Cemented versus screw-retained posterior implant-supported single crowns: A 24-month randomized controlled clinical trial.

OBJECTIVES: To compare the incidence of biological and technical complications of cemented and screw-retained monolithic lithium-disilicate implant-supported posterior single crowns. MATERIAL AND METHODS: Forty-one subjects with a total of 56 implants received randomly allocated 28 cemented and 28 screw-retained crowns. In the screw-retained group, monolithic lithium-disilicate restorations were luted to titanium bases extraorally. In the cemented group, monolithic lithium-disilicate crowns were cemented on individualized titanium abutments intraorally. All restorations were examined according to modified FDI criteria within 2 weeks of inserting the crowns (baseline) and after 12 (n = 46) and 24 (n = 43) months. Bone loss was evaluated by standardized radiographs at baseline and 12 months. RESULTS: After 12 months, the incidence of mucositis (positive bleeding on probing) was 14.2% (screw-retained) and 17.9% (cement-retained). The gingival and plaque index and a mean marginal bone loss between 0.03-0.15 mm showed no significant difference between the groups. In the cemented group, cement residues were detected at baseline at two restorations (6.9%) by radiographic examination. A complete digital workflow was realized in most cases (85.7%). At 24 months, no restoration had failed, and no chipping of the ceramic had occurred. In the screw-retained group, screw loosening occurred in one implant. In both groups, there was obvious deterioration in the quality of 32% of the occlusal and of 18% of the proximal contact points. CONCLUSIONS: The type of retention mode of monolithic implant-retained lithium-disilicate posterior crowns had no influence on the biological and technical complication rate.

Monolithic restorations on customized titanium abutments - a cast-free approach without the necessity of gingiva management for impression taking.

The present application report describes a cast-free and chairside workflow that enables the manufacturing of monolithic restorations on custom-made abutments without damaging the periimplant soft tissue for impression taking. An easily achievable checklist for the individualization of standard abutments is presented so that the shape of the abutment is compatible with especially developed software after optical impressions. The principle of the method contains an extraoral impression of the finish line of the abutment and an intraoral impression that indicates the abutment position in relation to the adjacent teeth. The software needed for the semi-automated registration of the intra- and extraoral impression operates with .stl data and can be provided by the corresponding author on request.

A chairside concept for increasing the vertical dimension of occlusion in the maxilla and mandible.

An entirely digital concept has previously been proposed for the reconstruction of the occlusal plane in the case of wear-induced loss of the vertical dimension of occlusion (VDO). The concept, however, calls for a face scan. Since this technology is less frequently available than a facebow, the concept discussed in this article proposes a combination of analog and digital techniques. It takes into account the problem of redefining the occlusal plane in the case of occlusal alteration, and tries to avoid a situation where the chairside digital design of the occlusal surfaces is performed without any anatomical references. Such a situation poses a significant risk if the treatment indication for bite elevation exists in both the maxilla and the mandible.

Antagonist wear by polished zirconia crowns.

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.

Optical profilometry versus intraoral (handheld) scanning.

AIM: The aim of this study was to evaluate the difference in maximum height loss values obtained from datasets based on optical profilometry and intraoral scanning. Additionally, two analysis applications were tested with respect to their correspondence. MATERIALS AND METHODS: To obtain baseline data, the occlusal surface of a metal phantom tooth was scanned by optical profilometry [WLP] and an intraoral scanner [IOS]. Then, wear was simulated at two locations of the tooth, three times each ([wear1], [wear2], and [wear3]), and the surface was captured after each status of wear, applying [WLP] and [IOS]. The maximum vertical height loss was evaluated by comparing the 3D datasets of [WLP] and [IOS] at [wear1], [wear2], and [wear3] with the baseline data of [WLP] and [IOS], respectively. For this purpose, two commercially available applications, Geomagic Qualify and Oracheck, were used. RESULTS: Apart from one outlier of 16% difference between the data obtained from [WLP] and [IOS], the maximum difference was 12.6%, which was equal to a metrical value of 15 µm. For the corresponding values, which were calculated with Geomagic Qualify and Oracheck at identical wear facets, maximum differences between +7% and -6.7% were obtained. CONCLUSIONS: According to this in vitro study, the wear measurement on the basis of [IOS] seems to be a cost-effective, quick, and easily applicable tool for clinical screening purposes, with an acceptable reliability. With respect to the minor variations between each other, the Geomagic Qualify and Oracheck measurement applications are equivalent.

The face scan as a means for the visualization of complex prosthetic reconstructions.

The face scan can serve as a means for the visualization of planes relevant for extensive prosthetic reconstructions. The key prerequisite is the availability of data in stl format for further processing in different software programs. The method is described in this article by a patient case.