The polymerization process of composite resins should be carried out carefully, with a correct technique for inserting the material, respecting the recommended manufacturer times and using suitable light-curing equipment. Direct composite resins have a lower fracture toughness and lower color stability than ceramics⁴. Also, due to their physical properties and the microbubbles that form from handling the material, direct composite resins generally require periodic maintenance to maintain their surface and interface with the tooth structure, taking both esthetics and optimal biologic aspects into account.

Indirect composite resin restorations are made on extraoral models mounted on an articulator. These models can be obtained analogically from impression materials or digitally through the use of intraoral scanners. The latter method is preferred for resolving cases with multiple restorations or for situations in which the objective is to reduce clinical time.

Laboratory fabrication aims to minimize some of the limitations of the material. It can provide a higher degree of polymerization and, consequently, better physical properties such as flexural strength, abrasion resistance, fracture toughness, hardness, and color stability. The adhesive cementation can compensate for the polymerization shrinkage during restoration fabrication. Composite resins are repairable and cause low wear on the opposing teeth.

Despite all the advantages mentioned here, the dentist must consider that tooth preparations should have divergent walls, and thus increased preparation is required. The need for an intraoral impression or intraoral scan and more than one appointment should also be considered, and laboratory costs must also be taken into account.

Indications preferred by the author

Direct composite resins are routinely used for conservative restorations in anterior and posterior teeth. They are an excellent option in teeth with chromatic changes or where contour modifications are required because they allow the dentist to control many variables in terms of morphology as well as the management of shade changes. They are the first treatment option in posterior teeth whenever the structural condition allows, as is discussed later in this chapter [Figures 4-01 to 4-05].

[Figure 4-01A–H] The alteration of tooth morphology and chromatic aspects of anterior teeth can be performed effectively with direct composite resin restorations (Case 1 [A–D] and Case 2 [E–H]).

[Figure 4-02A–D] Composite resin restorations can be a solution with good longevity when their indications and the necessary technical recommendations are respected. Photographs [A] and [B] show the initial situation of a 14-year-old patient after the completion of orthodontic treatment in 1998. Photographs [C] and [D] show the patient’s restorations in 2019, after 21 years in the mouth, presenting some esthetic changes concerning shade and interfaces but with preserved morphology and an acceptable general condition.

[Figure 4-03A–D] The indication of composite resin for the restoration of discolored teeth allows the control of esthetic factors by the dentist. In these cases, tooth preparations should follow the morphologic and chromatic needs of the tooth.

[Figure 4-04A–C] To maintain a minimally invasive approach, composite resins can be used in conjunction with ceramics. In this case, a full crown was planned for tooth 21 due to the high degree of destruction, while tooth 11 would receive composite resin restorations to harmonize the esthetics of the smile.

[Figure 4-05A–C] Composite resin restorations for posterior teeth can have considerable longevity, as can be seen in this case carried out in 1996 (Z250; 3M, USA) [A,B] and reassessed after 24 years [C]. It is necessary to consider that the conditions of these restorations in the long term will depend on some factors related to the patient such as the remaining tooth structure, functional and parafunctional patterns, habits, commitment to daily oral hygiene, and periodic follow-up.

Indirect composite resins are mainly indicated for posterior teeth in inlays and onlays, usually when structural destruction is significant, due to the possibility of effective restoration of dental morphology, the coverage of weakened cusps, and the reestablishment of interproximal contact points [Figure 4-06A–C].

[Figure 4-06A–C] In extensively weakened teeth, especially those that have undergone endodontic treatment [A], indirect restorations with cuspal coverage are recommended. A core buildup of adhesive material was performed with the objective of structural reinforcement and leveling of the walls, and tooth preparation was performed [B]. The indirect composite resin restoration after cementation [C].

Ceramics

Dental ceramics have favorable esthetic characteristics and physical properties and are ideal for various indications. In this chapter, ceramic restorative materials are classified into three families: 1) glass matrix ceramics; 2) polycrystalline ceramics; and 3) resin matrix ceramics.

1. Glass matrix ceramics

The family of glass matrix ceramics can be subdivided into three subgroups: feldspathic ceramics, leucite-reinforced glass-ceramics, and lithium disilicate-reinforced glass-ceramics. Full crowns and metal-ceramic fixed prostheses are also discussed because they form part of the material selection.

Feldspathic ceramics

Feldspathic ceramics are materials with high esthetic potential although they are dependent on the expertise of the DLT for layering to achieve natural results and a precise marginal fit. They have a flexural strength of around 90 to 120 MPa and a fracture toughness of 1.2 MPa/m^0.5. These characteristics are critical during the laboratory and clinical manipulation of these materials and limit their indication for patients with signs of parafunction. Crystalline particles, such as leucite or fluorapatite, may be added in small proportions to increase their resistance, modify their optical properties, or adjust their thermal expansion coefficient to be used on metallic infrastructures⁵.

Feldspathic ceramic blocks are available for milling with a flexural strength of around 140 MPa. This increase in flexural strength is due to the reduction of porosities, impurities, and microcracks inherent in the laboratory sintering process of these blocks. However, because they are industrially processed blocks, the esthetic result may be limited, especially in single-unit restorations. Extrinsic pigments, called “staining,” or even additional ceramic layering may be required.

Adhesive cementation considerably increases the strength of ceramics⁶. Their internal surface must be etched with 10% hydrofluoric acid (HF) for 60 to 90 seconds (s). Sandblasting the internal surface with aluminum oxide (Al2O₃) is not recommended due to the risk of cracks⁷. After application of the HF, wash vigorously with air-water spray and place in an ultrasonic bath with distilled water for 5 minutes (min). The ceramics should then be dried with air and receive one layer of silane, which should be dried after 1 min. They can then receive a resin without fillers, or the cement directly, as long as they have an adequate viscosity.

Indications preferred by the author

Feldspathic ceramics are suitable for veneers and full crowns in adult patients with morphologic alterations in the anterior teeth. They allow excellent results in cases of shade discrepancies. However, the amount of tooth preparation depends on the degree of the disharmony and the dexterity of the DLT. Due to their low mechanical properties, they should only be indicated for posterior teeth as a veneering material over metallic or ceramic frameworks [Figure 4-07A,B].

[Figure 4-07A,B] After conversations with the patient depicted in Figure 4-02, it was decided to remove the restorations and fabricate feldspathic ceramic veneers for the anterior teeth.

Leucite-reinforced glass-ceramics

Leucite crystals are added to the ceramic matrix at about 40% to 50% (by volume) to increase its strength and modify its optical properties.

Leucite-reinforced glass-ceramics can be utilized – analogically or digitally – in three different ways: 1) For the reproduction of the final anatomy in a monolithic block; 2) For the elaboration of the final morphology, strategically reduced in esthetic areas (cutback) and complemented by the layering of feldspathic ceramic with partial coverage; 3) To be used for the infrastructure (coping) and complemented by a full-coverage feldspathic ceramic layer.

Although layering allows for a potentially superior esthetic result, the final strength of the restoration will be related to the intrinsic mechanical properties of the feldspathic veneering ceramic and the possibility of technical failures such as the incorporation of bubbles, cracks, or impurities during the fabrication process. On the other hand, monolithic materials have the advantage of being uniform and having superior mechanical properties when used in the thicknesses recommended by the manufacturer. However, color correction of darkened substrates with these materials is critical due to their inherent translucency, especially for single-unit restorations.

These restorations can be made in the dental laboratory by pressing at high temperatures or milling prefabricated blocks in CAD/CAM systems. The pressed materials have high predictability regarding their manufacturing technique and a low cost, but they tend to be monochromatic and dependent on staining techniques with extrinsic stains. The prefabricated blocks have gradients of saturation or translucency, enabling superior esthetic results with less dependence on staining techniques. It should also be noted that tooth preparations need well-defined margins, rounded angles, and a precise finish⁸, as the burs of the CAD/CAM system have difficulty reproducing irregular margins⁹.

The injected leucite-reinforced ceramics have a flexural strength of around 140 MPa and fracture toughness of 1.3 MPa/m^0.5. Values of 185 MPa have been reported for milled ceramics due to the homogeneity of their composition¹⁰. Such values make these ceramics widely used in esthetic cases, but they have a more restricted indication when parafunctional activities are diagnosed during the clinical examination.

[Figure 4-08A–L] presents various treatments with feldspathic ceramic veneers and crowns on anterior teeth.

[Figure 4-08A–L] Examples of esthetic and interdisciplinary treatments with feldspathic ceramic veneers and crowns on anterior teeth.

The dentist and DLT should be attentive to the selection of available products. For example, in the IPS Empress Esthetic System¹⁰ (Ivoclar Vivadent, Liechtenstein), 12 types of ingots with 7 different degrees of translucency are currently available for pressed restorations. IPS Empress CAD (Ivoclar Vivadent) has options with high translucency, low translucency, and multi-block (polychromatic, color transition, translucency, and fluorescence).

According to the manufacturer’s recommendations, these ceramics should have their internal surface etched with HF at 5% for 60 s. After acid etching, they should be vigorously washed with air-water spray and placed in an ultrasonic bath with distilled water for 5 min. They should then be air dried and receive a layer of silane, which should be dried after 1 min. The ceramics can then receive the application of a resin without filler or cement, as long as they have an adequate viscosity.

Indications preferred by the author

These materials have similar indications to feldspathic ceramics used for veneers or full crowns on anterior teeth (up to the premolar region), in addition to inlays, onlays, and veneers. It is recommended to avoid them in areas with a high concentration of forces or in patients with parafunctional activities. Due to their varied commercial availability, they allow the selection of ingots or blocks that are more translucent when the substrate’s color is favorable or less translucent when masking is required. Due to their milling characteristics and optical properties, leucite-reinforced glass-ceramics have shown satisfactory results in CAD/CAM systems. Single-unit cases usually require the cutback technique for individualization [Figure 4-09A–C].

[Figure 4-09A–C] Clinical case performed with leucite-reinforced glass-ceramic veneers on teeth 11 and 21.

Lithium disilicate-reinforced glass-ceramics

Lithium disilicate crystals are added to the glass matrix at about 70% (by volume) to improve its physical properties. Lithium disilicate-reinforced glass-ceramics have broad indications such as veneers, full anterior crowns, full posterior crowns, inlays, onlays, and three-unit fixed prostheses (up to the premolar region).

Like leucite-reinforced glass-ceramics, these materials can be processed analogically or digitally. A cut-back or a coping with a ceramic layer can be used to achieve the final morphology. The restorations can be pressed at high temperatures or milled as prefabricated blocks in CAD/CAM systems. Although the layered technique allows a potentially superior esthetic result, the final strength of the restoration will be related to the strength of the veneering material and the possibility of the incorporation of bubbles, cracks, or impurities during the fabrication.

Lithium disilicate-reinforced glass-ceramics have excellent mechanical properties due to the high concentration of randomly oriented needle-shaped crystals, which hinder the propagation of cracks¹¹. The pressed restorations have a flexural strength of around 400 MPa and a fracture toughness of 2.75 MPa/m^0.5. The milled variations have a flexural strength of 360 MPa because they have lithium disilicate crystals of a reduced size, and a fracture toughness of 2.25 MPa/m^0.5/12. These materials are often chosen by this author in cases with high functional demands (FDs) and signs of parafunctional activity.

The dentist should pay attention to the shape, finish line, and polish of tooth preparations when the work is performed in CAD/CAM systems, since such systems have difficulty reproducing irregular finishing lines⁹. Another aspect related to tooth preparation is that due to the high translucency of some ingots or blocks of this material, different thicknesses between teeth will cause different optical effects.

Lithium disilicate-reinforced glass-ceramics have excellent esthetic potential, with varying degrees of opacity, translucency, and fluorescence. The clinician should be aware that different ingots or blocks have different degrees of fluorescence, which may compromise the esthetic results¹³.

For the pressed technique with the IPS e.max Press system¹², for example, different products with specific indications are available as ingots of varied translucency or opalescence (high translucency, low translucency, medium opacity, high opacity, and “impulse” [values and varied opalescences]). For the IPS e.max CAD system, blocks with high translucency, low translucency, and medium opacity are available. In this author’s practice, materials with high translucency are typically used over partial preparations when the color of the substrate is favorable and for full crowns of medium or high translucency, depending on the substrate and the value of the adjacent teeth.

According to the manufacturer’s recommendations, these ceramics should have their internal surface etched with HF at 5% for 20 s. Sandblasting with Al₂O₃ particles is not indicated due to possible cracking of the material⁷. After acid etching, they should be vigorously washed with air-water spray, but an ultrasonic bath with distilled water does not seem to be critical for this material¹⁴. They should then be air dried and receive a silane layer, which should be dried after 1 min. The ceramics can then receive the application of a resin without fillers or cement, as long as they have an adequate viscosity.

Indications preferred by the author

This type of ceramic has a wide range of indications. It is recommended for anterior veneers and full crowns, for anatomical and chromatic restorations, and in cases where greater structural strength is required, as is explained later in this chapter. It can be used in inlays, onlays, overlays, veneers, and full crowns in posterior teeth.

Due to the many commercially available options of this material, it is possible to select ingots or blocks that are more translucent when the substrate color is favorable, or more opaque when masking is required. Lithium disilicate-reinforced glass-ceramics have shown satisfactory results in CAD/CAM systems due to their milling characteristics and optical and mechanical properties. In single-unit cases, the cutback technique is usually required to customize the restorations [Figure 4-10A,B].

[Figure 4-10A,B] Previous restorations were made with lithium disilicate-reinforced glass-ceramics using the cut-back technique to obtain a more personalized layering and natural esthetics.

Metal ceramics

Full crowns and metal-ceramic fixed prostheses have been used for over 60 years, with high survival rates reported in the literature¹⁵. The esthetic potential of these materials largely depends on tooth preparation and DLT expertise. They require considerable preparation (average 1.0 to 1.2 mm) and intrasulcular positioning of the margins in esthetic areas. In order to achieve satisfactory esthetic results, the DLT must have the necessary knowledge and technical experience with opacification and ceramic layering.

Feldspathic ceramics that cover a metallic infrastructure have compressive strength between 350 and 550 MPa¹⁶ but low flexural strength and fracture toughness. Due to the presence of leucite crystals, used to adapt the coefficient of thermal expansion of the ceramic to the metal, this material has a fracture toughness about 50% higher than feldspathic ceramics for covering a zirconia infrastructure¹⁷, in addition to being more resistant to cyclic fatigue, which explains its excellent clinical longevity^18–20.

Cementation of metal-ceramic restorations can be performed with traditional cement, such as zinc phosphate and resin-modified glass ionomer, or even with chemically polymerized resin (preferably) or types of dual-cure cements.

Indications preferred by the author

Although the development of new all-ceramic or resin materials has reduced some of the indications for metal-ceramic crowns, they can replace existing prostheses – especially in posterior teeth – with intrasulcular margins, metallic intraradicular retainers, and dental implants. This material is also a good choice in cases of tooth- or implant-supported fixed prostheses due to its strength and longevity^21,22. It is advisable to recommend metal ceramics once the patient is aware of the reasons for their indication as well as their limitations, especially in patients with high esthetic expectations (EEs) [Figure 4-11A–F].

[Figure 4-11A–F] A metal-ceramic crown with a ceramic shoulder made in an anterior tooth with a discolored substrate.

2. Polycrystalline ceramics

Polycrystalline ceramics are subdivided into four subgroups: alumina, stabilized zirconia, zirconia-reinforced alumina, and alumina-reinforced zirconia. This family of materials has a crystalline structure capable of providing strength and fracture toughness to the material. However, the absence of a vitreous phase results in a limited degree of translucency and restrictions to etching their internal surface with HF²³. This text addresses polycrystalline ceramics that are more widely used today.

Yttrium oxide partially stabilized zirconia (Y-TZP)

Zirconia, or zirconium dioxide, is a polymorphic material with three crystalline phases: monoclinic, tetragonal, and cubic²³. In its pure state, zirconia is monoclinic at room temperature, presenting mechanical and optical properties unsuitable for dentistry. Adding an oxide (yttrium [~3% in mol]) stabilizes the zirconia in its tetragonal phase, which has more favorable physical properties for clinical use. In a more recent generation of zirconia, the incorporation of yttrium was performed in slightly higher proportions (~4% to 5% in mol), increasing the cubic phase in the material. This increase, associated with larger zirconia grains and the reduction in alumina content, improved the optical characteristics, such as its degree of light refraction and reflection and the consequent perception of the value and translucency of the restoration, to the detriment of its mechanical properties like flexural strength and fracture toughness^24–27.

Zirconia restorations can be made in a monolithic manner, milled according to their final anatomy, stained to achieve the desired shade, milled according to the final morphology with cutback or even as infrastructure or copings, and complemented by stratification veneering ceramic [Figure 4-12A–D]. This way, they will have a less opaque and more natural appearance. However, their resistance is related to the veneering ceramic as well as the rigor of the DLT in following the manufacturer’s specifications regarding the firing and cooling cycles in order to avoid cracks and delamination^26,28,29.

[Figure 4-12A–D] Posterior restorations milled from CERASMART (GC). Tooth preparations [A,B] and crowns and onlays after cementation [C,D]. (Clinical case kindly provided by Dr. Luis Gustavo Barrote Albino.)

Zirconia has a flexural strength ranging from 300 to 1,590 MPa and a fracture toughness ranging from 2.3 to 8.0 MPa/m^0.5, depending on the percentage between its tetragonal and cubic phases²⁶. Translucent zirconia is found in polychromatic blocks containing gradients of cervical opacity and incisal translucency, such as KATANA Zirconia ML (Multi-Layered), KATANA Zirconia STML (Super Translucent Multi-Layered), and KATANA Zirconia UTML (Ultra Translucent Multi-Layered) (Kuraray, Japan), indicated for full crowns, inlays, onlays, and even veneers, due to its translucency and natural color gradient. However, the translucency increase is accompanied by a mechanical decrease due to an increase in the cubic phase. Thus, ML has about 50% cubic phase (by weight), STML about 65%, and UTML about 75%³⁰. The flexural strength of the latter is only 300 to 350 MPa³¹.

There are some concerns regarding zirconia’s long-term stability such as the low-temperature degradation that occurs in the mouth due to contact with moisture, occlusal stresses, temperature changes, and polishing, in addition to the significant amount of chipping and delamination reported in the literature^32–34.

The cementation of zirconia is predictably performed by sandblasting its internal surface at a distance of 10 millimeters (mm) with Al₂O₃ particles between 27 and 50 micrometers (μm), in circular motions, with low pressure (up to 2 bars/30 psi), for about 20 s. This is followed by the application of a ceramic primer containing the phosphate monomer 10-methacryloyloxydecyl dihydrogen phosphate (MDP), e.g. Ceramic Primer (Kuraray, Japan), and a resin cementing agent^7,35–37. Conventional types of cement may also be indicated in cases of full crowns or fixed zirconia prostheses when the tooth preparations have acceptable retention and resistance forms.

Indications preferred by the author

This material is used for cases of anterior and posterior full crowns, especially where there are severe structural impairments or unfavorable substrate discoloration. It can be used for fixed prostheses over teeth and implants. Although translucent zirconia is indicated for veneers, this author has not used it thus far for this indication due to the lack of long-term results concerning the stability of its adhesive interface.

3. Resin matrix ceramics

This category comprises materials with a resin matrix concentration greater than 80% (by weight) of ceramic particles^23,38. The industrial polymerization process under high pressure and heat significantly increases the degree of conversion and the percentage of cross-linking in the polymer network, improving its characteristics. The physical properties of these materials such as flexural strength, fatigue strength, elastic modulus, and low wear of the opposing dentition³⁹ make them particularly suitable for inlays, onlays, and full posterior crowns. They can also be used for full anterior crowns or even veneers. However, in this author’s opinion, their esthetic attributes do not make them the material of choice for restoring the buccal surfaces of maxillary anterior teeth.

According to Duarte Jr et al³⁸, based on the method of incorporating the ceramic in the resin matrix, these materials can be divided into:

a) Nanoceramic resin: This consists of a highly polymerized resin matrix reinforced with silica nanoparticles, sometimes accompanied by zirconia (approximately 80% by weight). Examples include Lava Ultimate (3M ESPE), Grandio (VOCO), Shofu Block HC (Shofu), and CERASMART (GC). The flexural strength of Lava Ultimate is between 170 and 180 MPa, and that of CERASMART is between 220 and 240 MPa^40,41.

b) Polymer-infiltrated ceramic: This is composed of a pre-sintered feldspathic ceramic block (86% by weight) infiltrated with polymers (14% by weight), e.g. Vita Enamic (Vita Zahnfabrik).

High translucency blocks are commercially available and generally indicated for minimally invasive restorations, and low translucency blocks are used for full crowns. All these materials are milled quickly and accurately in CAD/CAM systems due to their reduced hardness and low friability^40,42,43. In addition, they behave well at reduced thicknesses, providing good adaptation and marginal integrity⁴⁴. External characterization agents have the potential to customize the material to achieve a good esthetic result, but they have questionable longevity^45,46. Clinically, they are materials that are easy to try in, adjust, polish, or repair, when necessary.

All resin matrix ceramics need to be cemented with adhesive types of cement, having protocols for optimizing results according to the general recommendations below (subject to specific requirements for each product):

a) Nanoceramic resin: After clinical adjustment, clean the restoration in an ultrasonic bath with distilled water for 5 min; sandblast with AI₂O₃ from 27 to 50 μm for 5 to 20 s, depending on the size, until the surface becomes dull; wash vigorously with air-water spray; clean with alcohol and air dry for 20 s; use the ceramic primer or universal agent from the cement system for 20 s and then air dry for 5 s; apply dual-cure cement and light cure for 20 s on each side of the restoration^47,48.

b) Polymer-infiltrated ceramic: After clinical adjustment, clean the restoration in an ultrasonic bath with distilled water for 5 min; etch with 5% HF for 60 s (note: sandblasting with AI₂O₃ is optional); wash vigorously with air-water spray; clean the restoration with alcohol and air dry for 20 s; apply one layer of silane without agitating and allow it to react for 60 s; rub in the universal cementing agent for 20 s and dry for 5 s; apply dual-cure cement and cure for at least 60 s on each side of the restoration^47,49,50.

Indications preferred by the author

Resin matrix ceramics have similar indications to those of indirect composite resins; that is, they are mainly used for posterior teeth in cases of inlays, onlays, overlays, and veneers when the structural destruction is significant due to the possibility of the effective restoration of the dental morphology, covering of weakened cusps, and restoration of interproximal contact points. These materials can also be used to restore the lingual surface of anterior teeth.

[Table 4-01] presents a summary of indications, tooth preparation requirements, and technical comments regarding restorative materials.

[Table 4-01] Summary of indications, tooth preparation requirements, and technical comments regarding restorative materials.

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