Shade Selection in Dentistry

Aesthetic dentistry imposes several demands on the artistic abilities of the dentist and the technician, therefore knowledge of the underlying scientific principles of color is essential.

“Color is the result of the physical modification of light by colorants

as observed by the human eye and interpreted by the brain”

Color combination not only improves aesthetics but also makes the restoration appear natural and attractive. Color cannot be perceived without light, which is a form of electromagnetic energy visible to the eye.

Perception of color

As light enters the eye through the cornea and lens, an image is focused on the retina. The amount of light entering the eye is controlled by the iris, which dilates or constricts depending on the level of illumination. The retinal rods and cons can adjust the variation of light intensity.

Quality of Light

The quality of light source is the most influential factor when determining tooth shade.

The ideal light source is natural light, occurring around mid-day for accurate color comparison.

The time of the day, month and weather conditions affect the color of sunlight. If the light source changes, then the light reflected from an object changes too; in that case, a different color is perceived. The absence of ideal conditions has led to the use of artificial lighting for color matching. The light source that approximates standard daylight is ideal for shade matching.

Three dimensions of color

Color is usually described according to the Munsell color space in terms of hue, value, and chroma.

Hue is the attribute of a color that enables the clinician to distinguish between different families of color, whereas value indicates the lightness of a color. Chroma is the degree of color saturation.

When color is determined using the Munsell system, value is determined first followed by chroma. Hue is determined last by matching with shade tabs of the value and chroma already determined.


Properties of Colour

Translucency

Human teeth are characterized by varying degrees of translucency, which can be defined as the gradient between transparent and opaque.

With increased translucency, light is able to pass the surface and is scattered within the restoration.

Fluorescence

Fluorescence is the absorption of light by a material and the spontaneous emission of light in a longer wavelength. In a natural tooth, it primarily occurs in the dentin because of the higher amount of organic material.

Opalescence

Opalescence is the phenomenon in which a material appears to be of one color when light is reflected from it and of another color when light is transmitted through it.

Metamerism

The change in color perception of two objects under different lights is called metamerism.


Measurement of Colour

Manual method: Shade guides

Tabs of similar hue are clustered into letter groups while chroma is designated with numerical values (1-4).

Instrumental method: Colorimeters, Spectrophotometers and Spectroradiometer.


Shade Guides

Shade Selection is a procedure which provide patients an aesthetic restoration that harmoniously blends to the patient’s existing dentition. Clinicians often lend up with compromised restoration because they encounter difficulty in interpreting a multi-layered structure of varying thickness, opacities and optical surface characteristics.

• Early shade guides were derived from tooth colors that were considered pleasing rather than from the distribution of shades found in the general population.

• Clark introduced a custom shade guide in 1931 based on visual assessment of human teeth, recorded in Munsell Hue, Value and Chroma.

• A new generation of shade guides has been developed to address these deficiencies.

Shofu offered the Natural Color Concept while Vita introduced a 3-dimensional shade guide system (Vita 3D-Master).

Vita System 3D-Master Shade Guide

Guidelines for Visual Shade Matching

  1. Shade Matching should be made under balanced lighting and in an appropriate shade-matching environment (with grey colour wall/ cabinets).
  2. Remove bright colours from field of view that influences the shade matching e.g. makeup, tinted eye glasses, lipstick and bright clothes.
  3. The teeth to be matched should be clean. If necessary, stains should be removed by prophylaxis.
  4. Evaluate shade under multiple light sources to avoid problem of metamerism (e.g. natural daylight and fluorescent light).
  5. Shade matching should be made at the beginning of a patient’s visit. Tooth colour increases in value when the teeth are dry.
  6. The patient should be viewed at eye level so that the most colour-sensitive part of the retina is used.
  7. A viewing working distance is approximately 25 cm.
  8. Shade matching should be made quickly (less than 5 seconds), with the shade tab placed directly next to the tooth being matched. The dentist should be aware of the eye fatigue, particularly if very bright fiber optic illumination has been used.
  9. The dentist can rest eyes between viewing by focusing on a neutral gray surface before a matching, to balance all the colour sensors of the retina.

Limitations of shade guides

• Does not cover the complete color space of natural teeth color.

• Shades are not systematic in their color space.

• Lack of consistency among the individual dentist in matching colors.

• None of the commercially available shade guides are identical.

• Quality control issues regarding color mismatches of shade tab and porcelain batches from the same manufacturer.

• Limitations of the instrumental method

• Translucency mapping is inadequate.

• Positioning of the probe or mouth piece seems to be critical to the repeatability of the measurement.

• Limited area is measured.

• Designed to measure flat surfaces.

• Prone to edge loss effects

• Cosmetic and bright colored clothes should be removed.


OTHER Limitations of shade guides

  • Fail to account for the variability found in natural teeth, e.g. fluorescence, opalescence, translucency, enamel thickness, and objectivity.
  • Effects of surface texture on light reflection.

However, there are special lights that are colour corrected to emit light with a more uniform distribution of colour that can be utilized, e.g. Optilume TrueShade.

Click onto image for more infomation

Instruments Used for Shade Selection

A) Colorimeter

A trichromatic colorimetric measurement tool that provides an objective assessment of color characteristics from light passing through the primary filters of red, green and blue. It simulates the way the human eye perceives color.

– Detector, signal conditioner and software

– 3 or 4 photo-diodes with filters

B) Spectrophotometer

Clinical evaluation of a dental color analysis system: The Crystaleye Spectrophotometer®

3 principle elements: a standard light source “D65”

– Means to direct the light source to an object and receive the light reflected or otherwise returned from the object.

– Determines the intensity of received light as a function of wavelength.

– Provide most accurate color measurements.

Note: [D65] is intended to represent average daylight and has a correlated colour temperature of approximately 6500 K.

Shade Guides with Technology

Vita EasyShade® V

VITA Easyshade® V

The VITA Easyshade V digital spectrophotometer was developed for precise, fast and reliable shade determination of natural teeth and ceramic restorations.

ShadeScan

•First system to combine digital color imaging and colorimetric analysis

• Handheld device with fiber optic cable, halogen light source

• Image recorded on flash card hence no computer required

• ShadeScan software for shade and translucency mapping in basic Vitapan classical shades

Shadepilot

The digital shade matching technology that allows totally accurate evaluation of spectral data, unaffected by light sources in the surgery or other ambient light.

– end –

References:
Contemporary fixed prosthodontics ; Rosensteil, Lang, Fujimoto; 3rd ed.
Fundamental of fixed prosthodontics ; Shillingburg et al, 3rd ed.
https://www.vita-zahnfabrik.com/
http://www.dentsplyestore.com.au/www/770/files/shadepilot_brochure_en.pdf
https://borea-dental.com/en/resources/faq/spectrophotometer-vs-colorimeter/

Complete Denture – Repair, Reline & Rebase

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Repair

WHAT IS COMPLETE DENTURE REPAIR?

Dentures may fracture during function or when it is dropped on hard surface. The key to repair a denture is the accuracy of resassembling & alignment of the broken parts in their original position.

 

Procedures for repair of :

Midline Fracture

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1) Broken parts are assembled & fixed together with sticky wax on the polished surface.

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2) Assembled parts may be strengthened with burs or plastic sticks or match sticks.

3) Any undercut on the fitting surface is blocked out with wax or clay.

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4) The fitting surface is painted with separating medium (Vaseline).

5) Stone plaster is poured into the fitting surface. After stone setting, the denture is removed from the cast and cleaned from any traces of sticky wax.

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6) Fractured edges are reduced, widened (8-10 mm) along the fracture line and beveled towards the polished surface to increase bonding surface area.

7) Dove tail cuts may be made to strengthen the repair joint.

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8) The cast is painted with separating medium and the denture is secured to the cast with rubber bands.

9) Self cure acrylic resin is applied to the modified fracture area until the area is overfilled.

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10) An alternate method is to wax  and contour the fracture line to the desired form using base plate wax, followed by flasking, wax elimination, packing with self cure acrylic resin and placing in the flask under press for 2 hrs.

11) Deflasking, finishing and polishing is then done in the usual manner.

 

With Missing or Lost Part

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Broken flange

1) An impression is made with the denture placed in patient mouth.

2) After pouring the cast, either self cure acrylic resin is applied to replace the missing part, or wax is added and carved to resemble the broken denture part, followed by flasking, packing, curing, finishing & polishing.

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With Missing or Broken Teeth

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1) Fractured teeth are cut away with burs.

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2) On the lingual side, enough acrylic is removed and dove tailed.

3) Teeth of same size, shape & shade are positioned in proper alignment and waxed with base plate wax.

4) Carve the artificial gingiva in the tooth region.

5) Do flasking leaving the replaced tooth uncovered by the plaster.

6) Pack acrylic in the tooth region, cure, deflask, and finish.


 

Reline

WHAT IS RELINING?

Resurfacing or correction of denture adaptation to underlying tissues by the addition of a new resin material to its fitting surface without changing its occlusal relation.

Addition of Material to the tissue side of a denture to improve its adaptation to the supporting mucosa.

Diagnosis: Occlusal disharmony

  1. Loss of stability and retention
  2. Irritation and inflammation on one side
  3. Teeth stained on one side

 

Reline Indications

Whenever the denture loses or has poor adaptation to the underlying tissues, while all other factors as occlusion, esthetics, centric relation and denture base material are satisfactory.

  • Loss of retention
  • Instability
  • Food under denture
  • Abused mucosa

 

Dentures Evaluation

  • Overextension
  • Irritation of peripheral bordersCD_244

 

Reline Contraindications

  1. Worn out dentures
  2. Vertical dimension loss greater than 7 mm
  3. Significant mucosal inflammation
  4. Poor denture esthetics
  5. Denture related speech problems
  6. Severe tooth wear
  7. Severe vertical overlap with tooth wear (posterior tooth concept)
  8. Severe occlusal wear (CD evaluation)

Procedures for reline:

First, the patient is instructed to leave his denture out of his mouth at least 48 hrs to allow for recovery of tissues and reduce irritation caused by ill-fitted denture.

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1. Prepare the worn denture

  • Any undercuts are removed from the denture base
  • Check peripheral extensionsCD_245
  • Indicate amount of peripheral reduction requiredCD_250CD_241CD_246

 

  • Tissue Conditioner preparation: Peripheral reduction + Tissue surface, to provide a definite edge for addition of new resin material.CD_257
  • The denture old resin material is thoroughly cleaned and roughened.

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2. Border Molding

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3. Palatal surface vented

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4. Seat denture with impression material until wash comes through vents

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5. Take final impression

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9. Identify post palatal seal (post-dam) in impression, before pouring it up with gypsum. Identify on impression so technician can scribe the seal.

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10. New acrylic resin material is packed, and the denture is cured in pressure curing unit containing water at 45°C for 20 min to prevent porosity of new resin material and warpage of the old resin material (release of internal stresses).CD_242

11. Finishing and polishing

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When both upper and lower dentures need relining, lower denture should be completed first. The upper may be relined against a stable lower denture.

The denture should be clinically remounted to perfect the occlusion.


 

Rebase

It is a process of readaptation of a denture to the underlying tissues by replacing the denture base material with a new one without changing its occlusal relation.

 

Rebase Indications

When the existing denture base is unsatisfactory e.g. stained, crazed or porous.

 

Procedures for rebase:

1. An impression is made with the denture and a cast is obtained.

2. An occlusal and incisal index of the teeth is made in plaster using Hooper duplicator. The posts of the lower part of the duplicator are seated in the upper part to maintain the relationship of the casts to the plaster index.CD_262

3. The denture with the impression material are removed from the cast.

4. Artificial plastic teeth are sectioned from the denture and all base material around the teeth is removed. (porcelain teeth are removed by flaming)

5. Teeth are placed and held in position in the index using sticky wax on the labial and buccal surface.

6. A layer of base plate wax is placed over the ridge of the cast.

7. The upper part of the duplicator is closed and denture teeth are waxed to the proper thickness and contour to the cast.CD_243

8. The cast is removed, flasked and processed in the usual manner.

9. After deflasking, the cast is reattached to the upper part of the duplicator to adjust any occlusal errors.

10. Occlusion of rebased denture is further perfected by clinical remount.

 

– end –

 

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A denture rebase practice of mine

Denture Base Problems

WHAT ARE THE PROBLEMS OCCUR IN DENTURE BASE?

A) Analysis of Porosity problems:

a. Internal porosity: P/L heterogeneity and air incorporation (spherical pores)

b. Internal porosity: localized boiling (common in thicker portions)

c. External porosity: insufficient pressure or dough (surface blisters and pores) Commonly occur sites – Flanges (Buccal, Labial, Lingual)

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B) Dimensional Changes on Processing:

  1. Expansion on heating flask.
  2. Expansion on polymerization exotherm.
  3. Contraction on polymerization.
  4. Contraction on cooling to room temperature.
  5. Expansion on swelling in water.
  6. Expansion on thermal change.CD_224

 

C) Cracks and Crazes:

  • Created by thermal and mechanical cycling

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Processed Complete Denture Problems

 

Altered Vertical Dimension Occlusion

  • Increased OVD – most common (0.25 – 0.5 mm is acceptable)
  • However, if > 0.5 mm, has to do selective grinding

 

Tooth Shift

  • Lateral shift
  • Twisted

Reasons can be due to:

  1. Baseplate wax is unstable, and denture teeth can drift easily in trial denture.
  2. Setting expansion of the stone used to flask the wax denture.
  3. Resin packing pressures during trial packs and final close
  4. During polymerization, the resin expands and contracts, possibly moving teeth.

 

Liquid / Powder Ratio

It is important to use correct the powder-liquid ratio. If…

a. Excess monomer (liquid)

  • Increased polymerization shrinkage.
  • Increased time necessary to reach packing consistency.
  • Increased porosity.

 

b. Insufficient monomer

  • Decreased wetting of polymer
  • Increased handling difficulty
  • Decreased amount of polymerization

 

– end –

Complete Denture – Finishing

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Main Steps on Finishing and Polishing

1.Remove the excess with the acrylic bur.

2.Smooth with sandpaper fixed on mandrill.

3.Do polishing using brushes of different sizes with pumice.

4.Rinse the denture, and then use special very fine particles powder with special brushes to gain the final polished denture.

5.In all these procedures avoid the rise of temperature of the denture.

Note:

  • Do not trim the tissue side of dentures.
  • Keep dentures hydrated at all times except when you’re working on them.CD_220

 

Types of Polishing instruments

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Remounting and Selective grinding (Occlusal Adjustment)

After finishing the denture, remount it on the articulator (if we use the semi-adjustable) by taking the new vertical dimension and centric relation.

Occlusal adjustment is the final procedure that will be done before the insertion of the dentures.

 

Selective grinding

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The selective grinding (occlusal adjustment) is the process of elimination of the high spots or the pre-mature contacts in all positions of the mandible including:

A) Centric relation position.

B) Antero-posterior or protrusive position.

C) Lateral movement position.

 

Advantages of occlusal adjustment

  • To insure the equal distribution of the occlusal forces over all the denture supporting tissues including the bone.
  • To obtain the denture stability during function.
  • To provide comfort to the patient.

 

A) In centric position premature contacts

The following laws should be respected:

  • The shape of the cusps must be conserved (the active cusps are spherical and the non active cusps are triangular in shape).
  • The non-active cusps which can be modified are the upper buccal and lower lingual cusps.
  • All primary cusps must be situated in the fossae or embrasures.
  • The active cusps must not be modified in centric pre-maturities.CD_222

 

B) In protrusive pre-maturities

The selective grinding is done according to this formula:

MI-DS inclines:

Do grinding to the mesio-inferior (mesial incline of the lower posterior teeth) and disto superior inclines (distal inclines of the upper posterior teeth) only.

 

C) In lateral movement pre-maturities

  • Working side pre-maturities: Grind the internal inclines of the secondary (non active cusps).
  • Non-working side pre-maturities: Grind the mesial internal incline of the active cusps.

 

After completion of the selective grinding procedures, remove the denture from the articulator, do polishing specially for the teeth using pumice and brush.

The denture now is ready to be inserted in the patient mouth.

 

– end –

 

Complete Denture – Flasking, Dewaxing & Packing

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WHAT IS FLASKING?

Flasking is the process of investing the cast with the waxed denture in a flask to make a sectional mold that is used to form the acrylic resin denture base. Therefore it is also known as investing.

 

Components of a Flask

The flask is a metallic mold that supports the models and the try in denture during the flasking procedure.

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It is composed of 3 parts:

  1. The base in which the model & the try-in denture will be placed.
  2. The mid-part in which the teeth will be located.
  3. The cover


Flasking / Investing Procedure

  1. Flask must close fully and accurately without resistance. If a flask fails to do this, air-blows, distortion or excess increase in vertical dimension may occur.
  2. The model with the sealed try in denture must be covered with very thin layer of Vaseline.CD_203
  3. Any undercut should be covered by wax.
  4. All parts of the flask must be clean and covered by thin layer of Vaseline from inside.
  5. Models with the sealed (try in) are to be placed in cold water for 10 min. before flasking.
  6. Thin mixture of POP poured in the base of the flask, place the model, teeth should be vertical.
  7. All the parts of the model should be covered with POP and all the wax and teeth must be uncovered.CD_201
  8. After setting of POP cover it by thin layer of cold mold seal or Vaseline.
  9. Prepare a mixture of gypsum, put the mid part in its correct place and pour the gypsum without covering the occlusal surfaces.
  10. After setting of this layer also cover it with cold mold seal.
  11. Fill the flask with another layer of gypsum, cover it, put the flask under mild pressure to prevent gypsum from expanding, wait for complete setting.CD_204

 

Dewaxing / Wax Elimination ProcedureCD_206

  1. After setting of gypsum, wax elimination procedure is to be done.
  2. Put the flask in boiling water for 5-7min.
  3. Separate the 2 parts of the flask.
  4. Remove the shellac base plate and the wax using the boiled water and detergent.
  5. Place the clean flask in open air to dry and cool it. CD_208

Note:

  • Remove ALL wax residue since acrylic resin will NOT adhere to a surface coated with wax.
  • Any residual wax will contaminate the acrylic resin and prevent bonding between teeth and the denture base.

 

Acrylic Packing Procedure

1. Isolate the gypsum of the flasking by using one of these systems of isolation:

  • Physical separator or isolator: tin foil.
  • Chemical isolator: solution of alginate (cold mold seal). It reacts with the calcium of the gypsum to form a film of insoluble calcium alginate.

2. Use the brush, move it in one direction to spread the cold mold seal.

3. The cold mold seal should be thin and even on all the parts of the mold except the teeth which should not be separated. If the teeth covered by cold mold seal, they will not adhere to the denture base.

4. Mixing

  • Acrylic resin is a resinous plastic material of various esters of acrylic acid. It is used as a denture base material.  It is formed of a powder and liquid.Powder:  polymethyl methacrylate PMMA (polymer) + Benzoyl peroxide (initiator) +pigments.
    Liquid:  methyl methacrylate (monomer) + hydroquinone (inhibitor)Powder and liquid are mixed in a ratio of 3 to 1 by volume for an average sized denture.

Stages of acrylic mixing

  1. A sandy stage : where a fluid mass occur due to the settling of the polymer into the monomer.
  2. A stringy or fibrous stage: where the monomer starts to attack the polymer. In this stage the mix is tacky, sticky and adheres to the sides of the mixing jar.
  3. Smooth dough like stage: where the monomer diffuses into the polymer.
  4. Rubber like stage: further penetration of the monomer into the polymer. In this stage the acrylic resin cannot be packed or molded being too stiff.
  5. Stiff stage : hard

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5. Packing of acrylic

  • It is the procedure of application of acrylic resin into the mold and pressing the flask by using sufficient pressure to compensate for the contraction of the acrylic after polymerization to prevent shrinkage and porosity.

Put acrylic in the mold, press in a clamp, do curing immediately.CD_211

Note:

Too early– (Stage II) – acrylic resin has too low viscosity to densely fill the mold. Results in porosity in the final prosthesis.

Too late– (Stage IV) – inability to close the flask, loss of detail and increase in vertical dimension of occlusion in final prosthesis, as well as, movement and/or fracture of teeth.

  • Acrylic placed into mold cavity and covered with cellophane for trial pack.CD_212
  • Flask pressed until excess acrylic squeezes out around edges.
  • Acrylic flash to be trimmed away, small amount of acrylic to be added where needed. Take note of the wrinkles from cellophane.CD_213
  •  The mold is full when the acrylic is pressed smooth and dense. A small amount will be added at wrinkles.
  • Close the upper and lower parts of the flask together.CD_214

 

Curing of Acrylic

The packed mold is heated (cured) in an oven or in water bath. Temperature and time should be controlled.

Two water bath heating techniques may be used:

a) Heating the flask in a special bath of water, beginning from the room temperature until reaching 72°C for 16 hours.

b) Heating the flask in an ordinary water bath beginning from the room temperature, until reaching 72°C, lasting for 2 hours, then the temperature is raised to boiling for another 1 hour.

This technique takes shorter time but there is a likelihood to be distorted during de-flasking. Also, the free monomer is more.


 

Cooling of the flask / Bench Cooling:

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After curing, the flask is to be cooled slowly on the bench in its water bath.

The slow cooling will permit the relief of the internal stresses caused by the difference in contraction between the acrylic and the mold material.


 

De-flasking Procedure

It is the procedure of opening the flask after curing of acrylic resin. It should be done carefully to prevent the breakage of the denture. It includes the following steps:

  1. Remove the flask from the clamp.
  2. Remove the upper and lower lids.CD_216
  3. Separate the 2 parts of the flask with attention using the plaster knife.
  4. Liberate the denture with its model, then try to remove the model carefully. If there is undercut, split the model into 2 or 3 parts to remove them easily.
  5. After gaining the denture, remove the excess of acrylic using the acrylic bur.

 

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– end –

 

 

Complete Denture – Wax-Up and Gingival Contouring

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 My 3rd complete denture waxing up practice

The denture base that replaces the bone and tissues should have natural aesthetic and easy for the patient to maintain it’s hygiene. Also, it should be well contoured to harmonize with the muscles and shaped to such that retention and stability are helped.

 

WHAT ARE THE CRITERIA FOR WAXING UP A COMPLETE DENTURE?

Sulcus

  • The denture base should be extended fully into the sulcus to achieve a good seal between the denture periphery and the tissues.

 

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Denture base

  • Once the teeth are secured in position, all areas of the denture base, particularly those distal to the molars, which are regularly removed during the registration stage, should be replaced using wax.
  • This non-occluding part of the denture will allow the tongue to brace the lower denture if properly contoured.

 

Buccal and lingual flange extension

  • The width of the buccal and lingual flanges on both upper and lower dentures should be constructed to fit fully into the sulcus of the working models.
  • Care should be taken to ensure that the flange does not encroach onto the buccal or lingual frenum.CD_198

 

Buccal and lingual flange contour (polished surface shape)

  • The contour of the buccal and lingual flanges of the denture, can have a major effect on denture stability.
  • Fully contoured dentures, which take into account the muscles of mastication, allowing the muscles to act with the denture contours to help keep the denture in place.
  • The lingual surfaces of the lower denture should be shaped to provide maximum room for the tongue in such a way as to allow the tongue to rest on the denture base and direct forces such that they help to retain it in  contact with the underlying tissues and bone and not dislodge it.

 

Palate

  • The palate should generally be smooth and extend to the junction of the hard and soft palate.
  • The shape of the anterior palate can have a significant effect on speech and this should be assessed and modified at the try-in stage.

 

Gingival contour

  • The gingival area should be sculptured to create an as aesthetic and natural situation as possible (Waxing Up).
  • Older patients, for example, would be expected to have receding gum levels, and although filling embrasures with pink acrylic would certainly allow the dentures to be cleaned readily, it would look false for an elderly patient.
  • So a degree of compromise is needed to create a gingiva that reflects the tooth arrangement and the patient’s age but still allows the denture to be relatively self-cleaning or easily cleaned by the patient.

 


 

Denture Waxing Up Procedure

 

A) Add wax to the denture base

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B) Carve the wax to create the artificial gingiva with the following criteria:

  1. The peripheries must be thick and rounded (3mm), except the posterior palatal seal area which should be thin.
  2. The buccal and labial surfaces must be convex to allow for free movement of the buccinator and orbicularis oris muscles.
  3. Lingual surface inclined inwards, from above downwards.
  4. The interdental papilla concave.
  5. The root areas convex.

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In general, artificial gingiva can be divided into 3 parts:

  • i) The superior part: near denture periphery, the thickness is determined by the final impression (about 3mm).
  • ii) The middle part: should be concave to allow for free muscle movement.
  • iii) The lower part: in the region of the roots, must be convex, while the interdental papillae is concave and tapered in young, and rounded in old age.

 

C) Stippling the gingiva contour

  • It is the procedure of the reproduction of the minute creases and pits that occur in the natural gums which give the orange peel appearance. This is done on the labial surfaces of the upper and lower flanges.

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Example of a stippling effect

 

D) Give a shine to the waxed up gingiva by moderately polishing it with soapy water and soft brush.

 

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 – end –

 

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Still needs a lot of stippling practice!

Complete Denture – Selection & Arrangement of Artificial Teeth

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During the occlusal registration stage, the positioning of the anterior teeth and the selection of size, shape and shade is incorporated. The duplication of aesthetics can be determined based on the patient’s natural teeth or through their existing dentures.

Technicians copy and retain the features of the existing dentures by having an impression. Having photographs of the patient wearing their dentures can also be very useful in establishing shortfalls or positive aspects about the dentures’ appearance.


Anterior teeth selection

The basic considerations in selecting anterior teeth are:

  1. Tooth size
  2. Tooth form
  3. Tooth colour
  4. Tooth material

1 ) Selection of Tooth Size

  • Tooth size is selected to give an overall proportion between the teeth and face
  • Size of a tooth should be analyzed three dimensionally :
  1. height (occlusogingival)
  2. width (mesiodistal)
  3. thickness (labiolingual)

e.g. Height of the tooth is selected in proportion to the length of the face.

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To establish the overall width of the six anterior teeth, the distance between the canines can be determined using various methods:

  1. Marking the corners of the mouth on the rim with the mouth at rest.
  2. Measuring the width of the nose at its widest point with the mouth at rest. Add 5 mm to this measurement to allow for the curvature of the teeth.
  3. The width of the two central incisors may be estimated using the philtrum width.
  4. The height of the central incisor should be equal to or greater than the height of the smile line above the incisal edge.
  5. This high smile line should ideally be marked onto the wax rim of the registration rim during the registration stage by the clinician.CD_155
  6. Larger central incisors should be used for people with a high lip line.

Size of the face :

  • Using the Trubyte tooth indicator or a Facebow, the width of six maxillary anterior teeth can be estimated:TS 01
  • Average width of the maxillary central incisor is estimated to be 1/16th of the bizygomatic width (Width of the face measured between the zygoma (in mm) )TS 02
  • The combined width of the maxillary anterior teeth can be estimated by dividing the bizygomatic width by 3.3.

2 ) Selection of Tooth Form

Three factors are used as guide:

  1. The form and profile of the face
  2. Dentogenic concept – Age, sex and personality

Theory given by J. LEON WILLIAMS, which states that the shape of the teeth should be inverse of the shape of the face.

The labial surface of the anterior teeth should be in harmony with the face.

Facial forms can be grouped into:

  1. Square
  2. Tapering
  3. Square tapering
  4. OvoidTS 03

—Facial profiles can be grouped into

  1. Class I – Straight
  2. Class II – Concave
  3. Class III – Convex

Dentogenic concept

Dentogenics is the art, practice and technique of creating the illusion of natural teeth in artificial dentures and is based on the elementary factor influenced by sex, personality and age of the patient. It was first described by Frush and Fisher.

Sex:

  • In females, the incisal angles of the maxillary anterior teeth are more rounded and the teeth have lesser angulation. While in males, the incisal angles are rounded to a lesser degree.
  • In males, the incisal edges are parallel to the lips. In females, they follow the curve of the lower lip.
  • In females, the distal surface of central Incisor is rotated more posteriorly and the lateral incisors are placed anteriorly to the central incisors.
  • The distal surface of the cuspids is rotated more posteriorly in females, and in men, it is visible and prominent.

TS 04TS 05

Personality:

  • Soft, delicate personality is associated with women and vigorous personality is associated with men.
  • Large, vigorous type of patients can be given the teeth of size and form with prominent markings, different from those of a delicate appearing patient.
  • Personality types can be Delicate, Medium pleasing and Vigorous.
  • The size, shape and form of the teeth can be manipulated to suit the respective personality.

Age:

  • The colour of the teeth changes with age. Lighter shades are selected for younger and darker shades for older patients.
  • Wear patterns like attrition and abrasion can be shown in the denture teeth.
  • Inter-incisal distance increases with age. Also, the loss of muscle tonus can lead to the sagging of the lower lip. Hence, mandibular anteriors can be given more visibility.
  • Old patients have gingival recession & this can be reproduced in the dentures.TS 06

Steps to determine denture teeth shape:CD_158

  1. Use the patient’s old dentures if they are happy with the teeth.
  2. Select teeth based on the inverted shape of the patient’s face to determine whether the teeth should be square, tapered, ovoid or oblong.
  3. Select teeth based on the shape of the patient’s upper palate.
  4. Masculine and feminine moulds are always available for selection.

CD_159


3 ) Selection of Tooth Colour

CD_156

Colour is described using the terms ‘value’ (lightness), ‘chroma’ (saturation) and ‘hue’ (colour). As age progresses darker teeth should be selected for older patients.

  1. Colour of the teeth should blend with patient’s age, skin, hair and eyes.
  2. Shade selection can be done on the basis of age, sex, skin complexion and patient preference.
  3. As a general rule, bright teeth for young patients with fair skin and dark teeth for aged with dark skin is suitable.
  4. Some of the colour characteristics of natural teeth that can be reproduced are:
    • Neck of the teeth have a more pronounced yellow colour
    • Incisal edges are more translucent than the middle third
    • Canines are more darker than incisors
    • Attrition facets and gingival recession
    • Stains

CD_157


4 ) Selection of Tooth Material

Most of the artificial teeth are made up off either air fired or vacuum fired porcelain or acrylic resin.

Both materials have its advantages and disadvantages, and provides a base for dentist to select the advantageous material for each case.

CD_160

Denture Teeth / Denture Base Attachment Mechanisms

1. Gross mechanical retention (holes,pin, undercuts)

2. Micromechanical retention (bur roughening, grinding, sandblasting)

3. Chemical bonding (denture base monomer penetration into teeth)

  • Minimizes interfacial leakage and staining (hygienic and aesthetic problem)
  • Facilitates stress-transfer preventing cracks or crazes near interface with base

CD_161

Porcelain Teeth Acrylic Teeth
Aesthetic Higher (advantage) Less (disadvantage)
Attachment to the denture base Mechanical (disadvantage) Chemical (advantage)
Density Higher (disadvantage) Lower (advantage)
Brittleness Higher (disadvantage) Lower(advantage)
Compatibility with the denture base Lower (disadvantage) Higher (advantage)
Hardness Higher (advantageous by less abrasion) Less (disadvantage)
(disadvantage when adjustments needed) (advantage when adjustments needed)
Forces to the supporting soft tissues Higher (disadvantage) Lower (advantage)
Tissue biocompatibility Higher (advantage) Less (disadvantage)

Posterior teeth selection

General requirements of posterior teeth selection

  • Selection is done in accordance with the size and contour of the lower residual ridge, since it offers lesser support to the occlusal forces
  • Should satisfy the masticatory efficiency
  • Should contribute to denture stability
  • Should be comfortable to the underlying tissues
  • Should not cause any bony resorption
  • Should not create any sound on impact
  • Should satisfy aesthetics

Factors influencing the selection of posterior teeth are :

  1. Size
  2. Form
  3. Colour
  4. Material

1 ) Size of the posterior teeth

Factors considered for size selection are

  • Buccolingual width
  • Mesiodistal width
  • Occlusogingival height

Buccolingual width

Should be narrower than that of the natural teeth to decrease the amount of stress to the supporting tissues during function .

This also helps in the development of the correct form of polished surfaces of the denture, thus helping to maintain the denture in position over the ridge.

The width should be still enough to hold the food during mastication.

Mesiodistal width

The space between the distal of the canine and the anterior border of the retromolar pad is available for posterior teeth arrangement.

A measurement of this space is an efficient method to select the proper tooth size.

When the ridge is poor or the lower molar slope is steep, smaller teeth should be selected.

Occlusogingival height

Controlled by the available interarch distance at the established occlusal vertical dimension.

Should be filled with more of tooth material and minimal denture base material.

Long posterior teeth are generally more aesthetic in appearance than shorter teeth.

A harmony of tooth size between the canine and the first premolar is necessary for natural appearance.


2 ) Form of the occlusal surfaces

Form of the occlusal surfaces is selected on the basis of the occlusal surfaces desired and the type of occlusion planned.

Condylar inclination, shape and height of the residual ridge, Incisal guidance, plane of occlusion, compensating curves and ridge relationship are the factors that influence the form selection.

Based on this, the forms of posterior teeth can be grouped as :

—  Anatomic  (Cusp angle 33⁰)

—  Semi anatomic ( Cusp angle 20⁰)

—  Non anatomic ( 0 degree or Cusp-less teeth or Monoplane teeth)

TS 07

  • Anatomic teeth are used when a balanced occlusion in centric and eccentric positions are desired.
  • If eccentric dis-occlusion and centric occlusion is desired, then anatomic or semi anatomic teeth are selected.
  • If the ridges are poor or a horizontal incisal guidance is selected, then non anatomic teeth are used.TS 08

Anatomic Teeth

Use for patients with:

  • Aesthetic concerns
  • Coordinated jaw movements
  • Denture opposing natural teeth

Non-Anatomic Teeth

  • No overbite
  • Normal overjet (1-2 mm)
  • Jaw size discrepancies (Class III)
  • Severe ridge resorption
  • Uncoordinated jaw movements
  • Poorer aesthetics, due to lack of cuspal inclinesTS 10TS 09

3 ) Colour

  • Should be harmonized to the shade of anterior teeth
  • Maxillary first premolars are used more often for aesthetic purpose than function. So it’s advisable to select premolar teeth with lighter colour than the other posterior teeth, but not lighter than anterior teeth.
  • Generally the shades of posterior teeth are slightly darker than anterior teeth.

4 ) Material

Similar to the selection of material for the anterior teeth, a choice can be made between acrylic and porcelain teeth based on the requirements.


Positioning The Denture Teeth

ANATOMICAL LANDMARKS & AIDS USED TO POSITION DENTURE TEETH

A) Lip Line

CD_164

  • Highest point of upper lip when smiling
  • Cervical necks lie at or above this line
  • If shorter teeth are selected, aesthetics compromised

CD_163

B) Palatal Midline

  • Extend through middle of incisive papilla and mid-palatal raphe
  • Check for symmetry  (If not symmetrical, adjust rim)CD_165

C) Midline & Canine Reference

  • Line passing through distal of incisive papilla
  • Perpendicular to the palatal midline
  • Intersects cusp tips of the canines

CD_166

D) Incisive Papilla

  • On average, facial of central incisors should be 8-10 mm anterior to this line.CD_167.jpg

E) Retromolar Pads

  • Distal border of the lower denture.
  • A point two-thirds the way up the retromolar pads may be used to approximate the occlusal plane.

CD_168

F) Center of Ridge – Posterior

  • Maxillary lingual cusps should be centered over this line
  • Mandibular teeth must be on the centre of the ridge
  • Ensures denture stability
  • Reduces fulcruming forces during function

CD_169

G) Center of Ridge – Anterior

  • If anterior teeth are too facial to center of ridge, fulcruming tilting and dislodging occur

CD_170


Arrangement of the Maxillary Anterior Teeth

Setting Upper Anterior Teeth:

  • Incisal edges of central incisors & canines at level of the occlusal plane
  • Laterals Incisors placed approximately 0.5 mm – 2 mm above the occlusal plane
  • Circumference (labial contour) follows arch shape
  • Look for Symmetry where the right and left maxillary anterior teeth should be positioned symmetrically on either  side of the arch

A) Maxillary Central Incisor

CD_171.jpg

  1. First an upper central incisor is placed to one side of the centre line, replacing the labial contour of the upper wax block, and just touching the occlusal plane.
  2. Incisal edges placed more anteriorly than their necks to support the lips in a slightly prominent and natural position.
  3. The long axis of the tooth is parallel to the vertical axis when viewed from the front.
  4. The long axis of the tooth is sloping labially when viewed from the side.
  5. The incisal edge of the tooth evenly contacts the occlusal plane.

B) Maxillary Lateral Incisor

CD_172

  1. The lateral incisor should be positioned with the incisal edge 0–2 mm off the occlusal plane.
  2. This will vary according to the age of the patient; older patients would not normally be expected to have a ‘youthful’ step between their centrals and laterals, due to wear of the centrals and canines.
  3. Incisal edges placed more anteriorly than their necks to support the lips in a slightly prominent and natural position.
  4. The long axis of the tooth is tilted towards the midline when viewed from the front.
  5. The long axis of the tooth is sloping labially when viewed from the side. The inclination of the slope is greater than that of the central incisor.
  6. The incisal edge is 2 mm above the level of the occlusal plane. And the edge is tilted towards the midline.

C) Maxillary Canine

CD_173

  1. The canines should be positioned to show their mesial aspects when viewed from the front.
  2. The incisal edge should just touch the occlusal plane.
  3. The neck of the canine should be prominent and more anteriorly placed than the incisal edge to emphasise the canine eminence and to support the lips.
  4. The long axis of the tooth is parallel to the vertical axis when viewed from the front. A mild mesial tilt is supposed to improve its aesthetics.
  5. The cuspal tip of the canine touches the plane of occlusion.

Setting Upper Posterior Teeth:

  • The upper posterior teeth are set over or slightly buccal to the ridge, such that their occlusal surfaces lie slightly buccal to the lower ridge.
  • The teeth are positioned to create a compensating curve.
  • The steepness of the curve depends on the condylar angle, the cusp angle of the teeth and incisal guidance angle.
  • The steeper the angle, the steeper the compensating curve needs to be.
  • The curve of Spee should match the condylar angle to maintain contact between the teeth in protrusive excursions.

D) Upper 1st PremolarCD_180

  1. The long axis of the tooth is parallel to the vertical axis when viewed from the front.
  2. The buccal cusp touches the occlusal plane and the palatal cusp is positioned about 0.5 mm above  the occlusal plane.

E) Upper 2nd Premolar

CD_181

  • The long axis of the tooth is parallel to the vertical axis when viewed from the front.
  • The long axis of the tooth is parallel to the vertical axis when viewed from the side also.
  • Both the buccal and palatal cusps should touch the occlusal plane.

F) The Upper 1st Molar

CD_182.jpg

  • The long axis incline distally and buccally.
  • The mesiopalatal cusp contact with the occlusal plane.
  • This tilt give the lateral curve.

F) The Upper 2nd Molar

CD_182b.jpg

  • The long axis of the tooth is tilled buccally when viewed from the front.
  • The long axis of the tooth is tilted distally when viewed from the side
  • No cusp touch the occlusal plane but the mesiopalatal cusp should be the nearest cusp to the occlusal plane.
  • This is to create the compensatory curve.

Arrangement of the Mandibular Anterior Teeth

a) Mandibular Central IncisorCD_184

  • The long axis of the tooth is parallel to the vertical axis when viewed from the front.
  • The long axis of the tooth slopes slightly labially when viewed from the side.
  • The incisal edge of the tooth should be 2 mm above the plane of occlusion.

b) Mandibular Lateral IncisorCD_185

  • The long axis of the tooth is parallel to the vertical axis when viewed from the front.
  • The long axis of the tooth slopes slightly labially when viewed from the side but not so steeply as the central incisor.
  • The incisal edge of the tooth should be 2 mm above the plane of occlusion.

c) Mandibular CanineCD_186

  • The long axis of the tooth is very slightly tilted lingually when viewed from the front.
  • The long axis of the tooth slopes slightly mesially when viewed from the side.
  • The canine tip is slightly more than 2 mm above the occlusal plane.

d) Mandibular 1st PremolarCD_187

  • The long axis is parallel to the vertical plane.
  • The buccal cusp of the mandibular 1st PM should engage the mesial marginal ridge of the maxillary 1st PM.
  • Lingual cusp is below the occlusal plane while the buccal cusp is 2 mm above the occlusal plane.

e) Mandibular 2nd PremolarCD_188

  • The long axis is parallel to the vertical plane.
  • The buccal cusp tip should engage the embrasure between the maxillary 1st PM and 2nd PM.
  • Its 2 cusps are about 2mm above the occlusal plane.
  • The central fossa of the mandibular 2nd premolar and the 1st premolar are over the crest of the ridge.
  • The teeth need to be set over the crest of the ridge to maximise denture stability and support.CD_189

f) Mandibular 1st MolarCD_190

  • The long axis of the tooth slopes slightly lingually when viewed from the front.
  • The lingual cusp is below the occlusal plane and the buccal cusp should be 2 mm above the occlusal plane.

g) Mandibular 2nd MolarCD_191

  • The long axis of the tooth slopes slightly lingually when viewed from the front
  • Both the cusps are 2 mm above the level of the occlusal plane.

Important notes:

Overjet & Overbite:CD_183

  • Avoid too much overbite or too little overjet.
  • Increasing overbite steepens the angle, separating posterior teeth more quickly.
  • Increasing overjet shallows the angle, separating the posterior teeth less quickly.

Lingual Centric Occlusion:CD_192

  • Make sure that the palatal cusps of the maxillary 2nd molar occlude properly with the central fossa of the mandibular 2nd molar.

Summary

  • Teeth selection should be in harmony with patient’s face, sex and age for a successful fabrication of complete denture prosthesis.
  • Teeth should be positioned in harmony with intraoral and circumoral muscle activity and adjusted so that they occlude and articulate evenly.
  • Several different prosthetic tooth molds have been produced, and each has some purported advantages. In the absence of a clear advantage, tooth molds, selected should be aesthetically pleasing and have a simple procedure to set up.
References
1.Sheldon winkler: essentials of complete dentures  prosthodontics. 2nd edn, W. B. Sauders company,
2.Charles M. Heartwell, Jr; Arthur O. Rahn: Syllabus of Complete Dentures, Fourth edition; published by Lea & Febiger Philadelphia
3.Zarb-Bolender ; Prosthodontic treatment for edentulous patients.. Twelfth edition

– end –

Complete Denture – Occlusion in CD

 

CD_123.jpg

The occlusal schemes provided for complete dentures differ significantly from those found in most natural dentitions. Unlike natural teeth, the artificial teeth act as a single unit. Hence, there should be a minimum of three contact points (usually one anterior and two posterior) between the upper and lower teeth at any position of the mandible for even force distribution and stabilization of the denture.

Therefore, occlusion in a complete denture is defined as any contact between the incising or masticating surfaces of the maxillary and mandibular teeth which deals with the relationship of the maxillary and mandibular teeth is dental articulation.

 

Ideal requirements of complete denture occlusion

  • Stability of the denture & its occlusion when the mandible is in both centric & eccentric relations.
  • Balanced occlusal contacts.
  • Functional lever balance should be obtained by vertical tooth to ridge crest relationship.
  • Cutting, penetrating and shearing efficiency of occlusal surface.
  • Minimal area of contact to reduce pressure while crushing food.
  • Incisal clearance during posterior functions.
  • Sharp ridges, cusps & sluiceways to increase masticatory efficiency.

 

Types of Occlusion

  1. Balanced occlusion
  2. Monoplane occlusion
  3. Lingualised occlusion

 


 

Balanced occlusion

Balanced occlusion refers to the occlusal scheme that is provided for dentures and its features:

  • Inter-cuspal position (ICP) = retruded contact position (RCP) or Centric Occlusion (CO);
  • working side and balancing side contacts in lateral excursions
  • anterior and posterior contact in protrusive excursions.

 

A) Maximum Intercuspal Position

CD_124.jpg

The ICP contacts are established on the artificial teeth to coincide with the RCP that  recorded at the registration stage. Having ICP and RCP coincident allows the wearer to function from centric relation, which is considered the optimal position for function and comfort.

CD_125

 

B) Working side and Balancing side 

CD_126

The side to which the mandible is moving toward is called the working side. The side that is opposite the working side (Moving from) is called the balancing side or Non-working side.

In natural occlusion, the teeth contact on the working side but usually disclude on the non-working side in lateral excursions.

CD_127
Natural Occlusion

However in complete denture, the occlusion is designed to provide stability; therefore the non-working side teeth also contact in lateral excursions to prevent the denture from tipping, giving rise to the term ‘balancing side’.

CD_128
Denture Occlusion

 

C) Protrusion

CD_129

During protrusive excursions, the anterior teeth contact and simultaneous contact should be provided between the posterior teeth to prevent the dentures from dislodging.

 

D) Retrusion

This is mandibular position refers to the tooth contacts during movement of the mandible in a posterior direction. Movement of the mandible in the posterior direction is called “retrusion” just as movement in the anterior direction is called “protrusion”.

 

Objectives of Balanced Occlusion

  1. To improve the stability of denture.
  2. To reduce resorption of the residual ridge and soreness.
  3. To improve oral comfort & well being of the patient.

 

Factors influencing balanced occlusion

CD_130

A balance of these five factors is required for balanced occlusion = Hanau’s quint

  • A) Incisal guidance (IG)
  • B) Condylar guidance (CG)
  • C) Cuspal angulation / cusp height (CH)
  • D) Plane of occlusion or occlusal plane (OP)
  • E) Curve of Spee (CC)

 

A) Incisal Guidance

CD_131

  • During protrusive movements, mandibular teeth move downward & forward called as incisal guidance.
  • Incisal guide angle should be acute with suitable vertical and horizontal overlap to achieve balanced occlusion.
  • Shallow incisal guidance will produce less posterior teeth separation during protrusive movement.
  • Steep Incisal guidance will produce greater posterior teeth separation during protrusive movements.CD_132

 

B) Condylar Guidance

CD_133

  • Shallow condylar guidance produces lesser tooth separation during protrusion.
  • A steep condylar inclination with produce greater tooth separation during protrusion.

 

C) Cusp Height

  • The greater the separation of the teeth, the greater must be the height of the cusps of the posterior teeth.CD_138

D) Occlusal Plane

CD_136

  • The plane of occlusion is an imaginary line that touches the incisal edges of anterior teeth and the  the occlusal cusps of the posterior teeth.
  • The plane of occlusion can also be altered to decrease the posterior tooth separation during protrusion movement. CD_137Note: plane of occlusion should never be tilled more than 10 deg.

 

E) Curve of Spee (anteroposterior curve)

CD_134

  • If the teeth are viewed from the lateral the Curve of Spee is an imaginary anteroposterior curve extending from the tip of the mandibular canine along the buccal cusp tips of the mandibular posterior teeth.
  • Degree of curvature in the Curve of Spee height varies for patients and is based on their cusp size and height of the teeth.
  • Allows for the normal functional protrusive movement of the mandible.
  • The posterior teeth separation during protrusive movement can be decreased by increasing the curvature of curve of spee.CD_135

 


 

Curve of Wilson (lateral curve)

CD_139

  • Also found on the posterior teeth.
  • Is a continuous imaginary line extending across the occlusal surfaces of teeth from the buccal cusp tips to the lingual cusp tips, across the arch (laterally and over the lingual and then buccal cusps.
  • Allows for those exquisite movements which are used in chewing functions.

Vertical and Horizontal Overlap

Vertical overlap is known as OVERBITE. The extension of maxillary teeth over mandibular teeth in a vertical direction when the teeth are in CO.

CD_140

Horizontal overlap is known as OVERJET. This is the projection of maxillary teeth over mandibular antagonists in a horizontal direction.

 


Common Occlusal Relationships

In examining the occlusal relationships, much attention is centered around the first molar, incisor teeth and canine relationship.

 

Angle’s Classification

Edward Angle, a dentist who developed a classification of the normal and abnormal ways that people bring their teeth into centric occlusion – Angle’s Class I, II, III.

Each of Angle’s Classifications are based on the position of the mesiobuccal cusp of the maxillary first molar relative to the mesiobuccal developmental groove of the mandibular first molar.

 

A) Molar-Occlusal Relationship

 

Class I:

  • A person has a normal profile.
  • Mesiobuccal cusp of the maxillary first molar falls in the mesiobuccal groove of the mandibular first molar when teeth are in CO (centric occlusion).CD_141

Class II:

  • Person has a retruded profile (retrognathic profile).
  • The mesiobuccal cusp of the maxillary first molar falls anterior to the mesiobuccal groove of the mandibular first molar in CO.CD_142

Class III:

  • Person has a protruded (prognathic profile)
  • Mesiobuccal cusp of the maxillary first molar falls posterior to the mesiobuccal groove of the mandibular first molar in CO.CD_143

 

In conclusion for Angle’s Class I, II & III:

CD_144
Top: class I ; Middle: class II ; Bottom: class III

B) Incisor Relationship

Class I:

  • The lower incisor edge occlude on or lie below the cingulum plateau of upper incisors.CD_145

Class II Division 1:

  • The lower incisor edges occlude behind the cingulum plateau of the upper incisors.
  • The upper incisor are normally inclined or proclined.
  • Increased over jet.CD_146

Class II Division 2:

  • The lower incisors edges occlude behind the cingulum plateau of the upper incisors.
  • The upper incisors are retroclined.CD_147

CD_148

Class III:

  • The lower incisors edges occlude anterior to the cingulum plateau of the upper incisors.CD_149

 

C) Canine Relationship

Class I:

  • The maxillary permanent canine occludes in the embrasure between the lower canine and first premolar.CD_150

Class II:

  • The maxillary canine occludes anterior to the embrasure relationship between lower canine and first premolar.CD_151

Class III:

  • The  maxillary canine occludes posterior to the embrasure between the lower canine and first premolar.CD_152

 

 

– end –

Complete Denture – Articulators

CD_105.JPGWHAT IS AN ARTICULATOR?

Articulator is a mechanical device which represents the temporomandibular joints and the jaw members to which maxillary and mandibular casts may be attached to simulate jaw movements.

 

Purpose of the Articulator

  • To hold the maxillary and mandibular casts in a determined fixed relationship.
  • To simulate the jaw movements like opening and closing.
  • To produce border movements (extreme lateral and protrusive movements).

CD_112.jpg

Requirements of the Articulator

  • It should hold casts in the correct horizontal relationship.
  • It should hold casts in the correct vertical relationship.
  • The casts should be easily removed and reattached.
  • It should open and close in a hinge movement.
  • It should be made of non-corrosive and rigid materials that resist wear and tear.
  • It should not be bulky or heavy.
  • There should be adequate space present between the upper and lower members.

 

Advantages of the Articulator

  1. Allow the operator to visualize the patient’s occlusion, especially from the lingual view.
  2. Patient cooperation is not a factor when using an articulator once the appropriate interocclusal records are obtained from the patient.
  3. The refinement of complete denture occlusion in the mouth is extremely difficult because of shifting denture bases and resiliency of the supporting tissues. This difficulty is eliminated when articulators are used.
  4. Reduced chair time, patient’s appointment time.
  5. The patient’s saliva, tongue and cheeks are not factors when using an articulator.

 

Structure of an ArticulatorCD_106

A) Upper member: triangular metal plate – represent maxilla.

 

 

B) Lower member: L shaped frame – represent mandible.

 

 

C) Incisal pin (vertical rod) separates the upper and lower triangular component in the anterior end.

 

D) Incisal table is a table on the lower member which the incisal pin rest on.

 


 

Classification of Articulators

►Based on the theories of occlusion

►Based on the type of inter-occlusal record used

►Based on the ability to simulate jaw movement

►Based on the adjustability of the articulator

A) Articulator Type Based On The Ability To Simulate Jaw Movements

i) Class I

  • Simple articulators capable of accepting single static registration.
  • Only vertical motion is possible.
  • Used in few cases where a tentative jaw relation is done.

ii) Class II

  • Permit horizontal and vertical movement.
  • Do not orient the movement of TMJ with a face-bow.

iii) Class III

  • Permit horizontal and vertical movements.
  • Accept face-bow transfer but this facility is limited.
  • Can not allow total customization of condylar pathways.

iv) Class IV

  • Accept three-dimensional dynamic registration.
  • Capable of accurately reproducing the condylar pathway for each patient.
  • Allow point orientation of the casts using a face bow transfer.

 

B) Articulator Type Based On the Adjustability Of The Articulator

Classified as:

  • i) Non-adjustable.
  • ii) Semi-adjustable.
  • iii) Fully-adjustable.

 

i) Non-Adjustable ArticulatorCD_107.jpg

  • Open and close in a fixed horizontal axis.
  • Have a fixed condylar path.
  • The incisal guide pin ride on an inclined plate in a fixed inclination.

 

ii) Semi-Adjustable ArticulatorCD_108.jpg

  • Have adjustable horizontal condylar paths.
  • Adjustable lateral condylar paths.
  • Adjustable incisal guide table.
  • Adjustable intercondylar distances.
  • They do accept face-bow transfer but this facility is limited.

Semi-adjustable articulator is further divided into 2 groups:

  1. Arcon articulator
  2. Non-arcon articulator
Arcon = ar (articulator) + con (condylar)

>> Arcon Articulator

  • condylar elements is attached to the lower member of the articulator.
  • Condylar guidance is attached to the upper member of the articulator.
  • This articulator resembles the TMJ.

>> Non-Arcon Articulator

  • Condylar elements are placed on the upper portion of the articulator.
  • Condylar path guidance is attached to the lower member.
  • This articulator is the reverse of the TMJ

 

iii) Fully Adjustable ArticulatorCD_109

  • Capable of being adjusted to follow the mandibular movement in all directions.
  • Have numerous adjustable readings, which can be customized for each patient.
  • They do accept face-bow transfer.

 

 


 

Facebow recordingCD_110

For semi adjustable articulator: A facebow transfers the distance between the hinge axis and the tooth being restored from the patient to the articulator.

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Bennett movementCD_113.jpg

►The Bennett movement is the lateral movement of the condyle .

►The ability to adjust the Bennett movement is also found on some semi-adjustable articulators.


 

Articulating the Denture

CD_1141. Soak the models in water.

 

 

2.Trim the base of both models flat and parallel with the occlusal surface.

 

 

 

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3.Make three grooves in the base of both models.

►These should be in the form of “ V ” – there should be no undercuts.

►Put a light coat of a separating medium in the relocation grooves (either sodium alginate or petroleum jelly).

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4.Attach maxillary and mandibular models with the record bases together.

5.Check the height of models with the height between the upper and lower arms of the articulator.

 

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6.The upper member of the articulator is raised with the mounting ring attached and impression plaster is placed in the center of the base.

 

The upper member of the articulator is lowered until the guide pin comes in contact with the guide table.

 

Excess plaster from above the ring is removed and the plaster surface is smoothed and then allowed to fully set.

 

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7.To seat and affix the mandibular cast to the record base, the operator will:

  • Seat the mandibular cast.

 

  • Seal it in place on the record base.

 

 

 

 

  • Close the articulator to CD_120.jpgensure that at least 3 mm clearance exists between the inferior surface of the mandibular cast and the mandibular mounting ring.
  • If this is not so, the undersurface of the mandibular cast must be adjusted until sufficient clearance is achieved.
  • Care may need to be taken to avoid accidentally perforating the cast in the greatest depths of the lingual vestibules.

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CD_121

 

8.Clean it up, using water, your fingers and the palm of your hand.

  • Rinse articulation and clean under running water.
  • Allow the articulation to stand until the final set is complete.

 

 

 

– end –

 

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My first complete denture articulator practice

Complete Denture – Occlusal Registration

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WHAT IS OCCLUSAL REGISTRATION?

The occlusal registration stage records the information required to produce the trial dentures.

 

Jaws Relationship Record

  • Maxillary record base and occlusion rim are used to transfer the correct relationship of the maxillary master cast relative to the condylar elements and axis of orbital plane of the articulator.
  • Combination of both upper and lower record base and occlusion rims are used to transfer the correct horizontal and vertical position of the mandibular master cast relative to maxillary master cast.

 

Various Term Used in Jaw Relation

A) Vertical jaw relation: is the amount of separation between mandible and maxilla in the frontal plane. It is affected by the teeth and musculature.

B) Horizontal jaw relation: is the relationship of mandible to the maxilla in a horizontal plane.

C) Centric jaw relation: is the relation of mandible to the maxilla when the condyles are in the uppermost and rearmost position in the glenoid fossa.CD_081.jpg

D) Eccentric jaw relation: Any relationship other than the centric jaw relation.

E) Intercuspal  Position ICP: The jaw relationship in which maximum occlusal contact occurs.CD_082.jpg


Essential Recordings made during occlusal registration

  1. Occlusal Plane
  2. Lip Support
  3. Centre Line
  4. Vertical Dimension
  5. Centric Relation
  6. Smile lines
  7. Canine lines

Occlusal Plane & Lip Support

CD_083.jpg

  • The occlusal plane is the plane at which the upper and lower teeth occlude. It passes through the incisal edge of the central incisors and curves upwards as it travels towards the molars.
  • The labial surfaces of the anterior teeth or rim also provide support for the lips. Added wax into the labial surface of the rims to support the lips to achieve the correct labial contour to the face.

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The occlusal plane is significant in providing:

  • Suitable aesthetics
  • Phonetics
  • Function

 

 

The correct position of occlusal plane and lip support is determined using a combination of:

A) Anatomical landmarks

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—The incisal papilla may be used to assess the position of the labial surface of central incisors, which are typically 9–10 mm anterior to the middle of the incisal papilla.

 

B) Aesthetics

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  • Looking at the soft tissues around the top lip can help to assess the labial positioning.
  • The patient should have a natural profile.
  • With the lip at rest, the amount of tooth or rim visible is used to determine the vertical height of the occlusal plane.
  • Lips should be unstrained
  • Naso-labial angle ≈ 90°
  • Philtrum depressed
  • Vermilion border showing

 

C) Phonetics

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  • When ‘F’ is pronounced, the incisal edge of the maxillary incisors should just touch the wet–dry border of the lower lip.

 

D) Existing denture

  • An existing denture is an excellent guide when establishing the occlusal plane of the new denture.
  • The position of the teeth can be measured using the Alma gauge and duplicated on the registration rim or new denture.

    CD_086
    Alma gauge
  • Alternatively, a copy denture technique may be used.

 

Adjusting  the upper rim

  • If the upper rim needs to be adjusted by removing wax from the rim, this can be achieved using a hot rim inclinator until the block is parallel with the reference plane.
  • The upper occlusal rim anteriorly recommended to be 1-2 mm below the lip line at rest (anterior lip line).
  • The occlusal plane of the upper registration rim is adjusted to be parallel to the ala-tragal (or Camper’s) line.CD_089
  • A Fox plane can be used where mediolaterally the occlusal plane parallels the pupils of eyes.CD_090
  • A Foxes occlusal plane indicator held against the upper rim allows the occlusal plane to be viewed extraorally. At the same time, any handy straight implement can be held along the ala-tragal line to compare the reference plane to the occlusal plane of the upper rim.

 

Lower lip supportCD_093

  • The labial aspect of the lower rim is harmonized with the lower lip to ensure that the denture will remain seated during speech.
  • A useful check is to ask the patient to pronounce the letter ‘E’, which pulls the lower lip against the labial aspect of the rim.
  • Neutral zone techniques may be indicated in cases where positioning the lower rim or teeth is difficult.CD_094
  • Posteriorly, the occlusion rim intersects 1/2 – 2/3 up the retromolar pad.
  • Unstrained lips.
  • Vermilion border showing.
  • Anterior height even with the corners of the mouth when the lip is relaxed.
  • 1-2 mm horizontal overjet in anterior & posterior in centric position.

Midline, Smile Line & Canine LineCD_091

  • The midline is marked on the upper rim in line with the midline of the face.
  • The smile and canine lines are useful in selecting the size of tooth to be placed.
  • The height of the central incisor should be equal to or greater than the height of the smile line above the incisal edge.
  • The distance between the canines can be determined from the corners of the mouth at rest.CD_092

 

Vertical Dimension

There are two vertical dimensions that are routinely measured:CD_097

  • The Vertical Dimension of lower facial height when the teeth are in Occlusion VDO.
  • The Vertical Dimension of lower facial height when the teeth are in Rest VDR.
  • To establish a functional vertical dimension the VDO must be less than the VDR to allow the occluding surfaces to separate at rest.
  • The difference between the two is called the ‘freeway space’ and is significant because it allows the muscles of mastication periods of rest.
FREEWAY SPACE = VDR - VDO
  • The lower rim is adjusted such that it occludes evenly with the upper rim while allowing approximately 2–4 mm of freeway space.

 

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Excessive Occlusal Vertical Dimension

  • Increase lower facial height
  • Sore muscles (Stretching of facial muscles)
  • Soft tissue sore spots (Trauma to denture bearing area)
  • Rapid bone resorption.
  • Difficulty in swallowing and speech
  • Cheek biting

 

 

 

CD_103

Inadequate Occlusal Vertical Dimension

  • Collapsed Appearance – chin too close to the nose
  • Protruding jaw. (decrease lower facial height)
  • Fatigue when chewing
  • Sore muscles or joints
  • Difficulty in swallowing
  • Loss of lip fullness
  • Loss of muscle tone

 

 


 

Centric Relation

  • The centric relation is the relationship between the maxilla and mandible when the jaw is in its optimal position (when the condyle heads seat uppermost and rearmost position of the glenoid fossa).
  • The most commonly used method to position the mandible in centric relation is to ask the patient to curl the tip of the tongue to the soft palate, encouraging the condyles to seat.CD_098
  • To check that the position is correct, the procedure is repeated several times and the positions compared to ensure they coincide.
  • To record this position, ‘V’-shaped notches are cut into each rim and the exercise above repeated with silicone bite registration material between the rims.CD_099
  • Well adjusted occlusal rims united & casts returned to lab. Then casts mounted on an articulator so that the teeth can be set up.

CD_100

 

– end –

 

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My first practice making occlusal rim