The o r i e n t a t i o n and d i r e c t i o n of rods in d e n t a l e n a m e l C l a u d i o P i n h e i r o F e r n a n d e s , D . D . S . , M.D.S.,* a n d Orlando Chevitarese, D.D.S., Ph.D.**
Lund University, Maim6, Sweden; and Federal University of Rio de Janeiro, Rio de Janeiro, Brazil E n a m e l rods are c o m m o n l y a c c e p t e d as p e r p e n d i c u l a r l y oriented to the tooth surface and this concept has influenced the d e s i g n of c a v i t y preparations. This i n v e s t i g a t i o n studied the orientation and direction of e n a m e l rods at the outer third of the e n a m e l plate. Fifteen h u m a n m o l a r s w e r e r a n d o m l y s e l e c t e d and sectioned in the buccolingual, m e s i o d i s t a l , and coronal directions. A n g u l a t i o n s of the rods at the outer surface w e r e m e a s u r e d by use of a protractor s u p e r i m p o s e d on the micrographs t a k e n by s c a n n i n g electron microscope. The m e a n angulation for axial s u r f a c e s w a s 60 d e g r e e s . The e n a m e l rods w e r e c o n s i s t e n t l y parallel to the long axis of the tooth w i t h 5 5 - d e g r e e m e a n angulation. The conclusion w a s that e n a m e l rods are not p e r p e n d i c u l a r to the surface except at the edge of the cusps and o c c a s i o n a l l y at the c e r v i c a l area. (J PROSTHET DENT 1991;65:793-800.)
O p e r a t i v e dentistry texts, replete with statements regarding tooth preparation, emphasize that enamel rods are often perpendicular to the surface of the enamel. The question that arises is whether this is an accurate statement that can be verified histologically. Several studies have demonstrated opposing views because the rods are often oriented toward the occlusal surfaces. 15 This histologic alignment of the enamel rods influences the cavity preparation for several restorative materials.
*Graduate student, Department of Prosthetic Dentistry, Lund University. **Professor of Dental Materials, Research Division for Dentistry, Federal University of Rio de Janeiro. 10/1/27554
Fig. 1. Buccolingual section at light microscope (original magnification ×30), framed areas indicate location of SEM micrographs.
THE J O U R N A L OF P R O S T H E T I C D E N T I S T R Y
Unsupported enamel rods are considered a hazard for composite resin restorations because of their brittleness. 6-8 Composite resins are also affected by unsupported enamel because of polymerization shrinkage during the setting period. 9-11 Conversely, histologic appraisal of enamel before tooth preparation is not widely done. Perhaps the proposals of Marzouk et al. 6 regarding cavity preparations should be considered histologically supported cavosurface configurations. This investigation determined the orientation and direction of the enamel rods at the outer third of the enamel plate of axially and coronally sectioned molars. MATERIAL
AND
METHODS
Fifteen permanent, intact human maxillary and mandibular molars were randomly divided into three groups. Group I. Five teeth were axially sectioned buccolingually, parallel to the long axis of the tooth with a carborundum
Fig. 2. Mesiodistal section at light microscope (original magnification )
Lund University, Maim6, Sweden; and Federal University of Rio de Janeiro, Rio de Janeiro, Brazil E n a m e l rods are c o m m o n l y a c c e p t e d as p e r p e n d i c u l a r l y oriented to the tooth surface and this concept has influenced the d e s i g n of c a v i t y preparations. This i n v e s t i g a t i o n studied the orientation and direction of e n a m e l rods at the outer third of the e n a m e l plate. Fifteen h u m a n m o l a r s w e r e r a n d o m l y s e l e c t e d and sectioned in the buccolingual, m e s i o d i s t a l , and coronal directions. A n g u l a t i o n s of the rods at the outer surface w e r e m e a s u r e d by use of a protractor s u p e r i m p o s e d on the micrographs t a k e n by s c a n n i n g electron microscope. The m e a n angulation for axial s u r f a c e s w a s 60 d e g r e e s . The e n a m e l rods w e r e c o n s i s t e n t l y parallel to the long axis of the tooth w i t h 5 5 - d e g r e e m e a n angulation. The conclusion w a s that e n a m e l rods are not p e r p e n d i c u l a r to the surface except at the edge of the cusps and o c c a s i o n a l l y at the c e r v i c a l area. (J PROSTHET DENT 1991;65:793-800.)
O p e r a t i v e dentistry texts, replete with statements regarding tooth preparation, emphasize that enamel rods are often perpendicular to the surface of the enamel. The question that arises is whether this is an accurate statement that can be verified histologically. Several studies have demonstrated opposing views because the rods are often oriented toward the occlusal surfaces. 15 This histologic alignment of the enamel rods influences the cavity preparation for several restorative materials.
*Graduate student, Department of Prosthetic Dentistry, Lund University. **Professor of Dental Materials, Research Division for Dentistry, Federal University of Rio de Janeiro. 10/1/27554
Fig. 1. Buccolingual section at light microscope (original magnification ×30), framed areas indicate location of SEM micrographs.
THE J O U R N A L OF P R O S T H E T I C D E N T I S T R Y
Unsupported enamel rods are considered a hazard for composite resin restorations because of their brittleness. 6-8 Composite resins are also affected by unsupported enamel because of polymerization shrinkage during the setting period. 9-11 Conversely, histologic appraisal of enamel before tooth preparation is not widely done. Perhaps the proposals of Marzouk et al. 6 regarding cavity preparations should be considered histologically supported cavosurface configurations. This investigation determined the orientation and direction of the enamel rods at the outer third of the enamel plate of axially and coronally sectioned molars. MATERIAL
AND
METHODS
Fifteen permanent, intact human maxillary and mandibular molars were randomly divided into three groups. Group I. Five teeth were axially sectioned buccolingually, parallel to the long axis of the tooth with a carborundum
Fig. 2. Mesiodistal section at light microscope (original magnification )
