Outcome Evaluation of Ceramic Crowns Using Two Different Dental Cements
Condition: Sensitivity to Dental Cements; Dental Crowns; Dental Three-unit Bridges
MeSH terms: Hypersensitivity
Study type: Interventional

Summary: 
      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 restoration.

      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.
    

Detailed description: 
      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.
    

Intervention name(s): Full ceramic crowns or 3-unit fixed partial dentures.
Intervention type(s): Device
Intervention description(s): Subjects who met the inclusion/excluson criteria received two ceramic crowns or one three-unit dental bridge on posterior teeth. The crowns and dental bridge were cemented using two different dental adhesives. Follow-up to assess sensitivity of the crowns/bridges occur at 24 hrs. and 1 week post seating by telephone. Clinical visits to assess sensitivity and the integrity of the crowns/bridges occur at 6, 12, 18 and 24 months post seating of the restorations.
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: 2 crowns per subject or one dental bridge with two retainer crowns for a total of 72 Teeth.
Masking: Single (Participant)
Primary purpose: Basic Science
Keywords: dental cement; ceramic crowns; three-unit bridges; sensitivity