A Restorative Challenge: Tetracycline-Stained Teeth

INTRODUCTION
Porcelain veneers are the restoration of choice in many aesthetic restorative situations involving anterior teeth.^1,2 Tooth structure preservation; excellent aesthetics; the ability to change tooth alignment, incisal plane, and spacing; and their high strength (once bonded to the teeth) make veneers preferable over full crowns in the aesthetic zone for many dentists and patients alike, when adequate sound tooth structure exists.

Masking dark tooth shades is a challenge with thin porcelain veneers. Dentists often choose to restore dark teeth with full crowns because of the difficulty of overcoming “shine-through” shadowing, which is sometimes seen when attempting to restore tetracycline-stained teeth with porcelain veneers.^3-6 Today, the circumferential removal of tooth structure of anterior teeth for full crowns is never a first choice if an equally aesthetic and more conservative restorative choice is possible.^1,2

This premise is doubly true of the lower incisor teeth. Full-crown reduction of mandibular anterior teeth greatly compromises them and makes them very prone to snapping off at the gingival line. By slightly modifying the normal tooth preparation and veneer fabrication, excellent porcelain veneer results in these complex situations (where masking of darkly stained teeth is desired) may be attained.

Background
Tetracycline has been used as an antibiotic for more than 65 years to treat infections of the respiratory tract, skin, genital, and urinary systems; pneumonia; and more recently, acne. It is in a class of drugs known as tetracycline antibiotics and works by preventing bacteria from growing or spreading.^7,8

While tetracycline is an effective antibiotic, it can also produce untoward side effects, including the dark staining of teeth. A report by Schuster and Shwachman⁹ in 1956 was among the first to identify tetracycline staining in the teeth of children who had been prescribed the drug during formative tooth development, and several reports that followed reinforced these findings.^9-14 Since that time, tetracycline’s effects on both deciduous and adult teeth have been well documented in the literature.

In almost all cases, tetracycline staining in adult teeth occurs as a long-term side effect of being prescribed the drug in infancy or as young children, from 3 months up to about 7 years of age.^15,16 If a clinician considers the teeth that demonstrate tetracycline staining versus the time frame in which adult teeth begin to develop (ie, anterior teeth first: upper centrals, lower centrals, and lower laterals at 3 to 4 months of age; canines at 4 to 5 months of age; and upper laterals at 10 to 12 months of age; followed by posterior dentition),¹⁵ he or she can determine when the drug was prescribed.

It is important to note that there are a relatively small number of documented cases of staining in the permanent teeth of patients who as adults had been prescribed minocycline, a tetracycline derivative, for the treatment of acne.^8,17-19 Along these same lines, tetracycline can also affect the deciduous teeth of children who were prescribed it in infancy or whose mothers took the drug later in pregnancy.^15,20 These points are relevant to the topic being presented, but a full discussion of them is outside the scope of this article.

The process of tetracycline staining in permanent teeth may take months or years to fully unfold. When ingested during infancy or early childhood, tetracycline has the ability to bind to and chelate calcium ions in teeth that have not fully formed, thus incorporating itself deep within the tooth structure.^8,18,21 The dose and duration of tetracycline treatment, as well as the age and weight of the child at the point(s) the drug was taken, will impact the extent to which staining and discoloration becomes evident. Teeth that have been exposed to tetracycline will initially appear fluorescent yellow; upon eruption and exposure to light, the staining will transition throughout time to a brown, gray, or bluish hue.^8,15,17,19 Because this transition can take years to develop, the treating clinician often finds that those who wish to mask the stains may be older patients who are just realizing that childhood tetracycline use may be to blame for their dark or discolored teeth.

Feldspathic porcelain is often preferred by laboratory technicians over leucite-reinforced pressed porcelain for the restoration of anterior adult teeth due to the more aggressive preparation required for the latter as well as, some say, the less lifelike results that are produced. When considering restorative options for anterior teeth (ie, veneers versus full crowns), it is preferable to reduce as little enamel/tooth structure as possible because they are so much smaller than posterior teeth. Also, anterior teeth with full crowns are more prone to fracture than teeth restored with porcelain veneers; the biting angle of maxillary anterior teeth (not along the long axis of the teeth) exacerbates fracture risk in bruxers and those who use their teeth to bite into hard foods.

Unless it is the only alternative, lower anterior teeth simply should not be restored with full crowns. Once 1.0 to 1.5 mm of tooth structure is removed circumferentially from lower incisors, the remaining tooth structure resembles a toothpick. Although the crown probably will not break, the tooth itself is at a substantial risk later of snapping off at the gumline. Lower incisors that have been prepared for full crowns also are more prone to needing endodontics.

CASE REPORT
Examination and Findings
A middle-aged woman in good health presented with a chief complaint of an unaesthetic smile due to intrinsic tooth discoloration; the cause was early childhood prescription of tetracycline for ear infections. A comprehensive examination of the teeth and supporting structures found darkly stained teeth, worn anterior teeth, no maxillary anterior tooth display with lips in repose, a relatively flat upper lip when in repose, a low lip-line that did not expose the maxillary gingival margins when the patient smiled, the maxillary incisal plane non-parallel to the pupillary line and lower lip, worn posterior crowns and bridge, facial abfraction and decay, gingival recession, and old amalgam fillings. The patient complained of tooth sensitivity, especially of the posterior teeth. She reported a history of bruxism, but had never worn a nightguard.

Clinical Treatment
Step one of the treatment for this patient was a wax-up on stone study models of the maxillary and mandibular teeth to ideal tooth shape, length, and incisal planes (Figure 1). The study models were mounted on a semi-adjustable articulator (Hanau Articulator [Whip Mix]) with an arbitrary face-bow in centric occlusion. A vinyl polysiloxane (VPS) matrix (Express STD/firm set base/catalyst and Imprint 4 Super Quick Light wash [3M ESPE]) was made on the waxed-up models for provisional restoration fabrication (Figure 2). Because the anterior teeth were to be restored with porcelain veneers, 0.5 mm of wax was added to the facial surfaces of the anterior stone teeth so that the veneer provisional restorations would be thick enough to work with.

Figure 1. Wax-up on maxillary and mandibular stone models of the teeth.	Figure 2. A vinyl polysiloxane matrix was fabricated using the waxed-up models for the fabrication of the provisional restorations.
Figure 3. Mandibular anterior teeth were prepared for porcelain veneers, and mandibular bicuspids and first molars were prepared for full crowns.	Figure 4. Veneer preparations, extended through the interproximal contacts.
Figure 5. Retraction cord was placed circumferentially in the sulcus of the bicuspid and molar teeth preparations.	Figure 6. A polyether impression taken of the prepared teeth, using a custom tray.

Step 2 was preparation of the mandibular anterior teeth for porcelain veneers and the mandibular bicuspids and first molars for full crowns (Figure 3). The second molar teeth were not prepared at this time in order to preserve the patient’s existing vertical dimension of occlusion. Thoughtful tooth preparation is important. The anterior veneers should be 0.5 to 1.0 mm in thickness throughout the veneer when covering dark teeth, allowing enough space for the laboratory team to block out the dark tooth shade and to create lifelike restorations. These marginal preparations are cut with small chamfer diamonds and most often extend into the dentin. As previously stated, it is always desirable to bond to enamel; however, unfortunately, optimal aesthetics do not allow for more conservative tooth preparation in situations where the teeth are darkly stained. Enamel in the apical quarter of anterior teeth is generally 0.3 to 0.5 mm thick. These are not cases for translucent margins that create a contact lens effect.

Ideally, the entire veneer preparation remains in enamel. Studies consistently show that the bond strength of porcelain/resin to enamel is stronger and more durable than porcelain/resin bonded to dentin. If the gingival margins of the teeth are seen when the patient smiles, it may be necessary, in cases where the veneer is masking dark teeth, to extend the tooth preparations into the dentin to create more space for blocking out the dark natural tooth shade in the veneer; 0.5 to 1.0 mm of space must be available for porcelain veneer fabrication to cover dark teeth so the laboratory technician has enough room for opacious and translucent porcelain.

As previously stated, enamel in the apical quarter of teeth is generally 0.3 to 0.5 mm thick. This marginal preparation extension is often needed in maxillary teeth but may not be necessary in mandibular anterior teeth. In this case, the gingival margins of the mandibular teeth were not visible when the patient smiled, so the marginal teeth preparations were performed with a thin, flame-shaped diamond bur (Brasseler 8862-012 [Brasseler USA]). Between 0.3 and 0.5 mm of marginal tooth structure was prepared, allowing the preparations to remain completely in enamel. It is also important that the veneer preparations extend through the interproximal contacts and that the veneers cover the incisal edge of the teeth (Figure 4).

The mandibular provisional restorations were fabricated by flowing bis-acryl provisional material (Protemp Plus [3M ESPE]) into the VPS matrix fabricated on the waxed-up model. Retraction cord was placed circumferentially in the sulcus of the bicuspid and molar teeth preparations (Gingi Plain Z-Twist, size 00 [Gingi-Pak]) (Figure 5). Cord was not placed in the sulcus of the incisors and cuspids because those sulci were extremely shallow and the tissue fragile.

A polyether impression with a custom tray was taken of the prepared teeth (Impregum Penta Soft medium body and Garant Soft light body [3M ESPE]) (Figure 6). A second “security” impression was taken with reversible hydrocolloid (VanR Hydrocolloid [DUX Dental]), followed by a face-bow record and a VPS (Imprint 4 Bite [3M ESPE]) occlusal registration record of the prepared teeth. A full-face, high-quality photograph was taken of the patient with lip retractors in place and the teeth parted. This photo was taken to sent to the laboratory technician to allow confirmation of the precision of the face-bow mounting, and also to view the intensity of the dark teeth shade to be blocked out.

The provisional restorations were seated with unfilled resin, without dentin primer (Scotchbond Unfilled Resin [3M ESPE]) (Figure 7). Once the provisional restorations were in place, the excess unfilled resin was blown off onto a 2- x 2-in gauze pad with the operatory air syringe and cured 20 seconds on both the facial and lingual surfaces with a curing light (Demetron LC [Kerr]). Another full-face photograph was taken of the patient with lips retracted so the laboratory technician could view the provisional restorations in relation to the pupillary line, representing a flat plane to the floor or tabletop (Figure 8). A hydrocolloid impression was taken of the mandibular teeth with the provisional restorations. A vacu-formed matrix was fabricated and given to the patient to wear while sleeping to protect the provisional restorations.

Figure 7. Provisional restorations were seated with unfilled resin.	Figure 8. Full-face photograph (with lips retracted) was taken to send to the laboratory technician.
Figure 9. Restorations were etched and cemented with veneer luting resin.	Figure 10. Veneers and composite are initially cured to quick-set the cement, then excess material was broken off with the back edge of a scaler.
Figure 11. Restorations were polished with fine, high-speed diamond burs, followed by rubber wheels and diamond paste.	Figure 12. Crowns were seated on the mandibular bicuspids and first molars.

Figure 13. Facial marginal tooth preparations of maxillary anterior teeth were prepared more aggressively, extending subgingivally.

Porcelain veneer fabrication for dark teeth is very specific if the dark shade is to be completely blocked out, preventing a “blue glow” through the cemented restorations. When fabricating the porcelain veneers, the first layer of porcelain placed must be very thin and almost 100% opacious. The second porcelain layer builds up the basic structure of the veneer and is 50% opacious porcelain. The third layer is 30% opacious porcelain and 70% translucent porcelain (Fortress/Mirage). Porcelain veneers placed on dark teeth must be more opaque than veneers placed on teeth with a normal hue, chroma, and value. It is important the final hue, chroma, and value of the restoration be determined completely in the porcelain veneer. The filled resin luting cement should not be counted on to block out the darkness or affect the color.

When the feldspathic porcelain veneers and porcelain-fused-to-zirconia (PFZ) crowns returned from the laboratory, the provisional restorations were removed. The prepared teeth were cleaned with pumice and water in a rubber cup, and then wiped with Tubulicid Red (Global Dental Products) to remove the smear layer formed from debris on the prepared surfaces of the teeth. (Tubulicid removes the smear layer without opening the dentinal tubules.) The restorations were tried on the teeth, verifying fit, ideal interproximal contacts, hue, chroma, and value and then etched and cemented with low-viscosity veneer luting resin (Rely X, B 0.5 [3M ESPE]) (Figure 9). It is important that the excess luting resin is not removed until an initial set has been achieved with a curing light. The veneers/luting composite are initially cured for about one second per veneer to quick-set the unfilled resin luting cement so the excess material may be broken off with the back edge of a scaler (Figure 10). If the excess unfilled resin is removed in the flowable state, resin will be pulled out of the veneer-tooth interface microgap, leaving a void between the prepared tooth and veneer. Bacteria in this microvoid, which is normally 25 to 100 µm, can lead to staining, gingival inflammation, and decay. If the excess filled resin is peeled off in pieces after initial light set, the veneer-tooth microgap is completely filled and sealed.

Once the excess filled resin has been peeled away from the margins, the restoration is cured completely with curing lights on the facial and palatal surfaces. Marginal and occlusal adjustment and polish are next, using high-speed fine diamond burs (Brasseler 8878-012 and 8392-016 [Brasseler USA]) with a light touch and high water spray, followed by rubber wheels (Shofu Dental) and diamond paste (Figure 11).

The PFZ crowns were next seated using a resin cement (Rely X) on the mandibular bicuspids and first molars following silica impregnation (Rocatec [3M ESPE]) of the zirconia core in the laboratory (Figure 12). Since the topic of this article is porcelain veneers, the full-crown seating technique will not be addressed.

The maxillary anterior teeth and left first and second bicuspids were prepared for porcelain veneers in a slightly different method than the mandibular anterior teeth. The gingival sulci of maxillary anterior teeth are generally not as tight and fragile as the sulci of the mandibular anterior teeth, and the margins of the maxillary anterior teeth are more often visible when a patient speaks and smiles. The facial marginal tooth preparations of the maxillary anterior teeth are prepared a bit more aggressively, extending subgingivally at least 0.5 mm and, ideally, 1.0 mm to 1.5 mm (Figure 13).

Prior to marginal preparation, size zero nonimpregnated retraction cord (GingiBraid 0N VanR [DUX Dental]) was placed in the facial gingival sulcus. The cord outlines and protects the apical aspect of the sulcus, preventing the diamond bur from invading the biologic width. This cord also provides a bit of facial retraction during tooth preparation. The cord does not extend into the interproximal areas because multiple adjacent, maximally placed circumferential cords might strangulate the papillae, resulting in loss of the papillae.

Provisional veneer restorations are fabricated in a similar fashion to the mandibular provisional. A medium-sized retraction cord (Gingi Plain Z-twist 00) was placed lightly into the facial sulcus of each prepared tooth (Figure 14). The cord was placed lightly into the sulcus and only on the facial aspect. If this thicker cord is placed maximally and circumferentially into the sulcus, the papillae might be strangulated and lost. This cord may be impregnated or nonimpregnated with hemostatic agent, depending on bleeding. Normally a hemostatic agent is not necessary. This second cord was left in place for 5 to 10 minutes, only for gingival retraction of the coronal aspect of the sulcus.

A polyether impression (Impregum Soft [3M ESPE]) with custom tray was taken, followed by a second “security” reversible hydrocolloid impression. Just before the first impression was placed, the prepared teeth were gently rinsed with VanR PrepWet (DUX Dental), then water, to thoroughly wet and lubricate the retraction cord, soft tissue, and teeth so the second, size one cord, may be atraumatically removed from the sulcus. Polyether is hydrophilic, so a damp impression environment is desirable.

Like the mandibular records, an arbitrary face-bow record was taken as well as high-quality photographs of the full face, with the lips retracted and the teeth slightly parted, so the laboratory technician could verify the face-bow mounting record was correct and observe the actual dark shade of the teeth to be blocked out.

The provisional restorations were trimmed, polished, and placed, like the mandibular provisional. High-quality photographs were taken of the provisional restorations. A hydrocolloid impression of the provisionals was taken and poured in stone. The photos and stone provisional model were sent with the case to the laboratory technician to serve as a guide for porcelain veneer length and alignment, as well as incisal plane.

The final porcelain veneer restorations were seated in the same manner as the mandibular restorations. Following restoration of the posterior teeth, a hard polymer, flat-plane, centric relation occlusion nightguard was fabricated.

Final before and after photos are shown (Figures 15 to 17).

DISCUSSION
Veneers fabricated with feldspathic porcelain are excellent restorations for restoring dark, tetracycline-stained teeth. The entire veneer, including the margins, must be 0.5 to 1.0 mm thick so the laboratory technician has enough room for opacious and translucent porcelain to block out the dark tooth shade and create a natural-appearing restoration. This normally requires a small chamfer margin, with the tooth preparation often extending into the dentin. The entire interproximal and incisal surfaces should be included in the teeth preparation to prevent dark show through.

The feldspathic porcelain veneers are created in 3 layers. The first layer is very thin and is 100% opacious porcelain. The second layer is 50% opacious and 50% translucent porcelain and builds up the basic structure of the veneer. The third layer is 30% opacious and 70% translucent porcelain. The hue, chroma, and value of the final restoration should be controlled entirely in the porcelain veneer. The luting composite must not be counted on to influence the final appearance of the restoration or to block out the dark tooth shade.

CLOSING COMMENTS
Restoring dark, tetracycline-stained teeth with conservative porcelain veneers can be a real challenge. If the tooth preparations and veneer fabrication are not correct, there is the danger of a “bluish” tone to the final product due to influence of the dark tooth shade. Light chamfer versus featheredge marginal finish lines, including the interproximal contacts in the tooth preparations and careful placement of opaque porcelain in the veneers, are essential for pleasing restorative results.

References

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Dr. Cutbirth graduated from Baylor Dental College in 1979, then completed a 2-year fellowship there and became a member of the teaching faculty at the Pankey Institute in Florida for 20 years. He currently practices restorative dentistry in Waco, Tex (wacosedationdentist.com) and is director of the Center for Aesthetic Restorative Dentistry (centerforard.com), located in Dallas, a hands-on restorative teaching center for practicing dentists. He has lectured and published extensively on the topics of systematic restoration of the severely worn dentition with vertical dimension increase, diagnosis and treatment of occlusal problems and facial pain, complex aesthetic restorative dentistry, ridge modification and bone grafting for small-diameter implant utilization, and the most effective and productive dental practice systems. He can be reached at (254) 772-5420 or via email at card1611@gmail.com.

Disclosure: Dr. Cutbirth is an occasional lecturer for 3M ESPE but has received no compensation for writing this article.