Teething
Teething, also known as the eruption of primary dentition, is the natural process by which an infant's first set of 20 deciduous (primary) teeth emerge through the gums.[1][2][3] It typically begins between 6 and 10 months of age, with signs possibly appearing as early as 3 months and first teeth sometimes not erupting until 12 months or later.[1][2][3] The process starts with the lower central incisors, followed by the upper central incisors, and proceeds in a predictable sequence, with all primary teeth usually in place by around 30 months of age.[1][3] Teething involves the teeth pushing through soft gum tissue, which can cause temporary discomfort but is a normal developmental milestone and does not typically lead to serious health issues.[1] Common associated signs include drooling and gum swelling (detailed in later sections); however, teething does not cause fever, diarrhea, excessive crying, diaper rash, or respiratory infections—these symptoms require medical evaluation for other causes.[4][1][3]Introduction and Basics
Definition
Teething is the natural process by which an infant's primary (also known as deciduous or milk) teeth emerge through the gums into the oral cavity.[3] This developmental event marks the initial stage of dentition, involving the gradual breakthrough of these teeth from their underlying positions in the jawbone.[5] While dentition encompasses the full development and eruption of both primary and permanent teeth throughout life, teething specifically denotes the eruption phase limited to the 20 primary teeth in early infancy.[6] These primary teeth serve as placeholders, guiding the alignment of future permanent dentition, and are eventually shed between ages 6 and 12.[6] Teething occurs universally in all healthy infants as a standard physiological milestone, though the exact timing varies individually.[7] By approximately age 3, a complete set of 20 primary teeth has erupted in nearly every child.[8]Typical Timeline
Teething in infants typically commences between 6 and 10 months of age, with the lower central incisors emerging as the first primary teeth in most cases.[9][10] The process continues progressively until completion around 2.5 to 3 years of age, at which point all 20 primary teeth have usually erupted.[11][12] Variations in the teething timeline are common and often influenced by genetic and ethnic factors, with eruption tending to occur earlier in European populations and later in South American ones.[13] Premature eruption can happen as early as 3 months, while delayed onset up to 12 to 15 months is generally not a cause for concern unless accompanied by other developmental or health issues.[14][15] The active phase of discomfort associated with each tooth's eruption typically lasts 1 to 2 weeks, though symptoms may fluctuate during this period.[16][17]Biological Process
Tooth Development
Tooth development, or odontogenesis, for primary (deciduous) teeth begins prenatally during the sixth week of gestation, when the oral ectoderm interacts with neural crest-derived mesenchyme to form the dental lamina—a thickened band of epithelial tissue along the developing jaw ridges.[18] This lamina serves as the primary structure for initiating tooth formation, with ectodermal cells proliferating and invaginating into the underlying mesenchyme to create epithelial buds that represent the earliest tooth germs, typically by the eighth week.[19] These buds mark the initiation stage, where reciprocal signaling between the epithelium and mesenchyme dictates the number, position, and shape of the 20 primary teeth.[18] The developmental process progresses through distinct histological stages: bud, cap, and bell. In the cap stage (around the ninth week), the bud deepens and forms a cap-like enamel organ enclosing a condensation of mesenchymal cells known as the dental papilla, which will later differentiate into the tooth's inner structures.[18] By the bell stage (tenth to fourteenth weeks), the enamel organ fully envelops the papilla, establishing the histological foundation with the outer enamel epithelium, stellate reticulum, stratum intermedium, and inner enamel epithelium.[19] The successional lamina, a lingual extension of the dental lamina, begins forming during this period to initiate permanent tooth buds beneath the primary ones, though primary tooth development remains the focus.[18] Hard tissue formation commences in the late bell stage, with initial calcification of the crowns starting in the fourth fetal month for all primary teeth, including central and lateral incisors, canines, and molars.[20] Postnatally, the processes of dentinogenesis and amelogenesis continue and complete the mineralization of the primary teeth. Dentinogenesis involves odontoblasts from the dental papilla secreting an organic matrix that mineralizes into dentin, beginning prenatally but extending into infancy, with crown completion around 1.5–3 months for incisors and 11–12 months for second molars.[21] Amelogenesis follows, as ameloblasts from the inner enamel epithelium deposit enamel over the dentin, forming the hardest tissue in the body through hydroxyapatite crystallization; this phase also concludes postnatally.[18] The resulting tooth structure consists of an outer enamel layer for protection, a supportive dentin core, and an inner pulp chamber containing nerves, blood vessels, and connective tissue for nourishment.[22] Adequate maternal and infant nutrition, particularly calcium for hydroxyapatite formation and vitamin D to facilitate its absorption and promote mineralization, is essential during these stages to prevent defects like enamel hypoplasia.[23] These prenatal and postnatal phases culminate in the mature primary dentition ready for eruption, the visible stage of teething.[18]Eruption Mechanism
The eruption of teeth through the gingiva involves a coordinated process of tissue resorption and remodeling, primarily driven by the activity of odontoclasts and supported by inflammatory mediators. Odontoclasts, multinucleated cells similar to osteoclasts, resorb the overlying alveolar bone and gingival tissue to create a pathway for the tooth crown to emerge. This resorption is initiated when the dental follicle signals the recruitment and differentiation of precursor cells into odontoclasts, which then degrade mineralized tissues through acidification and enzymatic action. Inflammatory mediators, such as prostaglandins and interleukins, further facilitate this breakdown by promoting localized tissue degradation without systemic involvement.[24] Central to this mechanism is the dental follicle, a connective tissue sac enveloping the developing tooth, which orchestrates the eruption by producing key regulatory molecules. The follicle secretes colony-stimulating factor-1 (CSF-1), which stimulates the formation of odontoclasts from mononuclear precursors, and downregulates osteoprotegerin to enhance RANKL-mediated osteoclastogenesis. Additionally, it releases enzymes like matrix metalloproteinases (MMPs) that remodel the extracellular matrix, allowing for the degradation of collagen and other gingival components. This follicular coordination ensures precise timing and prevents excessive resorption, maintaining the integrity of surrounding structures.[25] The physical movement of the tooth during eruption results from a combination of biomechanical forces, including root elongation and increased vascular pressure within the periodontal ligament. As the root continues to grow, it exerts upward pressure on the tooth, while hydrostatic forces from blood vessels in the dental pulp and follicle contribute to the coronal displacement. These forces propel the tooth at an average rate of approximately 0.7 mm per month in primary dentition, allowing gradual emergence over several weeks.[26][24] An accompanying inflammatory response, characterized by localized release of cytokines such as IL-1 and TNF-α, induces mild gingival swelling and erythema to accommodate tissue expansion. This controlled inflammation differs from infectious processes, as it is self-limiting and resolves with eruption completion, without bacterial involvement or fever. Such cytokine activity supports the remodeling but is typically subclinical in healthy individuals.[24][26]Clinical Signs and Symptoms
Recognized Symptoms
Teething in infants is commonly associated with a range of mild symptoms stemming from the eruption of primary teeth through the gums. These symptoms are typically localized to the oral area and surrounding regions, arising from increased saliva production, gum inflammation, and discomfort during the process. Evidence from prospective studies indicates that while not all infants experience every symptom, those that do often show signs in the days immediately surrounding tooth emergence. Not all infants experience these symptoms, and their presence and intensity can vary.[27] Excessive drooling is one of the most frequently reported symptoms, occurring as the infant's salivary glands become more active in response to gum irritation. This increased saliva can lead to skin irritation around the mouth and chin, resulting in a mild facial rash characterized by red, chapped, or inflamed skin. The rash develops from prolonged exposure to moisture and is usually self-limiting once drooling subsides.[27][1] Infants may exhibit irritability due to the discomfort of tender, swollen gums as teeth push through the tissue. This gum sensitivity often prompts increased chewing, biting, or rubbing on objects, such as fingers, toys, or teething rings, as a way to alleviate pressure and provide relief.[27][3] A mild elevation in body temperature, typically not exceeding 100.4°F (38°C), can occur as a result of local inflammation in the gums rather than systemic infection. This low-grade increase is distinct from fever and resolves quickly without intervention. Symptoms associated with teething generally persist for 3 to 8 days per tooth, aligning with the period from just before eruption to shortly after. The intensity of these symptoms may vary slightly depending on the sequence and type of teeth erupting.[27][1][8]Order of Tooth Eruption
The eruption of primary teeth follows a predictable sequence in most infants, beginning with the central incisors and progressing posteriorly to the molars. The first teeth to emerge are the mandibular central incisors, typically between 6 and 10 months of age, followed closely by the maxillary central incisors at 8 to 12 months.[11][28] Next in the sequence are the lateral incisors, with the mandibular laterals erupting at 10 to 16 months and the maxillary laterals at 9 to 13 months. The first primary molars then appear around 14 to 18 months in the mandible and 13 to 19 months in the maxilla, often causing more noticeable discomfort due to their larger size compared to incisors.[11][29] The canines follow at 17 to 23 months in the mandible and 16 to 22 months in the maxilla, and the process concludes with the second molars at 23 to 31 months in the mandible and 25 to 33 months in the maxilla, completing the set of 20 primary teeth.[11][28]| Tooth Type | Mandibular Eruption (months) | Maxillary Eruption (months) |
|---|---|---|
| Central Incisors | 6-10 | 8-12 |
| Lateral Incisors | 10-16 | 9-13 |
| First Molars | 14-18 | 13-19 |
| Canines | 17-23 | 16-22 |
| Second Molars | 23-31 | 25-33 |