CLASS II AMALGAM RESTORATIONS Amalgam restorations that restore one or both of the proximal surfaces of the tooth Initial Tooth Preparation Occlusal outline form (occlusal step).The occlusal outline form of a Class II tooth preparation for amalgam is similar to that for the Class I tooth reparation. enter the pit nearest the involved proximal surface with a punch cut using a No. 245 bur oriented as illustrated in Fig. 17-41, A and B. the long axis of the bur and the long axis of the tooth crown should remain parallel during cutting procedures. Proper depth of the initial entry cut is 1.5 to 2 mm , 1.5 mm as measured at the central fissure, and approximately 2 mm on the prepared external walls. While maintaining the same depth and bur orientation, move the bur to extend the outline to include the central fissure and the opposite pit (see Fig. 17-41, Cand D). For the very conservative preparation, the isthmus width should be as narrow as possible and no wider than one quarter the intercuspal distance . The pulpal floor should be prepared to a uniform depth (and is usually flat). Maintaining the bur parallel to the long axis of the tooth crown creates facial, lingual walls with a slight occlusal convergence, which provides favorable amalgam angles at the margins. It may be necessary to tilt the bur to diverge occlusally at the distal wall if extension of the distal margin would undermine the marginal ridge of its dentinal support (see Fig. 17-41, B and Q. During development of the pit area of the preparation, extension to include any facial and lingual developmental fissures radiating from the pit may be indicated. The pit area provides dovetail retention form, which may prevent displacement of the completed restoration. (see Fig. 17-41, E).
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CLASS II AMALGAM RESTORATIONS
Amalgam restorations that restore one or both of the proximalsurfaces of the tooth
Initial Tooth Preparation
Occlusal outline form (occlusal step).The occlusal outline form of aClass II tooth preparation for amalgam is similar to that for the Class Itooth reparation. enter the pit nearest the involved proximal surface with apunch cut using a No. 245 bur oriented as illustrated in Fig. 17-41, A andB. the long axis of the bur and the long axis of the tooth crown shouldremain parallel during cutting procedures. Proper depth of the initial entrycut is 1.5 to 2 mm , 1.5 mm as measured at the central fissure, andapproximately 2 mm on the prepared external walls. While maintainingthe same depth and bur orientation, move the bur to extend the outline toinclude the central fissure and the opposite pit (see Fig. 17-41, Cand D).For the very conservative preparation, the isthmus width should be asnarrow as possible and no wider than one quarter the intercuspaldistance . The pulpal floor should be prepared to a uniform depth(and is usually flat). Maintaining the bur parallel to the long axis ofthe tooth crown creates facial, lingual walls with a slight occlusalconvergence, which provides favorable amalgam angles at themargins. It may be necessary to tilt the bur to diverge occlusally atthe distal wall if extension of the distal margin would undermine themarginal ridge of its dentinal support (see Fig. 17-41, B and Q.During development of the pit area of the preparation, extension toinclude any facial and lingual developmental fissures radiating fromthe pit may be indicated. The pit area provides dovetail retentionform, which may prevent displacement of the completed restoration.(see Fig. 17-41, E).
resistance form (occlusal step)is provided by:
(1) the pulpal wall being relatively flat and smooth and perpendicular toforces directed with the long axis of the tooth
(2) providing enough thickness of restorative material to prevent itsfracture under mastication (1.5-2mm depth).
(3) slightly rounding the internal line angles to reduce stressconcentration in tooth structure
(3) restricting the occlusal outline form (where possible) to areasreceiving minimal occlusal contact[1/4 inercuspal distance]
(4) the proximal wall should be parallel or slightly diverge occlusaly toremove unsupported enamel .
(5) cavosurface angles approximately 90 degrees(90-110)º to ensure thatno undermined enamel rods remain on the proximal margins andadequate thickness for amalgam
retention form (occlusal step)is provided by:
1-the occlusal convergence of facial and lingual walls occlusaly
2- flat pulpal floor
3- restricting the occlusal outline form to areas receiving minimalocclusal contact[1/4 inercuspal distance]
Proximal outline form (proximal box).
The objectives for extension of proximal margins are to:
1-Include all caries, faults, or existing restorative material.
3-Establish (ideally) not more than 0.5 mm clearance with the adjacentproximal surface facially, lingually, and gingivally.
The initial procedure in preparing the outline form of the proximal box isthe isolation of the proximal enamel by the proximal ditch cut. This is avery important procedure in conservative tooth preparation and is,therefore, With the same orientation of the bur, position it over the DEJ inthe pulpal floor next to the remaining marginal ridge (Fig. 17-44, A).Allow the end of the bur to cut a ditch gingivally, while the bur is movedfacially and lingually along the DEJ. Extend the ditch gingivally justbeyond the caries or the proximal contact, thus creating an axial wallthat follows the faciolingual contour of the proximal surface (see Fig.17-44, D). The location of final proximal margins (i.e., facial, lingual,gingival) should be established with hand instruments (i.e., chisels,hatchets, gingival marginal trimmers) in conservative proximal boxpreparations. Otherwise, these margins may be overextended to achieve90-degree cavosurface margins with the No. 245 bur (see Fig. 17-44, E).Extending gingival margins into the gingival sulcus should be avoidedwhere possible because subgingival margins are more difficult to restoreand may be a contributing factor to periodontal disease . The proximalditch cut may be converge occlusaly to ensure that the faciolingualdimension at the gingival is greater than at the occlusal (see Fig. 17-44,G). However, the shape of the No. 245 inverted cone bur should providethis converge. The occlusal converge contributes to retention form and
provides for desirable extension of the facial and lingual proximalmargins to include defective tooth structure or old restorative material atthe gingival level. Proximal margins having cavosurface angles of 90degrees are indicated. Cavosurface angles of 90 degrees ensure that noundermined enamel rods remain on the proximal margins
. In addition, remove the weakened enamel along the gingival wall byusing the enamel gingival marginal trimmer in a scraping motion. If thegingival cavosurface margin is in enamel, it will usually require a slightbevel. Ideally the minimal clearance of the completed gingival marginwith the adjacent tooth is 0.5 mm.
Final Tooth Preparation
Removal of any remaining defective enamel and infected cariousdentin. Removing any remaining enamel pit and fissure and infectedcarious dentin on the pulpal wall in Class II preparations is accomplishedin the same manner as in the Class I preparation. The presence of infectedcarious dentin on a portion of either the pulpal wall (floor) or axial walldoes not indicate deepening the entire wall. Infected carious dentin isremoved with a slowly revolving round bur of appropriate size or adiscoid-type spoon excavator or both. To enhance good resistance form,the occlusal step should have pulpal seats at initial preparation depth,perpendicular to the long axis of the tooth in sound tooth structure (Fig.17-49).
Pulp protection. The reader is referred to this same step in toothpreparation in class I amalgam restoration.
Secondary resistance and retention forms. Secondary resistance form infinal tooth preparation involves both resistance of the remaining toothstructure against fracture from oblique forces and resistance of restorativematerial against fracture. Restricting extensions of external walls providesthe former; the latter is enhanced by using the gingival margin trimmer tobevel or round the axiopulpal line angle (Fig. 17-53), thereby increasingthe bulk of and decreasing the stress concentration within the restorativematerial. Proximal retention locks in the axiofacial and axiolingual lineangles significantly strengthen the isthmus of a Class Il restoration, FIG .17-53 .The occlusal convergence of the facial and lingual walls and thedovetail design provide sufficient retention form to the occlusal portion ofthe tooth preparation. The occlusal convergence of the mesiofacial andmesiolingual walls offers retention in the proximal portion of thepreparation against displacement occlusally. To enhance retention form of
the proximal portion, proximal locks may be indicated to counterproximal displacement. Many operators use proximal locks routinely toensure that each portion of the tooth preparation is independentlyretentive. To prepare a retention lock, use a No. 169L bur with air coolant(to improve vision) and reduced speed (to improve tactile "feel" andcontrol). The bur is placed in the properly positioned axiolingual lineangle and directed to bisect the angle (Fig. 17-54, A) approximatelyparallel to the DEJ (Fig. 17-55). This positions the retention lock 0.2 mminside the DEJ.
Procedure for finishing external walls. The preparation walls andmargins should not have unsupported enamel and marginal irregularities(if present, they require correction). It has been demonstrated that lessmarginal leakage occurs if the margins are straight and smooth . Ideallythere should be a 90-degree cavosurface angle at the proximal margin.The occlusal line angle may be 90 to 110 degrees. This angle aids inobtaining a marginal amalgam angle of 90 degrees (no less than 80degrees). Clinical experience has established that this "butt joint"relationship of enamel and amalgam creates the strongest margin.
Amalgam is a brittle material and may fracture under occlusal stress if itsangle at the margin is less than 80 degrees.
Final procedures: cleaning, inspecting, desensitizing, and bonding.
resistance form (proximal box)is provided by:
(1) the gingival wall being relatively flat and smooth and perpendicular toforces directed with the long axis of the tooth
(2) cavosurface angles approximately 90 degrees are indicated. to ensurethat no undermined enamel rods remain on the proximal margins andadequate thickness for amalgam
(3) the buccal and lingual walls shoud be diverge proximally to opencontact and remove unsupported enamel.
(4) Axiopulpal line angel should be beveled o prevent stressconcentration area to restoration
(5) slightly rounding the internal line angles to reduce stressconcentration in tooth structure
(6) gingival cavosurface margin in enamel require a slight bevel usinggingival marginal trimmer to remove unsupported enamel.
retention form (proximal box)is provided by
1-the occlusal convergence of facial and lingual walls occlusaly
2-the dovetail design of the occlusal step.
3-flat gingival wall.
4- Proximal retention locks in the axiofacial and axiolingual line angles
