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Halitosis is chronic, endogenous malador that is etiologically classified from type 0 to 5—physiologic, oral, airway, gastroesophageal, bloodborne, and subjective, respectively.1 Halitosis measurement methods should cover each of the three malodor sources: the mouth, nose cavity, and breath.
The diagnostic tests currently used in halitosis examination can be divided into direct and indirect (Figure 1). Direct tests include self-assessment of the odor or other people’s assessment, and the determination of odorous substances by halitometry or gas chromatography. Indirect tests determine the presence of some bacterial species, metabolic products generated by microorganisms in vitro or their enzymes.
Patients become concerned when either they themselves or others detect the odor at a socially unacceptable level. For this reason self-assessment or assessment by other people are prominent among all diagnostic testing.
Halitometers should be used for confirmation of halitosis, comparing similar cases, and monitorizing the therapy effect. This test gives a quantification of the gases but not of the halitosis. Organoleptic examination is highly subjective and has not been standardized. There are many methods and different protocols to examine halitosis; however, which among them is most predictable has not been clearly determined.
Self- or Other People’s Assessments
Asking individual patients about the level of their own halitosis is the simplest way to gauge how much the patient is affected by the condition. However, there is no statistically significant correlation between self-assessment and measurable halitosis levels by objective methods.2,3 This is due to the fact that patients with halitosis may not be aware of the situation, or they become inured to their own malodor over time,4 because olfactory desensitization in objective halitosis patients can cause “false-negative” results in self-assessing halitosis.5,6 It has been observed that psychopathological factors can lead to misdiagnosis (false positive) of halitosis.7
Although there are some conflicting findings in the literature, subjective opinion generally correlated well with objective evaluation of halitosis.8-13 Significant associations between self-reported oral malodor, socio-demographic or medical history, and oral hygiene variables were also found.9 In actuality, self-assessment is the primary diagnostic criterion for halitosis and is the main reason patients seek treatment for the condition. Their initial visit commonly stems from a complaint by another person or their own suspicion. Therefore, despite the general reluctance of people to mention the halitosis of another out of politeness,14 the most descriptive question of the medical history and the most convincing tool to determine the result of a halitosis treatment is self- or other people’s assessment that covers the three sources of malodor. Those patients who self-assess their halitosis are usually at least type 5 halitosis patients.
Studies argue that organoleptic assessments (sniffing the patient’s breath and scoring the level of malodor by an examiner such as a general practitioner, periodontist, or dental hygienist) are regarded as the gold standard for measuring halitosis and are significantly related to volatile sulfur compounds (VSCs)15-17 and amines.18,19 However, volatiles, or odorous gases, that can be detected by the human olfactory system are limited. For instance, the human nose is less sensitive to ammonia,20 though breath that has the smell of ammonia is considered halitosis.14,21 The latter nonstandard preparation and test protocols for organoleptic measurement have been used, but even the scales used for scoring of malodor are often changed.
Before performing organoleptic measurement, antibiotics should be ceased at least 3 weeks prior22; others proscribe them for 4 to 8 weeks.2,23 Some investigators forbid patients to drink, eat, chew, rinse, or smoke for at least 2 hours,24-26 although some extend it to 4 hours, or prohibit odorous foods for 24 or 48 hours before the appointment. Some allow restricted oral hygiene (tooth brushing without using toothpaste) 2 to 3 hours prior to the patient’s appointment, while some prohibit even drinking water for an hour. Some practitioners prefer to examine their patients in the morning, while others favor the afternoon or evening.27 A pre-measurement protocol is not truly standardized thus far.
It is a challenge to ask individuals to fast for hours and not clean their mouth to cause (or exacerbate) halitosis, which is a previously described mechanism for inducing morning breath.1 Even people with no halitosis will have malodor in their mouth under those conditions.
Organoleptic measurement protocols available in the literature also vary. Patients may be asked to exhale either with or without a tube inserted into the mouth,2,23,24 or to count aloud to 10 while their breath is evaluated by the examiner.14 Lips are kept closed for 30 seconds,26 60 seconds,28 2 minutes,27 or 3 minutes,29 after which the oral air is assessed by the examiner from 5 cm to 15 cm,29 5 cm to 10 cm,27 or 10 cm.30,31 Another method is having patients hold their breath for a while before exhaling with their mouth 20 cm from the examiner (a pipette could be used).21
Modified methods of organoleptic assessments have been widely applied and include the following:
• Spoon test—A spoon is sniffed 5 cm away 5 seconds after scraping the dorsum of the tongue.25
• Floss test—A piece of unwaxed floss is sniffed 3 cm away after flossing through the interdental regions of teeth.14
• Salivary odor test—The subject spits out 1 mL to 2 mL of saliva into a glass tube32 or 0.7 mL to 0.8 mL of saliva into a petri dish,33 after which it may or may not be incubated at 37°C for 5 minutes, then evaluated from a distance of 4 cm.34
• Glass rod test—A glass rod (15 cm x 0.5 cm) test consists of sniffing the saliva from a distance of 2.5 cm away after the saliva sample has been inserted and stirred three times.34
These four aforementioned tests are categorized as organoleptic.35 Other such assessments include:
• Wrist-licking test—This consists of sniffing the wrist from a distance 3 cm after licking it and waiting for 524 or 1,014 seconds.
• Tongue-coating test—A 2 cm x 2 cm piece of gauze—some use a scraper, periodontal probe, or dental floss—is applied to the dorso-posterior surface of the tongue and drawn anteriorly for 2 cm to 3 cm, then immediately evaluated.29
• Prosthesis test—If the patient wears a removable denture, the prosthesis odor can be scored.14
• Tonsil test—This involves subjectively assessing the odor of the tonsils.36
It is known that some odorants (eg, indole, methylamine, and cadaverine) do not increase malodor when added to bulk saliva24 because they are resolved in the dental plaque37; however, they become detectable when saliva is dried or agitated.15,38 Some organoleptic tests (eg, floss, spoon, gauze, wrist licking) are often found to be false-positive, even in patients with no pathologic halitosis, so their diagnostic values are questionable.
The severity of the odor sniffed by the examiner is usually numerically scored from less strong to extremely strong. Some investigators use a 3-point,28 4-point,26,34,39 5-point,23,40 6-point,15 or 10-point15 scale; even half-scores are used occasionally. Nonstandardized scaling of organoleptic scoring will obviously cause misinterpretation of findings.
That 50% of patients feel embarrassed or otherwise dislike the testing process1 may also be a disadvantage of organoleptic testing (n = 283). To minimize this issue, individuals can instead be asked to breathe inside a plastic bag, which the examiner sniffs afterwards.21 Sometimes, a privacy screen is used to hide the direct-sniffing contact from the patients, who assume that they have undergone a specific malodor examination instead.23 Some examiners place a non-transparent wall with a hole to separate patients.41 A syringe method is recommended to obtain a higher degree of privacy for the patient.22,42 A questionnaire by the authors asked dental practitioners (n = 151) this question: “Do you smell the breath of your halitosis patients?” A total of 133 practitioners (88%) declined to smell patients’ breath because they found it unpleasant.
Variable factors (eg, age, gender, individual odor memory of examiner, time of day, temperature and humidity of room air, etc.) affect organoleptic scoring, which makes the organoleptic assessment unreliable and, therefore, not reproducible.15,43 Further, assessment is extremely subjective, emotional, instinctive, learnable, intuitive, and is also subject to the socioeconomic background or examiner’s experiences; also, there is not yet international calibration44 and standardization.
Chemical and Enzymatic Tests
Some studies45,46 hypothesized a potential relationship between halitosis and particular bacterial species, but others found no clear association.47 The authors consider merely labeling bacteria as either odorigenic or not to be an oversimplification, given that every bacterium is odorigenic.48,49 Nevertheless, there are tests that colorimetrically indicate oral bacteria or their by-products in the mouth.
Beta-galactosidase test—β-galactosidase is an enzyme that catalyzes the hydrolysis of lactose to monosaccharides. It is only synthesized by lactose-positive bacterial species (eg, Peptostreptococcus productus IIa or Actinomyces denticolens). The β-galactosidase test detects an enzyme that may be related to odorigenic bacteria present in the medium. Although β-galactosidase activity has been correlated with malodor,50 it can be associated with physiologic halitosis, which is not necessarily associated with oral problems,51 nor truly reflects halitosis level.52
Indole test—Indole, ammonia, and pyruvate are the result of the deaminating process of tryptophan by tryptophanase. Indole is methylated to skatole. Each of these components have a bad odor. The indole test exhibits the presence of indole, which is one of the odorous compounds in halitosis,34 but no clear correlation was found between odor concentrations and the indole amounts.38
Ninhydrin test—Low molecular-weight amines and amino-acid levels may provide information on halitosis caused from bacterial putrefaction. The ninhydrin test is a simple, rapid enzymatic test that can provide information on halitosis-related bacterial putrefaction.8 It can be used qualitatively (eg, for chromatographic visualization) or quantitatively (eg, for peptide sequencing). Typically, α-amino acids give a blue-purple product, whereas proline, a secondary amine, gives a yellow-orange product.
Lead acetate test—The lead acetate test is also used to detect sulfurs present in the medium. For this test, saliva taken from a patient is incubated overnight26 or 30 minutes29 in an agar plate containing Pb-acetate (0.02%); afterwards, a black color indicates sulfur content. If there were a method to instantly quantify sulfur content, it would make it possible to more accurately estimate the VSC content of saliva.
BANA test—A hydrolase enzyme of hydrolyzing benzoyl-DL-arginine-naphthylamide (BANA) is present on commercially available test strips. BANA strips turn blue, indicating a positive result, if the three particular bacteria—Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia—are present in the medium with this hydrolase.53,54 The specificity and sensitivity of the BANA test is over 80%, and its predictability for periodontal disease is greater than 83%.55 However, these three bacteria are not the unique oral species that have the BANA hydrolase enzyme. Bacteria identification software,56 using its library, was able to find 37 more bacteria that can hydrolyze arginine, showing the BANA test to be unreliable.
It is important to note that the above chemical and enzymatic tests are used to diagnose only malodor of oral origin by searching for the presence of bacteria or their products, but cannot be used to diagnose nasal or alveolar malodor.
There are other enzymatic methods for diagnosing halitosis that principally use base peptidase enzymes of the three aforementioned bacteria and of some Capnocytophaga strains.57 Other methods utilize colorimetric hydrogen sulfide sensors, engineered both as an optical fiber, capable of measuring reflectance change of an immobilized reagent,58 or as thin reactive films of chromophores.59
A bioelectronic nose, capable of detecting the oxygen consumption induced by an enzymatic reaction with methyl sulfide, has also been developed.60 Detected levels are in the range of 0.2 µg/l to 0.4 µg/l.61
Stress or unsuitable environmental conditions compel bacteria to unpredictable metabolic pathways. Therefore, all of the above chemical and enzymatic test results may vary from ancestral expectation of those bacteria. This is another reason why chemical and enzymatic tests may not be descriptive enough for halitosis diagnosis.
Gas chromatography (GC) is highly sensitive for VSCs but impractical.62 A GC-based portable device (OralChroma™, FIS Inc.) is capable of quantifying sulfur family gases. Other portable halitometers include: Halimeter® (Interscan), Breathtron® (New Cosmos Electric Co., LTD.), the Twin Breasor™ (GC Co.), Probe/Perio (Diamond General Development Corporation), and B/B Checker® (Taiyo).
Some authors63 found 3,481 VOCs in the mouth or alveolar air of healthy subjects, while others64 found 400 to 700. Sulphide detectors cannot cover all of these gases. There is a need for new halitometers to detect sulfur, nitrogen, and organic-based gases (at least H2S, NH3, VOC, H2). There are industrial portable gas detectors capable of detecting more than four gas groups that could potentially be utilized.1 Sensor systems for monitoring the simple gases with a breath test kit (BreathTracker, QuinTron), electronic noses like FF-2A (Shimadzu) and Cyranose® 320 (Sensigent), and a bioelectronic gas sensor to detect sulfur family and trimethyl amine have been developed to measure halitosis.65 Some of them use chemical sensor arrays for the detection of the odorant profile (halitoprint) based on an algorithm,66 which covers many gases.
Halitometers are generally used to detect orally originated malodor. They are only occasionally used for alveolar or nasal malodors, depending on the measurement method used. The halitometers mentioned can detect gases but not halitosis, and should be used only for confirmation, comparing similar cases, and monitoring the therapy of halitosis; they should not be used for diagnostic purposes alone because halitometric readings are meaningless in the absense of a halitosis complaint.
Patients typically consult a healthcare professional for halitosis when the malodor is detected by themselves or they received feedback from others in their social environment. Organoleptic test methods, including directly sniffing oral air or indirectly sniffing a sample, such as floss or a spoon, are subjective and not reproducible. Chemical and enzymatic methods briefly estimate presence of bacteria or their enzymes but do not prove halitosis. Halitometric assessment, especially multigas detecting systems, are very objective and reproducible and can detect odorous gases in a wide spectrum; however, if the patient does not complain about halitosis, then halitometeric readings are of little value since there seems to be no problem. Therefore, halitometers should be used for confirmation of halitosis, comparing similar cases, and monitorizing the therapy, but not for diagnositic purposes alone.
Diagnosing and resolving this condition is important to patients’ self esteem and quality of life. Therefore, it is important to give strong consideration to the patient’s self-assessment, which may include feedback from others in their social environment, rather than solely rely on objective examination methods such as halitometer readings or testing the enzymatic activity of the saliva.
The authors had no disclosures to report.
About the Authors
Murat Aydin, DDS, PhD
Doctor of Philosophy in Microbiology
Halitorium International Halitosis Research Group
Curd M.L. Bollen, DDS, PhD, MSc
Director, Mondcentrum Parimplant
Department of Periodontology USA
BioCore, Richmond, Virginia
Murat Eren Özen, MD
Private Adana Hospital
Halitorium International Halitosis Research Group
Queries to the author regarding this course may be submitted to firstname.lastname@example.org.
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