Dentist’s preferences on vital and nonvital tooth bleaching: findings from a Guatemalan survey

Aim: The present study aimed to investigate if the Guatemalan dentist’s options on tooth bleaching could be influenced by their time in clinical practice, the level of specialization or their working place. Methods: A representative sample of dentists working in clinical practice in Guatemala was selected. Data were collected using a self-administered questionnaire with information related to gender, professional characteristics (time since graduation in years and working place) and preferences regarding vital (at-home or in-office; type and concentration of bleaching agent) and the nonvital tooth bleaching (bleaching agent used). The analysis was performed and the association between preference for bleaching technique and independent variables were investigated using Fisher’s exact test. Results: 200 dentists were interviewed. More than half of dentists were male (57.0%) with time since graduation between 11 and 20 years (n= 64; 32.3%). Dentists mostly (60.5%) preferred in-office technique for vital bleaching, with 10-20% Carbamide peroxide (CP) as the preferred agent (50%). For nonvital teeth, the preferred agent (46.8%) was 37% Hydrogen Peroxide (HP). About the associations, younger dentists (< 20 years of graduation) selected mostly in-office technique, while those with more than 20 years indicated more the at-home technique. Also, the dentists working in private practice chose more frequently in-office technique. Thus, the in-office technique was more popular among Guatemalan dentists, with 10-20% CP and 37% HP selected as favorite bleaching agents for vital and nonvital techniques, respectively. Conclusion: The time of clinical practice and working place influenced some choices.


Introduction
Esthetics plays a pivotal role in modern society. Discolored or darkened teeth could impair individuals´ social life and negatively impact the oral health-related quality of life (OHRqO) 1 . Whiter and aligned teeth are considered central requirements for satisfaction with teeth appearance [2][3][4][5] . Aesthetic dental treatments are highly desired for individuals in several studies 6,7 . A survey with university students observed that 74% of them desired to carry out an esthetic treatment in their teeth and 16% have already bleached their teeth at least once in their lives 7 . Similar results were observed in a population study in adults, where 86% desired to bleach their teeth 6 .
Indeed, tooth bleaching is one of the treatments most popular in dental clinics. There are different bleaching agents with variate concentrations (generally ranging from 10 to 37%) available for professional use. These products are mainly based on hydrogen peroxide (HP) or carbamide peroxide (CP), which breaks down into HP and urea. These oxidizing chemical agents can be used for vital or nonvital tooth bleaching; while sodium perborate (SP) is used exclusively for nonvital tooth bleaching [8][9][10] . Moreover, low concentration agents [10-22% CP and 6% HP] are used at home by the patients under professional supervision, which is defined as an at-home technique; and high concentrations [>30% CP or HP] are applied only in the dental office by the dentist in the so-called in-office technique 11 . Bleaching agents seem to be able to improve tooth color for vital and nonvital teeth 12 . The bleaching effect is also capable to positively impact in the OHRQoL 13 . When comparing at-home and in-office vital bleaching protocols, a systematic review found similar results between both techniques 14 . These techniques have also been reported to exhibit similar side effects: tooth sensitivity and gingival irritation 15 . Considering the large number of products available in the market and the different techniques, most of the time the choice of bleaching technique and agents relies on the professional opinion. In fact, a survey with Brazilian dentists showed that the decision for vital or nonvital bleaching protocols was impacted by the post-graduation training, time since graduation and working place 16 .
There is none study in Central America evaluating the preference of dentists regarding the vital and nonvital bleaching techniques and materials. Therefore, the present study aimed at the Guatemalan dentist's options for vital or nonvital tooth bleaching and additionally to investigate if their choices could be influenced by dentists characteristics (the time in clinical practice, the level of specialization or their working place).

Materials and Methods
The present study was reported following the STROBE guideline (Strengthening the Reporting of Observational Studies in Epidemiology).

Study design, setting and study size
The present self-administered survey was carried out in Guatemala, a country located in Central America with a population of around 17.3 million. Guatemalan dentists are registered in the "Colegio Estomatológico de Guatemala", which maintains actualized the respective dentist's address and telephones. In 2015, 2,258 dentists were registered being distributed in all Guatemalan territory. A representative sample of this population was calculated considering an α error of 5%, power of 80% and a prevalence of 50% (unknown) of the outcome. Thus, a sample of 181 individuals was estimated. Considering potential losses and refusals, we added around 20% to the initial sample, thus comprising 220 individuals. Dentists were designated systematically, selecting at random the first position in the list. Subsequent individuals were selected by calculating the sample interval. Selected dentists were initially contacted by cellphone and invited to participate. Individuals that agreed to participate scheduled a meeting to deliver and complete the self-administered questionnaire. The questionnaires were personally delivered and collected after filling in by the participant. They have included only active graduated dentists that carry out clinical practice in the Republic of Guatemala. Data were collected using a self-administered questionnaire including 12 questions related to demographic information (sex), professional characteristics (time since graduation in years), and information regarding bleaching techniques. All participants that agreed to participate in the study signed an informed consent form. All data collection was performed during May of 2016.

Independent Variables
Independent variables were collected regarding the gender of participants, time since graduation was continuously collected and then categorized in a) ≤10; b) 11 to 20; c) 21 to 30; d) >30 16 . Dentists were also asked about their level of specialization and categorized in general practitioners (no post-graduation) and specialists (with post-graduation training) 17 . The place of work was also assessed by the question "Where do you get your professional clinical practice from most of the time?" The answers were categorized as "private" and "public/university".

Outcome
The outcomes of present studies were the choice of the vital bleaching technique and the materials used in vital and nonvital tooth bleaching 16 .
1. Considering vital teeth, "What is your favorite protocol to bleach vital teeth?". Two possible answers were possible: a) at-home; b) in-office 2. In cases of vital teeth "What is your first choice to bleach discolored vital teeth?": a) 10% carbamide peroxide (CP); b) 15 to 22% CP; c) 37% of CP; d) 37% of HP or e) over-the-counter (OTC) products; 3. In cases of nonvital teeth "What is your first choice to bleach discolored nonvital teeth?" a) 10% to 22% CP; b) 37% CP; c) 37% HP; d) sodium perborate (SP) + water/or HP.

Statistical methods
Data were tabulated in Excel™ (Microsoft Corporation) software. Descriptive analysis was performed and the association between outcome and independent variables was investigated using Fisher's exact test. All the analyses were done with Stata 12.0 (StataCorp, College Station, TX, USA) software package. Confidence intervals of 95% were calculated and a level of significance of a ≤0.05 was used for the analyses.

Results
A total of 200 dentists participated of present study, which were mainly in the Guatemala City (n=135; 67.5%) followed by Sacatepéquez (n=18; 9.0%) and Chimaltenango (n=16; 8.0%). while 20 (9.1 %) of dentists declined to participate. More than half of dentists were male (n= 114; 57.0%) with time since graduation between 11 and 20 years (n= 64; 32.3%) followed by individual with less than ten years since graduation (n=48; 24.2%) ( Table 1). Most of the dentists worked in private practice (n=170; 92.9%). Regarding the technique for bleaching vital teeth, 10.8% of dentists reported not to perform vital bleaching. Considering only those participants who performed tooth bleaching, most of the dentists (n=95; 60.5%) carried out the in-office technique. The bleaching agent of choice by most Guatemalan dentists was the carbamide peroxide between 10-22% (n=88; 50.0%). Regarding nonvital bleaching, hydrogen peroxide was the material used by 46.8% (n=65) of the surveyed dentists. Table 2 shows the association between the choice of the vital bleaching technique and independent variables. An association was found between the time since graduation and the type of vital bleaching technique (p=0.017). Younger dentists (<20 years) indicate more in-office technique while dentists with more than 30 years since graduation indicate more at-home. Although post-graduation training did not was associated with vital bleaching therapy (p=0.194), the place of work was a factor that influenced the choice of professionals (p=0.021). Dentists in public/university place work choose more at-home vital bleaching compared with individuals that work in private practice, which preferred mostly in-office. Regarding the association between the materials used for nonvital tooth bleaching (table 3), no association was observed with time since graduation (p=0.319), post-graduation training (p=0.714) and place of work (p=0.447). Similarly, no association was observed between the choice of vital bleaching materials and time since graduation (p=0.271), post-graduation training (p=0.085) and place of work (p=0.911).

Discussion
The overall results of the present questionnaire-based survey showed that professionals' characteristics such as place of work and time since graduation influenced the dentist's decision concerning indication of at-home or in-office vital tooth bleaching. To investigate the opinion of dentists is a useful tool to understand what is happening in the dental clinic in real life for different procedures, including the preferences for tooth bleaching 17,18 .
In this study, in-office dental bleaching was largely preferred (60.5%) by Guatemalan dentists over at-home (39.5%) for vital tooth bleaching. A systematic review showed that both techniques are effective in bleaching capacity 14 . Although the literature showed that while different concentration agents exhibit similar efficacy 12 , the use of therapies with lower peroxide concentration has been recommended as the first choice because they usually are associated with less sensitivity during treatment 19 . Moreover, an in vitro study showed that higher concentrations of peroxide in bleaching materials can degrade more easily than peroxides with lower concentrations and thus affect its effectiveness 8 . In fact, 60.5% of dentists choose the in-office protocol, of which 50% indicated CP 37% or HP 37% and 10.5% indicated the CP 10-22%, concentrations used to at-home. This result could be explained due to possible higher sensitivity indices observed at higher concentrations. However, it is important to note that the use of CP in low concentrations (10-22%) is indicated only in the at-home technique. The choice of approach to tooth vital bleaching of Guatemalan dentists was different from those reported by Demarco et al. 16 (2013), which investigated dentists in the south of Brazil. In this study, Brazilian dentists preferred more (78.1%) at-home than in-office bleaching 16 . Also, the main dentist characteristic associated with the indication of bleaching treatments was the post-graduation training and younger dentists 16 . Dentists with post-graduation preferred to indicate at-home bleaching, like as younger dentists 16 . In our study, we have not observed any influence of post-graduation training in the choice of vital bleaching technique. However, the place of work was an important factor associated with dentist preferences. Thus, a dentist that works in public or university prefers more an at-home approach compared that in-office. The choice for this kind of treatment in private practice could be related to the higher control of the treatment for the dentist or related to the belief that in-office could produce a faster or more strong bleaching effect, which is not demonstrated by a systematic review comparing at-home and in-office treatments 14 .
Moreover, we identify that time since graduation was another factor that influences the indication of vital bleaching technique. Older dentists (between 21 and 30 and more than 30 years since graduation) prefer more at-home tooth bleaching to the vital tooth. These results do not corroborate with Brazilian dentists, were younger dentists indicate more at-home than older dentists 16 .
Concerning the nonvital bleaching, 37% hydrogen peroxide was the favorite bleaching agent in this present study. Indeed, this agent has been largely been used to carry out bleaching treatments in nonvital teeth for more than 70 years 20 . Hydrogen peroxide is no longer indicated for application in nonvital bleathing into the pulp chamber due to the risk of external cervical resorption. Therefore, Sodium Perborate can be a safer alternative to hydrogen peroxide as an intracoronal bleaching agent. Some studies have also suggested that 35% carbamide peroxide present similar efficacy of 35% hydrogen peroxide even as is more safety 21,22 . Also, in the Brazilian study, above 30% Hydrogen Peroxide was the preferred bleaching agent for nonvital treatments 15 . Considering the materials used by Guatemalan dentists, we did not observe any association regarding time since graduation, post-graduation training or place of work, both to vital as nonvital tooth bleaching. These results corroborate with a study carried out in Brazil, which did not found an association between materials used for nonvital tooth bleaching and dentist's characteristics 16 . A possible explanation for differences between the studies that evaluated dentists' preferences can be linked to differences in dental schools. A study investigated the attitudes of the final-year students from three European dental schools towards bleaching 23 , and found important differences between these schools (concerning confidence, teaching received in bleaching and attitudes to provision of bleaching and recommendations to patients).
Students declared to feel more confident about providing nonvital bleaching than vital bleaching. Besides, the complete understanding of mechanisms that professional decision making is a hard task and can englobe several levels of comprehension, beginning in the professional knowledge 17,24 , influenced by the school of dentistry and, also, can be influenced by patients' characteristics [25][26][27] . Some patient's characteristics could influence the decision making of health professionals [25][26][27] . Moreover, it was observed that competition affected the clinical decision-making of dentists in Canada 28 . Dentists located in regions with competitive pressure from other dentists presented an odds 63% higher to indicate a more aggressive approach than dentists located in medium competitive regions. Also, the dentist in very low competitive areas presented an odds 31% higher to indicate aggressive dentistry treatments when compared with medium density regions 28 . Therefore, considering the Brazilian and Guatemalan distribution of dental schools and Dentists we found some differences that could help us. The dentist labor market in Brazilian is very competitive in capitals and this decreases considering interior country 29 ; similarly, dentist Guatemalan distribution is concentered (around 75%) in the capital.
Moreover, some straight points must be highlight. Practice-based studies carried out in dentists' clinical practice have paramount relevance to understanding factors influencing the clinician's preference of a specific technique/material over another. Yet, we included dentists from all regions of Guatemala through a representative sample of all countries. Moreover, some limitations could also be emphasized. There were more than 9.1 % of the dentists included in the initial sample size that refused to participate in the study. Also, considering that we applied a self-applied questionnaire, some dentists did not answer all the questions, making the numbers of respondents different for each question.
Thus, the present findings demonstrated that the place of work and the time in the clinical practice affected dentists' choices for vital tooth bleaching techniques. In-office bleaching using carbamide peroxide at lower concentrations is preferred by the Guatemalan dentists.