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Biomedical subjects

I Krejci

Publications and source records attributed to I Krejci.

At least 37 records · Page 2Linked to original sources
PubMed1999

Resin composites in the post-amalgam age.

Resin-based composites are now being used as either amalgam substitutes or amalgam alternatives for the direct placement of box-shaped, stress-bearing restorations in posterior teeth. The expected longevity of these restorations is 8 years. With amalgam substitutes, preservation of enamel and dentin and restoration of tooth form and function must be warranted for the full length of the envisaged service life. In addition, with amalgam alternatives, the restoration must be, and must remain, imperceptible at a normal talking distance. The limiting factor with amalgam substitutes is the elevated risk of secondary caries, which is a result of the marginal openings that are unavoidably associated with the nature of the operative technique. Restorations in permanent teeth using amalgam substitutes most likely fail in some critical aspect of the Swiss Dental Society quality guidelines. With amalgam alternatives, the high cost and the demanding operative technique remain the main criticisms. However, amalgam alternatives, if they are placed using a sophisticated operative technique resulting in perfectly adapted restorations, meet the high expectations outlined in the Swiss Dental Society quality guidelines and fit the clinical concept of the post-amalgam age.

Bicuspid↗
PubMed1998

Adhesive crowns and fixed partial dentures fabricated of ceromer/FRC: clinical and laboratory procedures.

Ceramic optimized polymer and fiber-reinforced composite materials represent a significant development in prosthetic dentistry. When utilized in conjunction with adhesive luting techniques, exceptionally conservative crown and bridge restorations may be achieved. This article discusses utilization of these materials in inlay and onlay restorations, as well as clinical and laboratory procedures for fabrication, preparation, and seating of adhesive crown and bridge restorations. The initial results of restorations utilizing these innovative materials are presented.

Ceramics↗
PubMed1998

Principles of proximal cavity preparation and finishing with ultrasonic diamond tips.

Conventional treatment of proximal cavities can result in significant damage to the adjacent dentition. This paper describes a recently developed technique of proximal cavity preparation and finishing by use of selectively diamond-coated, ultrasonically driven instruments. By using these instruments for composite, compomer, ceramic, amalgam, and even gold restorations, the inadvertent damage to neighboring teeth is completely avoided. This article demonstrates the effective utilization of the diamond-tipped ultrasonic instruments for the preparation of primary lesions and the replacement of existing restorations.

Dental Caries↗
PubMed1997

Three-dimensional measurement of enamel loss caused by bonding and debonding of orthodontic brackets.

A mechanical computerized three-dimensional scanner with a resolution of 1 micron was used to assess loss of enamel caused by orthodontic bonding and debonding. A total of 2646 measurements was performed on six human premolars. The results showed an average loss of enamel of 7.4 microns. The range was between 1 and 52 microns, which may account for discrepancies with earlier studies that measured only a few points per tooth surface.

Acid Etching, Dental↗
PubMed1997

Dentin bonding: effect of tubule orientation on hybrid-layer formation.

In an attempt to compare the morphology of the resin-dentin interface in areas where the dentinal tubules run perpendicularly or at an angle to the cavity surface with that of areas where they run parallel to it, we studied a dentin adhesive system using transmission electron microscopy and fluorescence confocal laser scanning microscopy. The design of the study included the simulation of the normal hydrostatic pressure within the pulp and the dentinal tubules. Following acid etching of the dentinal surface with maleic acid/HEMA, the smear layer was removed, and a superficial zone was demineralized in such a way that the exposed collagenous dentin matrix retained its integrity. Confocal laser scanning microscopal investigations using primer labeled with rhodamine B showed that the penetration of the primer occurred not only vertically via surface porosities, but mainly laterally, via the dentinal tubules. The adhesive resin labeled with fluorescein completely infiltrated the demineralized layer, thereby forming a hybrid layer. The orientation of the dentinal tubules had a profound effect on the formation of the hybrid layer. In areas with perpendicular tubule orientation, the layer was 3.2 +/- 0.8 microns thick, showing solid 27.2 +/- 0.8 microns long resin tags in the dentinal tubules, and a network of tiny tags in their side-branches. In areas with parallel tubule orientation the layer was significantly thinner (1.3 +/- 0.6 microns) and resin tags were absent.

Acid Etching, Dental↗
PubMed1996

Advanced adhesive restorations: the post-amalgam age.

Due to patient demand for biocompatible, safe, and tooth-colored restorations, the use of amalgam as a restorative material has been declining. Currently, the profession of operative dentistry is in a state of transition from the amalgam age to the post-amalgam age. The learning objective of this article is to discuss the current state of the art of tooth-colored restoratives--amalgam substitutes and amalgam alternatives--used either as direct or laboratory fabricated restorations nationally and internationally. Adhesive dentistry is discussed in detail, with tooth preparation as the key element. The challenges facing the clinician during the transition period include clinician education, restorative concepts and teaching competence, costs, prevention, and maintenance.

Composite Resins↗
PubMed1995

Kynurenic acid and 5,7-dichlorokynurenic acids improve social and object recognition in male rats.

The present study describes the effect of kynurenic (KYNA) and 5,7-dichlorokynurenic (DCKA) acids, acting as selective antagonists at the glycine site on the NMDA receptor complex, upon short-term memory of male rats. Oxiracetam (OXIR) or pramiracetam (PRAM) were used as reference compounds. In the social recognition test, adult animals were injected SC with a drug or vehicle immediately after the first exposure to a juvenile male, 21-24 days old, and reexposed to the same or a novel juvenile 120 min later. Time spent by adults in social investigation of juveniles was measured. Animals treated with KYNA or DCKA (0.3, 3 and 30 mg/kg in both cases) and OXIR (30 and 60 mg/kg) had significantly reduced investigation time when reexposed to the same juvenile as compared to controls. No reduction of investigation time was found in those drugged animals reexposed to a novel juvenile. The findings suggest that KYNA and DCKA improved retention of memory for olfactory stimuli in adult male rats. In the object recognition test, the duration of exploration of two identical objects during the sample trial and the familiar and a new object during the choice trial, performed 60 min later, was evaluated. Drugs or vehicles were administered SC 30 min prior to the sample trial. On choice one, animals treated with KYNA or DCKA (0.6 and 30 mg/kg in both cases) and PRAM (30 mg/kg) spent more time in exploring a new object than the familiar one as compared to controls. This suggests that the drugged animals were able to remember the familiar object.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Time required to remove totally bonded tooth-colored posterior restorations and related tooth substance loss.

OBJECTIVES: The study was conducted to measure the time required to remove large totally bonded tooth-colored posterior restorations and related tooth substance loss. This information was collected to determine if there were differences between bonded restorations and conventional restorations. METHODS: Molars were restored with the following materials: amalgam, composite, glass ionomer cement or glass ceramic cusp coverages. After submitting them to an in vitro aging process, they were attached to a lower jaw model in a phantom head. Six dentists removed the test restorations under standardized, quasi-clinical conditions. RESULTS: While the amalgam was completely removed, some glass ionomer cement vestiges were found. In the glass-ceramic group, the margins were covered with remnants of the composite luting agent in several places. The most restorative material was left in the composite group. The loss of tooth structure after removal of amalgam, glass ionomer cement, composite and glass ceramic was 17.6 mm3, 19.6 mm3, 39.9 mm3 and 41.8 mm3, respectively. When comparing the removal time, the glass ionomer group scored best with an average of 11.9 min followed by the amalgam group with an average of 15.2 min, followed by 24.9 min for the composite group and 30.4 min for the glass ceramic group. SIGNIFICANCE: The removal of totally bonded posterior restorations made of composite and ceramic is more technically demanding and more time-consuming than the removal of glass ionomer and amalgam restorations.

Acrylic Resins↗
PubMed1994

Wear and marginal adaptation of composite resin inlays.

MOD inlays were made with conventional, coarse hybrid, fine hybrid, and two microfilled composite resins. They were adhesively luted in six extracted human molars for each group and were subjected to longitudinal, in vitro testing. Final wear ranged from 46.8 +/- 18.6 microns for fine hybrid composite resin to 132.0 +/- 39.3 microns for conventional composite resin for the inlays and from 19.3 +/- 6.6 microns for homogeneous microfilled composite resin to 136.3 +/- 65.1 microns for coarse hybrid composite resin on enamel antagonists. The wear of the luting composite resins ranged from 11.2 +/- 11.2 microns to 20.0 +/- 23.6 microns. Marginal adaptation at the beginning of the test exceeded 88.7% of "continuous margin" for all groups in enamel. However, marginal gaps were evident in dentin without dentinal adhesives. Marginal adaptation of the microfilled composite resin inlays deteriorated during loads even when a dentinal adhesive and an inlay primer were used. The margins of the other composite resin inlays remained stable during load application.

Acrylic Resins↗
PubMed1994

New adhesives in Class V restorations under combined load and simulated dentinal fluid.

OBJECTIVES: This study compared the efficacy of three dentinal adhesives using the "all etch" technique (All-Bond 2, Bisco; Scotchbond MP,3M Dental Products Co.; OptiBond, Kerr) with a dentinal adhesive which still uses phosphoric acid to condition enamel and a self-etching primer for dentin (A.R.T.-Bond, Coltene/Whaledent). METHODS: Eight V-shaped mixed Class V restorations were placed per group in extracted human premolars. The restorations were subjected to 1,200,000 mechanical occlusal cycles (max. force 49 N; frequency 1.7 Hz) and 3,000 simultaneous thermal cycles (5-50-5 degrees C). Dentinal fluid was simulated using 1:3 diluted horse serum and fed into the pulp chamber both during restoration and loading. Percentages of "continuous margin" were assessed on SEM replicas of enamel and dentinal margins at 200x magnification immediately before and after stressing, respectively. RESULTS: No significant differences were observed before stress between the materials either in enamel or in dentin. After stress, however, OptiBond and A.R.T.-Bond performed significantly better in dentin than the two other adhesives (Kruskal-Wallis, Mann-Whitney; p < 0.05). Although high initial values were observed, All-Bond 2 and Scotchbond MP were not stress-resistant under simulated physiological conditions. SIGNIFICANCE: The predicted clinical potential of All-Bond 2 and Scotchbond MP is inferior to that of OptiBond and A.R.T.-Bond.

Acid Etching, Dental↗
PubMed1994

Effects of thermocycling and occlusal force on adhesive composite crowns.

The aim of this in vitro study was to provide first quantitative data on the marginal adaptation and the required load to fracture of adhesive composite crowns with and without adhesive composite cores. Eighteen caries-free extracted human premolars were restored using fine hybrid composite crowns with margins located entirely in dentin. Six crowns were adhesively luted to dentin stubs, six to endodontically treated teeth with adhesive titanium posts and adhesive composite cores, and six to adhesive composite cores without posts. Another ten unprepared teeth served as a control. All restored teeth were subjected to long-term occlusal and thermal stresses. The marginal adaptation was evaluated in the SEM before and after loading. Load to fracture was recorded at the end of the stress. Before stressing, 72.2 to 85.0%, and after stressing, 51.9 to 66.2% of "continuous margin" were recorded at the dentin-luting composite interface. The best results after stressing were achieved with crowns luted to adhesive composite cores without titanium posts. At the luting composite-composite crown interface, 61.6 to 88.7% of "continuous margin" before and 57.7 to 75.5% after stressing were recorded. The required load to fracture the restored teeth ranged from 72.0 to 89.2% of the unrestored, unloaded control. Adhesive composite cores without titanium posts yielded the best results.

Bite Force↗
PubMed1994

Scanning electron microscopic and clinical examination of composite resin inlays/onlays up to 12 months in situ.

In this limited clinical study, 30 posterior adhesive fine-particle hybrid composite resin inlays/onlays were placed. After 12 months in situ, 29 of the restorations were reexamined. The evaluation was carried out using clinical parameters and the scanning electron microscope. None of the restorations showed fractures, recurrent caries, or a clinically visible loss of substance. All restored teeth were vital. The radiopacity of the material was clinically sufficient. Only the color match, because of a suboptimal shade range, and the perfect removal of excess luting composite resin proved to be problematic. Furthermore, slight abrasion of the luting composite resin was observed, although the abrasion had no influence on the quality of the marginal adaptation. In the scanning electron microscope excellent marginal quality was observed initially (98.9% continuous margin) as well as after 12 months (94.9% continuous margin). The evaluated composite resin inlay/onlay system has proved to be reliable during 12 months in situ.

Adult↗
PubMed1994

[Amalgam as the measure in filling therapy. A determination of its place].

As the value of amalgam restorations is increasingly being questioned in modern dentistry, the clinical potential of amalgam restorations in general has been evaluated in this literature review. The major factors limiting the longevity of amalgam restorations are operator- and patient-related. Both factors will likewise influence the longevity of any new restorative concepts. Nevertheless, amalgam restorations remain the standard against which alternative materials are evaluated. Amalgam restorations are slowly loosing ground to the use of tooth-colored materials, which are gaining in popularity. However, amalgam can not currently be withdrawn from the list of possible restorative materials used for patients in Switzerland.

Costs and Cost Analysis↗
PubMed1994

[Clinical and long-term scanning electron microscopic studies of composite inlays].

24 composite inlays, which were thoroughly documented for postgraduate education purposes were recalled after 13.3 and 30.5 months on average. The clinical evaluation yielded very good results after 13.3 and good results after 30.5 months, respectively. Marginal gaps were observed in 6.6% at the tooth-composite cement and in 27.1% at the composite cement-inlay-interface after 13.3 months using replica technique and SEM. There values were not significantly different from the findings at 30.5 months. The adhesive failures between inlay and composite cement were preferably located in large, multisurfaced restorations. No significant differences were found between direct immediate inlays and lab-made indirect inlays and between molar and premolar restorations, respectively.

Composite Resins↗
PubMed1994

Mesio-occlusodistal amalgam restorations: quantitative in vivo data up to 4 years. A data base for the development of amalgam substitutes.

Wear and marginal quality of 14 mesio-occlusodistal amalgam restorations (Dispersalloy) were quantitatively analyzed in this in vivo study. Wear rates, measured as maximum vertical loss of substance in the occlusal contact area, were 41, 50, 57, 79, 82, 123, 165, and 215 microns after 1, 2, 3, 6, 9, 24, 36, and 48 months, respectively. In the contact-free occlusal area an expansion of 2 to 9 microns was recorded. The micromorphology of the tooth-amalgam interface significantly changed within the first 9 months after restoration placement. The percentages of marginal opening increased from 91% to 100%, marginal restoration fracture from 49% to 89% and underfilled margin from 50% to 78%. Amalgam restorations have clinically proved successful despite their poor marginal adaptation and their inferior wear resistance compared to enamel. Thus, the wear resistance of amalgam substitutes, preferably metal-free, tooth-colored restorative materials, would not necessarily have to exceed that of amalgam to replace it. The wear data generated may serve as guiding figures in the development of amalgam substitutes.

Adult↗
PubMed1994

Wear of CAD/CAM ceramic inlays: restorations, opposing cusps, and luting cements.

Six standard mesio-occlusodistal restorations in extracted mandibular human molars and six opposing palatal cusps from maxillary human first molars were prepared per group. The occlusal contact areas of the restorations and of the opposing enamel cusps were digitized with a three-dimensional scanner. The specimens were exposed to a clinically correlated long-term in vitro wear test. Dicor MGC, Cerec Vita Mk I porcelain, Cerec Vita Mk II V7R porcelain, and Cerec Mk II Vita V7K porcelain were tested. The mean wear of these ceramic materials at the end of the long-term test ranged from 24.3 +/- 10.3 microns (Cerec Vita Mk II V7R) to 88.0 +/- 37.3 microns (Dicor MGC). The mean wear of the opposing human enamel cusps ranged from 93.5 +/- 30.8 microns (Cerec Vita Mk II V7R) to 224.3 +/- 117.4 microns (Cerec Vita Mk I). All ceramic materials except Dicor MGC wore less than did previously measured standards, such as natural human enamel and amalgam. However, because the wear of opposing enamel cusps was high with Dicor MGC and with Cerec Vita Mk I the total wear of these two materials--the sum of the restoration's and the opposing tooth's wear--was higher than that of the standards. Only the new fine porcelain Cerec Vita Mk II V7R showed a total wear comparable to that of enamel, because of its moderate abrasivity against opposing enamel. The wear of the two luting composite resins was measured at the end of the test. Both luting composite resins wore more than did the ceramic inlays and surrounding enamel, leaving a shallow ditch around the restorations.

Ceramics↗
PubMed1994

[Composite polymers--an amalgam substitute for deciduous tooth cavities?].

In this prospective clinical study, 29 class II restorations in deciduous teeth were placed in 17 patients using the recently developed compomer Dyract. The restorations were clinically and macrophotographically evaluated immediately after placement and after 6 months in situ. In addition, marginal adaptation and loss of substance were quantitated using replicas. Clinical and macrophotographical findings were excellent. Quantitative marginal analysis scored 92.5% "continuous margin" immediately after placement of the restorations and 95.4% after 6 months. Mean loss of substance at the margins of the restorations was 20.8 microns with a standard deviation of 64.6 microns. Providing that the positive results of this short term study are confirmed by long term data, Dyract may replace amalgam in deciduous teeth.

Child↗