Comparative Evaluation of Metal-ceramic Bond Strengths of Nickel Chromium and Cobalt Chromium Alloys on Repeated Castings: An In vitro Study.
BACKGROUND
Recasting the base metal alloys is done as a routine procedure in the dental laboratories whenever there is casting failure or to decrease the unit cost of a fixed partial denture. However, this procedure may affect the metal ceramic bond. Furthermore, it is unclear, as to which test closely predicts the bond strength of metal-ceramic interface. The aim was to compare the bond strength of nickel chromium (Ni-Cr) and cobalt chromium (Co-Cr) alloys with dental ceramic on repeated castings using shear bond test with a custom made apparatus.


METHODS
Sixty metal ceramic samples were prepared using Wiron 99 and Wirobond C, respectively. Three subgroups were prepared for each of the groups. The first subgroup was prepared by casting 100% fresh alloy. The second and third subgroups were prepared by adding 50% of fresh alloy and the remnants of the previous cast alloy. The bond load (N) between alloy and dental porcelain was evaluated using universal testing machine using a crosshead speed of 1 mm/min, which had a 2500-kgf load cell. Mean values were compared using oneway analysis of variance with post-hoc Tukey's test and Student's t-test.


RESULTS
The mean shear bond load of A0 (842.10N) was significantly higher than the load of A1 (645.50N) and A2 (506.28N). The mean shear bond load of B0 (645.57N) was significantly higher than the load of B1 (457.35N) and B2 (389.30N).


CONCLUSIONS
Significant reduction in the bond strength was observed with the addition of the first recast alloy (A1 and B1) compared with the addition of second recast alloy (A2 and B2). Ni-Cr alloys (664.63N) showed higher bond strengths compared to that of Co-Cr alloys (497.41N). The addition of previously used base metal dental alloy for fabricating metal ceramic restorations is not recommended.
Head, Department of Prosthodontics and Crown & Bridge, Drs. Sudha & Nageswara Rao Siddhartha Institute of Dental Sciences, Chinaoutapalli, Gannavarm, Andhra Pradesh, India.
Kaleswara Rao
KR
Atluri
Post Graduate, Department of Prosthodontics and Crown & Bridge, St. Joseph Dental College, Eluru, Andhra Pradesh, India.
Tapan Teja
TT
Vallabhaneni
Senior Lecturer, Department of Prosthodontics and Crown & Bridge, Drs. Sudha & Nageswara Rao Siddhartha Institute of Dental Sciences, Chinaoutapalli, Gannavarm, Andhra Pradesh, India.
Durga Prasad
DP
Tadi
Senior Lecturer, Department of Prosthodontics and Crown & Bridge, Drs. Sudha & Nageswara Rao Siddhartha Institute of Dental Sciences, Chinaoutapalli, Gannavarm, Andhra Pradesh, India.
Sriharsha Babu
SB
Vadapalli
Reader, Department of Prosthodontics and Crown & Bridge, Drs. Sudha & Nageswara Rao Siddhartha Institute of Dental Sciences, Chinaoutapalli, Gannavarm, Andhra Pradesh, India.
Sunil Chandra
SC
Tripuraneni
Reader, Department of Prosthodontics and Crown & Bridge, Drs. Sudha & Nageswara Rao Siddhartha Institute of Dental Sciences, Chinaoutapalli, Gannavarm, Andhra Pradesh, India.
Premalatha
P
Averneni
Cobalt chromium alloys; custom made apparatus; metal-ceramic bond; nickel chromium alloys; recasting