RESUMEN
Aim and background This study aims to determine the stress distribution on the prepared tooth at the margins with shoulder and radial shoulder finish lines when an occlusal load of 300N was applied to ceramic, zirconia, and polyether ether ketone (PEEK) crowns. Materials and methods Six models of mandibular first molar teeth were fabricated. The tooth models were subdivided into two groups with shoulder and radial shoulder margins, respectively (n = 18). The teeth were restored with three different prosthetic crown materials (ceramic, zirconia, and PEEK). To simulate the typical forces experienced by a prosthetic crown material in a lower posterior tooth during chewing and biting, an occlusal load of 300N was applied to each of the samples, and the maximum principal stress (Pmax) and von Mises stress were calculated, respectively. These samples were then compared and evaluated to determine the material best suited as a prosthetic crown material of choice for a lower posterior tooth. Results Among the materials used, the maximum principal stress value was the least in PEEK crowns. The von Mises stress value was highest for the zirconia crown with shoulder margin and was least for the PEEK crown with a similar margin. Conclusion PEEK as a crown material was found to be a better choice for lower posterior teeth as there was the least maximum principal stress at the margin, irrespective of either shoulder or radial shoulder finish line used.
RESUMEN
BACKGROUND: The process of respiration is the primary factor of the posture of the jaws and tongue. Thus, a changed respiratory form like mouth breathing can change the posture of the head, jaw, and tongue. This, in turn, could change the equilibrium of pressure on the jaws and teeth thus affecting jaw growth and teeth positions. The influence of nasorespiratory function on craniofacial growth has stimulated interest and debate for more than a century. Mouth breathing is the reason for numerous orthodontic glitches such as a mouth breather's face evolving aberrantly because of of functional disruptions triggered by chronic airway obstruction. The relationship between nasorespiratory function and dentofacial development remains controversial despite the long-standing clinical concern of orthodontists, so there was a need to evaluate and compare the relationship between head posture, airway inadequacy, and craniofacial morphology in mouth breathers and nasal breathers. METHODOLOGY: Forty patients were selected and divided equally into two groups: mouth breathers and nasal breathers. Patients were diagnosed as mouth breathers based on physical examination and a history of chronic allergic rhinitis, adenoid, and tonsil enlargement. Lateral cephalograms were taken for all patients in the natural head position (NHP) with the Planmeca Proline XC Dimax3 x-ray machine (Planmeca, Helsinki-Uusimaa, Finland). All lateral cephalograms were traced and analysis was done to check airway, head posture, and craniofacial morphology. Descriptive statistics were performed to obtain the means and standard deviation of all the sample sizes. Unpaired t test was performed between nasal breathers and mouth breathers to check and evaluate the relationship. RESULT: Mouth-breathing patients varied from nasal-breathing patients in airway adequacy and craniofacial morphology. A little, but not statistically significant, difference was seen in head posture between the two groups. CONCLUSIONS: Early interception of mouth breathing in patients could be very helpful, as the postural changes in the mouth-breathing patients, if continued for a longer period of time, could be the reason for severe skeletal deformities as well as dental malocclusion.
