Shade Selection & Lab Instruction in FPD

DEPT.OF PROSTHODONTICS & CROWN & BRIDGE

North Bengal Dental College & Hospital

IntroductionTo provide aesthetic restorations to the patients,the dentist

must understand the scientific as well as artistic basis of shade selection.To accomplish this,a through knowledge of the concepts of colour & light is necessary with clear communication to the laboratory.

Colour: An attribute of things that results from the light they reflect,transmit or emit in so far as this light causes a visual sensation that depends on its wavelegth.

Light: Light is a form of visible energy that is part of the radiant energy spectrum.Visible light spectrum ranges from 400-700 nm.

Colour mixing: In the additive or light-mixture colour mixing system;red,green,blue are the primary colours.Mixing two primary colours produces a secondary colour.

Red+green=yellow ; Green+blue=cyan ;Red+blue=magentaThis system applies only to combining lights & illuminants.

In the subtractive or pigment-mixture system,the secondary colours in the additive system yellow-cyan-magenta are the primary colours.

Yellow+cyan=green ; Cyan+magenta=blue ;Magenta+yellow=redIn dental ceramics both additive & subtractive

concepts are used.

Colour description:Two systems may be used to describe colour:

1. Munsell (1915) colour order system-more visually descriptive:the system describes colour possessing three dimensions-

i. Hueii. Valueiii. Chroma

2. Cielab (1976) colour system-more quantitative

Colour of human teeth:Spectrophotometer studies shows a hue range

of 6 YR to 9.3 Y,a value range of 4-8 & a chroma range from 0-6. Hence the human teeth lie in the yellow-red to yellow portion of colour wheel,with value range in the lighter portion,which indicates that very dark teeth are uncommon.The chroma range is towards the lower scale,which indicates that strong colours are not found.

Colour perception:This involves the participation of three factors:

1. The observer2. The object being observed3. The light sourceObserver:Perception of colour depends on

the observer’s visual individuality.It depends on the age,duration of the exposure of the eye,fatigue,colour blindness.

Object: When light falls on an object,it is absorbed,reflected,transmitted or refracted depending on the light transmitting ability of the object.This produces characteristic quality of that colour.

Light source: The light source utilized has a definite effect on the perception of colour.There are commonly three available source-natural daylight,incandescent light & fluorescent light.LED lights are also being used currrently.

Example: of commercially available colour corrected lights are-Demetron shade light & Vita-Lite.

Metamerism:An object appears to be having different colours when viewed under different light source.

Principles of Shade Selection

1. Teeth to be matched must be clean2. Remove bright colors from field of view

- makeup / tinted eye glasses- bright gloves- neutral operatory walls

3. View patient at eye level4. Evaluate shade under multiple light

sources5. Make shade comparisons at beginning of

appointment6. Shade comparisons should be made

quickly to avoid eye fatigue

Shade GuidesShade matching is performed either visually

(using shade guide) or by electronic shade taking devices or by shade distribution chart.

Visual : Most convenient and common method of

making shade selectionsGuides consist of shade tabs

◦ Metal backing◦ Opaque porcelain◦ Neck, body, and incisal color

Select tab with the most natural intraoral appearance

Commercial Shade Guides in visual method

• Vita Classic

• Vitapan 3D –Master

• Extended Range Shade Guides

Vita Classic Shade Guide• Very popular shade guide• Tabs of similar hue are clustered into letter

groups– A (red-yellow) – B (yellow)– C (grey)– D (red-yellow-gray)

• Chroma is designated with numerical values• A3 = hue of red-yellow, chroma of 3

A B C D

Red/Yellow Yellow GreyGrey

Red/Yellow

Vita Classic Shade Guide

Manufacturer recommended sequence for

shade matching

1. Hue Selection

2. Chroma Selection

3. Value Selection

4. Final Check / Revision

Vita Classic – Step 1 (Hue Selection)

• Four categories representing hue– A, yellow-red– B, yellow– C, gray– D, red-yellow-gray

• Operator should select hue closest to that of natural tooth

• Use area of tooth highest in chroma for hue selection– Difficult to select hue for teeth low in

chroma

Vita Classic – Step 2 (Chroma Selection)

• Hue selection has been made (B)

• Chroma is selected from gradations within the B tabs– B1, B2, B3, B4

• Several comparisons should be made– Avoid retinal fatigue– Rest eyes between comparisons

(blue-gray)

Vita Classic – Step 3 (Value Selection)

• Use of second, value ordered shade guide is recommended

• Value oriented shade guide– B1, A1, B2, D2, A2, C1, C2, D4, A3, D3, B3, A3.5, B4, C3, A4, C4,

• Value best determined by squinting with comparisons made at arms length – Decreases light– Diminishes cone sensitivity, increases

rod sensitivity– Tooth fading first has a lower value

Vita Classic – Step 4 (Final Check / Revision)

• Potential Problem– Following value selection, tabs

selected for hue and chroma may not coincide with shade tab selected for value

Vita Classic – Step 4 (Final Check / Revision)

• Possible Findings / Solutions– Value of shade tab < natural teeth

• Select new shade tab with higher value

• Cannot increase value of restoration with extrinsic staining

• Will only increase opacity, light transmisison

– Value of shade tab > natural teeth• Select new shade tab with lower

value (or)• Bridge difference with intrinsic or

extrinsic staining

VITAPAN 3D-MASTER Shade Guide

Vita-3D – Step 1• Determine the lightness level (value)

• Hold shade guide to patient’s mouth

• Start with darkest group moving right to left

• Select Value group 1, 2, 3, 4, or 5

Vita-3D – Step 2• Select the chroma

• From your selected Value group, remove the middle tab (M) and spread the samples out like a fan

• Select one of the three shade samples to determine chroma

Vita-3D – Step 3

• Determine the hue

• Check whether the natural tooth is more yellowish or more reddish than the shade sample selected

Vita-3D – Step 4

• For more precise shade, intermediate levels for hue, value, and chroma can be given– 2.5M2 = value between 2M2 and 3m2– 3M1.5 = chroma between 3M1 and 3M2– 3M2 / 3L2.5 = hue between 3M2 and

3L2.5

Vita-3D – Value Modification

• For more precise shade, intermediate levels for value, chroma, and hue can be given– 2.5M2 = value between 2M2 and 3M2

Vita-3D – Chroma Modification

• For more precise shade, intermediate levels for value, chroma and hue can be given– 3M1.5 = chroma between 3M1 and

3M2

Vita-3D – Hue Modification

• For more precise shade, intermediate levels for value, chroma and hue can be given– 3M2 / 3L2.5 = hue between 3M2 and

3L2.5

Extended Range Shade Guides

• Most shade guides do not cover all the colors in the natural dentition

• Some porcelain systems extend the typical range

• Bleached shades

• Dentin shades

• Custom shade guides

Electronic shade taking devices These are electronic instruments which record

the colour of the tooth.They allow an improved understanding of colour perception & its correlationwith clinical aspects.

They are divided into two categories:1.Colourimeters: It measures the absorbance of

different wavelengths of light in a solution,e.g.Shade eye-Shofu

2.Spectrophotometers:It quantitatively measures the reflection or transmission properties of a material as a function of wavelength,e.g.Easy shade-Vita.

Shade distribution chartThe tooth is divided into incisal,middle & cervical portions

& the colour of each region is matched independently.Various patterns of translucency must be recognized to

attain good results.In younger patients the incisal enamel is thick & very translucent.As translucency increases the value decreases.Over years of function,this enamel is lost.Similarly the thickness of the enamel on the buccal aspect also decreases & allows the dentine to dominate the shade.

Individual characteristic are then marked.The surface of the tooth or the restoration determines how much of light is reflected away.This produces changes in the perceived colour of restoration.Younger teeth show a great deal of surface characterization like stippling,developmental lobes,ridges & striations.Older teeth,due to wear show a smoother,highly polished surface.

.

Lab instructions To make a high-quality fixed prosthesis, all members

of the dental team must understand what they can reasonably expect from each other. A mutual knowledge of individual limitations is also critical.The dentist who does not understand and appreciate the challenges faced by the technician is at a serious disadvantage when prescribing and delegating laboratory procedures . Critical to the development of sound clinical judgment is a thorough understanding of technical procedures and their rationale.

MUTUAL RESPONSIBILITIESGood communication is the key to a dental team's technical

success. This requires a close working relationship between the dentist and laboratory technician.Anticipating satisfactory results is absolutely unrealistic if the dentist does not have a reasonable amount of experience with, and a thorough understanding of, dental laboratory procedures.

The American Dental Association (ADA) has issued guidelines to improve the relationship between dentist and technicians.

The dentist, being duly licensed, should:(1) Provide the laboratory with signed written instructions

detailing the work which is to be performed and prescribing the appropriate materials to be used;

(2) Provide the laboratory with accurate impressions,casts, interocclusal records or mountings;

(3) Identify the margins, postdam, borders, relief and/or prosthetic design on all submitted cases;

(4) Furnish a shade description, photograph,drawing or shade button that most closely achieves the desired results;

(5) Provide a verbal or written approval for thelaboratory to proceed with the fabrication of the prosthesis or approve modifications, if notified by the laboratory that a submitted case may have questionable areas or unclear instructions and submit written approval to the laboratory after the item in question has been clarified;

(6) Retain a copy of the written instructions for aperiod of time as may be required by law;

(7) Follow appropriate laboratory infection control protocol as outlined in the ADA's infection control guidelines.

The dental laboratory should:(1) Produce dental prostheses following the

written instructions provided by the dentist and using the impressions, casts, interocclusal records or mountings as submitted;

(2) Review the case with the prescribing dentist for clarification if a question arises;

(3) Match the shade as described in the original instructions, within the limitations of the materials available for use;

(4) Notify the dentist immediately if it is determined that work on the case cannot proceed;

Section 3 Laboratory Procedures(5) Fabricate the prostheses in a timely manner;(6) Inform the dentist of the materials used in

the fabrication of the case;(7) Follow appropriate laboratory infection

control protocol as outlined in the ADA's infection control

RESPONSIBILITIES OF THE DENTISTThe dentist has the overall responsibility for the treatment

rendered. Delegating many procedures to auxiliary personnel is possible if all the necessary information is provided to enable them to deliver high-quality service. However, errors such as insufficient tooth reduction, uncertainty about the location of tooth preparation margins, improper interocclusal records and articulations, and ambiguity in communicating the desired shades for esthetic restorations to the technician hamper this responsibility

WORK AUTHORIZATIONIn addition to certain general information that is required by law, a

work authorization form (Fig. 16-8)should include the following:1. General description of the restoration to be made2. Material specification (e.g., ADA Type IV gold)3. Desired occlusal scheme4. Connector design for FPDs5. Pontic design, including the material specification for tissue

contact6. Substructure design for metal-ceramic restorations7. Information regarding the shade selection for esthetic

restorations8. Proposed RPD design (if applicable)9. Date of the next scheduled patient appointment

Shade Selection: With the prevalence of metalceramic restorations,

dentists and technicians have become acutely aware of the difficulty involved in communicating shade selection. A thorough understanding of the principles of color science and the use of internal and surface colorants is essential to both parties. Many dentists and technicians have found a diagram of the tooth that allows specifications of multiple shades helpful (Fig. 16-10). 11 The diagram should be large enough to designate a cervical shade, an incisal shade, and any applicable individual characterization. Diagrams on most preprinted laboratory prescription forms do not provide adequate space (see Fig. 16-8), so other space must be available. A separate entry regarding the value or brightness can be helpful. When selecting a shade, the dentist should use a guide that corresponds to the ceramic system used by the technician. On occasion, it may not be possible to obtain a match with a simple shade guide (e.g., the Vita Lumin vacuum system). In those cases an alternative guide or a shade distribution chart (outlined in Chapter 23) should be used. The dentist must have excellent color perception skills and should be able to precisely transfer those onto a written prescription that includes a large, detailed diagram that allows the ceramist to accurately reproduce the shade observed and described by the clinician. Close communication and cooperation are obviously necessary, and a trial porcelain firing may be needed.

A practical alternative to written color communicationis the use of light-cured, resin-based stainingkits to custom-stain a shade-tab. The closest matchingshade-tab is selected and modified using stainsmixed with liquid resin. Once the desired match hasbeen obtained, the resin is light-cured, and the cus-tomized tab is sent to the dental laboratory. The ceramistthen has an actual reference and can comparethe work and make the required modifications, thusensuring predictable success. If esthetic requirements are extensive or difficultto communicate through the means described above,involving dental laboratory personnel in the shadeselection process may be helpful. The ADA takes theposition that when a dentist requests the assistanceof a dental laboratory technician in the shade selectionprocess, this does not constitute the practice ofdentistry by the technician, provided the activity isundertaken in consultation with the dentist and thatit complies with the dentist's written instructions.Such assistance is most appropriately providedin the dentist's office.'

Fig. 16-10. A shade distribution chart must be adequatein size to permit inclusion of enough detail. Subtle differencesobserved in cervical shades are identified, as are surfacedetails such as hypocalcification, incisal translucency,and stains.

Sample Laboratory Prescription form

Reference1.Contemporary Fixed

Prosthodontics-Rosensteil,Land,Fujimoto

2.Fundamental of FPD – Shillingburg3.Textbook of Prosthodontics-V

Rangarajan,TV Padmanabhan4.www.google.com

Thank YOU