Long-term occlusal tooth wear at the onset of permanent dentition.

OBJECTIVES: This study quantified the long-term occlusal wear in the natural posterior teeth and the associations per tooth type within the dentition. METHODS: The sample included 70 orthodontically treated subjects (52 females and 18 males; median age, 14.3 years), followed for a 12.7-year period. They were consecutively selected with no tooth wear-related criteria. Post-treatment (T1) and follow-up dental casts (T2) were scanned and superimposed through three-dimensional methods. Occlusal wear volume of posterior teeth and tooth wear patterns were investigated through non-parametric statistics and analysis of covariance. RESULTS: There were no significant differences between contralateral teeth. The average occlusal wear per posterior tooth was 2.3 mm3, with 65.2% of teeth showing values greater than 1 mm3. Males, mandibular teeth, and first molars exhibited slightly greater wear levels than females (median, 2.57 and 2.21 mm3, respectively; p = 0.005), maxillary teeth, and first or second premolars, respectively. In all first premolars and in the mandibular second premolars, the buccal cusps were primarily affected with no other distinct patterns. There were weak to moderate correlations between tooth types, apart from certain strong correlations detected in males. CONCLUSIONS: Posterior tooth wear was highly prevalent after a 13-year period starting at the onset of permanent dentition. The detected patterns are in accordance with the concept of canine guidance occlusion that is transforming into group synergy through function. CLINICAL RELEVANCE: The widespread tooth wear occurrence and the high intra- and inter-individual variability underline the need for individual patient monitoring to identify high-risk patients at early stages.

Accuracy of facial skeletal surfaces segmented from CT and CBCT radiographs.

The accuracy of three-dimensional (3D) facial skeletal surface models derived from radiographic volumes has not been extensively investigated yet. For this, ten human dry skulls were scanned with two Cone Beam Computed Tomography (CBCT) units, a CT unit, and a highly accurate optical surface scanner that provided the true reference models. Water-filled head shells were used for soft tissue simulation during radiographic imaging. The 3D surface models that were repeatedly segmented from the radiographic volumes through a single-threshold approach were used for reproducibility testing. Additionally, they were compared to the true reference model for trueness measurement. Comparisons were performed through 3D surface approximation techniques, using an iterative closest point algorithm. Differences between surface models were assessed through the calculation of mean absolute distances (MAD) between corresponding surfaces and through visual inspection of facial surface colour-coded distance maps. There was very high reproducibility (approximately 0.07 mm) and trueness (0.12 mm on average, with deviations extending locally to 0.5 mm), and no difference between radiographic scanners or settings. The present findings establish the validity of lower radiation CBCT imaging protocols at a similar level to the conventional CT images, when 3D surface models are required for the assessment of facial morphology.

Accurate gingival recession quantification using 3D digital dental models.

OBJECTIVES: To develop and validate a method for accurate quantitative assessment of gingival recessions based on superimposition of serial 3D digital models. MATERIALS AND METHODS: Gingival recessions of mild (0.5-2 mm) and increased (3-7 mm) severity were simulated on stone casts and surface models were created. The outlines of the gingival margins of the mild (A) and severe recessions (B) were compared to the original gingival margins following 3D best fit superimposition through a gold standard technique (GS), which used intact adjacent structures, and the tested method (CC), which used single tooth crowns at the position of recessions, as superimposition reference. The primary outcome was the distance between the most apical point of each corresponding gingival margin along the respective tooth long axis. RESULTS: For mild recessions, the median difference of the test methods (CC_A) from the reference method (GS_A) was 0.008 mm (IQR: 0.093; range: - 0.143, 0.147). For severe recessions, the median difference of the test method (CC_B) from the reference method (GS_B) was 0.009 mm (IQR: 0.091; range: - 0.170, 0.198). The proposed method (CC) showed very high intra- and inter-operator reproducibility (median: 0.025 and 0.033 mm, respectively). CONCLUSIONS: The suggested method offers highly accurate monitoring of gingival margin changes and diagnosis of gingival recessions using 3D digital dental models. The method is applicable irrespective of changes in tooth position or form, allowing for assessments over any time span. CLINICAL RELEVANCE: The accurate detection and visualization of gingival margin changes in 3D will enhance diagnosis and patient-doctor communication.

Effect of hydration on the anatomical form of human dry skulls.

In radiology research soft tissues are often simulated on bone specimens using liquid materials such as water, or gel-like materials, such as ballistic gel. This study aimed to test the effect of hydration on the anatomical form of dry craniofacial bone specimens. Sixteen human dry skulls and 16 mandibles were scanned with an industrial scanner in dry conditions and after water embedding. Ten skulls were also embedded for different time periods (5 or 15 min). The subsequent 3D surface models were best-fit superimposed and compared by calculating mean absolute distances between them at various measurement areas. There was a significant, primarily enlargement effect of hydration on the anatomical form of dry skeletal specimens as detected after water embedding for a short time period. The effect was smaller in dry skulls (median 0.20 mm, IQR 0.17 mm) and larger in mandibles (median 0.56 mm, IQR 0.57 mm). The effect of different water embedding times was negligible. Based on the present findings, we suggest to shortly hydrate the skeletal specimens prior to reference model acquisition so that they are comparable to hydrated specimens when liquid materials are used as soft-tissue simulants for various radiologic research purposes.

Precision of a Hand-Held 3D Surface Scanner in Dry and Wet Skeletal Surfaces: An Ex Vivo Study.

Three-dimensional surface scans of skeletal structures have various clinical and research applications in medicine, anthropology, and other relevant fields. The aim of this study was to test the precision of a widely used hand-held surface scanner and the associated software's 3D model generation-error in both dry and wet skeletal surfaces. Ten human dry skulls and ten mandibles (dry and wet conditions) were scanned twice with an industrial scanner (Artec Space Spider) by one operator. Following a best-fit superimposition of corresponding surface model pairs, the mean absolute distance (MAD) between them was calculated on ten anatomical regions on the skulls and six on the mandibles. The software's 3D model generation process was repeated for the same scan of four dry skulls and four mandibles (wet and dry conditions), and the results were compared in a similar manner. The median scanner precision was 31 µm for the skulls and 25 µm for the mandibles in dry conditions, whereas in wet conditions it was slightly lower at 40 µm for the mandibles. The 3D model generation-error was negligible (range: 5-10 µm). The Artec Space Spider scanner exhibits very high precision in the scanning of dry and wet skeletal surfaces.

Association of Craniofacial Patterns with the Curve of Spee and the Time Required for Orthodontic Levelling.

The curve of Spee (CoS) is an important parameter for an individualized treatment plan. The available information regarding a potential association of the depth of the curve of Spee with various skeletal craniofacial characteristics is conflicting and it is also unknown whether certain craniofacial parameters affect the duration of the levelling phase of orthodontic treatment. A prospective sample of 32 patients with mild to moderate crowding that underwent orthodontic treatment with full fixed appliances was used to study these topics. The craniofacial characteristics were captured on pre-treatment lateral cephalometric radiographs and measurements of the CoS were performed on the initial 3D digital dental models using the Viewbox 4 software. Non-parametric statistics and Spearman's correlations were applied. Weak negative correlations were detected between the CoS depth and the SNA and SNB angles. There was no other association between the CoS and craniofacial parameters, including various anteroposterior measurements. Furthermore, there was no significant association of any craniofacial parameter with the duration of the levelling. Contrary to certain clinical beliefs, it can be argued that the craniofacial characteristics are not associated with the CoS and the time required for its levelling in subjects with moderate pre-treatment CoS depth.

Reliability of cephalometric superimposition for the assessment of craniofacial changes: a systematic review.

BACKGROUND: Superimposition of serial cephalometric radiographs enables the assessment of craniofacial changes over time, and therefore, several methods have been suggested in the literature. OBJECTIVE: The aim of the present study is to summarize and critically evaluate the available evidence on the reliability of methods used to superimpose serial cephalometric radiographs. SEARCH METHODS: Electronic searches were performed in MEDLINE, EMBASE, Google Scholar, and Cochrane Databases, without time limit (last update: 1 November 2020). Unpublished literature was searched on the Open Grey and Grey Literature Report databases. SELECTION CRITERIA: Studies that tested the accuracy, precision, or agreement between different cephalometric superimposition techniques, used to evaluate the craniofacial changes due treatment or growth. DATA COLLECTION AND ANALYSIS: Reference lists of relevant articles were screened and authors were contacted, if needed. All study selection steps, data extraction, and risk of bias (QUADAS-2 tool) assessments were performed independently by two authors on predefined forms. RESULTS: There were 27 eligible studies. From these, 17 tested superimpositions methods on the anterior cranial base, 10 on the maxilla and 12 on the mandible. There were three studies that compared superimpositions on the cranial base with those on the maxilla and one that compared the cranial base with the mandibular superimposition. There was high heterogeneity among studies in terms of sample size, growth, radiographic machines, selection criteria, superimposition methods, references, and outcomes measured. Furthermore, almost all studies presented important methodological limitations, with only two studies having unclear risk of bias and the rest 25 presenting high risk. CONCLUSIONS: Currently, there is no cephalometric superimposition method that has been proved to deliver accurate results. There is an urgent need for further research in this topic, since this is a primary assessment method to assess craniofacial changes over time for several relevant disciplines. REGISTRATION: PROSPERO (CRD42020200349).

Effect of the timing of second molar bonding on the duration of the mandibular arch levelling: a randomized clinical trial.

INTRODUCTION: This study investigated the effect of the timing of second molar bonding on the time required for the levelling of the mandibular dental arch. TRIAL DESIGN: Single-centre two-arm parallel randomized clinical trial using random permuted blocks. Allocation concealment was achieved through sealed envelopes. There was blinding in outcome assessment, but not of patient or operator. METHODS: Thirty-six patients (12-18 years old) with mild to moderate crowding and fully erupted mandibular second molars were assigned randomly (1:1 ratio) in two groups. Group A started fixed orthodontic treatment by bracket bonding in both jaws. Initial wire was 0.014" NiTi. Lower second molar tubes were bonded at the time of 0.016" x 0.022" NiTi wire placement. Group B was same as Group A, but second lower molars were bonded at the first appointment. Placement of the 0.017" x 0.025" stainless steel wire in the mandibular arch was considered the primary endpoint of the trial, indicating the completion of the levelling phase. The days required from bonding to the endpoint comprised the main outcome. Non-parametric statistics were applied. RESULTS: There were two dropouts in each group. The compared groups had similar baseline characteristics regarding age, sex, overjet, overbite, space in the dental arch, average Curve of Spee (CoS), and maximum CoS. Group A tended to require more days for levelling (median: 203 days) than Group B (median: 168 days). However, this difference was not statistically significant (P = 0.128). From the tested occlusal factors, only initial overjet was found to be moderately associated with the days required to complete levelling of the mandibular arch (r = 0.45, P = 0.009). CONCLUSIONS: In the frame of the current study, the duration of the levelling phase of orthodontic treatment with fixed appliances was not affected by the timing of second molar inclusion in the appliance. Future research could aim in cases with deep CoS to generalize the present findings and in larger sample sizes.

Longitudinal 3D Study of Anterior Tooth Wear from Adolescence to Adulthood in Modern Humans.

In modern humans, tooth wear can easily be observed as a loss of tooth substance, but its precise measurement is problematic. The aim of this longitudinal cohort study was to determine the precise amount of occlusal tooth wear in the anterior permanent dentition from adolescence to adulthood. Corresponding tooth crowns from serial 3D digital dental models of 72 individuals were best fit-approximated by applying novel, highly accurate 3D superimposition methods. The superimposed crowns were simultaneously sliced on intact structures, and the differences in the volumes of the subsequent occlusal parts were calculated. Over a thirteen-year period, there was an average loss of anterior occlusal surfaces of 1.58 mm3 per tooth. Tooth surface loss in at least one tooth was higher than 1 mm3 in 93.1% of the human subjects. Tooth wear severity differed by sex and tooth type, with males showing higher values versus females and upper canines versus other anterior teeth. The study revealed the endemic occurrence of occlusal anterior tooth wear, highlighting the need for monitoring of the condition in the population to identify high-risk patients and enable timely interventions. The novel methods applied here on 3D digital models are recommended for this.

3D Occlusal Tooth Wear Assessment in Presence of Limited Changes in Non-Occlusal Surfaces.

The study aimed to develop an accurate and convenient 3D occlusal tooth wear assessment technique, applicable when surfaces other than the occlusal undergo changes during the observation period. Various degrees of occlusal tooth wear were simulated in vitro on 18 molar and 18 premolar plaster teeth. Additionally, their buccal and lingual surfaces were gently grinded to induce superficial changes and digital dental models were generated. The grinded and the original tooth crowns were superimposed using six different 3D techniques (two reference areas with varying settings; gold standard: GS). Superimposition on intact structures provided the GS measurements. Tooth wear volume comprised the primary outcome measure. All techniques differed significantly to each other in their accuracy (p < 0.001). The technique of choice (CCD: complete crown with 30% estimated overlap of meshes) showed excellent agreement with the GS technique (median difference: 0.045, max: 0.219 mm3), no systematic error and sufficient reproducibility (max difference < 0.040 mm3). Tooth type, tooth alignment in the dental arches, and amount of tooth wear did not significantly affect the results of the CCD technique (p > 0.01). The suggested occlusal tooth wear assessment technique is straightforward and offers accurate outcomes when limited morphological changes occur on surfaces other than the occlusal.

3D Method for Occlusal Tooth Wear Assessment in Presence of Substantial Changes on Other Tooth Surfaces.

Early diagnosis and timely management of tooth or dental material wear is imperative to avoid extensive restorations. Previous studies suggested different methods for tooth wear assessment, but no study has developed a three-dimensional (3D) superimposition technique applicable in cases where tooth surfaces, other than the occlusal, undergo extensive morphological changes. Here, we manually grinded plaster incisors and canines to simulate occlusal tooth wear of varying severity in teeth that received a wire retainer bonded on their lingual surfaces, during the assessment period. The corresponding dental casts were scanned using a surface scanner. The modified tooth crowns were best-fit approximated to the original crowns using seven 3D superimposition techniques (two reference areas with varying settings) and the gold standard technique (GS: intact adjacent teeth and alveolar processes as superimposition reference), which provided the true value. Only a specific technique (complete crown with 20% estimated overlap of meshes), which is applicable in actual clinical data, showed perfect agreement with the GS technique in all cases (median difference: -0.002, max absolute difference: 0.178 mm3). The outcomes of the suggested and the GS technique were highly reproducible (max difference < 0.040 mm3). The presented technique offers low cost, convenient, accurate, and risk-free tooth wear assessment.

An accurate and efficient method for occlusal tooth wear assessment using 3D digital dental models.

Tooth or material wear in a dentition is a common finding that requires timely diagnosis for management and prevention of further loss or associated esthetic or functional impairment. Various qualitative and quantitative methods have been suggested to measure tooth or material wear, but they present with limitations, such as imprecision, subjectivity, or high complexity. Here we developed and assessed an efficient 3D superimposition method to accurately measure occlusal tooth wear on 3D digital dental models. For this purpose, teeth on plaster casts were manually grinded on their occlusal surfaces to simulate various degrees of tooth wear. The casts were scanned using a surface scanner. Grinded tooth crowns (T1) were segmented and compared to the original crowns (T0) using five 3D surface superimposition techniques and a gold standard technique (GS). GS measurements were obtained by using intact adjacent structures as superimposition references. The technique of choice (complete crown with 30% estimated overlap of meshes) showed the best reproducibility (maximum difference < 0.050 mm3) and excellent agreement with the GS technique (median difference: 0.032 mm3). The suggested 3D superimposition method offers a highly efficient and accurate tool for tooth wear assessment, which could be applicable to clinical conditions.

The effects of fixed orthodontic retainers on periodontal health: A systematic review.

INTRODUCTION: The objective of this systematic review was to assess the available evidence in the literature for the effects of fixed orthodontic retainers on periodontal health. METHODS: The following databases were searched up to August 31, 2019: Medline, EMBASE, the Cochrane Oral Health Group's Trials Register, CENTRAL, ClinicalTrials.gov, the National Research Register, and Pro-Quest Dissertation Abstracts and Thesis database. Randomized controlled trials (RCTs), controlled clinical trials, cohort studies of prospective and retrospective design, and cross-sectional studies reporting on periodontal measurements of patients who received fixed retention after orthodontic treatment were eligible for inclusion. The quality of the included RCTs was assessed per the revised Cochrane risk of bias tool for randomized trials (RoB 2.0), whereas the risk of bias of the included cohort studies was assessed using the Risk Of Bias In Nonrandomized Studies of Interventions tool. A modified version of the Newcastle-Ottawa scale was used for cross-sectional studies. RESULTS: Eleven RCTs, 4 prospective cohort studies, 1 retrospective cohort study, and 13 cross-sectional studies fulfilled the inclusion criteria. The quality of evidence was low for most of the included studies. In contrast to the general consensus, 2 RCTs, 1 prospective cohort study, and 2 cross-sectional studies reported poorer periodontal conditions in the presence of a fixed retainer. The results of the included studies comparing different types of fixed retainers were heterogeneous. CONCLUSIONS: According to the currently available literature, orthodontic fixed retainers seem to be a retention strategy rather compatible with periodontal health, or at least not related to severe detrimental effects on the periodontium.

Effect of orthodontic treatment with 4 premolar extractions compared with nonextraction treatment on the vertical dimension of the face: A systematic review.

INTRODUCTION: Our aim was to assess the available evidence for the effects of orthodontic treatment with 4 premolar extractions on the skeletal vertical dimension of the face compared with nonextraction treatment. METHODS: Electronic database searches (MEDLINE, EMBASE, Cochrane Oral Health Group's Trials Register, and CENTRAL) of published and unpublished literature and hand searches of eligible studies were performed, with no language or publication date restrictions. Two authors performed data extraction independently and in duplicate. Risk of bias was assessed. RESULTS: After application of the eligibility criteria, 14 studies were included in this systematic review. All were retrospective. Risk of bias ranged from moderate to critical. Ten studies investigated patients with various skeletal vertical patterns and classes of malocclusion and found no difference between extraction (Ex) and nonextraction (Nonex) treatment in regard to the vertical dimension. Only 2 studies found statistically significant increases in the nonextraction groups, one in N-Me (Ex: +1.5 mm; Nonex: +5.5 mm; P <0.05) and one in SN-GoGn (Ex: -0.9°; Nonex: +0.8°; P <0.05), but without a concurrent significant change in other vertical measurements such as FMA. Two other studies showed opposite findings regarding N-Me (Ex: +2.3 mm; Nonex: +0.9 mm; P <0.05) and FMA (Ex: +0.3°; Nonex: -2.0°; P <0.05). CONCLUSIONS: Although the quality of evidence ranged from moderate to low, there was considerable agreement among these studies, suggesting that orthodontic treatment with 4 premolar extractions has no specific effect on the skeletal vertical dimension. Thus, an extraction treatment protocol aiming to reduce or control the vertical dimension does not seem to be an evidence-based clinical approach.