Abstract
Objectives:
To investigate treatment outcomes of different restorative techniques undertaken by dental therapists for primary molar carious lesions in a sample of children in New Zealand primary care.
Methods:
This was a randomized controlled trial with children aged 3 to 8 y in New Zealand’s Whanganui region. Children meeting inclusion criteria were randomly allocated to treatment with either the Hall technique (HT), in which a stainless-steel crown (SSC) is placed without any carious tissue removal or tooth preparation, or a non-Hall conventional restorative approach (NHT), including tooth preparation with selective carious tissue removal; this included SSC, amalgam, composite, or glass ionomer cement (GIC) restorations. Restorative outcomes after 12 and 24 mo were categorized as success, minor failure, or major failure.
Results:
Of the 295 eligible children, 149 and 146 were allocated to the HT and NHT groups, respectively, with a total of 570 carious primary molars treated by 13 dental therapists. The participant follow-up rates at 12 and 24 mo were 95% and 91%. SSCs were the most commonly used restoration in the NHT group (60%), followed by GIC (28%). SSCs were the most successful restorations regardless of whether they were placed with the HT or NHT, with success rates of 89% and 92% at 12 mo and 85% and 86% at 24 mo. In the NHT group, the treatment material was a predictor of minor failure at 12 and 24 mo, with significantly more failures with GICs.
Conclusions:
SSCs placed by dental therapists are a highly successful restoration for the primary dentition, regardless of whether they are placed with the HT or conventionally. The high failure rate of glass ionomer restorations means that they cannot be recommended for widespread use in New Zealand primary care (Australian New Zealand Clinical Trials Registry, ACTRN12614000844640).
Knowledge Transfer Statement:
The findings of this study can be used by policy makers and clinicians when deciding on which materials and which approach to use to maximize success and to minimize retreatment rates when providing restorative treatment for carious primary molars in children’s primary oral health care. Results also suggest that undertaking research in the primary care setting may enhance translation of new knowledge and techniques into clinicians’ hands.
Introduction
In New Zealand, most children receive publicly funded dental care provided by dental therapists in the Community Oral Health Service (COHS). Dental therapy practice is a subset of the practice of dentistry. In the COHS, dental therapists independently examine and treat children from 2 to 11 y of age, and they maintain a consultative working relationship with a dentist or dental specialist. The fully defined scope of practice for dental therapists in New Zealand can be found on the website of the Dental Council of New Zealand (n.d.). The 2009 New Zealand Oral Health Survey (Ministry of Health 2010) found that in the 2- to 11-y age group, nearly all children (90%) had had a dental examination in the previous 12 mo, more than two-thirds (68%) had caries experience, and there was a high restorative index, with only 17% having untreated carious lesions present. However, there remain very high numbers of children treated under general anesthesia for dental caries (Hunt et al. 2018), and early childhood caries is highly prevalent, with one New Zealand study finding that 41% of children had been affected by the time that they entered school at 5 y of age (Aung et al. 2019).
Despite the high restorative index, there has been little research on the outcomes of the restorative care provided in this country. A feasibility study in a New Zealand region in 2011 explored the introduction of the Hall technique (HT) after audit data had found a high rate of glass ionomer restoration placement and replacement in children. The study found that dental therapists were adept at using the HT, with promising outcome data at 6-mo follow-up (Boyd et al. 2017). The HT involves cementing a preformed stainless-steel crown (SSC) onto a carious primary molar, with no caries removal, tooth preparation, or local anesthesia. It is a technique that embraces minimal intervention dentistry and use of a less invasive dental treatment approach for children. The technique was shown to have much higher success than glass ionomer cement (GIC) restorations (92% vs 52%, respectively) at 48-mo follow-up in a randomized controlled trial (RCT) with general dentists in Scottish primary care (Innes et al. 2011). A New Zealand quasi-experimental study in primary care, with dental therapists performing the procedures, also found that the success of the HT was much higher than conventional restorative treatment with amalgam or GIC (94% vs 68%) after 2 y of follow-up (Boyd et al. 2018). Similar success for the HT was shown in an RCT in Germany, in which pediatric dentists or pediatric dentistry trainees provided the treatment and the HT was compared with compomer restorations. At 2.5 y, the success rate was 92% for the HT and 67% for the compomer restorations (Santamaria et al. 2017).
There have been no RCTs on the outcomes of restorative treatment of dental caries in primary care in New Zealand children. Accordingly, the aim of this RCT was to investigate clinical and radiographic outcomes of the HT and non-Hall conventional restorative care (NHT) in primary molar approximal carious lesions in New Zealand primary care, with 3- to 8-y-old children at 1- and 2-y follow-up.
Methods
This was a primary care RCT, with children randomized to intervention with either the HT or NHT upon recruitment to the study. The primary outcome was success or failure based on clinical and radiographic measures combined at 1- and 2-y follow-up to give composite outcomes of success, minor failure, or major failure (Table 1), as defined by Innes et al. (2007). Ethical approval for the study was obtained from the Northern B Health and Disability Ethics Committee (14/NTB/39). A feasibility study conducted from 2011 to 2012 (Boyd et al. 2017) indicated procedural success rates of 82.0% for conventional treatment and 96.0% for the HT at 6-mo follow-up. Based on these data for sample size calculations, a conservative power analysis suggested that a minimum of 103 children was needed in each arm (assuming α = 0.05 and ß = 0.90). Assuming 33% loss to follow-up over 2 y, we aimed to recruit 137 children in each arm. The study was registered with the Australian New Zealand Clinical Trials Registry (ACTRN12614000844640).
Outcome Criteria.
Based on Innes et al. (2007)
The eligible study population comprised children aged 3 to 8 y attending for their next dental examination from 37 schools and preschools in New Zealand’s Whanganui region COHS. They were invited to take part in the study, with written consent and assent obtained from the parent and child, respectively, before proceeding. Information on child age, address, and ethnicity was obtained from parents. Other sociodemographic information included an area-based deprivation score: the NZDep2013 (Atkinson et al. 2014). The NZDep2013 allocates each address a deprivation score, ranging from 1 (least deprived) to 10 (most deprived). All dental therapists participated together in 2 d of training in study protocols, which included practical clinical procedures and calibration exercises. The practical training included a hands-on session with study models on the HT and the placement of separating elastics, as well as radiography training. In the calibration sessions, all dental therapists discussed and completed sample study documentation, using photographic images of teeth with various stages of carious lesions and radiographs with carious lesions at various stages, which encouraged consideration of the pulp-dentine complex and dentoalveolar complex. Recruitment commenced on July 7, 2014, and was completed on December 20, 2014.
Screening and Baseline
All children underwent a comprehensive clinical examination by 1 of the 13 calibrated dental therapists. Visual examination was conducted under dental light with a flat dental mirror, blunt explorer, and triplex air syringe. Teeth were washed and dried and cotton roll isolation used to maintain a dry field. Caries status was systematically recorded for each surface. Only the clinical status of the primary dentition was recorded for this study. The examining clinician also took a set of bitewing radiographs using a standardized bitewing holder at baseline. These were developed and read by the examining clinician and by 2 dental specialists (one in pediatric dentistry, the other in dental public health). No magnification was used in reading radiographs, and surfaces that could not be read were recorded as such.
To be included in the study, children were required to have no complicating medical history 1 and at least 1 radiographically detectable proximal carious lesion in the primary molars, with healthy pulp 2 and with a score of P3 or P4 in the following radiographic scoring system: P0, no radiolucency; P1, radiolucency in outer half of enamel; P2, radiolucency in inner half of enamel; P3, radiolucency <0.5 mm into dentine; P4, radiolucency >0.5 mm into dentine but confined to dentine’s outer half. Teeth had to have more than half the root structure remaining. If a child had >1 tooth affected by a proximal lesion, >1 tooth was included. Children were excluded if they were unable to have radiographs taken, had no carious lesions present or into dentine at the P3 or P4 level, were medically compromised, did not have parental consent, or did not assent to participation in the study. At baseline, the dental therapists completed history and examination documentation for each child. This included assessing and recording temporomandibular joint health, absence/presence of open bite, the study tooth, the sites and depth of the carious lesions, the presence/absence of marginal ridge breakdown, and gingival health. The children were randomly allocated (in randomly permuted blocks generated by L.A.F.P. with SPSS 24 [IBM]) to 1 of 2 groups undisclosed to the examiners (A, HT; B, NHT); the details were sealed in envelopes held by the research assistant and delivered to the dental therapists’ assistants. The assistant informed the dental therapist the intervention group to which the child was allocated, and the designated treatment was provided by that dental therapist.
Treatment
The HT was carried out according to the user’s manual (Innes and Evans n.d.). Separating elastics were provided for dental therapists to use prior to the HT when needed. No carious tissue removal, tooth preparation, or local anesthesia was undertaken. Preformed, precrimped SSCs were supplied by 3M and cemented with 3M RelyX Luting Plus Resin Modified GIC. In the NHT group, dental therapists used the materials that were currently in use in this District Health Board, which were amalgam (SDI GS-80), composite (GC G-aenial), GIC (GC Fuji IX), or SSCs according to their usual clinical judgment. The non-Hall restorations and SSCs were placed according to District Health Board protocols, in which local anesthetic was administered as required, rotary and hand instruments were used to excavate the carious dental tissue with a selective caries removal approach used to avoid pulp exposure, and dental materials were placed according to the manufacturer’s instructions. A rubber dam was rarely used, with cotton roll isolation used to maintain a dry field.
Follow-up Examination Clinical and Radiographic Measures
Participants were clinically examined after 12 and 24 mo by 1 of the 13 dental therapists. At 12 and 24 mo, they assessed the children and recorded data on temporomandibular joint health, the absence/presence of open bite, gingival health, whether any further treatment had been required for the study tooth, and the condition of the study tooth, including signs and symptoms of pulp pathology. Two specialist dentists (D.H.B. and K.N.F.) experienced in assessing bitewing radiographs of children examined all baseline and follow-up radiographs. The dental specialists were calibrated prior to reading radiographs. Intra- and interexaminer reliability was assessed by re-examining every 10th set of radiographs at the end of each day of reading. The intraclass correlation coefficient for the interexaminer reliability score was 0.85, and the intraexaminer scores were 0.86 and 0.88. Baseline radiographs were assessed for quality and positioning and to confirm that study tooth/teeth had fulfilled the inclusion criteria. At follow-up, the radiographs were again assessed for quality and positioning, and the study tooth was assessed for presence of the restoration and for signs of pulp health/disease (by pathologic interradicular radiolucency/root resorption) and assigned composite outcomes of success, minor failure, or major failure, as previously described.
Data Analysis
Data were entered and analyzed with SPSS 24. Following the computation of univariate descriptive statistics, differences among proportions were tested for statistical significance (α = 0.05) via cross-tabulations and χ2 tests; differences with continuous variables were tested for statistical significance with analysis of variance (and 1-way analysis of variance to identify post hoc differences among >2 groups). To allow for some participants having had >1 tooth restored, we used multilevel modeling (with the melogit command in Stata 15.1; StataCorp) to examine the contribution of treatment type and baseline carious lesion depth to the occurrence of major failure by 12 and 24 mo.
Results
Baseline Characteristics
Of the 556 patients examined, 295 children (53.1%) fulfilled the inclusion criteria and were randomized for treatment: 149 for HT and 146 for NHT (Appendix Fig. 1). In total, the outcomes of 570 carious primary teeth were analyzed, with 273 and 297 teeth from the HT and NHT groups, respectively (Appendix Fig. 2).
Children’s sociodemographic characteristics are summarized by treatment group in Table 2. There were no significant differences between treatment groups by sex, age, ethnicity, and deprivation. Of the 570 teeth treated, nearly half were mandibular second molars (41.0%), and about one-third were maxillary second molars (29.8%). There was no significant difference between treatment groups, apart from baseline dmfs.
Sociodemographic Characteristics at Baseline by Intervention.
NZ, New Zealand.
Parentheses contain column percentage unless noted otherwise.
Row percentage.
Baseline clinical characteristics of teeth receiving treatment are shown in Table 3. Of the 570 teeth, 273 (47.9%) were treated with the HT. In the NHT group, 297 teeth were treated with 4 approaches; more than half (59.6%) of the teeth received a conventional SSC, while over one-quarter (28.3%) received a glass ionomer restoration. A similar distribution of caries depth was observed in both treatment groups.
Baseline Clinical Characteristics of Teeth Receiving Treatment: Hall and Non-Hall.
There were 24 cases where radiographic depth could not be coded (12 in each group).
P < 0.05.
Follow-up Findings
Of the 295 children, 279 (94.6%) and 269 (91.2%) were followed up at 12 and 24 mo, respectively (Appendix Fig. 1). The Appendix Table presents the characteristics of the 26 children lost to follow-up at 24 mo as compared with those who were followed up. More of the former were Ma-ori or from the HT group. Of the 570 teeth treated, 535 (93.8%) and 462 (81.0%) were followed up at 12 and 24 mo (Appendix Fig. 2). There were 2 teeth that had exfoliated and 6 teeth that had been extracted by 12 mo, with 48 exfoliated and 12 extracted by 24 mo.
Clinical and radiographic outcomes at 12 and 24 mo by treatment are summarized in Table 4. By 12 mo, more than three-quarters (86.5%) of all treated teeth were successful, with no significant differences between the treatment groups (88.6% HT and 84.5% NHT). There had been a very small number (2.8%) of major failures after 12 mo, again with no difference between the treatment groups. In the NHT group, the treatment material was a significant predictor of minor failure at 12 mo, with more failures in the glass ionomer treatment group (P < 0.001).
Clinical Outcome (by Tooth) at 12 and 24 mo by Treatment.
Values are presented as n (%). The 12 extracted teeth are included in the failure categories.
SSC, stainless-steel crown.
P < 0.001.
Depth could not be recorded for 24 teeth at baseline.
P < 0.05, Hall vs. non-Hall.
SSCs had the greatest success by 24 mo, regardless of treatment group. There had been only 26 (5.5%) major failures by 24 mo, with nearly all having been treated with a SSC and no difference between the treatment groups. At 24 mo, nearly half of the glass ionomer–treated teeth showed minor failure (P < 0.001). In lesions that had had their caries depth recorded as P4 at baseline, there was a higher success rate in the HT group by 24 mo (P < 0.05). The multilevel modeling of major failure by 12 and 24 mo (Table 5) showed no significant differences by technique, baseline caries depth, or material used.
Outcome of Multilevel Modeling of Major Failure.
Used as an ordinal variable (stainless-steel crown = 1, glass ionomer cement = 2, amalgam = 3, composite = 4).
Discussion
This RCT investigated the 1- and 2-y clinical and radiographic outcomes of 2 restorative treatment approaches (HT and NHT) for managing interproximal carious lesions in primary molars in 3- to 8-y-old children in New Zealand primary care. SSCs were the most successful restorative treatment, regardless of whether they had been placed with the HT or a conventional technique. This SSC success is consistent with other studies (Innes et al. 2011; Ludwig et al. 2014; Santamaria et al. 2017; Boyd et al. 2018). Only a small number of amalgam and composite restorations were placed, and these showed success rates similar to one another. GIC restorations showed poor outcomes, with more than a third of these failing at 1 y and almost half at 2 y. Conventional GIC has been shown to have poor performance in proximal class II restorations in primary molars, mainly due to fracture of the material and debonding from the dentine (Chadwick and Evans 2007). It seems wise to limit the use of this material in primary care to clinical situations where the restoration is required to last for less than a year. Resin-modified GIC may be a superior material, provided that its use is limited to small cavities. It has yet to be evaluated in New Zealand primary care.
Although the strengths of the study lie in the use of random allocation to the different treatment groups, a large number of participants, and excellent follow-up at 2 y, there are several weaknesses to consider. A number of dental therapists (n = 13) provided the treatment, and there were likely differences among them. However, all dental therapists undertook treatment in both arms of the study, so any individual differences are unlikely to have had an effect on the difference in outcomes between the treatment groups. Dental therapists in this study had a range of experience in the profession, with some recent graduates and some more experienced, and this is representative of the current New Zealand COHS workforce. Given that the patients are typical of those seen nationally, the findings are likely to be applicable across the country. Since the majority of treatment in the NHT arm of the study was with SSCs and GIC, there were only small numbers of teeth treated with composite and amalgam, and so the success rates for these materials must be regarded with some caution. The success rates for composite resin and amalgam were reasonably high and similar at 1 y, although composite success declined considerably at 2 y (from 95.0% to 73.7%). Nonetheless, further investigation of composite restorations in the New Zealand primary care setting may be justified because the up-front costs of this material are lower than those of SSCs. Dental therapists were allowed to choose their preferred restorative material in the NHT arm of the study, and this may have had an effect on outcomes because they may have chosen to place SSCs on the extensive, deep carious lesions and the other restorative materials on small, shallow carious lesions. This would be expected to lead to more favorable outcomes with the non-SSC materials, which was not the case.
Despite the known durability of SSCs (Innes et al. 2015; Seale and Randall 2015), they were rarely used until the past decade—except in the hands of pediatric dental specialists—because of perceived barriers to their use (Threlfall et al. 2005; Bell et al. 2010). Although it was not our intention to compare conventionally placed SSCs with HT, such a comparison was possible because dental therapists chose to use SSCs more than any other restorative material in the NHT arm of the study. This reflects a change in practice in New Zealand primary care and may be due to the international introduction of the HT, which is seen as a simpler way for clinicians to place SSCs and which has increased publicity about the success of SSCs. In addition, recent research conducted within the New Zealand COHS on outcomes of its restorative treatment (Foster Page et al. 2014; Boyd et al. 2017; Boyd et al. 2018) has raised awareness within the COHS of the poor outcomes with GIC restorations (which had been the most popular restorative choice), and this may have been translated into the change in practice reported here. Furthermore, it has been proposed that the participation of clinicians in research generates benefits over and above the research findings and may include changes in practitioner behavior, such as the uptake of new treatments earlier than they would otherwise have occurred (Krzyzanowska et al. 2011). This might also explain the greater use of SSCs by dental therapists in this RCT.
In this study, a selective caries removal approach was used in the NHT arm to avoid pulp exposure. Selective removal of carious tissue and indirect pulp therapy are techniques with good success, with added advantages of preservation of tooth structure and lower treatment time and complexity (Qudeimat et al. 2007; Ricketts et al. 2013; Schwendicke et al. 2013; Smail-Faugeron et al. 2016; Dhar et al. 2017). In a tertiary center where treatment was conducted by pediatric dentistry trainees and specialists, the success rate for compomer restorations was 64% after 2.5 y with a selective caries removal approach (Santamaria et al. 2017). Others have, however, reported high success (89%) with a selective caries removal approach and composite restorations at 2 y (Franzon et al. 2015). The use of selective caries removal and/or the HT alongside early diagnosis of carious lesions and preventive dental care is an essential component of contemporary evidence-based primary dental care for children (Innes et al. 2019). While there has been uptake of these modern restorative options in the Whanganui COHS, more research is needed to determine whether this reflects practice throughout the rest of New Zealand primary care and to explore the use of evidence-based diagnostic and caries-preventive strategies in that setting.
Differences between conventionally applied SSCs and HT have not previously been evaluated in a primary care RCT, although the success rates of the 2 techniques were comparable in a retrospective audit in a US specialist pediatric practice (Ludwig et al. 2014), a retrospective study in 2 UK pediatric dental specialist centers (Banihani et al. 2018), and a prospective practice-based RCT in Sudan in which a dental therapist placed the HT and a dentist carried out the conventional SSCs (Elamin et al. 2019). The success rates for HT and conventional SSCs in our RCT were also similar, suggesting that the success is due to the durability and seal provided by the crown itself, rather than the placement technique. However, our success rates were slightly lower than those of the US and UK studies, and this may be explained by the latter studies being retrospective, based in specialist centers (where success rates are generally higher than in primary care), and having a shorter period of follow-up. Nonetheless, the success rates for HT in our RCT are slightly lower than the 92% success reported in primary care at 23 mo in Scotland (Innes et al. 2007) and the 94% success observed in the previous evaluation at 2 y in New Zealand primary care (Boyd et al. 2018). The multilevel modeling revealed no effect of baseline characteristics or treatment material/method on major failure. The reason may be the small numbers of major failure overall and/or the fact that all teeth were treated with a selective carious tissue removal approach, which is likely to improve outcomes.
The findings of this study are important because it is the first RCT to examine the outcomes of restorative dental care with different techniques carried out by dental therapists in New Zealand primary care. GIC performed poorly, and HT and conventionally applied SSCs performed equally well at 2 y follow-up. The dental therapists in the study have already changed their practice in favor of SSC and can continue to use either HT or conventionally applied SSCs effectively. However, they now need to translate the findings of this study into reducing the use of conventional GIC in primary molar interproximal carious lesions. Composite, amalgam, and resin-modified GIC restorations need further study in this primary care setting.
Author Contributions
D.H. Boyd, contributed to conception, design, data acquisition, analysis and interpretation, drafted and critically revised the manuscript; W.M. Thomson, contributed to design, critically revised the manuscript; S. Leon de la Barra, contributed to data analysis and interpretation, critically revised the manuscript; K.N. Fuge, contributed to data acquisition, analysis, and interpretation, critically revised the manuscript; R. van den Heever, B.M. Butler, F. Leov, contributed to data acquisition, critically revised the manuscript; L.A. Foster Page, contributed to design, data acquisition, analysis, and interpretation, drafted and critically revised the manuscript. All authors gave final approval and agree to be accountable for all aspects of the work.
Supplemental Material
DS_10.1177_2380084420933154 – Supplemental material for A Primary Care Randomized Controlled Trial of Hall and Conventional Restorative Techniques
Supplemental material, DS_10.1177_2380084420933154 for A Primary Care Randomized Controlled Trial of Hall and Conventional Restorative Techniques by D.H. Boyd, W.M. Thomson, S. Leon de la Barra, K.N. Fuge, R. van den Heever, B.M. Butler, F. Leov and L.A. Foster Page in JDR Clinical & Translational Research
Footnotes
Acknowledgements
We are grateful to the Whanganui District Health Board for supporting the study, to the research assistant Noeline Barrows and manager Barbara Dewson, and to the dental therapists, children, and their families who took part.
A supplemental appendix to this article is available online.
This study was funded by a grant from Cure Kids New Zealand, and stainless-steel crowns and cement were provided by 3M.
The authors declare no potential conflicts of interest with respect to the authorship and/or publication of this article.
Notes
References
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