To Evaluate & Compare Retention of Complete Cast Crown in Natural Teeth Using Different Auxiliary Retentive Features with Two Different Crown Heights - An In Vitro Study.

BACKGROUND & OBJECTIVES: To evaluate the retention of complete cast crowns in teeth with adequate and inadequate crown height and to evaluate the effects of auxiliary retentive features on retention form complete cast crowns. MATERIALS AND METHODS: Sixty freshly extracted human premolars. They were divided into 2 major groups depending upon the height of the teeth after the preparation. Group1 (H1): prepared teeth with constant height of 3.5 mm and Group 2 (H2): prepared teeth with constant height of 2.5 mm. Each group is further subdivided into 3 subgroups, depending upon the retentive features incorporated. First sub group were prepared conventionally, second sub group with proximal grooves and third subgroups with proximal boxes preparation. Castings produced in Nickel chromium alloy were cemented with glass ionomer cement and the cemented castings were subjected to tensional forces required to dislodge each cemented casting from its preparation and used for comparison of retentive quality. The data obtained were statistically analyzed using Oneway ANOVA test. RESULTS: The results showed there was statistically significant difference between adequate (H1) and inadequate (H2) group and increase in retention when there was incorporation of retentive features compared to conventional preparations. Incorporation of retentive grooves was statistically significant compared to retention obtained by boxes. Results also showed there was no statistically significant difference between long conventional and short groove. CONCLUSION: Complete cast crowns on teeth with adequate crown height exhibited greater retention than with inadequate crown height. Proximal grooves provided greater amount of retention when compared with proximal boxes.

A Functional Stress Analysis in the Maxillary Complete Denture Influenced by the Position of Artificial Teeth and Load Levels: an In-vitro Study.

The fracture of complete dentures fabricated using Polymethyl methacrylate resin constitutes a challenge to the clinician and remains an unresolved problem. To determine whether gradual increase in load or different posterior teeth positions in maxillary denture would influence the pattern of stress. Two groups of maxillary dentures were fabricated with different posterior teeth positions (Group I with teeth on the crest of the ridge; Group II with buccal to the crest of the ridge.) using casts prepared from prefabricated edentulous molds, with 5 dentures in each group. Two strain gauges were cemented on to the midline of each denture, one on the anterior palatal area and other on the posterior palatal area. The dentures were loaded from 0 to 110 N in steps of 10 N, and the strains induced were measured. Differences of the stress magnitudes between the 2 groups were statistically analyzed using Mann-Whitney U test. The anterior palatal area of the maxillary denture was dominated by a tensile stress, which was greater in the group II than in group I. The posterior palatal area was dominated by compressive stress but the outer placement of the maxillary teeth caused a significant decrease in the compressive stress. The high anterior tensile stress with compressive stress in the posterior palatal area during loading may be responsible for denture base fractures that initiate from the anterior palatal area. The buccal placement of posterior teeth may play a role in the fatigue fracture of the maxillary denture.