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INCISAL ATTRITION





Video Recording, Live Stage, at Pacific Dental Conference, Vancouver, March 7,2014.


I was honored to be asked to be one of the six clinicians to perform a procedure on the live stage at the largest dental conference in Canada. This 90 minute Live demonstration recorded at the Pacific Dental Conference demonstrates the preparation and restoration of three maxillary incisors for a patient using composite resin. Eventually it will be edited for brevity, but for now it is posted as a summary of the clinical method described below. https://drive.google.com/file/d/0B0wH1JsC2atGMzh4VTlDM2xKTEU/edit?usp=sharingexternal link



BEGINNINGS: THE FAILURE OF PREPLESS RESTORATION

Fifteen years ago I began placing composite in unprepared attrition defects. Many lecturers recommended this approach at the time, and some still do. However, it has proven to be a short-lived technique. Despite an appeal to our conservative instincts, being a reversible procedure, requiring no reduction, it is unfortunately doomed to a short lifespan, and for good reasons. Let us look at these reasons….

  1. There is usually insufficient and inconsistent depth for load dissipation into the dentin. We all know that composite, when used in thin layers, is prone to flaking and disintegration.
  2. Because there is not a consistent depth to the preparations, and darkened sclerotic dentin is not removed, the inconsistent aesthetic results are seen
  3. The enamel is unprepared . When there is no preparation, bond strengths are poor,due to the etch-resistance of older, highly fluoridated enamel. As well, the enamel surface consists of amorphous, re-mineralized enamel. We want to gain access to the structural rods which underlie this layer.
  4. There is no removal of pellicle, plaque, or acquired smear layer that might be on the dentin surface. Dentin bonding may therefore be contaminated by biofilm in addition to sclerotic dentin and smear layer.
  5. Finally, the prep form created by natural attrition is usually saucer-shaped. In GV Black terms, this offers poor resistance form. This promotes rotation of the material under load. This translates into shear forces between the composite and the tooth structure,straining the bond, because there is no form to contribute to retention.

This illustrates an important point: in bonded composite restorations, you can often succeed with reduced classic retention form. But you cannot ignore it altogether. We still have to engineer the case. Alternative streams of retention i.e. sufficient area, sufficient depth, preparation form, attention to occlusal contacts, are still needed to ensure success. Adhesion works best when combined with extra-coronal and intra-coronal retention form and classic dental restorative acumen.

I call the design for Incisal Attrition a “belts and suspenders preparation”, because some GV Black thinking is still necessary. See The New Paradigm of Composite Resin

Over time, some early prep-less cases survived, more by chance rather than by intention. Overall lifespan was still short because the teeth would continue to wear, and before long the shallow increments of composite at the enamel interface would wear away, leaving an island of composite surrounded by a moat of dentin. The enamel rim, no longer bonded and supported composite,resumed disintegrating as before.

The EUREKA case

After a few years of this futility I was faced with a challenge case. It opened the door to a better technique.

A new patient, a big and muscular man, presented with a desperate situation. His small teeth showed extreme attrition. Functionally, his dentition was exposed to very high load, imposed upon his very small teeth, which were separated by diastemas throughout the mouth. It was a disastrous combination. The anterior occlusion was entirely in dentin by this time, and coronal loss was at a staggering 50% level. The teeth were melting like snowballs in July.

Obviously he was bruxing. His budget was too low to allow the use of crowns, not to mention the difficulty of realizing decent aesthetics on very small teeth. As well, his caries index was too high to make crowns advisable.

When I took x-rays, there was no sign of pulps in any of the teeth – they were all extremely calcified. Because nothing else could be done to stave off the collapse of this patient’s mouth, I took a deep breath and prepped into dentin on all the maxillary and mandibular incisors to a depth of 1.2mm- about 2/3 of the length of a 330 bur. A perimeter rim of thin enamel remained around these intracoronal preparations. I restored the teeth with Z100, the toughest new kid on the block at the time, 1996.

A year later this patient returned. Unbelievably, 11 of 12 restorations were still intact. I re-restored the lost one, and five years later, these 12 were still intact! Incredible! I had discovered a new modality. Today, (2014), these restorations are still intact and preserving what little tooth structure remains, photo below.


A typical maxillary incisor case

The photos below illustrate the preparation and typical outcome for two maxillary central incisors suffering from Linguo-incisal attrition and concomitant dentinal staining and some accompanying deterioration of the facial outline form. No attempt was made to idealize other aspects of the smile, only to restore the weakened and deteriorating incisal edge within the confines of the existing bite. The resin used was 3M Espe Z-250, shade D3. Equally convincing outcomes have been achieved with Tokuyama Estelite, shade A3.5, which is warmer in hue. Experience has shown me that the best esthetics are obtained with a single shade of resin, closely matched in hue and value to the host tooth, with high "metamerism" or blending properties. The difficulty of layering and controlling placement in these small preparations precludes consistency when layering. Equally, placement of flowable resin is difficult to control.As it is higher in contraction and lower in physical properties than paste resin, why use it? A very satisfactory result can be obtained with this seemingly-too-simple approach, but all attempts at greater complexity have met with frustration.







Typical mandibular attrition cases prep and post-op


Subsequent evolution of Incisal Treatment: Extreme Resin Makeovers


I have placed over 3000 individual restorations for many hundreds of patients. New resins have appeared and been tested and subsequently adopted. Because of this highly successful clinical performance,I have taken on more and more challenging cases, exploring this concept to the limit. I have lengthened worn maxillary teeth, and now am restoring vertical dimension to gain full crown length, against natural teeth,and against full dentures – i.e.- direct full mouth reconstruction, Extreme Resin Makeovers. A CUD case is detailed at Extreme Resin Makeovers

A dentate case, detailed below, with severely collapsed natural teeth in severely shortened dental arches, was treated in 2006, and was completed in one day without anesthesia. This case has survived with minimum maintenance- 10 of the 12 teeth have seen no further treatment. One tooth lost vitality; after endodontic treatment, the root was re-restored using a passive parallel sided stainless post. A second tooth de-coronated, and was electively de-vitalized and restored similarly. Cosmetically, as an aside, I think the maxillary teeth are too white in shade but the patient, or rather the patient's wife, prefers it.

Some aesthetic imperfections were corrected the following day, and two more appointments were needed to complete the posterior teeth and prepare for a maxillary overdenture. But,at the point of photographing this first stage, the 12-tooth makeover, we were tired, and ready to go home!



Obviously, I have a great deal of confidence in this restorative approach to attrition. Its success has also informed preparation design for Class IV restorations that join a worn or compromised incisal edge. This is detailed below in this guide.

Properly executed, this approach produces durable, painless, conservative, attractive, and inexpensive restorations, which are endodontically and periodontally innocuous.

For some time I worried about possible pulp exposure in entering the incisal edge, but there is a fortunate biological synergy, in that, typically, where there is no enamel on the incisal edge, the pulp immediately begins to calcify and retreat apically. In this way nature conveniently makes way for dentists to prepare into dentin with a bur.

In 18 years of using this procedure, preparing almost four thousand teeth, I have never had an exposure. Post-operative sensitivity is never seen.

It is prudent to enter the dentin cautiously, however, when preparing the incisors, to maintain good control over these small and delicate preparations where tactile cues guide preparation as much as visual cues.

ANESTHESIA

Often, these restorations can be placed without anesthesia. Quixotically, this may be the case even if the teeth have cervical sensitivity.

When cervical sensitivity is elicited by handpiece water spray and/or the HVE, it can be eliminated without resorting to anesthesia by topical fluoride varnish on the cervical defects. Alternatively the neck of the tooth can be wrapped with occlusal indicator wax (Kerr). Another approach is the use of a syringeable rubber dam material, such as Dam Cool (Danville Dental) at www.Danvilledental.com.external link can be used to encase the sensitive areas. All these methods exclude air from sensitive cervical areas during the appointment and provide relief from cervical hypersensitivity.

If anesthetic is preferred, a short-acting epinephrine-free anesthetic such as Carbocaine 3%,(Cooke-Waite) is usually sufficient.

On the lower arch bilateral mental injections are the placement of choice. In the maxilla, lesser quantities of infiltration are often sufficient.


ETIOLOGY

Why is incisal wear exaggerated in some patients? Usually the pattern is multi-factorial, involving one or many of the following categories of etiology: age, acidity, excess function,untreated traumatic injuries, and familial occlusal patterning. Regardless of etiology, restorations remain the same. What must change is clinical management and follow-up to respect and control etiological factors.

#Age itself is the dominant agent: in the typical attrition- related lesion, the patient is in the fourth to fifth decade of life. Normal wear breaks through the enamel into dentin on one or more teeth in the upper or lower incisors.
#Occlusal factors
  1. Opposing porcelain crowns may create accelerated wear on individual teeth.
  2. Loss of posterior teeth, shifting excess function onto anterior teeth.
  3. Parafunction - Bruxism and clenching
  4. Occlusal disharmony: plunger cusps forcing excursive paths into narrow functional envelopes, accelerating wear in specific zones
  5. Tooth mal-positions- rotations, crowding
  6. Deep overbite
#Acidity
  • gastro-esophogeal reflux or GERD
  • Bulimia
  • Excessive use of acidic carbonated bottled soft drinks,
  • acidic fruit juices
  • Vinegar exposure as in salad dressings
  • some wines
  • Street drug use such as crack cocaine and methamphetamine.
#Familial Genetics
  • Some families have a trend towards anterior destruction for no obvious reason. Working in a small community, as I do, I see extended families spanning three or even four generations. In some family lines, occlusions are all worn flat, featuring exposed dentin by early middle age, with accompanying premature wear of the anterior teeth. Unfortunate dental genes!
#Untreated traumatic fracture A fracture in early life is untreated, the tooth passively erupts and wear is accelerated relative to the adjacent teeth because no enamel is present on the fractured tooth.




#Incisal Attrition in younger patients - a growing segment of the dental population

While incisal attrition is most prevalent in patients aged 50 or more, today younger patients are presenting with advanced attrition when the following are occurring: See Acid Erosion for more information and for treatment modalities

  1. Heavy function
  2. Parafunction
  3. Poor posterior occlusion
  4. Exaggerated Curve of Spee (slide above)
  5. Acid dissolution from food/drink exposures
  6. Abrasion from opposing porcelain




INDICATIONS FOR TREATMENT

Early interception

Early interception is desirable when the neighboring teeth are still relatively normal in form. If postponed, the final appearance of the restored teeth will be compromised by an overall loss of vertical dimension, and, often, shortening of the clinical crown due to passive eruption, i.e. teeth erupting out of the alveolus to compensate for the attrition of the incisal edge.

Clinical judgment dictates the appropriate time for intervention. From my observation, there is no serious acceleration of generalized attrition until:
  • the incisal edge shows cratering of the dentin
  • the width of the dentin exposed is large enough to accept a 330 bur.

Then it is time to treat. By the time exposed dentin has become the width of the 330 bur, penetration into the tooth is easy, pulpal regression has begun, and there is little risk of undermining perimeter incisal edge enamel with this bur, if angled correctly.

Incipient lesions


In some cases, exposure of the dentin on the incisal edge leads the patient to request treatment before attrition has advanced sufficiently to meet the above rule of thumb. Clinically, dentin staining is darkening and spoiling an otherwise perfect smile,
the maxillary lingual enamel walls have begun to crumble, perhaps due to a malposed opposing tooth. How does one treat these incipient lesions?

In the past I recommended a 169L bur to prepare the tooth, because of its excellent tactile feedback, small diameter, and good control. Its dome-ended counterpart, the 1169L, lacks good control, tending to "skate" rather than penetrate with surety. However, over the last 7 years I have seen that the sharp internal line angle created by the sharp end of the 169L has lead to a small incidence of localized fracturing of enamel from the perimeter of small numbers of incisors- possibly, to quantify, about 5% of the time. To attempt to overcome this weakness, the original SSW Fissurotomy bur is now being used. This bur has good penetration control, but a fairly substantial taper, so discretion is required to limit over-removal of the facial and lingual walls of enamel. As well, air abrasion is used to ensure that all enamel surfaces are fresh-cut to optimize bonding, noting that air-abraded enamel tends to reveal fractured enamel more readily, and also to ensure that the inner aspect of the enamel rim is fully debrided of etch-resistant hyper-fluoridated amorphous enamel. Since following that protocol, which identifies weak enamel and removes it, and rod-ends are exposed and engaged for optimum bonding, this fracture problem has virtually disappeared. Note that with the fissurotomy bur, there is no mechanical retentive interlock with the dentin, but there is still dentin penetration.


THE PREPARATION

The objectives for the preparation are as follows

  • The enamel perimeter should be a minimum of ½ mm deep
  • Perimeter enamel rod should be lightly cut, providing rod-end bonding, not rod-edge bonding
  • All enamel should be freshly cut to enhance adhesion
  • Floor of preparation should be into dentin
  • Dentin should provide resistance and retention form

SeeHistological Basis for Enamel Margins and "Preparations In Composite Resin Part I: Principles And Instrumentation For Class V, Cusp Tips, And Incisal Attrition" Oral Health Journal, December 2011 Pgs.48-61

This article covers 5 enamel preparation axioms for Incisal Attrition, Class V, and Cusp tip restorations, and appropriate instrumentation.See http://www.oralhealthgroup.com/news/preparations-in-composite-resin-part-i-principles-and-instrumentation-for-class-v-cusp-tips-and/1000738881/?type=Print%20Archivesexternalexternal link link

DEPTH

How deep a penetration is necessary? Tooth wear has been measured in various studies; The following article found 30 microns to be a normal wear rate.Lambrechts P,Braem M,Vuylsteke-Wauters? M, Vanherle G. Quantitative in vivo wear of human enamel J Dent Res 1989;68: 1752-1754
There are really two parts to the preparation- the enamel rim, and the dentin retention. The perimeter enamel of the incisal edge should be cut to an average inciso-gingival depth of half a millimeter. This confers wear-ability over a worthwhile span - a decade or more, ideally, before dentin is encountered anew. The extent of cutting and hence thinning to the enamel on all sides- facial,proximals, and lingual should be absolutely minimal ,i.e.,only enough to optimize etching. Further thinning the enamel periphery only weakens it.

The preparation then descends a further 0.4 to 0.5 mm. into dentin to interlock the resin with the dentinal structure.

In attrition cases, we can assume that wear is accelerated, but simple arithmetic calculates that 30 microns a year in a normal patient means that 300 microns- roughly a third of a millimeter- equates to a decade of wear. Because these preparations are bonded to the enamel to the depth of 0.4 to 0.5 of a millimeter, one should see a lifespan of 13 to 17 years from these restorations before dentin exposure recurs. Clinical experience has borne this out, in fact , as I approach that lifespan with my early work, these restorations are still consistently functional.

As the preparation descends into dentin, the floor and walls should be kept entirely in dentin. To accomplish this, the handpiece must be angulated so that it follows the apical tapering of the tooth outline, with additional inclination to negate the convergence of the 330 bur. The base of the preparation must be in dentin not enamel. It is essential that the perimeter enamel should not be undercut. The photos below indicate the inclination of the handpiece as the preparation approaches the proximal extension, in an exaggerated way.



The schematics below illustrates the cross-sectional form.



After initial preparation, the tooth should be examined under high magnification for remaining incisal dentin. The intra-oral camera is helpful here, as well as the microscope. Failure to establish a 360 degree cavosurface in enamel leads to premature failure of the restoration. An island of composite will be prematurely surrounded by a moat of dentin, which resumes rapid wear and allows enamel chipping to proceed unchecked, as in the photo below, where an island of composite leaves the perimeter enamel unbonded and unprotected, and chipping resumes unabated.



What explains the effectiveness of this restoration? Two reasons:
  1. The Brinnell hardness of a typical resin is around 8.5, enamel is 9.8, while dentin is 6.8. The Brinnell scale is logarithmic, so that an incisal edge restored in resin is therefore 100 times harder than the dentin surface. Consequently, the restoration reduces the rate of ablation of the incisal edge by 99 percent.The wear of one day now takes 100 days.
  2. The perimeter enamel is fresh cut and end-bonded to composite, held cohesively to the underlying structure by adhesive dentistry's best and most reliable bond. The rationale for this approach derives from a pivotal article: Munichika T Suzuki K Nishiyama M Ohasi M Horie K. A comparison of the tensile bond strengths of composite reins to longitudinal and transverse sections of enamel prisms in human teeth J Dent Res 1984: 63:1079-1082. The excerpt below is of paramount importance to adhesive dentistry in all disciplines.


“CRYSTALS WITHIN THE ENAMEL ROD CYLINDERS RUN PARALLEL TO THE LENGTH OF THE ENAMEL RODS, WHICH ARE IN TURN APPROXIMATELY PERPENDICULAR TO THE EXTERNAL SURFACE” “WHEN THE TRANSVERSE SECTION OR FACE OF THE CRYSTAL, RATHER THAN ITS SIDE, IS EXPOSED TO ACID,THE CENTRAL CORE OF THE CRYSTAL IS MOST SUSCEPTIBLE TO ACID DISSOLUTION" "RESIN BOND STRENGTHS ARE TWICE AS HIGH WHEN ADHERING TO THE ACID-ETCHED ENDS OF THE CRYSTALS AS COMPARED TO THE SIDES OF THE CRYSTALS”

The effect of failing to engage rod ends is that bond strengths are effectively halved relative to rod-end margins. White line and/or brown line ensue, along with microleakage and premature restoration loss. All of our data on bond strengths derives from fresh-cut bovine enamel. The clinical necessity is to ensure that all our restorations meet this basic and unavoidable histologically-based criterion.


ESCALATIONS IN COMPLEXITY

Well-aligned mandibular incisors in which the enamel perimeter is still virtually intact are the simplest prototype from which more advanced applications evolve, specifically:

  • The minishoe: when chipped,irregular and weak facial enamel is seen
  • Lingual shoe, mandibular tooth
  • Lingual shoe, maxillary tooth
  • Cusp tip lesion
  • Junction with a Class III lesion
  • Wear through lingual surface
  • Junction with abfraction lesion
  • Vertical augmentation in rehabilitation

These contingencies will now be covered.

WEAK OR IRREGULAR PERIMETER ENAMEL: THE "MINISHOE"
This treatment applies to the lingual margin of the lower incisors, and to the facial margin of the upper teeth.

After preparation, the remaining enamel may be very thin and transparent. This becomes more obvious if the preparation is transilluminated with a fiber optic source, handpiece light, or operatory light.

If this very thin and fragile enamel shows crazing, it may be cohesively failing. If horizontal fracture lines are seen, it is best to remove the enamel to the level of the horizontal fracture. Otherwise, it is likely that this weak fragment will detach from the adjacent enamel under polymerization contraction forces. As such, it is contributing nothing to retention and actually weakens the entire restoration.

An effective way to ascertain the decide if the cohesion of a weakened edge is suspect, is to lightly and respectfully pull the thin enamel towards the center of the tooth with a hand instrument such as the H6/7 scaler.

Force applied to the tooth in this way mimics the effect of polymerization contraction forces. A pulling force serves to assess the sturdiness of the remaining tooth structure. It is often surprising, however, that very thin enamel may still be quite robust.

But if the enamel fails, the margin should be instrumented back with judicious use of the H6/7 until sound structure is reached. If the amount of missing tooth is now large, it should be restored with a bevel, as will be detailed later in this article.

When the enamel defect is small, irregular,only slightly below full incisal height,without horizontal fracture and still strong, ,a "mini-shoe" is indicated. This is accomplished by lightly reducing the defect with the apical third tip of a 7902 FG carbide at slow rpm with a delicate touch. A mini-bevel of less than ten degrees is sufficient. Following this, lightly air-abrade the bonding surfaces. The goal of these steps is to eliminate fluoridated and amorphous enamel; this prepares for optimum bonding without sacrificing sound enamel unnecessarily. Only 10 microns needs to be removed, from Summitt and Robbins "Fundamentals of Operative Dentistry, third edition, Quintessence, pg 8.

It should be noted that in a typical mini-shoe, the final enamel rod orientation is minimally beveled to achieve rod end-bonding. There is no attempt to produce esthetic blending by employing a long bevel to mesh the resin shade to the that of the shoe. The intention is to keep the amount of resin added so minimal that it does not attract attention negatively. If a blending resin is selected, often termed a "metameric" resin, as opposed to an opaque, densely-hued material, esthetic results can be very good. The translucent result is youthful and pleasing. If the patient has very dense incisal characterization, a more densely hued resin may be indicated.

The success of the mini-shoe is counter-intuitive. However, it has proven durable even in very thin overlays, in this author's experience. The probable reason for its durability is that the loads are primarily compressive on the shoe,and only incidentally in other planes. The primary shear and displacement loads are borne by the rest of the restoration. I often describe the "minishoe" as "hitchhiking" along with the main restoration. The mini-shoed enamel is not carrying the main retentive burden of the restoration, and, hence, this limited edge-bonding proves sufficient, and there is no staining as would possibly arise from rod-side bonding.




The pictures below illustrate before and after views of a mini-shoe. This tooth had sufficient dentin exposure on the incisal edge that a thin edge of enamel was standing proud. A quick bite on the tine of a fork did the rest.



MANDIBULAR LINGUAL SHOE

Lingual finish line

In the case of fractured mandibular lingual enamel, first ascertain the robustness of the fractured edge with a H6/7 scaler, just as described above. Remove any weak,crazed,undercut or friable enamel.

Once proven sound with scaling, a FG 7406 carbide is used to transform the irregular fracture line on the lingual tooth structure into a smooth and beveled finish line. This bullet-shaped bur correctly prepares the lingual margin; when the handpiece is held at ninety degrees to the cavosurface, the taper of the bullet-nose cuts the cavosurface margin to a small-angled bevel. See Conservative Composite Bevel. An article in Oral Health explaining this approach to margin design can be found at "Preparations In Composite Resin Part I: Principles And Instrumentation For Class V, Cusp Tips, And Incisal Attrition" Oral Health Journal, December 2011 Pgs.48-61 http://www.oralhealthgroup.com/news/preparations-in-composite-resin-part-i-principles-and-instrumentation-for-class-v-cusp-tips-and/1000738881/?type=Print%20Archivesexternalexternal link link


Lingual surface preparation

A lingual extension of the resin will be carried past the prepared margin onto the lingual surface to create a buttress conferring resistance against lingual displacement.The method of exposing rod ends on the lingual surface has undergone positive evolution over the last ten years. Earlier, the lingual surface gingival to the beveled lingual finish line was lightly prepared with a 7406 bur to establish fresh bonding area on the lingual surface. The intention was not to grossly remove tooth structure, but rather to remove the remineralized, amorphous, and highly fluoridated enamel surface which covers mature teeth to a depth of 10 microns. A long bevel was established 3mm to 5 mm gingival to the lingual beveled margin. This method exposed rod ends for optimum structural bonding, and eliminated the less etchable fluoridated layer. It was difficult, however, to carry the preparation well into the line angle, and equally difficult to control the placement of resin to this finish line. The photos below detail this earlier approach.



Our new approach to creating the lingual finish line is to sandblast the intended lingual bonding surface inside a Tofflemire band tightened to a positive seal at the gingival extent of the band. Simultaneously, the band protects adjacent teeth from unwanted air abrasion and creates a definitive finish line.

A new band is then placed as closely as possible to the same finish line and the tooth is bonded and resin placed inside the band. The finish line is determined solely by the location of the Tofflemire band, seating to several millimeters above the CEJ. The band enables positive condensation of resin to the prepared surface, and is a faster and more controlled method than free-handing. The photo below illustrates the rod-ends on the lingual surface exposed by removal of the amorphous fluoride-rich and etch-resistant remineralized enamel.





Restoration Design and Placement


The restoration is deliberately finished to a lingual over-contour. This forms a buttress to carry compression loads from the incisal onto the lingual surface, providing an intentional material path through which the compression forces on the incisal edge are transmitted down onto the lingual surface.

Without this buttress, compression and lingual displacing forces are borne by thin remaining incisal tooth structure. Clinically, early failure is seen without the lingual buttress.

Finishing this buttress can be problematic, because the finish line is indistinct. The following protocol optimizes this finishing: reduce excess shape using a FG 7406 to an indistinct flame-type margin at the presumed gingival level. Test for adhesion by pulling the margin incisally with a sharp H6/7 scaler. Poorly bonded composite peels back until the line where the tooth structure has been sandblasted. That is the correct finish line, where adhesion is optimum. Smooth this junction and polish with a FG Shofu Brownie point, wet, at low rpms. The Brownie point has the signifiant advantage of being quite aggressive when higher pressures are applied, yeet very delicate at lower rpms with a light touch. Other tapered finishing point systems do not always have this convenient dual personality.

When the patient is dismissed, advise them that perceptible extra bulk necessary for strength is present, and its purpose is to prevent future tooth breakage. When they understand that you are postponing a crown, they will likely accept the slight change in contour and be appreciative of your conservative instincts.

If the patient is not an appreciative personality type, I generally extend the dialogue to mention that lower crowns are the hardest in the mouth to perform, often suffering from poor aesthetics through under-reduction or pulpal death if sufficiently reduced. Unattractive over-contour is also very prevalent. I also mention subsequent accelerated wear to the opposing maxillary teeth from the abrasion of a mandibular porcelain crown. Sometimes we have to be very informative to win the patient over.

I personally think that crowns on the lower incisors have the poorest benefit-to-cost ratio of any crowns we place in dentistry. I avoid them like The Plague.


MAXILLARY LINGUAL SHOE

Unlike the lower incisor, over-contouring cannot be used in the maxillary teeth to augment the strength of the linguo-incisal restoration: we must conform to the occlusion. To offset this, the preparation requires deeper penetration into the incisal dentin, developing a deeper "mortise and tenon" interlock between the dentin and the resin, transferring loads from resin to dentin.

However, because normal function seats the restoration rather than dislodges it, the increase depth is usually less than half a millimeter. In the slide below, both central incisors present weak lingual enamel, which will be shoed.



The pencil line on the model below shows the anticipated finish line.



Preparation

First penetrate into the dentin with a 330 bur, to a suitable depth,at least 1.2 of a millimeter. Prepare the facial enamel so that the first 0.75mm to 1mm of depth is enamel,then penetrate into dentin a further 0.5 mm. Once this is done, bevel the lingual margin with A 7406 bur to produce a small-angled bevel, continuously from DEJ to cavosurface, at something under ten degrees.CCB margin - See Conservative Composite Bevel This is identical to the rationale for beveling the lingual margin of the mandibular linguo-incisal restoration, to engage rod ends.

However, two other concerns must be met; sufficient depth of resin for long lifespan, and sufficient thickness of enamel to accept contraction loads from polymerization. This is because thin enamel runs the risk of wearing through and opening the margin for renewed wear and erosion. Therefore, intentionally thicken the lingual enamel margin to a least 1/2mm. In deep overbites, this may significantly extend the footprint of the restoration in a gingival direction, sometimes several millimeters, often recruiting the centric stop off tooth structure and into the restoration. Because healthy tooth structure is being removed, this extension may seem intuitively destructive. On the contrary, this extension builds longevity in the result. The schematics below illustrate the preparation in cross-section.



The criteria for the preparation are as follows:
  • Adequate thickness of lingual enamel at the lingual cavosurface.
  • Centric occlusion not placed on the margin; instead, extended in a gingival direction until out of occlusion if necessary

The pictures below illustrate incisal breakdown, both facial and lingual, with accompanying discoloration of the incisal component. Tooth #11 will receive a facial mini-shoe, and both #11 and #21 require a lingual shoe. The restoration of the incisal contour and elimination of discoloration improves appearance markedly, despite the malpositions and misangulations of the teeth, and disharmonies of gingival form in the overall smile.


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CUSP TIPS

Restoring cuspids with exposed dentin; Method#1: The Intracoronal prep.


The model below shows a cusp tip preparation on a lower first bicuspid.The preparation is like that for an incisor, except that a 7404 or 7406 bur is used to extend a generous cavosurface bevel to all aspects of the outline. This is a necessity because the cusp tip is an area of rapidly changing enamel rod orientation, and physically irregular rod trajectories in a radial pattern, the so-called "gnarled enamel" see Summit and Robbins 2006, pg. 185-186 for histological discussion.Also, see See Cate, A.R. Ten. Oral Histology: development, structure, and function. 5th ed. 1998. ISBN 0-8151-2952-1.



Restoring cuspid guidance:cusp shoeing, Method #2: The Extracoronal prep

The case below shows restoration of lost cuspid guidance against an opposing long-standing PFG bridge, illustrating an important alternative to the above intracoronal prep design. When augmentation is being performed, less divergence of the walls required to ensure protection of the resin-to-tooth margin. Therefore,in contrast to the generous internal bevel recommended in Method#1,the internal walls are only slightly divergent in this prep. To protect the cavosurface, and often to regain cuspid disclusion, a 360 degree shoe is extended beyond the internal outline, a minimum of 2mm in extent, which generates extensive extracoronal bonding area - a generous "shoe". To complete the design, the preparation and the tooth margin beyond the finish line are sandblasted after a bevel is placed. This ensures that when the margin is feathered back in finishing, there is no risk of poor bonding, should the resin extend beyond the prepared finish line.

The restoration of these cuspids will protect incisal restorations, which are progressively destroyed as the cuspids fail to disclude them in protrusive excursions. the photos below illustrate the consequences from the parafunctional habits of a Class II Div II occlusion.





JUNCTION WITH A CLASS III LESION

When a Class III or IV meets an incisal edge worn into dentin, it is beneficial to prepare the incisal as well. If not, premature failure of the Class II incisal margin, chipping or dislodgement of the restoration, or aesthetic discontinuity between the shade of the composite and that of the incisal dentin. The cavosurface of the entire lingual outline form is conservatively bevelled; a 7404 bur is often used rather than the 7406, which may over-cut. The photos below illustrate the treatment of a lateral incisor demonstrating this wear pattern, i.e., linguo-incisal convergence. Tokoyama Estelite Shade A3.5 was used for its excellent blending characteristics, and established outstanding clinical performance, see The Dental Advisor for a 5-year clinical survey.







ADVANCED FACIAL WEAR:



Adequate enamel thickness.

Advanced wear of the facial surface on discluding surfaces sometimes produces very thin enamel at the perimeter of a wear facet. In the case above, there has been concomitant facial fracture, exposing a large volume of facial dentin. To ensure longevity, the preparations are extended peripherally in enamel until sufficient thickness of enamel is established, a minimum of 0.5 to 0.75mm.The correct cavosurface angle for rod-end bonding is established using the 7406, held perpendicular to the cavosurface, producing a CCB, See Conservative Composite Bevel. Near the CEJ, a Brasseler H284K.018 reaches more conveniently and produces a 45 degree bevel, which is appropriate for the thinner and relatively delicate enamel near the CEJ.

Adequate dentin thickness


Adequate thickness of 0.75 mm is needed to confer long lifespan to these advanced facial lesions. The 330 bur, whose cutting blade is 1,8 mm in length, helps to gauge the dentin reduction as it is being prepared. Alternatively, one can gauge inter-occlusal reduction with Kerr Occlusal Indicator wax, several layers thick, and have the patient occlude on a wax wafer two or three layers in thickness, to identify areas of insufficient reduction. Thin areas will be more transparent than the surrounding dark green of the wax layer. Another method to confirm reduction is quick-set VPS occlusal registration products, interposed and then calipered once set.

In deep overbite cases, adequate extension may remove as much as 50% of the footprint of the facial surface. This hardly seems the conservative thing to do. However, if the restoration is not adequately deepened and extended back to thick enamel, re-treatment will be premature, possibly in as little as five years. Bear in mind that the next escalation in invasiveness may be a full coverage crown, where we remove every last speck of enamel and dentin incursion is deeper yet.

In other words, while electively cutting greater depth in direct dentistry is not part of our habitual mode of thinking, it is more conservative than crown work, where we abandon this caveat and instead turn to the mindset of ensuring enough removal to meet the needs of the crown paradigm. We have to keep perspective despite the habitual mindset shifts incurred when changing paradigms.

If maximum aesthetic blending is desired, perimeter bevels can be increased to 45 degrees or even 60 degrees, rather than 6 to 12 degrees as in the CCB. A greater bevel is not necessary structurally, and becomes advantageous esthetically only when a metameric resin is chosen that blends to the host tooth in value, hue,and saturation. The pictures below illustrate preparations where larger bevels at the cavosurface were utilized. The Bandbender ,a custom-contoured circumferential matrix invented and sold by Dr. Walford was used to close the buccal margin and promote positive condensation of the resin, while establishing proper proximal contour and height of contacts. Without proper interproximal control, there will be no occlusal embrasures/spillways, contacts will be weak or non-existent. Equally important, without sufficient bulk below the contact, marginal ridges are prone to fracture and food impaction. See Bandbender



OPERATIVE EFFICIENCY

Efficient, low-frustration dentistry produces a better job. The following expediencies have proved critical.

  1. Treatment is coordinated by full sextant.
  2. Anesthesia, if needed, is a bilateral mental block, and is placed according to the method pioneered by Stanley Malamud. See www.drmalamed.com/external link for his teaching media.In synopsis, a bolus of anesthetic is placed adjacent to the foramen and induced into the foramen by finger pressure overlying the bolus. A quick-acting short-duration anesthetic, such as Carbocaine 3%, is frequently all that is needed. With this method, anesthesia is bilateral, quick, profound, painless,for the whole sextant. The lingual tissue and tongue remain unanesthetized, which prevents iatrogenic saliva ejector events, such as aspiration of the floor of the mouth, or chafe of a torus.
  3. The Hygoformic saliva ejector is employed to block investigative probes by a curious tongue. This wonderful adjunct minimizes swallowing, and keeps the patient in a stable configuration.see Isolation and Moisture Controland
Hygoformic Saliva Ejector Do not attempt to "make do" with a conventional saliva ejector. A rubber dam may also be used effectively, but active evacuation is always essential, because saliva accumulates uncomfortably behind the dam and leakage or sudden spasmodic swallows can be expected.
  1. Bilateral cotton rolls expand the lip away from the teeth, protecting the lip, making more room for a stable finger rest, and keeping the obicularis muscle from influencing cutting.
  2. The dental assistant is recruited to control the lower lip if the patient is still involuntarily contracting the Obicularis Oris muscle.The CDA places her thumb into the labial vestibule, stabilized against the alveolus, and places her first finger under the chin. The lower incisor prep is small and delicate and there must be exquisite control without unwanted extraneous inputs from the lip.
  3. Both hands are used by the operator to guide the handpiece head to optimize control, if needed.
  4. A new 330 bur is used to ensure delicately controlled cutting
  5. The bur cut is initiated with the “corner” of the bur, rather than the end, to avoid the possibility of skating off-target and iatrogenic damage.
  6. The intra-oral camera is used routinely for inspecting preps, to ensure that the preparation is fully extended to the enamel perimeter in all teeth. These small preps, on small teeth, require magnification at the I/O level or microscope to achieve a perfect job every time.
  7. Liquid etch is used with a brush to get complete insertion into all aspects of these small preps. In multiple preps, etchant is placed in a rhythm of placement of about two seconds in sequence, beginning on the CDA's side, and rinsing in sequence commensurately.
  8. A Monoject 412 syringe, filled with water is used to rinse off etchant in a controlled manner. Again, a rhythm of sequenced rinsing every two seconds maintains consistent etch times. If conventional A/W syringe is used, these small preparations have a tendency to splash back. Stopping to dry your face and glasses is not efficient nor patient-impressing. Other devices can be substituted, e.g., a Dialite plastic irrigation tip,attached to a 3cc luer-lock syringe. Dialite tips are available from Bisco Canada. Alternatively, a 3cc syringe can be used witha 22 gauge metal tip. The Monoject 412 10cc syringe is also convenient and effective, and holds a larger volume.

The shared goal of these rinsing options is to supply rinsing water with controlled and lower pressure and volume than the AW syringe, and as well, to use an irrigant that has not been treated with a waterline disinfectant, which can reduce bond strengths. See Reality Yearbook 2012 Pg. 144. for a report of a 25% drop in bond strength due to waterline disinfectant relative to distilled water.
  1. A Bendabrush, tip bent at 45 degrees, applies primer, ensuring thorough and speedy priming.
  2. No matrix strips are used unless a proximal wall is missing. This keeps the field unobstructed and thereby helps to prevent overfilling the preps. Matrix strips get in the way and promote overfilling.
  3. Overfilling is only required to compensate for thecontraction shrinkage expected, about 2%, and for the thickness of the oxygen-inhibited layer, another 10-20 microns on average. Any resin in excess of that is a waste of material and time.
  4. A anti-curing shield covers the operating light during placement. This allows continuous placement without fear of premature resin cure. A shield can be custom-made from a yellow transparent report cover, available from stationary suppliers. There are some aftermarket proprietaray shields available as well, at greater cost and with greater weight, which can upset the balance of the operatory light. Recently, manufacturers have started to build a yellow mode into operating lights.
  5. The goal is to block the curing wavelength completely. Amazingly, this plastic sheet absolutely blocks cure: resin under a sheet, curing wand directly on the other side of the film, results in no hardening of a resin increment. SeeBlocking Premature Cure
  6. In the smallest preps, a Hufriedy PICH is used to condense into the base of the preparation. The ends of this instrument resemble a Dycal application instrument; the shaft of the PICH, however, is full length and is much more ergonomic for the task of condensation.

  1. Larger preps require a smooth-ended amalgam plugger to ensure condensation to the base of the prep. Condensation is finished with a larger plugger, plastic instrument. or the egg-end of a Hufriedy 28/29 ball burnisher.

  1. With a lightly-held touch, the resin can be smoothed and adapted to the cavosurface by tactile means. The small end of the Hufriedy 26/27 also cleans up lingual overfill and gathers up any excess material. This overfill may be placed into the next tooth, reducing resin wastage and overfill.
  2. Reduced overfill equates to reduced finishing time, and lessened frustration. Frustrated dentists are more prone to over-cutting, making mistakes, and generating excess heat in finishing.
  3. 3M Espe Filtrk Z250, a commonly used resin, has high plasticity, which makes for placement qualities similar to some flowables. This produces a coherent functional result with little fuss.
  4. Z250 also has excellent metameric properties, so that the shade needs only to be correct in value to blend well.
  5. Z250 has fairly high shrinkage, 2.2% but, coupled with a Flexural Modulus of 9 GPa, still shows little tendency to crazing enamel. The best universal shade of Z 250 is D-3 for matching in the A3-A3?.5 range- not adhering that well to its stated shade, but very serviceable once you figure it out.
  6. As a rule of thumb, all materials placed in these preps should have the lowest contraction possible. In the author's clinical trials, most resins exceeding 2.3% contraction have produced visible enamel crazing. Unfortunately,excessive contraction excludes the majority of resins available today for these preparations. At the outset, before I understood how to quantify contraction stress, I accepted enamel crazing as an unavoidable downside. Now I know better.
  7. Estelite Sigma by Tokuyama (1.7%, Flexural Modulus, 8.6GPa) and Majesty Aesthetic from Kuraray, (1.9%, Flexural Modulus 10 GPa)are both also very effective.March 2014. See Resin Choices for Posterior Composites
  8. To compensate for unwanted resin stiffness,all are heated to 54 deg.C in the Calset Composite Heater. Viscosity is reduced markedly, cure time is reduced, polymerization shrinkage is reduced, photoconversion is increased, surface hardness is increased, and the thickness of the oxygen-inhibited layer is decreased. These are all highly desirable improvements in resin quality. See Heated Resinsfor relevant references.
  9. Estelite has excellent metamerism, and its wear properties have been excellent in two and five-year trials by The Dental Advisor. CRA has also given it high ratings. It is a very pretty material which is more faithful to its stated Vita shade than is Z250. Because of its lower shrinkage, it is the material that I use for at least half of my attrition cases now. It is somewhat harder to condense into preparations than Z250. Its handling is only slightly influenced by heating, but it a very plastic resin in its own right.
  10. Majesty Aesthetic is a little-known resin in North America, made by Kuraray, a powerhouse in the plastics world but lesser known in North America. It is without vices and attractive in cooler, lighter shades where less translucency and warmth is required than what one finds in Z-250 or Estelite.
  11. Research has shown that Z100 and Z250 are very hard- wearing surfaces, due to the very small filler particles.Estelite has larger filler particles but has shown equivalent wear-hardiness in clinical trials.(See review by the Dental Advisor)
  12. All these resins are very fast-curing materials. A 20 second cure exceeds the recommended cure times by a factor of three. High curability ensures full polymerization and optimum subsequent clinical properties.
  13. Curing time can be shortened by using two curing lights, if you have them, one in the hands of the assistant, one in the hands of the operator. This eliminates the frustration of 120 seconds of cure for six teeth. By using two lights it becomes a more tolerable 60-second process, or even 30 seconds in the case of a fast later-generation LED, allowing for outputs of 1500-2000 mW, and conferring the necessary joules to complete the cure.
  14. A snap cure is performed occasionally before the final cure, so that if something goes wrong, such as the patient having a coughing spell, all is not lost.
  15. Stable, wet finishing, free of convulsive swallowing, proceeds smoothly with the Hygoformic saliva ejector supplemented by the assistant's HVE. This increases control, reduces mistakes, or the temptation to finish dry, which will possibly abuse and overheat the resin.
  16. A 12-bladed finishing carbide, the 7902, is used for finishing, not a diamond finishing bur. This provides excellent tactile feedback, and leaves the enamel mirror-smooth once the margin is finished flush.
  17. Diamond finishing burs inevitably leave a rough, finely scored enamel surface. When rough enamel is polished, it will ablate at 1/10th the speed of the resin, being ten times harder. (The Brinell hardness of enamel is 9.8, that of most hybrid composites is 8.5. The scale is logarithmic, so that a difference of 1.2 is over ten times harder.) The clinical significance is that an abrasive effective enough to polish enamel will over-polish the composite. Make life easy- don't abuse the enamel by scratching it with a diamond in the first place.
  18. The H6/7 scaler is repeatedly used to check for flash, minimizing the need for rotary instruments. However, large amounts of lingual flash must be removed with the 7406 bur, because it is possible to rip off lingual enamel with a strong pull on a big piece of flash with a scaler.
  19. Two articulating forceps are used, one by the assistant, another by the operator, giving full registration in one application.
  20. A final check of the occlusion is made with Almore shimstock; the degree of grip between the incisors can be felt. If teeth posterior to the incisor group are fully occluded, one is certain that no prematurity exists.
  21. If the procedure is done without anesthesia, verification of correct occlusion is that much easier for the patient to confirm.
  22. The lingual enamel is wet polished with the FG Shofu Brownie at low rpms to restore smoothness which may have been roughened by the use of the 7406 finishing bur. If not polished,the patient’s may perceive roughness with their tongue just as you are raising the chair for dismissal. Better to polish preemptively.
  23. It builds confidence and patient rapport to preemptively ask the patient if there is noticeable roughness. When they so “no, it feels really nice and smooth,” you have a small bit of gratification built into the patient interaction, and of course we dentists are usually starved for gratification.
  24. Paint the preps after initial finishing with Caries Detector and have the CDA air thin it. This identifies flash and imperfect margins.
  25. The brown pigment from the Shofu Brownie point lodges in bubbles or voids that may have formed. This early identification of defects results. This avoids unhappy patients ,who may tell friends that your work is inadequate before you can fix it at recall. See Enhanced Finishing for more on this subject.
  26. The I/O camera is used to inspect the preps before dismissal. The high-contrast CCD chip and high illumination highlight deficiencies before they become committed flaws.

The sum of these steps is to make every aspect of the procedure as excellent as possible,a satisfying experience for the clinician, producing a controlled and durable restoration achieved effortlessly for the operator and patient.


EXTRAPOLATIONS AND ADVANCED CASES; VERTICAL AUGMENTATION

You can go farther with these ideas once you have gained confidence in this approach. Logically, if the concept of preparing into incisal dentin restores a tooth soundly in conformity with an existing bite, with imagination, couldn’t it also be used to augment tooth length if there was a need to do so?

Vertical rehabilitation of several mouths is documented below. Less adventurous, but quite achievable, is maxillary lengthening of worn teeth to restore the convex incisal smile line of youth, aesthetically following the curve of the lower lip.

The following cases show successes over a reasonable length of time, ten years being my definition of reasonable.
However, it is wise to understate one’s hopes to the patient by a good safety margin. As well, it is prudent to be explicit with the patient about who will bear the cost of re-treatment if and when it is needed.Lifespan is lifespan. There is no true permanence, only longevity. Even the best-placed conventional treatment, a ceramco crown, for example, will need re-treatment one day. Objectively, there should be some equation between cost and service life. If something cost four times as much, it should be expected to last four times as long, or, at the least, be tangibly better in some respect.

My experience, cost wise, is that these advanced composite extrapolations often factor out between one tenth to one quarter the cost of laboratory-modulated procedures. At this cost to service ratios, the direct composite service is excellent dollar value. For many patients, it is the only treatment that will ever be within their financial reach.Practitioners able to deliver these services are prepared for a "hard times" scenario in their practice if world and local economies continue to downturn.

As well, in our increasingly senior population, we can preserve appearance and function appropriate to fixed incomes and to the physically reduced treatment tolerance of patients in the later years of life.

WIRE AND COMPOSITE SPLINT WITH CHAIRSIDE-FABRICATED PONTIC

Sometimes, in vertical augmentation, enough space is gained to house a wire and composite splint, attaching to a deeply worn defect, and filling an edentulous space with a chairside fabricated composite pontic.





COMPLETE VERTICAL REHABILITATION



This 66-year-old female patient presented with 50% attrition of mandibular incisor height. Her acrylic CUD was the fourth in a sequence of full dentures. An initial porcelain-toothed prosthesis had scrubbed off her incisal enamel while she was in her third decade of life. Subsequent dentures in acrylic slowed the attrition but nonetheless she presents with extreme incisal attrition in her sixties.

We had stabilized her lower incisors about seven years earlier, with conservative resin incisal restorations conforming to the existing bite, as outlined above. Now, seven years later, she asked on examination if anything could be done to make her incisors longer. We were planning a new CUD, and she was remarrying.



We made a treatment plan to augment the incisors back to full length, and similarly increase the length of the posterior teeth, which were also abraded, and to lessen the Curve of Spee in the augmentation. Against this we would fabricate a new CUD, optimizing it for smile line, incisal length, with thickness compensating for resorption of the palate.



Articulator and Mock-up.

A facebow was taken of the original denture, and the models were mounted on a Hanau articulator. On the model,all the lower teeth were augmented to ideal height with expired composite resin, and the resulting extent of bite opening was noted.

More on this case

For more information on how this case was completed, see Vertical Rehabilitation with CUD