Direct Resin Restorations: Treatment Planning and Protecting the Dentin-Pulp Complex
Luiz N. Baratieri, CD, MS, PhD
Over the last decade, the use of composite resins for the direct restoration of posterior teeth has significantly increased due to aesthetic demands and the desire to preserve sound tooth structure during cavity preparation.1-4 With the development of adhesive systems5,6 and improved restorative resins,2,7,8 composite restorations are predictably successful (Figures 1-2-3).9 In order to restore posterior teeth with direct composite resin, however, the clinician must alter basic treatment concepts that apply to nonadhesive restorative techniques, which include diagnosis, cavity design, pulp protection, and restoration maintenance.10-12
Composite resin restorations are technique sensitive,10,13 particularly in the posterior region where access, visibility, and moisture are difficult to control.3,14 Despite these challenges, it is evident that composite resins are gaining popularity as the restorative material of choice.1,5,15 The objective of this article is to present updated information related to the use of composite resins for the restoration of the posterior dentition.
Advantages and Limitations
A primary advantage of adhesive composite resins to restore posterior teeth is the possibility of preserving sound tooth structure during cavity preparation (Figures 4-5-6-7-8-9).16,17 The preparation for a composite resin restoration is generally limited to access to the lesion/defect, removal of the diseased tissue, and development of a cavity form to facilitate matricing and application of the restorative material. It is not necessary to reduce sound tooth structure to provide “bulk for strength,” nor is it necessary to remove unsupported enamel or to provide mechanical retention.18,19
Secondly, composite resin restorations represent a significant aesthetic treatment option,20 enabling the fabrication of restorations with a natural appearance. The use of composite resins also provides strength to weakened tooth structure and postoperative comfort due to their low thermal conductivity.1,3,4,21
A precise restorative technique is essential in order to properly use this modality.12 Sensitivity to the moisture in the mouth, limited adhesion to dentin, and polymerization stresses generated during lightcuring6,22 represent the primary limitations associated with this technique. These factors are particularly relevant in the posterior quadrant, since it is more difficult to obtain appropriate isolation in these regions as compared to the anterior sector.3
The following factors can also be considered restrictions to the utilization of composite resins on the posterior dentition:3,4,13,23,24
• High coefficient of thermal expansion.
• Low elastic modulus.
• Questionable wear resistance in situations of heavy occlusal stress.
• Possibility of undercuring.
When the proper treatment protocol is maintained, direct composite resins are indicated for the following posterior applications1,3,4,15,25-27:
• Carious lesions where restorative treatment is required.
• Cervical noncarious lesions.
• Restoration replacement.
• Foundations for indirect restorations.
• Provisional restoration of periodontally, endodontically, and prosthetically treated teeth.
• Pit and fissure sealants without utilizing cavity preparation.
In the authors’ experience, the clinician should in each clinical circumstance consider that 1) adequate isolation is mandatory; 2) sound tooth structure must be preserved whenever possible; and 3) treatment should commence only after information on the prevention and treatment of etiologic factors (eg, dental caries and periodontal disease) has been delivered. While this article provides emphasis to the use of direct posterior composite resins on incipient and moderate sized carious lesions, the majority of these principles are applicable to other indications as well.
In order to evaluate the preoperative condition and the necessity of the composite resin restoration, bitewing and periapical radiographs must be recorded to assess the extent of the lesion and to establish the restorative strategy. Vitality tests, prophylaxis, occlusal analysis, shade selection, and, when appropriate, tooth separation, are important steps prior to the initiation of cavity preparation.27,28
While the shade of the composite is not as important in the posterior area as it is in the anterior dentition, several shade options are available in the contemporary composite resin systems, which enable the selection of the composite that best matches the adjacent natural dentition. Since maxillary premolars are often visible from the facial aspect, the shade of the composite resin contributes significantly to the successful restoration of these teeth. Resin tints and pigments are also available to create a lifelike composition when the occlusal area is to be restored. When a rubber dam is used, shade selection should be accomplished prior to its application, due to possible color shifts associated with dehydration.
The occlusal analysis may be an important process when the restoration involves the occlusal aspect, and should be completed prior to the isolation of the operatory field.4 The analysis of the interocclusal relationship between the tooth to be restored and the adjacent teeth can significantly simplify the occlusal adjustment phase of the procedure. The centric and eccentric stops should be registered with articulating paper prior to initiating preparation, and maintained in sound tooth structure or reproduced on the restoration.
Elastic rubber rings can be important diagnostic tools for proximal incipient lesions, facilitating separation that enables the visualization and assessment of the suspect area.27 This evaluation, when performed in conjunction with the anamnesis and the radiographic information, can determine the necessity of tooth restoration.28
Once anesthesia has been administered to the patient, the treatment site is isolated with a rubber dam, which can be applied once preparation has been initiated or even prior to the adhesive protocol. The cavity design for posterior composite resin restorations depends primarily on the size and shape of the existing defect. The preparation of cavities in moderatesized or incipient caries lesions is generally restricted to three steps: access to the lesion, removal of infected carious tissues, and establishment of a cavity convenience form (Figure 10). Proximal incipient lesions may require extensive sound tissue removal as compared to decayed tissue, and the need for restoration must be positively verified,29,30 since these lesions are not always indicated for restorative procedures. For interproximal incipient lesions, it can be useful to temporarily separate the involved teeth to simplify the instrumentation of the lesion. Occlusal and facial access can be performed to prevent the breakage of the marginal ridge.18
Although controversies regarding the use of caries detecting solutions have been raised,31 the authors believe that this is the optimal manner to identify the irreversible infected carious tissue and to guide caries removal. Unsupported enamel can be preserved if it does not compromise the application of matrices and the insertion and polymerization of the restorative material. Bevels are often unnecessary in posterior composite restorations, except in those areas where aesthetics is of paramount importance.32 The cavosurface angle should be clear and well defined, which sometimes can be achieved with reciprocating devices.
The preparation can be performed with high speed burs and diamonds under water irrigation. Carious dentin may be more effectively removed with slow speed carbide burs and dentin spoon excavators. When the restoration involves proximal lesions or defects, or when it is intended to replace defective restorations (either amalgam or composite resin), prewedging may be useful. This step protects the interproximal rubber dam and the papillae, prevents bleeding that could jeopardize the bonding procedures, and promotes a slight separation between the teeth that favor the achievement of adequate proximal contacts. Once the preparation has been completed, the wedge is removed, the matrix is applied, and the wedge is repositioned.
Matricing and Wedging
The selection and placement of matrices to restore proximal boxes with composite resin are very important for obtaining an adequate restoration. Individual thin precontoured metallic matrices are the most suitable to obtain adequate contour and proper interproximal contacts without overhangs (Figures 12 and 13). The technique for applying the matrices varies depending on the faciolingual extension of the proximal box. Alternative systems require the use of thin precontoured metallic matrices and a ring to maintain the position of the matrix and promote a slight separation between the tooth to be restored and the adjacent tooth. The placement and stabilization of the matrix with anatomic wooden wedges should, ideally, be performed prior to the application and polymerization of the adhesive system, which simplifies the application process (Figure 4). The clinician must not allow the fluid resin to accumulate adjacent to the matrix and the internal angles of the cavity. This “pooling” could result in failure and in the misdiagnosis of recurrent decay on the radiograph, since the majority of the fluid resins are not radiopaque.
Protection of the Dentin-Pulp Complex
The clinical need for a protective agent (base or liner) is one of the most controversial issues in restorative dentistry.33 In order to prevent injury to the pulp, it was once believed that it was necessary to apply bases or liners on the exposed vital dentin.34 Recently, however, the failure of restorations has been attributed to the inappropriate sealing of the tooth/restorative interface,35 and a modification of the concepts of “pulpal protection” has occurred.33,36-40
Studies have demonstrated that the pulp possesses an inherent ability to heal, repair, and form mineralized tissue bridges under several restorative materials.41,42 Bacterial leakage has been attributed as a key factor for triggering pulp inflammation and necrosis, regardless of the material used to cover dentin and pulp.43 Additional histological studies have indicated that restorative materials in direct contact with the pulp do not elicit inflammation, maintaining the pulpal metabolism with or without the hard tissue bridge formation, as long as a biological marginal seal is secured.43-45 These data support the concept that the repair of the pulpal tissue does not depend on the type of lining, base, or restorative material, but rather upon the capacity of the restorative material to effectively seal the tooth/restoration interface.
Adverse pulp responses associated with composite resin restorations have been attributed to a variety of factors (eg, nonconverted monomers, contraction stresses, bacterial leakage).4,46,47 As a result of these reports, composite resins and the adhesive systems have not always been regarded as biocompatible materials and, consequently, have been suggested by some not to be used directly on vital dentin. A base or liner has often been utilized to chemically and mechanically isolate the composite resin from the vital tissues. Calcium hydroxide was widely advocated for this purpose prior to 1990, but complications have been reported following its use.39,48 Lining the dentin with calcium hydroxide cement prevents the lined area from being etched and bonded, compromising the effectiveness of the adhesive techniques. The lack of adhesion between calcium hydroxide and tooth structure may also generate a gap at this interface40; this space can be colonized by bacteria and/or act as a “hydraulic pump,” stimulating the flow of the tubular fluid inward. This hydraulic pressure might be responsible for postoperative sensitivity, particularly to masticatory forces.49 Calcium hydroxide based cements may also be visible beneath composite resin restorations. Glass ionomer cements have been recommended as base materials for these restorations to act as dentin adhesive materials,50 mediating the adhesion between the natural tooth and the composite resin. Although glass ionomer cements have several positive properties (eg, fluoride release and effective thermal insulation), the weak bond strength and difficult handling properties of these materials have restricted their broad acceptance.
It is now generally accepted that the hybridization of the exposed dentin with an adhesive system is one of the most effective means of protecting the pulp-dentin complex under composite resin restorations, regardless of the depth of the preparation.6,39,44,45,51 While concepts such as adhesion, material placement, and finishing/polishing are also important considerations, they are beyond the scope of this presentation and will be discussed hereafter.
*Department of Operative Dentistry, School of Dentistry, Universidade Federal de Santa Catarina, Florianopolis, SC, Brazil
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