Teeth selection

Dr. Salah Kh. Al-RawiBDS, MSc, Dental Science, Prosthodontist (Baghdad University)

PhD, Maxillo-Facial Prostheses (Universiti Sains Malaysia, USM)
9-5-2016
Selection of teeth in complete denture

OBJECTIVES IN TEETH SELECTION

1- The teeth should be in harmony with the surrounding tissues.
2- They should maintain the vertical dimension.
3- They should be efficient for mastication.
4- Anterior teeth are selected predominantly based on esthetic, whereas the posterior teeth should be selected based on the function.
Selection of artificial teeth includes:
1- Selection of anterior teeth.
2- Selection of posterior teeth.

SELECTION OF ANTERIOR TEETH

Anterior teeth are primarily selected to satisfy esthetic requirements. Records of shade, size, and form of teeth could be obtained from pre-extraction records which include
1- Preserved extracted teeth.
2- Previous diagnostic casts with natural teeth.
3- Pre-extraction radiograph.
4- Pre-extraction photograph.


Factors to be considered when pre-extraction records are not available

1-Shade. 2- Size. 3- Form.

SHADE
It is the degree of darkness of the color. There are two basic shades, the yellow and grey, and the other shades vary in between.
The factors of shade selection
1- AGE
The younger the patient, the lighter the shade is preferred. The shade of natural teeth will be darkening with age because of
A- Deposition of secondary dentin.
B- Consequent reduction in size of the pulp chamber.
C- Wearing a way of enamel.
D- External staining of the exposed dentin from oral fluids, foods, or tobacco.
2- GENDER
The gender may affect the shade; it seems that females are given lighter and brighter teeth than males.

3- COMPLEXION

The color of the face should harmonize the shade of the teeth. Lighter teeth are suitable for lighter skin, while darker teeth are suitable for darker skin. Although people with dark skin seemed to have very light teeth, this is because of contrast in the skin and teeth color.
4- PATIENT PREFERENCE
Show the patient a complete shade guide and select the two tabs that are the lightest and the darkest, hold them against the patient lip and ask them to point to the one that they prefer this method called (method of pair comparison). More than two or three shades should be selected and comparison between them would help in final right selection.


SIZE
To select the size of anterior teeth, we have to consider the following:

1- LENGTH

The length of anterior teeth is controlled by:
a- Length of upper lip:
• In short lip more than 2 mm seen from the maxillary central incisors.
• In medium lip length 1.5-2 mm seen from the maxillary central incisors.
• In long lip nothing can be seen from the maxillary central incisors.

b- Level of the lower lip:

Length of mandibular anterior teeth should be with the
level of lower lip.
c- Inter-ridge distance:
When the space is available, it is more aesthetically acceptable to use a tooth long enough to eliminate the display of the denture base (teeth are more attractive in appearance than denture base materials).

2- WIDTH

a- The width from the tip of left canine to the tip of right canine is almost equal to the width of the nose (interalar width) when measured by the caliper. (Width of six anterior teeth = interalar width + 7 mm).

b- The width of maxillary central incisor equals approximately to 1/16 of bizygomatic width, and the width of maxillary anterior teeth equals to 1/3.36 of bizygomatic width.

c- Width of the anterior teeth can be measured on maxillary occlusal rim depending on the intraoral anatomical landmarks like: (buccal frenum, corner of the mouth, and canine eminence).

FORM

The form or outline of anterior teeth depends on the following factors

1- FACIAL FORM

According to frontal outline: The face could be classified into: square, ovoid, and tapering. The maxillary central incisor form should be in harmony with patient face.
According to profile: The face could be classified into: straight, convex, and concave. The labial surface of maxillary central incisor viewed from mesial aspect should be in harmony with profile of face.

2- GENDER

• Masculine form is associated with square, cuboidal, and angular form.
• Feminine form is associated with more rounded, ovoid, and tapering features.

3- AGE

In old patients the teeth tend to have square form due to attrition, more round features disappear and line angle quite seen in those patients.

4- PATIENT PREFERENCE

Allow the patient to select between the same size teeth but different forms. Set two different forms of teeth on the right and left sides of a piece of wax rope, and ask the patients which they prefer.

SELECTION OF POSTERIOR TEETH

Posterior teeth are selected for
1- Shade 2- Size 3- Occlusal form
1- SHADE

Shade of posterior teeth should be harmonized to the shade on anterior teeth, maxillary first premolars are sometimes used for esthetic more than function, so it is advisable to select premolar teeth with lighter color than the other posterior teeth, but not lighter than anterior teeth. Generally the shades of posterior teeth are slightly darker than anterior teeth.

2- SIZE

Occlusogingival height
It is determined by the available inter arch distance. The length of the maxillary first premolar should be comparable to that of maxillary canine to have the proper esthetic effect.
The height of posterior teeth usually divided into long, medium, and short. Long posterior teeth are generally more esthetic in appearance than are shorter teeth.

Buccolingual width

The buccolingual width of posterior teeth should be slightly narrower than natural teeth, because the broader occlusal surfaces which direct more stress during function to supporting tissue, leading to increase in the rate of ridge resorption. Broader teeth exceed into the tongue space leading to instability of the denture. Also, the teeth should not exceed into the buccal corridor space to avoid cheek biting.

Mesiodistal length

The combined mesiodistal lengths of all maxillary posterior teeth in that side of the arch should be equal to the distance between canine line, and anterior border of maxillary tuberosity.

For mandibular posterior teeth, the mesiodistal lengths should be equal to distance between the canine line and anterior border of retromolar pad. If the residual ridge anterior to retromolar pad area slopes upward, smaller teeth or even fewer in number must be used. Placing a tooth on an inclined plane (steep anteroposterior ridge slope) should be avoided, otherwise this would lead to forward displacement of the denture and dislodgment of denture occurs. Similarly the teeth should not be placed over displaceable tissues like the retromolar pad as it will cause tipping of the denture during function. In case with inadequate mesiodistal length, the premolar can be neglected.

3- OCCLUSAL FORM

There are two forms
a- Cusp form (anatomical teeth): They have anatomical teeth have cusp angles 33; 20; 5.
b- Non-cusp form (cuspless form): They also called monoplane, flat plane, or zero degree.
ADVANTAGES OF CUSP FORM TEETH
1- More efficient in chewing.
2- More acceptable esthetically.
3- More compatible with surrounding oral environment.
4- They can be arranged in balanced occlusion in eccentric position.
5- The cusp fossa relationship between the maxillary and mandibular posterior teeth forms a definite point for return to centric occlusion.

ADVANTAGES OF NON-CUSP FORM TEETH

1- Offer less resistance in non-masticatory movement like (bruxism); therefore less damaging to the supporting structure.
2- Offer less resistance to lateral forces therefore, they are indicated in excessively resorbed ridges.
3- Allow greater range of movement which is necessary in patient with malrelated jaws.