Abstract
Objectives
The aim of this paper is to examine cavity design for posterior resin composite restorations and to discuss various resin composite filling techniques.
Data
Literature with regard to cavity preparation for amalgam and resin composite restorations has been reviewed. An overview of available bulkfill resin composite systems is provided and a categorization of these systems according to their clinical application and their intended use is outlined.
Sources
A literature search was carried out by the authors in Medline.
Study selection
Pre-defined inclusion criteria based on keywords were included and reviewed.
Conclusions
Minimum cavity preparations are advised for posterior resin composite restorations, preserving the greatest amount of healthy tooth structure. For resin composite restorations only the lesion of caries needs to be removed with all remaining tooth structure protected for the bonding process. The anticipated outcome of this philosophy will result in increased survival of teeth. Newer bulkfill restorative resins offer many advantages such as reduces time for placement.
1
Introduction
When placed in optimal conditions and in low caries risk patients, resin composite restorations demonstrate comparable or even higher clinical performance to that of dental amalgam restorations .
Resin composites materials offer the potential of extended survival of the tooth and are more aesthetic than amalgam . Resin composites require different clinical skills and operative techniques to that used with dental amalgam restorations. These techniques have now been introduced into many undergraduate dental education programmes. Recent graduates are more experience in placing resin composite materials for the restoration of posterior teeth .
Resin composite restorations support the use of minimum cavity design . In contrast to dental amalgam, resin composites do not require a minimum thickness; and when bonded they support the remaining enamel and dentine requiring no additional retentive features .
The main disadvantage associated with the use of resin composite for restoring posterior teeth is shrinkage on polymerization. Stresses produced during polymerization are a leading cause of adhesive failure, resulting in postoperative sensitivity, marginal staining, and recurrent caries . This polymerization shrinkage creates stresses as high as 13 MPa between the resin composite material and tooth interface exceeding the tensile strength of the enamel often resulting in stress cracking and fracturing of the enamel .
When a resin composite is cured, the surrounding tooth structure may deform . This deflection can range from 4 to 6 μm, depending on the filling technique used . The higher the intensity of the light source, the greater the contraction force at the composite-tooth interface and so the use of high intensity plasma lights is not recommended. Intermittent or lower intensities lights improve the marginal integrity of the restoration because it permits dissipation of the polymerization stress . To achieve clinically successful posterior resin composite restorations, it is vital to maintain the integrity of the bond and the marginal adaptation to tooth enamel and dentin . Other shortcomings of resin composites are the long placement procedure and achievement of an adequate contact point.
The incremental technique is considered as the standard technique for posterior restorations. The thickness is limited to 2 mm maximum for optimal polymerization and degree of conversion . Combined with a three step total etch bonding technique, the restoration of a posterior cavity with resin composite can take much long to complete than an equivalent procedure using dental amalgam .
With the development and use of self-adhesive bonding systems the operator can shorten the bonding procedure and at the same time reduce postoperative sensitivity . Using bulk filling resin composite materials the total time taken to restore a posterior tooth with resin composite is similar to that of a dental amalgam restoration .
2
Cavity design
Greene Vardiman Black (1836–1915), published his concepts and ideas of cavity design for dental amalgam in his text Manual of Operative Dentistry in 1896. Further, he organized ‘Black’s Classification’ which is still in use today.
He established guidelines for cavity preparation, extension, retention and resistance form which applied to the mechanical requirements of dental amalgam. Design is based on the extent of the disease process and on the physical properties of amalgam. This means that the cavity must be at least 2 mm deep with design features such as undercuts, parallel walls and flat floors. It is also important that while finishing the cavity that the surface enamel is supported. In many cases, amalgam also requires the placement of a lining material.
A new cavity classification was published in 1998 in response to adhesive restorations by Mount and Hume . This emphasized the principle of minimum extension. An FDI review of minimal intervention was published in 2000 .
Further publications in 2001 , 2002 and 2003 lead eventually in 2006 to a publication which introduced the SiSta classification of cavity design .
Cavities for resin composite restorations are not predetermined by the physical properties of the material. The only criterion for the cavity design is the removal of the diseased tissue and as a result there are no standard cavities for resin composite restorations . Cavities can be of minimal depth , can have unsupported enamel at the cavo- surface margin, proximal walls and the cervical floor and do not require the placement of a base material. Unsupported enamel in the interproximal box is not removed with a bur or chisel as this can lead to bleeding from the interproximal papilla let alone loss of healthy enamel. The papilla can also be protected by pre-wedging which also assists in the development of a good interproximal contact. The cavosurface margins of proximal boxes to be restored with resin composite are smoothed and finished, but not bevelled .
In the following table ( Table 1 ) the authors suggest cavity designs for posterior resin composite restorations. These designs are based on the most frequent presentation of caries. Further, these designs may assist students and educators in standardizing resin composite techniques.
2
Cavity design
Greene Vardiman Black (1836–1915), published his concepts and ideas of cavity design for dental amalgam in his text Manual of Operative Dentistry in 1896. Further, he organized ‘Black’s Classification’ which is still in use today.
He established guidelines for cavity preparation, extension, retention and resistance form which applied to the mechanical requirements of dental amalgam. Design is based on the extent of the disease process and on the physical properties of amalgam. This means that the cavity must be at least 2 mm deep with design features such as undercuts, parallel walls and flat floors. It is also important that while finishing the cavity that the surface enamel is supported. In many cases, amalgam also requires the placement of a lining material.
A new cavity classification was published in 1998 in response to adhesive restorations by Mount and Hume . This emphasized the principle of minimum extension. An FDI review of minimal intervention was published in 2000 .
Further publications in 2001 , 2002 and 2003 lead eventually in 2006 to a publication which introduced the SiSta classification of cavity design .
Cavities for resin composite restorations are not predetermined by the physical properties of the material. The only criterion for the cavity design is the removal of the diseased tissue and as a result there are no standard cavities for resin composite restorations . Cavities can be of minimal depth , can have unsupported enamel at the cavo- surface margin, proximal walls and the cervical floor and do not require the placement of a base material. Unsupported enamel in the interproximal box is not removed with a bur or chisel as this can lead to bleeding from the interproximal papilla let alone loss of healthy enamel. The papilla can also be protected by pre-wedging which also assists in the development of a good interproximal contact. The cavosurface margins of proximal boxes to be restored with resin composite are smoothed and finished, but not bevelled .
In the following table ( Table 1 ) the authors suggest cavity designs for posterior resin composite restorations. These designs are based on the most frequent presentation of caries. Further, these designs may assist students and educators in standardizing resin composite techniques.
3
Adhesive process
3.1
Management of operatively exposed dentine
In most cases, liners/bases are not required under resin composite restorations, as they prevent the bond to dentine. There is evidence of no difference in outcome in terms of post- operative sensitivity when a resin composite is “bonded” or “based” . Placement of a liner for therapeutic purposes may be required in areas close to the pulp.
A recent review on direct and indirect pulp capping concludes that exposure of the vital pulp should be avoided at all times . Should a pulpal exposure occur, emerging evidence suggests that MTA is superior to calcium hydroxide . Newer products such as Biodentine have potential use in this situation .
3.2
Bonding
The bonding of resin composite to tooth structure can be achieved with one of four different etching systems: total-etch 3 step, total-etch 2 step, self-etch 2 step, and self-etch 1 step. The self-etch adhesives have increased in popularity due to their simplified technique and lower incidence of postoperative sensitivity . However, the acidic nature and permeability of simplified, self-etch adhesives make them incompatible with self-cured and dual-cured composites . One-step adhesives have a lower bonding effectiveness, attributed in part to the dissolution of hydrophilic and hydrophobic monomers in a highly concentrated solvent, which jeopardizes bond durability . Tay et al. has demonstrated that single-bottle adhesives, due to the lack of a more hydrophobic bonding resin layer, behave as permeable membranes after polymerization. They permit the continuous transudation of dentinal fluid and do not provide a hermetic seal for vital deep dentin. This may interfere with optimal polymerization of composites and resin cements.
The shear bond strengths of self-etching primer/adhesive systems and total- etch, 1-bottle systems to enamel have been shown to be much lower than the other systems, resulting in increased leakage and staining at the enamel- composite interface. The bonding of these self-etching primers to enamel may depend on their specific composition (pH) .
The conventional, 3-step, etch-and-rinse adhesives still perform favorably and are the most reliable in the long-term. Multiple studies comparing contemporary adhesives reveal that these adhesives remain the gold standard in terms of durability; whereas simplifying the clinical procedure results in loss of bonding effectiveness .
The 2-step total-etch systems exhibit slightly lower bond strengths than the 3- step systems after aging , the introduction of filled, 2-step total-etch systems demonstrate good bond strengths. These filled adhesives provide better coverage of the dentinal substrate. Filled adhesives are associated with a reduction in microleakage when compared to unfilled adhesives .
3.3
Selection and placement of restorative resin using incremental technique
The selection of resin composite is important for the success of the composite restoration. Hybrid and certain nano-particle hybrid resin composites are, in general, appropriate for use in posterior load-bearing situations. As a general rule, the resin composite selected should contain at least 60% filler by volume. Careful technique is required during the placement of resin composite to limit the adverse effects of polymerization shrinkage. According to Feilzer et al. the stress relieving flow is affected by the configuration of the restoration, known as the C-factor. The C-factor is the ratio of bonded (flow- inactive) to unbonded or free (flow-active) surfaces. An increase in the number of bonded surfaces results in a higher C-factor and greater contraction stress on the adhesive bond.
The occlusal restoration is the most common restoration to have post-operative sensitivity due to incorrect filling technique. Occlusal cavities have five bonded surfaces and have a high C-factor . Joining the opposing walls, buccal and lingual, in one-increment concentrates the contraction forces in the centre of the bulk of the resin composite. By avoiding the union of the buccal and lingual walls in any one increment the centre of contraction is directed towards the walls and away from the centre of the restoration.
One study has questioned the clinical significance of the C-factor for occlusal cavities. However, in this study extensive cavities were used which may have influenced the results .
Other advantages of the incremental technique are the improved shade and shape control of the restoration and complete curing of the composite. This technique tends to concurrently enhance the depth and adequacy of cure of the resin composite ( Photo 1 ).
