Influence of Silver Diamine Fluoride Application on the Restorative Treatment for Root Caries
Phase: NA
Conditions: Root Caries
Sponsor: The University of Hong Kong

 
 
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Study protocol, Version 2, 6 Dec 2022 
 
Title:   
Influence of silver diamine fluoride application on the restorative treatment for root caries 
 
Abstract: 
The number and percentage of older adults in most countries around the world are rapidly 
increasing. Hong Kong is facing the same challenge where the pace of population ageing is 
continuing and will be ramping up with the number of older adults (aged 65 or above) projected 
to nearly double in the coming 20 years. The increasing ageing population amplifies the 
society’s needs for dental care. With longer life-expectancy and more remaining natural teeth, 
older adults are at high risk to suffer from dental problems. As reported by the Department of 
Health, about one-fourth of non-institutionalised older adults in Hong Kong had root surface 
decay, and most of the decay remained untreated. Decayed roots, if left untreated, can cause 
pain, infection, tooth fracture or loss, which in turn will affect chewing ability, diet, and oral 
health‐related quality of life. Thus, it is needed to find effective ways to handle prevalent dental 
problems of older adults.  
 
At present, conventional approach of 'drilling and filling' is the most commonly used method 
to treat decayed dental roots. However, recent studies show that the conventional restorative 
approach is not a satisfactory treatment method due to its high annual failure rate. Therefore, 
in this study, aiming to improve the outcomes of treating root decay, we propose a novel 
approach to treat decayed roots by conjunctive use of silver diamine fluoride (SDF) solution 
and conventional restorative treatment. 
 
First of all, the proposed novel approach may potentially improve longevity of the fillings in 
decayed lesions. Further, with prior SDF application, the chance of secondary caries associated 
with the fillings may be reduced. As application of SDF can arrest and harden the decayed root 
lesions, it is expected that there will be less amount of soft carious tooth tissues to be removed 
for placement of fillings. Thus, this can preserve natural dental tissues from removing. Besides, 
the proposed method may have additional benefits for patients other than an improved clinical 
outcome (longevity of fillings). For instance, older adults who are medically compromised, 
require additional support and cannot tolerate invasive treatment (drilling and filling) at the 
moment, or have too many decayed roots to be treated at a single dental visit, can be applied 
with SDF first to control the progress of tooth decay. The fillings can be placed later when the 
situation allows. Besides, placement of fillings in SDF treated lesions can reshape and repair 
the decayed tooth to have improved appearance, which may improve patient-based subjective 
evaluations, e.g. satisfaction and oral health-related quality of life. 
 
Therefore, this study will generate valuable clinical evidence regarding the proposed novel 
approach in treating decayed dental roots. The treatment outcomes will be assessed both 
objectively (clinical indicators) and subjectively (patient-based outcomes). With the jointly 
comprehensive evaluations, the findings of the study will guide dental clinicians to make smart 
decisions when treating root decay for older adults. 
 
 
 
 

 
 
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Introduction 
An increasing ageing population with amplified dental treatment needs 
According to the Census and Statistics Department’s latest report, the pace of population ageing 
in Hong Kong is continuing and will be ramping up with the number of older adults (aged 65 
or above) projected to nearly double in the coming 20 years. The population of older adults in 
2019 was 1.3 million and it is projected to be 2.5 million (33% of the total population) in 2039, 
i.e. about one in every three people will be an older adult 1. Living longer and retaining more 
natural teeth, older adults are at potentially higher risks to have more dental problems. As 
reported by the Department of Health, about one-fourth of non-institutionalised older adults in 
Hong Kong had decayed tooth root surfaces, and most of these decayed lesions remained 
untreated 2. Decayed roots (root caries), if left untreated, can cause pain, infection, tooth 
fracture or loss, which in turn will affect chewing ability, diet, and oral health‐related quality 
of life (OHRQoL). In fact, the increasing ageing population amplifies the need to carry out 
effective dental treatments for older adults, and this is considered a great challenge faced by 
the Hong Kong society as reported by the Secretary for Food and Health 3.  
 
High effectiveness of silver diamine fluoride solution application in arresting root caries 
Our previous studies demonstrate that application of silver diamine fluoride (SDF) solution is 
highly effective in stopping and arresting the progress of decay in dental roots of older adults 
4, 5, and this finding is consistent with a study conducted overseas 6. Systematic reviews confirm 
the effectiveness of SDF in arresting root caries for older adults 7, 8. The American Dental 
Association (ADA) has published a guideline based on the up-to-date evidence to support the 
use of SDF for managing tooth decay 9. As a non-invasive procedure, application of SDF is 
simple, quick, painless and non-aerosol generated, the advantages of which makes it favoured, 
in particular, during the period of Covid-19 pandemic 10. However, an obvious drawback of 
SDF application is the black stain on the arrested caries lesions 4, which may raise aesthetic 
concern. 
 
Current restorative treatment for root caries remains controversial 
Conventional approach of 'drilling and filling' is still the most commonly used method to treat 
root caries lesions. However, a recent systematic review found that irrespective of various 
restorative materials used, high annual failure rates of restorations in root caries lesions were 
reported in majority of the clinical studies 11. Besides, insufficient data is available to clearly 
rule out if any difference with regard to restoration longevity between different restorative 
techniques, i.e. conventional restorative treatment vs. atraumatic restorative treatment 12. Since 
there is insufficient evidence to recommend any specific material or technique for routine use 
in placement of restorations in root caries lesions, it is necessary to further research in this area 
to seek for a novel approach to improve outcomes of restoring root caries lesions. 
 
Combination of SDF application and restorative treatment for root caries 
Potential improvement regarding clinical outcomes 
We propose a novel restorative approach to treat root caries lesions by combining SDF 
application and conventional restorative treatment. First, the antimicrobial effect of SDF can 
prevent caries formation around cavity margins. Laboratory studies showed that prior SDF 
application could increase resistance of restorations to secondary caries 13-15. The conjunctive 

 
 
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use of SDF may reduce the chance of new caries associated with restorations as well as the 
failure rate of restorations. Second, as the application of SDF can arrest and harden the caries 
lesions 16, it is expected that there will be less amount of soft carious tooth tissues to be removed 
for placement of restorations. This embodies the concept of the “minimal invasive dentistry” 
to remove and replace as little tissue loss as possible to preserve natural dental tissues 17. Third, 
as shown in laboratory studies, prior SDF application can increase the chemical bonding 
strength between glass ionomer cement (GIC) and dentine 18, 19, which implies potential to 
increase the success rate of restorations. Laboratory-based results show promise in conjunctive 
use of SDF application prior to restorative treatment, yet no clinical trial has been conducted 
to evaluate this novel restorative approach. 
 
Additional benefits  
Other than potential improvements in clinical outcomes, the conjunctive use of SDF application 
and restorative treatment may have additional benefits for patients. Older adults who are 
medically compromised, require additional support and cannot tolerate invasive treatment at 
the moment, or have too many decayed roots to be restored at a single dental visit, can receive 
SDF treatment first to control the progress of tooth decay. Dental restorations can be placed 
later when the situation allows. Besides, placement of restorations in SDF treated lesions can 
cover the black stain caused by SDF, which may improve patient-based subjective evaluations, 
e.g. satisfaction and oral health-related quality of life. 
 
Therefore, a well-designed randomized controlled trial (RCT) is needed to provide high-quality 
clinical evidence regarding the conjunctive use of SDF application and restorative approach in 
treating root caries of older adults. 
 
 
Aims and Hypotheses 
Based on our previous studies, we hypothesize that SDF application prior to placement of 
dental restorations is a novel approach to improve the outcomes of treating root caries lesions. 
 
The aim of the proposed study is to investigate the influence of prior SDF application on the 
restorative treatment for root caries. 
 
The objectives of the study are to 
1) Compare the success rate of restorations placed in root caries lesions that have prior SDF 
application or that of restorations placed without prior SDF application; 
2) Compare patient-based subjective evaluations on the two different approaches 
mentioned-above in treating root caries lesions. 
 
Hypotheses to be tested: 
1) Prior SDF application increases the success rate of restorations placed in root caries; 
2) Patient-based subjective evaluations of the treatment outcomes are better when SDF is 
applied to the root caries lesions prior to restoring the lesions. 
 
 

 
 
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Material and Method 
This study is designed as a two-arm randomized controlled clinical trial with 24-month follow-
up. This clinical trial will be conducted in accordance with the ethical principles that have the 
origin in the Declaration of Helsinki, and that are consistent with Good Clinical Practice (GCP) 
and the applicable regulatory requirements of ICH-GCP. 
 
Recruitment of participant 
Community-dwelling older adults attending community centres in different districts of Hong 
Kong will be invited to join the study. It is planned to recruit 184 older adults who have 
untreated decayed dental roots. An invitation letter with information on the purpose and 
procedures of the study will be sent to community-dwelling older adults through the 
community centre they are attending. Free dental examination will be offered, and older adults 
who have decay in their exposed dental roots will be invited to join the study. Written consent 
form will be obtained before any clinical procedures. Screening will be conducted in the 
community centre by an experienced dentist using a ball-ended CPI probe and a dental mirror 
attached to an intra-oral LED light source. Exposed dental root surfaces will be examined by 
the visual-tactile method. No radiograph will be taken during the dental screening. 
 
Inclusion criteria 
Older adults (aged 60 or above) with at least one untreated decayed dental root will be included 
in the study. 
 
Exclusion criteria  
Older adults who do not have self-care ability for basic daily activities, such as tooth brushing, 
will be excluded. Teeth with severe decay, for example those with signs of pulpal pathology, 
an abscess or discoloured, indicating for endodontic treatment will be excluded. Teeth that are 
indicated for extraction due to any reason, such as advanced periodontal disease, will also be 
excluded. 
 
Sample size calculation 
Sample size calculation is based on the primary outcome measure of this study which is the 
success rate of restorations placed in root caries lesions. Success of a restoration is defined as 
the restoration staying in place and without major defects or dental caries associated with it. 
According to a recent systematic review, the anticipated two-year success rate of restorations 
placed in root caries is 65% 12, and the success rate of the restoration placed in root caries with 
prior SDF treatment is expected to be 80%. With a statistical significance level set at 5%, a 
power of 80%, and an enrolment ratio of 1:1, the calculated minimal number of restorations 
required in each group is 138 (https://clincalc.com/stats/samplesize.aspx). Since more than one 
caries lesion may be found in a participant, the clustering effect on sample size is taken into 
consideration. It is anticipated that the number of decayed roots included per person is 2. A 
design effect of 1.15, assuming an intra-class correlation roh of 0.1, is used in the sample size 
calculation 20, 21. Thus, the minimal sample size needs to be multiplied by 1.15 to become 159. 
Furthermore, to compensate for a possible drop-out rate of 15%, the initial sample size is 
increased to 183 restorations per group. Therefore, 92 participants in each group will be 
recruited at baseline and the total number of enrolled participants will be 184. 
 

 
 
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Randomization 
The included older adults with decayed dental roots will first be divided into two strata: 
 
1) with a small amount of caries (high caries risk), which is defined as the presence of less 
than 4 untreated caries teeth; and 
2) with a large amount of caries (extremely high caries risk), which means 4 or more 
untreated caries teeth. 
 
The participants will then be allocated by a block randomization method (block size=6) into 
the following two study groups. An independent statistician who is not involved in the trial will 
generate a random-number table. The enrolled participants will be allocated into two study 
groups following the random-number table. 
 
 Group 1 (SDF group), the participants will be applied with SDF solution about 1 month 
before receiving dental restoration; 
 Group 2 (control group), the participants will be applied with a placebo (tonic water to 
mimic the bitter taste of SDF) about 1 month before receiving dental restoration. 
 
Intervention 
SDF and placebo application 
A micro-brush will be used to apply a 38% SDF solution (Saforide, Toyo Seiyaku Kasei Co., 
Osaka, Japan) on decayed root surfaces of participants in the SDF group after the dental 
screening in the community centre. The decayed root surfaces in control group participants will 
be applied with tonic water as placebo following the same procedures as in the SDF group. All 
participants will be instructed not to eat or drink for half an hour after the application. 
 
Dental restoration placement  
Around one month after the application of SDF/placebo, participants will have their decayed 
root lesions restored by dentists following the standard restorative procedures in the Prince 
Phillip Dental Hospital (PPDH). Soft carious tooth tissues, if any, will be removed by means 
of hand instruments and dental burs until the surface of the cavity is hard on probing. Local 
anaesthesia injection will be given on demand from the participant and recorded. After removal 
of carious dental tissues, the cavity will be cleaned with water from a 3-in-1 syringe and then 
dried. The prepared cavity will be restored with an adhesive dental material, light-cured glass 
ionomer cement (Fuji II LC, GC Corporation, Tokyo, Japan). The dentists who place the dental 
restorations will not be involved in the SDF/placebo application. 
 
Allocation concealment 
Based on the group allocation, a dentist will apply either SDF or placebo onto root caries 
lesions of the study participants. A dental assistant will follow the random-number table to dip 
dental micro-applicators in either SDF or tonic water, and then pass the micro-applicators to 
the dentist, so as to achieve the allocation concealment. The participants and the dentists who 
are responsible to carry out interventions are blinded to the group allocation. 
 
Data collection 
Clinical outcome 

 
 
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Eligible participants will receive a detail clinical examination before the application of 
SDF/placebo and also right before the placement of dental restorations. In the clinical 
examination, the International Caries Detection and Assessment System (ICDAS II) will be 
used to record the status of the root surfaces 23. The diagnosis of root surface status will be 
mainly made through careful visual inspection and aided by the use of a CPI probe, if indicated. 
Besides, other clinical parameters including the participant’s caries experience, dental hygiene, 
and prothesis status will be examined. The decayed, missing and filled tooth (DMFT) score of 
the participant will be recorded according to the World Health Organization (WHO) criteria 24. 
The presence of visible plaque on each of the exposed root surfaces, four surfaces per tooth, 
will be recorded without using any disclosing agent. The proportion of root surfaces with 
visible plaque will be calculated by dividing the number of exposed root surfaces with plaque 
by the total number of exposed root surfaces examined. Whether the participant wears a denture 
as well as the tooth surfaces in close proximity (within 3 mm) to a denture component will be 
recorded. 
 
Follow-up examinations will be carried out at the 6-, 12-, 18- and 24-month follow-ups by 
calibrated examiners who are not involved in the placement of restorations. The presence and 
status of the restoration will be assessed according to the criteria that are commonly used in 
other studies 22. The coding system is shown as following: 
 
0 = restoration present, no caries, no marginal defects or wear  
1 = restoration present, no active caries, slight defects or wear not greater than 0.5 mm 
2 = restoration present, marginal defects greater than 0.5 mm 
3 = restoration present, wear greater than 0.5 mm 
4 = restoration present, active caries found associated with the filling 
5 = restoration missing, no active caries, surface hard to gentle probing 
6 = restoration missing, active caries found, surface soft to probing allowing penetration of the 
tip of a blunt probe 
7 = restoration was replaced by a new restoration 
8 = tooth with signs of pulpal pathology or extracted due to caries 
9 = tooth missing due to any other reasons  
 
The study restorations will be assessed as success or failure. Codes 0 and 1 are considered as 
success of the restoration, and no further treatment is necessary. On the contrary, the restoration 
is regarded as failure when it has major defects (code 2 or 3), is associated active caries (code 
4), is missing (code 5 or 6), is replaced by a new restoration (code 7), and the tooth has signs 
of pulpal pathology or has been extracted due to caries (code 8).  
 
Duplicate examinations on about 10% of the participants will be carried out to assess examiner 
agreement regarding the status of restorations. 
 
Patient-based subjective evaluation 
Interviews using a structured questionnaire will be conducted to assess the patient-based 
subjective outcomes. The questionnaire consists of multiple sections: (i) participant’s 
sociodemographic background; (ii) satisfaction with their dental health conditions as well as 
the dental treatment process; and (iii) the OHRQoL. The Chinese version of General Oral 

 
 
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Health Assessment Index (GOHAI) will be adopted as a tool to assess the OHRQoL of the 
participants 25. It contains 12 questions covering three domains: physical function, pain and 
discomfort, and psychosocial function. The total GOHAI score is generated by adding up the 
score of each response to the 12 questions, and the total score ranges from 12 to 60. A higher 
score indicates a better perceived OHRQoL. 
 
The interviews will be conducted at baseline before and after the placement of restorations, the 
6-month follow-up and the 24-month follow-up by a trained interviewer. Before the interview, 
the participants will not be informed of their dental conditions to avoid possible bias. With data 
collected in the follow-up interviews, influence of the proposed novel restorative approach on 
patient perceived subjective outcomes can be analysed. 
 
Data processing and analysis  
Clinical charting forms and questionnaires will first be checked for completeness and obvious 
errors. The collected data will be entered into computers. Double entry will be carried out to 
detect any errors of entered data and the corrected data will be used for statistical analysis. 
 
Basic data analysis will be carried out by using the statistical software SPSS for Windows. Chi-
square test and t-test will be performed to assess the comparability between the two study 
groups regarding the demographic background, baseline dental caries experience and 
OHRQoL.  
 
Clinical outcomes of dental restorations at each follow-up examination will be classified as 
either success or failure according to the criteria mentioned above. A multi-level survival 
analysis for interval-censored data will be adopted. The first level is the restoration while the 
second level is the study participant. This analysis will account for the correlation (clustering) 
between observations of multiple restorations placed in the same participant. The analyses will 
be carried out using the statistical software SAS for Windows (SAS Institute Inc., Cary, N.C., 
USA). The level of statistical significance for all tests will be set at 0.05. McNemar's test and 
paired t-test will be adopted to assess the change in patient-based subjective outcomes 
including satisfaction with the treatment and OHRQoL. 
 
 
 
 
 

 
 
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