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.

Caries Detection on Intraoral Images Using Artificial Intelligence.

Although visual examination (VE) is the preferred method for caries detection, the analysis of intraoral digital photographs in machine-readable form can be considered equivalent to VE. While photographic images are rarely used in clinical practice for diagnostic purposes, they are the fundamental requirement for automated image analysis when using artificial intelligence (AI) methods. Considering that AI has not been used for automatic caries detection on intraoral images so far, this diagnostic study aimed to develop a deep learning approach with convolutional neural networks (CNNs) for caries detection and categorization (test method) and to compare the diagnostic performance with respect to expert standards. The study material consisted of 2,417 anonymized photographs from permanent teeth with 1,317 occlusal and 1,100 smooth surfaces. All the images were evaluated into the following categories: caries free, noncavitated caries lesion, or caries-related cavitation. Each expert diagnosis served as a reference standard for cyclic training and repeated evaluation of the AI methods. The CNN was trained using image augmentation and transfer learning. Before training, the entire image set was divided into a training and test set. Validation was conducted by selecting 25%, 50%, 75%, and 100% of the available images from the training set. The statistical analysis included calculations of the sensitivity (SE), specificity (SP), and area under the receiver operating characteristic (ROC) curve (AUC). The CNN was able to correctly detect caries in 92.5% of cases when all test images were considered (SE, 89.6; SP, 94.3; AUC, 0.964). If the threshold of caries-related cavitation was chosen, 93.3% of all tooth surfaces were correctly classified (SE, 95.7; SP, 81.5; AUC, 0.955). It can be concluded that it was possible to achieve more than 90% agreement in caries detection using the AI method with standardized, single-tooth photographs. Nevertheless, the current approach needs further improvement.

3D Printing in Dentistry-State of the Art.

Three-dimensional (3D) printing is a rapidly developing technology that has gained widespread acceptance in dentistry. Compared to conventional (lost-wax technique) and subtractive computer numeric controlled methods, 3D printing offers process engineering advantages. Materials such as plastics, metals, and ceramics can be manufactured using various techniques. 3D printing was introduced over three decades ago. Today, it is experiencing rapid development due to the expiration of many patents and is often described as the key technology of the next industrial revolution. The transition to its clinical application in dentistry is highly dependent on the available materials, which must not only provide the required accuracy but also the necessary biological and physical properties. The aim of this work is to provide an up-to-date overview of the different printing techniques: stereolithography, digital light processing, photopolymer jetting, material jetting, binder jetting, selective laser sintering, selective laser melting, and fused filament fabrication. Additionally, particular attention is paid to the materials used in dentistry and their clinical application.

Effects of prostaglandin E2 and D2 on cell proliferation and osteogenic capacity of human mesenchymal stem cells.

The manifestation of periodontitis-related inflammatory reaction is inevitably bound to the production of prostaglandins E2 and D2 which have been suggested to mediate osteoclastic and osteogenic effects within the affected tissue. We demonstrated the presence of PGE2 and PGD2 receptors on hMSCs on RNA level and with immunofluorescence. For each Prostaglandin, three concentrations were studied: 0.1; 0.5 or 1.0 µg/ml. A lower expression of EP1 and EP4 (PGE2 receptors 1 and 4) after stimulation with PGE2 was shown, thus a tendency to compromise osteogenic differentiation and metabolism. PGE2 induced a higher growth-rate during the first week, while a continuous inflammatory challenge determined a decrease of the proliferation of hMSCs. PGD2 inhibited cell growth irrespective of the duration of the stimulation. PGE2 and PGD2 have also negative effects on calcium deposition osteogenic, thus on differentiation of hMSCs. PGE2 and PGD2 seem to induce bone resorption also having indirectly a negative impact on the osteogenic differentiation of hMSCs. Thus, inhibitors of PGE2 and PGD2 can be used as adjunct to mechanical periodontal treatment.

3D printed replicas for endodontic education.

AIM: To assess the feasibility of producing artificial teeth for endodontic training using 3D printing technology, to analyse the accuracy of the printing process, and to evaluate the teeth by students when used during training. METHODOLOGY: Sound extracted human teeth were selected, digitalized by cone beam computed tomography (CBCT) and appropriate software and finally reproduced by a stereolithographic printer. The printed teeth were scanned and compared with the original ones (trueness) and to one another (precision). Undergraduate dental students in the third and fourth years performed root canal treatment on printed molars and were subsequently asked to evaluate their experience with these compared to real teeth. RESULTS: The workflow was feasible for manufacturing 3D printed tooth replicas. The absolute deviation after printing (trueness) ranged from 50.9 to 104.3 µm. The values for precision ranged from 43.5 to 68.2 µm. Students reported great benefits in the use of the replicated teeth for training purposes. CONCLUSION: The presented workflow is feasible for any dental educational institution who has access to a CBCT unit and a stereolithographic printer. The accuracy of the printing process is suitable for the production of tooth replicas for endodontic training. Undergraduate students favoured the availability of these replicas and the fairness they ensured in training due to standardization.

3D-printed model for hands-on training in dental traumatology.

AIM: To assess the feasibility of creating a realistic model for hands-on training in dental traumatology using 3D printing technology, and then to investigate the added value of working with the website dentaltraumaguide.org. METHODOLOGY: With the use of special software applications, a model was designed based on the CBCT of the maxilla of a real patient that imitated several traumatic dental injuries. The model was reproduced using a stereolithographic printer to use the specimens in a hands-on training course on dental traumatology for undergraduate students in their final year in the Department of Conservative Dentistry and Periodontology in Munich, Germany. During the course, half of the participants had access to dentaltraumaguide.org, whereas the others did not. The students were then assessed according to their theoretical knowledge and practical performance in simulated treatment. These data were analysed by Kolmogorov-Smirnov test, unpaired t-test and Mann-Whitney U test. Subsequently, the participants were asked to evaluate the model. RESULTS: The workflow for manufacturing a model of dental traumatology for training purposes was practical and relatively inexpensive. In the evaluation process, the model was considered to be highly realistic and useful during an instructive hands-on training course. There were significant differences between the two groups in favour of using the dentaltraumaguide.org website. CONCLUSIONS: 3D printing technology offers new possibilities for training specific dental treatments that are currently difficult to imitate. The online platform dentaltraumaguide.org assisted students in correctly managing traumatic dental injuries.

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.

Clinical studies in restorative dentistry: New directions and new demands.

Clinical research of restorative materials is confounded by problems of study designs, length of trials, type of information collected, and costs for trials, despite increasing numbers and considerable development of trials during the past 50 years. This opinion paper aims to discuss advantages and disadvantages of different study designs and outcomes for evaluating survival of dental restorations and to make recommendations for future study designs. Advantages and disadvantages of randomized trials, prospective and retrospective longitudinal studies, practice-based, pragmatic and cohort studies are addressed and discussed. The recommendations of the paper are that clinical trials should have rational control groups, include confounders such as patient risk factors in the data and analysis and should use outcome parameters relevant for profession and patients.

Academy of Dental Materials guidance-Resin composites: Part II-Technique sensitivity (handling, polymerization, dimensional changes).

OBJECTIVE: The objective of this work, commissioned by the Academy of Dental Materials, was to review and critically appraise test methods to characterize properties related to critical issues for dental resin composites, including technique sensitivity and handling, polymerization, and dimensional stability, in order to provide specific guidance to investigators planning studies of these properties. METHODS: The properties that relate to each of the main clinical issues identified were ranked in terms of their priority for testing, and the specific test methods within each property were ranked. An attempt was made to focus on the tests and methods likely to be the most useful, applicable, and supported by the literature, and where possible, those showing a correlation with clinical outcomes. Certain methods are only briefly mentioned to be all-inclusive. When a standard test method exists, whether from dentistry or another field, this test has been identified. Specific examples from the literature are included for each test method. RESULTS: The properties for evaluating resin composites were ranked in the priority of measurement as follows: (1) porosity, radiopacity, sensitivity to ambient light, degree of conversion, polymerization kinetics, depth of cure, polymerization shrinkage and rate, polymerization stress, and hygroscopic expansion; (2) stickiness, slump resistance, and viscosity; and (3) thermal expansion. SIGNIFICANCE: The following guidance is meant to aid the researcher in choosing the most appropriate test methods when planning studies designed to assess certain key properties and characteristics of dental resin composites, specifically technique sensitivity and handling during placement, polymerization, and dimensional stability.

Academy of Dental Materials guidance-Resin composites: Part I-Mechanical properties.

OBJECTIVE: The objective of this project, which was initiated from the Academy of Dental Materials, was to review and critically appraise methods to determine fracture, deformation and wear resistance of dental resin composites, in an attempt to provide guidance for investigators endeavoring to study these properties for these materials. METHODS: Test methods have been ranked in the priority of the specific property being tested, as well as of the specific test methods for evaluating that property. Focus was placed on the tests that are considered to be of the highest priority in terms of being the most useful, applicable, supported by the literature, and which show a correlation with clinical findings. Others are mentioned briefly for the purpose of being inclusive. When a standard test method exists, including those used in other fields, these have been identified in the beginning of each section. Also, some examples from the resin composite literature are included for each test method. RESULTS: The properties for evaluating resin composites were ranked in the priority of measurement as following: (1) Strength, Elastic Modulus, Fracture toughness, Fatigue, Indentation Hardness, Wear-abrasion (third body) and Wear-attrition (contact/two body), (2) Toughness, Edge strength (chipping) and (3) Wear determined by toothbrush. SIGNIFICANCE: The following guidance is meant to aid the researcher in choosing the proper method to assess key properties of dental resin composites with regard to their fracture, deformation and wear resistance.

Assessment of practical tasks in the Phantom course of Conservative Dentistry by pre-defined criteria: a comparison between self-assessment by students and assessment by instructors.

INTRODUCTION: Assessment of practical skills in undergraduate dental education has difficulties, including a lack of transparency/objectivity in student evaluations. This prospective study investigated whether agreement between student- and faculty-based assessments increased when students were trained to use the assessment criteria. MATERIALS AND METHODS: Assessment criteria were available for 6 tasks in the Phantom course of Conservative Dentistry: Class II cavity preparation, composite restoration, gold and ceramic partial crown preparation, trepanation and access cavity preparation, and root canal filling. Forty-two students were allocated to three different assessment training groups. Students' self-assessments of practical tests were compared with instructors' assessments, depending on training intensity and task type (Pearson's rho, ANOVA, Tukey's post hoc test, Kruskal-Wallis test). Students/instructors were questioned regarding benefits/drawbacks of the criteria. RESULTS: Student self-assessments showed either consent (24.2%), overestimation (31%) or underestimation (44.8%). Gender differences were negligible. Regarding passing/failing grades, more intensive training yielded significantly increased agreement only for preparation of gold partial crowns (rho = +0.313, P = 0.044). Ratings exhibited significant differences amongst tasks (P = 0.002), for example, trepanation assessment had significantly lower differences than gold or ceramic preparation assessments. These discrepancies decreased with increased training. Students consistently reported benefitting most from learning the criteria for gold preparations, followed by composite and ceramic preparations. They also reported that learning the criteria was beneficial for knowledge transfer/feedback. Instructors rated the criteria as helpful for task evaluation and feedback efficiency. CONCLUSIONS: Pre-defined assessment criteria may increase consistency between student self-assessment and instructor assessment depending on the task, improving transparency and feedback in dental education.

Criteria for the Replacement of Restorations: Academy of Operative Dentistry European Section.

The replacement of a restoration is one of the most common procedures in dentistry. However, the criteria for such intervention, excluding catastrophic failure and persistent discomfort and pain, continue to be the subject of considerable debate. The decision-making process remains subjective on the part of the treating clinician, while the evidence base for refurbishment and repair rather than replacement for the management of defective and failing restorations continues to grow and strengthen. This article, prepared as an Academy of Operative Dentistry European Section consensus publication, reviews existing criteria for the replacement of restorations and encourages practitioners to shift, if not already doing so, to considering the replacement of a restoration as a last resort rather than as a prudent action to be taken if in any doubt about clinical acceptability. Further research in the area, spanning the risk assessment of defective and failing restorations and new diagnostic tools and processes, together with work to enhance the evidence base of restoration repair vs replacement, would be of immense value.

The need for repeated dental care under general anaesthesia in children.

AIM: Though the use of advanced behaviour management may facilitate dental treatment in children, some patients still require comprehensive care under general anaesthesia (GA). This is especially true for young children and/or medically compromised children. Thus, this study aimed to provide information about children undergoing GA with regard to age, sex and medical conditions (ICD-10), repeated treatments, dental procedures and recall. MATERIALS AND METHODS: A total of 464 medically compromised children treated under GA in a dental university clinic between 2004 and 2012 were included. Patients` records were analysed retrospectively using SPSS (Version 21.0) and R for statistical analysis. RESULTS: More than 75% of the patients were younger than six years when receiving initial GA. The proportion of children subjected to repeated treatments was low, at 11% for a second and <2% for a third round of GA. The greatest proportion of dental care consisted of restorative therapy and tooth extractions. The recall behaviour observed between the first and second GA revealed no significant influence on the time elapsed in between events (p>0.05). CONCLUSION: Oral care in children with medical conditions is mostly caries-related, and repeated treatment may be necessary, though it was generally uncommon in this university-based study population.

Occlusal caries extension in relation to visual and radiographic diagnostic criteria: results from a microcomputed tomography study.

OBJECTIVE: This in vitro study aimed to evaluate occlusal caries extension in relation to visual and radiographic diagnostic criteria and their clinical value to indicate operative or preventive dental care. METHODS: A total of 196 third molars with clinically sound occlusal fissures or noncavitated lesions were collected. Before microcomputed tomography (µCT) investigation, each tooth was examined visually and radiographically. Kühnisch's µCT-based caries-extension index (CE index) was used to determine the caries depth on a numeric scale (0 = sound; 0.01-0.99 = enamel caries; 1.0-1.99 = dentin caries). Sensitivities (SEs), specificities (SPs), and area under the receiver operating characteristic curve (Az value) were also calculated. RESULTS: Based on µCT data, the following mean CE index values and standard deviations (SDs) were documented according to the visual criteria: sound = 0.6 (0.4); first visible signs = 0.9 (0.4); established lesions = 1.3 (0.3); microcavities = 1.4 (0.2); dentin exposure = 1.5 (0.2); and large cavities = 1.5 (0.3). The radiographic categories according to Marthaler (enamel caries [D0-2], caries in the outer half of dentin [D3], and caries in the inner half of dentin [D4]) were related to CE index values of 0.9 (0.4), 1.4 (0.2) and 1.6 (0.4), respectively. Caries detected visually or radiographically showed an SE of 84% and an SP of 85% (Az = 0.85). When both methods were used to predict dentin involvement simultaneously, SE = 27%, SP = 100%, and Az = 0.63; this combined visual and radiographic approach was associated with a perfect specificity and no false-negative decisions. The proportion of false-positive diagnoses was moderately high, and lesion extension in these cases was mainly limited to the outer 20% of the dentin. CONCLUSIONS: Our results might be useful for differentiating between preventive and operative dental care for pits and fissures.

Elevated serum 25(OH)-vitamin D levels are negatively correlated with molar-incisor hypomineralization.

To date, the precise etiology of molar-incisor hypomineralization (MIH) is uncertain. Vitamin D plays a key role in hard tissue formation. Therefore, this study aimed to analyze the relationship between serum 25-hydroxy-vitamin D (25(OH)D) status and dental health data obtained from 1,048 children in a 10-year follow-up of the Munich GINIplus and LISAplus birth cohorts. The dental examination included the diagnosis of MIH and recording of (non-)cavitated caries lesions in primary and permanent teeth. Serum 25(OH)D concentrations were taken from blood samples of the 10-year investigation and measured with a fully automated, modular system. Different logistic regression and Poisson hurdle models were calculated. MIH was diagnosed in 13.6% of the study population. Approximately 16.4% of the children demonstrated caries-related defects (D3-4MFS > 0). The mean season-adjusted concentration of 25(OH)D was 75.8 nmol/l (standard deviation 22.0 nmol/l). After adjusting for sex, age, body mass index, parental education, equivalent income, and television/personal computer (TV/PC) viewing hours, a 10 nmol/l increase in serum 25(OH)D concentrations was significantly associated with a lower odds ratio of having MIH (OR = 0.89; P = 0.006). Furthermore, higher 25(OH)D values were associated with a lower number of caries-affected permanent teeth. It is concluded that elevated serum 25(OH)D concentrations were associated with better dental health parameters.

Quantification of elutable substances from methacrylate based sealers and their cytotoxicity effect on with human gingival fibroblasts.

OBJECTIVES: Previous studies have shown that resin composites may cause persistent inflammation of oral or pulpal tissues as well as cell death through eluted substances. The aim of this study was to investigate the leaching of ingredients from commercial dental fissure sealers as well as their cytotoxic effects on human gingival fibroblast (HGF). METHODS: The sealers tested were: Helioseal(®) F, Helioseal(®) Refill, Fissurit(®) F, Grandio(®) Seal, Ultraseal XT(®) plus and Delton(®) FS. Ten discs of each sealer were respectively immersed in methanol or water and incubated at 37°C. The eluates were analysed by gas chromatography/mass spectrometry at day 1, 3 and 7. In the XTT-test, eight discs of each fissure sealer were immersed into medium. The eluates of the respective sealer were mixed and used undiluted and diluted with medium. HGF were incubated with the dilutions at 37°C for 24h. Then XTT-salt was added and the XTT-formazan formation was quantified. RESULTS: In eluates from polymerized sealers, comonomers (triethylene glycol dimethacrylate (TEGDMA)) and additives were found (e.g. camphorquinone (CQ), butylated hydroxytoluene, triphenylstibane). 7 d after the beginning of the experiments the highest amount of TEGDMA was found in the aqueous eluate from Grandio(®) Seal (9944.31 (2250.56) µmol/l). The most cytotoxic eluate found in the XTT-test was from Fissurit(®) F (EC50 value at 27.13 (7.04)%; (mean(SD)). SIGNIFICANCE: Because of the use of sealers in preventative dental medicine it should be taken into account that substances like TEGDMA or CQ, that are often causing allergic reactions, are elutable. Before using the sealers patients should be asked for allergic reactions to these substances.

Primary cancellous bone formation with BMP and micro-chambered beads: experimental study on sheep.

PROBLEM: The physiological reconstruction of cancellous bone defects in surgery of the locomotor system is an unsatisfactorily solved problem. AIMS: The aims of this study are to examine whether micro-chambered ß-tricalcium-phosphate (ß-TCP) beads provide a certain capillary force suctioning in blood and bone marrow thus forming a stable "negative"-replica of the bone marrow spaces. If so, a new approach for osteoconduction would yield primarily a scaffold of lamellar cancellous bone under load without a long-lasting remodeling process. Recombinant human bone morphogenetic protein (rhBMP) might even enhance all processes of defect healing, remodeling and ß-TCP resorption; gentamicin-loaded ε-caprolactone might protect the implant. MATERIAL AND METHODS: Ten sheep were operated on; the patella-groove model and the tibial head were used. A defect of 9.4 × 20 mm was created using wet-grinding-diamond instruments. Micro-chambered ß-TCP-beads of 4-6 mm with 0.35 mg rhBMP-7 + 0.1 g collagen per animal, or 1.5 g demineralized bone matrix (DBM) paste on the contra-lateral side were implanted. Both osteoinduction groups were compared with the defect in the tibial heads where plain micro-chambered ceramic beads were inserted. Added to the beads was 12.5 mg gentamicin sulphate in 12.5 mg ε-caprolactone-carrier. Outward diffusion was prevented using a 1-mm-thick press-fit inserted ceramic lid. The bone healing, remodeling and resorption of the ceramic in a right-left comparison of the patella groove and the tibial head was examined at 6 weeks, 2 and 3 months; one animal in reserve was followed for 14 months. The animals were perfusion-fixed, the vasculature micro-casted with an acrylate and nondemineralized processed, and with µ-CT and microscopically documented. RESULTS: A primary load-bearing spongiosa had developed around the beads, which shortened the remodeling process. The strong micro-chambered, resorbable ß-TCP-beads demonstrate high capillary strength, resorb blood and bone marrow, and represent a stable formative material which, as a carrier for the controlled local release of BMP, that accelerates bone healing, shortens resorption and remodeling compared with plain and DBM loaded implants. CONCLUSION: Micro-chambered beads represent the bone-forming element, BMP yields a fast defect healing and enhanced remodeling of bone and resorption of ß-TCP compared to delayed and incomplete reconstruction and resorption of ß-TCP on the DBM-side, the plain implants reached nearly the same reconstruction, but far later compared with the BMP loaded implants.

Resin-based composite light-cured properties assessed by laboratory standards and simulated clinical conditions.

SUMMARY The following parameters were varied: 1) irradiation technique: top and bottom polymerization according to the ISO standard, and polymerization from only the top, simulating clinical situations; 2) polymerization time: 5, 10, 20, and 40 seconds; 3) storage conditions: 24 hours in distilled water, thermocycling followed by storage for four weeks in artificial saliva or alcohol. Flexural strength (FS), flexural modulus (Eflexural), indentation modulus (E), Vickers hardness (HV), and degree of conversion (DC) were measured. The laboratory results were similar to those measured by mimicking clinical conditions only at high polymerization times and mild storage conditions (20 seconds and 40 seconds and storage for 24 hours in water, and 40 seconds with aging and storing in saliva). Significantly higher DC values were measured on the top than on the bottom of a 2-mm layer for all polymerization times. Overall, 5-second and 10-second irradiation times induced significantly lower DC values compared to the currently recommended polymerization times of 20 and 40 seconds at both the top and bottom of the samples. The initial DC differences as a function of irradiation time are leveled at 24 hours of storage but seem to do well in predicting long-term material behavior. A minimum irradiation time of 20 seconds is necessary clinically to achieve the best mechanical properties with modern high-intensity light emitting diode (LED) units.