Minimally Invasive All-ceramic Preparation for the Occlusal Face: The ‘V Preparation’
Michel Fages, DDS, MS, PhD; Bertrand Bennasar, DDS; and Jacques Raynal, DDS
ABSTRACT:
A clinical case illustrates and explains step by step a minimally invasive molar occlusal surface preparation for all-ceramic bonded restoration. The sequential use of calibrated burs, following the specific procedure, systematically and quickly, provides a perfectly calibrated reduction of the occlusal face even for an inexperienced practitioner. This preparation increases the bonding surface and optimizes the accommodation of constraints that provides a more resistant reconstruction and favors the preservation of the vital tooth. This procedure, called a “V preparation” or V prep, is discussed in the case report below.
In the past 10 years, in addition to caries, dentists have been confronted with erosion, a pathology growing exponentially.1 This increase is mainly due to the use of acidic drinks or gastric regurgitations associated with mechanical wear. This type of excessive wear is classified in the basic erosive wear examination (BEWE) index, based on the severity of substance loss.2,3
The index is as follows: 0 for no surface loss; 1 for initial loss of enamel surface texture; 2 for distinct defect, hard tissue loss (dentine), and less than 50% of the surface area; and 3 for hard tissue loss ≥50% of the surface area. In this article, the clinical case corresponds to a BEWE score of 3.
In most cases, the eroded teeth required reconstruction, in particular the occlusal surfaces of the molars. The adhesive techniques and ceramic materials currently available4-6 can be used to provide minimum treatment, preserving tooth vitality, without the need for peripheral restoration.7 “V preparations,” or “V preps,” are especially indicated for any type of occlusal surface lesion8,9 and were first suggested in the late 1990s by David Sutton and Hubert Stevie for CEREC users.10
They are a form of minimally invasive preparations for all-ceramic restorations.11 The subject of this article is to describe step by step this preparation.
Methodology and Clinical Case
The clinical case involved a preparation of a vital tooth No. 26 with a substantially damaged occlusal surface from erosion (Figure 1 and Figure 2). The patient was a 27-year-old man, who frequently drank sparkling sweet drinks and had good oral hygiene. Demineralization of the enamel provided loss of hard tissues (index score = 3), and a conservative approach was taken.
The treatment goal was to obtain a complete, 2-mm-deep homothetic reduction of the occlusal surface. Each step involved a specific procedure that required the use of specific rotary instruments. Those steps included: creating guides grooves, performing the cusp reduction, and finishing the preparation.
Guide grooves were created using a diamond bur that was 2.0 mm long and 0.9 mm in diameter. The bur was inserted into the long axis of the tooth until its abutment (Figure 3). A first mesio-distal guide groove joined the two marginal ridges, crossing the entire occlusal surface following the intercusp; similarly, a second groove joined the buccal face to the lingual face (Figure 4).
Then grooves began at the buccal cusps following the cusp ridges until they joined the lingual cusp on the opposite side (Figure 4). Thus, the guide grooves crossed the tooth along the lower (furrow: orange) and higher (cusp: green) ridges, and they were strictly 2 mm deep throughout the occlusal surface (Figure 5).
The cusp reduction was obtained by using a sweeping motion to connect the guide grooves. A cylindrical-conical green diamond bur with a total occlusal convergence of 7° was used (Figure 6 through Figure 8).
The tip of the bur was positioned at the bottom of the mesial and distal marginal ridge. It was sweeped transversally, without adding to the depth of the groove. The sweeping motion was guided by the grooves. The morphology of the preparation, at this point, appeared as a combination of “V” shapes in the palatal-lingual and mesio-distal directions (Figure 9 and Figure 10). It formed a butt joint between the tooth and ceramic material (Figure 9 through Figure 11). Then a cylindrical-conical red diamond bur, with a total occlusal convergence of 7°, was used to polish the occlusal surface, particularly the rough edges and periphery.
Insertion of the Restoration
A pressed12 or milled (CAD/CAM)13 glass-ceramic restoration was bonded using dual-cure adhesive resin cement (Figure 12 and Figure 13). In this case, Vitablocs® Mark II ceramic (Vita Zahnfabrik, vita-zahnfabrik.com) and RelyX™ Ultimate (3M ESPE, 3m.com) were used.
Everything rests on ceramic’s bonding ability and its capacity to accommodate compressive stresses. A peripheral preparation would reduce the enamel band and induce shear stresses at this level, which is not good for bonded ceramic. This proposal is excellent for sealed materials, such as gold, but would be advantageous for glass-ceramic materials. The procedure does not provide retention but a better setting, which is an asset.
The authors have used this technique in private practice for more than 5 years and regularly in the prosthetic department of the University Hospital of Montpellier in France for 2 years. They intend to publish the results after 3 years, and then at 5 years. To date, no failures have occurred.
Discussion
This type of preparation has many advantages. The bonding surface is considerably extended, and the depth of the reduction is uniform throughout the entire occlusal surface. Only the minimum thickness required by the restorative procedure and bonding materials is removed. The geometry of the prepared surface reproduces the original contour of the occlusal surface, and this ensures optimal coupling with the antagonist surfaces when constraints are present. The V and inverted V shapes provide the stability of the restoration and facilitate positioning during bonding. Guide burs should be as long as the thickness of the reconstruction material (glass-ceramic) and its bonding agent, which is usually 2 mm. The bur chuck makes it impossible to exceed this depth. Glass-ceramic material combines biocompatibility and biomimetic with a wear coefficient closer to enamel.14
The bonding agent must be extremely adhesive, and its modulus of elasticity should accommodate constraints at the dentin-enamel junction.15 It should also be transparent, in order to ensure optimal esthetics. Those preparations are indicated for restorations of the occlusal surfaces of premolars and molars in cases of carious teeth,8 the replacement of failing restorations (ie, amalgam fillings, composite fillings, defective inlays or onlays), and eroded teeth.16
They can also be performed if preparation is necessary in the case of vertical dimension augmentation. If the preparation needs to be less invasive, shallower gauges (1.0 mm or 0.6 mm) can be used.17
They are contraindicated if bonding is impossible, if the pulp is too near the surface, or if the decay is too severe, indicating peripheral restoration.18
Conclusion
The principle of the V preparation is simple and logical, but it is a delicate procedure, requiring the use of guide burs and an effective methodology. Once the technique has been mastered, the preparation is quick and simple, regardless of the type of occlusal surface being restored.
The sequential use of the specific burs in accordance with the step-by-step procedure provides immediately excellent results, even for inexperienced operators. It makes it possible to avoid more damaging preparations, and remains perfectly compatible with bio-integration restorative dentistry concepts.
ABOUT THE AUTHORS
Michel Fages, DDS, MS, PhD
Assistant Professor, Prosthetic Department, Faculty of Odontology, Montpellier, France
Bertrand Bennasar, DDS
Assistant Lecturer, Prosthetic Department, Faculty of Odontology, Montpellier, France
Jacques Raynal, DDS
Assistant Lecturer, Prosthetic Department, Faculty of Odontology, Montpellier, France
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