Research Article: A randomized clinical trial comparing Hall vs conventional technique in placing preformed metal crowns from Sudan

Date Published: June 3, 2019

Publisher: Public Library of Science

Author(s): Fadil Elamin, Nihal Abdelazeem, Isra Salah, Yousra Mirghani, Ferranti Wong, David John Manton.


Despite the high success rates of preformed metal crowns (PMCs) in children no randomized clinical trials compare methods of placement and none describe its use in Africa. Our aim was to compare survival and cost-effectiveness of PMCs placed by conventional techniques (CT) and biological Hall techniques (HT) using a prospective randomized control trial in a general dental practice from Khartoum. One hundred and nine and 103 PMCs were placed in randomly selected children (5-8years) with 1–2 carious primary molars using HT and CT respectively and followed for 2 years. Socioeconomic status, periodontal health, occlusion, anxiety, and procedure time were compared using student t-test. Kaplan–Meier survival rates and incremental cost effectiveness ratio (ICER) were compared between CT and HT. CT and HT groups were similar for age, gender, socio-economic status. Survival rates were high (over 90%) for both study arms and not statistically different (p>0.05). Anxiety scores were significantly higher in CT arm after 12 months compared to HT (p<0.001). Clinically, gingival and plaque indices were similar between groups (p>0.05) but occlusions were raised in nearly all subjects in the HT arm (p<0.05). Periodontal health improved, and occlusions adjusted over time in both arms. There were 3 (2.7%) and 6 (5.8%) minor failures, 7 (6.4%) and 6 (5.8%) major failures in HT and CT arms respectively. Mean procedure time was lower in HT (9.1 min) than CT (33.9 min); p<0.001. Mean PMC cost was US$2.45 and US$7.81 for HT and CT respectively. The ICER was US$136.56 more for each PMC placed by CT per life year. We show that PMCs have high survival outcomes in disadvantaged populations similar to results from developed countries. As HT can be carried out by less experienced dental operators and therapists, this biological approach provides a promising cost-effective option to manage caries in developing countries with limited resources.

Partial Text

Preformed metal crowns (PMCs) have excellent and higher success rates for treating carious primary molars in children compared to conventional restorations such as composite resin restorations, glass ionomer cements and amalgam [1–6]. They are routinely used in specialist paediatric practices in developed countries but relatively underutilised by general practitioners worldwide [6–10]. Restoration of carious molars is carried out using the conventional technique which involves total carious tissue removal. As the CT requires tooth modification and occlusal reduction, it usually requires the administration of local anaesthetic and rubber dam use [11,12]. Hence, it is regarded by general dental practitioners to be highly technical, requiring advanced training, including excellent child behaviour management skills. It is therefore highly unlikely to be widely used outside specialist settings and unlikely to be incorporated in routine care of deprived children from developing countries. The Hall technique (HT) on the other hand, requires either no, or partial, carious tissue removal, and no tooth modification or local anaesthesia. The PMC is cemented by the clinician using a gentle push aided by the child’s biting force. This biological approach has been shown to have high success rate [6].

The study was conducted in a general dental practice in Khartoum, Sudan (2014–2017). The practice has a throughput of 6000 to 6500 children per annum. Ethical approval was granted by the Khartoum Centre for Research and Medical Training Review Board on 11/9/2014 (Ref. Paed/Dent/11). Due to a clerical and managerial oversight, the trial was registered after enrolment of participants had started. This led to the retrospective inclusion of the study in the trials register (; identifier NCT03640013). Recruitment began in February 2015 and ended in March 2016. The protocol has been submitted with the manuscript as supporting information. The authors confirm that all ongoing and related trials for this drug/intervention are registered. All relevant data are within the paper. The trial ended in May 2018.

PMCs placed using the Hall or conventional techniques have excellent survival in deprived communities. HT is highly cost-effective in terms of materials, labour and time. HT induces less self-reported anxiety than the more invasive CT. Placing PMC using HT by therapists is a successful and cost-effective public health intervention for carious primary molars in communities and developing countries.




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