Introduction

Imagine a world where humans are born without teeth - not just as infants, but for life. How would we chew, speak, or even smile?. While this may sound like science fiction, for some, a similar reality exists due to a condition known as Tooth agenesis.

Tooth agenesis is a birth defect characterised by the absence of one or more teeth in primary dentition and permanent dentition, excluding the absence of third molars (wisdom teeth). Previously, “Congenital absence of teeth” was previously perceived as a result of failure in the early stages of tooth development. However, several authors have reported that the condition may be caused by a variety of hereditary or environmental factors.¹ Tooth agenesis may occur as an isolated condition or may occur in association with other dental anomalies or medical conditions. 

Globally, this condition is reported with a frequency range between 2.2% and 10.1%.² In the United Kingdom, the National Health Service has reported that a range between 3% and 5% of the population is born with missing teeth.

Common terminologies reported in the context of missing teeth:

• Hypodontia - It is characterised by the congenital absence of one to five teeth (excluding third molars)
• Oligodontia - It is a severe form of tooth agenesis characterised by congenital absence of six or more teeth (excluding third molars)
• Anodontia - It is a severe form of tooth agenesis characterised by the congenital absence of the entire dentition

The absence of teeth can lead to aesthetic, functional, and psychological concerns, highlighting the significance of further research on tooth agenesis and its treatment options. 

Studies have reported associations between tooth agenesis and other dental anomalies, such as Microdontia, Delayed eruption, Malocclusions, and Taurodontism. These correlations are crucial to initiate early diagnosis and treatment planning.¹ Therefore, in this article, we will explore the causes of tooth agenesis, its association with other dental anomalies, and management.

Causes of tooth agenesis 

Tooth agenesis is a complex interplay of genetic and environmental factors. Let's explore these causes and understand their impact:

Genetic causes

• Mutations in genes such as MSX1, PAX9, AXIN2, and EDA have been strongly associated with tooth agenesis.
• PAX9 mutations have been linked to hypodontia, particularly in molars, whereas

MSX1 mutations typically impact premolars and third molars. 

• AXIN2 mutations have been associated with severe oligodontia and an increased risk of colorectal cancer, implicating a more systemic impact

Environmental impact

• Prolonged radiation exposure
• Chemotherapy
• Maternal smoking and alcohol consumption
• Rubella 
• Nutritional deficiencies

The above-mentioned factors could negatively impact tooth development,  resulting in the absence of teeth. Upper lateral incisors, second premolars, and lower central incisors are commonly reported to be involved in this condition due to early fusion in developmental stages.²                                                                              

Is it syndromic or non-syndromic: Let’s debate 

Table 1: Syndromic Agenesis V/s Non-syndromic Agenesis: The table above outlines the key differences between syndromic and non-syndromic tooth agenesis, focusing on their etiological factors, clinical manifestations, diagnostic approaches, and treatment planning. This comparative analysis emphasises the necessity of genetic evaluation and a multidisciplinary approach for effective diagnosis and management.^3,4

Association of tooth agenesis with other dental anomalies

• Microdontia: Microdontia, particularly peg-shaped maxillary lateral incisors, is prevalent in hypodontia patients. The condition can be triggered by genetic changes that affect tooth development⁵
• Supernumerary Teeth: Although agenesis is defined by missing teeth, some patients have both missing and extra teeth in distinct areas of their mouth.   This contradiction points to a shared genetic cause that affects the regulation of the normal number of teeth⁶
• Delayed Eruption with Retained Primary Teeth: Patients with hypodontia frequently have delayed eruption of permanent teeth and extended retention of primary teeth. which affects occlusal development - the process by which teeth come into proper alignment - and complicates treatment planning⁷
• Malocclusion: Malocclusion is a condition causing the misalignment of upper and lower teeth. Class II and Class III malocclusions, deep bites, and midline discrepancies are usually associated with hypodontia. The absence of teeth could result from shorter arch lengths, different eruption patterns, and inadequate intercuspation⁸
• Taurodontism and Root Anomalies: Taurodontism, a disorder marked by larger pulp chambers and apically displaced furcations, is common in individuals with hypodontia. This disorder has been linked to mutations in the PAX9 and MSX1 genes⁹
• Enamel Hypoplasia: Enamel hypoplasia, characterised by thin and poor enamel formation, is common in individuals with hypodontia. This abnormality might be attributed to a decrease in ameloblast activity caused by genetic or environmental factors¹⁰

Clinical manifestations

• Altered occlusion or Malocclusion
• Facial asymmetry
• Compensatory Tooth drifting
• Spacing 
• Altered alveolar ridge development
• Dysphagia
• Dysphonia
• Taurodontism ^1,2

Diagnostic considerations

A multifaceted approach is needed to manage tooth agenesis, incorporating clinical examination, family and previous medical history, radiographic diagnosis, and genetic 

testing. Early diagnosis plays a significant role in optimising management strategies and patient outcomes.

Early diagnosis

• Early intervention: Early intervention facilitates improved orthodontic, prosthodontic, and restorative treatment planning.
• Multidisciplinary collaboration: Multidisciplinary collaboration among orthodontists, prosthodontists, and geneticists provides comprehensive treatment.
• Regular followups: Proactive monitoring in high-risk people can result in better functional and cosmetic outcomes.

Clinical examination

A thorough clinical examination (intraoral and extraoral) helps to identify missing teeth and other dental anomalies. Look for these indications:

• Missing teeth
• Retention of primary teeth
• Delayed eruption pattern
• Altered tooth morphology
• Malocclusion
• Spacing
• Soft tissue and skeletal abnormalities
• Facial abnormalities

Radiographic evaluation

Radiographic imaging is necessary to confirm the diagnosis and assess the severity of agenesis. 

• Periapical and Bitewing radiographs: Useful in assessing retained primary teeth and root characteristics.
• Panoramic: OPGs (Orthopantomograms) are useful to identify any missing teeth. These can also be helpful in assessing impacted teeth, roots, and alveolar bone depth
• Cone Beam Computed Tomography (CBCT): In cases with combined skeletal and dental involvement, this technique displays a 3-dimensional view of the bone (E.g., assessing bone depth for the safe placement of implants). This technique can also be useful in taurodontism and root malformations
• Lateral cephalogram: Useful in orthodontic procedures to assess the extent of skeletal and dental anomalies

Genetic testing 

• Family history and Previous medical history: Tooth agenesis is typically inherited in an autosomal dominant, autosomal recessive, or X-linked pattern. These familial patterns help medical professionals to predict the possibility of  inheritance and severity in siblings and future generations
• Genetic testing: Recommended in severe cases, mostly in syndromic ones. Mutations in the MSX1, PAX9, AXIN2, and EDA genes are most often linked with both non-syndromic and syndromic variants. AXIN2 mutations may be associated with an increased risk of colorectal cancer, emphasising the importance of systemic surveillance¹

Treatment options 

• Orthodontic evaluations and interceptors

Space management is feasible to achieve functional occlusion. Redistributing spaces while managing masticatory forces will aid in prosthodontic rehabilitation. It is crucial to address midline discrepancies and vertical dimension issues,, to maintain aesthetics and function. In teenagers and younger adults, growth modification appliances, such as space maintainers and retainers, are used to guide skeletal and dental growth and development at proper speed and direction.

• Conservative and Prosthodontic interventions

In cases where orthodontic space closure is not possible, resin-bonded bridges are used to close small spaces. In permanent dentitions, implants could also replace missing teeth. Where extensive space closure is needed, removable partial dentures could be used.^1,2,8

• Multidisciplinary collaboration

This is a rare congenital condition that needs a collaborative approach to achieve the best outcomes for patients. The team involves:

• Parents / Guardian
• Family Dental Surgeon
• Family GP
• Pediatrician
• Orthodontist
• Endodontist
• Prosthodontist
• Oral Maxillofacial Surgeon
• Geneticist 

Summary

Tooth agenesis is a congenital defect characterised by the absence of one or more teeth in primary or permanent dentitions (excluding third molars). The condition can be either non-syndromic or syndromic. The upper lateral incisors and lower premolars are among the most frequently reported teeth to be affected by tooth agenesis. Several authors have reported associations between this condition and various other dental and skeletal anomalies, such as microdontia, taurodontism, altered occlusion or malocclusion, delayed eruption, supernumerary teeth, root anomalies, and enamel hypoplasia.

Clinical examination and radiographic assessment are the cornerstones of diagnosing this condition. However, genetic testing is necessary due to its hereditary and environmental origins. Early detection facilitates strategic planning and regular follow-ups. A multidisciplinary approach involving a dental surgeon, general practitioner, paediatrician, orthodontist, endodontist, prosthodontist, oral and maxillofacial surgeon, and geneticist is essential to achieving the best patient outcomes.

FAQs

What is tooth agenesis, and how frequent is it among children?

Tooth agenesis occurs when one or more teeth fail to develop. It affects around 2 to 10% of the global population.  Second premolars and upper lateral incisors are the most common missing teeth.

How can I know if my child is missing teeth?

You might notice: 

• Permanent teeth erupt later than usual
• There are MORE spaces where the teeth should be
• Prolonged presence of baby teeth
• A clinical examination and X-rays can help a dentist confirm the diagnosis

Is tooth agenesis hereditary?

Yes, it usually runs in families. If you or a close relative has missing teeth, your child may be at a higher risk. Non-syndromic agenesis is associated with genetic alterations in MSX1, PAX9, and AXIN2. In certain situations, it may be accompanied by ectodermal dysplasia.

How does tooth agenesis affect my child's speech and feeding habits?

Yes, it depends on which teeth are missing. Missing front teeth may impact speech clarity, but missing molars or premolars might make chewing more difficult. Early intervention with orthodontics or prosthetics can assist.

What treatment choices are available to my child?

The number and location of missing teeth determine the appropriate treatment. Options include:

• Orthodontic therapy addresses spaces and prepares for future implants
• Dental implants or bridges are used as permanent replacements in older children
• Removable Partial Dentures are a temporary option for younger children

At what age should I seek help for my child?

Early detection is crucial!   If your child's permanent teeth do not appear on time (usually by age 7-8), see a Pedodontist. Orthodontic planning often begins between the ages of 10 and 12, with permanent options such as implants being explored when jaw growth is complete (17 to 20 years).