Longevity of Dental Fillings Utilizing 3D Printing

Introduction

In dentistry, filling materials are needed repairing damage caused by dental caries as well as for occlusal rehabilitation. Composite restorations can be performed using direct or indirect technique. There are some shortcomings linked with direct technique, such as polymerization shrinkage, and also their manufacturing can be demanding due to circumstances in the oral cavity. Partly due to these, approximately 8 out 10 regular users of dental services need repetitive repair or replacement of old restorations within 5 years. One solution for manufacturing high-qualified and long-lasting restorations is chairside CAD/CAM (computer-aided design and computer-aided manufacturing) technology that includes both subtractive and additive manufacturing techniques. Additive techniques, also called 3D printing techniques, may provide novel possibilities to overcome the challenges linked with the durability of dental fillings. They might be used to fabricate more complex restorations compared to subtractive techniques with a reasonable cost. In 3D printing, successive layers of material are deposited under computer control to create an object layer by layer. The objects, having practically any shape or geometry, are produced from a model or design in an electronic form. The 3D printable models may be created with a CAD software package and in many cases utilize the imaging data by a dental scanner which have become widely available with high resolution. 3D printing may enable higher restoration accuracy compared to subtractive manufacturing techniques, where the accuracy is limited by the milling unit and machining tools. Another benefit is its low material loss. 3D printing process is fast and likely in future to be used chairside at the dental office. Only a few studies addressing the possibilities of 3D printing in dental filling manufacture exist in the current literature. Based on a previous in vitro study by the imvestigators, the accuracy of 3D printing technique is at least at the same level as milling technique in fabrication of dental inlay and onlay fillings, and thus might be a clinically acceptable alternative to the subtractive milling technique. Additional clinical investigations are needed to confirm these findings. The aim of the present study is to compare the success of dental fillings prepared using 3D printing technique to those manufactured with the direct composite technique.

Material and Methods

At total, 100 adult patients are selected from dental care patients of the Health Centre of Kaarina, Kaarina, Finland, as volunteers. Written informed consent forms are obtained from all patients at the beginning of the study. Participation in the study is voluntary and causes no additional costs for the patient.

Each patient requires two Class II, III or IV cavities to be restored in the dentition. The randomizations are performed by noting each tooth to be restored (Fédération Dentaire Internationale \[FDI\] two-digit code) on one form and the type of restorative system (direct technique vs. indirect technique utilizing 3D printing) on a second. First, a tooth number is drawn blindly. Subsequently, a restorative system is allocated to this tooth by blind drawing. The clinical procedures of cavity preparation and restoration placement are performed by two experienced dentists.

Clinical Evaluation Restorations are rated independently by blinded dentists at the Institute of Dentistry, University of Turku, Finland, who are not involved with the insertion of the indirect and the direct restorations and are unaware of the group status of the fillings. The two evaluators are calibrated against a reference standard. This clinical assessment method results in ordinally structured data for the outcome variables.

Statistical Analysis Power analysis was used to estimate the sample size. In the calculation, the distributions for clinically excellent or acceptable restorations (direct 87% vs. indirect 93%) based on a previous study. Based a previous in vitro study, it was estimated that restorations based on 3D printing technique have at least as high success rate as indirect ceramic restorations, 96%. When the statistical significance was set p \<0.05, alpha coefficients 0.05 and beta value 0.2, the sample size n=150 tooth restorations per group was calculated. The number of patients for the study is estimated between 75 (when 4 restorations are performed for each patient) and 150 (2 restorations performed for each patient).

Descriptive statistics are used to describe the frequency distributions of the evaluated criteria. To analyse the failure rate (distributions of Charlie scored versus non-Charlie-scored restorations) for direct vs. indirect restorations, 2x2 tables are created. Non-parametric statistical procedures are used due to ordinally structured data for the assessment of the restorations. Mann-Whitney U-test is used to explore significant differences at different time points between direct and indirect restorations. The same test is used to detect differences between baseline and follow-up registration. The standard value considered to demonstrate statistically significant differences was set at p \<0.05.

Ethical issues

Participation in the study is voluntary and requires an informed consent of the patient. The patient has a right to refuse or interrupt his/her participation in the study at any stage. The patients are treated according to the good clinical practices. Quality of the treatment is suspected to be at least at the same level as in normal treatment methods for restorative care. During the study, the patients will have additional check-ups as, which is compensated with economical or other benefits. Patient data are saved in patient registers at the care-providing instances. Research data are saved and analysed anonymously using SPSS 25 (IBM Statistic Viewer) program.