Effect of Endodontic Access Location on Fracture Resistance of CAD/CAM Lithium Disilicate Mandibular Anterior Crowns

Objectives: This study assesses the influence of lingual, incisal, facial and no endodontic access cavity preparations on the fracture resistance of chairside computer-aided design and manufacturing (CAD/CAM) lithium disilicate crowns for mandibular right incisors.
Methods: Eighty lithium disilicate (E.max CAD) crowns for mandibular right central incisor were designed with a chairside CAD/CAM system (PrimeScan). The restorations were bonded with resin luting cement (Multilink Automix) with primer system (Monobond Plus) onto printed resin dies. The restorations were treated and divided into five groups (20 specimens/group): (1) crowns with no endodontic access (NoAc); (2) crowns with lingual endodontic access (LiAc); (3) crowns with incisal endodontic access (InAc); and (4) crowns with facial endodontic access (FaAc). Half of the restorations for each group (10 specimens) underwent 10,000 thermal cycles between 5° and 55 °C, followed by loading to measure compressive force until fracture. Scanning electron microscope (SEM) images of the fractured specimens were obtained. Data was analyzed with ANOVA test and Bonferroni’s correction, and alpha was set at .05.
Results: Crowns with no endodontic access provided the highest fracture resistance values, both with (T: 1218 N) and without thermocycling (NT: 1088 N), followed by crowns with lingual endodontic access (T: 898 N and NT: 1187 N), and crowns withfacial endodontic access (T: 893 N and NT: 1023 N). Crowns with incisal endodontic access displayed the lowest values (T: 720 N and NT: 822 N). The thermocycling process led to reduced fracture resistance values, regardless the presence of endodontic access.
Conclusions: The fracture resistance of chairside CAD/CAM lithium disilicate mandibular anterior crowns is influenced by thepresence and location of the endodontic access. Crowns with no endodontic access provide higher fracture resistance compared to any type of endodontic access. Crowns with endodontic access on the lingual and facial areas offer higher fracture resistance thanthose on the incisal surface.