Bone grafts have made it possible to resolve the problems of the insufficient thickness or height of the jawbone in many patients who require dental implants for either functional or esthetic reasons. Autologous bone is currently considered the “gold standard” for bone regeneration due to its osteoconduction, osteoinduction and osteogenesis-inducing properties . However, autologous bone grafts occasionally have significant drawbacks, such as increased postoperative morbidity, the need for a second surgery and the lack of sufficient bone mass at the donor site . Consequently, science has developed other therapeutic options, such as alloplastic grafts (synthetic bone substitutes), processed bone from species other than that receiving the graft (xenografts), and processed bone from different individuals of the same species (allografts) . Unfortunately, the literature reports some controversial issues regarding allografts related to possible graft rejection, virus transmission and other ethical concerns [15, 16]. Similarly, xenografts may produce zoonotic disease in some cases . These data may influence the opinions of clinicians and patients, and these opinions should determine the final treatment.
In general, the sociodemographic variables did not influence the refusal/acceptance rates of the various bone grafts options, and these results are consistent with those of a study by Hof et al. . Similarly, no significant differences were observed in the acceptance/refusal rates for the different bone grafts according to religious affiliation. These findings may be attributable to the fact that only two religious branches were included in the sample, i.e., Catholic and Evangelical. These are the predominant religions of the Chilean population, and both allow the use of grafts derived from humans and animals . Moreover, these findings demonstrate that the opinions about specific therapies are unique to each patient and not dependent on other factors.
Allografts were the bone grafts that elicited the highest refusal rate among respondents. 41 % declared that they would never accept this type of bone graft or would do so only as a last resort. A study involving 219 patients  who had received or were about to receive liver allotransplants reported on these patients' opinions about possible donor-related risks. Most patients wanted to be informed about the risk of infectious disease transmission (74.8 %). In the present study, 15 % of patients reported that they would refuse to accept a bone allograft due to fear of disease transmission from the donor.
Importantly, allografts are not available worldwide due to religious and ethical concerns . However, in this study no significant differences were observed in the refusal rates for allographs due to specific religious affiliation. Moreover, despite the finding of a significant relation between women and allograft refusal, we cannot dismiss the possibility that this finding was influenced by the predominance of females in the sample. Despite the percentage of women not being representative of the total population at regional level, it is close to the percentage of females that receive attention in our clinics (68 % of patients). In relation to the percentage of religious/non-religious, data from the last Chilean censusFootnote 1 showed percentages of 67 % Catholic, 16 % Evangelical and 11 % non-religious. Therefore, this study exhibited percentages closer to the national population census with 55.5 % of individuals who declared themselves Catholic, 20.8 % Evangelical and 23.5 % non-religious.
Bone allografts from living donors are primarily obtained from the femoral head of patients undergoing hip-replacement surgery . The donation criteria are quite strict, and over 50 % of willing donors are excluded. Accepted donors are tested for contagious diseases. Allograft bone from cadavers is also used, but in these cases information about the donor's lifestyle must be obtained from relatives, and this information may not always be reliable . Nonetheless, the risks and benefits of allografts should be discussed with the patient prior to the consent process . Such discussions are a part of the process of patient choice and essential to the principle of autonomy. Similarly, the clinician should be aware of the moral and ethical issues related to the use of allografts, the origins of the allografts, and the possible risks of disease transmission so as to respect the principles of beneficence and non-maleficence.
Regarding xenografts, 15 % of the patients reported that they would not accept this type of graft under any circumstance, and 18 % reported that they would approve of a xenograft only as a last resort. The main reasons for xenograft rejection were the fear of possible disease transmission and the belief that it is wrong to use animals for human benefit. Both of these opinions are valuable and must be considered by the clinician prior to the surgical procedure.
The ethical aspects of xenografts have also been a topic of discussion in the scientific community. Nelson  asked for the careful consideration of the ethical issues involved in the use of animal organs and the sacrifice of animal life for human benefit. McCarthy  reported that opponents of the use of animals may base their arguments on theological, philosophical and/or economic reasons. The rules and customs related to the use of products derived from animals may differ between different religions and individuals (Eriksson et al., 2013). For example, Hinduism does not allow the use of implants or products derived from cows or pigs, and Islam conflicts with the use of pig-derived products . This study did not detect significant relationships between religion and xenograft primarily because Christian religions (i.e., Catholic and Evangelical) accept the use of animal-derived products . In summary, some animal-derived products may cause conflicts with personal or religious beliefs that need to be considered prior to surgery.
In the case of autologous bone grafts, the majority of the patients who rejected their use provided reasons related to potential discomfort or postoperative pain at the donor site, whereas only 2 % mentioned religion. A study conducted by Nkenke and Neukam  reported that mandibular bone grafts are generally well-accepted procedures that also involve low objective and subjective morbidity rates. Banwart et al.  studied morbidity in 261 patients who had bone harvested from the iliac crest and concluded that serious complications can be avoided and those complications affecting the functions of the donor site were rare. In a study by Hof et al.  in which 150 patients were interviewed in relation to dental implants and bone grafts, 43 % chose a synthetic bone substitute material (alloplastic) to avoid donor site morbidity, and 23 % were able to undergo surgery to obtain an autograft from the hip. In the present study, only 8 % expressed that they would never accept the harvesting of an autologous bone graft from an extraoral donor site, for example, the tibia or hip.
Clinicians occasionally make decisions about the type of surgery and products used without concern for patient discussions, which violates the ethical principle of autonomy. Op den Dries et al.  found that 79.8 % of patients expressed the desire to be involved in decision-making regarding the advisability of accepting a liver transplant, 10.6 % wanted to make the final decision themselves, and only 9.6 % did not wish to be involved in the decision-making process. Therefore, the clinician must properly inform the patient without influencing his decision to obtain the patient’s opinion and informed consent for each product and procedure used in the treatment plan . The final decision may depend on several factors, but it is necessary for the patient to be well informed . In this sense, a professional must carefully consider the risks, costs and benefits of the type of bone graft to be used to achieve the final treatment outcome. Thus, the clinician must be sufficiently ethical and conscious of his duties to individuals and humanity.
One point that we wish to highlight is that despite the fact that all of the surveyed individuals were Christians, religion was one of the reasons for graft refusal. This finding was confusing for the authors but could be attributable to the differences that exist in individual religious interpretations . Unfortunately, this question was answered without explanation. Both individuals that answered wrote: “because the word of God says so” and “religious reasons”, but without further explanation.
Little is known about patients’ opinions regarding bone grafts ; however, in this study we observed that each patient had a different opinion and strong arguments for choosing to accept or reject each type of bone graft, and this needs to be understood by the clinician prior to treatment planning. Unfortunately, it was not possible to directly compare previous studies with the present study because four types of bone grafts were examined here that have only recently become conventional. Similarly, this study employed a quantitative approach to the patients’ opinions about bone grafts. However, further studies employing qualitative analyses are needed to understand the different opinions in greater detail.