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Biomedical subjects

S Rengo

Publications and source records attributed to S Rengo.

At least 19 recordsLinked to original sources
PubMed1999

Debonding of adhesively restored deep Class II MOD restorations after functional loading.

PURPOSE: To assess debonding due to functional loading at the cervical dentin margins of deep Class II MOD restorations prepared with a variety of adhesive restoratives in endodontically-treated teeth. MATERIALS AND METHODS: MOD preparations and endodontic treatment were carried out on extracted sound maxillary premolars. The cavities were restored with seven material combinations: Three different resin-based composites (RBC) (Z100, Herculite XRV or Clearfil RP with their respective bonding systems); two bonded amalgam combinations (Valiant with Superbond D or with Panavia 21) and two sandwich combinations [the RBC Tetric with the polyacid-modified RBC (compomer) Compoglass or Z100 with the resin-modified glass ionomer Fuji II LC]. For each group, half of the samples were exposed to mechanical functional loading and the other half served as control. Imperfect bond formation and debonding due to loading was determined by dye penetration. In addition, the dye penetration scores were correlated with the cusp fracture strengths of similarly prepared restorations of a previous study. RESULTS: After functional loading, the RBC in combination with hybridizing dentin bonding agents showed better preservation of marginal integrity than the sandwich restorations, which in turn performed better than the amalgam restorations (P < 0.05). Debonding correlated with reduction in fracture resistance. Under the conditions of this study, debonding of adhesive MOD restorations by functional loading can best be prevented by using RBC in combination with hybridizing dentin-bonding systems.

Analysis of Variance↗
PubMed1998

Inhibition by glass-ionomer cements of protein synthesis by human gingival fibroblasts in continuous culture.

The effects of several glass-ionomer cements (Baseline and Chem Fil of De Trey; Ketac Fil and Ketac Bond of ESPE; Vitrebond and Vitremer of 3 M) on the protein synthesis of cultured gingival fibroblasts were studied. The presence of cements in the culture medium inhibited protein synthesis, although the relative effectiveness varied significantly. The cements tested have been ranked in three groups, group A (Chem Fil and Ketac Fil), group B (Ketac Bond and Baseline) and group C (Vitrebond and Vitremer), showing 50, 75 and 100% reduction in protein synthesis, respectively. Incubation of cells with medium previously conditioned by Baseline and Ketac Fil caused only transient inhibition of protein synthesis followed by almost complete recovery. This recovery was not observed when the medium was conditioned with Vitrebond. A characterization of the factors determining the inhibitory effect of one cement in each group was attempted. The cements, irrespective of the type, produced small but reproducible decreases in the pH of the medium but released fluoride ions to a different extent. Both changes in the pH of the medium and in the fluoride concentration inhibited protein synthesis by cultured gingival fibroblasts. The different action of cements can be explained, at least in part, by a differing release of fluoride ions.

Aluminum Silicates↗
PubMed1997

Fracture resistance of endodontically-treated premolars adhesively restored.

PURPOSE: To investigate the cusp fracture resistance of endodontically treated teeth, adhesively restored with various materials. MATERIALS AND METHODS: MOD preparations and endodontic treatment was carried out on extracted sound maxillary premolars. The cavities were restored with the amalgam Valiant in combination with Superbond or Panavia bonding, the resin composites Z100, Herculite XRV or Clearfil RP with their respective bonding systems, Z100 in combination with the glass ionomers Ketac Fil, Fuji II and Vitremer, and Tetric in combination with Compoglass. Fracture resistance was measured by axial loading in an Instron testing machine. RESULTS: One of the restorative methods, resin composites in combination with dentin bonding systems in beveled MOD preparations rendered the tooth a cusp fracture resistance which did not differ significantly from that of sound natural teeth. Two other restorative methods, bonded amalgam and a sandwich of glass ionomer cement/resin composite in beveled preparations were significantly weaker in resisting cusp fracture than sound natural teeth, but still significantly stronger than the unrestored tooth with a MOD preparation. It was statistically apparent that several adhesive restorative systems could satisfactorily be used to restore teeth after endodontic therapy.

Analysis of Variance↗
PubMed1994

Photopolymerization of dental composite matrices.

The kinetic behaviour of dental composite is traditionally studied, considering only the isothermal behaviour, whereas a fast and highly non-isothermal bulk polymerization is expected as a consequence of the significant heat developed due to the exothermic nature of the polymerization reaction. In this paper the photopolymerization kinetics of a commercial dental composite activated by visible light are analysed by differential scanning calorimetry. This technique is applied to determine the degree of reaction and the glass transition temperature of thin layers of the composite matrix, at different isothermal cure temperatures. A phenomenological kinetic model is then integrated with an energy balance in order to analyse the cure behaviour of thicker composite layers. The full model results indicate that non-isothermal cure conditions may be achieved, obtaining higher values for the glass transition temperature and the degree of reaction.

Calorimetry, Differential Scanning↗
PubMed1990

[Ultrasound in endodontics: S.E.M. verification].

After giving a brief illustration of the complex morphology of the root canal system, the Authors discuss the use of ultrasound in Endodontics. Following a critical evaluation of the literature and of the mechanisms of ultrasonic instruments, they illustrate their experience through a wide selection of S.E.M. photographs of teeth treated in vitro with sodium hypochlorite at various concentrations and for different lengths of time. They demonstrate the synergistic action between ultrasound and irrigation solutions, and conclude that the best results are with 2.5% hypochlorite for 1 minute.

Dental Pulp Cavity↗
PubMed1989

[Cardiotoxicity of local anesthetics: dynamic electrocardiogram study].

Twenty-two cardiopathic patients (mean age 54.4 +/- 9.9 years) underwent dynamic electrocardiography during tooth extraction under local anesthesia (mepivacaine hydrochloride 2% plus adrenalin 1:200.000). Heart rate (p less than 0.001), systolic and diastolic blood pressure (p less than 0.001) significantly increased during tooth extraction returning to values near to basal level in the recovery period. No patients showed significant changes in ST segment. One patient with chronic atrial fibrillation presented an increase in ventricular rate (180 beats/min) and appearance of premature ventricular beats, spontaneously regressed. In conclusion, in cardiopathic patients dental operations by local anesthesia with vessel constriction it is possible, provided estimated clinical conditions of patients.

Adult↗
PubMed1988

[Finishing and polishing of an anterior hybrid composite--Herculite XR. SEM evaluation].

A study was a conducted in order to discover finishing and polishing effectiveness, by particular operative method, on HERCULITE XR, sub-micron hybrid composite. The study was realized on 35 incisors extracted for periodontal reasons, treated with "labial veneers" according to Jordan (1987), divided into 7 groups each containing 5, and finished with different technique. After treatment, the teeth were subjected to SEM examination. The results showed that the high speed finishing technique by twelve and thirty fluted carbide burs and final polishing with Command Ultrafine Luster Paste produces the smoothest and flatest surface of HERCULITE XR. Furthermore the HERCULITE XR/enamel margin doesn't appear fractured or disrupted. Since finishing and polishing rotary techniques in accordance with the characteristic of each type of composite resins.

Composite Resins↗