Having successfully negotiated the planning, preparation, impression and prescription of your crown, the cementation stage represents the culmination of all your efforts. This stage is not difficult, but a successful outcome needs as much care as the preceding stages. Once a restoration is cemented there is no scope for modification or repeat You have to get it right first time. Decemented crowns often have thick layers of residual cement suggesting problems with either initial seating or cement handling. When the fate of restorations costing hundreds of pounds depends on correct proportioning of cements and the quality of the mix, the value of a well-trained and experienced dental nurse is easy to see. Both dentist and nurse need a working knowledge of the materials they are handling.

Crowns and other extra-coronal restorations: try-in and cementation of crowns.

The relationship between metallic cast crowns and tensile strength according to cement types submitted to thermocycling was studied Seventy-two metallic crowns were cast with Verabond II Ni-Cr alloy and cemented in standardized preparations with 10o tapering Three types of finishing line (45-degree chamfered, 20-degree bevel shoulder and right shoulder) were made with diamond burs on bovine teeth Twenty-four metallic crowns in each group were randomly subdivided into three subgroups of 8 samples each according to the cement used: SS White zinc phosphate cement, Vitremer resin-modified glass ionomer cement, and Rely X resin cement and were submitted to thermocycling Retention was evaluated according to tensile load required to displace the metallic cast crowns from tooth preparations with an Instron testing machine ANOVA and Tukey's test showed a statistically significant difference among luting materials, with greater results for Rely X resin cement (249 kgf) followed by SS White zinc phosphate cement (133 kgf) and Vitremer resin-modified glass ionomer cement (101 kgf) The finishing line types did not influence the tensile resistance of the crowns fixed with the three cements Increased tensile resistance of metallic crowns fixed on bovine teeth was obtained with resin cement, independent of the finishing line types

/pdf/effect-of-cement-types-on-the-tensile-strength-of-metallic-4o9cczw3pi.pdf

Effect of cement types on the tensile strength of metallic crowns submitted to thermocycling

Der Langzeiterfolg einer prothetischen Versorgung ist von verschiedenen Faktoren abhangig. Die Grunde fur Misserfolge sind sehr unterschiedlich und reichen von Materialermudungen bis hin zu Verlusten durch Zementierfehler. Retentionsverlust ist eine haufige Komplikation bei festsitzenden Restaurationen (Hoffman, 2001; De Backer, 2006), wobei es die Aufgabe des Befestigungszementes ist, eine gute Retention zwischen prapariertem Zahn und Restauration herzustellen (Rosenstiel, 1998).
Ziel dieser Arbeit war es, festzustellen, ob und inwieweit die mechanischen Eigenschaften von Polycarboxylatzementen auf Abweichungen vom vorgeschriebenen Anmischverhaltnis reagieren. Dazu werden drei Vertreter dieser Klasse (Durelon®, Aqualox® und Carboco®) getestet.
Obwohl allgemein bekannt ist, dass sich durch Fehler wahrend des Mischungsvorganges die Materialeigenschaften der Zemente verschlechtern, gibt es bislang nur wenige Untersuchungen, die sich mit diesem Thema befassen. Nach Durchfuhrung dieser Studie lasst sich sagen, dass Abweichungen vom vorgeschriebenen Mischungsverhaltnis bei den getesteten Zementen Verschlechterung der mechanischen Eigenschaften mit sich bringen konnen. Das Ausmas der Veranderungen ist vom Zement abhangig.
Das Verschleisverhalten wurde mit Hilfe des Drei-Medien-Abrasionsversuchs untersucht. Der zeitliche Aspekt der Verschleisdaten wurde durch eine Datenerhebung nach 15.000, 20.000 und 50.000 Belastungszyklen berucksichtigt.
Um Veranderungen bezuglich der Harte festzustellen wurde die Harteprufung nach Vickers durchgefuhrt.
Des Weiteren wurde thermische Analyseverfahren mit Hilfe der DTA durchgefuhrt, mit der die Einblicke in der Aushartung der Zemente gewonnen werden konnten. Grundsatzlich wurde erwartet, dass mit steigendem Pulveranteil die mechanischen Eigenschaften der Carboxylatzemente steigen.
Beim Drei-Medien-Abrasionsversuch stieg die Abnutzung von allen untersuchten Zementen mit zunehmendem Flussigkeitsgehalt. Bei Aqualox® wurde dies am grosten ausgepragt.
Bei Vickers Harteprufverfahren wurde ebenfalls festgestellt, dass mit hoherem Pulveranteil die Werte steigen. Auserdem lasst sich feststellen, dass eine Erhohung des Flussigkeitsanteils bei Aqualox® und Carboco® starkere Auswirkungen bezuglich der Vickers Harte hatte, als eine Erniedrigung. Bei Durelon® wurde ganz Gegenteil festgestellt: Die Erhohung des Pulversanteils starkere Auswirkungen aufwies, als eine Erniedrigung. In diesem Verhalten ist Durelon® dem Harvard® Zement ahnlich (Trempler, 2008). Bezuglich Anmischen von Aqualox® mit dem Leitungs- bzw. destilliertem Wasser konnte kein Unterschied festgestellt werden.
Durch die DTA wurde bestatigt, dass mit dem erhohten Flussigkeitsgehalt die Proben deutlich groseren Enthalpieunterschied zeigten.
Zusammenfassend lasst sich sagen, dass durch Abweichungen von den vorgeschriebenen Mischungsverhaltnissen bei den getesteten Carboxylatzementen Verschlechterung bezuglich der mechanischen Eigenschaften auftereten konnen. Um letztlich jedoch eine eindeutige Aussage daruber treffen zu konnen, ab wann und inwieweit sich in der zahnarztlichen Praxis Mischungsfehler beim Zementieren klinisch negativ auswirken, ware es empfehlenswert, weitere Studien anzustellen. Moglich ware es eine im Kausimulator durchgefuhrte Untersuchung der Brucheigenschaften von Kronen, die mit korrekten und fehlerhaften Mischungsverhaltnis zementiert waren, nach funfjahriger Belastungszeit.

In vitro Untersuchung des Einflusses von Mischungsabweichungen auf die physikalischen Eigenschaften von Polycarboxylatzementen

The aim of this study was to evaluate the tensile bonding strengths of Fleck’s® zinc phosphate cement, Nexus™ RMGI (resin-modified glass ionomer) luting cement, and RelyX™ Ultimate adhesive resin cement on metallic crowns after thermocycling. Methods: Thirty extracted mandibular first molars with minimal caries and restoration were prepared to receive full metal crowns. The teeth were divided into 3 groups (n=10 each) based on the cement used. The cementation procedures were done following the manufacturers’ instructions for all the specimens, and the teeth were stored for 72 hours at room temperature. The prepared teeth with the cemented crowns were immersed in the thermocycling unit for 48 hours; then, the tensile bonding strength was measured using an Instron testing machine. A one-way analysis of variance was used to test for differences among the three groups at a P-value ≤ 0.05. Results: There was a significant difference (P=0.000) between the groups. The RelyX™ Ultimate cement had the strongest retentive force, and detachment occurred at a tensile force of 401.5 N. The Nexus™ RMGI cement had the lowest retentive effect and detachment occurred at an average tensile force of 133.7 N. The retentive strength of the Fleck’s® cement was in the middle and detachment occurred at 244.5 N. Conclusion: Within the study limitations, the RelyX™ Ultimate cement was the most retentive cement for the metallic crowns.

/pdf/retentive-strengths-of-three-different-commercial-luting-24e0z5x5tx.pdf

Retentive Strengths of Three Different Commercial Luting Cements on Metallic Substrate: An In Vitro Study

Objectives:
To compare the finger pressure applied by dentists during cementation and to examine the effect of gender and time of day on finger pressure.

/pdf/effects-of-finger-pressure-applied-by-dentists-during-tn78etfr4u.pdf

Effects of Finger Pressure Applied By Dentists during Cementation of All-Ceramic Crowns

Summary

The effect of three different powder/liquid ratios of one zinc phosphate cement on the early retention of a standard crown on metal and tooth dies was investigated. Two different seating pressures were evaluated. The results indicate that the effect of variation in the powder/liquid was not significant. The part played by the seating force was significant, the higher seating force resulting in a greater force being required for displacement after 1h. Greater forces of removal were required when tooth dies were used.

The effect of seating pressure and powder/liquid ratio of zinc phosphate cement on the retention of crowns.

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The effect of seating pressure and powder/liquid ratio of zinc phosphate cement on the retention of crowns.