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Biomedical subjects

R Labella

Publications and source records attributed to R Labella.

At least 19 recordsLinked to original sources
PubMed2001

Clinical wear performance of eight experimental dental composites over three years determined by two measuring methods.

The effect of matrix selection, filler composition, filler silanization, operator variations, and test site (dental clinic) on the wear rate of eight composites were evaluated. The wear was measured on replicas using both a microscopic and a laser scanning measuring method. The average wear rate on contact-free surfaces was 9.2 +/- 4.2 microm/month with the microscopic measurement and 8.5 +/- 3.7 microm/ month with the laser scanner over the 36-month period. The urethane-based composites performed significantly better than those which were bisGMA-based. Restorations placed at one dental clinic showed significantly lower initial wear. There was also a significant difference between the operators that was most pronounced during the first 6 months. The other variable (filler composition and silane treatment) did not affect the wear rate significantly.

Barium Compounds↗
PubMed1999

Polymerization shrinkage and elasticity of flowable composites and filled adhesives.

OBJECTIVES: The magnitude and kinetics of polymerization shrinkage, together with elastic modulus, may be potential predictors of bond failure of adhesive restorations. This study examined these properties in visible-light-cured resins, in particular new flowable composites and filled adhesives. METHODS: Polymerization shrinkage values were obtained by digital video imaging before and after light-curing; shrinkage kinetics were obtained by the "deflecting disk" method and the elastic modulus by analysis of the fundamental period of vibration. RESULTS: Flowable composites generally showed higher shrinkage than traditional non-flowable composites, while more densely filled adhesives presented lower shrinkage than lightly filled or unfilled resins. The elastic moduli of flowable composites were in the low-medium range, whilst the hybrid composites showed the highest values and the microfilled the lowest. More densely filled adhesives were more rigid than lightly filled and unfilled adhesives. The kinetics behavior was material dependent, mainly characterized by the coefficient of near-linear contraction between 10 and 40% of the final shrinkage and the time to reach 75% of the final shrinkage. SIGNIFICANCE: The higher shrinkage of flowable composites over that of hybrids may indicate a potential for higher interfacial stresses. However, their lower rigidity may be a counteracting factor. The microfilled composite showed low shrinkage and low rigidity, a combination that may prove less damaging to the interface. As the kinetics parameters tended to be material specific, no specific class of materials should be seen as more stress inducing until studies determine the relative importance of each examined parameter. The performance of adhesive resins as stress buffers also remains unpredictable.

Analysis of Variance↗
PubMed1999

A long-term evaluation of composite-bonded natural/resin teeth as replacement of lower incisors with terminal periodontitis.

BACKGROUND: In patients with severe peridontitis, lower incisors are prone to terminal breakdown. This study assessed the longevity of composite-bonded resin/natural teeth (reinforced only with a stainless steel mesh) as replacements for periodontally lost lower incisors. METHODS: Besides the longevity of the restoration, the periodontal condition of the abutment teeth, and the general satisfaction of the patient were evaluated retrospectively via a phone interview, in combination with an analysis of the patient's clinical dental file. RESULTS: The cumulative proportion of survival rate of these composite restorations was 80% after 5 years of function. No statistically significant difference was found between the survival distribution of one- and two-pontic bridges (P = 0.66). The abutment teeth demonstrated stable probing depths and a negligible loss in attachment (0.1 mm/year). The satisfaction ratings were also favorable. CONCLUSIONS: The data seem to suggest that composite bonding of 1 or 2 teeth can be considered a semi-permanent rehabilitation for the replacement of 1 or 2 periodontally lost lower incisors.

Adult↗
PubMed1998

Monomethacrylate co-monomers for dental resins.

Polymerisation shrinkage is widely recognised as a major drawback of resin based dental restoratives. Bis-GMA is often employed as the principal dimethacrylate monomer. Due to its high viscosity, Bis-GMA is normally mixed with large proportions of low viscosity glycol dimethacrylates. The purpose of this study was to determine whether the polymerisation shrinkage of Bis-GMA-based resins would be lower if alternative monomethacrylate co-monomers were used in place of conventional dimethacrylate co-monomers as viscosity modifiers. Conventional resins used were ethyleneglycol dimethacrylate and triethyleneglycol dimethacrylate; the alternative monofunctional co-monomers were tetrahydrofurfuryl methacrylate, hydroxypropyl methacrylate and isobornyl methacrylate. Model resins containing 54% mol/mol of co-monomer in Bis-GMA and 1% w/w of benzoyl peroxide as initiator were heat-cured at 70 degrees C for 8 h. Polymerisation shrinkage, degree of conversion and concentration of remaining methacrylate groups were calculated from density changes obtained gravimetrically. Other properties evaluated were Young's modulus, water uptake and viscosity of the monomer mixtures. The Bis-GMA-based resins exhibited lower shrinkage when mixed using the monomethacrylates rather than with conventional glycol dimethacrylates. Among the alternative co-monomers, tetrahydrofurfuryl methacrylate conferred the best balance of all measured properties.

Absorption↗
PubMed1998

Long-term strength of aesthetic restoratives.

Glass-ionomer cements have established an important role in clinical dentistry since their introduction over 20 years ago. More recently, in an attempt to enhance the strength of the material, resin additions have been made to conventional glass-ionomer cements. This study established the long term flexural strength of two hybrid glass-ionomer cements, by use of a bi-axial flexural strength test (Shell test), and compared the values with those obtained for a light curing composite resin and a conventional glass-ionomer cement. The results demonstrated that those materials with a high resin component relying on polymerization as the main method of setting had a greater initial flexural strength than those with little or no resin addition. Those materials where the glass-ionomer acid-base reaction provided a substantial contribution to the setting reaction showed an increase in strength as they matured, whereas a decline in strength with time was observed for those materials where the resin setting reaction predominated.

Acrylic Resins↗
PubMed1996

THFMA in dental monomer systems.

This study investigates the physical properties of a range of dental resins containing up to 30% by weight of tetrahydrofurfuryl methacrylate (THFMA). The principal monomer was 2,2-bis-(4(2-hydroxy-3-methacryloyloxypropoxy)-phenyl)-propane (bis-GMA) or 1,6-bis-(methacryloxy-2-ethoxycarbony lamino)-2,4,4-trimethyl-hexane (UDMA). Heat-cured resins were tested for Young's modulus, flexural strength, refractive index, polymerization shrinkage and degree of conversion. The results indicated that THFMA has negligible effects on the mechanical properties of bis-GMA and UDMA and on the refractive index of UDMA, whilst the other measured properties present a strong relationship with the concentration of the additive. The dental relevance of the results is discussed and it is concluded that there is scope for further research on the use of THFMA as a comonomer in resin-based materials for dental applications.

Acrylic Resins↗
PubMed1994

Novel hydroxyapatite-based dental composites.

Newly designed composite resins for dental applications have been studied. The matrix phases were based on 2,2 bis-4(2-hydroxy-3-methacryloyloxypropoxy)phenyl propane and a urethane dimethacrylate. Tetrahydrofurfuryl methacrylate was added as a diluent to both dimethacrylates in a proportion of 30 wt%. Heat-cured composite resins were obtained with filler weight fractions of 60% and 67%. After surface treating hydroxyapatite powder with a silane coupling agent, filler contents of 60%, 67% and 80% were employed. These materials were then evaluated for Young's modulus, flexural strength, diametral tensile strength and Vickers hardness. With the exception of Young's modulus, all mechanical properties of the tested materials were significantly improved when a silanized hydroxyapatite filler had been used.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1992

Novel acrylic resins for dental applications.

A heat-cured resin based on a copolymer of bis-phenol-A glycidyl methacrylate (bis-GMA) and tetrahydrofurfuryl methacrylate (THFM) was investigated. Workable pastes were made by adding 90/10 w/w bis-GMA/THFM copolymer powder to a 70/30 w/w monomer of the same composition. The organic filler content was 60-64% w/w. Young's modulus, flexural strength, impact strength, hardness, water absorption and desorption, linear thermal expansion, polymerization shrinkage and glass transition temperature were determined. The materials studied showed high elastic modulus, hardness and glass transition temperature. A relatively low linear thermal expansion was obtained but poor impact strength and low flexural strength, indicating brittleness. Acceptable values were obtained for water absorption.

Acrylic Resins↗
PubMedDate not supplied

[Proposed use of natural teeth for management of a prosthetic case].

Authors describe the case of a periodontopathic patient having seriously involved lower incisors. They used a splinting system consisting of a lingual metal bar using close healthy teeth as an anchor, and using previously extracted teeth of the patient to get a good aesthetical, psychological and functional result.

Dental Abutments↗
PubMedDate not supplied

[Water absorption by denture base resins].

In a review of the international literature about water absorption of denture base resins any effect on the physical properties of these polymers has been considered. The authors discuss the possibilities of controlling the final results on denture base function.

Absorption↗
PubMedDate not supplied

[Water absorption by composite resins].

A literature review about water absorption in dental composites has led to a number of hypotheses made for the variables affecting the experimental behaviour. It follows a discussion about the possible advantages and disadvantages of the fenomenon.

Absorption↗