Biomedical subjects

Ivo Krejci

Publications and source records attributed to Ivo Krejci.

At least 19 recordsLinked to original sources

PubMed2006

Bracket bond strength dependence on light power density.

OBJECTIVES: In order to reduce curing time for bracket bonding with light-cured composites, manufacturers increase the power density (PD) of light sources. The present study aims at investigating the relationship between PD and shear bond strength (SBS) at short exposure time. METHODS: Stainless steel brackets were bonded to bovine incisors using light-cured adhesive. Six groups of 20 incisors each were exposed to 4s of halogen light with different PD increasing from 500 to 3000 mW/cm(2) in steps of 500 mW/cm(2). Two more groups were exposed to a PD of 3000 mW/cm(2) for 6s (n=15) and 8s (n=19), thus simulating non-available PD of 4500 and 6000 mW/cm(2) for 4s. A halogen lamp with a PD of 1000 mW/cm(2) was used for 40s in the control group (n=15). After storage for 24h at 37 degrees C in water, SBS and adhesive remnant index (ARI) were recorded. RESULTS: SBS was significantly different among groups (ANOVA, p<0.001). SBS comparable to the control group could only be achieved with a PD of at least 3000 mW/cm(2). An exponential model described the relationship between SBS and PD. The best-fit curve based on this model reached 85% of the highest possible SBS at approximately 4000 mW/cm(2). ARI scores showed that higher PD was associated with better adhesion at the bracket/adhesive interface. CONCLUSIONS: Our findings show the SBS dependence on PD, and thus provide a valuable tool for the development of light-curing systems. An exponential model suggests that SBS enters a region of saturation and cannot be improved significantly by further increasing PD.

Adhesiveness↗

PubMed2006

Hydrothermal and mechanical stresses degrade fiber-matrix interfacial bond strength in dental fiber-reinforced composites.

Fiber-reinforced composites (FRCs) show great promise as long-term restorative materials in dentistry and medicine. Recent evidence indicates that these materials degrade in vivo, but the mechanisms are unclear. The objective of this study was to investigate mechanisms of deterioration of glass fiber-polymer matrix bond strengths in dental fiber-reinforced composites during hydrothermal and mechanical aging. Conventional three-point bending tests on dental FRCs were used to assess flexural strengths and moduli. Micro push-out tests were used to measure glass fiber-polymer matrix bond strengths, and nanoindentation tests were used to determine the modulus of elasticity of fiber and polymer matrix phases separately. Bar-shaped specimens of FRCs (EverStick, StickTech, and Vectris Pontic, Ivoclar-Vivadent) were either stored at room temperature, in water (37 and 100 degrees C) or subjected to ageing (10(6) cycles, load: 49 N), then tested by three-point bending. Thin slices were prepared for micro push-out and nanoindentation tests. The ultimate flexural strengths of both FRCs were significantly reduced after aging (p < 0.05). Both water storage and mechanical loading reduced the interfacial bond strengths of glass fibers to polymer matrices. Nanoindentation tests revealed a slight reduction in the elastic modulus of the EverStick and Vectris Pontic polymer matrix after water storage. Mechanical properties of FRC materials degrade primarily by a loss of interfacial bond strength between the glass and resin phases. This degradation is detectable by micro push-out and nanoindentation methods.

Biomechanical Phenomena↗

PubMed2006

A new shading concept based on natural tooth color applied to direct composite restorations.

OBJECTIVE: Patient demands have prompted manufacturers to improve intrinsic optical properties of resin composites and clinicians to refine application procedures. The aim of this study is to present a shading concept based on colorimetric L*a*b* and contrast ratio data of human dentin and enamel. METHOD AND MATERIALS: Extracted teeth of the A and B Vita shade groups (n = 8 per group) were sectioned according to 2 different planes to measure specific color (using the CIE L*a*b* system) and opacity (contrast ratio). Standardized samples of enamel and dentin shades of a new composite system (Miris, Coltène Whaledent) were submitted to the same colorimetric evaluation for comparison with natural tissues. RESULTS: Comparison of teeth from the Vita groups A and B having the same chroma showed limited variations regarding a* (green to red) and b* (blue to yellow) values; the only significant variation was the increasing b* values (yellow) with increasing chroma (A1 to A4 and B1 to B3). As for dentin contrast ratio, limited differences were reported, while enamel proved to increase in translucency with age (reduced contrast ratio). CONCLUSION: These data served as the foundation of the so-called natural layering concept, which makes use of 2 basic composite masses (dentin and enamel) that optically mimic natural tissues. This concept allows for simplified clinical application and layering of composite, as it uses only 1 universal dentin hue with several chroma levels and 3 enamel types for young, adult, and old patients, each exhibiting specific tints and translucency levels.

Acrylic Resins↗

PubMed2006

Biomimetic direct composite stratification technique for the restoration of anterior teeth.

The aim of this article is to describe a simplified layering technique based on a biomimetic approach for large anterior Class 4 restorations. The proposed layering technique is based on a modified layering technique where palatal enamel and dentin masses are replaced with the same quantity of a microhybrid enamel and dentin shade composites, respectively, while for the thin buccal enamel layer a microfilled resin composite is used. Transparencies and, whenever necessary, white spot characterizations, are created by interposing blue and white effect masses between dentin mamelons, under buccal enamel. The combination of a microfilled composite with a microhybrid composite substituting the same quantity of lost enamel and dentin better mimics the physical and optical characteristics of the natural tooth. The biomimetic composite restoration may be considered an interesting alternative to ceramics, minimizing invasiveness, chair time, and costs for patients.

Acrylic Resins↗

PubMed2006

Extended sealing of interproximal caries lesions.

In recent years the concept of minimally invasive dentistry has offered a more conservative approach to restoration of teeth with caries lesions. Several techniques have been suggested for treatment of proximal lesions, but their results have been less than ideal. The aim of this article is to present a new technique for ultraconservative restoration of small interproximal caries lesions that avoids the disadvantages of both the tunnel and the proximal slot restorative techniques. Two cases, of patients with high and low caries risk, are presented to illustrate the technique. The proposed technique can be considered the most conservative alternative to conventional Class 2 or slot-cavity treatment approaches.

Cariostatic Agents↗

PubMed2006

Indications and limitations of Er:YAG laser applications in dentistry.

PURPOSE: To describe the development, indications, and limitations of Er:YAG lasers in the dental field. METHODS: A review based on the literature search in PubMed and completed by other documents was performed. RESULTS: Based on the synthesis of the reviewed literature different topics concerning the Er:YAG effects and applications in dentistry are discussed and recommendations for the use of this type of laser are given.

Dental Equipment↗

PubMed2006

Marginal quality in enamel and dentin after preparation and finishing with an Er:YAG laser.

PURPOSE: To find the most appropriate Er:YAG laser parameters for an optimal marginal adaptation of Class V restorations in enamel and dentin. METHODS: Six saucer-shaped mixed Class V cavities were prepared in each of the eight experimental groups with an Erbium:YAG hard laser (Opus Duo) on extracted human molars in near contact mode with a conical 800 microm sapphire tip under continuous water spray by using different pulse energy and pps (pulse per second) parameters. The cavities were restored under the simulation of dentin fluid with Clearfil SE Bond and Clearfil APX PLT composite applied in two layers and light-cured. Marginal adaptation in enamel and dentin was quantified before and after simultaneous thermal (5-50-5 degrees C, 2 minutes each) and mechanical (max. 49N; 1,200,000 cycles) stresses by using the replica technique in a SEM under x200 magnification. RESULTS: With the exception of dentin margins before loading, significant differences for percentages of "continuous margin" and "enamel fractures" were detected before and after loading (P < 0.05, ANOVA, Student's t-test). A pulse energy of 100 mJ both on dentin and enamel was found optimal for finishing and smoothing the preparation margins after cavity preparation with 500 mJ or more.

Analysis of Variance↗

PubMed2005

Thermal risks from LED- and high-intensity QTH-curing units during polymerization of dental resins.

The aim of this study was to test the ability of an infrared (IR) camera to assess temperature changes and distributions in teeth below restorations when quartz-tungsten-halogen (QTH) and light-emitting diode (LED) curing lights were used to photopolymerize the restorative material. Our hypothesis was that the higher power density and broader spectral distribution of the QTH source would cause greater increases in tooth temperature than the LED source, and that these differences would be best demonstrated with the IR camera. Cavities were prepared on human third molars and restored with a resin composite restorative material. The material was light-cured using three light-curing sources using several exposure times. The external (outside the tooth) and internal (inside the pulp chamber) temperature changes during polymerization of the composite material were recorded over 360 s with thermocouples and an IR camera. Using thermocouples the maximum increase in external temperature (+17.7 degrees C) was reported for the Swiss Master light after 20 s of curing time while the minimum temperature rise (+7.8 degrees C) was reported for the Freelight 2. Whereas a 2.6 degrees C increase in internal temperature was observed after curing 20 s with the Freelight 2, 7.1 degrees C was reported after 60 s of light exposure to Astralis 10. Infrared images showed similar trends in external-internal rises in temperature as the thermocouples, although temperatures measured by the IR were generally higher. These results indicate that the higher power density QTH sources caused greater increases in tooth temperatures than the LED source and that thermocouples may underestimate the heat applied to the tooth.

Composite Resins↗

PubMed2005

Clinical performance and marginal adaptation of class II direct and semidirect composite restorations over 3.5 years in vivo.

OBJECTIVE: The study evaluated the clinical performance and marginal adaptation of direct and semi-direct class II composite restorations in a split-mouth design over 3.5 years. DESIGN: 44 upper posterior teeth in 11 adults with primary carious lesions were treated with 22 direct and 22 semi-direct restorations. Conventional cavities were prepared for both types of restorations. A fine fine hybrid composite (APH) and a multifunctional adhesive system (Prisma universal bond 3) were used for all restorations. The incremental "3-sited light curing" technique was applied to direct restorations. Semi-direct inlays were prefabricated on silicone casts and post-cured using light and heat. Clinical performance was evaluated using modified USPHS parameters, while marginal adaptation was judged on replicas, using SEM and a standardized evaluation technique. RESULTS: Clinical results after 3.5 years revealed a 100% retention rate with no fractures, sensitivity or recurrent caries for both types of restorations. SEM-evaluation of the occlusal margins showed at the tooth-restoration interface relatively low rates of marginal openings over the observation period (4-8%). Marginal restoration fractures ranged between 1 and 2%, marginal tooth fractures between 3 and 9%. Differences between the restorative techniques and after the different time observation periods were not statistically significant. Proportions of marginal fractures and openings at the restoration-luting composite interface were less than 10% after 3.5 years. CONCLUSION: The results indicated no significant differences for direct and semi-direct fine hybrid composite restorations in medium size cavities in posterior teeth with respect to clinical performance and marginal adaptation over 3.5 years.

Acrylic Resins↗

PubMed2005

Light-curing time reduction with a new high-power halogen lamp.

INTRODUCTION: Orthodontic brackets are routinely bonded with light-cured adhesives. Conventional halogen lights used in bonding have the disadvantage of a long curing time, and the available alternatives (laser and plasma lights) are expensive. Our aim was to investigate the minimum time necessary to bond brackets with a new, relatively low-priced, high-power halogen light. METHODS: Five groups of 15 deciduous bovine incisors were bonded with stainless steel brackets (Mini Diamond Twin, Ormco, Orange, Calif) by using different lamps and curing times. Three of the groups were bonded by using a high-power halogen light (Swiss Master Light, Electro Medical Systems, Nyon, Switzerland) for 2, 3, and 6 seconds, respectively. The fourth group, bonded with a fast halogen light (Optilux 501, Sybron Dental Specialties, Danbury, Conn) for 40 seconds, served as the positive control group. The fifth group, the comparison group, was bonded with a plasma light (Remecure, Remedent, Deurle, Belgium) for 4 seconds. After storage for 24 hours in the dark at 37 degrees C in water, shear bond strength was measured with a universal testing machine. RESULTS: A curing time of 2 seconds with the high-power halogen light negatively affected the bond strength and the probability of bond survival. The adhesive remnant index scores were not significantly different among the groups. Most failures (> 60%) occurred at the bracket base/adhesive interface. CONCLUSIONS: The high-power halogen light seems to be a cost-effective solution to reducing curing time. The recommended curing times to bond stainless steel brackets are 6 seconds and, with caution, even 3 seconds.

Analysis of Variance↗

PubMed2005

Resin composite shrinkage and marginal adaptation with different pulse-delay light curing protocols.

The aims of this study were, first, to measure shrinkage induced by different methods of pulse-delay light curing and, second, to verify their influence on the marginal adaptation of class V restorations in enamel and dentin. Eight groups, comprising seven groups (n = 6) with different pulse-delay parameters and a control group, were compared for dynamic linear displacement and force by using a fine hybrid composite. Based on these results, the pulse-delay curing procedure with the lowest shrinkage force was chosen and tested against the control group with respect to marginal adaptation in class V restorations (n = 8) before and after simultaneous thermal and mechanical loading. Statistically significant differences between groups were found for both shrinkage properties tested, with one pulse-delay group giving the lowest overall shrinkage values. However, the percentages of 'continuous margin' of this group, and of the control before and after loading, were not significantly different in dentin, whereas a significantly lower percentage of 'continuous margin' was detected in the pulse-delay group in enamel after loading.

Composite Resins↗

PubMed2004

Cytotoxicity and sealing properties of four classes of endodontic sealers evaluated by succinic dehydrogenase activity and confocal laser scanning microscopy.

The objectives of this study were to evaluate the cytotoxicity and sealing properties of four classes of endodontic sealers (PCS/Kerr, RoekoSeal/Roeko, TopSeal/Dentsply, and EndoREZ/Ultradent). For cytotoxicity testing (MTT method), the materials were either placed immediately in contact with cultured cells or 24 h after setting, then evaluated at three subsequent time points (24 h, 48 h, or 1 wk). For the leakage study, extracted human roots were obturated with acrylic cones and sealers and immersed for 48 h into rhodamine-labeled lipopolysaccharide. The roots were then observed under a confocal laser scanning microscope to estimate (semiquantitatively) the presence of the rhodamine-lipopolysaccharide (LPS) inside the canal. The results showed that cytotoxicity generally increased with time, and that most materials pose significant cytotoxic risks, particularly in the freshly mixed condition. Further, all materials showed significant leakage although there was large variation among teeth. Overall, the silicon-based material (Roeko Seal) was less cytotoxic and more effective in sealing root canals against LPS leakage than other materials.

Analysis of Variance↗

PubMed2004

Warming up to composites.

Patient demand for composite restorations has increased dramatically over the past decade. Anterior composites, for teeth that are visible when smiling, have been the standards of practice for many years. For the less visible teeth, it is estimated that the 50% mark for composite restorations in the posterior region was surpassed in 2000.

Composite Resins↗

PubMed2003

Microtensile bond strength between adhesive cements and root canal dentin.

OBJECTIVES: The hypotheses tested were that the bond strength of adhesive cements to root canal dentin (1) would be reduced as a function of configuration factor, polymerization process and type of luting material and (2) would be lowered near the apex of the tooth. METHODS: Human canines and premolars were prepared for post cementation using Single Bond/Rely X ARC, ED Primer/Panavia F, C and B Metabond, and Fuji Plus. The specimens were divided into two groups. For intact roots, the posts were luted using standard clinical procedures. For flat roots, the posts were applied directly into flat ground canals. All roots were sectioned into 0.6 mm thick slices, trimmed mesio-distally and stressed to failure at 1 mm/min. The muTBS of each slab was calculated as the force at failure divided by the bonded cross-sectional surface area. The results were compared using a one-way ANOVA and Tukey multiple comparison intervals (alpha=0.05). Least squares linear regression analysis was used to assess the effect of dentin location on bond strength. RESULTS: All cements showed significantly (p</=0.05) lower bond strengths in intact vs. flat roots. The muTBS of posts to intact roots were not significantly different for Single Bond/Rely X ARC and Panavia F, but both were significantly lower (p</=0.05) than the bonds produced by C and B Metabond and Fuji Plus cements. For Single Bond/Rely X ARC and Fuji Plus a significant decrease in bond strength was observed in dentin closer to the apex of the root. SIGNIFICANCE: Stresses from polymerization shrinkage and problems with adequate access to the root canal complicate the formation of high-strength bonds when cementing endodontic posts with resin cements.

Analysis of Variance↗

PubMed2003

In vitro evaluation of marginal and internal adaptation after occlusal stressing of indirect class II composite restorations with different resinous bases.

Composite inlays are indicated for large cavities, which frequently extend cervically into dentin. The purpose of this study was to compare in vitro the marginal and internal adaptation of class II fine hybrid composite inlays (Herculite, Kerr) made with or without composite bases, having different physical properties. Freshly extracted human molars were used for this study. The base extended up to the cervical margins on both sides and was made from Revolution (Kerr), Tetric flow (Vivadent), Dyract (Detrey-Dentsply) or Prodigy (Kerr), respectively. Before, during and after mechanical loading (1 million cycles, with a force varying from 50 to 100 N), the proximal margins of the inlay were assessed by scanning electron microscopy. Experimental data were analysed using non-parametric tests. The final percentages of marginal tooth fracture varied from 30.7% (no base) to 37.6% (Dyract). In dentin, percentages of marginal opening varied from 9.2% (Tetric Flow) to 30.1% (Prodigy), however, without significant difference between base products. Mean values of opened internal interface with dentin varied from 11.06% (Tetric Flow) to 28.15% (Prodigy). The present results regarding dentin adaptation confirmed that the physical properties of a base can influence composite inlay adaptation and that the medium-rigid flowable composite Tetric Flow is a potential material to displace, in a coronal position, proximal margins underneath composite inlays.

Compomers↗

PubMed2003

Replacement of missing teeth with fiber-reinforced composite FPDs: clinical protocol.

The concept of minimally invasive preparation protocols has resulted in reduced loss of critical tooth structures and maintenance of optimal strength, form, and aesthetics. While various treatment options have been described for single-tooth replacement, fiber-reinforced composite (FRC) fixed partial dentures (FPDs) provide a viable treatment alternative with proven mechanical properties, aesthetics, and function. This article presents several clinical scenarios in which minimally invasive adhesive FRC FPDs are provided to deliver enhanced predictability, strength, and durability.

Aged↗

PubMed2003

Linear displacement and force induced by polymerization shrinkage of resin-based restorative materials.

PURPOSE: To measure the linear displacement and force induced by polymerization shrinkage of a series of resin-based restorative materials. METHODS: The materials tested were 10 ultrafine midway-filled resin-based composites, mainly used in anterior restorations (Brilliant Dentin, Brilliant Enamel, Charisma F, Pertac II Aplitip, Prodigy, Resulcin, Sculpt-it, Synergy Duo, Tetric and Z100), 11 ultrafine compact-filled composites, suggested by the manufacturers as "amalgam substitutes" for posterior restorations (Alert, Ariston pHc, Definite, EXI-119, EXI-120, Nulite F, Prodigy Condensed, Prodigy High Viscosity, Solotaire, Surefil and Synergy Compact), and six polyacid-modified composites (Compoglass, Dyract, Dyract AP, Elan, F2000 and Hytac Aplitip), also known as compomers. Each property was measured for 180 seconds from the start of curing with the help of custom made devices in eight specimens for each material. Statistical evaluation of the data was performed with one-way ANOVA, Tukey's Studentized Range (HSD) Test (P= 0.05) and simple linear regression. RESULTS: Statistically significant differences among groups and among composites were found for both of the properties that were studied. The ultrafine compact-filled composites (amalgam substitutes) exhibited the least linear displacement, followed by the polyacid-modified composites (compomers) and the ultrafine midway-filled composites, with statistically significant differences among all groups. The groups followed the same order in the polymerization force, with only the compomer-amalgam substitute comparison not being statistically significantly different. The simple linear regression showed that the two studied properties were also highly correlated (r=0.89).

Analysis of Variance↗

PubMed2002

Crown fractures in the permanent dentition: pulpal and restorative considerations.

Crown fractures account for the highest percentage of all traumatic injuries in the permanent dentition. This review paper will discuss the different types of crown fracture, from the uncomplicated to complicated, including crown-root fractures. It will focus on two different aspects: the pulp, with an attempt to correlate epidemiological, experimental, histopathological and clinical studies, so that the clinician can better understand the underlying processes accounting for success or failure to maintain pulp vitality. Also, we will consider the restoration: knowledge about bonding to dentin and new material is evolving extremely quickly making it difficult for the clinician to keep up with the developments. If handled properly, prognosis of the pulp, after traumatic crown fracture, is good. Prognosis of the restoration has also improved considerably over the last few years, and it appears that this trend will continue in the future.

Composite Resins↗