Teeth begin forming long before they’re visible. The process starts during the fifth week of pregnancy, when the first tooth buds take shape inside a developing embryo’s jaw. From that point, it takes years of growth, hardening, and movement before a full set of adult teeth is in place. The biology behind it involves cells that build enamel and dentin, bone that reshapes itself to create a path, and a carefully timed sequence that unfolds from infancy through early adulthood.
Teeth Start Forming in the Womb
By the eighth week of pregnancy, small swellings called enamel organs appear along a band of tissue in the developing jaw. These are the earliest structures that will become individual teeth. Over the next several weeks, each swelling goes through a series of shape changes, progressing from a simple bud into a cap-like form and then into a bell shape. During these stages, the cells that will eventually produce enamel and the inner tooth tissue begin to differentiate and organize themselves.
By about 12 weeks, the inner layer of each developing tooth organ has taken on a columnar shape that defines what the crown will look like. Beneath that layer, a cluster of cells called the dental papilla forms, which will later become the tooth’s pulp (the soft, living core that contains nerves and blood vessels). A surrounding capsule called the dental follicle also develops at this stage. It will eventually become the ligament that anchors the finished tooth to the jawbone. All of this happens months before birth, meaning the blueprints for every baby tooth are already in place when a child is born.
How Enamel and Dentin Are Built
Two specialized cell types do the heavy lifting of constructing a tooth. Ameloblasts, which come from the outer tissue layer of the embryo, are responsible for building enamel. Odontoblasts, which come from deeper connective tissue, build dentin, the dense layer underneath enamel that makes up most of the tooth’s structure.
Ameloblasts work in a way that’s unlike almost anything else in the body. They form a single-cell-thick sheet that moves as a unified front, laying down a protein-rich scaffold as they go. This scaffold acts as a template for mineral crystals to grow into. The ameloblasts then switch roles: they break down and remove those proteins, replacing them with minerals until the enamel becomes the hardest substance in the human body. Once this process is complete, the ameloblasts die off. This is why enamel can’t regenerate. The cells that made it are gone for good.
Dentin formation follows a different path. Odontoblasts remain alive inside the tooth pulp throughout your life, continuing to deposit small amounts of dentin over time. This is why teeth can sometimes respond to damage by laying down a protective layer of new dentin on the inside, even in adulthood.
What Pushes a Tooth Through Bone and Gum
A fully formed crown sitting deep inside the jawbone still has to travel upward (or downward, for upper teeth) through solid bone and gum tissue before it can function. This journey, called eruption, relies on a coordinated process of bone remodeling. The dental follicle surrounding each developing tooth signals the bone above the crown to break down, carving an eruption path. At the same time, new bone forms beneath the developing root, pushing the tooth upward toward the surface.
Once the tooth’s tip reaches the top of the jawbone, the eruption rate increases. From there, collagen fibers in the ligament surrounding the root shorten and cross-link, generating a pulling force that draws the tooth through the gum tissue and into its final position. Root growth and continued bone formation at the base of the tooth socket contribute additional upward force. Even after a tooth breaks through the gum, its root continues developing for some time before reaching full length.
The dental follicle is so essential to this process that animal studies have shown eruption simply doesn’t happen when it’s removed. Without the follicle, the bone pathway never forms, and the tooth stays trapped.
The Eruption Timeline
Baby teeth typically start appearing between 6 and 12 months of age. The lower central incisors (the two front bottom teeth) usually come in first. By around 33 months, most children have all 20 primary teeth, with the four second molars being the last to arrive, usually after age 2.
The transition to permanent teeth begins around age 6, when the central incisors start to loosen and fall out. The first permanent molars also appear around this time, emerging behind the last baby teeth without replacing anything. The process continues gradually, with the last baby tooth, typically a canine or second molar, lost around age 12. By the mid-teen years, most of the 28 permanent teeth are in place.
Wisdom teeth, the third molars, are the final arrivals. They typically emerge between ages 17 and 25, though roughly 8 out of 10 people have at least one wisdom tooth that never fully comes in. Some people never develop them at all.
Nutrients That Teeth Need to Mineralize
Calcium and phosphorus are the two primary minerals that make up tooth enamel and dentin. They combine to form a crystalline structure called hydroxyapatite, which gives teeth their hardness and durability. Without adequate supplies of both minerals during development, teeth can form with thinner or weaker enamel.
Vitamin D plays a critical supporting role because it controls how efficiently the intestines absorb calcium and phosphorus from food. When vitamin D levels are low, even a calcium-rich diet may not deliver enough mineral to developing teeth. This is particularly relevant during pregnancy: maternal vitamin D deficiency has been linked to poorer mineralization of a child’s developing teeth. Fluoride also integrates directly into the crystal structure of tooth enamel during development, making the crystals more resistant to acid and decay.
When Teeth Don’t Come In as Expected
Sometimes teeth fail to erupt on schedule or don’t come in at all. The causes fall into two broad categories: physical obstruction and biological dysfunction. Crowded dental arches are a common physical cause. When there simply isn’t enough room in the jaw, teeth can become impacted, meaning they’re blocked from reaching the surface by neighboring teeth or bone.
On the biological side, some eruption failures have a genetic basis. A gene called PTH1R has been identified as the cause of familial primary failure of eruption, a condition where teeth cannot erupt despite having a clear path. Researchers now suspect that many eruption problems previously attributed to mechanical causes may actually stem from genetic variations affecting the bone remodeling process that teeth depend on to reach the surface. Ankylosis, where a tooth fuses directly to the surrounding bone and loses the ligament that normally allows movement, can also halt eruption. This sometimes happens after trauma to a tooth or the jaw.
Palatally impacted canines, where the upper eye teeth drift toward the roof of the mouth instead of erupting normally, are thought to have both genetic and developmental origins. These are among the most common eruption problems orthodontists manage, after wisdom teeth.