Feldspathic porcelain materials are indicated for anterior teeth when significant enamel is remaining. Occasionally, feldspathic porcelains may be used on bicuspids, but rarely on molars.
When deciding whether to use feldspathic veneers, it is also necessary to undertake a flexural risk assessment.
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- Flexural risk tends to be higher when bonding to higher levels of dentin because dentin tends to be more flexible than enamel.
- If bonding to enamel, the flexural risk is low to moderate.
- A simple but strong determinant of tooth flexure is to observe mesial–distal craze/fracture lines on the lingual. Tensile and shear stress risk assessments are also necessary when deciding on feldspathic porcelain veneers.
- Generally, higher tensile and shear stresses occur when there are large areas of unsupported porcelain, deep overbites or overlaps of teeth, bonding to more flexible substrates such as dentin and composite, bruxism is present, and the restorations are placed more distally. In these higher-risk clinical situations, a pressed or machined glass ceramic should be considered.
- Finally, there must be an absolute low risk of bond and seal failure when placing restorations fabricated from feldspathic porcelain.
Confirm Shade Selection
- Remove at least 0.5 mm-0.8 mm enamel.
- Removal of some enamel aids in achieving better bond strength, but care must be taken not to remove more than 0.5 mm-0.8 mm, especially in the proximal and cervical areas.
- Even though dentin adhesives have improved dramatically, porcelain bonding to enamel is better than porcelain bonding to dentin.
Depth Guide Cuts
- Prior to preparation always examine study models in order to avoid over-reducing areas of the tooth that may be rotated or lingually inclined.
- The use of a reduction guide is recommended.
- A diamond depth cut bur can be used to scribe horizontal depth cut grooves on the labial surface of any anterior tooth.
- Extend these grooves from mesial to distal, taking care not to damage the adjacent teeth that are not being prepared.
- It may be necessary to angle the bur in relation to the contour of the labial surface to achieve the appropriate depth for these guide cuts.
- The finish line of the preparation could end gingivally or supragingivally, approximately 0.5 mm incisal to cemento-enamel junction (CEJ).
- Do not place your gingival depth cut so as to cut into the cemento enamel junction area.
- Using a tapered diamond, reduce the remaining labial tooth structure between the depth cuts.
- Simultaneously create a chamfer ending 0.5 mm incisal to the CEJ.
- This reduction should also extend interproximally without breaking through the contact areas to prevent tooth movement during temporization.
Types of Veneer Preparation
- Incisal Chamfer Preparation (Interlock prep)
- The incisal edge is not reduced in length.
- This type of preparation is done in order to preserve the natural guiding palatal surface of the tooth, which is important functionally.
- Add an additional space for the incisal porcelain by creating a chamfer along the facial incisal margin using the tip of a tapered diamond.
Incisal Butt-Joint Preparation
- Prepare 0.5 mm depth cut grooves in the incisal edge.
- Using the tapered diamond remove the remaining incisal tooth structure.
- Then round the facial incisal line angle leaving a butt-joint margin along the lingual incisal edge.
- The incisal reduction should be 0.5 mm-1.0 mm.
- This type of preparation is done in order to increase the length of the tooth. The length can be increased from 0.5 to 2mm only.
Incisal Lingual Wrap Preparation
- Prepare 0.5 mm depth cuts in the incisal surface of tooth.
- Reduce the incisal surface in a manner similar to incisal butt-joint preparation.
- Reduce the mesial incisal and the distal incisal corners an additional 0.5 mm.
- Then using a diamond bur, extend the incisal chamfer to the palatal surface.
- This palatal chamfer should be a straight line mesial to distal.
- All incisal edges should be rounded.
- The lingual chamfer line on the wraparound preparation should be above or under the centric lingual contacts to avoid occlusal contact on the interface between porcelain and tooth structure.
- Contact should be either all on porcelain or on tooth structure.
- The incisal wrap prep is a popular option for several reasons. It can be used in most patients, easily fabricated by the technician and easily handled by the dentist due to positive seating on delivery.
The path of insertion for veneers is in the labial or incisal-labial direction.
- All undercuts and unsupported enamel in relation to this path must be removed.
- A silicone reduction guide is used in order to check the amount of reduction required.
- The reduction guide is designed to evaluate the amount of reduction at the incisal, middle third and cervical third of the tooth.
- Use of a reduction guide is particularly important when teeth are misaligned.
Check contraindications Final Impression
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- Strip contact area using a finishing strip prior to impression to improve visualization for lab technician.
- Place a # 0 cord to reveal the margin, which is left in place while taking the impression.
- Either Polyether or Polyvinyl Siloxane impression materials can be used according to manufacturer‘s instruction.
- Remove provisionals
- Use flour of pumice to clean all prepared tooth surfaces and wash thoroughly being careful to not induce gingival bleeding.
- Isolate and dry the teeth.
- Moisten the veneers with water and place them carefully on the prepared teeth to check fit and shade.
- Try-in paste can be used behind facings to check shades.
- If color adjustment is needed, select appropriate shade of try-in paste, apply to veneer, seat, and examine for color and fit.
- Clean the veneers by rinsing with water.
- You should verify with your laboratory technician but the veneers generally come already etched with hydrofluoric acid. Therefore a 30-second application of 37% phosphoric acid is used only for cleaning, not for etching.
- Rinse with water and dry.
- Apply silane to the etched porcelain surface for 60 seconds and air-dry.
- Always confirm that your silane is not expired as it can have a short shelf life.
- Pumice and wash the tooth preparation dry and isolate the teeth.
- When cementing multiple veneers, you must always start closest to the midline and work distally.
- Veneers are luted two at a time starting with the central incisors and continuing distally.
- Isolate the preparation interproximally with thin Mylar strips.
- Etch the preparation in the usual manner indicated by the manufacturer of the bonding agent being used and dry the area.
- Apply enamel/dentin-bonding system according to the manufacturer‘s instructions. Sixth or 7th generations (Self Etching) bonding agents are not recommended for veneers only prepared into enamel. Light cure the tooth (Adhesive) prior to seating the veneer.
- Apply unfilled resin, after primer if indicated, to the tooth surface and inside of the laminate veneer. Do not cure this layer at this time.
- Apply composite-resin luting cement to the veneer and gently place the veneer onto the tooth in an inciso-gingival direction. Remove excess material gently with a resincoated brush. Make sure that cement is visible at all the margins to avoid any voids.
- Hold the veneer and check the gingival margin for proper seating. Then, for each of the four regions (gingival, mesial, lingualincisal and distal) remove any additional excess. Light-cure the gingival margins first for 10 seconds, mesial, incisal and distal. After curing these four areas, cure for 60 seconds through the facial surface. Lightcure each area and margin of the veneer for 30 seconds (longer for thicker or more opaque veneers, or darker shades). (Check manufacturers‘ recommendations for curing time.)
- Remove gross excess using sharp hand instruments — CL carver or perio scaler. (# 12 scalpel blade)
- Using fine and extra fine diamond finishing burs, remove excess resin gingivally and inciso-lingually
- Finish the proximals using fine strips.
- Proceed to the next placement.
- Use porcelain polishing paste to regain a smooth porcelain surface whenever necessary.
- Check occlusion in all excursions and adjust as needed.
It is recommended post cementation to provide the patient a soft or a soft and hard (dual) night guard. This is done to protect the veneers.
"Do’s and Don’ts of Porcelain Laminate Veneers"
Chad J. Anderson, MS, DMD; Gerard Kugel, DMD, MS, PhD; Shradha Sharma, BDS, DMD
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