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Keywords:

  • Resin-based adhesive;
  • clinical trial;
  • non-carious cervical lesions;
  • dentine bonding

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Background:  The aim of this study was to evaluate the clinical performance of G-Bond all-in-one adhesive with Gradia Direct resin composite placed in non-carious cervical lesions (NCCLs) over a five-year period.

Methods:  Forty-seven restorations were placed in NCCLs in 10 subjects (age 45–75 years) after written informed consent was obtained. Institutional ethical approval for the trial was obtained before recruitment. Restorations were placed according to the manufacturer’s instructions and using 50% phosphoric acid to etch uncut enamel margins. Patients were recalled annually for five years and restorations reviewed for presence and marginal staining. Photographic records were obtained prior to restoration, immediately after placement and at each recall.

Results:  At five years, 6 of the original 10 subjects were available for recall, meaning 27 restoration sites could be evaluated. All restorations remained intact apart for one partial failure at four years. This resulted in a cumulative retention rate of 97.5% of restorations at five years. Marginal staining occurred around seven restorations during the study. Staining tended to be isolated to a few patients.

Conclusions:  It was concluded that G-Bond with Gradia Direct resin composite showed excellent results over the five years of the study. This material combination seems very suitable for the restoration of NCCLs.


Abbreviations and acronyms:
GIC

glass-ionomer cement

HEMA

hydroxyethyl methacrylate

NCCL

non-carious cervical lesions

Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The use of tooth coloured restorative materials continues to increase as the technology improves and patients continue to demand more aesthetic restorations. The critical link is the bond between tooth structure and the restorative material, especially when a cavity has few if any retentive features, as do non-carious cervical lesions (NCCLs), and in order to conserve tooth structure no preparation is undertaken.

As the population ages, the prevalence of NCCLs is increasing.1 These lesions can create significant disability for patients when the dentinal tubules remain open, causing various degrees of sensitivity and making eating and drinking a problem. Various means of treating dentine sensitivity are now available, with the most invasive, and usually the last resort, being the placement of a restoration. When restoration placement is required, the aim should be to limit removal of tooth structure, or where possible, rely solely on the adhesive ability of the restorative material for restoration retention. Hence, this is why glass-ionomer cement (GIC) has been frequently recommended as an ideal material due to its proven clinical adhesive durability and reliability.2 However, GICs, even the resin-modified materials, may not always achieve the aesthetic needs of some patients. Also, after a long period in the mouth, some GIC restorations can show deterioration of the surface which can detract from their aesthetics.3 The alternative material to GIC is resin composite with a resin-based adhesive. The resin-based adhesives have only recently been developed to an extent where clinical trial data are showing good retention rates, comparable with GICs, and limited marginal staining over the long-term.

The difficulty of achieving stable adhesion with resin-based adhesives is related to the bonding substrate. NCCLs only have a small enamel margin that may aid adhesion and therefore retention. However, a previous study indicated enamel margins only provide minimal assistance in improving retention rates.4 The remainder of the NCCL consists of dentine that has frequently undergone varying degrees of sclerosis. The lesions also commonly involve the root surface, where the dentine substrate varies further and can be a less reliable bonding substrate. It has been shown that different levels of dentine sclerosis in NCCLs can affect restoration retention.5 Laboratory studies have shown that resin-based adhesive systems can show a greater variation in bond strengths to sclerotic dentine compared with coronal dentine.6,7

Two-step self-etching priming systems have demonstrated reasonably good success for restoring NCCLs in a number of clinical trials.8,9 However, with the advent of the ‘all-in-one’ self-etching systems, there are few or no long-term data from clinical evaluations. The studies that have been published tend to be of short duration, but have concluded that all-in-one systems perform quite well in comparison to two-step self-etching or etch-and-rinse adhesives.10–12 Recently, a study reported a three-year trial of an all-in-one system which showed performance little different from a ‘gold-standard’ resin-based adhesive system.13

In laboratory adhesion studies, all-in-one systems performed less well than etch-and-rinse and two-step self-etch systems. One of the issues identified was the propensity for all-in-one systems to dissociate more easily when applied to the tooth surface.14 Should the uncured bonding resin dissociate when it is applied to the tooth surface, the infiltration into the dentine will be less than optimal, meaning the bond is poor and thus is likely to breakdown more quickly. It has also been noted that these types of resin adhesives act as semi-permeable membranes, allowing water to pass through more easily, which is also thought to lead to quicker hydrolysis of the bond.15 Therefore, it has been concluded that these resin adhesives are likely to degrade hydrolytically at a faster rate than other adhesive systems and clinically show poor retention rates and increased marginal staining. However, the clinical evidence remains weak, due to the short duration of the few published studies.

The aim of this study was evaluate the retention and marginal staining of restorations in NCCLs using an all-in-one resin-based adhesive, G-Bond (GC Corp, Tokyo, Japan) with resin composite over a period of five years. The unique aspect of the adhesive used in this evaluation is that it does not contain the hydrophilic monomer 2-hydroxyethyl methacrylate (HEMA) to promote adhesion. The one-year results were reported in 2007.16

Materials and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Forty-seven restorations were placed in NCCLs in 10 subjects (age range 45–75 years at trial commencement) presenting for treatment at the Royal Dental Hospital of Melbourne. Voluntary participation and informed written consent from all subjects was obtained prior to commencement of treatment. Approval for the clinical trial was obtained from Dental Health Services Victoria and Faculty of Medicine, Dentistry and Health Sciences Human Ethics Committees. Subjects were excluded from the trial if they exhibited severe periodontal disease or chronic gingivitis, rampant caries, poor oral hygiene or were potentially unable to attend recall visits. Teeth with lesions were identified for restoration, and varying numbers of lesions were restored per patient. The size of restored lesions varied from shallow (less than 1 mm deep), often exhibiting sensitivity to cold, as reported by the patient, to large (approximately 5 mm occluso-gingivally in height and approximately 2 mm deep). All restored teeth were in occlusion and the lesion shape varied from saucer-shaped to very angular.

All teeth were restored by one operator (MFB) with G-Bond (GC Corporation, Tokyo, Japan: batch number: 0404011) and Gradia Direct resin composite (GC Corporation; batch number: 0411102). Restorations were placed using the following procedure: the dentine and enamel were cleaned with a slurry of pumice and water on a slowly rotating rubber cup in a slow-speed handpiece, washed and dried, but not desiccated. The uncut enamel margin was etched with 50% phosphoric acid (Etching Liquid, GC Corporation; batch number: 0412202) for 30 seconds, washed and dried. One drop of G-Bond was dispensed, immediately applied to the NCCL with a brush, allowed to remain undisturbed for 10 seconds as described in the manufacturer’s instructions, blown with a strong air blast to evaporate the solvent and thin the adhesive, and light-cured for 10 seconds using an LED light with an output of 1000 mW/cm2. The resin composite was applied in one increment for the smaller lesions and cured for at least 40 seconds. For larger lesions, resin composite was placed incrementally, each increment being cured for 40 seconds. The restorations were contoured with fine composite finishing diamonds in an intermediate-speed handpiece under water spray and finished with Sof-Lex (3M-ESPE, St Paul, MN, USA) discs.

Subjects were recalled at six months, then annually for the following five years. The restorations were checked for presence or absence and for marginal staining. Photographs at 1:1 magnification were taken of the cavities prior to restoration, immediately after, then at six months and 1, 2, 3, 4 and 5 years. The photographs were also checked for restoration presence or absence, and colour match of the restoration with the surrounding tooth structure. Marginal discolouration was assessed by MJT from photographs, by comparing the test restoration against a standard set of photographs on a nine-point scale, whereby 0 represented no staining and 9 represented severe staining.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The distribution of restorations to teeth is shown in Table 1. All lesions exhibited sclerotic dentine of varying degrees, with some lesions having a matt surface, whilst others exhibited a shiny ‘burnished’ surface. Forty-two per cent of lesions were classified as deep, 17% shallow, with the remainder (37%) between these two groups. Twenty per cent of lesions were classified as ‘saucer-shaped’, having rounded contours (Fig. 1a) whilst 21% exhibited a sharp angular form (Fig. 1b). All teeth were in occlusion.

Table 1.   Distribution of restorations to teeth
TeethNumber restored
Upper anterior (including canine)13
Upper premolar7
Upper molar2
Lower anterior17
Lower premolar6
Lower molar2
Total 47
image

Figure 1.  Example of (a) a ‘saucer-shaped’ lesion; (b) and angular lesion.

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At one year, all patients returned for recall and all restorations were present. At two years, one patient with four restoration sites was unable to attend. All restorations reviewed were intact. Eight of the original 10 patients were available for recall at three years, which provided 40 restorations for evaluation, all of which were present. One tooth was extracted for reasons not associated with the restoration. One restoration had minor marginal staining at one year and at two years. Four restorations had slight staining, but this was regarded as clinically insignificant. This marginal staining remained unchanged at three years.

At the four-year recall, one further patient with four restorations was unable to attend, therefore seven patients were examined, totalling 36 restoration sites. Thirty restorations were intact and one, in a molar, was partially missing; the distal root portion of the restoration had failed whereas the mesial root was still intact (Fig. 2).

image

Figure 2.  Tooth 36: (a) restored at baseline; (b) partial failure of the restoration, where the distal portion has failed, leaving the mesial portion of the restoration intact. Marginal staining can be observed at the mesio-occlusal margin of the restoration associated with the crown margin and the root surface on the mesial aspect.

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At five years, another two patients were unable to attend recall, resulting in another nine restoration sites being unavailable for evaluation, leaving six patients with 27 restoration sites for examination. All restorations were intact, apart from the partial restoration loss from the molar tooth at four years. One further restoration showed the development of minor marginal staining at the five-year recall. Those restorations showing marginal staining at the four-year recall (seven restorations in total) showed progression of the degree of staining during the following 12 months. Four restorations with marginal staining were present in one patient. The degree of marginal staining was not at a level where patients made a comment or the restoration needed to be replaced (Fig. 3, 4 and 5). Restoration size was also not a factor with respect to degree of marginal staining.

image

Figure 3.  Tooth 43: (a) immediately after restoration; (b) at 5 years. Increased marginal staining is observed at the disto-gingival and disto-occlusal marginal regions. These two regions were often more difficult to finish without causing trauma to the tooth or soft tissues. The occlusal margin has a slight defect associated with further development of the NCCL.

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image

Figure 4.  Teeth 32, 33: (a) at baseline; (b) at 5-year recall. Minor superficial staining is observed on these restorations that could be removed by careful polishing of the restoration margins.

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The cumulative retention rates using survival analysis over the life of the trial are shown in Table 2. No sensitivity or caries was recorded for any of the teeth restored throughout the study period.

Table 2.   Cumulative loss rates at the end of each annual interval using life table (survival) analysis
Recall timeCumulative retention rate (%)
1 year100
2 years100
3 years100
4 years97.4
5 years97.4

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Although the current trial did not use a large number of restorations or patients, it still provides an indication of how this adhesive is likely to perform in general clinical practice. The number of restorations per patient varied, which has the potential to skew results, particularly if one patient receives a large number of restorations and either fails to attend recall or the oral environment is such that it can influence the success or otherwise of restorations. A good example of this is where many restorations show severe marginal staining, which is often patient-dependent due to dietary or smoking habits and oral flora. On the other hand, having numerous restorations in one patient also provides a more standardized environment, thus reducing some of the natural variation among individuals that can also influence restoration retention or marginal staining. A recent three-year study, which also used multiple restorations per patient, showed using sensitivity analysis that ‘patient factor’ had a relatively low sensitivity thus allowing supplementary information of restoration performance to be just as useful compared with placing one or two restorations per patient.13 In clinical practice, it is difficult to achieve the ‘ideal study’ unless very large numbers of patients and restorations are placed, which requires extensive resources, and a large patient pool for selection whose members are willing to return for recall over an extended time period. This is not the case in the Australian situation, which has a relatively small patient pool from which to select suitable patients. In addition, when large numbers of restorations are placed, it is common practice to use several practitioners for restoration placement. This can create a further variable of operator influence that may affect outcomes, although it may provide the opportunity of assessing the ‘dentist factor’. This is especially the case when a technique sensitive bonding agent is employed. Therefore, to achieve a good knowledge base, it is preferable to establish multicentre studies to conduct independent trials using similar protocols, thus creating a strong foundation of evidence for the successful use of resin-based adhesive systems.

G-Bond is one of the first resin-based adhesives that does not contain HEMA as the wetting agent to aid bonding to the moist dentine. One laboratory study showed the inclusion of HEMA in small quantities will enhance bonding to dentine.17 The current study seems to show that even without HEMA, the adhesion to the sclerotic dentine of the NCCL has not been compromised, as demonstrated by the excellent retention rates over five years at over 97%. A similar study has also shown outcomes that are quite comparable.13 Another study, using a different HEMA-free all-in-one system, was not as successful as the G-Bond.18 G-Bond is classified as a mild self-etching system and uses 4-MET and a phosphate ester as the functional monomers to achieve chemical bonding to tooth structure. In the study by Yoshida et al.,19 it was shown that the 4-MET monomer is able to form a salt with hydroxyapatite, thus demonstrating a chemical bond could be achieved with this monomer. However, in the same laboratory study,19 the bond of 4-MET to hydroxyapatite was also shown to deteriorate with time, which has been confirmed in other laboratories.20 However, if the bond is deteriorating, it seems to show little effect on the clinical retention of the restorations in the current trial, as well as another trial conducted by the present authors.21

The enamel surface was etched with 50% phosphoric acid according to the manufacturer’s instructions, which recommend the use of etch when the enamel remains uncut. The use of phosphoric acid etch on the enamel was most likely the reason why little staining was observed on these margins. In addition, little staining was observed along the gingival (dentine) margins of most restorations. At four years, 12 of 35 restorations showed marginal staining. It was interesting to note that most of the restorations exhibiting staining occurred in one or two patients. At five years, the marginal staining had progressed further, but no restoration exhibiting staining was observed that necessitated replacement.

Few restorations failed, so lesion size and degree of sclerosis was believed not to be a factor affecting retention, based on those restorations that could be examined at recall. Etching the enamel margins may have contributed to the very high retention rates in this study. However, the present authors have conducted a concurrent study which did not etch the enamel margins, showing a 100% retention rate for the G-Bond bonded restorations over three years.21 Hence, it would seem that enamel etching provides a small contribution to the success of restoration retention, other than perhaps reducing enamel marginal staining. The staining, when observed, was most often at the enamel margin on the disto-bucccal corners of the lesion (Fig. 5). This region was often difficult to finish due to the curvature of the tooth and restoration surface. It is believed that the resin in these locations was probably not as smooth as other parts of the restoration, e.g. gingival margins on dentine, hence a slightly rough surface or flash of material remained at the enamel margin, resulting in staining rather than breakdown of the bond in this region. This is possibly why it appears the enamel margins show a greater degree of staining. In everyday clinical practice, the staining would usually be removed by judicious repolishing and refinishing of enamel margins at a recall visit. In general, it seems the stain is more likely to be related to patient factors such as oral bacteria and diet rather than deterioration of the adhesive.

image

Figure 5.  Tooth 45 showing staining occurring on the disto-buccal margin of the restored NCCL.

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The three-year outcomes of a similar trial that also placed numerous restorations per patient showed a retention rate of just below 95% for G-Bond with Gradia Direct resin composite, in comparison with 94% for the three-step etch-and-rinse adhesive Optibond FL (Kerr, Orange, CA, USA), also with Gradia Direct.13 However, this study13 did note that marginal defects were more likely to occur in the all-in-one adhesive compared to the etch-and-rinse system, particularly at the enamel margin. This was not the case for the current trial. This may partly be due to the etching of the enamel, which was not done in the Van Landuyt study,22 or the fact that a bevel was not placed on the margins in the current trial but was placed in the Van Landuyt study.22 However, with both trials, if a defect was noted it could usually be eliminated if the margin was repolished. Another two trials comparing self-etching systems, of which G-bond was one of the adhesives, have also demonstrated good outcomes.10,12 A further trial has published 2-year results comparing Clearfil S3 (Kuraray Medical) and G-Bond, and showed that one restoration of each material was lost over this time period.11

One of the issues researchers claim about the all-in-one systems is their poor bond durability.23 Adballa and Feilzer24 showed that two all-in-one systems tested had a significant reduction in bond strengths over two years when bonded to bur-ground enamel. In addition, bond strength studies have concluded that the all-in-one systems exhibit a lower bond strength than two-step self-etch and etch-and-rinse systems to enamel and dentine.25,26 However, even though laboratory tests seem to indicate that these systems are not as successful as other adhesive systems, the current clinical evidence indicates all-in-one systems such as G-Bond perform very well. Van Landuyt et al.14 compared the ease of bonding of the all-in-one systems with multi-step systems and concluded ‘the all-in-one systems were not always better than two-step SE (self-etching) or etch-and-rinse systems’; but once again, the results of the current trial, as well as others, would refute this comment, as the clinical success of G-Bond in restoring NCCLs is as good as many other bonding systems that have been clinically tested under similar conditions. A recent study investigating marginal adaptation of Class V (cervical cavities) in a laboratory setting using thermal and mechanical stressing over 1 year concluded that G-Bond showed a mean 78% continuous margin, the best of the 12 systems tested.27 Hence, evidence based solely on bond test outcomes should not be the only basis to judge an adhesive and its potential success.

Unfortunately, not all patients could be recalled by the fifth year of the trial. Therefore, the results must be viewed with some caution since the performance of the censored restorations is unknown. With this qualification, it can be concluded that G-Bond is an excellent all-in-one resin-based adhesive suitable for the restoration of NCCLs.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The authors wish to thank the Royal Dental Hospital of Melbourne for the use of its facilities to conduct this trial. The trial was supported by GC Corporation, Tokyo, Japan.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
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