Impact of Occlusal Intercuspal Angulation on the Quality of CAD/CAM Lithium Disilicate Crowns

Abstract

Purpose Modification of intercuspal angulation (ICA) influences the amount of tooth structure removal, which may impact the retention and resistance form of the preparation. This study evaluated the impact of ICA on the marginal gap of CAD/CAM crowns and the influence that tooth structure removal, caused by variation of ICA, has on the resistance and retention form of the preparation. Materials and Methods Sixty ivorine molars were manufactured with various ICAs (100°, 110°, 120°, 140°, 160°, and 180°; 10 per group). The preparations were digitized using an intraoral scanner, and the crowns were designed using a design software. The designed crowns were then manufactured from lithium disilicate using a 3‐axis milling machine, with the “detailed mode” selected for the manufacturing. The marginal gap of each crown was evaluated using a stereomicroscope at 20× magnification. Then, the marginal integrity and the resistance form of the preparation were assessed by tactile‐visual evaluation, and they were given a categorical score. Crowns were then secured on their associated preparations using a temporary luting agent, and retention force was measured on a universal testing machine under tension with a 0.5 mm/min crosshead speed. Wilcoxon test followed by post‐hoc tests (α = 0.05) were used to evaluate the impact of the ICA on the marginal gap and the retention form of the preparation. Fisher's exact test followed by post‐hoc tests (α = 0.05) were used to assess the impact of the occlusal preparation design on the marginal integrity and the resistance form of the preparation. Results The marginal gap was significantly larger for ICA‐180 preparations (72 μm), compared to the other groups (ICA‐180 vs ICA‐100, ICA‐110, ICA‐120, and ICA‐160 p = 0.0001; ICA‐180 vs. ICA‐140 p = 0.0017). None of the crowns for ICA‐180 preparations had clinically acceptable resistance form. Preparations with ICAs of 100°, 110°, and 120° had a significantly higher value of retention than the other groups (ICA‐100 vs. ICA‐120 p = 0.0119; ICA‐100 vs. ICA‐140, ICA‐160, and ICA‐180 p < 0.0001; ICA‐110 vs. ICA‐140, ICA‐160, and ICA‐180 p = 0.0001; ICA‐120 vs. ICA‐180 p = 0.0017). Conclusions Crowns fabricated for preparations with various ICAs had clinically acceptable marginal adaptation. Variation in ICA impacts the loss of tooth structure. This loss of tooth structure may influence the resistance and retention form of the preparation.

Assessment of Tooth Preparations Submitted to Dental Laboratories for Fabrication of Monolithic Zirconia Crowns

“…Such a design may reduce milling times, improve accuracy, and expedite the treatment process, all of which will enhance the overall quality of CAD-CAM crowns [9,40]. However, two recent studies have demonstrated that preparing a nonanatomical occlusal surface leads to a significantly larger marginal gap on CAD-CAM crowns [9,41]. Preparing non-anatomical occlusal surface results in more tooth structure loss, a factor that may influence the resistance and retention form of the preparation [41].…”

“…However, two recent studies have demonstrated that preparing a nonanatomical occlusal surface leads to a significantly larger marginal gap on CAD-CAM crowns [9,41]. Preparing non-anatomical occlusal surface results in more tooth structure loss, a factor that may influence the resistance and retention form of the preparation [41].…”

Assessment of Teeth Prepared by Senior Dental Students for CAD/CAM Restorations

“…Similar to conventional complete coverage restorations, the longevity of all‐ceramic crowns is affected by the principles of tooth preparation such as total occlusal convergence (TOC), the occlusocervical/incisocervical dimensions, the presence or absence of undercuts, the amount of occlusal reduction, finish line form and depth, and finish of the preparation 5,6 . When one is preparing a tooth for an all‐ceramic crown using a complete digital workflow that includes recording with an intraoral scanning device (IOS) followed by crown fabrication with CAD/CAM technology, certain principles of tooth preparation such as the quality of the finish line design, line angle form, and design of occlusal surface (anatomical, semi‐anatomical, or non‐anatomical) become essential 7‐9 . In addition to an acceptable tooth preparation, the quality of a CAD/CAM crown is dependent on the optical scanner interface, defining internal settings of the restoration in the design software, the manufacturing process, and the type of material used for fabrication of the restoration 10‐17 …”

“…Previously, modifications on the anatomical features of the occlusal surface were suggested to compensate for the milling process; as a result, a simple practical occlusal reduction design with a non‐anatomical occlusal surface was recommended as this modification may reduce milling times, improve accuracy, and expedite the treatment process, thereby enhancing the overall quality of CAD/CAM crowns 8,33 . However, two recent studies found that preparing a non‐anatomical occlusal surface led to a significantly larger marginal gap 8,9 . In addition, preparing a non‐anatomical occlusal surface resulted in more tooth structure loss, a factor that may influence the resistance and retention form of the preparation 9 …”

“…However, two recent studies found that preparing a non‐anatomical occlusal surface led to a significantly larger marginal gap 8,9 . In addition, preparing a non‐anatomical occlusal surface resulted in more tooth structure loss, a factor that may influence the resistance and retention form of the preparation 9 …”