Biomedical subjects

J Sindel

Publications and source records attributed to J Sindel.

6 recordsLinked to original sources

PubMed1999

Crack formation of all-ceramic crowns dependent on different core build-up and luting materials.

OBJECTIVES: The aim of this in vitro study was to evaluate various core build-up and luting materials regarding their effect on crack formation of all-ceramic crowns. METHODS: Fifty-six freshly extracted sound human third molars were prepared according to a standardized procedure obtaining a circular shoulder of 1.5 mm with all margins located in dentin. Sixty percent of the dentin volume were removed and restored with totally bonded build-up composite resins or resin-modified glass ionomer cements (RMGIC) or compomers. Cast IPS-Empress caps were manufactured and luted with the different materials. For each material group, the volumes of the core build-ups and of the luting cements were determined. The caps were examined for cracks after 1, 3, 6, 9 and 12 months storage in 0.9% saline solution at 37 degrees C. RESULTS: The tested groups revealed no major differences in the percentage of the core build-ups and in the volume of the luting cements. After 12 months only the group with composite resin build-up and luting showed no crack formation. RMGIC/compomer build-up or RMGIC/compomer luting always resulted in cracking of the caps. CONCLUSIONS: Within the limits of this study it can be concluded that the hygroscopic expansion of RMGIC/compomer materials led to failure of all-ceramic crowns, when the materials are used for both core build-up or adhesive bonding.

Acrylates↗

PubMed1998

Evaluation of subsurface damage in CAD/CAM machined dental ceramics.

Commercial ceramics for dental computer aided design/computer aided manufacture (CAD/CAM) restorations suffer from surface chipping defects and microcracking. The influence of CAD/CAM machining of dental materials on the mechanical strength and extension of the damage zone was studied. Two different commercial dental ceramics, a feldspathic porcelain and a glass-ceramic, were CAD/CAM machined according to dental practice. The extension of the damage zone was analysed by a stepwise erosion of the surface, and the biaxial flexural strength was measured. To simulate the adhesive fixing of ceramic inlays, the specimens were sealed using a light-curing monomer. The different machining behaviour is dominated by the microstructure of the investigated materials. Owing to the high amount of glassy phase, the feldspathic porcelain shows extensive microcracking and chipping defects. The extent of the damage zone can be determined as 40-60 microm. Sealing of the surface did not affect the flexural strength of the machined samples. The dominating response to machining of the glass-ceramic is crushing and crumbling with a major contribution of plastic deformation on a microscopic scale. The extent of the damage zone is less than 20 microm. These cracks can be bridged by sealing of the surface, resulting in a substantial increase in strength.

Journal Article↗

PubMed1997

Compomers--a new bracket bonding generation in orthodontics?

Compomers are a new class of materials. With the compomer Dyract Ortho., specifically for bracket bonding, and with Prime & Bond 2.0, a one-component primer for enamel and dentin, DeTrey/Dentsply has developed alternative new materials. The aim of this in vitro study was to test the tensile bonding strength of these materials with different kinds of brackets. Twelve test groups, each with 30 prepared bovine incisors, were formed. Two primers, Prime & Bond 2.0 and PSA, were used. 50% of all teeth were first etched will 36% phosphoric acid. Three types of brackets--metal, ceramic and silan ceramic--were bonded with the compomer Dyract Ortho. For 90 teeth forming a control group, the composite Concise was used. When conditioning the enamel with 36% phosphoric acid, the compomer Dyract Ortho showed a similar tensile bonding strength to the composite Concise. This was not the case if metal brackets were used. Metal brackets had significantly less tensile bonding strength (p < 0.001). The interface of the compomer with the bracket was the main failure site. There was insufficient retention between the compomer and the foil mesh of the bracket base because of the strong consistency of the compomer. Without enamel etching, Dyract Ortho produced an acceptable result only in combination with the primer Prime & Bond 2.0 and silan ceramic brackets. As insufficient data are available to date, the use of compomers in clinical practice cannot yet be recommended.

Animals↗

PubMed1997

Viscous glass-ionomer cements: a new alternative to amalgam in the primary dentition?

Glass-ionomer cements offer advantages in the treatment of the primary dentition. New, colored, highly viscous glass-ionomer cements hold the promise of better abrasion properties. Owing to their high viscosity, their handling characteristics are similar to those of amalgam. Examination of their properties demonstrated increased resistance to abrasion in comparison to amalgam, although no improvement in fatigue or flexural resistance was found. Clinical experience extending over 2.5 years confirmed these results.

Dental Amalgam↗

PubMedDate not supplied

Dentin bond strength and marginal adaptation: direct composite resins vs ceramic inlays.

The aim of this in vitro study was to compare the dentin bond strength and marginal adaptation of directly and indirectly inserted restorations. A conically modified push-out test was designed to consider polymerization shrinkage and facilitate inlay placement. A total of 260 cavities were prepared into disks of freshly extracted human third molars and filled with direct composite resins or with adhesively luted ceramic inlays. Dentin adhesives of the third--(with self-etching primer: ART Bond, Syntac Classic), fourth--(with total etching: Scotchbond Multi-Purpose Plus), and fifth-generation (one-bottle adhesives: Syntac Single Component, Prime & Bond 2.1) were used in combination with one hybrid composite (Tetric) or luting composite (Variolink Low). Control groups did not use an adhesive. Polymerization of the bonding agent was carried out prior to insertion of the filling/inlay or afterwards simultaneously with the composite/luting composite. The thickness of the adhesive layer and luting composite was recorded, and after 7 days of storage and 24 hours of thermocycling (1150 cycles) replicas were made and extrusion testing performed. Fracture modes were determined and replicas were examined regarding marginal adaptation using SEM (X200 magnification). Precuring of the bonding resin increased dentin bond strength independent of the material combination or insertion mode (P < 0.05). In general, third- and fourth-generation dentin adhesives produced better results in bond strength and marginal adaptation than one-bottle systems (P < 0.05). In the third generation, ART Bond achieved significantly higher push-out values than Syntac (P < 0.05), but no better marginal adaptation. Cohesive fractures within the dentin were only observed in the inlay groups with precured resin. Precuring of the bonding resin is an important factor for both direct and indirect restorations. Nevertheless, precuring of the bonding resin prior to insertion of adhesive inlays cannot be recommended clinically, because the 120-micron luting spaces were too large. In simulated cavities, direct composite fillings with precuring achieved bond strengths similar to inlays without precuring. One-bottle adhesive systems performed poorly compared with multi-step adhesives of the third and fourth generation.

Analysis of Variance↗

PubMedDate not supplied

Repair strength of etched vs silica-coated metal-ceramic and all-ceramic restorations.

The purpose of this in vitro study was to examine shear bond strengths of composite resin to metal-exposed porcelain-fused-to-metal (PFM) and all-ceramic restorations after silica coating or etching with 5% hydrofluoric acid (HF). Specimens were fabricated for each of the following groups: two all-ceramic materials [a feldspathic porcelain (Vita Mark II) and a leucite-reinforced glass-ceramic (IPS Empress)], and one noble metal-ceramic (Orplid Keramik I alloy; Vita VMK 68 N felspathic veneer ceramic). These groups were repaired with resin composites after different pretreatment methods. In one metal-ceramic subgroup the surface exhibited a 50% metal and 50% ceramic exposure. In the silica-coating groups, the specimen surfaces were air abraded with silica acid-modified Al2O3 (CoJet Sand) and treated corresponding to the porcelain repair with resin composite. For control groups, the surfaces were etched with 5% HF for 60 seconds and treated in the same way as the silica-coated groups. After 24 hours of storage (distilled water, 37 degrees C) and an additional 24 hours of thermocycling (1150 x 5 degrees C/55 degrees C) the specimens were debonded using a shear bond strength test (n = 15). In all groups the silica coat repair achieved equal or significantly higher bond strengths than did the etching technique (p < 0.05, Mann-Whitney U test). In the metal-exposed group, the mean bond strength increased from 7.3 MPa to 16.3 MPa following the silica-coat repair. Results indicated that silica coating represents a suitable treatment for the intraoral repair of the materials tested in the present study.

Acid Etching, Dental↗