• oral tissues develop from ectoderm, mesoderm, and endoderm
• orofacial development & odontogenesis (tooth development) knowledge of formation of these three aspects is necessary

• process by which the embryo forms and develops
• fertilization
• formation of zygote
• formation of morula
• formation of blastcyst
• beginning of the implantation process

• fusion of male & female gametes (sperm, ovum) to form zygote
• usually occurs in the ampulla of the uterine tube (fallopian tube or oviduct)

• first structure formed after fertilization of ovum by sperm
• contains normal human complement of 46 chromosomes
• 23 maternal, 23 paternal

• euploidy - condition of having a normal number of chromosomes
• aneuploidy - condition of having less than or more than the normal diploid number of chromosomes
• monosomy - the lack of one of a pair of chromosomes
• trisomy - having three chromosomes of a particular type

• arising from monosomy
• occurs in 1 out of every 2500 female births
• instead of the normal XX sex chromosomes, only one X chromosome is present and fully functional
• 70-80% of cases the sperm is missing the second X chromosome
• common characteristics are - short stature, problems w/ovary function, cardiac abnormalities, kidney abnormalities

• both primary and permanent teeth may erupt too early
• children may be 10-12 before they loose any of their primary teeth
• many girls w/Turner syndrome have a high arch palate and may have to use a palate expander
• the teeth may have small roots which may interfere w/orthodontic treatment

• estimated at 1per 600-800 births making it the most common chromosomal abnormality
• in 90% of cases the extra chromosome was present in the oocyte
• maternal age influences the risk of conceiving a baby w/the syndrome
• in females pregnant between ages 20-24the incidence is 1/1500, at age 40 is is 1/100, age 49 1/11

• severe periodontal disease is seen in up to 90% of adults w/Downs Syndrome w/onset in the mid to late teens
• pts may need to be seen every three months for scaling and root planing
• they often have upper respiratory infections, leading to mouth breathing and dry mouth (xerostomia)

• triple X syndrome, XXX syndrome, trisomy X, tripo-X, 47, XXX
• occurs n about 1 in 1000 newborn girls
• symptoms vary widely, but tall stature is common
• often causes no unusual physical features or medical problems
• most females have normal sex drive, and are able to conceive children

• XXX males
• occurs in 1 in 500-1000 male births
• extra X chromosome has equal probability of coming from the oocyte or sperm
• characterized by gyencomastia (enlarged breasts), a rounded body type w/abnormal body proportions, sparse facial and body hair, small testies, and an inability to produce sperm
• about 40% of pts have taurodontism, which is characterized by an elongated and enlarged tooth pulp - incidence rate is about 1% in healthy XY individuals

• occurs in 1 in 800-1000 males. 5 to 10 boys w/47 XYY syndrom are born in the US each day
• typically causes no unusual physical features or medical problems
• increased height and excess physical energy
• most males w/XYY syndrome have normal sexual development and are able to conceive children
• they have significantly longer tooth roots than normal males and females

• first consists of two cells called blastomeres
• mitotic divisions of the blastomeres are called cleavage
• 2-cell, 4-cell, and 8-cell zygote
• the zona pellucida is still present in the zygote and inhibits growth of zyote
• any one cell in a zygote can form an entire human
• loated in oviduct
• pre-embryo exsits as a zygote for 2-3days

• after 3days of cleavage the preembryo is a solid ball called the morula
• the cells are interdependent, one cell can no longer form one entire human
• cells start to communicate w/each other
• usually enters into the uterus by day 4 following fertilization

• by day 5, a fluid-filled cavity called the blastocoele or blastocyst cavity forms w/in the mass of cells of the morula
• the preembryo is now called a blastocyst
• the blastomeres are no longer indentical in size and shape, and two distinct cell populations are formed
• divided into an inner cell mass or embryoblast
• cells of the inner cell mass will become the embryo
• outer cell mass or trophoblast will become the embryonic part of the placenta
• healthy blastocyst should "hatch" from it's zona pellucida by the end of day 6 - within 24hours after hatching, it should begin to implant into the uterine wall

• by the end of the first week of development the blastocyst attaches to the uterine endometrium
• the inner cell mass is attached to the uterine wall
• ideal implantation site is the back wall of the body of the uterus towards the mother's spine

• occurs when a fertilized egg implants outside of the uterus, and the placenta and embryo begin to develop there
• 1/100 pergnancies
• most common site within in oviduct where they are called tubal pregnancy (95%)
• ectopic pregnancies also occur in the ovary, abdomen, and cervix
• 40-50 women die each year from ectopic pregnancy in the US

• outer cell mass or trophablast differentiates into cytotrophoblasts and syncytiotrophblasts
• these cells contribute to formation of the placenta and fetal membranes
• endometrium
• hypoblast
• syncytiotrophblasts
• cytotrophoblasts
• epiblast
• blastocyst cavity

• trophoblast cells secrete many hormones including hCG
• in non-pregnant women hCG levels are undetectable
• during early pregnancy hCG levels double every two to three days

Pregnancy Detection

• most commonly used hormone used to detect pregnancy is the beta subunit of human chorionic gonadotropin (hCG)
• betahCG is detectable in blood 8-9 days after ovulation
• home pregnancy tests measure betahCG in urine
• HPT are most commonly used in the week after the missed menstrual period (fourth completed gestational week)