Experimental And Clinical Studies On Compressive Strength Of Prefabricated Inlay

Objective:As we all known, dental caries is one of the most common oral diseases, whose incidence ranks first in oral clinic. Dental caries is a chronic, progressive and destructive disease of tooth hard tissue caused primarily by bacteria. The characteristic is defect or absence of tooth form and function. Thus, the goal of treatment is to terminate its process, to protect dental pulp, to rehabilitate tooth form, function and aesthetic, and to maintain normal physiological relationships with adjacent tissues. There are two leading techniques in curing molar occlusal and proximal occlusal cavities: one is medical plugging whose filling materials includes silver amalgam, light cured composite resin and glass ionomer; the other is fixed prosthesis called inlay, such as alloy inlay, composite resin inlay and porcelain inlay. Both of the two techniques have advantages and disadvantages, meanwhile both are affected by material' s properties. Prepared cavity should have favorable retention form andresistance form. Generally speaking, plugging doesn't do well in rehabilitating tooth form and function, and that has something to do with the physical properties of materials. On the contrary, inlay is able to recover favorable form and masticatory function, but it has poor retention form. This study aims to explore a more favorable treatment called prefabricated inlay, which incorporates the advantages of the above two techniques and are expected to be used in clinic.Methods:1. 80 recently extracted human maxillary first molars are selected, without caries, cracking or any dental detect, and then are fixed in formalin for four hours. After scaling the calculus and debris, all the teeth are prepared in normal saline. 60 of the teeth were divided into five groups and 12 each, all of which are treated with root canal therapy. Then standardized class I and II cavities were prepared separately by the same dentist. The principle of cavity preparation is the same as that of silver amalgam filling.2. Make prefabricated inlay: Standardized class I and II cavities were prepared separately in the 20 surplus teeth. The undercut of cavities were filled with zinc oxide and then burnished by diamond burr. Make sure that the floor is plane and the walls are straight, so the wax inlay could be easily taken out and prefabricated inlay was finally finished. The tissue surfaces of alloy inlays were treated by aluminum oxidesandblasting. Different sizes of prefabricated inlays can be made according to the sizes of cavities. Before plugging, choose appropriate prefabricated inlay. If the inlay suited the cavity exactly, it only needed mild adjustment. Grind off zinc oxide in the cavity, try-in the inlay and adjust it, then put it in the right position with glass ionomer cement. However, if the inlay didn't suit the cavity well, some luting agent should be smeared on the walls of cavity, then light cured composite resin should be filled soon, and at the same time, the selected prefabricated inlay was pressed in. Wipe off the redundant resin. So after solidification of resin, it had cemented the prefabricated inlay in the sandblasting surface.3. Five groups of teeth were filled separately with glass ionomer, light cured composite resin, silver amalgam, prefabricated Ni-Cr alloy inlays and prefabricated Co-Cr inlays.4. The compressive strength of every group was tested and compared.5. Clinical trial: 88 decayed teeth were treated with root canal therapy and prefabricated Co-Cr inlays. The clinical effects were observed.Results:The compressive strength of prefabricated inlay groups(Ni-Cr and Co-Cr) was significantly higher than the other groups(glass ionomer,light cured composite, silver amalgam). Between the two inlay groups, prefabricated Co-Cr inlay group was higher than prefabricated Ni-Cr inlay group. Both of the two groups had lower missing ratio.Conclusion:This study used prefabricated inlays to fill the dental cavity. Alloy inlay has higher compressive strength and favorable integral properties. It hardly shrinks, distorts, breaks or falls off. Prefabricated inlay is able to recover dental form and proximal contour, and it also shortens the consulting interval. Furthermore, it has a reasonable price. Therefore, prefabricated inlay is a valuable treatment and can be generalized in clinic.