Experimental Study Of The Effects Of A Self-invented Shoulder File On The Marginal Fit Of Co-Cr Alloy Base Crown

Clinically, the marginal fit is an important criterion to juge whether a fixedprosthesis is well made. A margin lack of compactment or too short may bothlead to a higher failure rate for the applied restoration process. In order toachieve a better marginal fit for the prosthesis, scholars are mainly working onimproving the properties of moulding and basal crown material. They concentremore on material researchs. However, the impact of human factors during therestoration process has rarely given much attention or even been ignored. In fact,during the preparatory process of teeth, the instability of human hand makes itimpossible to maintain a constant force and interval, therefore the high-speedrotating diamond leaves several remarkable dents over the shoulder which mayeventually lead to a failed fixed prosthesis in terms of marginal fit. This articleaims at discussing if the method of treating shoulder with the help ofhand-maded tool can improve the marginal fit of Co-Cr alloy base crown.Objective: In this study, two group of Co-Cr alloy base crown are made: one is basedon the the routine procedure; the other is obtained after the application ofself-invented shoulder file. The entire procedure follows strictly therequirements of technical engineer department. Try the two group of Co-Cralloy base crown on, two group of silicon rubber film which indicate themarginal gap before and after are accordingly obtained. A statistical analysis ismade to study the effects of shoulder file on the Co-Cr alloy base crown. Try tounderstand if the method of planing can efficiently improve the marginal fit ofshoulder, which may provide a steady experimental basis for clinicalapplication.Methods:Based on a large number of pre-test, create two kinds of manuel tools(Shoulder File nominated by the author) which could theoretically play a role inpolishing on dentin: one with a rough edge which could polish; the other with asharp blade which could plane. Develp several articles for each type. Comparethe grinding effect of the created tools mentionned above with the tradionnal burby means of the naked eye and under the the stereomicroscope, then usingroughness-detective machine to measure the differences and making statisticalanalysis in order to investigate the validation of the statement that shoulder fileis capable of polishing the dentin.One should file which was made to plane was chosen to be theexperimental object. Prepare6Maxillary Central Incisors for the routine clinicaloperation in order to obtain their base crowns by means of waxing (using both inlay waxand cervical margin wax) and embedded casting, then try them on. Make the silicon rubberfilm of the gap between the base crowns and the toothand cut it in six. Afterwards measure thickness of marginal area of this film which is considered as the marginal gap (controlgroup) through stereo microscope (100×zoom). Take advantage of the new tool to improvethe form of the shoulder and obtain the data concerning about the marginalgap(experimental group) accordingly produced by repeating the same procedures mentionedabove. Statistical analysis which can prove the feasibility of treating shoulder with this newshoulder file was performed.Results:First of all, comparing the polishing effect of tradionnnal bur and theshoulder file, through the naked eye as well as the stereomicroscope observe thatthe mark left by shoulder file is more smooth. The statistical result ofroughness-detective machine shows that the polishing effect of the shoulder fileis as good as the TR-11EF polishing bur. In the experiment on the marginal fit ofCo-Cr alloy base crown, with stereo microscope(100×), observe that the form ofsilicon rubber film of the experimental group is more even and smooth than thatof the control group. The results of the Program SPSS indicate that the thicknessof silicon rubber film of the experimental group is [(33.77±2.16μm] which isobviously inferior to that of control group [(77.52±3.50) μm]. The difference issignificant in terms of statistics（p＜0.01）Conclusion:Based on the principle that sharp blade can plane, shoulder file can alsopolish the dentin and can clinically be applied in the treatment of shoulder. Theobservations by naked eye and under the stereomicroscope both showed that thesurface is more smooth and continuous after treatment. A further experiment onthe marginal fit of Co-Cr alloy base crown proved a remarkable improvement of smoothness of the shoulder after the application of shoulder file. It is expectedto develop a similar instrument for clinical purpose which could facilitate thework of prosthodontics doctors.