Evaluation of the effects of different groove length and thickness of the retainers on the retention of maxillary anterior base metal resin bonded retainers-an in vitro study

Objectives: The resin-bonded fixed partial dentures have gained immense popularity in recent years as they are more conservative, esthetic, economic and easily fabricated. However debonding is considered the most common cause of failure of resin bonded prosthesis. The objective of the study were to compare the effects of different groove lengths and thickness of retainers on retention of maxillary anterior base metal resin bonded retainers. Study Design: Twenty five metal dies of maxillary central incisor duplicated from pure typhodont teeth (maxillary left central incisors) prepared to receive retainer for resin bonded fixed partial denture having different test designs were made. Five test groups were made with each group having five specimens. Two groups were having preparation depth of 0.5mm and retention groove lengths of 3mm and 5mm. Two groups had preparation depths of 0.3 and 0.7mm with no groove preparation with retainer thickness of 0.3 and 0.7mm respectively. Fifth group with no groove preparation and preparation depth of 0.5mm was kept as control for all the groups. All the specimens were cemented using calibra (Dentsply) resin cement. Each specimen was subjected to tensile loading in vertical direction on universal testing machine (Instron 5569) at a crosshead speed of 1mm/min. \ Results: Groups with 5mm and 3mm groove length recorded higher mean vertical forces when compared to the group with no groove preparation. Group with 5mm groove length showed highest mean vertical forces. The group with 0.7mm retainer recorded higher mean vertical force values when compared to groups with 0.5mm and 0.3mm retainer thickness. Group with 0.3mm retainer thickness recorded the least mean vertical force value. Conclusion: Placement of the grooves increased the retention values almost 2 ½ times than the grooveless preparation and as the thickness of the retainers increased retention values also increased. Retention value was directly proportional to the groove length and retainer thickness. Key words:Groove length, retainer thickness, resin bonded bridges.