April 1, 2006
by Cory Seebach, DMD
With the recent surge in cosmetic dentistry more and more patients are walking into the office that have had their maxillary teeth restored with porcelain veneers and have a considerable shade difference between the mandibular and the maxillary teeth with the mandibular teeth being darker. After successive whitening appointments and the fabrication of whitening take home trays a lot of them will request a permanent fix with veneers. Porcelain veneers are an excellent choice for this. Unfortunately, low fracture resistance, potential for abrading structures against which it occludes and the difficulty in resurfacing and polishing the glazed surface continue to be the biggest problems associated with the material,1 and there are special considerations when thinking of restoring mandibular teeth with porcelain veneers. This case study reviews some specific concerns for preparing teeth and creating mandibular anterior veneers. The author follows the case from gathering pre-operative information, through the preparation day and follow-up period in temporaries to the final appointment when the restorations are bonded in place, adjusted and polished. Some comments are also made regarding follow-up care.
The 50-year-old male had had his maxillary arch restored with 10 bonded porcelain veneers in March 2002. They were restored for color and alignment reasons, and to renew some failing interproximal composite restorations. He was left with a considerable difference in color with the lower teeth darker in contrast to the top (Fig. 1) and he wanted the slight mal-alignment corrected (Fig. 2). Preoperative study models and radiographs were taken to assess the teeth and bone level. A periodontal exam revealed mild gingivitis with no pocketing depths >3mm (Fig. 3). The models were prepared and sent to the lab for a diagnostic wax up (Fig. 4). Providing esthetics with the correct anterior guidance is key in order to have occlusal stability long term. The blending of conservative esthetics with the traditional science of occlusion is creating a new standard of care for dental patients.2 Special attention to occlusion must always be made. This case had no pre-existing occlusal concerns or interferences.
Mock preparations were preformed on the study model and sent to the lab for a wax-up. The mock preparations were an important step as the smaller anterior teeth limit the amount of preparation that can be achieved without jeopardizing the teeth’s vitality. In this case only minor alignment correction was necessary and preparations were close to ideal. A preparation depth of approximately .4-.6mm was attempted. The preparation depth is very limited with the small size of the teeth. Under preparation of teeth for porcelain veneers has been relatively common and the placement of veneers on under prepared teeth can lead to periodontal and esthetic problems. The use of a depth gauge or index will help to appropriately prepare the teeth.3 In this case depth cuts were used to gauge the amount of reduction. It is always advisable to ensure you are well aware of the diameter of the burs you are using along the entire length. The operator used a small caliper to measure this and confirm it before starting (Figs. 5 & 6).
Preparations were based on personal experience taking into consideration a review of articles suggesting some advantages and disadvantages with the different options. Some considerations for preparation design and shape are the narrow teeth, angulations of the teeth and the lingual profile of the maxillary teeth. As a result of the thin preparations the design often results in laminates with thin edges, which exhibit a high risk of cracking during the bonding procedure4, therefore a pronounced chamfer preparation was chosen. There has been quite a bit of discussion in the literature as to whether or not the incisal edge should be included in the preparation of maxillary teeth, as the porcelain is sometimes the weakest link in the complex system: veneer, tooth and bonding.5
For esthetic reasons the author chose to include the incisal edge in the preparations, however aesthetic parameters and contact relationship between the incisors and canines in centric occlusion and during excursive movements are a major factor in determining the finish line of the porcelain on maxillary teeth,5 and the same is true for mandibular teeth. Some studies have claimed that preparation with incisal edge overlap contributed to a better distribution of loading forces.5 More recent studies have refuted this belief demonstrating little or no difference between types of incisal margins.6-8 The author’s experience is that the major factor for mandibular teeth is esthetics.
Several methods for controlling the amount of reduction were reviewed and the technique used was a technique based on a dimpling procedure9 but modified to use depth grooves rather than dimples. The length of the anteriors needs to be kept from being too elongated incisally, as an increase in length would cause protrusive interference on the already restored maxillary teeth. Thus, if the incisal edge is included in the preparation adequate preparation is needed for incisal porcelain. The vestibular gingival tissue is thin and a full periodontal exam is vital to eliminate any unforeseen soft tissue problems. Occasionally some tissue grafting or frenectomy procedure may be considered. With careful placement of margins and minimal tissue trauma there weren’t any soft tissue complications anticipated. Patient compliance was of extreme importance to maintain healthy supporting structures.
The preparation appointment starts with a consult regarding the diagnostic wax-up and discussion about shade matching. In this case it was agreed to match the shade of the maxillary veneers (Fig. 7). Although the shade can be communicated to the lab this way and with shade mapping, teeth are three-dimensional and the desired contours can be difficult to clarify.
Also, when the outline form of the teeth is changed (moving teeth, closing spaces) more information needs to be related to the lab10 by making a model of the temporaries and or sending the diagnostic wax-up back to the lab. In this case after reviewing the wax-up with the patient and agreeing on the set up it was decided to send the wax-up back to the lab to use as a guide when fabricating the final restorations.
A main concern is anesthetizing the mandibular teeth. The options being: bilateral mandibular inferior alveolar nerve blocks, bilateral mental nerve blocks, infiltration, intraligamental or intra-osseous injections. It should be noted that successful pulpal anaesthesia in mandibular teeth is not always achieved following the regional block, soft tissue anesthesia is not always an indicator of pulpal anesthesia and pulpal anaesthesia of the posterior teeth is not an indication of successful anaesthesia in the anterior teeth.11
The author’s experience has been in order to achieve full anesthesia required for proper preparations bilateral mandibular inferior alveolar blocks with supplemental buccal infiltration is a good method whereby you can proceed with treatment in a confident manner assuring the patient comfort the majority of the time. The most common approach to inferior alveolar anaesthesia is the traditional Halstead method. In this method, the inferior alveolar nerve is approached in the pterygomandibular space, via an intraoral route located just before the nerve enters the mandibular foramen.12 Once anesthetized a full arch rubber dam was placed to aid in the preparation. Preparation shape and minimal removal guidelines were followed as mentioned and are depicted by depth cuts (Fig. 8).
Preparation margins (Fig. 9) were finished at the gingival crest and only minor cauterizing and troughing were necessary with the diode laser (Diolase ST, Americ
an Dental Technologies, Corpus Christi, TX). A custom tray full arch impression was taken (Fig. 10) and the lab prescription was filled out with a color mapping of the front six teeth.
Numerous techniques and materials exist for fabricating provisional restorations, and every dental professional should be familiar with several methods to enable him or her to handle different situations.13 The temporaries were fabricated from the template (Fig. 11) made of Sil-Tech putty (Ivoclar, Amherst, NY.) (Fig. 12) relined with a light body polyvinyl-siloxane (Reprosil, Dentsply Caulk, Milford, DE) material from the diagnostic wax-up. The material for the temporaries was a bis-acryl material (Integrity, Dentsply Caulk, Milford, DE) which was bonded directly to the teeth in one piece after the teeth were thoroughly cleaned and pre-treated with an anti-microbial solution (Tublicid Red, Wright Dental Canada, Richmond Hill, ON) which was air dried onto the tooth. (Fig. 13)
Acrylic materials are used extensively in dentistry and occupational contact allergies to dental acrylates are well known, but allergic contact dermatitis and utricaria from dental resin-based products are considered rare among patients.14 The patient was instructed on scrupulous home care and given an end-tuft brush (Oral B, Belmont, CA) and post-op complication briefing as well as a cool gel pack to help minimize discomfort from inflammation. Photos show finished temporaries with a gloss coat of Temp Art (Sultan Chemists, Englewood, NJ.) (Fig. 14) applied. This gives a little shine to the otherwise dull acrylic appearance.
Three weeks allowed for the soft tissues to heal nicely (Fig. 15) and the patient is ready for bonding of the final restorations. The photo shows the temporaries held up extremely well and the patient did an excellent job maintaining gingival health. The healthy gingiva will aid in bonding in a clean and dry environment. The restorations are shown on the model (Fig. 16) prior to being seated on the teeth to check for fit, alignment, shape and over all design. Once anesthetized the temporaries were removed by placing several grooves interproximal and ‘wedging’ the pieces loose. (Figs. 17 & 18). The teeth were cleaned (Fig. 19) and the restorations were tried on with water to check fit and esthetics (Fig. 20).
After the patient’s approval the restorations were removed and the rubber dam was placed in order to bond the veneers in place. It is very important to seal off the floor of the mouth when placing the rubber dam to eliminate moisture contamination and minimize humidity. In this case, placing a modified dry angle and sealing around the edges accomplished it with fast setting bite registration material (Regisil 2X, Dentsply Caulk, Milford, DE) (Fig. 21). It is imperative to have hands free ability to keep the preparations clean and dry for all teeth beyond the gingival margins.
Once isolated the preparations were scrubbed with a chlorhexidine scrub (Consepsis scrub, Ultradent, South Jordan, UT) and washed. Each tooth was acid etched with 37.5% phosphoric acid (Kerr, Orange, CA) for 12-15 seconds and rinsed thoroughly. Excess water was dabbed away with a micro brush (Microbrush International, Grafton, WI) leaving a wetted surface.
The bonding agent (Onestep, Bisco, Schaumburg, IL) was applied liberally and air-dried slowly. Each tooth was cured leaving the prepared surface ready for the restoration. The inside of the veneer was micro etched and acid etched (Porcelain etch, Bisco, Schaumburg, IL) and coated with a silane primer (Bisco, Schaumburg, IL). The luting cement used was a dual-cured luting composite (Variolink II, Ivoclar, Amherst, NY). When seating restorations to teeth, luting composite displays advantages such as low solubility, good fracture resistance and optical properties.
However, dual-cured luting composites have shown severe color changes when visible light curing was not applied15 thus it is extremely important to ensure adequate curing with a light or laser. The luting cement was loaded and each individual veneer was tacked in place for 3 seconds. Excess cement was removed and each contact flossed once. The restorations were cured from the facial and lingual and a #12 blade was used to remove most of the cured cement. Once the rubber dam was removed very minimal adjustment and polishing were required (Fig. 22). Immediate post cementation there was slight gingival irritation (Fig. 23).
By bonding in a controlled environment you can be very confident healing will be swift and excellent. The patient exhibited some concern with the bite and agreed to try a short week or two accommodation period. Final adjustment of the bite is often difficult due to the bilateral anesthesia. Postoperative instructions were given and the patient was instructed to return to the office for a two-week follow-up appointment.
Two weeks of healing allowed the tissues to completely heal (Fig. 24) and minor bite adjustments were not necessary at this time. Patient co-operation and satisfaction was been excellent and crucial to a successful result. Size, shape; contour and color all compliment the previously restored maxillary teeth.
The important and special considerations when restoring the mandibular teeth with veneers as apposed to the maxillary teeth involve the size difference in the available tooth structure and frailness of the thin soft tissue. The anatomy of the nerve distribution must be considered in order to proceed with confidence in a pain free manner. Care must be taken by the lab to prevent any protrusive interference, and to match the color as desired. The placing of a sealed rubber dam for the bonding of the restorations is extremely important and its ease has been illustrated. Follow-up pictures at three months show the excellent esthetic result, (Fig. 25) the healthy tissues (Fig. 26) and the happy patient (Fig. 27). Placement of mandibular anterior veneers can be a very successful and gratifying procedure if you start with a clear vision of the end in mind.
Long-term treatment for this patient should include fabrication of a nighttime bruxing avoidance device and regular maintenance period visits with complete periodontal evaluation and dental exam.
The author acknowledges and emphasizes the importance of a team approach to attaining successful results. Success is a result of an extremely motivated and co-operative patient, talented and knowledgeable porcelain artists, the hygiene treatment team, and the clinical chair side assistants. It is definitely a group effort and always worth it when you are able to take the results beyond beautiful.
Dr. Seebach maintains a private practice in Campbell River, BC, focusing on cosmetic and implant dentistry.
Oral Health welcomes this original article.
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