Premolars: The replacement teeth for baby teeth

Permanent premolars (permanent premolars) are placed between the anterior and molars. Eight premolars are found in the permanent dentition. Of these, 4 on each arc and two in each quadrant. The main function of the premolars is to assist the canines in tearing and stabbing food. They complement the grinding of the molars during chewing. Other functions are to support the corners of the mouth, enhance the smile appearance, and maintain verticality.

content

• 1. Introduction to premolars (RCNs)
• Time to grow
• 2. Upper molars
• 3. Lower premolars
• 4. The difference between the upper and lower premolars

1. Introduction to premolars (RCNs)

Terms

In English, RCN is also known by another common name "bicuspid" (two-pack teeth). However, RCNs are not always bipartite, so this designation is not widely used. The word for RCN in English and French is "premolar, premolaire", which is often translated into Vietnamese as "pre-jam", "pre-mortem". Although this term is still quite common and seems acceptable in translation, it is not biologically appropriate.

Time to grow

As we all know, there are 8 premolars (also known as premolars) on the human permanent teeth. The erupting RCNs replace the primary molars. They erupt between the ages of 9 and 11, before the eruption of the 2nd molars. The upper and lower first (first premolars 1) erupt relatively simultaneously (at about 9 years of age). This was followed by second RCNs (2 premolars) at about 11 years of age.

>> You can see more: The stages and time of teething of children that mothers should know .

4 premolars of the upper jaw

Quantily

Primitive humans had four premolars in each quadrant, or 16 per person. Over time, the central premolars – the teeth closest to the front of the mouth – were lost. Paleontologists refer to these medial premolars as 3rd and 4th premolars.

Body shape, function

The premolars occupy the position between the canines and the molars on the dental arch. Morphologically, they can be seen as a transition between canines and molars. We already know that canines have a wedge-shaped cusp suitable for biting or tearing. While molars have many segments and wide chewing surfaces, suitable for chewing and grinding functions.

RCN has at least one large and sharp cusp (outer cusps of the lower premolar). Or have 2-3 packs and have a relatively small chewing surface compared to molars (molars), suitable for stamping function. The RCNs and molars form a group of posterior teeth.

Summary of features of the premolar group:

1. Have at least 2 packs.
2. There is an outer pack and one or two inner packs.

2. Upper molars

Premolars 1 upper and lower jaw

• The upper RCNs 1 and 2 are more similar than the lower RCNs 1 and 2. Meanwhile, the lower RCNs look more different.
• The above RCNs have 2 large, prominent, relatively equal sizes. This is not true for the lower RCN.
• When viewed from the occlusal side, the upper RCNs are significantly larger in size than the mesial and distal sizes. In the lower RCN, these dimensions are roughly equal.
• When viewed from the side, the upper RCNs have an outer contour that is only slightly slanted inward, from the point of maximal lateral convexity to the apex of the lateral fascia. The lower RCNs have a stronger inward inclined outer contour.
• When viewed from above, the upper RCNs have a maximal internal convexity in the middle third. The inferior RCNs have maximal internal convexity in the occlusal third.

Size and age of eruption of upper premolars

3. Lower premolars

The lower RCN 1 from a purely functional point of view can be viewed as a canine. While the lower RCN 2 is like a miniature molar . Therefore, these two teeth do not resemble each other as much as the two RCNs above.

Premolars 2 upper and lower jaws

Features of the lower premolar arch:

• The size of the outside is much larger than that of the inside.
• The crown of the tooth has an outer-inner dimension that approximates the mesio-distal size.
• Viewed from the side, the outline is heavily tilted inward.
• The maximum convex point is about the occlusal third.
• The middle groove is curved inward.

Size and age of eruption of lower premolars

4. The difference between the upper and lower premolars

There are several common features that distinguish the upper RCN from other posterior teeth and the mandibular RCN:

• The upper first and second RCNs appear to be more similar than those of the lower molars. However, the crown of the first RCN in the upper jaw is usually larger than that of the second tooth. In addition, in the lower jaw, the first RCN was significantly smaller than the teeth of the same type.
• From the mesial and distal sides, the mandibular crown appears to be lingual in relation to the root. While the crowns of the upper molars are more aligned.
• The upper RCN has 2 chewing surfaces of approximately equal size. The lower RCNs may have more than two packs. The inner cusps of the lower teeth are usually less prominent than the outer cusps.
• The outer band was longer than the inner band in all RCNs. This difference was most prominent for the mandibular first RCN, and least prominent for the maxillary second RCN.
• The first RCN in the upper jaw is usually bipedal. While other RCNs have one pin.

Premolars are teeth that have a transitional shape between canines and molars. They perform the function to support the process of grinding and tearing food of the molars. Permanent RCNs erupt at the ages of 9-11, to replace the primary molars. When the baby molars are lost early, it will delay the eruption of permanent premolars. Therefore, we need to protect the baby molars until the time of tooth replacement is appropriate, to avoid early loss of caries.

Doctor Truong My Linh