•The transmitted irradiance passing through a crown-shaped specimen can be predicted.•The calculation model allows for adapting clinical workflow and material choice.•Variation in curing parameters ...shows negative effect on the transmission of light.•Highest transmitted irradiances occur for perpendicular incidence in direct contact.
To predict the clinically relevant transmitted irradiance that is available for luting when a CAD/CAM restoration is inserted. The influence of irradiance, exposure distance, light curing unit (LCU) angulation and direction of polymerization is analyzed when curing through crowns of different thicknesses.
Three modern CAD/CAM resin-based composites (RBCs) were used to produce 45 crown-shaped specimens. The distance between fissure and crown base was set at 1.0, 1.5 and 2.0 mm (n = 5). Transmitted irradiance, while using a violet-blue LCU, was measured with a photo-spectrometer. 180 exposure conditions per specimen were investigated by variation in LCU curing mode, angulation, exposure distance and direction. Data was analyzed using univariate ANOVA followed by Tukey HSD (α = 0.05) and comparison of 95% confidence intervals.
The CAD/CAM-RBC’s decadic absorption coefficient ranges from 0.317 mm−1 to 0.387 mm−1 and the reflection correcting factor for crowns ranges from 0.305 to 0.337. Transmitted irradiance decreases significantly with increasing exposure distance and decreasing incident irradiance. For tilt angles greater than 10°, transmitted irradiances are significantly reduced (−11% for 20°, −23% for 30°). Significantly lowest transmitted irradiances were measured for vestibular curing direction (up to −15%).
A calculation model can predict the transmitted irradiance through a CAD/CAM restoration in dependence of restoration thickness and radiant emittance. The practitioner can be supported by this model to adapt material choice of dental restoration and adhesive system to the individual situation. Variation in exposure conditions shows negative effect on the transmission of light and should be limited.
To develop a laboratory technique for improving the retention of crowns, the present study investigated the effects of micro retentive grooves (MRGs) on the inner surface of CAD/CAM resin composite ...crowns on the pull-out bond strength. MRGs with four different depths were prepared for the inner surface of the CAD/CAM crown (0 μm: MRG0, 25 μm: MRG25, 50 μm: MRG50, 100 μm: MRG100). MRG0 was divided into two groups as controls by different surface treatments: air abraded with alumina, and not blasted (Con). A silane coupling agent was applied to all specimens. The crowns were then bonded to standard stainless-steel abutments using self-adhesive resin cement following the manufacturer’s instructions. Pull-out tests were conducted, and pull-out bond strength (N) was obtained. The number of repetitions was set to five with five conditions. It was found that the largest strength of 492.2 (79.9) N was obtained in MRG50, and the smallest of 55.1 (17.5) N in Con, indicating that MRG50 was about nine times stronger than Con. The strength of MRG was significantly larger than the others except for MRG100 (p<0.05). Thus, the bond strength of CAD/CAM resin composite crowns could be improved by preparing the inner surface of MRGs. MRG with a depth of 50 μm showed the highest bond strength.
The article focuses on newly emerging Czech words (see neologisms and neosemantisms). The reasons for the formation of such lexemes were given and their importance was selectively emphasized. Several ...examples of creating new lexical and word-formation structures were cited, and problematic linguistic connections from the point of view of political correctness were also specified. New lexical adhesions were narrowed down mainly with the prefix korona-, but also words profiling other artifacts or activities were quoted: Czech rouška – English mask, Czech distanční vzdělávání/výuka – English distance learning, Czech společenský odestup/rozestup – English social distance, Czech eRecept – English e-prescription. etc. Some of these newly created names are experiencing a real renaissance due to the much higher attendance as they have shifted from the periphery towards the center of the language.W artykule skoncentrowano się na nowo powstających słowach w języku czeskim (patrz neologizmy i neosemantyzmy). Podano przyczyny powstawania takich leksemów oraz zwrócono wybiórczo uwagę na ich znaczenie. Przywołano parę przykładów tworzenia nowych tworów leksykalnych i słowotwórczych oraz wyszczególniono także problematyczne połączenia językowe z punktu widzenia poprawności politycznej. Skupiono się na nowych zrostach leksykalnych głównie z przedrostkiem korona-, ale także przywoływano słowa profilujące inne artefakty lub czynności: czes. rouška – pol. maseczka, czes. distanční vzdělávání/výuka – pol. nauczanie zdalne, czes. společenský odestup/rozestup – pol. dystans społeczny, czes. eRecept – pol. e-recepta. itp. Niektóre z tych nowo powstałych nazw przeżywają prawdziwy renesans ze względu na zdecydowanie większą frekwencję, ponieważ przesunęły się z peryferii w kierunku centrum języka.
Aim To investigate ex vivo the fracture resistance and failure mode of direct resin composite complete crowns with and without various root canal posts made on maxillary premolars.
Methodology The ...clinical crowns of 40 human extracted single‐rooted maxillary premolars were sectioned at the cemento‐enamel junction. The canals were prepared with Gates Glidden drills up to size 4. Thirty samples were provided with standardized post spaces in the palatal canal and all roots were embedded in acrylic. Minimal standardized preparations in the canal entrances were made. Groups of 10 samples were treated with (i) prefabricated metal posts, (ii) prefabricated glass fibre posts, (iii) custom‐made glass fibre posts, and (iv) no posts (control). Posts were cemented with resin cement and resin composite complete crowns were made. All specimens were thermocycled (6000×, 5–55 °C). Static load until fracture was applied using a universal loading device (crosshead speed 5 mm min−1) at a loading angle of 30°. Failure modes were categorized as favourable and unfavourable failures.
Results No significant difference was observed between the mean failure loads (group 1: 1386 N, group 2: 1276 N, group 3: 1281 N, and group 4: 1717 N, P > 0.05), nor between frequencies of failure modes (P > 0.05). All failures were fractures of the resin composite crown in combination with tooth material (cohesive failures).
Conclusions Within the limits of this laboratory investigation it is concluded that severely damaged and root filled maxillary premolars, restored with direct resin composite complete crowns without posts have similar fracture resistances and failure modes compared to those with various posts, which suggest that posts are not necessarily required.
Aim This study aims at an analysis of the clinical and technological aspects that decisively influence the clinical esthetic finality, as reflected in a representative number of clinical cases ...diagnosed with partially reduced edentation, the therapeutic choices being represented by metal ceramic, namely metal composite restorations. Material and Method: The factual material was represented by a number of 25 clinical cases diagnosed with partially reduced edentation, the therapeutic solutions being represented by metal ceramic, namely metal composite bridges, the analysis of the multiple factors that influence the technological algorithm of certain representative practical cases leading to pertinent conclusions regarding the individualization of the clinical technological algorithm. Results and Discussions :Out of the extremely large and diverse range of esthetic restorative materials, ceramic remains the “uncrowned queen of restorative materials”, ensuring that sense of naturalness so much sought after by its translucent similarity to dental enamel. Conclusions:The particular conditions of the prosthetic field influence the clinical technological details of the treatment algorithm, its clinical finality being that of masking deficits or excesses, in full agreement with the corrective proprosthetic interventions
Aim
To investigate stress transmitted by various restorative materials given for a full veneered implant‐supported crown through implants in the bone.
Methods
A 2‐D finite element model of dental ...implant with an abutment and full crown was designed. The materials used for stress dissipation were zirconia, full ceramic, full metal crown, composite crown, and acrylic crown. Adequate boundary conditions were applied, as was a vertical load of 100 N.
Results
The highest stress value was exhibited for the zirconia prosthesis model, and maximum stress dissipation for the same model was observed around the cervical region of the abutment and abutment‐implant junction (24.877 Mpa).
Conclusion
Within the limitations of this study, it was concluded that an occlusal material with a low modulus of elasticity, such as acrylic resin, dampens the occlusal impact forces, thereby decreasing its effect on the bone‐implant interface.
Back ground: Fiber reinforcement was introduced to clinical dentistry for the first time in the 1960s when investigators attempted to reinforce polymethyl- methacrylate dentures with glass or carbon ...fibers. It has recently been shown that crowns, bridges and posts made of FRC can be used successfully in dental practice and they are esthetically more acceptable than conventional metal ceramic crown. Aims: A prospective comparative cross-sectional study was performed involving 60 patients who attended in the out patients department of Prosthodontics, Faculty of Dentistry, BSMMU during the period of January 2007 to December 2008. Objective: Compare fiber-reinforced composite crowns and metal ceramic crowns according to attrition of opposing teeth. Methods: Clinical data were recorded from the randomly selected 60 patients divided in to tow groups experimental and control. Attrition of opposing teeth was indexed after California Dental Associations quality evaluation system. Results: In group A patients, 12(40.0%) were male and 18(60.0%) female. In group B patients 14(46.7%) were male and 16(53.3%) were female. All the patients were in grade I in both groups after 4 months. After 8 months all patients were in grade I in group A and 29(96.7%) patients were in grade I in group B. After 12 months all patients were in grade I in group A and 28(93.3%) patients were in grade I in group B. The difference was not statistically significant (p>0.05) in chi square test. Conclusion: The Fiber Reinforced Composite crown represents a valuable development in field of Prosthetic Dentistry. DOI: http://dx.doi.org/10.3329/updcj.v4i1.21161 Update Dent. Coll. j: 2014; 4 (1): 21-26
Abstract Objectives The aim of this in vitro study was to evaluate the static load-bearing capacity and the failure mode of endodontically treated maxillary incisors restored with complete crowns ...made of experimental composite resin (FC) with short fiber fillers, with and without root canal posts. Further aim was to evaluate the effect of fiber-reinforced composite resin (FRC) on the failure mode of the restoration. Material and methods The experimental composite resin (FC) was prepared by mixing 22.5 wt.% of short E-glass fibers (3 mm in length) and 22.5 wt.% of semi-interpenetrating polymer network (IPN) resin with 55 wt.% of silane treated silica fillers. The clinical crowns of 30 human extracted maxillary incisors were sectioned at the cemento-enamel junction. Five groups of direct complete crowns were fabricated ( n = 6); Group A: made from particulate filler composite resin (PFC) (Grandio Caps, VOCO, control), Group B: PFC with fiber post (everStick, StickTeck), Group C: made from PFC with everStick fiber post and FRC-substructure, Group D: made from FC, Group E: made from FC with FRC-substructure. The root canals were prepared and posts were cemented with resin cement (ParaCem Universal). All restored teeth were stored in water at room temperature for 24 h before they were statically loaded with speed of 1.0 mm/min until fracture. Data were analyzed using ANOVA ( p = 0.05). Failure modes were visually examined. Results ANOVA revealed that restorations made from experimental fiber composite resin had higher load-bearing capacity (349 N) ( p < 0.05) than the control restorations (173 N). No significant difference was found in load-bearing capacity between restorations reinforced with FRC-substructure and those without ( p > 0.05). Conclusions Restorations made from short glass fiber containing composite resin with IPN–polymer matrix showed better load-bearing capacity than those made with either plain PFC or PFC reinforced with fiber post.
PDF
