The Salvadora persica tree is considered as the main source of siwak in many countries. It is commonly found in Algeria, Egypt, India, Nigeria, Pakistan, Saudi Arabia, Sri Lanka, Uganda and Zimbabwe (42). With regards to research done on siwak, the same source of siwak is also utilised in most in-vivo and in-vitro studies. Siwak from S.persica tree is the most common use for oral hygiene. The siwak practice started at young age population in countries such as India, Sudan, Tanzania, Saudi Arabia and Yemen (8, 10, 43–46). This early exposure to siwak use explains why the prevalence of siwak use increases in young adult and highest in elderly as its use is likely to have become a habit from a young age and persist till old (47–49).
Our review found that the main reasons of choosing siwak as an oral hygiene tool is likely to be due to religous beliefs (6, 9, 16, 47). In addition, the specific features of siwak in its natural form had been claimed to ease its application on the teeth; specifically its small head may facilitate better access to the posterior teeth. Moreover, the availability of the source of supply which is direct from a tree contributes to its low cost. All these factors promote the use of siwak for oral hygiene care (9). Almost 85% of users reported to feel fresh and whiter teeth after the use of siwak (6). Other users noticed the absence of gum bleeding and improved oral health, and perceived oral health benefit of siwak use, and these factors has influenced them to choose siwak over toothbrush (16).
The clinical benefits of siwak on periodontal health
The oral hygiene and gingival health of siwak users were found to be comparable to tooth brush users (24, 29, 34, 50). Moreover, significant antiplaque and antigingivitis effects were discovered in the randomised controlled clinical trials and analysed in this review (31, 33, 41, 51, 52). Equally important is the finding that significantly greater reductions of plaque and gingivitis scores were observed when siwak was used as an adjunct to the toothbrush (35, 36). These observations indicate that siwak was either equally effective as toothbrush for mechanical plaque removal or in some studies its use was seen to be superior. These positive benefits support the World Health Organisation (WHO) recommendation on the use of siwak as an alternative measure to the toothbrush for oral hygiene care (22).
The mechanical plaque removal is the standard management of periodontitis as for preventive and therapeutic measures. As such, self-performed mechanical plaque removal (SPMPR) is important to improve the periodontal health and prevent primary periodontitis (Needleman et al, 2015). The mechanical effect of siwak seems proven to distrupt the bacterial plaque and improved the periodontal health as shown by the lower gingivitis score, probing pocket depth and fewer sites of pocket ≥ 4mm, found in siwak users (26, 53). However, the effect of siwak on subgingival plaque microbiota was found to be inconsistent.While higher quantities of Aggregatibacter actinomycetemcomitans, Veillonella parvula, Actinomyces israelii, Capnocytophaga gingivalis and Streptococcus intermedius were reported in siwak users (54), A. actinomyctemcomitans quantities were observed to be lower compared to toothbrush users (31). Yet recently Rifaey et al. reported that there was no significant difference of A. actinomycetemcomitans between siwak and toothbrush user (36).
These observations contradict findings from an in-vitro study which recorded benzyl isothiocyanate (BITC) as the major antibacterial compound of S.persica extract that is responsible to inhibit gram negative bacteria, including A. actinomycetemcomitans, Porphyromonas gingivalis and Streptococcus Mutan (55). P. gingivalis was the most sensitive to BITC and essential oil, compared to A. actinomycetemcomitans and Haemophilus influenza (56). Antibacterial activity against gram negative bacteria was highly evidenced in water-based preparation of S.persica extract (57). Furthermore, periodontal pathogens (Streptococcus mutans, Prevotella intermedia & Peptostreptococcus and Candida albicans) were significantly sensitive to both water and alcohol extractions (58). There seems to be a discrepancy in the effects of siwak on the subgingival microbiota between in-vitro and in-vivo study. The reason could be due to unstandardised protocol in preparation of specimen. For instance, there was unmeasured quality of the freshly cut siwak used for everyday toothbrushing in the clinical trials. Instead, the essential oil used in laboratory tests was extracted from the fresh cut of S. persica and standardised to contain the highest concentration of antibacterial compound and produce optimum effects.
The differences in the frequency of siwak practice in the clinical trials may contribute to the inconsistent reports related to the antibacterial effects of siwak (31, 34–36, 41). According to Albabtain et al. (2018), antibacterial compounds in the siwak brushes reduced significantly from baseline, after being used more than once. The reduction of the same antibacterial compounds was also observed in the saliva, and the compound disappeared after ten minutes (56). There were several clinical trials that applied the extended duration of siwak brushing than conventional toothbrush practice and this measure should give more chance of getting the benefit from released chemical compounds (33, 52).
The quantified microbiota plaque in those studies were collected from subgingival areas of the study participants (31, 36, 54). These subgingival areas are naturally formed, when the gingival margin is sealed at the cervical of tooth (cementoenamel junction) through junctional epithelium, creating a narrow space between tooth surface (59). Such anatomical arrangement may limit the mechanical action of siwak and as a result, subgingival plaque remains undisturbed. The architecture of established multispecies community of oral biofilm make them tolerant to antibacterial compound (60), unless an appropriate method, such as by using siwak or any other toothcleaning method is able to remove the subgingival plaque within these areas.
The adverse effect of siwak practice on periodontal health
Most of the reported clinical trials did not describe the details of siwak practice, either concerning the technique of tooth cleaning, the duration or the time taken in using the siwak (31, 33, 35, 36). The lack of information in these studies raises concerns about their reproducibility and may cause any oral health benefits discovered from their research to be deemed as be less meaningful.
Eid and co-workers noted of significant gingival recessions on the labial surface of premolars and central incisors of siwak users (39). In addition, Baeshen and co-workers also found signs of traumatised tissues on the gingiva. The horizontal toothbrushing is common and easiest to apply, and according to Bergström and co-workers, this method is highly associated with gingival recession and abrasion (61). The most common method of siwak use observed among users was vertical and/or horizontal directions (24, 29, 40, 52).
In spite of reductions in plaque, gingivitis and periodontal pocket depth among siwak users, there appears to be more sextants associated with clinical attachment loss (28). In a case study, one patient presented with severe tooth surface loss on buccal and lingual surfaces, as well as generalised recession, but there was absence of any periodontal pocket. Investigations to locate any etiologic factor prior to restorative treatment suggested that siwak practice may be a probable cause. The patient used the average sized siwak in scrubbing motion on all tooth surfaces, horizontal on buccal and vertical on lingual (40). Incorrect method of brushing and hard texture of siwak fibers were suspected as the cause of the gingival recession, tooth abrasion and signs of oral soft tissue trauma in long term siwak users (5). This might explain the higher incidence of gingival recession in populations that use traditional oral hygiene tools such as siwak (23). It is undeniable that hard bristle contributes to the occurrence gingival recession (62). Nevertheless, the most important toothbrushing factors that have been associated with the development and progression of gingival recession are frequency and method of brushing (63).
The frequency of toothbrushing in siwak user was between one to five times per day (24, 29), although siwak use may be expected to be at least five times daily or more, based on Islamic religious advice. Siwak is also reported to be frequently used on special days like Friday and during religious special events (16). The extreme frequency and lengthy oral hygiene practice are secondary influence factors for the development and progression of gingival recession (63). Recently, a survey among a small group of Muslim siwak users while visited a Mosque in Kuala Lumpur, reported that most of method and siwak practice was according to religious advice (7). However, the method of siwak practice by Prophet (saw) was not clearly understood in most of Malaysian population (64). Thus, the instruction on proper method of siwak practice is required with consideration of optimum clinical effectiveness and safety on the oral soft tissues.
Integration of oral hygiene instruction with self-performed mechanical plaque removal is expected to prevent soft tissue trauma and achieve high standard of daily plaque control (65). Appropriate oral hygiene education should include knowledge on proper method of siwak practice for existing siwak users and communities of siwak users from different cultures and beliefs. Even among Asian dental educators, knowledge and awareness towards siwak practice is still lacking and this needs to be addressed if proper use of siwak is to be advocated (66).