Sound Dental Arch

Question 1

What is the sound dental arch?

Answer 1

Term used to describe the ideal arrangement of teeth and their supporting structures.
Has 3 main functions:
1. Prevention of disease
2. Balance of occlusal forces
3. Protection of gingivae and periodontium.
Any slight deviation from the sound dental arch leaves the oral cavity susceptible to attack.

Four main factors that make up the sound dental arch:

1. Tooth form and function
2. Alignment
3. Occlusion
4. Gingivae

Question 2

Tooth form and function

Answer 2

In order that the teeth perform their function , they should conform to their set morphological pattern. In addition to this the following 6 characteristics should exist:

1. Sound dental arch should possess correct number of teeth.
2. Smooth enamel- enamel should be smooth to prevent notches for colonisation of bacteria and trapping of food particles.
3. Tooth contour - labial/ buccal and lingual/ palatal surfaces should possess correct degree of contour. The contour is to deflect food away fro, the gingival margin at an angle that facilitates its return to the occlusal surfaces for mastication . Contour of teeth most prominently developed in areas where food is propelled with greatest force during mastication. Ie buccal of molars.
4. Cingulum - present on palatal or lingual surfaces it has a similar function to tooth contour. After incision and during mastication it deflects food back into oral cavity.
5. Marginal ridges - keep foods within confines of the tooth surface during mastication. Marginal ridges most developed on teeth bearing most masticatory force.
6. Curvature of cervical line - mesial and distal surfaces of anterior teeth show a greater curvature of the cervical line than those of posterior teeth. An extension of alveolar bone called interdental bony septum projects into this area. Gives more support to single rooted teeth to prevent drifting. More support on mesial surface than distal to prevent mesial drifting.

Question 3

Tooth contour

Answer 3

Normal contour - food is deflected away from the gingival crevice.
Over contoured - food is forced and moved into vestibular area.
Under contoured - food forced into the gingival crevice.

Question 4

Occlusion

Answer 4

The term used to describe the relationship between occlusal or incisal surfaces of the teeth in maxillary arch to those in Mandibular arch when in a position of rest. Ideal occlusion known as ANGLES CLASS 1.

Question 5

Gingivae

Answer 5

To complete the sound dental arch the gingivae should be healthy: pale pink, firm, stippled , and scalloped. They should cover the CEJ and terminate at knife edge at the gingival crevice. Crevice should be 1.5-2mm deep . Interdental papillae should completely fill the interdental spaces to contact area.

Question 6

Alignment

Answer 6

Shape of arch is perfect semi eclipse, with the incisal edge of the anterior teeth and buccal cusps of the posterior teeth forming a continuous arch.
3 further considerations:
1. Contact areas - each tooth except for central incisors and posterior molars contact mesially and distally at a precise centrally located contact area. Two main functions are to prevent food packing and provide added support and resistance to occlusal forces.
2. Embrasures - space between the teeth situated occlusally to contact area. They’re rounded and smooth. Function is to: allow food to splay off during mastication, prevents food packing , reduce occlusal forces , also known as spillways.
3. Interdental spaces - spaces between two teeth cervical to the contact area. To achieve a sound dental arch this space should be filled with interdental papillae to prevent food packing. Main function is protection.

Question 7

Other factors assisting the sound dental arch

Answer 7

Sound dental arch should evacuate all masticated food by using its self cleansing mechanism.
Tongue - assists self cleansing mechanism by returning food to occlusal surfaces, forms food into a bolus before deglutition , dislodges remaining food particles, sensitive especially to temp.
Palate - assists tongue in first two functions, acts as sturdy structure for tongue to work against, also very sensitive.
Cheek and lips - help to return food to occlusal surfaces, muscular forces along with tongue maintain tooth alignment.
Saliva - lubrication of food to aid in bolus formation , antibacterial properties, washes over teeth after removing remaining food particles after deglutition , reduces acidity, prevents drying of mucosa.