The purpose of this study is to determine whether a novel material of S-PRG fillers containing in a daily-used resin denture base and their capability of fluoride release and recharge to elevate the salivary fluoride level and prevent dental caries in Thai middle-aged patients between 35-60 years of age who wear the resin denture.

The study design is a 1.5-year, double blind randomized clinical trial, with 150 volunteers between 35-60 years of age wearing palatal removable partial denture containing with/without S-PRG fillers. This study will be performed in 3 local government hospitals located around Bangkok metropolitan, Ministry of Public Health, Thailand. The subjects will be assigned to the control group; resin denture base containing without S-PRG fillers and the experimental group; resin denture base containing 20% by weight of S-PRG fillers. Two parameters we can measure are; (1) Salivary fluoride level, accessed at different time point; on day 1, 14, 15 and at 3, 12 months after wearing the denture, and (2) Caries incidence using ICDAS-II, taken at 18 months.

Regarding an agreement with the participating dentists and dental assistants in the hospitals, patients in the waiting list of removable partial denture are screened according to our eligible criteria. If they meet eligibility criteria, a complete description is follow:

"If you agree to participate in the study, at today's visit we will ask you some questions about your medical and dental health such as what medication that you are presently taking, and whether you use fluoride supplement except for toothpaste. You do not have to answer every question. The dentist will do a brief examination of your mouth looking to see if you have any decay. You will not be able to participate in this study if you have obvious untreated tooth decay.

Following completion of the questionnaire and examination, we will do a simple test on your saliva. We will collect stimulated saliva by having you to chew a piece of wax for 5 minutes. You will spit all the saliva formed during those 5 minutes into a cup. We will measure the volume of the saliva produced. You will have to have a normal flow rate to participate.

Collecting this information, doing the saliva test, and completing the dental examination will take about 30 minutes of today's appointment. You may refuse to participate in any of the saliva test or answer any question or item in the questionnaire. If that is the case, you will not qualify for the study. If you do qualify and agree to take part, the dentist will take a mold of your mouth to make an upper resin denture to replace your missing teeth for you to wear. This is a routine dental procedure. Some subjects may gag while the mold is being taken for the denture. The dentist has methods to help you control the gagging reflex.

Depending on which group you are assigned, your resin denture will be made from standard material or the standard material containing some new type of biological material. This new material we are testing is being used in the formulation of dental product as filling materials.

At the next appointment, approximately two week later, you will come in to have the denture fitted for you. Slight discomfort may occur at the gum margin where the denture can pinch. The plate will be adjusted to relieve any pinching. On rare occasions, allergy to the resin denture base may occur. We will stop your participation in the study if you have an allergy to the resin denture.

We will give you the resin denture and need you to wear it all day excluding when you sleep at night. You must take it out to brush your teeth. You may clean the denture with water and the same toothbrush that you use to brush your teeth before keeping the denture in the denture storage box. We do not want you to use anything else on the denture except material we supply. You will receive a box for keeping your denture, toothbrush and toothpaste to brush your teeth at home.

At the first 14 days once you receive the denture, we do want you to soak your denture in a denture storage box containing tap water every night when you sleep. After that we will supply you a tube of fluoride gel for storing the denture instead of tap water. We will ask you to apply the gel (approximately 1 cm of length) to the denture and spread out totally on both side of the denture before keeping in the denture box during sleeping every night for 1.5 years.

After wearing the denture, you will be asked to return to the clinic for check-up and recall. We will collect your saliva while wearing the denture periodically for a total of six times within one year according to our schedule for the analysis of the fluoride level.

At 1.5 years, you will be asked to return to the clinic and the dentist will do a dental examination for follow-up. That will conclude your participation in the study.

We will assess the salivary fluoride at different time point during 1 year. The fluoride level of saliva will show us the capability of the new material on the fluoride release and recharge. The follow up period will be extended for 6 more months. The caries information collected at 1.5 years will show us the incidence of new caries. All procedures will be done at the dental clinic of the hospital. The subjects will be identified by a number assigned only. The principle investigator and the project coordinator will have to access to the code which will remain locked at all time. The saliva collected from the subjects will be discarded immediately after complete analysis.

The sample size assessment is considered based on the long term outcome, caries incidence, and the short term outcome, salivary fluoride concentration, of the study. The optimal sample size to address both outcomes in the study and allow for a 20% drop out rate would be 75 subjects per group (150 total) to provide sufficient statistical power to detect the difference in mean caries incidence between the control and the intervention group.

Collected data will be entered into a computer database and analyzed with STATA software version 12 for Windows. The statistical significance level will be set at α = 0.05.

The analysis plan for salivary fluoride level at each phase of follow up is based on two-sample t test and linear regression adjusting for confounders (age, number of remaining teeth).

Data analysis for caries incidence will be recorded per surface using ICDAS-II severity scores at 1.5 years. The caries outcome is defined as score 1 to 6 and 1 to 2 for root caries. Two-sample t test or linear regression with adjusting for age will be performed to assess the different between the control and the intervention group in the mean number of new surface caries (dmfs) ± standard deviations at 1.5 years follow-up examination.

Inclusion Criteria:

• Compliance: Understands and is willing, able and likely to comply with all study procedures and restrictions
• General Health: Good general health with no clinically significant and/or relevant abnormalities of medical history or oral examination that could interfere with subject safety during the study period
• Salivary Flow: Have a salivary flow rate in the range of normal values (unstimulated whole saliva flow rate > 0.15 ml/minute; gum base stimulated saliva flow rate ≥ 1 ml/minute)
• Oral condition: a) At least 6 teeth remaining natural upper teeth in good condition, including at least 2 posterior teeth. b) Adequate remaining natural or artificial lower teeth for proper function. c) Do not use fluoride supplement excluding toothpaste. and d) Present of caries risk or filling at least 1 surface.

Exclusion Criteria:

• Exhibited signs of xerostomia
• Serious oral pathology (e.g. extensive dental caries, periodontal disease)
• Pregnant or lactating women
• Frequent mouthwash or fluoride supplement use
• Unable to have basic self-care ability (including oral hygiene practice)
• History of allergies, metabolic diseases such as diabetes, or other medical conditions that could interfere with the study.
• Be caries free in oral cavity

The study was followed for 1.5 years. This period of time collected for adverse event data.

Adverse event were assessed and monitored during the study. However, no adverse event was found.