Influence of additive and subtractive zirconia and lithium disilicate manufacturing on tensile bond strength and surface topography.

STATEMENT OF PROBLEM: Although bonding is important for long-term clinical success, studies on the bonding of additively manufactured ceramics are sparse. PURPOSE: The purpose of this in vitro study was to determine the influence of manufacturing methods, additive (LCM) versus subtractive (CAM). and ceramic materials, zirconia (ZrO2) and lithium disilicate (LiSi), on the tensile bond strength (TBS), failure mode, and surface roughness of ceramics. MATERIAL AND METHODS: A total of 240 ceramic specimens (n=60/group; 2×2×10 mm) were prepared. Two additively manufactured (LCM-printed) ceramics, LiSi and ZrO2 (Lithoz), subtractively manufactured LiSi (IPS e.max CAD), and subtractively manufactured ZrO2 (KATANA Zirconia HTML PLUS) were evaluated. From each material, 40 specimens were bonded together (n=20 ceramic-ceramic specimens/group), and 20 specimens were bonded to equally sized human dentin specimens (n=20 ceramic-dentin specimens/group). The ZrO2 specimens were airborne-particle abraded (Al2O3, 50 µm, 0.1 MPa), and the LiSi specimens were etched with hydrofluoric acid. Then, a universal primer (Monobond Plus) was applied. After the dentin was coated with an etch-and-rinse adhesive (Syntac Classic), the specimens were bonded with luting composite resin (Variolink Esthetic DC), light polymerized for 40 seconds, thermally aged (10 000 cycles between 5 °C and 55 °C), tested for TBS, and statistically analyzed (1- and 3-way ANOVA and Weibull analysis). The ceramic surface was examined with scanning electron microscopy, and surface roughness was measured with digital microscopy before and after surface pretreatment. RESULTS: TBS varied between 5.88 ±2.22 MPa and 6.34 ±2.26 MPa in the ceramic-dentin groups and 12.40 ±1.56 MPa and 18.82 ±5.92 MPa in the ceramic-ceramic groups. No significant difference was observed regarding the manufacturing method and material for different bonding conditions (P>.05). Additive and subtractive LiSi showed the highest reliability with m=18.27. The ceramic-ceramic specimens failed cohesively in the luting composite resin, whereas the ceramic-dentin specimens failed adhesively. CONCLUSIONS: The manufacturing method and material used had little effect on bond strength values or surface properties. The recently introduced printed materials performed similarly to conventionally milled materials.

Influence of the design of 3D-printed indirect bonding trays and experience of the clinician on the accuracy of bracket placement.

PURPOSE: The aim was to investigate the influence of three different three-dimensional (3D)-printed bonding tray designs and professional experience on accuracy of indirect bracket placement. METHODS: Virtual bracket placement was performed on a scanned dental model using OnyxCeph software (Image Instruments, Chemnitz, Germany). Three different designs for indirect bonding trays (open, semi-open, and closed design) were created and produced using a 3D printer. To analyze the influence of professional experience, one of the three tray designs was produced twice. In this case, bracket placement was performed by an inexperienced dentist. Bracket positions were scanned after the indirect bonding procedure. Linear and angular transfer errors were measured. Significant differences between the target and actual situation were analyzed using the Kruskal-Wallis and χ2 test. RESULTS: All bonding tray designs resulted in comparable results. The results of the unexperienced dentist showed significantly higher deviations than those for the experienced orthodontist in the torque direction. However, the mean values were comparable. The open tray design exceeded the clinically acceptable limits of 0.25 mm and 1° more often. The inexperienced dentist exceeded these limits significantly more often than the experienced orthodontist in the vertical and torque direction. The immediate bracket loss rate showed no significant differences between the different tray designs. Significantly more bracket losses were observed for the inexperienced dentist during the procedure compared to the experienced orthodontist. CONCLUSIONS: The bonding tray design and professional experience had an influence on the exceedance of clinically relevant limits of positioning accuracy and on the bracket loss rate.

Retrospective clinical study on the performance and aesthetic outcome of pressed lithium disilicate restorations in posterior teeth up to 8.3 years.

OBJECTIVES: Evaluation of cumulative survival and complication rate of monolithic lithium disilicate inlays and partial crowns performed by supervised undergraduate students up to 8.3 years of clinical service. MATERIALS AND METHODS: In this retrospective clinical study 143 lithium disilicate posterior restorations (IPS e.max Press) were examined according to the FDI criteria. A standardised questionnaire was used to determine patient satisfaction. The aesthetic outcome was evaluated by dentists and dental technicians using intraoral photographs. Data were descriptively analysed. Cumulative survival and success rates were calculated using Kaplan-Meier estimation. RESULTS: The cumulative survival rate of lithium disilicate restorations was 97.5% after a mean service time of 5.9 years and 95.0% after 8.3 years. The cumulative success rate decreased from 94.4% after 5.9 years to 30.7% after 8.3 years. Repairs were required for 7 restorations (4.9%), and 5 (3.5%) were classified as failures. The results of the questionnaire indicate a high level of patient satisfaction. The subjective aesthetics were assessed more critically by dental technicians compared to dentists. CONCLUSION: Lithium disilicate posterior restorations survived successfully up to 8.3 years when carried out by undergraduate students. CLINICAL RELEVANCE: Pressed lithium disilicate glass ceramic inlays and partial crowns are reliable treatment options in posterior teeth.

Influence of decision-making algorithms on the diagnostic accuracy using the current classification of periodontal diseases-a randomized controlled trial.

OBJECTIVES: To examine the influence of the decision-making algorithms published by Tonetti and Sanz in 2019 on the diagnostic accuracy in two differently experienced groups of dental students using the current classification of periodontal diseases. MATERIALS AND METHODS: Eighty-three students of two different clinical experience levels were randomly allocated to control and study group, receiving the staging and grading matrix, resulting in four subgroups. All diagnosed two patient cases with corresponding periodontal charts, panoramic radiographs, and intraoral photographs. Both presented severe periodontal disease (stage III, grade C) but considerably differed in complexity and phenotype according to the current classification of periodontal diseases. Controls received the staging and grading matrix published within the classification, while study groups were additionally provided with decision-trees published by Tonetti and Sanz. Obtained data was analyzed using chi-square test, Spearman's rank correlation, and logistic regression. RESULTS: Using the algorithms significantly enhanced the diagnostic accuracy in staging (p = 0.001*, OR = 4.425) and grading (p < 0.001**, OR = 30.303) regardless of the clinical experience. In addition, even compared to the more experienced control, less experienced students using algorithms showed significantly higher accuracy in grading (p = 0.020*). No influence on the criteria extent could be observed comparing study groups to controls. CONCLUSION: The decision-making algorithms may enhance diagnostic accuracy in dental students using the current classification of periodontal diseases. CLINICAL RELEVANCE: The investigated decision-making algorithms significantly increased the diagnostic accuracy of differently experienced under graduated dental students and might be beneficial in periodontal education.

Cytotoxicity of 3D printed resin materials for temporary restorations on human periodontal ligament (PDL-hTERT) cells.

OBJECTIVES: Various dental resin materials are available for the fabrication of temporary restorations using modern additive printing methods. Albeit these materials are placed for several months in intimate contact with dental hard and soft tissues, including the gingival crevice, there exists only insufficient evidence on the biocompatibility of these materials. This in vitro study aimed to delineate the biocompatibility of 3D printable materials on periodontal ligament cells (PDL-hTERTs). METHODS: Samples of four dental resin materials for additive fabrication of temporary restorations using 3D printing (MFH, Nextdent; GC Temp, GC; Freeprint temp, Detax; 3Delta temp, Deltamed), one material for subtractive fabrication (Grandio disc, Voco) and one conventional temporary material (Luxatemp, DMG) were prepared with a standardized size according to the manufacturer's instructions. Human PDL-hTERTs were exposed to resin specimens or eluates of the material for 1, 2, 3, 6 and 9 days. For determination of cell viability, XTT assays were performed. In addition, the expression of the proinflammatory cytokines interleukin 6 and 8 (IL-6 and 8) was assessed in the supernatants with ELISA. Cell viability and the expression of IL-6 and 8 in presence of the resin material or their eluates was compared with untreated controls. Immunofluorescence staining for IL-6 and IL-8, as well as scanning electron microscopy of the discs after culturing, were performed. Differences between groups were analyzed with Student´s t-test for unpaired samples. RESULTS: Compared to untreated control samples, the exposure against the resin specimen induced strong reduction of cell viability in case of the conventional material Luxatemp (p < 0.001) and the additive material 3Delta temp (p < 0.001) irrespective of the observation period. On the contrary, the presence of eluates of the various materials induced only minor changes in cell viability. Considering IL-6 (day 2: p = 0.001; day 6 and 9: p < 0.001) and IL-8 (day 1: p = 0.001; day 2, 3, 6, 9: p < 0.001) their expression was strongly reduced in presence of the eluate of Luxatemp. Except for IL-6 at day 1 and 6 also the material 3Delta temp caused significant reduction of both proinflammatory mediators at any time point. SIGNIFICANCE: The conventional material Luxatemp and the additive material 3Delta temp appear to severely affect cell viability when in direct contact with PDL-hTERTs. The other tested materials of this new category of additive materials and the subtractive material Grandio seem to induce only minor changes in direct contact with these cells. Therefore, they could serve as a viable alternative in the fabrication of temporary restorations.

The Detection of Dental Pathologies on Periapical Radiographs-Results from a Reliability Study.

(1) Background: Caries, periapical lesions, periodontal bone loss (PBL), and endo-perio lesions are common dental findings that require an accurate diagnostic assessment to allow appropriate disease management. The purpose of this reliability study was to compare the inter- and intra-rater reliability for the detection of the above-mentioned pathologies on periapical radiographs. (2) Methods: Fourteen dentists (three with more than two years and eleven with less than two years of work experience) participated in a training workshop prior to data acquisition. A total of 150 radiographs were assessed by all raters in two rounds. Cohen's Kappa (CK) values and a binary logistic regression were calculated. (3) Results: The reliability was found in a moderate and substantial range of agreement: caries (mean inter-rater CK value/first round 0.704/mean inter-rater CK value/second round 0.659/mean intra-rater CK value 0.778), periapical lesions (0.643/0.611/0.768), PBL (0.454/0.482/0.739) and endo-perio lesion (0.702/0.689/0.840). The regression model revealed a significant influence of the clinical experience, and furthermore, periapical pathologies and PBL were identified less reliably in comparison to caries and endo-perio lesions. (4) Conclusions: The dentist's ability to detect the chosen pathologies was linked with significant differences. Periapical lesions and PBL were identified less reliably than caries and endo-perio lesions.

The Dentist's Ability to Detect Different Restorative Procedures on Periapical Radiographs-Results from a Reliability Study.

(1) Background: This in vitro reliability study aimed to determine the inter- and intra-examiner reliability for the detection of direct fillings, indirect crown restorations, root canal fillings and implants on periapical radiographs. (2) Methods: Fourteen dentists (<2 years of clinical experience = 11; >2 years of clinical experience = 3) participated in this diagnostic reliability study in which included a theoretical and practical educational training prior to data collection. The image set of periapical radiographs (N = 150) was examined in two evaluation rounds by all the dentists. Cohen's Kappa (CK) and a binary logistic regression model were computed. (3) Results: The inter- and intra-examiner reliability were found to be in almost perfect agreement: direct fillings (1st round 0.859/2nd round 0.844/intra 0.910), indirect crown restorations (0.932/0.926/0.955), root canal fillings (0.920/0.886/0.941) and dental implants (0.994/0.988/0.987). The binary logistic regression model revealed that the "evaluation round" and "dentist's clinical experience" had no significant influence, but for the "diagnostic category"; small, but statistically significant differences were documented. (4) Conclusions: The reliability for detecting direct and indirect restorations, root canal fillings or implants on periapical radiographs was found to be high in the present reliability study on periapical radiographs.

Influence of DLP and SLA printer technology on the accuracy of surgical guides for implant dentistry in free-end situations.

AIM: The present in vitro study aimed to compare the accuracy of the implant position inserted by surgical guides manufactured by three different 3D printers (one SLA and two DLP) and a subtractive manufacturing technique for a free-end situation. MATERIALS AND METHODS: Surgical guides were manufactured using three different 3D printers, one SLA printer (Form 2; Formlabs) and two DLP printers (D20 II; Rapid Shape, and SolFlex 350; W2P Engineering). Surgical guides manufactured using the conventional CAD/CAM-based subtractive method served as controls. In total, 48 surgical guides were printed and assessed for accuracy. The guides were used for the placement of implants at tooth position 37. The postoperative implant position was digitally scanned for metric comparison with the preoperatively planned implant position. RESULTS: Significant differences were found when the SLA and DLP printers were compared. The SLA printer showed significantly lower accuracy in implant displacement at crest (P = 0.032) and angular displacement (P = 0.049) compared with the two DLP printers. The DLP printers showed comparable values to the control group. The results were within an acceptable clinical range. CONCLUSION: DLP technology seems to be superior to conventional SLA technology in terms of the accuracy of 3D-printed surgical guides when used for placement of implants in free-end situations.

Idiopathic Multicentric Castleman Disease Occurring Shortly after mRNA SARS-CoV-2 Vaccine.

Idiopathic Multicentric Castleman Disease (iMCD) is a potentially life-threatening systemic disease whose complex symptomatology is due to cytokine dysregulation. We, herein, present a case of severe iMCD occurring in a previously healthy young man shortly after mRNA SARS-CoV-2 vaccination, responding to interleukin-6 blockade with siltuximab. Six months after the completion of siltuximab, the patient remained without any signs of iMCD or inflammation, indicating a temporal trigger of the disease. This case not only adds to the potential pathogenetic spectrum of MCD, but also extends the clinical picture of potential but rare adverse events following COVID-19 immunization.

Effects of resin materials dedicated for additive manufacturing of temporary dental restorations on human gingival keratinocytes.

OBJECTIVE: This study investigated the effect of eluates of conventional and 3D-printed resin materials for manufacturing temporary dental restorations on gingival keratinocytes. METHODS: Three-dimensional (3D)-printed resin materials: 3Delta temp (Deltamed), NextDent MFH (Nextdent), Freeprint temp (Detax), GC temp (GC), were compared to Grandio disc (Voco) and Luxatemp (DMG). Human gingival keratinocytes (IHGKs) were exposed to eluates of the materials and XTT assays were performed at 24 h, 48 h, 72 h, or 144 h. For quantification of the proinflammatory response, the protein amount of IL-6 and 8 was determined in the supernatants using ELISA. One-way ANOVA with post hoc analysis was used to compare differences in cell viability and IL-6 and IL-8 levels between groups. RESULTS: At 24 h, and more remarkably at 48 h, a significant decrease in cell viability occurred for the 3D-printed materials compared to the untreated IHGKs, but also compared to Grandio disc and Luxatemp. Except for the expression of IL-8 in presence of the eluate of Grandio disc at 24 and 48 h, all tested materials caused attenuation of IL-6 and 8 from IHGKs for any observation period. CONCLUSIONS: The materials for additive manufacturing affect cell proliferation differently than the subtractive manufactured material Grandio disc and the conventional material Luxatemp. CLINICAL SIGNIFICANCE: In comparison to conventional and subtractive manufactured restorations, 3D printed temporary restorations might induce more negative effects on the gingival and probably also on pulpal health since viability and the proinflammatory response of oral keratinocytes are more intensively affected by these materials.

Bracket transfer accuracy with two different three-dimensional printed transfer trays vs silicone transfer trays.

OBJECTIVES: To compare the transfer accuracy of two different three-dimensional printed trays (Dreve FotoDent ITB [Dreve Dentamid, Unna, Germany] and NextDent Ortho ITB [NextDent, Soesterberg, the Netherlands]) to polyvinyl siloxane (PVS) trays for indirect bonding. MATERIALS AND METHODS: A total of 10 dental models were constructed for each investigated material. Virtual bracket placement was performed on a scanned dental model using OnyxCeph (OnyxCeph 3D Lab, Chemnitz, Germany). Three-dimensional printed transfer trays using a digital light processing system three-dimensional printer and silicone transfer trays were produced. Bracket positions were scanned after the indirect bonding procedure. Linear and angular transfer errors were measured. Significant differences between mean transfer errors and frequency of clinically acceptable errors (<0.25 mm/1°) were analyzed using the Kruskal-Wallis and χ2 tests, respectively. RESULTS: All trays showed comparable accuracy of bracket placement. NextDent exhibited a significantly higher frequency of rotational error within the limit of 1° (P = .01) compared with the PVS tray. Although PVS showed significant differences between the tooth groups in all linear dimensions, Dreve exhibited a significant difference in the buccolingual direction only. All groups showed a similar distribution of directional bias. CONCLUSIONS: Three-dimensional printed trays achieved comparable results with the PVS trays in terms of bracket positioning accuracy. NextDent appears to be inferior compared with PVS regarding the frequency of clinically acceptable errors, whereas Dreve was found to be equal. The influence of tooth groups on the accuracy of bracket positioning may be reduced by using an appropriate three-dimensional printed transfer tray (Dreve).

Influence of 3D-printing method, resin material, and sterilization on the accuracy of virtually designed surgical implant guides.

STATEMENT OF PROBLEM: Three-dimensional printing has introduced new manufacturing methods. However, information on the influence of the specific printing technology, material, sterilization, and the comparison between printing and milling on the accuracy of surgical guides is lacking. PURPOSE: The purpose of this in vitro study was to evaluate the influence of the manufacturing method (printing and milling), printing technology stereolithography (SLA) and digital light processing (DLP), material, and sterilization on the accuracy of digitally designed surgical implant guides. MATERIAL AND METHODS: Resin patient replicas with a single edentulous space were used to place 132 implants with digitally designed surgical guides. The accuracy of postoperative implant position was analyzed for the manufacturing method (printing and milling), resin materials, and preoperative autoclaving. To determine 3D accuracy, angular displacement, mean horizontal crestal, apical displacement, and the linear vertical displacement at the apex were calculated separately for each group (n=12). In addition, the surgical guides were qualitatively analyzed by using field emission scanning electron micrograph. RESULTS: The postoperative angular deviation ranged from 0.76 ±0.52 degrees (Rapidshape D20II with NextDent SG) to 2.43 ±0.64 degrees (Form2 with NextDent SG) (P<.001). Linear horizontal displacement at the crest was smallest for Rapidshape D20II with 3Delta Guide (0.27 ±0.08 mm) and highest for Form2 with NextDent SG (0.54 ±0.10 mm) (P<.001). Linear horizontal displacement at the apex ranged from 0.36 ±0.10 mm (SolFlex 350 with V-Print SG) to 0.89 ±0.32 mm (Form2 with NextDent SG) (P<.001). Considering the vertical position displacement was no more than 0.43 ±0.07 mm (Form2 with NextDent SG) short of the apex, none of the implant tips were displaced apically. Preoperative autoclaving differentially impaired the accuracy of surgical guides. CONCLUSIONS: The specific manufacturing technique, the 3D printing device, the resin material, and the application of preoperative sterilization all affected the accuracy of the postoperative implant position. Irrespective of the manufacturing method, all implants were placed within the commonly accepted safety distance.

Influence of the tooth position, guided sleeve height, supporting length, manufacturing methods, and resin E-modulus on the in vitro accuracy of surgical implant guides in a free-end situation.

PURPOSE: The study aims to evaluate the effect of tooth position, sleeve height, supporting length, resin E-modulus, and manufacturing method on the accuracy of dental implants placed in vitro fully guided in a lower jaw free-end situation. MATERIAL AND METHODS: Using resin clones of a patient case providing a free-end situation 384 implants has been experimentally placed guided. The accuracy of postoperative implant position analyzed depending on the tooth position (first and second molar), sleeve height (2 and 6mm), supporting length (tooth no. 37-33 and 37 43), resin E-modulus (<2,000, >2,000, and >3,000 MPa), and manufacturing method (milled, printed). To determine the three-dimensional accuracy angular deviation, mean crestal, apical deviation, and the linear vertical deviation at apex were calculated separately for each group (n = 12). RESULTS: The accuracy of implant placement using milled guides was affected only by the tooth position, indicating stronger deviation of implants replacing second molars than first molars. Considering printed guides, the implant position was influenced by tooth position, sleeve height, and supporting length. Linear vertical deviation >1 mm was found for printed materials with the lowest E-modulus at tooth position no. 37. Logistic regression analysis revealed a significant lower odds for linear vertical deviation >1 mm for materials with higher E-modulus (OR: 0.04; 95% CI:0.01-0.97; p = .048) and higher ratio for smaller sleeve height (OR: 2.77; 95% CI:1.20-6.38; p = .017). CONCLUSION: Accuracy of implant placement in a free-end situation lacking distal tooth support is superior for milled as compared to 3D-printed surgical guides. When using 3D-printed surgical guides, smaller sleeve heights and extended tooth support improve the accuracy of implant placement.

Three-body wear of luting composites and influence of the ACTA wheel material.

The aim of the study was to investigate the wear of luting materials (Variolink Esthetic LC/DC, Multilink Automix, Panavia V5 paste) compared to a resin composite (Tetric EvoFlow) with an ACTA-machine (three-body-wear simulator) using steel and 3D-printed polymer wheels. Wear was measured (software Match3D) and statistically analyzed (ANOVA). Worn surface was examined with a field-emission-scanning-electron-microscope. Finite element analysis was carried out to analyze differences in the mechanical stress of the two different sample wheels. Using the steel wheel, Variolink Esthetic DC exhibited significantly less wear than Tetric EvoFlow after 200,000 cycles (p=0.037). Luting composites on polymer wheels exhibited significantly lower wear values compared to the steel wheels (p<0.001). Finite element analysis showed higher stresses for the steel wheel compared to the polymer wheel. Mechanical properties of the sample wheels had a high influence on wear properties. Dual- or auto-polymerizing materials seem to have a small advantage over the light-curing materials.

In vitro investigation of the influence of printing direction on the flexural strength, flexural modulus and fractographic analysis of 3D-printed temporary materials.

The aim of this in vitro study was to evaluate the effect of printing direction and aging on the mechanical strength of 3D-printed temporary resin-based composites. Three hundred and sixty specimens (2×2×25 mm³) out of three materials were DLP printed. Specimens were either stored in distilled water for 24 h at 37°C or additionally subjected to thermocycling. Flexural strength (FS) and flexural modulus (FM) were evaluated in a three-point bending test considering three printing directions. Fractography was carried out by light microscopy, surfaces were categorized according to fracture origin. FS ranged from 93.2 to 159.9 MPa and 76.8 to 135.1 MPa in nonaged and aged specimens in the material sequence: Freeprint temp

Two-body wear and fracture behaviour of an experimental paediatric composite crown in comparison to zirconia and stainless steel crowns dependent on the cementation mode.

OBJECTIVES: The purpose of this in vitro study was to assess the two-body wear and fracture behaviour of an experimental additive manufactured composite crown in comparison to zirconia and stainless steel crowns and its cementation protocol for primary molars. MATERIAL AND METHODS: Three different paediatric crowns - experimental composite crowns (CCs, 3M), zirconia crowns (ZCs, NuSmile), and stainless steel crowns (SSCs, 3M)-were cemented with an experimental resin-modified glass ionomer cement (RMGIC, 3M) and two self-adhesive cements (SACs; RelyX Unicem Automix 2, 3M; BioCem, NuSmile). Seven groups, each with eight specimens, were thermally cycled (55 °C/50 °C) and dynamically loaded (50N/ 1.2Hz) in a masticatory simulator with steatite antagonists. The areal and volumetric material loss of all specimens before and after 1,200,000 masticatory cycles was evaluated with a 3D profilometer. Light and scanning electron microscopy were used for qualitative analysis. Pairwise comparisons between all the groups were performed using the Mann-Whitney U test (p < 0.05). RESULTS: Microscopic imaging revealed different wear patterns for each material. Lowest fracture rates were documented for the CCs. In contrast, all the SSCs showed perforations. The CCs cemented with RMGIC showed the highest significant volumetric wear (6.3 ± 0.72 mm³), followed by the SSCs cemented with RMGIC (3.6 ± 1.79 mm³) and CCs cemented with SAC (3.5 ± 1.92 mm³). No significant differences were found in terms of the wear among all the other groups, ranging between 0.4 ± 0.25 and 0.6 ± 0.32 mm³. CONCLUSION: The volume loss of the tested crowns differed for each material and was dependent on the type of cementation. With regard to in vitro wear and fracture patterns, cementation with SAC may increase the clinical performance of CC paediatric crowns.

Shrinkage vectors in flowable bulk-fill and conventional composites: bulk versus incremental application.

OBJECTIVES: Sufficient depth of cure allows bulk-fill composites to be placed with a 4-mm thickness. This study investigated bulk versus incremental application methods by visualizing shrinkage vectors in flowable bulk-fill and conventional composites. MATERIALS AND METHODS: Cylindrical cavities (diameter = 6 mm, depth = 4 mm) were prepared in 24 teeth and then etched and bonded with OptiBond FL (Kerr, Italy). The composites were mixed with 2 wt% radiolucent glass beads. In one group, smart dentin replacement (SDR, Dentsply) was applied in bulk "SDR-bulk" (n = 8). In two groups, SDR and Tetric EvoFlow (Ivoclar Vivadent) were applied in two 2-mm-thick increments: "SDR-incremental" and "EvoFlow-incremental." Each material application was scanned with a micro-CT before and after light-curing (40 s, 1100 mW/cm2), and the shrinkage vectors were computed via image segmentation. Thereafter, linear polymerization shrinkage, shrinkage stress and gelation time were measured (n = 10). RESULTS: The greatest shrinkage vectors were found in "SDR-bulk" and "SDR-increment2," and the smallest were found in "SDR-increment1-covered" and "EvoFlow-increment1-covered." Shrinkage away from and toward the cavity floor was greatest in "SDR-bulk" and "EvoFlow-increment2," respectively. The mean values of the shrinkage vectors were significantly different between groups (one-way ANOVA, Tamhane's T2 test, p < 0.05). The linear polymerization shrinkage and shrinkage stress were greatest in Tetric EvoFlow, and the gelation time was greatest in "SDR-bulk." CONCLUSIONS: The bulk application method had greater values of shrinkage vectors and a higher debonding tendency at the cavity floor. CLINICAL RELEVANCE: Incremental application remains the gold standard of composite insertion.

Development and evaluation of an interdisciplinary teaching model via 3D printing.

The investigation aimed to assess the feasibility of creating an interdisciplinary training model simulating endodontic, restorative as well as implantologic treatment procedures by using 3D printing technology. A CBCT scan of the mandible of a real patient was initially taken. The generated DICOM-data were converted to a STL-file, which was further processed to design spaces for exchangeable replica teeth, a bone segment and an adapter to fix the model in a mannequin's head. After the manufacturing process, the model was evaluated by dental students performing a root canal treatment, the insertion of a glass fibre post and the insertion of an implant. The workflow allowed a simple and cost-effective way of manufacturing a single model, which is suitable for several training scenarios in the fields of endodontics, prosthodontics and implantology. The model was rated as being comparable to the real patient situation and offers repetitive treatment simulations. The present workflow is a feasible way of using DICOM-data and 3D printing for an interdisciplinary training model. The dental schools can design models according to their own curriculum and put the focus on a patient centered education.

Monomer release from surgical guide resins manufactured with different 3D printing devices.

OBJECTIVES: The aim of this study was to assess the post curing monomer release of resins applicable for 3D printing of surgical implant guides in dependency of printing technique and storing media using high performance liquidchromatography. MATERIAL AND METHODS: Specimens of Nextdent SG, Freeprint Splint, Fotodent Guide, 3Delta Guide, and V-print SG (n = 4) were additively manufactured with the corresponding DLP/SLA printing devices (Rapidshape D20II, Form2, Solflex350). Postprocessing was done according to the manufacturer's specifications. Subsequently, samples were eluted in methanol and water for 3 days and analyzed with gas chromatography/mass spectrometry (GC/MS). RESULTS: A total of twelve different substances released from the tested resin materials. The highest eluted concentration for MMA in methanol was 20.27 ± 8.60 µg/mL followed by 12.66 ± 3.38 µg/mL of HPMA. HEMA was found at concentration of 11.17 ± 2.43 µg/mL in methanol and 1.15 ± 0.11 µg/mL in water. TPGDA and TEGDMA reached maximum concentration in methanol of 4.29 ± 0.54 µg/mL and 5.07 ± 0.93 µg/mL and in water of 0.79 ± 0.19 µg/mL and 0.36 ± 0.14 µg/mL, respectively. Significant difference was found for the material Nextdent SG manufactured on SLA and DLP printing device for THFMA (p = 0.041), TEGDMA (p = 0.026), TPGDA (p = 0.05) and EGDMA (p = 0.06). The amount of monomers released into water did not reach the detection threshold for V-print SG. SIGNIFICANCE: The study revealed significant influence of the printing technique and resin material on the elution of monomers. The elution in methanol and water was significantly different. While the relative amount of eluted monomers from 3D printed guides is comparable to conventional direct composites and below toxic relevant concentrations, the absolute amount of monomer can rise in a clinic situation due to the size of the guides.

Meta-analysis of the longevity of commonly used pit and fissure sealant materials.

OBJECTIVE: This systematic literature review and meta-analysis compared the clinical retention of primed or adhesively bonded sealants to that of conventional sealant materials. METHODS: A search of the MEDLINE, EMBASE and CENTRAL databases identified 3707 abstracts published prior to 12/31/2017, of which 335 clinical publications were analysed in detail. A total of 67 studies included information about sealant retention after 24, 36, or 60 months of follow-up. A meta-analysis using a random effects model was conducted to calculate the pooled estimate of the retention rates for the five groups of sealants. Subgroup moderator analysis was performed to compare the pooled retention rate estimate (RRE) of primed sealants against those of the other groups. RESULTS: Primed sealants had a 2-year pooled RRE of 43.2% (95% CI: 30.5-55.8), which was significantly inferior to those of auto-polymerizing (80.8%, 95% CI: 72.2-89) and light-polymerizing sealants (68.4%, 95% CI: 60.2-76.7). Fluoride-releasing and light-polymerizing sealants had the highest 3-year pooled RREs (86.4%, 95% CI: 73.4-99.3 and 83.1%, 95% CI: 75.6-90.7, respectively). SIGNIFICANE: The results of this meta-analysis suggest that primed sealants cannot be fully recommended for clinical practice due to their moderate survival rates. Auto-polymerizing, light-polymerizing and fluoride-releasing sealants continue to be considered the reference standards for pit and fissure sealants. However, future generations and developments of primed sealant materials may change this position.