Effects Of Luting Agent And Abutment Height On Bonding Performance Of Implant-coping Interface

Background:Many dental practitioners and patients consider cement retention as a better option in implant-supported prostheses because of the significant advantages of passive fitness, optimal occlusion, esthetics, and stress distribution to the prosthetic components and bone-implant interface. Implant abutments make connections between the implants in bone and the superstructures in oral environment with emergence profiles as natural teeth. Titanium has been widely used in the fields of implant dentistry because of its favorable biocompatibility, high resistance to corrosion, low density, and light weight. It is also one of the best materials for Implant abutments.Factors influencing the retention of implant prostheses include geometry of abutment (height, taper, diameter etc.), abutment surface roughness, luting agent and clinical cementation techniques. Among them surface roughness and luting agents are more controllable clinically. The present study firstly evaluates the adhesion of different luting cements to titanium in combination with surface conditioning methods; secondly compares the tensile bond strengths of different luting agents cementing restorations to short abutments with the apllicaton of compressive cyclic loading. This study provides clinical guides for the impant-supported cement-retained restoration.Part I:The effect of four luting cements on shear bonding strength to basic metalsObjective:To compare shear bond strengths and adhesion failure modes of four cements between titanium and cobalt-chromium alloy.Methods:Eighty discs with thickness in 3mm cutting by diameter of 5mm titanium rod paired with eighty cobalt-chromium alloy rod. Their bond surfaces were smoothed with silicon carbide papers (320,400,600,800 and 1000 grit). Half of titanium discs and all the cobalt-chromium alloy rods were airborne-particle abraded with 120-mum oxide aluminum. Then four cements Fuji I, Fuji CEM, RelyX Unicem and Super-Bond were applied on them respectively according to the Manufacturers’instructions. All specimens were stored in distilled water at 37℃ for 24 hours and then tested in shear mode by an Universal material testing machine (SANS, CMT6103). Adhesion failure modes were observed under a scanning electron microscope (Hitachi,3700N).Results:The shear bond strength values (MPa) of the four luting cements Fuji I, Fuji CEM, RelyX Unicem and Super-Bond with/without sandblasting were 5.94±2.30/14.29±3.03, 15.00±2.88/18.51±2.79,23.37±2.25/30.45±3.67 and 26.54±3.45/33.69±3.54 respectively. The air-abraded groups had higher shear bond strength than the untreated groups. One-way ANOVA analysis showed statistical difference significantly (P<0.01). LSD(Least-Significant Difference) test showed significant difference(p<0.05) in subgroups except for the two groups Fuji I with sandblasting and Fuji CEM without sandblasting(p=0.60). The scanning electron microscope revealed an increase on surface roughness of pure titanium with sandblasting. The failure modes including adhesive failure in pure titanium surface, cr-co alloy surface or both, the rate of adhesive failure in pure titanium surface decreased with sandblasting.Part Ⅰ:The effect of luting agents on retention of short implant abutmentsObjective:Aim to evaluate the retentive strength of different luting agents on short implant abutments.Methods:Thirty-two implant abutment/analog assemblies were divided randomly into two groups. The axial height of abutments in group I was unchanged, while the remaining abutments were reduced to 3mm. Co-Cr copings were casted for each abutment. Each group was subgrouped for cemention with the luting agents Fuji CEM or Super-Bond. After the copings were cemented onto the implant abutments, the specimens were stored for 24 hours in 37C° water, then subjected to 100,000 cycles on a chewing simulator (provided by state key laboratory of West China Stomatological College) with a vertical load of 75N. At a crosshead speed of 1 mm/min, the dislodging force of the copings along the long axis of the implant/abutment complex was recorded using a universal testing machine(SANS,CMT6103).Results:The following values for the mean and standard deviation of cement failure loads for each group were obtained:Fuji CEM,160.68±55.10N(3mm); Fuji CEM,213.37±23.54N(4mm); Super-Bond,706.83±12.42N(3mm); Super-Bond,1048.63±183.77N(4mm). The Kruskal-Wallis test showed significant differences among the groups (P<0.01). LSD test showed significant difference between the mean rank retention values of different luting agents (p<0.05). The mean tensile strengths of 4 mm abutments were higher than 3mm ones.Conclusions:1. Sandblasting increased the shear bond strength of Fuji I, Fuji CEM, RelyX Unicem and Super-Bond cements to titanium disc and cobalt-chromium alloy. The two resin cements RelyX Unicem and Super-Bond showed the highest bond strengths. With sandblasting, the pure titanium surface showed an increasing surface roughness and a decreasing adhesive failure rate.2. The retention of Super-Bond on implant abutment was significantly higher than Fuji CEM. An increasing abutment height showed a significant increase in bond strength for the two tested cements. These results might suggest Fuji CEM luting agent as the material of choice for provisional cementation because it allows easier removal of the prosthesis and maintain enough retention to prevent loosening of the restoration. The resin cement Super-Bond, even in situation of short clinical crown, should be served as permanent cement.3. Short abutments (3-4mm) may achieve desired amount of retention by using relatively strong luting agents.