The Restoration With Box Retention Form On Short Molars

Objective: To evaluate the feasibility of the cavity box retention form used in toothpreparation through clinical observation on four types of crown restorations; To providethe basic data for clinical restorative procedure in short molars through an experimentalstudy of the relation between different abutment height and retention force.Methods: Patients with60short molars were selected from First Affiliated Hospital ofXinjiang Medical University, experimental groups were divided into onlay group,endocrown group, post and core endocrown group, the box retention were used in allexperimental groups. Short molars in control group were restored by post and core crown,evaluate the clinical effect, all the patients were followed-up and examined fromanatomical form, marginal adaptation, secondary caries, gingivitis, abutment tooth loose,food impaction, and patient’s satisfaction; Collecting48extracted teeth with completecrown, after preparation they were divided into3mm group,2mm group,1mm groupaccording to abutment height. Eight full crowns and eight endocrowns restorations inevery group. Record the maximum load power after tensile test by Microcomputer controlelectron universal testing machine, direction of tension with tooth length axis was0°and15°, the speed was1.0mm/min. Statistical analysis was carried out on average result ofeach group.Results: qualified19(82.61%) among23cases of onlay, qualified18(85.71%) among21cases of endocrown, qualified19(95.0%) among20cases of post and core endocrown,qualified21(84.0%) cases among25cases of traditional post and core crown. Fourgroups of short molars prosthesis have showed different clinical effect, difference wasstatistically significant (P<0.05). The acceptability of traditional post and core crown washigher than onlay. Clinical effect between prosthesis of endocrown with post and corecrown basically no difference. The acceptability of post and core endocrown was higherthan traditional post and core crown, and showed low failure rate; Experimental datashowed that, retention force of endocrown higher than full crown, with the decrease of the abutment height, retention force was decreased in each prosthesis. Prosthesis in the sametype showed different retention force on the basis of different abutment height beforebonding (F=143.407, P=0.000), the result showed a significant difference between everytwo group for3mm,2mm and1mm (P<0.01). Prosthesis showed different retention forceon the basis of different abutment height after bonding (F=216.579, P=0.000). Comparedfull crown restoration for3mm abutment with endocrown restoration for2mm abutment, itshowed no significant difference (P>0.05). Endocrown prosthesis of3mm abutmentshowed the highest retention force.Conclusion: Cavity box retention form improves the retention force of short molarseffectively. Endocrown shows as good clinical effect as post and core crown. Short molarsmay satisfy the basic retention condition when abutment height≥2mm after preparation.Endocrown has better clinical application value on crown restoration for short molars.