Magnification—a New Look at a Long-known Optical Property of Dentin

Visualization of Pulpal Structures by SWIR in Endodontic Access Preparation

Endodontic access preparation is one of the initial steps in root canal treatments and can be hindered by the obliteration of pulp canals and formation of tertiary dentin. Until now, methods for direct intraoperative visualization of the 3-dimensional anatomy of teeth have been missing. Here, we evaluate the use of shortwave infrared radiation (SWIR) for navigation during stepwise access preparation. Nine teeth (3 anteriors, 3 premolars, and 3 molars) were explanted en bloc with intact periodontium including alveolar bone and mucosa from the upper or lower jaw of human body donors. Analysis was performed at baseline as well as at preparation depths of 5 mm, 7 mm, and 9 mm, respectively. For reflection, SWIR was used at a wavelength of 1,550 nm from the occlusal direction, whereas for transillumination, SWIR was passed through each sample at the marginal gingiva from the buccal as well as oral side at a wavelength of 1,300 nm. Pulpal structures could be identified as darker areas approximately 2 mm before reaching the pulp chamber using SWIR transillumination, although they were indistinguishable under normal circumstances. Furcation areas in molars appeared with higher intensity than areas with canals. The location of pulpal structures was confirmed by superimposition of segmented micro-computed tomography (µCT) images. By radiomic analysis, significant differences between pulpal and parapulpal areas could be detected in image features. With hierarchical cluster analysis, both segments could be confirmed and associated with specific clusters. The local thickness of µCTs was calculated and correlated with SWIR transillumination images, by which a linear dependency of thickness and intensity could be demonstrated. Lastly, by in silico simulations of light propagation, dentin tubules were shown to be a crucial factor for understanding the visibility of the pulp. In conclusion, SWIR transillumination may allow direct clinical live navigation during endodontic access preparation.

The power of light - From dental materials processing to diagnostics and therapeutics

Harnessing the power of light and its photonic energy is a powerful tool in biomedical applications. Its use ranges from biomaterials processing and fabrication of polymers to diagnostics and therapeutics. Dental light curable materials have evolved over several decades and now offer very fast (≤ 10 s) and reliable polymerization through depth (4-6 mm thick). This has been achieved by developments on two fronts: (1) chemistries with more efficient light absorption characteristics (camphorquinone [CQ], ~30 L mol-1 cm1 [ʎmax 470 nm]; monoacylphosphine oxides [MAPO], ~800 L mol-1 cm-1 [ʎmax 385 nm]; bisacylphosphine oxide [BAPO], ~1,000 L mol-1 cm-1 [ʎmax 385 nm]) as well mechanistically efficient and prolonged radical generation processes during and after light irradiation, and; (2) introducing light curing technologies (light emitting diodes [LEDs] and less common lasers) with higher powers (≤ 2 W), better spectral range using multiple diodes (short: 390-405 nm; intermediate: 410-450 nm; and long: 450-480 nm), and better spatial power distribution (i.e. homogenous irradiance). However, adequate cure of materials falls short for several reasons, including improper selection of materials and lights, limitations in the chemistry of the materials, and limitations in delivering light through depth. Photonic energy has further applications in dentistry which include transillumination for diagnostics, and therapeutic applications that include photodynamic therapy, photobiomodulation, and photodisinfection. Light interactions with materials and biological tissues are complex and it is important to understand the advantages and limitations of these interactions for successful treatment outcomes. This article highlights the advent of photonic technologies in dentistry, its applications, the advantages and limitations, and possible future developments.

Does luminosity and smear layer influence 810 nm laser energy transmission through human dentine?

PURPOSE

The aim of this study was to evaluate the influence of luminosity values and smear layer on transmission characteristics of 810 nm near infrared laser energy through dentine, using extracted human teeth.

METHODS

A total of 200 teeth treated with endodontic medicaments to cause discolouration (Ledermix, Doxypaste or Odontopaste) were selected, to give a range of values for tooth shade (luminosity values). Sectioned teeth had smear layer created or removed. Near-infrared laser energy transmission was assessed using an 810 nm diode laser (90 mW, CW mode) with the tip placed at 2 mm and 4 mm from the external root surface, and a laser power metre.

RESULTS

Both tooth shade and smear layer had independent attenuating effects. Transmission of laser energy was significantly lower in teeth with darker shades. There was a strong positive correlation between relative luminosity (lighter tooth colour) and transmitted laser power (r = 0.9271 for the Spearman rank correlation, P = 0.0022). When a smear layer was present, this significantly reduced the transmission of laser energy through the sample, compared to when no smear layer was present.

CONCLUSION

The results of this laboratory study highlight the attenuating influence of a darker tooth shade and the presence of smear layer on the transmission of 810 nm light when directed onto the surface of human dentine. Such effects may be relevant to photo biomodulation, Photodynamic Therapy and other dental laser treatments.

Determination of the spectrally resolved extinction coefficient of human dental enamel using collimated transmission spectroscopy

OBJECTIVES

The determination of the extinction coefficient of human dental enamel to deliver further optical properties of enamel to improve the understanding of light propagation in teeth and to improve restoration materials.

METHODS

The extinction coefficient was measured within a spectral range of 300-980 nm using a collimated transmission setup. 35 specimens from 16 donors were examined. The donors were categorized by age and the researched specimen were categorized by tooth type, tooth quality and lateral expansion of the enamel to clarify the influence of these parameters.

RESULTS

The obtained spectrally resolved extinction coefficient was accurately described by a power law, which agrees with theoretical scattering models. The results were evaluated with regard to the influence of parameters such as subject age, tooth type, enamel sample quality and enamel width. For this purpose, both the average values of multiple measurements of a single sample in a defined spectral range as well as the curve slope of the averaged results versus wavelength were compared.

SIGNIFICANCE

The results provide detailed information about the optical properties of human enamel. The wide spectrum investigated provides important information for the evaluation of the main scatterers and the optical impression under any light condition. However, the deviation of the extinction coefficient varies less between the mean values for the specimens grouped by several parameters than between the specimens themselves within a group. This indicates a unique optical behaviour for every specimen and this requires consideration in the development of artificial materials.

Attenuation of near-ultraviolet, visible and near-infrared light in sound and carious human enamel and dentin

Objectives

This in vitro study aimed to investigate the optical attenuation of light at 405, 660 and 780 nm sent through sound and carious human enamel and dentin, including respective individual caries zones, as well as microscopically sound-appearing tissue close to a carious lesion.

Materials and methods

Collimated light transmission through sections of 1000–125-µm thickness was measured and used to calculate the attenuation coefficient (AC). The data were statistically analysed with a MANOVA and Tukey’s HSD. Precise definition of measurement points enabled separate analysis within the microstructure of lesions: the outer and inner halves of enamel (D1, D2), the translucent zone (TZ) within dentin lesions and its adjacent layers, the enamel side of the translucent zone (ESTZ) and the pulpal side of the translucent zone (PSTZ).

Results

The TZ could be distinguished from its adjacent layers and from caries-free dentin at 125 µm. Sound-appearing dentin close to caries lesions significantly differed from caries-free dentin at 125 µm. While sound and carious enamel exhibited a significant difference (p < 0.05), this result was not found for D1 and D2 enamel lesions (p > 0.05). At 405 nm, no difference was found between sound and carious dentin (p > 0.05).

Conclusions

Light optical means enable the distinction between sound and carious tissue and to identify the microstructure of dentin caries partially as well as the presence of tertiary dentin formation. Information on sample thickness is indispensable when interpreting the AC.

Clinical relevance

Non-ionising light sources may be suitable to detect lesion progression and tertiary dentin.

Transmission of 940 nm diode laser to the radicular area during its application as root canal disinfectant

To measure the transmitted laser power in the coronal, middle and apical root thirds during vertical and horizontal irradiation of laser. 14 mm length whole roots and longitudinal root sections were irradiated using a 940 nm diode laser with 0.5 W in continuous mode for 5 s. A power detector was placed in front of the root apex for the vertical transmitted power measurement and placed laterally to root surface for the horizontal transmission experiment. The transmitted power from the root apex vertically was 53% of the irradiated power, while for the horizontal transmission experiment for the coronal, middle and apical root thirds were 25.6%, 40.4% and 41.3%, respectively. Irradiation of root canals with 940 nm laser power can be transmitted during vertical irradiation in more than 50% of the samples, whereas less transmission happens with horizontal irradiation at apical and middle root third than coronal.

Cavity Disinfection With a 445 nm Diode Laser Within the Scope of Restorative Therapy - A Pilot Study

Introduction: Cavity disinfection is necessary to prevent a progressive infection of the crown dentin and pulp. Increasing intolerance and resistance to antiseptics and antibiotics as well as the controversy over the effects of those on the dental hard tissue and composite have prompted the investigation of alternative treatment options. The objective of this pilot study is to evaluate the antibacterial potential of a diode laser with a wavelength of 445 nm in the cavity preparation using the bacterium Streptococcus salivarius associated with caries in conjunction with the characteristics and influences of dentin on light transmission. Methods: The bactericidal effect of the laser irradiation was determined in culture experiments by using caries-free human dentin samples on bacteria-inoculated agar. For this, dentin discs (horizontally cut coronal dentin) of 500 µm and 1000 µm thicknesses were produced and irradiated with the laser with irradiation parameters of 0.7-1 W in a cw-mode and exposure times of between 5-30 s. Based on the different sample thicknesses, the penetration depth effect of the irradiation was ascertained after the subsequent incubation of the bacteria-inoculated agar. Additional influential parameters on the irradiation transmission were investigated, including surface moisture, tooth color as well as the presence of a smear layer on the dentin surface. Results: The optical transmission values of the laser radiation for dentin were significantly dependent on the sample thickness (P = 0.006) as well as its moisture content (P = 0.013) and were independent of the presence of a smear layer. There was a 40% reduction in bacteria after the radiography of the 500-µm-thick dentin samples, which was shown as the lowest laser dose (443 J/cm²). Conclusion: These findings indicate that the diode laser with light emission at a wavelength of 445 nm is interesting for the supportive cavity disinfection within the scope of caries therapy and show potential for clinical applications.

New fluorescence and reflectance analyses to aid dental material detection in human identification

INTRODUCTION

The identification of aesthetic dental materials during clinical dental examination can be challenging especially as patients and dental manufacturers place great emphasis on filling materials being as close as possible in appearance to the natural tooth. This makes dental identification in a forensic setting even more complicated.

OBJECTIVE

The aim of this study was to develop a simple method using photographic analyses to determine differences in fluorescence and reflectance between brands and shades.

METHOD

Three discs of 95 shades of resin composites (n = 285) were produced. Photographs were taken using a digital single-lens reflex (DSLR) camera attached to a dark box illuminated by an ultraviolet (UV) flashlight (wavelength 385 ± 10 nm) in a standardised manner. Images were analysed using an image software. The lightness (L) component according to the CIELAB was recorded. Kruskal-Wallis test was used to compare the mean lightness of the different samples followed by Dunn's test for multiple comparisons. The level of significance was set at P < 0.05.

RESULTS

L values ranged from 238.81 to 49.74. Fluorescence and reflectance were categorized according to crescent L values into 5 categories and organized into a Fluorescence and Reflectance Scale. Overall, dentin shades showed similar L values when compared to the same enamel shade from the same manufacturer. Comparison of L values for shades A1E and A3.5E demonstrated that darker shades had lower L values.

CONCLUSIONS

UV light allowed the recording of the Lightness component of CIELAB of a composite with little variation between images. The Fluorescence and Reflectance Scale allows the examiner to identify a specific brand or restrict the possibilities down to two brands. This information could help in cases of identification especially when ante-mortem data is limited.

Transillumination and HDR Imaging for Proximal Caries Detection

The purpose of this study was to develop an in vitro model for the validation of near-infrared transillumination (NIRT) for proximal caries detection, to enhance NIRT with high-dynamic-range imaging (HDRI), and to compare both methods, using micro-computed tomography (µCT) as a reference standard. Both proximal surfaces of 53 healthy or decayed permanent human teeth were examined using the Diagnocam (DC) (KaVo) and NIRT with HDRI (NIRT-HDRI). NIRT was combined with HDRI to improve the diagnostic performance by reducing under- and overexposed image areas. For NIRT-HDRI, an exposure series was captured and merged into a single HDR image. A classification was applied according to lesion depth. All surfaces were assessed twice by 2 trained examiners, and additionally with µCT for validation. The Kappa statistic was used to calculate inter-rater reliability and agreement between DC and NIRT-HDRI. Inter-rater reliability (weighted Kappa, wκ) showed very good agreement for the DC (0.90) and NIRT-HDRI (0.96). The overall agreement (wκ) was almost perfect (0.85). In the individual categories (0 to 4), the agreement (simple Kappa) ranged from almost perfect (category 4) to moderate (1 and 2) to substantial (categories 0 and 3). Sensitivity and specificity of sound surfaces, enamel, and dentin caries ranged from 0.57 to 0.99 and were similar for both methods in the different categories. NIRT-HDRI had a higher sensitivity for sound surfaces and enamel caries, as well as a higher specificity for dentin caries. Regarding the obtained images, HDRI allowed for the detection of caries within a greater range of luminance levels, resulting in a more detailed visualization of structures without under- or overexposure. However, HDRI this did not improve the diagnostics significantly. Distinguishing between a processed demineralized enamel and dentin lesions appears to be a problem specific to NIRT and cannot be balanced using HDRI.

"Metabolism of Odontoblast-like cells submitted to transdentinal irradiation with blue and red LED"

OBJECTIVES

The present study evaluated the trans-dentinal effect of light emitting diodes (LEDs) irradiation on the metabolism of odontoblast-like cells.

METHODS

Seventy-two dentin discs (0.2mm thick) were obtained from human molar teeth. MDPC-23 cells (20,000 cells/disc) were seeded on the pulpal side of the discs using DMEM, supplemented with 10% fetal bovine serum (FBS). After 12h, the culture medium was replaced with DMEM containing 0.5% FBS. After additional 12h, blue (455±10nm) or red (630±10nm) LEDs were used at irradiances of 80 and 40mW/cm², respectively, to irradiate the occlusal side of the discs. The energy doses were fixed at 2 or 4J/cm². Cell viability, alkaline phosphatase activity (ALP), total protein production and collagen synthesis were evaluated 72h after irradiation. Data were submitted to Kruskal-Wallis and Mann-Whitney tests (α=0.05).

RESULTS

Red light promoted proliferative effects at the energy dose of 4J/cm²_. Conversely, cell cultures irradiated with 2J/cm² emitted by the blue light showed reduced viability. ALP production was stimulated by red light in comparison with blue light at 4J/cm². Total protein production was reduced after exposure to blue light at 4J/cm², while no effect was observed on collagen production.

CONCLUSIONS

Irradiation with red LED at 4J/cm² bio-stimulated the viability of odontoblast-like cells, whilst blue light had unfavorable effects on the cellular metabolism.

Evaluation of the effects of fluoride-releasing varnish on dentin demineralization using optical coherence tomography

Effects of a fluoride-releasing varnish containing surface reaction-type prereacted glass ionomer (S-PRG) filler on dentin demineralization were examined using optical coherence tomography. Bovine incisors that were sliced and treated with undersaturated 0.1 M lactic acid buffer solution (DE group). A thin film of varnish-containing S-PRG filler was applied before demineralization (PRG group). Control was maintained in artificial saliva. Using optical coherence tomography of selected locations on the dentin surface, peak intensity (dB) and width (μm) at 1/e(2) were obtained and integrated values calculated. Although alterations in integrated values were different in each group, there was a slight but not significant increase in those for the control group and a slight but significant increase for the De group. For the PRG group, integrated values were doubled seven days after experiment initiation, followed by a significant increase. Fluoride-releasing varnish containing S-PRG fillers prevented dentin demineralization as detected by optical coherence tomography.

Transmission of Curing Light through Moist, Air-Dried, and EDTA Treated Dentine and Enamel

Objective. This study measured light transmission through enamel and dentin and the effect of exposed dentinal tubules to light propagation. Methods. Light attenuation through enamel and dentin layers of various thicknesses (1 mm, 2 mm, 3 mm, and 4 mm) was measured using specimens that were (1) moist and (2) air-dried (n = 5). Measurements were repeated after the specimens were treated with EDTA. Specimens were transilluminated with a light curing unit (maximum power output 1869 mW/cm(2)), and the mean irradiance power of transmitting light was measured. The transmission of light through teeth was studied using 10 extracted intact human incisors and premolars. Results. Transmitted light irradiance through 1 mm thick moist discs was 500 mW/cm(2) for enamel and 398 mW/cm(2) for dentin (p < 0.05). The increase of the specimen thickness decreased light transmission in all groups (p < 0.005), and moist specimens attenuated light less than air-dried specimens in all thicknesses (p < 0.05). EDTA treatment increased light transmission from 398 mW/cm(2) to 439 mW/cm(2) (1 mm dentin specimen thickness) (p < 0.05). Light transmission through intact premolar was 6.2 mW/cm(2) (average thickness 8.2 mm) and through incisor was 37.6 mW/cm(2) (average thickness 5.6 mm). Conclusion. Light transmission through enamel is greater than that through dentin, probably reflecting differences in refractive indices and extinction coefficients. Light transmission through enamel, dentin, and extracted teeth seemed to follow Beer-Lambert's law.

Photodynamic Inactivation of Root Canal Bacteria by Light Activation through Human Dental Hard and Simulated Surrounding Tissue

Introduction: Photodynamic inactivation of bacteria (PIB) may be a supportive antimicrobial approach for use in endodontics, but sufficient activation of photosensitizers (PS) in root canals is a critical point. Therefore, aim of this study was to evaluate the ability of PS absorbing blue (TMPyP) or red light (Methylene Blue; MB) for light activation through human dental hard and simulated surrounding tissue to inactivate root canal bacteria.

Methods: A tooth model was fabricated with a human premolar and two molars in an acrylic resin bloc simulating the optical properties of a porcine jaw. The distal root canal of the first molar was enlarged to insert a glass tube (external diameter 2 mm) containing PS and stationary-phase Enterococcus faecalis. Both PS (10 μM) were irradiated for 120 s with BlueV (20 mW/cm²; λ_em = 400–460 nm) or PDT 1200L (37.8 mW/cm²; λ_em = 570–680 nm; both: Waldmann Medizintechnik), respectively. Irradiation parameters ensured identical numbers of photons absorbed by each PS. Three setups were chosen: irradiating the glass pipette only (G), the glass pipette inside the single tooth without (GT) and with (GTM) simulated surrounding tissues. Colony forming units (CFU) were evaluated. Transmission measurements of the buccal halves of hemisected mandibular first molars were performed by means of a photospectrometer.

Results: PIB with both PS led to reduction by ≥ 5 log₁₀ of E. faecalis CFU for each setup. From transmission measurements, a threshold wavelength λ_th for allowing an amount of light transmission for sufficient activation of PS was determined to be 430 nm.

Conclusion: This study can be seen as proof of principle that light activation of given intra-canal PS from outside a tooth may be possible at wavelengths ≥ 430 nm, facilitating clinical application of PIB in endodontics.

Metabolic activity of odontoblast-like cells irradiated with blue LED (455 nm)

Blue light emitting diodes (LEDs) are frequently used in dentistry for light activation of resin-based materials; however, their photobiostimulatory effects have not yet been fully investigated. This study aimed to investigate the effect of blue LED (455 nm) on the metabolism of odontoblast-like cells MDPC-23. Energy doses of 2 and 4 J/cm(2) were used at 20 mW/cm(2) fixed power density. MDPC-23 cells were seeded at 10,000 cells/cm(2) density in Dulbecco's modified Eagle's medium (DMEM) containing 10 % fetal bovine serum (FBS). After 12 h, the culture medium was replaced with new DMEM supplemented with 0.5 % of FBS, and the cells were incubated for further 12 h. After that, single irradiation was performed to the culture, under selected parameters. Cell viability evaluations (Alamar Blue Assay, n = 12), number of viable cells (Trypan Blue Assay, n = 12), morphological analysis by scanning electron microscopy (SEM, n = 2), gene expression (n = 6) of alkaline phosphatase (Alp), collagen (Col-1a1), and dental matrix protein (Dmp-1) (quantitative polymerase chain reaction (qPCR)) were performed 72 h after irradiation. Data were analyzed by Kruskal-Wallis, ANOVA, and Tukey tests (p < 0.05). Direct light application at 4 J/cm(2) energy dose had no negative effects on cell viability, while irradiation with 2 J/cm(2) reduced cell metabolism. None of doses affected the number of viable cells compared with the control group. The two energy doses downregulated the expression of Alp; however, expression of Col-1a1 and Dmp-1 had no alteration. Cells presented change in the cytoskeleton only when irradiated with 2 J/cm(2). In conclusion, the blue LED (455 nm) irradiation, under the evaluated parameters, had no biostimulatory effects on MDPC-23 cells.

Dentin translucency and color evaluation in human incisors, canines, and molars

STATEMENT OF PROBLEM

For restorations with excellent esthetics, an understanding of the optical properties of human dentin is needed. Little information is available on the translucency and color parameters of dentin and its relationship to tooth type and position.

PURPOSE

The purpose of this in vitro study was to investigate the translucency and CIELab color coordinates of human dentin in both anterior (incisors and canines) and posterior teeth (molars) by using spectrophotometric and spectroradiometric assessment methods.

MATERIAL AND METHODS

Uniformly thick specimens (2 mm) of midcoronal human dentin were taken from 33 central and lateral incisors, 7 canines, and 33 molars (all maxillary teeth). The CIELab color coordinates were measured with a clinical spectrophotometer (Easyshade Compact) and a noncontact spectroradiometer (SpectraScan PR-704). The translucency parameter (TP) was calculated. Bland-Altman plots and Wilcoxon signed rank tests for paired samples were used to assess the agreement of the 2 measurement techniques. The differences between anterior and posterior dentin specimens regarding color coordinates and the translucency parameter were analyzed using Mann-Whitney-Wilcoxon rank sum tests.

RESULTS

Statistically significant differences between spectrophotometric and spectroradiometric measurements of the TP and CIELab color coordinates were found in both groups of dentin specimens (P<.05). TP values of molar dentin specimens were significantly higher than those of the anterior ones, regardless of the assessment method (P<.001). Dentin specimens of the anterior teeth exhibited higher L∗ values but lower a∗ and b∗ values on both black and white backgrounds compared with molar dentin specimens.

CONCLUSIONS

The dentin of anterior teeth was found to be lighter but less translucent and less chromatic than in molars, regardless of the assessment method used.

Dentine scattering, absorption, transmittance and light reflectivity in human incisors, canines and molars

OBJECTIVES

To evaluate, using Kubelka-Munk reflectance theory, the scattering (S), absorption (K), transmittance (T) and light reflectivity (RI) of incisors, canines and molars human dentine.

METHODS

Eighty-one human teeth (incisors, canines and molars) were used in this study. All teeth crowns were sectioned using a water-cooled diamond saw at low speed. The obtained dentine samples were polished to a final thickness of 2mm. The relative spectral radiance was measured against black and white backgrounds, using a spectroradiometer in a viewing cabinet with D65 illuminant. Kubelka-Munk equations were used to calculate the scattering and absorption coefficients, transmittance and light reflectivity. Kruskal-Wallis rank sum test was performed to compare the mean values of Kubelka-Munk coefficients of human incisors, canines and molars dentine samples followed by Kruskal-Wallis multiple comparison tests for pairwise comparisons.

RESULTS

The spectral behavior of S, T and RI exhibited similar trends for all three types of dentine samples. However, highly significant differences (p<0.001) were found between their magnitudes in the three types of dentine samples (p<0.001). Only the magnitudes of the K coefficients were found to be similar (p=0.235) between incisors, canines and molars. Canine's dentine samples showed highest S and RI values, while human molars dentine samples exhibited highest K and T values.

CONCLUSIONS

Within the limitations of this study, the optical properties of human dentine are strongly influenced by the type of tooth. The results of the present study can be used as reference in the development of aesthetic dental restorative materials.

CLINICAL IMPLICATIONS

The significant differences identified in the optical behavior of the dentine from the three types of teeth have to be taken into consideration by the dentist and the dental technician when pursuing biomimetics with any restorative material in esthetic dentistry.

Scattering properties of a composite resin: Influence on color perception

Background:

The properties of the composite materials and the clinical expertise while layering them carry many esthetic implications in restorative dentistry.

Aims:

The aim of the present study is to assess the influence of scattering properties of G-aenial A2 shade on color perception when used in esthetic restorations.

Materials and Methods:

Two composite resins were evaluated in this study: Gradia Direct (shade A3) and G-aenial (shade A2). A colorimetric evaluation according to the CIE L*a*b* system, relative to standard illuminant A against a white background, was performed to assess the referred chameleonic properties of G-aenial when used in simulated clinical situations.

Statistical Analysis Used:

The differences in color change between the test group G-aenial and the test Group Gradia Direct were considered clinically not perceptible (ΔE* <3.3). Differently, the differences in color change were considered clinically perceptible (ΔE* >3.3) between the control group G-aenial and the control group Gradia Direct and between the test group G-aenial and the control specimens obtained with G-aenial. The CIE Lab parameters which brought to ΔE were investigated using t-test (P < 0.05).

Results and Conclusions:

Color harmonization in simulated clinical conditions depends on different factors related to dentine and to composite resins. In this study dentine variables were dropped in order to analyze the influence of thickness and of the composition of the composite resin.

Fabrication and characterization of biomimetic ceramic/polymer composite materials for dental restoration

OBJECTIVE

Conventional dental composites with randomly dispersed inorganic particles within a polymer matrix fail to recapitulate the aligned and anisotropic structure of the dentin and enamel. The aim of the study was to produce a biomimetic composite consisting of a ceramic preform with graded and continuously aligned open pores, infiltrated with epoxy resin.

METHODS

The freeze casting technique was used to obtain the hierarchically structured architecture of the ceramic preforms. Optical and scanning electron microscopy (SEM) and differential thermal analysis and thermogravimetry (TG-DTA) were used to characterize the samples. Three point bending test and compression test were also performed.

RESULTS

All analysis confirmed that the biomimetic composite was characterized by a multi-level hierarchical structure along the freezing direction. In the bottom layers close to the cooling plate (up to 2mm thick), a randomly packed ceramic with closed pores were formed, which resulted in incomplete infiltration with resin and resultant poor mechanical propertiesof the composite. Above 2mm, all ceramic samples showed an aligned structure with an increasing lamellae spacing (wavelength) and a decreasing wall thickness. Mechanical tests showed that the properties of the composites made from ceramic preforms above 2mm from cooling plate are similar to those of the dentin.

SIGNIFICANCE

The fabrication processing reported in this work offers a viable route for the fabrication of biomimetic composites, which could be potentially used in a range of dental restorations to compete with the current dental composites and ceramics.

Light transmission characteristics of dentine and resin composites with different thickness

OBJECTIVE

The purpose of this study was to evaluate the light transmission characteristics of dentine and resin composites with different thickness.

METHODS

Disks of bovine dentine and three resin composites (Estelite Σ, Beautifil II and Clearfil Majesty) of OA2 shade were prepared with various thicknesses (0.5, 1.0 and 2.0mm). Using a goniophotometer, the distribution graphs of the light transmission intensity of each specimen were obtained, and diffusion factor (DF) as an indicator for a diffuse transmission property and peak-gain (G0) for a straight-line transmission property were calculated. Their colors were measured on black and white backings using a reflection spectrophotometer to calculate translucency parameter (TP). The data of each value (G0, DF and TP) were analyzed by two-way ANOVA and Dunnett's T3 for post hoc test (p=0.05). Regression analyses were used to determine the correlation between G0, DF, TP values and the thickness.

RESULTS

Regardless of the thickness, dentine had lower TP values than the resin composites. 0.5 mm-thick specimens of dentine and resin composite produced various G0 and DF values, with dentine exhibiting significantly lower G0 and higher DF than the resin composites (p<0.05), whereas with the 1.0 and 2.0mm-thick specimens, they were closely aligned. For dentine, G0 and DF increased in inverse proportion to the thickness (G0: R(2)=0.962, p<0.001; DF: R(2)=0.891, p<0.001).

CONCLUSIONS

Dentine had different light transmission characteristics from resin composite, depending on the thickness.

CLINICAL SIGNIFICANCE

Dentine has different light transmission characteristics (straight-line and diffusion) from resin composite, depending on thickness. Resin composite restoration might be different to accurately reproduce light transmission characteristics of dentine substrate.

The effect of distance and tooth structure on laser fluorescence caries detection

The DIAGNOdent, a device used in caries detection, uses a laser to excite fluorescence from pigments in carious tooth structure. In clinical use assessing occlusal surfaces, distance and tooth structure may separate the instrument's tip from the fluorescent source.The aim of this in vitro study was to examine the effect of distance and tooth structure on laser fluorescence (LF) readings.In one set of experiments, a porphyrin pigmentin oil suspension was used as a LF signal source. Thin slices of enamel and dentin were obtained from extracted molars. Pigment-induced LF readings were obtained when these slices were placed between the porphyrin pigment and the LF instrument's tip. The effect of either demineralized or intact tooth tissue on pigment-induced LF readings was assessed.In other experiments on extracted molars with small occlusal caries, LF readings were taken from pit/fissure sites before and after removal of the occlusal surface.LF readings are proportional to pigment con-centration and inversely proportional to the distance between the suspension and the instrument's tip. Enamel, demineralized enamel,dentin, and demineralized dentin all caused significant reductions in LF signal, all readings being taken with the same tip-pigment distance. Demineralized enamel (white with intact surface) caused the most reduction.After sectioning of carious teeth, there was a significant increase in LF readings.The results of this study indicate that distance and the presence of tooth structure between the carious lesion and the instrument's tip reduce LF readings. These results indicate that anatomic factors interfere with the LF device's ability to assess occlusal caries. DIAGNOdent readings should not be relied on when making diagnostic decisions.

Measurement of the refractive index of human teeth by optical coherence tomography

We describe a novel method based on optical coherence tomography (OCT) for the accurate measurement of the refractive index of in vitro human teeth. We obtain the refractive indices of enamel, dentin, and cementum to be 1.631+/-0.007, 1.540+/-0.013, and 1.582+/-0.010, respectively. The profile of the refractive index is readily obtained via an OCT B scan across a tooth. This method can be used to study the refractive index changes caused by dental decay and therefore has great potential for the clinical diagnosis of early dental caries.

Absolute transmitted light plethysmography for assessment of dental pulp vitality through quantification of pulp chamber hematocrit by a three-layer model

After confirming that the gingival circulation had little effect on transmitted light plethysmography measurement in the upper central incisor in both in vivo experiments and numerical Monte Carlo simulation studies, a three-layer model comprising of a pulp chamber sandwiched between two dentin layers has been introduced to quantify the pulp chamber hematocrit (Hctp) from the measured optical density. Two-flux theory was utilized to derive a mathematical equation for transmitted intensity in terms of tooth dimensions, Hctp, and light-source wavelength. Each layer was assumed homogeneous so as to represent its optical properties by the bulk absorption and scattering constants. The mean error between the Hctp estimate based on the three-layer-model equation and the Hctp actual in the extracted model tooth was -0.00115 with standard deviation (SD) of 0.00733 at 522 nm wavelength, while for 810 nm +0.09157 and 0.02493. The Hctp estimate of the upper central incisor in 10 young volunteers at 522 nm using the three-layer model ranged from 0.002 to 0.061 with the mean of 0.032. The Hctp change reflects blood volume shift in the pulp microcirculation to possibly indicate dental pulp vitality.