The Comparison Of The Denture Base Fabricated By The Injection-molded Technique And The Conventional Compression Technique

Acrylic resin polymers were introduced as a denture base material in1937,Today, the majority of the denture bases are heat-cured PMMA. Compressionmolding is a conventional technique described in textbooks on complete andpartial dentures. But the technique is time-consuming. Furthermore, Manyfactors in the laboratory procedures can lead to deformation of the denture baseduring the construction of the complete dentures, such as, the proportion of thepowder and the monomer which composed the PMMA is not well controlled,the uneven pressure while compressing, the speed and the time is not wellretained and so on. In the1950s, Authors made a new procedure for rapidprocessing of PMMA resin with an automatic pressure cooker and used in theclinic. This new procedure can shorten laboratory working time, but associatedinstrument should be used that was very heavy. And the dimensional stability,the residual monomer of the denture base was not improved made by theprocedure, which limited the promotion of the rapid processing procedure.Attempts to overcome the problems associated with compression moldinghave resulted in the development of the injection system. A new injection system can shorten more laboratory working time. The plaster model is not destroyedafter the completion of the denture base. The dentist can check the incisal pinopening, dimensional accuracy and the adaptation of the denture base. Becauseof these advantages of the injection system, the injection resins become moreand more popular.As a new technique, the dimensional accuracy of the denture base havebeen carried out both in home and abroad. However, emphasis has been focusedon the adaptation, the residual monomer of the denture base rationally. Recentreport have been shown the acylic resin made by injection system have asignificantly little bond strength of the acylic resin denture teeth. But theVertex-dental company has invented a new product--Acrybond to strength thebond of the acylic resin and the acylic resin denture teeth. It is not well studiedweather the Acrybond can improve the bond strength or not.Objective: The purpose of this in vitro study was to contrast the adaptation,the residual monomer and the bond strength of the denture base fabricated bytwo different techniques: the injection-molded technique and the conventionalcompression technique. It can provide experimentally theoretical support for theclinic.Methods:1. The adaptation of the denture base fabricated by two different techniques:the injection-molded technique and the conventional compression technique:Two test groups, each with10maxillary denture bases. Group1was fabricatedby injection-molded technique and Group2was fabricated by the conventionalcompression technique. The gap between the stone and the denture base wasmeasured with a stereoscopic microscope at five referential positions in eachsection. The data were submitted to t-test.2. The residual monomer of the denture base fabricated by two differenttechniques: the injection-molded technique and the conventional compressiontechnique:20test specimens were fabricated by different techniques. The residual monomer content was determined using high-performance liquidchromatography (HPLC) and expressed as a percentage of residual monomer.The data were submitted to t-test.3. The bond strength of the denture base fabricated by two differenttechniques: the injection-molded technique and the conventional compressiontechnique:30test specimens were fabricated by different techniques and dividedinto3groups. Group1was fabricated by the injection-molded techniquewithout Acrybond. Group2was fabricated by the injection-molded techniquewith Acrybond. Group3was fabricated by the conventional compressiontechnique. The shear bond strength was examined and the data were submittedto LSD-t testResults:1. The adaptation of the injection-molded ones was better than thecompression ones (P<0.05). The gap between the stone and theinjection-molded resin denture base at the five referential positions respectivelywas: A(0.1258±0.0199)mm; B(0.0842±0.0255)mm,; C(0.2315±0.0778)mm;D(0.1251±0.0333)mm; E (0.1475±0.0251)mm. And the gap between the stoneand the conventional compression ones was: A(0.2688±0.0819)mm;B(0.1614±0.0520)mm; C(0.4243±0.0595)mm; D(0.1780±0.0451)mm; D(0.2680±0.0598)mm.2. Comparing the residual monomer content of the specimens, statisticaldifferences were found (P<0.05). The residual monomer of the injection-moldedresin was more than the compression one. Group1was:(0.5235±0.1212)%.Group2was:(0.0610±0.0084)%.3. The shear bond strength of the injection-molded resins without theAcrybond was (11.499±1.147) Mpa.The shear bond strength of theinjection-molded resins with the Acrybond was (16.344±3.095) Mpa and theshear bond strength of conventional compression resins was (14.484±1.826)Mpa. Comparing the shear bond strength of the Group1and the others, statistical differences were found (P<0.05). But comparing the Group2and theGroup3, statistical differences were mot found (P>0.05).Conclusion:The findings indicate that resin fabricated by the injection-molded has abetter adaptation than the compression ones, but the residual monomer contentwas more than the compression one. The adhesive bond strength of theinjection-molded could be improved with using Acrybond. The injection-moldedresin can be used and promoted in the clinic.