Search PubMed⌕ Search

Biomedical subjects

N Krämer

Publications and source records attributed to N Krämer.

At least 19 recordsLinked to original sources
PubMed2006

Antagonist enamel wears more than ceramic inlays.

Wear phenomena of ceramic inlays are not fully understood. The aim of the present study was to evaluate ceramic wear, antagonist enamel wear, and luting cement wear over 8 years. The two-fold null hypothesis was that there would be (1) no difference in wear behavior between ceramic and enamel, and (2) no influence of filler content of luting composites on composite wear. From 96 restorations, 36 Class II inlays from 16 participants were selected. For inlays with opposing enamel cusps (n=17), replicas of inlays and enamel were scanned with a 3-D laser scanner. Luting gaps of inlays (n=36) were analyzed with a profilometer, including 3-D data analysis. Ceramic and enamel wear increased between 4 and 8 years, with significantly higher values for enamel after 6 years (p<0.05). Luting gap wear increased continuously up to 8 years (p<0.05), with no influence of luting composites (p>0.05) and location of teeth (p>0.05).

Adult↗
PubMed2003

Effect of preparation mode on Class II resin composite repair.

Complete removal of failed posterior resin composite fillings is time-expensive and involves the risk of removing sound tooth substance. In any case of failure within the composite material, intra-oral repair would be favourable. This in vitro study was conducted to examine the effect of different preparation and bonding modes on integrity of repaired restorations. Forty-eight direct Class II resin composite restorations (Syntac Classic/Tetric Ceram) were placed in extracted human third molars. The specimens were stored for 365 days and then replaced partially by removing the central part of the proximal box with all margins located in composite. The partial repairs were placed with the same materials after pre-treatment with a silicon carbide bur and Syntac Classic (n = 8). Preparation modes have been (i) box-only parallel, (ii) box-only with undercuts, (iii) box with undercuts and additional occlusal retention. The repairs were performed either with (i) Tetric Ceram or with (ii) Tetric Flow as thin lining covered with Tetric Ceram. Before and after thermomechanical loading (100 000 cycles of 50 N and 2500 cycles between +5 and +55 degrees C in an artificial mouth), marginal quality between aged and freshly applied composite was evaluated by SEM at x200 magnification and microleakage was observed by light microscopy at x50 magnification. Box-only preparations exhibited a better fatigue resistance than preparations with additional occlusal retention. This observation was independent from the presence of undercuts (P < 0.05). An intermediary layer of flowable resin composite tended to result in better marginal quality, however, not being statistically significant.

Biocompatible Materials↗
PubMed2002

Altered methylation pattern of the G6 PD promoter in Rett syndrome.

Rett syndrome (RTT) is a neurodevelopmental disorder that almost exclusively affects girls. Recently mutations in MECP2, that encodes the methyl CpG binding protein 2 (MeCP2), have been found to cause RTT. MeCP2 has a role in gene silencing. It binds to methylated cytosine in the DNA and recruits histone deacetylases. We studied the methylation pattern of the promoters of two X chromosomal genes, G6 PD and SYBL1, in patients with RTT and in a control group. Both genes undergo X inactivation which correlates with promoter methylation. A 1 : 1 ratio of methylated versus non-methylated alleles was expected. In the control group a median ratio of 47 : 53 of methylated to non-methylated alleles was found at the G6 PD promoter locus. In 22 patients with RTT the median ratio was significantly different, 33 : 67 (p < 0.0001). Analysis of the SYBL1 promoter revealed an almost identical median ratio of methylated versus non-methylated alleles (RTT 47 : 53; control 49 : 51), however, the range was wider in the RTT group (RTT 23 : 77 to 56 : 44; control 43 : 57 to 55 : 45). There was no apparent correlation between G6 PD promoter methylation status and mutations in the MeCP2 gene or the severity of the clinical phenotype in our patient group. The finding of reduced methylation at the G6 PD promoter is an interesting finding and suggests that there could be widespread dysregulation of X chromosomal genes in Rett syndrome.

Chromosomal Proteins, Non-Histone↗
PubMed2001

Clinical performance of a condensable metal-reinforced glass ionomer cement in primary molars.

OBJECTIVE: Aim of the present study was to evaluate the clinical suitability of the condensable metal-reinforced glass ionomer cement Hi-Dense in classes I and II cavities of primary molars. METHODS: Seventeen children received a total of fifty four Hi-Dense fillings (nineteen class I and thirty five class II). The restorations were clinically assessed at baseline, after one and after two years of clinical service according to modified USPHS codes and criteria. The restorations were replicated in each recall and representative samples were qualitatively analysed under a SEM. RESULTS: Over the observation period of two years, five restorations failed due to total retention loss, two fillings needed replacement because of persisting hypersensitivity, one filling was lost because of an unsuccessful endodontic treatment, and four restorations remained intact until natural exfoliation (Two year survival rate: 92% for Class I and 66% for Class II). The SEM analysis of surfaces and marginal areas exhibited an inferior adhesive performance primarily in proximal areas, whereas a negative step formation due to wear was frequently observed in occlusal parts. CONCLUSIONS: The results clearly indicate that the condensable, metal-reinforced GIC Hi-Dense reveals no enhanced performance and lifetime expectancy for class II restorations in primary molars when compared to other non-resin-modified GICs.

Cermet Cements↗
PubMed2001

Effect of surface treatment on fatigue behaviour between Tetric Ceram inlays and Variolink luting composite.

The effect of pre-treatment of composite inlays on bonding performance between a resin composite inlay and a luting composite has not been fully studied. The aim of the present study was to evaluate the influence of three different pre-treatment modes on fatigue bond strength and marginal adaptation. One hundred twenty resin composite discs (Tetric Ceram) were made as simulated inlays and randomly assigned to four groups (n=30): Without treatment (WT), hydrofluoric acid etching for 15 s + silanating (HF), roughening with a silicon carbide bur (SC), and silica coating + silanating (CO). Luting composite cylinders (Variolink II low) were bonded to the discs using Heliobond, and after 24 h in water at 37 degrees C, quasistatic shear bond strengths (n=l) and fatigue bond strengths (n=20; 5,000 cycles) were measured. Thirty-two third molars received occlusomesial Class II cavities (n=8), and direct resin composite inlays were luted with identical methods and materials. Before and after thermomechanical loading (100,000x50 N, 2,500 x +5 degrees C/+55 degrees C), replicas were made and examined (SEM, x200). CO and SC exhibited significantly higher bond strengths and adhesive fatigue limits than HF and WT (P<0.05). After thermomechanical loading, CO (98% continuous margin) and SC (95% continuous margin) demonstrated that they provide significantly more fatigue resistance than HF (88%).

Acid Etching, Dental↗
PubMed2001

Clinical performance and margin analysis of ariston pHc versus Solitaire I as posterior restorations after 1 year.

The resin composite Ariston pHc (pHc means pH control) was introduced as an alternative for fast amalgam replacement. The aim of the present study was to evaluate clinically the behaviour of this non-bonded resin composite material, promising the release of fluoride, calcium, and hydroxy ions, in comparison to a bonded resin composite (Solitaire I) in class I and II cavities. Ninety-nine cavities in 31 patients were restored in a controlled prospective clinical study. Fifty fillings were placed with Ariston pHc as per the manufacturer's instructions, i.e. neither with enamel etching nor with the use of rubber dam. The same patients received 49 Solitaire I restorations totally bonded with Solidbond using rubber dam. At baseline, after 6 months, and after 12 months, two investigators given the same instructions examined the restorations, according to modified USPHS codes and criteria. Forty selected restorations (20 Ariston, 20 Solitaire) were additionally analysed via replicas, using a stereo light microscope (SV 11, Zeiss, Germany) at 130x magnification. After 12 months, 95 restorations were rated clinically acceptable (6% failure rate for Ariston pHc; 2% for Solitaire). Statistically significant differences were computed for both materials regarding the criterion "filling integrity". Further statistically significant deterioration for Ariston pHc between the three evaluations has been detected for the criteria "tooth integrity" (enamel cracks) and "marginal adaptation" (gap formation/Friedman 2-way ANOVA; p<0.05). With Ariston the criterion "hypersensitivity" also increased significantly after 1 year in comparison to Solitaire. The microscopic margin analysis revealed significantly increasing marginal deficiencies over time for both materials regarding the criteria "perfect margin", "gap formation", and "negative step" (P<0.05; Friedman 2-way ANOVA).

Adult↗
PubMed2000

Rett syndrome: analysis of MECP2 and clinical characterization of 31 patients.

UNLABELLED: Only recently have mutations in MECP2 been found to be a cause of Rett Syndrome (RTT), a neuro-developmental disorder characterized by mental retardation, loss of expressive speech, deceleration of head growth and loss of acquired skills that almost exclusively affects females. We analysed the MECP2 gene in 31 patients diagnosed with RTT. Sequencing of the coding region and the splice sites revealed mutations in 24 females (77.40%). However, no abnormalities were detected in any of the parents that were available for investigation. Eleven mutations have not been described previously. Confirming two earlier studies, we found that most mutations are truncating and only a few of them are missense mutations. Several females carrying the same mutation display different phenotypes indicating that factors other than the type or position of mutations influence the severity of RTT. Four females with RTT variants were included in the study. Three of these presented with preserved speech while the fourth patient with congenital RTT lacked the initial period of normal development. Detection of mutations in these cases reveals that they are indeed variants of RTT. They represent the mild and the severe extremes of RTT. CONCLUSIONS: mutations in MECP2 seem to be the main cause for RTT and can be expected to be found in approximately 77% of patients that fulfil the criteria for RTT. Therefore analysis of MECP2 should be performed if RTT is suspected. Three mutation hotspots (T158M, R168X and R255X) were confirmed and a further one (R270X) newly identified. We recommend screening for these mutations before analysing the coding region.

Alleles↗
PubMed2000

Adhesive luting of indirect restorations.

PURPOSE: To describe the potential of adhesive luting procedures with respect to (1) material characteristics and classifications, (2) film thickness, (3) overhang control, (4) bonding to different inlay materials, (5) adhesion to tooth substrates and the problem of hypersensitivities, (6) wear of luting composites, and (7) clinical performance. MATERIALS AND METHODS: A literature review of relevant studies of various in vitro and in vivo studies enables an overview of possibilities and limitations of adhesively luted indirect restorations. RESULTS: (1) Resin-based composites are the material of choice for adhesive luting. Both material properties and wear behavior of fine particle hybrid-type resin-based composites are superior to other materials. The use of compomers is questionable due to hygroscopic expansion and possible crack formation as proven for IPS Empress caps in vitro and in vivo. (2) Recent luting cements exhibit excellent flow characteristics with mean film thicknesses ranging between 8 microm and 21 microm. The ultrasonic insertion technique is recommended for viscous luting composites or conventional restorative composites utilizing their thixotropic properties. (3) For successful overhang control, good fit of the restoration (during luting) and high radiopacity of the cement (after luting) are indispensable. Overhang control is estimated easier when the ultrasonic insertion technique is applied. (4) The pre-treatments of ceramic inlays using hydrofluoric acid or silica coating result in effective bonding; for pre-treatment of resin-based composite inlays, silica coating is promising as well. (5) Bonding to enamel and dentin is proven clinically acceptable, but it should be performed with multi-step systems providing separate primers and bonding agents producing a perfect internal seal with almost no hypersensitivities. Dual-cured multi-step bonding agents provide the most promising potential. (6) The viscosity and filler content of the resin composite used for luting does not influence the wear characteristics within the marginal luting area in vivo. However, the ultrasonic insertion technique involving high viscosity materials provides enhanced handling characteristics for luting of tooth-colored inlays. (7) Clinical results with tooth-colored inlays and veneers are promising over periods of up to 10 yrs, including use in severely destroyed teeth.

Acid Etching, Dental↗
PubMed1999

Fatigue behaviour of different dentin adhesives.

The aim of this in vitro study was to compare quasistatic and cyclic fatigue dentin bond strength of modern adhesive systems representing different generations. One hundred and fifty cavities were made in discs of freshly extracted human third molars and filled with direct resin composite restorations. Dentin adhesives of different generations (SY = Syntac Classic, multi-step system with self-etching primer; SE = Syntac Classic with additional phosphoric acid etching prior to application of the self-etching primer; SB = Scotchbond Multi-Purpose Plus, multi-step system with total etching; PE = Prime & Bond 2.1, single-step system with and without [PB] total etching) were used in combination with one hybrid composite. After 21 days of storage, 10 specimens for each adhesive system were subjected to thermocycling (1150 cycles) for 24 h and were afterwards debonded in a push-out test. Another 20 specimens were tested with cyclic fatigue according to the staircase method with 5000 cycles for each specimen. Static and cyclic push-out bond strengths, respectively, for each group were (MPa): SY 16.9 +/- 0.9 and 14.2 +/- 1.7, SE 17.5 +/- 1.8 and 14.8 +/- 3.4, SB 18.5 +/- 1.7 and 13.9 +/- 2.1, PB 14.6 +/- 2.2 and 7.2 +/- 2.4, PE 13.4 +/- 2.2 and 6.8 +/- 1.8. Both quasistatic and dynamic bond strengths revealed better values for the multi-step systems (P < 0.05). All adhesive systems tested revealed a significant fatigue behaviour which was more pronounced for the one-bottle system with a decrease of about 50% independent of additional dentin etching.

Adhesiveness↗
PubMed1999

Internal adaptation and overhang formation of direct Class II resin composite restorations.

The aim of the present in vitro study was to evaluate different restorative concepts for posterior resin composite fillings in terms of internal adaptation and overhang formation. Eighty standard occluso-distal cavities with and without a 1.5-mm bevel were restored in a phantom head using Syntac Classic and Tetric Ceram with and without Tetric Flow as thin lining or Solid Bond and Solitaire with and without FlowLine. The restorations were finished intraorally and afterwards subjected to thermal loading (1150 x +5 degrees C/+55 degrees C) for 24 h. The proximal margins of the original specimens were analyzed for overhangs under a stereo light microscope (100-fold magnification) before and after intraoral control with loupes, including additional polish. Afterwards the teeth were cut longitudinally, replicated, and their internal integrity analyzed under a SEM (200-fold magnification). The combination of flowable and viscous composites resulted in enhanced internal adaptation for both adhesive systems. However, Syntac Classic exhibited superior adaptation characteristics compared with Solid Bond. In terms of overhang formation, the use of flowable materials always led to higher percentages of marginal overhangs in beveled cavities. Higher viscous materials alone resulted in higher percentages of underfilled margins of beveled than box-shaped cavities. It was clear that the use of magnifying glasses during finishing was beneficial for reducing marginal overhangs up to 40%.

Composite Resins↗
PubMed1999

Crack formation of all-ceramic crowns dependent on different core build-up and luting materials.

OBJECTIVES: The aim of this in vitro study was to evaluate various core build-up and luting materials regarding their effect on crack formation of all-ceramic crowns. METHODS: Fifty-six freshly extracted sound human third molars were prepared according to a standardized procedure obtaining a circular shoulder of 1.5 mm with all margins located in dentin. Sixty percent of the dentin volume were removed and restored with totally bonded build-up composite resins or resin-modified glass ionomer cements (RMGIC) or compomers. Cast IPS-Empress caps were manufactured and luted with the different materials. For each material group, the volumes of the core build-ups and of the luting cements were determined. The caps were examined for cracks after 1, 3, 6, 9 and 12 months storage in 0.9% saline solution at 37 degrees C. RESULTS: The tested groups revealed no major differences in the percentage of the core build-ups and in the volume of the luting cements. After 12 months only the group with composite resin build-up and luting showed no crack formation. RMGIC/compomer build-up or RMGIC/compomer luting always resulted in cracking of the caps. CONCLUSIONS: Within the limits of this study it can be concluded that the hygroscopic expansion of RMGIC/compomer materials led to failure of all-ceramic crowns, when the materials are used for both core build-up or adhesive bonding.

Acrylates↗
PubMed1999

IPS Empress inlays and onlays after four years--a clinical study.

OBJECTIVE: Ceramic inlays are used as esthetic alternatives to amalgam and other metallic materials for the restoration of badly damaged teeth. However, only limited clinical data are available regarding adhesive inlays and onlays with proximal margins located in dentine. In a prospective, controlled clinical study, the performance of IPS Empress inlays and onlays with cuspal replacements and margins below the amelocemental junction was examined. MATERIALS AND METHODS: Ninety-six IPS Empress fillings were placed in 34 patients by six clinicians. The restorations were luted with four different composite systems. The dentin bonding system Syntac Classic was used in addition to the acid-etch-technique. At baseline and after 6 months, one, two and four years after placement the restorations were assessed by two calibrated investigators using modified USPHS codes and criteria. A representative sample of the restorations was investigated by scanning electron microscopy to evaluate wear. RESULTS: Seven of the 96 restorations investigated had to be replaced (failure rate 7%; Kaplan-Meier). Four inlays had suffered cohesive bulk fractures and three teeth required endodontic treatment. After four years in clinical service, significant deterioration (Friedman 2-way Anova; p < 0.05) was found to have occurred in the marginal adaptation of the remaining restorations. Seventy-nine percent of the surviving restorations exhibited marginal deficiencies, independent of the luting composite. Neither the absence of enamel margins, nor cuspal replacement significantly affected the adhesion or marginal quality of the restorations. CONCLUSION: After four years, extensive IPS Empress inlays and onlays bonded with the dentin bonding system Syntac Classic were found to have a 7% failure rate with 79% of the remaining restorations having marginal deficiencies.

Adult↗
PubMed1999

Direct posterior composite restorations with a new adhesive system: one-year results.

PURPOSE: Syntac Sprint is a new one-bottle adhesive based on the total-etch and total-bond technique. The aim of this study was to compare the new restorative system consisting of Syntac Sprint and the resin composite Tetric Ceram with the clinically proven combination of the dentin adhesive Syntac Classic and the resin composite Tetric. MATERIALS AND METHODS: In a controlled prospective clinical study, 47 cavities (36 premolars, 11 molars; 29 maxillary, 17 mandibular; 6 occlusal, 33 occluso-approximal, 7 MOD, 1 > 3 surfaces) in 33 patients (17 female, 16 male) were filled. Twenty-five fillings were placed with the combination Syntac Sprint/Tetric Ceram under total etching and total bonding conditions. In thirteen restorations, Syntac Sprint was precured prior to the application of the resin composite; in the other twelve cases, restoration and adhesive were cured simultaneously. The control group consisted of 22 cavities restored with Syntac Classic plus the composite Tetric. At baseline and after 6 and 12 months, two calibrated investigators examined the restorations with modified USPHS codes and criteria. RESULTS: The criteria marginal integrity and integrity of the tooth deteriorated significantly between the baseline and the 6- and 12-month investigations (Friedman 2-way ANOVA; p < 0.05). No differences were found in the criteria surface roughness, color matching, anatomic form, step formation, integrity of the filling, proximal contact, hypersensitivity, or satisfaction. After one year, all fillings were in good condition. There was no significant difference between the Syntac Sprint/Tetric Ceram and Syntac Classic/Tetric groups for any criterion (Kruskal-Wallis; p > 0.05). CONCLUSION: Within the limits of this study, Tetric Ceram fillings in combination with Syntac Sprint were clinically successful after one year.

Acrylates↗
PubMed1997

Viscous glass-ionomer cements: a new alternative to amalgam in the primary dentition?

Glass-ionomer cements offer advantages in the treatment of the primary dentition. New, colored, highly viscous glass-ionomer cements hold the promise of better abrasion properties. Owing to their high viscosity, their handling characteristics are similar to those of amalgam. Examination of their properties demonstrated increased resistance to abrasion in comparison to amalgam, although no improvement in fatigue or flexural resistance was found. Clinical experience extending over 2.5 years confirmed these results.

Dental Amalgam↗
PubMed1996

Comparison of two- and three-body wear of glass-ionomers and composites.

The two-body and three-body wear of glass-ionomers (GIC), visible light cured glass-ionomers (VLC-GIC), and composites were compared. The wear simulations were performed for the two-body wear in an artificial mouth and for the three-body wear with the so-called ACTA machine. The tested materials were different conventional glass-ionomers, light cured glass-ionomers, composites, and amalgam. The wear rates of 8 specimens of each material for the two-body and 16 for the three-body wear test were compared. After 10(5) cycles with each testing device, the wear shapes were measured. All measurements were related to the wear rate of amalgam. For the two-body wear method, the worn materials were qualitatively judged by scanning electron microscopy. The two different wear testing methods lead to similar results with slight differences in ranking. Amalgam showed the lowest wear rates with both methods. Photac Fil, a newly developed VLC-GIC, showed dramatically lower wear resistance than composites and conventional GIC with both methods. Further investigations are necessary to identify the material-specific parameters influencing the wear behaviour of a material in relation to different wear testing methods.

Acrylic Resins↗
PubMed1994

Effect of Helicobacter pylori on dbc-AMP stimulated acid secretion by human parietal cells.

This study examines the effect of different H.p. strains (A-D) on dbc-AMP stimulated acid secretion by human parietal cells in vitro. H.p. strains A and D reduced acid secretion dose-dependently between 20 and 80%. In contrast, H.p. strains B and C had little or no effect. We conclude that H.p. strains vary in their ability to suppress acid secretion, and that the site of inhibition lies beyond the c-AMP level, possibly involving the K+H(+)-ATPase of the parietal cell. Interference with acid secretion may facilitate H.p. colonization of the stomach and may prove to be an important pathogenetic factor.

Aminopyrine↗
PubMed1991

[Individually controlled sedation using Midazolam].

Midazolam might be an alternative to general anesthesia for noncooperative children. 40 children were treated during 94 midazolam sedations to evaluate the potential dental therapy. An average of 2 fillings and 1 endodontic treatment was possible per sedation. The initial Midazolam dosage was 0.6 mg/kg. Every 15 min another 0.3 mg Midazolam/kg were administered to maintain the treatability of the children. 30 min after the initial Midazolam dosage dental treatment could be started. The average duration of a sedation was 76 min. Our results suggest that sedations complement under dental treatment general anesthesia.

Anesthesia, Dental↗