example, tipping of the buccal surface of the upper molar and lingual surface of the lower molar compensates for transverse maxillary deficiency.
4.2 Soft Tissue Factors
4.2.1 Fullness and Tone of the Lips
The fullness and tone of lips can have an effect on the dentition, as they can result in positioning of the incisors in the labiolingual direction. The effects can include the following:
Lips that lack muscular tone and are flaccid – incisors tend to be proclined.
Strap‐like lips:Lips are tense and the incisors tend to be retroclined.The term highly active lip can also be used to describe this.
Lower lip line:The lower lip should cover one‐third to one‐half of the upper incisor crowns.More than one‐half coverage = retroclined upper incisors.Less than one‐third coverage = proclined upper incisors.
4.2.2 Lip Competency
Lip competency looks at how the lips are when the patient is at rest. There are two types of lip competency:
Competent lips, which is where minimal effort is required to achieve an oral seal.
Incompetent lips, which is where excessive muscular activity is required to achieve an oral seal.
With incompetent lips the following features can be found:Can often be associated with a low lower lip line.Swallowing patterns may occur to achieve an anterior oral seal. If excessive muscular activity or forward mandibular posturing is not possible to achieve, then the following swallowing patterns can occur:Tongue to lower lip results in incisor proclination.Lower lip to palate results in upper incisor proclination and lower incisor retroclination.Tongue to upper lip results in upper incisor proclination.
4.2.3 Macroglossia (Large Tongue)
The size of the tongue can affect the development of the dentition. The tongue can also impede incisor eruption and anterior open bite (AOB). The tongue can present with two types of tongue thrusts:
Adaptive tongue thrust: this can be corrected and stopped once the positions of the teeth are corrected. It is seen when the tongue is forced between the teeth.
Endogenous tongue thrust: this is where the tongue is thrusted forward between the teeth, but is a habit that may not be stopped once tooth positions have been corrected. This can result in relapse.
4.2.4 Enlarged Adenoids
Adenoids are large glands which are located by the soft palate in the roof of the mouth. Enlarged adenoids can result in the development of an AOB due to constant mouth breathing. This has the effect of the molars over‐erupting and resulting in an increased LAFH.
4.2.5 Generalised Pathology of Muscles
Muscle weakness can also have an effect on the dentition. Weak muscles enable the teeth to move due to the lack of support of the soft tissues surrounding the dentition.
4.3 Local Factors
Local factors are divided into three groups:
Variation in tooth number
Variation in tooth size
Variation in tooth position.
4.3.1 Variation in Tooth Number
4.3.1.1 Hypodontia
Hypodontia is known as missing teeth.
Hypodontia is found when there is an absence of one or more primary or secondary teeth, excluding third molars.
The most common cause can be genetic, with a family history of hypodontia.
The most common missing teeth are upper third molars (U8s), lower third molars (L8s), lower premolars (L5s), upper lateral incisors (U2s), upper premolars (U5s), and lower central incisors (L1s).
4.3.1.2 Supernumerary
Supernumerary teeth are extra teeth.
Supernumerary teeth are found when there are excessive teeth in the normal series.
The most commonly found supernumerary is in the anterior maxillary region.
The types that can be found are conical, also known as mesiodens, tuberculate, supplemental, and odontomes.
4.3.1.3 Early Loss of Deciduous Teeth
There could be numerous reasons for early loss of deciduous teeth.
Common causes could be caries, trauma, or root resorption.
Early loss could result in crowding and space loss, which could possibly lead to impaction.
For example, early loss of a lower deciduous E can result in mesial movement of the lower first molar, making no space for the lower premolar to erupt, resulting in impaction.
4.3.1.4 Extraction of Permanent Tooth
Most commonly a first permanent molar.
Extraction of a first permanent molar can result in crowding and space loss, which could possibly lead to impaction.
Reasons for a first permanent tooth being extracted could be poor diet and oral hygiene, which can lead to caries.
4.3.2 Variation in Tooth Size
4.3.2.1 Macrodont
A large tooth is known as a macrodont.
This tooth will present with a large clinical crown.
Macrodonts can be associated with supernumaries.
A clinical feature that can result from macrodonts is dental crowding.
4.3.2.2 Microdont
A small tooth is known as a microdont.
This tooth will present with a small clinical crown.
Microdonts
