International Journal of Computerized Dentistry, 03/2017

Objectives: To prove the biocompatibility of biomaterials applied in biomedical devices, in vitro testing is crucial to render a material fit for medical application. The material of choice for dental implants is commercially pure titanium (cp-Ti), while other materials such as zirconia and polyetheretherketone (PEEK) are considered highly promising due to their functional and esthetic properties. The aim of this study was to determine whether PEEK with defined mean surface roughness and composition could achieve results equal to titanium or zirconia. Materials and methods: Disks measuring 14 mm in diameter and 1 mm in thickness made from cp-Ti, yttria-stabilized zirconia (Y-TZP), and filled PEEK with a smooth surface finish were used for cell culture experiments. Human fetal osteoblasts (hFOB) were cultured in vitro on each material to observe changes after 1, 3, and 7 days regarding cell viability and lactate dehydrogenase (LDH) release. Additionally, mRNA expression of proliferative factors PCNA and Ki67 and cellular adhesion (vinculin mRNA expression and immunofluorescence staining) were analyzed after 3 days in the culture. Results: In hFOB cultures, adhesion and viability were decreased on PEEK platelets, while LDH release remained stable. No significant difference was observed in cp-Ti and Y-TZP when compared to the control. Conclusions: The performance of cp-Ti and Y-TZP was equal to the control in all tests. It seems that highly polished PEEK in this particular composition cannot be recommended for osseointegrated implant applications due to decreased osteoblast attachment. Further investigations are recommended, especially in surface structures optimized for osseointegration. Keywords: biocompatibility, osteoblasts, polyetheretherketone, PEEK, titanium, zirconia

Objectives: Computer-aided technologies can help to minimize clinical complications of zirconia-based restorations such as veneering porcelain fractures. The aim of this study was to evaluate different veneering approaches for zirconia single crowns regarding contact wear, fracture strength, and failure mode. Methods: Six different types of computer-aided design (CAD) crowns were manufactured and conventionally cemented on 10 metal dies each: three groups with a zirconia framework and a CAD/CAM-fabricated veneering cap ("digital veneering system": DVS, CAD-on, Infix CAD), zirconia-based crowns with pressed veneering caps (Infix Press), zirconia framework containing the dentin layer with only the incisal enamel material added (dentin-core), and conventional substructure with powder buildup veneering porcelain (layering technique). All specimens were submitted to artificial aging (120,000 mechanical cycles, 50 N load, 0.7-mm sliding movement, 320 thermocycles). After contact wear was measured with a laser scanning system, fracture resistance and failure mode were examined using a universal testing machine and a scanning electron microscope. Statistical analysis was performed at a significance level of 5%. Results: No statistical difference was revealed regarding the contact wear of the restorations (P = 0.171; ANOVA). No significant difference was found regarding the fracture resistance of the crowns (P = 0.112; ANOVA). Failure analysis revealed three different failure patterns: cohesive veneering fracture, adhesive delamination, and total fracture, with a characteristic distribution between the groups. Significance: All tested specimens survived artificial aging and exhibited clinically acceptable wear resistance and fracture resistance. Digital veneering techniques offer a promising, time- and cost-effective manufacturing process for all-ceramic restorations and may usefully complement the digital workflow. Keywords: CAD/CAM, all-ceramic, chipping, digital veneering, single crown, zirconia

Aim: The aim of this in vivo study was to measure antagonist wear caused by polished monolithic posterior zirconia crowns over a 24-month period using the intraoral digital impression (IDI) technique. Materials and methods: Thirteen zirconia crowns were placed in nine patients. The crowns and adjacent teeth were captured using an intraoral scanner (Lava C.O.S.). The corresponding antagonist teeth and the respective neighboring teeth were also scanned. Scanning was performed immediately after the restoration (baseline) as well as 12 and 24 months after crown placement. Geomagic Qualify software was used to superimpose the follow-up data sets onto the corresponding baseline data set, identify wear sites, and measure maximum vertical height loss in each individual wear site. Overall antagonist wear was then determined as the mean of wear rates measured in all of the individual antagonist units. In addition, wear rates in enamel and ceramic antagonists were analyzed as part of the scope of this study. Results: The maximum mean wear with standard deviation (SD) in the overall sample with a total of nine patients, 13 antagonist units, and 98 evaluable wear sites was 86 ± 23 µm at 12 months, and 103 ± 39 µm at 24 months. The maximum mean wear in the enamel antagonist subgroup was 87 ± 41 µm at 12 months, and 115 ± 71 µm at 24 months; and in the ceramic antagonist subgroup 107 ± 22 µm at 12 months, and 120 ± 27 µm at 24 months. Conclusions: The wear rates determined in this study are comparable to those of existing studies. The IDI technique of wear analysis can be carried out in a practical manner and produces useful results. Keywords: wear, zirconia, monolithic, antagonist, clinical, digital, intraoral scan

Marginal integrity is important for the longevity of a restoration. An increase in the marginal discrepancy after cementation contributes adversely to the longevity of a restoration. In the past, the preferred method to overcome this discrepancy was to create internal space for the cement by using a number of coats of a die-spacing material. In the digital age, however, this method is no longer the only option. Currently, an amount of die spacer is engineered into the computer program and forms part of the milling process. The present study attempted to identify the optimal setting of the Spacer parameter that a) is necessary for the complete cementation of a Cerec milled all-ceramic crown, and b) does not compromise the strength of the crown postcementation. Keywords: cement space, die spacer, CAD/CAM, Cerec, crown seating, crown strength, all-ceramic crown, parameters

Purpose: The purpose of this study was to determine whether there is a significant difference in the fracture strengths of hybrid computer-aided design/computer-aided manufacturing (CAD/CAM) blocks and fiber posts for post and core restorations in both ferrule and nonferrule pulpless mandibular canines. Materials and method: Forty extracted human mandibular canines were divided into ferrule and nonferrule groups and restored with hybrid CAD/CAM blocks using either the CAD/CAM system or fiber posts (control). Thus, there were four subgroups of ten specimens each. A 45-degree oblique load was applied with a crosshead of 0.5 mm/min, and the fracture loads were recorded. The mode of fracture was evaluated using an optical microscope at 3× magnification, and the data were tabulated and statistically analyzed using the Mann-Whitney U test and the t test, respectively, for the existence of significant difference at a 0.05 significance level. Results: No statistically significant difference was found between the fracture strength under oblique loading when using hybrid CAD/CAM blocks and fiber posts in both ferrule and nonferrule groups. The failure mode distribution of the nonferrule group presented no unfavorable failures, whereas failures in the ferrule groups were spread out between the Favorable and Unfavorable groups. Conclusions: The results show that hybrid CAD/CAM blocks can be considered as an alternative restorative system in post and core restorations. Further basic and clinical research should be conducted to support the improvement of this system. Keywords: CAD/CAM, post and core, anatomic posts, digital impression, fracture resistance

The increasing use of dental implants rather than fixed cantilever bridges for standard dental restorations has led to the development of multiple materials in this field. The goal in modern dentistry in recent years has been to achieve results in implantology that match the natural dentition in esthetics and function. Constant efforts have been made to achieve a perfect emergence profile, and to individualize the surrounding periimplant soft tissue. Powder-free digital scanning is now possible, which allows for the computer-assisted design/computer-assisted manufacturing (CAD/CAM) of ready-to-fit customized immediate implant abutments in various appropriate materials. Since lithium disilicate can be used as a hybrid abutment for restorations, many patients today can more easily afford a customized solution. Apart from the esthetic advantages in the transition area of the crown, the microscopic characterization of the emergence profile is also relevant. Numerous research studies have shown that the optimal surface of titanium abutments is neither too rough nor too smooth. Following these studies, various methods have been used to establish the same proven roughness for zirconia and lithium disilicate surfaces. The present study looks at different polishing methods and glaze firing processes. Keywords: surface roughness, dental abutment, lithium disilicate, emergence profile

The objective of this follow-up study was to examine the performance of Cerec 1 inlays and onlays in terms of clinical quality over a mean functional period of 25 years. Out of 200 Cerec 1 inlays and onlays placed consecutively in 108 patients in a private practice between 1989 and early 1991, 141 restorations could be reevaluated in 65 patients after up to 26 years and 10 months. All ceramic inlays and onlays had been generated chairside using the Cerec 1 method, and had been seated adhesively using bonding composite. At follow-up examinations, the restorations were classified based on modified United States Public Health Service (USPHS) criteria. According to the Kaplan-Meier analysis, the success rate of Cerec 1 inlays and onlays dropped to 87.5% after up to 27 years. In 19 patients, a total of 23 failures were found. Of these failures, 78% were caused by either ceramic fractures (65%) or tooth fractures (13%). The reasons for the remaining failures were caries (18%), and endodontic problems (4%). Three-surface restorations had a significantly higher failure risk (P 0.05) than one-, two-, and four-surface restorations, and restorations in premolars presented a lower failure risk than those in molars. The survival probability of 87.5% after up to 27 years of clinical service of Cerec 1 computer-assisted design/computer-assisted manufacturing (CAD/CAM) restorations made of Vita Mark I feldspathic ceramic proved to be highly acceptable in private practice. Keywords: feldspathic ceramic, CAD/CAM, Cerec 1, chairside, survival estimate, long-term results