Endodontic Access Effect on Full Contour Zirconia and Lithium Disilicate Failure Resistance.

OBJECTIVES: To evaluate the effect of endodontic access on the failure load resistance of both adhesively and conventionally luted, full-contour monolithic yttria-stabilized zirconium dioxide (Y-TZP) and adhesively luted lithium disilicate (LD) crowns cemented on prepared teeth. METHODS AND MATERIALS: Seventy-two human maxillary molars were prepared per respective guidelines for all-ceramic crowns with one group (n=24) restored with LD and the other (n=48) receiving Y-TZP crowns. Preparations were scanned using computer-aided design/computer-aided milling (CAD/CAM) technology, and milled crowns were sintered following manufacturer recommendations. All LD crowns and half (n=24) of the Y-TZP crowns were adhesively cemented, while the remaining Y-TZP specimens were luted using a conventional glass ionomer cement (GIC). One LD group, one Y-TZP adhesive group, and one GIC-luted group (all n=12) then received endodontic access preparations by a board-certified endodontist: the pulp chambers were restored with a dual-cure, two-step, self-etch adhesive and a dual-cure resin composite core material. The access preparations were restored using a nano-hybrid resin composite after appropriate ceramic margin surface preparation. After 24 hours, all specimens were loaded axially until failure; mean failure loads were analyzed using Mann-Whitney U test (α=0.05). RESULTS: Endodontic access did not significantly reduce the failure load of adhesively luted LD or Y-TZP crowns, but Y-TZP crowns with GIC cementation demonstrated significantly less failure load. CONCLUSIONS: These initial findings suggest that endodontic access preparation may not significantly affect failure load resistance of adhesively luted Y-TZP and LD crowns. Definitive recommendations cannot be proposed until fatigue testing and coronal seal evaluations have been accomplished.

Middle ear disease and hearing impairment in northern Tanzania. A prevalence study of schoolchildren in the Moshi and Monduli districts.

A total of 854 schoolchildren from one urban and one rural district in northern Tanzania were examined for the presence of middle ear pathology and hearing loss by means of pneumotoscopy and screening audiometry (air conduction). The prevalence of chronic otitis media (COM) was 1.6%, with no difference between urban and rural children. Scarred and sclerotic tympanic membranes were found in 10.9% of urban children and in 15.1% of rural children, the difference being significant. Hearing loss within the speech frequency range in all the children studied was found in 37% of the urban children and in 18% of the rural children. However, the prevalence of hearing loss above 30 dB HL was 3% in both districts. High frequency loss was significantly more common among urban than among rural children. Undetected severe hearing impairment/deafness was found in three children in the rural district, while none was found in the urban district.