| Abstract|| |
Introduction: Conventional Class II cavity preparations used for restoring small lesions with amalgam may be inappropriate for composite resin restorations due to the extensive cavity form, large occlusal contact area, and thin or missing margins of the tooth. Cavity preparation in the proximal areas as per the precepts of Clark is a conservative method of caries excavation and tooth preparation.
Materials and Methods: Conventional Class II and Clark's Class II cavities were prepared on the mesial surfaces of 60 molars. All cavities were given a standard buccolingual width of 2 mm, an occlusogingival height of approximately 3.5 mm and an axial depth of 1.5 mm. These were then restored using flowable composites or resin-modified glass-ionomer cement liners and nanohybrid composites. The compressive bond strength was tested with a universal testing machine.
Results: The compressive bond strength was the highest for Clarks Class II cavity preparation with a lining of flowable composites. Conventional Box only Class II cavities restored with flowable liners showed the next best result.
Conclusion: Clark's class II cavity preparation can be used as efficiently as the conventional Class II box preparation with the advantage of preserving more tooth structure, more precise tooth preparation, good bond strength and better esthetics.
Keywords: Cavity configuration; Clark's cavity preparation; flowable liner; resin-modified glass-ionomer cement
|How to cite this article:|
Kumar T, Sanap A, Bhargava K, Aggarwal S, Kaur G, Kunjir K. Comparative evaluation of the bond strength of posterior composite with different cavity configurations and different liners using a two-step etch and rinse adhesive system: In vitro study. J Conserv Dent 2017;20:166-9
|How to cite this URL:|
Kumar T, Sanap A, Bhargava K, Aggarwal S, Kaur G, Kunjir K. Comparative evaluation of the bond strength of posterior composite with different cavity configurations and different liners using a two-step etch and rinse adhesive system: In vitro study. J Conserv Dent [serial online] 2017 [cited 2018 Feb 21];20:166-9. Available from: http://www.jcd.org.in/text.asp?2017/20/3/166/218315
| Introduction|| |
There has been a continuous decline in the overall use of amalgam over the last few decades and an increase in the use of the composite the causes are:
- Health concerns and environmental considerations regarding amalgam
- The clinicians need for an adhesive material that requires minimum invasive cavity preparation,
- Patient demand for tooth-colored restorations in posterior teeth.,,
Posterior composites; with good case selection, proper adhesion, and insertion, do provide successful and predictable restorations, that closely mimic the natural appearance of teeth. Consequently, the use of posterior composites has demonstrated a marked increase, with improvements in the physical properties of materials, instruments, better adhesion to dentin and appropriate restorative techniques.,
Conventional Class II cavity preparations used for restoring small lesions with amalgam may be inappropriate for composite resin restorations due to the extensive cavity form, large occlusal area particularly in the areas of occlusal contact, and compromised gingival enamel. Preparations which aim to preserve tooth structure include the facial slot, tunnel, and box-only preparations. A box-like cavity in the proximal areas is suitable only for small interproximal lesions, leading to good access and visibility.
Dental composite resins encounter the common problem of 2%–4% of volumetric shrinkage during the polymerization process. Contraction subsequent to polymerization leads to stress within the composite filling, leading to a marginal microleakage. In spite the progress in the development of newer dentinal adhesives, no existing systems are able to compensate the creation of gaps at the dentin/restoration interface.
The configuration of the cavity plays an important role in the durability of the restoration. The boxy of a conventional Class II preparation creates sharp internal line angles, promotes crack initiation, and leaves dentin vulnerable to fracture.
Dr. David Clark introduced a new form of cavity preparation that advocated separate occlusal and proximal cavity preparations with margins extending into the enamel. Clark promotes preparations that are based on the adhesive capability of restorative materials and are engineered to resist tooth fracturing.
The use of liners is recommended for reducing the polymerization shrinkage. The flowable restorative resins contain lesser fillers (60%–70% by weight and 46%–70% by volume) and a greater proportion of resin matrix than hybrid resins. It is for this reason that manufacturers often advise the use of flowable composites as liners in areas of limited access or compromised flow, such as irregular internal surfaces and proximal boxes of class II preparations.
This study was conducted to check the strength of composites when used as a restorative material in different cavity preparations and liners.
| Materials and Methods|| |
Sixty caries free extracted multi rooted molars of permanent dentition were used for the study. The teeth were debrided ultrasonically and were then mounted in acrylic blocks such that the cemento-enamel junction was exposed. Class II cavities with Clarks configuration were prepared on the mesial surfaces of 30 molars. Each cavity had a standard buccolingual width of 2 mm, occlusogingival height of 3.5 mm and an axial depth of 1.5 mm. The occlusal, proximal, and gingival margins of the cavity preparation had disappearing/serpentine margins in enamel (approximately 3 mm).
- Group A: Clarks Class II cavity preparation was lined with resin-modified glass-ionomer cement (RMGIC) liner (n = 10)
- Group B: Clarks Class II cavity preparation was lined with flowable Composite Liner (n = 10)
- Group C: Clarks Class II preparation was left without liner (n = 10)
- On the mesial surfaces of 30 teeth Class II box-only cavities were prepared. All cavities had a standard buccolingual width of 2 mm, occlusogingival height of 3.5 mm and axial depth of 1.5 mm
- Group D: Class II box only preparation lined with RMGIC liner (n = 10)
- Group E: Class II box only preparation lined with flowable composite resin liner (n = 10)
- Group F: Class II box only preparation without liner (n = 10) (control group).
In Group A, the RMGIC (Vitrebond, 3M ESPE) was placed on the cavity floor to a thickness of approximately 1 mm and cured. The cavities were etched with 37% phosphoric acid for 15 s, rinsed with water and blot dried. The bonding agent was then applied to the dentin surface. The adhesive resin was thinned with a low-pressure air stream and light-cured for 20 s. The packable composite was placed over this and cured.
In Group B, flowable resin was injected onto the gingival floor of the cavity to a thickness of approximately 1 mm and light cured. The packable composite was placed in the cavity and cured.
In Group C, the cavity was etched and bonded. The packable composite was placed over this and cured.
- Group D. Procedure was same as for Group A
- Group E. Procedure was same as for Group B
- Group F. Procedure was same as for Group C.
All cavity preparations and restorations were done using dental loupes (4X). A polyester matrix band was used as a matrix around the tooth. Each cavity was then restored with a packable composite. The restorative resin was applied in oblique layers of 2–3 mm increments and cured for 20 s. All the composite restorations were finished and polished with a composite polishing kit, Super Snap (Shofu).
The teeth were thermocycled and then subjected to a compressive load in an Instron Universal testing machine until fracture. The diameter of the plunger was 0.2 mm and the cross head speed was 3 mm/min.
The data were analyzed using the Student's Unpaired t-test of difference for comparison between two samples. One-way ANONA test (Tukey-Kramer multiple comparison test) was applied to compare fracture load (N) in all six groups together. Probability, P < 0.05: considered as statistically significant. Statistical analysis software SYSTAT version 12 (By Cranes software's, Bengaluru, Karnataka, India) was used to analyze data.
| Results|| |
The compressive bond strength was highest for Clarks Class II cavity preparation with flowable lining. The compressive bond strength of Class II box only cavity with flowable liner was lower than Clarks Class II cavity preparation with flowable lining but did not show statistically significant difference from it. The compressive bond strength of Clarks Class II cavity preparation without liner was lower than the flowable liner group. No statistically significant differences were seen in the Class II box only preparation without any lining. Clark's cavities showed similar results to the conventional box only preparation. All the Clarks Class II cavities preparation with RMGIC lining showed significantly lower compressive bond strength than all the other groups [Table 1].
|Table 1: Bond strength of different material with different cavity preparation|
Click here to view
| Discussion|| |
The primary advantage of adhesive composite resin to restore posterior teeth is the possibility of preserving sound tooth structure during cavity preparation. It is futile to reduce sound tooth structure to provide “bulk for strength,” is not necessary to remove unsupported enamel or to provide mechanical retention.
The Fissurotomy NTF Bur (SS White, Lakewood, NJ, USA) is ideal for ultraconservative micro preparations of pit and fissure defects.
Simplified two-step etch-and-rinse adhesives combine the primer and adhesive resin into one application. Ethanol-water-based etch-and rinse adhesives are still considered to be the “gold standard” in terms of bond durability, particularly in demanding cavity preparations that have exposed dentin margins.
The failure patterns observed in this study were mostly adhesive. The reason for this could be the hydrolytic degradation of the adhesive system, impairing bonding resistance, and favoring breakdown of the adhesive interface. The present study showed that the Clarks cavity preparation has better compressive bond strength than a conventional box only Class II cavity preparation. The reason for this could be beveled restorations generally exhibit better fracture resistance and less gap formation. Beveled margins provided a series of advantages, such as removing the nonprismatic enamel surface, which is rich in fluoride, increasing surface energy and enhancing the surface area of enamel, thereby improving adhesion and marginal sealing and providing a better esthetic result for the restoration. The only disadvantage of a bevel is the additional removal of sound enamel structure.,,
Two components of the tooth substrate can be used to bond to collagen fibrils and hydroxyapatite crystals. Binding to collagen fibrils can be achieved only by hydrogen bonds; however, these are relatively weak and unstable, especially in an aqueous environment. However, the calcium available in hydroxyapatite can serve as a receptor for stronger ionic bond formation. Therefore, more the enamel margin better is the bonding. Nordbø et al. did a clinical trial to check the long-term (10 years) performance of saucer shaped cavities and found that these are preferable to the box preparation.
In the present study, it is seen that there is no significant difference between the fracture loads of Clarks Class II cavity preparation without liner and box only Class II without liner. The reason for this could be that since Clarks cavities are saucer shaped the packable composite does no adapt properly to the cavity. Whereas, the flowable liner makes the adaptation into the small irregularities, better.
The RMGIC groups had lower fracture resistance than the flowable groups. The bond strength between glass ionomer and resin composite has been described as very weak; therefore, the interface between the glass ionomer and the resin can almost be considered an inadequate bonded surface. Moreover, the mechanical strength of the glass ionomer is lower than that of resin composite, resulting in poor compensation of the stress absorber.
The bond strength flowable composite bond strength to enamel 20 MPa and to dentin is 17 MPa, whereas RMGIC has bond strength of 14 MPa to enamel and 11 MPa to dentin.
The authors did not find any documented or published literature on comparative studies with Clark's cavity preparations.
So, the limitations of this study are:
- The Clarks cavity was not restored exactly according to Dr. Clark's recommendations. However, the aim of this study was to check the influence of the cavity design and the materials used and not the influence of the technique of restoration. Other studies should be done to check the influence of the restoration process
- Results of this in vitro research should be verified with clinical scenario
- There is no reference from literature with regards to clinical or laboratory performance of Clarks Class II cavities.
| Conclusion|| |
The Clark's class II cavity preparation can be used as efficiently as the conventional Class II box preparation with the advantage of preserving more tooth structure, more precise tooth preparation, good bond strength, and better esthetics.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Dr. D. Y. Patil Dental College & Hospital, Dr. D. Y. Patil Vidyapeeth, Pimpri, Pune -18, Maharashtra
Source of Support: None, Conflict of Interest: None