PTA assembly

PTA assembly

1. INTRODUCTION

Creating a prosthesis that meets aesthetic, functional, mechanical and biological requirements is the objective that determines the choice and assembly of artificial teeth. 

2. DEFINITION OF THE MOUNTING

This is the stage in the laboratory which consists of making wax models bearing artificial teeth prefiguring the finished prosthesis.

3. ASSEMBLY OBJECTIVES
4. Aesthetic objective:

  The harmony of the face and the restoration of the smile will depend on:

• The height of the lower floor.
• The orientation and position of artificial teeth.
• The choice of prosthetic teeth.
• The character of the false gum.

2. Mechanical objective:

The durability of prosthetic retention and stability.

3. Functional objective:

Restore and improve chewing and phonation function.

4. Biological objective: 

Preserve as much as possible the biological integrity of the support surfaces on the mucosal and bone plane, while respecting the principles of assembly.

5. Psychological objective:

Contribute to the reintegration of the patient into society (totally edentulous patients are affected in their communication and relationships with others), and this will depend on the patient/practitioner relationship.

4. PREREQUISITES FOR ASSEMBLY

1. Drawing the marks on the models:

 * The tracing on the upper model: -median sagittal plane.

-ridge line

-position of the canine tips

-anterior limit of the tuberosity.

-line passing through the center of the retroincisive papilla.

-line of the bottom of the vestibule.

*The tracing on the lower model: -median sagittal plane.

-line of the ridge crest and its anterior and posterior extension.

-anterior support zone between the top of the anterior crest and the bottom of the vestibule (ACKERMANN area)

-anterior limit of each trine.

2. The upper occlusion model  :

Used to determine and record the RIM, it is equipped with a wax rim adjusted in position, volume and orientation so as to prefigure the situation of the teeth.

Some points must be engraved on the bead:

• The inter-incisal midpoint taking the symmetry of the face as a reference.
• The projection of the lower edge of the upper lip during the forced smile in order to determine the line of the necks.
• The position of the canine tips which is located at a tangent to the wings of the nose  

 (LEE index).

PTA assembly

3. The prosthetic occlusion plane:

The upper model is set parallel to the Camper plane posteriorly, and to the bipupillary line anteriorly, thus defining the prosthetic occlusion plane.

4. Transfer to articulator:

Following the determination of the intermaxillary relationship, the models are transferred to the articulator.

Positioning the models relative to each other allows for precise objectification of the space available for the teeth.

• The projection of the inter-ridge axis.

This axis is the one which, in the frontal plane, joins the summits of the maxillary and mandibular crests.

PTA assembly

5. CHOOSING ARTIFICIAL TEETH

In complete prosthesis, the choice of anterior and posterior teeth is conditioned by aesthetic considerations (ant teeth) and functional considerations (post teeth). This choice is under the exclusive responsibility of the dental surgeon who is made according to the following criteria: materials, size, shape, shade.

1. Choosing anterior teeth 

The choice of anterior teeth is a very important step, it is often the key to success or failure in the eyes of the patient.

1. materials  : the choice is relatively limited since it is only between ceramic (porcelain) and plastic (acrylic resin)

Ceramic Resin

Benefits

-natural appearance with different translucency -shock resistance

-chemical, mechanical and aesthetic stability -easy grinding on all sides

-abrasion resistance -progressive abrasion 

-possible make-up and characterization -chemical bond with the base

-excellent retention at the base thanks to the crampons -easy makeup using several techniques

– easy disassembly by heating – reasonable cost price. 

Disadvantages

-very limited grinding possibilities -difficulty in dismantling them

-great fragility, particularly of the free edge -lack of sharpness in the eyes of the patient -no chemical bond with the base -adhesion of certain foods

-appearance over time of an unsightly colored border -loss of aesthetic quality over time -gold studs sometimes annoying -lack of translucency  

-complex makeup requiring baking in the oven

-price

Indications

-young patient very concerned about their aesthetics -always except contraindications

-patient requiring porcelain anterior teeth -need for significant grinding

                  -very elderly patients

                  -floating crests.

Contraindications

-resin posterior teeth -patients requiring ceramic posterior teeth

-very elderly patients

-requires significant grinding

-reduced available space in height

2. size, shape, color:

		Upper anterior teeth	Lower anterior teeth
DIMENSION	width	Mathematical formula linking facial landmarks: -LEE larg bloc inc/c sup=distance qi separates the inter-incisor point from the wing of the nose.	-Their overall width represents 4/5 of the width of the upper teeth.-Narrower to allow horizontal overhang.
	height	-inter-ridge distance: long upper antlers so as not to reveal the false gum when smiling.-Smile: the teeth touch the lower lip.	-Residual space between the Inc sup and the lower crest.-It is advisable to choose them short (end to end in propulsion without loss of post contact)
SHAPE	Face shape	Square face: square toothTriangular face: triangular toothOvoid face: round toothMixed face: rectangular tooth	The appearance of inc inf is often neglected, it is necessary to think about discarding overly juvenile forms with thin free edges and to consider abrasions in elderly people.
	profile	Curvilinear profile: rounded teethFlat profile: flat teeth
	sex	Female sex: teeth soft and rounded, incL narrower and rounded at the distal edge (LOMBADI)Male sex: tooth vigorous and square
	age	Elderly: inc abraded with a cracked free edge.
	SkinEyesHair	-Light skin: white-grey teeth-Redheads: teeth with a greyish tendency-Blue eyes/blond hair pair: white to grey teeth.-Brown eyes/brown hair pair: teeth with a yellowish brown tone
	personality	– Vigorous personality: saturated tooth – Delicate personality: more saturated tooth
	Age	Older people: teeth are yellower, more saturated, less shiny, less translucent.

5.2 Choice of posterior teeth: the posterior teeth are chosen essentially according to functional criteria, they must nevertheless satisfy certain aesthetic requirements (the 1st pm is visible).

The choice therefore depends on: – the state of the underlying tissue.

– muscular, ligamentous, joint capacity of the patient.

-chewing habits of the patient.

5.2.1 Materials: As with ant teeth, the decision is essentially between ceramic and resin, but improved resins exist, and it has also been proposed to use partially or totally metallic grinding faces.

Ceramic Resin 

Benefits

-low wear ensuring the durability of the occlusion -chemical bond with the base

-maximum masticatory efficiency -perfect polishing

– excellent retention at the base thanks to the crampons – easy grinding on all sides

– easy disassembly by heating – softer contact and absence of noise during occlusion 

Disadvantages

-no neuro-articular adaptation of the occlusion

by abrasion – difficulty in dismantling them

 -occlusal noise sometimes annoying -low resistance to abrasion

– very limited grinding – no lasting occlusal stability

-no chemical bond with the base -reliable masticatory efficiency

-difficulty polishing after grinding

-price

Indications

-always except contraindications -patient fearing the clicking of porcelain.

-deficient covering and/or underlying tissues.

-insufficient inter-ridge distance.

-very elderly patients.

Contraindications

-very elderly patients -patients requiring perfect occlusal stability 

-reduced available height space -porcelain anterior teeth (absolute CI)

– need for significant grinding

-floating crests

5.2.2 dimension, shape, color:

	Posterior teeth
Dimension	Vestibulo-lingual width	The vestibulo-lingual diameter is proportional to the relief of the crest: – thin, flat or concave crest: narrow tooth. – high, wide crest: wide tooth.
	Mesio-distal length	Proportional to the length of the crest-canine tip to the anterolateral limit of the tuberosity at the maxilla.-canine tip to the anterolateral limit of the trigone at the mandible.
	Height	-According to the inter-ridge space identified on the articulator – 1st pm at the same height as the canine (a little shorter because it is visible when smiling)
Tint	-secondary-must be in harmony with the shade of the anterior teeth.-1st pm less saturated than the canine, 2nd pm more saturated than the 1st pm-molars must never appear lighter than the anterior teeth.

Note 7: when the length of the arch is not sufficient, it is possible to mount one less tooth or to replace a molar with a premolar.

2. ASSEMBLING TEETH IN BIMAXILLARY PROSTHESIS

Gysi’s assembly:

This assembly continues to have an almost universal value, it is also chosen by many prosthetics specialists, uses anatomical teeth.

1 assembly of anterior teeth

*The principles of assembly:

• The free edges of the upper antlers reproduce the external contour of the maxillary rim determined clinically.
• The central incisors are placed on either side of the interincisal point.
• The mounting of the ant teeth must provide support for the lips.
• The line joining the free edges of the upper incisors must harmonize with the edge of the lower lip (more curvilinear in women, straight in men)

PTA assembly

• In the maxilla, the favorable conditions of stability of the base make it possible to locate and orient the anterodental teeth according to the aesthetic conditions (outside the support area)

• In the mandible, the lower mechanical value of the base, on the other hand, requires the assembly of the ant teeth inside the support area: the incisors and canines are placed on the external slope of the edentulous crest, and its free edge does not exceed the bottom of the vestibule.
• The assembly of the lower teeth must respect the shape of the lower arch.
• The free edge of the mandibular incisors is often located 1 mm below the edge of the lower lip.
• The position of the upper incisors in relation to the lower incisors should have a vertical and horizontal overhang of approximately 1 mm.

*assembly itself:

	Horizontal plane	Frontal plan	Sagittal plane
Upper central incisor	-Mounted 6mm in front of the retroincisive papilla	-Vertical-In contact with the POP by its free edge.	Vetibulo-versée of 5°
Upper lateral incisor	Its free edge is continuous with that of the central one	-located 1 mm above the POP.-inclined distally by 10°.	-Vetibulo poured 10°
Canine sup	-the position of the 2 canine tips must be symmetrical (in alignment with the retro-incisive papilla)	-canine tip rests on the mounting plane.-is parallel to the lateral.	-vertical
Lower central incisor	-its heel is placed 1.2mm in front of the crest.-its edge is 1mm from the lingual face of the central sup: over bite.	-edge is parallel to the POP-vertical-the central upper covers it by 1mm	-slightly vestibulated.
Lower lateral incisor	-the horizontal overhang must be respected.-the free edges are inscribed in the curve of the upper free edges.	– inclined in this direction mesially by 5°	-vertical
Lower canine		Tilted mesially by 10°	-slightly lingual.

PTA assembly

2 mounting of posterior teeth

This step is important because it determines the stability and effectiveness of the prostheses.

The assembly of these teeth must comply with certain requirements:

*static requirements:

• The upper posterior teeth will be mounted so that their palatal cusps project onto the inter-crest axis.
• The occlusal plane is located parallel and at an equal distance from the 2 crests both in the frontal and sagittal planes.
• The maxillary intercuspal grooves must be aligned, corresponding to the alignment of the tips of the mandibular vestibular cusps.

*dynamic requirements:

• The occlusal surfaces must achieve a curve with superior concavity in the sagittal plane called the SPEE curve, the main purpose of which is to promote the achievement of a balanced occlusion in propulsion and diduction.
• Respect for the WILSON curve, which allows harmonious occlusal sliding of the lower vest cusps on the upper vest cusps (internal slope) during the lateral movement.
• The assembly must be perfectly symmetrical in order to avoid destabilization of the prostheses.

*physiological requirements:

• The posterior teeth must be placed within the POUND tolerance area, which is determined from the trigone and the position of the lower canines, its lingual limit must be in accordance with the functional freedom of the tongue.

*assembly itself:

	Horizontal plane	Frontal plan	Sagittal plane
1st PM sup	-the mesiodistal grooves are aligned in a straight line	Its 2 cusps rest on the mounting plane.	-mounted perpendicular to the POP
2nd PM sup		Bicuspid contact with POP	Perpendicular to the POP
1st M sup	-is vestibulated by 20° to avoid biting the cheek when chewing.	Only the mesioplatinum cusp is in contact with POP.	-the occlusal face is tilted back and up by 6° in order to initiate the SPEE curve.
2nd M sup	-same version	-is out of contact with POP	– its occlusal face is in extension with that of 1st M (6°) – this orientation is due to the curvature of the mandibular crest.
1st M infThe assembly begins with its installation.	-the cuspid teeth are arranged in the POUND area.-the cuspid tips form a coalescing curvature	The M and PM are mounted astride the inter-ridge axis	-its central fossa receives the mesioplatinum cusp of the 1st M sup.-its median cusp is closely related to the mesiovest cusp of the 1st M sup.-placed in the center of the curvature of the mandibular arch.
2nd PM inf			-its vest cusp is placed between the 2 upper PM, and in contact by its distal face with the palatine cusp of the 2nd upper PM.
2nd M inf			– inclined from bottom to top and from front to back. – its central furrow vest receives the transverse crest of the mesio vest cusp of the 2nd M inf.
1st PM inf			-intercalated between 1st PM and the lower canine.

-dynamic equilibrium requires the coordination of factors:

QUINT of HANAU: Thielmann formula

POxCOxPC / Tc Ti =Constance

PO: occlusal plane

CO: occlusion curve

PC: cusp slope

Tc: condylar trajectory

Ti: incisal trajectory

PTA assembly

  Untreated cavities can reach the nerve of the tooth.
Porcelain veneers restore a bright smile.
Misaligned teeth can cause headaches.
Preventative dental care avoids costly treatments.
Baby teeth serve as a guide for permanent teeth.
Fluoride mouthwash strengthens tooth enamel.
An annual checkup helps monitor oral health.
 

PTA assembly