In Vitro Investigation of Material Combinations for Meso- and Suprastructures in a Biomimetic Approach to Restore One-Piece Zirconia Implants

The aim of this study was to find a suitable material combination to avoid cement excess in the marginal region of one-piece zirconia implant-supported restorations by means of a hybrid crown consisting of a meso- and a suprastructure. One-piece zirconia implants (n = 120) were embedded in epoxy resin. Microfilled resin composite mesostructures (n = 60), designed as caps, were bonded on the implant abutment with a primer only. A molar crown was constructed and cemented with a resin cement on top of the mesostructure as a suprastructure out of feldspar ceramic (n = 12), lithium-disilicate (n = 24), or zirconia (n = 24). Fracture load (n = 6) and retention force (n = 6) were measured immediately after storage in distilled water at 37 °C for 24 h, as well as after an additional exposure to artificial aging in a chewing simulator and simultaneous thermal cycling. For the measurement of the fracture load, monolithic crowns made of the employed restorative materials and identical in shape to the hybrid crowns served as controls (n = 6 each). Fracture load values for feldspar ceramic and lithium-disilicate hybrid crowns were slightly higher than those for the respective monolithic crowns at baseline and after aging, which was statistically significant only for feldspar crowns after aging. In contrast, fracture load values for zirconia monolithic crowns were higher than those for zirconia hybrid crowns, which was only statistically significant after aging. Artificial aging reduced the fracture load of feldspar and lithium-disilicate crowns both for hybrid and monolithic crowns. The effect was only statistically significant for lithium disilicate hybrid crowns. The fracture load for hybrid and monolithic zirconia crowns was increased by artificial aging without reaching statistical significance. The retention force of lithium-disilicate and zirconia hybrid crowns was not affected by artificial aging. Taking into account retention force and fracture load, lithium-disilicate hybrid crowns showed promising results.

Measuring perception of mental well-being in patients under isolation precautions: a prospective comparative study

OBJECTIVES

Isolation precautions (IP) are applied to prevent transmission of pathogens in healthcare settings. Potential negative health outcomes experienced by patients have been previously described but results remain conflicting. We aimed at evaluating the psychological impact of IP in adult patients in isolation using a novel psychological assessment tool.

STUDY DESIGN

Prospective matched cohort study.

SETTING

Tertiary care centre in Switzerland.

PARTICIPANTS

Hospitalised patients under IP and non-isolated patients were matched by ward, age and illness severity.

OUTCOME MEASURES

We measured surrogates of mental and social well-being by using the Pictorial Representation of Illness and Self Measure (PRISM) instrument once during hospitalisation. PRISM is a visual psychometric instrument that has been validated as a quantitative measure of suffering. Smaller distance in self-to-illness separation (SIS) signifies higher importance for a patient.

RESULTS

156 patients agreed to participate of which 63 were under IP and 93 were matched controls. Median (IQR) duration of isolation was 5 days (2-10). The median SIS (IQR) for perceived inferior nurses' care was 22.8 (18.5-24.3) and 23.8 (23.3-25.5) for isolated and non-isolated patients, respectively (p<0.001). Similarly, median SIS (IQR) was significantly smaller in isolated than non-isolated patients for avoidance by visitors with 17.5 (7.7-22.0) and 22.2 (21.8-22.6), for loneliness with 7.5 (3.6-16.0) and 18 (10.2-21.6) and for feeling impure with 19 (17.0-21.5) and 21.5 (18.9-22.1), respectively (all p values<0.05).

CONCLUSIONS

IP to prevent transmission of pathogens may negatively impact mental and social well-being. Measures to alleviate adverse effects of IP should be taken routinely.

Loading capacity of CAD/CAM-fabricated anterior feldspathic ceramic crowns bonded to one-piece zirconia implants with different cements

OBJECTIVE

This study evaluated the loading capacity of CAD/CAM-fabricated anterior feldspathic ceramic crowns bonded to one-piece zirconia implants with different cements.

MATERIAL AND METHODS

Fifty one-piece zirconia implants were embedded in epoxy resin. The abutment aspect of one implant was optically scanned and a standardized upper canine was designed with CAD-software. Fifty feldspathic ceramic crowns were milled, polished, and mounted on the implants either without any cement, with a temporary cement or with three different composite resin cements after surface pretreatment as recommended by the manufacturers (n = 10). After storage in distilled water at 37°C for 24 hr, specimens were loaded until fracture on the palatal surface of the crown at an angle of 45° to the long axis of the implant and loads until fracture were detected and compared. Compressive strength of the investigated cement materials was determined. Statistical analyses were done with One-way ANOVA followed by post hoc Fisher LSD test (α = 0.05).

RESULTS

The cements revealed significantly different compressive strength values (temporary cement: 37.1 ± 7.0 MPa; composite resin cements: 185.8 ± 21.3, 277.9 ± 22.1, and 389.0 ± 13.6 MPa, respectively). Load-at-fracture values had an overall mean value of 237.1 ± 58.2 N with no significant difference among the composite resin cements (p > 0.05). Fracture load values with the temporary cement or without cement were significantly lower (p < 0.002).

CONCLUSIONS

CAD/CAM-fabricated anterior feldspathic ceramic crowns bonded to one-piece zirconia implants provide sufficient resistance to intraoral forces.

Organic Pillared Clays

Commonly used organophilic clays are modified by alkylammonium cations which hold apart the aluminosilicate layers permanently. The cations fill the interlayer space and are contemplated as flexible pillars, resulting from the mobility of the alkyl chains. Therefore, the interlayer distance varies depending on the layer charge and on the alkyl chain length. Contrary to these cations, rigid pillaring cations guarantee a constant interlayer distance without occupying the interlayer by themselves and show special adsorption properties such as hydrophilic behavior contrary to the generally hydrophobic ones. Smectites were modified by flexible organic cations, e.g., dimethyldioctadecylammonium, and by rigid ones, e.g., tetraphenylphosphonium. Their adsorption properties are compared. Our investigations showed improved adsorption properties for rigid organic cations on smectites using 2-chlorophenol as pollutant. Best adsorption results are achieved using pillaring cations in combination with low charged smectites, especially at low pollutant concentrations. The properties of organic modified smectites are discussed by a pollution intercalation model. The intercalation process of an organic pollutant into an organic modified smectite is expressed by a two-step Born-Haber cycle process: (i) the formation of an adsorbing position by layer expansion and (ii) the occupation of the adsorbing position by the pollutant. The first step of the formation of the adsorbing position is an endothermal transition state which lowers the total intercalation energy and therefore worsens the adsorption behavior. Thus, an already expanded organophilic smectite will show improved adsorption behavior. The formed adsorbing position state on organic modified smectites is comparable to the pillared state of inorganic pillared clays. Copyright 2001 Academic Press.