Dental Laboratory Form Question And Answers

 Dental laboratory form

Dental laboratory form Synonym

Work authorization form.

Dental laboratory form Definition

The written instructions submitted to a dental laboratory by a dentist along with the work.

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Dental laboratory form Items to be sent to the laboratory

• Properly prepared and articulated master cast with interocclusal records or mountings.
• Diagnostic cast with specific design and requirements drawn on it.
• Shade guide for the replacement prosthesis.
• Impressions with poured casts.
• Dissected dies.
• Work authorization order.
• Appropriate laboratory infection control protocol needs to be followed.

Dental laboratory form Work authorization order should include

• Signature of the dentist.
• Date of the authorization.
• Name and address of the patient.
• Date of case returned for try-in or completion.
• Telephone number of dentist and dental technician.
• General description of the restoration to be made.
• Designs of gingival margins, pontic designs, anterior and posterior.
• Exact location of metal and porcelain joining on occlusal surface.
• For fixed-removable, rests and guide planes designs need to be drawn.
• The desired occlusal scheme.
• Connector design for fixed partial dentures.
• Pontic design, including the material specification for tissue contact.
• Substructure design for metal–ceramic restorations.
• Materials specification.
• Instructions on articulation and shade selection with type of tooth replacement.

Dental laboratory Objectives

• Acts as a good line of communication between the dentist and the laboratory
• The technician can carry out the work according to the dentist’s clinical requirement
• Instructions written can be clarified
• The quality of the work done by the dentist and by the laboratory can be improved
• Also serves as a legal protection form for the dentist and laboratory technician
• Protects the public from the illegal practice of dentistry
• Establishes the separate responsibility of the dentist and the laboratory technician.

Dental laboratory Preparation margins

Should be outlined on the die or ensure that the impressions can give the accurate margin demarcation.

Dental laboratory Articulation
Cast with interocclusal record helps to accurately articulate the casts.

Dental laboratory Occlusion

Should designate the location of the occlusal contacts.

Dental laboratory Desirable occlusal schemes

• Cusp-fossa
• Cusp-marginal ridge (If positive stops are not present).

Dental laboratory Connectors

To specify the connectors to be cast, preceramic soldered and postceramic soldered.

Pontic and substructure design

• Type of pontic replacement need to be drawn (ridge lap, modified ridge lap)
• To instruct specifically if wax pattern is to be evaluated.

Shade selection

• A diagram of the tooth with multiple shades, (as cervical shade, an incisal shade and individual characterization), needs to be charted for easy identification and accuracy
• Also a shade guide matching the tooth to be replaced is placed.

Evaluation for accuracy

• A wax pattern try in to review the contours of retainers and pontics
• A metal substructure try in for metal–ceramic restorations
• A final try in to evaluate the contours, texture and staining of a metal–ceramic restoration.

Dahls Appliance

This concept was proposed by Dahl in 1975 for localized anterior tooth wear cases. The first design included a cobalt chromium partial denture with anterior bite plane which caused a posterior disocclusion.

Dahls Principle

There was a reestablishment of posterior occlusion due to a combination of intrusion of anterior teeth (40%) and extrusion of posterior teeth (60%) in a period of 4–6 months. The degree of space created ranged between 1.8 mm and 4.7 mm.1

Dahls Advantage

• The vertical dimension of occlusion can be increased within the physiologic limits
• The steep incisal guidance angle is reduced
• Favorable biomechanical situation is reached
• Once the posterior occlusion is reestablished there is enough space to restore the anterior teeth with definitive restorations
• This is specifically used for localized anterior tooth wear
• A conservative method for good esthetics.

Dahls Disadvantages

Time consuming, increased treatment time and extra laboratory procedures.

• Material is placed on the palatal aspect of anterior teeth for re-establishment of inter-occlusal space
• The thickness of the material placed is equal to the amount of space required
• No mucosal-borne component is present
• The bite plane in anterior ensures that occlusal forces are directed along the long axis of the teeth
• Stable inter-occlusal contacts
• No interference to the movement of the posterior discluded teeth.

Modification in Dahls appliance

• Presently fixed appliances or materials are used
• The palatal surfaces of anterior teeth can be build up using cemented cast metal appliance or resin materials.

Dahls appliance Recent advancement

• This technique includes a single stage procedure instead of the original two step procedure
• Here restorative space is gained by cementing the restoration in supraocclusion
• Direct bonded composites are employed commonly as they are less expensive, reversible and easy to adjust and favorable wear properties.

Dahls appliance Advantages

• Restore esthetics and function
• Less treatment time, cost and final control over esthetics
• Easy to retreat, repolish, repair and is a reversible process.

Dahls appliance Limitations
The higher wear rate than porcelain and prone to staining.

Contraindications of direct bonding

• In cases of periodontal disease or short root length direct bonding can cause tooth displacement in a nonaxial direction leading to drifting
• If less than two thirds of root length.

Techniques for composite build up

The techniques apply to cases where dentoalveolar compensation has occurred, and there is insufficient space for restorations.

• Free-hand technique
• Matrix-guided technique.

Procedure

• Clinical evaluation of space required either by intraoral examination or by articulated study casts mounted
• Shade selection is done
• A diagnostic wax-up is done on the articulated cast.

Clinical procedure

• Old restorations are removed in order to improve bond strength
• Tooth surfaces are cleaned with pumice and a polishing brush
• Retraction cord is placed
• A long bevel at the enamel margins improves the transition between tooth and composite, decrease internal stresses and increases the bonding surface area
• Good moisture control is ensured by use of rubber dam, cotton wool rolls and saliva ejectors.

Free-hand technique

Free-hand technique Advantages
The free-hand technique may avoid a visit for impression taking and can be carried out in a single treatment session.

Free-hand technique Limitation
Good clinical skill and moisture control.

Free-hand technique Procedure

• First step: Both canine cingulum region build up—Composite is added to the cingulum region of both upper canines and the mandible manipulated into the retruded axis and closed into the uncured resin until the desired anterior space is achieved4
• Recheck OVD and bilateral cingulum contact
• Second step: Individual incisor build up—Each individual incisor is build up in the cingulum area and finally the entire contacts are finished with the aid of a matrix strip. After each incisor build up the midline is checked
• The occlusion is checked with thin articulating paper to ensure even contact and protective guidance in protrusive and lateral excursions
• The posterior teeth will be out of occlusion and should be monitored over subsequent months until contact is re-established.

Matrix technique

Matrix Technique Advantage
Palatal anatomy and the position of the incisal edges are guided by the matrix.

Matrix Technique Limitation
Depends on the clinical skill of the diagnostic wax up.

Matrix Technique Procedure

• Models are mounted on a semiadjustable articulator in retruded axis by face bow transfer
• A diagnostic wax up which is 1–2 mm clear from gingival margin palatally is made in the desired vertical dimension
• A transparent silicone matrix (Memosil Heraeus-Kulzer, Hanau, Germany) is adapted just beyond the incisal edges of the diagnostic wax up
• This matrix aids as a template for composite build up on the palatal cingulum area but clear of the proximal contact areas
• The composite is cured and the matrix removed
• Proximal areas are built up with the help of a matrix strip
• The occlusion is checked to create even contact on the restorations at the new vertical dimension, with canine guidance in excursive movements.

Management of tooth surface loss (TSL)

Classification of tooth surface loss (Grippo)

Tooth Surface Loss Erosion
Erosion is the loss of tooth substance by acid dissolution by either intrinsic or extrinsic origin. Extrinsic sources are carbonated drinks and alcoholic beverages. Intrinsic sources include gastrooesophageal reflux, bulimia, etc.

Tooth Surface Loss Abrasion
The pathological wear of tooth substance through biomechanical frictional process. (e.g. tooth brushing and abrasive food).

Tooth Surface Loss Attrition
The loss of tooth substance as a result of tooth to tooth contact during normal function or parafunction (e.g. bruxism—is the grinding of teeth during nonfunctional movements of the masticatory system).

Abfractions (stress lesions)
Is the pathologic loss of tooth substance caused by biomechanical loading forces. Causes stress at the cervical area resulting in a lesion which is typically wedge shaped with sharp line angles.
Types: Hairline cracks, striations, saucer shaped and semi-lunar shaped.

Flowchart 1: Treatment options for tooth wear

Features of different types of tooth surface loss

• Flattening of cusps or incisal edges and wear facets on occlusal or palatal surfaces – Attrition
• Cervical lesions with defined margins and smooth surface – Abrasion
• More rounded and shallow lesions and have a cupping effect – Erosion
• Measured by tooth wear indices. Commonest is Smith and Knight.

The effects of tooth surface loss

• Reduction in vertical tooth height and horizontal tooth width leading to loss of vertical dimension of occlusion (increased free way space)
• Forward posturing of the mandible
• Dentoalveolar compensation seen in some cases maintaining the vertical dimension.
• Unesthetic.

Treatment plan (Flowchart 1)

• To evaluate if to confirm to the existing centric occlusion or to reorganize in centric relation
• To evaluate if centric occlusion is in centric relation.

The conformative approach

• Criteria for conformative approach
• The patient with centric occlusion occurring in centric relation
• The patient does not have any deflecting contacts and will not need other restorations for tooth loss
• When there is no temporomandibular disorder.

The reorganised approach

If the above criteria is not present and there is lack of freeway space then a reorganised approach is considered.

Tooth Surface Loss References

• Grippo JA. A new classification of hard tissue lesions.
• Smith BG, Knight JK. An index for measuring wear of teeth.
• Kelleher M, Bishop K. Tooth surface loss: an overview.
• Gray R M J, Davies S J, Quayle A. A clinical approach to temporomandibular disorders: Splint therapy.

Flowchart for surgical procedure in implant placement.

Flowchart 2, 3 and 4 gives the surgical procedure in implant placement.

Flowchart 2: Steps in surgical procedure in implant placement

Second stage surgery

Flowchart 3: Steps in second stage surgical procedure in implant placement

After 4–6 weeks post second stage surgery

 All-ceramic restoration

• The first all-ceramic crowns introduced by Land in 1903
• In 1965, McLean and Hughes formulated aluminous porcelain in which 50% aluminum oxide increases the strength and baking temperature.

Ceramics Definition

Ceramics are defined as man made solid objects formed by baking raw materials at high temperatures.

From Greek word ‘keramos’ meaning burnt stuff.

Composition of all ceramics

Feldspathic dental porcelain with high amounts of alminum oxide.

Classification of all-ceramic systems

• Conventional powder–slurry ceramics – Optec HSP, Duceram LFC
• Castable ceramics – Picon, Dicor Plus
• Machinable ceramics – Cerec vitablocs Mark 1, Mark 2, Dicor MGC, Celay
• Pressable ceramics – IPS Empress, Optec Pressable Ceramic
• Infiltrated ceramics – In-Ceram.

Conventional powder–slurry ceramics

Available as

• Powders to which water is added to produce a slurry
• Available in various shades and translucencies, with characterizing stains and glazes.

Manufacturing

• Leucite crystals are dispersed in a glassy matrix by controlling their nucleation and crystal growth.
• The leucite and glassy matrix fuse together during the baking process.
• The build-up and contouring of the crown can be done by using the powder–slurry technique on semipermeable die material.

Ceramic Restoration Advantages

• Greater strength than conventional feldspathic porcelain due to its leucite content
• Does not require a core as with aluminous porcelain jacket crowns
• The body and incisal porcelains can be pigmented to provide desired shade and translucency
• Does not require special processing equipment
• These restorations fit accurately.

Ceramic Restoration Disadvantages

• Their high leucite contents can cause increased wear to opposing teeth.

Other types

Duceram LFC

• Hydrothermal low-fusing ceramic
• Composed of an amorphous glass containing hydroxyl ions.

Duceram LFC Advantages

• Greater density, higher flexural strength, greater fracture resistance and lower hardness than feldspathic porcelain
• No special laboratory techniques or equipment required.

Duceram LFC Uses

• For fabrication of ceramic inlays, veneers and full-contour crowns.

Duceram LFC Procedure

• Base layer
  Duceram Metal Ceramic–(a leucite-containing porcelain)—is placed on a refractory die using powder–slurry techniques and baked at 930°C.
• Over base layer
  Duceram LFC is applied using the powder–slurry technique and baked at a relatively low temperature (660°C).

Castable ceramic systems

Castable ceramic systems Available as

• Solid ceramic ingots, which are cast using lost-wax and centrifugal-casting technique
• Only one shade is available
• Staining is done to obtain proper shading of the final restoration.

Castable ceramic systems Picon
This is a polycrystalline glass-ceramic material, in which glass is heat-treated under controlled crystallization.

Picon Procedure

• When solid ceramic ingots are cast at 1350°C, a transparent glass crown is obtained.
• This crown is then heat-treated at 1075°C for 10 hours.
• “Ceramming” causes partial crystallization (55%) of tetra-silicic-mica-like crystals.
• For final restoration colorant stains are baked on the surface of the glass–ceramic material.

Picon Advantages

• Easier as it is a lost wax technique
• The transparent crown after heat treatment at 1075°C for 10 hours forms an opaque crown, which increases fracture resistance and strength
• Less abrasive to opposing tooth structure.

Dicor Plus
This is a shaded feldspathic porcelain veneer applied to the Dicor substrate.

Dicor Plus Disadvantages

• Abrasive to opposing teeth
• Requires a special high-temperature, electric-heated casting unit
• Fracture of the restorations is common.

Machinable ceramics

Available as:

• Ceramic ingots in various shades
• Used in computer-aided design and computer-aided manufacturing (CAD–CAM) procedures
• The machined restoration are stained and glazed to the desired characterization.

Cerec vitablocs Mark 1
This is a feldspathic porcelain, used with the Cerec system
Composition and properties are the same as feldspathic porcelain used for porcelain-fused-to-metal restorations.

Cerec vitablocs Mark 2
This is a feldspathic porcelain of increased strength with less abrasive wear of the opposing tooth structure.

Dicor MGC

• Contains fluorosilicic mica crystals in a glass matrix
• It has greater flexural strength than the castable Dicor and Cerec
• Less abrasive wear of the opposing tooth structure than Cerec Mark I.

Celay

• Can be used for CAD-CAM-and copy-milling technique
• Identical in physical properties to Cerec Vitablocs Mark II.

Celay Disadvantage

Marginal fit is not good.

Pressable ceramics

Available as:

• Ceramic ingots, which are melted at high temperatures and pressed into a mould created by lost-wax technique
• Can be made to full contour, or can be built up using feldspathic porcelain.

IPS Empress

• This is a feldspathic porcelain supplied in ingot form
• The ingots are heated and moulded under pressure to produce the restorations.

Procedure:

• The ceramic ingot is placed under the plunger and heated to 1150°C
• The plunger presses the molten ceramic into the mould
• The final shade of the crown is done by staining or veneering. (Cut back technique of wax pattern).

Optec Pressable Ceramic
This is a type of feldspathic porcelain with increased leucite content, processed by moulding under pressure and heat.

Advantages of IPS and OPC

• Produce strong, translucent, dense and etchable ceramic restorations
• Useful in fabricating ceramic veneers.

Disadvantages
Require special equipment to fabricate the restorations.

Infiltrated ceramics

Available as:

• Powder (aluminum oxide or spinel), which is fabricated into a porous substrate, and a glass, which is infiltrated at high temperature into the porous substrate
• The infiltrated ceramic is then veneered using conventional feldspathic porcelain technique.

In-Ceram

• The spinel cores are more translucent than the aluminum oxide cores
• The core is made from fine-grained particles that are mixed with water to form a suspension referred to as a ‘slip’.

Procedure

• The slip is placed on a gypsum die and baked at 1120°C for 10 hours to produce the opaque, porous core.
• An appropriate shade of glass powder is applied to the core, which is baked again at 1100°C for four hours.
• During this process, the molten glass infiltrates the porous alumina core by capillary action.

Ceramic Restoration Advantages

• Extremely high flexure strength
• The aluminum oxide or spinel crystals limit crack propagation and the glass infiltration reduces porosity
• Provides an accurate fit.

Ceramic Restoration Disadvantages

• Cannot etch internal surface; hence a resin cement, such as Panavia 21TC is recommended
• Not as esthetic as other systems
• Requires specialized equipment to fabricate a restoration.