Fracture Resistance of A Newly Proposed Occlusal Veneer Design Using Two Different CAD/CAM Ceramic Materials

Abstract

Statement of the Problem:Management of severe occlusal erosive lesions constitutes a challenging therapeutic approach to the restorative dentist. Bonded occlusal veneers have been introduced as a conservative solution to traditional onlays or complete coverage crowns. Still, there is lack of information and conflict in the data concerning the mechanical performance of the occlusal veneer materials and designs.Purpose: The purpose of this in vitro investigation was to evaluate and compare the fracture resistance and failure mode of a newly proposed occlusal veneer design constructed of zirconia reinforced lithium silicate and hybrid ceramic materials with the conventional design restored with the same tested materials. Materials and Methods:Two mandibular first molars of a typodont were chosen to perform the master preparations; one for the conventional planar occlusal veneer design, and the second for the proposed modified design which consisted of occlusal veneer preparation with circumferential chamfer finish line and two shallow proximal slots. Ten elastomeric impressions were taken for each design using the putty and light polysiloxane addition silicone impression material. The twenty impressions were poured using type IV dental stone to produce twenty stone casts, ten for each design. Each group of stone casts was subdivided randomly into two equal subgroups according to the ceramic material to be tested; the zirconia reinforced lithium silicate "Celtra Duo" and the hybrid resin nano ceramic "Lava Ultimate". All the occlusal veneers were fabricated using the CAD/CAM Cerec InLab SW 4.2.5 System. The veneers were then checked on both the stone casts and the master preparation on the typodont for perfect seating, after the Celtra veneers were crystallized and glazed and the Lava veneers being subjected to finishing and polishing. The preparations were duplicated to obtain twenty epoxy casts over which the occlusal veneers were adhesively cemented using a standard bonding protocol. The samples were then subjected to thermal cycling program. All the samples were individually mounted on the Instron testing machine with a loadcell of 5 KN and fracture test was done by compressive mode of load applied occlusally using a metallic rod with spherical tip (5.6 mm diameter) at cross-head speed of 1mm/min. The load required to fracture was recorded in Newton and tabulated to be statistically analyzed. The fractured specimens were examined to detect the mode of failure. (2900)Carl Hany Halim E.D.

Marginal fit and fracture resistance of advanced lithium disilicate occlusal veneer with different preparation designs

“…(34) While in the minimally invasive chamfer design, there is less enamel exposed at the margins which decrease surface area for bonding which in turn decreases the fracture resistance, in addition to that thinner finish lines are generally contraindicated for allceramic restorations as they trigger wedging effect at the margins (35) . This results in agreement with Carl H et al (2019) (36) and, Lorio et al (2011) (37) , who found that the shoulder design showed the highest fracture resistance mean value while the chamfer one recorded the lower mean value. To a statistically significant degree, the configuration of the finish line affected the fracture resistance for ceramic posterior occlusal veneers.…”

Wear behavior of bonded occlusal veneers constructed from machine milled glass and polymer infiltrated ceramics in contact with enamel: An in vitro study

“…In our study, we used tabletops with 1.5 mm thickness which was supported by Andrade et al [5] study which evaluated the impact of several ceramic materials "IPS e.max CAD, Vita Enamic, and Lava Ultimate" with different thicknesses (0.6 mm and 1.5mm) on the fracture resistance of occlusal veneers and concluded that the occlusal veneers of IPS e.max CAD, VitaEnamic, and Lava Ultimate, with thicknesses of 0.6 mm and 1.5 mm, obtained fracture resistance similar to those of intact teeth. The conventional planar preparation was done to follow the occlusal anatomy with 1.5mm occlusal reduction at the cusp tip and 1mm reduction at the fossa to confirm the sufficient thickness of the occlusal veneers which comes in accordance with Halim et al [8] who conducted a study to detect the fracture resistance and failure mode of "zirconia reinforced lithium silicate and hybrid ceramic" occlusal veneers with two preparation designs conventional planar preparation and modified design, and it was concluded that both designs offered fracture resistance mean values that exceeded the clinically accepted range with the two tested materials To standardize the preparation in all the tested samples we executed the main preparation on a typodont lower right first molar tooth and duplicated the prepared typodont tooth using epoxy resin to get 16 epoxy resin dies as replicas of the prepared typodont tooth, which was confirmed by Nawafleh et al [24] who confirmed that the use of (die) materials such as epoxy resin or acrylic resin are not difficult to standardize and fabricate, on the other hand, natural teeth are inconstant in size, shape, and condition, creating difficulty in standardizing tooth preparation. In our study, we used occlusal veneers in different materials to test wear rather than a flat sample in accordance with Heintze et al [10] who assessed the difference in wear resistance between flat samples and anatomical samples (crowns) in four different ceramic materials (Empress, e. max press, IPS Eris and Pro Cad) opposed with Empress stylus using Ivoclar wear method which disclosed significant differences among flat samples and crowns.…”

Marginal accuracy of Cad/Cam occlusal veneers fabricated from glass and hybrid ceramics with two preparation designs: An in vitro study

“…Fixed prosthodontists have been pushed into more conservative treatment methods by recent advancements in restorative materials, construction technology and adhesive techniques. Occlusal veneers are thought to be the most recent therapeutic option for conservatively treating the problem of advanced erosive lesions [8] .…”