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 Table of Contents  
Year : 2016  |  Volume : 13  |  Issue : 1  |  Page : 11-17

Effect of occlusal loading on microleakage of wedge-shaped abfraction-like cavities restored with three different esthetic restorative materials

Conservative Dentistry Department, Faculty of Dentistry, Alexandria University, Alexandria, Egypt

Date of Submission22-Feb-2016
Date of Acceptance17-Mar-2016
Date of Web Publication26-Jul-2016

Correspondence Address:
Wegdan M Abdel-Fattah
Conservative Dentistry Department, Faculty of Dentistry, Alexandria University, 86 Lafizon St. Boulkley, Alexandria - 2394
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1687-8574.186941

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Noncarious cervical lesions are a very common occurrence in clinics. They also represent one of the less durable types of restorations and have a high index of loss of retention, marginal excess, and secondary caries.
Aim of the study
Considering the aspects related to abfraction and the materials frequently used in its restoration, we conducted an in-vitro study to investigate the relationship between occlusal loading and the microleakage of cervical wedge-shaped esthetic restorations.
Materials and methods
Sixty wedge-shaped cavities in extracted upper premolars were divided into three groups (n=20). Group I was restored with GrandioFlow, group II was restored with Compoglass F, and group III was restored with PhotacFil Quick Aplicap. Half of the specimens from each group were subjected to occlusal loading (2 kg for 5 min at a rate of 120 cycles/min for 600 cycles) on the buccal cusp, and the other half were used as controls without loading. All teeth were then thermocycled. The teeth were water-sealed and immersed in methylene blue solution for 3 h. The samples were cut buccolingually and the leakage scores were assessed for all groups at the occlusal and cervical walls using a steriomicroscope.
There was no significant difference between loaded and unloaded tested restorations neither at the occlusal nor at the cervical margin.
Occlusal loading did not have an effect on the margins of cervical abfraction-like lesions.

Keywords: abfraction, cervical lesions, microleakage, occlusal loading

How to cite this article:
Abdel-Fattah WM. Effect of occlusal loading on microleakage of wedge-shaped abfraction-like cavities restored with three different esthetic restorative materials. Tanta Dent J 2016;13:11-7

How to cite this URL:
Abdel-Fattah WM. Effect of occlusal loading on microleakage of wedge-shaped abfraction-like cavities restored with three different esthetic restorative materials. Tanta Dent J [serial online] 2016 [cited 2019 Jan 23];13:11-7. Available from: http://www.tmj.eg.net/text.asp?2016/13/1/11/186941

  Introduction Top

Noncarious cervical lesions (NCCL) are commonly encountered and raise considerable restorative challenges for the dentist. It involves the loss of hard tissue and, in some instances, restorative material at the cervical third of the crown and subjacent root surface, through processes unrelated to caries. Although it is accepted that NCCLs have a multifactorial etiology, the relative contributions of the various processes remain unclear [1]. The occurrence of NCCL is very common on anterior and premolar teeth because they are of a smaller size [2].

The role of occlusal loading in the development of NCCL is becoming increasingly prominent. It is suggested that high occlusal loads result in large stress concentrations in the cervical region of the teeth. These stresses may be high enough to cause disruption of the bonds between the hydroxyapatite crystals, eventually resulting in the loss of cervical enamel [3]. The stresses create microfractures in the enamel or dentin adjacent to the gingival region. These fractures propagate in a direction perpendicular to the long axis of the tooth, leading to a localized defect around the cementoenamel junction [4].

The theory of abfraction is based primarily on engineering analyses that demonstrate theoretical stress concentration at the cervical areas of teeth. They are typically wedge-shaped and display a size proportional to the magnitude and frequency of tensile force application. Although the role of occlusal forces in the etiology of abfraction lesions has been widely discussed, it was found that lateral forces and occlusal forces, which cause cuspal flexure, are the cause of the breakdown of tooth structure in the cervical region [5]. It was proposed that bruxing produced most of the destructive forces on the tooth structure, which was supported by stress studies conducted by Litonjua et al. [6].

As abfraction lesions implicate enamel and dentine margins, class V NCCL represent a challenge to the dental profession due to their position, which make it difficult to provide a long-lasting restoration [7]. It is well known that enamel and dentin respond differently to masticatory stresses. Although these tissues are intended to support each other, they can react to occlusal forces independently. Dentin has shown low compressive and high tensile stresses at the cementoenamel junction, whereas enamel has demonstrated a reverse trend [8].

Stress concentration at the cervical region is responsible not only for the development of cervical lesion but also for restoration retention failure. Combining chemical adhesion and restorative materials of appropriate elastic properties are promising in long-term success [9].

Occlusal forces increase microleakage and gap formation at the cement/dentinal margin. Continual occlusal loading produces displacements and stresses under the buccal cervical enamel and dentin, increasing crack initiation and encouraging loss of restoration [10]. A critical factor for restorative success is represented by the selection of the restorative materials. These issues dictate the restoration's integration in an area of the tooth, which involves multiple biomaterials and experiences complex stresses.

The demand for restoration of cervical defects, such as cervical erosion and root caries, has increased significantly in recent years [11]. Currently, the materials of choice indicated for restoring cervical lesions include glass ionomer cements, resin-modified glass ionomer cements, polyacid-modified resin-based composites (compomers), and composites resins [12]. However, there is no unanimous recommendation for one material or another, because of a fundamental lack of understanding on how the restorative elastic properties affect the retention rate of cervical restorations.

Considering the information related to abfraction lesions and the materials used for their restoration, this study was conducted to investigate the effect of oclusal loading on the microleakage of cervical wedge-shaped restorations.

  Materials and Methods Top

A total of 60 human maxillary first premolars free from decay, cracks, or previous restorations were selected for the study. All patients are informed about the purpose of the study and using of their extracted teeth according to ethics committee of Faculty of Dentistry b, Tanta University. Teeth were thoroughly cleaned and stored in physiological saline solution at room temperature before use. Wedge-shaped abfraction-like cavities were prepared with occlusal margin in enamel and cervical margin on cementum using a flat-end cylindrical diamond bur no. 012 (Komet Dental MANI, Tochigi, Japan) at 45° to the cement–enamel junction on the buccal surface of each tooth [13]. Complete penetration of the bur diameter was used as a guide to establish a standardized dimension of preparation in all specimens. The preparation was performed with a water-cooled high-speed handpiece. The bur was replaced after every five preparations.

The teeth were randomly divided into three groups (n = 20) and restored with different materials. Group I teeth were restored with Grandio flow (Voco, Cuxhaven, Germany), a nanohybrid flowable composite resin; group II teeth were restored with Compoglass F (Ivoclar Vivadent, Schaan, Liechtenstein), a polyacid-modified composite resin; and group III teeth were restored with Photac Fil Quick Aplicap (3M ESPE; St Paul, Minnesota, USA) a resin-modified light-cured glass ionomer.

For both groups I and II, cavities were acid-etched using 35% phosphoric acid Scotchbond Etching gel (3M ESPE) and rinsed with water for 15 s, and then blot-dried before the application of Single Bond adhesive (3M ESPE) in two consecutive coats. The teeth were gently air dried with oil-free compressed air from an air syringe for 5 s and light-cured for 10 s. After adhesive application, cavities of both groups were filled with the respective materials, flowable composite (Grandio Flow) and polyacid-modified composite resin (Compoglass F), according to the manufacturer's instructions. Both materials were injected in the cavity and then light-cured for 40 s using Optilux light curing unite (Kerr, USA). For group III teeth restored with Photac Fil Aplicap, the cavities were only rinsed with water and air dried. Photac Fil resin-modified glass ionomer was injected directly into the cavity with no acid etching or conditioning and then light-cured for 40 s. All restorations were finished and polished with Soflex discs (3M ESPE).

Teeth were embedded in self-curing acrylic resin in a metallic cylindrical mold (20 mm in diameter and 30 mm in height), with the cervical margin of the restoration placed at 1 mm below the rim of the cylinder. To simulate the periodontal ligament, the roots were covered with a layer of rubber base impregum impression material (3M ESPE).

Ten teeth of each group were subjected to occlusal loading of 2 kg for a period of 5 min at a rate of 120 cycles/min with a total of 600 cycles in a mechanical load cycling machine [14]. The load was applied vertically with a steel stylus at the buccal cusp of the occlusal surface, parallel to the long axis of the teeth. The remaining ten teeth from each group were not subjected to any load and were used as controls.

All teeth were then stored in distilled water at 37°C until thermocycled for 500 cycles from 5 to 55°C with 1-min dwell time and a transfer time of 30 s.

For microleakage test, the tooth surface was sealed with sticky wax. All external surfaces were covered with two layers of nail varnish except for 1.0 mm around the restorations, and then immersed in a 2% methylene blue solution for 3 h [15]. The specimens were rinsed in running water and then dried. The teeth were sectioned buccolingually with a low-speed diamond saw under water spray.

The dye penetration depth along the cavity walls (including both occlusal and gingival margins) was measured with a stereomicroscope (Olympus SZ 11; Japan) at ×5 magnification and using a digital camera (Olympus E330; Japan).

The microleakage scores were recorded separately for both occlusal and cervical walls using the following criteria [16]: score 0, no evidence of dye penetration; score 1, dye penetration into one-third the distance of the cavity dentinal wall (mild microleakage); score 2, dye penetration more than one-third the distance of the cavity dentinal wall but short of the cavity base (moderate microleakage); and score 3, dye penetration into the total depth of the v-shaped cavity and into the pulp (severe microleakage).

  Results Top

The data for the microleakage scores of dye penetration for the loaded and unloaded restorations at both occlusal and cervical walls were analyzed using and the Mann–Whitney U-test. At the occlusal and cervical walls, there was no significant difference in microleakage scores between loaded and unloaded restorations for any of the tested materials. At the cervical margin the P values were 0.739 for Grandio Flow, 0.481 for Compoglass F, and 0.218 for Photac Fil. However, at the occlusal wall the P values were 1.000, 0.739, and 4.36 for Grandio Flow, Compoglass F, and Photac Fil, respectively, at a 0.05 level of significance ([Table 1] and [Table 2]).
Table 1: Microleakage scores for loaded and unloaded teeth at the cervical wall

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Table 2: Microleakage scores for loaded and unloaded teeth at the occlusal wall

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The Kruskal–Wallis test was used for comparing the scores of dye penetration between the three tested materials, with no load cycling. There was no significant difference between the three tested materials at the cervical wall (P = 0.342) or the occlusal wall (P = 0.368) for the unloaded groups at a 0.05 significant level. Moreover, there was no significant difference between the three tested materials at the cervical wall (P = 0.119) or the occlusal wall (P = 0.135) for the load-cycled groups at a 0.05 level of significance ([Table 1] and [Table 2]).

For the unloaded control group, the occlusal wall did not show any dye penetration except for one Photac Fil resin-modified glass ionomer restoration (10%) with a score 1; for the cervical wall, Photac Fil showed 20% restoration with score 1 and 10% restoration for Compoglass F polyacid-modified composite resin with a score 1.

When teeth were subjected to occlusal load, one of the restorations in group III (restored with Photac Fil) was lost. The cervical wall showed more microleakage scores than that of the occlusal wall for all tested materials, with dye penetration score 1 at the occlusal margin for two Photac Fil restorations (22.22%), whereas for the cervical margin three teeth from the same group showed score 1, accounting for 33.33%, and one tooth with score 2, accounting for 11.11%. For the loaded Compoglass restorations (group II), two restoration (20%) showed score 1 at the occlusal wall, whereas at the cervical wall three teeth showed leakage score 1, accounting for 30% of the restorations. The flowable composite Grandio Flow (group I) did not show any leakage neither at the occlusal nor the cervical margins when no load was applied, but with load cycling only one tooth (10%) showed score 1 at the cervical margin only ([Figure 1],[Figure 2],[Figure 3],[Figure 4]).
Figure 1: Microleakage score 0 for Grandio Flow at both occlusal and cervical walls.

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Figure 2: Microleakage score 1 for Compoglass F at cervical wall and score 0 at occlusal wall.

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Figure 3: Photac Fil score 2 at cervical wall and score 1 at occlusal wall.

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Figure 4: Lost Photac Fil restoration.

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  Discussion Top

This study compared the microleakage of three different esthetic materials in cervical abfraction-like lesion after occlusal loading. The most desirable property that a restorative material should have is an adequate, complete, and a long-lasting seal of the margins of the restoration. Microleakage is more critical in margins with little or no enamel, which characterizes most of the noncarious class V cavities [17]. The cervical margins of such restorations may be at the cementum or dentin surfaces. The adhesion between composites and dentin is not as strong as with enamel; therefore, the material can be dislodged toward occlusal during polymerization contraction, causing a bad adaptation of the restoration at the cervical margins [18].

In the present study, when comparing the cervical and the occlusal margins of the restorations, the cervical wall of most of the restorations showed more scores of microleakage. This is in agreement with the findings of Yap et al. [17] and Van Meerbeek et al. [19]. As abfraction lesions implicate enamel and dentine margins, class V NCCL represent a challenge to the dental profession due to their position, which makes it difficult to provide a long-lasting restoration [2].

Occlusal loads and dental substrates are considered the most important factors affecting the clinical performance and retention of NCCL restorations [20]. The different locations of the loads generating tension may affect cervical restorations in different ways, and the magnitudes of the defects may be related directly to the intensity and frequency of local tensions. It is generally believed that occlusal load applied to the buccal cusp promotes cervical compressive tensions [13]. In our study, the load was applied on the buccal cusp of the premolar teeth; thus, it was expected that it will affect the cervical wedge-shaped restorations and the marginal quality of these restorations. However, this was not true in our results, as no statistically significant difference was found for microleakage scores between the loaded and unloaded restorations. This might be due to the low load (2 kg) and loading cycles (120 cycles/min) applied on the teeth in our study. It was observed by Francisconi et al. [13] that when specimens were subjected to a load of about 15 kg for 144 h it showed a higher percentage of marginal gaps in the loaded group compared with the unloaded control group. In contrast, the results of Jang et al. [21]is not in agreement with ours, as gingival margins had significantly more microleakage compared with occlusal margins when suffering from occlusal forces to the same degree.

In the current study, there was no significant difference in leakage scores when flowable composite (Grandio Flow), compomer (Compoglass F), or resin-modified glass ionomer (Photac Fil) were used in both unloaded and loaded conditions, with Grandio Flow composite groups presenting the least scores. This might be as a result of the high modulous of elasticity of Grandio Flow imparted from its nanotechnology filler loading [22]. Moreover, flowable composites have a shock-absorbing ability, which help in compensating for contraction stresses in polymerization shrinkage of a restoration [23].

Some authors also claim that the lower elastic modulus and increased flexibility of flowable composites support the materials and the inability to flex with tooth structure, and thus resist fracture and reduce the stresses of polymerization shrinkage [24]. As compomer also has a lower flexural modulus of elasticity, a shock-absorbing ability similar to flowable composite [25], it can be explained why there were no statistically significant microleakage differences between Grandio Flow and Compoglass compomer. In a finite-element study, it was concluded that restorative materials with a low modulus of elasticity are successful in abfraction lesions at moderate tensile stresses [26].

According to current results, the largest degrees of microleakage were observed in Photac Fil Aplicap with no statistically significant difference between the other studied materials. The elastic modulus of the resin-modified glass ionomer Photac Fil used in this study might not be sufficient to withstand the occlusal force and prevent microleakage, especially at the dentine margin.15 Moreover, Photac Fil was applied to tooth surface with no bonding agent, and so this might explain the higher leakage scores and loss of one of the restorations during the study. Urabe et al. [27] and Senawongse et al. [28] reported that elastic modulus of dentin was greater than those of the low-viscosity resins and resin composite. Meanwhile, in a previous study by Van Meerbeek et al. [29], it was concluded that the low-flow flowable composite demonstrated a greater elastic modulus compared with high-flow flowable composite. However, Senawongse et al. [15] in their study suggested that the application of flowable composites reduced the marginal leakage at the dentin margin of wedge-shaped composite restorations to compensate for the stresses generated by occlusal force.

Tyas [30] recommended that RMGIC be the first preference for restoration of NCCLs or, in esthetically demanding cases, a RMGIC/IC liner / base be laminated with resin composite. Meanwhile, Vandewalle and Vigil [31] recommended that NCCLs suspected of being caused primarily by abfraction be restored with a microfilled resin composite that has a low modulus of elasticity, as it will thus flex with the tooth and not compromise retention. However, a 7-year study found no statistically significant difference between failure rates of three resin composites of different stiffness used to restore NCCLs [32]. This was contradicted by Browning et al. [7], who found that class V lesions restored with materials of higher modulus of elasticity enabled better stress distribution. However, no significant difference was found between materials with different elastic moduli; it is desirable that the elastic modulus of a restorative material matches that of the tissue it replaces [33].

Abfraction lesions present primarily at the cervical region and are typically wedge-shaped, with sharp internal and external line angles [11]. It should be noted that when restoring such lesions clinicians are not treating the etiology but are merely replacing what has been lost. There are no generally accepted, specific guidelines in the literature stating when abfraction lesions should be restored. That is why the clinician must consider the etiologic factors such as bruxism, premature contacts, and wear facets contributing to the lesion when the indicated treatment is restoration[34],[35]. Moreover, there are problems with restoring NCCLs and include difficulty in obtaining moisture control, gaining access to subgingival margins, and high failure rates [36],[37].

Logic and good clinical judgment would suggest that they should be restored when clinical consequences such as dentin hypersensitivity have developed or are likely to develop in the near future. Esthetic demands of the patient may also influence the decision to restore these lesions [35].

The influence of restorative materials on the margins of cervical restorations subjected to occlusal loading, however, requires further investigation.

  Conclusion Top

Occlusal loading of abfraction-like lesions restored with flowable composite resin (Grandio Flow) did not show any microleakage for the occlusal and cervical walls. However, Compoglass F polyacid modified composite and Photac Fil resin-modified glass ionomer resin showed mild leakage at both occlusal and cervical margins.

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Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1], [Table 2]


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