The effective minimum cement thickness of zinc phosphate cement for luted non‐precious crowns

Abstract

Non-precious metal crowns were prepared for natural teeth which were ground to a taper angle of 5 degrees. The movement of the crowns on teeth during repeated try-on seating was measured with a micrometer. Increasing the applied load from 2 to 10 kg resulted in an average crown movement of 63 micron. For most samples this movement continued when try-on was repeated. Casting irregularities were found to create furrows on some regions of the axial tooth surface during try-on seating. The diameter of the ADA specification consistency disk for zinc phosphate cement was found to depend strongly on the P:L ratio and the ambient temperature. The castings were cemented with zinc phosphate cement of controlled consistency. Cementation with a load of 10 kg gave rise to an average crown elevation of 54 micron and a range of measurements between -8 and 113 micron. The effective minimum cement thickness corresponding to this average was calculated to be 4.7 micron. Small negative values of elevation were attributed to deepening of tooth furrows during cementation. An analysis is given of data from the literature, relevant to the cement flow and irregularities in cement thickness.

The effects of die‐Spacidng on post‐cementation crown elevation and retention

“…This phenomenon has been described as 'uncemented grip' or 'frictional fit' and is a known limiting factor in crown seating 29 but its role in retaining the cast restoration has only been investigated to a limited degree.…”

“…Increased convergence angle also favo u r e d decreased crown elevation in the study of Eames et al 2 Studies have further demonstrated variations in the seating of cast restorations due to the various materials and techniques involved in the impression, die construction and casting procedures. Grajower et al 29 have demonstrated the variability in cement film thickness produced with changes in the powder:liquid ratio and ambient temperature for zinc phosphate cement. A delay in seating following mixing of the cement also has been shown to result in increased seating discrepancies.…”

“…He proposed that providing a cement space may prevent the formation of large agglomerates thus reducing their effectiveness in arresting crown seating and allowing an increased gap for expression of excess cement. Grajower et al 29 stated that contact between internal surface irregularities of the crown and the prepared surface of the tooth may also arrest crown seating and that the provision of a cement space reduces the likelihood of this contact taking place.…”

“…29 Jorgensen 35 described a 'filtration effect' of zinc phosphate cement where approximation of two glass slabs separated by a film of cement was arrested by aggregates of powder. Jorgensen noted also that the viscosity of the cement increased rapidly with time rendering the expression of excess cement increasingly difficult.…”

Avaliação da adaptação marginal de copings metálicos fundidos em ligas de níquel-cromo, níquel-cromo-berílio e em titânio comercialmente puro em função da aplicação de espaçadores

“…Os dados obtidos (µm) foram submetidos à análise estatística (ANOVA) e teste de Tukey (p<0.05). Para a condição material, a liga VB (118,73) não apresentou diferença estatisticamente significante em relação à liga VB II (93,40), sendo que estas apresentaram diferença estatisticamente significante em relação ao 35). Em relação ao fator espaçador, houve diferença estatisticamente significante entre as três condições (G0=177,31; G1=121,51 e G2=81,66).…”