Análisis de las hojas de registro en UETE.

As has already been discussed, there are indications from the literature that certain aspects of infant development may act as barriers to dyadic toothbrushing, mainly coming in the form of difficult infant behaviour during toothbrushing (AAPD, 2011b; Amin and Harrison, 2009; Hoeft et al., 2009; Huebner and Riedy, 2010; Mofidi et al., 2009; Olley et al., 2011b; Riedy et al., 2001; Spitz et al., 2006). However, other aspects of infant development may also influence the emergence of toothbrushing as a dyadic process through infancy.

Towards the end of the first year of life, gross motor skills develop in order to allow infants to walk unaided, and alongside this, fine motor skills including object grapsing and manipulation also develop. An international study conducted by the WHO

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examined windows for achievement of six gross motor skills in infants from Ghana, India, Noway, Oman and the USA (WHO, 2006). Between the ages of 4 – 24 months, 816 infants were examined bi-monthly by trained fieldworkers until each of six milestones was achieved in order to generate standard data of how infants should develop and allow identification of delayed development. Additionally, caregivers provided self-reported dates of when each infant was observed by them to have achieved each milestone. Table 2.1 provides this caregiver self-report data around infant gross motor skills milestones.

Table 2.1- Ages at which infants reach gross motor skills milestones

Gross motor skill Mean age reached

(months) Range (months) Confidence interval Sitting unaided 6.0 3.8 – 9.2 1.1

Standing with assistance 7.6 4.8 – 11.4 1.4

Crawling on hands and knees 8.5 5.2 – 13.5 1.7

Walking with assistance 9.2 5.9 – 13.7 1.5

Standing alone 11.0 6.9 – 16.9 1.9

Walking alone 12.1 8.2 – 17.6 1.8

Although these data provide indications as to when most infants should reach each of these developmental milestones, the data should be interpreted with some caution. This is because caregiver self-reports were taken as the ‘exact’ date when each infant reached each milestone if a trained fieldworker had not examined an

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infant on the day that the milestone was reached or a fieldworker had not been available to conduct an examination that month. As caregivers may be reassured by their infant reaching milestones either early or on time, caregiver provided dates may have over-inflated the precocity of milestone achievement for their infant. Additionally, these data come from outside of the UK, so it is unknown whether the ages of milestone achievement identified in the WHO (2006) study provide reliable comparisons for infants residing in the UK.

Unfortunately, the WHO Growth Reference Study Group that collected the

international gross motor skills data (WHO, 2006) have not as yet collected similar

data for fine motor skills. However, standardised assessments such as the Bayley

Scales of Infant Development (Bayley, 2006), and reviews by the American Academy of Pediatrics (AAP- Gerber et al., 2010) have provided norms for ages at which a number of fine motor skills milestones are expected to be reached. The Bayley Scales assess fine motor skills such as grasps, with scores for fine motor skills increasing as grasps become more complex. For example, the first grasp type infant’s exhibit is a whole hand grasp, which allows infants to grasp objects like rattles and emerges at the age of around 2-months (Gerber et al., 2010).

As infants develop further, the ‘inferior-palmer’ followed quickly by the ‘palmar’ grasp emerge at around the age of 4 – 6 months (Gerber et al., 2010; Law et al., 2010) and is assessed with the Bayley Scales via the infant being required to grasp a crayon without using the thumb. Following this, the ‘transitional’ or ‘radial-palmar’

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grasp emerges around the age of 6 – 7 months (Gerber et al., 2010), which is a palmar grasp that incorporates the use of the thumb and is assessed by the infant grasping a crayon. This is then followed by the yet more complex ‘radial-digital grasp’, which emerges at the age of around 8 – 9 months (Gerber et al., 2010) and allows the infant to pick up objects such as blocks using the pad of the thumb and the other fingertips. Soon after the emergence of the radial-digital emergence comes the ‘inferior pincer’, and then the ‘pincer’ grasp at the age of around 8 – 10 months (Gerber et al., 2010), which is similar to the radial-digital grasp, but allows grasping of smaller objects such as pellets.

Further in infant development, the yet more complex ‘tripod grasp’ emerges which allows fine control of objects such as crayons. The final grasp assessed by the Bayley Scales is the ‘dynamic’ grasp which is essential for the fine control of objects such as pencils when engaging in writing. If this final grasp type is exhibited between the ages of 3 – 3.5 years, this would indicate typical development. See Figure 2.3 for photographs depicting each of the grasps that emerge throughout infancy.

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Crude palmer grasp (4 – 5 months) and palmer grasp (5 – 6 months)

Radial-palmer grasp (6 – 7 months) and radial-digital grasp (8 – 9 months)

Inferior pincer grasp (8 – 9 months) and pincer grasp (10 – 12 months) Figure 2.3- Grasp types that emerge through the first 12-months of life

The onset of walking unaided frees up an infant’s hands allowing them to develop these fine motor skills (Biringen et al., 2008; Karasik et al., 2011; Wijnhoven et al., 2004) and is facilitated via caregiver encouragement (Karasik et al., 2008), in addition to caregiver direction and teaching and infant persistence (Banerjee and Tamis- LeMonda, 2007; Bober et al., 2001). Once infants are able to grasp objects a key

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motor skill emerges, in which objects are manipulated and used as tools. Developmental psychologist Rachel Keen recently defined tool use as “using an object to act on the environment to accomplish a goal” (Keen, 2011), which would imply that when tool use emerges in infancy, infants purposefully grasp objects and manipulate them, using them as a tool in a conscious planned way to achieve a goal. As infants develop and they are able to grasp tools in more sophisticated ways, they can achieve increasingly complex environmental change using tools (Cox and Smitsman, 2006). One of the first tools infants use to exert their will to change their environment is a spoon, which they use to engage in an important self-care task, that of self-feeding (Claxton et al., 2009; McCarty et al., 2001).