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» Articles -> Smile Magazine Issue 5 September 2007-> Simplifying the Layering Technique in Daily Practice
Dated : 2007-09-01
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Simplifying the Layering Technique in Daily Practice

 

 » By: Dr. Joseph Sabbagh

DDS, MSc, PhD
Cosmetic and operative dentistry

“Chargé d’enseignement”, Saint Joseph University-Lebanon
“Chargé de cours” Lebanese University-Beirut, Lebanon
Lecturer, Dental College, Beirut-Lebanon
Fellow Researcher, Catholic University of Louvain, Belgium

PO Box 257.
1253/ 2020 Mansouriet El Metn
Lebanon josephsabbagh@hotmail.com

 

 

What is layering technique and why to use it?

Resin composites are widely used in our daily practice to answer the increasing aesthetic demand of our patients. In the past, clinicians were using hybrid and microfilled composites to combine in the same restoration optimal mechanical to aesthetic properties. Nowadays, and due to the improvement of composite systems, they can be used in anterior as well as in posterior restorations.

The layering technique or stratification is a modern concept allowing the dentist to achieve high aesthetic restorations using new systems of resin composites. It reproduces the shade and the colour of the tooth using the optical properties of dentine and enamel shades, and colour modifiers. It allows optimal light transmission within the restoration providing a more realistic depth of colour and surface characteristics of the tooth (Vanini, 1996). The anatomy and the shape of the tooth should guide the clinician in recreating the correct form and colour.

 

 » (Table 1)

Examples of previous and recent composites systems.

 

 

 

 

 

 

 

 

 

Beside providing a full control on the shade of the tooth, the layering technique has many advantages, such as improving resin adaptation on the cavity margins, and thus the optimal anatomical contour of the tooth. Also polymerisation shrinkage is reduced through the insertion of increments in such a way to decrease the configuration factor (C-Factor) (Versluis, 1996).

Resin composite systems can be considered according to their aesthetic properties (number of shades and opacities). Most of the previous systems of composites included a limited number of shades and only one opacity (Table 1). Recent kits of composites include a wide range of shades divided into three different levels of opacities; opaque, body and translucent. Depending on the depth of the cavity, at least one, two or three different opacities are used to restore the missing structure of the tooth, enamel and dentin.

Successful anterior restoration starts with an adequate shade selection, better known as “shade mapping” (Figure 1). Usually, the shade mapping of the tooth is determined according to three parts; the cervical, the body and the incisal thirds of the tooth.
A custom made shade guide is preferably used to select the shade, instead of the shade guide provided with the composite system. The latter has a different composition than the hand-made shade guide, fabricated from the same composite used for the restoration (Douglas 2003).
The thickness of enamel and dentine varies according to tooth anatomy and physiology. For instance, the cervical third of the upper canine is more yellowish than the rest of the anterior teeth, due to the thinner layer of enamel. This region is used to determine the shade of the dentine.
The shade body and the saturation of the tooth are determined by the median third of the tooth, while the incisal third (thick enamel layer) will determine the “vitality” of the tooth and its translucency (Douglas, 2003). Young patients have the incisal edges of their teeth more translucent due to the enamel thickness.

The physiological modifications that may occur during a tooth life cycle, will a affect the shade and the saturation of the tooth. According to the depth and the location of the cavity one, two or three opacities will be used for restoration.

» (Fig. 1)

Shade Selection

 

  

 

 

  

Starting from left: (Fig. 2 Case1): Preoperative view of the central (11) and the lateral incisors (22), presenting a defective Class IV and III restorations / (Fig. 3 Case 1): Cavities ready for restoration after rubber dam isolation, translucent Stopstrip matrix and wood-wedge placement. Note the irregular aspect of the bevel that enhances the esthetic outcome of the restoration / (Fig. 4 Case 1): Postoperative view reflecting the harmonious integration of composite restorations with tooth structure after using the layering technique.
          

Materials used for the layering technique

Composite materials are used to replace lost dental tissue, enamel and dentin. Consequently their properties must be as close as possible to those of the dental tissues. Regarding their mechanical properties, recent composite systems have excellent mechanical behaviour (Sabbagh et al; 2002). Concerning their optical and aesthetic properties, their refractive index, shades and opacities ensure the polychromatic effect, that mimics natural teeth appearance (Douglas, 2004 a). Also their polishability and color stability plays an important role in the aesthetic outcome.

» (Table 2)

Modern composite systems, with different opacities, used for layering technique.

 

 

Table 2 shows some examples of modern composite systems used for layering technique. Those systems include at least three different opacities used from the deep part of the cavity to the surface in order to replace the dentin and enamel.
Many factors influence the choice of the composite opacity and the thickness of the layer;  the age of the patient, the restored tooth, and the location of the cavity.

 

» Starting from left:

(Fig. 5 Case 2): Preoperative view a wide crown fracture on tooth number 11. /

(Fig. 6 Case 2): Field  isolation, matrix and wood-wedge placement.

  
Starting from left: (Fig. 7 to fig. 9 Case 2): Stratification steps using small increments of different opacities of resin composite.

 

 » (Fig. 10 Case 2)

Postoperative appearance of the class IV restoration following the finishing and polishing procedure.

             

 

Usually opaque dentin composite is selected for strength and color. Those materials have similar refractive properties and colors to that of dentin, and have enough resistance for most of stress bearing regions.  A three dimensional space around the dentin core must be managed for the translucent enamel layer in order to allow an internal diffusion of the light and a control of the restoration luminosity. The artificial enamel layer is the principal determinant of the value of the restoration (Douglas 2004 a) 

Achieving a predictable layering technique

The bonding procedure will not be discussed in this paper, but the use of a performing adhesive system according to the manufacturers recommendations, is a very important element for the success of the restoration.

Several techniques and procedures such as the use of prefabricated translucent crowns, the use of a mock-up and the free hand techniques can be used to build imperceptible restorations. The free hand technique offers the possibility to reproduce the ideal proportions, shapes and anatomy (Vargas, 2006). In class III and IV restorations, the matrix is pushed tightly towards the palatal side of the tooth before inserting first, the opaque layer of composite. This will ensure a perfect adaptation and anatomy of the tooth, avoiding any palatal excess (Figure 3 Case 1).

The build up of the restoration will be performed using layers of composites, arranged in different geometrical aspects in order to reproduce the anatomy of the tooth (Figures 6-10). Each increment is gently placed and adapted to the cavity walls using a clean non-sticking condenser (Figure-8). Several instruments, usually thin, with various shapes and lengths will be used for this purpose. The number of layers is dictated by the volume of the cavity.

To prevent overbuilding of the dentin layer, it is imperative to monitor the thickness of the composite material, in order to allow sufficient space for the enamel layer. Moreover the opaque dentin layer must remain below the bevel performed on the buccal surface of the tooth to increase the surface of retention and improve the adaptation of the composite shade (Figure 7). Then the body shade of the restoration is placed (Figure 8), and on the incisal edge (class IV), enough space is managed for the enamel layer according to the age of the patient, and the size of the cavity. The colorless layer of enamel determines the value of the natural tooth (Figure 9).

The facial surface is then smoothened before polymerization, with a sable brush. In some cases, additional characterization can be achieved by the use of color modifiers and tints, in order to enhance the aesthetic result (Douglas, 2004 b). 

Each layer of composite will be polymerized from the facial and lingual side, using a powerful and efficient light-curing unit, with a minimum power of 600 mW/cm2. This will ensure optimal degree of conversion and thus optimal mechanical behaviour of the restoration. The finishing and polishing procedure of the restoration is a final step that must be done properly using the adequate instruments, (discs, burs and polishing paste) in order to ensure the harmonious integration of composite resin with the tooth structure (Figure 10).

Conclusion

Despite the development achieved in the field of resin composites and adhesive systems, the selection of a composite resin is not the only guarantee of a successful composite restoration. The use of an adequate bonding procedure, combined to an accurate layering technique will enable the dentist to attain excellence in direct anterior restorations while preserving tooth structure.

References

Douglas T, Color matching with composite resin: A synchronized shade comparison. Pract Periodont Aesthet Dent, 2003; 15(7) : 515-521.

Douglas T, Direct applications of a nanocomposite resin system, part 1. Pract Periodont Aesthet Dent, 2004 a; 16(6) : 417-422.

Douglas T, Direct applications of a nanocomposite resin system, part 2. Pract Periodont Aesthet Dent, 2004 b; 16(9) : 677-684.

Sabbagh J, Vreven J, Leloup G. Dynamic and static moduli of elasticity of resin based materials. Dent Mater 2002; 18: 64-71.

Vargas M, Pract Periodont Aesthet Dent, 2006; 18(8) : 501-507.

Versluis A, Douglas WH, Cross M, Sakaguchi RL; Does an incremental filling technique reduce polymerisation shrinkage stresses? J Dent Res 1996; 75(3) : 871-878.

Vanini L. Light and color in anterior composite restorations. Pract Periodont Aesthet Dent 1996; 8(7) : 673-683.

 

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