Table 2.

Inclusion and exclusion criteria

Criterion	Rationale for inclusion and exclusion
Population: Adult	An adult is person who has reached the age of maturity or adulthood [67]. The use of siwak as an alternative oral hygiene tool among adult who are physically and mentally fit, is considered independent behaviour, compared to children. The adults wearing fixed orthodontic appliance are excluded to minimise the effects of plaque-retentive factors and ease toothbrushing [21]
Concept: Effect of siwak on periodontal health Method and practice of siwak	The World Health Organization (WHO) recognises siwak as an alternate oral hygiene, but more research is needed [22]. It is derived from a common plant and comes in different diameter and length, as well as having distinct characteristics from toothbrushes [3]. Thus, the method and siwak practice may differ from the toothbrush and may have favourable and/or adverse effect on oral health, particularly periodontium. According to Shah et al. [23] traditional oral hygiene practises can harm the soft and hard tissues of the mouth
Context: Clinical benefit and adverse effect of siwak
Study type: Human studies and based on original data analysis	Studies that involved human population provide original data and comprehensive evidence on the clinical effects of intervention, including siwak
Date of publication: From 01 January 1990 to 24 June 2021	Many ancient people were known to use siwak, and the clinical benefit and adverse effect were recognised [3, 4]. Apart from the perceived oral hygiene benefit of siwak, religious beliefs are the primary reason of existing population continues to use it [6, 16]. As a result, the clinical effect of siwak should be observed and reported in academic journals between 1990 to 2021, to secure the recent and dated publication within past 30 years