STRUCTURAL-ANALYSES OF PLAQUE AND CARIES IN RELATION TO THE MORPHOLOGY OF THE GROOVE-FOSSA-SYSTEM ON ERUPTING MANDIBULAR 3RD MOLARS

Using 22 erupting human third mandibular molars, this study investigat ed: (1) the relationship between the morphology of the interlobal groo ve and the histological features of caries, (2) the ultrastructural fe atures of the interlobal groove contents, and (3) whether the morpholo gy of interlobal grooves influences the viability of the microorganism s. Posteruption time was classified as (1) <3 months (7 teeth), (2) 3- 12 months (8 teeth) and (3) >12 months but <18 months (7 teeth). The t eeth were pre-and postfixed, and buccolingual sections were prepared. The mesial/distal interlobal groove on 116 sections was classified as fissure-like or groove-like. All sections were embedded and ground, an d microradiographs were made. The interlobal groove contents were anal yzed on two sections from each tooth, one with a fissure-like and one with a groove-like morphology, giving a total of 44 sections. Eighteen teeth (82%) had evidence of caries. Severity of caries was associated with length of posteruption time. 'Fissures' were not more prone to c aries than 'grooves'. Tn about 70% of the 'fissures' caries had penetr ated deepest at the entrance rather than in the deeper parts. LM and T EM examinations from 1 tooth disclosed erythrocytes, enamel organ cell s and pioneers of microorganisms in the interlobal grooves. All other interlobal grooves were occupied by microorganisms, mainly gram-positi ve coccoids and small rods. Viable microorganisms were seen at the ent rance as well as at the bottom part of the 'grooves'. In 'fissures' vi able microorganisms were primarily observed at the entrance, while in deeper parts the microorganisms were less viable or dead. A moderate a ssociation was observed between the viability of the microorganisms an d differences in the depths of caries penetration in the fissures. Thu s, the internal morphology of the interlobal grooves influenced the co nditions for bacterial growth and this determined the location for car ies progression within the groove-fossa system.