhesive before sealant placement. This step minimized treatment time and potential errors in technique, and had better patient compliance. One self-etching adhesive clinically tested for 2 years was the Prompt L-Pop (3M ESPE, St Paul, MN, USA). The 2-year data show comparable sealant retention against normal etch and seal methods. Glass ionomers are also being used as a surface protectant because they can flow more readily into pits and fissures, as shown by their clinical effectiveness. The explanation could be attributed to the fact that fluoride content in glass ionomers is higher than in the tooth. When used as sealants, the ion exchange process causes fluoride ions to diffuse from the cement onto the tooth, transforming some of the hydroxyapatite into fluorohydroxyapatite, and making it more caries-resistant.

Official American Dental Association (ADA) guidelines recommend the use of glass ionomer sealers only on partially erupted teeth or deciduous teeth, and the use of resins on permanent teeth. The latest glass ionomer, Ketac Nano (3M ESPE Dental Products, St Paul, MN, USA), is nano-filled and could change the guidelines if clinical trials on wear rates are favorable. Currently, strong support in the literature favors bonding dental sealants or the use of glass ionomers as a pit and fissure sealant on surfaces determined to be at high risk for caries. The drawback, however, is the lack of long-term clinical longevity data.

Glass ionomer materials

The use-based classification for glass ionomer materials includes crown cementation, restorations, liners and bases, fissure sealants, orthodontic cements, and buildups in non–stress-bearing situations. ADA classification for glass ionomers include type 1, which are cements, and type 2, which are filling materials (class 2, 3, 5).

Glass ionomers have been one of the most widely researched dental materials since their introduction in the 1970s. They have a coefficient of thermal expansion similar to dentin and can be bulk-filled and finished faster than a composite. The newer generations of glass ionomer materials are faster setting and no longer sensitive to hydration or desiccation during setting. They are used more regularly as intermediate restorations, adhesive cavity liners (sandwich technique), and atraumatic restorative material. However, their use in load-bearing situations is still unreliable.

One main advantage of glass ionomer materials is their chemical bonding ability to tooth structure, making them more resistant to leaks. Compared with resin system bonding, glass ionomer bonding is more degeneration-resistant and does not breakup, unlike the hydrolytic degradation of the hybrid layer of the resin system. Literature from laboratory studies supports the application of these adhesive materials to perform therapeutic actions on demineralized tissues because of the potential for bother uptake of fluoride ions and release and recharge by fluoride-containing toothpastes. However, clinical trials supporting this work are still uncertain.

The most recently accepted uses of glass ionomers have been as a liner and base under deep composite restorations, which has been referred to as the sandwich technique , Deep cervical lesions and proximal boxes of class II cavities whose gingival floor is on root surfaces are areas where there is increased diameter of dentinal tubules that will affect the bond strength because of increased chances of hydrolytic degradation. Because of their chemical bonding capabilities, glass ionomer adhere to these surface better then dental adhesive-bonding agents. Based on evidence-based dentistry protocols, the recommendation is to treat the surfaces with a polyacrylic acid conditioner, which is rinsed before glass ionomers are applied. This weak acid modifies the smear layer by leaving the smear plugs behind, improving the seal and eliminating postoperative sensitivity. A new self-conditioner for resin-modified glass ionomers, recently developed by Fuji (GC America, IL, USA), does not require rinsing before applying the glass ionomer material. Both Fuji II and Fuji IX (GC America, IL, USA) have unique automix dispensing capsules, simplifying placement of these materials. Resin-modified ionomers, such as Fuji II LC, are routinely used as liners at 1 mm or less, and a material such as Fuji IX or Riva (SDI, Bensenville, IL, USA) is preferred for larger areas of dentin replacement.

Based on abundant evidence, conventional and metal-modified glass ionomers are not recommended in class 2 restorations in both primary and permanent molars. To compensate for this, resin-modified glass ionomer cements were developed to produce better mechanical properties than the conventional ones. The resin hydroxyethyl methacrylate (HEMA) or bis-glycerol methacrylate was added to the liquid. The resin modification of these cements allowed the base curing reaction to be supplemented by a light or chemical curing process, allowing for a command set. The obvious advantages were better fracture toughness, increased tensile strength, and a decrease in desiccation and hydration problems. The limiting factors were the setting shrinkage, which was found to be greater than with conventional cements, and the limited depth of cure with more opaque lining cements. The mean age of these failed glass ionomer restorations at replacement in permanent teeth in general practice was found to be 5.5 years for patients older than 30 years. Secondary caries, bulk fracture (1.4%–14%), and marginal fracture (from poor anatomic form) constituted the main reasons for failure.

In developing countries, highly viscous glass ionomer materials have became popular in atraumatic restorative treatment techniques for class 1 restorations in posterior teeth. In class 2 restorations, these high viscous glass ionomers are still considered satisfactory after 3 years of clinical service, despite large percentages of failed restorations. However, a recently concluded retrospective study showed that the failure of class 2 restorations with these materials rose to 60% at 72 months. It was hypothesized that caries-like loss of material was seen on radiographs and that the presence of proximal contacts promoted disintegration of these materials.

In effort to provide easier manipulation and reduced variability of the physical properties, dental material companies have introduced a paste/paste glass ionomer dispensing system. Examples include the Ketac Nano (3M ESPE Dental Products, St Paul, MN, USA) light-curing glass ionomer, which is the first paste/paste resin-modified glass ionomer developed with nanotechnology. The nano fillers are blended with fluoroaluminosilicate technology. Laboratory studies support these nano-ionomers, but clinical data will prove their ultimate efficacy.

Vanish XT (3M ESPE Dental Products, St Paul, MN, USA) is a newly developed resin-modified glass ionomer material that releases fluoride, calcium, and phosphate. It is currently used as a site-specific, light-cured durable coating that provides an immediate layer of protection to relieve dentinal hypersensitivity through occluding the dentinal tubules.

The newer generations of glass-ionomers are anticipated to be amino acid–modified and non–HEMA-containing glass ionomers materials, because they are being researched extensively to reduce deficiencies of the present generation of glass ionomers, especially in terms of their strength. The technique of ultrasound application to improve the mechanical properties during hardening of the glass ionomer cement seems promising and intriguing.

Glass ionomer materials

The use-based classification for glass ionomer materials includes crown cementation, restorations, liners and bases, fissure sealants, orthodontic cements, and buildups in non–stress-bearing situations. ADA classification for glass ionomers include type 1, which are cements, and type 2, which are filling materials (class 2, 3, 5).

Glass ionomers have been one of the most widely researched dental materials since their introduction in the 1970s. They have a coefficient of thermal expansion similar to dentin and can be bulk-filled and finished faster than a composite. The newer generations of glass ionomer materials are faster setting and no longer sensitive to hydration or desiccation during setting. They are used more regularly as intermediate restorations, adhesive cavity liners (sandwich technique), and atraumatic restorative material. However, their use in load-bearing situations is still unreliable.

One main advantage of glass ionomer materials is their chemical bonding ability to tooth structure, making them more resistant to leaks. Compared with resin system bonding, glass ionomer bonding is more degeneration-resistant and does not breakup, unlike the hydrolytic degradation of the hybrid layer of the resin system. Literature from laboratory studies supports the application of these adhesive materials to perform therapeutic actions on demineralized tissues because of the potential for bother uptake of fluoride ions and release and recharge by fluoride-containing toothpastes. However, clinical trials supporting this work are still uncertain.

The most recently accepted uses of glass ionomers have been as a liner and base under deep composite restorations, which has been referred to as the sandwich technique , Deep cervical lesions and proximal boxes of class II cavities whose gingival floor is on root surfaces are areas where there is increased diameter of dentinal tubules that will affect the bond strength because of increased chances of hydrolytic degradation. Because of their chemical bonding capabilities, glass ionomer adhere to these surface better then dental adhesive-bonding agents. Based on evidence-based dentistry protocols, the recommendation is to treat the surfaces with a polyacrylic acid conditioner, which is rinsed before glass ionomers are applied. This weak acid modifies the smear layer by leaving the smear plugs behind, improving the seal and eliminating postoperative sensitivity. A new self-conditioner for resin-modified glass ionomers, recently developed by Fuji (GC America, IL, USA), does not require rinsing before applying the glass ionomer material. Both Fuji II and Fuji IX (GC America, IL, USA) have unique automix dispensing capsules, simplifying placement of these materials. Resin-modified ionomers, such as Fuji II LC, are routinely used as liners at 1 mm or less, and a material such as Fuji IX or Riva (SDI, Bensenville, IL, USA) is preferred for larger areas of dentin replacement.

Based on abundant evidence, conventional and metal-modified glass ionomers are not recommended in class 2 restorations in both primary and permanent molars. To compensate for this, resin-modified glass ionomer cements were developed to produce better mechanical properties than the conventional ones. The resin hydroxyethyl methacrylate (HEMA) or bis-glycerol methacrylate was added to the liquid. The resin modification of these cements allowed the base curing reaction to be supplemented by a light or chemical curing process, allowing for a command set. The obvious advantages were better fracture toughness, increased tensile strength, and a decrease in desiccation and hydration problems. The limiting factors were the setting shrinkage, which was found to be greater than with conventional cements, and the limited depth of cure with more opaque lining cements. The mean age of these failed glass ionomer restorations at replacement in permanent teeth in general practice was found to be 5.5 years for patients older than 30 years. Secondary caries, bulk fracture (1.4%–14%), and marginal fracture (from poor anatomic form) constituted the main reasons for failure.

In developing countries, highly viscous glass ionomer materials have became popular in atraumatic restorative treatment techniques for class 1 restorations in posterior teeth. In class 2 restorations, these high viscous glass ionomers are still considered satisfactory after 3 years of clinical service, despite large percentages of failed restorations. However, a recently concluded retrospective study showed that the failure of class 2 restorations with these materials rose to 60% at 72 months. It was hypothesized that caries-like loss of material was seen on radiographs and that the presence of proximal contacts promoted disintegration of these materials.

In effort to provide easier manipulation and reduced variability of the physical properties, dental material companies have introduced a paste/paste glass ionomer dispensing system. Examples include the Ketac Nano (3M ESPE Dental Products, St Paul, MN, USA) light-curing glass ionomer, which is the first paste/paste resin-modified glass ionomer developed with nanotechnology. The nano fillers are blended with fluoroaluminosilicate technology. Laboratory studies support these nano-ionomers, but clinical data will prove their ultimate efficacy.

Vanish XT (3M ESPE Dental Products, St Paul, MN, USA) is a newly developed resin-modified glass ionomer material that releases fluoride, calcium, and phosphate. It is currently used as a site-specific, light-cured durable coating that provides an immediate layer of protection to relieve dentinal hypersensitivity through occluding the dentinal tubules.

The newer generations of glass-ionomers are anticipated to be amino acid–modified and non–HEMA-containing glass ionomers materials, because they are being researched extensively to reduce deficiencies of the present generation of glass ionomers, especially in terms of their strength. The technique of ultrasound application to improve the mechanical properties during hardening of the glass ionomer cement seems promising and intriguing.

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Oct 29, 2016 | Posted by in General Dentistry | Comments Off on Advances in Dental Materials
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