Oral Health and Herbal Medicine by Khalid Rehman Hakeem, Waseem Mohammed Abdul, Mohd Muzzammil Hussain, and Syed Shoeb Iqbal Razvi. Basel, Switzerland: Springer Nature; 2019. ISBN: 978-3-030-04335-3. Softcover, 46 pages. $69.99.
The purpose of this book is to provide examples of medicinal plants that have been used traditionally for, and are considered valuable against, dental disease. Not only is it difficult to understand the book’s target audience, but, with four authors, the presentation is uneven and sometimes professionally questionable. A clear and succinct presentation of each topic was needed. Some critical details are missing, glossed over, or referenced rather than clarified in the text. The lack of coordination among authors was evident, since discussions about certain facets, such as dental disease, were found throughout the book rather than being concentrated in one place. Generally, I found the content disappointing, since much of the richness of Middle Eastern and Indian dental ethnobotany was not included, and other examples, seemingly picked at random, lacked a long tradition of use. Moreover, the book should have been copy-edited appropriately, since colloquial use of English by some of the authors is evident rather than the type of English expected in a scientific publication.
A significant omission was the lack of information about the acquisition of normal oral microflora and how changes in the microbiota can occur normally throughout a person’s lifetime. The understanding of this concept, and how the organisms involved could be affected by using traditional plants or extracts and compounds, is pivotal to oral health maintenance. While it was stated that many of these natural products have been valuable for ameliorating dental disease, many details, including relevant clinical studies, were not emphasized or were omitted altogether.
The chapter “Oral Diseases and Their Severity” did not include discussions of a number of oral issues, such as halitosis; infections such as candidiasis (often a predictor of malignancy or AIDS), herpetic gingivostomatitis, aphthous stomatitis, and actinomycosis; other bacterial infections causing cellulitis and osteomyelitis; or systemic infections with oral manifestations. Since many of these conditions were cited in the chapter on herbal dentistry, it would have been logical to describe these topics in this chapter. In addition, descriptions of plaque-associated diseases were incomplete and did not differentiate between those that cause various types of caries or periodontal disease. Also, because the mechanisms of these bacteria can differ, so can their susceptibility to certain compounds found in the herbal remedies used to treat them.
However, the focus on how dental disease and certain odontoperiopathic (periodontal disease-causing) organisms can predispose individuals to cardiovascular disease, stroke, and respiratory disease does have merit. Similarly, it is interesting that the book links diabetes mellitus (and its ability to impair healing capacities) to an increase of periapical lesions (i.e., lesions affecting the apex of a tooth root) that require endodontic interventions. Other noteworthy topics include periodontal disease as a predictor for end-stage kidney disease and dental plaque as a possible nidus of infection for gastric ulcers.
Chapters 4 and 5 include several examples of culinary oils, herbs, and spices that are used traditionally for dental purposes. It would have been valuable to include their ethnobotanical origins and the rationale for their selections. Culinary herbs and spices in fresh or dried forms generally are considered safe when used for food or healing purposes, but their essential oils can cause adverse reactions. This is appropriately discussed for the European herbal remedies that use thyme (Thymus vulgaris, Lamiaceae) and sage (Salvia officinalis, Lamiaceae). However, the text lacks warnings about the allergenic potential of many essential oils used in dentistry, such as tea tree (Melaleuca alternifolia, Myrtaceae) oil, for example.
Chapter 4 (“Traditional Information About Herbal Medicine of Oral Activity”) focuses on several culinary oils that are used in the practice of “oil pulling.” Nowhere in the discussion is India, or perhaps other adjacent countries, mentioned as the source of this practice. In Ayurveda, the use of oils in therapy is commonplace, with the theory that compounds from these medicated oils are absorbed through the skin by massage. While it follows that certain bioactive substances may act in a similar way on the oral mucosa, the theory that these oils “pull” toxins from plaque has not been proven. Throughout the chapter, these oils are referred to only by their common names and lack appropriate binomials to identify their plant sources. Some are mentioned in a cursory way, and those mentioned in more detail, such as sesame (Sesamum indicum, Pedaliaceae) oil, should have been placed in Chapter 5 (“Role of Medicinal Plant Species in Oral Health Sector”). Any additional studies associated with their bioactive components or those that affect odontoperiopathic organisms should have been included. None of the clinical trials to support oil pulling were cited in Table 6.1. The last paragraph of the chapter, which describes Tanzanian plants used for dental purposes, is an outlier and not relevant to the theme of Chapter 4.
Some choices, such as ginger (Zingiber officinale, Zingiberaceae), seem trivial compared to others that were omitted, such as oil of cloves (Syzygium aromaticum, Myrtaceae). Clove oil contains a relatively significant amount of eugenol, which is present in many plants that are prized worldwide for toothache. Moreover, since Listerine® (Johnson & Johnson Inc.; New Brunswick, New Jersey) mouthwash was cited in so many studies in Chapter 6 (“Oral Health Care Products Obtained from Medicinal Plants”), it is surprising that two of its ingredients, eucalyptol from Eucalyptus globulus (Myrtaceae) and methyl salicylate from oil of wintergreen (Gaultheria procumbens, Ericaceae), were not included in Chapter 5.
Research into the mechanistic actions of plants used primarily as foods has led to some of them being used as herbal remedies for medical and dental purposes. This is not explained in the descriptions of either cranberry (Vaccinium macrocarpon, Ericaceae) or green tea (Camellia sinensis, Theaceae). For example, the discovery only a few decades ago that cranberry juice is valuable for the treatment of urinary tract infections has made it a popular Western herbal remedy for this purpose. Additional work followed to determine if cranberry could also affect the adherence and co-aggregating capacities of plaque-forming bacteria. Several studies have indicated that cranberry polyphenols have the ability to prevent the colonization, adhesion, and proteolytic activity of certain periopathic bacterial species and inhibit fibroblast inflammatory responses, but these studies were not cited. Also, the book’s claims that cranberry affects squamous cell carcinoma are based only on in vitro studies.
Clinical observations regarding the regular consumption of green tea and a decrease in the incidence of periodontal disease were not given as the rationale for selection of this non-oxidized form of C. sinensis. A review of references in PubMed would have provided better insights into green tea’s clinical efficacy. For example, studies have demonstrated its ability to sustain oral hygiene and that it is a useful adjunct to scaling and root planing. A mechanistic study, which indicated that green tea polyphenols can enhance gingival keratinocyte integrity by protecting against invasions of certain periopathic species, was not included. There was also no mention of green tea’s high fluoride content, which might contribute to its clinical efficacy.
In Chapters 5 and 6, the rationale for selecting certain medicinal plants was not fully explained, and some binomial identifiers were not complete or correct. Also, information about the plant part and preparation was often lacking. In some instances, therapeutic claims were linked to known bioactive compounds or in vitro antibiotic or mechanistic studies without providing evidence from human clinical trials. The therapeutic claims for evening primrose (Oenothera biennis, Onagraceae) and caraway (Carum carvi, Apiaceae), for example, are supported by rodent studies only
The root of black cohosh was cited by its pharmacopeial name (Rhizoma Cimicifugae racemosae) rather than its binomial (Actaea racemosa, Ranunculaceae). The only purported dental use of black cohosh, to “relieve cramps in the jaw or neck,” was not included. The choice of this plant derived from Native American pharmacopeias is unusual, since in Western herbal medicine it is used primarily for the treatment of hot flashes and other menopausal conditions.
Some important clinical trial information was not cited in Chapter 5, such as for twig or oil extracts of neem (Azadirachta indica, Meliaceae), twig extracts of miswak (Salvadora persica, Salvadoraceae), or mouthwash containing flower extracts of chamomile (Matricaria chamomilla, Asteraceae). All should have been described in more detail and incorporated into Table 6.1. Turmeric (Curcuma longa, Zingiberaceae) root is used traditionally in Ayurveda and traditional Chinese medicine for a wide variety of dental disorders. While turmeric was referenced, clinical trials supporting its value in reducing plaque and gingival indices and as an ingredient as a dental sealant were missing from the discussion.
Other plants/products cited as having value because of their traditional uses for dental conditions in Western Asia, India, and the Middle East still lacked appropriate clinical evaluations. For example, tulsi (Ocimum tenuiflorum, Lamiaceae) has long been used in Ayurveda for a wide variety of conditions, including dental disorders. While found in the references, information about how its leaves are used fresh or powdered in a dentifrice (a paste or powder for cleaning the teeth), and how its antimicrobial and anti-inflammatory nature may be responsible for its capacity to treat gum disorders, is missing in the text.
Chapter 5 cites plant uses under a variety of categories related to their reported efficacies. In some instances, I do not understand why certain plants were put into one category and not another. For example, neem was cited under “Plants Used to Maintain Oral Health” and miswak was cited under “Plants Used in the Treatment of Oral Disease.” Not only are they traditionally used in similar ways, but their dental products also are considered valuable for dental hygiene as well as to ameliorate dental diseases. Their bioactive compounds have been well studied, and clinical evaluations have been made. No references were made to neem’s widespread popularity as a chew stick in India and parts of Africa. I was surprised that the value of miswak was not highlighted by the authors, since, as the prophet Mohammed’s favored chew stick, it is valued in Islamic traditional dental hygiene.
Generally, what often is missing when citing any of these plants is information regarding their incorporation into dental products or details of clinical trials to support their efficacy. Also, I would not have cited bloodroot (Sanguinaria canadensis, Papaveraceae), a native North American plant, since it was not traditionally used for dental purposes and its alkaloids can intercalate with DNA. A mouthwash containing bloodroot has been responsible for inciting leukoplakia and squamous cell carcinoma.
While I appreciate that much effort was made in preparing this book, its value as a reference is limited.
Memory Elvin-Lewis, PhD, is Professor Emerita of Biology at Washington University in St. Louis, Missouri, and a world authority on the use of plants for oral health.