**1. Introduction**

Traditionally, oral health has been defined as "a state of being free from mouth and facial pain, oral diseases and disorders that limit an individual's capacity in biting, chewing, smiling, speaking and psychosocial well-being" [1]. In view of more emphasis given to 'absence of disease' in this definition, a broader description for oral health has recently been suggested [2]. This broader definition advocates the definitions adopted by global and national organizations and reiterates the importance of recognising dentistry as an arena providing care and supporting oral health, rather than purely treating disease. According to the new definition, oral health is multi-faceted and includes the ability to speak, smile, smell, taste, touch, chew, swallow and convey a range of emotions through facial expressions with confidence and without pain, discomfort, and disease of the craniofacial complex, as well as being a fundamental component of general health and physical and mental wellbeing [2,3]. While proponents of this new definition aimed to reach consensus on a universal definition of oral health, this has not eventuated [4]. Global oral health aims to provide optimal oral health for all and to eradicate global health inequalities via health promotion, disease prevention and appropriate oral care strategies that incorporate common factors and resolutions, and recognise that oral health is integral to overall health [4].

**Citation:** Amarasena, N.; Chrisopoulos, S.; Jamieson, L.M.; Luzzi, L. Oral Health of Australian Adults: Distribution and Time Trends of Dental Caries, Periodontal Disease and Tooth Loss. *Int. J. Environ. Res. Public Health* **2021**, *18*, 11539. https:// doi.org/10.3390/ijerph182111539

 Paul

 B. Tchounwou

Received: 15 September 2021 Accepted: 28 October 2021 Published: 2 November 2021

Academic Editor:

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Oral diseases predominantly comprise tooth decay (dental caries), gingival (periodontal) disease and oral cancers [5,6]. Dental caries, which is considered the most prevalent chronic disease worldwide [7], occur when microorganisms of dental biofilm (a sticky colourless film of bacteria build-up on the tooth surfaces) start to metabolize fermentable carbohydrates in the diet, in particular, free sugars, into acidic by-products. These acidic by-products can locally destroy (demineralise) the hard tooth structure (enamel and dentine) and initiate dental caries' development. Frequent consumption of high free sugar and insufficient exposure to fluoride are the main contributing factors for dental caries [5–7]. While making enamel more resistant to acid attack, fluoride mainly acts topically to inhibit demineralisation through its presence at low concentrations in the oral fluids [5,7]. With periodontal disease, tissues that support and surround the tooth (gums, periodontal ligament and alveolar bone) are affected mainly by dental biofilm accumulated at the neck of the tooth where the tissues meet the gums (gingival margin), causing gingivitis (bleeding of the gums) [5,6]. This may lead to a more destructive form of disease, i.e., periodontitis, in susceptible individuals, particularly among those who are immunocompromised [5,6]. Poor oral hygiene, accompanied by inadequate plaque removal, is the main cause of periodontal disease, while tobacco smoking is a major risk factor associated with periodontal disease [5,6]. If left untreated, both dental caries and periodontal disease lead to tooth loss, and these two oral diseases are the major causes of tooth loss. Oral diseases affect nearly 3.5 billion people universally. Of them, approximately 2.3 billion and 530 million present with dental caries of the permanent and primary (baby) dentitions, respectively [8,9]. In 2010, severe periodontitis was ranked as the sixth-most prevalent health condition, afflicting 743 million people globally with an incidence of 701 cases per 100,000 person years [10]. Although the prevalence of severe tooth loss declined from 4.4% in 1990 to 2.4% in 2010, 158 million people worldwide were edentulous in 2010 [10].

In regard to the oral health status of Australians (based on data published prior to the National Study of Adult Oral Health 2017–18), 42% and 24% of children aged 5–10 years and 6–14 years, respectively, had experienced dental caries in their primary teeth and permanent teeth, whereas almost a quarter of Australian dentate adults aged 15 and over had untreated decay [11]. The prevalence of periodontal disease in Australian dentate adults aged 15 years and over was 22.9%, whilst 4.4% of the adult population were edentulous [11]. The present study aims at describing the distribution and time trends of dental caries, periodontal disease and tooth loss in Australian adults based on findings from the National Study of Adult Oral Health 2017–18 (NSAOH 2017–18).

#### **2. Materials & Methods**

Study methodology, including computation of sample size, has been described in previous studies [12,13]. Briefly, a cross-sectional study of a random sample of Australians aged 15 years and over was carried out across all Australian states and territories, employing a three-stage stratified probability sampling design. The first stage of selection included sampling of postcodes within states/territories, mainly by means of systematic sampling with probability of selection proportional to the number of households within the postcode, followed by selecting individuals aged 15 years and over within selected postcodes from the Medicare database provided by the Australian Government Department of Human Services (DHS). Accordingly, the final sample size required 15,200 interviews to be conducted, in order to complete 7200 oral examinations.

Interviews were conducted online or by telephone (CATI—computer-assisted telephone interview) by trained interviewers using a questionnaire based on previous surveys [11,14]. Self-reported information about oral health and related characteristics such as age, sex, Indigenous identity, residential location, schooling/educational qualifications, eligibility for public dental care, dental insurance and usual reason for a visit to the dentist was collected. Calibrated dental practitioners conducted oral examinations following a standardised protocol in public dental clinics run by the relevant state or territory dental health services. Inter-examiner reliability relative to a gold standard examiner was assessed

by conducting replicate pairs of examination with 101 study participants. Dentate participants who consented to an examination were included for oral examinations. Although there were nine measures of oral health status, as described in detail elsewhere [15], the current analysis was confined to assessment of coronal caries (dental decay in tooth crown), gingivitis and periodontal destruction, and presence/absence of teeth (tooth loss).

#### *2.1. Dental Caries (Coronal Caries)*

All teeth present were subdivided into five tooth surfaces and assessed for dental caries using visual criteria without an explorer. The five tooth surfaces were mesial, buccal, distal, lingual and occlusal (for back teeth: premolars and molars)/incisal (for front teeth: incisors and canines). The mean number of decayed tooth surfaces per person denotes the severity, or burden, of untreated dental caries in people. The number of decayed, missing and filled tooth surfaces (DMFS) indicates lifetime experience of dental caries in a given person, since it has been regarded that cavities in enamel cannot heal and treatment of dental decay, either as a filling or extraction, leaves a permanent sign of disease [12].

### *2.2. Periodontal Disease*

Clinical assessment for periodontal disease was conducted among those who had no medical contraindications for periodontal probing. Gingivitis and periodontitis were the two types of diseases assessed, as per the following criteria:

**Gingivitis:** Inflammation of the marginal gingival tissues around six index teeth (if present: the most anterior molar tooth in each dental quadrant + right upper central incisor + left lower central incisor) were assessed using the gingival index of Loe and Silness [16].

**Periodontitis:** The US National Health and Nutrition Examination Survey (NHANES) methods were employed to assess periodontal tissue destruction [17]. Assessments were made on three aspects (mesio-buccal, mid-buccal and disto-buccal) of all teeth present, except third molars (wisdom teeth), using a periodontal probe. To describe the prevalence of moderate and severe periodontitis, a case definition developed by the US Centers for Disease Control and Prevention (CDC) and the American Academy of Periodontology (AAP) was used [17]. Accordingly, moderate periodontitis was defined as the presence of either at least two proximal sites not on the same tooth with attachment loss of 4 mm or more, or at least two such sites that had pockets of 5 mm or more. Severe periodontitis was defined as having at least two proximal sites not on the same tooth with attachment loss of 6 mm or more, plus at least one periodontal pocket with a depth of 5 mm or more.

**Tooth loss:** Complete tooth loss (edentulism) was assessed based on the answer to the following interview question: 'Do you have any natural teeth?', with response categories of 'Yes'/'No'. Existing natural teeth included crowns and caps, while dental implants were not considered natural teeth. For participants aged less than 45 years, the examiners distinguished between missing teeth that had been removed due to dental decay or periodontal disease and teeth missing due to any other reason. For participants aged 45 years or more, a removed or an absent tooth was recorded as missing.

To ensure representativeness of the target population, all data were weighted to population benchmarks [13]. Data files were managed and summary variables were computed using SAS software version 9.4 (SAS 9.4; SAS Institute Inc., Cary, NC, USA). Proportions, means and their 95% confidence were calculated where relevant.
