Evaluation of surface roughness of resin veneers finished and polished by different techniques

Four different resin veneers and composite resins were evaluated for surface roughness after finishing and polishing. The resins were prepared against celluloid strip and finished then polished by four different methods imitating the clinical methods. The surface roughness of these resins was evaluated using surface profile tester. The results of this study showed resin veneers prepared against celluloid strip has the highly polished surface. Finishing and polishing veneers in the oral cavity should be done using white flexible disk or rubber abrasive point with polishing gel to get highly polished surface comparable to that obtained using celluloid strip

Scanning electron microscopic study of acid and laser etched enamel and dentin

Specimens of human dental enamel and dentin were topically etched with two acid etching solutions including 37% phosphoric acid and 10% maleic acid. While another group of specimens were exposed to laser irradiation for etching at different exposure times. All the specimens were studied using SEM for evaluation and comparison. The results showed that 10% maleic acid produce mild etching to both enamel and dentin and it can be used as a universal etchant. Application of Nd: YAG laser to enamel caused etching with some cracking and voids to the depth comparable to that achieved with phosphoric acid etching. Lasing dentine causes melting of dentine and closure of exposed dentinal tubules while three minutes laser etching exposed dentinal tubules again

Evaluation of some properties of acid etching composite cements

A study was conducted to evaluate the strength properties and bond strength ofseven composite adhesive resin cements to enamel, chromium cobalt and nickelchromium. The cements were bonded to etched enamel, sandblasted chromiumcobalt and nickel chromium. Panavia Ex cement showed a highly significantbond strength than the six other cements. The coefficient of correlationbetween both strength properties and bond strength was 0.78. It was concludedthat Panavia Ex cement was superior for strength properties and bonding toetched enamel, chromium cobalt, and nickel chromium and this work suggestsusing this type of cement for cementing Maryland bridges

Creep of composite resins

Creep characteristics of 16 composite resins having three different fillersystems were evaluated under two aging conditions [1 day and 7 days]. Theresults showed a big variation among the creep values obtained. Microfill andhybrid composite have a high creep compared to the fine particles composite. The filler percentage did not correlate with the creep values obtained for fineparticles and hybrid composite, but it had a high negative correlation valuewith microfill composite

Wear of anterior and posterior composites under accelerated aging

The two-body abrasion, compressive strength, and single-pass sliding parameters of three anterior and four posterior composites were determined. Single-pass samples were aged for 900 hours in a weathering chamber. Compressive strength was not correlated with either two-body abrasion or single-pass sliding parameters. The quarters-filled composites had the lowest values of two-body abrasion. The light-cured composites were among the composites with high values of two-body abrasion and track width before aging

Effect of setting expansion of some dental stones upon the accuracy of poured dies

This investigation has shown that the setting expansion of three dental stones when measured according to the ADA Specification No.25, was lower than that expansion when determined by a dial gauge method. The values of setting expansion from this test and percentage deviation of the diameter of extra coronal stone dies from the base diameter of the st and ard preparation were identical

Effect of cross head speed on the tensile strength of some composite resins

Diametral tensile strength was measured for four composite resins under different tensile load speed. The results showed that crushing speed have a statistically significant effect on the tensile strength. A constant slow speed is very important in determining the tensile strength and it should not be more than 0.05 cm/minute. The four materials tested have different values depending on the type and content of filler

study of the characteristic retentive behaviour of the cements

Cement film thickness, mechanical properties, retention and adhesive properties of some cements were evaluated. The cement film thickness has a high correlation with the effective maximum grain size of the cements used. There was no correlation between the strength properties tested and the retention of the cements. Glass ionomer and polycarboxylate cements showed a greater increase in retention after one month

Effect of confined surface on the dimensional changes of high copper amalgam

Dimensional changes for two high copper amalgams were measured for free samples and restricted samples having smooth and rough inner surfaces. The samples were prepared according to ADA specification No. 1. The experiment was conducted at 50C in air for maximum period 30 weeks. The amalgam tested had high expansions for unrestricted cylinders [82 un/cm for Dispersallcy and 134 um/cm for Optaloy11]. While the expansion in the restricted glass-tube showed very low values for Dispersallcy 3 um/cm and 30 um/cm for Optaloy11. There was no significant difference between the samples prepared in a glass tubes having smooth and tough surfaces. This present study, which is principally concerned with the dimensional changes of two high copper amalgam in a confined glass tubes having smooth and tough surfaces has arrived to the following conclusions: 1] There are wide differences between the expansion of the dental amalgam as a free sample and in a restricted sample stimulating the cavity in the tooth regardless to the surface conditions. 2] For restricted samples, Dispersalloy showed about 2.1-3.6 Um/cm. 3] Most of the amalgam expansions for bathe conditions recorded in the first 10 weeks of the experiment. A phase changes of gamma I towards Beta I in dental amalgam restorations has resulted in dimensional changes. As observed clinically, these dimensional changes may be partly cause some of the extrusion of amalgam restorations. For this reason, the dimensional stability as amalgam is an important aspect for clinical behavior. A phase change of gamma I to beta I in the silver-tin mercury system occurs slowly at body temperature [37C] and more rapidly at 50 to 60C [7,2].Most of the works were done to study the dimensional changes that occurs during hardening for the first 24 hours [3-8]. As well as more after 40 weeks at 42. 37. 60C in air for the samples [3-8].The present work was conducted to study the effect of confined surface on the dimensional stability of two high - copper amalgam alloys

in vitro study: the effect of coca-butter application on the surface property of some glass ionomer cements

The purpose of the present work was to study the effect of coca butter application over the cement against the surface property for three brands of glass ionomer cement. The effect of water storage on the surface property of the cement was also studied. Scratch resistance test for cement surface was performed using a vicker Hardness apparatus under a load of 200 gm. And a speed of 0.5 m/min. Width of the scratch was measured using a stereo-microscope. The results showed that application of coca butter on cement surface had no effect for increasing scratch resistance. There was no significant difference among all the brands of cement tested for the scratch width. For all the brands investigated, the width of the scratch was not varied after four month of water storage

comparative evaluation of the retention of two different posts and their effect on the strength property of the roots

A total of eighty freshly extracted human maxillary central incisors and canines were used for post hole preparation after been filled with gutta percha by the ordinary methods. Roots were divided into two groups. The first group was subjected to retention analysis, while the second to mechanical stress one. Each group of teeth was subdivided according to the post design into two subgroups; the first received threaded posts, ten of diameter 2 and ten of diameter 6. The second subgroup received casted posts, ten of diameter 2 and ten of diameter 6. The difference in post diameter had no significant effect on the retention of threaded posts while it played an important role in the casted ones. When both post designs subjected to a 450 angle load, fracture of the roots at their cervical one third occurred