Ricci and Fahl - Nature Mimicking Layering With Composite Resins Through A Bio Inspired Analysis 25

17088240, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/jerd.13021 by Aline Girotto - CAPES , Wiley Online Library on [09/02/2023].
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Received: 20 December 2022 Revised: 12 January 2023 Accepted: 13 January 2023
DOI: 10.1111/jerd.13021
CLINICAL ARTICLE
Nature-mimicking layering with composite resins through a

bio-inspired analysis: 25 years of the polychromatic technique
Weber Adad Ricci DDS, MS, PhD, Assistant Professor 1,2 |

Newton Fahl Jr. DDS, MS, Clinical and Scientific Director, Adjunct Professor 3,4,5
1
Department of Social Dentistry, Sao Paulo
State University UNESP, Araraquara, Brazil Abstract
2
Private Practice, Sao Carlos, Brazil Objectives: For decades, the dental community has discussed which materials
3
Private Practice, Curitiba, Brazil would be the ideal substitutes for lost tooth structure. Initially, the biomimetic
4
Fahl Center, Curitiba, Brazil
5
approach advocated that feldspathic ceramics would be the material of choice for
University of North Carolina at Chapel Hill,
Chapel Hill, North Carolina, USA enamel. However, given the complexity of obtaining excellent dental technicians
and the financial cost, are composite resins a suitable replacement? The optical
Correspondence
Newton Fahl Jr., Private Practice, Rua properties with opalescence and fluorescence effects, as well as this material's
Visconde do Rio Branco, 1335 – sala high fracture toughness, indicate it as a long-lasting restorative material. How-
24, 80420-210 – Curitiba, PR, Brazil.
Email: newton@fahl.com.br ever, because this material depends on the operator's expertise, knowledge of
layering techniques and the selection of each material for the different layers is
required. Thus, knowledge of the polychromatic technique through a bioinspired
approach is necessary to obtain results of life-like restorations. This article aims to
review the polychromatic layering technique (PLT), considering the optical and
mechanical properties of dentin and enamel and correlating these properties with
current composite resins to guide clinicians in selecting the most suitable restor-
atives for their clinical challenges.
Clinical Considerations: The polychromatic layering technique is revisited, cross-
referencing the properties of dentin and enamel with current composite resin restor-
atives and their biomimetic properties. The effectiveness and predictability of the
PLT are corroborated in clinical cases of varying degrees of difficulty requiring differ-
ent layering strategies.
Conclusion: After the bio-inspired analysis, using nature as a model to be understood
and followed, it is possible to note how the polychromatic technique remains current
and viable in mimicking nature, providing esthetic and natural results in the layering
of composite resins.
Clinical Significance: Composite resins effectively replicate the optical and mechani-
cal characteristics of natural dentin and enamel through the bioinspired approach
presented by the polychromatic layering technique.
KEYWORDS
bioinspiration, biomimetic, composite layering, dental tissues, light propagation
J Esthet Restor Dent. 2023;1–12. wileyonlinelibrary.com/journal/jerd © 2023 Wiley Periodicals LLC. 1

17088240, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/jerd.13021 by Aline Girotto - CAPES , Wiley Online Library on [09/02/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
2 RICCI and FAHL JR.
1 | I N T RO DU CT I O N
Restorative dentistry, for decades, has been looking for materials and
techniques to replace the tooth structure affected by injuries. In the
research of developments for new products, countless alternatives
are presented with the promise of being ideal substitutes. As a result,
the industry has periodically introduced restoratives combining opti-
mal mechanical and nature-mimicking properties. In addition, numer-
ous in vitro and in vivo studies have scrutinized materials and
methods to establish scientific and clinical grounds for consistently
creating restorations that emulate dental tissues.1–5
Skilled ceramists use elaborate stacking techniques to artistically
achieve high-quality results that mimic the living tissues (Figure 1). In the
same way, composite layering techniques have been introduced with sig-
FIGURE 1 Single unit ceramic crown on maxillary left central
nificant clinical acceptance and application, aiming at the quest for resto- incisor.
rations that go unnoticed by the most attentive observer6–8 (Figure 2A,B).
The clinician's critical challenge has consistently been producing
restorations that mingle natural tissues' characteristics with synthetic
restoratives according to biomimetic principles. Biomimetics is an (A)
interdisciplinary field in which principles from engineering, chemistry,
and biology are applied to the synthesis of materials, synthetic sys-
tems, or machines that have functions that mimic biological processes.
In this scenario, ceramics are considered the materials closest to den-
tal structures by the biomimetic dental school of thought—feldspathic
porcelain, particularly—as they closely emulate dental enamel's mechanical
and optical characteristics.9 Because enamel is very similar to glass due to
its high mineral content, the calcium phosphate crystals (hydroxyapatite)
and other constituent minerals of this acellular layer give it an anisotropic
behavior and a light dispersion like that found in porcelain10
(Figure 3A–D). However, the definition of an ideal synthetic substitute
can only be defended with deeper pondering. Porcelain is credited with
being more abrasive to opposing enamel than composite resins. Addition- (B)
ally, its manufacturing technique also requires more invasive tooth prepa-
rations and a more complex and costly workflow due to the increased
time and cost of the laboratory process.
Although immersing in materials science per se seems fascinating,
the choice of a substitute synthetic material prompts reasoning that
extends beyond mechanical and optical properties found in biomimet-
ics to consider the overall scope of restorative dentistry as a field of
health promotion.
Whether with resins or ceramics, the restorative process depends on
the technical skill of the human being; in other words, it is operator-
dependent.11 However, ceramic works are more expensive and depend
on an experienced ceramist who, in most cases, is not the dentist himself.
Thus, the purpose of this article is to carry out a conceptual analysis not F I G U R E 2 (A and B) Single unit composite restoration on
only through biomimetics but through the broader look of bioinspiration maxillary right central incisor.
for the choice of materials and techniques that can be introduced more
simply in the daily lives of clinicians. Furthermore, this article aims at
understanding the natural tissues and the characteristics of currently 2 | T H E CH O I C E O F C O M P OS I T E R E S I N A S
available composite restoratives while scrutinizing and revisiting a logical A R E S T O R I N G M A T E RI A L
pathway for their selection and application according to a widely
accepted technique published by one of the authors in 1995—the poly- In many countries, academic discussions argue about the best restor-
chromatic layering technique.12 ative material when comparing composites versus ceramics. Often
RICCI and FAHL JR. 3
F I G U R E 3 (A–D) Add-on
(A) (B)
feldspathic ceramic contact-lens
type fragment.
(C) (D)
defended even passionately, this analysis makes no sense when the beings, this may be a challenging task. Plain logic indicates that the
focus is on the patient. Longevity studies demonstrate that both best substitute for enamel should be tissue-engineered enamel itself.
materials can be used successfully in dental restoration for decades, Without this possibility, a deep study of the element to be copied
benefiting people in terms of esthetics and function.11,13 Mechani- must be done, and the search for how to restore it can have a deeper
cally, the physical properties of composite resins have historically meaning when nature is analyzed more broadly. Bioinspiration ana-
been optimized by the often ceramic filler particles of this composite lyzes the target element and looks for other forms of intelligent design
(hybrid) material. With this, a perfect balance can be obtained in the present in nature (Figure 5). For example, suppose the tooth presents
proportion of the organic and inorganic components. In this way, even a dentin/enamel junction with a stable and long-lasting chemical and
with simple layering techniques using a single shade and opacity, micromechanical bond. Why can adhesives not be produced by study-
esthetic and functional results can be achieved with resins, unlike ing glues synthesized by mussels that can attach them to the mineral
ceramics, which invariably depend on complex implementation tech- content of rocks even when submerged in water?16 Dental bioinspira-
niques (Figure 4A–C). tion seeks answers in nature to restore nature itself when damaged.
Another favorable factor for using composite resins is their addi- Thus, it does not focus only on the target element but analyzes beings
tive application technique. Because composite resins are directly from other specimens and classes to offer viable repair alternatives.
applied in the mouth, creating a path of insertion, as in the case of However, like biomimetics, studies should always be initiated by the
indirect restorations, is unnecessary. This direct approach implies natural object, which is the focus of the copying process.
more significant preservation of healthy dental structures, keeping
Contemporary Dentistry in an additive and not amputative era.14
Finally, the high operational cost of ceramic works and the need 3.1 | The enamel
for an outsourced laboratory service—only sometimes readily available
across different countries and their socioeconomic realities—make This acellular tissue is the hardest in the human body. Its formulation
resins an attractive proposal that places the clinician as the protago- and formatting are intriguing. Its chemical base is mineral, consisting
nist of a successful esthetic/functional restoration. of approximately 95% calcium phosphate and 5% organic matter,
which gives it high resistance to friction, demonstrated through tribol-
ogy analysis.17 However, it has little ability to withstand plastic defor-
3 | THE N ATURAL TOOTH I N T HE mation before fracture. So, this is a tissue of low fracture toughness.
C O N T E X T OF BI O I NS P I R A T I O N Toughness is the ability of a material to resist crack propagation.
Despite the sigmoid prisms arrangement and the presence of proteins
Dental biomimetics is a concept that seeks to imitate the structure to associated with a combination of diversely oriented prims in the inter-
15
be restored in the choice of replacement materials. With this, the prismatic area, its fracture toughness is about four times lower than
natural element is studied, and substitutes of similar characteristics that of dentin18 (Figure 6). Thus, the primary function of this outer
are selected whenever eligible. However, when dealing with living layer that covers the tooth is to be a protective barrier to the
(A)
(B)
F I G U R E 5 Bioinspiration example. Study of the wing of a

butterfly to produce lenses and even cosmetics with an unrivaled light
dispersion.
(C)
FIGURE 6 Enamel cracks demonstrating its low fracture

toughness.
F I G U R E 4 (A–C) Monochromatic composite resin restoration
showing excellent esthetic results.
molecules that compose it will scatter the light with a wavelength of a

underlying cell layers, allowing masticatory efficiency due to coronal bluish appearance. The wavelength of visible light is between 400 and
rigidity and protecting the dental organ from wear over a lifetime of 700 nm. If the size of the particles that make up an object is greater
occlusal service. The organized morphological aspect of this tissue than the wavelength, the light does not decompose into its chromatic
grants it an anisotropy, not behaving equally depending on the direc- components. All wavelengths are equally dispersed, which is why it is
tion of the applied load. seen as white when passing through a cloud. When the components
An essential aspect of the optical context of this layer is the are smaller, the light assumes a predominance of blue. For composi-
molecular weight of hydroxyapatite, which is 502 g/mol with an tions greater than one-tenth of the wavelength, the scattering
approximate size of 20–70 nm. Despite being a birefringent structure, described as Mie will occur, where blue is no longer predominant, yel-
its average refractive index is 1.63.19 The light scattering on this sub- low and red becoming more evident. This physical phenomenon
strate will be of the Rayleigh type.20 The small size of the mineral makes it possible to explain the opalescent effect in enamel. The
FIGURE 7 Opalescent effect.
FIGURE 9 Dentin yellow color.
The peritubular region presents isotropic behavior, and the orientation

of the tubules shows probable isotropy.21
The optics of this tissue is related to collagen molecular weight of
approximately 300,000 g/mol and size between 180 and 280 nm; the
intertwining of fibrils creates collagen networks with sizes in μm. The
FIGURE 8 Enamel cracks barred in dentin.
refractive index is 1.54. In this context, Mie-type scattering will occur,
as previously mentioned. This higher molecular weight of the dentin
incident light demonstrates the blue in this layer. On the other hand, components will not allow the sensation of the blue hue but the visu-
the reflected light will present an orange tone since the blue scatter- alization of the reddish-yellow hue (brown), which explains the tones
ing has already occurred during the passage of light inside the enamel of group A of the Vita Classical shade guide as the most frequently
(Figure 7). found in dentin22 (Figure 9). It should also be noted that this increased
amount of protein creates an effect called fluorescence in this sub-
strate, which is more intense in areas close to the dentin/enamel junc-
3.2 | The dentin tion than close to the pulp. With age, the deposition of higher mineral
content as secondary and tertiary dentin will decrease this effect23
Dentin is the tissue that presents a mixture of organic and inorganic (Figures 10 and 11).
components in a balanced way to promote fracture resistance. About
70% of this tissue is of mineral origin (calcium phosphate), and 18%
comprises collagen fibrils. This organic material has high resistance to 4 | BIOINSPIRED ANALYSIS
plastic deformation, making dentin approximately 10 more resistant
to bending than enamel. This behavior is due to an intriguing network When the target element (the natural tooth) is studied, it becomes
formed by collagen types I, III, and V. Due to this more elastic charac- apparent that enamel and dentin are tissues with very different physi-
teristic, dentin offers high resistance to crack propagation (high frac- cal (mechanical and optical) behaviors. Despite the similarity in its pri-
18
ture toughness). As a result, the cracks formed in the enamel will mordial constitution, dentin resists fracture, presenting a greater
lose energy as they pass through the junction and reach the dentin optical density and a perception of warmer tones of the visible light
(Figure 8). The directional behavior of the load is complex in dentin. spectrum. Enamel, on the other hand, has the function of resisting
F I G U R E 1 0 Tooth crown
fluorescence 3D chart. Note how
the effect is more intense from
JED to the pulp.
compared to metals depending on the direction and constitution of

their fibers. They may also undergo industrial transformations creating
materials of very high density and resistance.24 In this scenario, when
dental hybrid composites are processed to balance their organic and
inorganic phases, materials can be produced with superior mechanical
characteristics. An increase in density can be obtained by balancing
different sizes and compositions of the inorganic phase and improving
properties and bonds in the organic mesh. Historically, the first com-
posite resins had low abrasive resistance. The modification in the size
and composition of the loads provided materials with high resistance
to fracture and wear. Studies show composite resins behave like
enamel when annual wear rates are verified in vivo.25
Moreover, their flexural strength and elasticity bring them closer
to the mechanical characteristics of natural dentin. With this, a com-
posite resin can be categorized as a unique replacement for lost tooth
structure, fulfilling the mechanical strength role of dentin and the
abrasive strength role of enamel. On the other hand, their fragility lies
in the potential of longitudinal chemical instability since these mate-
rials present a leaching process by hydrolytic degradation in water.26
However, advances in light curing devices, especially formulations
with industrial conversion (prefabricated CAD/CAM blocks), tend to
improve the chemical stability of this material.
5 | T H E CH O I C E O F C O M P OS I T E R E S I N A S
F I G U R E 1 1 Comparison of fluorescence between old (left) and
A S I N G L E SU B S T I T U T I O N M A T E R I A L F O R
young (right) teeth. LOS T N A T U RA L T I S S U E A N D I T S
M E C H A N I C A L A N D OP T I C A L I N T E R A C T I O N S
attrition and increasing masticatory efficiency through coronal rigidity, 5.1 | Mechanics
scattering cooler shades of visible color. Within a biomimetic concept,
considering the restorative materials currently present in dental prac- Even though composite resins have very similar base formulations,
tice, resins would be substitutes for dentin, while feldspathic ceramics their mechanical behavior can vary dramatically depending on brand
would be substitutes for enamel. However, despite natural dentin names due to the different uses of filler particles. This approach is so
having low wear resistance and natural enamel having low fracture impactful that the current ranking factor for resins is particle size.27
resistance and low toughness, studies of hybrid systems help us to Two factors must be considered in this analysis. (1) Particles at the
understand that in bioinspiration, an intermediate design model could nanometer scale present an industrial deficiency in the silanization
supply the structural loss of these two materials with only a single process, compromising the mechanical properties of these materials.
restorative material. We have examples of natural bone composites, For this reason, fillers smaller than 50 nm were grouped into clusters
dentin, and even wood. The latter present specimens with hardness patented for a specific brand of resin (Figure 12) (Filtek Supreme
Ultra, 3 M, Minnesota, USA). (2) Large particles considerably increase

the fracture resistance but reduce the wear resistance, the polish, and,
to a lesser degree, the flexural strength, which could be improved by
increasing the small particle content of the organic phase.28 There-
fore, as the portion that will reconstitute dentin and enamel has dif-
ferent individual characteristics, it would be more logical to choose
materials with different constitutions for each layer. The innermost
portion of a resin buildup represents the structural reinforcement des-
ignated by natural dentin. In this constitutive layer of the restorative
core, resins with high mechanical properties, especially fracture tough-
ness, should be chosen. On the other hand, the outer layers need a
smoothness provided by polishing, avoiding increased biofilm reten-
tion, improving chromatic stability, and high wear resistance.
F I G U R E 1 2 SEM of a nanofill clustered composite resin. 5.2 | Optics

Courtesy: Marcos Vargas.
Following the principles of light scattering in natural teeth, the dentin
layer has higher density and, therefore, Mie-type scattering, empha-
sizing reddish-yellow hues.20 Thus, most studies analyzing the natural
color of dentin indicate a high predominance of the hue of Group A
on the Vita shade designation, as mentioned above. This phenomenon
occurs when light is scattered in particles larger than 450 nm, increas-
ing the chromatic effect of longer wavelength colors. However, parti-
cles with sizes within the visible light spectrum must be present for
light decomposition in the material to occur. By this analysis, resins
with characteristics suitable for dentin should contain particles rang-
ing from nanometer to micrometer scale, with a predominance of
medium-sized than micro or nanoparticles (Figure 13). This concentra-
tion will give the dentin layer a higher optical density, making it more
opaque. This phenomenon happens in the natural model. However, it
suffers variations according to a greater or lesser degree of dentin
mineralization in the different areas of the crown and aging. Thus, the
dentin will become more opaque from the cervical to the incisal third
and from the outermost area to the area closest to the pulp
(Figure 14A,B). With aging and increasing mineralization of the dentin
FIGURE 13 SEM of a nanohybrid composite resin. structure,29 fluorescence and opacity will decrease due to protein loss,
F I G U R E 1 4 (A and B) Tooth
(A) (B)
crown opacity 3D chart. Green
area is the most opaque part,
follow by blue tones (medium
opaque) and pink
(transluscent area).
(A)
(A)
(B)
(B)
(C) F I G U R E 1 6 (A and B) Images demonstrating the translucent and

opaque enamel lamellae and the blind analogy.
making the aged tooth more translucent in the dentin layer. It will also
become less reflective of visible light, generating a grayish appearance
of low luminosity (Figure 15A–C).
When the enamel is analyzed, a curious situation can be noticed.
Enamel is not a translucent material as commonly advocated by clini-
cians. Instead, it presents an organized arrangement of opaque and
highly translucent lamellae in horizontal layers to the crown—when
viewed from a facial perspective—compared analogously to a partially
open blind. Therefore, the enamel will function as an optical fiber in
F I G U R E 1 5 Comparison of opacity by age. (A) Extracted teeth the hypermineralized prismatic lines capturing the color of the dentin
(photographed with transmitted light) of older adult (left) and young underneath. In addition, the enamel will have a highly opaque behav-
(right). The older tooth is more translucent. Young and aged teeth ior in the protein-rich interprismatic areas (Figure 16A,B). If this were
show distinct opacity/translucency levels. (B) The young tooth is
not, the tooth would seem bluish even in the face of warmer dentin
brighter. (C) The older tooth lost the luminosity.
(A)
(B)
(C)
F I G U R E 1 7 (A–C) Cutback being performed and a value-

modifying achromatic composite resin layer applied. Post-operatory
result. FIGURE 18 Layering diagram in the polychromatic layering
technique.
colors. This constitution explains the enhanced light reflection in

young patients due to the thicker layer of this tissue. Abrasion and literature. A single layer of enamel with only one opacity will only be
attrition decrease this characteristic with age, making the enamel able to reproduce some of the nuances of opacity and translucency
more translucent overall and exacerbating the teeth’ low luminosity visible along the crown. Therefore, enamel shades of higher opacity,
with aging. Another essential factor is that composite resins cannot that is, higher value, should be used in the middle third area, giving
perfectly reproduce this unique characteristic because the material high luminosity to this region, especially in young patients. However,
does not present an organized distribution of phases. The latter is one a cutback and the use of enamel shades that reproduce the optical
of the factors that most corroborates the naturalness of the polychro- aspect produced by the junction of the buccal and palatal translucent
matic technique compared to other techniques described in the lamellae will provide adequate luminosity and a natural appearance to
the restoration (Figure 17A–C). For this purpose, inner opalescent and spectrum will favor natural optics, high fracture toughness, and
external resin masses of varying opacities are recommended. abrasive resistance.
Layer 2: This is the core layer, the most important for the fracture
resistance of the tooth/restoration compound. Because it is an inner
6 | S E L E C T I O N OF CO M P O S I T E R E S I N layer, fracture toughness is far more critical than wear resistance. This
B RA N D S F O R T HE D I F F E R E N T A RE A S O F T H E layer defines the primary hue and chroma of the tooth. One chroma
POLYCHROMATIC TECHNIQUE more saturated than the desired final shade should be chosen for the
cervical and middle third. The most prevalent hue for this dentin layer
Initially described by one of the authors of this article, the poly- is A in the VITA Classical shade guide. The opacity should block the
chromatic layering technique (PLT) is based on the rationally orga- mouth's dark background and allow for proper mamelon design and
nized distribution of five layers that reproduce the optical morphology. In this zone, classic microhybrids and larger-particle
characteristics of the natural tooth. The conceptual diagramming nanohybrids, predominant in their composition, will generate a high
of the arrangement of the layers by the polychromatic technique is resistance and a Mie-type dispersion, providing a reddish-yellow hue.
represented in Figure 18. Layer 3: This layer fills the depressions in-between, around,
and over the mamelons and has little influence on the final
strength due to its small quantity. However, it significantly contrib-
7 | LAYERS IN THE POLYCHROMATIC utes to the occurrence of opalescence. The beauty of incisal layer-
TECHNIQUE ing depends on this layer. A correct opalescence allows a through-
and-through transmission of light, like the natural enamel's translu-
Layer 1: In this palatal/lingual layer, the resin must elicit high abra- cent lamellae, accentuating the Rayleigh type's blue dispersion. For
sion/attrition resistance, as it is the path for anterior and canine accentuated Rayleigh scattering, the material must have nano-
guidance. High fracture toughness is also required, significantly metric particles and particles that promote light scattering
increasing the resistance of this area to functional loads. As it is a (between 180 and 700 nm). Its refraction in the organic matrix
region that challenges the reproduction of natural enamel, the stands differently than in the inorganic phase. High translucency
material must have a milky-white semitranslucent characteristic. nanocluster and hybrid resins produce the best results for
The milky-white halo along the incisal edge and the bluish opales- this area.
cent halo internally to it can be achieved by adjusting the thickness Layer 4: This layer must be resistant to abrasion due to the
of this milky-white semitranslucent layer to allow optical changes. sliding of food during cutting and hygiene techniques through
The choice should fall on micro-hybrid and nano-hybrid materials brushing. The area of the cervical and middle third primarily cov-
whose particle size composition encompasses nanometric and ered by this layer will define the final color of the tooth. In this
micrometric scales. The significant filler size variation will allow the zone, the sum of the dentin and the thickness of the enamel, with
correct scattering of light and dispersion into blue wavelengths its opaque and translucent lamellae acting as an optical fiber bring-
when these types of particles are present. Thus, variations between ing the dentin color, will generate the zone of higher light reflec-
20 and 180 nm (blue effect) and particles within the visible light tion in the crown. In order to achieve high wear resistance and
TABLE 1 List of commercially available composite resin brands categorized according to filler and colorimetric characteristics.
Layers Composite classification Color characteristics Brands

1 Nanohybrids (medium and large fillers) Achromatic, translucent, milky Vita-l-escence PF; Estelite Posterior PCE; Forma
Incisal or WE; Miris 2 NR; Inspiro Skin Neutral SN;
Renamel Nano Incisal Light; Venus diamond I;
Essentia LE; Gradia Direct NT or WT; Filtek
Supreme WE
2 Microhybrids or Nanohybrids (large O, Opaque, Dentin, D GrandioSO O colors; Enamel HRI UD colors;
fillers) Herculite XRV D colors; Vita-l-escence Vita colors;
Empress Direct D colors; Inspiro I colors; Renamel
Microhybrid Vita colors; Miris S colors.
3 Nanohybrids (micro fillers) Colors with high translucency and Filtek Supreme GT; Harmonize Incisal Blue; Essentia
effects OM; Vita-l-escence IrB; HRi OBN
4 Nano, micro or nanohybrids (micro Body colors or semi-opaque enamels Renamel microfill Vita colors; Estelite Sigma O
fillers) colors; Estelite Omega E colors; Harmonize E
colors; Herculite Ultra E colors
5 Nano, micro or nanohybrids (micro Achromatic (incisal) Renamel microfill IM; Estelite Sigma CE; Harmonize
fillers) Clear; Herculite Ultra Incisal; Filtek Supreme CT
(A) (B) (C) (D)
(E) (F) (G) (H)
(I) (J) (K) (L)
(M) (N)
F I G U R E 1 9 A step-by-step clinical case demonstrating the polychromatic layering technique for Class IV restorations. As part of a clinical
trial, brands of similar properties were used for each layer on each central incisor. No differences can be perceived between the two restorations
in the result. (A) Pre-operative condition. (B–D) Dentin and enamel shades are selected according to their distinct properties. (E) Bevel.
(F) Adhesive protocol. (G) Palatal shell with a milky-white semitranslucent composite. (H) Dentin layer. (I) Translucent enamel (opalescent effect).
(J) Body (chromatic) enamel. (K) White effect enamel. (L) Value (achromatic) enamel. (M and N) Follow-up after rehydration.
polishability, nanofilled and especially microfilled composites must to ensure a long-lasting functional behavior. Below is the indication of
be used. Nanohybrids with a predominance of nano and micropar- each brand according to the current literature and the authors'
ticles are also indicated. These materials must contain chromatic research and clinical experience regarding the characteristics of each
characteristics that will act synergistically with the opacity of the material available on the market (Table 1).
dentin. Thus, VITA-based resins of higher opacity designated by The polychromatic technique predictably restores the anterior
the manufacturer as “body” or natural translucency enamels will dentition seamlessly, provided the composite resins are selected
be essential allies in masking transition lines, especially in Class III according to their optimal mechanical and optical properties, and a
and IV restorations. methodical restorative protocol is followed. However, choosing the
Layer 5: This final layer aims to emphasize or modulate the effects optimal shades for each layer from among the available brands may
obtained in the underlying layers. It must present high polishability and be challenging, especially when the clinician needs to gain hands-on
wear resistance like the previous layer. In addition, this resin must have a familiarity with the vast array of commercial possibilities. Therefore,
noticeable opalescent effect that increases significantly with thickness. the authors recommend keeping a select combination of shades that
Frequently, there is a decrease in luminosity compatible with the natural- clinicians can repeatedly master in their day-to-day challenges. Once
ness of the incisal third. In young teeth, the opposite may occur due to the fundamental concepts of bioinspired protocols are fully mastered,
histological changes in the enamel. The same category of materials should combining different brands in a single case will no longer be a chal-
be preferred as the previous layer (nanofills, microfills, or small particle lenge and thus can provide esthetic results of high magnitude
nanohybrids) to avoid “islands” with different degrees of polishing in the (Figure 19A–N).
final buccal layer. However, concerning translucency, they must be achro-
matic (non-VITA based) to only generate chromatic expressions by effect
and not by pigments. 8 | CONC LU SION
For the longevity of the restoration, the right choice of material in
each of these five regions is paramount. To that effect, an analysis of After the bio-inspired analysis, using nature as a model to be
the mechanical properties of the composite resins must be carried out understood and followed, it is possible to note how the
polychromatic technique remains current and viable in mimicking 13. Morimoto S, Rebello de Sampaio FB, Braga MM, Sesma N, Ozcan M.
nature, providing esthetic and natural results in the layering of Survival rate of resin and ceramic inlays, onlays, and overlays: a sys-
tematic review and meta-analysis. J Dent Res. 2016;95(9):985-994.
composite resins.
14. Kopperud SE, Staxrud F, Espelid I, Tveit AB. The post-amalgam era: Nor-
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How to cite this article: Ricci WA, Fahl N Jr.. Nature-
sons for failure. Dent Mater: Off Publ Acad Dent Mater. 2015;31: mimicking layering with composite resins through a bio-
1214-1224. inspired analysis: 25 years of the polychromatic technique.
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15-22.

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17088240, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/jerd.13021 by Aline Girotto - CAPES , Wiley Online Library on [09/02/2023].

Nature-mimicking layering with composite resins through a

Weber Adad Ricci DDS, MS, PhD, Assistant Professor 1,2 |

J Esthet Restor Dent. 2023;1–12. wileyonlinelibrary.com/journal/jerd © 2023 Wiley Periodicals LLC. 1

F I G U R E 5 Bioinspiration example. Study of the wing of a

FIGURE 6 Enamel cracks demonstrating its low fracture

molecules that compose it will scatter the light with a wavelength of a

FIGURE 7 Opalescent effect.

FIGURE 9 Dentin yellow color.

The peritubular region presents isotropic behavior, and the orientation

compared to metals depending on the direction and constitution of

Ultra, 3 M, Minnesota, USA). (2) Large particles considerably increase

F I G U R E 1 2 SEM of a nanofill clustered composite resin. 5.2 | Optics

(C) F I G U R E 1 6 (A and B) Images demonstrating the translucent and

F I G U R E 1 7 (A–C) Cutback being performed and a value-

colors. This constitution explains the enhanced light reflection in

Layers Composite classification Color characteristics Brands

(A) (B) (C) (D)

(E) (F) (G) (H)

(I) (J) (K) (L)

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