In dentistry, the cingulum (Latin: girdle) is an anatomical feature of the tooth and refers to the small raised area of anterior teeth, which includes the central incisors, lateral incisors and canines. It makes up the bulk of the tooth near the gum line and is located at the back of the tooth (on the side closest to the tongue). The convexity of the cingulum from one side of the tooth to the other side resembles a girdle circling the back of the tooth at the cervical third of the anatomical crown. The cingulum represents the developmental lobes at the back of the teeth.
The tooth crown develops from primary growth centres known as developmental lobes. Normal teeth generally consist of three to five lobes. In anterior teeth, the front side of the teeth generally develop from three lobes known as the facial lobes, while the back side of the teeth develops from one lobe known as the lingual lobe. The cingulum develops from the lingual lobe. As the tooth matures over time, the cingulum eventually becomes more defined, which contributes to its overall shape and function.
Originally, the cingulum’s main function was to provide protection for the gingiva (gums) in early mammals. Later on, as teeth evolved, the cingulum was formed as a structural reinforcement to provide support to the tooth and spread the force generated from the incisal or cuspal edge throughout the tooth during chewing or by asymmetrical loads placed on the tooth. This is because it greatly reduces tensile strains in the enamel caused by forces. The size and shape of the cingulum has an effect on the amount of strain the tooth is able to withhold. It also plays a role in directing food during chewing.
Anatomical features Cingulum is an inverted V shaped ridge found on lingual surface at the cervical third of anterior teeth. The majority of a lingual surface's cervical third is made up of the cingulum. All anterior teeth are formed from four centers of development, referred to as lobes. Three are located on the facial side of the tooth, and one on the lingual side. The three mamelons, or bumps, on the incisal edge of the incisors when they first erupted are remnants of the lobes from which the tooth formed. The cingulum forms from this lingual lobe of development. In contrast, posterior teeth developed from 4 to 5 lobes. Instead of cingulum, posterior teeth have multiple cusp for grinding. There are clear distinctions between primary and permanent teeth in the cingulum. Primary teeth have more prominent and well-developed cingulum compared to their permanent teeth, particularly in the anterior teeth. Besides, the canines have a highly noticeable cingulum, but the maxillary cingulum is more prominent than the one on mandibular canines.
Function The cingulum plays a significant role in dental occlusion, particularly concerning the stability and function of anterior teeth. The cingulum of maxillary anterior teeth provides a contact area for the incisal edges of mandibular anterior teeth in centric occlusion. It helps in distributing occlusal forces evenly, reducing excessive stress on individual teeth. The cingulum guides mandibular movement, particularly in protrusive and lateral movements. It plays a role in anterior guidance, ensuring smooth occlusal function and protecting posterior teeth from excessive wear. It contributes to the stability of the dental arch by maintaining proper tooth position and contact.
The contour of the cingulum influences the deflection of food away from the gingival margin, potentially reducing food impaction and contributing to periodontal health. Proper curvature can aid in protecting the gingiva during mastication.
The cingulum serves as a reinforcement point by adding bulk to the lingual surface of anterior teeth, enhancing their resistance to fracture and stress. This additional enamel thickness improves the tooth's ability to withstand occlusal forces, reducing the risk of fractures, especially in incisors and canines. The cingulum contributes to tooth stability by providing an anchoring surface for the periodontal ligament fibers. In canines, the well-developed cingulum aids in canine guidance, which protects posterior teeth from excessive lateral forces. Studies suggest that the morphology of the cingulum directly influences the load-bearing capability of anterior teeth, particularly in canines where it plays a critical role in guiding occlusion. Finite element analysis models indicate that the presence of a well-defined cingulum reduces stress concentration in enamel and dentin, improving tooth longevity.
Role in Speech and Phonetics Various anatomical features of teeth, including the cingula, interact with oral structures during speech. They collectively contribute to speech sound articulation.
Speech production and articulation
Speech occurs when air flows from the lungs to the larynx, where vocal cords vibrate and create sound. This airflow continues into the oral cavity. Articulators, such as the tongue, lips, teeth, alveolar ridge and hard palate, then shape the air in certain ways to form speech sounds.
Consonants are speech sounds produced by a partial or complete blockage of airflow through the vocal tract. The tongue is majorly involved in articulating consonants by creating these blockages when it contacts other structures in the oral cavity. The cingula of anterior upper teeth can play an indirect role in tongue placement for some consonants.
Normal speech involves correct synchronisation between the vocal organs to create precise speech sounds. Alterations in any of these structures can affect tongue placement and airflow patterns. Thus, producing perceived speech distortions which are regarded as speech sound disorders (SSDs). For sounds that require teeth, changes in tooth anatomy and position can therefore contribute to changes in speech. Some speech sounds are more impacted by dental abnormalities than others, depending on the areas the sound is articulated. Dental deviations in the anterior part, majorly affect lip and tongue placement in alveolar, dental and palatal sounds.
Impact of malocclusions on articulation
Malocclusions, including crossbites and anterior open bites, influence articulatory movements, leading to speech sound distortions, omissions or substitutions. Additionally, craniofacial anomalies (such as clefts) can cause orofacial muscle imbalances and with alterations in the function of the orofacial region, speech challenges arise.
The relationship between SSDs and malocclusion is multifactorial and complex. It is related to specific anatomical structures, oral habits, muscular alterations but perhaps to language-specific traits also.
Anterior open bite
Anterior open bite is the occlusal feature most often associated with SSDs. Prolonged non-nutritive sucking is a common cause. This habit is related to speech disorders and myofunctional disorders, which reduce oro-motor abilities. In regards to teeth, proclination of upper incisors and retroclination of lower incisors occurs. The edges of lower incisors do not make contact with the cingula of upper teeth like in an ideal Class I occlusion. This impacts the articulation of linguo-alveolar sounds (/t/, n/, /d/, /l/) and lateral sounds (/l/, /ll/). Sibilant sounds (/s/, /ch/ and /z/) and fricatives affricatives (/v/, /f/) are also impacted as no occlusion between anterior teeth creates an air outlet. This is associated with lisping.
Class II Division 1
In Class II Division 1 malocclusions, bilabial (/p/, /b/, /m/) sounds can be distorted. Due to prominent overjet, the lower lip makes contact with the incisal edges of upper incisors rather than creating a seal with the upper lip. For fricative sounds (/f/, /v/) there is a difficulty in managing air flow anteriorly. Air is forced through the interproximal spaces and gaps between incisal edges of the teeth and the lower lip moves beneath the maxillary incisors, so there is a distortion in these speech sounds.
Class III
In Class III malocclusions, upper incisors are anterior to lower incisors. This affects the articulation of sibilant fricatives /s/ and /z/. The tongue is unable to reach the palatal side and cingula of upper teeth or the alveolar ridge due to its placement under the lower incisors, which creates misarticulation. Labiodental fricatives /f/ and /v/ are also affected as the lower lip has difficulty meeting the upper incisors. Individuals with this type of occlusion often make compensatory articulation gestures for these speech sounds. The upper lip touches the lower incisors for /f/ and /v/ and tongue touches the incisal edge of upper incisors for /s/ and /z/.
Edge-to-edge bites
In edge-to-edge bites, incisal edges of upper and lower incisors meet with no overlap. The phoneme /t/ has been reported as difficult to articulate in such malocclusions.
Dental corrections
Orthodontic treatment can help correct malocclusions and improve articulation as a result. Teeth can be aligned into an ideal occlusal relationship where the lower incisors occlude with or lie below the cingulum plateau of the upper incisors. A combination of orthodontics and speech therapy may be required to rectify some malocclusion and speech challenges. In other cases, orthognathic surgery with orthodontics plus postoperative speech therapy may be necessary.
Denture Design and Speech Intelligibility
In prosthodontics, for complete and partial dentures, features like the cingulum and palatal contour are incorporated to improve speech intelligibility. These features enable natural tongue positions and allow areas of articulation on the palate and anterior teeth which can contribute to easier articulation. In a maxillary complete denture, if tooth position, occlusal vertical dimension, occlusal plane and palatal contours are approximated accurately to the patient’s tongue, speech clarity can be improved.
Variation and Abnormalities The cingulum can vary in size and how prominent it is. Some teeth may have a more prominent cingulum, while others may have one that is less visible. Certain conditions or abnormalities can also affect the cingulum due to genetic factors, developmental defects, or environmental influences.
Hypoplasia
Enamel hypoplasia is sometimes mistaken for enamel hypomineralization. Enamel hypomineralization occurs when the enamel does not fully harden, leading to weak, discolored teeth that can break easily. It appears as soft, bumpy, or decayed areas on the enamel, usually affecting molars and incisors as they develop.
On the other hand, enamel hypoplasia is when the enamel does not form properly, causing it to be too thin or missing in certain areas, including the cingulum. It appears as brown or yellow stains and exposes the dentin underneath. Hypoplasia is a type of amelogenesis imperfecta, a condition where the enamel is either absent or extremely thin, making teeth more likely to break. The enamel present remains hard but is weak.
Enamel development issues are common. One of the most widespread causes of enamel hypoplasia—amelogenesis imperfecta—affects about 1 in 700 people in developing countries. In the U.S., it is rarer, affecting about 1 in 14,000 people.
There are several reasons why these conditions develop. According to the Indian Journal of Dentistry, they happen when there is a disruption in how enamel forms. To understand this, we need to look at ameloblasts—cells that create enamel. These cells go through six stages: morphogenetic, organizing, formative, maturative, protective, and desmolytic. Enamel hypoplasia occurs during the formative stage, leading to pitting, grooves, or even a complete lack of enamel.