Biomedical subjects

A Sahafi

Publications and source records attributed to A Sahafi.

4 recordsLinked to original sources

PubMed2005

Resistance to cyclic loading of teeth restored with posts.

This in vitro study evaluated the effect of presence of post, presence of core, and of shape, type, and surface treatment of posts on resistance to cyclic loading of crowned human teeth. For all teeth, crowns designed without ferrule were cast in sterling silver and luted with resin cement (Panavia F). Each tooth underwent cyclic loading of 600 N at two loads per second until failure. Teeth that had only been crowned showed significantly higher resistance to cyclic loading than teeth with cores or with post and cores. No significant differences were found between teeth restored with cores only or with post and cores, irrespective of surface-treatment of the posts. Teeth restored with parallel-sided cast post (ParaPost XP) and cores showed significantly higher resistance to cyclic loading than teeth with either tapered cast posts or untreated prefabricated posts of titanium alloy (ParaPost XH) or glass fiber composite (ParaPost Fiber White). No significant difference was found between teeth restored with parallel-sided cast post and cores and teeth restored with untreated prefabricated posts of zirconia (Cerapost). Surface treatment of posts significantly increased the resistance to cyclic loading compared with untreated posts. When posts are used, surface treatment is recommended.

Alloys↗

PubMed2001

Soft-start polymerization and marginal gap formation in vitro.

PURPOSE: To determine the effect of soft-start polymerization of resin-based composites on the marginal gap formation in dentin cavities. MATERIALS AND METHODS: Cylindrical cavities were prepared in dentin in extracted human molars. The cavities were distributed into 8 groups. The teeth in groups 1-4 were treated with Scotchbond Multi-Purpose and restored with Z100, and the teeth in groups 5-8 were treated with OptiBond FL and restored with Herculite XRV. The restorations were light-cured for 40 s by four different curing modes. The marginal gap formation was measured in a light microscope after a 20 min water-storage, and the wall-to-wall contraction was calculated as the widest gap in percent of the cavity diameter. RESULTS: Soft-start light curing did not influence wall-to-wall contraction in dentin cavities. OptiBond FL and Herculite XRV showed less wall-to-wall contraction than did Scotchbond Multi-Purpose and Z100. CLINICAL SIGNIFICANCE: The soft-start polymerization procedures studied did not improve the marginal adaptation of two resin composites bonded to dentin cavities compared with conventional polymerization.

Analysis of Variance↗

PubMed2001

Effect of pulse-delay curing on in vitro wall-to-wall contraction of composite in dentin cavity preparations.

PURPOSE: To determine the effect of pulse-delay curing of resin composite on marginal gap formation in dentin cavity preparations. MATERIALS AND METHODS: Cylindrical cavities were prepared in extracted human molar dentin and were distributed into 8 groups (A-H). The cavity preparations were treated with a dentin-bonding agent (Prime & Bond NT) and filled with a light-cured resin composite (Z100). The restorations were irradiated initially for 1, 2 or 3 seconds at a power density of 425 mW/cm2. Following water storage for varying time intervals, the restorations were re-exposed for 10 seconds at 750 mW/cm2. Marginal gap formation was measured by light microscopy after 20 minutes of water-storage, and the wall-to-wall contraction was calculated as the widest gap in percent of cavity diameter. RESULTS: Pulse-delay curing in combination with a waiting time of at least 1 minute between exposures reduced wall-to-wall contraction in dentin cavities compared to continuous-cure control.

Analysis of Variance↗

PubMed2000

Characterization of resin composites polymerized with plasma arc curing units.

OBJECTIVES: Newly developed curing units (plasma arc curing units) operate at relatively high intensity and are claimed to result in optimum properties of resin composites in a short cure time. This study was conducted to determine a number of characteristics of resin composites polymerized by plasma arc curing units. METHODS: The investigated polymerization characteristics were quantity of remaining double bonds, depth of polymerization, flexural strength and modulus, and wall-to-wall polymerization contraction. The investigated plasma arc curing units were Apollo 95E and 1000 PAC. The conventional curing unit XL 3000 was used as baseline. RESULTS: Irradiation with Apollo 95E resulted in a higher quantity of remaining double bonds than did XL 3000, whereas the results obtained with 1000 PAC depended on the resin composite. The depth of cure with the plasma arc units was equal to or less than that obtained with the conventional unit, depending on the resin composite. The flexural strength did not depend on the curing unit. The flexural modulus resulting from curing with Apollo 95E was less than that resulting from curing with XL 3000 in 3 out of 4 comparisons. The wall-to-wall polymerization contraction was equal to or less with the plasma arc units than with the conventional unit. SIGNIFICANCE: Plasma arc curing units make it possible to polymerize resin composite in much shorter times than conventional curing units. However, the polymerization characteristics associated with the units may be less than optimal.

Composite Resins↗