Machine learning assisted 5-part tooth segmentation method for CBCT-based dental age estimation in adults.

BACKGROUND: The utilization of segmentation method using volumetric data in adults dental age estimation (DAE) from cone-beam computed tomography (CBCT) was further expanded by using current 5-Part Tooth Segmentation (SG) method. Additionally, supervised machine learning modelling -namely support vector regression (SVR) with linear and polynomial kernel, and regression tree - was tested and compared with the multiple linear regression model. MATERIAL AND METHODS: CBCT scans from 99 patients aged between 20 to 59.99 was collected. Eighty eligible teeth including maxillary canine, lateral incisor, and central incisor were used in this study. Enamel to dentine volume ratio, pulp to dentine volume ratio, lower tooth volume ratio, and sex was utilized as independent variable to predict chronological age. RESULTS: No multicollinearity was detected in the models. The best performing model comes from maxillary lateral incisor using SVR with polynomial kernel ( = 0.73). The lowest error rate achieved by the model was given also by maxillary lateral incisor, with 4.86 years of mean average error and 6.05 years of root means squared error. However, demands a complex approach to segment the enamel volume in the crown section and a lengthier labour time of 45 minutes per tooth.

Effect of composite radiopacity and margin location of the restoration on the diagnosis of secondary caries.

This research aimed to evaluate the effect of the radiopacity of a Bulk-Fill composite (X-TraFil, VOCO, Germany) and a Conventional composite (P60, 3M ESPE, USA) and assessment of the margin location in the enamel and dentin on the diagnosis of secondary caries. 76 intact premolars with MOD preparation were divided into two equal groups and filled with the conventional and bulk-fill composite. Four regions were considered to simulate carious lesions (two regions in enamel and two regions in dentin). In each group, half of the regions in the dentin and half in the enamel were randomly selected for secondary caries simulation and filled with a wax-plaster combination while the remaining regions stayed intact. Bitewing imaging was done using the PSP digital sensor. Five examiners reviewed the images, and lesions were recorded. Caries diagnosis indicators and paired-sample t-test were used for statistical analysis. The reproducibility and accuracy of the examiners' responses were evaluated using the kappa and agreement coefficient (α=0.05). The sensitivity, specificity, and accuracy of diagnosing secondary carious lesions in enamel were significantly better under conventional than bulk-fill composite. Similarly, the sensitivity and accuracy of diagnosing secondary caries in dentin were significantly higher under conventional composite than bulk-fill composite (p<0.05). No significant differences were found in the agreement and kappa coefficient between conventional and bulk-fill composites in the enamel and dentin (p>0.05). The diagnostic accuracy of carious lesions was higher under conventional composite than bulk-fill composite. However, the location of the secondary was ineffective in caries diagnosis.

Characterizing the microstructures of mammalian enamel by synchrotron phase contrast microCT.

The enamel of mammalian teeth is a highly mineralized tissue that must endure a lifetime of cyclic contact and is inspiring the development of next-generation engineering materials. Attempts to implement enamel-inspired structures in synthetic materials have had limited success, largely due to the absence of a detailed understanding of its microstructure. The present work used synchrotron phase-contrast microCT imaging to evaluate the three-dimensional microstructure of enamel from four mammals including Lion, Gray Wolf, Snow Leopard, and Black Bear. Quantitative results of image analysis revealed that the decussation pattern of enamel consists of discrete diazone (D) and parazone (P) bands of rods organized with stacking arrangement of D+/P/D-/P in all mammals evaluated; the D+ and D- refer to distinct diazone bands with juxtaposed rod orientations from the reference plane. Furthermore, the rod orientations in the bands can be described in terms of two principal angles, defined here as the pitch and yaw. While the pitch angle increases from the outer enamel to a maximum (up to ≈ 40°) near the dentin enamel junction, minimal spatial variations are observed in yaw across the enamel thickness. There are clear differences in the decussation parameters of enamel across species that are interpreted here with respect to the structural demands placed on their teeth. The rod pitch and band width of enamel are identified as important design parameters and appear to be correlated with the bite force quotient of the four mammals evaluated. STATEMENT OF SIGNIFICANCE: The multi-functionality of tooth enamel requires both hardness and resistance to fracture, properties that are generally mutually exclusive. Ubiquitous to all mammalian teeth, the enamel is expected to have undergone adaptations in microstructure to accommodate the differences in diet, body size and bite force across animals. For the first time, we compare the complex three-dimensional microstructure of enamel from teeth of multiple mammalian species using synchrotron micro-computed tomography. The findings provide new understanding of the "design" of mammalian enamel microstructures, as well as how specific parameters associated with the decussation of rods appear to be engineered to modulate its fracture resistance.

Use of micro-computed tomography and scanning electron microscopy with energy-dispersive spectroscopy to distinguish natural white spot enamel lesions from sound enamel in human premolars.

PURPOSE: The aim of the present study was to develop a novel method for distinguishing white spot lesions (WSLs) from sound enamel in human premolars using micro-computed tomography (micro-CT) and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), and to examine differences in surface morphology, chemical composition, and mineral density (MD) between these two areas. METHODS: Fourteen premolars with natural WSLs on the enamel surface of the crowns were examined. After sectioning the teeth, each specimen containing WSLs adjacent to intact enamel was examined for MD, surface morphology, and atomic percentages (At%) of chemical components using micro-CT and SEM/EDS, respectively. Differences between these areas of the same specimen were analyzed statistically using paired t-test. RESULTS: SEM images highlighted increased roughness and irregularity in the lesion area. EDS analysis revealed significant reductions in calcium (Ca), phosphorus (P), fluorine (F), chlorine (Cl), and sodium (Na) levels at the lesion surface in comparison to intact enamel (P < 0.05). The decreases in the MD of the lesions were statistically significant in comparison to sound enamel (P < 0.05). CONCLUSION: These findings provide standard measurements for evaluating the essential characteristics of WSLs and intact enamel, being vital for assessment of treatment outcomes and development of innovative biomaterials for management of hypo-mineralized enamel lesions.

Variation in enamel prism size in primate molars.

OBJECTIVE: This study examines whether larger enamel prism diameters accommodate a greater enamel volume from the enamel-dentine junction (EDJ) to the outer-enamel surface (OES) in primate molars, and how prism size relates to enamel thickness and crown location. DESIGN: We assessed variation in enamel prism diameter in relation to crown location and enamel thickness in catarrhine lower molars (n = 14 species) and one platyrrhine. Prism diameter and enamel thickness were recorded in four locations (lingual lateral; lingual cuspal; buccal cuspal; buccal lateral), using a buccal-lingual section through the centre of the mesial cusps. Ten prism diameter readings were collected at inner (near the EDJ), outer (near the OES) and middle (between the two locations) enamel for each location. RESULTS: Mean prism diameter values for each species were similar (range: 4.06 µm to 5.81 µm). Prism diameter enlarged from inner to outer enamel, suggesting larger prisms help accommodate the increase in enamel volume from the EDJ to the OES. Average prism diameter does not associate with enamel thickness. Instead, cuspal positions had significantly smaller prism diameter at the EDJ than lateral positions, and larger prism sizes at the OES, leading to an overall similar prism diameter mean for all positions (Lingual lateral: 5.11 µm; Lingual cuspal: 5.04 µm; Buccal cuspal: 4.78 µm; Buccal lateral: 4.99 µm). CONCLUSIONS: Our study revealed consistent average enamel prism diameters in various crown locations of lower primate molars, potentially contributing to the mechanical integrity and functional optimization of enamel in primates.

Evaluation of Dental Enamel Thickness in Maxillary Teeth of Alouatta guariba clamitans, Alouatta caraya, and Sapajus nigritus by Cone Beam Computed Tomography.

Tooth enamel thickness is widely studied in primates and is important in differentiating taxa and in interpreting diet and feeding behavior. The objective of this study was to measure enamel thickness and discuss whether the results can be associated with different feeding patterns. Thirty-four syncraniums of Alouatta guariba clamitans, Alouatta caraya, and Sapajus nigritus were subjected to cone beam computed tomographic (CBCT) scans, and the dental enamel was measured in different regions of the crown using the multiplanar reconstruction tool. The differences observed indicate that for many variables and teeth, A. guariba clamitans showed significantly higher values compared to the other 2 species, with the exception of the cuspid region. Although the A. guariba clamitans is a folivorous species, it showed thicker enamel for most of the variables. CBCT was efficient in performing the measurements, allowing analysis of the syncraniums.

Sexual dimorphism in the three-dimensional detailed crown structure of maxillary first premolars.

OBJECTIVES: Maxillary first premolars have a unique shape because of their curvature features, positional relationship of the cusps, and most prominent points, making them different from other teeth. This study aimed to quantitatively analyze the detailed three-dimensional morphometric structure of maxillary first premolars and sexual dimorphism. METHODS: The study participants were 60 elementary and junior high school students (30 boys and 30 girls) in Japan. The distance between landmarks was measured using the three-dimensional coordinates of plaster casts, and the data collected was statistically analyzed. RESULTS: Sexual dimorphism was greater in the lingual cusp, showing greater variation in size than the buccal cusp. Boys exhibited significantly larger relative distances in the mesiodistal and buccolingual directions than girls; particularly, regarding mesiodistal diameter of the central groove, mesial slope of the buccal cusp, and distal slope of the lingual cusp. These results may be due to a slight difference in the timing of secondary enamel knots between boys and girls during the developmental stage, which was reflected in the sexual dimorphism of the completed teeth. Curvature features, cusp positions, and most prominent points were considered individual traits because they were not interrelated. CONCLUSIONS: Subtle differences during the developmental stage may lead to sexual dimorphism of the completed crown. Furthermore, the morphological characteristics of the maxillary first premolars may be related to their location in the dental arch.

Age and sex related change in tooth enamel thickness of maxillary incisors measured by cone beam computed tomography.

BACKGROUND: To measure adequate enamel thickness of maxillary incisors in planning enamel reduction for a porcelain laminate veneer restoration in relation to chronological age and sex by using cone beam computed tomography (CBCT) in an Iraqi subpopulation. METHODS: From 81 CBCT images, 324 maxillary incisors were examined. Enamel thickness was measured at both mesial and distal regions of the tooth in three different levels: cervical, middle, and incisal (occlusal) 1/3 at a sagittal section. Measurements were made for the following tooth areas using CBCT: facial enamel thickness at 1, 3, and 5 mm from the cementoenamel junction (CEJ), palatal enamel thickness at 5 mm from the CEJ (5 mm P), facial and palatal enamel thickness at the incisal edge (IFP), mid incisal enamel thickness (IET), and the incisal edge enamel-pulp distance (IEPD). Relationships of enamel thickness with age and sex were evaluated using Independent t-test, Mann-Whitney U-test and the Pearson correlation coefficient, a simple linear regression analysis used for statistical analysis. RESULTS: Significant differences (P < 0.05) were found in terms of an inverse association between enamel thickness and chronological age at all measurements above the CEJ and the regression model for the mid-incisal enamel thickness was (R2 of 0.4). In contrast, there was an increase in IFP, palatal, and IPED enamel thickness with age. Also, significant differences were found in enamel thickness between males and females, the enamel being thicker in females in relation to facial enamel thickness, enamel palatal thickness above CEJ and IET, while for IEPD, the enamel thickness was greater in males compared to females. CONCLUSION: The measurements for enamel thickness outcome variables in relation to chronological age revealed significant differences for each measured distance and there were statistically significant differences in enamel thickness between males and females at all measurements except at IFP. These results demonstrate that CBCT can be used for noninvasive, accurate measurements of enamel thickness in both sex.

Optimizing the use of low-frequency ultrasound for bacterial detachment of in vivo biofilms in dental research-a methodological study.

OBJECTIVES: Low-frequency, low-intensity ultrasound is commonly utilized in various dental research fields to remove biofilms from surfaces, but no clear recommendation exists in dental studies so far. Therefore, this study aims to optimize the sonication procedure for the dental field to efficiently detach bacteria while preserving viability. MATERIALS AND METHODS: Initial biofilm was formed in vivo on bovine enamel slabs (n = 6) which were worn by four healthy participants for 4 h and 24 h. The enamel slabs covered with biofilm were then ultrasonicated ex vivo for various time periods (0, 1, 2, 4, 6 min). Colony-forming units were determined for quantification, and bacteria were identified using MALDI-TOF. Scanning electron microscopic images were taken to also examine the efficiency of ultrasonications for different time periods. RESULTS: Ultrasonication for 1 min resulted in the highest bacterial counts, with at least 4.5-fold number compared to the non-sonicated control (p < 0.05). Most bacteria were detached within the first 2 min of sonication, but there were still bacteria detached afterwards, although significantly fewer (p < 0.0001). The highest bacterial diversity was observed after 1 and 2 min of sonication (p < 0.03). Longer sonication periods negatively affected bacterial counts of anaerobes, Gram-negative bacteria, and bacilli. Scanning electron microscopic images demonstrated the ability of ultrasound to desorb microorganisms, as well as revealing cell damage and remaining bacteria. CONCLUSIONS: With the use of low-frequency, low-intensity ultrasound, significantly higher bacterial counts and diversity can be reached. A shorter sonication time of 1 min shows the best results overall. CLINICAL RELEVANCE: This standardization is recommended to study initial oral biofilms aged up to 24 h to maximize the outcome of experiments and lead to better comparability of studies.

Longitudinal assessment of dental erosion-abrasion by cross-polarization optical coherence tomography in vitro.

This study tested a novel in vitro dental erosion-abrasion model and the performance of cross-polarization optical coherence tomography (CP-OCT) in longitudinally monitoring the simulated lesions. Thirty human enamel specimens were prepared and randomized to receive three dental erosion-abrasion (EA) protocols: severe (s-EA, lemon juice/pH:2.5/4.25%w/v citric acid), moderate (m-EA, grapefruit juice/pH:3.5/1.03%w/v citric acid) and no-EA (water, control). EA challenge was performed by exposing the specimens to acidic solutions 4x/day and to brushing 2x/day with 1:3 fluoridated toothpaste slurry, for 14 days. Enamel thickness measurements were obtained using CP-OCT at baseline (D0), 7 (D7) and 14 days (D14) and micro-computed tomography (micro-CT) at D14. Enamel surface loss was measured with both CP-OCT and optical profilometry at D0, D7 and D14. Data was analyzed with repeated-measures ANOVA and Pearson's correlation (r) (α = 0.05). CP-OCT enamel thickness decreased over time in the s-EA group (D0 >D7 > D14, p < 0.001) and m-EA group (D0 > D14, p = 0.019) but did not change in the no-EA group (p = 0.30). Overall, CP-OCT and micro-CT results at D14 correlated moderately (r = 0.73). CP-OCT surface loss was highest for s-EA (p <0.001) but did not differ between moderate and no-EA (p = 0.25). Enamel surface loss with profilometry increased with severity (no-EA>m-EA>s-EA, p < 0.001). D14 surface loss was higher than D7 for both methods except for the no-EA group with profilometry. CP-OCT and profilometry had moderate overall correlation (r = 0.70). Our results revealed that the currently proposed in vitro dental erosion-abrasion model is valid and could simulate lesions of different severities over time. CP-OCT was a suitable method for monitoring the EA lesions.

Microcomputed Tomography Mineral Density Profile as Reference Standard for Early Carious Lesion Activity Assessment.

Early caries diagnosis is crucial to treatment decisions in dentistry and requires identification of lesion activity: whether a carious lesion is active (progressively demineralizing) or arrested (progressively remineralizing). This study aimed to identify microtomographic (micro-CT) differences between active and arrested smooth surface enamel lesions, to quantify those micro-CT differences by creating thresholds for ex vivo caries activity assessment to serve as a future reference standard, and to validate those thresholds against the remaining sample. Extracted human permanent teeth (n = 59) were selected for sound surfaces and non-cavitated smooth surface carious lesions. Each surface was then examined for caries activity by calibrated individuals via visual-tactile examination using the International Caries Classification and Management System (ICCMS) activity criteria. Each tooth was scanned via micro-CT and the mineral density was plotted against lesion depth. The area under the curve (AUC) was calculated and represented the loss of density for the outermost 96 µm of enamel. AUC thresholds obtained from micro-CT were established to classify sound, remineralized, and demineralized surfaces against the gold standard examiner's lesion assessment of sound, inactive, and active lesions, respectively. The established AUC thresholds demonstrated moderate agreement with the assessment in identifying demineralized lesions (k = 0.45), with high sensitivity (0.73) and specificity (0.77). This study demonstrated quantifiable differences among demineralized lesions, remineralized lesions, and sound surfaces, which contributes to the establishment of micro-CT as a reference standard for caries activity that may be used to improve clinical and laboratorial dental caries evaluations.

Quantitative analysis of the degree of demineralization for bleached enamel by optical coherence tomography.

BACKGROUND: Tooth bleaching imparts whitening effects along with adverse effects such as increased tooth sensitivity and enamel surface changes. Herein, we employed optical coherence tomography (OCT), a nondestructive optical detection technique, for evaluation of tooth enamel after treatment with peroxide-based bleaching agents. METHODS: Fifteen enamel samples were bleached using 38% acidic hydrogen peroxide-based bleach, subjected to OCT scanning, and then cross-sectioned and imaged under polarized light microscopy (PLM) and transverse microradiography (TMR). OCT cross-sectional images were compared with PLM and TMR. The depth and severity of demineralization produced in the bleached enamel were measured by OCT, PLM, and TMR. Comparison between the three techniques was performed using Kruskal-Wallis H non-parametric test and Pearson correlation. RESULTS: In comparison with PLM and TMR, OCT clearly detected the changes in the enamel surface after hydrogen peroxide bleaching. Significant correlations (p<0.05) were observed in lesion depth between OCT and PLM (r=0.820), OCT and TMR (r=0.822), and TMR and PLM (r=0.861). There was no statistically significant difference in demineralization depth values measured by OCT, PLM, and TMR (p>0.05). CONCLUSION: OCT can allow real-time, non-invasive imaging of artificially bleached tooth models and automatically measure the early changes in the enamel lesion structure upon exposure to hydrogen peroxide-based bleaching agents.

Multi-resolution Correlative Ultrastructural and Chemical Analysis of Carious Enamel by Scanning Microscopy and Tomographic Imaging.

Caries, a major global disease associated with dental enamel demineralization, remains insufficiently understood to devise effective prevention or minimally invasive treatment. Understanding the ultrastructural changes in enamel is hampered by a lack of nanoscale characterization of the chemical spatial distributions within the dental tissue. This leads to the requirement to develop techniques based on various characterization methods. The purpose of the present study is to demonstrate the strength of analytic methods using a correlative technique on a single sample of human dental enamel as a specific case study to test the accuracy of techniques to compare regions in enamel. The science of the different techniques is integrated to genuinely study the enamel. The hierarchical structures within carious tissue were mapped using the combination of focused ion beam scanning electron microscopy with synchrotron X-ray tomography. The chemical changes were studied using scanning X-ray fluorescence (XRF) and X-ray wide-angle and small-angle scattering using a beam size below 80 nm for ångström and nanometer length scales. The analysis of XRF intensity gradients revealed subtle variations of Ca intensity in carious samples in comparison with those of normal mature enamel. In addition, the pathways for enamel rod demineralization were studied using X-ray ptychography. The results show the chemical and structural modification in carious enamel with differing locations. These results reinforce the need for multi-modal approaches to nanoscale analysis in complex hierarchically structured materials to interpret the changes of materials. The approach establishes a meticulous correlative characterization platform for the analysis of biomineralized tissues at the nanoscale, which adds confidence in the interpretation of the results and time-saving imaging techniques. The protocol demonstrated here using the dental tissue sample can be applied to other samples for statistical study and the investigation of nanoscale structural changes. The information gathered from the combination of methods could not be obtained with traditional individual techniques.

Variation in enamel and dentine mineral concentration and density in primate molars.

OBJECTIVE: Variation in enamel and dentine mineral concentration and total effective density can be reliably collected using Micro-CT scans. Both variables are suggested to reflect mechanical properties such as hardness and elastic modulus in dental tissues, meaning Micro-CT methods allow relative composition and mechanical properties to be collected non-destructively. DESIGN: 16 lower molars from 16 Catarrhine primates were Micro-CT scanned alongside hydroxyapatite phantoms using standardized settings and methods to calculate mineral concentration and total effective density. Mineral concentration, total effective density and thickness of dentine and enamel were calculated for four cusps, representing each 'corner' of the tooth and four lateral crown positions (i.e., mesial, buccal, lingual and distal). RESULTS: The results show mean mineral concentration and total effective density values were higher in areas of thicker enamel, while the opposite was observed for dentine. Buccal positions had significantly higher mineral concentration and total effective density values than lingual areas. Cuspal positions had higher mean values than lateral enamel, for both dentine (mineral concentration cuspal: 1.26 g/cm3; lateral: 1.20 g/cm3) and enamel (mineral concentration cuspal: 2.31 g/cm3; lateral: 2.25 g/cm3). Mesial enamel had significantly lower values than other locations. CONCLUSIONS: These common patterns across Catarrhine taxa may be linked to functional adaptations related to optimization of mastication and tooth protection. Variation in mineral concentration and total effective density may also be associated with wear and fracture patterns, and can be used as baseline information to investigate the effect of diet, pathological changes and aging on teeth through time.

Evaluation of enamel thickness of mandibular incisors.

OBJECTIVE: To measure enamel thickness at the proximal surfaces of the mandibular incisors, using micro-computed tomography (micro-CT) scans. MATERIAL AND METHODS: Forty-one single-rooted mandibular incisors were selected and analyzed according to anatomical characteristics, to form three groups: Group 1 - central incisors (n = 18); Group 2 - right lateral incisors (n = 10); and Group 3 - left lateral incisors (n = 13). First, enamel thickness at the proximal contact areas of the mandibular incisors was measured. Second, the mesial and distal surfaces of the lateral incisors were compared. Finally, the relationship between the tooth width and the mean enamel thickness was determined. Each tooth was scanned with a micro-CT scanner, and the image was processed with SCANCO micro-CT onboard analysis software. RESULTS: There were no statistically significant differences in mean enamel thickness between the mesial and distal surfaces for each lateral incisor, or between contralateral lateral incisors. In all surfaces analyzed, the upper zones had statistically significantly thinner enamel (0.52 ± 0.10 mm) when compared to the middle and lower zones (0.60 ± 0.08 mm and 0.59 ± 0.08 mm, respectively). There was no correlation (r =0.07) between enamel thickness of the mandibular incisor and the tooth width. CONCLUSIONS: The enamel thickness of the mandibular incisors is similar on the mesial and distal surfaces, with the thinnest layer located at the upper zone.

The influence of age and orthodontic debonding on the prevalence and severity of enamel craze lines.

BACKGROUND: Craze lines may cause esthetic concerns, especially when noted on the incisors. Various light sources with additional recording apparatus have been proposed to visualize craze lines, but a standardized clinical protocol is yet to be determined. This study aimed to validate the application of near-infrared imaging (NIRI) from intraoral scans to evaluate craze lines and to determine the influence of age and orthodontic debonding on their prevalence and severity. METHODS: The NIRI of maxillary central incisors from a full-mouth intraoral scan and photographs from an orthodontic clinic (N = 284) were collected. The prevalence of craze lines and influence of age and orthodontic debonding history on severity were evaluated. RESULTS: Craze lines were detected reliably as white lines distinguishable from dark enamel using the NIRI from intraoral scans. The craze line prevalence was 50.7%, which was significantly higher in patients 20 years or older than in patients younger than 20 years (P < .001), with more frequent severe craze lines for those 40 years or older than in patients younger than 30 years (P < .05). Prevalence or severity was similar between patients with and without an orthodontic debonding history regardless of the type of appliance. CONCLUSION: The prevalence of craze lines in the maxillary central incisor was 50.7%, with a higher prevalence in adults than in adolescents. Orthodontic debonding did not affect the severity of craze lines. PRACTICAL IMPLICATIONS: Craze lines were reliably detected and documented by means of applying NIRI from intraoral scans. Intraoral scanning can provide new clinical information on enamel surface characteristics.

Translucency and Radiopacity of Dental Resin Composites - Is There a Direct Relation?

OBJECTIVES: The purpose of this study was to correlate the translucency degree of varying resin composites with their radiopacity. METHODS AND MATERIALS: Twenty-four resin composites (conventional or bulk-fill) of various shades and opacities were selected from the following manufacturers: 3M ESPE (nanofilled), Ivoclar (nanohybrid), and FGM (microhybrid). Resin composite samples (n=5) were prepared (5-mm diameter × 1.5-mm thickness) for comparison using prepared samples of human dentin and enamel as controls. The translucency of each sample was measured using the translucent parameter (TP) method with a digital spectrophotometer (Vita Easyshade) and CIEL*a*b* color system over white and black backgrounds. The samples were also x-rayed using a photostimulable phosphor plate system for measurement of their radiopacity (in mmAl). All data were analyzed using one-way ANOVA and Student-Newman-Keuls (α=0.05); data for TP and radiopacity were correlated using the Spearman correlation test. RESULTS: Overall, the translucent shades and bulk-fill resin composites showed greater translucency than the other resins. While "body" and "enamel" shades demonstrated intermediate translucency to dentin and enamel, the "dentin" shades were more standardized, showing similar translucency to human dentin. All tested resin composites showed similar or greater radiopacity to human enamel, except the Empress Direct (Ivoclar) resin with Trans Opal shade, which was not radiopaque. Dentin and enamel showed radiopacity similar to 1 and 2 mmAl (millimeters of aluminum), respectively. CONCLUSIONS: The resin composites investigated in this study differed regarding their translucency degree and radiopacity level, without any positive relationship between the two properties.

Assessing Enamel Wear of Monolithic Ceramics With Micro-CT and Intra-oral Scanner.

OBJECTIVE: This in vitro study aimed to investigate enamel wear against 3 monolithic ceramics using 2 methods of measurement. METHODS: Three groups of standard flat monolithic ceramic specimens including zirconia-reinforced lithium silicate glass (Vita Suprinity, VITA Zahnfabrik), yttria-stabilised tetragonal zirconia (Lava Esthetic Zirconia), and lithium disilicate glass (IPS e.max Press, Ivoclar Vivadent) were prepared, with human enamel used as the control group. Each specimen was subjected to the 2-body wear test at 49 N for 250,000 cycles. Enamel antagonists were evaluated with micro-computed tomography (CT) and intra-oral scanner, allowing 3-dimensional images of vertical wear and volumetric loss of enamel antagonists to be calculated. One-way analysis of variance followed by Student-Newman-Keuls post hoc tests were used to examine the differences in vertical wear/volumetric loss amongst the groups. Paired t tests and intra-class correlations were used to compare vertical wear/volumetric loss between the micro-CT and intra-oral scanner groups. RESULTS: No significant difference in vertical wear was found amongst all groups. More volumetric loss was found in all test groups than in the control group (P < .001), but no significant difference was found amongst the test groups. There was a moderate positive correlation (r = 0.535, P = .033) between the vertical wear and volumetric loss. No significant difference between the 2 methods of measurement was found. CONCLUSIONS: Monolithic ceramics induce more enamel wear than natural teeth. Both micro-CT and intra-oral scanners can be used for measuring tooth wear with similar performance.

Phenotypic variability in LAMA3-associated amelogenesis imperfecta.

OBJECTIVE: Amelogenesis imperfecta (AI) is defined as inherited enamel malformations. LAMA3 (laminin alpha-3) encodes a critical protein component of the basement membrane (laminin-332). Individuals carrying heterozygous LAMA3 mutations have previously been shown to have localized enamel defects. This study aimed to define clinical phenotypes and to discern the genetic etiology for four AI kindreds. MATERIALS AND METHODS: Whole-exome analyses were conducted to search for sequence variants associated with the disorder, and micro-computed tomography (µCT) to characterize the enamel defects. RESULTS: The predominant enamel phenotype was generalized thin enamel with defective pits and grooves. Horizonal bands of hypoplastic enamel with chalky-white discoloration and enamel hypomineralization were also observed and demonstrated by µCT analyses of affected teeth. Four disease-causing LAMA3 mutations (NM_198129.4:c.3712dup; c.5891dup; c.7367del; c.9400G > C) were identified. Compound heterozygous MMP20 mutations (NM_004771.4:c.539A > G; c.692C > T) were also found in one proband with more severe enamel defects, suggesting a mutational synergism on disease phenotypes. Further analyses of the AI-causing mutations suggested that both α3A (short) and α3B (long) isoforms of LAMA3 are essential for enamel formation. CONCLUSIONS: Heterozygous LAMA3 mutations can cause generalized enamel defects (AI1A) with variable expressivity. Laminin-332 is critical not only for appositional growth but also enamel maturation.

Three-dimensional characterization of naturally developed early caries lesions using high-resolution micro-computed tomography.

OBJECTIVES: The goal of this micro-Computed-Tomography (µCT) study was to characterize the structural parameters of natural, early proximal enamel caries lesions and correlate them with two-dimensional radiographic findings. METHODS: Extracted human premolar teeth with ICDAS score 2 proximal lesions were examined using visual-tactile, µCT and simulated bitewing radiographs (BTX). Sound enamel and caries-lesions' structural and mineral density (MD) parameters were analyzed which included surface layer (SL) status and thickness, depth of lesion, and MD. RESULTS: Thirty-six extracted premolars with 54 proximal early enamel caries lesions were analyzed. Lesions varied notably in lesion depth and MD. SL thickness ranged between 20 and 139µm. Three teeth (5.6%) had micro-cavitations upon the µCT examination despite being "clinically" non-cavitated. Cavitation status had no significant association with µCT nor BTX radiographic depth. Depth of lesions correlated weakly but statistically significantly with mineral loss (ML) at body of lesion (r=0.301, p=0.027). SL thickness also correlated negatively with ML at SL (r=-0.501, p<0.001). CONCLUSIONS: Early proximal enamel lesions with ICDAS 2 score as determined by visual-tactile examination exhibited a wide range of lesion parameters and cavitation status when examined by µCT. Visual-tactile examination may fail to detect micro-cavitations in enamel surface that are detectable by µCT. CLINICAL SIGNIFICANCE: Clinicians have direct access to early proximal enamel lesions during orthodontic separation, exfoliation, extraction or restoration of adjacent teeth. This study invites the clinician to consider more decisive management options in high risk individuals (e.g. micro-invasive techniques), given the finding of vast structural variability of such lesions.