Primary, Mixed, and Permanent Dentition: Eruption, Arch Development, and Occlusion

Flashcards covering primary, mixed, and permanent dentition characteristics, eruption sequences, arch development, leeway spaces, and Andrews' 6 keys of orthognathic occlusion.

How many teeth are in the primary dentition compared to the permanent dentition, and what clinical clasp does the absence of premolars favor?

There are $20$ teeth in the primary dentition compared to $32$ in the permanent dentition; the absence of premolars makes the Schwartz clasp more suitable.

What are the characteristic size and root features of primary teeth compared to permanent teeth?

Primary teeth have smaller and shorter clinical crowns, equators positioned more gingivally, and roots that are more spread out to create space for premolars.

What are the morphological forms of primary incisors, canines, and molars?

Primary incisors are spade-shaped, canines are spear-shaped, and molars are rhomboid-shaped.

What is the normal eruption timeline for each group of primary teeth?

First incisors erupt at $6-8\,\text{months}$, second incisors at $8-12\,\text{months}$, first molars at $12-16\,\text{months}$, canines at $16-20\,\text{months}$, and second molars at $20-30\,\text{months}$.

What defines premature and late eruption in the primary dentition, and what is the acceptable time range for eruption?

Premature eruption occurs before $4\,\text{months}$ of age, late eruption occurs after $1\,\text{year}$ of age, and the acceptable time range is $1\,\text{year}$ after the expected time.

What are the timelines for root formation and root resorption in primary teeth?

Root formation finishes $1^{\text{st}}-2^{\text{nd}}\,\text{year}$ after tooth eruption, and root resorption begins $2.5-3\,\text{years}$ after full root formation.

What are the periods of primary dentition development and when does development of the apical base begin?

Primary dentition formation lasts from $6\,\text{months}$ to $2.5/3\,\text{years}$, stable primary dentition lasts from $3-6\,\text{years}$, and development of the apical base begins at $4\,\text{years}$.

According to Vladislavov, how does spacing in primary arches affect secondary tooth alignment, and where are primate spaces located?

Arches with diastemas and gaps ($>0.5\,\text{mm}$) guarantee proper alignment of secondary teeth in $80\%$ of cases, whereas arches without diastemas result in improper alignment of secondary incisors in $75\%$ of cases. Primate spaces are located anterior to the canine in the maxilla and posterior to the canine in the mandible.

What are the normal sagittal occlusal relationships for overjet and canines in the primary dentition?

The normal overjet is $0-4\,\text{mm}$ (with an overall normal range of $2-6\,\text{mm}$), and the upper canine cusp tip occludes with the contact point between the lower canine and the primary lower first molar.

What are the three terminal plane relationships in primary dentition and their clinical classification?

1. Flush terminal plane (normal: maxillary and mandibular terminal planes are at the same anteroposterior level); 2. Mesial step (normal: mandibular plane is more anterior than the maxillary plane); 3. Distal step (pathological: mandibular plane is more posterior than the maxillary plane).

Why is a moderate deep bite not considered pathological in the primary dentition?

Because two physiological bite openings are expected to occur during development.

What is the key exception to the rule that permanent teeth are larger than primary teeth?

The mesiodistal ($\text{MD}$) diameter of primary molars is greater than the mesiodistal ($\text{MD}$) diameter of premolars.

What is the eruption sequence and timeline for permanent teeth in the maxilla and mandible?

Eruption sequence in maxilla is $6, 1, 2, 4, 3, 5, 7$ and in mandible is $6, 1, 2, 3, 4, 5, 7$. Ages: $6\,\text{y/o}$ (1st molars and central incisors), $7\,\text{y/o}$ (lateral incisors), $8\,\text{y/o}$ (1st premolar), $9\,\text{y/o}$ (canines), $10\,\text{y/o}$ (2nd premolars), and $12\,\text{y/o}$ (2nd molars).

At what root development stage does a secondary tooth migrate through bone, and when is root formation complete?

A secondary tooth moves through bone when $1/2$ of its root length has formed, and root formation finishes $3-4\,\text{years}$ after eruption.

What are the two phases of early mixed dentition ($6-9\,\text{years}$)?

Phase I ($6.5-7\,\text{years}$) is characterized by active growth of the anterior dental arch segment; Phase II ($7.5-9\,\text{years}$) is characterized by root formation of erupted teeth and moderate arch growth.

What are the two phases of late mixed dentition ($9-12\,\text{years}$)?

Phase I ($9-10.5\,\text{years}$) shows no active growth of the dental arch as premolars erupt; Phase II ($10.5-12\,\text{years}$) involves premolar root formation, canine eruption, and active dental arch growth.

What is leeway space, and what are its values in the maxilla and mandible?

Leeway space is the difference between the greater combined mesiodistal diameter of primary molars and the smaller combined diameter of succedaneous premolars, measuring approximately $1.5\,\text{mm}$ in the maxilla and $2.5\,\text{mm}$ in the mandible.

What are the upper and lower arch forms in mixed dentition, and what is the deepest point of the Curve of Spee?

The upper dental arch is semi-elliptical and the lower dental arch is U-shaped. The Curve of Spee has its deepest point of $1.5\,\text{mm}$ located at the premolars.

How do anterior and posterior arch dimensions change during mixed dentition?

Anterior length increases by $2.2\,\text{mm}$ in the maxilla and $1.3\,\text{mm}$ in the mandible during incisor/canine/1st molar eruption; posterior segment length decreases by $2-2.5\,\text{mm}$ in the maxilla and $2.5-3\,\text{mm}$ in the mandible as leeway space is consumed by the mesial movement of molars.

What are the three physiological bite openings described in dental development?

a. Eruption of the 1st primary molar and complete occlusion; b. Eruption of the 1st secondary molar and complete occlusion; c. Complete occlusion of canines and 2nd secondary molars.

What defines the 'ugly duckling stage' of upper lateral incisors, and how does it resolve?

Upper lateral incisors erupt with distovestibular inclination; spontaneous uprighting occurs naturally with the eruption of the permanent canines.

When does active jaw growth take place in the permanent dentition, and what does late growth during the $17-20^{\text{th}}\,\text{year}$ cause?

Active jaw growth occurs at $12-13.5\,\text{y/o}$ and continues to age $15$ (when root formation of permanent 2nd molars is complete); late growth during the $17-20^{\text{th}}\,\text{year}$ leads to crowding of the lower anteriors.

How is space created for the alignment of permanent 2nd and 3rd molars in the maxilla and mandible?

In the maxilla, space is provided by bone apposition in the tuberosity area; in the mandible, space is provided by bone resorption of the ramus.

What are Andrews' 6 keys of orthognathic occlusion?

1. Molar relationships (Class I); 2. Mesiodistal ($\text{MD}$) inclination of teeth; 3. Labiolingual inclination of teeth; 4. Lack of teeth rotations; 5. Presence of full proximal contact between teeth in dental arch; 6. Flat presence of curve of Spee.