Background: Dental crowns are ideal restoration to protect teeth that have been extremely worn down, broken, weakened by caries, and heavily filled or root canal treated. They can be also used for aesthetic purposes. Full crown preparation requires more tooth removal than other restorations and is associated with dentine exposure. When a two-stage crown fabrication is planned, there is a risk of bacterial contamination of the pulpal tissue through dentine and eventually vitality loss. The main objective of this protocol is to assess whether immediate sealing of the exposed dentine surface following crown preparation of back teeth can lead to a decrease in microleakage and bacterial infiltration from the oral environment.
Methods: This protocol, immediate dentine sealing of crown preparations, demonstrates a model for a one year, three years and six years follow-up, in-vivo, randomised controlled trial with a balanced treatment allocation of 1:1 (immediate dentine sealing vs. delayed sealing). The treatment will include tooth preparation, impression taking, temporary crown placement and full crown fit on a posterior tooth.
Discussion: The results of the study would provide insight into the question of whether immediate sealing of dentine after crown preparation reduces the bacterial ingression and incidence of vitality loss of teeth. The results would also help to provide evidence based suggestions for clinicians and other researchers.
This dissertation consists of literature review and a representation of the study design and methodology, followed by data management, statistical analysis and quality assurance of proposed study. Other sections are allocated to ethical consideration and reflection on thesis procedure.
No portion of the work referred to in the dissertation has been submitted in support of an application for another degree or qualification of this or any other university or other institute of learning.
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I have great pleasure to express my gratitude to my Tutor
(Juliette Kendall). She has been most helpful and supportive throughout.
Introduction, Research question and PICO
Restoring teeth with full-coverage crowns is a routine treatment in general dental practice. This normally requires two visits, one for crown preparation and impression taking and one for final cementation of the crown once the restoration has been produced in the dental laboratory. Provisional crowns which will be provided to protect the tooth between two visits could cause problems since they are not bonded to the prepared tooth surface permanently and require removal prior to final cementation. Problems may occur if the bacteria from oral cavity gain access to the pulpal tissue. The consequence could be pulp inflammation or even irreversible pulp infection, which requires endodontic treatment. There are some evidence in the literature that suggests that applying a sealant material on the freshly prepared teeth may reduce the invasion of the pulp by bacteria (Magne et al., 2007). Any effort needs to be made to reduce the risk of vitality loss in teeth requiring a full-coverage crown.
There are other alternatives to reduce the bacterial ingression like CAD/CAM technology. This method allows restoring a tooth with a crown in a single visit. Reis 2006 believes that using this system may decrease the possibility of bacterial infection of the pulp as there is no need for provisional coverage of the prepared tooth.
1.2 Research question
Protecting the exposed dentine with a sealant after a crown preparation requires some additional steps and is more expense and time-consuming than the traditional procedure. The research question is if it is clinically necessary to seal the exposed dentine immediately after the preparation with a dentine sealing agent or not.
Population: NHS and private patients between the age of 18 and 58 years of age in general dental practice requiring full-coverage crowns of a posterior tooth.
Intervention: Sealing the exposed dentine of prepared teeth for full crown coverage with a dentine sealing agent instantly after the preparation before taking a final impression and temporisation.
Control: Not sealing the exposed dentine of prepared teeth for full crown coverage with a dentine sealing agent instantly after the preparation.
Outcome measure: Comparing the vitality loss of the prepared teeth for full crown restoration at one year, three years and six years.
Aims and objectives
The aim of the study is to evaluate the efficiency of instant sealing of posterior teeth prepared for full crown coverage prior to impression taking and temporisation in terms of vitality loss compared with teeth without any sealant application.
The primary objective is to assess whether an instant sealing of prepared posterior teeth for full crown restorations with a dentine sealant results in a reduction in vitality loss.
To organise a clinical trial and to allocate two groups of participants (NHS and private) aged between 18 and 58 requiring a crown on a posterior tooth. One group will have their prepared teeth covered and one group not.
To analyse the achieved data and to determine whether there is a difference between groups in terms of loss of vitality.
The assumption of this protocol is the proposition that the instantaneous sealing of exposed dentine after crown preparation, will help against the bacterial contamination of the pulpal tissue and decreases the probability of the treated tooth requiring root canal treatment in the future.
3.2 Search Strategy
The strategy conducted for this literature review included an electronic search of the following databases: EMBASE (1995 – Oct 2011), MEDLINE (1995 – Oct 2011) and Cochrane Library. The reference list includes hand-searched articles and key journals related to researching.
Key words: REFER TO KEY WORD EITHER HERE OR APPENIX
Where tooth destruction by dental disease is extensive, restoration may only be possible with full coverage restorations or crowns. There is a big number of NHS and private patients in UK requiring a full coverage of posterior teeth due to failed huge previous restorations, fractured cusps or following a root canal therapy. Tooth preparation for full coverage crown requires more tooth removal than other restorations. It should be carried out in a conservative way. The reason is to reduce the post-preparation sensitivity and pulp tissue protection in vital teeth and to maximise the remaining tooth structure.
3.4 Crown Preparation and pulp
Health of pulp tissue can be affected by any restorative treatment. This is due to a continuous extension between dentinal and pulpal fluid (Pashley 1992).
Preparation for a full-coverage restoration requires removal of most of the enamel resulting in an exposed dentine surface and may affect the pulp. In one study by Jackson et al. (1992) irreversible pulpitis occurred in
5.7% of cases in which crowns were placed. The bigger the exposed dentine surfaces during tooth preparation like for a crown, the greater the risk of bacterial infiltration from the oral environment (Pashley, 1990).
Saunders and Saunders (1998) considered the vitality loss in adults who received full crowns in a dental hospital based on radiographic analysis and found that 19% of the patients in the study have lost vitality of the prepared teeth.
A study by Cheung et al. (2005) aimed to investigate the influence of factors connected with pulpal damage in teeth restored with porcelain fused to metal (PFM) crowns or crowned as a fixed bridge abutment. The study reveals that the preparation for either of the restorations requires a considerable reduction of dentine and may cause trauma to pulp tissue but the survival rate of pulp in single-unit crowns is higher than in abutment teeth.
Bergenholtz and Nyman (1984) and Karlsson (1986) demonstrated a permanent pulpal damage rate of 1% year for vital teeth following a crown restoration.
3.5 Crown Vs. other restorations
Many previous studies have supported the use of indirect intracoronal restorations (porcelain or composite) in vital teeth as advantageous against full-coverage restorations due to their less invasively preparation and more conservative nature (Jackson, 2008, Magne et al., 1996, Dietschi et al., 1994). They have been also considered to be easier to do than a crown and are no more expensive than crowns or root canal treatments.
A literature review by Kerschbaum and Voß 1981 showed that inlay restorations at 10 years have 9.5% lower rate of vitality loss compared to full crown restorations. When aesthetic aspect is not the first priority properly designed and provided inlays and onlays have the same longevity and durability as crowns (Jackson, 2008).
Cusp replacement with resin composite can be considered as alternative to traditional cusp replacement by crowns due to advanced adhesive technology. Deliperi et al. (2006) highlight that if the bonding agent is not stressed, an acceptable success rate could be achieved by using this method. According to van Dijken et al. (2001) an indirect cusp replacement restoration with ceramic might be considered indicated. This has the benefit of saving valuable remaining tooth substance and eventually avoiding endodontic therapy.
3.6 Dentin Bonding
There are recommendations in the literature for sealing the dentine with a Dentine Bonding Agent (DBA) following crown preparations in order to minimise the associated complications like hypersensitivity (Clinical Research Associates 1993). Dentine bonding agents have shown to be advantageous over the smear layer itself due to their mechanical retention (Nakabayashi et al. 1982) and moisture and acid resistance (Brunton et al. 2000). Over the last decades they have been considered as a modern way of sealing exposed dentine (Ferrari M. et al. 1999, Swift EJ et.al 2001).
Some authors have compared the effectiveness of DBA with smear layer as a natural barrier. Pashley (1984) states that dentine permeability can be reduced up to 98% when smear layer is produced by slow or fast rotary headpieces but it would not last for more than a few days due to acidic PH from the oral cavity (Kerns DG. et al. 1991) .There are several advantages of DBAs over the smear layer like hybrid layer as described by Nakabayashi (1982) and resisting moisture and acid (Brunton et al. 2000).
The result of various in-vitro studies on humans teeth (Pashley et al. 1992, White et al. 1992, Al-Fawaz et al. 1993) and animals teeth (Suzuki et al. 1994) supports the idea of sealing the dentine of prepared teeth for a crown restoration. A literature review by Lam, C.W. and Wilson, P.R. (1999) revealed that dentine sealing with bonding agents prior to crown cementation could be beneficial due to fluid flow reduction in dentine tubules.
Magne (2005) believes that immediate application of dentine bonding agents or Immediate Dentine Sealing (IDS) prior to impression taking can reduce the postoperative sensitivity and bacterial contamination. 35% H3PO4 is normally used to remove the smear layer before DBA application.
There are different ways of sealing dentinal tubules after the preparation. Edward and swift (2009) reviewed several in vitro research studies on the immediate dentine sealing technique in a critical appraisal and came to following conclusions. First, immediate sealing of fresh dentin improves the resin adhesion and the bond strength will be affected by late application. Second, the IDS provide a mechanical barrier which minimises the postoperative sensitivity, bacterial contamination and eventually the necessity of local anaesthesia.
Most Practitioners prefer to use self-etch-adhesives. However, Magne et al. (2007) believe that a three-step, etch-and-rinse adhesive has shown to be more efficient. In order to avoid complications after the IDS, some clinical steps need to be taken. The appearance of an O2 -inhibitory layer is not desirable and should be prevented by light-curing the dentine adhesive twice under a glycerine coating. This step avoids the reaction between inhibitory layer and impression material. The reaction between temporary crown and sealed tooth should also be prevented by applying a separating material.
The influence of dentine on antimicrobial effect of ingredients added to one-step dentine sealants was assessed by Gondim et al. (2008) and revealed a reduced affectivity after polymerisation with UV light.
3.7 Temporary Crowns
Temporary crowns are provisional restorations that are fitted on the teeth between preparation and fit appointment. They have various functions, mainly dentine protection and tooth movement prevention. Their role is often overlooked by practitioners (Wassel et al. 2002). Pre-formed crowns (plastic, metal) and self or light cured resins are usually used in the dental practices as convenient for temporary restorations.
Many temporary crowns have poor-fitting margins based on production procedure and material used. Some materials create a gap between the temporary and the prepared tooth due to polymerisation shrinkage (Robinson and Hovijitra, 1982)( Tjan et al. 1987).
Cervical border of a temporary crown is the primary area to be reached by bacteria from the oral environment. Richardson et al. (1991) believe that dentine in the cervical margin shows higher permeability than dentine in other surfaces of the prepared tooth and that confirms the importance of good marginal adaptation of temporary crowns.
A paper by Cagidiaco et al. (1996) considers the exposure of vital pulp tissue to bacterial contamination and irritants after dentine preparation in the base of a cavity, especially if temporary shows an unsatisfactory sealing. Exposed dentinal tubules after a crown preparation provide a way for transfer of substances between the pulpal tissue and periphery (Garberoglio and Brannstrom M. 1976). These tubules are expected to be sealed by cement. Different researchers (White et al. 1992, White et al. 1994, Lyons. et al, 1997, Baldissare. et al. 1998, Goldman et al. 1992) have found microleakage to be present after either permanent or temporary crown cementation.
Literature review supports the evidence of benefit of immediate dentine bonding as a technique during temporisation of indirect provided restorations but reveals a lack of in vivo evidence. This fact supports the requirement for this clinical study.
Study design & methodology
The study design and methodology will be presented in accordance with the CONSORT explanation for reporting on clinical trials (Moher et al., 2010).
4.1 Trial Design
This will be a randomised controlled parallel two-armed trial-pragmatic group trial to take place over the duration of a six-year period. The study will provide a 1:1 allocation ratio. One molar tooth will be randomly chosen per participant. The evaluation of the outcome will take place at one year, three years and five years (Fig 1).
4.1.1 Changes to trial design
The Data Monitoring Committee (DMC) will have access to the un-blinded data. The study protocol may be altered by DMC due to their recommendations.
Participant selection will take place utilising new and existing patient population that attends the dental practice. Recruitment will be on a continuous basis until the required numbers of participants have been enrolled into the study (see section 5 for sample size calculation). This will ensure the pragmatic nature of the trial as no proactive recruitment of patients from leaflet drops and advertising will take place. A trained member of staff will administrate the consent process once a patient has been identified as having an eligible tooth suitable for the study.
4.2.1 Inclusion criteria for participants:
Healthy adult patients between 18-58 years of age
Provide a written informed consent, understand spoken and written English.
Regular attenders (at least every six months) with a two-year record
Require a full coverage of a Molar (Upper or Lower arch)
With a crown
Selected tooth must be periodontally healthy.
Selected tooth must be vital and without any history of pulpitic symptoms within the last 12 months.
Are able to attend follow-up appointments.
In terms of periodontal status, the chosen teeth for study have to have a BPE less than three mm as per guidelines published by British Society of Periodontology (BSP). The teeth must be also radiographically free of any pre-operative pathological signs meaning intact pulp with no evidence of radiopaque foreign materials in the pulp chamber and/or root canals(s) and no periradicular radiolucent area.
4.2.2 Exclusion criteria for participants:
Irregular attenders to dental practice
History of pulpitic symptoms in the last 12 months
Patients participating in any other medical trials
Notable medical history change or pregnancy
Existing periapical pathology (radiographically)
Periodontal pockets more than three mm
Pulpal exposure or extending caries into the pulp chamber
Vulnerable adults or children
4.3 Study location and settings
The trial will take place in twenty dental practices based in the United Kingdom. General Dental Practitioners with more than five years’ experience and qualification in a post-graduate restorative dentistry will be recruited.
Patients may be disqualified if they experience medical complications or refuse to attend routine check-ups. A patient may also be withdrawn from
the study if the tooth suffers from a trauma, requires extraction or develops pockets deeper than 3mm due to insufficient oral hygiene. Information on all patients, including the reason for the withdrawal will be collected and added to trial data report. Patients may also choose to withdraw from the study themselves.
Initial selection process will include all teeth that are suitable per patient.
To maintain allocation concealment and to limit the occurrence of selection bias (Vickers A.J. 2006) a remote allocation officer in the central generates the allocation of teeth for either the intervention or control group. The participant’s initials, gender, date of birth and tooth notation will be submitted to a centre securely, where randomisation will occur within the patients to select the eligible tooth and to allocate the patient to the treatment or control group using a computer generated sequential number list. The trial will include only one allocated tooth per patient per control or treatment group. The indication of allocation will be sent to the general dental practitioner in an envelope with the patient’s identification code and the tooth number. The code for trial remains hidden until the clinical procedure to treat all eligible teeth is ready. At this time, it will be opened by the operator but not revealed to the participants.
The randomisation will be balanced to a 1:1 ratio for each provider in each practice. Simple randomisation is suitable to generate a balanced group. Balance between the groups at each location will be verified by the trial allocation operator regularly.
4.6 Baseline assessment
A baseline examination will be carried out by operators once the suitable patients have completed the consent procedure. The assessment will include:
Patient’s Identification, age and gender
Medical and social history
Musculoskeletal assessment, Soft tissue profile, TMJ
Oral Hygiene, periodontal assessment, soft tissue, occlusal analysis, vitality testing, Ridge mapping,
Radiographic evaluation of tooth prior to preparation
Reason for Crown placement
4.7 GDP training
Each of the operators will attend a one-day training program on techniques. Clinical consensus will be ensured and standardised in a discussion with investigators in a separate session and will include a clinical protocol for the preparation of teeth for a full coverage with a crown, impression taking and temporisation. Additional clinical protocols will be prepared for immediate dentine sealing after preparation and for final cementation of the restoration. A clinical team member will be appointed as the independent observer to evaluate the compliance to the study criteria.
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All materials and Instruments used will be applied as per manufacturer’s instructions. The Crown system used in the study is Cercon ht (Dentsply) full Contour Zirconia. The high strength of zirconia-based ceramic restorations increases the indications for choice. They can be a near ideal choice for restoring crowns, fixed partial dentures, and implants in aesthetic areas. Because of their high strength, zirconia-based ceramic restorations can be cemented with traditional cements or bonded with adhesive resin cements. Like gold, Cercon ht has a simple, clinical protocol, requiring conservative tooth reductions of as little as 0.5 to 1.0 mm. A feature that is friendly to both patient’s dentition and dentist’s chair time. All clinical and laboratory techniques for teeth involved in the study are specified as per Dentsply protocol.
A universal self-priming dental adhesive system (Prime & Bond NT Dual cure, Dentsply) and a dual cure resin cement (Calibra, Dentsply) will be used to bond the indirect restoration to the tooth. The literature supports the chosen material for this proposed study (Barnes et al., 2006).
4.8.1 Intervention protocol for Immediate Dentine Sealing (IDS)
The teeth will be sealed immediately after preparation with Prime & Bond NT Dual Cure (Dentsply). To avoid any bond contamination, retraction cord will be placed before dentine sealing. The protocol for dentine bonding is as manufacturer’s instructions:
Clean freshly instrumented dentine with water spray and air dry.
It is recommended not to etch dentine to minimize the possibility of post-operative sensitivity.
Place 1-2 drops of Prime & Bond NT adhesive into a clean plastic mixing well. Place an equal number of drops of Self Cure activator into the same mixing well. Mix Contents for 1-2 seconds with a clean, unused brush tip.
Immediately apply mixed adhesive/activator to thoroughly wet all the tooth surfaces. These surfaces should remain wet for 20 seconds and may necessitate additional application of mixed adhesive/activator.
Remove excess solvent by gently drying with clean, dry air at least for 5 seconds. Surface should have a uniform glossy appearance.
Cure mixed adhesive/activator for 10 seconds using a curing light. Check curing light for minimum curing output of at least 550mw/cm2 and a spectral output, including 470nm (peak absorption of the CQ photoinitiator).
Exactly the same procedure will be used for the control group prior to final bonding of the Crown.
4.8.2 Protocol for Impression taking
Study Group (IDS)
In practice, freshly cut dentin is present only at the time of tooth preparation (before impression). Freshly cut dentin is the ideal substrate for dentin bonding. Most studies on Dentine Bonding Agents (DBA) bond strength use freshly prepared dentin (Magne 2005). There is a possibility for the oxygen inhibition layer of filled resin of the dentine bonding agent to inhibit the setting of the impression material. The bonded teeth have to be cleaned with pumic and a rubber prophylactic cup and washed with water and air dried before the impression (Magne and Nielsen, 2009b). Impressions will be taken with an A-silicone double-mix technique (Aquasil ultra, Dentsply) as per manufacture’s Instruction.
Control Group (no sealing)
Impressions will be taken as per study group without sealing the dentine with DSA.
4.8.3 Protocol for temporisation
Study Group (IDS)
A prefabricated light curable temporary Crown (Protemp Crown temporisation material, 3M ESPE) will be fitted on the prepared tooth standard temporary cements. The occlusion will be controlled and if necessary adjusted.
A temporary crown will be fitted as above without any DBA application and after Impression taking as per clinical consensus guidelines.
4.8.4 Protocol for final cementation
Study group (IDS)
Just prior to the luting procedures (when placing the final restoration), it is recommended to roughen the existing adhesive resin using a coarse diamond bur at low speed or by microsandblasting (Magne 2005). The tooth and the restoration will be treated as per manufacturer’s instructions, and the crown can be cemented with dual cure resin (Calibra, Dentsply).
The same procedure as for study group will be carried out except the adhesive resin roughening step.
The outcome measures will be assessed, and the CRF forms updated at baseline and at recall appointments of 1 year, 3 years and 5 years. Any relevant clinical incident between these times affecting the trial tooth needs to be recorded on CRF. Base-line findings and post-operative taken periapical (PA) of each trial tooth at one year and five years will be studied, assessed and recorded by two blind assessors. These precalibrated, independent observers will examine the radiographs and categorize the periapical status of the selected teeth according to a written set of criteria
(Cheung et al. 2005) (Table 1). Categories 1, 2 or 3 are deemed to be associated with a non-vital pulp. If there are any disagreement, a third assessor will be involved as an arbitrator before a final score is reached.
The protocol for Periapicals will adhere to the guidelines produced by the faculty of General Dental Practitioners (Pendlebury et al., 2004). An Independent assessor will audit each practice participating in the study to ensure compliance with radiology regulations (IRMER).
Every effort will be made to prevent disclosure of the exact nature of the study aim and to which arm of the study the participants have been allocated. This will be specified to minimise assessment reactivity, which has been hypothesised by McCambridge and Strang (2005).
The date collection statistician who assesses and calculates the outcome results will also be blinded to the individual patient allocation to limit detection bias. The operators will not be blinded but the allocation of whether the tooth is to be control or intervention will be concealed until intervention procedure is to be carried out.
4.11 Follow up
An important selection criterion to minimise drop-out is the eligibility of the patients to be regular attenders at the relevant dental practices. Patients lost to follow up will be recorded..
No evidence of radiopaque foreign material
in pulp chamber and/or root canal(s),
and no periradicular radiolucent area
Widening of the PDL
Widening of the apical part of the periodontal ligament space, not exceeding two times the width of the lateral periodontal ligament space
Radiolucency in connection with the apical part of the root, the diameter exceeding two times the width of the lateral periodontal ligament space
Tooth with radiopaque material in pulp chamber (if discernible) and/or root canal(s)
Table 1- Radiographic categorization of pulpal status (Cheung et al. 2005)
This study will not be utilising any investigational medicinal products; it will therefore be classed as a non- Clinical Trial of an Investigative Medicinal Product trial (non-CMITP). All untoward incidents will be adverse events rather than adverse reaction. The study is also compatible with Data Protection and Mental Capacity Act. The treatment options being studied are non-life threatening on non-vulnerable adults with no risk of harm and no unknown or uncertain risks. A Data Monitoring Committee (DMC) will be appointed who makes recommendations, as required, to the chair of the Trial Steering Committee. This committee is responsible for ensuring that the intervention and control techniques will be carried out under the guidance provided by the EU directive for Good Clinical Practice.
4.12.1 Assessment of Safety
There are no expected unexpected adverse events since the intervention is used routinely in general dental practice. The using of etching gel has expected adverse events should it come into contact with the soft tissues (Material Safety Data Sheet (MSDS) sheet). All other dental materials involved (Prime & Bond NT Dual Cure, Calibra dual cure resin cement (Dentsply), Protemp Crown temporisation material, 3M ESPE) are fully licensed within the medical devices regulations for use in dentistry in UK. All operators are experienced dental practitioners having handled these materials routinely and will be trained in dealing with expected adverse reactions should the product inadvertently come into contact with pati
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