Crown Try-In and Adjustments

Clinical Try-In and Adjustment

• This is done once the lab procedure is complete.
• It is done before final finishing and cementation.
• There are three stages:
  • Pre-operative evaluation of crown or fixed bridge on its die.
  • Seating on the tooth.
  • Evaluation of the seated restoration.
• It can be performed with or without anesthesia, however, it is preferable without anesthesia.
• There is unimpaired tactile sensation, this is valuable during occlusal adjustment.
• Anesthesia is sometimes used if the patient is uncooperative.
• It is important to check the crown fit on the cast before trying it in the patient, this helps anticipate problems with:
  • Marginal fit
  • Aesthetics
  • Articulation
• Checking the crown on the cast should be done with good light and under magnification.
• The restoration should be seated on the die without any pressure.
• Prior to the try-in procedure, inspect the inner surface of the restoration, check for:
  • Nodules and bubbles, remove these with a small round bur
  • No contact between the die and the internal surface of the restoration
  • A uniform space for the luting agent to spread evenly must be present, identified any contacts and relieve these via selective grinding

Seating the Restoration on the Prepared Tooth

• Remove temporary restoration
• Clean the prepared tooth from any remnant of cement, this ensures proper seating of restoration
• Use a Backhaus towel clamp or GC pliers
• Seat the restoration on the prepared tooth with pressure

Evaluation Sequence of the Seated Crown

• Proximal contacts
• Marginal integrity
• Retention and stability
• Occlusion
• Polishing or characterization and glazing

Proximal Contacts

• The location, size, and tightness of a restoration's proximal contacts correlate with those of the natural teeth.
• Excessive contact prevents complete seating, and causes marginal discrepancy.
• Open contact leads to food impaction.
• The use of unwaxed floss compares the contacts with others in the dentition.
• The use of 0.05 mm shim stock (thin Mylar film) is a reliable indicator of proximal contact.
• Satin finish helps identify excessive tightness in metal restoration; shiny spots indicate binding, and adjustment is necessary.

Interproximal Contact Area Examination

• The contact should be as tight as other areas in the mouth, use dental floss
• Heavy resistance indicate a heavy contact and it must be reduced.
• No resistance indicate an under-contoured (deficient contact) area.

How to Correct Proximal Contacts

Metal Crown or Retainer

• A deficient proximal contact is remedied by repeating the restoration or adding solder to that area.

Porcelain Restoration

• The contact area can be identified with red pencil or thin marking tape.
• A tight proximal contact in unglazed porcelain can be adjusted with a cylindrical stone.
• Glazed restoration adjustment can be achieved through diamond-impregnated silicone points or diamond polishing paste
• A deficient proximal contact is corrected by adding porcelain (lab).

Incomplete Seating

• If the contact area is perfect but the crown does not seat completely, interferences may be present (metal bubbles or undercut)
• Use pressure indicating paste or spray, placing it inside the crown restoration
• Seat the crown with pressure, then remove and inspect for shiny areas (pressure)
• Relieve any interference areas
• Repeat until complete seating is achieved; if it fails, refabricate the restoration

Evaluating Complete Seating

• The margin of the restoration is critical, complete fitness between the restoration margin and finishing line of the preparation is necessary

Types of Marginal Defects

• Short margin (under extension, shoulder or ledge); the margin lies short of the finish line
• Long margin (overextension, overhang); the margin lies beyond the finish line
• Open margin; margin within the finish line with space between the restoration margin and prepared tooth
• Overcontoured; margin within the finish line, but the gingival third shows excessive bulk

Poor Fitting Margins Lead To

• Cement dissolution
• Plaque retention, which affects gingival health
• Recurrent caries

Checking Marginal Integrity

• To check marginal integrity use:
  • Visual
  • Radiographic
  • Explorer

Visual

• Evaluate the supra gingival margin or margin that have easy access with:
  • Direct or indirect visual (mirror)
  • Magnification apparatus (eye loops or microscope)

Radiographic

• Used to detect interproximal margins that cannot be seen by eye
• Use angle of beam (parallel technique to detect interproximal margin)

Explorer

• Probe is used to check the marginal integrity of the crown, especially the subgingival margin.
• Varying tip size probes should be used, along with varying approaching angles

Checking Marginal Integrity with a Probe

• Move the probe from the restoration toward the tooth surface; a smooth passage indicates an acceptable crown margin
• If there is any interpretation during this movement it shows under extended margin.
• If the probe catches when moving from the tooth surface toward the restoration margin, this indicates overextended margin (correction leads to open margin)
• Smooth probe passage in both directions indicates correct margin extension.
• Space between the restoration and tooth surface at the area indicates an open margin.

Assessing Retention and Stability

• Evaluate the restoration for stability on the prepared tooth; no rocking or rotation with applied force.
• Correct instability from a nodule; remake if due to distortion

Occlusion Adjustment

• After complete seating, adjust the occlusal relationship in all mandible movements (centric and eccentric) using articulating paper
• Any occlusal prematurity should be relieved
• Occlusal adjustment is done using high-speed diamond burs
• The treatment is remaking (metal) or refiring (Porcelain) in cases of teeth that are out of occlusion
• Metal crowns are then ready for margin finishing.

Objectives of Marginal Finishing

• Obtain at least a 1mm wide margin closely adapted to the tooth surface at the finish line to prevent microleakage.
• Subgingival margins are finished on the die with a burnisher to avoid tooth and periodontal tissue damage.
• Supragingival margins can be finished directly on the tooth; improve margin adaptation using a burnisher or dull bur

Polishing and Characterization for Metal Restorations

• The objective provides a smooth, shiny restoration surface that is less susceptible to plaque accumulation or deposition.
• Polishing provides:
• Glossy surface
• Plaque resistance
• Tarnish/corrosion resistance
• Good appearance
• Surface defects and roughness are removed by grinding with abrasive particles on grinding stones, rubber wheels, or paper discs, or applied as abrasive paste
• A commonly used abrasive is Tripoli on a soft Robinson bristle brush

Polishing for Porcelain in PFC and All-Ceramic Crown Restorations

Contour & Shade

• Must evaluate before glazing
• Use water or saliva to moisten, reflecting light, similar to a glazed restoration
• Verify shade and contour of the gingival third; excessive bulk may cause periodontal disease

Incisal Edge

• Establish position and shape on anterior teeth
• It is important for good esthetics and function
• Maxillary anterior teeth incisal edges align with the curvature of the lower lip during relaxation

Incisal Embrasures

• Incisal embrasures enhance separation, and their absence draws attention, revealing an artificial appearance

Surface Texture

• Duplicate surface detail & reproduce natural defects
• Avoid over-characterizing restorations

Glazing

• Colorless glass powder is applied to fired crowns/bridges create a glossy surface, duplicate natural tooth luster, and for characterization
• Insufficient glazing leads to:
  • Rough surface that may lead to abrasive wear of the opposing dentition
  • Increased rate of plaque accumulation
  • Inflammation of soft tissues it contacts
  • Reduction in the strength of a ceramic restoration

Polishing

• Provides a precise degree of luster and distribution than glazing
• Polishing dental ceramics is a way of restoring luster after adjustment by grinding
• Done using silicone wheels or diamond polishing paste

Cementation of Crowns and Bridges

• Achieving good planning, preparation, impression, and prescription
• The cementation stage is important, and requires care like the preceding stages
• Once a restoration is cemented, there is no scope for modification or repetition

Permanent Cementation

• Crown restorations on prepared teeth are hold using luting material (agent) in two ways:
  • nonadhesive (mechanical luting and micromechanical bonding)
  • chemical adhesion (molecular adhesion)
• Dental cement does not contribute to the retention of the restoration.

Luting Agent Qualities

• The material acts as an adhesive to hold the crown restoration to the tooth structure.
• Luting agents can be either permanent or temporary

Bonding Mechanisms

• Non-adhesive (mechanical) luting - Involves filling macro-spaces between the tooth and the restoration, creating a mechanical bond
• Micromechanical bonding - Irregularities are produced on enamel via phosphoric acid; on ceramics, via hydrofluoric acid; and on metal, via electrolytic chemical etching and sandblasting
• Molecular adhesion - Physical forces and chemical bonds between molecules of two different substances

Ideal Luting Agent Properties

• Low film thickness (≤25µm)
• Adequate strength (minimum 70 MPA)
• Low viscosity and solubility
• Adequate working time
• Reasonable setting time
• Good sealing and biocompatibility

Function of Cement

• Securing lasting retention of the restoration to the prepared tooth
• Sealing the gap against fluid and bacteria penetration
• Acting as an insulating barrier against thermal and galvanic activity

Factors Affecting the Retention of Cemented Cast Restorations

• The preparation's geometrical relations and retentive properties
• Biophysical factors: the restoration's accuracy of fit, metallurgical characteristics, and inside surface texture
• Mechanical properties of the luting agent: compressive strength, tensile strength, shear strength, adhesive property, and film thickness
• Difference in thermal expansion coefficient between tooth, restoration, and cement

Types of Dental Cementing Agents

• Cements classified as soft or hard
• Soft cements are for provisional cementation during trial assessment
• Hard cements are for definitive cementation: conventional, resin, or a hybrid

Conventional Cements

• Rely on an acid-base reaction, forming an insoluble salt (the cement) and water; examples includes:
  • Zinc phosphate
  • Zinc polycarboxylate
  • Glass ionomer
• Resin cements, set by polymerization
• Hybrid cements, relay on acid-base reaction and polymerization

Zinc Phosphate Cement Qualities

• Traditional luting agent with a compressive strength of 14000-16000 PSI (cavity varnish decreases pulp effect)
• With a low pH at the time of cementing (around 3.5)
• It comes in two separate containers: powder and the liquid

Zinc Phosphate Cement Advantages

• It is the oldest luting agent

Zinc Phosphate Cement Disadvantages

• It is an Irritant
• Little effect on the retention of the restoration

Zinc Phosphate Cement Recommendations

• Good default cement for conventional crowns and posts with retentive preparations
• Working time can be extended by incremental mixing and a cooled slab for multiple restorations

Zinc Silicophosphate Cement Properties

• Compressive strength of 22000 PSI with a highly acidic pH that affects pulp health
• Mixture of zinc phosphate & silicate cement
• Film thickness, compressive strength & tensile strength in the range of ZPHC with slight lower solubility
• It have anti-cariogenic property due to fluoride content

Zinc Silicophosphate Cement Disadvantages

• Low pH and pulpal irritation

Zinc Silicophosphate Cement Use

• No longer used

Poly-Carboxylate Cement Properties

• Adheres to enamel, dentine, and stainless steel (not gold alloy)
• High bond strength to enamel (1300 PSI), but lower to dentine (480 PSI)
• The pH before setting is 4.8, but attains a relatively neutral pH level after setting
• Large poly-acrylic acid molecules have less effect on the pulp, and low film thickness optimizes fit and margin integrity

Poly-Carboxylate Cement Recommendations

• Recommended for vital or sensitive teeth
• Useful to retain an unretentive provisional crown

Glass Ionomer Cement Properties

• Similar acidity to zinc phosphate
• Compressive strength of 18600 PSI (low tensile strength)
• Bonds to enamel and dentine (more to enamel)
• Releases fluoride, inhibiting secondary caries
• Sensitive to early moisture contamination

Glass Ionomer Cement Recommendations

• Good for general prosthodontic use; fluoride release may benefit patients
• Avoid using with hypersensitive teeth.
• Used for conventional crowns in patients with a high rate of caries and may be used as an alternative to zinc phosphate

Resin Luting Cement

• They have a range of formulations, and are classified by polymerization method (chemical, light cure, dual cure) and the presence of dentin bonding mechanisms
• Chemical cure is for metal restoration, light cure is for ceramic restorations

Resin Luting Cement Advantages

• Chemical bond to the tooth structure
• High strength
• Reduced fracture for ceramic restorations
• Low solubility

Resin Luting Cement Disadvantages

• Difficult to remove excess after setting
• High cost
• Irritant to pulp

Resin Luting Cement Recommendations

• Need to used with an effective dentine bonding agent
• Choice material for porcelain veneers, ceramic crowns, composite restoration, and resin-bonded ceramic crowns
• Improves retention where the preparation geometry is sub-optimal

Resin Luting Cement Types

Adhesive Resin Cement

• Two-component system: one bottle (self-etch), one syringe
• Time-consuming etching and bonding
• Sensitive procedure

Self-Adhesive Resin Cement

• One-component type
• Time-saving, no etching, or bonding
• Easy to use

Resin Modified Glass Ionomer Cements and Compomers Properties

• They combine resin strength and insolubility with fluoride release
• Intended to overcome moisture sensitivity
• Moisture absorption sets the glass ionomer in composites
• High bond strength to dentine, to form a thin film layer, and release fluoride
• They are:
  • Moisture-tolerant
  • Show low solubility
  • Show low microleakage
  • Show less post-cementation sensitivity

Resin Modified Glass Ionomer Cements and Compomers Recommendations

• It is good for metal or metal ceramic crowns where preparation retention is borderline
• Delayed cement expansion may cause ceramic fracture or root fracture

Resin Modified Glass Ionomer Cements and Compomers Delivery Techniques

• Hand mixing
• Applicap/maxicap capsule
• Automix (syringe or clicker dispenser)

Selection Types

• The selection type for crown restoration is complex

Factors Affecting Cement Type Selection

• Availability of different cement type
• Properties of materials
• Restoration material of the crown and its flexural strength
• Optical properties and esthetic demands
• Ability to maintain a dry field
• Margin location
• Chewing forces
• Remaining tooth structure
• Preparation design (retentive/non-retentive)

Types of Luting

• Weak restorations (ceramic with low flexural strength under 350 MPa) like all-porcelain, all-composite crowns, inlays, onlays, and veneers are adhesively bonded with strong cements.
• Increase in strength is attributed to the cement filling defects and prevent crack propagation, or to the resin cement's mechanical properties
• High-strength ceramics (flexure strength of more than 350 MPa), lithium disilicate, and zirconia restoration requires adhesive luting
• Adhesive luting and conventional cementation can be used for metal restorations

Considerations based on Translucency (Optical)

• High-translucent restorations must not be cemented with an opaque cement
• Translucent ceramic restorations needs adhesive luting
• Metal or opaque high-strength zirconia restorations can use adhesive luting or conventional cementation

Dry Field Considerations

• Intolerance of adhesive bonding procedures to contamination demands dry environment with a rubber dam to prevent contamination
• Inability to maintain a dry field, i.e., subgingival preparation margins and posterior areas on the mandibular arch, contraindicate traditional full-adhesive bonding

Preparation Design

Non-Adhesive Mechanical Luting

• Zinc phosphate cement can be used when all the following are true:
  • Tooth preparation provides mechanical retention
  • Pulp of the tooth is not a concern
  • Endodontically treated teeth or teeth with heavy amalgam or composite filling.
• More biologically compatible alternatives exist that are:
  • Polycarboxlate
  • GIC
  • Compomer

Inadequate Retention

• If teeth feature inadequate-retentive features
• If the depth of the preparation is a concern for the vitality of pulp
• If resin cements are suitable for bonding porcelain, cast ceramic, and composite restorations and are recommended for teeth with inadequate preparation
• Non-retentive minimal-invasive restorations and additional measures may be needed
• Clinician determines clinical factors

Temporary Cements

• Soft cements made-up of classical plain zinc oxide and eugenol are classical
• The eugenol acts as a bacteriostatic or bactericidal, arrest production of toxin by the microorganism

Plain ZnOE Disadvantages

• Eugenol limits polymerization
• Use is limited in permanent cases because:
  • Poor oral durability is a result of eugenol loss
  • Possesses low compressive strength

Temporary-Cement Zinc Oxide (Non-Eugenol) Advantages

• It is Eugenol-free prevent resin polymerization
• Low film thickness helps help with fit
• High adhesion

Cementation Technique With ZPC (Mechanical Bonding)

• Remove the temporary crown and any residues of cement from the prepared tooth via cleaning with water and pumice.
• Rinse, and dry without desiccating the tooth
• Placement of cotton roll isolation (dry field of operation)
• Varnish and cavity used for partial protection of pulp, 2 layers are applied
• Slowly mix the cement in small area to reduce acidity
• Coat a clean, dry casting restoration/prep with cement
• Seat the casting crown on the tooth with pressure - instruct the patient to bite down on a wooden stick or cotton roll for 3-4 minutes for complete seating
• Remove excess cement from interproximal areas, gingival cervicals, and underneath the bridge using a dental probe and floss when the cement has been set
• Check occlusion next

Cementation of All-Ceramic Crowns and Bridges

• Excessive forces and surface damages may lead to fractures and cracks as ceramic brittleness is lower than metal.
• Enhance resistance via adhesive bonding
• Follow Clinical, laboratory bonding protocols
• Etch-able are the silica-based ceramics: feldspathic, Leucite-reinforced feldspathic porcelain (IPS Empress®), and lithium-disilicate glass-ceramic (IPS e-max®)
• Non Etch-able are the non-silica-based ceramics such as aluminum oxide and zirconium oxide

Etching Non-Etchable Metals Treatment

• Etching using 5% HFL gel for 20 seconds and then apply 60 seconds of silane coupling agent and then rinse

Cementation Procedure when Using Adhesive Bonding

• Remove the temporary crown, thoroughly rinse
• Isolate
• Treat Internal Surface where appropriate
• Follows manufacturers recommendation to use bonding agents
• Prepare the tooth being careful not to etch and following manufacturers recommendations
• Light cure/Remove cement, apply bonding agent again and light cure and check occlusion