Maret 14, 2017
welcome to the university of michigan dentistrypodcast series promoting oral health care worldwide. this carious lesion requires a class i restoration.there is staining of the fissures and pits that the explorer can penetrate and catch. the tooth being worked on is a second molar.however it has been mounted in the first molar position in this instance in order to facilitateaccess. this leaves an open distal contact. the tooth is in contact with the opposingarch. as a guide for cavity preparation and restoration, mark the centric stops with articulatingpaper by tapping the teeth together. these blue marks show the supporting cusps on thebicuspids and molars. the centric stops are
compromises on the incline planes of the mesialbuccal and also the distal lingual incline of the molar. the rubber dam has been applied to isolatethe operating site. note the floss and the rubber dam clamp as a safety precaution. thisparticular preparation will be started with a number two round bur. the bur align in twodirections. first, perpendicular to the plane across the tips of the buccal to lingual cusp.and second, a plane across the mesial to distal marginal ridges. remove the bur very slightlyfrom contact while maintaining the established alignment and start the bur rotating. thisremoval before activation of the bur tends to prevent breakage of the flutes to the bur.initial penetration is through enamel and
approximately one-half millimeter into dentinwith extension into each of the carious fissures and enamel faults carried out at that depth.the air-water spray is used as a coolant. a sweeping motion of the bur is an effectivemethod of round bur use. this is a radiograph of the tooth being prepared.the superimposed number two round bur shows the relationship of enamel thickness to thediameter of that bur and is an effective method of measuring to help guide the depth of penetration. this histological ground section shows dentinaltubules, enamel, dentinoenamal junction, and the number two round bur at the dentinoenameljunction. this is the depth mentioned earlier, approximately one-half millimeter into dentin.
in this particular tooth the cavity is approximatelyone and a half times the depth of the diameter of the head. this depth was established byplacing the bur head against the radiograph of the tooth as was shown and using the buras a measuring device. after completion of initial outline forms switch to a straightfissure bur number 56 in this case. maintain the depth previously established when usingthe round bur. align the bur and keep this alignment during tooth tissue removal. notethe height of the cutting flutes you can see above the surface of the preparation and usethis height as a guide for maintenance of pulpal floor depth. widen the isthmus andlean the bur slightly into the buccal groove. lean the bur into the distal marginal ridgearea to establish a full taper or divergence.
this also prevents undercutting the enamelrods and maintains a maximum bulk of dentin under the remaining ridge. at the mesial,the bur is tipped in a similar manner with the hand position adjusted for that area. this histological section shows the relationshipof the fissure bur to the direction of enamel rods in the marginal ridge area. this outline form, both internal and external,results in use of the straight fissure bur. notice that the width of the isthmus in themesial section is nearly ideal. there is a wider section than ideal into buccal groovearea and also the distal isthmus because the carious lesion in the floor has underminedthe enamel.
in the lingual groove and central pit areathere is a small whitish area of enamel still present beneath the arrow. this is not ideal and the cavity needs tobe deepened slightly. using the same fissure bur at ultra speedsplane the floor lightly to remove the remaining enamel. refinement and retention are done using aslow speed handpiece and a straight fissure bur. use a two-handed approach with the fingersof the left hand steadying the head of the handpiece. while refining the preparation;pulpal floors, walls, and margins, the bur is slipped tight, is tipped slightly at thedistal marginal ridge area in order to prevent
undermining the enamel rods. lean the burslightly toward the buccal wall and more exaggerated into the buccal groove again because of thepattern of the enamel rods. the slow speed handpiece should be run fairly rapidly witha light touch during this smoothing procedure while proceeding completely around the preparation.slow rotation may result in irregularity of the wall outline. this is the outline form after refinement.again note the walls are smooth, the isthmus is nearly ideal on the mesial but wide onthe distal. now that the external and internal outline forms have been established, cariesremoval is carried out. caries remain in the distal and buccal areas.
the spoon excavator is used to remove grosssoft caries. notice the peeling effect when doing this procedure on soft carious dentin. after the gross caries have been removed witha spoon excavator and the remaining tooth structure beneath feels fairly firm, checkthe soundness of the dentin with an explorer. take care during this procedure not to exertheavy force towards the pulp. a large round bur is now used in a slow speedhandpiece. in this particular case, a number four round steel bur has been chosen to removethe remaining carries. it is operated at a fairly slow speed using a brushing actionwith air used intermittently to blow away the debris. remove all the peripheral cariesprogressing toward the deeper center portion
of the carious lesion. cleanse the cavity with a small amount ofwater on a cotton pellet and dry it gently with cotton or air. check this again with the explorer to makesure all caries have been removed and only firm dentin remains. after all caries are removed retention formis placed. in this case a straight fissure bur is being used. retention is placed bytipping slightly under the cuspal areas. do not place retention under the groove extensionsor into the marginal ridge areas because this would result in weakening of the tooth. retentionshould not be excessive and cause undermining
of the enamel. cleanse preparation with water on a cottonpellet and again dry carefully. place the double-ended [west coast?] cementinstrument into the preparation to get a general idea of the amount of cement that will beneeded. since b&t is being used cavity varnish is not required at this time. place the cement into the cavity. in thiscase it is placed in two increments, the buccal and distal areas in which caries requiredremoval of dentin beyond the ideal depth of cavity preparation. coat the instrument with cement powder andadapt the cement into the pulpal floor area
that has been extended in the caries removaloperation. clean the cement from the margins and fromthe retentive areas with a spoon excavator. be sure to remove the cement from all areasof retention. this is the outline of the preparation andthe outline of the base in the floor of the preparation. again note that the base coversonly that area removed beyond the ideal depth. apply cavity varnish to the entire cavitypreparation including the walls, floor, and margins. use a small wisp of cotton on anendodontic file to do this. pretest the amalgam pluggers in the preparation to make sure theywill fit into all areas of the preparation. in this case the condenser cannot reach thebottom of the floor of the mesial extension.
a smaller condenser or a [west coast?] pluggercan be used. pre-try the carvers at this time also. a number26 spoon is being used for this preparation. ride the spoon on the marginal area and notinto the preparation itself. try the 5c carver, the discoid end being usedhere. in use with the cleoid end of the 5c, notethat the cleoid end should not extend further than half-way across the preparation becausethat would remove amalgam from the opposite margin. place an increment of amalgam intothe central area and begin condensation. condense with a firm, rocking motion. as the deeper portion is filled progress tolarger condensers when possible.
the preparation should be overfilled. placethe condenser at right angles to the tooth surface to begin formation of the centralgroove and overpack the margins. do not push the amalgam back into the preparation butallow it to spill over the edges of the tooth. mercury-rich amalgam is removed during condensationby this overfilling. start carving with a number 26 spoon to removethe excess. keep the spoon riding on the margins and do not allow it to carve into the depthsof the cavity. carefully carve around all the margins progressingaround the preparation in an orderly manner. then use a 5c discoid end to define the margins. air may be used to remove the excess amalgam.
the cleoid end of the 5c carver is used todefine the central groove, the lingual groove, and also the buccal and supplemental grooves.the distal and central pits are also established with this instrument. again note the cleoidend should not extent further than half-way across the preparation because that wouldremove amalgam from the opposite margin. the rubber dam is removed. check the occlusionby tapping the teeth together lightly. examine the restoration for burnished areas resultingfrom contact. areas that show any burnishing in this areslightly relieved with a 5c carver. check the occlusion again by tapping the teethtogether gently with blue carbon paper. this particular restoration has a very dark bluecontact area which needs to be relieved slightly
since all the contact areas should have auniform density of color from the carbon. after making occlusal adjustment with thecontacts, check the occlusion again. press the teeth more firmly together and check workingand balancing excursions. in this case, there's a very long slide that needs to be removed. after the adjustments have been made checkthe occlusion again. always be sure to include working and balancing excursions. the entire restoration is burnished usinga conical burnisher or round ball burnisher after the occlusion has been established.accentuate the grooves and do not burnish heavily in the centric stop areas.
a thorough burnishing will greatly minimizethe time needed to complete the finishing and polishing at a subsequent appointment.finishing and polishing should take place a minimum of 24 hours after placement of therestoration. after a minimum of 24 hours, examine the restorationfor areas of attrition which would indicate high occlusion. check the margins with a cowhorn explorer with the tine held perpendicular to the margins. check the occlusion with carbon paper includingworking and balancing excursions. note the centric stop area is still maintained. a definite pattern should be followed duringthe finishing procedures working from coarser
to finer abrasives during the procedure. with a slow speed handpiece start finishingby using a small round finishing bur to accentuate the grooves. operate the bur at a fairly rapidspeed using a very light, brushing action. use the small round finishing bur only inthe deep grooves and not across the broad surfaces of the restoration. next use a small pear-shaped finishing burto emphasize the grooves and to start widening them. move around the restoration in a definitepattern. when using a new, sharp finishing bur it may be operated in reverse to preventexcessive amalgam removal. lastly, a large pear-shaped finishing buris used with a light brushing action over
the rough surfaces of the restoration. takecare not to destroy the centric stop areas by overfinishing with the burs. examine the restoration with an explorer overall the margins. a catch from tooth to filling means excess filling material, a catch fromfilling to tooth means short or overfinished margins. areas that have a slight catch atthe base of deep grooves are adjusted with a thin flame-shaped bur. the bur is used ina back and forth motion level with the restoration. begin the polishing procedure with a slurryof xxx silex and a black rubber cup. follow the contours of the restoration. placethe cup into the grooves and around the cusp tips so as not to destroy the anatomy builtinto the restoration.
after polishing the entire restoration withsilex rinse the tooth thoroughly. place a clean, fresh rubber cup in the handpiece.a slurry of tin oxide is used for final polish. if a fresh rubber cup is not used or the toothnot rinsed thoroughly the remaining particles of silex will scratch the final polish producedby the tin oxide. follow the anatomy again in the final polish. when the polishing of tin oxide is completerinse the tooth thoroughly. make a final check on the margins with theexplorer. and also make a final check with the occlusionwith articulating paper. this concludes the class i amalgam and wouldprovide a patient many years of service.
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