Humans begin to develop teeth while still in the womb and, in fact, the process usually starts sometime around 6 to 8 weeks of gestation (https://en.wikipedia.org/wiki/Human_tooth_development#). By about 4 months of gestation the hard tissues of the teeth form. Infants are usually born with the dental tissue present but below the gum line. It is only sometime after birth that the first set of teeth, called the deciduous or baby teeth, actually grow out of the gum tissue. These baby teeth are usually all present by the time a child is about 33 months of age, but there is some variation in this. In general the first tooth to erupt through the gum-line is an incisor in the front region of the lower mandible or jaw. 

The next teeth that erupt above the gum include the second central incisor and then the four incisors of the upper mandible. The molars and rest of incisors then make their way through the gum-lone. The cuspids are the pointed teeth that are actually canines, and these come in next. The final teeth of the jaw are the last of the molars, which come in by the time the child is about 2 to 3 years of age.

The deciduous teeth are not permanent and are eventually replaced over time with permanent adult teeth. Interestingly the permanent teeth do also start to develop during fetal development and not all the baby teeth are lost at once. The first tooth to fall out is usually an incisor, and the last teeth to be lost are the molars. The last of the baby teeth usually are lost when the child is about 12 years of age.

Each tooth is comprised of three layers, an innermost pulp layer, dentin and then an outermost enamel layer. Dentin is a tough material that has a similar structure to that of bone and the enamel provides one more layer of protection for the tooth. 

 Types of teeth that we have and how teeth can be replaced if lost

All humans have incisors, canines, premolars and molars. These teeth have slightly different functions with incisors being used for biting, canines for tearing flesh and premolars and molars for grinding and chewing up food.

While it is not too serious for a child to damage or break a baby tooth, it is a problem in the case of a permanent tooth. This is because permanent teeth are your adult teeth which are not replaced. The only really good solution to losing a tooth is to get a dental implant done. These are not cheap though, and in some cases a person may require dentures if too many teeth have been lost. This is a poor substitute for natural teeth. A better option, if at all possible, is to have a bridge that is attached to either two natural teeth or one or two dental implants. This at least makes a more functional form of dentition than a denture.