Biomedical subjects

C M Kreulen

Publications and source records attributed to C M Kreulen.

At least 19 recordsLinked to original sources

PubMed2006

[In vitro fracture behaviour of composite crowns with and without posts].

The failure load and failure mode of severely damaged endodontically treated maxillary premolars were examined within a laboratory study. The premolars were divided into 4 groups. The first of which was restored with prefab metal posts, the second with prefab fibre posts and the third with custom-made fibre posts; all 3 receiving direct resin crowns. In a 4th (control) group no post-space preparation was performed and no posts were placed; a direct resin composite complete crown was made. After thermocycling, all specimens were statically loaded in a universal test machine until failure, under an angle of 30 degrees. There was no significant difference between the mean failure loads. Failure was merely due to unfavourable, non-repairable fractures (ending below the simulation of bone level). This study suggests that posts are not necessarily required to increase the failure load of direct resin composite crowns, however, clinical studies are necessary to confirm these findings.

Bicuspid↗

PubMed2005

A comparison of fatigue resistance of three materials for cusp-replacing adhesive restorations.

OBJECTIVES: To investigate the fatigue resistance and failure behaviour of cusp-replacing restorations in premolars using different types of adhesive restorative materials. METHODS: A class 2 cavity was prepared and the buccal cusp was removed in an extracted sound human upper premolar. By using a copy-milling machine this preparation was copied to 60 human upper premolars. In groups of 20 premolars each, direct resin composite restorations, indirect resin composite restorations and ceramic restorations were made. All restorations were cusp replacements made in standardized shape and with adhesive techniques. Cyclic load (5 Hz) was applied starting with a load of 200 N (10,000 cycles) followed by stages of 400, 600, 800 and 1000 N at a maximum of 50,000 cycles each. Samples were loaded until fracture or to 2,10,000 cycles maximum. In case of fracture, the failure mode was recorded. RESULTS: No differences were seen in fracture strength between the three groups (Wilcoxon P = 0.16). No differences were observed with regard to failure mode above or below the cemento enamel junctions (chi2 P = 0.63). The indirect resin composite and ceramic restorations showed significantly more combined cohesive and adhesive fractures than the direct resin composite restorations, which showed more adhesive fractures (chi2 P = 0.03 and 0.002). CONCLUSIONS: The results of this study suggest that ceramic, indirect resin composite and direct resin composite restorations provide comparable fatigue resistance and exhibit comparable failure modes in case of fracture, although the indirect restorations tend to fracture more cohesively than the direct restorations.

Acrylic Resins↗

PubMed2005

Ex vivo fracture resistance of direct resin composite complete crowns with and without posts on maxillary premolars.

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 (6000x, 5-55 degrees C). Static load until fracture was applied using a universal loading device (crosshead speed 5 mm min(-1)) at a loading angle of 30 degrees . 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.

Bicuspid↗

PubMed2005

Can internal stresses explain the fracture resistance of cusp-replacing composite restorations?

The aim of this study was to explore and compare the results of occlusal load application to cusp-replacing composite restorations, studied by means of finite element (FE) analysis and in vitro load tests. A three-dimensional (3D) FE model was created with a set up similar to an in vitro load test that assessed the fatigue resistance of upper premolars with buccal cusp-replacing resin composite restorations. Occlusal load was applied to two geometries (with and without palatal cuspal coverage), and the tooth-restoration interface and composite material stresses were calculated. Subsequently, safety factors were calculated by dividing the material strength values by the obtained stresses. The highest safety factors were observed for the restorations with cuspal coverage. This was consistent with the load test, in which cuspal coverage led to higher fracture resistance. Furthermore, the FE analysis predicted that failure of the tooth-restoration interface is more likely than failure of the composite material. Correspondingly, the load test showed predominantly adhesive failures of the restorations. Although the described test methods did not lead to a complete understanding of the failure mechanism, it can be concluded that the FE analysis provides additional information with regard to the differences in fracture behaviour of these types of restorations.

Adhesiveness↗

PubMed2004

[Research methods in dentistry 5. The finite element method].

The finite element method is a commonly applied experimental research technique. The method comprises computer simulation of constructions under load and of internal mechanical processes, which enables the study of effects of geometrical and material variations. The analysis shows internal stresses and, consequently, predictions can be made of possible failure. In dentistry, the method is applied in disciplines, such as orthodontics, oral and maxillofacial surgery, implantology en restorative dentistry.

Computer Simulation↗

PubMed2003

A three-dimensional finite element model of the polymerization process in dental restorations.

Restoration of dental restorations with resin composite is hampered by shrinkage of the material during the polymerization process. In this study, we simulated the polymerization process in a detailed three-dimensional finite element model of a human upper premolar with a cusp-replacing restoration. It was analyzed how the stress patterns changed during polymerization and it was assessed whether immediate failure of the restoration is likely to occur and if so, which locations within the restoration are at highest risk and what the clinical implications of these findings are for clinical practice. It was found that the stresses increased rapidly during polymerization and decreased again in the post-polymerization phase. At the interface, tensile stresses relaxed to a higher degree than the shear stresses. Stress values in the composite material and at the interface with the tooth tissue were lower than the reported strength values suggesting that immediate failure is unlikely. The safety factor against mechanical failure of the interface, however, was relatively low indicating that the interface between the composite material and the tooth tissue is at a higher risk for failure than the bulk of the restoration. Stress relaxation was less effective in areas where the interface surface was irregular. In common practice, irregular interface surfaces are used to increase the retention of the restoration. This study indicates that the increased retention may be compromised to some extent by higher shrinkage stresses. The fact that stresses considerably decreased during the post-polymerization period suggests that mechanical loading should be limited during the first few hours after restoration.

Bicuspid↗

PubMed2003

Does layering minimize shrinkage stresses in composite restorations?

Polymerization shrinkage of resin composites may impair restoration longevity. It is hypothesized that layering, rather than bulk, techniques result in less stress in the tooth-restoration complex. The aim of this study was to compare shrinkage stresses for different restorative techniques used for cusp-replacing restorations with direct resin composite. In a 3-D FE model, the dynamic process of shrinkage during polymerization was simulated. Time-dependent parameters (shrinkage, apparent viscosity, Young's modulus, Poisson ratio, and resulting creep), which change during the polymerization process, were implemented. Six different restorative procedures were simulated: a chemically cured bulk technique, a light-cured bulk technique, and 4 light-cured layering techniques. When polymerization shrinkage is considered, a chemically cured composite shows the least resulting stress. The differences seen among various layering build-up techniques were smaller than expected. The results indicate that the stress-bearing locations are the interface and the cervical part of the remaining cusp.

Chemical Phenomena↗

PubMed2003

[A finite element model of a cusp-replacing adhesive restoration].

This article describes the development of a three-dimensional finite element model of a premolar, based on a micro-scale computed tomographic data-acquisition technique. Using the model shrinkage stresses were analysed during and after the polymerisation process of resin composite. The stress patterns generated were three-dimensional. The results of this study indicate that failure of the interface is more probable than failure of the composite material. The described procedure is a relatively easy method to produce a highly detailed 3-D finite element model of a premolar with an adhesive cups-replacing restoration.

Bicuspid↗

PubMed2003

[Minimal invasive treatment of cuspal fractures of premolars].

This article describes the cusp-replacing adhesive restoration as a minimally invasive alternative for crowns after cuspal fracture of premolars. To demonstrate the importance of this treatment option for daily practice, the results of an incidence study of cuspal fractures are reported. Subsequently, the development of clinical guidelines and procedures as applied in a clinical study of adhesive cusp-replacing restorations are described.

Bicuspid↗

PubMed2003

[The restoration of endodontically treated teeth: the minimally invasive (post-) core buildup?].

The rebuilding of endodontic treated teeth is a common situation in general dental practice. The final (post-) core buildup, with or without a crown, should protect the restoration as well as the tooth against fracture, should prevent debonding of the restoration, should not permit leakage and should provide an acceptable esthetic result. Several factors influencing these properties are described. The (post-) core buildup in relation to the concept of minimally invasive dentistry is discussed. In conclusion, there is no unambiguous guideline for restoring endodontically treated teeth. Standardised in vitro and in vivo studies are needed.

Composite Resins↗

PubMed2003

[Fiber-reinforced adhesive partial dentures].

Dental applications of fiber-reinforced polymers include adhesive partial dentures. Dental resin composite materials can be reinforced by several types of fibres. Fiber orientation, proper wetting of the fibers by the resin and fiber volume are important. An application of fiber reinforced composites is the composite inlay bridge. This paper deals with some aspects of this type of adhesive partial denture. Advantages include the satisfactory esthetics and the minimally invasive character. Not clear yet is the long-term survival. The adhesive properties of fiber-reinforced adhesive partial dentures require an adaptation of the current dental philosophy, in which direct and indirect restorative techniques can be combined. An increase in knowledge and experience is needed to determine the dental applications.

Composite Resins↗

PubMed2001

Occlusal stability in shortened dental arches.

Shortened dental arches consisting of anterior and premolar teeth have been shown to meet oral functional demands. However, the occlusal stability may be at risk as a result of tooth migration. The aim of this nine-year study was to investigate occlusal stability in shortened dental arches as a function over time. Occlusal stability indicators were: 'interdental spacing', 'occlusal contacts of anterior teeth in Intercuspal Position', 'overbite', 'occlusal tooth wear', and 'alveolar bone support'. Subjects with shortened dental arches (n = 74) were compared with subjects with complete dental arches (controls, n = 72). Repeated-measurement regression analyses were applied to assess age-dependent variables in the controls and to relate the occlusal changes to the period of time since the treatment that led to the shortened dental arches. Compared with complete dental arches, shortened dental arches had similar overbite and occlusal tooth wear. They showed more interdental spacing in the premolar regions, more anterior teeth in occlusal contact, and lower alveolar bone scores. Since the differences remained constant over time, we conclude that shortened dental arches can provide long-term occlusal stability. Occlusal changes were self-limiting, indicating a new occlusal equilibrium.

Adult↗

PubMed2001

[Meta-analysis of anterior veneer restorations in clinical studies].

A systematic review was used to make an inventory of clinical studies on veneer restorations. Based on a protocol articles were selected that were subsequently assessed for their quality. With 'failure of the restoration' as a study outcome, survival data of the restorations were generated from the selected studies and a mean survival result was composed. Porcelain veneer restorations showed an acceptable 3-year survival, which was favourable to the 3-year survival of preformed acrylic veneers. The quality assessment expressed that reports on clinical studies should be more standardised in order to make it easier to compare the results of different studies.

Acrylic Resins↗

PubMed2000

Time-and-motion study on class II copy-milled ceramic inlays.

OBJECTIVES: To obtain an estimate of working times of Class II copy-milled ceramic inlays as an indication of their efficiency, and to analyse factors of influence. METHODS: In a controlled clinical trial, 173 MO/DO or MOD ceramic inlays of the Celay system were constructed in 101 patients. Treatment was carried out by seven dentists. The inlays were replacements of existing amalgam restorations in both molar and premolar teeth. Net-times needed for the treatment and for the laboratory stage were registered. Variables of influence on the working time were assessed by using ln-working times in ANOVA. Differences of working times were expressed as the relative difference between the upper and lower value of each variable (Delta). RESULTS: The mean clinical treatment time was 67(+/-22)min. The laboratory stage required 60(+/-17)min working time. 'Cavity modification technique' (composite basing/conventional, Delta=17%), 'clinical operator' (seven dentists, Delta=57%), and 'size of the restoration' (large/medium, Delta=16%) significantly influenced the clinical treatment time (p<0.001). Although the dentists were familiar with inlay construction, they showed a 25% decrease in working time towards the end of the study. CONCLUSIONS: Class II copy-milled ceramic inlays in this time-and-motion study required about 125min of working time. Working time increased by applying composite basing and making large restorations. The dentist influenced working times, while efficiency increased over time. Dentists needed more laboratory time to produce an inlay than the dental technician.

Adult↗

PubMed2000

A systematic review of single-tooth restorations supported by implants.

OBJECTIVES: To make an inventory of clinical studies on single-tooth restorations supported by implants using a systematic review procedure and to aggregate overall survival results. DATA SOURCES: Papers referring to single-tooth implants were located by a MEDLINE search 1990 to April 1998. Three hundred and twenty references were found, and they were subjected to a systematic review procedure. STUDY SELECTION: A three-step inclusion/exclusion procedure was applied to identify papers that represented: good scientific practice (GSP), reported results of all patients, implants and crowns for more than 2years, and had sufficient data to generate life-table analyses. The outcomes were 'implant failure' and 'crown completion'. Nine studies survived. These data showed an overall mean GSP of 0.37 with a predicted 4year implant survival of 97% (n=459), and an uncomplicated crown maintenance of 83% (n=240). CONCLUSION: Single-tooth implants show an acceptable short-term survival of 4years, but crown complications are common.

Clinical Trials as Topic↗

PubMed1999

Cost-effectiveness of composite resins and amalgam in the replacement of amalgam Class II restorations.

OBJECTIVES: The replacement of an old amalgam Class II restoration is a common treatment and will remain so for decades. In addition to effectiveness, possible adverse health effects and esthetics, the costs of the treatment options will play a role in the choice of material. The aim of this study was to yield information on the relative cost-effectiveness of the use of composite resins and amalgam for the rerestoration of amalgam Class II restorations. METHODS: As part of a larger randomized clinical trial, treatment effectiveness and treatment costs were estimated in 73 composite and amalgam Class II posterior re-restorations. The main treatment outcome was longevity. Secondary outcomes included need of repair and quality of the margin while in situ. Costs were analyzed from the perspective of dentistry, assuming a treatment strategy aimed at offering 'value for money'. From this perspective, differential costs were based on personnel costs as approximated by treatment time. RESULTS: Replacing an amalgam Class II restoration with amalgam is associated with lower costs than replacing with a composite resin. A sensitivity analysis, considering type of composite, increasing proficiency with the material, and time needed for future removal of material, demonstrated that these differences are fairly robust. The materials performed equally well for the first 5 years after placement with respect to longevity. Differences in secondary outcomes were minor and not all in favor of the same material. CONCLUSIONS: It is tentatively concluded that amalgams are more cost-effective than composites for replacing existing Class II amalgam restorations.

Adolescent↗

PubMed1999

Bacterial counts in carious dentine under restorations: 2-year in vivo effects.

Little is known about the long-term effects of fluoride-releasing materials on carious dentine in vivo. The aim was to investigate the 2-year influence of a resin-modified glass ionomer cement (RM-GIC) and amalgam on the bacteriological counts of carious dentine that remained under class I restorations. To enable a split-mouth design, 33 molar pairs in 33 patients (mean age 15.1 years, SD 1.4) were selected, based on clinically and radiographically diagnosed occlusal dentine caries. The enamel of the carious molars was removed, and the carious dentine was sampled under aseptic conditions just beneath the dentinoenamel junction. The molars were alternately restored with RM-GIC or amalgam without further removal of carious dentine. The samples were processed for microbiological determination of total viable counts (TVC), mutans streptococci (MS), and lactobacilli (LB). The molar pairs of 25 patients were reevaluated after 2 years using the same clinical techniques and were permanently restored after complete caries removal. Both materials showed a substantial decrease in numbers of TVC and LB of the carious dentine after the 2-year period. Compared to amalgam, the decrease in the numbers of LB was significantly more pronounced for RM-GIC. No microorganisms were detected in only 11 molars (6 RM-GIC and 5 amalgam) after the 2-year period. Based on this study, we suggest that complete removal of carious dentine is still the best conservative treatment, irrespective of the restorative material used.

Adolescent↗

PubMed1998

Observer variation in the assessment of resin composite.

OBJECTIVES: The aim of this study was to compare the type of information obtained from log-linear modelling vs Cohen's kappa statistics on observer variation in the assessment of marginal adaptation in composite inlays and amalgam restorations. METHODS: Marginal adaptation of Class II resin composite inlays and amalgam restorations was clinically assessed by two observers, four years after placement. Each of 52 patients received 4 different restorations, three composite (Herculite XR, Clearfil CR Inlay and Visiomolar) inlays and one Tytin restoration. The results were evaluated by Cohens Kappa statistics and log-linear modelling. RESULTS: The overall Cohen's kappa was 0.45, ranging from poor to good for the four materials. Log-linear modelling confirmed that the observers agreed beyond chance but this agreement depended on the performance of the material. Marginal adaptation of Visiomolar (ESPE) inlays was somewhat inferior compared to the other materials. The assessment of Clearfil CR (Kuraray) inlay was difficult using this clinical evaluation procedure. SIGNIFICANCE: Using log-linear modelling it is possible to look at observer agreement and material performance at the same time. This combined approach is important because agreement may depend on material performance.

Chi-Square Distribution↗