Margareta Rinastiti

Biofilm Formation on Dental Restorative and Implant Materials

Biomaterials for the restoration of oral function are prone to biofilm formation, affecting oral health. Oral bacteria adhere to hydrophobic and hydrophilic surfaces, but due to fluctuating shear, little biofilm accumulates on hydrophobic surfaces in vivo. More biofilm accumulates on rough than on smooth surfaces. Oral biofilms mostly consist of multiple bacterial strains, but Candida species are found on acrylic dentures. Biofilms on gold and amalgam in vivo are thick and fully covering, but barely viable. Biofilms on ceramics are thin and highly viable. Biofilms on composites and glass-ionomer cements cause surface deterioration, which enhances biofilm formation again. Residual monomer release from composites influences biofilm growth in vitro, but effects in vivo are less pronounced, probably due to the large volume of saliva into which compounds are released and its continuous refreshment. Similarly, conflicting results have been reported on effects of fluoride release from glass-ionomer cements. Finally, biomaterial-associated infection of implants and devices elsewhere in the body is compared with oral biofilm formation. Biomaterial modifications to discourage biofilm formation on implants and devices are critically discussed for possible applications in dentistry. It is concluded that, for dental applications, antimicrobial coatings killing bacteria upon contact are more promising than antimicrobial-releasing coatings.

Immediate repair bond strengths of microhybrid, nanohybrid and nanofilled composites after different surface treatments

OBJECTIVES To evaluate immediate repair bond strengths and failure types of resin composites with and without surface conditioning and characterize the interacting composite surfaces by their surface composition and roughness. METHODS Microhybrid, nanohybrid and nanofilled resin composites were photo-polymerized and assigned to four groups: (1) no conditioning (Control), (2) no conditioning, polymerized against a Mylar strip (Control, with strip), (3) intermediate adhesive resin (IAR) application, and (4) chair-side silica coating, silanization and intermediate resin application (SC). Resin composites, similar as their substrates, were adhered onto the substrates. Shear force was applied to the interface in a universal testing machine and failure types were evaluated under light microscopy. Surface characterization was done by contact angle measurements, X-ray photoelectron spectroscopy, scanning electron and atomic force microscopy. RESULTS Significant effects of the resin composite type and surface conditioning were observed. Conditioning the composites with their IARs does not result in significant improvements in bond strength compared to the control with strip (bond strengths between 14.5 and 20.0 MPa). SC increased the bond strength in all composites except TE by an average 8.9 MPa, while in all composites the surface roughness increased from 7 to 384 microm. Failure types in this group were exclusively cohesive. Physico-chemical modelling of the composite surfaces showed that the surfaces were dominated by the resin matrix, with a major increase in silica-coverage after SC for all composites. CONCLUSION Intermediate adhesive resin conditioning did not improve the composite-to-composite immediate repair strength. Silica coating and silanization followed by its corresponding IAR, strongly increased repair bond strengths and provided exclusively cohesive failures in the substrate in all composites.

Effect of Biofilm on the Repair Bond Strengths of Composites

Composite restorations degrade during wear, but it is unknown how wear affects the composite surface and influences composite-to-composite bonding in minimally invasive repair. Here, it is hypothesized that in vitro exposure of composites to oral biofilm yields clinically relevant degradation of composite surfaces, and its influence on composite-to-composite bonding is determined. Biofilms on composite surfaces in vitro increased their roughness and decreased filler particle exposure, except for a microhybrid composite, similar to effects of clinical wear in palatal appliances. Failure shear stresses after intermediate-adhesive-resin application were significantly lower after aging by in vitro exposure to biofilms, while silica-coating maintained the same failure stress levels as in non-aged composites. Failure modes were predominantly cohesive after silica-coating, while intermediate-adhesive-resin application yielded more adhesive failure. It is concluded that in vitro exposure to oral biofilm is a clinically relevant aging condition, and that silica-coating is to be preferred for the repair of aged composites.

Comparison of shear and microtensile failure stresses in the repair of dental composite restorations

Failure of dental composite restorations frequently occurs. To preserve tooth structure, repair of existing restorations can be done by relayering (composite-to-composite-bonding). This study compares shear and microtensile failure in composite-to-composite-bonding. Disk-shaped and rectangular-blocks of a nanohybrid and nanofilled composite were prepared for shear and microtensile measurements, respectively. Half of all specimens were aged using thermocycling. Non-aged and thermocycled specimens were conditioned by intermediate-adhesive-resin-application (IAR-application) or silica-coating and silanization followed by IAR-application (SC-application). Resin composites, of the same kind as the substrate, were adhered onto the substrates and shear or microtensile forces applied to the interface. Significant differences between shear and microtensile failure stresses, effects of conditioning, aging and composite types were observed. Mean failure shear stresses (7 – 28 MPa) were significantly lower than microtensile ones (32 – 53 MPa), regardless of aging or conditioning, with average standard deviations approaching 50%. The dependability of the bonds, indicated by its Weibull modulus, was similarly low in shear and microtensile modes. Failures after shear were more frequently cohesive than after application of a tensile force, except in thermocycled composites after IAR-application. Clinically, restorations are mainly exposed to shear and shear evaluations are to be preferred over microtensile ones, also since Weibull moduli are similar for both modes. Hence, considering the high percentages of cohesive failure in shear combined with the low Weibull moduli, this study indicates that the least dependable link in composite-to-composite-bonding is the composite itself and not the adhesive interface, with the exception of bonding created after thermocycling by IAR-application.

Biomaterials in Dentistry

Dental materials are used for the replacement of destroyed or lost structures and for the restoration of disturbed functions of the orofacial organ (hard tooth substance, teeth, and soft tissues of the mouth). Among the main challenges in restorative dentistry in Indonesia are the caries, recurrent caries due to the leakage or restoration failure that may lead to infection of the pulp and periodontal tissue. Therefore, it is desirable to develop dental materials having ability to seal the marginal interface between material and tooth structure, bioactivity to promote remineralization and good bonding with tooth structure and antimicrobial capabilities. This chapter describes dental materials in restorative dentistry, the most common dental problems in Indonesia, and the development of local bioactive dental materials by utilizing the diversity of natural resources in Indonesia.

Semi-automatic determination of root canal length in dental X-ray image

In this paper we propose a new approach to determine the length of root canal in dental X-ray image semi-automatically. The approach consists of a sequence of the following procedures: preprocessing procedure using contrast stretching method, segmentation procedure using active shape model to find the area of root canal and thinning procedure to find centerline of the root canal area. The length of the extracted centerline to be the length of root canal. Active shape model able to find root canal area in the image, and the length of root canal can be determined. Hence, semi-automatic determination of root canal length in dental X-ray image is feasible.

Strength and displacement of open cell designs of coronary stent in responding of various inflated pressures

Coronary stent metal-based, either Bare Metal Stent or Drug Eluting Stent types, has been the best method for treatment patient with cardiovascular blood blockage. Although non-metal stent has been introduced with claiming of absorbable characteristic, this metal type is still applicable up to now. Various materials and designs of strut-link are commercially exists. Design a new stent, is not only medical aspect such as anti-thrombosis and restenosis as the main ultimate goal, but also doctor and engineering aspects need to be considered. In engineering point of view, beyond biocompatibility and mechanical properties of material, design of strut and link with closed and open cell play important role to address those needs. This paper simulated how open cell stent structure with diameter of 2mm and the length of 20mm was designed to allow standing on radial pressure of 0.8, 1.6 and 2 MPa generated by inflated balloon that may occur during stent placement. Results of the investigation will be discussed.

Synthesis of hydroxyapatite from local bovine bones for biomedical application

This paper presents the method of obtaining hydroxyapatite from animal (bovine) bones. Bovine hydroxyapatite (BHA) was produced from bovine bone in bulk form by de-fatting process followed by calcination process at temperature of 900°C. The calcined products were characterized using x-ray diffraction (XRD) and Fourier transformed infrared (FT-IR) spectroscopy. The BHA phase are highly crystalline with irregular form of particles (particle size < 45 µm).