Five-year Clinical Evaluation of a Nanofilled and a Nanohybrid Composite in Class IV Cavities
The purpose of this study was to evaluate a nanofilled and a nanohybrid composite, in combination with manufacturer-recommended etch-and-rinse adhesives, in class IV cavities. Thirty-four patients aged 14-46 years (mean age, 27.1 years) comprised the study group. Twenty-six patients received two class IV restorations and eight patients received four class IV restorations. For each patient, half the number of restorations were performed using a nanohybrid composite (Ceram X duo) and the remaining half used a nanofilled resin composite (Filtek Supreme XT), with two- (XP Bond) and three-step (Scotchbond Multipurpose) etch-and-rinse adhesives, respectively. Two experienced examiners evaluated the restorations for retention, color match, marginal discoloration, wear/loss of anatomic form, caries formation, marginal adaptation, and surface texture to compare the baseline (after placement) and annual recalls over 5 years. The cumulative success rates for the Filtek Supreme XT and Ceram X duo restorations after five years were 86.2% and 89.7%, respectively. Four Filtek Supreme XT and three Ceram X duo restorations failed. There was no statistically significant difference between the nanofilled and nanohybrid composites at any of the evaluation periods for any of the parameters evaluated. Despite the limited number of restorations, all restorations were clinically acceptable regarding retention, color match, marginal discoloration, wear or loss of anatomic form, the formation of caries, marginal adaptation, and surface texture, except the failed restorations. Fracture was the main cause of restoration failure.SUMMARY
INTRODUCTION
The increasing demand for esthetic treatment of anterior teeth indicates that the causes of restoration failure, beyond caries and fracture, occur largely in anterior restorations. However, long-term clinical trials are required to determine the validity of this supposition. Another important consideration is whether aspects of the composite formulation used, such as filler size, affects the clinical performance of anterior restorations.1
Various composites are available for anterior restorations.1 In anterior teeth, the esthetic appearance, color matching, and polishability are important. Anterior composites usually have small filler particles to increase smoothness, but this also reduces the fracture strength and Young's modulus of the materials.2 However, nanotechnology has enabled recent advances in dental composite restorations.3 Consequently, a new category of composite resins, known as nanocomposites, has been developed.3,4 Although all filler particles should be nanometer-sized in true nanocomposites, the term “nanotechnology” is occasionally used inappropriately when describing materials. At present, two distinct dental composites, nanofillers and nanohybrids, contain nanoparticles. Nanofilled composites use nanoparticles (1-100 nm) throughout the resin matrix, whereas nanohybrids contain conventional fillers (0.4-5.0 μm), with nanometric particles.3 Increasing the filler load by adding these particles improves the mechanical properties and polishability of the composite surfaces.5
Several nanocomposite products are available on the market.6 A new nanofilled composite was recently developed that contains nanometric particles (combination of 20 nm nonagglomerated/nonaggregated nanosilica) and nanoclusters (primarily 2- to 20-nm loosely bound zirconia/silica particle agglomerates).6,7 Another nanocomposite is the ormocer-based nanoceramic composite, Ceram X (Dentsply-DeTrey, Konstanz, Germany), which contains a methacrylate-modified silicon dioxide-containing nanofiller (10 nm) and glass fillers (1.1-1.5 μm); furthermore, the conventional resin matrix is largely replaced by a matrix replete with highly dispersed methacrylate-modified polysiloxane particles (2-3 nm).6 The various esthetic composite system formulations also include a vast range of shade options for dentin and enamel layers, as well as several areas of the teeth, such as the incisal edge, body, and cervical. Thus, clinicians are able to choose a shade-layering technique, according to the esthetic needs of the patients.3
In contrast to class I, II, III, and V cavity configurations, stresses are generated in class IV restorations through the incisal angle, which challenges the tooth-restoration interface.8 There are also greater challenges to the tooth-restoration bonded interface because of the lack of mechanical retention in the majority of class IV restorations.1 The etch-and-rinse method remains the most effective approach to achieving efficient and stable bonding to enamel.9 Also, etch-and-rinse adhesives, which result in higher resin-dentin bonds, are more durable than most one- and two-step dentin adhesives.10
To date, no published studies have evaluated the longevity of highly stressed class IV nanofilled and nanohybrid restorations. Therefore, we aimed to evaluate a nanofilled and a nanohybrid composite, in combination with their manufacturer-recommended etch-and-rinse adhesives, in class IV cavities.
METHODS AND MATERIALS
Study Design
The brands, chemical compositions, and manufacturers of the materials used are shown in Table 1. The restorations were placed between August 2008 and February 2010 at the Department of Restorative Dentistry, Faculty of Dentistry, Istanbul University. In total, 34 patients (9 males and 25 females) aged between 14 and 46 years (mean age, 27.1 years) comprised the study group. Table 2 lists the inclusion and exclusion criteria for the patients.11-14 Twenty-six patients received two class IV restorations and eight patients received four class IV restorations, due to primary caries of the anterior teeth. A total of 84 restorations were included in the final analysis. The distribution of class IV restorations, according to adhesive/composite combination and tooth number, is presented in Table 3. Opposing and adjacent tooth contacts were present for all teeth.14
Treatment Protocol
For the 26 patients who received two class IV restorations, one was performed with a nanofilled resin composite (Filtek Supreme XT, 3M ESPE, St Paul, MN, USA), whereas the other was performed with a nanohybrid composite (Ceram X duo). Similarly, for the eight patients who received four class IV restorations, two were performed with Filtek Supreme XT, whereas the other two were performed with Ceram X duo. The nanohybrid and nanofilled resin composites were applied in combination with two-step (XP Bond, Dentsply-DeTrey) and three-step (Scotchbond Multipurpose, 3M ESPE) etch-and-rinse adhesives, respectively (Table 1). The nanohybrid composite and tooth number were randomly selected by flipping a coin. This approach was first used for the patients with two restorations, and the same randomized approach was then used to select the nanofilled and nanohybrid resin composite and tooth number, respectively, for the patients with four restorations. After randomization, the number of restorations per patient with Filtek Supreme XT was equal to the number of Ceram X duo restorations.
Restoration Procedure
The teeth were first cleaned using a pumice-water slurry and a rubber cup to remove the pellicle and any residual dental plaque. All material was used in accordance with the manufacturer's instructions (Table 1). Cavity preparation was limited to the removal of caries. The cavity margins included the proximal area and the incisal surface, as well as the extended facial and lingual surfaces, depending on the amount of tooth structure missing. All enamel margins were beveled at a 45° angle to the external cavosurface, using a high-speed, water-cooled, rotary handpiece, with a medium-grit diamond bur. The width of the bevel was approximately 0.5-2.0 mm, depending on the amount of tooth structure missing and the retention perceived necessary.15 After the cavities were prepared, the cavity treatment and restorative placement were performed with strict attention to the manufacturer's instructions. Isolation was achieved with cotton rolls and saliva ejectors.16 Cavity treatment, application, and polymerization of the dentin adhesives were performed by the same experienced practitioner (HSS), who was familiar with the materials being used in the study. After the shade selection, all cavities were restored using a Mylar strip and wooden wedge to rebuild the anatomic form and proximal teeth contacts. The composite was incrementally applied, when the restorations had depths of more than 2 mm. The first composite layer was applied on the pulpal walls and light-cured (Table 1). A second layer was then applied and light-cured, as per the first layer.16 Care was taken when closing the strip, to not pull with excessive force because the soft material could be extruded incisally, resulting in an under-contoured restoration. In this instance, composite was added to achieve the appropriate contour and contact.15 Light-curing, contouring, and finishing were performed, as per our previous publication.14
Evaluation
Two experienced examiners evaluated the restorations, using a dental explorer and mirror, according to the modified United States Public Health Service (USPHS) criteria (Table 4).17-19 The examiners were not involved in the operation and insertion of the restoration procedure and were fully blinded to the experimental protocol. For consistency, both examiners observed sets of photographs as reference material to illustrate the scoring for each criterion. Both examiners then clinically evaluated 20 class IV restorations, which were not included in the study, with a two-day separation between the examinations. The evaluation phase of the study began after obtaining at least 85% intra- and inter-examiner agreement in the calibration phase.20 Color match, wear or loss of anatomic form, marginal discoloration, caries, marginal adaptation, and surface texture were evaluated at baseline (after placement) and at five annual recalls. Restorations were scored as follows: alpha = ideal clinical condition; bravo = clinically acceptable; charlie = unacceptable condition, restoration requires replacement; and delta = restoration fractured, mobile, or missing, immediate replacement required. Conflicts in scoring were resolved through consensus.17,20
Statistical Analysis
All analyses were performed using SPSS for Windows version 20.0 (SPSS, Chicago, IL, USA). Data were statistically analyzed using Friedman's test, to examine changes that occurred during the five-year evaluation period (Table 5). Whenever a statistically significant difference was identified, Dunn's test was used for multiple comparisons between each recall time interval for each composite. The Mann-Whitney test was used to evaluate the differences between the two composite materials. The probability of clinical survivability of the two composite types was determined using Kaplan-Meier survival analysis (Figure 1). p<0.05 was considered statistically significant. Inter- and intra-examiner agreements were tested using Cohen's κ.
Citation: Operative Dentistry 43, 3; 10.2341/16-358-C
RESULTS
Ten patients, which accounted for 26 restorations, exited from the study during the five-year evaluation (13 Filtek Supreme XT and 13 Ceram X duo restorations; Figure 2). Cumulative recall rates at baseline and at all five annual follow-ups are provided in Table 5. Cohen's κ (0.89) demonstrated strong agreement between the examiners, and there was no statistical difference between their findings (p>0.05). The cumulative failure and success rates, according to Kaplan-Meier survival analysis, are shown in Table 5. At two years, one Filtek Supreme XT had failed due to postoperative sensitivity (pulpitis) and one Ceram X duo restoration had failed due to fracture. The success rate was 97.1% for both restorations. At three years, one Filtek Supreme XT and two Ceram X duo restorations had failed because of fracture, with cumulative success rates of 93.9% and 90.9%, respectively. There were no restoration failures at four years, thus providing cumulative restoration success rates of 93.1% for Filtek Supreme XT and 89.7% for Ceram X duo. At five years, one Filtek Supreme XT restoration was lost and one Filtek Supreme XT restoration failed because of fracture. Thus, the cumulative success rates for the Filtek Supreme XT and Ceram X duo restorations were 86.2% and 89.7%, respectively.
Citation: Operative Dentistry 43, 3; 10.2341/16-358-C
Two of four failed Filtek Supreme XT restorations were located in the mesial region of the right central incisor. One restoration was located in the mesial region of the left central incisor and one restoration was located in the mesial region of the right lateral incisor. One of three failed Ceram X duo restorations was placed in the mesial region of the right lateral incisor. One restoration was located in the mesial region of the left lateral incisor, and one restoration was placed in the distal region of the left lateral incisor.
The direct clinical evaluation rates, at baseline and at the five annual recalls, are shown in Table 5. At five years, with the exception of the four failed Filtek Supreme XT and three Ceram X duo restorations, no restorations were clinically unacceptable, regarding any of the evaluation criteria. Moreover, there were no statistically significant differences between Filtek Supreme XT and Ceram X duo restorations, in any of the evaluation periods, for any of the evaluation parameters.
At five years, 92% of Filtek Supreme XT and 84.6% of Ceram X duo restorations exhibited alpha color matches. Regarding the marginal discoloration, 16% of Filtek Supreme XT and 11.5% of Ceram X duo restorations showed bravo discoloration. However, the discoloration was superficial and was located on an unspecific part of the enamel. It did not penetrate toward the pulp at the edge of the restoration and could be polished away. Regarding wear and anatomic form, 88% of the Filtek Supreme XT and 96.2% of the Ceram X duo restorations were assessed as alpha at five years. Regarding marginal adaptation, three (6.3%) Ceram X duo restorations and two (7.4%) Filtek Supreme XT were regarded as unacceptable (charlie) at three and five years, respectively, and had to be replaced at the end of the five-year period. For caries and surface texture, 100% of both the Filtek Supreme XT and Ceram X duo restorations were graded as alpha at five years.
DISCUSSION
A meta-analysis about the clinical effectiveness of anterior restorations concluded that new clinical research on contemporary resin materials was warranted, owing to the few studies that exist regarding class IV restorations, most of which were performed between 1980 and 2000 with older materials.21 Incisal edge class IV restorations are exposed to high masticatory loads.1 Thus, the mechanical and physical properties of a restorative material are as important as its esthetic features. Ideal esthetic restorative materials should simulate natural teeth in color, texture, and translucency and also have adequate strength, wear, and sealing characteristics.22 Nanocomposite systems were shown to have a high translucency, polish, and polish retention similar to microfilled composites and maintained the physical and wear resistance properties of various hybrid composites.23 Therefore, the present study evaluated the five-year clinical performance of a nanofilled and a nanohybrid composite, in combination with their manufacturer-recommended etch-and-rinse adhesives, in class IV cavities.
In the current study, the five-year survival rates for Filtek Supreme XT/Scotchbond Multipurpose restorations and Ceram X duo/XP Bond restorations were 86.2% and 89.7%, respectively. In contrast, a relatively long-term clinical study (up to 20 years) found a 100% anterior restoration five-year survival rate, which included class III and IV restorations.2 The discrepancy between this finding and the current results may be due to differences in the number of restorations (51 vs 84 class IV restorations, respectively) and the material and patient characteristics. Also, in contrast to the present study, which only included one type of cavity (class IV), a 100% success rate was previously reported in class III/IV restorations at five years.24 This high success rate in composite restoration success in recent years is a result not only of improved restorative materials and bonding systems but of increased clinician expertise. However, teeth having a combination of endodontic access and two-type cavities (class III/IV), as well as a comparably lower number of class IV restorations (16 restorations),24 may explain the variable success rate. In another study, 4 of 45 class III/IV restorations, with two-step etch-and-rinse adhesive, failed at 48 months.25 However, in accordance with the present study findings, van Dijken showed a cumulative survival of more than 80% in the Kaplan-Meier survival curve for a composite restorative material (Pekafil) at five years, in a maximum 14-year follow-up of class IV restorations.22 Also, fractures accounted for 11 of 43 restorations (25.6%), with a Kaplan-Meier estimate of 9.9 years,22 corroborating our findings that found fracture was the main reason for class IV restoration failure.22 Furthermore, in agreement with the present study results, a meta-analysis reported 10-year survival rates for class III and IV restorations as 95% and 90%, which corresponded to annual failure rates of around 0.5% and 1%, respectively.21 A systematic review that investigated the long-term survival of class III and IV anterior restorations showed annual failure rates between 0% and 4.1%.1 Moura and others reported a lower survival rate (77.8%) than that found in the present study for class IV restorations at three years.8 However, in the study by Moura and others,8 the restorations were placed by undergraduate dental students and the main cause of failure was restoration loss due to poor adhesiveness. The authors stated that restoration debonding might have resulted from the operators' lack of experience with the adhesives, coupled with the stresses generated at the incisal angle, which challenge the tooth-restoration interface of class IV restorations.8
In the present study, two Filtek Supreme XT restorations failed because of a fracture in the restoration. One Filtek Supreme XT was lost. According to the evaluation criteria, these three restorations received delta scores for marginal adaptation. Likewise, all three Ceram X duo restorations failed because of a fracture in the restoration. These restorations were also rated delta for marginal adaptation. Although four Filtek Supreme XT and three Ceram X duo restorations exhibited marginal discoloration at five years, this discoloration was clinically acceptable (bravo) and did not cause failure in the restorations. In contrast to the current findings, Deliperi reported alpha scores for all class III/IV microhybrid composite restorations regarding marginal discoloration and marginal integrity.24 Häfer and others reported that at 48 months, 4 of 45 class III/IV restorations, with two-step etch-and-rinse adhesive, failed due to marginal integrity (two restorations), marginal discolorations (one restoration), and loss of vitality (one restoration).25 In these two previous studies,24,25 class III and IV restorations were evaluated together. Therefore, cavity location and size, as well as variability of the bonding substrate, may reflect the variation in failure rates reported in the literature. A meta-analysis reported that the failure rate of class IV restorations was twice that of class III restorations at 10 years (10% vs 5%).21 In a maximum 14-year follow-up study of class IV restorations, fracture was the main cause of failure, which occurred in 11 of 43 (25.6%) composite restorations (Pekafil).22 Another study reported that esthetics (43%), and anatomic form (26%), were the main reasons that anterior restorations (class III and IV) failed, whereas fracture (22%) had an annual failure rate of between 0.5% and 1.8% during a maximum of 20 years.2 Thus, although the evaluation period of these two above mentioned studies were longer (14 and 20 years, respectively) 2,22 than our study (five years), fracture was a common reason for failure across all three studies.
It has been stated that loss of material or fracture failures in class IV restorations are probably directly associated with increased wear and incisal stresses.22 A systematic review on the long-term survival of anterior class III and IV restorations reported that tooth or restoration fracture was the most frequent cause of failure among the studies.1 Class IV restorations that involve the incisal edge in anterior teeth are subjected to high masticatory loads, and hence, fracture is a possible clinical outcome.1,2,8 Furthermore, most class IV restorations do not include mechanical retention, which may lead to challenges associated with the bond interface of the restoration.1 Thus, these aforementioned assumptions were probably the reasons that fracture was the main cause of failure for the Filtek Supreme XT and Ceram X duo restorations.
No restorations in the present study exhibited failure due to marginal discoloration. In support of our findings regarding marginal adaptation and marginal discoloration, it has been reported that marginal integrity is not linked to the method or system of tooth conditioning, which confirms that detectable margins do not necessarily mean there will be stained margins.21 Also, the bonding to enamel is essential for a good seal and the prevention of marginal discoloration because 100% of the visible margin of class III/IV restorations is usually located in the enamel. The use of 37% phosphoric acid in enamel etching remains the most successful approach to form a microretentive pattern, which permits good bonding to ground enamel.21,26 In the present study, the nanofilled (Filtek Supreme XT) and nanohybrid (Ceram X duo) composites were used in combination with their manufacturer-recommended etch-and-rinse adhesives, which may have contributed to the lack of failed restorations, with regard to marginal discoloration. A meta-analysis regarding the clinical effectiveness of direct anterior restorations concluded that less discoloration was seen at restoration margins when enamel etching was performed with phosphoric acid compared with restorations that used other conditioning systems.21
At five years, there was no statistically significant difference between the nanofilled and nanohybrid composite restorations, with regard to the color match. However, the nanofilled composite (Filtek Supreme XT) restorations were considered to have a better color match than the nanohybrid composite restorations. In contrast, our previous study found a comparably greater restoration percentage for a color match at four years, in which the same composites were used to restore space closure in buildup restorations on anterior teeth.14 This difference may be associated with the difference in restoration type. In our previous study,14 restorations were applied only to the enamel, whereas the present study included enamel and dentin as the bonding substrates. Conversely, other studies that used a microhybrid or a highly filled hybrid composite material showed more color change than the present study at three or five years,8,24 which could be due to differences between the teeth and operator skills. In one of these previous studies, the restorations were applied to endodontically treated and bleached teeth,24 whereas in the other study, the restorations were performed by undergraduate dental students.8 Another contributing factor may be the differences between size and type of composite fillers used. It has been stated that the initial gloss of many restoratives was quite good, but in hybrid composite (microhybrids, nanohybrids), plucking of the larger fillers, caused loss of gloss.3 In contrast, the nanoclusters were sheared at a rate similar to the surrounding matrix during abrasion in the nanofilled composite, allowing the restorations to maintain a smoother surface for long-term polish retention,3 which could explain the improved color match in the nanofilled compared with nanohybrid composite restorations at five years, as found in the current study.
Although no statistically significant difference was found between the nanofilled and nanohybrid composites, the nanofilled composite restorations exhibited a lower percentage of ideal restorations than the nanohybrid composite restorations, with respect to wear. However, a similar percentage of ideal restorations were previously obtained in buildup restorations for the same composite materials on anterior teeth at four years.14 Conversely, a higher percentage of ideal restorations was found in class III/IV restorations or buildup restorations on anterior teeth at three, four, and five years.8,14,24 These conflicting percentages of ideal restorations may be due to differences among the types of composites used and/or restoration types. A previous meta-analysis on the clinical effectiveness of direct anterior restorations reported that the loss of anatomic form was material dependent.21
In the present study, neither the nanofilled nor nanohybrid composites exhibited caries adjacent to their margins. These findings are in accordance with previous studies.8,14,24 A low rate of secondary caries (4 of 43 Pekafil restorations) was observed in class IV restorations in a maximum 14-year follow-up study.22 Also, secondary caries were largely absent in a maximum 20-year clinical study of anterior restorations that included class III and IV cavities.2 Differences in evaluation times between these two studies and our study may account for the slight difference in the rates of secondary caries because a longer evaluation time may increase the risk of caries. It was reported that caries adjacent to the restoration were infrequent and seen less often in anterior restorations.1,21 Therefore, anterior restorations are probably more likely to be replaced because of esthetic demands, trauma fracture, and loss of retention, which may explain the different functional demands of anterior and posterior teeth.1 Moreover, etch-and-rinse adhesives were used in the current study for the nanofilled and nanohybrid composites. Enamel etching with phosphoric acid reduces the occurrence of marginal discoloration, which, in turn, may reduce the replacement of restorations due to the confusion between stained margins and caries at the margin or may be due to esthetic reasons.21
In the present study, all of the nanofilled and nanohybrid composite restorations, showed ideal (alpha-rated) surface texture. These findings are in accordance with previous studies.14,24 In addition, the dental nanocomposite system showed equivalent translucency, polish, and polish retention properties to those of microfill composites and maintained the physical and wear resistance of several hybrid composites.23 Therefore, the use of nanotechnology-based modern composites in the present study could have resulted in improved surface texture.
CONCLUSIONS
Despite the limited number of restorations, no statistically significant differences were found between the nanofilled and nanohybrid composite restorations in any of the clinical criteria evaluated. The main cause of restoration failure was restoration fracture. Modern nanofilled and nanohybrid composites may provide good long-term results in class IV cavities. However, more long-term clinical studies are warranted.
Kaplan-Meier survival analysis, showing the time interval (years).
Flow diagram history of restorations.
Contributor Notes