The restoration of indirect partial and full coverage restorations in dentistry necessitates
the use of a luting agent to act as a means of mechanical and potentially, chemical
retention of the restoration. Upon the introduction of the first generation of glass Ionomer
cements for use as a luting agent, an elevated short-term post operative hypersentivity was
reported. In part, this adverse event was considered to be due to a desiccating effect of
the cement as water is utilized in the setting reaction and thus a desiccation of the
dentinal tubules was proposed as a potential mechanism leading to disruption of the
neurosensory odontoblasts. Further materials development in the field of dental cement
luting agents has lead to the introduction to the current market of resin formulations that
have an alternative mechanism of setting. Consequently, there are anecdotal reports of a
decrease in the incidence of post-operative sensitivity but no comparison with the effect of
conventionally used dentin desensitizing agents as a part of the bonding process of the
The purpose of this trial is a single blinded parallel design randomized clinical trial to
evaluate the perceived incidence of post-operative sensitivity when full coverage all
ceramic crowns or short-span three unit fixed partial dentures (dental bridge) is fabricated
in the posterior part of the mouth. The dental crowns or bridges will be bonded with
conventional glass ionomer cement or a Urethane dimethacrylate / Bis-GMA composite resin
dental cement. Outcome measures will be both objective clinical criteria and the use of a
calibrated pain survey instrument.
Background and Significance: The development of porcelain crowns for the predictable
restoration of teeth has been brought about by the development of bonding techniques to
enamel and dentin with the use of multi-step total etch adhesive systems along with the
evolution in small particle hybrid resin composites as adhesive luting agents. One of the
most common post-operative concerns of patients following delivery of full coverage crowns
and bridges is sensitivity to thermal conditions in the mouth (cold water, ice cream, etc.)
(Goodacre, Bernal et al. 2003). In order to understand the biological basis for these
materials it is important to understand the anatomy and neurophysiology of dentin. The
following is adapted from a paper provided by Dr. Charles Cox (Professor, University of
Alabama School of Dentistry) concerning dentin structure and mechanisms for reduction of
dentin hypersensitivity .
Dentin is a vital tissue, harder than bone but weaker than enamel with a physiological
elasticity preventing tooth fracture. Dentin is approx. 74% mineral; the organic phase
being approx. 26% type-1 collagen with small amounts of proteins and water. The collagen
matrix is secreted as a biologically "plastic" material, which hardens by a variety of
mechanisms. Normal dentin is composed of millions of tubules or canals, running from the
pulpal wall to the Dentin-Enamel Junction (DEJ). The dimensions of these tubules or canals
varies depending on the position within the dentin structure. For instance, tubule diameter
at the DEJ is 0.06 µm, and 3.0 µm at the pulpal wall (approx. 60,000 tubules / mm2). Most
tubules are filled with fluid, an odontoblast cell process, collagen, and occasional
non-myelinated pulpal nerves coursing approx. 150 µm towards the DEJ (Ten Cate 1998).
In normal (non-anesthetized) patients, Gysi (1900) reported that fluid distortion on the
cavity floor caused sharp pain. Brännström et al. (1966, 1969, 1976, 1979, 1980, 1996)
demonstrated dentin hypersensitivity (sharp pain) is the result of rapid fluid movement in
the tubule complex, aggravated by aggressive air-drying. Physiological testing in various
animal studies (Heyeraas 1985, Narhi 1983, 1985) confirmed the fluid pulsing or hydrodynamic
mechanism (Brännström 1966) as the prime cause of sudden dentin pain. Physiologically, any
rapid bi-directional fluid flow is the result of a sudden shift in tubule fluid from stimuli
(i.e. cold or rapid airflow; Brännström 1996).
Management of dentin hypersensitivity is only one part of a successful dental complete
coverage restoration (dental crown or bridge). In evaluating the clinical service-life of
porcelain crowns there are three aspects of the bonding environment that needs to be
considered. These consist of the tooth preparation, the adhesive and the tooth or crown
preparation and the fit of the porcelain restoration to the tooth preparation. All ceramic
restorations need enamel and dentin reduction of at least 1.5 mm along with a smooth
shoulder and avoidance of sharp edges to avoid crack formation on the intaglio surface,
proper esthetics, physiological contours and strength of the final restoration.(Goodacre,
Campagni et al. 2001) Dental preparation for full coverage restorations (1.5 to 2 mm
clearance which often means 1.5 - 2 mm loss of tooth structure) are inherently
non-conservative and with a reduced amount of remaining tooth structure there is an elevated
risk of post-operative sensitivity.
In today's society, having a dental restoration that provides minimal post-operative
sensitivity is only part of the demand from patients. There is an increasing expectation
for esthetic, "life-like" restorations that simulate if not replicate the natural tooth.
This is complicated especially in patients with heavy occlusion or are missing teeth. The
development of CAD/CAM milling technologies has laid the groundwork for use of high strength
heat-pressed zirconia [tetragonal zirconia polycrystals (TZP) a yttrium partially stabilized
polycrystal structure] as a supporting framework for supporting an esthetic, "life-like"
Lucite-base veneering ceramic material to provide an all ceramic form of full coverage
dental restorations for individual teeth or replacement of a single missing tooth with a
3-united fixed partial denture ("dental bridge"). The use of press porcelain crown
technology has allowed the improvement of fit of refractory die porcelain crown fabrication
relative to conventional Pt foil techniques and may lead to greater predictability and
reduced microleakage (with enhanced service life of the dental restoration). The potential
for an enhanced service life may depend on a combination of silination with a bifunctional
bis-GMA primer and dual cured composite resin luting agent which may seal microcracks within
the intaglio surface of the porcelain and a sufficient bond to tooth structure for a
reasonable service life.
Inclusion and Exclusion Criteria:
- Subject shall be in need of a maximum of two porcelain crowns on their posterior
teeth. In the case of missing single teeth, the adjacent retainers shall be in need
of complete coverage restorations and provide sufficient support for a conventional
3-unit fixed partial denture.
- Cantilever pontics shall not be performed.
- Prospective teeth shall be vital and not in need of root canal endodontic therapy.
- The tooth in question shall be "responsive" to conventional Endodontic tests. These
tests shall include a positive response to thermal stimulation (CO2 ice) and/or
electric pulp testing (EPT).
- The tooth in question shall be in occlusion with the opposing dentition. Subjects
shall have an Angle Class I occlusion with preferably canine eccentric lateral
guidance. In selected cases a mutual protected occlusion is acceptable if lateral
guidance can be minimized on the restorations at risk. Subjects with intraoral
ornamental metallic devices (e.g., posts, etc) shall be excluded.
- The tooth in question shall not be a retainer for a Removable Partial Denture (i.e.,
a surveyed crown) although the tooth may lack a mesial or distal contact.
- The tooth in question shall have periodontal stability (probing depths < 3mm, dental
mobility < 1).
- The tooth shall not be in need of surgical crown lengthening for reasons of
restoration or periodontal status.
- Subjects involved in other clinical trial protocols utilizing a similar protocol as
proposed shall be excluded.
- The subject shall not have any known allergies to any materials used in this
protocol. Subjects who need antibiotic prophylaxis for SBE are acceptable for
- Subjects of child bearing age shall have a urine pregnancy test. Pregnant subjects
shall be excluded.
- Subjects shall be available for a potential recall period of five years