Original study - ZZI 03/2016

Survival and complication rates of implant-supported CAD/CAM lithium-disilicate single crowns

Eric André Noack1, Peter Gehrke2

Introduction: New digital technologies facilitate the fabrication of CAD/CAM lithium-disilicate crowns on teeth
and implants. Due to the limited data available only little is known about the influence of the CAD/CAM process on the clinical complication rate of all-ceramic implant restorations. The aim of this cohort study was to retrospectively analyze the survival and the technical/biological complication rates of implant-supported fixed lithium disilicate ceramic single crowns, milled using a CAD/CAM system, and cemented on titanium abutments.

Material and Method: One hundred and ninety-two implants were placed in 91 patients (58 female and 33 male) and provided with single crowns after a mean healing period of 3.86 months.

Results: After a mean of 45.8 months, implant survival rate was 99.5 %. Within the observation period of seven years the cumulative success rate and the cumulative survival rate of the prosthetic superstructure was 87.5 % and 94.3 % after a mean of 41.9 months, respectively. Loss of single crowns was recorded in 11 cases, of which 10 were caused by technical reasons. Four crowns were lost due to loosening of the abutment screw, and 3 were lost due to the actual abutment fracturing. Two more were lost because the entire crown fractured/major chipping at the crown margin and one crown had to be removed because of a prosthetic schedule change. Periimplantitis as a biological complication was recorded in 8 cases, from which one implant/single crown had to be removed due to major inflammation.

Conclusion: Based on the promising results of the study, CAD/CAM lithium disilicate ceramic single crowns are a valuable restorative alternative in implant therapy.

Keywords: Implant-supported CAD/CAM crowns; lithium-disilicate; titanium abutments; prosthetic complications

Cite as: Noack EA, Gehrke P: Survival and complication rates of implant-supported CAD/CAM lithium-disilicate single crowns. Z Zahnärztl Implantol 2016; 32: 202–213

DOI 10.3238/ZZI.2016.0202–0213

Introduction and problem

Implantology is becoming increasingly important in dental treatment due to its various advantages. Dental implants are used for replacing lost teeth and thus restoring the masticatory function and esthetics. The standard indication for implants includes treatment of edentulous and partially edentulous jaws and single-tooth gaps [2]. Single crowns on implants have a similarly high survival rate to the actual implant [13]. The survival rate of single implants after five years is over 96.0 % [27] and still 94.9 % after 10 years [1]. Based on these good long-term results, restoration of single-tooth gaps in the anterior and posterior region using single implants has proven to be a suitable alternative to conventional bridges restorations. According to current reviews PFM crowns have high survival rates of 89.4 % after 10 years and are therefore still the gold standard in the treatment of single implants [13, 15, 23]. Innovative technologies (e.g. Computer-Aided Design/Computer-Aided Manufacturing, CAD/CAM) have now become firmly established in dentistry and enable predictable, high-quality restorations [6, 17]. Following the market launch of IPS e.max. CAD ceramic (Ivoclar Vivadent GmbH, Ellwangen, Germany) in 2007, the CEREC 3D (Sirona Dental Systems GmbH, Bensheim, Germany) CAD/CAM system also allows fabrication of all-ceramic implant crowns. CEREC 3D simplifies and accelerates fabrication of ceramic inlays, onlays, veneers, partial crowns and crowns for anterior and posterior teeth and enables patient treatment in a single session [18]. The high success rates in the literature confirm the practical feasibility of the CEREC method [24, 25].

In addition to the proven PFM restorations, therefore, all-ceramic crowns have also gained in importance in recent years. IPS e.max CAD lithium-disilicate glass ceramics, among others, are also increasingly used for prosthetic treatment of implants thanks to their good mechanical properties. The IPS e.max CAD blocks used for the grinding process in the CEREC system are manufactured in the casting-press process, a glass technology process. The lithium metasilicate crystals (Li2SiO3 ) created by partial crystallization give the material good malleability with simultaneous relatively good strength and edge stability. The partially crystallized state gives the material a characteristic blue color (Fig. 1, 2). The grain size of the plate-shaped crystals is in the range of 0.2–1.0 µm. After contouring the crown in the CAD/CAM system, the restorations are tempered and lithium disilicate crystals (Li2Si2O5 ) form, which give the crown its final shade and required high strength (Fig. 3) [7]. The structure of the fully crystallized e.max CAD comprises approx. 70.0% fine-grain lithium-disilicate crystals embedded in a glass matrix.

After grinding the fully anatomical restorations in a CAD/CAM system, the instant glaze IPS e.max CAD Crystal/Glaze is applied and the restoration is then simultaneously crystallized and glazed in a dental furnace. The glaze can be applied as a paste using a brush or sprayed on in a quicker working process. A good bond forms between the glaze layer and lithium-disilicate ceramic. The transition has no bubbles or cracks (Fig. 6). Clinical studies on the use of CAD/CAM-fabricated glass ceramic crowns on implants were not yet available at the time of the market launch of the e.max CAD ceramic system. To what extent the fabrication technique using CAD/CAM procedures influences the clinical complication rate of all-ceramic, implant-supported restorations could not be finally assessed to date due to the sparsity of data [10].

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