Overall, a total of 388 records were identified through literature searches. After removal of duplicates and initial screening, 85 studies were reviewed in full for eligibility. Across all searches, 22 articles met the criteria for inclusion and were included in the final synthesis. Two articles from the grey literature were also incorporated. Figure 1 illustrates the selection process at each stage of the review.
PRISMA 2020 flow diagram of study selection
All studies were observational and most employed a cross-sectional design (n = 20). Only one study used a comparison group from the general population; however, some compared their results against available data from national dental health surveys. Table 1 and Table 2, and online Supplementary Tables 1 and 2 provide a summary of the findings, categorised by oral health outcomes for each vulnerable group examined.
People experiencing homelessness
Ten studies on clinical oral health outcomes and homelessness were included.13,14,15,16,17,18,19,20,21,22,23 In addition, the 2017 Groundswell Healthy Mouth report24 was included from the grey literature (online Supplementary Table 1).
Studies reported that people experiencing homelessness had high levels of untreated dental caries, with 71–76% of participants requiring restorative treatment.16,17 Compared to the general population, people experiencing homelessness had more missing and carious teeth and fewer filled teeth.13,15,16,17 The mean number of decayed, missing, and filled permanent teeth (DMFT) among the samples ranged from 15.5 to 16.9, with most studies showing that the largest DMFT component was missing teeth.13,14,15,17,18,19 Additionally, the Groundswell study revealed that 46% of its participants reported having ‘holes in teeth’.24
Periodontal disease was examined in four studies.15,16,17,19 They pointed to very high levels of periodontal disease among people experiencing homelessness, with the majority needing periodontal treatment. One study found that only 15% of people experiencing homelessness showed no signs of debris, bleeding, or pocketing,16 while another observed that only 8% showed no apparent symptoms of gingival or periodontal disease,15 while the Groundswell study indicated that 56% reported ‘bleeding gums,’ 45% experienced ‘bad breath,’ and 44% had ‘loose teeth’.24
Three studies on tooth loss were identified.13,17,19 In the largest (n = 853), the prevalence of edentulousness was 6% among relatively young adults (mean age 34 years).13 In another study on a smaller cohort of older people experiencing homelessness (mean age 55 years), the prevalence of edentulousness was about 30%, with most not using dentures.19 According to the Groundswell study, seven-in-ten participants reported having lost teeth since becoming homeless. Of these, 17% attributed tooth loss to acts of violence, and 12% to accidents.24
Only two small-scale studies were identified for odontogenic infections18,19 and the same was the case for oral cancer.13,15 One study on odontogenic infections (n = 44) reported that 4.6% of participants had abscesses,18, while the other study (n = 70) found that 54% of individuals had one or more teeth with obvious pulpal involvement.19 Regarding oral cancer, one study reported that out of 853 participants, 61 had suspicious oral mucosal lesions, with five requiring referral.13 Another study (n = 317) reported that 5% of the sample had soft tissue lesions, with two cases ultimately diagnosed as oral cancer.15
Six peer-reviewed articles focused on subjective oral health, including oral health-related quality of life (OHRQoL).13,14,15,17,18,20 Comparisons with the general population revealed that a higher proportion of people experiencing homelessness experienced poorer OHRQoL.13,14,17,18 The most frequently reported oral impacts were physical pain, psychological discomfort, and psychological disability. For instance, a study from Scotland found that 25% of participants frequently felt self-conscious and 23% felt embarrassed about their mouth’s appearance.13 The Groundswell study highlighted that 87% of participants reported experiencing oral impacts occasionally or more frequently, a contrast to the 39% reported in the Adult Dental Health Survey (ADHS) 2009.24
Three papers were found in relation to oral health-related behaviours.13,21,22 The Groundswell study found that only 35% of people experiencing homelessness brushed their teeth twice-daily, a much lower prevalence than the 75% reported in the ADHS 2009. Additionally, 60% of the participants were categorised as high sugar users, compared to 50% in the wider population.24
Five papers examined dental service use among people experiencing homelessness.13,16,19,21,23 One study on 853 participants revealed that 41% had visited a dentist in the previous year, primarily due to dental pain.13 This finding aligns with a London-based study (n = 201), where over 40% attended a dentist due to pain,16 and another study using patient records data (n = 349), where 40% presented with pain.23 Other reasons for visiting the dentist included missing teeth, swellings and periodontal problems.21 Barriers for regular attendance included cost, lack of perceived need, fear, low priority, and fatalism.19,21 Barriers hindering people experiencing homelessness from accessing dental care reported by the Groundswell study included lack of motivation (about 30% believing their teeth were beyond repair), confusion regarding NHS entitlement (58%), cost concerns (23%), fear (24%), and previous negative treatment experiences (12%).24
Prisoners
Six peer-reviewed papers relating to clinical outcomes among prisoners met the inclusion criteria (online Supplementary Table 2).25,26,27,28,29,30 These examined caries, oral sepsis, periodontal disease, and oral cancer. No studies assessed tooth loss or traumatic dental injuries. In addition, findings from grey literature, i.e., the 2019 Scottish Oral Health Improvement Prison Programme (SOHIPP) survey were also included (n = 559).31
Generally, prisoners had more decayed, fewer sound and fewer filled teeth compared to the general population.25,27,30 Across studies, the DMFT index ranged from 12.3 to 15.6, with missing teeth being its largest component.
In relation to odontogenic infections, one study (n = 122) found that 16% of the sample exhibited signs of diffuse swelling or the presence of a chronic abscess or sinus.26 Another study on female prisoners (n = 103) reported a significantly higher prevalence of oral sepsis (40%) compared to the general population (7%).30 Prisoners also had a higher prevalence of gingival bleeding, calculus, and deep periodontal pocketing compared to the general female population. For example, 62% of the prisoners had periodontal pockets of 4 mm or more, in contrast to 41% in the ADHS 2009.30 Additionally, two other studies on relatively young prisoner populations indicated high periodontal treatment need.25,26
While no peer-reviewed studies addressed tooth loss among prisoners, the 2019 SOHIPP report revealed that 75% of prisoners (mean age 32.1 years) retained at least 20 teeth, and 4% were edentulous.31
One study with 122 participants noted that three individuals were referred to secondary care due to suspicious oral lesions,26 while the 2019 SOHIPP indicated that 8.3% of prisoners had at least one oral lesion that warranted monitoring or further referral.31
Four studies on subjective oral health measures were identified.25,26,29,30 They suggest that prisoners generally perceive their oral health as poor and express dissatisfaction with it. Two studies reported a significantly higher prevalence of oral impacts among prisoners compared to the ADHS 2009 population.29,30 For instance, 73% of prisoners experienced at least one oral impact on their daily life, in contrast to 34% in the ADHS 2009. The most common impacts related to difficulty eating (55%), problems smiling (37%), emotional stability (32%), and difficulty relaxing (30%).30 The 2019 SOHIPP survey found that the most frequently reported oral impacts were ‘feeling self-conscious’ (38%) and ‘feeling embarrassed’ (32%).31
Three papers investigated oral health-related behaviours in prisoners.25,26,30 The 2019 SOHIPP report revealed that 44% reported using tobacco products. The study also inquired about toothbrushing habits, finding that 89% of participants brushed their teeth in prison, with 73% maintaining this habit both at home and in prison.31 One study found that high sugar intake was more prevalent among female prisoners (66%) than in the general population (16%).30
In terms of service use, a large proportion of prisoners attended the dentist within the last year.25,26,29,30 However, they visited the dentist mainly when in trouble, which was also the case for this population before imprisonment. One study showed that compared to the general female population, the prevalence of regular dental attendance was considerably lower for female prisoners (67% versus 33%), whereas the prevalence of visiting the dentist only when in trouble was much higher (22% versus 41%).30 The SOHIPP 2019 found that 78% of prisoners reported accessing dental services in prison, compared to 74% who had ever accessed dental care inside or outside prison. However, the study also highlighted barriers to accessing care, including difficulty securing appointments (40%), limited availability of treatment visits (32%), and dislike of the prison dental service (6%).31
Gypsy, Roma and Traveller communities
Only one small study on 37 Traveller children was identified (Table 1).32 Approximately two-thirds of the children had caries, assessed as visually obvious decay. The prevalence of twice-daily tooth brushing was low (40%) and a moderate to highly cariogenic diet was consumed by 95% of the children. Around 85% had visited a dentist within the last two years.32
Looked-after children
Four articles, reporting on studies from different parts of the country and using different methodological designs, met the eligibility criteria for inclusion (Table 2).33,34,35,36
Caries and dental trauma were the only clinical outcomes assessed, with evidence suggesting higher levels of both conditions among looked-after children. A study in Bradford found that only 42% of children under a child protection plan were caries-free, compared to 68% among the control group of children not under such a plan. Significant differences in primary dentition caries persisted even after adjusting for gender and area deprivation. Children with a protection plan also had more caries in permanent teeth than the control group, but the differences were not significant.33 School-based epidemiological data in North East London showed that a higher proportion of looked-after children had caries (54%) and dental trauma (41%) than non-looked-after children, where the prevalence was 10% for caries and 4.5% for trauma.34
With regards to subjective oral health measures, only the North East London-based study provided relevant information, with looked-after children experiencing higher levels of dental pain than those not looked after (12.5% versus 7%).34
Service use measures were assessed in three studies.33,35,36 The Bradford study showed that children under a child protection plan were less likely to be registered with a dentist and attended dental services less frequently than non-looked-after children.33 In a large data linkage study in Scotland, a lower percentage of looked-after children regularly attended dental services compared to non-looked-after children (51% versus 63%). This study also found that at age five, looked-after children were more likely to need urgent dental treatment and were more often subject to teeth extractions under general anaesthesia than their counterparts (23% versus 10% and 9% versus 5%, respectively).35 A case-control study in Wales reported that children in care visited the dentist less frequently and were more likely to require treatment upon these visits compared to non-looked-after children.36
Sex workers, and asylum seekers and refugees
No articles were identified for these vulnerable groups.
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