Nanotechnology in Operative Dentistry

CHAPTER

Nanotechnology in Operative Dentistry: A Perspective Approach of History, Mechanical Behavior, and Clinical Application

4

E.G. Mota,1 and K. Subramani2 1

Pontifical University of Rio Grande do Sul (PUCRS), Porto Alegre, RS, Brazil 2 Department of Orthodontics, University of Kentucky, Lexington, KY, USA

CONTENTS   4.1 Introduction.....................................................................................................................................50   4.2 Historical Review: Nanotechnology Applications in Operative Dentistry..............................................50   4.3 Biomimetics....................................................................................................................................50   4.4 Fillers in Composite Resins..............................................................................................................52   4.5 SEM and EDS Evaluation..................................................................................................................53   4.6 Filler Weight Content (wt%).............................................................................................................54   4.7 Water Sorption................................................................................................................................54   4.8 Mechanical Behavior.......................................................................................................................56 4.8.1 Compressive Strength............................................................................................... 57 4.8.2 Diametral Tensile Strength........................................................................................ 58 4.8.3 Flexural Strength and Flexural Modulus...................................................................... 59 4.8.4 Microhardness.......................................................................................................... 60 4.8.5 Nanohardness.......................................................................................................... 62 4.8.6 Wear Resistance....................................................................................................... 62   4.9 Clinical Applications........................................................................................................................66 4.10 Conclusions....................................................................................................................................68 Acknowledgments.....................................................................................................................................68 References...............................................................................................................................................68

Emerging Nanotechnologies in Dentistry. DOI: 10.1016/B978-1-4557-7862-1.00004-3 © 2012 Elsevier Inc. All rights reserved.

49

50

CHAPTER 4  Nanotechnology in Operative Dentistry

4.1  INTRODUCTION Since the pioneering research in the 1950s, numerous innovations have been applied in operative dentistry. Composite resin technology has continuously evolved since its inception by Bowen as a reinforced Bis-GMA (bisphenol A-glycidyl methacrylate) system [1]. This color-based filling material is basically composed by a triad: organic phase (dimethacrylates), inorganic phase (silanated fillers), and initiator/activator system. One of the most important breakthroughs in composite resin technology was the development of photocurable resin material. This was followed by the development of reduced filler particle size and increased filler loading which significantly improved the universal applicability of light-cured composite resins. Resin composites are widely used in dentistry and have become one of the most common aesthetic restorative materials due to their mechanical strength, excellent aesthetics properties, moderate cost (when compared to ceramics), ability to bond with the tooth, improved formulation, simplified clinical procedures, and the decline in amalgam usage due to mercury toxicity. During the last few decades, the increasing demands in aesthetic dentistry have led to the development of resin composites for direct restorations with improved physical and mechanical properties, aesthetics, and clinical longevity. The latest innovation in the field has been the introduction of nanofilled materials, by combining nanometer scale particles and nanoclusters in a conventional resin matrix.

4.2 HISTORICAL REVIEW: NANOTECHNOLOGY APPLICATIONS IN OPERATIVE DENTISTRY The term “nanotechnology” was coined by the researcher named Norio Taniguchi in 1974. Nanotechnology aims at the creation and utilization of materials and devices at the level of atoms, molecules, and supramolecular structures, and in the exploitation of unique properties of particles with size ranging from 0.1 to 100 nm (1 nm  109 m). Nanofilled composite resin materials are believed to offer excellent wear resistance, strength, and ultimate aesthetics due to their exceptional polishability and luster retention [2]. In operative dentistry, nanofillers constitute spherical silicon dioxide (SiO2) particles with an average size of 5–40 nm (0.005–0.04 μm). However, this 0.04-μm scale filler is not new in dentistry. In the 1970s, the minifilled composites (0.04 μm, i.e., 40 nm) were launched in the marketplace. The nanometer scale filler particles have been already applied in composite resins. So, the following question can be asked: What is the difference between this resin and the actual nanofilled resins? The answer lies in the manufacturing procedure. While the colloidal silica from the 1970s obtained by pyrogenic method allows a maximum load of 55 wt%, the ordered growth of nanofillers allows up to 87 wt% of inorganic phase (for details of filler weight content, refer to Figure 4.4). It was only in 2003 that the primary results of a nanofilled composite were published in the Journal of American Dental Association by Mitra et al. [3]. The authors reported improvements in optical properties, similar mechanical behavior when compared to microhybrid material, and same polishability of minifilled resins.

4.3  BIOMIMETICS The early stages of dental materials as a science were characterized by answering how the natural and artificial material behaves. The development and discovery of new materials were based on fortuitous

4.3  Biomimetics

Acc.V Spot Magn Det WD 20.0 kV 3.0 25000 x SE 9.8

51

2 µm

FIGURE 4.1 Scanning electron microscopy (SEM) of nanoclusters.

observations, i.e., the acid etch surface observed by Buonocore and then applied to dental enamel, or mixing materials in order to improve properties which were shown to be effective as seen in published manuscripts of Wilson and Kent since 1968 up to 1972 that culminated in the development of glass ionomer cement. The following decades of 1980s and 1990s were comprised by testing and discussing which dental material behaves similarly to dental hard tissues. While exhaustion of this subject was reached, nanotechnology field has gained attention. Therefore, a new question was asked: How nanotechnology can be used to create materials capable of simulating the physical and mechanical behavior of enamel/dentin? Biomimetics has been the answer to this question. Biomimetics has been described as the science that applies nanotechnology to create materials and devices that imitate nature. According to Saunders (2009) [4], biomimetics is supporting numerous improvement on nanofillers used in restorative materials in dentistry. Besides the size that allows a higher amount of inorganic phase into the composite, the shape, i.e., nanoclusters (Figure 4.1), nanorods, nanotubes, and nanofibers, has a significant and positive influence on resin bonded composites’ mechanical property. The nanosized fillers inserted into resin composites lead to better physical and mechanical characteristics. An optical advantage of high aesthetic potential, due to nanofillers of size 20 nm smaller than visible light wavelength that ranges from 400 to 800 nm, enhances the translucency and color (refer to Section 4.9). Significant augmentation of microhardness, diametral tensile, compressive and flexural strengths are recorded when nanofillers are incorporated. Further composition changes as CaPO4 nanostructures [5], caries preventive CaF2 nanoparticles, and recombinant amelogenins are being added in order to synthesize biomimetic composites. Therefore, in the near future, nanofilled

52

CHAPTER 4  Nanotechnology in Operative Dentistry

composites shall not be used as a simple bioinert way of enamel/dentin replacement, but as a complex, biomimetic, and biointeractive material.

4.4  FILLERS IN COMPOSITE RESINS Since the first formulation of composite resins in the 1960s, a basic triad is used: monomer, silane treated filler, and initiators. The filler used by Bowen [1], in 1963, consisted of milled quartz particles with average size ranging from 8 to 12 μm (8,000–12,000 nm) as shown in Figure 4.2. Due to the aesthetic limitations of macrofilled composites (lack of surface gloss), the minifilled composites were introduced in the 1970s. The filler material was produced by a pyrogenic method allowing a maximum load of 55 wt%, with better polishability, however with a significantly lower mechanical strength. It was only in the 1980s and 1990s, mixtures of previous filler materials were tested. These hybrid fillers (600–2,000 nm) were commercialized as hybrid, microhybrid, and condensable (whiskershaped) composites. Improvement in the mechanical strength was achieved; however, the polishability was still a limitation. A maximum load of filler from 70 to 77 wt% was recorded then. Still, the particle size of conventional composites were not similar to the size of the hydroxyapatite crystal, dentinal tubule, and enamel rod, and that there was a potential for compromise in adhesion between the macroscopic restorative material and the nanoscopic (1–10 nm in size) tooth structure [6].

P : 10,000 x

10.0 kV

1 µm

AMRAY

#0000*

FIGURE 4.2 SEM of irregular macrofiller. Source: Hörlle, Hirakata, and Mota (2008).

4.5  SEM and EDS Evaluation

53

However, the milling procedure cannot normally reduce the filler particle size below 100 nm. Thus, nanotechnology has been used as an innovative way to manufacture fillers from the controlled growth of an initial molecule (bottom-up approach), resulting in homogeneity in shape and size (in the range between 5 and 20 nm). The Filtek Supreme (3MEspe, St. Paul, MN, USA) was the commercial milestone of nanotechnology application in operative dentistry in the beginning of this century. This composite resin was a combination of aggregated zirconia/silica cluster filler with a primary particle size of 5–20 nm and nanoagglomerated 20 nm silica filler in 78.5 wt%. Over the last few years, a combination of microhybrid and nanofilled composites has been commercialized. This new combination has increased the filler weight content up to 87% by filling spaces between larger particles with smaller ones, and has retained optical and mechanical characteristics which are known to be exclusive to nanofilled composites.

4.5  SEM AND EDS EVALUATION SEM has been used to analyze the shape and size of the filler particles and as a qualitative method to classify the composite resins [7]. Comparative SEM images of nanofilled composites are presented in Figure 4.3. Morphological comparisons show that there are similar patterns between Esthet-X (Dentsply, Caulk, Milford, USA) and Grandio (Voco, GMBH Cuxhaven, Germany). High amount of irregular fillers are seen with additional load of small nanofillers around and/or over them occupying the empty spaces. The same pattern was registered to both enamel and dentin shades. A completely different pattern can be seen with Filtek Supreme XT (3MEspe, St. Paul, MN, USA) with high amount of rounded, uniform size fillers in both enamel and dentin shades. Following the classification proposed by Lutz and Phillips in 1983 [8], all evaluated composites could be classified as microhybrid, except the Filtek Supreme XT which is an exclusive nanofilled composite in accordance to Mitra et al. [3] and Beun et al. [9].

(A) P:20.000 x

(B) 10.0 kV 1 µm AMRAY

#0000*

P:20.000 x

(C) 10.0 kV 1 µm AMRAY

#0000*

P:20.000 x

10.0 kV 1 µm AMRAY

#0000*

FIGURE 4.3 SEM: (A) Nanoclusters of Filtek Supreme XT, the exclusive nanofilled composite. (B) Esthet-X filler, a microhybrid composite with additional load of nanofillers. (C) Grandio, a high filled microhybrid composite with additional load of nanofillers. Source: Hörlle, Hirakata, and Mota (2008).

54

CHAPTER 4  Nanotechnology in Operative Dentistry

Table 4.1  Descriptive Table of Components (wt%) Recorded from Nanofilled Composites Submitted to EDS Composite Resins

Ba

Al

O

Si

Esthet-X Enamel Esthet-X Dentin Filtek Supreme XT Enamel Filtek Supreme XT Dentin Grandio Enamel Grandio Dentin

37.56 37.00       5.18

6.15 6.05     10.38 10.12

23.37 17.42 40.79 37.38 36.93 33.27

32.92 39.53 59.26 62.62 52.70 51.42

, not recorded.

When fillers were analyzed with energy dispersive spectroscopy (EDS), the following components were observed: aluminum (Al), barium (Ba), silicates (Si), and other heavy metals used to increase the radio opacity (Table 4.1). For clinical inference, the composites with Ba and Al (Esthet-X) shall be more evident in X-ray and for clinical longevity of the filling. For Grandio, the dentin shade must be inserted in deeper increments which is more radiopaque when compared to the enamel shade (as seen in the X-ray in Figure 4.26B).

4.6  FILLER WEIGHT CONTENT (WT%) Thermogravimetric analysis is used to evaluate filler concentration in percentage by weight. The specimens of composite were inserted in a platinum container and subjected to 20°C/min temperature increase until 700°C (TGA 2050, TA Instruments, New Castle, DW, USA) in a nitrogen saturated atmosphere. The temperature of organic matrix degradation and filler weight percent (wt%) were recorded. The amount of inorganic residues was established by stabilization of the weight of the sample. The determination of the inorganic content was performed by weighing the mass of the composite specimen before and after the entire elimination of the organic phase [10]. The filler weight content of common nanofilled composites ranged from 75.75 to 87 wt% (see Figure 4.4 and Table 4.2). In the relevant literature, it can be seen that there is a strong positive correlation between filler content and mechanical properties. Xu [9] concluded that there was a uniform improvement of elastic modulus and hardness when filler load was enhanced. Similarly, Sabbagh et al. [11] recorded a strong correlation (r  0.82) between the filler weight content and elastic modulus of composite resins. Thus, the following section will describe the mechanical properties of nanofilled composites.

4.7  WATER SORPTION Water absorption by composite materials is a diffusion-controlled process, and the uptake of water occurs largely in the resin matrix [12]. The water sorbed by the polymer matrix can cause filler/ matrix debonding (Figure 4.4, or even hydrolytic degradation of the fillers [13] and may reduce the

4.7  Water Sorption

100

139.29°C

98

95

406.74°C

94 92

6.339% (1.105 mg) 437.62°C

90

(A)

0

100

200

300 400 Temperature (°C)

500

278.52°C 6.758% (0.6089 mg) 315.55°C

90

401.81°C

85 Residue: 87.00% (15.17 mg)

88 86

136.50°C 5.105% (0.4600 mg) 179.55°C

244.71°C Weight (%)

Weight (%)

105

4.626% (0.8065 mg)

100

96

55

600

9.737% (0.8773 mg) Residue: 76.80% 436.31°C (6.920 mg)

80

700

75

(B)

0

100

200

300 400 Temperature (°C)

500

600

700

105 100 258.64°C 6.185% (1.385 mg) 304.08°C

Weight (%)

95 90

399.59°C

85

13.13% (2.940 mg)

80 75

(C)

434.36°C

0

100

200

300 400 Temperature (°C)

500

Residue: 76.54% (17.14 mg) 600

700

FIGURE 4.4 Comparative charts of thermogravimetry analysis of nanofilled enamel shade composites. (A) Grandio, (B) Esthet-X, and (C) Filtek Supreme XT. Source: Pires and Mota (2008).

Table 4.2  Descriptive Table of Filler Weight Content (wt%) of Nanofilled Composites Evaluated by Thermogravimetric Analyses Composite Resin

wt%

Esthet-X Enamel Esthet-X Dentin Filtek Supreme XT Enamel Filtek Supreme XT Dentin Grandio Enamel Grandio Dentin

76.8 75.75 76.22 76.54 87 86.89

56

CHAPTER 4  Nanotechnology in Operative Dentistry

mechanical properties of the composite materials [14]. Water sorption also results in increased overall weight. Solubility, leaching, and hydrolytic degradation is a result of either the breaking of chemical bonds in the resin or softening through the plasticizing action of water [15]. When resin samples are immersed in water, some of the components, such as unreacted monomers or fillers, dissolve and leach out of the sample. The release of these components may influence the initial dimensional changes of the composite, the clinical performance, the aesthetic aspect of the restoration, or the biocompatibility of the material [15]. Solubility therefore results in weight reduction. Water sorption and solubility measurements were performed as described by Oysaed and Ruyter [16]. Ten disk specimens were used for each material. The diameter and the thickness of the specimens were measured and the volume (v) was calculated. The disks were conditioned in a desiccator for 3 days, containing calcium sulfate at 37°C until a constant weight had been achieved (w0). The disks were placed in a glass vial containing 100 ml of distilled water. The vials were wrapped by aluminum foil to protect from light and placed in an incubator at 37°C and at intervals removed, blot dried, and weighed. This was continued until the weight change/week was less than 0.32 μg (constant weight—w1). The disks were removed from the water and replaced in a desiccator for 24 h and then reweighed for the last time (w2). These steps were carried out to evaluate water sorption (WS) and water solubility (WSL), in μg/cm3.

where

WS  w1  w2 /V WSL  w0  w2  V

w0 is the sample weight before immersion w1 is the sample weight after immersion w2 is the sample weight after immersion and desiccation For water sorption and solubility, statistical differences were recorded when nanofilled composites were compared. The exclusive nanofilled composite, Supreme XT, was more susceptible to water uptake. This can be explained by the higher contact surface of nanosized fillers. Samples cured with halogen device were less sensitive in water (Figures 4.5 and 4.6).

4.8  MECHANICAL BEHAVIOR In 1983, the composite resin materials were classified according to the average size of inorganic filler that became a standard. Based on the size, composite resin is classified as macroparticulated or traditional (up to 50 μm), hybrid (8–30 μm), microhybrid (0.7–3.6 μm), and microparticulated or minifilled (0.04–0.2 μm) [8]. Due to many differences between materials classified in the same group, other methods for classification were suggested based on mechanical properties [7,17]. Compressive strength, diametral tensile strength, flexural strength, and hardness have also been evaluated [18,19], due to a direct influence of composition in the mechanical behavior [20]. However, different composites are available in the market and are classified just by inorganic filler size, suggesting that resins of the same group would have similar mechanical behavior. Therefore, the following described mechanical properties and results will show a dissimilar behavior.

4.8  Mechanical Behavior

57

3.5 3

µg/cm3

2.5 2 1.5 1 0.5 LED

0 Esthet-X

Halogen

Venus Supreme XT

FIGURE 4.5 Comparison of water sorption (μg/cm3) between nanofilled composites when photocured by two different sources.

2

µg/cm3

1.5 1 0.5 LED

0 Esthet-X

Halogen Venus

Supreme XT

FIGURE 4.6 Comparison of solubility (μg/cm3) between nanofilled composites when photocured by two different sources. Source: Retamoso, Mortari, Hörlle, and Gonçalves (2009).

4.8.1  Compressive Strength The compressive measurement test induces stress into the sample tested (in order to quantify the maximum strength, the filler and polymeric resin can withstand). This mechanical property results in higher cohesive strength of the material. Resin-based restorations in functional areas are submitted

58

CHAPTER 4  Nanotechnology in Operative Dentistry

200

MPa

150 100 50 Enamel

0 Esthet-X

Dentin Grandio

Supreme XT

FIGURE 4.7 Graphic representation of compressive strength (MPa) of nanofilled composites in dentin and enamel shades. Source: Balbinot and Mota (2006).

up to 800 N. The relation between the maximum strength (N) applied on a sample divided by the sectional area (mm2) results in the maximum compressive strength in megapascal (MPa). A comparative view in Figure 4.7 describes the compressive strength of nanofilled composites. The compressive strength ranges from 146.63 to 206.08 MPa. There was no statistical difference between them and in both shades (Anova and Tukey, P  0.18).

4.8.2  Diametral Tensile Strength This in vitro methodology was developed to test the cohesion of materials when subjected to tensile stress. However, when brittle materials are exposed to tensile stress, they are most likely to break easily. The diametral tensile test applies a compressive load into a cylindrical-shaped sample, resulting in elongation as an indirect tensile strength. This mechanical property is calculated (MPa) as a relation of two times the maximum strength recorded under the relation of π, diameter and height of the sample. The diametral tensile strength (MPa) ranged from 34.87 to 50.26 (Figure 4.8). There was a significant difference between the composites (P  0.02). Supreme XT enamel shade was statistically higher than Esthet-X Dentin. The other composites and shades did not differ from both resins studied [21]. Besides the results after 24 h of storage, the effect of artificial accelerated aging on mechanical properties has also been recorded [22]. Samples of nanofilled composites were submitted up to 300,000 mechanical cycles of 80 N at 37°C. Figure 4.9 presents the effect of this load on nanofilled composites. The results (MPa) ranged from 41.6 (Esthet-X) to 53.39 (Supreme XT). No differences were recorded between composites submitted up to 300,000 mechanical cycles and the samples which were not submitted to the mechanical loading cycle. This means that nanofilled composites might support the masticatory load better than other microhybrid composites.

4.8  Mechanical Behavior

59

50

MPa

40 30 20 10 Enamel

0 Esthet-X

Dentin Grandio

Supreme XT

FIGURE 4.8 Graphic representation of diametral tensile strength (MPa) of nanofilled composites in dentin and enamel shades. Source: Balbinot and Mota (2006).

50

MPa

40 30 20 10 Mechanical load

0 Esthet-X

Control Venus

Supreme XT

FIGURE 4.9 Comparative graph of diametral tensile strength of nanofilled composites submitted up to 300,000 cycles of 80 N. Source: Rigo and Mota (2009).

4.8.3  Flexural Strength and Flexural Modulus The flexural strength (Figure 4.10) measurement was carried out according to the International Standardization Organization specification 4049 due to the capability to test complex stress (compressive, tensile, and shear) simultaneously using one sample. The flexural modulus (GPa) is the relation of flexural strength to the deformation of materials. The higher the flexural or elastic modulus of a material, the higher the energy required to deform it. In

60

CHAPTER 4  Nanotechnology in Operative Dentistry

140 120

MPa

100 80 60 40 20

Enamel

0 Esthet-X

Dentin Grandio

Supreme XT

FIGURE 4.10 Comparative graph of flexural strength (MPa) of nanofilled composites in enamel and dentin shades. Source: Balbinot and Mota (2006).

14 12

GPa

10 8 6 4 2

Enamel

0 Esthet-X

Dentin Grandio

Supreme XT

FIGURE 4.11 Comparative graph of flexural modulus (GPa) of nanofilled composites in enamel and dentin shades. Source: Balbinot and Mota (2006).

literature, 12–14 GPa has been reported as elastic modulus of human dentin. Restorative materials are expected to perform like natural dentin; however, different behavior is presented in Figure 4.11.

4.8.4  Microhardness The hardness test measures the ability of a material to be indented or abraded by another material. In dentistry, microhardess is commonly used due to smaller sample dimensions and multiple

4.8  Mechanical Behavior

61

FIGURE 4.12 Microhardness impressions using Vickers (A) and Knoop (B) indenters of Supreme XT and Grandio, respectively. Source: Rogério, Rigo, and Mota (2006).

120 100 KHN

80 60 40 20

Mechanical Load

0 Supreme XT

Control Esthet-X

Venus

FIGURE 4.13 Comparative graph of Knoop microhardness of nanofilled composites when submitted up to 300,000 cyclic loads. Source: Rigo and Mota (2009).

compositions of the materials. Two main methods are described in the literature: Vickers or Knoop. Vickers indenter is associated to brittle materials and use a square-shaped indenter tip (Figure 4.12A). However, some researchers classify composite resins as elastic materials due to the organic phase and use Knoop point with “V” shape (Figure 4.12B). The potential resistance to wear is mainly explained by hardness. Resin composites fillings in functional areas are more susceptible to abrasion. In Figure 4.13, the exclusively nanofilled composite

62

CHAPTER 4  Nanotechnology in Operative Dentistry

800 700 600 MPa

500 400 300 200 100 0

Esthet-X

Grandio

Supreme XT

FIGURE 4.14 Comparison of nanohardness. Source: Rosa and Mota (2009).

Supreme XT showed the highest average microhardness when compared to Esthet-X and Venus. However, there was no significant effect of 300,000 load cycles on the hardness. This is a completely different behavior when compared to minifilled and microhybrid composites [22]. At the same time, this gives an indication of higher clinical longevity which must be considered.

4.8.5  Nanohardness Since the use of nanofillers started, the term “nanohardness” has been introduced. The use of a nanoindenter with a Berkovich diamond tip with a nominal radius of 5,000 nm has been widely used. A nanoindenter measures the hardness and elastic modulus of a material on an extremely smaller surface scale of 50 nm [23]. Nanohardness results ranged from 350 to 770 MPa (Figure 4.14), far less than 4,350 from enamel recorded by Machado [23].

4.8.6  Wear Resistance According to O’Brien and Yee [24], clinical wear mechanisms of composite resin are described as follows: (1) organic matrix wear, (2) loss of filler bond to the matrix, (3) shear of filler, (4) matrix cohesive failure, and (5) exposure of air blisters. Some of these phenomena still occur in nanofilled composites and can be seen in Figures 4.15–4.19. Morphological aspects observed in SEM in different simulated periods of three body wear show rounded fillers exposed by the organic phase removal, small cracks, and loss of fillers due to debonding.

4.8  Mechanical Behavior

FIGURE 4.15 Sample exposed to three body wear test.

0.2 0.18 0.16

µm

0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 24 hours

6 months

1 year

2 years

FIGURE 4.16 Comparative wear Ra (μm) of Supreme XT after 24 h, 6 month, 1 and 2 years of three body simulated test. Source: Braun and Oshima (2008).

63

64

CHAPTER 4  Nanotechnology in Operative Dentistry

FIGURE 4.17 Morphological aspect of Filtek Supreme XT after finishing and polishing (8,000). The organic phase covers entirely the fillers. Source: Braun and Oshima (2008).

FIGURE 4.18 Morphological aspect of Filtek Supreme XT after 1 year of simulated wear (8,000). It is possible to observe the removal of superficial organic phase exposing rounded particles and nanoclusters. Source: Braun and Oshima (2008).

4.8  Mechanical Behavior

FIGURE 4.19 Morphological aspect of Filtek Supreme XT after 2 years of simulated wear (8,000). Small cracks and filler debonding can be observed. Source: Braun and Oshima (2008).

FIGURE 4.20 Morphological aspect of Filtek Supreme XT after 4 years of simulated wear (8,000). Source: Braun and Oshima (2008).

65

66

CHAPTER 4  Nanotechnology in Operative Dentistry

FIGURE 4.21 Morphological aspect of Filtek Supreme XT after 6 years of simulated wear (8,000). A similar pattern can be observed compared to 1, 2, and 4 years suggesting maintenance of roughness as presented in Figure 4.15. Source: Braun and Oshima (2008).

The wear resistance depends upon the filler weight content (as described in Section 4.6), organic phase, and silanization. In 2002, Kim et al. [25] suggested the use of smaller particles in order to improve the filler load, reducing the exposure of organic resin to wear that was confirmed later by Yesil et al. [26]. The effect of this wear (Figure 4.20) in a nanofilled composite (Supreme XT) is measured by surface roughness (μm) and is presented in Figure 4.21.

4.9  CLINICAL APPLICATIONS The following clinical report (Figures 4.22–4.26) illustrates an interproximal restorative procedure in a 20-year-old male patient with nanofilled composite resin.

FIGURE 4.22 The clinical protocol followed all conservative procedures, removing only the affected hard tissues. The beginning aspect of the interproximal cavity (A) and the X-ray confirmation (B).

4.9  Clinical Applications

67

FIGURE 4.23 After complete removal of a decayed tissue (A), the adhesive protocol was total acid etch with 37% phosphoric acid for 15 s in dentin and 20 s in enamel followed by water rinse and gently air blow; two consecutive layers of one-bottle adhesive and light curing for 20 s with 1,000 mW/cm2 LED light source.

FIGURE 4.24 Hybridization aspect of preparation (A). The nanofilled composite resin Grandio A2 dentin and A1 enamel shades were used, incrementally inserted (B) and light cured for 20 s each increment with 1,000 mW/cm2 LED light source.

FIGURE 4.25 (A) Filling aspect immediately after matrix removal and (B) presents the immediate aspect after finishing and polishing.

68

CHAPTER 4  Nanotechnology in Operative Dentistry

FIGURE 4.26 Figure (A) shows the filling after 1 week and the final X-ray (B) with radiopacity for further radiographic control.

4.10  CONCLUSIONS In dentistry, nanofillers could be considered an inorganic particle with average size of 40 nm or 0.04 μm. This size, however, is not an innovation in dental composites, because the minifilled composites had the same 0.04 μm (40 nm) filler particles since the 1970s. The real innovation is the nanofiller manufacture and the possibility of improving the load of inorganic phase [21]. The effect of this high filler load is widely recorded in terms of mechanical properties. Microhybrid composites with additional load of nanofillers are the best clinical choice. The next research frontier in operative dentistry is the manufacture of a filler material with shape and composition that can closely mimic the optical and mechanical characteristics of the natural hard tissues (enamel and dentin).

Acknowledgments The authors would like to thank the associated professors Prof. Dr Hugo Mistuo Silva Oshima and Prof. Dr Luciana Mayumi Hirakata and the students of Dentistry Graduate Program of Pontifical Catholic University of Rio Grande do Sul, Brazil.

References [1] R.L. Bowen, Properties of a silica-reinforced polymer for dental restorations, J. Am. Dent. Assoc. 66 (1963) 57–64. [2] Y. Xia, F. Zhang, H. Xie, N. Gu, Nanoparticle-reinforced resin-based dental composites, J. Dent. 36 (6) (2008) 450–455. [3] S.B. Mitra, D. Wu, B.N. Holmes, An application of nanotechnology in advanced dental materials, J. Am. Dent. Assoc. 134 (2003) 1382–1390.

References

69

  [4] S.A. Saunders, Current practicality of nanotechnology in dentistry. Part 1: Focus on nanocomposite restoratives and biomimetics, Clin. Cosm. Inv. Dent. 1 (2009) 47–61.   [5] H.H. Xu, L. Sun, M.D. Weir, S. Takagi, L.C. Chow, B. Hockey, Effects of incorporating nanosized calcium phosphate particles on properties of whisker-reinforced dental composites, J. Biomed. Mater. Res. B. Appl. Biomater. 81 (1) (2007) 116–125.   [6] D.A. Terry, Direct applications of a nanocomposite resin system: Part 1: The evolution of contemporary composite materials, Pract. Proced. Aesthet. Dent. 16 (2004) 417–422.   [7] H. Hosoda, T. Yamada, S. Inokoshi, SEM and elemental analysis of composite resins, J. Prosthet. Dent. 64 (1990) 669–676.   [8] F. Lutz, R.W. Phillips, A classification and evaluation of composite resin systems, J. Prosthet. Dent. 50 (1985) 480–488.   [9] S. Beun, T. Glorieux, J. Devaux, J. Vreven, G. Leloup, Characterization of nanofilled compared to universal and microfilled composites, Dent. Mater. 23 (1) (2007) 51–59. [10] J. Sabbagh, L. Ryelandt, L. Bachérius, J.J. Biebuyck, J. Vreven, P. Lambrechts, et al., Characterization of the inorganic fraction of resin composites, J. Oral. Rehab. 31 (11) (2004) 1090–1101. [11] J. Sabbagh, J. Vreven, G. Leloup, Dynamic and static moduli of elasticity of resin-based materials, Dent. Mater. 18 (2002) 64–71. [12] M. Braden, R.L. Clarke, Water absorption characteristics of dental microfine composite filling materials, Biomaterials 5 (1984) 369–372. [13] K.J. Söderholm, M. Zigan, M. Ragan, W. Fischlschweiger, M. Bergman, Hydrolytic degradation of dental composites, J. Dental Res. 63 (1984) 1248–1254. [14] A. El-Hadary, J.L. Drummond, Comparative study of water sorption, solubility, and tensile bond strength of two soft lining materials, J. Prosthet. Dent. 83 (2000) 356–361. [15] J.L. Ferracane, Elution of leachable components from composites, J. Oral Rehab. 21 (1994) 441–452. [16] H. Oysaed, I.E. Ruyter, Composites for use in posterior teeth: mechanical properties tested under dry and wet conditions, J. Biomed. Mater. Res. 20 (1986) 261–271. [17] B.R. Lang, M. Jaarda, R.F. Wang, Filler particle size and composite resin classification systems, J. Oral. Rehab. 19 (1998) 569–584. [18] T. Brosh, Y. Ganor, I. Belov, R. Pilo, Analysis of strength properties of light-cured resin composites, Dent. Mater. 15 (1999) 174–179. [19] D.S. Cobb, K.M. MacGregor, M.A. Vargas, G.E. Denehey, The physical properties of packable and conventional posterior resin-based composites: a comparison, J. Am. Dent. Assoc. 131 (2000) 1610–1615. [20] E.C. Say, A. Civelek, A. Nobecourt, M. Ersoy, C. Guleryuz, Wear and microhardness of different resin composite materials, Oper. Dent. 28 (2003) 628–634. [21] E.G. Mota, H.M. Oshima, L.H. Burnett, Jr., L.A. Pires, R.S. Rosa, Evaluation of diametral tensile strength and Knoop microhardness of five nanofilled composites in dentin and enamel shades, Stomatologija 8 (3) (2006) 67–69. [22] P.N. Gomes, S.C. Dias, M.R. Moyses, L.J. Pereira, B.G. Negrillo, J.C. Ribeiro, Effect of artificial accelerated aging on Vickers microhardness of composite resins, Gen. Dent. 56 (7) (2008) 695–699. [23] C. Machado, W. Lacefield, A. Catledge, Human enamel nanohardness, elastic modulus and surface integrity after beverage contact, Braz. Dent. J. 19 (1) (2008) 68–72. [24] W.J. O’Brien, J. Yee, Jr., Microstructure of posterior restorations of composite resin after clinical wear, Oper Dent. 5 (3) (1980) 90. [25] K. Kim, J.L. Ong, O. Okuno, The effect of filler loading and morphology on the mechanical properties of contemporary composites, J. Prosthet. Dent. 87 (2002) 642–649. [26] Z.D. Yesil, S. Alapati, W. Johnston, R.R. Seghi, Evaluation of the wear resistance of new nanocomposite resin restorative materials, J. Prosthet. Dent. 99 (6) (2008) 435–443. [27] H.H.K. Xu, Dental composite resins containing silica-fused ceramic single-crystalline whiskers with various filler levels, J. Dent. Res. 78 (1999) 1304–1311.