Zinc oxide phosphate cement (Harvard)

Indications

Powder: approx. 80% zinc oxide, 10% magnesium oxide & additives for firmness & oral stability
Liquid: phosphoric acid, water, ion additives (e.g. zinc, reduce reaction speed)
The surface of the alkaline powder is dissolved through the acidity of the liquid
The reaction is exothermic (heat is generated)

good mechanical properties
offers good insolation against chemical, thermal, bacterial influences (underfilling)
easy to process & affordable
easy removal of excess cement because there is no chemical connection to the tooth
quite thin, which enables a good fit of the restoration

when setting, pH drops to 3.5 (MILLER 1997) ², which can lead to an acid shock for pulp, which is why pulp protection is recommended; pH is only neutral again after 48 hours
Dentures stick to the abutment tooth only through physical wedging effect, which is why a preparation is smoothed but not polished³ (AYAD et al. 1997)
relatively soluble in the oral environment

Powder & liquid are mixed in portions and with light pressure in the appropriate ratio
Setting time up to 8 min
Reseal powder & liquid immediately as liquid pulls water & powder can accumulate with CO2, which makes the cement porous
longer setting time by mixing on a cooled glass plate (Voß and MEINERS 1989).
shorter processing and setting time
- high ambient temperature
- quick powder addition
Powder-rich mixtures give the best results, since the oral resistance increases with the amount of powder.

Breustedt A: Lehrmaterialien für das Selbststudium auf dem Gebiet der stomatologischen Werkstoffkunde, Humbold-Universität Berlin, 1964.
Miller M: Befestigungszemente - Indikation und Alternativen. Phillip Journal 14 (1997) 385-386
Ayad MF, Rosenstiel SF, Salama M: Influence of tooth surface roughness and type of cement on retention of complete cast crowns. J Prosthet Dent 77 (1997) 116-121.
Voß R, Meiners H: Fortschritte der Zahnärztlichen Prothetik und Werkstoffkunde, Band 4, Hanserverlag, 1989, 394- 408.