Composite Over-Molding of the Worn Lower Incisor

INTRODUCTION
I still recall coming out of dental school and doing my first examination on my mother. She had several large, discolored, but noncarious silicate restorations in her maxillary incisors. I conferred with her hometown dentist, expressing an interest in using composite resin to restore the slightly crowded and structurally intact 4 incisors. He had suggested that crowns would be a more "permanent" solution. Well, it has been 23 years and she is on her second set of crowns. Additionally, the "instant ortho" crowns left her with undersized incisors. I remember thinking to myself at the time, "Wouldn't it be great to have a toothshaped matrix, create featheredge margins, and inject composite to provide a less invasive and more natural result?" Although I was an inexperienced rookie straight out of school, I should have listened to my own intuition.

Today, armed with a balanced blend of flowable and paste composites, an understanding of adequate composite tooth preparations, and anatomic anterior matrices, we can do things "they" told us we could not do. In "their" defense, porcelain crowns or porcelain veneers were the only predictable choice for these situations based on past experience and a G. V. Black mindset.

In this article, I will outline modern tooth preparations, matrixing techniques, injection molding, and finishing protocols for aesthetic composite reconstruction of the stained and worn lower incisor. In my previous article (published in the February 2012 issue of Dentistry Today available on our Web site at dentistrytoday.com) about the treatment of severe black triangles of the lower incisor, I discussed the unique challenges that lower incisors present. Perhaps one reason that we see so many aesthetic treatments of maxillary incisors and so few treatments of mandibular incisors is that most of us simply dislike treating these tiny teeth with their odd rootcrown transition. We avoid them like tax preparation.

Lower Incisors: Challenges and Aesthetic Promise
As humans age, their facial musculature changes and the upper incisors tend to disappear from sight (Figures 1 and 2). Meanwhile, the lower incisors, as the lips droop a little, become more and more visible. Their aesthetic importance is multiplied by the display of the incisal edge during speech as the mandible rotates open. Many dentists, myself included, have treated these areas by using an inverted cone carbide bur to cut a retentive preparation, leaving a small channel in the dentin, and then restoring with composite. This treatment looks great at first but has a poor track record that includes sliver fractures of the undermined enamel. Undermined enamel cannot be strengthened by composite.1 Even if the incisal enamel does not chip, the bond nearly always deteriorates within a year or 2 as the incisal occlusion overwhelms the marginal interface. Dentin begins to surface, leading to stain and unsightly debonding of the dentin-composite margin. After a few disappointing long-term outcomes, dentists often stop treating this problem or resort to overly aggressive porcelain therapies. The Table outlines the necessary steps for long-term composite over-molding of the worn lower incisor. Because incisal edges require a minimum of 1.5 mm of incisal clearance, the clinician must evaluate whether the clearance should be created with uniform tooth reduction of the teeth to be restored, or instead by opening the vertical dimension with addition to the posterior teeth and canines with a full-arch approach. No-prep occlusal posterior composites that can be placed over enamel, or sandblasted composite and amalgam, are all predictable options (an excellent choice in some cases, including the case I will present in my next article in Dentistry Today). In this patient's particular situation, aggressive incisal reduction was chosen, as the patient would not benefit from an increase in vertical dimension of occlusion (VDO). Additionally, the patient's posterior teeth were not amenable to simple occlusal composite addition restorations to open the VDO because of extensive PFM crowns.

Figure 1. Low magnification preoperative view of the commonplace aesthetic and functional dilemma of exposed dentin in a 58-year-old woman. Figure 2. High magnification view of the preoperative condition. Dentin exposed to direct occlusion
is an aesthetic liability because of its tendency to darken. It also wears much more rapidly than enamel.
Figure 3. Depth cuts of 1.5 mm are the minimum required for adequate composite strength. Additionally, facial incisal reduction prevents the inevitable "white line" that so often appears when adjusting occlusion. Figure 4. The depth cuts are then joined. If performed with copious water coolant, no anesthesia is required in most cases when cuts involve dentin. Interestingly, that is almost never the case in
posterior teeth.

Depth cuts of 1.5 mm, similar to a porcelain veneer preparation (Figure 3), are critical to ensure adequate composite thickness. I have performed this treatment on hundreds of mature adults and as long as water coolant is used, the patients almost never require anesthesia. This is the polar opposite of cutting into the dentin of posterior teeth which nearly always requires pulpal anesthesia. Next, a 3.0mm wide facialincisal slice (Figures 3 and 4) (that should not enter into dentin) provides the facial wrap necessary to move occlusal contact away from potential marginal areas. A lesser, shorter slice is advisable for the lingualincisal edge. In cases where the teeth are so badly worn that these depth cuts and slices will remove the last vestiges of enamel, opening the VDO, instead of incisal reduction, should be reconsidered. It is doubtful that a mostly dentinbased adhesion will retain these heavily loaded restorations.

Once the depth cuts are connected and facialincisal and lingualincisal slices finished, the dentin should receive a countersink of at least 0.5 mm. This should not be undercut; rather, one should create divergent walls similar to the draw of the fissurotomy bur (Original Fissurotomy Bur [SS White Burs]) (Figure 5). This additional clearance provides 3 benefits:

1. Composite performs optimally with a 2mm thickness when in occlusion and when covering dentin. The thin, infinity edge compositeenamel margins of posterior teeth are not applicable on the incisal edge area. A thin composite here will debond or chip right away.

2. The darker dentin which can show through composite is further removed without overpreparing precious enamel.

3. Mechanical resistance of the incisal trench aids in placement of the composite, keeping the composite from sliding around.

The reader is reminded that the tapering trough along the incisal edge should not undermine enamel rods (Figure 6). The final preparation step is the lightening of the contacts to make placement of the nonmetal matrix possible without prying the teeth apart, which can be painful to the patient and is technically challenging. An additional benefit of the ContacEZ (ContacEZ Restorative Strip System [ContacEZ]) (Figure 7) is the removal of calculus just apical to the contact area. The new handlebased abrasive instruments (such as the ContacEZ) have the unique ability to wedge the teeth apart as they lighten the contact. These are a huge improvement over traditional lightening strips. If the contact is a little tight, the Clark Explorer (Bioclear) or endodontic explorer is inserted between the teeth and gently levered to gain additional temporary tooth separation to allow full insertion of the matrices.

Once the contacts are lightened, A103 Bioclear (Bioclear) anterior matrices are fitted (Figure 8). In this case, the gingival ends of some of the matrices were trimmed back slightly to eliminate excess curvature (Figure 9). For decades, dentists have improvised with crown formers, labored to burnish metal matrices, or created "gizmos" in the lab or their garage to achieve this kind of shape. Thank goodness, the suffering is over. The patent pending anatomic matrices at only 50µm thickness can now make both tight contacts and great curves.

Figure 5. The tip size and taper of the Original Fissurotomy Bur (SS White Burs) make it the ideal bur to "countersink" the dentin of the lower incisors. Figure 6. Finished preparation for the lower incisor over-molding.
Figure 7. (Image from another case) The red ContacEZ (ContacEZ) is "knifed" be­tween tight contacts to lighten and clean the contact. The Bioclear Matrix is easily inserted after this step. Traditional strips destroy the contact and can lead to sawing of the patient's lip. Figure 8. The ideally shaped A-103 Bioclear Matrix (Bioclear) is now easily slid into position, from incisal to gingival. The intimate fit plus the sealing pressure of the heavy rubber dam together create a perfect
gingival seal without using a wedge.
Figure 9. Facial view of 2 Bioclear A-103 matrices specifically designed for the lower incisors. The shape, size, and fit are so ideal that we can create crownlike contours and aesthetics with relative ease.

The Porcelain/Composite Tipping Point
One reason that composite is underutilized today for tooth reconstruction is the negative experiences of past treatments performed with a flat matrix and cumbersome composite placement. Injection molding of a balanced amount of a robust flowable and a creamy paste make all the difference. Instead of struggling with the unfriendly handling of a stiff paste, we simply inject "light body, then heavy body" composites that provide a seamless and mostly paste continuum. The other porcelain/composite tipping point is the finishing. In the past, I have treated similar cases with a flat matrix and a G. V. Black mindset. I started the procedure with good intentions and a good attitude. After struggling with the placement, I suffered and ran overtime with the finishing. The embrasure finishing was excruciating, especially near the gingival aspect. The smallness and odd access angles of the lower incisors compounded all of the other problems. When I finally finished, one hour overtime, I thought to myself, "Never again!"

Table. Lower Incisor Over-Molding Guidelines
DOs DON'Ts
Create 1.5 mm of incisal clearance Prep just the incisal edge dentin with an inverted cone
Create another 0.5 mm of dentinal clearance using an original fissurotomy bur, "countersinking" the dentin Undermine enamel while cutting a "channel" in the exposed dentin
Give 0.75 mm of incisofacial reduction Leave occlusal contacts on margins
Total-etch (rinse-etch with phosphoric acid) Rely on self-etch alone

Blow air on the incisors to assess the need for anesthesia

Assume that anesthesia is required, even when
performing appropriate aggressive incisal reduction

Changing the Way We Think About Composite
Aesthetically bonded porcelain is at its best and least invasive when it goes on the tooth. When it goes around the tooth, it requires a mutilatory preparation because the preparation must be tapered for adequate draw, thus allowing the insertion of the unyielding porcelain. And, unless the tooth is heavily prepared or restored with zirconia, light preparation can lead to compromises that lead to restorations that are more prone to fracture and have aesthetic and functional limitations. I am delighted to announce that composite can be at its best when it wraps around the tooth, which is only practical to perform with injection molding and an anatomic or diastema closure matrix system. In Figure 10 we see an incisal view of 2 Bioclear matrices in position during whole tooth etching of a one of the lower incisors treated in this case.

Injection Molding of Composite—Goodbye G. V. Black, Hello D. J. Clark
This is where it gets interesting…and a little exciting. In the G. V. Black era (which unfortunately has still not ended) from 1890 to today, we had regimented cavity preparations that had walls, margins, and were bounded by grossly contaminated tooth surfaces; perfect for gold and amalgam, hopelessly flawed for composite. In today's dentistry (starting now), injection overmolding has 4 fundamental requirements:

1. The entire tooth should be blasted to remove biofilm (Prophy Plus [Bioclear] or ProphyJet [DENTSPLY Professional])

2. The interproximals are fitted with sectional anatomic matrices

3. The entire tooth is acidetched (Figure 10)

4. Scotchbond Universal (3M ESPE) is applied to the entire tooth, massaged into dentin for 20 seconds, airthinned, and then lightcured. Filtek Supreme Ultra flowable composite (3M ESPE) is then injected into the cervical areas but not lightcured (Figure 11). Next, the creamy Filtek Supreme Ultra paste composite, or a heated stiff paste composite, is injected from the facial, lingual, and then the occlusal. The paste composite displaces most of the flowable composite outwardly through the small partition between the matrices, at midfacial and midlingual.

Figure 10. Occlusal view of the Bioclear A-103 matrices loaded with blue etchant. Note that excess etch exits facially and lingually where the 2 matrices come together. Excess indicates that that the matrices are filled and the etchant has reached the entire tooth. Figure 11. The anatomic matrices, unlike flat mylar that falls away from the tooth, must be teased away from its adapted position by inserting the tip of the canula of the flowable syringe, and then immediately afterwards with the paste syringe tip (paste not pictured).
Figure 12. Several dry Benda Brushes (Centrix) are utilized to wipe away excess flowable composite that can squirt past the matrix, in the same manner that excess cement is cleared away from the margins of a porcelain veneer before light-curing. Figure 13. Midcase photograph showing 3 different stages of injection molding. Note the crownlike contours and seamless composite surfaces. At only 50-µm thickness, tight contacts are consistent. Crown formers or thick polycarbonate forms cannot be used in this way (patent pending).
Figure 14. Step 2 of the Clark 3-Step Polish sequence is the use of coarse pumice in a disposable cup. It leaves a nice matte finish with omnidirectional, shallow scratches. Figure 15. Step 3 is the use of the diamond impregnated Jazz polisher (SS White Burs). Heavy pressure, constant movement, and constant water coolant are key.

The excess is removed; embrasures are wiped clean and dry with disposable brushes (Figure 12). The mass is lightcured. Sounds like a porcelain veneer, doesn't it? Well, it is very similar. And almost unrelated to what we have done in the past when it comes to operative dentistry. In order to form tight contacts, and because the teeth are not wedged for this type of case, it is safer to matrix only one or 2 teeth at a time (Figure 13).

Composite Finishing: You Aren't Finished Until the Surface Is Smoother Than Porcelain
Composite polishing is not like any other kind of finishing (Figures 14 and 15). What works well to polish porcelain, gold, amalgam, or acrylic usually fails when it comes to composite. Discs create flat, ugly, unnatural contours that are a dead giveaway that you have a filling on your tooth. Other systems have complicated and expensive components that just don't work to create the mirror smooth yet wavy, undulating surface that you see in Figures 16 to 18. The 3step Clark polish follows gross contouring which is accomplished with discs, diamond burs, and carbides. Once the shape is close, we move to finishing/polishing:

Step 1: A brownie point at medium speed with water coolant is used to marginate and undulate (run the brownie up and down the mammelon groove areas to create 2 vertical striations).

Step 2: Wetted coarse pumice is then utilized in an inexpensive disposable cup. Remember that it should be replenished every few seconds; otherwise you risk overheating the tooth, wasting your time, and heat damaging the composite.

Step 3: The Jazz Polisher (SS White Burs) is implemented with an interesting dance of heavy pressure, constant movement, and copious water coolant. (Please see my technique video, "Dr. Clark's 3Step Composite Finishing," in the Dentistry Today video library at the Web site dentistrytoday.com, at the Bioclear Web site bioclearmatrix.com, or on YouTube. Other injection molding technique videos and articles are also available online.)

Figures 16 and 17. Facial and lingual postoperative views of the incisor overmold treatment. By locking the composite under the contact with anatomic curved matrices, the strength, aesthetics, and black triangle closure capabilities are quite stunning.
Figure 18. High magnification view (12x) of the natural looking finish. Unlike the flat, grainy finish created by discs, the Clark approach leaves a
"living" yet incredibly polished surface.

CLOSING COMMENTS
At first glance, the preparations in this article may seem too aggressive for composite. Remember that once the incisal edge is restored in this manner, the wear of the tooth will slow down significantly. Be reminded that many of the new composites wear at the same rate as enamel, far slower than the dentin it replaces. If these edges are not protected and rebuilt, these lower incisor teeth can suffer a snowball effect, in terms of wear, since the percentage of dentin exposed at the incisal edge increases as the enamel disappears. It is common to see older patients with lower incisor weardown to the gum line, especially when they are opposed by porcelain crown or veneers on the maxillary incisors. Pulpal necrosis in these severely worn lower teeth is also not uncommon.
This pulpal friendly, slightly aggressive yet preventive procedure can become a significant tool of the renaissance dentist's bag of tricks. Whether for aesthetics, prevention, or both, I encourage the reader to consider the significance of this treatment modality.


Reference

  1. Latino C, Troendle K, Summitt JB. Support of undermined occlusal enamel provided by restorative materials. Quintessence Int. 2001;32:287291.

Dr. Clark founded the Academy of Microscope Enhanced Dentistry, an international association formed to advance the science and practice of microendodontics, microperiodontics, microprosthodontics, and microdentistry. He is a course director at the Newport Coast Oral Facial Institute in Newport Beach, Calif. He is codirector of Precision Aesthetics Northwest in Tacoma, Wash, and an associate member of the American Association of Endodontists. He lectures and gives handson seminars internationally on a variety of topics related to microscopeenhanced dentistry. He has developed numerous innovations in the fields of microdental instrumentation, imaging, and dental operatory design. He is proud to join with the CR Foundation in the "Update Series" lectures and also to participate in the important research at their world class facility in Provo, Utah. He is also developing new techniques and materials to better restore endodontically treated teeth, including the endorestorative casting. A 1986 graduate of the University of Washington School of Dentistry, he can be reached at This e-mail address is being protected from spambots. You need JavaScript enabled to view it or at lifetimedentistry.net.

Disclosure: Dr. Clark has a financial interest in the Bioclear Matrix System.