Mouth Preparation For The Removable Partial Denture

Mouth Preparation For The Removable Partial Denture

Mouth preparation is part of the treatment-planning phase carried out to enhance the success of the fixed partial denture.

Mouth Preparation helps to:

• Relieve symptoms
• Removes the etiologic factors causing the symptoms
• Repairs the damages caused by the etiologic factors
• Maintains dental health.

Read And Learn More: Fixed Partial Denture Short Essay Question And Answers

The order of procedures in mouth preparation

• Diagnosis and treatment planning.
• Treatment to relieve the presenting symptoms.
• Surgical procedures.
• Endodontic procedures.
• Periodontal procedures.
• Orthodontic realignment, if necessary.
• Definitive occlusal treatment.
• Prosthetic rehabilitation.
• Follow-up.

Surgical procedures

• Extractions
  • Abutment tooth detrimental to the design of fixed partial denture
  • Residual roots tips
  • Impacted or unerupted supernumerary teeth
  • Malposed teeth, which is grossly extruded or drifted which cannot be corrected by restorations.
• Cyst and odontogenic tumors
• Hyperplastic tissue
  • Surgical excision by scalpel, curette, or electrosurgery.
• Bony spines and knife-edge ridges
• Dentofacial deformity
  • Surgical correction of a jaw deformity can be made in horizontal, sagittal, or frontal planes.
• Implant-supported fixed prostheses
  These are placed under controlled oral surgical procedures if required for fixed partial denture.

Endodontic procedures

• Endodontically treated tooth are restored with crowns
• Caries tooth are restored by amalgam, composite, glass ionomer, pin-retained restoration or post and core depending on extend of damage.

Periodontal procedures

The periodontal procedures follow surgical procedures.

Objectives of periodontal therapy

• Removal of all etiologic factors causing periodontal disease
• Elimination of all pockets
• Creating physiologic gingival and osseous architecture
• Establishment of functional occlusal relationships
• Plaque control program and definitive maintenance schedule.

Evaluation of abutment tooth for periodontal health

• Evaluating pocket depth especially in the abutment tooth
• Check bleeding on probing, for sulcular health
• The extent and pattern of bone loss
• The degree of mobility present
• Any traumatic occlusion.

Diagnostic aids

Diagnostic aids which are used include:

• Periodontal probe
• Mouth mirror
• Curved explorers
• Furcation probes
• Diagnostic casts
• Roentgenograms.

Evaluating pocket depth

Periodontal probe is used circumferentially around each tooth and depths are recorded in distobuccal, mesial, mesiobuccal, distolingual, lingual and mesiolingual aspects of each tooth.

Crown lengthening procedures

Done when clinical crown height is less and when retention will be compromised.

Orthodontic Treatment

• Minor orthodontic tooth movement can be done to upright a malpositioned abutment tooth
• Can improve axial alignment
• Will create pontic space and will improve embrasure form in the fixed prosthesis
• It can direct occlusal forces along the long axis of the teeth.

Definitive occlusal treatment

Done to make intercuspal position coincident with centric relation and to remove eccentric interferences.

Mouth Preparation Contraindications

• Bruxers, when too much tooth structure needs to be removed
• Angle Class 2 and a skeletal Class 3
• Excessive wear
• Temporomandibular pain.

Prosthetic rehabilitation and Follow-up

Whether removable, fixed or implant supported, the patient needs to be recalled after prosthetic rehabilitation.

 Requirements of a crown.

Crown Definition

Artificial crown is a fixed restoration of the major surfaces or the entire coronal part of a natural tooth that restores anatomy, function and esthetics, usually of metal, porcelain, synthetic resin, or combinations.

Requirements of a Crown

• An ideal retainer needs to support and connect the body of the bridge with the abutment
• It should restore the form, function and esthetics of the abutment
• Should impart strength to tooth
• Should have harmonious occlusion
• Should have good marginal adaptation and a smooth gingival margin with a supportive relationship to the gingival margin
• An artificial crown should have strength, stability, and retention
• An artificial crown should replicate the exact contours of missing tooth to maintain oral hygiene and periodontal health
• Artificial crown should maintain occlusal plane
• Should be biocompatible with tooth and its adjacent tissues
• Retainer should be constructed without injury to pulp and supporting structures
• Should protect and maintain the pulp against thermal and galvanic shock
• Should provide safety for the tooth during the lifetime of the restoration
• Should provide self-cleaning property
• Should be resistant to corrosion and tarnish
• Should be a conservative preparation with uniformity of reduction of the abutment tooth
• Load should be dispersed to the more receptive areas of the abutment
• There should be large surface contact between the abutment and a retainer
• Complete metal crowns should provide desirable guide planes for RPD
• It should be made of rigid material to withstand the forces
• Should maintain vertical dimension and should have the property of resistance to wear.

 Double Arch Impression Technique

Other names

Closed bite double arch method/dual quad tray, double arch, triple tray, accu-bite, closed mouth impression.

Double Arch Impression Requirements

• The articulator must have an incisal pin or other metal-to-metal contact
• There should be a positive stop in articulator or natural teeth should be present to maintain vertical dimension. Limited to single castings with good interdigitation
• Should have sufficient space distal to the terminal tooth for tray approximation.

Double Arch Impression Advantages

• Physical deformation of the mandible during opening is minimized
• Shifting of teeth during maximum intercuspation is copied
• Less impression material is required
• Chance of gagging sensation is less.

Double Arch Impression Disadvantages

• Tray is not rigid
• It is not a functionally generated technique
• Distribution of the impression material is not uniform.

Impression procedure

• After selecting the correct tray, the trays crossbar is positioned distal to last tooth
• The patient is asked to close the mouth to observe complete bilateral closure and patient’s comfort.

Loading light-body material

• Automatic gun dispensing:
  • Activated by placing a replaceable cartridge and mixing tip into the gun and squeezing the trigger, which expresses the material.
• Manual mixing:
  • 6 by 8 inches of impression material is mixed with a pliable spatula against the pad with circular motion combining the two strands
  • A figure of eight motion is used to flatten the mixture onto the mixing pad (mixing time 1 minute)
  • The pad is placed near the edge of a table (waist high).

Loading the mixed material

The mixed material is loaded onto the syringe at a slight angle while scraping the pad.

Cord removal

The 2 mm excess of cord is grasped with forceps and teased slowly with a gentle continuous pressure toward the occlusal surface.

Impression method

• The light body loaded onto the syringe is injected into inaccessible areas first, and then the prepared tooth surface completely.
• The high-viscosity elastomer is manipulated and “overfilled” bilaterally, tray is seated and the crossbar is positioned distal to the last tooth in that arch.
• The patient is asked to slowly close mouth and the interdigitation is observed on the opposite arch. The patient is asked to continue interdigitation until the material sets.

Tray removal

• The patient is asked to open mouth; generally the impression adheres to one arch.
• A finger is placed on either side of the tray and tray is removed with equal pressure bilaterally.
• Evaluate the final impression.

Pour die

Excess impression material is removed and die stone is poured, dowel pin is positioned and stone is allowed to set.

Articulation

• After making working cast, it is attached to a hinge articulator with incisal pin or vertical dimension stop.
• Sticky wax is placed around tray. Boxing wax in half length-wise is adapted to both upper and lower arches at one time and sealed to prevent the stone from entering the opposite side of the impression.
• Small openings are made in boxed wax to accommodate the boxed impression within the articulator for correct positioning of the impression.
• The tray is positioned, in the center of articulator, parallel to the tabletop, and centered from side to side.
• First the opposing side without dies are poured and articulator arm closed into unset stone. Then the dowel pins are placed without interfering with the closure of the articulator arm on the working side. This side is poured after lubricating the die(s). The articulator arms are closed until incisal pin contacts the lower arm. Unset stone is removed around tip of dowel pin(s) to facilitate removal.
• After complete setting of gypsum the impression tray is removed from articulator, the cast is separated from the impression tray.
• Casts and separate die(s) are evaluated.

 Double Mix Technique

Impression technique

• After a stock tray is selected, tray adhesive is applied; the impression putty is mixed and placed in tray
• A polyethylene sheet is used to cover the putty material and impression is seated in the patient’s mouth
• The complete set of the impression is ensured by fingernail testing and the tray is removed.

Relieving the tray

A sharp hand instrument is used to remove uniform amount of impression material from the tissue surface.

After gingival retraction evaluate tissue displacement, check the finish line area(s), and leave cord(s) in place for 8–12 minutes.

Manipulation of light body material

• After measuring the arch length of tray, one times the length of the tray low-viscosity elastomer is dispensed.
• A mixing pad, (6 by 8 inches) or an automatic gun dispensing system is used.
• The low-viscosity impression material is mixed with a circular motion combining the two strands.
• A figure of eight motion is used to blend and flatten the mixture onto the mixing pad. (mixing time less than l minute).

Loading the impression material

• The syringe is loaded by holding it at a slight angle while scraping the pad.
• Screw on the tip and insert the plunger.
• While the plunger is inserted into the syringe, the cord is removed.
• After evaluating retraction site for seepage, hemorrhage, or debris, first syringe inaccessible areas as distal lingual finish line and then the entire area of preparation.
• The syringe is positioned so the elastomer is ahead of the tip’s orifice.

Tray Insertion

• Insert the low-viscosity impression material into the tray slightly less than the depth of the external borders.
• Seat the tray from posterior to anterior, allowing the excess to extrude anteriorly.
• Seat the tray firmly in position.
• The tray should not be moved while the material is setting.

Final impression

After the final set is over, tray is removed parallel to the preparation(s) path of withdrawal and impression is evaluated.

Rinse impression with ambient water, and dry with short, small bursts of compressed air.

Evaluate set impression

• The area 0.5 mm beyond visible finish line should be visible.
• There should be no show-through in any areas of the impression, except at tissue stops
• There should be no shiny smooth areas, no voids present, there should be no thin areas leaving the finish line unsupported.

Making working cast

• Position the dowel(s) into the impression.
• Insert one extra dowel pin on either side of the working dies.
• This ensures die removal despite errors during sectioning
• Check dowel position in impression for parallelism and retention and add paper clips or orthodontic wire for retaining the second pour to the first.
• Pour first layer of stone, wait for initial set of stone.
• Lubricate die areas, bead and box impression.
• Pour second layer of stone for the base.

Question 10. Adhesives in dentistry/dentin bonding agents.

Adhesives in Dentistry Indications

• Direct resin composite restorations (caries, fractures, reshaping)/pit and fissure sealants
• Bond all-ceramic restorations (veneers, inlays, onlays, crowns)
• Bond amalgam/core build ups
• Resin-retained fixed partial dentures
• Orthodontic brackets
• Treatment for dentinal hypersensitivity
• Repair fractured porcelain and composite.

Classification of dentin bonding agents

• First generation – Hydrophobic monomers, bond strengths- 2–3 MPa, chemical bond to calcium (Cervident – SS White 1965).
• Second generation – Phosphorous-ester monomers – increased surface wetting, 5–6 MPa bond strength and smear layer predominately intact (Scotch bond).
• Third generation – Mildly acidic hydrophilic monomer, preparation by acid etch, modified/altered smear layer, moderate bond strength (Scotch Prep).
• Fourth generation – Multi step, conditions dentin by removing smear layer, primes and then adhesive. High bond strength (3M Multipurpose).
• Fifth generation – One step, combined primer and adhesive high bond strength.(Onestep).
• Sixth generation – Two types, one with combined primer and conditioner (AdheSe), moderate bond strength and another type with conditioner, primer and adhesive, low bond strength (Prompt-L-Pop).
• Seventh generation – All in one adhesives, combined conditioner, primer and adhesive, one-step, low bond strengths (G Bond).

Another classification based on type of use

Etch and rinse (i.e., total-etch) – three step (conditioner, primer and adhesive) or two step (primer and adhesive) 4th and 5th generation

Self-etch – 6th and 7th generation

Resin-modified glass ionomer – two step.

Depending on type of bonding

Wet Bonding – Acetone- and ethanol-based primers displace remaining water and carry monomers into collagen (One step)

Dry bonding – Water-based primers can check etching more reliably as self rewetting (Optibond).

Etch and rinse three steps

Conditioner
Acids, such as phosphoric, citric, maleic and nitric are used. They etch the enamel and also remove the dentinal smear layer exposing the collagen fibrils. Rinse after etching time is over and keep moist.

Primer
Are hydrophilic monomers dissolved in acetone, alcohol or water. After application, lightly air dry. Primers are bifunctional monomer that links the hydrophilic collagen to the hydrophobic resin (E.g. HEMA) by displacing water in dentin and promoting infiltration into collagen.

Adhesive resins
Are unfilled or lightly-filled monomers, such as Bis-GMA, UDMA, TEGDMA. They form resin tags linking primer to composite resin.

Etch and rinse two steps
Conditioner followed by an application of a combined primer and adhesive. It is highly technique sensitive and multiple layers need to be applied (E.g. Optibond Solo plus, Prime and Bond NT).

Advantages of etch and rinse
Long-term studies available, good etch pattern, separate etch is confirmative of proper etching.

Disadvantages of etch and rinse
Technique sensitive and over etching can happen. If the moistness after conditioning is not present ineffective penetration occurs.

Self etch two steps
Combined conditioner and primer followed by adhesive resin (AdheSE)

Composition

• Acidic monomers – MDP Di-HEMA-Phosphate, MA 154, Phenyl-P, MAC-10 and 4-META
• Cross-linking monomers – Bis-GMA, UDMA,TEGDMA, GDMA and HEMA
• Solvent – Water based.

Self etch one step

Combined conditioner primer and adhesive (Prompt-L-Pop, ibond, etc).

Self etch Advantages
Good dentin conditioning with simultaneous infiltration of resin, no post-conditioning rinse and reduced application time.

Self etch Disadvantages
Low bond strength, few clinical data.

Resin-modified glassionomer
Polyacrylic acid removes smear layer and exposes collagen. Mechanical bonding occurs by formation of hybrid layer and chemical bonding through carboxyl groups with calcium in tooth (Fuji bond LC).