Monomer elution from nanohybrid and ormocer-based composites

Recently, a paper on monomer elution from resin-based composites by my research team has been accepted for publication in the leading peer-reviewed journal on dental materials. The paper is available online under "Articles in press" and awaits publication in the paper format of Dental Materials. For reprints, you may contact me at vesna.miletic@gmail.com 

Abstract

Dent Mater. 2010 Dec 17. [Epub ahead of print]

Monomer elution from nanohybrid and ormocer-based composites cured with different light sources

Manojlovic D, Radisic M, Vasiljevic T, Zivkovic S, Lausevic M, Miletic V.

University of Belgrade, School of Dentistry, Department of Restorative Dentistry
and Endodontics, Rankeova 4, 11000 Belgrade, Serbia.

OBJECTIVES: To study monomer elution from four resin-based composites (RBCs)cured with different light sources.  
METHODS: Twenty-eight premolars were randomlyallocated to four groups. Standardized cavities were prepared and restored with ananohybrid (Filtek Supreme XT or Tetric EvoCeram), an ormocer (Admira) or a microhybrid RBC (Filtek Z250) which served as control. Buccal restorations were cured with a halogen and oral restorations with an LED light-curing unit. Elution of diurethane dimethacrylate (UDMA), Bisphenol A diglycidylether methacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) was analyzed using high-performance liquid chromatography (HPLC) 1h to 28 days post-immersion in 75% ethanol. Data were analyzed using multivariate and repeated measures analysis of variance (α=0.05).  
RESULTS: The greatest elution of UDMA and BisGMA occurred from Tetric EvoCeram and the least from Filtek Z250 (p<0.05). LED and halogen light-curing units gave similar results for all RBCs (p>0.05) except Tetric EvoCeram which showed greater elution for the LED unit (p<0.05). TEGDMA was below the limit of quantification. HEMA eluted in similar concentrations from Filtek Supreme and Tetric EvoCeram (p>0.05).  
SIGNIFICANCE: The two nanohybrid RBCs eluted more cross-linking monomers than the ormocer and the control microhybrid RBC. Continuous elution over 28 days indicates that RBCs act as a chronic source of monomers in clinical  conditions. Light source may affect monomer elution since differences were found  for one out of four RBCs. Mathematical models for elution kinetics of UDMA and BisGMA indicated two elution mechanisms.

News from jobs.ac.uk

PhD Studentship (full time, 3 years)

Toxicological Studies of Endocrine Disrupting Chemicals in Dental Patients
Peninsula College Of Medicine And Dentistry Graduate School

This studentship aims to investigate the baseline and post-treatment urine and saliva concentrations of Bisphenol A and phthalate plasticisers in paediatric and adult patient populations entering Peninsula Dental School (PDS) Clinics.

The post will involve chromatographic (LC-MS/MS) analysis of biological samples and potentially, advanced mathematical modelling of data obtained. We are therefore looking for someone with a science background (BDS, BMBS, BSc Biomedical Sciences/Biology/Pharmacology/Chemistry or similar) with an aptitude for mathematics.

Stipend:  £13,590 
UK/EU candidates only
Closing date: 21 February 2011

For more information, click here

Dental Materials Conferences 2011

89th General Session & Exhibition of the IADR
40th Annual Meeting of the AADR
35th Annual Meeting of the CADR
March 16-19, 2011
San Diego, California, USA
More information on the IADR website. Click here for the online scientific programme. More than 4000 abstracts are expected to be featured at the conference. Traditionally, the greatest number of sessions will cover many aspects of dental materials, from chemistry and properties to clinical performance.

45th Meeting of the Continental European Division (CED) and Scandinavian Division (NOF) of the IADR
August 31-September 3, 2011
Budapest, Hungary
More information on the IADR CED website. Deadline for abstract submission is March 25, 2011. Click here to submit your abstract. The CED-IADR will provide considerable support to young researchers through as many travel stipends as possible.

21st European Dental Materials Conference
August 24-26, 2011
Turku, Finland
“Current trends in moving toward non-metallic materials”
More information on the conference website. Click here for the tentative scientific programme. Dental Materials Summer School will be organized prior to the conference.

2011 Conference of the Academy of Dental Materials
October 13-15, 2011.
Bahia, Brazil
For more information, click here. Topics at this conference: What is the future? When to market? Where will the material be used?

International Dental Materials Congress
May 27-29, 2011
Seoul, Korea
"Moving Dental Materials from the Laboratory to the Clinic"
Visit the Congress website for more information. Click here for the scientific programme.

Clinical evaluation of dental restorative materials - Part III: FDI criteria

In 2007, recommendations for conducting clinical trials approved by the FDI were published in several peer-reviewed journals. These recommendations not only addressed designing protocols for clinical trials but also challenged the Ryge criteria with an in-depth discussion of  clinical evaluation criteria and suggested a new approach in clinical evaluation of dental restorative materials and operative techniques.

In August 2010, an update of the "FDI clinical criteria for the evaluation of direct and indirect restorations" was published  by Hickel et al. in the Journal of Adhesive Dentistry and Clinical Oral Investigations. A lot of clinical examples were presented in the paper to illustrate various ratings.

The new FDI criteria set a different background for the evaluation of dental restorations by introducing 3 groups of criteria: esthetic, functional and biological. Each of these groups has subgroups with 16 evaluation criteria in total. These are:

Esthetic criteria

1. Surface luster
2. Staining: (a) surface and (b) margin
3. Color match and translucency
4. Esthetic anatomical form

Functional criteria

1. Fracture of material and retention
2. Marginal adaptation
3. Occlusal contour and wear 
4. Approximal anatomical form: (a) contact point and (b) contour
5. Radiographic examination, where applicable
6. Patient's view

Biological criteria

1. Postoperative sensitivity and tooth vitality
2. Recurrence of caries, erosion, abfraction
3. Tooth integrity
4. Periodontal response
5. Adjacent mucosa
6. Oral and general health

For all three groups, the following gradings are used for evaluation:

1. Clinically excellent/very good
2. Clinically good
3. Clinically sufficient/satisfactory
4. Clinically unsatisfactory
5. Clinically poor

When judging a dental restoration using the FDI criteria, the score for each group is dictated by the most severe grading among the criteria for that particular group. Similarly, the overall score is determined by the worst grading among the groups. For example, if the functional criteria are unacceptable, the overall score is unacceptable. Detailed description of each grading is given in the previously mentioned paper: "FDI World Dental Federation - Clinical Criteria for the evaluation of direct and indirect restorations".

It is not mandatory to apply all of the FDI criteria in each study. In each particular study, the examiners should determine which criteria match their intended purposes best.

Gradings for the FDI criteria are substantially more detailed and sensitive than the Cvar and Ryge criteria and their modifications suggested by other authors. These detailed gradings challenge the training and calibration procedure of the examiners. To allow an easier and more efficient training, reduced variability in judgment and greater coherence in multi-centric studies, an online calibration system was established at www.e-calib.info. It is emphasized by the authors of the FDI criteria that the e-calibration system does not replace the clinical setting but shortens clinical training significantly.

Beside their use in clinical trials, the FDI criteria are recommended for quality assessment of restorations by general dental practitioners in their everyday practice and as guidelines whether or not a restoration needs refurbishment, repair or replacement. Refurbishment is a minimal intervention such as polishing or contouring when no additional material is placed. Repair is a minimal intervention which requires additional material to be placed with or without a minimal preparation in the restoration or dental tissues.

Clinical investigators are strongly advised to use the new FDI criteria when designing and conducting clinical trials. However, the criteria are "not indefinitely fixed and defined" so investigators are asked for feedback and encouraged to contribute to the e-calib database with high quality images of clinical cases.

References

Hickel R, Peschke A, Tyas M, Mjör I, Bayne S, Peters M, Hiller KA, Randall R, Vanherle G, Heintze SD. FDI World Dental Federation - clinical criteria for the evaluation of direct and indirect restorations. Update and clinical examples. J Adhes Dent. 2010 Aug;12(4):259-72. doi: 10.3290/j.jad.a19262.

Hickel R, Roulet JF, Bayne S, Heintze SD, Mjör IA, Peters M, Rousson V, Randall R, Schmalz G, Tyas M, Vanherle G. Recommendations for conducting controlled clinical studies of dental restorative materials. Science Committee Project 2/98--FDI World Dental Federation study design (Part I) and criteria for evaluation (Part II) of direct and indirect restorations including onlays and partial crowns. J Adhes Dent. 2007;9 Suppl 1:121-47.

Clinical evaluation of dental restorative materials - Part II: Modified Ryge criteria

Cvar and Ryge criteria[1] for clinical evaluation of dental restorative materials were first published in 1971 and re-evaluated in 1980 by Ryge.[2] Another post explains the original Cvar and Ryge criteria in greater detail. Also, read about the new FDI criteria in a separate post.

Modified criteria, often called modified Ryge criteria are mostly used in contemporary clinical evaluations of dental restorative materials. Modifications usually depend on the aim of the study i.e. the type(s) of restorations that are being compared. Here are some studies reporting on clinical performance of restorative materials based on modified Ryge criteria.

Gallo et al.[3] conducted a three-year clinical evaluation of two flowable composites, Tetric Flow (Ivoclar Vivadent) and Esthet-X Flow (Dentsply/Caulk) which were used to restore Class I caries lesions. The authors used the original Cvar and Ryge criteria with two additional criteria: (1) retention and (2) polishability. Table 1 presents the codes and descriptions for each criterion. It should be noted that polishability is rated using more than the original 4 codes, introducing subtle differences in rating. This may, however, affect the variability of diagnostic judgement and intra- or inter-examiner reliability as it becomes more difficult to differentiate between e.g. Bravo B-a and B-b or C and D. Also, the term “unacceptable polish” comes as a rather unexpected vague description in contrast to detailed codes A-D and it is unclear what unacceptable means. For some dentists, “Rough and dull or satin, not reflective” may be completely “Unacceptable polish”. An obvious principle adopted by Cvar and Ryge in their original criteria should also be applied when modifying these criteria by introducing new ones – keep it simple.

Table 1. Codes and descriptions of two additional criteria, as used in Gallo et al.
(Click on the table)

Poon et al.[4] conducted a 3.5-year clinical evaluation of a packable (SureFil, Dentsply DeTrey) and a conventional (SpectrumTPH, Dentsply DeTrey) composite used with a self-etch adhesive system. Not only did the authors add more criteria, they also modified the descriptions of the original Cvar and Ryge criteria. Additional criteria were: (1) Retention, (2) Surface texture, (3) Surface staining, (4) Postoperative sensitivity and (5) Gingival bleeding in Class II restorations. All criteria in this study, with the exception of Postoperative sensitivity and Gingival bleeding, were rated as Alfa (A) or Bravo (B), where A was defined as “restorations meet all clinical standards with a range of excellence” and B was “though not ideal, restorations have a range of acceptability”. The rating for Postoperative sensitivity and Gingival Bleeding were “absent” or “present”.

Swift et al.[5] compared the 3-year clinical performance of two-step total-etch adhesives (OptiBond Solo, SDS Kerr and Prime & Bond 2.1, Dentsply Caulk). Their additional criteria were: (1) Retention, codes as in Table 1, (2) Postoperative sensitivity and (3) Other failure. The latter two were rated as “none” or “present”.

Moncada et al.[6] conducted a 3-year clinical trial to compare various treatment options for Class I and II restorations (sealed margins, repair, refurbishment, replacement or no treatment). Unlike previous cited papers, Moncada et al. did not use all of the original Cvar and Ryge criteria but selected only the following: (1) Marginal adaptation, (2) Anatomic form and (3) Caries. Also, they added two new criteria: (1) Surface roughness and (2) Luster, described in Table 2.

Table 2. Codes and descriptions of two additional criteria, as used in Moncada et al.
(Click on the table)

Kihn and Barnes[7] investigated clinical longevity of porcelain veneers after 4 years. They substituted Anatomic form from the original Cvar and Ryge criteria with Postoperative sensitivity which was rates “absent” or “present”.

Hamilton et al.[8] used modified Ryge criteria to evaluate pit and fissure restorations after 1 year of clinical service. Instead of the original Caries criterion, the authors added Surface smoothness which was rated as follows:

A - As smooth as natural adjacent tooth structure
B - Not as smooth as natural tooth structure but not pitted
C - Not as smooth as natural tooth structure and pitted

Hamilton et al.[8] also modified Margin discoloration and Margin adaptation to include subrating as described in Table 3. Quantification of discoloration along the margin was used and restorations rated as B1 for less than 50% of exposed margin or B2 for greater than 50% of exposed margin. A subtle one-way catch with an explorer during the assessment of margin adaptation was tolerated and rated as A2 instead of B. Also, code D for margin adaptation (Restoration mobile, fractured or missing in part of the tooth) was not taken into account, most likely because none was found.

Table 3. Modifications of the original Cvar and Ryge criteria by Hamilton et al.
(Click on the table)

Conclusions

Based on this short literature review, it is apparent that in contemporary clinical evaluation of restorative materials and treatment modalities, the original Cvar and Ryge criteria are modified in some way based on study objectives. These modifications include:

(1) Additional criteria are introduced: Retention, Polishability, Postoperative sensitivity, Surface roughness, Surface staining, Luster, Gingival bleeding; 

(2) Not all of the original Cvar and Ryge criteria are used; 

(3) Subrating are introduced to increase the precision of clinical judgment or the quality of the original criteria is reduced either through poorer description of rating or by excluding rating.

Despite the limitations, Cvar and Ryge rating scales, with or without modifications, remain the most frequently used method of clinical evaluation of dental restorative materials and operative techniques.

References

1. Cvar and Ryge criteria for the clinical evaluation of dental restorative materials. First published in U.S. Department of Health, Education, and Welfare, U.S. Public Health Service 790244, San Francisco Printing Office 1971:1–42. Reprinted in Clinical Oral Investigations 2005;9:215–232.

2. Ryge G. Clinical criteria. Int Dent J 1980;30:347-58

3. Gallo JR, Burgess JO, Ripps AH, Walker RS, Maltezos MB, Mercante DE, Davidson JM. Three-year clinical evaluation of two flowable composites. Quintessence Int. 2010 Jun;41(6):497-503.

4. Poon EC, Smales RJ, Yip KH. Clinical evaluation of packable and conventional hybrid posterior resin-based composites: results at 3.5 years. J Am Dent Assoc. 2005 Nov;136(11):1533-40.

5. Swift EJ Jr, Perdigão J, Wilder AD Jr, Heymann HO, Sturdevant JR, Bayne SC. Clinical evaluation of two one-bottle dentin adhesives at three years. J Am Dent Assoc. 2001 Aug;132(8):1117-23.

6. Moncada G, Martin J, Fernández E, Hempel MC, Mjör IA, Gordan VV. Sealing, refurbishment and repair of Class I and Class II defective restorations: a three-year clinical trial. J Am Dent Assoc. 2009 Apr;140(4):425-32.

7. Kihn PW, Barnes DM. The clinical longevity of porcelain veneers: a 48-month clinical evaluation. J Am Dent Assoc. 1998 Jun;129(6):747-52.

8. Hamilton JC, Dennison JB, Stoffers KW, Welch KB. A clinical evaluation of air-abrasion treatment of questionable carious lesions. A 12-month report. J Am Dent Assoc. 2001 Jun;132(6):762-9.

Clinical evaluation of dental restorative materials - Part I: Cvar and Ryge criteria

Nearly 40 years ago John F. Cvar and Gunnar Ryge wrote that, although mechanical properties of the available dental restorative materials were well known, clinical scientific data were scarce. The lack of evidence-based studies was the result of the lack of well-defined measures to evaluate the clinical performance of dental materials. As a fast and relatively reliable solution, Cvar and Ryge developed the rating scales which assess five characteristics of dental restorative materials indicative of their aesthetics and functionality.(1) With some modifications, these criteria are still used in clinical evaluation of dental materials and operative techniques. Read about modified criteria and the new FDI criteria in separate posts.

The original Cvar and Ryge criteria or characteristics used for material clinical evaluation are color match, cavo-surface marginal discoloration, anatomic form, marginal adaptation and caries. Codes Alfa, Bravo, Charlie and Delta are used to rate the restorations according to the assigned descriptive values for each characteristic (Table 1). The rating is conducted in a clinical setting, usually by two examiners (dentists) and a recorder (e.g. dental assistant), by visual inspection of the restoration with the use of a mirror if necessary. In addition, an explorer is used to rate marginal adaptation and the presence of caries.

In 1980, Ryge published another paper on clinical criteria in which he systematically set out an approach in clinical assessment of restorative materials using the original Cvar and Ryge criteria.(2) In addition to the previously developed rating scales, Ryge introduced a classification of restorations. The four categories are:

1. Restorations within a range of excellence,
2. Restorations which are acceptable although showing minor deviations from the ideal,
3. Restoration which should be replaced for preventive reasons to avoid the likelihood of future damage and
4. Restorations which require immediate replacement.

Table 1. Original Cvar and Ryge criteria used to evaluate non-metallic restorations. (Click on the table)

References

1. Cvar and Ryge criteria for the clinical evaluation of dental restorative materials. First published in U.S. Department of Health, Education, and Welfare, U.S. Public Health Service 790244, San Francisco Printing Office 1971:1–42. Reprinted in Clinical Oral Investigations 2005;9:215–232.

2. Ryge G. Clinical criteria. Int Dent J 1980;30:347-58

ADA: WHO releases report on dental materials, amalgam

American Dental Association - WHO releases report on dental materials, amalgam

Dental amalgam is rapidly fading out from dental practice due to the increased use of aesthetic restorative materials, particularly resin-based composites, for restorations in posterior teeth. However, the debate about the safety of dental amalgam seems to be a never-ending subject. Amalgam opponents go as far as to request this material to be banned due to the toxicity and health issues associated with mercury (oral lesions, autoimmune disorders, chronic illnesses etc.)

In a recent report, the World Health Organization (WHO) states that dental amalgam remains a dental restorative material of choice reaffirming the safety of this material. Nevertheless, the WHO report emphasizes that alternative materials and preventive measures should be further improved and implemented.

In 2009, ADA and FDA agreed that dental amalgam should not be restricted from dental practice since the scientific literature supports amalgam as "a valuable, viable and safe choice for dental patients". Read more about this in another post.

It seems that amalgam will eventually cease to be used in dentistry not because of its safety issues but because of considerable improvements of aesthetic materials.