Efficacy of Co-Cr-Mo UCLA abutment for internal tapered implant

Abstract

Introduction & Purpose: There are various abutment materials for the dental implant restoration. Although gold alloy has been the choice of material, titanium and zirconia has been used widely for abutment materials of cement type restorations due to substantial gold price increase. For screw type restorations, plastic abutment that can be cast with Ni-Cr or Co-Cr alloy has been introduced. However, casting procedure might cause roughness and irregularities that can influence the stability of restoration. Recently, many implant companies have brought out premachined UCLA abutment with Co-Cr-Mo alloy on the market. Co-Cr-Mo alloy has been used in orthopedic implant for a long time due to excellent biocompatibility. Nevertheless casting and firing procedure for fabricating the porcelain fused metal crown can change the properties of Co-Cr-Mo alloy. To date there have been limited studies on the Co-Cr-Mo UCLA abutment (CCM abutment). The purpose of present study is to evaluate the efficacy of CCM abutment by investigating the surface change and surface roughness of abutment after casting and firing procedure for porcelain fused crown fabrication and by examining the removal torque value and wear pattern on the interface between abutment and fixture after functional loading by chewing simulator.Materials & Methods: I. Examination of abutment surface after casting & firing procedure: Six gold abutments and six CCM abutments were used. Three of six gold UCLA abutments were untreated (Group A) and the remaining three were cast with type III gold (Group B). Three of six CCM abutments were untreated (Group C) and the remaining three were cast with Ni-Cr alloy (Group D). Cast abutments have undergone porcelain firing cycle and bead blasting (CCM Only). The SEM photograph was taken to examine the surface change and surface roughness value of Ra was measured. II. Analysis of removal torque value and wear pattern after chewing simulation. Sixteen internal tapered implant fixtures were divided into 2 groups (CCM and gold group). Screw-retained prostheses were made using CCM abutment and gold UCLA abutment and they were connected to implant fixture to 30 Ncm torque. Thermocyclic functional loading of 5 kg was applied in wet condition by chewing simulator. A target of 1.0 x 106 cycles was defined. After cyclic loading, removal torque values were recorded. Interface between implant fixture and abutment was evaluated by scanning electronic microscopy (SEM).Results: After casting procedure, irregularities or deformation was not found on all specimens. Mean surface roughness value Ra for groups A, B, C, D were 0.119 ㎛, 0.320 ㎛, 0.094 ㎛, and 0.212 ㎛ respectively. After thermocyclic functional loading, mean removal torque value of gold group and CCM group were 14.88 ± 3.66 Ncm and 14.66 ± 3.58 Ncm respectively. In SEM analysis, remarkable wear patterns were observed at the interface of abutment in gold group, but there were no remarkable wear patterns at the interface of fixture in gold group and at the interface of fixture and abutment in CCM group.Conclusion: 1. Surface roughness value of CCM group after firing and bead blasting procedure was smaller than that of gold group after firing procedure. 2. After chewing simulation, there was no statistically significant difference in removal torque value between both groups. 3. On SEM photographs, wear patterns were observed only at the interface of abutment in gold group. Based on limited present study, CCM abutment can be alternative to gold abutment for internal tapered implant. However, consideration on biological aspect and long-term clinical study is needed in the future