Abstract. as an iterative approach. We strongly believe

Abstract. Even though tooth extraction is one of the common surgical procedure
in dental field, it needs an extensive knowledge and practical experiences when
handling the dental extraction equipment. Otherwise, it will be more complex or
even at worse case, it causes damages to patients’ mouth area. So, it is very
important to have a sound knowledge on the instruments to be used, especially
on extraction forceps. So, the knowledge on extraction forceps should be
disseminated properly. After identifying this need, as a first stage we
gathered the information regarding the dental extraction forceps from the
experts in the field. Then we started developing ontology as a second stage. Finally
the developed ontology was evaluated in two folds; by using inbuilt tools and
by ontology experts as an iterative approach. We strongly believe that our novel
approach on dental extraction forceps ontology can support the dental students,
dentists as well as their assistants to improve the knowledge and helpful in learning
practices. Our next step is to model the ontology for whole extraction process
and to develop a knowledge management system on dental extraction forceps.

Keywords: dental
forceps, ontology, knowledge sharing, health care, extraction

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A tooth is one of
the hardest part in most of the vertebrates which is calcified structure and
situated inside jaws 1. Tooth performs a very important function of the body which is
breaking down of foods. It also gives aesthetic value to appearance of a person.
Dentistry is a branch of medicine which deals with the dentition, and related
structures and tissues in the face. A dental extraction is the removal of teeth
from the dental alveolus in the alveolar bone 1, 2. There are many reasons for dental extractions, but mainly done if
a tooth has been damaged by decay or broken 3. Other reasons are such as a crowded mouth, infection,
supernumerary or malformed tooth, and even because of cosmetic purposes (to
remove tooth of poor appearance). The branch of dentistry that deals primarily
with extractions is oral surgery 1. There are two types of extractions performed in the dental field:

A simple extraction, which is
performed on a tooth which can be seen inside the mouth. In a simple extraction
procedure, the dentist will hold the tooth with specialized pliers called
“extraction forceps” and move them front and back in order to loosen the tooth
from the jaw before getting rid off the tooth 1, 4.

A surgical extraction, which is
a more complex procedure done by the surgeon.

The forceps is an exaggerated version pair
of pliers. It is made up of three parts; the blades, the joint and the handles.
In general, forceps which are designed for the extraction of anterior (front)
teeth in the maxilla (upper), the blades and handles are in the same line while
for the maxilla posterior (back) teeth the handles form a curve with the
blades. In forceps used for the extraction of mandibular (lower) teeth the
blades and handles are at an angle of approximately ninety degrees between them

Sometimes different terminologies are used to express the same concept.
Due to the unstructured, incomplete, general nature and varied formats of the information,
the knowledge is not reaching everybody 5. Further, computers needs to understand the
meaning or semantics of the information clearly. Semantic web enables this
understandings to computers 6. Ontologies are powerful mechanism for representing knowledge
presented in semantic web 7.

Ontologies are
widely used for various purposes such as knowledge management, e-commerce,
natural language processing, intelligent integration of information and
semantic web 8.

Ontology provides
a structured view of domain knowledge and act as a repository of concepts in
the domain 9. This structured view is essential to facilitate knowledge sharing,
knowledge aggregation, information retrieval, and question answering. Ontology
provides precise and well-defined relationships, strong semantic capabilities,
inference mechanism, and reasoning support. Therefore, ontology can be used to
find a response to queries within a specified context in the domain of dental
extraction 7, 9, 10. According
to Thomas Gruber 11 “an ontology is an explicit
specification of a conceptualization”.

Further, the
context has also been decided to con?ne the study to a particular Sri Lankan
hospital. The key reasons are based on the geographical location of the
researcher, practicality and ease of access to those hospitals and
comparability of research data due to hospital’s same jurisdiction, same
economic and regulatory regimes governing their operation.

The aim of this work is to contribute to an
improvement in the management and usage of dental extraction forceps in hospitals
by developing an ontology-driven solution that organizes and describes clearly
related knowledge.

The remainder of the paper is organized as follows. Section 2
describes the literature review and the related work. Section 3 discusses the contextual
information while section 4 explains the need for a new dental extraction
forceps ontology. Section 5 describes designing approach for modelling dental
extraction forceps. The ontology evaluation and verification methods are
described in the section 6. Section 7 concludes this paper and presents
directions for future work.

Related work and literature

Modelling knowledge by using ontologies in the
medical domain is an active research field 12. Even though health sector is being supported by number of
biomedical ontologies such as GALEN, the Uni?ed Medical Language Source, the
Systemic Nomenclature of Medicine which focus on general scope of the
biomedical domain 13, and the Gene Ontology (GO) which is one of the earliest and most
frequently used vocabularies 14, there are a very few ontology on dental domain on the health
sector. Ontology-based systems provide reusable terminology resources and they
can be used to improve the management of complex systems for different context
information which can be captured and validated 12.

The information needed for a domain may be
available from leaflets, and mass media in different formats such as text,
audio, video 9. The
use of ontologies in health domain mainly focused on the representation and
re-organization of medical terminologies. Ontologies
can help build more powerful and more interoperable information systems in
healthcare. The
most significant benefit that ontologies in the health sector is its ability to
support integration of knowledge and data 15. Even though ontologies are used in the information system (IS)
design, the ontology development in health sector is more challenging because
of its complexity and the level of detail in it 13.

Having discovered this research gap we have
focused on our attention to develop a dental extraction forceps ontology to
represent information needs according to tooth extraction context. That is, we
intend to develop an ontology-based knowledge framework to manage extraction
forceps-related knowledge. This would assist the doctors and their assistants
in the dental hospitals to manage extraction forceps knowledge.

Contextual Information

According to Dey 16, context is any information which can be used to describe the
situation of a participant in meaningful way. Our main target groups are
dentists and people associated with dental in Sri Lanka such as assistants in
dental hospitals, researchers and information specialists. In order to identify
dental extraction context clearly, we have extracted domain speci?c knowledge by
using the following reliable knowledge sources;

Related field experts from Sri
Lankan universities, Sri Lankan hospitals by using formal and informal
interviews, discussions.

Research articles, online
articles and books 1-4, 17-20.

Newspapers, radio and

By analyzing information gathered from
various sources, we have identi?ed what information is required by the dentists
and other related personnel. We identified the information needed to dentists
and their assistants in the form of questions for our study. Some of them are
in Table 1.

1. Dental Extraction Problems

What are the tooth of child and adult?

What are the different types of

What are the positions of the tooth
located in the mouth?

Which is the most suitable extraction
forceps to extract a particular tooth?

Which is the most suitable extraction
forceps to extract a particular tooth if the crown is damaged, i.e. if only
root is there?

What are the different shapes of

Need for a New Dental
Extraction Forceps Ontology

There are 32 teeth on an adult called as permanent dentition and 20
teeth on a child called as primary dentition. Further each tooth has a crown
and a root. Generally when extraction is done, the root also comes with the
crown. But in some special cases like broken tooth, while extracting crown,
roots stays in the jaw socket 4. Further, some
teeth are very difficult to extract from its socket for various reasons, such
as tooth’s position, the shape of the tooth roots and the integrity of the

During the extraction process, the force to be applied should strictly
be limited to the tooth that is to be extracted. Many cases of simple
extraction procedures, before proceeding the extraction process, the forces are
diverted from the tooth to areas such as bone surrounding the tooth, in order to
ensure adequate bone removal.

All the tooth in human are not in same shape and size. So, each tooth
needs to be extracted using different types of dental extraction forceps. Choosing
the appropriate extraction forceps is the important part for the protection for
jaws and other neighboring tooth which will be affected if the forceps slips
away while extracting. If the specific extraction forceps are not used for a
tooth, then there will be more complications 21 such as incomplete extraction in which a tooth root remains in the
jaw, prolonged bleeding, swelling,
bruising, nerve injury or even
extraction of wrong tooth 1.

Further, if proper extraction forceps are used by the dentist, his or
her extraction will be easy as each extraction forceps are made by using the
knowledge of physics. For example, extraction forceps are made smaller in size
for children in order to apply less force and larger in size for adults in order
to apply more force. If we take another example, tooth on deep end in the jaw
(wisdom tooth) needs a different mechanism to extract than the tooth in the
front part of the jaw (incisors) 4. So extraction forceps are made “L” shape for deeper end and straight
for central area. Therefore, usage of specific extraction forceps for specific
tooth is very important for patients’ health as well as for the easiness of the

The information and knowledge needs to be
provided in a structured and complete way and in a context speci?c manner. Ontologies
emerge as one of the more appropriate knowledge management tools for supporting
knowledge representation, processing, storage and retrieval. By considering the
importance of sharing the knowledge on dental extraction, ontology for dental extraction
forceps is developed.

Our Design Approach

Figure 1 describes the basic steps in the roadmap
of our ontology modelling approach.

1. Our design methodology

main focus is on simple extraction, more specifically on extraction forceps
because these extraction forceps plays an important role on tooth extraction 4. Grounded theory was used for data
collection. According to Strauss 22 grounded theory is a general methodology for developing theory in
grounded data through systematically gathering and analysing. One of the key
feature of grounded theory is that both data collection and analysis are
interrelated and iterative. So, we can start analysis as soon as the first data
are collected 23. Two dentists with extensive knowledge on dental (mainly on
extraction) and an expert on ontology engineering took part.

Competency Questions (CQ) are a set of
questions that the ontology must be capable of answering using its axioms 24. CQs work as requirement’s speci?cation of the dental extraction
forceps ontology. If CQs contains all the necessary and suf?cient axioms that
correctly answer the CQs, it is possible to know whether an ontology was
created correctly 7. Our ontology aims to answer competency questions. Some of them
shown in table 2.

2. Some competency questions

Which tooth are in upper left side of an

Which extraction forceps is needed to
extract the root of left second premolar of an adult?

What is the tooth of lower left central
incisor of a child in the mouth?

Which extraction forceps is needed to
extract the normal left central incisor of a child?

Which extraction forceps are S shaped?


We get the
relevant data in order to answer these problems through extensive literature
survey and expert collaboration. We categorized the “Person” into two; “Adult”
and “Child”. The “Parts” of the tooth is divided into “Crown” and “Root”.
“Positions” also categorized as “Upper”, “Lower”, “Left” and “Right”. Tooth
have “Specific Names”. They were classified into “Molar”, “Premolar”, “Canine”
and “Incisor”.

There are three international standard
systems for naming teeth: the universal numbering system, the palmer notation
method and the two-digit FDI world dental federation notation. In this paper,
we followed two-digit FDI world dental federation notation WHO and by other
organizations such as the International Association for Dental Research. It
provides a system for designating teeth or areas of the oral cavity using two
digits 17. We declared these notations into “ToothNotation” class.

Since there are no standards for forceps
classification, we formalized the forceps into two main category; Crown Forces
and Root Forceps. Here what we meant by crown is the full tooth which includes
both parts; crown and root. Further we divided each forceps into many sub
classes. The high level class hierarchy is shown in Figure 2

2. The high-level class hierarchy of dental extraction forceps

The basic high level ontology concepts are
identi?ed as Person, Tooth, Tooth Parts, Tooth Specific Name, Forceps, and
Position. Secondly, sub-classes of defined high-level ontology concepts, their
properties and their relationships are also identified. For example, Tooth
Specific Name has Canine, Incisor, Pre-molar and Molar as its sub-classes and
Lateral Incisor and Central Incisor are sub-class of Incisor. These sub classes
are related to their superclass by “is a”
relation 7.

Making the ontology manually is tedious and time-consuming task 9. According to Vasanthapriyan 7, the principles, methods and tools for initiating, developing and
maintaining ontologies are investigated in ontology engineering approach. There
are many different methodologies proposed to model the ontologies in many
literatures 24-27.
After reviewing all, we selected Grüninger and Fox’s methodology 24 for our work as it publish a formal approach for designing the
ontology and also it provides a framework for evaluating the developed ontology

Grüninger and Fox’s methodology 24 focuses on building ontology based on ?rst-order logic (FOL) by
providing strong semantics. The associative relationships are to identify the
concepts and relationships with meaningful relations, and to de?ne the
relationships and their inverse relationships. Table 3 shows some associative
relationships including their inverse.

3. Associative relationships with inverse.





hasSpecificName, isSpecificNameOf



hasUsedToPluck, isPluckedBy



hasPosition, isPositionOf






hasCrown, isCrownOf



Datatype properties
link an individual to an XML Schema Datatype value or an rdf literal. In other
words, they describe relationships between an individual and data values. A
datatype property can also be used in a restriction to relate individuals to
members of a given datatype.













The ontology was
implemented by using the Protégé-OWL Ontology Editor 5.1. Part of the dental
extraction forceps ontology is shown in the figure 3

3. Part of dental extraction forceps ontology

In our scenario, we introduce Description
Logic (DL) which is a decidable fragment of FOL since we are designing with OWL
2 Web Ontology Language 28 for sematic web. We have evaluated the competency questions to see
whether the ontology meets the dentists’ requirements during the internal
design process. The DL expressions have been used to query the ontology. For
this purpose, we used DL query facility which is available in Protégé-OWL Ontology
Editor 5.1. Some of the DL query and their answers are shown in table 4.

5. Some of DL query used and their outputs

Competency questions

DL query


What forceps are used to pluck T55

Forceps and hasUsedToPluck
value T55

Instances (2)

What are the dentitions which consists
specific name canine?

and hasSpecificName value Canine

Instances (8)

What is the position of T34 dentition?

Position and
isPositionOf value T34

Instances (1)
·   LowerLeft

What is the specific name of T28

and isSpecificNameOf value T28

Instances (1)
·   ThirdMolar

Ontology Evaluation and

Internal Evaluation

In order to avoid the defects when using
the ontology, its quality should be verified and validated 29. So, the last stage of our methodology consisted of an evaluation
of the ontology by experts in the ?eld ontology and by using inbuilt FaCT++
1.6.5 reasoner.

Further, in order to detect potential
pitfalls which can lead to modelling errors, we used an online ontology
evaluator called OOPS! (http://oops.linkeddata.es/)
29. This evaluator evaluates human understanding, logical consistency,
modelling issues, real world representation and semantic applications for the
developed ontology. The summary of the pitfall encountered, brief description
and description of how those are handled are shown table 5.

6. Pitfall, description and solution proposed




Missing annotations (156 cases | Minor)

Human understandable comments not

Included the ontology annotations

Missing domain or range in properties
(11 cases | Important)

Object and (or) datatype properties
without domain or range

Added the missing domain and range

Inverse relationships not explicitly
declared (32 cases | Minor)

Proper inverse relationship are not

Included missing inverse relationships

Using different naming conventions in
the ontology (8 cases | Minor)

Ontology elements are not named on same

Corrected by using uniform naming

Expert Evaluation

We evaluated the
ontology with the help of ontology expert by examining the de?ciencies of the
artifacts we used. The expert is not an author and not related to our research
team. There were many methods to evaluate the ontologies in literature 7. Our ontology expert considered the following layers to perform
evaluation; (a) syntax, (b) structure, (c) semantics and (d) representation. The
main objectives of expert evaluation are; (a) whether the software testing
ontology meets its’ requirements, standards, (b) coverage of the software
testing domain and (c) checking for internal consistencies.

This methodology allows us a better focus because
each level has a different evaluation objective. Table 6 summarizes the aspects
of the evaluation method used and Table 7 shows the suggestions and
improvements highlighted by the ontology expert. Based on Ontology expert’s
responses, comments, and suggestions the ontology was redeveloped.

7. Discussion topic of ontology expert



Discussion topic


Syntax of the formal language used

Standard syntax is used


Correctness of the concepts and the

Whether is describes is-a relationship
between concepts

Tools used in checking structure


Terms used to represent the knowledge

Understandable names of concepts and


Structural representation of the

Proper taxonomy

8. Review summary of ontology expert

Discussion topic

Ontology expert

Standard syntax is used

Manchester syntax was followed

Whether is describes is-a relationship
between concepts

All concepts follows is-a relationships

Tools used in checking structure

Whole ontology was viewed using OntoGraph

Understandable names of concepts and

2 concepts and 8 object properties do
not have understandable names.

Proper taxonomy

Clearly viewed in OntoGraph

Conclusions and future works

Tooth extraction is
one of the common surgical procedure in the field of dental, which mainly
depends on knowledge and experience of the dentists. Therefore in this
research, great importance is given to knowledge for dental extraction forceps,
and the potential benefits of managing dental extraction forceps knowledge, an
ontological approach to represent the necessary dental extraction forceps
knowledge within the dentists’ context was developed 10.

Identification of the suitable extraction
forceps for the given case is resolved by developing a domain ontology on
dental extraction forceps. Designing this type of ontology is not a simple
task, because we need to gain vast domain knowledge. This research presents
dental extraction forceps ontology to represent dental extraction forceps
domain knowledge which includes dental extraction forceps concepts, properties
and their relationships. We believe our dental extraction forceps ontology can
support other hospitals to improve the sharing of knowledge and learning

Our future works have two main parts.
Firstly we are planning to expand our research to whole extraction process
which includes all the devices used in the extraction process. Secondly, the
development of knowledge management portal for our expanded research in order
to disseminate the knowledge on dental extraction process. Even though previous
work has demonstrated knowledge sharing methods for various domains such as
software testing 7, 10, economics 30 etc., a very little research into dental knowledge sharing using
domain ontologies has been conducted. So our plan is to develop of knowledge management
portal in the domain of dental extraction.


We acknowledge the
experts and other personnel who directly and indirectly involved in order to
complete the research work successfully.