صناعة / د . هالة
ثاني اسنان موصل10 / 3 / 2016
صناعة / د . هالة
ثاني اسنان موصل10 / 3 / 2016
Selection of artificial teeth
When selecting and arranging teeth for complete denture, there are four factors to be considered(Objectives):1.Esthetics
2.Masticatory function
3.Correction of speech defects
4.Preservation of the remaining tissue and muscle tone
Primary selection of the teeth must be carried out at the first appointment. Selection of anterior teeth
pre-extraction guides for teeth selection :
1. Diagnostic casts with natural teeth.
2. Pre-extraction photographs.
3. Pre-extraction radiographs.
4. Observation of teeth of close relatives.
5. Preserved extracted
Post extraction guide: when pre-extraction guides are not available we depend on the following factors :
A. Shade (color). B. Size. C. Form.
A) Shade: Shade mean degree of darkness of the color. There are two basic shades, the yellow and gray are the basic shades, and the other shades vary in between . Also it should be compatible with the general coloring of the skin, hair and eyes.The factors of shade selection are:-
(1. Age. 2. Sex. 3. RACE. 4. Patient –preference)
1. Age: The younger the patient, the lighter the color is preferred. The color of natural teeth darken with age because of deposition of secondary dentin , wearing away of enamel and external staining from oral fluids, foods or tobacco.
2. Sex: The sex may effect color, it seems that females given brighter teeth than males.
3. race: The color of the face should harmonize the color of teeth. Lighter teeth are suitable for lighter skin, while darker teeth are suitable for darker skin, although darker people with dark skin seemed to have very light teeth. This is because of contrast in the skin and tooth color.
4. Patient preference (method of pair comparison):-
Show the patient a complete shade guide and select the two tabs that are lightest and darkest, hold them against the patient lip and ask them to point to the one that they prefer. More than two or three shades should be selected and comparison between them would help in final right selection.
B) Size To select size of anterior teeth we have to consider the following:
(1. Length. 2. Width. 3. Method of pair comparison.)
1. Length:- The length of upper anterior teeth is controlled by:-
* Inter-ridge distance.
* Length of upper lip:
A. In short lip more than 2mm seen from upper central incisor.
B. In medium lip 1-1.5 mm seen from upper central incisor.
C. In long lip nothing can be seen from upper central incisor.
The length of lower anterior teeth should be with level of lower lip.
2. Width:
A: The width of upper central incisor equals Approximately 1/16 of bi- Zygomatic width ,and width of upper ant teeth equal to 0.3 bi-Zygomatic width.
B. The width from the tip of left canine to the right canine is almost equal to the width of the nose when measured in a straight line by a caliper.
If the base of the nose is wide the central incisor should be wide, if the root of the nose is narrow the lateral incisor should be narrow.
C. Width of anterior teeth can be measured on upper occlusion rim depending on Labial frenum(mid line), corner of the mouth( Incisal papilla & cuspid eminences)By: drawning aline from the distal termination of the eminence (or anterior to buccal frenum attachment) following the contour of the ridge , reaching the anterior border of incisal papilla, then terminate distal to canine eminence of opposite side A mark is placed at occlusion rim at each corner of the lips when the patient is relaxed
C. Form:-
The form of anterior teeth(ex; rounded ,ovoid or tapered teeth) depends on the following:
1. Face form. 2. Sex, age and personality. 3. Method of pair comparison.
1. Face form:- According to frontal out-line, face could be classified into square, ovoid and tapering. The upper central incisor form should be in harmony with patient face.
2. Sex, age and personality:- Sex: Masculine form is associated with square, cuboidal and angular form. While feminine form associated with more rounded, ovoid and tapering features.
Age: In old patients the teeth tend to have square form due to attrition, more round features disappears and line angle quite seen in those patients.
Personality: It seems reasonable that a large vigorous type of persons have teeth of a size and form with prominent markings, different from those of a delicate appearing woman.
3. Method of pair comparison
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 artificial teeth
Posterior teeth are selected for shade( color), buccolingual width, mesiodistal length, vertical height (occluso-gingival length) and occlusal form.
1- Shade (color):
Shade of posterior teeth should be harmonized to the shade of anterior teeth, maxillary first premolars are sometimes used for esthetic more than function, so it's 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 (post. Contain dentin more than ant.).
2- Buccolingual width:-
The buccolingual width of posterior teeth should be slightly narrower than natural teeth to decrease occlusal surfaces which direct less stress during function to supporting tissue, and also enhance the development of the correct form of polished surfaces of the denture.
3- Mesiodistal width:
The mesiodistal width of posterior teeth should be equal to the distance between canine line and anterior border of maxillary tuberosity for upper teeth. For lower teeth should be equal to distance between canine line and anterior border of retro molar pad area.(the width with in design limit)
Note : Placing a tooth on an inclined plane should be avoided, otherwise dislodgment of denture occur.
4- The occlusogingival height
The occlusogingival height or length is controlled 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, short, medium. Long posterior teeth are generally more esthetic in appearance than are shorter teeth.
5- Occlusal form:
There are two forms:-
a) Cusp form (anatomical teeth): Anatomical teeth have cusp angles 30, 20 degrees.(angle between the cusp tip and flat occluosal plane)
b) Non cusp (cuspless) form teeth: also called monoplane or zero degree teeth.
Disadvantage of cusps on teeth is that alveolar resorption which cause reduction in vertical dimension and the interlocking of the cusps causes the lower denture to be displaced forwards and the upper backward causing damage to the underlying tissues.Materials of artifcial teeth:-There are two main types:
1. Porcelain teeth:We have vacuum fired and air fired. The vacuum is better because they are harder and have luster. Generally porcelain teeth are preferred particularly for young person because they look more vital, very smooth and difficult to abrade.
2. Acrylic teeth:
They are made from acrylic resin, indicated when there is insufficient inter-occlusal distance, and grinding becomes necessary, also in situation where there are opposing natural teeth, partial denture and gold bridge. They are inferior when they are compared with porcelain because they can not maintain luster for long time and abraded easily.
