<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>scott_s</author><text>Unfortunately, it&amp;#x27;s not accurate to say there is no evidence. There &lt;i&gt;is&lt;/i&gt; evidence, it&amp;#x27;s just old evidence. For some reason, Newsweek decided to focus on the fact that there is no evidence that fluoridation is helpful for &lt;i&gt;adults&lt;/i&gt;, and that the evidence for children is almost all from before 1975. That is important since behaviors may have changed post-1975.&lt;p&gt;The &amp;quot;Plain language summary&amp;quot; from the authors - their words, so this is the authors of the study synthesizing their conclusions for a lay audience - is clear:&lt;p&gt;&lt;i&gt;Data suggest that the introduction of water fluoridation resulted in a 35% reduction in decayed, missing or filled baby teeth and a 26% reduction in decayed, missing or filled permanent teeth. It also increased the percentage of children with no decay by 15%. Although these results indicate that water fluoridation is effective at reducing levels of tooth decay in children&amp;#x27;s baby and permanent teeth, the applicability of the results to current lifestyles is unclear because the majority of the studies were conducted before fluoride toothpastes and the other preventative meaures were widely used in many communities around the world.&lt;p&gt;There was insufficient information available to find out whether the introduction of a water fluoridation programme changed existing differences in tooth decay across socioeconomic groups.&lt;p&gt;There was insufficient information available to understand the effect of stopping water fluoridation programmes on tooth decay.&lt;p&gt;No studies met the review’s inclusion criteria that investigated the effectiveness of water fluoridation for preventing tooth decay in adults, rather than children.&lt;/i&gt;&lt;p&gt;This is from &lt;a href=&quot;http:&amp;#x2F;&amp;#x2F;onlinelibrary.wiley.com&amp;#x2F;doi&amp;#x2F;10.1002&amp;#x2F;14651858.CD010856.pub2&amp;#x2F;abstract&quot; rel=&quot;nofollow&quot;&gt;http:&amp;#x2F;&amp;#x2F;onlinelibrary.wiley.com&amp;#x2F;doi&amp;#x2F;10.1002&amp;#x2F;14651858.CD010856...&lt;/a&gt;. Thanks to HN user giarc (&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;news.ycombinator.com&amp;#x2F;item?id=9807427&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;news.ycombinator.com&amp;#x2F;item?id=9807427&lt;/a&gt;) for pointing it out.</text><parent_chain><item><author>jessriedel</author><text>Just so everyone is clear: this review found that there is little evidence that water fluoridation has any benefits.  It does not dispute that fluoride in toothpaste reduces tooth decay.&lt;p&gt;&amp;gt; Studies that attest to the effectiveness of fluoridation were generally done before the widespread usage of fluoride-containing dental products like rinses and toothpastes in the 1970s and later, according to the recent Cochrane study. So while it may have once made sense to add fluoride to water, it no longer appears to be necessary or useful, Thiessen says.&lt;p&gt;&amp;gt; It has also become clear in the last 15 years that fluoride primarily acts topically, according to the CDC. It reacts with the surface of the tooth enamel, making it more resistant to acids excreted by bacteria. Thus, there&amp;#x27;s no good reason to swallow fluoride and subject every tissue of your body to it, Thiessen says.&lt;p&gt;&amp;gt; Another 2009 review by the Cochrane group clearly shows that fluoride toothpaste prevents cavities.</text></item></parent_chain></comment><story><title>Water Fluoridation May Not Prevent Cavities, Scientific Review Shows</title><url>http://www.newsweek.com/fluoridation-may-not-prevent-cavities-huge-study-shows-348251</url></story>
<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>mikeyouse</author><text>The theory I&amp;#x27;ve encountered is that fluoridation previously had an impact on cavity-prevention before people were actually brushing their teeth with fluoridated toothpaste. Now that toothbrushing is much more common, the impact has waned.&lt;p&gt;Late edit;&lt;p&gt;Here&amp;#x27;s a look at toothbrushing frequency in Europe by country from 1994 - 2010:&lt;p&gt;&lt;a href=&quot;http:&amp;#x2F;&amp;#x2F;i.imgur.com&amp;#x2F;VVBldAy.jpg&quot; rel=&quot;nofollow&quot;&gt;http:&amp;#x2F;&amp;#x2F;i.imgur.com&amp;#x2F;VVBldAy.jpg&lt;/a&gt;&lt;p&gt;Just imagine how much improvement you&amp;#x27;d see from if the chart started in the 1940&amp;#x27;s and 1950&amp;#x27;s when many cities began fluoridating their water supplies. Not to mention that many early toothpastes were often ineffective at preventing cavities by primarily relying on baking soda and peroxide.&lt;p&gt;(Full brushing frequency study: &lt;a href=&quot;http:&amp;#x2F;&amp;#x2F;eurpub.oxfordjournals.org&amp;#x2F;content&amp;#x2F;25&amp;#x2F;suppl_2&amp;#x2F;20&quot; rel=&quot;nofollow&quot;&gt;http:&amp;#x2F;&amp;#x2F;eurpub.oxfordjournals.org&amp;#x2F;content&amp;#x2F;25&amp;#x2F;suppl_2&amp;#x2F;20&lt;/a&gt; )</text><parent_chain><item><author>jessriedel</author><text>Just so everyone is clear: this review found that there is little evidence that water fluoridation has any benefits.  It does not dispute that fluoride in toothpaste reduces tooth decay.&lt;p&gt;&amp;gt; Studies that attest to the effectiveness of fluoridation were generally done before the widespread usage of fluoride-containing dental products like rinses and toothpastes in the 1970s and later, according to the recent Cochrane study. So while it may have once made sense to add fluoride to water, it no longer appears to be necessary or useful, Thiessen says.&lt;p&gt;&amp;gt; It has also become clear in the last 15 years that fluoride primarily acts topically, according to the CDC. It reacts with the surface of the tooth enamel, making it more resistant to acids excreted by bacteria. Thus, there&amp;#x27;s no good reason to swallow fluoride and subject every tissue of your body to it, Thiessen says.&lt;p&gt;&amp;gt; Another 2009 review by the Cochrane group clearly shows that fluoride toothpaste prevents cavities.</text></item></parent_chain></comment><story><title>Water Fluoridation May Not Prevent Cavities, Scientific Review Shows</title><url>http://www.newsweek.com/fluoridation-may-not-prevent-cavities-huge-study-shows-348251</url></story>