Root Formation, Attachment Apparatus, Periodontium, and Tooth Eruption

Fifty question-and-answer flashcards covering root formation, the attachment apparatus, cementum, alveolar bone, periodontal ligament, bone remodeling, tooth eruption, and shedding of primary teeth.

When does root formation begin in relation to crown development?

After the outline of the crown has been established but before the full crown is calcified.

Which structure elongates to form Hertwig’s epithelial root sheath?

The cervical loop.

What combined structures determine the shape and number of dental roots?

The epithelial root sheath and the epithelial diaphragm.

Which odontogenic cells are triggered by the epithelial root sheath?

Odontoblasts.

The presence of what tissue triggers cementoblast differentiation?

Dentin.

What junction is established when cementum begins to form?

The dentinocemental junction (DCJ).

List three clinical considerations related to root development.

Enamel pearls, accessory root canals, and epithelial rests of Malassez.

What is the inorganic content percentage of cementum?

Approximately 45–50%.

What is the typical color of cementum?

Yellowish.

At what anatomic landmark does cementum formation start?

The cervical line or cementoenamel junction (CEJ).

In roughly what percentage of teeth does cementum overlap enamel at the CEJ?

About 60%.

In roughly what percentage do cementum and enamel meet edge-to-edge at the CEJ?

About 30%.

In roughly what percentage is there a gap between cementum and enamel at the CEJ?

About 10%.

What mnemonic is used to recall the three CEJ relationships?

“OMG” (Overlap, Meet, Gap).

Which type of cementum contains living cells within lacunae?

Cellular cementum.

What term describes excessive thickening of cementum?

Hypercementosis.

What collagen fibers insert into cementum to anchor the periodontal ligament?

Sharpey’s fibers.

What is the process called when cementum is broken down and removed?

Cementum resorption.

What percentage of alveolar bone is inorganic material?

Approximately 65%.

Name the three principal layers of alveolar bone.

Cortical plate, alveolar bone proper, and cancellous bone.

Give three synonymous terms for alveolar bone proper.

Cribriform plate, lamina dura, and bundle bone.

Which layer of alveolar bone shows the lamina dura on radiographs?

Alveolar bone proper.

Into what bone do Sharpey’s fibers insert on the socket side?

Alveolar bone proper.

From which embryonic tissue does the periodontal ligament originate?

Mesodermal cells of the dental sac.

What are the three main fiber groups of the periodontal ligament?

Gingival fibers, transseptal fibers, and alveolodental fibers.

Besides support, what sensations does the periodontal ligament convey?

Pressure and temperature sensations.

True or False: The periodontal ligament has its own blood, lymphatic, and nerve supply.

True.

What term describes the natural forward movement of teeth toward the midline?

Mesial drift.

Which cells dissolve bone during orthodontic compression?

Osteoclasts.

Which cells lay down new bone on the tension side?

Osteoblasts.

During tipping movement, which side of the tooth socket undergoes compression and resorption?

The side toward which the crown is tipping.

What stage of tooth eruption begins while the crown is still developing within bone?

The pre-eruptive stage.

Which eruption stage starts once root formation commences?

The eruptive (prefunctional) stage.

Which stage of eruption starts when teeth reach occlusion and continues until loss?

The post-eruptive stage.

What is supraeruption and when does it occur?

Movement of a tooth beyond the occlusal plane due to absence of an opposing tooth.

Name two proposed mechanisms that drive tooth eruption.

Alveolar bone formation and vascular pressure.

List three factors that contribute to shedding of primary teeth.

Position of the permanent tooth, enzymes from the enamel organ, and intermittent physiological root resorption.

What is ankylosis in deciduous teeth?

Fusion of the tooth root to alveolar bone, eliminating the periodontal ligament.

Give one reason a primary tooth might be retained in the mouth.

Absence of a permanent successor (other acceptable answers: ankylosis, malpositioned permanent tooth, unresorbed root fragments).

How can a malpositioned permanent tooth cause retention of its primary predecessor?

If the permanent tooth erupts too far lingually it fails to resorb the primary root properly.

What leftover epithelial cells within the periodontal ligament can become cystic?

Epithelial rests of Malassez.

Which tissue, cementum or alveolar bone, is more highly mineralized?

Alveolar bone (65% inorganic vs. 45–50% in cementum).

What is an enamel pearl?

A small, spherical enamel projection on a root surface.

What are accessory root canals?

Extra canals that connect the pulp chamber with the periodontal ligament.

Which eruption stage ends when the tooth is exfoliated?

The post-eruptive stage.

Why is alveolar bone proper also called the cribriform plate?

It contains numerous small holes that allow blood vessels and nerves to pass between bone and the periodontal ligament.

What two broad categories describe cementum based on presence of cells?

Acellular cementum and cellular cementum.

Which category of cementum predominates on the coronal two-thirds of the root?

Acellular cementum.

Which category of cementum is found mainly on the apical third and in furcations?

Cellular cementum.

What intermittent pattern characterizes physiological root resorption during shedding?

Alternating periods of active resorption and rest/repair.