Influence of two different cement space settings and three different cement types on the fit of polymer-infiltrated ceramic network material crowns manufactured using a complete digital workflow.

OBJECTIVES: The study evaluates the influence of two spacer settings and three resin luting materials on the marginal and internal fit of polymer-infiltrated ceramic network (PICN) material crowns manufactured using a complete digital workflow. METHODS: Optical impressions of fifty identical dies were performed using the 3M scanner (software version 5.0.2). Twenty crowns were designed using Ceramill Mind (version 3.4.10.1163), from which ten with spacer setting of 50 µm (G1) and ten with 80 µm (G2). Thirty crowns (spacer setting of 50 µm) were divided into three groups corresponding to the resin materials used as follows: RelyX Unicem (RX), Variolink Esthetic (VLE), and Nexus 3 (NX3). All crowns were milled from Vita Enamic blocks. After micro-CT scanning, absolute marginal discrepancy (AMD), internal gap (IG), total cement space volume (TCV), and marginal porosities (VP) were measured. RESULTS: Significant difference was detected on the VP between the RX and NX3 group (p = 0.033). The mean values of all parameters were the following: AMD (µm): G1 182.6, G2 253.7, RX 210.8, VLE 195.5, NX3 186.6; IG (µm): G1 215.6, G2 173.1, RX 171.1, VLE 198.6, NX3 203; TCV (mm3): G1 22.9, G2 20.49, RX 17.57, VLE 17.49, NX3 20.59; VP (mm3): G1 0.26, G2 0.34, RX 0.32, VLE 0.46, NX3 0.54. CONCLUSIONS: Fit of PICN material crowns was not significantly influenced by increasing the spacer settings and cementation with different resin materials. Additionally, RelyX Unicem showed significantly less porosities as compared with Nexus3. CLINICAL RELEVANCE: Both 50 µm and 80 µm virtual spacer settings can be suggested for the manufacture of PICN crowns when Ceramill Mind (version 3.4.10.1163) is used. Furthermore, a self-adhesive system can be recommended for the cementation.

Effect of two different primers on the shear bond strength of metallic brackets to zirconia ceramic.

BACKGROUND: In view of the increasing demand of adult orthodontics for esthetic purposes, adult treatment with brackets has become an important issue. One essential factor for the quality of such treatment is bracket bonding on ceramics. For testing the adhesive bond between the bracket and the ceramic surface it is important to consider the static or cyclic loading that goes along with it. METHODS: Metallic Brackets were adhesively fixed on zirconia ceramic blocks in a simulated leveling phase using two different primers (Monobond S and Monobond Etch & Prime). Half of the metallic brackets were activated using a 0.14-nickel titanium wire, while the other half remained non-activated. Shear bond testing (SBT) was performed after thermocycling. Furthermore the Adhesive Remnant Index (ARI) was analyzed. RESULTS: SBT resulted in significantly higher shear bond values when Monobond Etch & Prime was used compared to the use of Monobond S. Activation of the brackets did not show different results in comparison to the non-activated brackets. The ARI did not indicate cement remnants on the ceramic surface, regardless of the primer and the activation status. CONCLUSIONS: The use of Monobond Etch & Prime has great potential for the bonding of brackets on dental zirconia ceramics.

Shear bond strength of different materials used as core build-up to ceramic.

PURPOSE: To determine the performance of a resin composite material specially developed for core build-ups in comparison with conventional restorative materials. METHODS: 90 roughened ceramic blocs were divided into three groups; one group (n=30) was used for the core build-up material (Gradia Core) and the other two groups (n=30, each) were used for two conventional restorative materials (Tetric EvoCeram, Compoglass F). After adhesive fixation, specimens of each material were subdivided in accordance with the storage conditions (thermocycling or water storage). Shear bond strength was measured and fracture behavior was analyzed. RESULTS: Gradia Core presented significantly higher shear bond strength values than the conventional restorative material Tetric EvoCeram, both after 24 hours water storage as well as after thermocycling. Compoglass F did not show any statistically significant differences compared to the other materials, independent of the storage condition. However, Compoglass F resulted in numerically higher shear bond values than Tetric EvoCeram, but lower shear bond values than Gradia Core. Within the same materials, no statistically significant differences occurred regarding the storage conditions. CLINICAL SIGNIFICANCE: The specific core build-up material provided stronger bonding properties when luted to feldspar ceramic than conventional restorative materials, making it a suitable supporting material when high-quality esthetic restorations are needed for restoring decayed, but vital teeth.

Comparison of marginal fit of cemented zirconia copings manufactured after digital impression with lava™ C.O.S and conventional impression technique.

BACKGROUND: Evaluation of the marginal fit of cemented zirconia copings manufactured after digital impression with Lava™ Chairside Oral Scanner in comparison to that of zirconia copings manufactured after conventional impressions with polyvinyl siloxane. METHODS: A prepared typodont tooth #36, was replicated 40 times with a vinyl silicone and precise model resin. The dies were randomly divided into two groups according to the impression taking technique. Digital impressions with Lava™ C.O.S. and conventional impressions were taken according to the group. Subsequently zirconia copings were manufactured and cemented on their respective dies with zinc oxide phosphate cement. After embedding in resin, mesio-distal section of each coping was performed with a diamond saw in order to obtain two slices. One half of the specimen was used for evaluation with an optical microscope (OM) and the other half for evaluation with a scanning electron microscope (SEM). Marginal gap (MG) and absolute marginal discrepancy (AMD) were measured mesial and distal on each slice. RESULTS: No significant difference of the marginal parameters between the digital and the conventional group was found. The mean values for MG in the digital group were 96.28 µm (+/-43.21 µm) measured with the OM and 99.26 µm (+/-48.73 µm) measured with the SEM, respectively. AMD mean values were 191.54 µm (+/-85.42 µm) measured with the optical microscope and 211.6 µm (+/-96.55 µm) with the SEM. For the conventional group the mean MG values were 94.84 µm (+/-50.77 µm) measured with the OM and 83.37 µm (+/-44.38 µm) measured with the SEM, respectively. AMD mean values were 158.60 µm (+/-69.14 µm) for the OM and 152.72 µm (+/-72.36) for the SEM. CONCLUSIONS: Copings manufactured after digital impression with Lava™ C.O.S. show comparable marginal parameters with the copings manufactured after conventional impression with polyvinyl syloxane. The mean MG values of both groups fit in the clinically acceptable range.

Knowledge, application and how about competence? Qualitative assessment of multiple-choice questions for dental students.

Background: Many medical schools train their faculty members to construct high cognitive level multiple choice questions (MCQs) that demand a great deal of analytical and critical thinking, application, and competence. The purpose of this study is to determine the cognitive levels of MCQs by using Moore's Expanded Outcomes Framework and to understand whether the quality of MCQs has an effect on students' assessment performance.Methods: Four trained faculty members analysed 100 randomly selected questions developed at the University Clinic of Dentistry (UCD) and 100 questions developed by the National Board of Dental Examinations (NBDE). Moore's framework was applied to assist the review process.Results: The majority of questions was at the level of declarative knowledge followed by questions at the level of procedural knowledge. The cognitive level of UCD questions from 2002 to 2009 was significantly lower than that of NBDE questions but increased in questions written from 2010 to 2018. The improvement of quality of MCQs had no impact on assessment performance of students.Conclusion: The enhanced cognitive levels of UCD MCQs written 2010-2018 coincides with the implementation of a faculty training program for writing high-ordered MCQs. In addition, this study shows that the use of Moore's expanded framework is on par with other known taxonomies in supporting educators in writing items and reviewing the process.Abbreviations: MCQs: Multiple Choice Questions; UCD: University Clinic of Dentistry; NBDE: National Board of Dental Examinations.

Micro-CT evaluation of marginal and internal fit of cemented polymer infiltrated ceramic network material crowns manufactured after conventional and digital impressions.

PURPOSE: Purpose of this study was to evaluate the accuracy of fit of cemented polymer infiltrated ceramic network (PICN) material crowns manufactured after digital and conventional impression techniques using micro computed tomography (CT). Furthermore to determine the cement space volume and porosities in the cement layer. METHODS: A molar typodont tooth was prepared for PICN material crowns and replicated thirty times. The dies were randomly divided into three groups of 10 specimens each according to the impression technique: 3M True Definition Scanner (TDS), cara TRIOS (Trios) and Impregum Penta Soft (Impregum). PICN material crowns were milled for each specimen from Vita Enamic blocks and cemented on their respective dies. The absolute marginal discrepancy (AMD), internal fit (IG), total cement space volume (TVC) and marginal porosities (VP) were measured using Micro-CT. RESULTS: Mean and standard deviations values in µm for the AMD were: TDS 140.1 (28.4); Trios 253.7 (56.8); Impregum 220.2 (101.1). IG values in µm: TDS 173.1 (27.7); Trios 222.2 (22.4); Impregum 211.6 (55.9). TVC in mm3: TDS 19.82 (2.9); Trios 23.67 (2.01); Impregum 23.77 (5.09). VP in mm3: TDS 0.38 (0.09); Trios 0.36 (0.10); Impregum 0.51 (0.31). CONCLUSIONS: TDS group showed significantly better marginal and internal fit than the Trios group. No difference of the parameters was detected between the Impregum and both digital groups which implies that the digital impression technique is suitable in the manufacturing process of PICN material crowns.

Comparison of Bleaching Products With Up to 6% and With More Than 6% Hydrogen Peroxide: Whitening Efficacy Using BI and WI D and Side Effects - An in vitro Study.

The aim of this study was to evaluate the effect of bleaching agents containing different concentrations of hydrogen peroxide (HP) on color-change and on enamel-surface in bovine teeth. Furthermore the influence on cell viability and proliferation was investigated. Two hundred and forty teeth were randomly assigned into four groups (home bleaching ≤6%, in-office bleaching ≤6%, in-office bleaching > 6% HP, and control group). Bleaching was performed after artificial staining and the bleached index (BI) as well as the whiteness index (WI D ) was measured at several time points. Chemical analysis for HP concentrations and the pH of the bleaching products was done. Furthermore, enamel surfaces of randomly selected specimens were analyzed using scanning electron microscopy (SEM) and cytotoxicity of the tested bleaching products was evaluated in vitro using dental pulp cells (DPCs) and L929 cells. A statistically significant whitening effect was observed in almost all products. As expected all investigated products resulted in decreased cell viability, however, with different values of LC50 (median lethal concentration). SEM analysis showed an analog of enamel alterations with decreasing pH, increasing exposure time, and increasing HP concentration. Bleaching agents containing a low HP concentration are considered to be effective and to have less damaging effects on enamel and tested cells.

Hypoxia-based strategies for regenerative dentistry-Views from the different dental fields.

The understanding of the cell biological processes underlying development and regeneration of oral tissues leads to novel regenerative approaches. Over the past years, knowledge on key roles of the hypoxia-based response has become more profound. Based on these findings, novel regenerative approaches for dentistry are emerging, which target cellular oxygen sensors. These approaches include hypoxia pre-conditioning and pharmacologically simulated hypoxia. The increase in studies on hypoxia and hypoxia-based strategies in regenerative dentistry highlights the growing attention to hypoxia's role in regeneration and its underlying biology, as well as its application in a therapeutic setting. In this narrative review, we present the current knowledge on the role of hypoxia in oral tissues and review the proposed hypoxia-based approaches in different fields of dentistry, including endodontics, orthodontics, periodontics, and oral surgery.

Evaluation of the Morphological Characteristics of Laser-Irradiated Dentin.

OBJECTIVE: The aim of this study was to investigate the effect of different energy settings of Er:YAG laser irradiation on dentin surface morphology with respect to the number of opened dentinal tubules. BACKGROUND DATA: An ideally prepared dentin surface with opened dentinal tubules is a prerequisite for adhesive fixation. No study, however, has yet compared the numbers of opened dentinal tubules with regard to statistical differences. METHODS: Conventional preparations using a bur with or without additional acid etching acted as control groups. Dentin specimens were prepared from human third molars and randomly divided into eight groups according to the energy settings of the laser (1, 1.5, 4, 6, 7.5, and 8 W) and two controls (bur and bur plus acid etching). After surface preparation, dentin surfaces were analyzed with a scanning electron microscope, and the number of opened dentinal tubules in a defined area was counted. RESULTS: The control groups showed smooth surfaces with (bur plus acid etching) and without opened dentinal tubules (bur), whereas all laser-irradiated surfaces showed rough surfaces. Using the energy setting of 4 W resulted in significantly more opened dentinal tubules than the conventional preparation technique using the bur with additional acid etching. In contrast, the energy setting of 8 W showed significantly fewer opened dentinal tubules, and also exhibited signs of thermal damage. CONCLUSIONS: The Er:YAG laser with an energy setting of 4 W generates a dentin surface with opened dentinal tubules, a prerequisite for adhesive fixation.