Esthetic dental restorations, whe-ther porcelain veneers, all-ceramic restor-ations, or esthetic metal ceramics, have aspecific space requirement for ideal es-thetics. Understanding the individual es-thetic materials requirements for estheticsand long-term durability is paramountfor restorative success. Controlling theamount of tooth reduction for any giventype of restoration has been historicallyproblematic, with either over- or under-re-duced preparations being impressionedand sent to the laboratory. Students andpracticing dentists have demonstrated itto be very difficult to judge the amountof tooth structure removal and prepara-tion taper.

Many techniques to control reductionhave been discussed, from using depth cuts,a clear matrix to “see through” and judgethe amount of space available, to relin-ing shell provisionals with acrylic on theprepared teeth and then measuring space.

All of these techniques are problematic.Clear, see-through matrixes are easily dis-torted and can be of varying thicknessesdepending on the amount of heat andsuction used to create them. The distor-tion caused just by removing them fromthe cast after fabrication prevents accu-rate seating during the preparation ap-pointment. These should only be used tojudge “gross” reduction during full-crownpreparations. Relining shell temporarieswith acrylic and then measuring the fa-cial thickness to see if enough estheticspace is available is overly time consum-ing and has the potential problem of lock-ing into undercuts, making temporaryremoval difficult.

Using depth cuts can be a very accurateway to remove specific amounts of toothstructure. The problem with this techniqueis that depth cuts are only useful if, once youremove a specified amount of tooth struc-ture (ie, 0.7 mm for a porcelain veneer), you

replace or “restore” that 0.7 mm, as the0.7-mm depth cut is your only reference.This does not take into account the final3-dimensional (3-D) form and position-ing at which the tooth needs to end up.This is really a smile design issue, as theesthetic position of the teeth needs to bepredetermined prior to a bur evertouching the tooth. What is needed issome method to design the smile, get thepatient’s esthetic acceptance, and ideallytry the new design out functionally tosee if the patient will adapt to it, before abur ever touches the tooth.

THE BONDED MOCK-UPA smile design wax-up is completed basedon the patient’s esthetic desires and func-tional needs (Figure 1). A matrix is madewith lab putty (Figure 2) and tried in themouth to verify complete seating. Manytimes in an esthetic design there are ad-ditive components to the design (ie, the

LABtaLkLaboratory perspectives from the inside out.

96 INSIDE DENTISTRY—JANUARY 2007

Controlling Tooth Reductionand the Bonded Mock-Up: Part 1Edward A. McLaren, DDS, MDC, Maggie Bazos

Edward A. McLaren, DDSDirector

UCLA Center for Esthetic Dentistry

Founder and DirectorUCLA Master Dental Ceramist Program

Adjunct Associate ProfessorUCLA School of Dentistry

Los Angeles, California

Maggie BazosSenior Resident

UCLA Master Dental Ceramist ResidencyProgram

Los Angeles, California

Figure 5 Image demonstrating the etching patternfor bonded mock-ups.

Figure 6 Placing the primer/adhesive combi-nation over the whole surface of the tooth.

Figure 7 The adhesive is air thinned and sub-sequently light polymerized.

Figure 8 Placing bis-Acryl into the matrix. Thetip is placed at the incisal edge and back-filled.

Figure 1 Diagnostic wax-up in “white” wax of teethNos. 5 through 12.

Figure 2 Putty matrix made on the diagnosticwax-up used for the bonded mock-up.

Figure 3 The area marked in red has been“reduced” on the cast.

Figure 4 Placing the notch in the frenum area.

Figure 9 The fully loaded matrix is seated. Figure 10 The excess material is removed. Figure 11 There should be only a very thin “flash”of material beyond the edge of the proposed margins.

Figure 12 The flash is removed with round-ended carbide burs.

teeth are being built up) but there are alsosubtractive parts of the design (eg, a lineangle is being brought back lingually). Ifthere was stone removed on the cast to re-shape the teeth esthetically then similaramounts of tooth structure need to beremoved by esthetic tooth recontouringto be able to seat the matrix, allowing forthe subtractive design done on the pre-operative casts (Figure 3). A notch is cutinto the matrix in the frenum area toallow visualization of proper and com-plete seating (Figure 4).

Bonded mock-ups can be done witheither composite or bis-Acryl temporarymaterials. For longer-term stabilization(more than 3 months) the bonded mock-up should be done with composite. Usingbis-Acryl is much simpler than conven-tional composite. It has the disadvantageof much higher wear potential than com-posite and should only be used short term.

Generally, cotton roll isolation is ade-quate for these procedures as long-termbonding is not necessary or even desirablesince in a short time the mock-up will beremoved. The teeth are then etched with32% or 37% phosphoric acid. It is ex-tremely important to only etch a specificarea. The etching pattern should coverthe facial only (for veneers that are facialincisal veneers) and etch to 1 mm to 2 mmshort of the anticipated final veneer mar-gin. Do not etch the marginal area (Figure5) because during the preparation ap-pointment, when preparing the marginalarea (finish line), this area of bis-Acryl willeasily flake off, facilitating margin place-ment. Also, if this area has been etchedand bonded to with bis-Acryl there is thepotential of leaving small amounts at thefinal margin preparation, possibly affect-ing long-term marginal seal. After 20 to30 seconds, the etching material is rinsedwith copious amounts of water. The sur-face of the teeth is air-dried; since most ofthe time this procedure is done to enamel,over-drying is not a problem. The authoruses a primer and adhesive combinationon the whole surface of the tooth, eventhe unetched areas (Figure 6). This willcreate a minimal seal on unetched areasto help prevent leakage and staining atthe margins during the trial restorationphase. The primer/adhesive is air-thinnedand then light-polymerized (Figure 7).Bis-Acryl is then loaded into the matrix.The tip of the syringe should be placedin contact with the incisal edge or deepestarea of the matrix (Figure 8) and slowly

98 INSIDE DENTISTRY—FEBRUARY 2007

Figure 13 Bonded mock-up after 5 weeks. Figure 14 A 0.5-mm depth-cutting bur is usedduring the initial phase of preparation.

Figure 15 Pencil lines are drawn at the depth ofthe bur cuts.

Figure 16 A course diamond bur is then usedacross the whole facial surface.

back-filled. This will minimize the chanceof trapping air bubbles. An amount slight-ly more than is anticipated to be necessaryin order to not have any voids should beplaced in the matrix. The matrix is thencompletely seated in the mouth (Figure 9).

Once the matrix is seated the materialis allowed to set until it reaches a rubberyor doughy stage. The excess material be-yond the edge of the matrix is easily re-moved at this stage with an instrument(Figure 10). The material is allowed toset fully and the matrix is removed. If thematrix fits well there should only be athin “flash” of material beyond the antic-ipated veneer margins (Figure 11). Anyexcess material is trimmed with compos-ite trimming carbides (Figure 12). It isrecommended to use carbides that have around tip, as there is minimal chance todamage tooth structure. It is importantto open up the gingival embrasure to en-sure that the patient can floss in theseregions as the mock-up is left splintedtogether. Occlusion is adjusted in centricand all excursive movements. It is not re-commended to have the patient wear anocclusal splint at this point, as one of thegoals of this phase of treatment is to seeif the patient will adapt functionally tothe proposed anatomical changes. Themock-up can then be adjusted as neces-sary for esthetic requirements. If addition-al material is needed then a bonding agentis applied to the area and flowable com-posite is built up freehand to the desiredshape and cured. The patient wears thisuntil esthetic and functional acceptanceis obtained and has held up quite well forseveral weeks (Figure 13). This techni-que has proven to be a great patient mot-ivator to accept proposed treatment.

CONTROLLING REDUCTIONOnce the smile design has been estab-lished and a 3-D model has been mockedup and bonded in the patient’s mouth, itis fairly easy to control reduction. Becausethe final 3-D positions of the teeth areknown, depth cuts become useful andpractical. As stated earlier, the amount ofreduction is specific to a material. Forbonded porcelain it is possible to fabri-cate veneers 0.3 mm thick. The thicknessof the veneer is based on the desired colorchange from the color of the preparedtooth.1 For the benefit of illustration a0.6-mm to 0.7-mm thick veneer is planned.

To obtain a relatively uniform prepa-ration of 0.6 mm to 0.7 mm, a depth cut-ter of slightly less depth is used. This isbecause once the preparation is finishedwith fine diamonds it ends up removing0.1 mm to 0.2 mm more than the depthcutter. For the reduction mentioned, a0.5-mm depth cutter is used across thefacial surface (Figure 14). A simple tech-nique the author uses is to draw pencillines at the base of the depth cuts (Figure15). Then, a coarse diamond bur is used toa depth across the whole facial surface upto the depth of the pencil marks (Figure16). The incisal reduction is done the same

INSIDE DENTISTRY—FEBRUARY 2007 99

Figure 17 Using a 1.4-mm diameter bur tomake depth cuts along the incisal edge.

Figure 18 Several depth cuts were made atthe incisal edge.

Figure 19 Controlled incisal edge reduction of1.4-mm.

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way in that a specific sized bur is used tocreate depth cuts (Figure 17 and Figure 18).The same bur is then used to remove ma-terial in between the depth cuts to obtainadequate incisal reduction (Figure 19).At this point the preparation is evaluatedfor any remaining mock-up material.Many times the preparation is still in themock-up material. If this is the case,then the remaining mock-up materialneeds to be removed. With a diamond,lightly prepare down to the bis-Acrylinterface. The material near the marginwill just flake or fall away as it was notbonded to the tooth. The last step in theprocess is to place the margin. For con-servative veneers the author uses a finechamfer diamond to place a 0.3-mm to0.4-mm chamfer finish line (Figure 20).Any sharp line angles, such as the facialincisal line angle, are rounded so as notto concentrate stress in the porcelain re-storation. All of the teeth to be preparedcould have been done simultaneouslyusing this technique with equal results.Figure 21 demonstates the final prepara-tions of teeth Nos. 5 through 12. Figure22 is the pre-op condition of the case inthis article. The benefit of this techniqueis conservation of tooth structure. As canbe seen in this case, once ideal reductionwas obtained, the preparation was still inthe bonded mock-up material. Only aminimal amount of tooth structure wasactually removed to establish the periph-eral margin. With the normal techniqueof only using depth cuts with no beginningreference, unnecessary tooth structurewould have been removed. Figures 23 and24 are the final bonded porcelain veneersdone using the refractory technique.

REFERENCE1. McLaren EA. Porcelain veneer preparations:

to prep or not to prep. Inside Dentistry. 2006;

2(4)76-79.

100 INSIDE DENTISTRY—FEBRUARY 2007

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Figure 20 The final margin placement was donewith a fine diamond.This image has only one toothprepped for demonstration purposes.

Figure 21 Final preps maxillary anterior teeth. Figure 23 Postoperative view of eight porcelainveneers that were prepared using this technique.

Figure 22 Preoperative view of the patientpresented in this article.

Figure 24 Smile view with the new restora-tions demonstrating dento-facial harmony.