Comparison of strains for new generation CAD-CAM implant-supported crowns under loading.

PURPOSE: The behavior of implant-crowns fabricated from recently introduced CAD-CAM zirconia-reinforced lithium silicate ceramic (ZLS) or a hybrid ceramic containing resin-reinforced glass network (HC) for strains around the implant platform is not well-known. A force absorption capacity of the latter has been claimed by the manufacturer. The aim of this study was to measure and compare recently introduced ZLS and HC with commonly used CAD-CAM implant crown materials for strain distribution around the implant platform. METHODS: Four implants (Legacy 1; Implant Direct) were placed into a resin block. Zirconia abutments (Straight contoured stock abutment; Implant Direct) were torqued into the implant fixtures to support crowns that were milled from a virtual design using four different CAD-CAM materials (Vita Suprinity PC (ZLS), Vita Enamix (HC), IPS Emax, ZirCAD Zirkonzahn) (N = 20). The crowns were cemented with a resin cement, loaded and strain values were recorded. Three-dimensional digital image correlation (3D-DIC) was used to measure compressive and tensile strains around the implant platforms. The tensile and compressive strains were recorded for each test and first analyzed for equality of variance using Levene's test, and further tested using a 2-way ANOVA repeated measures analysis of variance (α = .05). RESULTS: The data analysis showed no statistically significant effect of crown material on the generated strains (P > .05). Compressive strains were significantly higher than the tensile strains (P < .05). One of the HC crowns fractured during loading. CONCLUSIONS: Strains generated around implant platform when new generation CAD-CAM crown materials were used was similar to strains observed when CAD-CAM zirconia and lithium disilicate crowns were used. New generation crown materials did not have a significant load absorption effect to change or minimize the strains generated around the implant platform.

Conservative treatment and follow-up of type III dens invaginatus using cone beam computed tomography.

Dens invaginatus is a well-recognized phenomenon, and its endodontic treatment poses a challenge, especially for peri-invagination lesions with vital pulp. Here we describe the outcome of conservative treatment and follow-up in a case of type III dens invaginatus. Cone-beam computed tomography was used for diagnosis and follow-up. Pulp vitality was preserved with endodontic treatment of only an invaginated canal. At the 24-month follow-up examination, the tooth was asymptomatic and repair of the lesion was evident radiographically. This case was managed successfully with endodontic treatment of the invagination. (J Oral Sci 56, 307-310, 2014).