1

Introduction

In modern operative dentistry focus is on minimal removal of tooth tissues and on application of adhesive restorative materials that possibly perform therapeutic actions on demineralized dentin. Glass ionomer cements (GIC) have been shown to have the potential for release and uptake of fluoride ions. While it is supposed that these materials may have caries preventive and remineralizing effects, it is still unclear what the clinical implications of this phenomenon might be . The major drawbacks of conventional GIC have been the relatively low fracture toughness and higher rate of occlusal wear, compared to amalgam and modern composite restorative materials. For use in Class II restorations, conventional and metal modified GIC were previously not considered materials of choice, neither in primary nor in permanent molars . Although the highly viscous glass ionomer materials, which were introduced in the market not before 1995, achieved superior physical properties compared to traditional GIC by optimizing polyacid and particle size distribution and resulting in a high cross-linkage in the GIC matrix , the reputation of glass ionomers did not change significantly: they are nowadays mostly still considered a semi-permanent restoration material for Class I and Class II fillings in permanent teeth.

However, some promising prospective longitudinal data of highly viscous GIC were shown in the ART (atraumatic restorative treatment) approach, e.g. in a prospective longitudinal study a total of 1117 Class I and Class II GIC (Fuji IX [GC Europe, Leuven, Belgium] and Ketac Molar [3MEspe, Seefeld, Germany]) and amalgam restorations which were placed in permanent teeth of 370 and 311 children, respectively, by 8 dentists. The cumulative survival rates after 6.3 years were 66.1% for GIC and 57.0% for amalgam. Differences between the GIC were not significant . However, it has to be considered that the relationship between Class I and Class II restorations was around 10:1 and ART conditions are not comparable to private practice conditions. Studies on highly viscous GIC not performed under ART conditions in Class I and II cavities are scarce, but also promising. In a study on 169 Class I ( n = 67) and Class II ( n = 102) GIC restorations (Fuji IX) in 116 patients placed by 3 dentists the survival rate was 98% after 2 years. The main reason for replacement was fracture of the filling . In a 6-year retrospective clinical study 116 Class II GIC restorations (Fuji IX GP) in 72 patients placed by 2 dentists in a private practice were examined. Until 1.5 years no failures were observed. From 1.5 to 3.5 years survival dropped to 93%. After 3.5 years failure rate increased and at 6 years survival was 60% .

Nowadays, GIC may also be an interesting alternative in terms of economical aspects which are very important in public health systems with a kind of basic and economic approach. They may be a valuable solution for the dentist and the patient in cases, where the patient does not accept an amalgam filling, but is not able or willing to pay additional costs for layered composite resin restorations.

To overcome the disadvantages of classical GIC, a unique concept called EQUIA (GC Europe, Leuven, Belgium) was introduced in 2007 which tries to combine the main advantages (self-adhesion, bulk application, improved mechanical properties) of the highly viscous GIC (Fuji IX GP Extra) with a nano-filled, light curing varnish (G-Coat Plus) to provide protection in the early maturation phase for improved strength and an improved surface hardness. So far, only results of one clinical prospective short-term study under ideal university environment conditions have been published .

The aim of the present retrospective cohort study was to evaluate the clinical performance of EQUIA used in a private practice environment in order to clarify, if a highly viscous GIC protected with a nano-filled, light curing varnish might be suitable as a permanent restoration material in Class I and/or Class II cavities under private practice conditions.

2

Materials and methods

In the present retrospective cohort study 151 Class I ( n = 26) and Class II ( n = 125) EQUIA restorations which were placed in permanent molars ( n = 94) and premolars ( n = 57) in 43 patients were evaluated at 4.5× magnification by one experienced dentist (last author) according to the modified USPHS criteria ( Table 1 ). Restorations had been placed in six German general practices (2 in Bavaria, 2 in North Rhine-Westphalia, 1 in Hesse, and 1 in Saxonia), in the years 2007 and 2008 by six experienced dentists. For all restorations (encapsulated) Fuji IX GP Extra (GC Corporation, Tokyo, Japan) was applied in bulk according to the manufacturer’s instructions without pre-conditioning the cavities. In case of Class II restorations circumferential or sectional metal matrices were applied. The self-curing restorations were finished after hardening using diamond finishing burs under water cooling. Finally accessible surfaces of the fillings were covered with the nano-filled, light curing varnish G-Coat Plus (GC) which was cured using a dental light curing unit for 20 s.

The random selection of practices, patients and fillings had been performed as follows: In October 2008 GC Europe sent a questionnaire to all their French, Dutch, Italian and German customers which began using EQUIA in different indications between market introduction in March 2007 and September 2008 to evaluate the general customer satisfaction with the product. A total of 254 European private practices answered the questionnaire and provided rough encoded information on the total number of placed restorations, indications, processing of the material, customer satisfaction, and their principal willingness or declining to be decoded and to take part in a potential retrospective clinical study.

The authors of the present study analyzed the encoded data in order to verify the chance to run a retrospective study in 2009/2010 on a representative number of those early EQUIA restorations in Class I and Class II indications, which had a life-span of around 2 years. The actual number of Class I and Class II restorations was unfortunately not determinable from the questionnaire.

For the above mentioned purpose the encoded practices were selected in a first step according to the following criteria:

• •

  Placement of more than 100 restorations in total.

• •

  Begin of using EQUIA between March and September 2007.

• •

  Use of EQUIA in (semi-)permanent Class I and Class II indications.

• •

  No cavity conditioner used before placement.

• •

  Use of G-Coat Plus according to the manufacturer’s instructions.

• •

  Regular check-ups of the patients.

• •

  Approval to take part in a potential retrospective clinical study.

After this first selection step 18 practices were left, which had given their principal willingness to take part in the planned retrospective study and they were, therefore, decoded.

In the second selection step those practices were contacted by the author and the planned study was explained in detail. They were asked again for their willingness to take part in the retrospective study in 2009/2010 including two visits in their practice. They were also asked for the possibility to filter Class I and II EQUIA restorations in their practice administration software, which fulfilled the above mentioned criteria and were placed in the given time frame.

The remaining six practices after this second selection step were visited (November 2009–January 2010) for personal training of study details and patients with EQUIA Class I and Class II restorations which will have been at least 18 months old at the planned (second) evaluation visit were selected by the participating dentists using the practice administration software. Only patients, who attended the practice at a regular basis for periodic checkups, were included in the study. No mentally or physically disabled patients, nor difficult to treat patients were included. The final patient group consisted of 22 male and 21 female patients. Data on the restorations were collected exclusively during routine check-ups and treatments between February and May 2010 in patients who agreed to contribute. Patients’ and practice data were immediately encoded again for further evaluation.

Significant relationships between groups were evaluated using the Pearson’s Chi-square-test at the 95% level of confidence. Results p ≤ 0.05 indicate that the frequency distribution of the defined events within the sample is not consistent with a particular theoretical distribution at the 95% level of confidence.

2

Materials and methods

In the present retrospective cohort study 151 Class I ( n = 26) and Class II ( n = 125) EQUIA restorations which were placed in permanent molars ( n = 94) and premolars ( n = 57) in 43 patients were evaluated at 4.5× magnification by one experienced dentist (last author) according to the modified USPHS criteria ( Table 1 ). Restorations had been placed in six German general practices (2 in Bavaria, 2 in North Rhine-Westphalia, 1 in Hesse, and 1 in Saxonia), in the years 2007 and 2008 by six experienced dentists. For all restorations (encapsulated) Fuji IX GP Extra (GC Corporation, Tokyo, Japan) was applied in bulk according to the manufacturer’s instructions without pre-conditioning the cavities. In case of Class II restorations circumferential or sectional metal matrices were applied. The self-curing restorations were finished after hardening using diamond finishing burs under water cooling. Finally accessible surfaces of the fillings were covered with the nano-filled, light curing varnish G-Coat Plus (GC) which was cured using a dental light curing unit for 20 s.

The random selection of practices, patients and fillings had been performed as follows: In October 2008 GC Europe sent a questionnaire to all their French, Dutch, Italian and German customers which began using EQUIA in different indications between market introduction in March 2007 and September 2008 to evaluate the general customer satisfaction with the product. A total of 254 European private practices answered the questionnaire and provided rough encoded information on the total number of placed restorations, indications, processing of the material, customer satisfaction, and their principal willingness or declining to be decoded and to take part in a potential retrospective clinical study.

The authors of the present study analyzed the encoded data in order to verify the chance to run a retrospective study in 2009/2010 on a representative number of those early EQUIA restorations in Class I and Class II indications, which had a life-span of around 2 years. The actual number of Class I and Class II restorations was unfortunately not determinable from the questionnaire.

For the above mentioned purpose the encoded practices were selected in a first step according to the following criteria:

• •

  Placement of more than 100 restorations in total.

• •

  Begin of using EQUIA between March and September 2007.

• •

  Use of EQUIA in (semi-)permanent Class I and Class II indications.

• •

  No cavity conditioner used before placement.

• •

  Use of G-Coat Plus according to the manufacturer’s instructions.

• •

  Regular check-ups of the patients.

• •

  Approval to take part in a potential retrospective clinical study.

After this first selection step 18 practices were left, which had given their principal willingness to take part in the planned retrospective study and they were, therefore, decoded.

In the second selection step those practices were contacted by the author and the planned study was explained in detail. They were asked again for their willingness to take part in the retrospective study in 2009/2010 including two visits in their practice. They were also asked for the possibility to filter Class I and II EQUIA restorations in their practice administration software, which fulfilled the above mentioned criteria and were placed in the given time frame.

The remaining six practices after this second selection step were visited (November 2009–January 2010) for personal training of study details and patients with EQUIA Class I and Class II restorations which will have been at least 18 months old at the planned (second) evaluation visit were selected by the participating dentists using the practice administration software. Only patients, who attended the practice at a regular basis for periodic checkups, were included in the study. No mentally or physically disabled patients, nor difficult to treat patients were included. The final patient group consisted of 22 male and 21 female patients. Data on the restorations were collected exclusively during routine check-ups and treatments between February and May 2010 in patients who agreed to contribute. Patients’ and practice data were immediately encoded again for further evaluation.

Significant relationships between groups were evaluated using the Pearson’s Chi-square-test at the 95% level of confidence. Results p ≤ 0.05 indicate that the frequency distribution of the defined events within the sample is not consistent with a particular theoretical distribution at the 95% level of confidence.