9: Direct Composite Restorations

Direct Composite Restorations

Overview

M. Veneziani

Over the last 15 years socioeconomic changes, decreased caries prevalence, the greater esthetic demands of patients, and finally the controversy about the potential toxicity of amalgam have contributed to the introduction of new materials and the development of new techniques for esthetic restorations in the posterior, which are being used alongside traditional restorative materials and are progressively replacing them (Nathanson, 1991).

In the early 1990s the Geneva School still recommended the use of silver amalgam even for small Class II restorations up to the distal surface of the canine (Figure 9-1).

Today tooth restoration techniques are radically different from those employed 15 years ago. Conservative dentistry has undergone a radical change, and today rehabilitation with adhesive techniques—following a strict operative protocol—of posterior teeth with medium and large carious lesions, and even with cuspal coverage, is considered correct and beneficial (Figure 9-2).

Reasons for Employing Adhesive Dentistry in the Posterior

The indications for use of amalgam are limited to few cases (see Chapter 5), essentially because esthetic adhesive composites have evolved considerably and offer significant advantages (Dietschi and Spreafico, 1997). They are tissue sparing, they strengthen the residual dental tissues, they ensure good esthetics, and they permit reintervention.

The routine use of adhesive restorations is also a result of improved materials, shifts in disease prevalence, longevity, their suitability for all types of cavities, and the fact that they address the “amalgam phobia” of patients.

Longevity

These materials also have a satisfactory life (Figure 9-8). According to Skeeters and colleagues (1998), 95% of restorations retain their function after 15 years; for Kohler and colleagues (1998) the 5-year duration depends on proper selection of cases and caries susceptibility.

Hoby and colleagues (1998) argue that after 5 years of function, marginal adaptation in premolars with Class II cavities seems more comparable to that of similar cavities with amalgam fillings. According to van Dijken (2000) the survival rate of composite inlays applied with intraoral technique is 83% at 11 years. A major review of the literature on the clinical survival of direct and indirect restorations since 1990 (Manhart and colleagues, 2004) reports an average annual failure of 2.2% for direct composite restorations and 2.9% for composite inlays.

Suitable for All Types of Cavities

Composites can be used for preventive restorations, for small, medium, and large Class I and II restorations, and those that are gradually more complex, culminating with full cuspal coverage—all of which are performed with the same material applied with different techniques (direct, semidirect, indirect). Figure 9-9 exemplifies some of the benefits listed previously.

Direct Class I Restorations in the Posterior

Adhesive Cosmetic Restorations in the Posterior

A restoration can be defined as the clinical procedure for replacing lost dental hard tissues after a carious or traumatic process. This therapeutic act should meet the core objectives of restorative dentistry with respect to shape, functional and esthetic parameters, and maximum preservation of residual healthy tissues by ensuring durability, predictable results, and a lower risk of secondary caries.

For many years metals used for both direct and indirect techniques were considered the only viable treatment option for restorations in the lateral sectors. Amalgam was the first choice for conservative dentistry for a long time, and today—despite the various alarmist campaigns regarding its potential toxicity—it continues to have important indications (Ferrari and Patroni, 2000).

Initially resins were used only in the anterior for both small and large restorations, with excellent results in terms of restoring shape, color, function, and esthetics (Figure 9-10).

Today the latest evolution of enamel-dentin adhesive systems and composite materials has completely changed the therapeutic approach to carious lesions in the posterior, allowing greater preservation of sound dental tissues during preparation of the cavities (adhesive techniques do not require any drilling for mechanical retention) and also offering better reliability and esthetics (Figure 9-11).

In a publication dated 1998, the American Dental Association outlined the indications for cosmetic restorations in the posterior (see box below).

The general principles of cavity preparation for adhesive posterior restorations call for perfect insulation of the field with a rubber dam, maximum tissue sparing, and preservation of healthy structures even in the presence of enamel that is not fully supported.

Cavity shape depends on the extent of the carious lesion or the preexisting restoration. As opposed to what is done with silver amalgam, additional mechanical retentions are not required, because they would be detrimental for the residual healthy dental tissue.

Moreover, preventive extension gives way to the “prevention of extension” principle (Toffenetti, 2001).

Direct and Indirect Posterior Composite Restorations

In general, small and medium intracoronal cavities—whose size, by definition, is less than half the distance between cusps—are an indication for direct restorations, whereas for the treatment of large and multiple cavities (rehabilitation of quadrants or arches) with the possible need for cuspal coverage, it is advisable to employ an indirect technique or a technique that calls for the use of cement, owing to the adverse effects of polymerization shrinkage of a large mass of material.

Even in the case of thin and low cervical enamel (thickness <0.5 mm and height <1 mm) it is advisable to use a luted technique, either semidirect or indirect, in order to minimize shrinkage of the material in such a limited substrate.

With greater thicknesses and heights (>1 mm) all three techniques can be used, and in such cases the choice is based mainly on the size of the cavity (see Figure 9-12).

Indications

According to the classification of G.V. Black (1908), Class I cavities are those located in the anatomic depressions of the tooth. Therefore they involve occlusal pits and fissures of molars and premolars, labial and palatal fossae of molars, and cingulum depressions of canines and incisors.

Class II cavities instead involve the proximal surfaces of molars and premolars (Marmasse, 1980).

In addition to good operative access, the presence of enamel on the entire cavity perimeter and the absence of excessively pronounced cervical concavities are basic requirements.

Composite is considered the material of choice for small-to-medium Class I cavities.

The approach is extremely conservative and strengthens the remaining tooth structure, which is not possible with metals (Eakle, 1986).

In such clinical situations, adhesive techniques are utterly reliable, given the presence of abundant enamel throughout the cavity margin and the possibility of direct control and reintervention, because the edges can be inspected fully.

The method is relatively simple to perform and the esthetic outcome is predictable (Figure 9-13).

Cavity Preparation Techniques

Cavity preparation techniques for direct adhesive restorations in the posterior can be divided into minimally invasive preparations and conventional preparations.

In reality, for all types of adhesive preparation—which are unquestionably more straightforward than those for metal materials—cavity shape is dictated solely by the extent of the caries or preexisting restoration, the careful removal of carious tissue combined with rounding of the internal angles, and accurate definition and finishing of cavity margins.

Minimally Invasive Preparations

The term minimally invasive dentistry refers to all diagnostic and therapeutic procedures whose goal is maximum preservation and respect for healthy dental tissues. Therefore it is not limited solely to restoration techniques, but above all includes the indications listed in the box.

The main goal of modern restorative dentistry based on the minimally invasive approach thus lies in the ability to avoid or defer the performance of restoration (Peters and McLean, 2001a).

The application of these principles within clinical restorative techniques, considered secondary to disease control and caries prevention, has led to the development of increasingly sophisticated techniques and tools, including the following (Peters and McLean, 2001a):

Atraumatic Restorative Technique

ART (World Health Organization [WHO], 1994) is used only in special circumstances, particularly in countries with inadequate healthcare, when limited dental equipment is available (emergency home treatment), and in certain circumstances (e.g., the elderly, uncooperative patients). It can also be performed by nurses and auxiliary personnel. It involves control and stabilization of existing active carious lesions by partial removal of carious tissue with hand instruments. Self-hardening glass-ionomer cement is applied to create a sort of indirect pulp capping and promote remineralization of pathologic residual dentin.

The limits of the procedure are mainly related to the operational difficulties determined by the use of hand instruments (Van Amerongen, 1996).

Sonic Instruments

Sonic oscillating systems have recently been developed for the treatment of small primary interproximal caries in order to simplify the procedure and at the same time achieve controlled reduction of cavity extension.

The most recent literature tends to consider rotary instruments more difficult to use, requiring greater operating skills and longer operating times. Nevertheless, the main advantage is that the prepared surfaces are more regular.

Sonic instruments, on the other hand, are characterized by greater ease of use and safety for the adjacent teeth owing to their special shape with a smooth nonworking flat portion, which is set toward the marginal surface of the adjacent tooth, and a diamond convex working portion for cavity shaping (Figure 9-15).

In the case of interproximal cavities, when there are no nonworking surfaces for either burs or sonic tips, protection of the adjacent teeth with metal strips and dental wedges is crucial.

According to some authors, a combination of rotary and ultrasound instruments ensures a more conservative approach (Krejci, Dietschi, and Lutz, 1998; Galimberti and colleagues, 2001; Sheets and Paquette, 2002).

These instruments are particularly useful in minimally invasive Class II cavities, which can be classified as tunnel and slot cavities.

Tunnel cavities are preparations that, starting from the marginal fossa, reach the interproximal carious area without completely removing the marginal ridge below which the carious process started. This is a more conservative approach. Closed tunnel cavities are preparations in which only the carious dentin is removed and the interproximal enamel wall is maintained. The preparation is referred to as an open tunnel when there is involvement and removal of the demineralized enamel (Pope and colleagues, 1993; Peters and McLean, 2001a).

Slot (or box) preparations can further be divided into vertical (occlusal) preparations (Figure 9-16) and horizontal (bucco-palatal) preparations (Figure 9-17).

According to many authors, the tunnel has no advantages over the slot. Moreover, tunnel preparations are harder to perform, involve more difficulties in the removal of carious dentin because of the limited access, and have an increased risk of pulp involvement and fracture of the marginal ridge (Papa and colleagues, 1993; Peters and McLean, 2001a; Ericson and colleagues, 2003) (Figures 9-18 and 9-19).

Chemical-Mechanical Systems

Chemical-mechanical systems are based on the treatment of carious dentin by antibacterial substances such as metronidazole, tetracycline, and chlorhexidine.

The purpose is enzymatic digestion of the dentin substrate affected by caries through the action of collagenase and proteinase.

A recently marketed innovative system dissolves denatured collagen with sodium hypochlorite and amino acids, followed by mechanical hand removal with extremely sharp excavators.

This system is quite effective for removing carious dentin, has no adverse effects on pulp vitality or the composition of pulp and dentin, and does not interfere with adhesive processes. Moreover, there is less need for anesthesia (Ericson and colleagues, 1999; Bongenhielm and Young, 2001; Hossain and colleagues, 2003) (Figure 9-20).

Air Abrasion

Air abrasion is a very widespread system that uses a pressure jet of aluminum oxide particles measuring 27 to 50 microns. It involves the use of nozzles with a diameter of 200 to 800 microns and a working distance of 0.5 to 2 mm.

It permits very conservative and selective opening of dental grooves for diagnostic and therapeutic purposes.

The main advantages are the lack of vibration and noise and a reduced need for anesthesia.

It is particularly effective in removing hard tissues, but significant difficulties are encountered with softened tissues because aluminum oxide particles tend to bounce off them, drastically reducing the abrasive effect of the particles. Furthermore, the procedure requires acid conditioning of the enamel-dentin substrate for the adhesive procedures.

This system should be avoided when removing amalgam, and it is not ideal for treating deep carious lesions.

In addition, the problems of dust and contamination of the environment should be taken into account (Rinaudo, Cochran, and Moore, 1997; White and Eakle, 2000; Malmstrom, Chaves, and Moss, 2003) (Figures 9-21 and 9-22).

Laser Systems

Among the laser systems introduced recently in dentistry, the erbium:yttrium-aluminum-garnet (Er:YAG) laser is suggested for both interventions on soft tissue and preparations of dental hard tissues.

This instrument was approved by the FDA in 1997 for caries removal and dental preparation and subsequently for applications in the field of restorative dentistry.

Its mechanism of action is based on high-energy absorption and rapid evaporation of water molecules, generating microexplosions resulting in mechanical removal of the substrate (Hibst and Keller, 1989).

According to some authors, the effects determined by the use of the Er:YAG laser on the pulp are equivalent to those of a turbine handpiece (Cozean and colleagues, 1997).

The laser action increases the resistance of enamel and dentin to acid exposure, with adhesion values that are lower for irradiated dentin compared with untreated tissue (Kameyama and colleagues, 2000).

Cavity preparation is also slower compared with conventional rotary instruments.

Greater difficulties have also been reported in obtaining standardized well-shaped cavities and smooth surfaces.

In any case, laser surface conditioning cannot replace etching with orthophosphoric acid (Poggio and colleagues, 2000).

Ozone Therapy

The principle that led to the development of these innovative methods is based on the need to preserve carious dentin through disinfection rather than removal. However, this objective is not shared unanimously by the scientific dental community.

The treatment is based on the antimicrobial effect of ozone gas, a strong oxidizing agent found in nature as triatomic oxygen (O3).

Exposing carious dentin to ozone supposedly leads to a significant reduction of cariogenic bacteria in primary root caries (Baysan, Whiley, and Lynch, 2000).

Other studies support the possibility of an effective treatment even for occlusal pit caries (Holmes and Lynch, 2000).

Some authors are cautiously hopeful about these promising initial results, encouraging further investigation and confirmation by researchers (Ericson and colleagues, 2003).

Materials for Minimally Invasive Restorations

The selection criteria for these materials are based on the parameters listed in the box.

Composites and glass-ionomers are undoubtedly the most widely used materials. Some authors consider glass-ionomers to be more conservative than composites because of the possibility of maintaining areas of partially demineralized dentin by relying on the remineralizing properties of these materials.

Instead, composites always require complete removal of demineralized dentin to obtain an optimal adhesive bond (Mount and Ngo, 2000; Mount, 2003).

Small cavities are often more difficult to layer owing to the absence of voids and porosity. It may be useful to apply flowable composites on the cavity floor, and they can be combined with the application of microhybrid composites with superior physical and mechanical properties on the surface of the cavity (Chuang and colleagues, 2001; Opdam, Roeters, and de Boer, 2003) (Figure 9-23).

Preventive Preparation

Preventive resin restoration (PRR) (Simonsen and Stallard, 1977; Simonsen, 1980) concerns superficial caries of pits and fissures, which affect the dentin only partially (Figures 9-24 and 9-25).

It represents a transitional clinical situation between conventional sealing and microcavity and essentially consists of a seal whereby the opening of a groove also involves a small portion of dentin.

As a rule, this involves selective ameloplasty and sealing of adjacent pits and fissures without dentin exposure.

A direct bulk technique is employed for preventive restorations, because the thickness of the layer is irrelevant in terms of shrinkage reduction.

Operative Sequence for Preventive Resin Restorations

1. Careful isolation of the field with a rubber dam.

2. Cleaning with a brush and water jet and pumice or bicarbonate jet.

3. Thorough inspection and examination of the pit.

4. Possible selective opening of the pit if enamel lesion is suspected, using rose-head microburs at low speed or diamond needle burs at medium speed.

5. Etching and enamel-dentin bonding.

6. Execution of small restorations with bulk layering of a light-curing composite. PRRs are often combined with traditional sealings of the adjacent pits and fissures (Figure 9-26). According to some authors, traditional sealants (not filled) obtain better results in vivo in terms of microleakage than flowable composite and compomer. However, the ability of sealants to penetrate seems to be closely related to the shape of the groove (Duangthip and Lussi, 2003).

7. Application of a specific sealant or flowable composite on the intact pits and fissures.

8. Possible simultaneous curing of adhesive and sealant agents (Peters and McLean, 2001b).

9. Finishing and polishing.

Adhesive Preparation

Adhesive preparation (Lutz and colleagues, 1976; Porte and colleagues, 1984) applies to primary deep carious lesions whose extent is the sole determinant of cavity size. It entails rounding of the angles and definition of cavity margins through careful finishing (chamfering) of the enamel (Figure 9-27). In reality, chamfering of the occlusal portion simply means rounding the enamel to adjust the edges and improve the definition of cavity margins (Figure 9-28). A proper chamfer is not required, because, by virtue of their orientation at this level, the enamel prisms are already cut crosswise by the finishing bur (cylindric or a needle type) placed perpendicular to the occlusal surface (Schwartz, Summit, and Robbins, 1996).

Materials

In the posterior sectors, the most widely used materials are hybrid microfilled composites, possibly combined with flowable composites. These hybrid composites are characterized by a content of miniparticles with an average size of 0.5 to 1 micron and pyrolytic silica particles of 0.04 micron.

The latest products have been improved even further by introducing nanoparticles measuring 5 to 100 nanometers.

These materials are highly filled (70% to 80% by weight, 60% by volume) and have excellent physical and mechanical properties, optimal surface characteristics (polishing), a modulus of elasticity similar to that of dentin, and wear behavior comparable to that of enamel and amalgam (10 to 50 microns/year) (Willems and colleagues, 1993).

On the cavity floor, in direct contact with the enamel-dentin adhesive, it is advisable to use materials with a low modulus of elasticity (Young’s modulus 4 GPa), flowable composites that are more elastic than dentin (18 GPa), and microhybrid composites with higher internal flow that can compensate for shrinkage stress.

Flowable composites are used in a thin layer to improve the fit between the adhesive and the composite and reduce the risk of postoperative sensitivity, especially in the most unfavorable cavity configuration. In this regard, it is certainly important to consider the cavity C-factor, described by Feilzer, De Gee, and Davidson (1987), which considers the relationship between cavity configuration and shrinkage stress based on the relationship between bonded and unbonded surfaces—in other words, the inversely proportional relationship between the number of cavity walls and preservation of adhesion (Davidson, De Gee, and Feilzer, 1984).

A high number of cavity surfaces implies a limited internal flow with higher shrinkage and the risk of alteration of the adhesive bond.

Polymerization stress is thus minimal when the material can flow freely—that is, when the number of unbonded surfaces is higher than the number of surfaces involved in the restoration.

In Class I and V cavities with an unfavorable C-factor (with five bonding surfaces and only one unbonded surface), the internal flow of the material is limited, whereas the stress that can alter the adhesive bond is greater.

The application of more flexible materials in the deepest areas of these cavities, such as flowable composites, is desirable to compensate for stress and improve the fit between adhesive and composite (Dietschi and colleagues, 1995; Dietschi and Spreafico, 1998; Scheibenbogen-Fuchsbrunner and colleagues, 1999).

Layering

The color choice of material for direct posterior restorations is generally quite simple, especially compared with what is required for anterior ones. Some manufacturers have reduced the number of masses by offering a single dentin shade and different chromas.

A key factor, as always, is careful evaluation of the characteristics of the tooth to restore and the adjacent teeth, as well as the corresponding contralateral tooth before isolation with the rubber dam. The choice of dentin chroma depends mainly on the type of tooth and the age of the patient. Enamel masses, which are usually opalescent and have a high value, will depend on the color and thickness characteristics of the adjacent natural enamel. To increase the natural effect and create a greater depth for the restoration, intensive whitish masses on the enamel ridges and pigments can be used, as appropriate, to characterize pits and fissures.

Layering techniques for direct posterior restorations can be classified as bulk technique, horizontal layering technique, oblique layering technique, and layering technique in three increments.

Jan 1, 2015 | Posted by in Dental Materials | Comments Off on 9: Direct Composite Restorations
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