International Journal of Computerized Dentistry, 03/2018

Purpose: The aim of this study was to investigate the fracture strength of computer-aided design/computer-aided manufacturing (CAD/CAM) posterior ceramic crowns with and without post-milling manual enhancement of occlusal morphology (MEOM), as indicated especially with early CAD/CAM restorations that have limited capacity to generate natural occlusal morphology. Materials and methods: A mandibular molar of an acrylic tooth model was prepared to receive a CAD/CAM all-ceramic crown and was used as a master die to fabricate 80 prepared tooth replicas using an epoxy resin with an elastic modulus (E) of 18 GPa. The crown was designed using Cerec software's Biogeneric Copy Design mode (Sirona). Eighty identical monolithic crowns were fabricated by milling four types of ceramic blocks. Forty monolithic crowns (10 of each ceramic system) were randomly selected as the control group, and MEOM was performed for each of the other 40 crowns by a certified dental technician. Restorations were crystallized and glazed according to the manufacturers' instructions and firing protocols. All crowns were cemented to their respective die using resin cement, and loaded to fracture at a crosshead speed of 0.5 mm/min. The resultant fractures were classified into three modes. Data were statistically analyzed using the nonparametric Mann-Whitney U test at α = 0.05. Results: The MEOM treatment decreased the fracture load for all ceramic brands. Conclusion: The MEOM procedure should be considered detrimental for monolithic CAD/CAM-generated crowns and should thus be avoided. Keywords: CAD/CAM, monolithic posterior crown, fracture strength, occlusal morphology, machinable ceramic, cementation, feldspathic ceramic, leucite-reinforced glass-ceramic, lithium disilicate glass-ceramic, zirconia-reinforced lithium silicate glass-ceramic

Different concepts are used for the analysis and transfer of mandibular movements to virtual or conventional articulating systems. Some common procedures and analyses include the determination of the terminal hinge axis. However, despite the widespread use of different methods for hinge axis determination, very little information on the applicability and quality of these methods is currently available in the literature. The aim of this study was to provide an overview of the methods already being applied and to search for novel algorithmic methods, comparing them with respect to achievable accuracy and indication. This comparison was based on new extensive computer simulations, where the influence of measurement noise on the result of the hinge axis position could be investigated. The assumptions used for the simulations were set so that the conditions allowed for the most accurate hinge axis determination: this comprised a pure rotation during mouth opening, within an incisal pathway of 15 mm, a measurement accuracy of 50 µm, and an optimal positioning of the entire measurement setup. The results of the computer calculations show that the best accuracy can be guaranteed by the novel least squares method, introduced in this article for temporomandibular joint (TMJ) measurements. Additionally, only methods tracking two and more (iterative or parallel) independent markers or equivalent jaw position measurements provide enough information for reliable accuracy. Using actual technical equipment, the highest accuracies can be achieved in a TMJ-near measurement setup. However, even in that best-possible setup, the error of hinge axis determination cannot be expected to be less than ±1 mm. For a better characterization of actual electronic recording systems, manufacturers need to provide more insight into the evaluation processes. Keywords: terminal hinge axis, jaw tracking, temporomandibular joint, accuracy, computer simulation

Purpose: The aim of this clinical study was to test whether or not digital workflows for the fabrication of crowns render different clinical outcomes from the conventional pathway with respect to (1) crown quality, and (2) time efficiency. Material and methods: For each of the 10 patients in need of one tooth-supported crown, five monolithic crowns were produced out of lithium disilicate reinforced glass ceramic. Four different optical impression and associated computer-aided design/computer-aided manufacturing (CAD/CAM) systems were used for crown fabrication (digital workflows): (1) Lava C.O.S. scanner and Lava C.O.S. and CARES CAD software, centralized CAM (group L); (2) Cadent iTero scanner, CARES CAD software and centralized CAM (group iT); (3) Cerec Bluecam, Cerec Connect CAD software, followed by laboratory-based CAM (group CiL); and (4) centralized CAM (group CiD). The conventional crown (group K) was fabricated based on a conventional silicone impression followed by a conventional wax-up and heat press technique. The examiners were blinded and evaluated the crowns clinically at the bisque-bake stage (initial try-in), and subsequently after finalization by a dental technician (final try-in). For the assessment of crown quality, modified United States Public Health Service (USPHS) criteria were used. Treatment times were recorded for clinical evaluation and adjustment. The quality ratings were analyzed descriptively. For both the continuous and ordinal outcomes, the non-parametric paired Wilcoxon test was applied, together with an appropriate Bonferroni correction to evaluate the differences between treatment groups. The results of the statistical analysis were interpreted globally at the significance level P = 0.05. Results: The clinical evaluation during the initial and final try-ins demonstrated similar clinical outcome measures for crowns generated with the four digital workflows and the conventional workflow. No statistically significant differences of crown quality in any state were found between groups (P > 0.005). The total clinical treatment times measured were: 456 ± 240 s for L; 655 ± 374 s for iT; 783 ± 403 s for CiL; 556 ± 285 s for CiD; and 833 ± 451 s for K. No statistically significant differences in treatment times were found between the groups (P > 0.05). Conclusions: Within the limitations of the present study, the monolithic ceramic crowns resulting from the four different CAD/CAM systems did not differ from the conventionally produced crowns with respect to the clinical quality rating and the treatment time efficiency. Keywords: digital workflow, conventional workflow, CAD/CAM, monolithic crown, time efficiency, clinical quality

Objective: To clinically evaluate computer-aided design/computer-aided manufacturing (CAD/CAM)-fabricated molar endocrowns after 6 months and 1, 2, and 3 years of clinical service. Materials and methods: 289 patients with 321 molars (267 patients with one endocrown, two patients with two endocrowns, and ten patients with three endocrowns) exhibiting extensive coronal loss of substance participated in the study. Endocrown preparations were scanned, and endocrowns designed and machined with the Cerec CAD/CAM system. The endocrowns were adhesively seated using a composite luting agent, and assessed using clinical United States Public Health Service (USPHS) criteria at baseline, 6 months, and 1, 2, and 3 years after placement. Patient satisfaction was evaluated using a questionnaire. Results: None of the 289 endocrowns failed during the observation period. The high clinical rating criteria (97.2%) and the high satisfaction percentage (98.0%) remained practically unchanged (P > 0.05) throughout the follow-up assessments at 6 months and after 1, 2, and 3 years. Conclusion: Monolithic zirconia endocrown restorations represent an effective method of restoring posterior teeth after root canal therapy. Based on the short-term observation period of the present study, monolithic zirconia endocrowns can be considered a reliable restoration for endodontically treated molars with extensive coronal loss of substance. Keywords: monolithic zirconia endocrowns, CAD/CAM fabrication, clinical short-term rating, patient acceptance

This study evaluates the symmetry of initial proposals for anterior tooth restorations delivered by the Cerec software. By using a symmetric preparation model and a special angulation gauge for restoration axes, the study proves that the restoration proposals are symmetric with respect to the median sagittal plane. Keywords: Cerec, biogeneric, initial proposal, symmetry, anterior tooth restoration

Vita Enamic is a durable hybrid ceramic that can be processed with efficient computer-aided design/computer-aided manufacturing (CAD/CAM) support. The porous sintered feldspar ceramic block that is infiltrated with polymer does not require a ceramic furnace after being ground out. Instead, it only needs to be finished and polished. This makes one-time chairside treatment possible. In addition to the well-known monochromatic Vita Enamic blocks, a multichromatic version with integrated shade gradient and a super-translucent version have been developed. The goal of this application study is to demonstrate these new indications with their material benefits in the anterior and posterior regions using four different case studies. Keywords: Computer-aided design/computer-aided manufacturing (CAD/CAM), hybrid ceramics, multi-chromaticity, super-translucence, Cerec

Objective: In most cases, according to our treatment concept, a presurgical orthodontic treatment (POT) is performed on patients with cleft lip and palate (CLP). The aim of this case report is to demonstrate a completely digital workflow for the production of a palate plate. Materials and methods: For the assessment of the maxillary arch, a digital impression of the jaw was made on two patients with an intraoral scanner (Cerec Omnicam Ortho). After reconstruction of a virtual model from the scan data, appropriate areas of the jaw could be blocked out and a plate constructed. This was printed with a DLP three-dimensional (3D) printer (SHERA EcoPrint D30) with class IIa biocompatible material. After minor surface finishing, the plates could be incorporated in the patients' mouths. Results: The scans could be performed in a short time without affecting the very young patients. All clinically relevant areas for the production and digital measurement of the models could be recorded. The plates showed an extremely good fit, and there were no differences in wear compared with a conventionally manufactured plate. Conclusion: For the first time, a risk-free digital impression of the edentulous jaw in CLP babies with a subsequently completely digitally constructed and 3D-printed palatal plate could be shown. Keywords: cleft lip and palate (CLP), computer-aided design/computer-aided manufacturing (CAD/CAM), three-dimensional (3D) printing, plate

Missing or reduced buccal bone plates and a reduced vertical dimension still represent challenges in bone grafting and require a three-dimensional (3D) reconstruction. The protocol presented in this short technical note describes the clinical application of a patient-specific, titanium lattice structure for customized bone regeneration (CBR). A 3D projection of the bony defect is generated, and an individualized titanium lattice structure designed using computer-aided design/computer-aided manufacturing (CAD/CAM) procedures and rapid prototyping. By confirming this design interactively, the surgeon is integrated into the design process. The aim of this technical note is to describe the principle of a novel and modern digital workflow, and describe a possible improvement to the common hand-configured lattice structure graft technique. The new protocol presented in this note facilitated and shortened surgery time, and may be a successful and predictable procedure for rebuilding an atrophied complex bone defect. Keywords: individualized dentistry, customized bone regeneration, CAD/CAM technology, grafting procedures, individualized lattice structure, titanium mesh