Bio-Emulation biomimetically emulating nature utilizing a histo- anatomic approach; visual synthesis.pdf

CLINICAL RESEARCH Bio-Emulation: biomimetically emulating nature utilizing a histo- anatomic approach; visual synthesis Panaghiotis Bazos, DDS Emulation, Athens, Greece Pascal Magne, DMD, MSc, PhD Associate Professor, Don and Sybil Harrington Foundation, Chair of Esthetic Dentistry, Herman Ostrow School of Dentistry, University of Southern California, Los Angeles, USA Correspondence to: Panaghiotis Bazos DDS 33 Vasilissis Sophias Avenue 106 75 Athens, Greece. Tel: +30 210 722 2329; E-mail: [email protected] 330 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ BAZOS/MAGNE Abstract A thorough understanding of the spatial The main goals for this article are to cog- distribution pertaining to the histo-ana- nize histo-anatomic visualization by in- tomic coronal structures and dynamic troducing: (1) Dynamic light interaction, light interaction of the natural dentition (2) the 9 elements of visual synthesis, provides the dental team with the ulti- (3) dynamic infinite optical thickness, mate strategic advantage with regards and (4) amplified visual perception ef- to optical integration of the final restor- fect of the hard dental tissues. Further- ation. The second part of this two-part more, a diversification of photographic article will attempt to provide insight on illumination techniques will be illustrat- the illumination interactivity and the spa- ed in order to juxtapose optical asso- tial arrangement of the coronal elements ciations between the enamel/dentinoe- of natural teeth through the utilization of namel complex/dentin nexus. this knowledge in the clinical and techni- cal restorative approach. (Int J Esthet Dent 2014;9:330–352) 331 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ CLINICAL RESEARCH DENTIN OPACIFICATION FLUO R E L A T I V E DEC TRANSPARENCY FLUO ENAMEL TRANSLUCENCY OPAL Fig 1 Relative attribution: although translucent by nature, the coronal structural elements can be graded with regards to their relative dynamic light interactivity and unique optical expression. Introduction luster (S/G/L) should also be appraised in conjunction with translucency, opal- In the modern dental practice, recreat- escence and fluorescence (T/O/F) as ing the optical features of the intact tooth part of the process of visual assessment presents a formidable task, due to the in- (Fig 2). herent translucent nature of enamel, the dentinoenamel complex (DEC) and den- tin. Translucent materials offer a signifi- Dynamic light interaction cant color measurement challenge since they interact with light in a far more com- Reflection and refraction plex manner than most other materials. in enamel and dentin While being translucent by nature, when coronal structures, such as enam- Incident light ray interactivity with a tooth el, the DEC and dentin, are compared can be: among each other, they seem to pos- Reflected specularly and/or diffusely sess relative translucency, transpar- from its surface (Fig 3) ency and opacity respectively (Fig 1). Refracted and either: Anachronistic traditional visual estima- – scattered within it and subsequently tion approaches that solely employ the reflected, a process largely respon- Munsell color model system based on TJCMFGPSDPMPSQFSDFQUJPO 'JH hue, chroma, and value (H/C/V) domi- – transmitted diffusely through it (re- nate the dental market appear to be lating to the properties of transpar- inadequate when conveying the perti- ency, translucency and opacity) nent information among the dental team (Fig 5) members (clinician/technician/patient). – absorbed within it (the electromag- Further information regarding the de- netic energy is transformed to other scription of surface texture, gloss, and forms of energy, eg, heat, photolu- 332 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ BAZOS/MAGNE S G L descriptive H C V objective T O F subjective 9 Elements Fig 2 Dynamic light interaction will generate the visual synthesis which is influenced by nine elements: surface texture, gloss and luster (S/G/L); hue, chroma and value (H/C/V) and translucency, opalescence and fluorescence (T/O/F). Incident Light Ray Diffuse Reflection Specular Reflection Reflection Fig 3 The term reflectance is used to denote the fraction of light energy that is reflected by the surface of a given material. If the surface is not plane but curved, as is the case with enamel above, it may still be considered to be made up of many very small, elementary plane surfaces. DENTIN DEC ENAMEL 1.63 Refraction Fig 4 The term refraction is used to denote a change in direction of propagation of light waves as a result of its traveling at different speeds at different points among the wave front between mediums of varying optical densities. Primary subsurface scattering is denoted by the radial arrow depictions. 333 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ CLINICAL RESEARCH T H G LI T N E ID C IN DENTIN T H G LI D TE IT SM R E N F A L TR E C T E D L IG H T DEC ENAMEL Fig 5 Light interactivity model. From the cervical to the incisal regions, the dominance of the dentin core gradually gives way to that of the enamel shell respectively, achieving a brief equilibrium in the middle region. Multi-directional forms of scattering (colored arrows) and refractive index variations between the enamel/dentinoenamel complex/dentin substrates create infinite photonic pathways, collectively rendering a unique visual synthesis depending upon the incident light direction and intensity. 334 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ BAZOS/MAGNE minescence, photoelectric effect Light guiding by scattering etc) in enamel and dentin – re-radiated with a lower energy state (eg, fluorescence) The heterogenous composition and asymmetric directional distribution of Relative refractive index the hard dental tissue structural compo- nents add to the level of complexity with Due to the fact that enamel and dentin regards to microscopic light interactivity. are heterogeneous hydrated substrates Natural waveguides,8 such as enamel of variable inorganic and organic com- and dentin, are differentiated from con- position, one must consider collectively ventional optical fibers by being non- the volume fraction of their individual uniform and containing scattering parti- elemental component’s refractive index cles. Nonetheless, they have the ability (RI), resulting in their respective relative to collect light and transport it purposely refractive index (RRI). Moreover, de- towards the pulp chamber (Fig 5).9-12 pending on the localized mineral content Scattering generally implies a forced of these substrates, minor fluctuations deviation of light from a straight trajec- in the RI may ensue, with the highest tory by localized non-uniformities (scat- values always occurring within the more terers), found upon or within the me- mineralized locations.1,2 dium through which it interacts, without The structural orientation and the ar- the loss of energy. Reflection, refraction rangement of the enamel prisms do not and diffraction represent various forms seem to have a significant effect on light of scattering. With regards to enamel attenuation, resulting in an RRI value of and dentin, multiple scattering path- 1.63. Unlike enamel, the structural ori- ways are prevalent. In the quantum pic- entation and arrangement of the dentin ture, when the wavelength (frequency) tubules seem to play a significant role of the scattered light is the same as the with regards to the RRI of dentin. Tra- incident light, elastic scattering occurs. ditionally, dentin has been cited with a Conversely, when the emitted radiation HFOFSBMJ[FE33*WBMVFPG3 Contem- has a wavelength different from that of porary localized RRI values for dentin the incident radiation, inelastic scatter- subadjacent to the dentinoenamel com- ing occurs. plex (DEC) include 1.60 (cervical), 1.56 The inorganic component of the den- NJEEMF BOE JODJTBM tal hard tissues is responsible for elastic The DEC, being an organic proteina- scattering; via Rayleigh scattering (rath- ceous continuum5 that is dominated pri- er isotropic, only depending on the po- marily by Type I collagen, has an RRI larization of the wavelength) in the case WBMVFPG6,7 of enamel and via Mie scattering (rather anisotropic, forward scattering is pre- dominant) in the case of dentin,13 while the organic component of the dental hard tissues is responsible for inelastic scattering; via fluorescence. 335 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ CLINICAL RESEARCH a b c d e f Fig 6 The frontal longitudinal tooth section was submerged in distilled water and photographed on a black background. Despite using the same amount of direct reflective illumination per exposure, a direc- tional change of 90 degrees reveals stunning and complex light transmissive and reflective pathways, emphasizing the optical anisotropy of dentin. Sharp details and remarkable contrast within the dentin shade is seen (c). Pronounced backscattering across the enamel prisms and the dentin tubules render a diffuse appearance obscuring critical details as evident in depiction (d), based on incident light direction. Paral- lel illumination with respect to the long axis of the tooth present on the left and perpendicular on the right. 336 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ BAZOS/MAGNE Dentin tubule direction at the DEC parallel 0° oblique ¡ POV perpendicular 90° Fig 7 Dentin subadjacent to the DEC exhibits a transitional orthogonal rotational orientation from cervical to incisal with regards to the dentin tubules. Hence, despite the fact that cervical dentin is thicker, due to the parallel orientation of of the tubules, it is rendered more translucent. The opposite happens with respect to incisal dentin, despite the fact that it is thinner, due to the perpendicular orientation of the tubules, it is rendered more opacious. In the case of enamel, major random DEC, scattering is decreased due to scattering occurs on the ultrastructur- low tubule density with small tubule size, al level from the hydroxyapatite (HAp) compared to the dentin directly adja- crystal subunits, whereas minor random cent to or above the pulp due to high scattering occurs on the microstructural tubule density with large tubule size.21 level due to the prism sheaths/interpris- Thus there exists a significant translu- matic material orientation in conjunc- cency gradient, that of superficial den- tion with the sinuous paths of Hunter- tin which is more translucent and that of Schreger bands. The scattering deep dentin, which is three times more coefficient appears to increase with opacious.22 Additionally, the regional shorter wavelengths,16 while thin enam- variation of dentin tubule orientation is of el sections also exhibit a Fraunhofer dif- particular relevance with regards to light fraction pattern in the plane perpendicu- transmission, rendering cervical dentin lar to the enamel prisms,17 acting as a as highly transmissive, middle dentin diffraction grating which in turn may be as moderate, and incisal dentin as low responsible for generating iridescent re- (Fig 7). flections (Fig 6). Conversely, the DEC lacks significant In the case of dentin, multiple direc- scatterers. The elevated lateral light dif- tional scattering occurs on the micro- fusion that occurs at the DEC has been structural level due to the presence and described as the “glass layer” or “high spatial arrangement of the dentin tubules diffusion layer” or “brilliance zone.” and the collagen fiber mesh. In Factors that may be considered for this contrast with enamel, the scattering co- enhanced light diffusion is that the in- efficient does not change significantly ner aprismatic enamel presents a more with wavelength.20 Directly below the uniform HAp crystal orientation, con- 337 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ CLINICAL RESEARCH Fig 8 Direct illumination is used to enhance the sensation of surface topography of the maxillary central incisors. Moderate wear is viewed on the vertical developmental lobular heights of contour whereas the concave depressions have retained parts of their original horizontal structural anatomy; diffuse light was utilized via indirect illumination to enhance the sensation of gloss and luster. 338 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ BAZOS/MAGNE sequently producing an elevated light- Luster flux density concentration at this junc- Luster describes the qualitative correla- tion,25,26 while the underlying mantle tion of the visual appearance produced dentin exhibits low tubule density and by the reflection of light with the enamel small tubular size, providing minimal surface. Also known as contrast gloss, scattering. Furthermore, the change in luster can be somewhat subjective, ex- the RRI between dentin and enamel re- pressed in relative terms such as satin- sults in partial reflections of light at this like, pearly, metallic, glass-like (Fig 8). junction and theoretically, when condi- tions are favorable for short distances, Objective color elements localized total internal reflections may be attained. Hue Hue Is defined as the name that distin- guishes one family of colors from an- The nine elements other. Hue is specified as the dominant range of wavelengths in the visible spec- of visual synthesis trum that yields the perceived color.27 Descriptive surface elements The base shade of dentin primarily de- termines the hue of a tooth.28,29 Hue can Surface texture be considered the quality of pigment Surface texture describes the physical (Figs 9 and 10). characteristics of the enamel surface, being directional (vertical developmen- Chroma tal lobes/horizontal cervical ridges) and Chroma is defined as the saturation, structural (perikymata). Perpetual sur- intensity, or strength of the hue. Unlike face texture adaptation is a function of value, which occurs independently of the inherent microstructure at eruption hue, chroma is only present when there and the subsequent physical and chem- is hue.30 Chromaticity is an objective ical processes that modify it: attrition, specification of the quality of a color abrasion, and erosion (Fig 8). regardless of its value, that is, as de- termined by its hue and chroma, and Gloss is readily visualized via cross-polarized Gloss describes the visual perception reflective photography (Figs 9 and 10). based on the interaction of light with the physical characteristics of the enamel Value surface, relating to the ability to reflect Value is defined as the relative white- light in a specular (“glossy appearance” ness or blackness of a color and is de- observed on polished convex con- termined by comparing it to a gray of tours) or diffuse (“matte appearance” similar brightness. Value is also called observed within concave depressions) lightness, brightness or luminance manner. Like color, it exhibits physical, (Figs 9 and 10). physiologic, and psychological aspects (Fig 8). 339 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ CLINICAL RESEARCH Fig 9 The intact teeth comprising the maxillary triad were extracted concurrently due to periodontal reasons and deemed as exemplary dental specimens for exploring interdental structural and optical inter-relationships. Aggressive acidulation led to the selective enamel dissolution and revealed the dentin substructure. Lobular coalescence is particularly prevalent in the central incisor. 340 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ BAZOS/MAGNE C + M HUE ++ I +++ C +++ M CHROMA ++ I + C ++ M VALUE +++ I + Fig 10 The objective color elements as viewed and estimated; general congruency is observed among the cervical (C), middle (M) and incisal (I) thirds amongst the maxillary triad. A multitude of hues is found at the incisal third due to the phenomena of opalescence and counter-opalescence. Chroma is more pro- nounced at the cervical third due to the thickness of dentin.31 In all instances Value is highest at the middle third, due to the fact that the enamel and dentin present an equilibrium in terms of thickness ratios.32 341 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ CLINICAL RESEARCH Fig 11 The longitudinal histological tooth section of a maxillary central incisor, 1 mm in thickness, was submerged in distilled water and photographed via transmissive illumination (upper) and reflective illumina- tion (lower) to epitomize the opalescent nature of enamel. Subjective optical elements wide to 8 μm high) meet this property be- cause the HAp subunit crystals exhibit Translucency UIJDLOFTTFTPGUPON BOEXJEUIT Translucency is defined as a gradi- PGUPON'PSUIBUSFBTPOUIFTIPSU ent between transparency (complete blue wavelengths reflect preferentially transmission of light) and opacification from the enamel, while the longer am- (complete reflection of light). The light ber wavelengths transmit accordingly transmission of enamel has been shown through it (Fig 11). to be wavelength specific, age related and is influenced by its state of hydra- Fluorescence tion. A decrease in translucency during An example of photoluminescence is a dehydration is explained as a result of phenomenon in which invisible UV light an increased difference in refractive in- is absorbed and then re-emitted almost dices between the enamel prisms and immediately (10-8 s) at a less energet- the surrounding medium when water is ic wavelength in the visible spectrum. replaced by air.33 Enamel and dentin both possess fluo- rescent properties, with dentin generally Opalescence exhibiting three times the intensity than Known as the Rayleigh scattering ef- that of enamel35 upon longitudinal sec- fect; enamel demonstrates this dichroic tion, emitting a white-blue luminescence effect, which is caused by scattering after excitation, imparting additional vi- particles with typical dimensions much tality and brightness to the natural tooth smaller than the wavelength of illumina- appearance predominantly in UV rich tion used. The mineral crystals present environments only. The DEC also exhib- JO UIF FOBNFM QSJTN NFBTVSJOH μm its elevated fluorescence due to the col- 342 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ BAZOS/MAGNE ENAMEL DENTIN + +++ Fig 12 A submerged maxillary premolar was photographed with reflected long wavelength UV illumina- tion (365 nm), enabling the visualization of dentin exhibiting three times the fluorescence intensity than that of enamel. Note that the DEC also exhibits pronounced fluorescence. lagen-rich, highly cross-linked composi- of that material either on a white or black tion, with primary intrinsic (endogenous) background, defines its infinite optical fluorophores being the aromatic amino thickness (IOT). acid tryptophan36,37 and the collagen Although light transmission in enamel cross-linking agent hydroxypyridium at 1 mm has been tentatively measured (Fig 12).38 to be 66% ± 11%, while that of dentin at NN JT one must con- sider the significance of sample loca- Dynamic infinite optical tion, the relative thickness distribution of both tissues as well as stage of tissue thickness maturation. Perceived color can be considered a With regards to dynamic aging on combination of the reflected color of the the macrostructural level, enamel inad- translucent enamel layer plus the color vertently goes through a volumetric re- reflected from the underlying relatively duction via functional wear, mechanical opacified dentin layer. As the enamel abrasion and chemical erosion, result- and dentin layers vary inversely in rela- ing externally in a hyperpolished sur- tive thickness from cervical to incisal, face. Conversely, internally the dentin the amount of color contribution from volume increases via secondary and the two tissues will be reciprocal (vice tertiary dentin deposition. WFSTB 'JHTBOE o On a microstructural level, a signifi- The thickness of a given translucent cant reduction in the porosity of the material at which any further material ad- enamel is due to posteruptive matura- dition does not alter the transmission of tion via hypermineralizationo and light, nor the perceived reflected color homogenization leading to HAp crys- 343 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ CLINICAL RESEARCH ENAMEL THICKNESS AVERAGE FACIAL C oNN 0.26–0.30 mm oNN 0.3 mm M 0.80–0.99 mm 0.80–0.92 mm 0.80–0.90 mm 0.9 mm I 1.00–1.19 mm 0.90–1.02 mm 0.86–1.00 mm 1.0 mm ENAMEL +++ IOT +++ translucen cy gradien additional t material th ickness (+ ++) does not alter op tical expres sion Infinite Optical Thickness Fig 13 Individual and pooled averages with regards to labial enamel thickness for the maxillary triad at the cervical (C), middle (M) and incisal (I) thirds. tal elongation,52 while in a homologous appearing more transparent grey (lower manner, hypermineralization of dentin value) due to less light scattering. ensues via natural tubular obliteration, Further research is desired in order rendering dentin more translucent over to estimate the dynamic IOT values for time. enamel and dentin at different stages of Due to this dynamic cycle of events, tissue maturation, thus establishing uni- juvenile enamel, which is thicker, pos- versal industry standards for composite sesses a texturized surface and is com- resins and etchable ceramics. Possess- posed of small HAp crystals, appearing ing knowledge of the dynamic IOT and to be translucent white (higher value) the degree of translucency and opacity due to more light scattering, while adult of dental resins and etchable ce- (and senior) enamel, which is thinner, is ramics at given thicknesses will auto- characterized by a polished surface and matically enable clinicians and techni- composed of large HAp crystals, thus cians to strategize accordingly in order 344 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ BAZOS/MAGNE DENTIN THICKNESS AVERAGE FACIAL C 2.5 mm 1.8 mm 2.2 mm 2.2 mm M 1.9 mm NN NN 1.6 mm I 0.2 mm 0.2 mm 0.2 mm 0.2 mm DENTIN +++ IOT +++ translucen cy gradien t additional material th ickness (+ ++) does not alter op tical expres sion Infinite Optical Thickness Fig 14 Pooled averages with regards to labial dentin thickness for the maxillary triad at the cervical (C), middle (M) and incisal (I) thirds. to provide adequate tooth reduction to a stunning effect; an optical illusion of meet the specific objectives that are re- magnification55 and spatial proximity is quired. perceived with regards to the underlying dentin mamelons. This apparent mag- nification manifests in an incisobuccal Amplified visual direction, creating an optical illusion with regards to the position and dimension perception effect of dentin mamelons. This optical illusion Due to the convex lens-like shape of is subdued in part by the birefringent enamel in conjunction with possessing nature of enamel, obscuring details ren- an RRI of 1.63, optical distortion oc- dering a hazy net appearance (Fig 15). curs. Thus, light being refracted within Concurrently, dentin also exhibits mag- enamel, the DEC and subsequently in- nification properties56,57 due to the di- ternally reflected from dentin produces vergent radial fanning of the dentin tu- 345 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ CLINICAL RESEARCH apparent dentin mamelons actual dentin mamelons Fig 15 Enamel is responsible for creating an optical illusion of the apparent versus the actual position with regards to the visualization of the underlying incisal dentin. bules when light is reflected internally graphic techniques aimed at increasing from the deeper strata. the accuracy and objectivity of dental shade evaluation and laboratory com- munication. In order to minimize the Diversification of user-dependent error in future clinic- al practice, it is necessary to develop photographic illumination standardized, reproducible imaging techniques modalities and objective image analysis Intact dental specimens provide the ul- methods (Figs 16 and 17). timate reference for the perpetual de- votion of time and attention to acquire Reflective Illumination the needed knowledge with regards to visual interpretation.58,59 Direct reflective illumination utilizing a Over the last decade, there has been macro twin flash, via manual standardi- profound interest in alternative photo- zation of power output, remains the pho- 346 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ BAZOS/MAGNE Fig 16 Facial illumination techniques from top to Fig 17 Palatal illumination techniques from top to bottom: reflective, reflective cross-polarized, reflec- bottom: reflective, reflective cross-polarized, reflec- tive UV and transillumination. tive UV and transillumintion. 347 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ CLINICAL RESEARCH tographic standard for providing pre- estimation of incisal enamel distribu- dictable and repeatable levels of light tion. Opalescence may also be visually for shade estimation. Indirect reflective assessed and gauged via this type of illumination (Lumiquest, Pocket Bounc- photography. To obtain such an image ers,) on the other hand, aids in revealing intraorally, a fiber optic transilluminator fine surface texture details. is utilized (Micro-Lux, AdDent). Reflective cross-polarized illumination Discussion This photography technique significant- The restorative task is elaborated along ly mitigates unwanted specular reflec- four levels of integration: biological, tions which obscure the fine details of functional, mechanical, and optical. dental structures23,60, while providing a To meet contemporary challenges, the high contrast/hypersaturated dental im- dental team must enhance its capacity age to be objectively analyzed via a cali- in all four levels equally. brated RAW workflow utilizing a generic From an optical standpoint in ambi- software program (Adobe Photoshop) ent light, enamel can be considered in the CIE L*a*b color space. To obtain isotropic, with the visual gradient being such a photographic image intraorally, expressed in the vertical direction (cer- a cross-polarization filter is utilized (po- vical/incisal) due to thickness variation, lar_eyes, Emulation). whereas dentin can be considered ani- sotropic, with the visual gradient being UV Illumination expressed: a) in a radial direction due to the dentin tubule attributes of diam- Ultraviolet Illumination is utilized in or- eter and density (qualitiative), and b) in a der to induce fluorescence and aid in horizontal zonal direction (cervical/mid- the selection of the restorative material dle/incisal) due to thickness variation (etchable ceramics and resins) with a and differing RRI indexes (quantitative). similar fluorescence intensity,61-63 pro- Hue and chroma are predominately viding the restoration with optimal inte- determined by the properties of dentin, gration primarily in the event of exposure dynamically changing over time as sec- to a UV dominant lighting environment, ondary deposition occurs. In some in- such as a dancehall or a nightclub. To stances, as in the cases of severe incisal obtain such an image intraorally, a cus- wear, dentin can be breached to such tom modified xenon flash tube is utilized an extent that external chromophores (fluor_eyes, Emulation). become readily absorbed, resulting in infiltration staining (Fig 10). Transillumination While the opacity of dentin provides and establishes a baseline for value, the Transillumination reveals histo-anatomic luminosity is predominately regulated by relative opacity levels (transparent den- the properties of enamel. The surface tin vs opaque) and visual quantitative texture influences the primary interac- 348 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ BAZOS/MAGNE CENTRAL LATERAL CANINE Fig 18 Stone replicas facilitate visual assessment and rumination of the variability between enamel and dentin surface topography. Mesiobccal (left) and Mesiopalatal (right) oblique views of central incisor, lateral incisor and canine (top to bottom). Generalized external enamel macromorphological congruency is seen upon the dentin counterpart, with amplified vertical corrugations, providing added roughness and waviness that is critical to be emulated during restorative stratification techniques. 349 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ CLINICAL RESEARCH tion of the incident light. A highly tex- they opt to employ; a trilaminar technique tured surface renders higher amounts of (enamel/DEC/dentin) for a simplex inter- diffuse surface scattering, thus elevat- pretation or a pentalaminar technique ing the perceived value, appearing to (Exo enamel/eso enamel/DEC/exo den- be more translucent. This is in contrast tin/eso dentin) for a complex one. The to a smooth surface, which would ex- utilization of this knowledge in the clin- hibit lesser amounts of diffuse surface ical and technical restorative approach scattering, thus demoting the perceived is to be described thoroughly in articles value, and appearing to be more trans- that will be published in future issues of parent. The relative thickness of enamel this journal. dictates the proportional amount of dif- fuse subsurface scattering (quantita- tive), while the degree and postmatura- Conclusion tion stage of the HAp crystals affects the type of photonic interaction (qualitative). This article presented fundamental yet Transparency, translucency and simplified photonic interactions with re- opacification are all visual representa- gards to the histoanatomic elements, ren- tions of the amount of light that is scat- dering the final visual synthesis. It should tered and subsequently reflected to the be emphasized that a thorough under- observer by the microstructural features standing of the light propagation within of a given substrate. Embracing the the coronal structures is a prerequisite paradigm shift of thinking in terms of dy- in order to elucidate color and shade, namic light interactivity via the principle however mastery of spatial distribution of scattering enables the clinician and of the three-dimensional histoanatomic technician to choose the level of sophis- relationships is paramount in the quest tication within the stratification protocol for restorative dental emulation (Fig 18). 350 THE INTERNATIONAL JOURNAL OF ESTHETIC DENTISTRY 70-6.&t/6.#&3t"656./ BAZOS/MAGNE References 9. Altshuler GB, Erofeev AV. 21. Garberoglio R, Brännström Lasers in Dentistry. Chicago: M. Scanning electron Quintessence Publishing, microscopic investigation of 1. Hariri I. Estimation of the 1995. human dentinal tubules. 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