Nobio has developed dental restorative materials with long term antibacterial properties in order to fight recurrent decay/caries around restorations. These composites with incorporated non-leaching antibacterial agents might overcome the vicious circle of newly developed cavities around freshly placed fillings.

The investigators will ask lower partial denture wearers to allow them to place a "gap model" with the Nobio-composite and enamel slab in one denture flange. In the other denture flange a gap model with a standard composite will be placed as control. In the laboratory the investigators will test with established methods for demineralization/caries prevention in the test and control enamel slabs, respectively.

As a major issue in dentistry, it has been stated that two-thirds of all restorative dentistry involves the replacement of failed restorations. Secondary caries indicates a lesion developing at the margins of an existing restoration and is the major reason for replacement of amalgam and composite resin restorations in operative dentistry.

In research the use of experimental intra-oral caries models dealing with caries prevention has increased. The most realistic experimental model is the in vivo model that uses living teeth, followed by the in situ model using specimens with natural surfaces held in the mouth during the experimental period. In situ models have the potential to study both fundamental aspects of the caries process as well as more applied research problems in caries prevention in human subjects without actually causing caries in the natural dentition.

To simulate a failed interface between a tooth and a restoration, a gap can be formed between an enamel slab and the restoration prior to a cariogenic challenge. The "gap-model" will be inserted for instance into the denture flanges, and the cariogenic challenge occurs inside the mouth during the wear period..

Nobio has developed dental restorative materials with long term antibacterial properties in order to fight recurrent decay around restorations. These composites with incorporated non-leaching antibacterial agents might overcome the vicious circle of newly developed cavities around freshly placed fillings. The ongoing caries activity due to bacteria around the filling may be interrupted by quaternary ammonium silica dioxide (QASi) particles incorporated in the test composite at 1.2% (by weight). These particles are members of the Nobio Antimicrobial Particle (NAP) family (Nobio, Israel). QASi are synthesized to form a high concentration of antimicrobial groups that are covalently-bound onto a carrier core, such as silica. The resulting micro or nano-sized QASi particles are mixed with other fillers of the dental composite material, during manufacturing. Following in situ placement and light-initiated polymerization, QASi particles are permanently retained in the final dental restoration. Laboratory studies have shown that the quaternary ammonium silica particles are potent antibacterial agents, do not leach out in contrast to other antimicrobials or caries preventive active substances, inhibit the breakdown of the composite, and maintain antibacterial activity over time.

The study is an in situ study. Subjects, wearing lower partial dentures with acrylic flanges on both sides of the mouth will be recruited. On each side of the denture an enamel slab will be placed next to a composite, separated by a tiny gap. On one side of the denture the composite will be Nobio's antibacterial composite, on the other side a regular composite (a Nobio composite w/o particles or another commercial composite will serve as control material. Enamel slab and composite will be recessed into the flange, allowing microbial plaque to accumulate on top of it and especially in the gap.

After wearing the dentures for four weeks with the slabs, decalcification - ΔZ mineral loss - in the enamel slabs adjacent to the gap will be determined by cross-section microhardness testing in the laboratory. Average ΔZ mineral loss will be calculated for the Nobio group and the control group, and difference will be tested for statistical significance.

Inclusion Criteria:

• aged between 18 and 80 years,
• have at least six natural teeth remaining and have a recent history of dental caries
• wearing lower partial denture (with replaced teeth on both sides of the mouth)
• willing to wear their denture during the night
• are in good health, of either gender
• are in good current oral health with no active caries or periodontal disease (but with a history of caries)
• have an understanding of the study
• have saliva flow within the normal range (stimulated saliva flow rate of greater than 0.7 ml/minute)
• no antibiotics for the last three months
• willing to comply with all study procedures and protocols,
• residing in San Francisco or other nearby locales with community water fluoridation (to eliminate water fluoridation as a potential confounding variable)
• able to give written consent themselves
• must be able to read and understand English
• willing to sign the "Authorization for Release of Personal Health Information and Use of Personally Unidentified Study Data for Research" form; data will only be used for research

Exclusion Criteria:

• subjects who have less than 6 natural teeth remaining
• subjects who have used a 5,000 ppm fluoride toothpaste in the last 6 months
• subjects who have used Chlorhexidine or any other antimicrobials (cetylpyridinium etc.) in the last 6 months
• show evidence of extremely poor oral hygiene
• subjects suffering from systemic diseases, significant past or medical history with conditions that may affect oral health or oral flora (i.e. diabetes, HIV, heart conditions that require antibiotic prophylaxis)
• taking medications that may affect the oral flora or salivary flow (e.g. antibiotic use in the past three months, drugs associated with dry mouth / xerostomia)
• other conditions that may decrease the likelihood of adhering to study protocol
• in-office fluoride treatment within the last three months
• subjects who will leave the area and are unable to complete the study

25 participants contributed 25 lower partial dentures. Each partial denture had two flanges - one side for the Nobio unit, the other side as the control composite unit

Four weeks study period, while wearing the composite inside the denture flanges

Subjects are not aware, which side of the denture will harbor the gap model with the Nobio composite and which side harbors the traditional composite.

Laboratory microhardness measurements will be conducted while keeping the operator blind.