CAD/CAM-generated high-density polymer restorations for the pretreatment of complex cases: a case report

Complex rehabilitations represent a particular challenge for the restorative team, especially if the vertical dimension of occlusion (VDO) needs to be reconstructed or redefined. The use of provisional acrylic or composite materials allows clinicians to evaluate the treatment objective over a certain period of time and therefore generates a high predictability of the definitive rehabilitation in terms of esthetics and function. CAD/CAM technology enables the use of prefabricated polymer materials, which are fabricated under industrial conditions to form a highly homogeneous structure compared with those of direct fabrication. This increases long-term stability, biocompatibility, and resistance to wear. Furthermore, they offer more suitable CAD/CAM processing characteristics and can be used in thinner thicknesses than ceramic restorative materials. Also, based on the improved long-term stability, the transfer into the definitive restoration can be divided into multiple treatment steps. This article presents different clinical cases with minimally invasive indications for CAD/CAM-fabricated temporary restorations for the pretreatment of complex cases.     

Computer-aided evaluation of preparations for CAD/CAM-fabricated all-ceramic crowns

Objective

The aim of this study was the evaluation of preparations from general dental practitioners for zirconia crowns and their correlation with clinical recommendations using a digital approach.

Material and method

Seventy-five datasets of left first upper molars (FDI 16) prepared for single zirconia crowns by general dental practitioners were analyzed using a computer-aided design software (LAVA^TM Design; 3M ESPE, Seefeld, Germany) and a 3D-inspection software (COMETinspect®plus version 4.5; Steinbichler Optotechnik, Neubeuern, Germany). Evaluated parameters were convergence angle, undercuts, interocclusal reduction, abutment height, and design of preparation margin.

Results

The mean convergence angle was determined to be 26.7°. The convergence angle in the mesiobuccal to distopalatal dimension was significantly the highest (31.7°), and the abutment height showed a mean value of 4.1 mm. Convergence angle and abutment height showed a negative correlation. Seventy-three percent of the evaluated locations revealed a margin design conforming to ceramic restorations. In over 30 % of the cases, the interocclusal reduction was insufficient. Generally, no preparation fulfilled all recommendations. Five (6.66 %) of the preparations fulfilled four criteria, 16 (21.33 %) preparations fulfilled three criteria, 31 (41.33 %) fulfilled two criteria, 17 (22.66 %) preparations fulfilled one criterion, and 6 (8 %) fulfilled no criterion.

Conclusions

Within the limitations of this study, most general dental practitioners seem to have difficulties fulfilling all clinical recommendations given for the preparation of zirconia crowns. The presented digital approach seems to be a useful method to evaluate the preparation geometry.

Clinical relevance

The correct preparation geometry represents an important prerequisite for the success of all-ceramic full crowns. As preparations clearly need to be improved, the approach presented could be the basis of a future tool to increase preparation quality in practice and education by direct objective feedback.     

Precise Placement of Single‐Retainer Resin‐Bonded Fixed Dental Prostheses with an Innovative Splint Design

Single‐retainer resin‐bonded fixed dental prostheses (RBFDPs) are difficult to position due to the pressure of soft tissue at the pontic area and the single‐retainer design. This clinical report describes an innovative technique for the insertion of single‐retainer RBFDPs. An incisal inserting splint is used to position the RBFDPs reliably. With the help of grooves in the buccal and incisal area of the splint, the precise positioning of the splint on the adjacent teeth and the RBFDP can be controlled. Also, a hole in the retainer wing region of the splint gives access for pressure application on the wing during the bonding process. With the aid of this method, 25 single‐retainer FBFDPs were inserted in the correct position in a case series. The splint described here allows the precise insertion of single‐retainer RBFDPs and simplifies delivery.     

A new method for the evaluation of the accuracy of full-arch digital impressions in vitro

Objectives

Introducing a new approach to evaluate the accuracy of digital impression methods for full-arch scans, avoiding “best-fit alignment.”

Materials and methods

A lower jaw model with a straight metal bar between the second molars of both quadrants was directly digitized using an intraoral scanner (True Definition, TRD, n?=?12) and indirectly digitized (D810, CON, n?=?12) after impression and plaster cast. A dataset of the bar from a coordinate measuring machine served as reference (REF). Datasets obtained from test groups were analyzed using inspection software to determine the aberration of the bar length, the linear shift (in X-, Y-, Z-axis) and the angle deviation (α _overall, α _coronal, α _horizontal) caused by the digitalization method. Mann–Whitney U and unpaired two-sample Student’s t test were implemented to detect differences. The level of significance was set at 5 %.

Results

Concerning the bar length, no significant differences were found between groups. In view of the linear shift, CON showed significantly higher values than TRD in Y-axis (p?=?0.003) and in Z-axis (p?=?0.040). Regarding the angle measurement, TRD showed significant smaller values than CON for α _overall (p?=?0.006) and for α _coronal (p?=?0.005).

Conclusions

This in vitro study shows that intraoral scanning systems seem to show the same or even higher accuracy than the conventional impression with subsequent indirect digitalization.

Clinical relevance

Intraoral scanners have proven excellent accuracy for single teeth or small spans. However, insufficient data is available about their accuracy for full-arch scans. The presented new approach seems to be suitable to precisely analyze differences in the accuracy of different digitalization methods without using best-fit alignment.