Bovine tooth is a substitute for human tooth on bond strength studies: A systematic review and meta-analysis of in vitrostudies

Highlights

  • Bovine teeth can be used as a substitute of human teeth on bond strength studies.

  • Both substrates—enamel and dentin of bovine teeth seems to be similar to human ones considering bond strength values.

  • Bovine primary teeth should be used carefully as a substitute of human primary teeth considering the number of studies comparing these substrates.

Abstract

Objectives

This study aimed to systematically review the literature to compare the bond strength values achieved from human and bovine teeth of in vitro studies.

Data and source

The PubMed/MEDLINE, ISI Web of Science and Scopus electronic databases were searched to select laboratorial studies that evaluated adhesive systems bond strength to human and bovine teeth. No publication year or language restriction was considered.

Study selection

From 1,285 potentially eligible studies, 15 were selected for full-text analysis, 11 were included in the systematic review and 9 in the meta-analysis. Two authors independently selected the studies, extracted the data and assessed the risk of bias. Mean differences were obtained by comparing bond strength values between human and bovine teeth (overall analysis), and considering enamel and dentin separately (subgroups analysis). Statistical analysis was performed using RevMan5.1, with random effects model, at a significance level of p = 0.05.

Results

No significant difference was found between human and bovine teeth (p = 0.35), either for enamel (p = 0.07) or for dentin (p = 0.93) substrates. Low to moderate heterogeneity was found on the meta-analysis. All included studies in the systematic review scored between medium and high risk of bias.

Conclusions

Bovine teeth can be a reliable substitute for human ones on bond strength studies of adhesive systems to both enamel and dentin substrates.

Introduction

Buonocore introduced adhesive dentistry in 1955 and, over the last 60 years, a huge technique development was accomplished; hundreds of products were introduced and replaced, aiming to achieve superior adhesive materials with more effective bonding approaches. Despite of the distance of clinical and in vitro data, many of the development aforementioned is based on data obtained from in vitro studies , which have been not claimed to be the only predictor to clinical performance of adhesive materials, but also, it is a valid tool to evaluate several parameters of products and techniques .

Extracted human teeth are usually preferred in bond strength studies , however sound human teeth have become difficult to obtain in the amount required for the laboratory tests, mainly based on the development of non-invasive or minimally invasive approaches in restorative dentistry, and on the decreasing in dental caries over the last decades. Furthermore, when human tissues are involved in laboratorial studies, ethical aspects demands attention and are time consuming.

Bovine teeth have been used for a long time as an alternative dental bonding substrate , mainly due to the ease to obtain a collection of bovine teeth and to the possibility of standardizes the tooth age, diet and other environmental conditions, reducing substrate discrepancy bias . Those aspects are not possible to control when dealing with human teeth. Based on this, bovine teeth have been used in bond testing . Several studies comparatively evaluated both substrates aiming to establish the suitability of bovine tooth for substitute human counterparts . In these studies, a wide variation of methodologies is employed and a range of materials is found. Moreover, despite being similar in some morphological aspects , the literature is not clear if bovine hard tissues can be reliably used as a substitute of human teeth.

To the best of our knowledge, there is no strong evidence supporting the deliberate use of bovine tooth for evaluating adhesive systems, nor the extrapolation of the bond strength values for human substrates. Thus, the aim of this study was to systematically review the literature for in vitro studies that evaluated the adhesive bond strength to dentin or enamel, using human and bovine teeth substrates.

Methods

The systematic review was conducted according to the Cochrane Handbook and PRISMA statement ( i.e ., Preferred Reporting Items for Systematic Reviews and Meta-analyses ).

The following research question was formulated to address the literature and outline the search strategy: Can bovine teeth be used as substitute for human teeth in laboratory dental adhesive bond strength studies?

Search strategy

The MEDLINE via PubMed, ISI Web of Science and Scopus electronic databases were searched to identify studies that could be considered. The following search strategies were performed: computer search of database, review of reference lists of all included studies, and contact with authors. The search was undertaken to identify literature up to June 13th, 2016.

The computer database search in MEDLINE via PubMed was performed using specific medical subject headings (MeSH) and keywords as follows: ((bovin*) AND (((dentin* adhesive*) OR bond*) OR adhesive system*)) AND ((((((((((((((((((((((((((((((((dentition permanent[MeSH Terms]) OR Permanent Dentition) OR Dentition; Secondary) OR Secondary Dentition) OR Dentition; Adult) OR Adult Dentition) OR Tooth; Deciduous[MeSH Terms]) OR Deciduous Tooth) OR Dentition; Deciduous) OR Deciduous Dentition) OR Deciduous Dentitions) OR Dentitions; Deciduous) OR Dentition*; Primary) OR Primary Dentition*) OR Milk Tooth) OR Tooth; Milk) OR Primary Teeth) OR Teeth; Deciduous) OR Deciduous Teeth) OR Teeth; Primary) OR Tooth; Primary) OR Milk Teeth) OR Teeth; Milk) OR Baby Teeth) OR Teeth; Baby) OR Baby Tooth) OR Tooth; Baby) OR Primary Tooth) OR dentin*[MeSH Terms]) OR Dental Enamel[MeSH Terms]) OR enamel)). For ISI Web of Science and Scopus the following search terms were used: (bovin*) AND (human) AND (bond strength) OR (adhesive system*). No publication year or language limit was considered.

Selection, inclusion and exclusion criteria

Firstly, titles and abstracts were reviewed independently by two authors (FZMS and AF) and selected per their consensus for further assessment considering the following inclusion criteria: in vitro studies that comparing bond strength of adhesive systems to bovine and human dental hard tissues, regardless of the methodology of the bond strength test employed. If consensus was not reached, the abstract was set aside for further evaluation.

The references of all selected studies were manually searched for further relevant studies that could fulfill the inclusion criteria.

The full texts of all studies that full-filled the inclusion criteria for eligible papers were then reviewed independently by two authors (FZMS and AF) considering the exclusion criteria: studies that evaluated bond strength to brackets or glass ionomer cements (not combined with adhesive systems); papers that compared different substrates ( i.e. , human primary teeth to bovine permanent teeth; or bovine enamel vs. human dentin) or that did not perform comparisons under the same bond strength test methodology. Any disagreements in the eligibility criteria were solved by discussion and consensus by a third reviewer (ROR). The eligibility of studies between the authors showed substantial agreement, with a kappa score of 0.84.

Data extraction

Two authors (FZMS and AF) performed the data extraction by means of a standardized sheet in Microsoft Office Excel 2013 (Microsoft Corporation, Redmond, WA, USA). A protocol for data extraction was defined: the authors categorized similar information into groups according to the main outcomes of interest. For each paper, the following data were systematically extracted: publication year; country; type of teeth used; sample size; adhesive system evaluated, time of storage before test; the bond strength test used and the substrates evaluated. Bond strength mean values (in MPa) and standard deviations (SD) were extracted from the data.

For studies that did not report the precise bond strength values and that showed the results in graphs or figures, corresponding authors were contacted 3 times by e-mail, with 2 weeks interval, if any information was missing. If no information was provided, the study was excluded from the systematic review.

Risk of bias assessment

Two authors (FZMS and AF) independently evaluated the risk of bias of each included study considering a score described in previous systematic reviews of in vitro studies . The description of the following parameters were checked in each study: randomization of the teeth for experimental groups, sample size calculation, teeth free of caries, specimen with similar cross section, failure mode evaluation, material applied following manufactureŕs instructions, adhesive and testing procedures performed by a single operator, specimen tested by a blinded operator. If the parameter was described on the text, the study received a “yes” on that specify parameter, otherwise it had a “no”. The risk of bias was classified according to the sum of “yes” received as follows: 1–3 = high, 4–5 = medium, 6–8 = low risk of bias.

Data analysis

For the meta-analyses, the pooled effect estimates were obtained by comparing means from human and bovine teeth, irrespective of the substrate (enamel or dentin), as well as considering the subgroups, according to the type of substrate – enamel and dentin – separately. For studies that evaluated several adhesive systems, the values were extracted and one mean for each condition was calculated by a formula according to the Cochrane Statistical Guidelines , to obtain a single sample size, mean and standard deviation values for experimental (bovine) and control (human) groups. In the selected studies, only the data of interest were extracted to be analyzed in the meta-analysis. If the study performed a separate group with storage or aging, only immediate bond strength values were considered for analysis.

The statistical differences between-groups were performed in Review Manager (RevMan version 5.3 software, Cochrane Collaboration, Copenhagen, Denmark, 2014) using a random-effect method. Statistical significance was defined as a P-value ≤0.05 (Z test). The amount of specimens was considered as the amount of experimental units. Forest plots were created to illustrate the meta-analysis.

Statistical heterogeneity among studies was assessed via the Cochran Q test, with a threshold p value of 0.1, and inconsistency (I 2 ). Values up to 60% were considered as not important to moderate heterogeneity.

Methods

The systematic review was conducted according to the Cochrane Handbook and PRISMA statement ( i.e ., Preferred Reporting Items for Systematic Reviews and Meta-analyses ).

The following research question was formulated to address the literature and outline the search strategy: Can bovine teeth be used as substitute for human teeth in laboratory dental adhesive bond strength studies?

Search strategy

The MEDLINE via PubMed, ISI Web of Science and Scopus electronic databases were searched to identify studies that could be considered. The following search strategies were performed: computer search of database, review of reference lists of all included studies, and contact with authors. The search was undertaken to identify literature up to June 13th, 2016.

The computer database search in MEDLINE via PubMed was performed using specific medical subject headings (MeSH) and keywords as follows: ((bovin*) AND (((dentin* adhesive*) OR bond*) OR adhesive system*)) AND ((((((((((((((((((((((((((((((((dentition permanent[MeSH Terms]) OR Permanent Dentition) OR Dentition; Secondary) OR Secondary Dentition) OR Dentition; Adult) OR Adult Dentition) OR Tooth; Deciduous[MeSH Terms]) OR Deciduous Tooth) OR Dentition; Deciduous) OR Deciduous Dentition) OR Deciduous Dentitions) OR Dentitions; Deciduous) OR Dentition*; Primary) OR Primary Dentition*) OR Milk Tooth) OR Tooth; Milk) OR Primary Teeth) OR Teeth; Deciduous) OR Deciduous Teeth) OR Teeth; Primary) OR Tooth; Primary) OR Milk Teeth) OR Teeth; Milk) OR Baby Teeth) OR Teeth; Baby) OR Baby Tooth) OR Tooth; Baby) OR Primary Tooth) OR dentin*[MeSH Terms]) OR Dental Enamel[MeSH Terms]) OR enamel)). For ISI Web of Science and Scopus the following search terms were used: (bovin*) AND (human) AND (bond strength) OR (adhesive system*). No publication year or language limit was considered.

Selection, inclusion and exclusion criteria

Firstly, titles and abstracts were reviewed independently by two authors (FZMS and AF) and selected per their consensus for further assessment considering the following inclusion criteria: in vitro studies that comparing bond strength of adhesive systems to bovine and human dental hard tissues, regardless of the methodology of the bond strength test employed. If consensus was not reached, the abstract was set aside for further evaluation.

The references of all selected studies were manually searched for further relevant studies that could fulfill the inclusion criteria.

The full texts of all studies that full-filled the inclusion criteria for eligible papers were then reviewed independently by two authors (FZMS and AF) considering the exclusion criteria: studies that evaluated bond strength to brackets or glass ionomer cements (not combined with adhesive systems); papers that compared different substrates ( i.e. , human primary teeth to bovine permanent teeth; or bovine enamel vs. human dentin) or that did not perform comparisons under the same bond strength test methodology. Any disagreements in the eligibility criteria were solved by discussion and consensus by a third reviewer (ROR). The eligibility of studies between the authors showed substantial agreement, with a kappa score of 0.84.

Data extraction

Two authors (FZMS and AF) performed the data extraction by means of a standardized sheet in Microsoft Office Excel 2013 (Microsoft Corporation, Redmond, WA, USA). A protocol for data extraction was defined: the authors categorized similar information into groups according to the main outcomes of interest. For each paper, the following data were systematically extracted: publication year; country; type of teeth used; sample size; adhesive system evaluated, time of storage before test; the bond strength test used and the substrates evaluated. Bond strength mean values (in MPa) and standard deviations (SD) were extracted from the data.

For studies that did not report the precise bond strength values and that showed the results in graphs or figures, corresponding authors were contacted 3 times by e-mail, with 2 weeks interval, if any information was missing. If no information was provided, the study was excluded from the systematic review.

Risk of bias assessment

Two authors (FZMS and AF) independently evaluated the risk of bias of each included study considering a score described in previous systematic reviews of in vitro studies . The description of the following parameters were checked in each study: randomization of the teeth for experimental groups, sample size calculation, teeth free of caries, specimen with similar cross section, failure mode evaluation, material applied following manufactureŕs instructions, adhesive and testing procedures performed by a single operator, specimen tested by a blinded operator. If the parameter was described on the text, the study received a “yes” on that specify parameter, otherwise it had a “no”. The risk of bias was classified according to the sum of “yes” received as follows: 1–3 = high, 4–5 = medium, 6–8 = low risk of bias.

Data analysis

For the meta-analyses, the pooled effect estimates were obtained by comparing means from human and bovine teeth, irrespective of the substrate (enamel or dentin), as well as considering the subgroups, according to the type of substrate – enamel and dentin – separately. For studies that evaluated several adhesive systems, the values were extracted and one mean for each condition was calculated by a formula according to the Cochrane Statistical Guidelines , to obtain a single sample size, mean and standard deviation values for experimental (bovine) and control (human) groups. In the selected studies, only the data of interest were extracted to be analyzed in the meta-analysis. If the study performed a separate group with storage or aging, only immediate bond strength values were considered for analysis.

The statistical differences between-groups were performed in Review Manager (RevMan version 5.3 software, Cochrane Collaboration, Copenhagen, Denmark, 2014) using a random-effect method. Statistical significance was defined as a P-value ≤0.05 (Z test). The amount of specimens was considered as the amount of experimental units. Forest plots were created to illustrate the meta-analysis.

Statistical heterogeneity among studies was assessed via the Cochran Q test, with a threshold p value of 0.1, and inconsistency (I 2 ). Values up to 60% were considered as not important to moderate heterogeneity.

Results

Search and selection

Fig. 1 depicts a flowchart summarizing the selection process for studies according to the PRISMA statement . From 1,285 potentially eligible studies by the search strategy in PubMed/MEDLINE, ISI Web of Science and Scopus, 15 were duplicates and 1255 were excluded since they did not meet the eligibility criteria. The first screening resulted in 15 studies remained for full-text reading , from which 5 studies were excluded because: evaluated brackets , compared different comparable substrates (primary human vs . permanent bovine) , used different tests parameter for comparison (different cross-sectional bonded area) and evaluated the bond strength of other materials than adhesive systems . As one study was included from the references , 11 studies were included in the systematic review. However, 2 of them were not included in the meta-analyses due to lack of numerical data , even after three attempts to contact the authors by e-mail.

Fig. 1
Flowchart diagram of study selection according to PRISMA statement.

Descriptive analysis

Table 1 shows descriptive extracted data from the included studies in systematic review. All studies were published between 1990 and 2013, with 6 studies published after 2000 . The majority of the studies were conducted in Brazil (n = 4) and United States (n = 2) . In this collection, 16 adhesive systems were evaluated including every commercially available adhesive classification: 3- and 2-step etch-and-rinse systems, 2- and 1-step self-etch systems. Six studies evaluated several adhesive systems in both substrates and 5 evaluated only one adhesive. Most evaluated system were: 1) Scotchbond Multi-Purpose (a.k.a. Scotchbond), considered in four studies and 2) Scotchbond 2 (a.k.a. Single Bond), evaluated in 2 studies . Six studies compared etch-and-rinse with self-etch systems and 5 evaluated only etch-and-rinse systems .

Table 1
Descriptive data from included studies in systematic review.
Paper Country Type of human tooth a Number of teeth per group Storage/ageing Adhesive system Bond strength test b Substrates
Fowler et al. United States Molars and premolars 40 2 weeks Scotchbond 2 d SBS Permanent enamel and dentin
Galhano et al. Brazil Single rooted 10 24 h All Bond 2 PO Permanent root dentin
Kaplan et al. Argentina Premolars 40 1 week Scotchbond
Bondlite
Prisma Universal Bond
Gluma
TBS Permanent dentin
Krifka et al. e Germany * 88 24 h Syntac Assortment
Adper Prompt L-pop
iBond Gluma
Clearfil Protect Bond
SBS Primary enamel and dentin
Lopes et al. Brazil Molars 20 24 h Scotchbond MP
Clearfil Liner Bond 2V
SBS Permanent enamel and dentin
Muench et al. Brazil Molars 30 2 weeks Prime & Bond 2.1
Single Bond
Etch&Prime 3.0
TBS Permanent dentin
Reis et al. Brazil Molars 10 24 h Single Bond μTBS Permanent enamel and dentin
Retief et al. United States Molars 25 24 h Scotchbond 2 SBS Permanent dentin
Rüttermann et al. Germany Molars 80 24 h Clearfil SE
Optibond FL
SBS Permanent enamel and dentin
Saunders United Kingdom Premolars 60 2400 termocycles Scotchbond
Topaz
Gluma
3M experimental agent
SIBS Permanent dentin
Shahabi et al. e Australia Central incisors, first premolars and third molars c 48 h Scotchbond Multi Purpose SBS Permanent enamel
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Nov 23, 2017 | Posted by in Dental Materials | Comments Off on Bovine tooth is a substitute for human tooth on bond strength studies: A systematic review and meta-analysis of in vitrostudies
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