Periodontal disease is an infection that causes inflammation of the tooth supporting structures, which results in the destruction of the periodontal ligament and alveolar bone, and eventually, tooth loss. The aetiology of the disease is oral biofilm. Therefore, the regular mechanical removal of biofilm, among others, is necessary to prevent and stop the disease progression. Biofilm and biofilm retentive calculus are removed via periodontal debridement. Subgingival debridement is an important procedure that is initially performed in the non-surgical periodontal therapy phase. According to the first European Workshop on Periodontology, subgingival debridement involves gently instrumenting subgingivally to disrupt and/or remove the biofilm. Various techniques are involved in subgingival debridement, with hand instruments and ultrasonic or sonic instruments being the most common, while modalities like air polishing are gaining momentum.

Mechanical periodontal debridement using hand instruments like curettes, sickles, hoes or files, and power driven instruments such as sonic or ultrasonic scalers, is generally known as root surface debridement (RSD). This modality is considered to be the gold standard of periodontal therapy. The usage of hand instruments has been advocated for their efficiency and the fact that it allows tactile sensation and operator control. However, various drawbacks from these instruments have been noted. Hand instruments and scalers are both technique sensitive, time consuming, and may cause irreversible hard tissue damage when used regularly. Besides, anatomical variations such as grooves, concavities and enamel pearls as well as deep pockets and furcation involvement, can influence debridement quality. Since periodontal therapy is performed regularly, being time efficient, acceptable to patient, and causing minimal tissue damage are important determinants. As such, treatment that causes minimal abrasion to root surface while being highly effective in biofilm removal would be a preferable choice.

One such treatment is air polishing. Air polishing was introduced in 1945 for the purpose of cavity preparation. Over time, its use expanded to periodontal debridement. Stain and biofilm are removed by the abrasive "slurry" which is formed by mixing together pressurised air, a jet of water and a stream of small particles. Sodium bicarbonate was the only abrasive powder available from the late 1970s until 2004. It is non-toxic and water soluble, with a mean size of up to 250μm. It has been shown to be safe and efficient to be

used on intact enamel surfaces. However, due to its abrasiveness, it could not be used on demineralised enamel surfaces. A study showed that regardless of parameters such as working time, powder and water setting, working distance, and angulation of the handpiece, substantial damage to the root occurs from sodium bicarbonate, concluding that it is contraindicated for use in exposed root surfaces. In order to overcome this problem, glycine based powders were then produced. In the in vitro study showed that glycine powder proved to have low abrasiveness towards cementum and dentine, while being efficient at plaque removal. The powder had a mean particle size of 45μm - 60μm, and was 80% less abrasive compared to sodium bicarbonate. More recently, erythritol powders have been used in air polishing. Erythritol is a sugar alcohol that is non-toxic, chemically neutral, and water soluble, and has been widely used as an artificial sweetener and food additive. Due to comparable physical properties to glycine and chemical characteristics allowing binding of antiseptic substances, it has been suggested for subgingival biofilm removal. Moreover, a recent study has shown erythritol to have an inhibitory effect on some periodontal bacteria, including P. gingivalis.

Advancements in air polishing devices have also occurred, mainly involving a disposable nozzle design to access the periodontal pocket directly, thus allowing the abrasive slurry to be delivered into moderate-to-deep periodontal pockets. The nozzle has a thickness of 0.7mm, which is within the diameter range of most periodontal probes, thereby allowing it to be inserted to the base of the pocket with minimal force. Besides, the new design resulted in a drop of pressure of the jet spray by 1 bar, thus reducing the risk of emphysema and allowing the nozzle to be used subgingivally.

The usage of air polishing in supportive periodontal therapy (SPT) has been extensively studied. However, minimal studies on the adjunctive use of air polishing in the management of active periodontitis have been conducted. One such study studied demonstrated that the effect of adjunctive subgingival glycerine powder air polishing (GPAP) in chronic periodontitis. It was a single blinded, 6 month study using the split mouth design with one of the outcomes being the reduction in the volume of gingival crevicular fluid (GCF). RSD followed by flushing of pockets with water was carried out in the control group, while RSD was followed by GPAP in the test group. Both groups showed significant reduction in periodontal parameters, and no significant differences between the two groups were seen. The test group showed significant reduction in GCF volume compared to control at 3 months, although at 6 months, no difference between the two groups was noted. Since GCF volume is an objective measure of subclinical inflammation, this study suggested that GPAP as an adjunct to RSD may improve periodontal inflammation in the short term.

Another study by Park et al. aimed to identify the clinical and microbiological effects of adjunctive subgingival erythritol powder air polishing (EPAP) in initial therapy. It was a 3 month study using a split mouth design in which treatment for the test group involved RSD and subgingival EPAP, whereas only RSD was done in the control group. Both groups showed significant changes in clinical parameters, and no difference was seen between the groups. Total bacterial count between baseline and 1 month after treatment decreased in both groups, but the decrease was significant in the test group. Between 1 month and 3 months after treatment, total bacterial count increased in both groups, but the increase was more significant in the control group. It appears that supplementing RSD with EPAP may have an effect on the total bacterial count. EPAP was also noted to have an anti-microbial effect, since the P. gingivalis count after 1 month treatment was significantly lower in the test group. This study concluded that both modes of treatment were clinically and microbiologically effective for initial therapy.

However, both studies were conducted using a split mouth design. Such a design has a risk of crossover effects, thus limiting intra-individual comparisons as local therapy can have systemic effects that are able to influence outcomes in different sites in the same individual. Therefore, there is a need to conduct a study using the parallel mouth design to identify the effects of adjunctive use of air polishing in periodontitis patient. Nevertheless, with new and more expensive technology, the question of cost effectiveness is not uncommon. Resources in health care such as time, money, and materials are often limited. This necessitates health economic evaluations to be carried out. One such evaluation is a cost effectiveness analysis that identifies the relationship between incremental resource consumption and outcome gain for various interventions. No such study has been conducted with regards to the cost effectiveness of air polishing. Therefore, the aim of this study is to investigate the adjunctive use of EPAP in NSPT and determine its cost effectiveness in the management of periodontitis.