Lecture 11: Development of Permanent Dentition

What is the most important characteristic of permanent tooth eruption compared to primary dentition?

Permanent teeth show much more variation in eruption timing and sequence

Which gender erupts permanent teeth earlier?

Girls by 5-6 months (except 3rd molars)

What is the most common eruption sequence in the lower arch?

Canine → first premolar → second premolar

What eruption sequence is associated with serial extraction cases?

First premolar → second premolar → canine

Which lower arch eruption pattern minimizes crowding?

Canine → first premolar → second premolar

What eruption sequence is associated with crowding?

First premolar → second premolar → canine

What does the eruption order chart show for the lower arch?

First molars, incisors, premolars, canines, and second molars

Around what age do first molars erupt?

6 years

Around what age do incisors erupt?

7-8 years

Around what age do premolars erupt?

10-12 years

Around what age do canines erupt?

11-12 years

Around what age do second molars erupt?

12 years and up

What clinical problem is associated with high buccal canines?

Ectopic eruption due to lack of arch space

What is the recommended management for palatally displaced canines?

Redirect eruption path by extracting primary canines

What is the most common eruption sequence in the maxilla, with 1 being the central incisors and 7 being the second molars?

6-1-2-4-5-3-7

What is the most common eruption sequence in the mandible, with 1 being the central incisors and 7 being the second molars?

6–1–2–3–4–5–7

What does the “timing is consistent within a dentition” principle mean?

Early eruptors tend to erupt all teeth early, and late eruptors erupt all teeth late

What should be investigated if eruption is asymmetric between left and right sides?

Pathology, ankylosis, impaction, or eruption disturbance.

Which teeth are most commonly crowded due to eruption sequence issues?

Maxillary canines and mandibular second premolars

What local factor can hasten permanent tooth eruption?

Periapical pathology of a primary tooth

If a primary tooth is extracted during active eruption, what happens to eruption time?

Eruption accelerates

If a primary tooth is extracted BEFORE root formation of the permanent tooth, what happens to eruption time?

Eruption is delayed

What does the “2/3 root formed” rule refer to?

Extraction accelerates eruption only when the permanent tooth has ≥ 2/3 root formation.

If a patient has a pulpotomy, what happens to the eruption of the permanent tooth?

May accelerate eruption if inflammation stimulates the follicle

What local factor slows eruption?

Premature extraction of a primary tooth before root formation of the permanent successor

What are the three major dimensional changes in dental arches?

• Arch width

• Arch length

• Arch perimeter

What drives arch width increase in the maxilla?

Alveolar process growth and buccal eruption of premolars and canines

Why does the maxilla gain more arch width than the mandible?

The divergent maxillary alveolar process allows more lateral growth

True or False: The sequence 4–5–3 is associated with crowding.

True

True or False: Premature extraction slows eruption

True

True or False: Arch width increases after canine eruption

False: it stops after canine eruption

Why does crowding occur?

Crowding occurs when the arch perimeter is insufficient for erupting teeth

How does poor eruption sequence effect the first molars?

It can cause mesially tipped first molars, blocking second molars

What does “dental eruption → wider placement” mean?

Permanent teeth erupt more buccally, requiring alveolar bone apposition

Why does intercanine width stop increasing after canine eruption?

Because the canines lock the arch form, preventing further lateral expansion

At what ages does the arch width growth?

4, 7 and 10 years, corresponding to general somatic growth spurts

Why does the maxilla gain more width than the mandible?

The divergent maxillary alveolar process allows more lateral bone apposition

Why do premolars erupt buccaly in the maxilla?

It contributes to arch width increase in the maxilla

What is arch perimeter?

The total length of the dental arch measured along the contact points

Which arch is easier to expand— maxilla or mandible? Why?

Maxilla— there’s more bone to grow

Why is mandibular expansion difficult?

The mandible lacks midline sutures and has dense cortical bone

What factors limit arch perimeter loss in the maxilla?

• Greater labial angulation of incisors

• Greater arch width increases

• Smaller leeway space

The maxilla may gain ______ of arch perimeter during eruption

Up to 3 mm

______ can create space when arch perimeter is insufficient.

Interproximal reduction

What happens to the occlusion when the Curve of Spee is flat? When it’s steep?

• Flat curve = stable occlusion

• Steep curve = deep bite tendency

Mandibular function influences _____ development.

Curve of Spee

When do third molars erupt?

17-18 years, often impacted

Removing impacted third molars is reasonable to prevent _____.

Pathology

Extracting third molars does NOT prevent ____ — correlation ≠ causation.

Relapse

What could happen to chin projection if the Curve of Spee became steep?

May coincide with growth spurts and chin projection

Why does arch perimeter decrease during mixed dentition?

Because primary molars are wider mesiodistally than premolars, and their loss reduces available space

Why is mandibular expansion unstable?

The mandible lacks sutural adaptability, so expansion relies on tooth tipping, which relapses

True or False: Extraction decisions should be based on pathology risk, not relapse prevention.

True

True or False: Maxillary arch perimeter is identical in males and females.

True

True or False: Retaining third molars always causes pathology.

False: risk increases but is not universal

Arch form is typically ______ and should guide treatment.

Stable

Arch perimeter loss is greatest in the _____.

mandible