Biomedical subjects

K G Boberick

Publications and source records attributed to K G Boberick.

7 recordsLinked to original sources

PubMed2001

Lifetime predictions for resin-based composites using cyclic and dynamic fatigue.

Because dental restorative materials undergo fatigue in use, testing is often performed in the laboratory to evaluate material responses to cyclic loading. The purpose of this study was to compare the lifetime predictions resulting from two methods of fatigue testing: dynamic and cyclic fatigue. Model composites were made in which one variable was the presence of a silanizing agent, and specimens tested in 4-point flexure. Cyclic fatigue was carried out at a frequency of 5 Hz, while dynamic fatigue testing spanned seven decades of stress rate application. Data were reduced and the crack propagation parameters for each material were calculated from both sets of fatigue data. These parameters were then used to calculate an equivalent static tensile stress for a 5-year survival time. The 5-year survival stresses predicted by dynamic fatigue data were approximately twice those predicted by cyclic fatigue data. In the absence of filler particle silanization, the survival stress was reduced by half. Aging in a water-ethanol solution reduced the survival stresses by a factor of four to five. Cyclic fatigue is a more conservative means of predicting lifetimes of resin-based composites.

Acrylic Resins↗

PubMed1999

1998 Judson C. Hickey Scientific Writing Award. Use of a flexible cast for the indirect fabrication of provisional restorations.

Efficient fabrication of a clinically acceptable provisional restoration for a fixed partial denture is an important part of treatment success. Fabrication of provisional restorations that uses the indirect technique produces accurate fitting provisional restorations without the chemical and thermal irritation associated with direct fabrication. With a typodont model, an indirect method is presented that uses an elastic cast for fabrication of multiple unit provisional restorations for fixed partial dentures. The cast is available within 6 minutes of impression making, can be trimmed with a sharp scalpel, and provides flexibility that allows easy separation of the acrylic provisional from the cast. The cast can also be used to evaluate the clinical acceptability of the preparations before impression making. This method has also been successfully used for the fabrication of acrylic provisional restorations for onlay preparations.

Acrylic Resins↗

PubMed1999

Use of a flexible cast for fabrication of multiple post-coping overdenture restorations.

Direct intraoral fabrication of multiple post-coping restorations for an overdenture in the same arch can be a time-consuming chairside clinical procedure. In addition, accurate intraoral fabrication of resin patterns with intracrevicular margins is not always possible as a result of limited access. This article presents a direct-indirect method that uses an elastic cast for fabrication of multiple post-coping restorations with intracrevicular margins. Custom post patterns are fabricated directly in the root canal with autopolymerizing resin (Duralay). An impression is made of the remaining tooth structure, which also includes the post patterns, and a flexible cast is poured chairside. The cast is available within 6 to 8 minutes of impression making and can be trimmed similar to a stone die. The procedure also provides flexibility that allows separation of the cast from the impression without fracture of the custom post pattern or cast. The fabrication of the post-coping restoration can be completed in the laboratory, or if necessary, completed chairside and verified intraorally, before dismissing the patient.

Dental Abutments↗

PubMed1999

Size effect in resin/glass composite flexure strengths.

The objective of this study was to test the hypothesis that composite restorative materials possess an elastic-brittle nature and therefore will exhibit a size effect for flexure strength data. The experimental material consisted of 20 wt% 60:40 BISGMA:TEGDMA, 10 wt% colloidal silica, and 70 wt% Sr glass and was cured by light irradiation. Two sizes of flexure specimens were fabricated: 3.2x1.6x35 mm, and 6.25x3.1x35 mm. Half of the specimens made were soaked to equilibrium weight gain in 50:50 ethanol:water. The fracture strengths were measured in four-point bending tests. The beams under load were modelled by the finite element package ABAQUS. A statistical fracture mechanics methodology embodied in a public domain computer program called CARES/LIFE, developed by NASA, utilized the ABAQUS input and the fracture strengths of the smaller specimens to predict the fracture strengths of the larger specimens. In making the computation it used an approach that combines a Weibull distribution of flaw size with Batdorf's fracture mechanical model for failure at a material flaw. Both the soaked and unsoaked specimens exhibited Weibull behaviour, with shape parameters ranging from 4.04 to 8.15. Soaking had a clearly detrimental effect on the strengths of specimens of both sizes, and produced a comparable percentage reduction in the estimated scale parameter of the fracture strength distribution. Both the soaked and unsoaked specimens also exhibited a clear and comparable size effect, i.e. the larger specimens had a fracture strength that was lower than that of the smaller specimens by roughly the same percentage. Moreover, the magnitude of the size effect was well predicted by the CARES/LIFE methodology for both the soaked and the dry specimens. The elastic-brittle character of both soaked and unsoaked composite specimens was validated by load-deflection data, the magnitude of the Weibull shape parameters of the observed fracture strength data (<10), and the observed effect of specimen size. The accuracy of CARES/LIFE in predicting the magnitude of the observed size effect in beams of two different sizes strongly suggests that CARES/LIFE will be useful for computation of failure probabilities for clinically relevant structures.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1998

Dimensional stability of record bases fabricated from light-polymerized composite using two methods.

STATEMENT OF PROBLEM: Record bases fabricated from resin-based composite, which undergoes polymerization shrinkage during curing, can distort during curing to produce significant gaps along the posterior border. PURPOSE: This study evaluated the pattern of gap formation that occurs over the palatal area of a maxillary record base fabricated from light-cured composite (Triad), and determined whether changes in the fabrication method affects the size and pattern of gap formation. Effects of composite width and passage of time on gap formation were also analyzed. MATERIAL AND METHODS: Twenty record bases were fabricated with two methods: (1) according to the manufacturer's directions, the entire surface of the record base was exposed to the curing light; and (2) the palatal area of the record base was covered with foil to prevent light penetration, and the base was light cured in three stages with readaptation of the uncured composite between stages. Ten record bases from each group were tested 1 hour after fabrication; the remaining 10 from each group were tested 7 days after fabrication. Measurements of adaptation were made at three points representing the right and left ridge crests and midpalatal areas. The first measurement was taken at the posterior border and subsequent measurements were made at 5 mm increments after reduction of the posterior border of the cast and record base with a model trimmer. RESULTS: Dimensional changes were observed in both procedures. The largest discrepancy occurred at the posterior border of record bases fabricated using method 1. Mean gap formation at the posterior border in this group after 1 hour was 454, 729, and 334 microm and 483, 841, and 330 microm after 7 days at points A, B, and C, respectively. Record bases fabricated with procedure 2 demonstrated mean gap sizes at the posterior border after 1 hour of 219, 421, and 208 microm and 267, 403, and 192 microm after 7 days at points A, B, and C, respectively. No significant influence of composite width on gap size was found. CONCLUSION: The average gap size due to stage curing (method 2) was never greater than the corresponding gap that arose from the use of the manufacturer's recommendations (method 1). Limiting the amount of surface area exposed to the curing light and readapting the uncured composite to the cast between curing episodes can significantly reduce the mean gap size occurring at the posterior border.

Acrylic Resins↗

PubMedDate not supplied

An accurate chairside technique for fabricating a temporary restoration for ITI single-tooth implant.

Current implant restoration techniques depend upon a well-fitting, anatomic provisional restoration--especially at the restoration margin--to promote healthy soft tissue contours, which are necessary for successful final restorations. The ITI implant system presents a particular challenge in this regard because of the configuration of the implant head and shoulder, especially when these are placed subgingivally. A chairside method for obtaining an accurate marginal fit and customized contours in the single-tooth provisional restoration is described and illustrated.

Dental Implants, Single-Tooth↗

PubMedDate not supplied

Post and core fabrication for divergent canals with a cast post and core and a prefabricated dowel.

A post and core fabrication technique for multirooted teeth with divergent canals uses a combination cast post and core and prefabricated dowel. This method modifies and improves a previously reported method by using a nickel-silver technique post during casting to preserve the channel in the resin core pattern. Following casting, the nickel-silver post is dissolved with nitric acid. Minimal hand instrumentation with a post drill leaves a clean and accurate channel for cementation of an accessory prefabricated stainless steel or titanium post.

Dental Casting Technique↗