Ceramic Veneer Preparation Techniques

Preparation Designs for Ceramic Veneers: Key Factors and Techniques

• Veneers are a type of partial extracoronal restoration usually indicated for anterior aesthetic rehabilitations.

• The main purpose of a veneer is to cover the labial-proximal surfaces and potentially the incisal border of the anterior teeth to correct color discrepancies, shape, texture, function, and position of the elements in the dental arch.

• There are several preparation designs for ceramic veneers, which vary according to the extent of the preparation and depend on several factors such as the amount of remaining tooth structure, presence of previous restorations, length of the clinical crown, and presence of endodontic treatment.

• Preparation for laminate veneers requires great stringency and a great deal of training, as no rectification can be made once the procedure is completed. Experience is required for mastery of 0.3-0.5 mm reductions.

• Enamel removal is necessary to ensure the bond strength of the resin composite to the tooth surface. Due to its poor retention capacity, the aprismatic top surface of mature teeth that have not been prepared must be removed or at least roughened.

• The more the bonding surfaces are located in dentin, the lower the success rate. This could be explained by the difference in the elastic modulus between the substrate and the ceramic. The lower this ratio, the better the fracture resistance.

• To ensure the bond strength of the resin composite to the tooth surface, it is necessary to reduce the enamel. However, rigidity in the tooth is due to the amount of enamel thickness, and thus, the more enamel that is removed, the more the tooth flexes.

• The shape of the preparations also influences the appearance and longevity of a restoration. Without reduction, the teeth will be larger and more labially positioned, and failure to remove proximal enamel can result in the finish line placed too far labially and encroachment on the embrasure areas, resulting in exposure of unsightly porcelain margins that may be difficult to finish.

• The continuing evolution of bonding processes to dental structures makes it possible to implement more conservative restorative techniques and enables the use of minimally invasive preparations.

• In teeth with slight or no discoloration, extremely thin ceramic veneers have emerged, requiring minimal tooth reduction that is limited to merely smoothing sharp angles and eliminating undercuts.

• Ceramic veneers are of limited use in situations requiring major correction. Therefore, very precise planning is necessary as the anatomy and the shade of the restoration are directly affected by the preparation design."Preparation for Ceramic Veneers: A Guide for Dentists"

• Enamel reduction should be minimal and only as much as necessary for placement of the veneer

• Young individuals or those with large pulps may not be good candidates for enamel reduction

• Patient's psychological state and feelings about tooth reduction or veneers should be considered before proceeding with any reduction

• The goal of preparation is to create enough space for the ceramic material while maintaining as much enamel as possible

• No-prep veneers have become popular but have limitations and may not be suitable for all cases

• Orthodontic movement can create the necessary thickness for final restorations without unnecessary tooth reduction

• Final objective and thickness of restoration should be considered to avoid overcontouring of the tooth

• Advantages of no-prep veneers include preservation of sound tooth structure and reduced clinical time for impression-taking stepProvisional and Conventional Preparation for Ceramic Veneers

Provisional Preparation:

• The veneer bonds exclusively to the enamel, but has several disadvantages.
• The manufacturing process is meticulous and increases the risk of fracture during various steps of the process.
• The critical cementation process and thoughtful maintenance are necessary for maintaining the aesthetic result.
• These veneers do not involve areas of dynamic visibility, which become visible with the natural darkening of the dental substrate.
• Extensive preparation is required when the potential treatment requires it, which can lead to biological irritation to the pulp and impairment of adhesion.
• The preparation is extended to the proximal surfaces and overlaps the free edge in what was commonly referred to as "palatal overlap."
• The palatal overlap led to mechanical complications related to the repositioning of the palatal margin in the area of greatest functional stress, the cingulum.
• This type of preparation resulted in excessive dentin exposure and frequent debonding of the restoration due to functional overload during occlusion.
• If the preparation needs to be extended palatally over the incisal edge, care must be taken to avoid mistakes due to the overbulked interior surface of the incisal edge, which will make it impossible to seat the veneer properly and result in an inaccurate fit at the cervical margin.
• Straight-type incisal terminations are preferably chosen when reduction is necessary because they advocate a passive fit in the labial-palatal direction without a deliberate insertion axis, greater preservation of tooth structure, and lend absolute confidence in the bonding mechanisms.

Conventional Preparation:

• The preparation follows three main stages applied to four main areas of the tooth.

• The three main stages to get the final veneer preparation are cutting, refinement, and finishing & polishing.

• Each tooth surface (incisal, cervical, labial/buccal, mesial or distal) will pass by these stages of preparation.

• The first step for the dental practitioner is to control their hand during tooth preparation for ceramic veneers, and the key point here is the depth cutters.Porcelain Veneer Preparation Techniques

• Depth cutters always remove the same amount of tooth regardless of position or inclination, which can be destructive for inexperienced dentists.

• Four essential rules for preparation: no cervical groove, incisal groove 2mm from free edge, 0.5mm in buccal at coronal two-thirds, and 1.5-2mm at the free edge.

• Vertical depth cuts should be prepared with rounded-ended conical diamond burs to preserve the convergence of the buccal surface.

• Horizontal depth cuts can be made with a special three-tier diamond depth cutter and marked with a pencil or marker.

• Homogenization of the grooves is done respecting the buccal convexity.

• Proper margin definition is essential for good veneer fit, stability, and higher adhesion values.

• There are four basic tooth surface preparations: incisal edge preparation, cervical margin preparation, labial/buccal surface triple angulation, and creation of a proximal slide.

• Two basic techniques for incisal finish lines are the intramural preparation or the feathered incisal preparation.

• A flat shoulder should be used at the incisal edge instead of a chamfer margin to avoid weakening the final restoration.

• A wheel-shaped diamond bur can be used for incisal preparation, but care must be taken to protect the neighboring sound teeth.

• It is essential to have knowledge about the thickness of the labial enamel of a natural tooth to preserve enamel as a guide whenever possible.