The use of phonetics is one of several guides that can be used by the restorative dentist during the assessment and restoration of structurally compromised teeth. To accomplish this, an understanding of the basic mechanisms involved in producing sounds during speech can facilitate the application of these techniques during patient management. This review discusses the basic principles of speech sounds production. This is followed by a discussion of the clinical applications of the different phonetic tests in the assessment and management of dentate and partially dentate patients with structurally compromised dentitions.
CPD/Clinical Relevance: Phonetic tests are among the many guides used in the assessment and management of dentate patients with structurally compromised dentitions. The clinician should be familiar with the basic principles and applications of these tests to be able to assess and manage patients in daily practice.
Article
Emad S Elsubeihi
The execution of active restorative care for dentate patients with a compromised dentition as a result of acquired or congenital disease processes should be based on appropriate comprehensive treatment plans geared towards addressing patients' needs. This requires the thorough gathering of information through detailed history-taking and clinical examination supplemented with essential investigations where required. Further procedures, such as a diagnostic wax-up and direct or indirect mock-up, may also be required to finalize the treatment plan and obtain patients' consent before embarking on irreversible restorative procedures. During restorative procedures, fabrication of provisional restorations should be optimized to act as a blueprint for the final restorations (Figure 1). Phonetic tests are among the many guides the clinician can use during these procedures to ensure that the restorations are in harmony with functional and aesthetic determinants. Photographic records of patients performing phonetic tests are helpful during treatment planning. The following is a review of the basic mechanisms involved in sound production and their applications for the management of dentate and partially dentate patients with compromised dentitions.
Figure 1.
(a) Intra-oral frontal view showing extensive destruction of teeth structure due to tooth wear. (b) Pre-operative assessment of teeth display using prolonged pronunciation of /e/. (c) Same phonetic test with provisional restorations. (d) Same phonetic test after insertion of final restorations.
Phonemes are not graphemes
In writing, words consist of spelling letters known as graphemes. However, as speech is the expression of spoken word by articulating sounds, in phonology words are considered to consist of speech sounds called phonemes.1 To avoid confusion created by regular orthography, different phonetic alphabet systems have been developed. Among these, the ‘International Phonetic Alphabet’ is the most widely accepted system.2 Phonemes are written in between angle slashes, for example /s/. On their own, phonemes do not symbolize an object or a concept.2 However, when put together, phonemes distinguish one word from another. For example, the phoneme /t/ on its own does not convey a meaning, however, when placed with other phonemes, such as /teeth/, it then conveys a meaning. It follows, therefore, that substituting one phoneme with another one changes the meaning of the word. For example, the words ‘beat’ and ‘bead’ are written phonemically as /bit/ and /bid/, showing that replacing the last phoneme gives the word a different meaning.2
The number of phonemes varies per language, with most languages having 20–40 phonemes that are classified into consonants and vowels.
Generation of sounds
Speech appears to be a daily effortless function. However, research has shown that it is a very complicated motor act involving numerous areas in the nervous system and the co-ordination of an estimated 100 muscles of the respiratory, laryngeal and supra-glottal articulatory systems to convert a discretely specified linguistic message to a continuous stream of sounds that can be understood by others.3,4
Once neural motor signals are planned and initiated, efferent pathways are transmitted from the primary motor cortex along several cranial and spinal nerves (via corticobulbar and corticospinal tracts of the pyramidal system) to the various muscles of respiration and the vocal tract in order to initiate and modulate the production of sounds.5
Role of vocal tract in speech production
The transmitted neural signals generate speech by forcing a volume of air from the lungs through bronchi and trachea and into the vocal tract. Most human sounds are produced by an egressive (outgoing) pulmonic airstream where the lungs take in air rapidly and exhale it slowly.6 This enables the production of long phrases on single expirations punctuated with quick inspirations at meaningful linguistic breaks.6
Air then passes through the trachea and into the larynx. The larynx contains the vocal folds with the glottis that is the opening between the vocal folds. The glottis divides the vocal tract into subglottal and supraglottal vocal tracts. The vocal folds act as a valve that can be adjusted in various ways through the actions of muscles and ligaments, which control the laryngeal cartilages to give different acoustic effects to sounds transforming air flow into audible sound (phonation or voicing).7 The vocal folds can be abducted (spread apart) where the air passes between them unimpeded.7 This results in the production of voiceless sounds. On the other hand, when the vocal cords are adducted (drawn together), the air from the lungs repeatedly pushes them apart as it passes through creating a vibration effect.7 This results in sounds with the desired pitch (frequency of vibration), and loudness (intensity of sound). Sounds produced in this manner are called voiced sounds.
Once the pitch and loudness is produced, the sound is further modified through resonators and articulations by the different structures and cavities of the supraglottal vocal tract, transforming sound into intelligible speech.
The larynx is the main resonator with the nasopharynx and oropharynx as the two primary resonating systems. Air then passes from the pharynx into the oral or nasal cavity. The movement of the soft palate controls the passage of air into the oral or nasal cavity. Sounds produced while the soft palate is lowered allow air to escape into the nasal cavity, resulting in production of nasal or nasalized sounds.7 On the other hand, sounds produced with the soft palate raised results in the production of oral sounds. Nearly all speech sounds are emitted from the mouth, however, English words such as ‘ran’, ‘ram’, ‘rang’ all end in nasal consonants.8 The facial and cranial sinuses also add resonance properties to sounds.
The oral cavity is extremely important in the production of speech sounds. By varying the relationships of the so-called articulators, lips and tongue, to the palate and teeth, one can produce a variety of sounds. This part of speech sounds production, the so-called articulation, is the most important from the restorative dentist's perspective.
Oral articulators can also be classified into passive and active articulators. An active articulator is the articulator that does all or most of the moving during a speech production. Active articulators include the lower lip, the tongue, and the mandible with attached lower teeth. A passive articulator is the articulator that makes little or no movement during a speech production. Passive articulators include the upper lip, maxillary teeth, the various parts of the upper surface of the oral cavity, and the back wall of the pharynx.
Based on place of articulation, consonants can be classified into bilabial, labiodental, linguodental, linguoalveolar, linguopalatal, and linguovelar sounds (Table 1).
Sound
Examples
Articulation
Bilabial sounds
/p/ (Paris)/b/ (Baby)/m/ (Mother)
Contact between upper and lower lips
Labiodental sounds
/f/ (Fifty five)/v/ (Vienna)
Contact of maxillary anterior teeth with lower lipIn /f/ the incisal edge of maxillary incisors contacts vermilion border of lower lip
In /v/ the incisal edge of maxillary incisors contacts the lower lip inside vermilion border
Linguodental sounds
/th/ (Thirty three)
Tip of the tongue extends about 3 mm between maxillary and mandibular teeth (except in patients with Class II type 1 malocclusion)
Linguoalveolar sounds
Known as sibilants (sharp sounds)/s/ (Mississippi)/z/ (Zoo)/t/ (Too)/d/ (Dot)
Tip of the tongue with the most anterior part of the palate or the palatal surface of maxillary anterior teeth while maxillary and mandibular incisors are end to end but not touching. Among sibilants, /s/ is of special importance in restorative dentistry. It can be typical or atypical /s/
Typical /s/: Produced by moving the mandible forward and upward bringing the incisal edges of maxillary and mandibular anterior teeth to an almost edge-to-edge relation with a space of about 1.0–1.5 mm between incisal edges of maxillary and mandibular incisors. The tip of the tongue moves forward close to, but not touching, the maxillary anterior teeth. Simultaneously, a sagittal groove is formed near the midline by the anterior part of the tongue.Atypical /s/: The incisors are not brought to edge-to-edge position, instead they maintain an overlap between the maxillary and mandibular teeth. This is seen in a smaller percentage of the population, particularly those with Class II occlusion.
Linguopalatal sounds
/sh/ (Shadow)/ch/ (Churchill)/j/ (Jar)
Contact between dorsum of the tongue and the palate.
Linguovelar sounds
/k/ (Kick)/g/ (Gun)
Contact between posterior part of the tongue and the soft palate. These sounds have very limited use in restorative treatment.
Phonetics as a guide during restorative treatment
The assessment of teeth displayed during smiling and function can be facilitated by using different phonetic sounds. In addition, they also guide the clinician in appropriate dimensions and positioning of teeth in occluso-cervical, anterio-posterior and medio-lateral directions. Furthermore, they facilitate the establishment of vertical dimension of occlusion (VDO) in cases where alteration of the VDO is required.
Assessment of teeth display
It is crucial during aesthetic analysis to record the amount of tooth display at rest and during function before executing restorative treatment.
The /m/ (m sound) is useful to provide information about the incisal length of the maxillary central incisors exposed at rest. This can be achieved by asking the patient to repeat words containing /m/ such as ‘Emma’ at regular pauses.9 In the interval between one pronunciation and the next, the clinician can record (using photographs) and evaluate the amount of tooth display at rest (Figure 2). This will help him/her to decide about modifications required in the length of maxillary incisors. The lip position, while using the word ‘Emma’, has been shown to be reproducible within a small range both in the same day and between treatment sessions.10 The amount of the maxillary central incisors normally visible at rest varies between individuals according to their age, sex, and length of upper lip. In patients younger than 30 years of age, the amount of maxillary incisor exposure at rest is approximately 3.5 mm in females and 2.0 mm in males.11 These measurements decrease as the patient gets older.11
Figure 2.
(a) Schematic representation of midsagittal view showing the relationship of articulators during pronunciation of /m/. (b) Diagram of occlusal view of maxilla showing no contact of tongue with maxilla during pronunciation of /m/ – compare this with Figure 7b. (c) Assessment of anterior teeth display at rest using /m/ by pronouncing repeated ‘Emma’ word (picture is taken at pause between repeated ‘Emma’ word).
Maximal teeth display is another important factor which clinicians should evaluate before and during restorative treatment. The amount of maximal teeth (and gingival) display depends on lip mobility that affects the lip movement from rest to its highest position, otherwise known as smile line or lip line.12
Prolonged pronunciation of /e/ as in ‘cheese’ is another phonetic test used to evaluate the maximal length of the maxillary incisors at maximal display during speech.13 The clinician may observe the space between upper and lower lips when a patient is pronouncing extended /e/ (Figure 3). The size of this space varies from one patient to another, depending on age, sex, as well as lip length and mobility. The reproducibility of the lip line position using static recording (photographs) during the pronunciation of the extended /e/ has not been confirmed. Recent studies suggest that the use of videography and computer software to select the highest lip line during speech rather than a static picture may be more valuable.14,15
Figure 3. Assessment of maximum teeth display using extended /e/ in a patient requesting increase in length of teeth. (a) Pre-operative view; (b) after indirect mock-up.
Generally, in young patients, the space between the upper and the lower lips would be occupied completely by the maxillary incisors during pronunciation of /e/.16 In these patients, with short maxillary anterior teeth occupying less than 50% of the space as a result of tooth wear, the clinician can increase the length of maxillary teeth to occupy as much as 80% of the space between the lips.17 This can be done provided that the increase is compatible with other phonetic and functional determinants.
In older patients the space between the upper and lower lips is only partially occupied by the maxillary incisors due to the reduced tonicity of the peri-oral muscles.18 The incisal edge of maxillary teeth may be a long way from the lower lip, which allows the clinician to increase the length to occupy more space, but not more than 50%.17
Patients may request an increased amount of teeth display to attain a more youthful appearance. A compromise between the patient's expectations and other functional determinants, such as appropriate anterior guidance, needs to be determined in consultation with the patient. Techniques such as diagnostic wax-up and mock-up are extremely helpful in discussions with the patient during the treatment plan phase. These changes should be confirmed during the provisional phase before fabrication of the final restorations (Figure 1).
Changes in occluso-cervical and anterio-posterior direction
The /f/, /v/ and /s/ can guide the clinician in determining changes in occluso-cervical and anterio-posterior position of the incisal edge of maxillary anterior teeth.
Use of /f/ and /v/ in determining occluso-cervical and anterio-posterior position of the incisal edge of maxillary anterior teeth
Pronunciation of /f/ and /v/ are produced by gentle contact between incisal edges of maxillary central incisors and lower lip (Table 1).
In short teeth, as in tooth wear cases, the length of the incisors can be increased to achieve contact at the vermilion border during production of /f/ (Figure 4) and inside the vermilion border during production of /v/ (Figure 5).
Figure 4.
(a) Schematic representation of midsagittal view showing the relationship of the different articulators during pronunciation of /f/. Lateral (b) and frontal (c) views showing the relation of maxillary teeth to the lower lip during pronunciation of /f/.Figure 5.
(a) Diagram showing the relationship of the different articulators during pronunciation of /v/. Lateral (b) and frontal (c) views showing the relation of maxillary teeth to the lower lip during pronunciation of /v/.
Excessive length of maxillary incisors will be associated with lower occlusal plan where the lower lip covers the labial surface of the maxillary teeth. In such a situation, the /f/ will sound more like a /v/.19 This is because the incisal edges of the maxillary anterior teeth will touch inside the vermilion border of the lower lip. In addition, there will be increased pressure on the lower lip manifested as indentations (Figure 6) during the pronunciation of /f/. Markedly short teeth, on the other hand, will be associated with a high occlusal plan, where the patient may compensate by increased mobility of the lower lip during pronunciation of these sounds. The /v/ will sound more like an /f/ because the lower lip will be over-closed and maxillary anterior teeth will touch outside the vermilion border of the lower lip.19
Figure 6. Frontal view showing long maxillary right canine tooth causing indentation in the lower lip during pronunciation of /f/.
The /f/ and /v/ can also guide the clinician during positioning of the incisal edge in anterio-posterior direction. As has already been alluded to, the incisal edges of the maxillary incisors touch the lower lip at the vermilion border during the pronunciation of the /f/ and inside the vermilion border during the pronunciation of the /v/ (Table 1 and Figures 4 and 5). Excessive labial positioning of maxillary central incisors may result in their incisal edges being placed outside the vermilion border during the production of /v/. In addition, maxillary incisors may trap the lower lip during the pronunciation of the /f/. Furthermore, the patient may feel bulkiness of teeth and may complain of difficulty when closing the lips together. Therefore, the vermilion border can be regarded as the facial limit of the position of the incisal edges of maxillary anterior teeth during pronunciation of these sounds.
Use of /s/ in determining the occluso-cervical and anterior-posterior position of the incisal edge of maxillary anterior teeth
The production of the /s/ by the oral articulators is variable,20 with the majority of the population demonstrating typical /s/ (Figure 7) and a smaller percentage of the population, particularly those with Class II occlusion, exhibiting atypical /s/ (Figure 8) during speech (Table 1). This subtle but important difference in the way patients pronounce the /s/ may influence its use during assessment of incisor teeth length and anterio-posterior position of their incisal edge.
Figure 7.
(a) Schematic representation of midsagittal view showing the relationship of different articulators during the pronunciation of typical /s/. (b) Occlusal view showing areas of contact between the tongue and palate during /s/. (c) Frontal view showing anterio-posterior relationship of maxillary and mandibular incisors during typical /s/.Figure 8.
(a) Frontal view showing relationship of maxillary and mandibular incisors during pronunciation of atypical /s/. (b) Schematic representation of incisors relationship during atypical /s/. (c) Schematic representation of typical /s/ as compared to that shown in (b).
In patients with typical /s/ sound, judgement can be made about the length of the incisal edges of the maxillary and mandibular incisors. Teeth length can be adjusted to maintain 1.0 to 1.5 mm space between the incisal edges of anterior teeth during pronunciation of the /s/ sound.20 If a space is required, on the other hand, reducing the length of mandibular incisors is performed provided that the maxillary anterior teeth length is compatible with other factors, such as teeth display, teeth proportions, functional determinants, and patient's expectations. Excessive space between the incisal edges of maxillary and mandibular teeth may result in lisping, which demands adjustment to the length of maxillary and/or mandibular incisors.
In patients with atypical /s/, information regarding the appropriateness of the length of the maxillary incisor teeth cannot be ascertained during /s/ production. In such patients, however, lack of space between maxillary and mandibular teeth may require adjustments of the incisal edges of mandibular teeth and/or adjustment to palatal surfaces of maxillary anterior teeth.
Effect of phonetics on the medio-lateral position of teeth
The bucco-palatal position of maxillary posterior teeth, particularly maxillary premolars, is very important in pronunciation of sibling sounds including /s/, /sh/ and /z/. It has been estimated that the sagittal groove formed by the upper anterior part of the tongue near the midline has a cross-section of about 10.0 mm2 during the production of /s/.21 It follows, therefore, that bulky lingual surfaces of premolar teeth, or teeth set up too palatally in the case of partially edentulous patients, will cause narrowing of the groove resulting in a whistle. In contrast, placement of these teeth too buccally would create a wider groove that can result in pronunciation of the /s/ as an /sh/, leading to lisping.21
Assessment of vertical dimension of occlusion
Changing the vertical dimension of occlusion (VDO) is frequently required in dentate patients with excessive loss of tooth structure, as in cases of generalized tooth wear. In such cases, the increase in the VDO is usually required to create space for the restoration and improve the aesthetics.
The use of /m/ has been suggested to assess the vertical dimension at rest. During this procedure, the patient is instructed to pronounce /m/ as in ‘mum’ while he/she is relaxed and in the upright position. A distance between two reference points placed on the patient's face (one on the tip of the nose and the other one on the chin) is immediately measured after the patient stops. The difference between this measurement and that taken with the teeth together represents the inter-occlusal space of about 2.0–4.0 mm.22 However, studies investigating English speakers have found that the inter-occlusal space is variable and ranges between 8.3 to 11.5 mm during pronunciation of /m/.23
While this phonetic test can provide information about the inter-occlusal space, another phonetic test using /s/ can be used to confirm these findings. During this method, which was originally described by Silverman,24 the pronunciation of /s/ creates a space of about 2.0 mm between the maxillary and mandibular teeth. This is best observed between the maxillary and mandibular premolars while the patient is pronouncing /s/ as there is minimal overlap between premolars as compared to anterior teeth (Figure 9).
Figure 9. Closest speaking space (between premolars) during pronunciation of /s/.
This space is called the closest speaking space. During assessment of VDO, it has been suggested that it is more reliable to use a variety of words containing different sibilant sounds as opposed to a single word.25 However, in addition to phonetic tests, it is wiser to confirm the VDO using other methods, such as swallowing and facial aesthetics.
A summary of different considerations during assessment of teeth positions in occluso-cervical, anterio-posterior and medio-lateral directions are shown in Figures 10 and 11.
Figure 10. Summary of different considerations during assessment of teeth positions in occluso-cervical direction.Figure 11. Summary of different considerations during assessment of teeth positions in anterio-posterior and medio-lateral directions.
Conclusions
Phonetic tests can help guide the clinician during the diagnosis and management of dentate and partially dentate patients requiring restorative treatment of compromised dentition. Knowledge of basic phonetic principles will improve the clinician's ability to use phonetic tests in the assessment of tooth display, as well as build up and/or positioning of teeth in occluso-cervical, anterior-posterior and medio-lateral directions. In addition, phonetic tests assist the clinician in determining the appropriate VDO.
