Direct Composite Restorations
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).
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).
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.
The need to perform composite restorations in the posterior is largely connected with the tissue-sparing principle—that is, the minimal sacrifice of sound hard tissues that results in an adhesive cavity rather than a conventional preparation (Figures 9-3 and 9-4).
The current trend is to restore the elastic properties of lost dentin by using composite materials with microhardness (a parameter related to the modulus of elasticity) very similar to that of dentin (Lutz, 1986) (Figure 9-5). This technique is used particularly for the restoration of endodontically treated teeth.
Modern composites have excellent physical and mechanical properties, a modulus of elasticity (10-26 GPa) comparable to that of dentin, and wear behavior similar to that of amalgam and enamel with in vivo abrasion of 10 to 50 microns per year, according to the literature.
Caries prevalence has undoubtedly decreased recently owing to the greater motivation of patients and prevention. Minimally invasive dentistry is thus more and more widespread, and it must necessarily rely on adhesive techniques.
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.
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.
Figure 9-9 Clinical case that underscores the main benefits of the adhesive approach. If treated with a traditional technique, this case would inevitably require root-canal treatment of tooth 16 and a subsequent preprosthetic restoration with a fiber post. The tooth would then require a crown-lengthening procedure to reestablish the proper biologic width, and a definitive crown, with severe biologic and financial implications. Instead, using the adhesive technique the procedure was limited to the removal of carious tissue from tooth 28, and the preparation of adhesive buildup and a composite inlay with the indirect technique on the plaster cast, which was then adhesively luted. This procedure respects the principles of sparing tissue, reinforcing the healthy tooth structure, ensuring esthetics, and permitting possible reintervention.
Direct Class I 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).
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).
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.
Among the most reliable classifications, that of the Geneva School (Dietschi and Holz, 1990) divides posterior cosmetic restorations into three categories corresponding to three basic techniques: direct, semidirect (intraoral and extraoral), and indirect techniques.
Regarding the selection criteria of the three methods, the main decision parameters (Dietschi and Spreafico, 1997) rely especially on the following:
Figure 9-12 Example of direct and indirect posterior composite restorations. A, The preoperative clinical picture shows the inadequate metal restoration of the lower right first molar. B, After isolation of the operative site with a rubber dam and removal of the amalgam restoration, the extent of infiltration becomes visible and a carious lesion of the distal surface of the second premolar (already evident on the preoperative bitewing radiograph) can be noted. C, The careful removal of carious tissue creates a large cavity and requires cuspal coverage of the molar (note also the scarce cervical enamel), an indication for indirect restoration, and a small cavity on the premolar, which calls for direct restoration. D, Application of the sectional matrix band to the premolar for the direct composite restoration. E, Buildup in composite material and preparation of the molar for indirect restoration, and complete direct restoration of the premolar. F, Composite overlay. G, Adhesive cementation of the overlay. H, Clinical check. I, The radiographic check shows the accuracy and proper fit of both 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.
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.
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.
Figure 9-13 Treatment of a quadrant by replacing inadequate metal restorations with direct composite restorations (Class I and II cavities). A, Clinical preoperative image. B, Isolation of the operative site with the rubber dam. C, Removal of amalgam and infiltrated tissue, and cavity preparation. D, Conversion of Class II cavities into Class I cavities through restoration of the missing marginal ridges. Knowledge of the layering techniques for occlusal cavities, which will also be used for all Class II cavities, is fundamental. E, Finished and polished restorations. F, Clinical check. G, Bitewing radiograph, which makes it possible to check adaptation of the material, especially in the cervical area.
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.
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 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):
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.
Traditional rotary instruments are unquestionably the most widely used tools in restorative dentistry, and today they can be combined with more up-to-date sonic systems and caries removal instruments based on chemical and mechanical systems (Figure 9-14).
Figure 9-14 A, Small multiblade and rose-head burs, indicated for the first nonaggressive inspection of the grooves; when used at low speed they remove only the decalcified enamel. B, Diamond burs with a thin shank and a small tip to selectively open and clean pits and fissures affected by caries (C). FG burs, for use with a reduction contra-angle handpiece (D).
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).
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).
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).
Figure 9-16 Example of vertical slot preparation.
Figure 9-17 Example of horizontal slot preparation. A, Isolation of the operative site with the rubber dam. The carious lesion on the first premolar is clearly visible. B, Horizontal slot cavity preparation below the marginal ridge and its preservation. C, Final restoration.
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).
Preparing a horizontal slot with rotary instruments alone can be difficult. After the first access is created with burs, cavity preparation can be completed with sonic tips. In nonesthetic and difficult-to-access areas it is advisable to perform the restoration with a material in a different color with respect to that of the adjacent tissue in order to facilitate finishing and checking of the cavity margins over time.
Figure 9-18 Treatment of an interproximal lesion with sonic instruments. A, Isolation of the operative site. Note the mesial carious lesions on the molar. B, Verification of instrument access. C, Final cavity preparation. D, Final restoration. E, Check after rubber dam removal.
In this case as well, rotary instruments are used to access the area. After a large portion of the marginal ridge has been removed, the preparation is completed with sonic tips in order to shape and finish the cavity.
Figure 9-19 Use of sonic instruments for the preparation of small interproximal cavities. A, Clinical preoperative image. B, Isolation of the site with a rubber dam and initial access to the carious lesions with rotary instruments. Note the obvious presence of carious dentin below the enamel of the marginal ridge. C, Completed excavation with burs (medium-speed diamond burs and carbide burs at low speed). D, Cavity preparation with sonic tips. E, Placement of the matrix band. F, Layering of the marginal ridge. G, Final restoration. H, Clinical check showing the color integration of the material.
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).
Figure 9-20 Treatment with a chemical-mechanical system. A, Isolation of the operative site. B, Removal of carious enamel with rotary instruments in order to gain better access to the lesion. C, Application of the gel (Carisolv), which should act for a few minutes before excavation of the softened tissue can commence. D, Instruments used to excavate the carious dentin. E, Cleaned cavity. F, Final restoration.
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 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.
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).
Figure 9-21 Tips for air abrasion.
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).
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).
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.
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.
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).
Considering that the various traditional and more modern methods of cavity preparation can be combined in order to streamline and enhance the outcome of individual procedures, “conventional” preparation can be classified into the following:
Figure 9-24 Preventive restorations. A, Isolation of the lower first molar of a young patient with a rubber dam: apparent carious involvement of pits and fissures. B, Preparation of small cavities. C, Implementation of preventive restorations with the bulk technique.
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.
Figure 9-25 A, Preoperative image of two lower molars with caries of the pits and fissures. B, Isolation of the operative site with a rubber dam. C, Selective opening of the carious grooves and execution of small rounded cavities. Note the extremely conservative approach: Cavity shape is dictated solely by the extension of the carious process. D, Preventive restorations performed with flowable composite combined with microhybrid composite, using the bulk technique for the superficial portions and horizontal layering for the deeper areas. E, Clinical check after rubber dam removal.
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).
Figure 9-26 Sealing of a lower left first molar of a young patient with mixed dentition. A, Clinical preoperative image. B, Isolation of the tooth with a rubber dam. C, Cleaning and cleansing with a bicarbonate jet and small ameloplasty of the affected grooves. D, Etching. E, Appearance of the grooves after etching. F, Adhesive procedures and sealant application (flowable composite). G, Sealed tooth.
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).
Figure 9-28 Second upper molar with carious grooves. A, Isolation of the tooth with a rubber dam. B, Initial opening of the grooves. C, Enlargement and deepening of the central cavity. Note the obvious dentinal extension of the caries. D, Completed preparation of the adhesive cavity: careful removal of carious tissue, rounding of the internal angles, and finishing of cavity margins. E, Composite restoration with direct technique and horizontal layering.
Conventional chamfer preparation is used for cavities created by the replacement of metals. The general shape of the cavity is dictated by the preexisting restoration. After removal of any residual infected tissue, preparation requires adjustment of the internal angles by rounding and finishing of the margins, which will transform the cavity into an adhesive cavity (Figure 9-29).
Figure 9-29 Replacement of old amalgam restorations. A, Preoperative image. B, Isolation of the operative site with the rubber dam. C, Removal of faulty restorations and preparation of the cavities. D, Adhesive procedures: selective enamel etching. E, Layering, finishing, and polishing the material. F, Final restorations.
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.
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).
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).
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.
During the shaping stages of the layering techniques, anatomic layering is required with the placement of the first layer of dentin mass, in order to recreate the proper inclination of cusp slopes. This must be combined with correct groove depth to create sufficient space for the next apposition of enamel masses (0.5 to 1 mm) and thus ensure a correct anatomic and esthetic result.