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Biomedical subjects

W G de Rijk

Publications and source records attributed to W G de Rijk.

At least 19 recordsLinked to original sources
PubMed2002

Weibull parameters of composite resin bond strengths to porcelain and noble alloy using the Rocatec system.

OBJECTIVE: The aim of the study was to determine the Weibull distribution parameters S(0) and m of the tensile bond strength of a composite resin sandwiched between a noble metal alloy and a feldspathic porcelain using the Rocatec system. METHODS: Specimens were prepared either as Au-Pt-Pd alloy cylinders alone or as alloy cylinders and a feldspathic porcelain. Surface treatments included 110 microm Al(2)O(3) sandblasting (Rocatec Pre), tribochemical silica coating (Rocatec Plus) and silane application (ESPE-Sil) prior to composite bonding. The tensile bond strengths of ceramic-resin-ceramic and metal-resin-metal specimens were determined before and after thermocycling at 5-60 degrees C for 1000 cycles. Statistical analyses were conducted using two parameter Weibull distributions determined by the characteristic strength (S(0)) at the 63% probability of failure, the Weibull modulus (m) and the 95% confidence intervals. RESULTS: With respect to the control group (no Rocatec) (7.5MPa), the Rocatec system significantly augmented the characteristic tensile bond strength S(0) of metal (17-18MPa) and porcelain (20-28MPa) groups. Thermocycling had no effect on the tensile bond strength of the metal samples and increased (not significant) the bond of the porcelain group. The Weibull modulus m for all groups ranged from 2.8 to 3.7. SIGNIFICANCE: This study confirmed the efficacy of the Rocatec system for bonding composite resin to metal or ceramic substrates. However, the variability of the strength of the bond is shown in the low Weibull modulus values obtained. This reflect the difficulties in controlling flaw formation and warrants research for future improvement.

Composite Resins↗
PubMed2000

Removal of fiber posts from endodontically treated teeth.

The removal of posts from endodontically treated teeth can be a major obstacle in the retreatment of teeth that have recurrent pathology, often leading to extraction of a tooth that could have been saved with endodontic retreatment. The use of a fiber post offers the advantages of a suitable elastic modulus and good bonding between post and cement, but also the advantage of easy removal, if so indicated by clinical findings. A special removal kit for fiber posts has been developed, and its use is illustrated, and described. The removal procedure can be completed in a very short time, usually less than 5 min. The tooth can then be restored with the same type and size of fiber post as was in the tooth prior to removal. Removal kits are found to be for single use only.

Carbon↗
PubMed1999

Tensile and shear stresses in the orthodontic attachment adhesive layer with 3D finite element analysis.

The tests commonly used for the evaluation of orthodontic adhesives measure tensile and shear bond strength. The two methods were compared with finite element analysis using a three-dimensional model and the effect of misalignment of the tensile and shear forces was calculated. Applying a shear load produces significant compressive and tensile stresses in the adhesive layer. Under ideal conditions of shear loading, the induced tensile stress is over 5 times the induced shear stress. The model shows that a tensile load induces predominantly tensile stresses in the adhesive layer. The calculations indicate that the tensile test method is a robust testing method with low sensitivity to misalignment of the applied load.

Adhesives↗
PubMed1997

Bond strength of visible light-cured glass ionomer orthodontic cement.

In this in vitro study, tensile strength tests were conducted with a visible light-cured glass ionomer cement (Fuji Ortho LC, GC America Inc.) bonded to extracted teeth under six different enamel surface conditions: (1) dry nonetched, (2) moist etched, (3) moist nonetched, (4) moist nonetched rebonded, (5) moistened with saliva substitute, and (6) moistened with human saliva. Two resin adhesives (Rely-A-Bond and Phase II, Reliance Orthodontic Products) were applied to dry and etched enamel and served as control agents. The glass ionomer cement approached the strength observed for resin adhesives and required the presence of moisture on the enamel surface for optimal performance.

Acid Etching, Dental↗
PubMed1995

Vectorial analysis of the equilibrium of forces transmitted to TMJ and occlusal biteplane splints.

A mechanical model (link quadrilateral bell crank) is used to demonstrate the equilibrium of normal force vectors transmitted to the masticatory system and maxillary occlusal biteplane splints with different designs. Occlusal contacts were imposed on the proposed models under the action of a masticatory force vector with an arbitrary value of 40 kgf. The consequence of this force action created different responses within the joint and at the level of the dentition. When compared to the intercuspal position in centric occlusion, intra-oral appliances with either smooth contacting surfaces or indentations, both with increased vertical dimension, forced the mandible to assume an anterior position with a concurrent increase of joint forces. The bite-splint that produced the least amount of joint force was the stabilization type with minimal increase of vertical dimension.

Biomechanical Phenomena↗
PubMed1994

Effect of cement film thickness on the fracture resistance of a machinable glass-ceramic.

OBJECTIVES: The aim of this study was to determine the fracture resistance of a machinable glass-ceramic plate cemented to a resin composite block as a function of the cement film thickness for two types of cement. METHODS: Ceramic plates were cemented to resin composite blocks using either zinc phosphate cement or a resin composite cement. For the zinc phosphate cement, the film thickness was 33 +/- 8 microns or 128 +/- 8 microns; for the resin composite cement, the thickness ranged from 26 +/- 11 microns to 297 +/- 48 microns. The elastic modulus was determined for each of the cements. Fracture loads were obtained by using a spherical steel indenter in the center of the glass-ceramic plate. The Weibull distribution was used for the statistical analysis. RESULTS: For glass-ceramic plates cemented with zinc phosphate cement, the fracture resistance was independent of the film thickness. When the resin composite cement was used, a gradual decrease of the fracture strength was observed that became statistically significant at a cement thickness of 300 microns or more. The characteristic fracture strength of glass-ceramic plates cemented with the resin composite cement was about 75% higher than when using the zinc phosphate cement. This difference is attributed to the bonding of the resin cement to the ceramic plate and the supporting structure. SIGNIFICANCE: The findings of this study suggest that the resistance to fracture due to indentation of the glass-ceramic may not be affected by the cement film thickness as much as previously thought.

Acrylic Resins↗
PubMed1994

Effect of surface treatments on the repair strength of a light-activated denture repair resin using censored data.

OBJECTIVES: The aim of this study was to evaluate the effect of three different chemical surface modifications on the bond strength of light-activated denture repair resin (Triad, Dentsply International) to a heat-cured resin (Lucitone, Dentsply International). METHODS: Transverse flexure test specimens were made, with surface treatment of 1) Triad bonding agent, 2) unreacted Lucitone monomer, and 3) a 1:1 mixture of methylene chloride and monomer, using two different application times (2 and 4 min). For all except one group, 18 specimens were made. The controls were solid single composition bars, 18 for each material. The elastic modulus in transverse flexure was measured for each material. The statistical analysis employed the Weibull distribution. Fracture strength values were obtained in a three-point flexure test. RESULTS: It was noted that many fractures occurred away from the interface and the center member of the test fixture. For those fractures, the observed fracture strength is a censored value of the fracture strength. Algorithms for the statistical treatment of censored data were used to get the maximum likelihood estimates of the fracture strength. A mechanical model showed that under three-point bending of a beam of two joined materials, fractures will occur in the part with the higher elastic modulus. This finding is indeed observed in the data. The 4 min monomer treatment showed the highest estimate of the bond strength (187.8 MPa). SIGNIFICANCE: Censored data can be used to obtain fracture strength estimates, and the censoring indicates that the bond strength may exceed the strength of the bulk material.

Acrylic Resins↗
PubMed1993

Occlusal contacts: vectorial analysis of forces transmitted to temporomandibular joint and teeth.

Despite relevant command of muscles in the chewing apparatus, occlusion of the upper/lower jaws is constrained by joints and opposing teeth. To describe this system performance, the link quadrilateral bell-crank comprised a suitable model to render vectorial analysis of forces transmitted to the masticatory system during mandibular elevation. Occlusal contacts were created in the above proposed model. No different mechanical responses in the system were found between maximum intercuspation contacts in centric occlusion as compared to long-centric reconstruction. There was a tendency for force decrease in joints and equal force distribution on dentition. Prematurities in centric relation, at least extent, and protrusive interferences produced concentration of forces at dentition and decrease of forces in the joint, while protrusive guidance tended to increase force in the joint.

Bite Force↗
PubMed1993

The accuracy of six impression techniques for osseointegrated implants.

PURPOSE: Six impression techniques were evaluated using tapered and square impression copings. MATERIALS AND METHODS: The absolute distortion was measured using a cast metal impression tray with fiduciary reference points external to the impression material. Measurements of the x, y, z coordinates on the master cast and the impressions were directly made with a travelling digitizing microscope. The difference between the coordinates of each of six sites in the impression and the corresponding reference site were compared. RESULTS: There was no significant difference between the techniques for the square copings but that there was a significant loss of accuracy in the z-axis with the tapered copings. CONCLUSIONS: No significant differences were noted.

Analysis of Variance↗
PubMed1992

Vectorial analysis of the instantaneous equilibrium of forces between incisal and condylar guidances.

Protrusive functional relationships between the upper and lower jaws are constrained by the structures of the temporomandibular joints (TMJs) and the opposing contacting surfaces of the anterior teeth. To check these biomechanical relationships, the link quadrilateral bell crank model was assumed in order to compute the instantaneous equilibrium of forces using vectorial analysis. Four anterior teeth configurations were analyzed to study the distribution of force components. The first represented normal bite (used as control), the second represented long anterior overjet, the third represented deep anterior overbite, and the fourth one represented freedom in centric. When three different interincisal contact positions were assumed, functional compromises concerning load/reaction between the TMJ and anterior dentition were found. In centric occlusion there was a tendency toward less loading in the joints and increased loading on the dentition. In intermediate positions and close to the edge-to-edge position, the mechanical tendencies were toward increased loading in the joints and decreased loading on the dentition.

Bite Force↗
PubMed1992

The regulatory process for dental devices: a researcher's view.

Comments from the three previous speakers ranged from moderate satisfaction to strong dissatisfaction with the regulatory process. Three different types of research are identified that seem to predict the ease of compliance with the 510(k) process. No one expressed satisfaction with the PMA application. It seems that current evaluation procedures inhibit the developing and marketing of new devices, but foster only enhancements to existing devices. The development of new evaluation methods is advocated to provide fast, inexpensive, but rigorous assessment of the clinical safety and treatment value of new devices.

American Dental Association↗
PubMed1990

Multidimensional internal setting expansion of a phosphate-bonded casting investment measured with strain gauges.

Strain gauges were used to determine the setting expansion of phosphate-bonded casting investments. The gauges were placed at the approximate site of the wax pattern. The isotropy of the expansion was evaluated with multidirectional strain gauges that measured the difference in expansion in two orthogonal directions. A large difference was found between the setting expansion measured externally (1% to 1.5%) and the method described here (0.01%). For casting rings lined with a nonasbestos layer, no statistically significant differences were found in the setting expansion parallel to the long axis of the ring and the expansion in the direction perpendicular to the long axis.

Dental Casting Investment↗
PubMed1990

Performance of dental biomaterials: conference report.

On August 13-18, 1989, a dental conference, entitled "Dental Biomaterials: Assessment of Performance Based on Engineering and Statistical Methods", was held in Santa Barbara, California. This conference was sponsored by the Engineering Foundation with co-sponsorship by the United States Army Institute of Dental Research, the United States Naval Dental Research Institute, Block Drug Co., Dentsply International, and the National Institute of Standards and Technology. The objective of this conference was to explore engineering and statistical methods for assessing the resistance of dental biomaterials to structural degradation and failure and for predicting the relative reliability of dental restorations and prostheses under clinical conditions. The conference was designed to evaluate the merits of established and new technology relative to the performance of dental materials. Analytical and experimental methods included fracture mechanics, conventional mechanical tests, adhesion tests, fractographic analysis, finite element analysis, statistical analysis, tribology, image analysis, x-ray diffraction, and scanning tunneling microscopy. The central theme was the development of a systematic approach to predict material performance under clinical conditions based on stress analysis, correlation of clinical data with in vitro data, and fracture surface characterization based on qualitative and quantitative methods. Supported in part by NIDR Grant No. DE06672.

Dental Materials↗
PubMed1985

Internal setting expansion of a dental casting investment measured with strain gauges.

A study was undertaken to investigate the feasibility of using strain gauges to evaluate the internal setting expansion of dental casting investments. A strain gauge was invested in the center of a casting ring to determine the linear setting expansion at the site of the wax pattern. The findings suggest that strain gauges can be used to measure setting expansion internally more accurately than volumetric or external surface measurement techniques. It was also found that winged strain gauges were more stable in the investment than wingless strain gauges.

Chemical Phenomena↗