Comparison of the Chairside Time and Fitness of Michigan Splints Fabricated With Conventional Method and Digital Method: A Self-Controlled Study

Research Article

Austin J Dent. 2023; 10(1): 1171.

Comparison of the Chairside Time and Fitness of Michigan Splints Fabricated With Conventional Method and Digital Method: A Self-Controlled Study

Fang Shuobo*

Peking University School of Stomatology, China

*Corresponding author: Fang Shuobo Peking University School of Stomatology, China. Email: fsbm1995@163.com

Received: March 23, 2023 Accepted: April 27, 2023 Published: May 04, 2023

Abstract

Purpose: To evaluate the chairside time and fitness of Michigan splints fabricated with conventional method and digital method.

Material and Methods: Two Michigan splints were fabricated with conventional method and digital method respectively for 16 participants. In digital workflow, the data of dentitions were obtained by model scanning. Michigan splints were then designed, occlusal surface modified with the aid of fully adjustable virtual articulator, and fabricated by 3D printing technology with light-cured acrylic resin. In conventional workflow, splints were fabricated using waxed up method and fabricated with heat-cured acrylic resin. The chairside time of insertion and occlusal adjustment were recorded. The retention and comfort were evaluated by participants using 10cm Visual Analog Scales (VAS). Highly flowable Polyvinyl Siloxane (PVS) filled the space between tissue side of splints and occlusal surface of the natural dentitions. The fitness of the splints was calculated by scanning the tissue sides of splints with and without PVS replicas respectively. All data were divided into conventional group (control group) and digital group (test group), and self-controlled method was adopted. Differences between two groups were analyzed by paired t-test.

Results: There was no statistical difference in insertion time between two groups (P=0.263). Test group took less chairside time for centric (605±436s vs. 945±427 s, P=0.007), protrusive (97.0±144s vs. 246±211s, P=0.036), and excursive (25.0±101s vs. 114±465s, P=0.026) occlusal adjustment than control group. The space of test group was significantly smaller than control group (350±120μm vs. 470±90.0μm, P<0.001). No statistical difference was detected in the scores of retention, comfort at postural position and comfort at centric occlusion between two groups (P≥0.113).

Conclusion: Michigan splints fabricated with digital method need less chairside time and showed better fitness than conventional method.

Keywords: Michigan splint; Digital workflow; Virtual articulator; 3D printing

Clinical Implications

Compared with conventional method, Michigan splints fabricated with digital method showed higher chairside efficiency and better fitness. However, the therapeutic effect of occlusal splints is still dependent on how well the occlusal adjustment is conducted instead of the method in which an occlusal splint is fabricated.

Introduction

The modern use of biteplanes or occlusal splints to eliminate temporarily occlusal interferences and to allow ideal seating of the condyles was initiated by Posselt in the 1950s [1]. The appliances were recommended for TMJ and muscular disturbances related to occlusal dysfunction. The stabilized splint is the mostly commonly used type of intraoral appliance and has the least potential for adverse effects to the oral structures [2]. The modifications incorporated in the Michigan splint beyond the flat stabilized splint have made it a significantly improved aid in the management of patients with occlusal dysfunction [1]. There are two conventional methods widely used in clinical routines to fabricate splints, including laboratory method and chairside method. The laboratory method is complex, labor-intensive and error-prone [3]. The chairside method is smelly, susceptible to biofilm adhesion and takes amount of chairside time.

With the application of Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) technology in the dentistry, several attempts have been launched to introduce digital method to the fabrication of occlusal splints [4-6]. Dedem et al [5] established a fully digital and plasterless fabrication workflow of Michigan splints. By assessing the fit, retention and number of initial occlusal contacts of splints, it was concluded that the Michigan splints fabricated with digital method showed some advantages over conventional method. However, there was lack of occlusal splints fabricated by conventional method as control in their study. Besides, the Michigan splints were milled from PMMA blocks, which took much processing time and inevitably wasted lots of material. 3D printing is another manufacturing process in which an object is formed layer by layer and the advantage is to produce complex shapes using less material than milling processes.

Fitness is crucial for each type of restorations. It is doubtful that a splint can behave as expected since the area between splint and teeth or soft tissue surface is much larger than other restorations, egg. Crown, bridge. This study describes a digital method of using virtual articulator to design occlusal contacts and using 3D printing to fabricate Michigan splints. The chairside time and fitness of splints fabricated with digital method were evaluated by this self-controlled study, and compared with those with conventional method.

Material and Methods

Participants

Healthy participants with complete dentition were recruited from graduate students of Peking University School of Stomatology. Inclusion criteria were Angle class jaw relations, and the vertical distance between upper and maximum opening of more than 40 millimeters. Exclusion criteria were oral infections, acute or chronic pain conditions temporomandibular disorders (diagnosed by one specialist using DC/TMD), various mucocutaneous diseases/disorders, medications affecting the nervous or muscle system. Written informed consents were obtained from all participants. The study was approved by Biomedical ethics committee of Peking University Hospital of Stomatology (PKUSSIRB-AF02).

A self-controlled design was applied in this study and paired t-test was adopted to analyze the differences. The primary outcome was that the difference of centric occlusal adjustment between both groups was up to 120 seconds. The sample size was calculated to be 13 with a significance level of 0.05, a power of 90%, and a SD of 132 seconds. 16 participants were recruited considering a 20% loss rate. Eight females and 8 males were included and the average age was 25 years.

Study Design and Statistical Method

One digital splint and one conventional splint were made for each participant, and the conventional splint was set as control and the digital splint was belonged to test group. The splints fabricated by digital or conventional method were delivered to the participants by one experienced clinician. The study data were input and analyzed in IBM SPSS 18.0 software. A normal test was conducted for variables firstly using Shapiro-Wilk test. Paired t-test and Wilcoxon test were then adopted to compare the differences of two groups according to the outcome of Shapiro-Wilk test. The level of significance was set at 0.05.

Mounting Plaster Model to Mechanical Articulator

Polyether (Impregum, 3M ESPE) impressions were made using metal stock trays (ASA Permalock; ASA Dental) and poured with type dental stone (Pemaco, Pemaco). Mandibular movements were recorded by ultrasonic jaw motion tracking device (ARCUS Digma, KaVo Dental GmbH), and individualized mandibular movement parameters were obtained. Upper jaw models were mounted onto the fully adjustable articulator (PROTARevo 7, KaVo Dental GmbH) with KaVo transfer system. The condyles were located in centric relation with bilateral manual manipulation technique [3]. The vertical dimension provided a thickness that maintained posterior teeth 1-2 mm apart. The therapeutic jaw relations were recorded by combining light-cured resin (Light-cured resin, Huge) and interim crown materials (ProtempTM 4, 3M ESPE). Mandibular movement parameters were set at the articulator joints and lower jaw models were mounted using jaw relation records.

Mechanical Articulator to Virtual Articulator

The occlusal transfer calibration objects (3Shape occlusal transfer calibration object, 3Shape A/S) and the transfer plates (3Shape transfer plate for PROTARevo, 3Shape A/S) were used for transferring the point cloud data and relative position of mounted models from mechanical articulator to virtual articulator. An appliance was designed to make sure that the occlusal transfer calibration object kept in the optimal position in the mechanical articulator, which had already obtained Chinese patent (Patent ZL 2021 1 0042483.1) (Figure 1). After the calibration objects were mounted to mechanical articulator with the appliance, the calibration objects in gypsum were scanned in a lab scanner (D2000, 3Shape A/S). Then the mounted models were scanned in the scanner under the transfer plate pattern and digital models were mounted onto a virtual articulator automatically.