Evidence has been accumulated over the past few decades to show that if dentists have a basic knowledge of children’s cognitive and socioemotional development, then they will be much better prepared for difficult situations that may emerge. The aim of this chapter is to provide the reader with an overview of the essentials of developmental psychology. It will describe those aspects of normal development that are most useful for dentists treating “typical” children of different ages. We use the term children for the age range 0–12 years, and the term adolescents for children between 13 and 18. For the 0–12 range we make a further division into infancy (0–1), toddlerhood (2–3), preschool years (4–5), and middle childhood (6–12).

The chapter starts with an overview of how to conceptualize psychological development, then follows more focused aspects relating to cognitive, emotional, and social development in preschoolers, school‐aged children, and adolescents. Finally, we present those aspects of the field of developmental psychopathology that we find most useful to pediatric dentistry.

Perspectives on psychological development

Long before developmental psychologists began to use scientific methods to study age‐related changes, philosophers proposed explanations of development based on everyday observations. Many of their questions and assertions about the nature of human development continue to be central to modern‐day developmental science.

The argument about nature versus nurture is one of the oldest and most central theoretical issues within both psychology and philosophy. Progress in both neuroscience, especially molecular biology, and developmental psychopathology since the millennium shift has however led to a new stance, where neuroscientists and developmental psychologists share a common interest in nature and nurture rather than nature or nurture. In the section “Developmental psychopathology” we will return to current ways of addressing this issue.

A biopsychosocial approach

Human life is produced by the interaction and modification of three major systems: biological, psychological, and social. It is the integration of these systems that leads to a complex, dynamic portrait of human thought and behavior.

The biological system is made up of all the processes necessary for the psychological functioning of the organism. Biological processes develop and change as a consequence of genetically guided maturation, environmental resources, exposure to environmental toxins, encounters with accidents and diseases, and lifestyle patterns of behavior.

The psychological system consists of mental processes central to a person’s ability to make meaning of experiences and take action. Emotion, motivation, memory, perception, problem solving, language, symbolic abilities, and our orientation to the future, all require the use of psychological processes. The psychological system provides the resources for processing information and navigating reality.

The social system is composed of processes through which a person becomes integrated into society. Societal influences include family organization; social support; culture; social roles; ethnic and subcultural influences; patterns of economic prosperity or poverty; and exposure to racism, sexism, and other forms of discrimination, to name only a few. The impact of the social system on psychological development results largely from interpersonal relationships, often relationships with significant others.

The biopsychosocial approach seeks to understand the internal experiences that are the product of interactions among biological, psychological, and social processes. Changes in one of the systems generally bring about changes in the others. At each period of life, children and adolescents spend much of their time mastering a unique group of developmental tasks that are essential for social adaptation. Solutions of developmental tasks will set children on different developmental trajectories with consequences for how future tasks will be solved. The importance of introducing time as a powerful ingredient in the interaction between the biological, psychological, and social systems has called for a new concept, the transactional model of child development.

Meaning is created out of efforts to interpret and integrate the experiences of the biological, psychological, and social systems. A primary focus of this meaning‐making is the search for identity. Children and adolescents establish categories that define who they are connected to or not, who they care or do not care about, and who they admire or reject or deny.

With this broad introduction to developmental science as the psychologist sees it, we now turn to more narrow aspects of child and adolescent development.

Aspects of psychological development

Child development is most often described using either a variable‐ or a person‐based approach. A variable‐based approach divides child development into components: cognitive, emotional, social, etc., and describes the development of each component through childhood and adolescence. The person‐based approach describes what is typical for a child of a certain age, whether preschooler, school‐aged child, or adolescent, using a number of components simultaneously. Both approaches have their advantages and disadvantages and the choice is more a matter of taste. No matter what, a child’s development is not divided into tidy packages labeled “physical development,” “social development,” and “language development” but is instead a coherent, integrated process. Nevertheless we will start by taking a look at particular processes and end with a more holistic approach.

Cognitive development

Cognition is the process of organizing and making meaning out of experience. Cognitive developmental theory focuses specifically on how knowing emerges and is transformed into logical, systematic capacities for reasoning and problem solving. Perhaps the most widely known and influential of the modern cognitive theorists is Jean Piaget [1]. Recent interest in the social framework within which cognition develops has been stimulated by the work of Lev Vygotsky [2].

Cognitive development according to Jean Piaget

According to Piaget (1896–1980), every organism strives to achieve equilibrium: a balance of organized structures (motor, sensory, or cognitive). When structures are in equilibrium they provide effective ways of interacting with the environment. Equilibrium is achieved through adaptation; a process of gradually modifying existing ways of organizing knowledge in order to take into account changes and discrepancies between what is known and what is being experienced. Adaptation is a two‐part process in which continuity and change interact. Assimilation, the tendency to interpret new experiences in terms of existing mental structures (schemas), contributes to the continuity of knowing, and it is balanced by accommodation, the tendency to modify familiar schemas in order to account for new dimensions of the object or event that are revealed through experience.

Piaget described cognitive development in terms of four stages, each of which is characterized by a unique capacity for organizing and interpreting information. At each new stage competencies of the earlier stages are not lost but are integrated into a qualitatively new approach to thinking and knowing.

The first stage, sensorimotor intelligence, is characterized by the formation of increasingly complex sensory and motor schemas that allow infants to organize and exercise control over their environment.

During the second stage, preoperational thought, children develop the tools for representing schemas symbolically through language, imitation, imagery, symbolic play, and symbolic drawing. Knowledge is, however, still very much tied to the child’s perceptions.

During the third stage, concrete operational thought, children begin to appreciate the logical necessity of certain causal relationships. They can manipulate categories, classification systems, and hierarchies in groups. They are more successful at solving problems that are clearly tied to physical reality than at generating hypotheses about purely philosophical or abstract concepts.

The final stage of cognitive development according to Piaget is formal operational thought. This level of thinking permits a person to conceptualize many simultaneously interacting variables. It allows for the creation of systems of laws, or rules that can be used for problem solving. Formal operational thought reflects the quality of intelligence on which science and philosophy are built.

Piaget’s theory has had an enormous influence on our understanding of cognition and the way we think about the reasoning capacities of children and adolescents. Some of this can be summarized as follows.

• Cognition has its base in the biological capacities of the human infant: knowledge is derived from action. Knowledge is constructed rather than passively absorbed.
• Discrepancies between existing schemas and contemporary experience promote cognitive development. Encounters with all types of novelty, especially experiences that are moderately distinct rather than widely different from what is already known, are important for advancing new ideas and new ways of organizing thought.
• Preschoolers and school‐aged children (not to mention infants and toddlers) think in different ways, and the ways they think are different from the ways (older) adolescents and adults think. This does not mean that their thinking is unorganized or illogical, but the same principles of logic that typically govern adult thought do not govern the thinking of young children.
• Children can approach problems using many of the principles that are fundamental to scientific reasoning. They can also begin to reason about their reasoning (e.g., explain how they arrived at a specific conclusion), but it takes formal operational thought to grasp and make use of meta‐cognition (i.e., thinking about thinking) in its more eloquent aspects.

Appearance and reality

The child’s movement away from egocentrism during the preschool years seems to be part of a much broader change in his or her understanding of appearance and reality. Flavell [3] has studied this in a variety of ways. In one procedure the experimenter shows a child a sponge that has been painted to resemble a rock. After the child has felt the sponge/rock and has answered questions about what it looks like and what it “really” is, a researcher might ask something like this:

“John [one of the child’s playmates] hasn’t touched this, he hasn’t squeezed it. If John just sees it over here like this, what will he think it is? Will he think it is a rock or will he think it is a sponge?”

“A sponge” says 3‐year‐old Minnie, who thinks that the playmate will believe the object is a sponge, because she herself knows it is a sponge.

“A rock” says 4‐year‐old Ken, who realizes that, because John hasn’t felt the sponge, he will have a false belief that it is a rock.

Investigators have also asked whether the child can grasp the false belief principle. Individuals who understand the false belief principle can look at a problem or situation from another person’s point of view in order to discern what kind of information can cause that person to believe something that is not true. A number of developmentalists have examined a theoretical notion known as theory of mind, or mentalization, a set of concepts that explain other people’s ideas, beliefs, desires, and behavior [3]. Adults and adolescents have a much more fully developed theory of mind than have children. However, research also suggests that young children’s degree of sophistication is greater than either Piaget or casual observers of children would expect, and that there are big individual differences with regard to when and how children’s mentalizing abilities develop.

Children’s development of a theory of mind shows that cognitive development is a relational process. The child learns to conceptualize the world around him or her by communicating with others. That cognitive development is an interpersonal endeavor is the hallmark of Vygotsky’s theory.

Cognitive development according to Vygotsky

The Russian psychologist Lev Vygotsky (1896–1934) argued that development can only be understood within a social framework. New levels of understanding begin at an interpersonal level as two individuals, initially an infant and an adult, coordinate their interactions. Further, Vygotsky claimed that cognitive development can only be understood in the context of culture, and that high‐level mental functions begin in external activity that is gradually reconstructed and internalized. He gave the example of pointing.

Initially, an infant will reach toward an object that is out of reach, stretching the hand in the direction of the object and making grasping movements with the fingers. As soon as the caregiver recognizes that the child wants the object and is able to satisfy the child’s request, the child begins to modify the reaching and grasping movement into a socially meaningful gesture—pointing. The individual grasping has become an interpersonal communication gesture, and the child has internalized an understanding of the special relationship between the desired goal, the caregiver as mediator, and pointing as a meaningful sign.

According to Vygotsky, a child’s learning of new cognitive skills is guided by an adult (or a more skilled child, such as an older sibling) who models and structures the child’s learning experience; a process later called scaffolding. Vygotsky [2] offered the concept of the zone of proximal development, which is the discrepancy between how difficult a problem (e.g., in math) a child can solve on his or her own relative to solving a problem under adult guidance or in collaboration with capable peers. Learning within the zone of proximal development sets into motion the reorganization and internalization of existing developmental competencies, which then become synthesized at a new, higher intra‐mental level.

Several specific implications of Vygotsky’s work can be inferred [4], of which at least three are of relevance for understanding child development in relation to dentistry, as follows.

• The mental structures and functioning of people raised in a specific culture will be different from those of people raised in other cultures. In contrast to Piaget, who viewed the emergence of logical thought as largely a universal process, Vygotsky considered the nature of reasoning and problem solving as culturally created.
• Individuals can promote their own cognitive development by seeking interactions with others who can help draw them to higher levels of functioning within their zone of proximal development.
• Teachers, whether formal or informal (like parents or dental personnel), must navigate their “lessons” so that they can scaffold the child’s learning within his or her zone of proximal development.

Adaptation, according to Piaget, or learning, according to Vygotsky, is effective only when the input is new (i.e., different from existing knowledge) but related enough to existing knowledge (i.e., within the zone of proximal development) to permit accommodation rather than assimilation (Piaget) and the building of more elaborate mental structures (Vygotsky) (Box 3.1).

Language development

Somewhere between 16 and 24 months, after an early period of very slow word learning (12–18 months typically), most children begin to add new words rapidly, as if they have figured out that things have names. For the majority of children, the naming explosion is not a steady, gradual process; instead, a vocabulary spurt begins once the child has acquired about 50 words. Noun learning precedes verb learning because infants lack the ability to associate words consistently with actions until about 18 months of age. During the preschool years, children continue to add words at a remarkable speed. At age 2½, the average vocabulary is about 600 words, about a quarter of which are verbs [5], and most children at this age are equipped with a language capacity that also enables them to begin to communicate verbally with unfamiliar adults, provided that (a) the adult adapts his or her way of speaking to the child’s level of cognitive understanding, and (b) the emotional contact is such that the child feels free to talk. By age 5 or 6, total vocabulary has risen to perhaps 15,000 words—an astonishing increase of 10 words per day. The momentous shift in the way children approach new words happens around the age of 3 years. Understanding the categorical nature of words helps children develop what we might think of as mental “slots” for new words. Once the slots are in place, children seem to organize automatically the linguistic input they receive from parents, teachers, peers, books, television programs, and other sources to extract new words and fill the slots as quickly as possible.

Even though most children are reasonably fluent in their first language by the age of 3 or 4 years, there are still many refinements to be made. Soon after young children have figured out inflections and basic sentence forms, such as negation and questions, they begin to create remarkably complex sentences, using conjunctions such as and and but to combine two ideas or using embedded clauses. During middle childhood, children become skilled at managing the finer points of grammar, such as understanding various ways of saying something about the past (I went, I was going, I have gone, I had gone, I had been going, etc.).

Children use language not only for communication with others, but also for “internal purposes”—to help control or monitor their own behavior. Such private speech, which may consist of fragmentary sentences, muttering, or instructions to the self, is detectable from the earliest use of words and sentences (Box 3.2).

Emotional development

Emotions, for example, fear, sadness, anger, and joy, are part of a complex set of interconnected feelings, thoughts, and behaviors. Plutchik [6] conceptualized emotions as part of a feedback system; a stimulus, which could be an internal experience, such as pain, or an external stimulus, such as a looming object, is perceived and given some meaning. The meaning is associated with a feeling and with its accompanying physiological state. These combine to create an impulse for action that, if expressed, is observed in behavior. Two aspects of emotions that are of special interest for this chapter are temperament and emotional regulation.

Temperament

Temperament is a theoretical construct that refers to relatively stable characteristics of response to the environment and patterns of self‐regulation [7]. Theorists have offered different views about the specific features of temperament and what accounts for the stability of these features. However, they all tend to agree that a primary feature of temperament is the child’s positive or negative reaction to environmental events, and that the stability of this reaction leads to a patterned reaction by others [8].

As early as the 1950s Thomas and co‐workers [9] studied temperament and were able to classify infants into three temperamental groupings: easy, slow to warm up, and difficult. Roughly 35% of the sample could not be classified into any of these categories (Table 3.1).

Later work on temperament identified activity level, sociability, and negative emotionality as traits with a substantial genetic influence [10]. Kagan and co‐workers [11] have identified behavioral inhibition as a relatively stable temperamental trait, which has been shown to be a vulnerability factor for the development of shyness and anxiety problems later in childhood.

Rothbart and Posner [12] have identified three broad temperamental factors in 3‐ to 7‐year‐old children: surgency/extraversion, negative affectivity, and effortful control. Surgency is primarily defined by positive emotionality and approach (including sensation‐seeking, activity level, impulsivity, smiling and laughter, and low shyness). Negative affectivity involves shyness, discomfort, fear, anger/frustration, sadness, and low soothability. Effortful control is defined by high inhibitory control, attentional focusing, low‐intensity (non‐risk‐taking) pleasure, and perceptual sensitivity.

To summarize, it makes sense to think of temperament as two basic processes:

• Reactivity—how easily aroused the child is, either positively or negatively. Both the very inhibited and the very impulsive child are highly reactive to environmental stimuli although his or her reactions have different origins in the brain and take very different forms.
• Control—how able the child is to handle his or her activated nervous system.

Both aspects of temperament are important in the dental situation, which for some children is packed with fear‐eliciting stimuli from which one wants to escape, and for others with a number of exciting things one wants to explore. In both cases it will be difficult for the child to sit still and follow instructions. Temperament is closely linked to the concept of emotion regulation to which we turn in a moment. Let us, however, conclude with the aspect of stability in childhood temperament.

Although temperament shows consistency over the period of infancy and toddlerhood, it is in no way written in stone. Temperament is in fact only modestly stable over longer periods of time—the level of stability depending on culture, measurement techniques, and methods of analysis. Temperamental characteristics are modified as they come into contact with socialization pressures at home and at school, as well as with new capacities to regulate behavior. Whether it is temperament itself (in terms of a biological propensity) that changes, or if the child simply learns to “hide” or “suppress” aspects of his or her temperament that are not culturally sanctioned, is a question of debate.

Tim is a typical example of shyness in a young child and how this can manifest during a dental visit (Box 3.3). Other examples of temperament are active, speedy children who jump into the chair right away, and are eager to have their teeth checked. These children are very restless and seem to have very little time for conversation, which is why it is difficult to get through with information or instructions. There are also children who get upset very easily when feeling uncomfortable, for example, when the dentist uses the water suction. But if just given some extra attention, these children are often able to feel a lot more at ease and to cooperate well.