International Journal of Computerized Dentistry, 03/2011

Objectives: The aim of this prospective clinical study was to assess the long-term clinical survival rate and the technical and biological complication rates of zirconia-based posterior FDPs. Materials and Methods: Forty-five patients in need of one or more posterior FDPs received 57 three- to fiveunit zirconia-based FDPs. The frameworks were fabricated by means of a prototype computer-aided manufacturing (CAM) system (direct ceramic machining, DCM), first processing zirconia in the white stage. The frameworks were veneered with a prototype veneering ceramic. The FDPs were adhesively placed. At baseline, 6 months, and 1, 2, 3, 5, 8 and 10 years of function, the FDPs were examined for technical and/or biological complications. Furthermore, the periodontal health of the abutment teeth (test) and untreated control teeth was analyzed. Statistical analysis was performed applying descriptive statistics, Kaplan-Meier survival and multiple mixed effects regression tests. Results: Twenty-one patients with 26 FDPs were examined at a mean observation time of 10.7 ± 1.3 years. A total of 16 FDPs were lost to follow-up. Fifteen FDPs had to be replaced due to technical/biological complications; hence, the 10-year survival rate of the FDPs was 67%. Three framework fractures occurred, resulting in a 10-year survival rate for the zirconia frameworks of 91.5%. Chipping/fracture of the veneering ceramic was detected in 16 FDPs over 10 years (complication rate 32%). A significant correlation of the span of the FDPs and the incidence of chipping was observed: 4- and 5-unit FDPs had a 4.9 times higher probability for chipping than 3-unit FDPs. Marginal discrepancy/degradation was found in 90.7% of the FDPs over 10 years. At 11 of the FDPs (complication rate 27%), secondary caries occurred. No difference of the periodontal health was found around test and control teeth. Conclusion: The zirconia frameworks exhibited very good long-term stability. However, the zirconia-based FDPs frequently exhibited problems such as marginal deficiency or chipping of the veneering ceramic. Both problems may be associated with the prototype status of the system. Keywords: zirconia, framework, fracture, long-term, FDP, chipping, marginal adaptation

This practice-based study evaluates the initial clinical performance of conventionally luted metal-ceramic and zirconia molar crowns fabricated with a prolonged cooling period of the veneering porcelain. Forty-nine patients were treated (group A: high precious alloy + low fusing porcelain; group B: zirconia crowns). All zirconia crowns were veneered with a modified porcelain firing cycle including a 6-minute cooling period. Ninety-two restorations (74 vital abutments/ 18 nonvital abutments) were evaluated after a mean observation period of 18.2 ± 4.6 months. No complete failures or loss of vitality were recorded in either group. Two events were recorded in group A (1 loss of retention/ 1 minor ceramic chipping 2 mm²). The third event occurred in group B (minor ceramic chipping 2 mm²). All ceramic defects could be polished intraorally. Statistical analysis revealed non-significant differences in success rates (p = 0.91) of metal-ceramic and zirconia crowns fabricated with a modified porcelain firing. The modified firing of the zirconia porcelain seems to decrease the risk for early ceramic chipping in the molar area, leading to a technical complication rate comparable to that of metal-ceramic crowns. Keywords: clinical trial, all-ceramic, zirconia, crown, chipping, success rate, veneering ceramic, PFM restoration

Purpose: To evaluate the influence of two different tooth preparation forms, two luting space settings and two cement types on the marginal and internal adaptation of all-ceramic crown copings produced using Cerec3^® CAD/CAM system. Materials and Methods: Forty working stone dies were made from two metal master casts (1. Tooth 36: with anatomic occlusal reduction, 2. Tooth 36: with flat occlusal reduction). Forty crown copings were milled using Vita In-Ceram 2000 YZ: 20 with an luting space settings of 0 = 100 µm and 20 with -50 = 50 µm. Copings were cemented using two cements (zinc phosphate cement, P21: Panavia21^®), then embedded and sectioned bucco-lingually and mesio-distally. Widths of marginal and internal gaps were measured using a light microscope at magnification of 40X. Data were submitted to one-way ANOVA, and statistical significance was set at p 0.05. Results: Copings with flat occlusal reduction and luting space settings of 100 µm had a better internal and marginal fit compared with copings with anatomic occlusal reduction and luting space settings of 50 µm, regardless of the cement used. P21 showed a significantly better fit compared with zinc phosphate cement. Conclusion: The presented Cerec3 CAD/CAM system can provide a marginal and internal adaptation which is comparable to that of conventional cast and conventional allceramic crowns. Keywords: all-ceramic copings, luting space setting, internal gap, marginal gap

We are currently developing new software for simultaneous visualisation and analysis of computerized recorded masticatory function and masticatory muscle activity. With the software, motion data recorded using the Jaw Motion Analyser and EMG data on masseter muscle activity can be uploaded in order to evaluate chewing activity immediately proximal to the occlusal surfaces. The software successfully differentiated between jaw opening and closing movements and filtered out muscle activity peaks, which were graphically depicted in the respective movement trajectories. This tracking strategy made it possible to visualize the movement sectors where chewing forces were effective and to estimate the strength of these forces. In the future, this software should improve our ability to analyze and assess the development of chewing forces. Therefore, it could provide a tool for optimal planning of implant-supported or CAD/CAM restorations. Keywords: masseter muscle activity, electromyography, jaw motion, masticatory movements, electronic motion analysis

Objective: Computer-assisted methods were used to evaluate different variants of surgically assisted rapid maxillary expansion (SARME) in terms of bone repositioning, new bone formation in the osteotomy gap, and bone quality before and after surgery. Materials and Methods: Twenty-nine patients (18 male, 11 female) with a mean age of 29 years (16 to 44 years) were included in the study. Surgically assisted rapid maxillary expansion with Le Fort I osteotomy was performed in all patients studied. High-resolution computed tomography (CT) was carried out directly before and 6 to 8 weeks after surgery. After registration of the preoperative CT data on the postoperative data, 3D models were constructed and superimposed. New bone formation in the osteotomy gap was visualized by means of a visualization procedure developed specifically for this purpose. Bone quality was analyzed by dividing the models into different anatomical segments. A qualitative comparison of the data was accomplished using a direct volume rendering procedure with a special transfer function. A quantitative comparison was carried out based on the pre- and postoperative histograms of each region. Results: Maxillary widening was confirmed in all patients by computer-assisted analysis. Four patients exhibited significant maxillary asymmetry after surgery. New bone formation within the osteotomy gap was irregular along the osteotomy lines but often symmetrical on both sides. The more symmetrical the osteotomy, the more symmetrical the new bone formation proved to be. In all but two cases, the postoperative qualitative and quantitative analyses showed a significant decrease in Hounsfield units, particularly in the vestibular bone. Conclusion: The differences in new bone formation in the osteotomy gap suggest that the type of surgical technique and distractor used influence the outcome. Our results indicate that SAME results in a decrease in bone quality, particularly in the vestibular bone. Computer-assisted analysis clearly results in an information gain. Keywords: surgically-assisted rapid maxillary expansion, maxilla, distractor, bone quality, new bone formation, medical visualization, 3D reconstruction, direct volume rendering, transfer function

For the individual dentist, the Ceramic Success Analysis (CSA) is a tried and tested internet-based platform for monitoring the clinical success of all-ceramic restorations. After compiling an insertion protocol and recording the findings from regular clinical follow-up examinations, an analysis follows which culminates in the re-evaluation of the indication and the treatment approach. The evaluations of the 12-year results confirm a high success rate for all-ceramic restorations. Factors which influence the long-term success are: tooth vitality, an indicated crown, the use of a two-bottle dentin adhesive, and the placement of rubber-dam in the adhesive cementation technique. Keywords: CSA, longitudinal study on ceramic restaurations, self-assessment

All-ceramic frameworks for crowns and bridges are now fabricated almost exclusively using CAD/CAM technology. They are usually made of high-strength oxide ceramics, the optical properties of which are esthetically unsatisfactory. Veneers, on the other hand, are manufactured manually. All veneering ceramics, without exception, belong to the mechanically weak class of glass ceramics, whose optical properties closely resemble those of the natural tooth structure. These materials are applied in multiple layers in order to mimic the internal structure of the natural teeth. The goal is to achieve a restoration that harmonizes with the surrounding natural dentition in terms of color, translucency and shape. This must be accomplished in accordance with the normal rules of good practice and in conformity with the anatomical and functional realities. Therefore, the fabrication of a working model and an antagonist model, which are mounted into a more or less complex articulator, is required.

The inexorable march of computers into all areas of dental practice started in the 1980s. In the early years, this technology was limited to accounting procedures that ran under text-based operating systems like MS-DOS without having many other capabilities. However, billing software was still a huge improvement over manual billing, which was the common practice of the day. In those days, it was necessary to fill out patient insurance forms by hand, and a dot matrix printer was used to print full-surface stickon labels, which had to be adhered to the originals of the insurance forms.