Donald Mettenburg

In vitro cytotoxicity of resin-containing restorative materials after aging in artificial saliva

Abstract Studies have reported that dental resin-based materials release substances which have biological liabilities. However, some current methods for detecting these substances may not be adequate to detect biologically relevant concentrations. In the current study, we hypothesized that resin-based materials exhibit cytotoxic effects and alter cellular function in vitro when high-pressure liquid chromatography (HPLC-UV detection) cannot detect any release of substances. We further hypothesized that this release continues even after aging the samples in artificial saliva. Five types of composite or compomer materials (Z-100, Tetric Ceram, Dyract AP, Solitaire, and Clearfil AP-X) and one organically modified ceramic material (Definite) were tested after aging in artificial saliva for 0, 7, or 14 days. Cytotoxicity was assessed using direct contact with fibroblasts and measurement of succinic dehydrogenase activity after 48 h of exposure post aging. Release of substances from the materials was assessed using HPLC with UV detection. Altered cellular function was estimated by measuring proliferation of MCF-7 cells with sulforhodamine staining. HPLC showed that whereas initial release of substances was higher without aging, this release dropped significantly after 7 or 14 days of aging, and was equivalent to the Teflon controls after 14 days for four of the materials (Tetric Ceram, Definite, Solitaire, and Clearfil AP-X). Without aging in saliva, all materials had cytotoxicities >50% of the Teflon negative controls. After 14 days of aging, all materials except the Definite continued to show severe cytotoxicity. Only the Definite could be tested for its ability to alter cellular function because of the continuing toxicity of the other materials. This modified ceramic material caused a significant proliferative effect on the MCF-7 cells indicating that sufficient substances were released to alter cellular function. We concluded that all of these commercially available resin-based dental materials continue to release sufficient components to cause lethal effects or alter cellular function in vitro even after 2 weeks of aging in artificial saliva.

Influence of filler addition, storage medium and evaluation time on biaxial flexure strength and modulus of adhesive systems

Abstract Objective. This study evaluated the effects of filler addition, storage medium and time on biaxial flexural strength and flexural modulus of six adhesive systems. Materials and methods. The adhesives were either unfilled resins: Single Bond, Prime&Bond 2.1 and One-Step; or filled resins: Single Bond Plus, Prime&Bond NT and One-Step Plus. Resin discs of each product (0.5 mm thick × 6.0 mm diameter) were prepared using silicon molds (n = 10). The discs were stored dry, in water, mineral oil or ethanol for 1 week or 3 months before biaxial flexural testing. Data were statistically analyzed by 3-way ANOVA and Tukeys post-hoc test (α = 0.05). The specimens were tested in a universal testing machine at 1.27 mm/min until failure occurred. Results. In general, the storage in ethanol led to significantly lower flexural strength and flexural modulus values than the other storage conditions for all adhesives in both storage periods. Filler addition increased flexural strength and flexural modulus for Prime&Bond NT, when it was stored dry or in water for 1 week. For Single Bond Plus, the filler addition resulted in higher flexural modulus, when it was stored for 1 week in oil and in ethanol. No significant differences in flexural modulus were observed between One-Step and One-Step Plus in any storage medium. Conclusions. Results suggested that filler addition does not necessarily have to increase the flexural strength and flexural modulus. Ethanol and oil storages tended to yield opposite effects.

Polymeric-Calcium Phosphate Cement Composites-Material Properties: In Vitro and In Vivo Investigations

New polymeric calcium phosphate cement composites (CPCs) were developed. Cement powder consisting of 60 wt% tetracalcium phosphate, 30 wt% dicalcium phosphate dihydrate, and 10 wt% tricalcium phosphate was combined with either 35% w/w poly methyl vinyl ether maleic acid or polyacrylic acid to obtain CPC-1 and CPC-2. The setting time and compressive and diametral tensile strength of the CPCs were evaluated and compared with that of a commercial hydroxyapatite cement. In vitro cytotoxicity and in vivo biocompatibility of the two CPCs and hydroxyapatite cement were assessed. The setting time of the cements was 5–15 min. CPC-1 and CPC-2 showed significantly higher compressive and diametral strength values compared to hydroxyapatite cement. CPC-1 and CPC-2 were equivalent to Teflon controls after 1 week. CPC-1, CPC-2, and hydroxyapatite cement elicited a moderate to intense inflammatory reaction at 7 days which decreased over time. CPC-1 and CPC-2 show promise for orthopedic applications.

Brushing-induced surface roughness of nickel-, palladium-, and gold-based dental casting alloys

STATEMENT OF PROBLEM Alloys with high nickel content have been increasingly used for dental prostheses. These alloys have excellent hardness, elastic modulus, and strength, yet have high corrosion rates when exposed to chemical or physical forces that are common intraorally. PURPOSE The purpose of the current study was to measure the susceptibility of several types of nickel-based alloys to brushing abrasion relative to gold- and palladium-based alloys. MATERIAL AND METHODS Au-Pt, Au-Pd, Pd-Ag, Ni-Cr, and Ni-Cr-Be dental alloys were brushed with a toothbrush (Oral-B Soft) and toothpaste (Ultrabrite) in a linear brushing machine, then the surface roughness was measured by profilometry (R(a), R(v), R(p)). Specimens (n=4) were brushed for 48 hours in a saline solution (pH 7). The effect of brushing was determined using 2-sided t tests (alpha=.05), and roughness among alloys postbrushing was compared using 1-way ANOVA with Tukey post hoc analyses (alpha=.05). RESULTS All polished alloy surfaces (before brushing) had roughnesses of <or=0.1 microm (R(a)). The Pd-Ag alloy was the most resistant to brushing. The Ni-Cr-Be alloy abraded the most, with a postbrushing surface roughness of >1 microm (R(a)). Ni-Cr alloys without Be had a postbrushing surface roughness of 0.25 microm (R(a)). Postbrushing roughness of all other alloys ranged from 0.1-0.25 microm (R(a)). R(v) and R(p) values behaved similarly to R(a) values for all alloys. CONCLUSIONS Although they have many excellent mechanical properties, Ni-Cr-Be alloys may be prone to degradation from brushing.

Mechanical Modeling of the Human Cricoid Cartilage Using Computer-Aided Design: Applications in Airway Balloon Dilation Research

Objectives: Balloon dilation is generally considered first-line treatment for airway stenosis. Some dilation systems utilize a compliant balloon that can conform around rigid structures. Others use a noncompliant balloon that does not conform, allowing for dilation of more rigid stenoses. We hypothesized that subglottic dilation with a noncompliant balloon increases the likelihood of fracture of the cricoid when compared to a compliant balloon. Methods: Three fresh human cricoid cartilages were placed in a universal testing system to determine the expansile force necessary for cricoid fracture. Using these data, a 3D printer was used to construct a synthetic cricoid model possessing near identical physical characteristics to the human cricoid. Simulated dilation was then performed on the model using a compliant and a noncompliant balloon. Results: Human cricoid fracture occurred at 97.25 N (SD = 8.34), and the synthetic cricoid model fractured at 100.10 N (SD = 7.32). Both balloons fractured the model in every replicate experiment. Mean balloon internal pressure at fracture was 7.67 ATM (SD = 1.21) for the compliant balloon and 11.34 ATM (SD = 1.29) for the noncompliant balloon. Conclusions: These data show that fracture of the cricoid is a valid concern in balloon dilation procedures where the balloon spans the subglottis. Furthermore, the hypothesis was rejected in that the compliant balloon system was at least as likely to fracture the cricoid model as the noncompliant.

Accuracy and precision of as-received implant torque wrenches

STATEMENT OF PROBLEM Previous implant torque evaluation did not determine if the target value fell within a confidence interval for the population mean of the test groups, disallowing determination of whether a specific type of wrench met a standardized goal value. PURPOSE The purpose of this study was to measure both the accuracy and precision of 2 different configurations (spring style and peak break) of as-received implant torque wrenches and compare the measured values to manufacturer-stated values. MATERIAL AND METHODS Ten wrenches from 4 manufacturers, representing a variety of torque-limiting mechanisms and specificity of use (with either a specific brand or universally with any brand of implant product). Drivers were placed into the wrench, and tightening torque was applied to reach predetermined values using a NIST-calibrated digital torque wrench. Five replications of measurement were made for each wrench and averaged to provide a single value from that instrument. The target torque value for each wrench brand was compared to the 95% confidence interval for the true population mean of measured values to see if it fell within the measured range. RESULTS Only 1 wrench brand (Nobel Biocare) demonstrated the target torque value falling within the 95% confidence interval for the true population mean. For others, the targeted torque value fell above the 95% confidence interval (Straumann and Imtec) or below (Salvin Torq). CONCLUSIONS Neither type of torque-limiting mechanism nor designation of a wrench to be used as a dedicated brand-only product or to be used as a universal product on many brands affected the ability of a wrench to deliver torque values where the true population mean included the target torque level.

Effect of Vital Tooth Bleaching on Solubility and Roughness of Dental Cements

STATEMENT OF PROBLEM Vital tooth bleaching may affect properties of dental cements used for fixed prostheses. PURPOSE The purpose of this study was to examine the effect of a combined in-office and at-home bleaching regimen on changes in surface roughness and depth loss of a variety of commercially available dental cements. MATERIAL AND METHODS Five cement classifications were tested: glass ionomer, resin-modified glass ionomer, resin,self-adhesive resin cement, and zinc phosphate. Cements were placed in multiple wells in plastic blocks. After setting,the surface profile of each block was determined, and average roughness and vertical height of cement surface from the specimen holder were recorded. Blocks were water stored (control) or subjected to in-office and at-home bleaching(n=12). Surfaces were rescanned and pre- and posttest parameter changes were calculated. Statistical analysis consisted of Mann-Whitney-Wilcoxon Rank Sum and Student t tests applied to control and bleaching parameterc hanges within the same cements. A family-wise alpha of .05 was maintained by using a Bonferroni-adjusted level of significance preset to .01 per test. RESULTS Zinc phosphate showed the only significant depth increase (P=.004) from bleaching: 0.9 +/- 0.7 microm deeper than the water-control group. Only resin-modified glass ionomer showed a significant (P=.004) increase in roughness from bleaching; values increased by 0.05 +/- 0.03 microm over the water-control group. CONCLUSIONS In-office and at-home bleaching significantly increased depth loss of zinc phosphate and increased resinmodified glass ionomer roughness. However, the absolute values of differences observed, as compared to the wateronly control, were considered to be clinically insignificant. (J Prosthet Dent 2009;102:148-154)

Biomechanical changes from long-term freezer storage and cellular reduction of tracheal scaffoldings.

To determine structural biomechanical changes in tracheal scaffolds resulting from cellular reduction and storage at −80oC.

Heat generation during removal of an abutment screw fragment from dental implants

Statement of problem: Little information is available on the effect of drilling speed on surrounding bone during the removal of an abutment screw fragment. Purpose: The purpose of this in vitro study was to compare, in vitro, the peak temperature increase during the removal of fractured abutment screws from implants placed in a porcine mandible, using drilling speeds of 600 or 2000 rpm. Material and methods: Twenty 4.3×13‐mm dental implants were placed in 10 dissected porcine mandibles: 2 implants per mandible, 1 on each side. Localized defects were created in 20 surface‐treated abutment screws, which were then tightened into each implant until a reproducible fracture occurred in each screw. The fractured screws were removed with a handpiece removal kit and irrigated with room‐temperature water at either 600 or 2000 rpm. The temperature rise at the implant surface was measured at 3 levels with 3 type‐K thermocouples. Repeated measure ANOVA was performed with the Tukey‐Kramer post hoc test for mean pair‐wise comparisons (&agr;=.05 for all tests). Results: Mean peak temperatures were significantly higher at 2000 rpm than at 600 rpm in the mid‐body (P<.001) and crestal (P=.003) regions but not in the apical (P=.225) implant locations. No significant differences in mean peak temperatures were found among the 3 locations using 600 rpm (P=.179). In the 2000‐rpm group, mean peak temperature in the mid‐body area was consistently higher than that in the apical (P<.001) area, and more instances of temperature rise above 56°C and 60°C were observed. In 1 implant from this group, the estimated peak temperature exceeded the bone damage threshold value (50°C for 30 seconds). Conclusions: A drilling speed of 2000 rpm during the removal of abutment screw fragments caused overheating of the outer surface of the implant which may damage the surrounding bone; a speed of 600 rpm appears to be safe.