by John Nosti, DMD, FAGD, FACE
Porcelain fracture can be one of the most disheartening
events to happen in a dental office. We have all experienced
recurrent decay on a restoration that we placed, or possibly reinfection
of a root canal that we performed, but no event seems
to sink the mood of a practice as a patient presenting with fracture
of a ceramic restoration that we have placed.
Many doctors shy away from placing all ceramic restorations
because they feel the porcelain-fused-to-metal counterparts are
superior in strength and will be the answer they seek in preventing
all ceramic fracture. Others have turned to full contour zirconia
crowns in an effort to outperform the evil "forces" that are
bestowed on our dentistry. Then there are those who don't place
all ceramic restorations at all because of the fear of fracture.
Beyond the confusion of which materials would be best
suited for cosmetic cases is when doctors should recommend
parafunctional control appliance after completing treatment.
What could be wrong with recommending every patient wear an
appliance after having cosmetic dentistry performed? First, are
you sure your patients are being 100 percent compliant with
your recommendations? Second, are you taking every precaution
necessary to ensure success of your restorations or are you
relying solely on the patient wearing an appliance?
The following is a set of guidelines I put together after performing
"cosmetic rehabilitations" and placing all ceramic restorations
for more than 10 years. Using these guidelines, in addition
to proper preparation and bonding protocols, should allow one to
limit the percentage of porcelain fracture in the office.
Guideline #1: Set up the occlusion as a parafunctional
appliance that cannot be removed. Research has indicated that
sleep bruxism is in part due to microarousals in the central nervous
system during sleep. Shortly following these microarousals,
rhythmic masticatory muscle activity (RMMA) occurs in
approximately 60 percent of the normal population¹ and 80
percent of patients with sleep bruxism.² Sleep bruxism is a parasomnia
and a parafunctional activity during sleep that is characterized
by clenching (tonic activity) and/or the repetition of
phases of muscle activity (phasic activity) that produce grinding
of teeth.³
Despite popular belief, these microarousals and RMMAs
occur independently of the type of occlusion present. This means
it is quite likely one doesn't stop bruxism with a change in occlusion.
So how does occlusion play a role? Deprogramming hyperactive
muscles, removing posterior interferences into closure and
setting up cosmetic cases with anterior guidance (immediate lateral
and protrusive guidance) will prevent posterior teeth from
contacting in excursive movements. When posterior teeth contact
elevator muscle force is increased. Removal of these posterior
contacts allows muscle contraction force to be reduced in excursive
movements.4 The result is a loss of potential harmful forces
placed on anterior all-ceramic restorations in excursive movements (shearing forces) that can result in porcelain fracture. This
occlusion doesn't stop parafunction but simply alters and reduces
forces that might have been responsible for the occlusal breakdown
present prior to restorations being placed. It is important
to test the new planned occlusion in temporaries to determine if
Guideline #1 is sufficient to resist parafunctional forces placed
on your new restorations.
Setting up the occlusion to resist parafunction should be considered
your chief protocol in porcelain protection. Patients who
don't have muscle pain or migraines associated with parafunction
are more likely to be non-compliant with protective appliances
compared to those with orofacial pain. The occlusion can be further
perfected with the use of Tekscan occlusal analysis. Actually
knowing the forces present on restorations and the timing of
occlusion is superior to the use of articulating paper alone.
The following guidelines are for patients who are highly
likely to experience porcelain fracture despite having a perfected
occlusion.
Guideline #2: Protect patients who present with broken
dentistry. Patients who present to your office in need of comprehensive
restorative dentistry with existing broken dentistry
should be considered highly likely to break dentistry in the
future. Patients who break solder joints, fracture bridgework or
present with multiple fractures to their existing dentition (in the
absence of large unsupported direct restorations) should be
informed ahead of time that they will require a protective appliance
once your dentistry is completed.
Guideline #3: Protect patients who break their temporaries
repeatedly. Patients you have placed in temporaries with
a corrected occlusion, as specified in Guideline #1, who present
to your office with fractured or missing temporaries should be
considered highly likely to break the final restorations as well.
This guideline might be subject to when and how the temporaries
fractured, i.e. biting on hard objects. Patients who report
consistently fracturing their temporaries during function might
have been placed in temporaries that violate their envelope of
function. Waking up from sleep with fractured temporaries or
under times of subconscious parafunctional activity should be
advised that a protective appliance is mandatory during sleep or
times when that activity occurs, i.e.: driving.
Guideline #4: Protect patients where anterior guidance is
not achievable. When anterior guidance is not achievable in all
excursive movements, a protective appliance should be strongly
suggested. There is a reason that the lateral incisor is the most
commonly fractured anterior ceramic in dentistry and here it
is… Verifying anterior guidance goes beyond just marking contacts
into closure and asking the patient to "grind left and right."
How often do you check your patients' crossover and latero-trusive
patterns? Patients that contact only on their lateral incisors
in crossover (Fig. 1) should have the option of either shortening
the length of the laterals or the opposing tooth/teeth, or should
be advised to wear a protective appliance. The same holds true
for patients who go into a latero-trusive movement and contact
their lateral incisor only. Adjustment recommendations should
be made to these patients to reduce the contacts or wear a protective
appliance.
Guideline #5: Protect patients who report with an ever increasing
diastema. One of the most common cosmetic corrections
sought out by patients is closure of diastemas. Prior to
treatment, a thorough history should be taken including questioning
patients if they have noticed that the space has increased
over time. If the patient reports that he/she has noticed a steady
increase in the space over time, a protective appliance should be
considered following definitive treatment. Checking for fremitus
in the teeth to be treated both pre- and post-operatively is
extremely important to rule out as a contributing factor. This
guideline has a tendency to be more forgiving than the others
when violated. Typically the patient will report within one
month post-cementation with a slight space where the original diastema was that can be easily closed with a combination
aligner/protective appliance.
Guideline #6: Protect patients who have their anterior
segments changed from Class III to Class I. Restoring anterior
segments from Class III to Class I typically involve a multitude
of factors and prosthetic concerns (Figs 2 & 3). One of the
main factors to be considered is the amount of porcelain that is
going to be placed unsupported at the incisal edge over the existing
teeth or preparation. Occlusal jumps involving increasing
lengths of 4mm or more over existing preparations should be
considered for protective appliances if the overbite is 2mm or
greater. Increasing vertical dimension is many times necessary to
facilitate such occlusal change. The combination of new occlusal
position and increased vertical dimension might result in a temporary
increase in bite force at maximum intercuspation. Even
if these patients have been stable in temporaries for a period of
time, it is still advised that they wear a protective appliance due
to the vast changes that have occurred.
Cosmetic dentistry can be a very rewarding aspect to add to
one's practice. Beyond the financial rewards are the emotionally
gratifying experiences that you will share with your patients.
Implementation of sound protocols, including knowledge of
preparation design, material selection, bonding techniques,
occlusion and parafunctional protection guidelines, will enable
you to practice more predictably, more confidently and keep
porcelain fracture to a minimum.
References
- Bender, Steven D. The Academy of Dental Therapeutics and Stomatolgy 2009.
- Luis de la Hoz-Aizpurua Jose, Esperanza Diaz Alonso, Roy Latouche A, Juan Mesa J. Sleep Bruxism.
Conceptual review and update. Med Oral Patol Oral Cir Bucal. 2011 Jan 3.
- Kato T, Thie NM, Huynh N, Miyawaki S, Lavigne GJ. Topical review: sleep bruxism and the role of
peripheral sensory influences. J Orofac Pain. 2003; 17(3):191-213.
- Ommerborn MA, Giraki M, Schneider C, Fruck LM, Zimmer S, Franz M, Raab WH, Schaefer R.
Clinical significance of sleep bruxism on several occlusal and functional parameters. Cranio. 2010
Oct;28(4):238-48.
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Author’s Bio |
Dr. John Nosti practices full time in Mays Landing and
Somers Point, New Jersey, with an emphasis on functional
cosmetics, full mouth rehabilitations, and TMJ dysfunction.
Dr. Nosti's down-to-earth approach and ability to
demystify occlusion and all-ceramic dentistry has earned
him distinction among his peers. He is privileged to instruct and mentor
live patient and hands on programs with the Clinical Mastery
Series and Dr. David Hornbook. He has lectured nationally on occlusion,
rehabilitations and technology. He is a member of the American
Dental Association, American Academy of Cosmetic Dentistry and
American Academy of Craniofacial Pain. Dr. Nosti also holds fellowships
in the Academy of General Dentistry and the Academy of
Comprehensive Esthetics. |
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