lab Flashcards
what is setting teeth based on
6 things
Occlusal plane
Labial contour
Crest of ridge
Axis of teeth
Curve of Spee/Wilson
Balanced occlusion
Occlusion Class
Class 1 = 1st molar mesial cusp sits in the lower 1st molar mesial groove
Upper canine slightly distal to lower canine
Class 2 = 1st molar meisial (over bite)
Class 3 = 1st molar distal (underbite)
Tooth selection considerations
Shape = arch shape, face, existing dentures
Size = intercanine distance, smile line, existing dentures
Colour = skin tones, existing, shade of teeth
Why are All adjustments made on lower
Lower is mobile upper is fixed
All should be set on the upper for lower teeth to be in correct position.
What is obtained from the upper (fixed)
Accurate occlusal plane
Vertical dimension
Contouring
Size and shape of teeth
Curve of Spee/Wilson
What type of special trays are there
Perforated-Alginate
Non-perforated = red compound, fast set material
What is a custom tray
Custom made device for patient to carry, confine and control impression material
* uniform space
* accuracy
* better for anatomy of patient
* comfort
Characteristics
Custom Tray
Well adapted
Dimensionally stable
Extensions = 2.3mm from peripheries
Smooth and round edges
Rigid
Retention holes - if needed
Stops
Have a handle
Eased frenems
Steam cleaned
Disinfected
Custom trays
What should they NOT be
Don’t let bind to model
Don’t react to impression material
Shouldn’t rock on model
Be overextended
Have voids or projections
What can custom trays be made from
Shellac = heat and time sensitive
Light cure = stable, uniform / brittle, rough surface
Tray compound =done chairside /heat and time sensitive, can distort
Thermoplastic = clear acurate / expensive
Acrylic resin = cheap/rigid
Why do we need to know LAndmarks
Where to extend trays
Sensitive areas avoid/impinge
Anatomical areas that need capturing
Design of prosthetic device
Identify abnormal conditions
Tori
Benign bone growth in mouth
90% bilateral
Not pathology
Bruxism, vitamin deficiencies, calcium rich supplements, genetics = cause
Mylohyoid ridge in prosthodontics
Posteriorly lies close to the residual ridge = needs to be relieved
* Covered by thin mucosa easily damaged by denture base
* Extension on lingual flange is to be beyond the palpable position of MR
* do not undercut
How to gum carve
6 things
• Buccally do not expose neck’s
• Lingually to marginal ridge height
• Do not expose cingulum’s
• Ensure there is no wax on the teeth
• Use wax carver to shape eminences
• Use wax carver to shape interproximal area’s
• Hollow out tongue space for the lower
Finishing setting teeth
- Round cervical margins with stipple brush
- Stipple buccal surface
- Brush flame only
- cervical margins
- Buccal roll
- Palate upper
- Lingual lower
- Check post dam
- Wash with cold soapy water
- Check occlusion
10 things
Model and wax build up
• • •
Cut post dam for maxillary
Seal wax up to model
Build up gum eminences
custom tray handle
- Must not interfere with the lip
- Dentate - the underside = same height as the anterior incisal edge
- Edentulous = allow room for the lip (expected height of new teeth)
- Should be parallel with the central axis of the mouth
- The handle should be parallel to the long axis of the teeth that are to be replaced
- The handle should be 3-4 mm thick, 8mm long, and 8mm high
Function of spacer in custom tray
- Allows tray to properly position in mouth during border molding
- Allow the impression to have an eventhickness of impression material
- Prevent distortion of the material at final stage
Spacer should be
- Constructed using wax
- Extended fully (but not overextended) as marked on model
- Be smooth
- Correct thickness
- Have stops placed in it
Where required
Subject to availability
Spacer thickness
wax sheets
Zince eugenol –> 0.5 = none
Elastomeric –> .5-1.5 = 1 sheet
Alginate –> 2-3 = 2 sheets
silicones –> 1.5-3 = 2 sheets
Plaster –> 4-5 = 3 sheets
Fabrication
what needs relieveing
Maxilla
incisal papilla
canine eminance
palatal fovea
sharp spiny ridge
any tori, bony prominance
ridge = tissue undercuts
Fabrication
What needs relieving
Mandible
Crest/ridge
mental foramen
genial tubercles
sharp spiny ridge
tori / bony prominance
ridge = tissue undercuts
Fabrication of
Spacer
- thickness dependant on material used
- uniform thickness
- full extensions of sulcus
- DO NOT extend past palatal fovea
- DO NOT extend past retro molar pad
- Min 3 stops
- max 4 stops
Fabrication
light cure material
- Fill stops with light cure material
- Adapt evenly = uniform thickness
- trim excess –> do not tear
- go to full extensions
- ease frenums
- place retention holes (not at periperhery)
Light cure
fabrication
5-10 mins
boil out remaining wax
Trimming custom tray
Mark deepest point on sulcus –> trim 2-3mm above
mark retromolar area
use acrylic bur to
* trim to marked lines
* round peripheries
* ease frenems
* trim post dam in front of fovea
* redrill holes (45)0
* roughen up tissue fitting surface
* Chamfer post dam to tissue (endentulous)
making model
Pour primary model
mix gypsum appropriatly
pour model
trim model = make land
* remeove imperfections
* mark sulcus depths
* mark frenems
* note landmarks
* mark central line
Duplication Process (Hydrocolloid)
- Soak model 30 minutes
- Pat dry model with paper towel
- Place in flask
- Pour Hydrocolloid and place in cold water, minimum
- of 3cm, for 1 hour
Calcium Sulphate Dihydrate
Plaster of Paris
Different plasters
- Impression plaster, ADA type I
- Model Plaster, ADA type II
- Model Stone, ADA type III
- Model Die Stone, ADA type IV
chemically identical.
The difference between plaster / stone / die stone
is the size and shape of the their particles.
has a great effect on the strength of the material
Purpose of balanced occlusion
- Teeth make contact eccentric and centric non functional or parafunctional activity
- Prevents breakage of artificial teeth
- establish bilateral and simultaneous occlusal contacts
working Movement
Occlusal contact between the maxillary bucccal cusps and the mandibular posterior teeth during lateral movement
Balanced movement
During right = max lingual cusps contact lingual incline of mandibular Buccal cusp
Protrusion movement
Balanced occlusion is achieved by:
* contact between maxillary Buccal cusps and lower posterior teeth
* contact between upper and lower incisal egde
Model prep for registration rims
- mark crest of ridge posteriorly
- mark anterior crest of ridge
- mark on land so it can seen once wax is placed
- wet model
Registration rims dimensions
Maxillary
* anterior vertical = 22mm
Anterior width = 5mm
Height tuberosity = 8mm
posterior width = 6mm
Mandible
* Anterior vertical = 18mm
Anterior width = 4mm
Height retro molar = 0 mm
Posterior width = 6mm
Registration rim requirements
Constructed on 2nd model
Stable
Adaptation
Correct dimensions
Height and width = natural dentition
Palate no more than 2mm thick
No covering of land area
Incorporate Buccal roll
Tapered on upper to avoid retromolar pad
Relieved Frenums
No extensions past post dam
Smooth, no voids
Centred over crest
Curvature follow curvature of arch
CUrve of spee
- anteroposterior compensating curve
- The curvature is related to the angle of the condylar guidance
- The curve isintroduced to provide balanced occlusion in protrusion
Fabrication = Curve of spee
- anteroposterior compensating curve
- starts with the second premolar
- buccal set on the occlusal plane, and progresses distally
- buccal cusps of the molars set progressively higher than theocclusal plane
- 6 and 7 tilt mesially to create an arc
Curve of Wilson
Mediolateral compensating curve
introduced to provide balanced occlusion in lateral excursions
Fabrication Curve of Wilson
- The long axis of the second premolar is set perpendicular to the occlusal plane
- molars are set with a slight tilt.
- The buccal cusps are set higher than the occlusal plane.
- Distal view –the necks of the 6 and 7 teeth are angled into the upper ridge creating an arc
- 6 and 7 lingual cusps are lower than the buccal cusps
what does a face bow record
Vertical dimension
Free-way space
Centric relation
Occlusal plane
Labial contour
Mid line
Intercanine distance
Smile line
Aids in tooth selection
