Optimal tooth reduction is a key requirement for esthetics, function, and longevity of fixed restorations, especially metal-ceramic and all-ceramic restorations.1 Adequate tooth preparation can provide uniform reduction and sufficient clearance to allow the necessary thickness of the final restoration without disturbing the periodontal health, esthetics, and structural integrity.2 The ability to re-treat the restored teeth should be considered by the clinician when choosing a conservative or an aggressive approach to treatment, especially for young adult patients.3 It is highly suggested that a conservative approach be used on any occasion possible as an alternative to treatment options that may sacrifice tooth structure.4 Veneers have become the most common conservative fixed restoration because they require only 25% to 50% of the tooth reduction necessary for complete-coverage crown restorations.5 Nevertheless, adequate buccal reduction is important to create optimal adhesion. Excessive buccal reduction can lead to compromised bond strength due to penetration of the dentin.6
In the late 1920s, Dr Charles Pincus described the first porcelain veneers retained by a denture adhesive during cinematic filming.7 Unfortunately, the restoration was fragile and it needed to be removed after filming because no adhesive system existed at that time for long-term attachment. Currently, veneer restorations show high survival rates. One study reported a success rate of 98.4% for 186 veneers placed over a period of 5 years.8 Another study showed a 93% success rate for 3,500 veneers after 10 years.9 The initial indications for porcelain veneers are for treating fractured, malformed, and discolored teeth. Today, veneers are included in more complex treatments such as full-mouth rehabilitations, restoration of endodontically treated teeth, and restoration of worn dentition.10–12
Tooth reduction guides are recommended to make uniform space for the restoration and avoid an undesirable situation, especially when the teeth are misaligned, tilted,rotated, or need significant alterations.13,14 For a fixed dental prosthesis, an ideal contour is established by means of the diagnostic wax-up, including any modification in vertical dimension and orientation in the plane of occlusion.15 Typical reduction guides are fabricated either with a polyvinyl siloxane (PVS) putty impression material or thermoplastic sheet.15,16 The reduction guide is seated intraorally and the clearance for the future restoration is evaluated visually and quantified. The PVS putty impression material is preferred for prosthodontic procedures because it duplicates and accurately transfers the diagnostic wax-up; however, a silicone putty guide is bulky and not practical for posterior use and requires additional procedures for the fabrication of interim restorations.17,18 A thermoplastic sheet is fairly easy to use on both anterior and posterior teeth. It allows adequate visual evaluation as well as measurement of the clearance using a periodontal probe placed through holes or slots made through the matrix. An accurate duplication of the axial/occlusal/incisal contours is obtained through pressure vacuum and intimate adaptation of the sheet over the duplicate cast of the diagnostic waxing, although the duplication of the occlusal/incisal surface details may be compromised. Evaluation of the reduction may not be accurate because the procedure is performed intraorally, the clear sheet blends with the tooth color, and the periodontal probe may not be calibrated for fixed restoration treatments.
Clinical verification of the tooth during preparation using a single type of guide can be problematic because the range of labial reduction for laminate veneers is small (0.3 to 0.9 mm). Veneer preparation without the use of reduction guides can result in either insufficient or excessive tooth removal.19,20 Thus, the aim of this article is to describe different types of tooth reduction guides for effective preparation of anterior teeth.
A 34-year-old female patient presented to the clinic with the chief complaint “I do not like my temporary crown and I want to improve my smile” (Fig 1a). The patient had recently moved to the United States and had unfinished dental treatment. She presented with a provisional crown on the maxillary right lateral incisor and was not satisfied with her smile. After detailed assessment, a diagnosis of Class I occlusion, generalized gingivitis, localized mild worn dentition of the maxillary anterior teeth, space between the maxillary right lateral incisor and canine, lack of tooth proportion, protruded maxillary right central incisor, rotated maxillary left central incisor, and stained anterior composite restorations (Figs 1b to 1e).
The patient was presented a comprehensive treatment plan that included oral hygiene instructions, dental prophylaxis, tooth whitening, orthodontic treatment, completion of the full-coverage crown on the maxillary right lateral incisor, and porcelain veneer restorations for the other five maxillary anterior teeth. The patient rejected tooth whitening and orthodontic treatment; she requested that only the prosthetic treatment be performed. She was informed that the diagnostic wax-up and mock-up would provide information about the tentative outcome.
Diagnostic casts were made and the diagnostic wax-up (Wax GEO Classic, Renfert) was fabricated to provide the patient with a harmonious smile, taking into account her wishes (Figs 2 and 3). After presentation of the diagnostic wax-up to the patient, a diagnostic mock-up was performed with temporary bis-acrylic material (Structur Premium, VOCO). The patient liked the initial result and consented to the treatment (Figs 4a and 4b).
Tooth Preparation with Reduction Guides
Following diagnostic mock-up removal, conservative tooth preparations were performed using different types of reduction guides. First a cast metal guide was fabricated using the lost-wax technique, and it was used to aid in the removal of the protruded surface of the maxillary left central incisor. The guide was placed and the protruded tooth surface was carefully removed with a fine diamond bur with a conical end (850, Jota AG) at high speed (Figs 5a to 5c). The main advantage of the cast metal reduction guide is that it is conservative and only allows for targeted tooth structure removal. Conservative tooth preparation (0.75 mm reduction) was provided on the facial surfaces of the six maxillary anterior teeth.
After initial tooth reduction, further reduction was performed with the aid of the clear thermoplastic reduction guide (Thermoplastics, Keystone Industries with 0.5 mm thickness). The guide was fabricated with a vacuum machine (Pro-Vac, Vacuum Formers). It was placed on the anterior teeth to evaluate overall tooth preparation. Then it was perforated with a diamond bur (6 HP Round 51 mm Overall Shank 2, Brasseler) in specific zones in order to insert the periodontal probe (CP-15 UNC color-coded single end probe, Hu-Friedy Qulix) to take measurements (Fig 6). Moreover, putty matrix guides (Platinum 85, Zhermack) were fabricated and used to evaluate incisal and two-plane reduction. The final space available for the future ceramic restorations was 0.75 mm on facial and 1.5 mm on incisal surfaces (Figs 7a and 7b). Crown tooth preparation for the right lateral incisor was refined prior to final impression.
Final Impression and Fabrication of Restorations
The final impression was made using the double-cord technique, first placing #000 cord followed by #0 cord on teeth with veneer preparation and cord #00 followed by cord #1 for the crown preparation (Retraction Cord Plain Knitted, Ultrapak) (Figs 8a and 8b). Impression trays (Rim-Lock Impression Trays, Dentsply Caulk) were loaded with PVS in heavy-body and light-body consistency (Virtual 380, Ivoclar Vivadent) and final impressions made (Fig 9). The final master cast was fabricated in type IV stone (Fuji-rock, GC America). Refractory feldspathic porcelain veneers were fabricated (Noritake Super Porcelain EX-3, Kuraray Dental) and the full-coverage crown was made of pressable feldspathic (Ex-3 Press, Kuraray Noritake (Figs 10a to 10e). Line angles were carefully defined during the finishing of the ceramic veneers (Figs 11a and 11b).
Bonding and Polishing
A dry try-in of the final restorations was performed to evaluate the fit and contours, and once the patient approved, the bonding procedure continued. A rubber dam (Dental Dam, Nic Tone) was placed from second premolar to second premolar and held with clamps (Clamp #00, Hu-Friedy) to achieve proper isolation. A clamp was also placed along the gingival margin of every tooth to be treated (Clamp B4, Brinker Hygenic), followed by sandblasting of the teeth with water and 29-micron aluminum oxide particles (AquaCare Aluminum Oxide Air Abrasion Powder, Velopex).
Surface treatment of teeth with veneers was carried out with total etch of the enamel using 37% phosphoric acid (Total Etch, Ivoclar Vivadent) for 15 seconds and gentle air drying, followed by primer application and gentle removal of excess with air. Fourth-generation adhesive was applied (Syntac, Ivoclar Vivadent), with gentle removal of excess by air. The ceramic restorations were etched with 37% phosphoric acid gel (Total Etch, Ivoclar Vivadent) for 15 sec-onds with gentle air-drying for 5 seconds, and then the light-shade bonding material was applied (Monobond Plus, Ivoclar Vivadent). Next, Variolink Esthetic LC (Ivoclar Viva-dent) was applied to the veneers, and the restorations were seated in place. Excess was removed followed by light curing (VALO cordless 6 oz, Ultradent) on the facial surface for 20 seconds, floss was used to clean the interproximal surfaces, followed by another light cure time of 20 seconds on each surface (palatal, mesial, and distal) of the veneer restorations. The single full-coverage crown was cemented with a dual-cure resin cement (Panavia V5, Kuraray Noritake) (Figs 12a to 12e).
Excess of adhesive and cement material was removed. The occlusion was checked and adjusted, and restorations were polished with polishing points (Dialite Feather Lite, Brasseler) and polishing paste (Dialite Intra-Oral Polishing Paste, Brasseler).
To protect the restorations, the patient was provided an occlusal guard to wear at night. She was pleased with the overall appearance of the restorations (Figs 13a to 13d). The 1-year follow-up evaluation displayed a good condition of the soft tissue and ceramic restorations (Fig 14).
The advancements in adhesive dentistry have enabled a more conservative approach to esthetic dental procedures. Patients seek esthetic treatments to improve their healthy appearance, dentofacial harmony, and physical condition— in dentistry as well as medicine. Esthetic-driven patients can easily recognize any small abnormality or discrepancy in the anterior teeth. Adequate reduction of tooth structure for veneer preparations without the aid of a tooth reduction guide is challenging. Overpreparation of teeth is a common mistake when guides are not used; this may lead to dentin exposure and decreased bonding properties. On the contrary, underpreparation of teeth will promote overcontoured restorations. The use of reduction guides is always indicated when preparing teeth for porcelain veneers. The clinician needs to become familiar with the different types of guides in order to use those most adequate for a particular case. Putty guides are the most commonly used to evaluate thickness and incisal reduction; however, they do not give a 360-degree view as does the clear matrix guide. Clear matrices can be perforated in order to evaluate tooth reduction of a specific area.
Despite the advantages of using these two types of matrices, both enable reduction of only a specific amount of tooth structure; therefore, in cases of protruded teeth requiring more reduction, a cast metal reduction guide or self-cured acrylic guide can provide the opportunity to selectively remove tooth areas that are protruded [Author: Is this sentence OK as edited?].
Controlled tooth preparation can provide the ideal space for final restorations fabricated conventionally by the dental technician or manufactured by milling. Moreover, conservative tooth preparation can save tooth structure that will be needed for future full-coverage crowns when the restorations need to be replaced. Since none of the current dental prostheses can be guaranteed to last forever, the clinician should always consider taking a conservative approach by controlling tooth reduction.
Ideal and conservative tooth preparations provide optimal space for adequate contour and thickness of the final indirect restorations. The use of different tooth reduction guides for the same tooth preparation will help the clinician tremendously to avoid over- or under-reduction of teeth for the fabrication of successful restorations.
The authors declare that there is no conflict of interest regarding the publication of this paper.