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.

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.

Histological evaluation of rabbit gingival wound healing transplanted with human amniotic membrane.

Human amniotic membrane has been used as a material to accelerate wound healing and reconstruct damaged organs. The aim of the present study was to assess histologically human amniotic membrane transplantation on rabbit's gingival wound. Three- to 4-month-old male rabbits were divided into 2 groups, i.e., control (group I) and amniotic membrane-transplanted animals (group II). Buccal gingival wounds were created by a punch-biopsy instrument and covered by a 5-layered human amniotic membrane for group II or left uncovered for group I. Gingival biopsies were taken at days 1, 3, 5, 7 and 10, processed for paraffin sections and stained with haematoxylin-eosin or von Gieson. Thickness of epithelial layer, the number of polymorphonuclear cells (PMN), fibroblasts and new blood vessels as well as density of collagen fibres were assessed. The results showed that the number of fibroblasts and new blood vessels, but not PMN, from group II was higher than that from group I (P < 0.05). Similarly, the epithelial thickness and density of collagen fibres from group II were significantly higher than those from group I (P < 0.05). The results of the present study indicate that amniotic membrane transplantation may induce rapid epithelialization and both granulation tissue and collagen formation but suppress inflammation, suggesting that amniotic membrane transplantation may promote rapid gingival wound healing in rabbits compared to secondary healing.