The Twin Block appliance is a removable orthodontic appliance that is used to help correct a backward positioned lower jaw in growing children. This appliance works by guiding the lower jaw forward to a specific position over a certain period of time. After completing the treatment, patients often experience improvements in their appearance, such as an improved bite, a more balanced facial profile and improved lip posture.

The investigators' interest is to compare two types of Twin Block appliances; traditional (conventional) and 3D-printed, by examining several factors, including the amount of bacteria that stick to them, the surface roughness, and the overall effectiveness of each type.

Surface roughness refers to the texture of the appliance's surface, which could influence how much bacteria can accumulate. Rougher surfaces may trap more bacteria, potentially leading to oral health issues such as bad breath, tooth decay, and gum problems. The study will also assess the effectiveness of both the conventional and 3D-printed Twin Block appliances, focusing on factors like how well they perform in improving jaw position and achieving the desired treatment outcomes.

Additionally, the investigators want to assess how these appliances affect the quality of life related to oral health. Participants will answer questions about their experience to help understand how the type of appliance impacts their daily lives, comfort, and overall well-being during the course of treatment.

RATIONALE OF STUDY

The rationale is to explore and address concerns related to the use of 3D printed resins with the Twin Block Appliance (TBA), in comparison to the conventional materials PMMA. The surface roughness of 3D printed resins, has been reported to be different from conventional materials and has been associated with increased microbial adhesion, particularly to Candida. This raises concerns about the potential oral health risks, such as dental caries and mucosal inflammation, when using 3D printed materials for orthodontic appliances.

Based on previous literature, it is postulated that bacterial load will be present on TBA surfaces, with the possibility of variation depending on the type of material used. This study aims to determine whether the microbial load decreases or increases based on the appliance material. Till date, there still remains a research gap specifically on microbial load in Twin Block appliances, making this study relevant in understanding the risks involved in the use of different materials in orthodontics.

Additionally, the study seeks to examine the effectiveness of 3D printed TBAs in reducing overjet and improving dental aesthetics, as well as the acceptability of these appliances by patients compared to conventional TBAs.

Furthermore, the study will compare the potential complications and treatment failures between conventional and 3D printed TBAs, aiming to demonstrate the practicality and feasibility of adopting 3D printing in the digital workflow for this appliance. By focusing on microbial adherence, surface roughness, treatment effectiveness, and oral health-related quality of life (OHRQoL), the study intends to provide valuable insights that could support the adoption of 3D printing technology in orthodontics while addressing the potential oral health risks associated with its use.

PRIMARY OBJECTIVES

1. To compare the microbial adherence between the conventional Twin Block appliance (TBA) and the 3D-printed Twin Block appliance (3D TBA).
2. To compare the impact of the appliances on the perception on dental aesthetics in patients wearing the TBA and 3D TBA.

SECONDARY OBJECTIVES

1. To compare the surface roughness of TBA and 3D TBA at baseline and after 6 months.
2. To determine the association between the surface roughness of TBA and 3D TBA with microbial adherence
3. To compare the impact of the appliances on the daily performances in patients wearing the TBA and 3D TBA.
4. To compare treatment effectiveness in the time required to reduce overjet within normal limits (<4mm)
5. To compare treatment effectiveness in achieving the skeletal and dental changes between TBA and 3D TBA.
6. To compare the risks for the potential complications and treatment failures between the TBA and 3D TBA.

SAMPLE SIZE ESTIMATION Sample size was determined using G*Power Software (Version 3.1.9.2). Sample size calculation was performed based on an alpha significance level of 0.05 and an effect size of 1.316 to achieve 80% power, to detect a significant difference between the groups. Based on the calculation, the total number of participants needed for this study is 11 participants per group. To anticipate a 36% drop out rate, the sample size required would be at least 15 participants per group.

METHODOLOGY

1. Recruitment

   • Participants will be recruited from the Orthodontic Postgraduate Clinic, Faculty of Dentistry, Universiti Malaya. They must meet inclusion and exclusion criteria for the study.
   • A total of 32 participants will be enrolled, with 16 males and 16 females, ensuring that gender is accounted for in the study.

2. Block Randomization

   • Block randomization will be performed using an online block randomization list generator (www.sealedenvelope.com) by another researcher who will not be involved in the clinical procedure.
   • A list will be generated and the random allocation sequences will be kept in sealed dark envelopes, labelled for gender and numbered accordingly
   • Participants will be assigned to two groups, either conventional TBA or 3D TBA based on the random allocation sequence and will be revealed when the envelopes are opened on the day of appointment.

3. Informed consent and assent

   • Prior to participation, patients and their parents will be provided with an information sheet and will be asked to give written consent and assent in their preferred language (English or Bahasa Melayu).
   • Once consent is obtained, participants will be randomly assigned to either the TBA or 3D TBA group.

Methodology based on objectives:

Primary objective 1: To compare the microbial adherence between the conventional Twin Block appliance (TBA) and the 3D-printed Twin Block appliance (3D TBA).

• Microbial adherence will be assessed at three time points: baseline (T0), 3 months (T1), and 6 months (T2) after appliance fitting.
• At the 3rd and 6th month follow up, the upper and lower Twin Block appliances will be placed separately in plastic containers filled with brain heart infusion (BHI) broth media, using sterilized tweezers, and sonicated in a water bath to dislodge microorganisms attached to the appliances.
• After sonication, the TBA will be removed from the containers, and the dislodged microorganisms will be transported to the Microbiology Lab for further processing.
• Samples will then be vortexed and serially diluted before plating on BHI, MSA, and SDA agar plates to allow enumeration of colony-forming units (CFU).
• Incubation will take place at 37°C for 18 to 24 hours and the plates showing CFU counts between 30 to 300 will be selected for enumeration.
• The researcher will be trained and assisted by a clinical microbiologist to perform the microbial colony count.
• The analysis will be performed in a sterile environment under a Class 2 Biosafety Cabinet.

Primary Objective 2: To compare the impact of the appliances on the perception of dental aesthetics in patients wearing the TBA and 3D TBA.

• Participants will complete the Psychosocial Impact of Dental Aesthetics Questionnaire (PIDAQ) at the following time points: baseline (T0), mid-treatment (T1), post-treatment (TF), and 3 months after final treatment (TF3).
• This questionnaire will assess participants' perceptions of dental aesthetics, including their psychosocial impact, to measure the appliances' effect on their self-esteem and social interactions.
• The PIDAQ will provide an objective measure of how wearing either the conventional TBA or 3D TBA affects dental aesthetics perception.

Secondary Objective 1: To compare the surface roughness of TBA and 3D TBA at baseline and after 6 months.

• Surface roughness will be measured three times in three different directions on each appliance using a profilometer at baseline (T0) and 6 months (T2) after appliance fitting

• The three measurements performed for each specimen will be used to calculate the average surface roughness (Ra) and will be recorded in micrometres (µm).

• The surface that it captures it best recorded on a flat surface, hence, the fitting surface and biting surface on the bite blocks of the upper and lower appliance will be used as reference point as the area of interest is similar for both conventional TBA and 3D TBA.

  -- Surface roughness is crucial because rough surfaces may promote microbial adherence, influencing the results of the microbial analysis.

• These measurements will be compared between the conventional TBA and the 3D TBA to assess the impact of different materials on appliance surface texture.

Secondary Objective 2: To determine the association between the surface roughness of TBA and 3D TBA with microbial adherence.

• After measuring the surface roughness at baseline and 6 months, a correlation analysis will be performed to assess the relationship between surface roughness and microbial adherence for both TBA and 3D TBA appliances.
• This analysis will help determine whether rougher surfaces contribute to higher microbial adherence.

Secondary Objective 3: To compare the impact of the appliances on the daily performances in patients wearing the TBA and 3D TBA.

• Participants will complete the Child Oral Impacts on Daily Performances (Child-OIDP) questionnaire at baseline (T0), mid-treatment (T1), post-treatment (TF), and 3 months after final treatment (TF3).
• The Child-OIDP assesses the impact of dental appliances on daily activities such as eating, speaking, and social interactions, providing insight into the patients' quality of life during treatment.
• This will allow comparison of the effects on daily function between TBA and 3D TBA.

Secondary Objective 4: To compare treatment effectiveness in the time required to reduce overjet within normal limits (<4mm).

• The overjet and other occlusal measurements (i.e canine relationships, molar relationships and overbite) will be recorded for the participants at the start of the study (T0), and every month for six months after the initial fitting of the Twin Block appliance (T0-T6)
• The target is to reduce overjet to less than 4mm, and the appliance's efficiency in achieving this will be compared between the conventional TBA and 3D TBA.

Secondary Objective 5: To compare treatment effectiveness in achieving the skeletal and dental changes between TBA and 3D TBA.

• Once the overjet is considered clinically corrected (<4 mm) and stable, the appliance will be removed, and the treatment will be deemed complete.
• Lateral cephalometric radiographs will be taken at baseline (T0) and end of treatment (TF) to assess skeletal and dental changes.
• Measurements on the lateral cephalogram using cephalometric parameters based on Pancherz analysis will be performed using Winceph (Rise Corporation, Japan).
• This data will provide insight into the treatment outcomes and compare the efficiency of the conventional and 3D TBA.

Secondary Objective 6: To compare the risks for potential complications and treatment failures between the TBA and 3D TBA.

• The study will also record failure of treatment rates, number of routine and emergency visits, number and nature of complications.
• Participants will be considered noncompliant (treatment failure) if overjet does not reduce by at least 10% within 6 months or if overjet fails to reach normal levels (<4mm) after 12 months.
• Breakage of the appliance more than 3 times over the initial 6-month period and/ or persistent poor oral hygiene with associated harms hindering treatment progress will also be regarded as a failure
• Details of adverse events (complications) in both groups, including breakages and harms reported during routine or emergency visits, will be collected from participants' notes using a data collection sheet and categorized according to their nature and severity.

STATISTICAL ANALYSES Results obtained will be computed using Statistical Package for Social Science (SPSS) software version 29.0.1 for Mac OS Catalina. Parametric tests will be applied for normally distributed data and non-parametric tests will be applied for non-normally distributed data. The level of statistical significance will be predefined at p < 0.05.

Inclusion Criteria:

1. Patients with Class II Division 1 incisor relationship
2. Overjet of ≥ 7mm
3. Age range of children: 10-12 years in females, 12-14 years in males
4. All permanent incisors and molars erupted
5. ICDAS ≥ score 3 and BPE ≥ 3
6. Able to understand English or Bahasa Melayu

Exclusion Criteria:

1. Patients with craniofacial syndromes (example: cleft lip and palate)
2. Patients with previous history of orthodontic treatment
3. Patients with hyperdivergent facial type (MMPA > 40º)
4. Untreated gingival disease (e.g.: gingivitis, periodontitis)

Investigator will be masked with the randomization sequance & allocation