CLASS II RESINS
Make small Class II tooth preparations! Unfortunately, one of
the most-used burs for Class II preparations is a #557. This bur cuts a
wide, right-angled slot in the tooth and, because of the cross-striations,
makes ultrasonic vibrations in the tooth, potentially causing cracks.
These particular burs should be abandoned. Since the mid-1970s, use
of small burs with rounded ends has been proven to be more acceptable
to retain tooth strength ( figure 2).
Use a proven matrix system. Open contact areas were a problem
with Class II restorations in the past. Several companies now dominate
the matrix system market for Class II restorations. Among them are
Dentsply, Garrison Dental, Greater Curve, Triodent, and Ultradent
Products. When any one of these matrices is used properly, there is no
reason to have open contacts on Class II restorations.
Use a potent disinfectant on tooth preparations. It has been
proven that microorganisms continue to live and create caries if tooth
preparations are not disinfected. Numerous disinfectants and
desensitizers are desirable to place on tooth preparations. Chlorhexidine,
benzalkonium chloride, and glutaraldehyde are examples. In vivo
research at Clinicians Report Foundation has shown that use of two
one-minute applications on tooth preparations will disinfect and
desensitize the tooth.
Upgrade to a state-of-the-art curing light. Several research
projects conducted in North American dental offices have shown that
most curing lights being used in general practices are not adequate due
to small-diameter curing guides, debris on the tip of the light guide, the
wrong angle on the tip of the guide, and—most importantly—improper
aiming and timing of the light. Examples of well-proven lights are: 3M,
Dentsply, GC, Ivoclar Vivadent, Kerr, Ultradent, and others ( figure 3).
Ensure that you are curing the resin well. Most current curing
lights can cure deeply. The light tip should be as close to the resin as
possible, and the light beam should be aimed perpendicular to the
surface of the resin. Not aiming the light perpendicular to the resin
surface markedly depreciates the energy getting to the resin.
Most companies now sell bulk-fill resins. Most of the bulk-fill products
are very good, but some dentists are not curing adequately. Regardless
of whether you are using the bulk-fill technique or not, test a sample
of the resin (approximately a 10-mm piece) out of the mouth to determine how deeply your light is curing. This simple test may surprise
you. Some lights cure only a few millimeters.
If using the bulk-fill resin procedure, I suggest using a normal bonding material and technique to place a small amount (approximately
0.5 mm) of resin in the depth of the box forms of Class IIs. Cure this
small amount of resin before placing and curing the subsequent bulk
portion. Research shows that this procedure reduces potential opening
of the gingival margin due to the 2% polymerization shrinkage of the
resin. In surveys we have conducted, most dentists prefer and still use
the incremental placement and curing procedure.
Another procedure to reduce or eliminate polymerization shrinkage
of resin in the box form is to place dual-cure resin in the box forms of
the prep. Example brands are Bulk EZ from Danville and HyperFIL
from Parkell. Inadequate curing is among the most deficient procedures
in the Class II resin-based composite technique, and it is doubtful that
many dentists know of this significant challenge.
Use air coolant while curing. The high-energy intensity of current
lights creates significant heat. An air stream from your air syringe applied to the tooth being treated while the resin is being cured is mandatory to keep the tooth cool, reduce postoperative tooth sensitivity, and
avoid subsequent need for endodontic treatment.
Do not overfill the tooth preparation. This common practice
requires significant finishing and produces lack of ability to locate the
tooth preparation margins without mutilating them. A technique that
allows optimum finishing and polishing is to place only about 0.5 mm
of resin over the tooth preparation margin. This allows adequate resin
excess for finishing and visibility of the margins.
Use sharp rotary instruments and gentle technique when
finishing. Finishing with either diamonds or carbides is well accepted. Most Americans use carbides, but both procedures work well.
Burs that have been proven to produce smooth surfaces and avoid
“white lines” (mutilated enamel and restorative material) are shown
in Figure 4.
I suggest a new, previously unused 7406 12-bladed bur for any occlusal surfaces that can be reached with this shape of instrument.
The sterilized 7406 bur can later be used for occlusal equilibration,
Figure 2: The DEXIS CariVu is
an adjunct to normal digital
radiographs and shows the actual
extent of proximal caries better
than digital periapical or bitewing
radiographs. The 329 and 330
burs shown allow small tooth
preparations to be made, thus
reducing potential subsequent
cusp breakage, making the
restorative process faster and
prolonging restoration longevity
when compared to large tooth
Figure 3: The Valo Grand curing light from
Ultradent Products is representative of the
desirable characteristics in a current light
with its wide curing tip and right-angle
direction of the light tip.