This paper collates some of the existing data on the clinical evaluations of resin-modified glass-ionomer cements (RMGICs) since their introduction two decades ago.
The relevant literature was considered and data reviewed under the headings of retention, marginal characteristics, material deterioration, secondary caries, color stability, as well as pulpal and biological effects.
The retention for RMGICs is generally good, with an annual failure rate over 13 years reported as being under 3%. However, more data is required on their performance in carious situations. Regarding marginal characteristics, they exhibit margins that are likely to deteriorate over time. From the limited data on the surface characteristics, they appear to exhibit some wear and loss of anatomic form, particularly in the mid to long term. Despite the fact that the studies reviewed for secondary caries varied in the initial caries status of lesions restored, the overwhelming conclusion is that this does not seem to be a problem. While their initial color match may be favorable, it appears that they change over time and may not be color stable. In the absence of more clinical data, it is difficult to draw conclusions on the pulpal and biological effects. The existing information primarily reports postoperative sensitivity, which fortunately does not seem to be an issue with RMGICs, and limited histopathology of the pulp, with mixed opinions.
The RMGICs appear to perform well in terms of retention, and secondary caries as well as postoperative sensitivity are not a problem. However, this is not necessarily true of their marginal characteristics, surface properties and color stability. More and long-term clinical research is required to establish compelling evidence of their behavior, particularly in terms of retention in carious cavities, surface properties and biological effects.
The quest for an ideal restorative dental material has been ongoing and this is nowhere more evident than in the realm of adhesive materials. Tooth-colored adhesive materials include the glass-ionomer cements (GICs), which were invented by Wilson and Kent in 1969 at the Laboratory of the Government Chemist in London, UK . As with most other materials, they too have been subjected to waves of improvements and developments. One such development was the introduction of the resin-modified glass-ionomer cement (RMGIC) materials patented in the late 1980s . This innovation was an attempt to help overcome the problems traditionally associated with the conventional GIC materials, i.e. moisture sensitivity and low physical properties (particularly their early mechanical strength). The RMGICs were thought of as an improvement over the original materials while still maintaining the clinical advantages of the traditional GICs, such as adhesion and fluoride release offering some protection against caries. In essence, the RMGICs are glass-ionomer cements with the incorporation of a small quantity of monomers as well as initiators involved in the polymerization reaction. Rapid acceptance of these materials by the dental profession saw subsequent similar materials appearing in the marketplace which were variations of the same theme. However, these latter materials are not considered as true GICs as they do not fulfill the requirements of a GIC of having a typical acid-based glass-ionomer reaction, unlike the RMGICs which are considered as GICs. By definition, the RMGICs contain a basic ion-leachable glass, a water-soluble polymeric acid, organic monomer/s and an initiator system .
The ultimate success, or otherwise, of a material is indicated by its longevity in the oral environment. As the initial laboratory tests of new materials do not always reveal their full limitations or assets, clinical data are essential to confirm their characteristics by solid empirical evidence. Unfortunately, at the present time, there is no consensus on the desired or ideal length of time of a clinical study to accurately predict the performance or life expectancy of restorative materials. Differences between studies often make comparisons difficult; the data from one may not be easily compared with another. In addition, sample size is a perennial issue and it is often not possible to extrapolate trends from small samples. Nevertheless, information gleaned from continual assessments is important in the hope that cumulative information adds to the body of evidence to help in making informed decisions regarding options for restoration. As a “major undertaking for general practitioners is the provision and assessment of dental restorations” , observations in clinical practice lend some valuable evidence if interpreted appropriately.
The RMGICs have been around for approximately twenty years now. They are used today in a variety of clinical situations, notably as liners/bases, luting agents and restorative materials. After two decades of use, it is reasonable to expect some level of evidence regarding their clinical performance. What has our experience in the past twenty years shown of these materials? Is there sufficient clinical information?
This paper collates some of the available data on the clinical evaluations of restorative RMGIC materials. It is not intended to be a systematic review of the subject. The relevant literature was considered and data reviewed under the headings of retention, marginal characteristics, material deterioration, secondary caries, color stability, as well as pulpal and biological effects.
Modern adhesive techniques are based on the premise that materials adhere to tooth structure and are retained within a cavity. Hence, retention is one of the most important criteria often used to assess the longevity of a restorative material. It is also one of the most commonly observed physical properties clinically.
One of the earliest clinical studies on RMGICs evaluated Class V abrasion lesions in 13 patients restored with one of three RMGICs; the retention rate at one year was found to be excellent (100%) . Subsequently, in another study the retention of one RMGIC at 18 months was found to be 95% . A more extensive study revealed no loss of RMGIC restorations in similar cavities even after two years . A large 18-month clinical trial of two commercially available (and one experimental) RMGICs confirmed the excellent retention, although the marginal seal remained a problem as cervical defects were noted as early as at the six-month recall . The aforementioned studies were conducted on non-carious Class V type of abrasion cavities. However, a study assessing restorations in carious as well as non-carious Class V cavities over three years found a survival rate of 93.3% for one RMGIC and 85.7% for another RMGIC . Whether the presence of carious lesions within that study lowered the retention rate is a tempting idea but difficult to confirm.
A small study comparing the clinical performance of several polyacid-modified composite resins with that of one RMGIC in non-carious abrasion lesions found that there was no statistically significant difference between the materials, with the RMGIC’s retention rate being 95% at two years . Similar findings were observed over five years with a retention rate of 93% for the same RMGIC . The longest assessment of these materials is provided in a 13-year evaluation of different adhesive systems which found the RMGIC to give among the best retention and lowest annual failure rate . It could be argued that as the study was performed on non-carious cervical lesions without enamel involvement, this gave the RMGIC a perceived advantage. However, it does not detract from the fact that the long period of observation highlighted the good performance of the RMGIC assessed and should not be overlooked.
In general, there does not seem to be a huge variation in retention rates between the studies reviewed in spite of differences such as sample sizes, products used and duration of clinical observation ( Table 1 ). The retention rates appear to be better in non-carious lesions and there is not enough information regarding their performance in carious situations. Although the latter point reflects the problems associated with clinical studies on carious cavities, it nevertheless highlights the need for more information regarding the materials’ performance in such lesions.
|Investigators||Number of restorations||Number of RMGICs||Types of cavities||Results: retention||Duration of study|
|Maneenut and Tyas (1995)||60||3||Class V, abrasion||100% retention||1 year|
|Neo et al. (1996)||21||1||Non-carious, cervical||95% retention||18 months|
|Abdalla and Alhadainy (1997)||80||3||Class V, abrasion||100% retention||2 years|
|Gladys et al. (1998)||122||3 a||Class V, abrasion/erosion||100% retention||18 months|
|Folwaczny et al. (2001)||82||2||Class V, carious and non-carious||93.3% and 85.7% survival||3 years|
|Ermis (2002)||20||1||Abrasion/erosion||95% retention||2 years|
|Loguercio et al. (2003)||16||1||Class V, non-carious||93% retention||5 years|
|Van Dijken and Pallesen (2008)||49||1||Non-carious, cervical||Lowest annual failure rate of 2.7%||13 years|
Evaluations of the marginal characteristics of a restoration over time are used as an indicator of the microleakage potential and maintenance or deterioration of esthetics. These characteristics may be assessed using parameters such as marginal integrity, adaptation or discoloration, either on their own or in combination.
One such evaluation of RMGICs found that the marginal adaptation was poor at 18 months (24% Alpha rating using USPHS criteria) and that marginal discoloration was apparent in some restorations (76% Alpha) . Another study found that margins that were perfect at restoration placement significantly deteriorated after six months . The margins either stabilized or showed a steady decline over the next 18 months, with the discrepancies being mainly small defects at the cervical margins of Class V lesions . These restorations concomitantly displayed superficial localized discoloration at the margins, although one RMGIC showed the least discoloration and was significantly better throughout the whole evaluation period than another one being assessed. Other researchers found that the marginal integrity and discoloration over three years was the worst with the RMGICs compared to a composite resin and a polyacid-modified composite resin . In contrast, some researchers observed that one RMGIC performed significantly better than a polyacid-modified composite resin after five years in non-carious Class V restorations . The criteria assessed were marginal adaptation (84.6% rated Alpha using USPHS criteria, 15.4% Bravo) and marginal discoloration (84.6% rated Alpha, rest rated Bravo). A summary of these studies is given in Table 2 .
|Investigators||Number of restorations||Number of RMGICs||Types of cavities||Marginal characteristics||Duration of study|
|Neo et al. (1996)||21||1||Non-carious, cervical||Marginal adaptation: 24% Alpha rating, marginal discoloration: 76% Alpha rating (USPHS criteria)||18 months|
|Gladys et al. (1998)||122||3 a||Class V, abrasion/erosion||Significantly deteriorated from 6 months; mainly small defects at the cervical margins||18 months|
|Folwaczny et al. (2001)||82||2||Class V, primary and secondary carious/non-carious||Marginal integrity (55–61% Alpha) and discoloration (48–71% Alpha) worst with RMGICs||3 years|
|Loguercio et al. (2003)||16||1||Class V, non-carious||Both marginal adaptation and discoloration: 84.6% Alpha rating (USPHS criteria)||5 years|
It is evident that there is considerable variation in the results for marginal characteristics of the RMGICs. However, it is important to bear in mind that direct comparisons may not be made with these studies as they vary in terms of the type of margins, placement of margins (whether on enamel or dentin), RMGICs used, as well as initial caries status of the cavities. Certainly the earlier studies appear to have worse results than the later ones. This may be due to different materials used or product evolution as they are constantly being reformulated and modified by manufacturers to improve properties. Nevertheless, when the available data is reviewed in the light of marginal properties, it is reasonable to conclude that the RMGICs exhibit margins that are likely to deteriorate over time.
Loss of anatomic form and wear could be interpreted as being consistent with deterioration of a material and may affect its longevity. In the short-term, the anatomic form of these materials appears reasonable (86% Alpha rating) . However, over a longer period, the RMGICs do not appear to perform well. In a three-year study, the surface texture and contours of restorations using two RMGICs were found to be the poorest compared with those of a composite resin and a polyacid-modified composite resin; only 9% or 16% were rated Alpha for surface texture while only 35% or 39% were rated Alpha for anatomical contours . In contrast, in a subsequent report, only 12.5% of RMGIC restorations showed loss of anatomical form (rated Bravo; 87.5% rated Alpha) after five years . However, 86% of the restorations were rated Bravo for surface texture in the same study. These studies are summarized in Table 3 .
|Investigators||Number of restorations||Number of RMGICs||Types of cavities||Material deterioration||Duration of study|
|Neo et al. (1996)||21||1||Non-carious, cervical||Anatomic form: 86% Alpha rating (USPHS criteria)||18 months|
|Folwaczny et al. (2001)||82||2||Class V, primary and secondary carious/non-carious||Surface texture (9% and 16% Alpha rating); anatomic contours (35% and 39% Alpha rating)||3 years|
|Loguercio et al. (2003)||16||1||Class V, non-carious||86% Bravo rating for surface texture; 87.5% Alpha rating for anatomic form||5 years|
It is reasonable to conclude from the limited data that the RMGICs exhibit some loss of anatomic form and surface wear, particularly in the mid to long term.
The detection of secondary caries after placement of a restoration in a cavity may be due to any one or more of several factors involving the material, the patient, the cavity and the operator or technique. In the absence of clearly defining factors involved in the occurrence or recurrence of the carious process, the presence of secondary caries is often interpreted as a function of the material properties if all other confounding factors are kept to a minimum. Cross comparison between studies is difficult but gives an idea of the general caries potential of the material.
In a study to establish the clinical performance of an RMGIC in non-carious cervical lesions, there was no secondary caries detected after 18 months . This observation was similar to another report in which no recurrence of caries was found at the one and two year recalls in Class V carious lesions . The absence of secondary caries was confirmed later by researchers evaluating RMGICs in mixed carious and non-carious Class V cavities over three years , as well as by others observing Class V non-carious RMGIC restorations over five years . In a separate study using an RMGIC in “open-sandwich” restorations in large Class II cavities, only one out of 239 restorations showed secondary caries after three years, although 43% of the patients were considered caries-risk patients . A summary of these studies is presented in Table 4 .
|Investigators||Number of restorations||Number of RMGICs||Types of cavities||Secondary caries||Duration of study|
|Neo et al. (1996)||21||1||Non-carious, cervical||No secondary caries observed||18 months|
|Abdalla et al. (1997)||60||2||Class V, carious||No secondary caries||2 years|
|van Dijken et al. (1999)||274||1||Class II, “open-sandwich”, primary caries and replacement restorations||Only 1 out of 239 restorations showed recurrent caries||3 years|
|Folwaczny et al. (2001)||82||2||Class V, carious and non-carious||No secondary caries||3 years|
|Loguercio et al. (2003)||16||1||Class V, non-carious||No secondary caries||5 years|