The effect of varying head tilt on the perceived color from composite resin and porcelain restorations: Simulating the effect of altering torque

Introduction

This study aimed to assess the effect of changes in tooth torque on the perceived color of composite and porcelain restorations.

Methods

A total of 30 patients with previous composite restorations and 30 patients with porcelain restorations on lateral and central incisors were selected. To simulate the effect of dental torque change, we asked the patients to tilt their heads upwards and downwards to represent buccal and palatal crown torque, respectively. Photographs were taken in 3 different positions (natural head position, 15° upward tilt, and 15° downward tilt). A laser alignment tool was used to help with head positioning. Color was measured on the 3 principal axes of the Commission Internationale de L’Eclairage, L∗, a∗, and b∗ color space using Photoshop software (Adobe, San Jose, Calif), and color differences were calculated. The midpoint of the clinical crown, both mesiodistally and incisogingival, was selected as the point of measurement. A general linear model was used to analyze the significance of changes in each value of different tooth torques. A t test was used to compare color changes of 2 different incisors (central and lateral) and overall color differences in the 2 types of restoration.

Results

Significant changes of the L∗ and a∗ values were found as a result of the change in head inclination, whereas b∗ values remained unchanged. It was found that buccal crown torque resulted in lighter and greener porcelain restorations. Composite restorations behaved similarly with the only difference being that the central incisors appeared bluer. Palatal crown torque resulted in a darker and redder porcelain restoration and a darker, redder, and yellower composite restoration. No significant differences were found between color changes in the central and lateral incisors. Furthermore, porcelain and composite restorations had similar color changes with alteration of head inclination.

Conclusions

Orthodontic changes of tooth torque alter the color perceived from composite and porcelain restorations.

Highlights

  • Changing tooth torque led to an alteration in perceived color from esthetic restorations.

  • The change in color was similar between the central and lateral incisors.

  • Composite resins and porcelain veneers behaved similarly with altering torque.

Torque correction of the anterior teeth is a common practice in routine orthodontic therapy, being most prominent in patients with Class II Division 2 malocclusions. A recent study by Ciucchi and Kiliaridis discovered that changing the inclination of a tooth can alter its color in the eyes of a fixed observer. It was found that buccal crown torque resulted in a lighter, redder (less green), and bluer (less yellow) perceived color, whereas palatal crown torque resulted in a darker and redder (less green) perceived color. On the basis of the results of this study, we can inform the patient beforehand that a correction of dental torque could lead to a change in how they perceive their tooth color. This information is valuable as it informs the patient about what to expect at the end of the treatment. Understanding this change is vital in patients with existing esthetic dental restorations in the form of composite resin restorations (CRR) or porcelain laminate veneers (PLV) as they are sensitive to any changes in their appearance.

The use of CRRs to restore worn teeth was first described by Bevenius et al. In this method, direct composite resin is applied on prepared tooth surfaces to achieve a desirable outcome. However, esthetic problems of anterior teeth are more commonly addressed using laminate veneer restorations. The popularity of PLV is due to its esthetic appeal, durability, and biocompatibility. , Tooth discolorations, rotated teeth, coronal fractures, congenital or acquired malformations such as peg-shaped lateral incisors, diastemas, discolored restorations, palatally positioned teeth, absence of lateral incisors, abrasions, and erosions are the main indications for direct laminate veneer restorations. , Although it is tempting to assume that the same changes of color with altering torque that happens in teeth occur for CRRs and PLVs, it should be noted that they have different optical properties compared with dental enamel and may therefore behave differently. ,

To the best of our knowledge, there are no studies in the existing literature that evaluates the effect of dental torque on perceived color. Therefore, we aimed to assess whether altering torque (buccal or palatal) results in a change of perceived color from CRRs and PLVs. The findings of this study will lead to a better understanding of how restorative material behaves during orthodontic treatment, which will be valuable to practitioners in orthodontics and restorative dentistry.

Material and methods

Thirty adult subjects with nanohybrid CRRs and 30 adult subjects with previous IPS Empress PLVs were randomly selected from the patients referred to a dental clinic. All patients were aged between 18 and 40 years. To avoid the effect of restoration discoloration and wear over time, we excluded patients who had incisor restorations older than 6 months from the study. Furthermore, patients with damaged restorations or visible gingival inflammation were also omitted. In addition, patients with evident dental crowding in the maxillary jaw or severe torque problems of the maxillary incisors diagnosed by a board-certified orthodontist based on clinical examination were not considered.

Clinical photographs were taken from the selected subjects in a controlled environment to be used as the basis for measuring tooth color. For this purpose, each patient was seated in an adjustable chair to ensure that the teeth are at the same vertical level as the camera. All teeth were cleaned before photography. Excessive saliva was removed to avoid the possible effects on the color determination. Because of the different amounts of tooth coverage by any individual’s lips, cheek retractors were used to eliminate any soft tissue interference. The light source in the photography room was a white neon light, augmented with a ring flash mounted on the camera. The position of the light source in relation to the patient was the same for all patients and all photographs. The photographs were taken at a set distance of 0.5 m with an ISO (International Organization for Standardization) of 100, F25, and a shutter speed of 125 (D90; Nikon, Tokyo, Japan) with a macro lens (Nikkor 105 mm; Nikon). For each patient, the first photograph was taken in a natural head position with the Frankfurt plane parallel to the floor, followed by 2 photographs with the patient’s head tilted at +15° and −15° to mimic the effect of varying torque.

For the first photograph, the patient was seated with the patient’s head in the natural position. The Frankfurt plane was marked on the patient’s face with a marker. To make sure that the angulation is accurately repeatable, we used a laser alignment tool. When the markings on the patient’s face coincided with the laser line, the first photograph was taken. Subsequently, the patients were asked to rotate head upward to the point where the Frankfurt plane on the patient’s face would make a 15° angle with the laser line, and the second picture was taken. A downward movement of the head was also performed in the same manner and the same extent for the third photograph. Informed consent was obtained from every patient before photography. All of the steps of the study were approved and verified by the local ethical committee.

All photographs were analyzed using the Photoshop imaging software (Adobe, San Jose, Calif, 2018). Commission Internationale de L’Eclairage, L∗, a∗, and b∗ (CIELAB) values were determined for each tooth in the middle of the clinical crown mesiodistally and gingiva-incisally. In CIELAB space, L∗ defines lightness (0 to 100), a∗ denotes the red-green value (−100 to +100), and b∗ the yellow-blue value (−100 to +100). The sum of change is expressed by the color difference (ΔE) value and is calculated as follows: <SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='a∗2+b∗2+L∗2′>a2+b2+L2a∗2+b∗2+L∗2
a ∗ 2 + b ∗ 2 + L ∗ 2
. In a study conducted by Johnston and Kao, it was shown that a color difference of 3.7 ΔE is acceptable, but if the difference exceeds this amount, it will be readily detected by the viewer. The values of color shade obtained in different head positions of the same individual were compared using a 1-way analysis of variance. Furthermore, the changes in ΔE values were compared between the 2 types of restorations using the Student t test. P values less than 0.05 were considered statistically significant.

Results

At the conclusion of the study, 3 photographs were taken from each patient. After analyzing the images and comparing the data, we found that tilting the patient’s head upwards (buccal crown torque) resulted in a significant increase in the L∗ value, which indicated a lighter perceived color. The a∗ value was decreased, meaning a greener color. The buccal crown torque of CRRs on the central incisors significantly decreased b∗ value, which translates to a bluer color. However, the same torque caused no significant changes in the b∗ value of CRRs of the lateral incisors and PLVs.

When the patient tilts his head downwards (simulating palatal crown torque), the L∗ value of the restoration decreases significantly, indicating a darker color. The a∗ value increases indicating a redder color component. The b∗ value of CRRs increases as the crown of the teeth move in a palatal direction, representing a yellower color. This value did not considerably change when we considered PLVs. The changes in the CIELAB values of CRRs and PLVs are represented by Figures 1 and 2 , respectively.

Jan 30, 2021 | Posted by in Orthodontics | Comments Off on The effect of varying head tilt on the perceived color from composite resin and porcelain restorations: Simulating the effect of altering torque
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