Preface
Finally, the intensive reading column of “The Tooth Preparation” is about to enter the climax part! Creating a smile that reflects personalized beauty for patients is one of the missions of us dentists. In this issue, we will bring you the guide to the preparation of abutment teeth for porcelain veneers! The dentist will also divide this part into a basic chapter and a clinical chapter, using two issues to explain in detail. The basic theory must be thoroughly mastered. If porcelain veneer restoration is carried out beyond the indications, it will definitely bring disastrous consequences to patients. Without further ado, let’s enter the basic chapter of the preparation of abutment teeth for porcelain veneers in this issue.
1.Characteristics of the Preparation of Abutment Teeth for Porcelain Veneers
· Preserve the enamel as much as possible
· Consider the path of insertion of the porcelain veneer and eliminate all undercuts
· According to the final restoration design, determine whether the margin is placed above or below the gingiva, whether to open the contact, and the area of dentin exposure, etc.
2.Indications for Porcelain Veneers (The classification method proposed by Yamazaki et al. in 2004)
Compared with composite resin veneers, porcelain veneers have more lasting aesthetic effects and stronger fracture resistance, but there is no statistical difference in the risk of detachment.
3.Thickness of Enamel
· The bonding of porcelain veneers depends greatly on the enamel. Therefore, a full understanding of the thickness changes of the enamel is required to correctly complete the preparation of abutment teeth.
· Using porcelain veneers to replace the lost labial enamel during the preparation of abutment teeth, there is no obvious change in the strength of the tooth structure.
· Once the dentin is exposed during the preparation of abutment teeth, in order to reduce dentin sensitivity, lower the risk of bacterial infection, reduce the gap between the porcelain veneer and the tooth structure, and increase the bonding strength, immediate dentin sealing is required before taking the impression.
4.Morphology of the Preparation of Abutment Teeth for Porcelain Veneers
· While preserving the enamel on the labial and proximal surfaces, ensure that the shape of the preparation is similar to the shape of the crown after the final restoration.
· The preparation of abutment teeth includes various designs such as closing large interdental spaces, only proximal slicing, minimally invasive (MI, minimal intervention) preparation after Mock-up, and non-prepared veneers.
5.Incisal Morphology of Porcelain Veneers
The incisal morphology includes four types: window, feathered-edge, butt joint incisal, and palatal chamfer. Chai et al. (2018) pointed out that the butt joint incisal can reduce the risk of porcelain veneer fracture and chipping.
6.Proximal Morphology of Porcelain Veneers ①
The position of the proximal margin depends on the proximal morphology of the porcelain veneer. Incorrect margin positions significantly affect aesthetics, cleaning, and the long-term prognosis of the restoration.
· For traditional porcelain veneers, the proximal margin should avoid exceeding the contact point. Remember not to prepare a jumping margin (Note: Japanese dental clinical jargon, referring to a sharp burr left on the outside after margin preparation).
· When there is an existing Class III cavity composite resin filling, if the proximal margin is prepared too short, the porcelain veneer may fracture due to the thermal expansion and contraction of the composite resin.
· When there is an existing Class III cavity composite resin filling, the proximal margin should be extended to the lingual side and the composite resin filling should be completely wrapped with the porcelain veneer to reduce the influence of the thermal expansion and contraction of the composite resin.
7.Proximal Morphology of Porcelain Veneers ②
When the interdental space is too large, the proximal margin can be extended to the lingual side to ensure an appropriate proximal morphology.
· When the interdental space is too large and the proximal margin is not extended to the lingual side but only stays on the labial side of the proximal surface
it is impossible to produce a smooth and natural proximal morphology of the porcelain veneer.
· When the proximal margin is extended to the lingual side, the proximal morphology of the porcelain veneer is smooth and natural.
8.Gingival Morphology of the Proximal Surface of Porcelain Veneers
When the interdental space is too large, the proximal margin needs to be prepared more gingivally, otherwise, an obvious black triangle will be caused, affecting aesthetics and cleaning.
· If the proximal margin is not prepared enough gingivally, it is difficult to close the gap above the gingival papilla.
· If the proximal margin is fully moved gingivally, even set below the gingiva, it is easier to close the gap above the gingival papilla.
9.Space Required for Porcelain Veneer Materials
· Porcelain veneer materials include feldspathic ceramics, lithium disilicate, zirconia, composite resins, etc.
· Due to the relatively thin enamel at the cervical area, an above-gingiva margin should be used as much as possible, with a margin width of about 0.3 – 0.5mm.
· The labial axial surface still requires three-sided preparation, with a preparation amount of about 0.5mm in the center of the labial surface and about 0.7mm near the incisal end.
· To ensure the strength and aesthetics of the incisal end, the preparation amount at the incisal end needs to be more than 1.5mm
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